ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev.3
(Generate patch)

Comparing libev/ev.3 (file contents):
Revision 1.59 by root, Tue Dec 25 07:16:53 2007 UTC vs.
Revision 1.98 by root, Thu Feb 28 02:17:11 2013 UTC

1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.16)
2.\" 2.\"
3.\" Standard preamble: 3.\" Standard preamble:
4.\" ======================================================================== 4.\" ========================================================================
5.de Sh \" Subsection heading
6.br
7.if t .Sp
8.ne 5
9.PP
10\fB\\$1\fR
11.PP
12..
13.de Sp \" Vertical space (when we can't use .PP) 5.de Sp \" Vertical space (when we can't use .PP)
14.if t .sp .5v 6.if t .sp .5v
15.if n .sp 7.if n .sp
16.. 8..
17.de Vb \" Begin verbatim text 9.de Vb \" Begin verbatim text
… …
23.ft R 15.ft R
24.fi 16.fi
25.. 17..
26.\" Set up some character translations and predefined strings. \*(-- will 18.\" Set up some character translations and predefined strings. \*(-- will
27.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left 19.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
28.\" double quote, and \*(R" will give a right double quote. | will give a 20.\" double quote, and \*(R" will give a right double quote. \*(C+ will
29.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to 21.\" give a nicer C++. Capital omega is used to do unbreakable dashes and
30.\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' 22.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
31.\" expand to `' in nroff, nothing in troff, for use with C<>. 23.\" nothing in troff, for use with C<>.
32.tr \(*W-|\(bv\*(Tr 24.tr \(*W-
33.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' 25.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
34.ie n \{\ 26.ie n \{\
35. ds -- \(*W- 27. ds -- \(*W-
36. ds PI pi 28. ds PI pi
37. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch 29. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
… …
46. ds PI \(*p 38. ds PI \(*p
47. ds L" `` 39. ds L" ``
48. ds R" '' 40. ds R" ''
49'br\} 41'br\}
50.\" 42.\"
43.\" Escape single quotes in literal strings from groff's Unicode transform.
44.ie \n(.g .ds Aq \(aq
45.el .ds Aq '
46.\"
51.\" If the F register is turned on, we'll generate index entries on stderr for 47.\" If the F register is turned on, we'll generate index entries on stderr for
52.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index 48.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
53.\" entries marked with X<> in POD. Of course, you'll have to process the 49.\" entries marked with X<> in POD. Of course, you'll have to process the
54.\" output yourself in some meaningful fashion. 50.\" output yourself in some meaningful fashion.
55.if \nF \{\ 51.ie \nF \{\
56. de IX 52. de IX
57. tm Index:\\$1\t\\n%\t"\\$2" 53. tm Index:\\$1\t\\n%\t"\\$2"
58.. 54..
59. nr % 0 55. nr % 0
60. rr F 56. rr F
61.\} 57.\}
62.\" 58.el \{\
63.\" For nroff, turn off justification. Always turn off hyphenation; it makes 59. de IX
64.\" way too many mistakes in technical documents. 60..
65.hy 0 61.\}
66.if n .na
67.\" 62.\"
68.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). 63.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
69.\" Fear. Run. Save yourself. No user-serviceable parts. 64.\" Fear. Run. Save yourself. No user-serviceable parts.
70. \" fudge factors for nroff and troff 65. \" fudge factors for nroff and troff
71.if n \{\ 66.if n \{\
… …
126. ds Ae AE 121. ds Ae AE
127.\} 122.\}
128.rm #[ #] #H #V #F C 123.rm #[ #] #H #V #F C
129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title "EV 1" 126.IX Title "LIBEV 3"
132.TH EV 1 "2007-12-25" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2013-02-28" "libev-4.11" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Subsection "EXAMPLE PROGRAM" 140.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1
143\& #include <ev.h>
144.Ve
145.PP
146.Vb 2 141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
147\& ev_io stdin_watcher; 149\& ev_io stdin_watcher;
148\& ev_timer timeout_watcher; 150\& ev_timer timeout_watcher;
149.Ve 151\&
150.PP 152\& // all watcher callbacks have a similar signature
151.Vb 8
152\& /* called when data readable on stdin */ 153\& // this callback is called when data is readable on stdin
153\& static void 154\& static void
154\& stdin_cb (EV_P_ struct ev_io *w, int revents) 155\& stdin_cb (EV_P_ ev_io *w, int revents)
155\& { 156\& {
156\& /* puts ("stdin ready"); */ 157\& puts ("stdin ready");
157\& ev_io_stop (EV_A_ w); /* just a syntax example */ 158\& // for one\-shot events, one must manually stop the watcher
158\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
159\& } 164\& }
160.Ve 165\&
161.PP 166\& // another callback, this time for a time\-out
162.Vb 6
163\& static void 167\& static void
164\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 168\& timeout_cb (EV_P_ ev_timer *w, int revents)
165\& { 169\& {
166\& /* puts ("timeout"); */ 170\& puts ("timeout");
167\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
168\& } 173\& }
169.Ve 174\&
170.PP
171.Vb 4
172\& int 175\& int
173\& main (void) 176\& main (void)
174\& { 177\& {
175\& struct ev_loop *loop = ev_default_loop (0); 178\& // use the default event loop unless you have special needs
176.Ve 179\& struct ev_loop *loop = EV_DEFAULT;
177.PP 180\&
178.Vb 3
179\& /* initialise an io watcher, then start it */ 181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
180\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181\& ev_io_start (loop, &stdin_watcher); 184\& ev_io_start (loop, &stdin_watcher);
182.Ve 185\&
183.PP 186\& // initialise a timer watcher, then start it
184.Vb 3
185\& /* simple non-repeating 5.5 second timeout */ 187\& // simple non\-repeating 5.5 second timeout
186\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187\& ev_timer_start (loop, &timeout_watcher); 189\& ev_timer_start (loop, &timeout_watcher);
188.Ve 190\&
189.PP 191\& // now wait for events to arrive
190.Vb 2
191\& /* loop till timeout or data ready */
192\& ev_loop (loop, 0); 192\& ev_run (loop, 0);
193.Ve 193\&
194.PP 194\& // break was called, so exit
195.Vb 2
196\& return 0; 195\& return 0;
197\& } 196\& }
198.Ve 197.Ve
199.SH "DESCRIPTION" 198.SH "ABOUT THIS DOCUMENT"
200.IX Header "DESCRIPTION" 199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
201The newest version of this document is also available as a html-formatted 202The newest version of this document is also available as an html-formatted
202web page you might find easier to navigate when reading it for the first 203web page you might find easier to navigate when reading it for the first
203time: <http://cvs.schmorp.de/libev/ev.html>. 204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
204.PP 205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
205Libev is an event loop: you register interest in certain events (such as a 222Libev is an event loop: you register interest in certain events (such as a
206file descriptor being readable or a timeout occurring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
207these event sources and provide your program with events. 224these event sources and provide your program with events.
208.PP 225.PP
209To do this, it must take more or less complete control over your process 226To do this, it must take more or less complete control over your process
… …
212.PP 229.PP
213You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
214watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
215details of the event, and then hand it over to libev by \fIstarting\fR the 232details of the event, and then hand it over to libev by \fIstarting\fR the
216watcher. 233watcher.
217.Sh "\s-1FEATURES\s0" 234.SS "\s-1FEATURES\s0"
218.IX Subsection "FEATURES" 235.IX Subsection "FEATURES"
219Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
220BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
221for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
222(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
223with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
224(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
225watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
226\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as 243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
227file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events 244loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
228(\f(CW\*(C`ev_fork\*(C'\fR). 245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
229.PP 247.PP
230It also is quite fast (see this 248It also is quite fast (see this
231benchmark comparing it to libevent 249benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
232for example). 250for example).
233.Sh "\s-1CONVENTIONS\s0" 251.SS "\s-1CONVENTIONS\s0"
234.IX Subsection "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
235Libev is very configurable. In this manual the default configuration will 253Libev is very configurable. In this manual the default (and most common)
236be described, which supports multiple event loops. For more info about 254configuration will be described, which supports multiple event loops. For
237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 255more info about various configuration options please have a look at
238this manual. If libev was configured without support for multiple event 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
239loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR 257for multiple event loops, then all functions taking an initial argument of
240(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument. 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259this argument.
241.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
242.IX Subsection "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
243Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
245the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
246called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
247to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
248it, you should treat it as some floatingpoint value. Unlike the name 267any calculations on it, you should treat it as some floating point value.
268.PP
249component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences 269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
250throughout libev. 270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
251.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
252.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
253These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
254library in any way. 293library in any way.
255.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
256.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
257Returns the current time as libev would use it. Please note that the 296Returns the current time as libev would use it. Please note that the
258\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
259you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
260.IP "ev_sleep (ev_tstamp interval)" 4 300.IP "ev_sleep (ev_tstamp interval)" 4
261.IX Item "ev_sleep (ev_tstamp interval)" 301.IX Item "ev_sleep (ev_tstamp interval)"
262Sleep for the given interval: The current thread will be blocked until 302Sleep for the given interval: The current thread will be blocked
263either it is interrupted or the given time interval has passed. Basically 303until either it is interrupted or the given time interval has
304passed (approximately \- it might return a bit earlier even if not
305interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
306.Sp
264this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR. 307Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
308.Sp
309The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
310with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
265.IP "int ev_version_major ()" 4 311.IP "int ev_version_major ()" 4
266.IX Item "int ev_version_major ()" 312.IX Item "int ev_version_major ()"
267.PD 0 313.PD 0
268.IP "int ev_version_minor ()" 4 314.IP "int ev_version_minor ()" 4
269.IX Item "int ev_version_minor ()" 315.IX Item "int ev_version_minor ()"
… …
281as this indicates an incompatible change. Minor versions are usually 327as this indicates an incompatible change. Minor versions are usually
282compatible to older versions, so a larger minor version alone is usually 328compatible to older versions, so a larger minor version alone is usually
283not a problem. 329not a problem.
284.Sp 330.Sp
285Example: Make sure we haven't accidentally been linked against the wrong 331Example: Make sure we haven't accidentally been linked against the wrong
286version. 332version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333such as \s-1LFS\s0 or reentrancy).
287.Sp 334.Sp
288.Vb 3 335.Vb 3
289\& assert (("libev version mismatch", 336\& assert (("libev version mismatch",
290\& ev_version_major () == EV_VERSION_MAJOR 337\& ev_version_major () == EV_VERSION_MAJOR
291\& && ev_version_minor () >= EV_VERSION_MINOR)); 338\& && ev_version_minor () >= EV_VERSION_MINOR));
292.Ve 339.Ve
293.IP "unsigned int ev_supported_backends ()" 4 340.IP "unsigned int ev_supported_backends ()" 4
294.IX Item "unsigned int ev_supported_backends ()" 341.IX Item "unsigned int ev_supported_backends ()"
295Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 342Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
296value) compiled into this binary of libev (independent of their 343value) compiled into this binary of libev (independent of their
… …
299.Sp 346.Sp
300Example: make sure we have the epoll method, because yeah this is cool and 347Example: make sure we have the epoll method, because yeah this is cool and
301a must have and can we have a torrent of it please!!!11 348a must have and can we have a torrent of it please!!!11
302.Sp 349.Sp
303.Vb 2 350.Vb 2
304\& assert (("sorry, no epoll, no sex", 351\& assert (("sorry, no epoll, no sex",
305\& ev_supported_backends () & EVBACKEND_EPOLL)); 352\& ev_supported_backends () & EVBACKEND_EPOLL));
306.Ve 353.Ve
307.IP "unsigned int ev_recommended_backends ()" 4 354.IP "unsigned int ev_recommended_backends ()" 4
308.IX Item "unsigned int ev_recommended_backends ()" 355.IX Item "unsigned int ev_recommended_backends ()"
309Return the set of all backends compiled into this binary of libev and also 356Return the set of all backends compiled into this binary of libev and
310recommended for this platform. This set is often smaller than the one 357also recommended for this platform, meaning it will work for most file
358descriptor types. This set is often smaller than the one returned by
311returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 359\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
312most BSDs and will not be autodetected unless you explicitly request it 360and will not be auto-detected unless you explicitly request it (assuming
313(assuming you know what you are doing). This is the set of backends that 361you know what you are doing). This is the set of backends that libev will
314libev will probe for if you specify no backends explicitly. 362probe for if you specify no backends explicitly.
315.IP "unsigned int ev_embeddable_backends ()" 4 363.IP "unsigned int ev_embeddable_backends ()" 4
316.IX Item "unsigned int ev_embeddable_backends ()" 364.IX Item "unsigned int ev_embeddable_backends ()"
317Returns the set of backends that are embeddable in other event loops. This 365Returns the set of backends that are embeddable in other event loops. This
318is the theoretical, all\-platform, value. To find which backends 366value is platform-specific but can include backends not available on the
319might be supported on the current system, you would need to look at 367current system. To find which embeddable backends might be supported on
320\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 368the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
321recommended ones. 369& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
322.Sp 370.Sp
323See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 371See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
324.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 372.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
325.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 373.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
326Sets the allocation function to use (the prototype is similar \- the 374Sets the allocation function to use (the prototype is similar \- the
327semantics is identical \- to the realloc C function). It is used to 375semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
328allocate and free memory (no surprises here). If it returns zero when 376used to allocate and free memory (no surprises here). If it returns zero
329memory needs to be allocated, the library might abort or take some 377when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
330potentially destructive action. The default is your system realloc 378or take some potentially destructive action.
331function. 379.Sp
380Since some systems (at least OpenBSD and Darwin) fail to implement
381correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
382\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
332.Sp 383.Sp
333You could override this function in high-availability programs to, say, 384You could override this function in high-availability programs to, say,
334free some memory if it cannot allocate memory, to use a special allocator, 385free some memory if it cannot allocate memory, to use a special allocator,
335or even to sleep a while and retry until some memory is available. 386or even to sleep a while and retry until some memory is available.
336.Sp 387.Sp
337Example: Replace the libev allocator with one that waits a bit and then 388Example: Replace the libev allocator with one that waits a bit and then
338retries). 389retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
339.Sp 390.Sp
340.Vb 6 391.Vb 6
341\& static void * 392\& static void *
342\& persistent_realloc (void *ptr, size_t size) 393\& persistent_realloc (void *ptr, size_t size)
343\& { 394\& {
344\& for (;;) 395\& for (;;)
345\& { 396\& {
346\& void *newptr = realloc (ptr, size); 397\& void *newptr = realloc (ptr, size);
347.Ve 398\&
348.Sp
349.Vb 2
350\& if (newptr) 399\& if (newptr)
351\& return newptr; 400\& return newptr;
352.Ve 401\&
353.Sp
354.Vb 3
355\& sleep (60); 402\& sleep (60);
356\& } 403\& }
357\& } 404\& }
358.Ve 405\&
359.Sp
360.Vb 2
361\& ... 406\& ...
362\& ev_set_allocator (persistent_realloc); 407\& ev_set_allocator (persistent_realloc);
363.Ve 408.Ve
364.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 409.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
365.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 410.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
366Set the callback function to call on a retryable syscall error (such 411Set the callback function to call on a retryable system call error (such
367as failed select, poll, epoll_wait). The message is a printable string 412as failed select, poll, epoll_wait). The message is a printable string
368indicating the system call or subsystem causing the problem. If this 413indicating the system call or subsystem causing the problem. If this
369callback is set, then libev will expect it to remedy the sitution, no 414callback is set, then libev will expect it to remedy the situation, no
370matter what, when it returns. That is, libev will generally retry the 415matter what, when it returns. That is, libev will generally retry the
371requested operation, or, if the condition doesn't go away, do bad stuff 416requested operation, or, if the condition doesn't go away, do bad stuff
372(such as abort). 417(such as abort).
373.Sp 418.Sp
374Example: This is basically the same thing that libev does internally, too. 419Example: This is basically the same thing that libev does internally, too.
… …
378\& fatal_error (const char *msg) 423\& fatal_error (const char *msg)
379\& { 424\& {
380\& perror (msg); 425\& perror (msg);
381\& abort (); 426\& abort ();
382\& } 427\& }
383.Ve 428\&
384.Sp
385.Vb 2
386\& ... 429\& ...
387\& ev_set_syserr_cb (fatal_error); 430\& ev_set_syserr_cb (fatal_error);
388.Ve 431.Ve
432.IP "ev_feed_signal (int signum)" 4
433.IX Item "ev_feed_signal (int signum)"
434This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
435safe to call this function at any time, from any context, including signal
436handlers or random threads.
437.Sp
438Its main use is to customise signal handling in your process, especially
439in the presence of threads. For example, you could block signals
440by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
441creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
442mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
443\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
389.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 444.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
390.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 445.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
391An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 446An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
392types of such loops, the \fIdefault\fR loop, which supports signals and child 447\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
393events, and dynamically created loops which do not. 448libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
394.PP 449.PP
395If you use threads, a common model is to run the default event loop 450The library knows two types of such loops, the \fIdefault\fR loop, which
396in your main thread (or in a separate thread) and for each thread you 451supports child process events, and dynamically created event loops which
397create, you also create another event loop. Libev itself does no locking 452do not.
398whatsoever, so if you mix calls to the same event loop in different
399threads, make sure you lock (this is usually a bad idea, though, even if
400done correctly, because it's hideous and inefficient).
401.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 453.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
402.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 454.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
403This will initialise the default event loop if it hasn't been initialised 455This returns the \*(L"default\*(R" event loop object, which is what you should
404yet and return it. If the default loop could not be initialised, returns 456normally use when you just need \*(L"the event loop\*(R". Event loop objects and
405false. If it already was initialised it simply returns it (and ignores the 457the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
406flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 458\&\f(CW\*(C`ev_loop_new\*(C'\fR.
459.Sp
460If the default loop is already initialised then this function simply
461returns it (and ignores the flags. If that is troubling you, check
462\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
463flags, which should almost always be \f(CW0\fR, unless the caller is also the
464one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
407.Sp 465.Sp
408If you don't know what event loop to use, use the one returned from this 466If you don't know what event loop to use, use the one returned from this
409function. 467function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
468.Sp
469Note that this function is \fInot\fR thread-safe, so if you want to use it
470from multiple threads, you have to employ some kind of mutex (note also
471that this case is unlikely, as loops cannot be shared easily between
472threads anyway).
473.Sp
474The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
475and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
476a problem for your application you can either create a dynamic loop with
477\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
478\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
479.Sp
480Example: This is the most typical usage.
481.Sp
482.Vb 2
483\& if (!ev_default_loop (0))
484\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
485.Ve
486.Sp
487Example: Restrict libev to the select and poll backends, and do not allow
488environment settings to be taken into account:
489.Sp
490.Vb 1
491\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492.Ve
493.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
494.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
495This will create and initialise a new event loop object. If the loop
496could not be initialised, returns false.
497.Sp
498This function is thread-safe, and one common way to use libev with
499threads is indeed to create one loop per thread, and using the default
500loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
410.Sp 501.Sp
411The flags argument can be used to specify special behaviour or specific 502The flags argument can be used to specify special behaviour or specific
412backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 503backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
413.Sp 504.Sp
414The following flags are supported: 505The following flags are supported:
… …
419The default flags value. Use this if you have no clue (it's the right 510The default flags value. Use this if you have no clue (it's the right
420thing, believe me). 511thing, believe me).
421.ie n .IP """EVFLAG_NOENV""" 4 512.ie n .IP """EVFLAG_NOENV""" 4
422.el .IP "\f(CWEVFLAG_NOENV\fR" 4 513.el .IP "\f(CWEVFLAG_NOENV\fR" 4
423.IX Item "EVFLAG_NOENV" 514.IX Item "EVFLAG_NOENV"
424If this flag bit is ored into the flag value (or the program runs setuid 515If this flag bit is or'ed into the flag value (or the program runs setuid
425or setgid) then libev will \fInot\fR look at the environment variable 516or setgid) then libev will \fInot\fR look at the environment variable
426\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 517\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
427override the flags completely if it is found in the environment. This is 518override the flags completely if it is found in the environment. This is
428useful to try out specific backends to test their performance, or to work 519useful to try out specific backends to test their performance, or to work
429around bugs. 520around bugs.
430.ie n .IP """EVFLAG_FORKCHECK""" 4 521.ie n .IP """EVFLAG_FORKCHECK""" 4
431.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 522.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
432.IX Item "EVFLAG_FORKCHECK" 523.IX Item "EVFLAG_FORKCHECK"
433Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after 524Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
434a fork, you can also make libev check for a fork in each iteration by 525make libev check for a fork in each iteration by enabling this flag.
435enabling this flag.
436.Sp 526.Sp
437This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, 527This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
438and thus this might slow down your event loop if you do a lot of loop 528and thus this might slow down your event loop if you do a lot of loop
439iterations and little real work, but is usually not noticeable (on my 529iterations and little real work, but is usually not noticeable (on my
440Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence 530GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
441without a syscall and thus \fIvery\fR fast, but my Linux system also has 531without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
442\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). 532\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
443.Sp 533.Sp
444The big advantage of this flag is that you can forget about fork (and 534The big advantage of this flag is that you can forget about fork (and
445forget about forgetting to tell libev about forking) when you use this 535forget about forgetting to tell libev about forking) when you use this
446flag. 536flag.
447.Sp 537.Sp
448This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR 538This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
449environment variable. 539environment variable.
540.ie n .IP """EVFLAG_NOINOTIFY""" 4
541.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
542.IX Item "EVFLAG_NOINOTIFY"
543When this flag is specified, then libev will not attempt to use the
544\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
545testing, this flag can be useful to conserve inotify file descriptors, as
546otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
547.ie n .IP """EVFLAG_SIGNALFD""" 4
548.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
549.IX Item "EVFLAG_SIGNALFD"
550When this flag is specified, then libev will attempt to use the
551\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
552delivers signals synchronously, which makes it both faster and might make
553it possible to get the queued signal data. It can also simplify signal
554handling with threads, as long as you properly block signals in your
555threads that are not interested in handling them.
556.Sp
557Signalfd will not be used by default as this changes your signal mask, and
558there are a lot of shoddy libraries and programs (glib's threadpool for
559example) that can't properly initialise their signal masks.
560.ie n .IP """EVFLAG_NOSIGMASK""" 4
561.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
562.IX Item "EVFLAG_NOSIGMASK"
563When this flag is specified, then libev will avoid to modify the signal
564mask. Specifically, this means you have to make sure signals are unblocked
565when you want to receive them.
566.Sp
567This behaviour is useful when you want to do your own signal handling, or
568want to handle signals only in specific threads and want to avoid libev
569unblocking the signals.
570.Sp
571It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
572\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
573.Sp
574This flag's behaviour will become the default in future versions of libev.
450.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 575.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
451.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 576.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
452.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 577.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
453This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 578This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
454libev tries to roll its own fd_set with no limits on the number of fds, 579libev tries to roll its own fd_set with no limits on the number of fds,
455but if that fails, expect a fairly low limit on the number of fds when 580but if that fails, expect a fairly low limit on the number of fds when
456using this backend. It doesn't scale too well (O(highest_fd)), but its 581using this backend. It doesn't scale too well (O(highest_fd)), but its
457usually the fastest backend for a low number of (low\-numbered :) fds. 582usually the fastest backend for a low number of (low-numbered :) fds.
458.Sp 583.Sp
459To get good performance out of this backend you need a high amount of 584To get good performance out of this backend you need a high amount of
460parallelity (most of the file descriptors should be busy). If you are 585parallelism (most of the file descriptors should be busy). If you are
461writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many 586writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
462connections as possible during one iteration. You might also want to have 587connections as possible during one iteration. You might also want to have
463a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of 588a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
464readyness notifications you get per iteration. 589readiness notifications you get per iteration.
590.Sp
591This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
592\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
593\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
465.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 594.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
466.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 595.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
467.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 596.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
468And this is your standard \fIpoll\fR\|(2) backend. It's more complicated 597And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
469than select, but handles sparse fds better and has no artificial 598than select, but handles sparse fds better and has no artificial
470limit on the number of fds you can use (except it will slow down 599limit on the number of fds you can use (except it will slow down
471considerably with a lot of inactive fds). It scales similarly to select, 600considerably with a lot of inactive fds). It scales similarly to select,
472i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for 601i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
473performance tips. 602performance tips.
603.Sp
604This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
605\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
474.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 606.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
475.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 607.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
476.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 608.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
609Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
610kernels).
611.Sp
477For few fds, this backend is a bit little slower than poll and select, 612For few fds, this backend is a bit little slower than poll and select, but
478but it scales phenomenally better. While poll and select usually scale 613it scales phenomenally better. While poll and select usually scale like
479like O(total_fds) where n is the total number of fds (or the highest fd), 614O(total_fds) where total_fds is the total number of fds (or the highest
480epoll scales either O(1) or O(active_fds). The epoll design has a number 615fd), epoll scales either O(1) or O(active_fds).
481of shortcomings, such as silently dropping events in some hard-to-detect 616.Sp
482cases and rewiring a syscall per fd change, no fork support and bad 617The epoll mechanism deserves honorable mention as the most misdesigned
483support for dup. 618of the more advanced event mechanisms: mere annoyances include silently
619dropping file descriptors, requiring a system call per change per file
620descriptor (and unnecessary guessing of parameters), problems with dup,
621returning before the timeout value, resulting in additional iterations
622(and only giving 5ms accuracy while select on the same platform gives
6230.1ms) and so on. The biggest issue is fork races, however \- if a program
624forks then \fIboth\fR parent and child process have to recreate the epoll
625set, which can take considerable time (one syscall per file descriptor)
626and is of course hard to detect.
627.Sp
628Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
629but of course \fIdoesn't\fR, and epoll just loves to report events for
630totally \fIdifferent\fR file descriptors (even already closed ones, so
631one cannot even remove them from the set) than registered in the set
632(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
633notifications by employing an additional generation counter and comparing
634that against the events to filter out spurious ones, recreating the set
635when required. Epoll also erroneously rounds down timeouts, but gives you
636no way to know when and by how much, so sometimes you have to busy-wait
637because epoll returns immediately despite a nonzero timeout. And last
638not least, it also refuses to work with some file descriptors which work
639perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
640.Sp
641Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
642cobbled together in a hurry, no thought to design or interaction with
643others. Oh, the pain, will it ever stop...
484.Sp 644.Sp
485While stopping, setting and starting an I/O watcher in the same iteration 645While stopping, setting and starting an I/O watcher in the same iteration
486will result in some caching, there is still a syscall per such incident 646will result in some caching, there is still a system call per such
487(because the fd could point to a different file description now), so its 647incident (because the same \fIfile descriptor\fR could point to a different
488best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work 648\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
489very well if you register events for both fds. 649file descriptors might not work very well if you register events for both
490.Sp 650file descriptors.
491Please note that epoll sometimes generates spurious notifications, so you
492need to use non-blocking I/O or other means to avoid blocking when no data
493(or space) is available.
494.Sp 651.Sp
495Best performance from this backend is achieved by not unregistering all 652Best performance from this backend is achieved by not unregistering all
496watchers for a file descriptor until it has been closed, if possible, i.e. 653watchers for a file descriptor until it has been closed, if possible,
497keep at least one watcher active per fd at all times. 654i.e. keep at least one watcher active per fd at all times. Stopping and
655starting a watcher (without re-setting it) also usually doesn't cause
656extra overhead. A fork can both result in spurious notifications as well
657as in libev having to destroy and recreate the epoll object, which can
658take considerable time and thus should be avoided.
498.Sp 659.Sp
660All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
661faster than epoll for maybe up to a hundred file descriptors, depending on
662the usage. So sad.
663.Sp
499While nominally embeddeble in other event loops, this feature is broken in 664While nominally embeddable in other event loops, this feature is broken in
500all kernel versions tested so far. 665all kernel versions tested so far.
666.Sp
667This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
668\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
501.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 669.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
502.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 670.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
503.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 671.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
504Kqueue deserves special mention, as at the time of this writing, it 672Kqueue deserves special mention, as at the time of this writing, it
505was broken on all BSDs except NetBSD (usually it doesn't work reliably 673was broken on all BSDs except NetBSD (usually it doesn't work reliably
506with anything but sockets and pipes, except on Darwin, where of course 674with anything but sockets and pipes, except on Darwin, where of course
507it's completely useless). For this reason it's not being \*(L"autodetected\*(R" 675it's completely useless). Unlike epoll, however, whose brokenness
676is by design, these kqueue bugs can (and eventually will) be fixed
677without \s-1API\s0 changes to existing programs. For this reason it's not being
508unless you explicitly specify it explicitly in the flags (i.e. using 678\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
509\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough) 679\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
510system like NetBSD. 680system like NetBSD.
511.Sp 681.Sp
512You still can embed kqueue into a normal poll or select backend and use it 682You still can embed kqueue into a normal poll or select backend and use it
513only for sockets (after having made sure that sockets work with kqueue on 683only for sockets (after having made sure that sockets work with kqueue on
514the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 684the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
515.Sp 685.Sp
516It scales in the same way as the epoll backend, but the interface to the 686It scales in the same way as the epoll backend, but the interface to the
517kernel is more efficient (which says nothing about its actual speed, of 687kernel is more efficient (which says nothing about its actual speed, of
518course). While stopping, setting and starting an I/O watcher does never 688course). While stopping, setting and starting an I/O watcher does never
519cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to 689cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
520two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it 690two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
691might have to leak fd's on fork, but it's more sane than epoll) and it
521drops fds silently in similarly hard-to-detect cases. 692drops fds silently in similarly hard-to-detect cases.
522.Sp 693.Sp
523This backend usually performs well under most conditions. 694This backend usually performs well under most conditions.
524.Sp 695.Sp
525While nominally embeddable in other event loops, this doesn't work 696While nominally embeddable in other event loops, this doesn't work
526everywhere, so you might need to test for this. And since it is broken 697everywhere, so you might need to test for this. And since it is broken
527almost everywhere, you should only use it when you have a lot of sockets 698almost everywhere, you should only use it when you have a lot of sockets
528(for which it usually works), by embedding it into another event loop 699(for which it usually works), by embedding it into another event loop
529(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for 700(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
530sockets. 701also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
702.Sp
703This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
704\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
705\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
531.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 706.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
532.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 707.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
533.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 708.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
534This is not implemented yet (and might never be, unless you send me an 709This is not implemented yet (and might never be, unless you send me an
535implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets 710implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
… …
539.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 714.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
540.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 715.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
541This uses the Solaris 10 event port mechanism. As with everything on Solaris, 716This uses the Solaris 10 event port mechanism. As with everything on Solaris,
542it's really slow, but it still scales very well (O(active_fds)). 717it's really slow, but it still scales very well (O(active_fds)).
543.Sp 718.Sp
544Please note that solaris event ports can deliver a lot of spurious
545notifications, so you need to use non-blocking I/O or other means to avoid
546blocking when no data (or space) is available.
547.Sp
548While this backend scales well, it requires one system call per active 719While this backend scales well, it requires one system call per active
549file descriptor per loop iteration. For small and medium numbers of file 720file descriptor per loop iteration. For small and medium numbers of file
550descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend 721descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
551might perform better. 722might perform better.
723.Sp
724On the positive side, this backend actually performed fully to
725specification in all tests and is fully embeddable, which is a rare feat
726among the OS-specific backends (I vastly prefer correctness over speed
727hacks).
728.Sp
729On the negative side, the interface is \fIbizarre\fR \- so bizarre that
730even sun itself gets it wrong in their code examples: The event polling
731function sometimes returns events to the caller even though an error
732occurred, but with no indication whether it has done so or not (yes, it's
733even documented that way) \- deadly for edge-triggered interfaces where you
734absolutely have to know whether an event occurred or not because you have
735to re-arm the watcher.
736.Sp
737Fortunately libev seems to be able to work around these idiocies.
738.Sp
739This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
740\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
552.ie n .IP """EVBACKEND_ALL""" 4 741.ie n .IP """EVBACKEND_ALL""" 4
553.el .IP "\f(CWEVBACKEND_ALL\fR" 4 742.el .IP "\f(CWEVBACKEND_ALL\fR" 4
554.IX Item "EVBACKEND_ALL" 743.IX Item "EVBACKEND_ALL"
555Try all backends (even potentially broken ones that wouldn't be tried 744Try all backends (even potentially broken ones that wouldn't be tried
556with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 745with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
557\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 746\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
558.Sp 747.Sp
559It is definitely not recommended to use this flag. 748It is definitely not recommended to use this flag, use whatever
749\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
750at all.
751.ie n .IP """EVBACKEND_MASK""" 4
752.el .IP "\f(CWEVBACKEND_MASK\fR" 4
753.IX Item "EVBACKEND_MASK"
754Not a backend at all, but a mask to select all backend bits from a
755\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
756value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
560.RE 757.RE
561.RS 4 758.RS 4
562.Sp 759.Sp
563If one or more of these are ored into the flags value, then only these 760If one or more of the backend flags are or'ed into the flags value,
564backends will be tried (in the reverse order as given here). If none are 761then only these backends will be tried (in the reverse order as listed
565specified, most compiled-in backend will be tried, usually in reverse 762here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
566order of their flag values :) 763()\*(C'\fR will be tried.
567.Sp 764.Sp
568The most typical usage is like this: 765Example: Try to create a event loop that uses epoll and nothing else.
569.Sp 766.Sp
570.Vb 2 767.Vb 3
571\& if (!ev_default_loop (0)) 768\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
572\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 769\& if (!epoller)
770\& fatal ("no epoll found here, maybe it hides under your chair");
573.Ve 771.Ve
574.Sp 772.Sp
575Restrict libev to the select and poll backends, and do not allow 773Example: Use whatever libev has to offer, but make sure that kqueue is
576environment settings to be taken into account: 774used if available.
577.Sp 775.Sp
578.Vb 1 776.Vb 1
579\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
580.Ve
581.Sp
582Use whatever libev has to offer, but make sure that kqueue is used if
583available (warning, breaks stuff, best use only with your own private
584event loop and only if you know the \s-1OS\s0 supports your types of fds):
585.Sp
586.Vb 1
587\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 777\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
588.Ve 778.Ve
589.RE 779.RE
590.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
591.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
592Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
593always distinct from the default loop. Unlike the default loop, it cannot
594handle signal and child watchers, and attempts to do so will be greeted by
595undefined behaviour (or a failed assertion if assertions are enabled).
596.Sp
597Example: Try to create a event loop that uses epoll and nothing else.
598.Sp
599.Vb 3
600\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
601\& if (!epoller)
602\& fatal ("no epoll found here, maybe it hides under your chair");
603.Ve
604.IP "ev_default_destroy ()" 4 780.IP "ev_loop_destroy (loop)" 4
605.IX Item "ev_default_destroy ()" 781.IX Item "ev_loop_destroy (loop)"
606Destroys the default loop again (frees all memory and kernel state 782Destroys an event loop object (frees all memory and kernel state
607etc.). None of the active event watchers will be stopped in the normal 783etc.). None of the active event watchers will be stopped in the normal
608sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 784sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
609responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 785responsibility to either stop all watchers cleanly yourself \fIbefore\fR
610calling this function, or cope with the fact afterwards (which is usually 786calling this function, or cope with the fact afterwards (which is usually
611the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 787the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
612for example). 788for example).
613.Sp 789.Sp
614Note that certain global state, such as signal state, will not be freed by 790Note that certain global state, such as signal state (and installed signal
615this function, and related watchers (such as signal and child watchers) 791handlers), will not be freed by this function, and related watchers (such
616would need to be stopped manually. 792as signal and child watchers) would need to be stopped manually.
617.Sp 793.Sp
618In general it is not advisable to call this function except in the 794This function is normally used on loop objects allocated by
619rare occasion where you really need to free e.g. the signal handling 795\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
620pipe fds. If you need dynamically allocated loops it is better to use 796\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
621\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
622.IP "ev_loop_destroy (loop)" 4
623.IX Item "ev_loop_destroy (loop)"
624Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
625earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
626.IP "ev_default_fork ()" 4
627.IX Item "ev_default_fork ()"
628This function reinitialises the kernel state for backends that have
629one. Despite the name, you can call it anytime, but it makes most sense
630after forking, in either the parent or child process (or both, but that
631again makes little sense).
632.Sp 797.Sp
633You \fImust\fR call this function in the child process after forking if and 798Note that it is not advisable to call this function on the default loop
634only if you want to use the event library in both processes. If you just 799except in the rare occasion where you really need to free its resources.
635fork+exec, you don't have to call it. 800If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
636.Sp 801and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
637The function itself is quite fast and it's usually not a problem to call
638it just in case after a fork. To make this easy, the function will fit in
639quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
640.Sp
641.Vb 1
642\& pthread_atfork (0, 0, ev_default_fork);
643.Ve
644.Sp
645At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
646without calling this function, so if you force one of those backends you
647do not need to care.
648.IP "ev_loop_fork (loop)" 4 802.IP "ev_loop_fork (loop)" 4
649.IX Item "ev_loop_fork (loop)" 803.IX Item "ev_loop_fork (loop)"
650Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 804This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
651\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 805reinitialise the kernel state for backends that have one. Despite the
652after fork, and how you do this is entirely your own problem. 806name, you can call it anytime, but it makes most sense after forking, in
807the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
808child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
809.Sp
810Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
811a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
812because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
813during fork.
814.Sp
815On the other hand, you only need to call this function in the child
816process if and only if you want to use the event loop in the child. If
817you just fork+exec or create a new loop in the child, you don't have to
818call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
819difference, but libev will usually detect this case on its own and do a
820costly reset of the backend).
821.Sp
822The function itself is quite fast and it's usually not a problem to call
823it just in case after a fork.
824.Sp
825Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
826using pthreads.
827.Sp
828.Vb 5
829\& static void
830\& post_fork_child (void)
831\& {
832\& ev_loop_fork (EV_DEFAULT);
833\& }
834\&
835\& ...
836\& pthread_atfork (0, 0, post_fork_child);
837.Ve
838.IP "int ev_is_default_loop (loop)" 4
839.IX Item "int ev_is_default_loop (loop)"
840Returns true when the given loop is, in fact, the default loop, and false
841otherwise.
653.IP "unsigned int ev_loop_count (loop)" 4 842.IP "unsigned int ev_iteration (loop)" 4
654.IX Item "unsigned int ev_loop_count (loop)" 843.IX Item "unsigned int ev_iteration (loop)"
655Returns the count of loop iterations for the loop, which is identical to 844Returns the current iteration count for the event loop, which is identical
656the number of times libev did poll for new events. It starts at \f(CW0\fR and 845to the number of times libev did poll for new events. It starts at \f(CW0\fR
657happily wraps around with enough iterations. 846and happily wraps around with enough iterations.
658.Sp 847.Sp
659This value can sometimes be useful as a generation counter of sorts (it 848This value can sometimes be useful as a generation counter of sorts (it
660\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with 849\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
661\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls. 850\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
851prepare and check phases.
852.IP "unsigned int ev_depth (loop)" 4
853.IX Item "unsigned int ev_depth (loop)"
854Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
855times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
856.Sp
857Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
858\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
859in which case it is higher.
860.Sp
861Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
862throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
863as a hint to avoid such ungentleman-like behaviour unless it's really
864convenient, in which case it is fully supported.
662.IP "unsigned int ev_backend (loop)" 4 865.IP "unsigned int ev_backend (loop)" 4
663.IX Item "unsigned int ev_backend (loop)" 866.IX Item "unsigned int ev_backend (loop)"
664Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 867Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
665use. 868use.
666.IP "ev_tstamp ev_now (loop)" 4 869.IP "ev_tstamp ev_now (loop)" 4
… …
668Returns the current \*(L"event loop time\*(R", which is the time the event loop 871Returns the current \*(L"event loop time\*(R", which is the time the event loop
669received events and started processing them. This timestamp does not 872received events and started processing them. This timestamp does not
670change as long as callbacks are being processed, and this is also the base 873change as long as callbacks are being processed, and this is also the base
671time used for relative timers. You can treat it as the timestamp of the 874time used for relative timers. You can treat it as the timestamp of the
672event occurring (or more correctly, libev finding out about it). 875event occurring (or more correctly, libev finding out about it).
876.IP "ev_now_update (loop)" 4
877.IX Item "ev_now_update (loop)"
878Establishes the current time by querying the kernel, updating the time
879returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
880is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
881.Sp
882This function is rarely useful, but when some event callback runs for a
883very long time without entering the event loop, updating libev's idea of
884the current time is a good idea.
885.Sp
886See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
887.IP "ev_suspend (loop)" 4
888.IX Item "ev_suspend (loop)"
889.PD 0
890.IP "ev_resume (loop)" 4
891.IX Item "ev_resume (loop)"
892.PD
893These two functions suspend and resume an event loop, for use when the
894loop is not used for a while and timeouts should not be processed.
895.Sp
896A typical use case would be an interactive program such as a game: When
897the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
898would be best to handle timeouts as if no time had actually passed while
899the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
900in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
901\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
902.Sp
903Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
904between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
905will be rescheduled (that is, they will lose any events that would have
906occurred while suspended).
907.Sp
908After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
909given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
910without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
911.Sp
912Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
913event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
673.IP "ev_loop (loop, int flags)" 4 914.IP "bool ev_run (loop, int flags)" 4
674.IX Item "ev_loop (loop, int flags)" 915.IX Item "bool ev_run (loop, int flags)"
675Finally, this is it, the event handler. This function usually is called 916Finally, this is it, the event handler. This function usually is called
676after you initialised all your watchers and you want to start handling 917after you have initialised all your watchers and you want to start
677events. 918handling events. It will ask the operating system for any new events, call
919the watcher callbacks, and then repeat the whole process indefinitely: This
920is why event loops are called \fIloops\fR.
678.Sp 921.Sp
679If the flags argument is specified as \f(CW0\fR, it will not return until 922If the flags argument is specified as \f(CW0\fR, it will keep handling events
680either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 923until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
924called.
681.Sp 925.Sp
926The return value is false if there are no more active watchers (which
927usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
928(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
929.Sp
682Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 930Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
683relying on all watchers to be stopped when deciding when a program has 931relying on all watchers to be stopped when deciding when a program has
684finished (especially in interactive programs), but having a program that 932finished (especially in interactive programs), but having a program
685automatically loops as long as it has to and no longer by virtue of 933that automatically loops as long as it has to and no longer by virtue
686relying on its watchers stopping correctly is a thing of beauty. 934of relying on its watchers stopping correctly, that is truly a thing of
935beauty.
687.Sp 936.Sp
937This function is \fImostly\fR exception-safe \- you can break out of a
938\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
939exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
940will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
941.Sp
688A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 942A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
689those events and any outstanding ones, but will not block your process in 943those events and any already outstanding ones, but will not wait and
690case there are no events and will return after one iteration of the loop. 944block your process in case there are no events and will return after one
945iteration of the loop. This is sometimes useful to poll and handle new
946events while doing lengthy calculations, to keep the program responsive.
691.Sp 947.Sp
692A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 948A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
693neccessary) and will handle those and any outstanding ones. It will block 949necessary) and will handle those and any already outstanding ones. It
694your process until at least one new event arrives, and will return after 950will block your process until at least one new event arrives (which could
695one iteration of the loop. This is useful if you are waiting for some 951be an event internal to libev itself, so there is no guarantee that a
696external event in conjunction with something not expressible using other 952user-registered callback will be called), and will return after one
953iteration of the loop.
954.Sp
955This is useful if you are waiting for some external event in conjunction
956with something not expressible using other libev watchers (i.e. "roll your
697libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 957own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
698usually a better approach for this kind of thing. 958usually a better approach for this kind of thing.
699.Sp 959.Sp
700Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 960Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
961understanding, not a guarantee that things will work exactly like this in
962future versions):
701.Sp 963.Sp
702.Vb 19 964.Vb 10
965\& \- Increment loop depth.
966\& \- Reset the ev_break status.
703\& - Before the first iteration, call any pending watchers. 967\& \- Before the first iteration, call any pending watchers.
704\& * If there are no active watchers (reference count is zero), return. 968\& LOOP:
705\& - Queue all prepare watchers and then call all outstanding watchers. 969\& \- If EVFLAG_FORKCHECK was used, check for a fork.
970\& \- If a fork was detected (by any means), queue and call all fork watchers.
971\& \- Queue and call all prepare watchers.
972\& \- If ev_break was called, goto FINISH.
706\& - If we have been forked, recreate the kernel state. 973\& \- If we have been forked, detach and recreate the kernel state
974\& as to not disturb the other process.
707\& - Update the kernel state with all outstanding changes. 975\& \- Update the kernel state with all outstanding changes.
708\& - Update the "event loop time". 976\& \- Update the "event loop time" (ev_now ()).
709\& - Calculate for how long to block. 977\& \- Calculate for how long to sleep or block, if at all
978\& (active idle watchers, EVRUN_NOWAIT or not having
979\& any active watchers at all will result in not sleeping).
980\& \- Sleep if the I/O and timer collect interval say so.
981\& \- Increment loop iteration counter.
710\& - Block the process, waiting for any events. 982\& \- Block the process, waiting for any events.
711\& - Queue all outstanding I/O (fd) events. 983\& \- Queue all outstanding I/O (fd) events.
712\& - Update the "event loop time" and do time jump handling. 984\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
713\& - Queue all outstanding timers. 985\& \- Queue all expired timers.
714\& - Queue all outstanding periodics. 986\& \- Queue all expired periodics.
715\& - If no events are pending now, queue all idle watchers. 987\& \- Queue all idle watchers with priority higher than that of pending events.
716\& - Queue all check watchers. 988\& \- Queue all check watchers.
717\& - Call all queued watchers in reverse order (i.e. check watchers first). 989\& \- Call all queued watchers in reverse order (i.e. check watchers first).
718\& Signals and child watchers are implemented as I/O watchers, and will 990\& Signals and child watchers are implemented as I/O watchers, and will
719\& be handled here by queueing them when their watcher gets executed. 991\& be handled here by queueing them when their watcher gets executed.
720\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 992\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
721\& were used, return, otherwise continue with step *. 993\& were used, or there are no active watchers, goto FINISH, otherwise
994\& continue with step LOOP.
995\& FINISH:
996\& \- Reset the ev_break status iff it was EVBREAK_ONE.
997\& \- Decrement the loop depth.
998\& \- Return.
722.Ve 999.Ve
723.Sp 1000.Sp
724Example: Queue some jobs and then loop until no events are outsanding 1001Example: Queue some jobs and then loop until no events are outstanding
725anymore. 1002anymore.
726.Sp 1003.Sp
727.Vb 4 1004.Vb 4
728\& ... queue jobs here, make sure they register event watchers as long 1005\& ... queue jobs here, make sure they register event watchers as long
729\& ... as they still have work to do (even an idle watcher will do..) 1006\& ... as they still have work to do (even an idle watcher will do..)
730\& ev_loop (my_loop, 0); 1007\& ev_run (my_loop, 0);
731\& ... jobs done. yeah! 1008\& ... jobs done or somebody called break. yeah!
732.Ve 1009.Ve
733.IP "ev_unloop (loop, how)" 4 1010.IP "ev_break (loop, how)" 4
734.IX Item "ev_unloop (loop, how)" 1011.IX Item "ev_break (loop, how)"
735Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1012Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
736has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1013has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
737\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1014\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
738\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1015\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1016.Sp
1017This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1018.Sp
1019It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1020which case it will have no effect.
739.IP "ev_ref (loop)" 4 1021.IP "ev_ref (loop)" 4
740.IX Item "ev_ref (loop)" 1022.IX Item "ev_ref (loop)"
741.PD 0 1023.PD 0
742.IP "ev_unref (loop)" 4 1024.IP "ev_unref (loop)" 4
743.IX Item "ev_unref (loop)" 1025.IX Item "ev_unref (loop)"
744.PD 1026.PD
745Ref/unref can be used to add or remove a reference count on the event 1027Ref/unref can be used to add or remove a reference count on the event
746loop: Every watcher keeps one reference, and as long as the reference 1028loop: Every watcher keeps one reference, and as long as the reference
747count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1029count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
748a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1030.Sp
749returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1031This is useful when you have a watcher that you never intend to
1032unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1033returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1034before stopping it.
1035.Sp
750example, libev itself uses this for its internal signal pipe: It is not 1036As an example, libev itself uses this for its internal signal pipe: It
751visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1037is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
752no event watchers registered by it are active. It is also an excellent 1038exiting if no event watchers registered by it are active. It is also an
753way to do this for generic recurring timers or from within third-party 1039excellent way to do this for generic recurring timers or from within
754libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1040third-party libraries. Just remember to \fIunref after start\fR and \fIref
1041before stop\fR (but only if the watcher wasn't active before, or was active
1042before, respectively. Note also that libev might stop watchers itself
1043(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1044in the callback).
755.Sp 1045.Sp
756Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1046Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
757running when nothing else is active. 1047running when nothing else is active.
758.Sp 1048.Sp
759.Vb 4 1049.Vb 4
760\& struct ev_signal exitsig; 1050\& ev_signal exitsig;
761\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1051\& ev_signal_init (&exitsig, sig_cb, SIGINT);
762\& ev_signal_start (loop, &exitsig); 1052\& ev_signal_start (loop, &exitsig);
763\& evf_unref (loop); 1053\& ev_unref (loop);
764.Ve 1054.Ve
765.Sp 1055.Sp
766Example: For some weird reason, unregister the above signal handler again. 1056Example: For some weird reason, unregister the above signal handler again.
767.Sp 1057.Sp
768.Vb 2 1058.Vb 2
769\& ev_ref (loop); 1059\& ev_ref (loop);
770\& ev_signal_stop (loop, &exitsig); 1060\& ev_signal_stop (loop, &exitsig);
771.Ve 1061.Ve
772.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4 1062.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
773.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)" 1063.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
774.PD 0 1064.PD 0
775.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4 1065.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
776.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 1066.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
777.PD 1067.PD
778These advanced functions influence the time that libev will spend waiting 1068These advanced functions influence the time that libev will spend waiting
779for events. Both are by default \f(CW0\fR, meaning that libev will try to 1069for events. Both time intervals are by default \f(CW0\fR, meaning that libev
780invoke timer/periodic callbacks and I/O callbacks with minimum latency. 1070will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1071latency.
781.Sp 1072.Sp
782Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR) 1073Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
783allows libev to delay invocation of I/O and timer/periodic callbacks to 1074allows libev to delay invocation of I/O and timer/periodic callbacks
784increase efficiency of loop iterations. 1075to increase efficiency of loop iterations (or to increase power-saving
1076opportunities).
785.Sp 1077.Sp
786The background is that sometimes your program runs just fast enough to 1078The idea is that sometimes your program runs just fast enough to handle
787handle one (or very few) event(s) per loop iteration. While this makes 1079one (or very few) event(s) per loop iteration. While this makes the
788the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new 1080program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
789events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high 1081events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
790overhead for the actual polling but can deliver many events at once. 1082overhead for the actual polling but can deliver many events at once.
791.Sp 1083.Sp
792By setting a higher \fIio collect interval\fR you allow libev to spend more 1084By setting a higher \fIio collect interval\fR you allow libev to spend more
793time collecting I/O events, so you can handle more events per iteration, 1085time collecting I/O events, so you can handle more events per iteration,
794at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and 1086at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
795\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will 1087\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
796introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. 1088introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1089sleep time ensures that libev will not poll for I/O events more often then
1090once per this interval, on average (as long as the host time resolution is
1091good enough).
797.Sp 1092.Sp
798Likewise, by setting a higher \fItimeout collect interval\fR you allow libev 1093Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
799to spend more time collecting timeouts, at the expense of increased 1094to spend more time collecting timeouts, at the expense of increased
800latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers 1095latency/jitter/inexactness (the watcher callback will be called
801will not be affected. Setting this to a non-null value will not introduce 1096later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
802any overhead in libev. 1097value will not introduce any overhead in libev.
803.Sp 1098.Sp
804Many (busy) programs can usually benefit by setting the io collect 1099Many (busy) programs can usually benefit by setting the I/O collect
805interval to a value near \f(CW0.1\fR or so, which is often enough for 1100interval to a value near \f(CW0.1\fR or so, which is often enough for
806interactive servers (of course not for games), likewise for timeouts. It 1101interactive servers (of course not for games), likewise for timeouts. It
807usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR, 1102usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
808as this approsaches the timing granularity of most systems. 1103as this approaches the timing granularity of most systems. Note that if
1104you do transactions with the outside world and you can't increase the
1105parallelity, then this setting will limit your transaction rate (if you
1106need to poll once per transaction and the I/O collect interval is 0.01,
1107then you can't do more than 100 transactions per second).
1108.Sp
1109Setting the \fItimeout collect interval\fR can improve the opportunity for
1110saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1111are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1112times the process sleeps and wakes up again. Another useful technique to
1113reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1114they fire on, say, one-second boundaries only.
1115.Sp
1116Example: we only need 0.1s timeout granularity, and we wish not to poll
1117more often than 100 times per second:
1118.Sp
1119.Vb 2
1120\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1121\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1122.Ve
1123.IP "ev_invoke_pending (loop)" 4
1124.IX Item "ev_invoke_pending (loop)"
1125This call will simply invoke all pending watchers while resetting their
1126pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1127but when overriding the invoke callback this call comes handy. This
1128function can be invoked from a watcher \- this can be useful for example
1129when you want to do some lengthy calculation and want to pass further
1130event handling to another thread (you still have to make sure only one
1131thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1132.IP "int ev_pending_count (loop)" 4
1133.IX Item "int ev_pending_count (loop)"
1134Returns the number of pending watchers \- zero indicates that no watchers
1135are pending.
1136.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1137.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1138This overrides the invoke pending functionality of the loop: Instead of
1139invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1140this callback instead. This is useful, for example, when you want to
1141invoke the actual watchers inside another context (another thread etc.).
1142.Sp
1143If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1144callback.
1145.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1146.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1147Sometimes you want to share the same loop between multiple threads. This
1148can be done relatively simply by putting mutex_lock/unlock calls around
1149each call to a libev function.
1150.Sp
1151However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1152to wait for it to return. One way around this is to wake up the event
1153loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1154\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1155.Sp
1156When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1157suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1158afterwards.
1159.Sp
1160Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1161\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1162.Sp
1163While event loop modifications are allowed between invocations of
1164\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1165modifications done will affect the event loop, i.e. adding watchers will
1166have no effect on the set of file descriptors being watched, or the time
1167waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1168to take note of any changes you made.
1169.Sp
1170In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1171invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1172.Sp
1173See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1174document.
1175.IP "ev_set_userdata (loop, void *data)" 4
1176.IX Item "ev_set_userdata (loop, void *data)"
1177.PD 0
1178.IP "void *ev_userdata (loop)" 4
1179.IX Item "void *ev_userdata (loop)"
1180.PD
1181Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1182\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1183\&\f(CW0\fR.
1184.Sp
1185These two functions can be used to associate arbitrary data with a loop,
1186and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1187\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1188any other purpose as well.
1189.IP "ev_verify (loop)" 4
1190.IX Item "ev_verify (loop)"
1191This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1192compiled in, which is the default for non-minimal builds. It tries to go
1193through all internal structures and checks them for validity. If anything
1194is found to be inconsistent, it will print an error message to standard
1195error and call \f(CW\*(C`abort ()\*(C'\fR.
1196.Sp
1197This can be used to catch bugs inside libev itself: under normal
1198circumstances, this function will never abort as of course libev keeps its
1199data structures consistent.
809.SH "ANATOMY OF A WATCHER" 1200.SH "ANATOMY OF A WATCHER"
810.IX Header "ANATOMY OF A WATCHER" 1201.IX Header "ANATOMY OF A WATCHER"
1202In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1203watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1204watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1205.PP
811A watcher is a structure that you create and register to record your 1206A watcher is an opaque structure that you allocate and register to record
812interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1207your interest in some event. To make a concrete example, imagine you want
813become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1208to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1209for that:
814.PP 1210.PP
815.Vb 5 1211.Vb 5
816\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1212\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
817\& { 1213\& {
818\& ev_io_stop (w); 1214\& ev_io_stop (w);
819\& ev_unloop (loop, EVUNLOOP_ALL); 1215\& ev_break (loop, EVBREAK_ALL);
820\& } 1216\& }
821.Ve 1217\&
822.PP
823.Vb 6
824\& struct ev_loop *loop = ev_default_loop (0); 1218\& struct ev_loop *loop = ev_default_loop (0);
1219\&
825\& struct ev_io stdin_watcher; 1220\& ev_io stdin_watcher;
1221\&
826\& ev_init (&stdin_watcher, my_cb); 1222\& ev_init (&stdin_watcher, my_cb);
827\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1223\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
828\& ev_io_start (loop, &stdin_watcher); 1224\& ev_io_start (loop, &stdin_watcher);
1225\&
829\& ev_loop (loop, 0); 1226\& ev_run (loop, 0);
830.Ve 1227.Ve
831.PP 1228.PP
832As you can see, you are responsible for allocating the memory for your 1229As you can see, you are responsible for allocating the memory for your
833watcher structures (and it is usually a bad idea to do this on the stack, 1230watcher structures (and it is \fIusually\fR a bad idea to do this on the
834although this can sometimes be quite valid). 1231stack).
835.PP 1232.PP
1233Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1234or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1235.PP
836Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1236Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
837(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1237*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
838callback gets invoked each time the event occurs (or, in the case of io 1238invoked each time the event occurs (or, in the case of I/O watchers, each
839watchers, each time the event loop detects that the file descriptor given 1239time the event loop detects that the file descriptor given is readable
840is readable and/or writable). 1240and/or writable).
841.PP 1241.PP
842Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1242Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
843with arguments specific to this watcher type. There is also a macro 1243macro to configure it, with arguments specific to the watcher type. There
844to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1244is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
845(watcher *, callback, ...)\*(C'\fR.
846.PP 1245.PP
847To make the watcher actually watch out for events, you have to start it 1246To make the watcher actually watch out for events, you have to start it
848with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1247with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
849*)\*(C'\fR), and you can stop watching for events at any time by calling the 1248*)\*(C'\fR), and you can stop watching for events at any time by calling the
850corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1249corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
851.PP 1250.PP
852As long as your watcher is active (has been started but not stopped) you 1251As long as your watcher is active (has been started but not stopped) you
853must not touch the values stored in it. Most specifically you must never 1252must not touch the values stored in it. Most specifically you must never
854reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1253reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
855.PP 1254.PP
856Each and every callback receives the event loop pointer as first, the 1255Each and every callback receives the event loop pointer as first, the
857registered watcher structure as second, and a bitset of received events as 1256registered watcher structure as second, and a bitset of received events as
858third argument. 1257third argument.
859.PP 1258.PP
… …
868.el .IP "\f(CWEV_WRITE\fR" 4 1267.el .IP "\f(CWEV_WRITE\fR" 4
869.IX Item "EV_WRITE" 1268.IX Item "EV_WRITE"
870.PD 1269.PD
871The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1270The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
872writable. 1271writable.
873.ie n .IP """EV_TIMEOUT""" 4 1272.ie n .IP """EV_TIMER""" 4
874.el .IP "\f(CWEV_TIMEOUT\fR" 4 1273.el .IP "\f(CWEV_TIMER\fR" 4
875.IX Item "EV_TIMEOUT" 1274.IX Item "EV_TIMER"
876The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1275The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
877.ie n .IP """EV_PERIODIC""" 4 1276.ie n .IP """EV_PERIODIC""" 4
878.el .IP "\f(CWEV_PERIODIC\fR" 4 1277.el .IP "\f(CWEV_PERIODIC\fR" 4
879.IX Item "EV_PERIODIC" 1278.IX Item "EV_PERIODIC"
880The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1279The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
900.PD 0 1299.PD 0
901.ie n .IP """EV_CHECK""" 4 1300.ie n .IP """EV_CHECK""" 4
902.el .IP "\f(CWEV_CHECK\fR" 4 1301.el .IP "\f(CWEV_CHECK\fR" 4
903.IX Item "EV_CHECK" 1302.IX Item "EV_CHECK"
904.PD 1303.PD
905All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1304All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
906to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1305gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
907\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1306just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1307for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1308watchers invoked before the event loop sleeps or polls for new events, and
1309\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1310or lower priority within an event loop iteration.
1311.Sp
908received events. Callbacks of both watcher types can start and stop as 1312Callbacks of both watcher types can start and stop as many watchers as
909many watchers as they want, and all of them will be taken into account 1313they want, and all of them will be taken into account (for example, a
910(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1314\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
911\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1315blocking).
912.ie n .IP """EV_EMBED""" 4 1316.ie n .IP """EV_EMBED""" 4
913.el .IP "\f(CWEV_EMBED\fR" 4 1317.el .IP "\f(CWEV_EMBED\fR" 4
914.IX Item "EV_EMBED" 1318.IX Item "EV_EMBED"
915The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1319The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
916.ie n .IP """EV_FORK""" 4 1320.ie n .IP """EV_FORK""" 4
917.el .IP "\f(CWEV_FORK\fR" 4 1321.el .IP "\f(CWEV_FORK\fR" 4
918.IX Item "EV_FORK" 1322.IX Item "EV_FORK"
919The event loop has been resumed in the child process after fork (see 1323The event loop has been resumed in the child process after fork (see
920\&\f(CW\*(C`ev_fork\*(C'\fR). 1324\&\f(CW\*(C`ev_fork\*(C'\fR).
1325.ie n .IP """EV_CLEANUP""" 4
1326.el .IP "\f(CWEV_CLEANUP\fR" 4
1327.IX Item "EV_CLEANUP"
1328The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1329.ie n .IP """EV_ASYNC""" 4
1330.el .IP "\f(CWEV_ASYNC\fR" 4
1331.IX Item "EV_ASYNC"
1332The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1333.ie n .IP """EV_CUSTOM""" 4
1334.el .IP "\f(CWEV_CUSTOM\fR" 4
1335.IX Item "EV_CUSTOM"
1336Not ever sent (or otherwise used) by libev itself, but can be freely used
1337by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
921.ie n .IP """EV_ERROR""" 4 1338.ie n .IP """EV_ERROR""" 4
922.el .IP "\f(CWEV_ERROR\fR" 4 1339.el .IP "\f(CWEV_ERROR\fR" 4
923.IX Item "EV_ERROR" 1340.IX Item "EV_ERROR"
924An unspecified error has occured, the watcher has been stopped. This might 1341An unspecified error has occurred, the watcher has been stopped. This might
925happen because the watcher could not be properly started because libev 1342happen because the watcher could not be properly started because libev
926ran out of memory, a file descriptor was found to be closed or any other 1343ran out of memory, a file descriptor was found to be closed or any other
1344problem. Libev considers these application bugs.
1345.Sp
927problem. You best act on it by reporting the problem and somehow coping 1346You best act on it by reporting the problem and somehow coping with the
928with the watcher being stopped. 1347watcher being stopped. Note that well-written programs should not receive
1348an error ever, so when your watcher receives it, this usually indicates a
1349bug in your program.
929.Sp 1350.Sp
930Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1351Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
931for example it might indicate that a fd is readable or writable, and if 1352example it might indicate that a fd is readable or writable, and if your
932your callbacks is well-written it can just attempt the operation and cope 1353callbacks is well-written it can just attempt the operation and cope with
933with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1354the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
934programs, though, so beware. 1355programs, though, as the fd could already be closed and reused for another
1356thing, so beware.
935.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1357.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
936.IX Subsection "GENERIC WATCHER FUNCTIONS" 1358.IX Subsection "GENERIC WATCHER FUNCTIONS"
937In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
938e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
939.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1359.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
940.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1360.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
941.IX Item "ev_init (ev_TYPE *watcher, callback)" 1361.IX Item "ev_init (ev_TYPE *watcher, callback)"
942This macro initialises the generic portion of a watcher. The contents 1362This macro initialises the generic portion of a watcher. The contents
943of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1363of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
947which rolls both calls into one. 1367which rolls both calls into one.
948.Sp 1368.Sp
949You can reinitialise a watcher at any time as long as it has been stopped 1369You can reinitialise a watcher at any time as long as it has been stopped
950(or never started) and there are no pending events outstanding. 1370(or never started) and there are no pending events outstanding.
951.Sp 1371.Sp
952The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1372The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
953int revents)\*(C'\fR. 1373int revents)\*(C'\fR.
1374.Sp
1375Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1376.Sp
1377.Vb 3
1378\& ev_io w;
1379\& ev_init (&w, my_cb);
1380\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1381.Ve
954.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1382.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
955.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1383.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
956.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1384.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
957This macro initialises the type-specific parts of a watcher. You need to 1385This macro initialises the type-specific parts of a watcher. You need to
958call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1386call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
959call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1387call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
960macro on a watcher that is active (it can be pending, however, which is a 1388macro on a watcher that is active (it can be pending, however, which is a
961difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1389difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
962.Sp 1390.Sp
963Although some watcher types do not have type-specific arguments 1391Although some watcher types do not have type-specific arguments
964(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1392(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1393.Sp
1394See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
965.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1395.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
966.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1396.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
967.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1397.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
968This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1398This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
969calls into a single call. This is the most convinient method to initialise 1399calls into a single call. This is the most convenient method to initialise
970a watcher. The same limitations apply, of course. 1400a watcher. The same limitations apply, of course.
1401.Sp
1402Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1403.Sp
1404.Vb 1
1405\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1406.Ve
971.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1407.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
972.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1408.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
973.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1409.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
974Starts (activates) the given watcher. Only active watchers will receive 1410Starts (activates) the given watcher. Only active watchers will receive
975events. If the watcher is already active nothing will happen. 1411events. If the watcher is already active nothing will happen.
1412.Sp
1413Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1414whole section.
1415.Sp
1416.Vb 1
1417\& ev_io_start (EV_DEFAULT_UC, &w);
1418.Ve
976.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1419.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
977.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1420.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
978.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1421.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
979Stops the given watcher again (if active) and clears the pending 1422Stops the given watcher if active, and clears the pending status (whether
1423the watcher was active or not).
1424.Sp
980status. It is possible that stopped watchers are pending (for example, 1425It is possible that stopped watchers are pending \- for example,
981non-repeating timers are being stopped when they become pending), but 1426non-repeating timers are being stopped when they become pending \- but
982\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1427calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
983you want to free or reuse the memory used by the watcher it is therefore a 1428pending. If you want to free or reuse the memory used by the watcher it is
984good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1429therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
985.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1430.IP "bool ev_is_active (ev_TYPE *watcher)" 4
986.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1431.IX Item "bool ev_is_active (ev_TYPE *watcher)"
987Returns a true value iff the watcher is active (i.e. it has been started 1432Returns a true value iff the watcher is active (i.e. it has been started
988and not yet been stopped). As long as a watcher is active you must not modify 1433and not yet been stopped). As long as a watcher is active you must not modify
989it. 1434it.
… …
996make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR 1441make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
997it). 1442it).
998.IP "callback ev_cb (ev_TYPE *watcher)" 4 1443.IP "callback ev_cb (ev_TYPE *watcher)" 4
999.IX Item "callback ev_cb (ev_TYPE *watcher)" 1444.IX Item "callback ev_cb (ev_TYPE *watcher)"
1000Returns the callback currently set on the watcher. 1445Returns the callback currently set on the watcher.
1001.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1446.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1002.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1447.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1003Change the callback. You can change the callback at virtually any time 1448Change the callback. You can change the callback at virtually any time
1004(modulo threads). 1449(modulo threads).
1005.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 1450.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1006.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" 1451.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1007.PD 0 1452.PD 0
1008.IP "int ev_priority (ev_TYPE *watcher)" 4 1453.IP "int ev_priority (ev_TYPE *watcher)" 4
1009.IX Item "int ev_priority (ev_TYPE *watcher)" 1454.IX Item "int ev_priority (ev_TYPE *watcher)"
1010.PD 1455.PD
1011Set and query the priority of the watcher. The priority is a small 1456Set and query the priority of the watcher. The priority is a small
1012integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR 1457integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1013(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked 1458(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1014before watchers with lower priority, but priority will not keep watchers 1459before watchers with lower priority, but priority will not keep watchers
1015from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). 1460from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1016.Sp 1461.Sp
1017This means that priorities are \fIonly\fR used for ordering callback
1018invocation after new events have been received. This is useful, for
1019example, to reduce latency after idling, or more often, to bind two
1020watchers on the same event and make sure one is called first.
1021.Sp
1022If you need to suppress invocation when higher priority events are pending 1462If you need to suppress invocation when higher priority events are pending
1023you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. 1463you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1024.Sp 1464.Sp
1025You \fImust not\fR change the priority of a watcher as long as it is active or 1465You \fImust not\fR change the priority of a watcher as long as it is active or
1026pending. 1466pending.
1027.Sp 1467.Sp
1468Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1469fine, as long as you do not mind that the priority value you query might
1470or might not have been clamped to the valid range.
1471.Sp
1028The default priority used by watchers when no priority has been set is 1472The default priority used by watchers when no priority has been set is
1029always \f(CW0\fR, which is supposed to not be too high and not be too low :). 1473always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1030.Sp 1474.Sp
1031Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is 1475See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1032fine, as long as you do not mind that the priority value you query might 1476priorities.
1033or might not have been adjusted to be within valid range.
1034.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 1477.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1035.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" 1478.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1036Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither 1479Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1037\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback 1480\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1038can deal with that fact. 1481can deal with that fact, as both are simply passed through to the
1482callback.
1039.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 1483.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1040.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" 1484.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1041If the watcher is pending, this function returns clears its pending status 1485If the watcher is pending, this function clears its pending status and
1042and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the 1486returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1043watcher isn't pending it does nothing and returns \f(CW0\fR. 1487watcher isn't pending it does nothing and returns \f(CW0\fR.
1044.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1488.Sp
1045.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1489Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1046Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1490callback to be invoked, which can be accomplished with this function.
1047and read at any time, libev will completely ignore it. This can be used 1491.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1048to associate arbitrary data with your watcher. If you need more data and 1492.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1049don't want to allocate memory and store a pointer to it in that data 1493Feeds the given event set into the event loop, as if the specified event
1050member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1494had happened for the specified watcher (which must be a pointer to an
1051data: 1495initialised but not necessarily started event watcher). Obviously you must
1496not free the watcher as long as it has pending events.
1497.Sp
1498Stopping the watcher, letting libev invoke it, or calling
1499\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1500not started in the first place.
1501.Sp
1502See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1503functions that do not need a watcher.
1052.PP 1504.PP
1505See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1506\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1507.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1508.IX Subsection "WATCHER STATES"
1509There are various watcher states mentioned throughout this manual \-
1510active, pending and so on. In this section these states and the rules to
1511transition between them will be described in more detail \- and while these
1512rules might look complicated, they usually do \*(L"the right thing\*(R".
1513.IP "initialised" 4
1514.IX Item "initialised"
1515Before a watcher can be registered with the event loop it has to be
1516initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1517\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1518.Sp
1519In this state it is simply some block of memory that is suitable for
1520use in an event loop. It can be moved around, freed, reused etc. at
1521will \- as long as you either keep the memory contents intact, or call
1522\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1523.IP "started/running/active" 4
1524.IX Item "started/running/active"
1525Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1526property of the event loop, and is actively waiting for events. While in
1527this state it cannot be accessed (except in a few documented ways), moved,
1528freed or anything else \- the only legal thing is to keep a pointer to it,
1529and call libev functions on it that are documented to work on active watchers.
1530.IP "pending" 4
1531.IX Item "pending"
1532If a watcher is active and libev determines that an event it is interested
1533in has occurred (such as a timer expiring), it will become pending. It will
1534stay in this pending state until either it is stopped or its callback is
1535about to be invoked, so it is not normally pending inside the watcher
1536callback.
1537.Sp
1538The watcher might or might not be active while it is pending (for example,
1539an expired non-repeating timer can be pending but no longer active). If it
1540is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1541but it is still property of the event loop at this time, so cannot be
1542moved, freed or reused. And if it is active the rules described in the
1543previous item still apply.
1544.Sp
1545It is also possible to feed an event on a watcher that is not active (e.g.
1546via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1547active.
1548.IP "stopped" 4
1549.IX Item "stopped"
1550A watcher can be stopped implicitly by libev (in which case it might still
1551be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1552latter will clear any pending state the watcher might be in, regardless
1553of whether it was active or not, so stopping a watcher explicitly before
1554freeing it is often a good idea.
1555.Sp
1556While stopped (and not pending) the watcher is essentially in the
1557initialised state, that is, it can be reused, moved, modified in any way
1558you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1559it again).
1560.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1561.IX Subsection "WATCHER PRIORITY MODELS"
1562Many event loops support \fIwatcher priorities\fR, which are usually small
1563integers that influence the ordering of event callback invocation
1564between watchers in some way, all else being equal.
1565.PP
1566In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1567description for the more technical details such as the actual priority
1568range.
1569.PP
1570There are two common ways how these these priorities are being interpreted
1571by event loops:
1572.PP
1573In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1574of lower priority watchers, which means as long as higher priority
1575watchers receive events, lower priority watchers are not being invoked.
1576.PP
1577The less common only-for-ordering model uses priorities solely to order
1578callback invocation within a single event loop iteration: Higher priority
1579watchers are invoked before lower priority ones, but they all get invoked
1580before polling for new events.
1581.PP
1582Libev uses the second (only-for-ordering) model for all its watchers
1583except for idle watchers (which use the lock-out model).
1584.PP
1585The rationale behind this is that implementing the lock-out model for
1586watchers is not well supported by most kernel interfaces, and most event
1587libraries will just poll for the same events again and again as long as
1588their callbacks have not been executed, which is very inefficient in the
1589common case of one high-priority watcher locking out a mass of lower
1590priority ones.
1591.PP
1592Static (ordering) priorities are most useful when you have two or more
1593watchers handling the same resource: a typical usage example is having an
1594\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1595timeouts. Under load, data might be received while the program handles
1596other jobs, but since timers normally get invoked first, the timeout
1597handler will be executed before checking for data. In that case, giving
1598the timer a lower priority than the I/O watcher ensures that I/O will be
1599handled first even under adverse conditions (which is usually, but not
1600always, what you want).
1601.PP
1602Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1603will only be executed when no same or higher priority watchers have
1604received events, they can be used to implement the \*(L"lock-out\*(R" model when
1605required.
1606.PP
1607For example, to emulate how many other event libraries handle priorities,
1608you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1609the normal watcher callback, you just start the idle watcher. The real
1610processing is done in the idle watcher callback. This causes libev to
1611continuously poll and process kernel event data for the watcher, but when
1612the lock-out case is known to be rare (which in turn is rare :), this is
1613workable.
1614.PP
1615Usually, however, the lock-out model implemented that way will perform
1616miserably under the type of load it was designed to handle. In that case,
1617it might be preferable to stop the real watcher before starting the
1618idle watcher, so the kernel will not have to process the event in case
1619the actual processing will be delayed for considerable time.
1620.PP
1621Here is an example of an I/O watcher that should run at a strictly lower
1622priority than the default, and which should only process data when no
1623other events are pending:
1624.PP
1053.Vb 7 1625.Vb 2
1054\& struct my_io 1626\& ev_idle idle; // actual processing watcher
1055\& { 1627\& ev_io io; // actual event watcher
1056\& struct ev_io io; 1628\&
1057\& int otherfd;
1058\& void *somedata;
1059\& struct whatever *mostinteresting;
1060\& }
1061.Ve
1062.PP
1063And since your callback will be called with a pointer to the watcher, you
1064can cast it back to your own type:
1065.PP
1066.Vb 5
1067\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1068\& {
1069\& struct my_io *w = (struct my_io *)w_;
1070\& ...
1071\& }
1072.Ve
1073.PP
1074More interesting and less C\-conformant ways of casting your callback type
1075instead have been omitted.
1076.PP
1077Another common scenario is having some data structure with multiple
1078watchers:
1079.PP
1080.Vb 6
1081\& struct my_biggy
1082\& {
1083\& int some_data;
1084\& ev_timer t1;
1085\& ev_timer t2;
1086\& }
1087.Ve
1088.PP
1089In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1090you need to use \f(CW\*(C`offsetof\*(C'\fR:
1091.PP
1092.Vb 1
1093\& #include <stddef.h>
1094.Ve
1095.PP
1096.Vb 6
1097\& static void 1629\& static void
1098\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1630\& io_cb (EV_P_ ev_io *w, int revents)
1099\& { 1631\& {
1100\& struct my_biggy big = (struct my_biggy * 1632\& // stop the I/O watcher, we received the event, but
1101\& (((char *)w) - offsetof (struct my_biggy, t1)); 1633\& // are not yet ready to handle it.
1634\& ev_io_stop (EV_A_ w);
1635\&
1636\& // start the idle watcher to handle the actual event.
1637\& // it will not be executed as long as other watchers
1638\& // with the default priority are receiving events.
1639\& ev_idle_start (EV_A_ &idle);
1102\& } 1640\& }
1103.Ve 1641\&
1104.PP
1105.Vb 6
1106\& static void 1642\& static void
1107\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1643\& idle_cb (EV_P_ ev_idle *w, int revents)
1108\& { 1644\& {
1109\& struct my_biggy big = (struct my_biggy * 1645\& // actual processing
1110\& (((char *)w) - offsetof (struct my_biggy, t2)); 1646\& read (STDIN_FILENO, ...);
1647\&
1648\& // have to start the I/O watcher again, as
1649\& // we have handled the event
1650\& ev_io_start (EV_P_ &io);
1111\& } 1651\& }
1652\&
1653\& // initialisation
1654\& ev_idle_init (&idle, idle_cb);
1655\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1656\& ev_io_start (EV_DEFAULT_ &io);
1112.Ve 1657.Ve
1658.PP
1659In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1660low-priority connections can not be locked out forever under load. This
1661enables your program to keep a lower latency for important connections
1662during short periods of high load, while not completely locking out less
1663important ones.
1113.SH "WATCHER TYPES" 1664.SH "WATCHER TYPES"
1114.IX Header "WATCHER TYPES" 1665.IX Header "WATCHER TYPES"
1115This section describes each watcher in detail, but will not repeat 1666This section describes each watcher in detail, but will not repeat
1116information given in the last section. Any initialisation/set macros, 1667information given in the last section. Any initialisation/set macros,
1117functions and members specific to the watcher type are explained. 1668functions and members specific to the watcher type are explained.
… …
1122watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1673watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1123means you can expect it to have some sensible content while the watcher 1674means you can expect it to have some sensible content while the watcher
1124is active, but you can also modify it. Modifying it may not do something 1675is active, but you can also modify it. Modifying it may not do something
1125sensible or take immediate effect (or do anything at all), but libev will 1676sensible or take immediate effect (or do anything at all), but libev will
1126not crash or malfunction in any way. 1677not crash or malfunction in any way.
1127.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1678.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1128.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1679.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1129.IX Subsection "ev_io - is this file descriptor readable or writable?" 1680.IX Subsection "ev_io - is this file descriptor readable or writable?"
1130I/O watchers check whether a file descriptor is readable or writable 1681I/O watchers check whether a file descriptor is readable or writable
1131in each iteration of the event loop, or, more precisely, when reading 1682in each iteration of the event loop, or, more precisely, when reading
1132would not block the process and writing would at least be able to write 1683would not block the process and writing would at least be able to write
1133some data. This behaviour is called level-triggering because you keep 1684some data. This behaviour is called level-triggering because you keep
… …
1138In general you can register as many read and/or write event watchers per 1689In general you can register as many read and/or write event watchers per
1139fd as you want (as long as you don't confuse yourself). Setting all file 1690fd as you want (as long as you don't confuse yourself). Setting all file
1140descriptors to non-blocking mode is also usually a good idea (but not 1691descriptors to non-blocking mode is also usually a good idea (but not
1141required if you know what you are doing). 1692required if you know what you are doing).
1142.PP 1693.PP
1143If you must do this, then force the use of a known-to-be-good backend
1144(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1145\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1146.PP
1147Another thing you have to watch out for is that it is quite easy to 1694Another thing you have to watch out for is that it is quite easy to
1148receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1695receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1149be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1696be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1150because there is no data. Not only are some backends known to create a 1697because there is no data. It is very easy to get into this situation even
1151lot of those (for example solaris ports), it is very easy to get into 1698with a relatively standard program structure. Thus it is best to always
1152this situation even with a relatively standard program structure. Thus 1699use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1153it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1154\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1700preferable to a program hanging until some data arrives.
1155.PP 1701.PP
1156If you cannot run the fd in non-blocking mode (for example you should not 1702If you cannot run the fd in non-blocking mode (for example you should
1157play around with an Xlib connection), then you have to seperately re-test 1703not play around with an Xlib connection), then you have to separately
1158whether a file descriptor is really ready with a known-to-be good interface 1704re-test whether a file descriptor is really ready with a known-to-be good
1159such as poll (fortunately in our Xlib example, Xlib already does this on 1705interface such as poll (fortunately in the case of Xlib, it already does
1160its own, so its quite safe to use). 1706this on its own, so its quite safe to use). Some people additionally
1707use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1708indefinitely.
1709.PP
1710But really, best use non-blocking mode.
1161.PP 1711.PP
1162\fIThe special problem of disappearing file descriptors\fR 1712\fIThe special problem of disappearing file descriptors\fR
1163.IX Subsection "The special problem of disappearing file descriptors" 1713.IX Subsection "The special problem of disappearing file descriptors"
1164.PP 1714.PP
1165Some backends (e.g. kqueue, epoll) need to be told about closing a file 1715Some backends (e.g. kqueue, epoll) need to be told about closing a file
1166descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means, 1716descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1167such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file 1717such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1168descriptor, but when it goes away, the operating system will silently drop 1718descriptor, but when it goes away, the operating system will silently drop
1169this interest. If another file descriptor with the same number then is 1719this interest. If another file descriptor with the same number then is
1170registered with libev, there is no efficient way to see that this is, in 1720registered with libev, there is no efficient way to see that this is, in
1171fact, a different file descriptor. 1721fact, a different file descriptor.
1172.PP 1722.PP
… …
1191.PP 1741.PP
1192There is no workaround possible except not registering events 1742There is no workaround possible except not registering events
1193for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to 1743for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1194\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. 1744\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1195.PP 1745.PP
1746\fIThe special problem of files\fR
1747.IX Subsection "The special problem of files"
1748.PP
1749Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1750representing files, and expect it to become ready when their program
1751doesn't block on disk accesses (which can take a long time on their own).
1752.PP
1753However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1754notification as soon as the kernel knows whether and how much data is
1755there, and in the case of open files, that's always the case, so you
1756always get a readiness notification instantly, and your read (or possibly
1757write) will still block on the disk I/O.
1758.PP
1759Another way to view it is that in the case of sockets, pipes, character
1760devices and so on, there is another party (the sender) that delivers data
1761on its own, but in the case of files, there is no such thing: the disk
1762will not send data on its own, simply because it doesn't know what you
1763wish to read \- you would first have to request some data.
1764.PP
1765Since files are typically not-so-well supported by advanced notification
1766mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1767to files, even though you should not use it. The reason for this is
1768convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1769usually a tty, often a pipe, but also sometimes files or special devices
1770(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1771\&\fI/dev/urandom\fR), and even though the file might better be served with
1772asynchronous I/O instead of with non-blocking I/O, it is still useful when
1773it \*(L"just works\*(R" instead of freezing.
1774.PP
1775So avoid file descriptors pointing to files when you know it (e.g. use
1776libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1777when you rarely read from a file instead of from a socket, and want to
1778reuse the same code path.
1779.PP
1196\fIThe special problem of fork\fR 1780\fIThe special problem of fork\fR
1197.IX Subsection "The special problem of fork" 1781.IX Subsection "The special problem of fork"
1198.PP 1782.PP
1199Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit 1783Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1200useless behaviour. Libev fully supports fork, but needs to be told about 1784useless behaviour. Libev fully supports fork, but needs to be told about
1201it in the child. 1785it in the child if you want to continue to use it in the child.
1202.PP 1786.PP
1203To support fork in your programs, you either have to call 1787To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1204\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child, 1788()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1205enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or 1789\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1206\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. 1790.PP
1791\fIThe special problem of \s-1SIGPIPE\s0\fR
1792.IX Subsection "The special problem of SIGPIPE"
1793.PP
1794While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1795when writing to a pipe whose other end has been closed, your program gets
1796sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1797this is sensible behaviour, for daemons, this is usually undesirable.
1798.PP
1799So when you encounter spurious, unexplained daemon exits, make sure you
1800ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1801somewhere, as that would have given you a big clue).
1802.PP
1803\fIThe special problem of \fIaccept()\fIing when you can't\fR
1804.IX Subsection "The special problem of accept()ing when you can't"
1805.PP
1806Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1807found in post\-2004 Linux) have the peculiar behaviour of not removing a
1808connection from the pending queue in all error cases.
1809.PP
1810For example, larger servers often run out of file descriptors (because
1811of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1812rejecting the connection, leading to libev signalling readiness on
1813the next iteration again (the connection still exists after all), and
1814typically causing the program to loop at 100% \s-1CPU\s0 usage.
1815.PP
1816Unfortunately, the set of errors that cause this issue differs between
1817operating systems, there is usually little the app can do to remedy the
1818situation, and no known thread-safe method of removing the connection to
1819cope with overload is known (to me).
1820.PP
1821One of the easiest ways to handle this situation is to just ignore it
1822\&\- when the program encounters an overload, it will just loop until the
1823situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1824event-based way to handle this situation, so it's the best one can do.
1825.PP
1826A better way to handle the situation is to log any errors other than
1827\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1828messages, and continue as usual, which at least gives the user an idea of
1829what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1830the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1831usage.
1832.PP
1833If your program is single-threaded, then you could also keep a dummy file
1834descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1835when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1836close that fd, and create a new dummy fd. This will gracefully refuse
1837clients under typical overload conditions.
1838.PP
1839The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1840is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1841opportunity for a DoS attack.
1207.PP 1842.PP
1208\fIWatcher-Specific Functions\fR 1843\fIWatcher-Specific Functions\fR
1209.IX Subsection "Watcher-Specific Functions" 1844.IX Subsection "Watcher-Specific Functions"
1210.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1845.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1211.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1846.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1212.PD 0 1847.PD 0
1213.IP "ev_io_set (ev_io *, int fd, int events)" 4 1848.IP "ev_io_set (ev_io *, int fd, int events)" 4
1214.IX Item "ev_io_set (ev_io *, int fd, int events)" 1849.IX Item "ev_io_set (ev_io *, int fd, int events)"
1215.PD 1850.PD
1216Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1851Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1217rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1852receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1218\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1853\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1219.IP "int fd [read\-only]" 4 1854.IP "int fd [read\-only]" 4
1220.IX Item "int fd [read-only]" 1855.IX Item "int fd [read-only]"
1221The file descriptor being watched. 1856The file descriptor being watched.
1222.IP "int events [read\-only]" 4 1857.IP "int events [read\-only]" 4
1223.IX Item "int events [read-only]" 1858.IX Item "int events [read-only]"
1224The events being watched. 1859The events being watched.
1225.PP 1860.PP
1861\fIExamples\fR
1862.IX Subsection "Examples"
1863.PP
1226Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1864Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1227readable, but only once. Since it is likely line\-buffered, you could 1865readable, but only once. Since it is likely line-buffered, you could
1228attempt to read a whole line in the callback. 1866attempt to read a whole line in the callback.
1229.PP 1867.PP
1230.Vb 6 1868.Vb 6
1231\& static void 1869\& static void
1232\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1870\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1233\& { 1871\& {
1234\& ev_io_stop (loop, w); 1872\& ev_io_stop (loop, w);
1235\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1873\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1236\& } 1874\& }
1237.Ve 1875\&
1238.PP
1239.Vb 6
1240\& ... 1876\& ...
1241\& struct ev_loop *loop = ev_default_init (0); 1877\& struct ev_loop *loop = ev_default_init (0);
1242\& struct ev_io stdin_readable; 1878\& ev_io stdin_readable;
1243\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1879\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1244\& ev_io_start (loop, &stdin_readable); 1880\& ev_io_start (loop, &stdin_readable);
1245\& ev_loop (loop, 0); 1881\& ev_run (loop, 0);
1246.Ve 1882.Ve
1247.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1883.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1248.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1884.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1249.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1885.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1250Timer watchers are simple relative timers that generate an event after a 1886Timer watchers are simple relative timers that generate an event after a
1251given time, and optionally repeating in regular intervals after that. 1887given time, and optionally repeating in regular intervals after that.
1252.PP 1888.PP
1253The timers are based on real time, that is, if you register an event that 1889The timers are based on real time, that is, if you register an event that
1254times out after an hour and you reset your system clock to last years 1890times out after an hour and you reset your system clock to January last
1255time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1891year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1256detecting time jumps is hard, and some inaccuracies are unavoidable (the 1892detecting time jumps is hard, and some inaccuracies are unavoidable (the
1257monotonic clock option helps a lot here). 1893monotonic clock option helps a lot here).
1894.PP
1895The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1896passed (not \fIat\fR, so on systems with very low-resolution clocks this
1897might introduce a small delay, see \*(L"the special problem of being too
1898early\*(R", below). If multiple timers become ready during the same loop
1899iteration then the ones with earlier time-out values are invoked before
1900ones of the same priority with later time-out values (but this is no
1901longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1902.PP
1903\fIBe smart about timeouts\fR
1904.IX Subsection "Be smart about timeouts"
1905.PP
1906Many real-world problems involve some kind of timeout, usually for error
1907recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1908you want to raise some error after a while.
1909.PP
1910What follows are some ways to handle this problem, from obvious and
1911inefficient to smart and efficient.
1912.PP
1913In the following, a 60 second activity timeout is assumed \- a timeout that
1914gets reset to 60 seconds each time there is activity (e.g. each time some
1915data or other life sign was received).
1916.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1917.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1918This is the most obvious, but not the most simple way: In the beginning,
1919start the watcher:
1920.Sp
1921.Vb 2
1922\& ev_timer_init (timer, callback, 60., 0.);
1923\& ev_timer_start (loop, timer);
1924.Ve
1925.Sp
1926Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1927and start it again:
1928.Sp
1929.Vb 3
1930\& ev_timer_stop (loop, timer);
1931\& ev_timer_set (timer, 60., 0.);
1932\& ev_timer_start (loop, timer);
1933.Ve
1934.Sp
1935This is relatively simple to implement, but means that each time there is
1936some activity, libev will first have to remove the timer from its internal
1937data structure and then add it again. Libev tries to be fast, but it's
1938still not a constant-time operation.
1939.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1940.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1941.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1942This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1943\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1944.Sp
1945To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1946of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1947successfully read or write some data. If you go into an idle state where
1948you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1949the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1950.Sp
1951That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1952\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
1953member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1954.Sp
1955At start:
1956.Sp
1957.Vb 3
1958\& ev_init (timer, callback);
1959\& timer\->repeat = 60.;
1960\& ev_timer_again (loop, timer);
1961.Ve
1962.Sp
1963Each time there is some activity:
1964.Sp
1965.Vb 1
1966\& ev_timer_again (loop, timer);
1967.Ve
1968.Sp
1969It is even possible to change the time-out on the fly, regardless of
1970whether the watcher is active or not:
1971.Sp
1972.Vb 2
1973\& timer\->repeat = 30.;
1974\& ev_timer_again (loop, timer);
1975.Ve
1976.Sp
1977This is slightly more efficient then stopping/starting the timer each time
1978you want to modify its timeout value, as libev does not have to completely
1979remove and re-insert the timer from/into its internal data structure.
1980.Sp
1981It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1982.IP "3. Let the timer time out, but then re-arm it as required." 4
1983.IX Item "3. Let the timer time out, but then re-arm it as required."
1984This method is more tricky, but usually most efficient: Most timeouts are
1985relatively long compared to the intervals between other activity \- in
1986our example, within 60 seconds, there are usually many I/O events with
1987associated activity resets.
1988.Sp
1989In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1990but remember the time of last activity, and check for a real timeout only
1991within the callback:
1992.Sp
1993.Vb 3
1994\& ev_tstamp timeout = 60.;
1995\& ev_tstamp last_activity; // time of last activity
1996\& ev_timer timer;
1997\&
1998\& static void
1999\& callback (EV_P_ ev_timer *w, int revents)
2000\& {
2001\& // calculate when the timeout would happen
2002\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2003\&
2004\& // if negative, it means we the timeout already occurred
2005\& if (after < 0.)
2006\& {
2007\& // timeout occurred, take action
2008\& }
2009\& else
2010\& {
2011\& // callback was invoked, but there was some recent
2012\& // activity. simply restart the timer to time out
2013\& // after "after" seconds, which is the earliest time
2014\& // the timeout can occur.
2015\& ev_timer_set (w, after, 0.);
2016\& ev_timer_start (EV_A_ w);
2017\& }
2018\& }
2019.Ve
2020.Sp
2021To summarise the callback: first calculate in how many seconds the
2022timeout will occur (by calculating the absolute time when it would occur,
2023\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2024(EV_A)\*(C'\fR from that).
2025.Sp
2026If this value is negative, then we are already past the timeout, i.e. we
2027timed out, and need to do whatever is needed in this case.
2028.Sp
2029Otherwise, we now the earliest time at which the timeout would trigger,
2030and simply start the timer with this timeout value.
2031.Sp
2032In other words, each time the callback is invoked it will check whether
2033the timeout occurred. If not, it will simply reschedule itself to check
2034again at the earliest time it could time out. Rinse. Repeat.
2035.Sp
2036This scheme causes more callback invocations (about one every 60 seconds
2037minus half the average time between activity), but virtually no calls to
2038libev to change the timeout.
2039.Sp
2040To start the machinery, simply initialise the watcher and set
2041\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2042now), then call the callback, which will \*(L"do the right thing\*(R" and start
2043the timer:
2044.Sp
2045.Vb 3
2046\& last_activity = ev_now (EV_A);
2047\& ev_init (&timer, callback);
2048\& callback (EV_A_ &timer, 0);
2049.Ve
2050.Sp
2051When there is some activity, simply store the current time in
2052\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2053.Sp
2054.Vb 2
2055\& if (activity detected)
2056\& last_activity = ev_now (EV_A);
2057.Ve
2058.Sp
2059When your timeout value changes, then the timeout can be changed by simply
2060providing a new value, stopping the timer and calling the callback, which
2061will again do the right thing (for example, time out immediately :).
2062.Sp
2063.Vb 3
2064\& timeout = new_value;
2065\& ev_timer_stop (EV_A_ &timer);
2066\& callback (EV_A_ &timer, 0);
2067.Ve
2068.Sp
2069This technique is slightly more complex, but in most cases where the
2070time-out is unlikely to be triggered, much more efficient.
2071.IP "4. Wee, just use a double-linked list for your timeouts." 4
2072.IX Item "4. Wee, just use a double-linked list for your timeouts."
2073If there is not one request, but many thousands (millions...), all
2074employing some kind of timeout with the same timeout value, then one can
2075do even better:
2076.Sp
2077When starting the timeout, calculate the timeout value and put the timeout
2078at the \fIend\fR of the list.
2079.Sp
2080Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2081the list is expected to fire (for example, using the technique #3).
2082.Sp
2083When there is some activity, remove the timer from the list, recalculate
2084the timeout, append it to the end of the list again, and make sure to
2085update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2086.Sp
2087This way, one can manage an unlimited number of timeouts in O(1) time for
2088starting, stopping and updating the timers, at the expense of a major
2089complication, and having to use a constant timeout. The constant timeout
2090ensures that the list stays sorted.
2091.PP
2092So which method the best?
2093.PP
2094Method #2 is a simple no-brain-required solution that is adequate in most
2095situations. Method #3 requires a bit more thinking, but handles many cases
2096better, and isn't very complicated either. In most case, choosing either
2097one is fine, with #3 being better in typical situations.
2098.PP
2099Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2100rather complicated, but extremely efficient, something that really pays
2101off after the first million or so of active timers, i.e. it's usually
2102overkill :)
2103.PP
2104\fIThe special problem of being too early\fR
2105.IX Subsection "The special problem of being too early"
2106.PP
2107If you ask a timer to call your callback after three seconds, then
2108you expect it to be invoked after three seconds \- but of course, this
2109cannot be guaranteed to infinite precision. Less obviously, it cannot be
2110guaranteed to any precision by libev \- imagine somebody suspending the
2111process with a \s-1STOP\s0 signal for a few hours for example.
2112.PP
2113So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2114delay has occurred, but cannot guarantee this.
2115.PP
2116A less obvious failure mode is calling your callback too early: many event
2117loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2118this can cause your callback to be invoked much earlier than you would
2119expect.
2120.PP
2121To see why, imagine a system with a clock that only offers full second
2122resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2123yourself). If you schedule a one-second timer at the time 500.9, then the
2124event loop will schedule your timeout to elapse at a system time of 500
2125(500.9 truncated to the resolution) + 1, or 501.
2126.PP
2127If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2128501\*(R" and invoke the callback 0.1s after it was started, even though a
2129one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2130intentions.
2131.PP
2132This is the reason why libev will never invoke the callback if the elapsed
2133delay equals the requested delay, but only when the elapsed delay is
2134larger than the requested delay. In the example above, libev would only invoke
2135the callback at system time 502, or 1.1s after the timer was started.
2136.PP
2137So, while libev cannot guarantee that your callback will be invoked
2138exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2139delay has actually elapsed, or in other words, it always errs on the \*(L"too
2140late\*(R" side of things.
2141.PP
2142\fIThe special problem of time updates\fR
2143.IX Subsection "The special problem of time updates"
2144.PP
2145Establishing the current time is a costly operation (it usually takes
2146at least one system call): \s-1EV\s0 therefore updates its idea of the current
2147time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2148growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2149lots of events in one iteration.
1258.PP 2150.PP
1259The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2151The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1260time. This is usually the right thing as this timestamp refers to the time 2152time. This is usually the right thing as this timestamp refers to the time
1261of the event triggering whatever timeout you are modifying/starting. If 2153of the event triggering whatever timeout you are modifying/starting. If
1262you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2154you suspect event processing to be delayed and you \fIneed\fR to base the
1263on the current time, use something like this to adjust for this: 2155timeout on the current time, use something like this to adjust for this:
1264.PP 2156.PP
1265.Vb 1 2157.Vb 1
1266\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2158\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1267.Ve 2159.Ve
1268.PP 2160.PP
1269The callback is guarenteed to be invoked only when its timeout has passed, 2161If the event loop is suspended for a long time, you can also force an
1270but if multiple timers become ready during the same loop iteration then 2162update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1271order of execution is undefined. 2163()\*(C'\fR.
2164.PP
2165\fIThe special problem of unsynchronised clocks\fR
2166.IX Subsection "The special problem of unsynchronised clocks"
2167.PP
2168Modern systems have a variety of clocks \- libev itself uses the normal
2169\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2170jumps).
2171.PP
2172Neither of these clocks is synchronised with each other or any other clock
2173on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2174than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2175a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2176than a directly following call to \f(CW\*(C`time\*(C'\fR.
2177.PP
2178The moral of this is to only compare libev-related timestamps with
2179\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2180a second or so.
2181.PP
2182One more problem arises due to this lack of synchronisation: if libev uses
2183the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2184or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2185invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2186.PP
2187This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2188libev makes sure your callback is not invoked before the delay happened,
2189\&\fImeasured according to the real time\fR, not the system clock.
2190.PP
2191If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2192connection after 100 seconds\*(R") then this shouldn't bother you as it is
2193exactly the right behaviour.
2194.PP
2195If you want to compare wall clock/system timestamps to your timers, then
2196you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2197time, where your comparisons will always generate correct results.
2198.PP
2199\fIThe special problems of suspended animation\fR
2200.IX Subsection "The special problems of suspended animation"
2201.PP
2202When you leave the server world it is quite customary to hit machines that
2203can suspend/hibernate \- what happens to the clocks during such a suspend?
2204.PP
2205Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2206all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2207to run until the system is suspended, but they will not advance while the
2208system is suspended. That means, on resume, it will be as if the program
2209was frozen for a few seconds, but the suspend time will not be counted
2210towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2211clock advanced as expected, but if it is used as sole clocksource, then a
2212long suspend would be detected as a time jump by libev, and timers would
2213be adjusted accordingly.
2214.PP
2215I would not be surprised to see different behaviour in different between
2216operating systems, \s-1OS\s0 versions or even different hardware.
2217.PP
2218The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2219time jump in the monotonic clocks and the realtime clock. If the program
2220is suspended for a very long time, and monotonic clock sources are in use,
2221then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2222will be counted towards the timers. When no monotonic clock source is in
2223use, then libev will again assume a timejump and adjust accordingly.
2224.PP
2225It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2226and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2227deterministic behaviour in this case (you can do nothing against
2228\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1272.PP 2229.PP
1273\fIWatcher-Specific Functions and Data Members\fR 2230\fIWatcher-Specific Functions and Data Members\fR
1274.IX Subsection "Watcher-Specific Functions and Data Members" 2231.IX Subsection "Watcher-Specific Functions and Data Members"
1275.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2232.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1276.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2233.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1277.PD 0 2234.PD 0
1278.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2235.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1279.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2236.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1280.PD 2237.PD
1281Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2238Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1282\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2239is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1283timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2240reached. If it is positive, then the timer will automatically be
1284later, again, and again, until stopped manually. 2241configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2242until stopped manually.
1285.Sp 2243.Sp
1286The timer itself will do a best-effort at avoiding drift, that is, if you 2244The timer itself will do a best-effort at avoiding drift, that is, if
1287configure a timer to trigger every 10 seconds, then it will trigger at 2245you configure a timer to trigger every 10 seconds, then it will normally
1288exactly 10 second intervals. If, however, your program cannot keep up with 2246trigger at exactly 10 second intervals. If, however, your program cannot
1289the timer (because it takes longer than those 10 seconds to do stuff) the 2247keep up with the timer (because it takes longer than those 10 seconds to
1290timer will not fire more than once per event loop iteration. 2248do stuff) the timer will not fire more than once per event loop iteration.
1291.IP "ev_timer_again (loop)" 4 2249.IP "ev_timer_again (loop, ev_timer *)" 4
1292.IX Item "ev_timer_again (loop)" 2250.IX Item "ev_timer_again (loop, ev_timer *)"
1293This will act as if the timer timed out and restart it again if it is 2251This will act as if the timer timed out, and restarts it again if it is
1294repeating. The exact semantics are: 2252repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2253timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1295.Sp 2254.Sp
2255The exact semantics are as in the following rules, all of which will be
2256applied to the watcher:
2257.RS 4
1296If the timer is pending, its pending status is cleared. 2258.IP "If the timer is pending, the pending status is always cleared." 4
1297.Sp 2259.IX Item "If the timer is pending, the pending status is always cleared."
2260.PD 0
1298If the timer is started but nonrepeating, stop it (as if it timed out). 2261.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2262.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2263.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2264.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2265.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2266.RE
2267.RS 4
2268.PD
1299.Sp 2269.Sp
1300If the timer is repeating, either start it if necessary (with the 2270This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1301\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. 2271usage example.
2272.RE
2273.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2274.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2275Returns the remaining time until a timer fires. If the timer is active,
2276then this time is relative to the current event loop time, otherwise it's
2277the timeout value currently configured.
1302.Sp 2278.Sp
1303This sounds a bit complicated, but here is a useful and typical 2279That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1304example: Imagine you have a tcp connection and you want a so-called idle 2280\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1305timeout, that is, you want to be called when there have been, say, 60 2281will return \f(CW4\fR. When the timer expires and is restarted, it will return
1306seconds of inactivity on the socket. The easiest way to do this is to 2282roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1307configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call 2283too), and so on.
1308\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1309you go into an idle state where you do not expect data to travel on the
1310socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1311automatically restart it if need be.
1312.Sp
1313That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1314altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1315.Sp
1316.Vb 8
1317\& ev_timer_init (timer, callback, 0., 5.);
1318\& ev_timer_again (loop, timer);
1319\& ...
1320\& timer->again = 17.;
1321\& ev_timer_again (loop, timer);
1322\& ...
1323\& timer->again = 10.;
1324\& ev_timer_again (loop, timer);
1325.Ve
1326.Sp
1327This is more slightly efficient then stopping/starting the timer each time
1328you want to modify its timeout value.
1329.IP "ev_tstamp repeat [read\-write]" 4 2284.IP "ev_tstamp repeat [read\-write]" 4
1330.IX Item "ev_tstamp repeat [read-write]" 2285.IX Item "ev_tstamp repeat [read-write]"
1331The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2286The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1332or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2287or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1333which is also when any modifications are taken into account. 2288which is also when any modifications are taken into account.
1334.PP 2289.PP
2290\fIExamples\fR
2291.IX Subsection "Examples"
2292.PP
1335Example: Create a timer that fires after 60 seconds. 2293Example: Create a timer that fires after 60 seconds.
1336.PP 2294.PP
1337.Vb 5 2295.Vb 5
1338\& static void 2296\& static void
1339\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2297\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1340\& { 2298\& {
1341\& .. one minute over, w is actually stopped right here 2299\& .. one minute over, w is actually stopped right here
1342\& } 2300\& }
1343.Ve 2301\&
1344.PP
1345.Vb 3
1346\& struct ev_timer mytimer; 2302\& ev_timer mytimer;
1347\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2303\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1348\& ev_timer_start (loop, &mytimer); 2304\& ev_timer_start (loop, &mytimer);
1349.Ve 2305.Ve
1350.PP 2306.PP
1351Example: Create a timeout timer that times out after 10 seconds of 2307Example: Create a timeout timer that times out after 10 seconds of
1352inactivity. 2308inactivity.
1353.PP 2309.PP
1354.Vb 5 2310.Vb 5
1355\& static void 2311\& static void
1356\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2312\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1357\& { 2313\& {
1358\& .. ten seconds without any activity 2314\& .. ten seconds without any activity
1359\& } 2315\& }
1360.Ve 2316\&
1361.PP
1362.Vb 4
1363\& struct ev_timer mytimer; 2317\& ev_timer mytimer;
1364\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2318\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1365\& ev_timer_again (&mytimer); /* start timer */ 2319\& ev_timer_again (&mytimer); /* start timer */
1366\& ev_loop (loop, 0); 2320\& ev_run (loop, 0);
1367.Ve 2321\&
1368.PP
1369.Vb 3
1370\& // and in some piece of code that gets executed on any "activity": 2322\& // and in some piece of code that gets executed on any "activity":
1371\& // reset the timeout to start ticking again at 10 seconds 2323\& // reset the timeout to start ticking again at 10 seconds
1372\& ev_timer_again (&mytimer); 2324\& ev_timer_again (&mytimer);
1373.Ve 2325.Ve
1374.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2326.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1375.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2327.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1376.IX Subsection "ev_periodic - to cron or not to cron?" 2328.IX Subsection "ev_periodic - to cron or not to cron?"
1377Periodic watchers are also timers of a kind, but they are very versatile 2329Periodic watchers are also timers of a kind, but they are very versatile
1378(and unfortunately a bit complex). 2330(and unfortunately a bit complex).
1379.PP 2331.PP
1380Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2332Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1381but on wallclock time (absolute time). You can tell a periodic watcher 2333relative time, the physical time that passes) but on wall clock time
1382to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2334(absolute time, the thing you can read on your calender or clock). The
1383periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2335difference is that wall clock time can run faster or slower than real
1384+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2336time, and time jumps are not uncommon (e.g. when you adjust your
1385take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2337wrist-watch).
1386roughly 10 seconds later).
1387.PP 2338.PP
1388They can also be used to implement vastly more complex timers, such as 2339You can tell a periodic watcher to trigger after some specific point
1389triggering an event on each midnight, local time or other, complicated, 2340in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1390rules. 2341seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2342not a delay) and then reset your system clock to January of the previous
2343year, then it will take a year or more to trigger the event (unlike an
2344\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2345it, as it uses a relative timeout).
1391.PP 2346.PP
2347\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2348timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2349other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2350those cannot react to time jumps.
2351.PP
1392As with timers, the callback is guarenteed to be invoked only when the 2352As with timers, the callback is guaranteed to be invoked only when the
1393time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2353point in time where it is supposed to trigger has passed. If multiple
1394during the same loop iteration then order of execution is undefined. 2354timers become ready during the same loop iteration then the ones with
2355earlier time-out values are invoked before ones with later time-out values
2356(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1395.PP 2357.PP
1396\fIWatcher-Specific Functions and Data Members\fR 2358\fIWatcher-Specific Functions and Data Members\fR
1397.IX Subsection "Watcher-Specific Functions and Data Members" 2359.IX Subsection "Watcher-Specific Functions and Data Members"
1398.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2360.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1399.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2361.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1400.PD 0 2362.PD 0
1401.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2363.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1402.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2364.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1403.PD 2365.PD
1404Lots of arguments, lets sort it out... There are basically three modes of 2366Lots of arguments, let's sort it out... There are basically three modes of
1405operation, and we will explain them from simplest to complex: 2367operation, and we will explain them from simplest to most complex:
1406.RS 4 2368.RS 4
2369.IP "\(bu" 4
1407.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 2370absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1408.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" 2371.Sp
1409In this configuration the watcher triggers an event at the wallclock time 2372In this configuration the watcher triggers an event after the wall clock
1410\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2373time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1411that is, if it is to be run at January 1st 2011 then it will run when the 2374time jump occurs, that is, if it is to be run at January 1st 2011 then it
1412system time reaches or surpasses this time. 2375will be stopped and invoked when the system clock reaches or surpasses
1413.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4 2376this point in time.
1414.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 2377.IP "\(bu" 4
2378repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2379.Sp
1415In this mode the watcher will always be scheduled to time out at the next 2380In this mode the watcher will always be scheduled to time out at the next
1416\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) 2381\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1417and then repeat, regardless of any time jumps. 2382negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2383argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1418.Sp 2384.Sp
1419This can be used to create timers that do not drift with respect to system 2385This can be used to create timers that do not drift with respect to the
1420time: 2386system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2387hour, on the hour (with respect to \s-1UTC\s0):
1421.Sp 2388.Sp
1422.Vb 1 2389.Vb 1
1423\& ev_periodic_set (&periodic, 0., 3600., 0); 2390\& ev_periodic_set (&periodic, 0., 3600., 0);
1424.Ve 2391.Ve
1425.Sp 2392.Sp
1426This doesn't mean there will always be 3600 seconds in between triggers, 2393This doesn't mean there will always be 3600 seconds in between triggers,
1427but only that the the callback will be called when the system time shows a 2394but only that the callback will be called when the system time shows a
1428full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2395full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1429by 3600. 2396by 3600.
1430.Sp 2397.Sp
1431Another way to think about it (for the mathematically inclined) is that 2398Another way to think about it (for the mathematically inclined) is that
1432\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2399\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1433time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2400time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1434.Sp 2401.Sp
1435For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near 2402The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
1436\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for 2403interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
1437this value. 2404microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2405at most a similar magnitude as the current time (say, within a factor of
2406ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2407\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2408.Sp
2409Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2410speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2411will of course deteriorate. Libev itself tries to be exact to be about one
2412millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2413.IP "\(bu" 4
1438.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 2414manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1439.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 2415.Sp
1440In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2416In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1441ignored. Instead, each time the periodic watcher gets scheduled, the 2417ignored. Instead, each time the periodic watcher gets scheduled, the
1442reschedule callback will be called with the watcher as first, and the 2418reschedule callback will be called with the watcher as first, and the
1443current time as second argument. 2419current time as second argument.
1444.Sp 2420.Sp
1445\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2421\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1446ever, or make any event loop modifications\fR. If you need to stop it, 2422or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1447return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2423allowed by documentation here\fR.
2424.Sp
2425If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1448starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). 2426it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2427only event loop modification you are allowed to do).
1449.Sp 2428.Sp
1450Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2429The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1451ev_tstamp now)\*(C'\fR, e.g.: 2430*w, ev_tstamp now)\*(C'\fR, e.g.:
1452.Sp 2431.Sp
1453.Vb 4 2432.Vb 5
2433\& static ev_tstamp
1454\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2434\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1455\& { 2435\& {
1456\& return now + 60.; 2436\& return now + 60.;
1457\& } 2437\& }
1458.Ve 2438.Ve
1459.Sp 2439.Sp
1460It must return the next time to trigger, based on the passed time value 2440It must return the next time to trigger, based on the passed time value
1461(that is, the lowest time value larger than to the second argument). It 2441(that is, the lowest time value larger than to the second argument). It
1462will usually be called just before the callback will be triggered, but 2442will usually be called just before the callback will be triggered, but
1463might be called at other times, too. 2443might be called at other times, too.
1464.Sp 2444.Sp
1465\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2445\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1466passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2446equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1467.Sp 2447.Sp
1468This can be used to create very complex timers, such as a timer that 2448This can be used to create very complex timers, such as a timer that
1469triggers on each midnight, local time. To do this, you would calculate the 2449triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1470next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2450next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1471you do this is, again, up to you (but it is not trivial, which is the main 2451you do this is, again, up to you (but it is not trivial, which is the main
1472reason I omitted it as an example). 2452reason I omitted it as an example).
1473.RE 2453.RE
1474.RS 4 2454.RS 4
… …
1477.IX Item "ev_periodic_again (loop, ev_periodic *)" 2457.IX Item "ev_periodic_again (loop, ev_periodic *)"
1478Simply stops and restarts the periodic watcher again. This is only useful 2458Simply stops and restarts the periodic watcher again. This is only useful
1479when you changed some parameters or the reschedule callback would return 2459when you changed some parameters or the reschedule callback would return
1480a different time than the last time it was called (e.g. in a crond like 2460a different time than the last time it was called (e.g. in a crond like
1481program when the crontabs have changed). 2461program when the crontabs have changed).
2462.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2463.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2464When active, returns the absolute time that the watcher is supposed
2465to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2466\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2467rescheduling modes.
1482.IP "ev_tstamp offset [read\-write]" 4 2468.IP "ev_tstamp offset [read\-write]" 4
1483.IX Item "ev_tstamp offset [read-write]" 2469.IX Item "ev_tstamp offset [read-write]"
1484When repeating, this contains the offset value, otherwise this is the 2470When repeating, this contains the offset value, otherwise this is the
1485absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). 2471absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2472although libev might modify this value for better numerical stability).
1486.Sp 2473.Sp
1487Can be modified any time, but changes only take effect when the periodic 2474Can be modified any time, but changes only take effect when the periodic
1488timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2475timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1489.IP "ev_tstamp interval [read\-write]" 4 2476.IP "ev_tstamp interval [read\-write]" 4
1490.IX Item "ev_tstamp interval [read-write]" 2477.IX Item "ev_tstamp interval [read-write]"
1491The current interval value. Can be modified any time, but changes only 2478The current interval value. Can be modified any time, but changes only
1492take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2479take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1493called. 2480called.
1494.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2481.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1495.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2482.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1496The current reschedule callback, or \f(CW0\fR, if this functionality is 2483The current reschedule callback, or \f(CW0\fR, if this functionality is
1497switched off. Can be changed any time, but changes only take effect when 2484switched off. Can be changed any time, but changes only take effect when
1498the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2485the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1499.IP "ev_tstamp at [read\-only]" 4 2486.PP
1500.IX Item "ev_tstamp at [read-only]" 2487\fIExamples\fR
1501When active, contains the absolute time that the watcher is supposed to 2488.IX Subsection "Examples"
1502trigger next.
1503.PP 2489.PP
1504Example: Call a callback every hour, or, more precisely, whenever the 2490Example: Call a callback every hour, or, more precisely, whenever the
1505system clock is divisible by 3600. The callback invocation times have 2491system time is divisible by 3600. The callback invocation times have
1506potentially a lot of jittering, but good long-term stability. 2492potentially a lot of jitter, but good long-term stability.
1507.PP 2493.PP
1508.Vb 5 2494.Vb 5
1509\& static void 2495\& static void
1510\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2496\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1511\& { 2497\& {
1512\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2498\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1513\& } 2499\& }
1514.Ve 2500\&
1515.PP
1516.Vb 3
1517\& struct ev_periodic hourly_tick; 2501\& ev_periodic hourly_tick;
1518\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2502\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1519\& ev_periodic_start (loop, &hourly_tick); 2503\& ev_periodic_start (loop, &hourly_tick);
1520.Ve 2504.Ve
1521.PP 2505.PP
1522Example: The same as above, but use a reschedule callback to do it: 2506Example: The same as above, but use a reschedule callback to do it:
1523.PP 2507.PP
1524.Vb 1 2508.Vb 1
1525\& #include <math.h> 2509\& #include <math.h>
1526.Ve 2510\&
1527.PP
1528.Vb 5
1529\& static ev_tstamp 2511\& static ev_tstamp
1530\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2512\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1531\& { 2513\& {
1532\& return fmod (now, 3600.) + 3600.; 2514\& return now + (3600. \- fmod (now, 3600.));
1533\& } 2515\& }
1534.Ve 2516\&
1535.PP
1536.Vb 1
1537\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2517\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1538.Ve 2518.Ve
1539.PP 2519.PP
1540Example: Call a callback every hour, starting now: 2520Example: Call a callback every hour, starting now:
1541.PP 2521.PP
1542.Vb 4 2522.Vb 4
1543\& struct ev_periodic hourly_tick; 2523\& ev_periodic hourly_tick;
1544\& ev_periodic_init (&hourly_tick, clock_cb, 2524\& ev_periodic_init (&hourly_tick, clock_cb,
1545\& fmod (ev_now (loop), 3600.), 3600., 0); 2525\& fmod (ev_now (loop), 3600.), 3600., 0);
1546\& ev_periodic_start (loop, &hourly_tick); 2526\& ev_periodic_start (loop, &hourly_tick);
1547.Ve 2527.Ve
1548.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2528.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1549.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2529.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1550.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2530.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1551Signal watchers will trigger an event when the process receives a specific 2531Signal watchers will trigger an event when the process receives a specific
1552signal one or more times. Even though signals are very asynchronous, libev 2532signal one or more times. Even though signals are very asynchronous, libev
1553will try it's best to deliver signals synchronously, i.e. as part of the 2533will try its best to deliver signals synchronously, i.e. as part of the
1554normal event processing, like any other event. 2534normal event processing, like any other event.
1555.PP 2535.PP
2536If you want signals to be delivered truly asynchronously, just use
2537\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2538the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2539synchronously wake up an event loop.
2540.PP
1556You can configure as many watchers as you like per signal. Only when the 2541You can configure as many watchers as you like for the same signal, but
2542only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2543default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2544\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2545the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2546.PP
1557first watcher gets started will libev actually register a signal watcher 2547When the first watcher gets started will libev actually register something
1558with the kernel (thus it coexists with your own signal handlers as long 2548with the kernel (thus it coexists with your own signal handlers as long as
1559as you don't register any with libev). Similarly, when the last signal 2549you don't register any with libev for the same signal).
1560watcher for a signal is stopped libev will reset the signal handler to 2550.PP
1561\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2551If possible and supported, libev will install its handlers with
2552\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2553not be unduly interrupted. If you have a problem with system calls getting
2554interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2555and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2556.PP
2557\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2558.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2559.PP
2560Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2561(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2562stopping it again), that is, libev might or might not block the signal,
2563and might or might not set or restore the installed signal handler (but
2564see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2565.PP
2566While this does not matter for the signal disposition (libev never
2567sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2568\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2569certain signals to be blocked.
2570.PP
2571This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2572the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2573choice usually).
2574.PP
2575The simplest way to ensure that the signal mask is reset in the child is
2576to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2577catch fork calls done by libraries (such as the libc) as well.
2578.PP
2579In current versions of libev, the signal will not be blocked indefinitely
2580unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2581the window of opportunity for problems, it will not go away, as libev
2582\&\fIhas\fR to modify the signal mask, at least temporarily.
2583.PP
2584So I can't stress this enough: \fIIf you do not reset your signal mask when
2585you expect it to be empty, you have a race condition in your code\fR. This
2586is not a libev-specific thing, this is true for most event libraries.
2587.PP
2588\fIThe special problem of threads signal handling\fR
2589.IX Subsection "The special problem of threads signal handling"
2590.PP
2591\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2592a lot of functionality (sigfd, sigwait etc.) only really works if all
2593threads in a process block signals, which is hard to achieve.
2594.PP
2595When you want to use sigwait (or mix libev signal handling with your own
2596for the same signals), you can tackle this problem by globally blocking
2597all signals before creating any threads (or creating them with a fully set
2598sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2599loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2600these signals. You can pass on any signals that libev might be interested
2601in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
1562.PP 2602.PP
1563\fIWatcher-Specific Functions and Data Members\fR 2603\fIWatcher-Specific Functions and Data Members\fR
1564.IX Subsection "Watcher-Specific Functions and Data Members" 2604.IX Subsection "Watcher-Specific Functions and Data Members"
1565.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2605.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1566.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2606.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
… …
1571Configures the watcher to trigger on the given signal number (usually one 2611Configures the watcher to trigger on the given signal number (usually one
1572of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2612of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1573.IP "int signum [read\-only]" 4 2613.IP "int signum [read\-only]" 4
1574.IX Item "int signum [read-only]" 2614.IX Item "int signum [read-only]"
1575The signal the watcher watches out for. 2615The signal the watcher watches out for.
2616.PP
2617\fIExamples\fR
2618.IX Subsection "Examples"
2619.PP
2620Example: Try to exit cleanly on \s-1SIGINT\s0.
2621.PP
2622.Vb 5
2623\& static void
2624\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2625\& {
2626\& ev_break (loop, EVBREAK_ALL);
2627\& }
2628\&
2629\& ev_signal signal_watcher;
2630\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2631\& ev_signal_start (loop, &signal_watcher);
2632.Ve
1576.ie n .Sh """ev_child"" \- watch out for process status changes" 2633.ie n .SS """ev_child"" \- watch out for process status changes"
1577.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2634.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1578.IX Subsection "ev_child - watch out for process status changes" 2635.IX Subsection "ev_child - watch out for process status changes"
1579Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2636Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1580some child status changes (most typically when a child of yours dies). 2637some child status changes (most typically when a child of yours dies or
2638exits). It is permissible to install a child watcher \fIafter\fR the child
2639has been forked (which implies it might have already exited), as long
2640as the event loop isn't entered (or is continued from a watcher), i.e.,
2641forking and then immediately registering a watcher for the child is fine,
2642but forking and registering a watcher a few event loop iterations later or
2643in the next callback invocation is not.
2644.PP
2645Only the default event loop is capable of handling signals, and therefore
2646you can only register child watchers in the default event loop.
2647.PP
2648Due to some design glitches inside libev, child watchers will always be
2649handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2650libev)
2651.PP
2652\fIProcess Interaction\fR
2653.IX Subsection "Process Interaction"
2654.PP
2655Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2656initialised. This is necessary to guarantee proper behaviour even if the
2657first child watcher is started after the child exits. The occurrence
2658of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2659synchronously as part of the event loop processing. Libev always reaps all
2660children, even ones not watched.
2661.PP
2662\fIOverriding the Built-In Processing\fR
2663.IX Subsection "Overriding the Built-In Processing"
2664.PP
2665Libev offers no special support for overriding the built-in child
2666processing, but if your application collides with libev's default child
2667handler, you can override it easily by installing your own handler for
2668\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2669default loop never gets destroyed. You are encouraged, however, to use an
2670event-based approach to child reaping and thus use libev's support for
2671that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2672.PP
2673\fIStopping the Child Watcher\fR
2674.IX Subsection "Stopping the Child Watcher"
2675.PP
2676Currently, the child watcher never gets stopped, even when the
2677child terminates, so normally one needs to stop the watcher in the
2678callback. Future versions of libev might stop the watcher automatically
2679when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2680problem).
1581.PP 2681.PP
1582\fIWatcher-Specific Functions and Data Members\fR 2682\fIWatcher-Specific Functions and Data Members\fR
1583.IX Subsection "Watcher-Specific Functions and Data Members" 2683.IX Subsection "Watcher-Specific Functions and Data Members"
1584.IP "ev_child_init (ev_child *, callback, int pid)" 4 2684.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1585.IX Item "ev_child_init (ev_child *, callback, int pid)" 2685.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1586.PD 0 2686.PD 0
1587.IP "ev_child_set (ev_child *, int pid)" 4 2687.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1588.IX Item "ev_child_set (ev_child *, int pid)" 2688.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1589.PD 2689.PD
1590Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2690Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1591\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2691\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1592at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2692at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1593the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2693the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1594\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2694\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1595process causing the status change. 2695process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2696activate the watcher when the process terminates) or \f(CW1\fR (additionally
2697activate the watcher when the process is stopped or continued).
1596.IP "int pid [read\-only]" 4 2698.IP "int pid [read\-only]" 4
1597.IX Item "int pid [read-only]" 2699.IX Item "int pid [read-only]"
1598The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2700The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1599.IP "int rpid [read\-write]" 4 2701.IP "int rpid [read\-write]" 4
1600.IX Item "int rpid [read-write]" 2702.IX Item "int rpid [read-write]"
… …
1602.IP "int rstatus [read\-write]" 4 2704.IP "int rstatus [read\-write]" 4
1603.IX Item "int rstatus [read-write]" 2705.IX Item "int rstatus [read-write]"
1604The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2706The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1605\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2707\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1606.PP 2708.PP
1607Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2709\fIExamples\fR
2710.IX Subsection "Examples"
1608.PP 2711.PP
2712Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2713its completion.
2714.PP
1609.Vb 5 2715.Vb 1
2716\& ev_child cw;
2717\&
1610\& static void 2718\& static void
1611\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2719\& child_cb (EV_P_ ev_child *w, int revents)
1612\& { 2720\& {
1613\& ev_unloop (loop, EVUNLOOP_ALL); 2721\& ev_child_stop (EV_A_ w);
2722\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1614\& } 2723\& }
2724\&
2725\& pid_t pid = fork ();
2726\&
2727\& if (pid < 0)
2728\& // error
2729\& else if (pid == 0)
2730\& {
2731\& // the forked child executes here
2732\& exit (1);
2733\& }
2734\& else
2735\& {
2736\& ev_child_init (&cw, child_cb, pid, 0);
2737\& ev_child_start (EV_DEFAULT_ &cw);
2738\& }
1615.Ve 2739.Ve
1616.PP
1617.Vb 3
1618\& struct ev_signal signal_watcher;
1619\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1620\& ev_signal_start (loop, &sigint_cb);
1621.Ve
1622.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2740.ie n .SS """ev_stat"" \- did the file attributes just change?"
1623.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2741.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1624.IX Subsection "ev_stat - did the file attributes just change?" 2742.IX Subsection "ev_stat - did the file attributes just change?"
1625This watches a filesystem path for attribute changes. That is, it calls 2743This watches a file system path for attribute changes. That is, it calls
1626\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2744\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1627compared to the last time, invoking the callback if it did. 2745and sees if it changed compared to the last time, invoking the callback
2746if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2747happen after the watcher has been started will be reported.
1628.PP 2748.PP
1629The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2749The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1630not exist\*(R" is a status change like any other. The condition \*(L"path does 2750not exist\*(R" is a status change like any other. The condition \*(L"path does not
1631not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2751exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1632otherwise always forced to be at least one) and all the other fields of 2752\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1633the stat buffer having unspecified contents. 2753least one) and all the other fields of the stat buffer having unspecified
2754contents.
1634.PP 2755.PP
1635The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2756The path \fImust not\fR end in a slash or contain special components such as
2757\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1636relative and your working directory changes, the behaviour is undefined. 2758your working directory changes, then the behaviour is undefined.
1637.PP 2759.PP
1638Since there is no standard to do this, the portable implementation simply 2760Since there is no portable change notification interface available, the
1639calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You 2761portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1640can specify a recommended polling interval for this case. If you specify 2762to see if it changed somehow. You can specify a recommended polling
1641a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2763interval for this case. If you specify a polling interval of \f(CW0\fR (highly
1642unspecified default\fR value will be used (which you can expect to be around 2764recommended!) then a \fIsuitable, unspecified default\fR value will be used
1643five seconds, although this might change dynamically). Libev will also 2765(which you can expect to be around five seconds, although this might
1644impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2766change dynamically). Libev will also impose a minimum interval which is
1645usually overkill. 2767currently around \f(CW0.1\fR, but that's usually overkill.
1646.PP 2768.PP
1647This watcher type is not meant for massive numbers of stat watchers, 2769This watcher type is not meant for massive numbers of stat watchers,
1648as even with OS-supported change notifications, this can be 2770as even with OS-supported change notifications, this can be
1649resource\-intensive. 2771resource-intensive.
1650.PP 2772.PP
1651At the time of this writing, only the Linux inotify interface is 2773At the time of this writing, the only OS-specific interface implemented
1652implemented (implementing kqueue support is left as an exercise for the 2774is the Linux inotify interface (implementing kqueue support is left as an
1653reader). Inotify will be used to give hints only and should not change the 2775exercise for the reader. Note, however, that the author sees no way of
1654semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 2776implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
1655to fall back to regular polling again even with inotify, but changes are
1656usually detected immediately, and if the file exists there will be no
1657polling.
1658.PP 2777.PP
1659\fIInotify\fR 2778\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2779.IX Subsection "ABI Issues (Largefile Support)"
2780.PP
2781Libev by default (unless the user overrides this) uses the default
2782compilation environment, which means that on systems with large file
2783support disabled by default, you get the 32 bit version of the stat
2784structure. When using the library from programs that change the \s-1ABI\s0 to
2785use 64 bit file offsets the programs will fail. In that case you have to
2786compile libev with the same flags to get binary compatibility. This is
2787obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2788most noticeably displayed with ev_stat and large file support.
2789.PP
2790The solution for this is to lobby your distribution maker to make large
2791file interfaces available by default (as e.g. FreeBSD does) and not
2792optional. Libev cannot simply switch on large file support because it has
2793to exchange stat structures with application programs compiled using the
2794default compilation environment.
2795.PP
2796\fIInotify and Kqueue\fR
1660.IX Subsection "Inotify" 2797.IX Subsection "Inotify and Kqueue"
1661.PP 2798.PP
1662When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only 2799When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
1663available on Linux) and present at runtime, it will be used to speed up 2800runtime, it will be used to speed up change detection where possible. The
1664change detection where possible. The inotify descriptor will be created lazily 2801inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
1665when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started. 2802watcher is being started.
1666.PP 2803.PP
1667Inotify presense does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers 2804Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1668except that changes might be detected earlier, and in some cases, to avoid 2805except that changes might be detected earlier, and in some cases, to avoid
1669making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presense of inotify support 2806making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
1670there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling. 2807there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2808but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2809many bugs), the path exists (i.e. stat succeeds), and the path resides on
2810a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2811xfs are fully working) libev usually gets away without polling.
1671.PP 2812.PP
1672(There is no support for kqueue, as apparently it cannot be used to 2813There is no support for kqueue, as apparently it cannot be used to
1673implement this functionality, due to the requirement of having a file 2814implement this functionality, due to the requirement of having a file
1674descriptor open on the object at all times). 2815descriptor open on the object at all times, and detecting renames, unlinks
2816etc. is difficult.
2817.PP
2818\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2819.IX Subsection "stat () is a synchronous operation"
2820.PP
2821Libev doesn't normally do any kind of I/O itself, and so is not blocking
2822the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2823()\*(C'\fR, which is a synchronous operation.
2824.PP
2825For local paths, this usually doesn't matter: unless the system is very
2826busy or the intervals between stat's are large, a stat call will be fast,
2827as the path data is usually in memory already (except when starting the
2828watcher).
2829.PP
2830For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2831time due to network issues, and even under good conditions, a stat call
2832often takes multiple milliseconds.
2833.PP
2834Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2835paths, although this is fully supported by libev.
1675.PP 2836.PP
1676\fIThe special problem of stat time resolution\fR 2837\fIThe special problem of stat time resolution\fR
1677.IX Subsection "The special problem of stat time resolution" 2838.IX Subsection "The special problem of stat time resolution"
1678.PP 2839.PP
1679The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and 2840The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
1680even on systems where the resolution is higher, many filesystems still 2841and even on systems where the resolution is higher, most file systems
1681only support whole seconds. 2842still only support whole seconds.
1682.PP 2843.PP
1683That means that, if the time is the only thing that changes, you might 2844That means that, if the time is the only thing that changes, you can
1684miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and calls 2845easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
1685your callback, which does something. When there is another update within 2846calls your callback, which does something. When there is another update
1686the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it. 2847within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2848stat data does change in other ways (e.g. file size).
1687.PP 2849.PP
1688The solution to this is to delay acting on a change for a second (or till 2850The solution to this is to delay acting on a change for slightly more
1689the next second boundary), using a roughly one-second delay \f(CW\*(C`ev_timer\*(C'\fR 2851than a second (or till slightly after the next full second boundary), using
1690(\f(CW\*(C`ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)\*(C'\fR). The \f(CW.01\fR 2852a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
1691is added to work around small timing inconsistencies of some operating 2853ev_timer_again (loop, w)\*(C'\fR).
1692systems. 2854.PP
2855The \f(CW.02\fR offset is added to work around small timing inconsistencies
2856of some operating systems (where the second counter of the current time
2857might be be delayed. One such system is the Linux kernel, where a call to
2858\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2859a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2860update file times then there will be a small window where the kernel uses
2861the previous second to update file times but libev might already execute
2862the timer callback).
1693.PP 2863.PP
1694\fIWatcher-Specific Functions and Data Members\fR 2864\fIWatcher-Specific Functions and Data Members\fR
1695.IX Subsection "Watcher-Specific Functions and Data Members" 2865.IX Subsection "Watcher-Specific Functions and Data Members"
1696.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2866.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1697.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2867.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
… …
1703\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2873\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1704be detected and should normally be specified as \f(CW0\fR to let libev choose 2874be detected and should normally be specified as \f(CW0\fR to let libev choose
1705a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2875a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1706path for as long as the watcher is active. 2876path for as long as the watcher is active.
1707.Sp 2877.Sp
1708The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2878The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1709relative to the attributes at the time the watcher was started (or the 2879relative to the attributes at the time the watcher was started (or the
1710last change was detected). 2880last change was detected).
1711.IP "ev_stat_stat (ev_stat *)" 4 2881.IP "ev_stat_stat (loop, ev_stat *)" 4
1712.IX Item "ev_stat_stat (ev_stat *)" 2882.IX Item "ev_stat_stat (loop, ev_stat *)"
1713Updates the stat buffer immediately with new values. If you change the 2883Updates the stat buffer immediately with new values. If you change the
1714watched path in your callback, you could call this fucntion to avoid 2884watched path in your callback, you could call this function to avoid
1715detecting this change (while introducing a race condition). Can also be 2885detecting this change (while introducing a race condition if you are not
1716useful simply to find out the new values. 2886the only one changing the path). Can also be useful simply to find out the
2887new values.
1717.IP "ev_statdata attr [read\-only]" 4 2888.IP "ev_statdata attr [read\-only]" 4
1718.IX Item "ev_statdata attr [read-only]" 2889.IX Item "ev_statdata attr [read-only]"
1719The most-recently detected attributes of the file. Although the type is of 2890The most-recently detected attributes of the file. Although the type is
1720\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 2891\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2892suitable for your system, but you can only rely on the POSIX-standardised
1721suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 2893members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1722was some error while \f(CW\*(C`stat\*(C'\fRing the file. 2894some error while \f(CW\*(C`stat\*(C'\fRing the file.
1723.IP "ev_statdata prev [read\-only]" 4 2895.IP "ev_statdata prev [read\-only]" 4
1724.IX Item "ev_statdata prev [read-only]" 2896.IX Item "ev_statdata prev [read-only]"
1725The previous attributes of the file. The callback gets invoked whenever 2897The previous attributes of the file. The callback gets invoked whenever
1726\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 2898\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2899differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
2900\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
1727.IP "ev_tstamp interval [read\-only]" 4 2901.IP "ev_tstamp interval [read\-only]" 4
1728.IX Item "ev_tstamp interval [read-only]" 2902.IX Item "ev_tstamp interval [read-only]"
1729The specified interval. 2903The specified interval.
1730.IP "const char *path [read\-only]" 4 2904.IP "const char *path [read\-only]" 4
1731.IX Item "const char *path [read-only]" 2905.IX Item "const char *path [read-only]"
1732The filesystem path that is being watched. 2906The file system path that is being watched.
1733.PP 2907.PP
1734\fIExamples\fR 2908\fIExamples\fR
1735.IX Subsection "Examples" 2909.IX Subsection "Examples"
1736.PP 2910.PP
1737Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 2911Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1738.PP 2912.PP
1739.Vb 15 2913.Vb 10
1740\& static void 2914\& static void
1741\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 2915\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1742\& { 2916\& {
1743\& /* /etc/passwd changed in some way */ 2917\& /* /etc/passwd changed in some way */
1744\& if (w->attr.st_nlink) 2918\& if (w\->attr.st_nlink)
1745\& { 2919\& {
1746\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 2920\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1747\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 2921\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1748\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 2922\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1749\& } 2923\& }
1750\& else 2924\& else
1751\& /* you shalt not abuse printf for puts */ 2925\& /* you shalt not abuse printf for puts */
1752\& puts ("wow, /etc/passwd is not there, expect problems. " 2926\& puts ("wow, /etc/passwd is not there, expect problems. "
1753\& "if this is windows, they already arrived\en"); 2927\& "if this is windows, they already arrived\en");
1754\& } 2928\& }
1755.Ve 2929\&
1756.PP
1757.Vb 2
1758\& ... 2930\& ...
1759\& ev_stat passwd; 2931\& ev_stat passwd;
1760.Ve 2932\&
1761.PP
1762.Vb 2
1763\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.); 2933\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1764\& ev_stat_start (loop, &passwd); 2934\& ev_stat_start (loop, &passwd);
1765.Ve 2935.Ve
1766.PP 2936.PP
1767Example: Like above, but additionally use a one-second delay so we do not 2937Example: Like above, but additionally use a one-second delay so we do not
1768miss updates (however, frequent updates will delay processing, too, so 2938miss updates (however, frequent updates will delay processing, too, so
1769one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on 2939one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1770\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation). 2940\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1771.PP 2941.PP
1772.Vb 2 2942.Vb 2
1773\& static ev_stat passwd; 2943\& static ev_stat passwd;
1774\& static ev_timer timer; 2944\& static ev_timer timer;
1775.Ve 2945\&
1776.PP
1777.Vb 4
1778\& static void 2946\& static void
1779\& timer_cb (EV_P_ ev_timer *w, int revents) 2947\& timer_cb (EV_P_ ev_timer *w, int revents)
1780\& { 2948\& {
1781\& ev_timer_stop (EV_A_ w); 2949\& ev_timer_stop (EV_A_ w);
1782.Ve 2950\&
1783.PP
1784.Vb 2
1785\& /* now it's one second after the most recent passwd change */ 2951\& /* now it\*(Aqs one second after the most recent passwd change */
1786\& } 2952\& }
1787.Ve 2953\&
1788.PP
1789.Vb 6
1790\& static void 2954\& static void
1791\& stat_cb (EV_P_ ev_stat *w, int revents) 2955\& stat_cb (EV_P_ ev_stat *w, int revents)
1792\& { 2956\& {
1793\& /* reset the one-second timer */ 2957\& /* reset the one\-second timer */
1794\& ev_timer_again (EV_A_ &timer); 2958\& ev_timer_again (EV_A_ &timer);
1795\& } 2959\& }
1796.Ve 2960\&
1797.PP
1798.Vb 4
1799\& ... 2961\& ...
1800\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.); 2962\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1801\& ev_stat_start (loop, &passwd); 2963\& ev_stat_start (loop, &passwd);
1802\& ev_timer_init (&timer, timer_cb, 0., 1.01); 2964\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1803.Ve 2965.Ve
1804.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 2966.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1805.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 2967.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1806.IX Subsection "ev_idle - when you've got nothing better to do..." 2968.IX Subsection "ev_idle - when you've got nothing better to do..."
1807Idle watchers trigger events when no other events of the same or higher 2969Idle watchers trigger events when no other events of the same or higher
1808priority are pending (prepare, check and other idle watchers do not 2970priority are pending (prepare, check and other idle watchers do not count
1809count). 2971as receiving \*(L"events\*(R").
1810.PP 2972.PP
1811That is, as long as your process is busy handling sockets or timeouts 2973That is, as long as your process is busy handling sockets or timeouts
1812(or even signals, imagine) of the same or higher priority it will not be 2974(or even signals, imagine) of the same or higher priority it will not be
1813triggered. But when your process is idle (or only lower-priority watchers 2975triggered. But when your process is idle (or only lower-priority watchers
1814are pending), the idle watchers are being called once per event loop 2976are pending), the idle watchers are being called once per event loop
… …
1818The most noteworthy effect is that as long as any idle watchers are 2980The most noteworthy effect is that as long as any idle watchers are
1819active, the process will not block when waiting for new events. 2981active, the process will not block when waiting for new events.
1820.PP 2982.PP
1821Apart from keeping your process non-blocking (which is a useful 2983Apart from keeping your process non-blocking (which is a useful
1822effect on its own sometimes), idle watchers are a good place to do 2984effect on its own sometimes), idle watchers are a good place to do
1823\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2985\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1824event loop has handled all outstanding events. 2986event loop has handled all outstanding events.
2987.PP
2988\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
2989.IX Subsection "Abusing an ev_idle watcher for its side-effect"
2990.PP
2991As long as there is at least one active idle watcher, libev will never
2992sleep unnecessarily. Or in other words, it will loop as fast as possible.
2993For this to work, the idle watcher doesn't need to be invoked at all \- the
2994lowest priority will do.
2995.PP
2996This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
2997to do something on each event loop iteration \- for example to balance load
2998between different connections.
2999.PP
3000See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3001example.
1825.PP 3002.PP
1826\fIWatcher-Specific Functions and Data Members\fR 3003\fIWatcher-Specific Functions and Data Members\fR
1827.IX Subsection "Watcher-Specific Functions and Data Members" 3004.IX Subsection "Watcher-Specific Functions and Data Members"
1828.IP "ev_idle_init (ev_signal *, callback)" 4 3005.IP "ev_idle_init (ev_idle *, callback)" 4
1829.IX Item "ev_idle_init (ev_signal *, callback)" 3006.IX Item "ev_idle_init (ev_idle *, callback)"
1830Initialises and configures the idle watcher \- it has no parameters of any 3007Initialises and configures the idle watcher \- it has no parameters of any
1831kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3008kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1832believe me. 3009believe me.
1833.PP 3010.PP
3011\fIExamples\fR
3012.IX Subsection "Examples"
3013.PP
1834Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 3014Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1835callback, free it. Also, use no error checking, as usual. 3015callback, free it. Also, use no error checking, as usual.
1836.PP 3016.PP
1837.Vb 7 3017.Vb 5
1838\& static void 3018\& static void
1839\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3019\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1840\& { 3020\& {
3021\& // stop the watcher
3022\& ev_idle_stop (loop, w);
3023\&
3024\& // now we can free it
1841\& free (w); 3025\& free (w);
3026\&
1842\& // now do something you wanted to do when the program has 3027\& // now do something you wanted to do when the program has
1843\& // no longer asnything immediate to do. 3028\& // no longer anything immediate to do.
1844\& } 3029\& }
1845.Ve 3030\&
1846.PP
1847.Vb 3
1848\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3031\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1849\& ev_idle_init (idle_watcher, idle_cb); 3032\& ev_idle_init (idle_watcher, idle_cb);
1850\& ev_idle_start (loop, idle_cb); 3033\& ev_idle_start (loop, idle_watcher);
1851.Ve 3034.Ve
1852.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3035.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1853.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3036.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1854.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3037.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1855Prepare and check watchers are usually (but not always) used in tandem: 3038Prepare and check watchers are often (but not always) used in pairs:
1856prepare watchers get invoked before the process blocks and check watchers 3039prepare watchers get invoked before the process blocks and check watchers
1857afterwards. 3040afterwards.
1858.PP 3041.PP
1859You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3042You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
1860the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3043the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1861watchers. Other loops than the current one are fine, however. The 3044watchers. Other loops than the current one are fine, however. The
1862rationale behind this is that you do not need to check for recursion in 3045rationale behind this is that you do not need to check for recursion in
1863those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3046those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1864\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3047\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1865called in pairs bracketing the blocking call. 3048called in pairs bracketing the blocking call.
1866.PP 3049.PP
1867Their main purpose is to integrate other event mechanisms into libev and 3050Their main purpose is to integrate other event mechanisms into libev and
1868their use is somewhat advanced. This could be used, for example, to track 3051their use is somewhat advanced. They could be used, for example, to track
1869variable changes, implement your own watchers, integrate net-snmp or a 3052variable changes, implement your own watchers, integrate net-snmp or a
1870coroutine library and lots more. They are also occasionally useful if 3053coroutine library and lots more. They are also occasionally useful if
1871you cache some data and want to flush it before blocking (for example, 3054you cache some data and want to flush it before blocking (for example,
1872in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3055in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1873watcher). 3056watcher).
1874.PP 3057.PP
1875This is done by examining in each prepare call which file descriptors need 3058This is done by examining in each prepare call which file descriptors
1876to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3059need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1877them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3060for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1878provide just this functionality). Then, in the check watcher you check for 3061libraries provide exactly this functionality). Then, in the check watcher,
1879any events that occured (by checking the pending status of all watchers 3062you check for any events that occurred (by checking the pending status
1880and stopping them) and call back into the library. The I/O and timer 3063of all watchers and stopping them) and call back into the library. The
1881callbacks will never actually be called (but must be valid nevertheless, 3064I/O and timer callbacks will never actually be called (but must be valid
1882because you never know, you know?). 3065nevertheless, because you never know, you know?).
1883.PP 3066.PP
1884As another example, the Perl Coro module uses these hooks to integrate 3067As another example, the Perl Coro module uses these hooks to integrate
1885coroutines into libev programs, by yielding to other active coroutines 3068coroutines into libev programs, by yielding to other active coroutines
1886during each prepare and only letting the process block if no coroutines 3069during each prepare and only letting the process block if no coroutines
1887are ready to run (it's actually more complicated: it only runs coroutines 3070are ready to run (it's actually more complicated: it only runs coroutines
1888with priority higher than or equal to the event loop and one coroutine 3071with priority higher than or equal to the event loop and one coroutine
1889of lower priority, but only once, using idle watchers to keep the event 3072of lower priority, but only once, using idle watchers to keep the event
1890loop from blocking if lower-priority coroutines are active, thus mapping 3073loop from blocking if lower-priority coroutines are active, thus mapping
1891low-priority coroutines to idle/background tasks). 3074low-priority coroutines to idle/background tasks).
1892.PP 3075.PP
1893It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 3076When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
1894priority, to ensure that they are being run before any other watchers 3077highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3078any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3079watchers).
3080.PP
1895after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 3081Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
1896too) should not activate (\*(L"feed\*(R") events into libev. While libev fully 3082activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
1897supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers 3083might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
1898did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other 3084\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
1899(non\-libev) event loops those other event loops might be in an unusable 3085loops those other event loops might be in an unusable state until their
1900state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to 3086\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1901coexist peacefully with others). 3087others).
3088.PP
3089\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3090.IX Subsection "Abusing an ev_check watcher for its side-effect"
3091.PP
3092\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3093useful because they are called once per event loop iteration. For
3094example, if you want to handle a large number of connections fairly, you
3095normally only do a bit of work for each active connection, and if there
3096is more work to do, you wait for the next event loop iteration, so other
3097connections have a chance of making progress.
3098.PP
3099Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3100next event loop iteration. However, that isn't as soon as possible \-
3101without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3102.PP
3103This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3104single global idle watcher that is active as long as you have one active
3105\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3106will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3107invoked. Neither watcher alone can do that.
1902.PP 3108.PP
1903\fIWatcher-Specific Functions and Data Members\fR 3109\fIWatcher-Specific Functions and Data Members\fR
1904.IX Subsection "Watcher-Specific Functions and Data Members" 3110.IX Subsection "Watcher-Specific Functions and Data Members"
1905.IP "ev_prepare_init (ev_prepare *, callback)" 4 3111.IP "ev_prepare_init (ev_prepare *, callback)" 4
1906.IX Item "ev_prepare_init (ev_prepare *, callback)" 3112.IX Item "ev_prepare_init (ev_prepare *, callback)"
… …
1908.IP "ev_check_init (ev_check *, callback)" 4 3114.IP "ev_check_init (ev_check *, callback)" 4
1909.IX Item "ev_check_init (ev_check *, callback)" 3115.IX Item "ev_check_init (ev_check *, callback)"
1910.PD 3116.PD
1911Initialises and configures the prepare or check watcher \- they have no 3117Initialises and configures the prepare or check watcher \- they have no
1912parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3118parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1913macros, but using them is utterly, utterly and completely pointless. 3119macros, but using them is utterly, utterly, utterly and completely
3120pointless.
3121.PP
3122\fIExamples\fR
3123.IX Subsection "Examples"
1914.PP 3124.PP
1915There are a number of principal ways to embed other event loops or modules 3125There are a number of principal ways to embed other event loops or modules
1916into libev. Here are some ideas on how to include libadns into libev 3126into libev. Here are some ideas on how to include libadns into libev
1917(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could 3127(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1918use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR 3128use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
1919embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 3129Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
1920into the Glib event loop). 3130Glib event loop).
1921.PP 3131.PP
1922Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, 3132Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1923and in a check watcher, destroy them and call into libadns. What follows 3133and in a check watcher, destroy them and call into libadns. What follows
1924is pseudo-code only of course. This requires you to either use a low 3134is pseudo-code only of course. This requires you to either use a low
1925priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as 3135priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1926the callbacks for the IO/timeout watchers might not have been called yet. 3136the callbacks for the IO/timeout watchers might not have been called yet.
1927.PP 3137.PP
1928.Vb 2 3138.Vb 2
1929\& static ev_io iow [nfd]; 3139\& static ev_io iow [nfd];
1930\& static ev_timer tw; 3140\& static ev_timer tw;
1931.Ve 3141\&
1932.PP
1933.Vb 4
1934\& static void 3142\& static void
1935\& io_cb (ev_loop *loop, ev_io *w, int revents) 3143\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1936\& { 3144\& {
1937\& } 3145\& }
1938.Ve 3146\&
1939.PP
1940.Vb 8
1941\& // create io watchers for each fd and a timer before blocking 3147\& // create io watchers for each fd and a timer before blocking
1942\& static void 3148\& static void
1943\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3149\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1944\& { 3150\& {
1945\& int timeout = 3600000; 3151\& int timeout = 3600000;
1946\& struct pollfd fds [nfd]; 3152\& struct pollfd fds [nfd];
1947\& // actual code will need to loop here and realloc etc. 3153\& // actual code will need to loop here and realloc etc.
1948\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3154\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1949.Ve 3155\&
1950.PP
1951.Vb 3
1952\& /* the callback is illegal, but won't be called as we stop during check */ 3156\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1953\& ev_timer_init (&tw, 0, timeout * 1e-3); 3157\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1954\& ev_timer_start (loop, &tw); 3158\& ev_timer_start (loop, &tw);
1955.Ve 3159\&
1956.PP
1957.Vb 6
1958\& // create one ev_io per pollfd 3160\& // create one ev_io per pollfd
1959\& for (int i = 0; i < nfd; ++i) 3161\& for (int i = 0; i < nfd; ++i)
1960\& { 3162\& {
1961\& ev_io_init (iow + i, io_cb, fds [i].fd, 3163\& ev_io_init (iow + i, io_cb, fds [i].fd,
1962\& ((fds [i].events & POLLIN ? EV_READ : 0) 3164\& ((fds [i].events & POLLIN ? EV_READ : 0)
1963\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3165\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1964.Ve 3166\&
1965.PP
1966.Vb 4
1967\& fds [i].revents = 0; 3167\& fds [i].revents = 0;
1968\& ev_io_start (loop, iow + i); 3168\& ev_io_start (loop, iow + i);
1969\& } 3169\& }
1970\& } 3170\& }
1971.Ve 3171\&
1972.PP
1973.Vb 5
1974\& // stop all watchers after blocking 3172\& // stop all watchers after blocking
1975\& static void 3173\& static void
1976\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3174\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1977\& { 3175\& {
1978\& ev_timer_stop (loop, &tw); 3176\& ev_timer_stop (loop, &tw);
1979.Ve 3177\&
1980.PP
1981.Vb 8
1982\& for (int i = 0; i < nfd; ++i) 3178\& for (int i = 0; i < nfd; ++i)
1983\& { 3179\& {
1984\& // set the relevant poll flags 3180\& // set the relevant poll flags
1985\& // could also call adns_processreadable etc. here 3181\& // could also call adns_processreadable etc. here
1986\& struct pollfd *fd = fds + i; 3182\& struct pollfd *fd = fds + i;
1987\& int revents = ev_clear_pending (iow + i); 3183\& int revents = ev_clear_pending (iow + i);
1988\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; 3184\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1989\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; 3185\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1990.Ve 3186\&
1991.PP
1992.Vb 3
1993\& // now stop the watcher 3187\& // now stop the watcher
1994\& ev_io_stop (loop, iow + i); 3188\& ev_io_stop (loop, iow + i);
1995\& } 3189\& }
1996.Ve 3190\&
1997.PP
1998.Vb 2
1999\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 3191\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2000\& } 3192\& }
2001.Ve 3193.Ve
2002.PP 3194.PP
2003Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR 3195Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2004in the prepare watcher and would dispose of the check watcher. 3196in the prepare watcher and would dispose of the check watcher.
2005.PP 3197.PP
2006Method 3: If the module to be embedded supports explicit event 3198Method 3: If the module to be embedded supports explicit event
2007notification (adns does), you can also make use of the actual watcher 3199notification (libadns does), you can also make use of the actual watcher
2008callbacks, and only destroy/create the watchers in the prepare watcher. 3200callbacks, and only destroy/create the watchers in the prepare watcher.
2009.PP 3201.PP
2010.Vb 5 3202.Vb 5
2011\& static void 3203\& static void
2012\& timer_cb (EV_P_ ev_timer *w, int revents) 3204\& timer_cb (EV_P_ ev_timer *w, int revents)
2013\& { 3205\& {
2014\& adns_state ads = (adns_state)w->data; 3206\& adns_state ads = (adns_state)w\->data;
2015\& update_now (EV_A); 3207\& update_now (EV_A);
2016.Ve 3208\&
2017.PP
2018.Vb 2
2019\& adns_processtimeouts (ads, &tv_now); 3209\& adns_processtimeouts (ads, &tv_now);
2020\& } 3210\& }
2021.Ve 3211\&
2022.PP
2023.Vb 5
2024\& static void 3212\& static void
2025\& io_cb (EV_P_ ev_io *w, int revents) 3213\& io_cb (EV_P_ ev_io *w, int revents)
2026\& { 3214\& {
2027\& adns_state ads = (adns_state)w->data; 3215\& adns_state ads = (adns_state)w\->data;
2028\& update_now (EV_A); 3216\& update_now (EV_A);
2029.Ve 3217\&
2030.PP
2031.Vb 3
2032\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); 3218\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2033\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); 3219\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2034\& } 3220\& }
2035.Ve 3221\&
2036.PP
2037.Vb 1
2038\& // do not ever call adns_afterpoll 3222\& // do not ever call adns_afterpoll
2039.Ve 3223.Ve
2040.PP 3224.PP
2041Method 4: Do not use a prepare or check watcher because the module you 3225Method 4: Do not use a prepare or check watcher because the module you
2042want to embed is too inflexible to support it. Instead, youc na override 3226want to embed is not flexible enough to support it. Instead, you can
2043their poll function. The drawback with this solution is that the main 3227override their poll function. The drawback with this solution is that the
2044loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does 3228main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2045this. 3229this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3230libglib event loop.
2046.PP 3231.PP
2047.Vb 4 3232.Vb 4
2048\& static gint 3233\& static gint
2049\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) 3234\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2050\& { 3235\& {
2051\& int got_events = 0; 3236\& int got_events = 0;
2052.Ve 3237\&
2053.PP
2054.Vb 2
2055\& for (n = 0; n < nfds; ++n) 3238\& for (n = 0; n < nfds; ++n)
2056\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events 3239\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2057.Ve 3240\&
2058.PP
2059.Vb 2
2060\& if (timeout >= 0) 3241\& if (timeout >= 0)
2061\& // create/start timer 3242\& // create/start timer
2062.Ve 3243\&
2063.PP
2064.Vb 2
2065\& // poll 3244\& // poll
2066\& ev_loop (EV_A_ 0); 3245\& ev_run (EV_A_ 0);
2067.Ve 3246\&
2068.PP
2069.Vb 3
2070\& // stop timer again 3247\& // stop timer again
2071\& if (timeout >= 0) 3248\& if (timeout >= 0)
2072\& ev_timer_stop (EV_A_ &to); 3249\& ev_timer_stop (EV_A_ &to);
2073.Ve 3250\&
2074.PP
2075.Vb 3
2076\& // stop io watchers again - their callbacks should have set 3251\& // stop io watchers again \- their callbacks should have set
2077\& for (n = 0; n < nfds; ++n) 3252\& for (n = 0; n < nfds; ++n)
2078\& ev_io_stop (EV_A_ iow [n]); 3253\& ev_io_stop (EV_A_ iow [n]);
2079.Ve 3254\&
2080.PP
2081.Vb 2
2082\& return got_events; 3255\& return got_events;
2083\& } 3256\& }
2084.Ve 3257.Ve
2085.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3258.ie n .SS """ev_embed"" \- when one backend isn't enough..."
2086.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3259.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
2087.IX Subsection "ev_embed - when one backend isn't enough..." 3260.IX Subsection "ev_embed - when one backend isn't enough..."
2088This is a rather advanced watcher type that lets you embed one event loop 3261This is a rather advanced watcher type that lets you embed one event loop
2089into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3262into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2090loop, other types of watchers might be handled in a delayed or incorrect 3263loop, other types of watchers might be handled in a delayed or incorrect
2091fashion and must not be used). 3264fashion and must not be used).
… …
2094prioritise I/O. 3267prioritise I/O.
2095.PP 3268.PP
2096As an example for a bug workaround, the kqueue backend might only support 3269As an example for a bug workaround, the kqueue backend might only support
2097sockets on some platform, so it is unusable as generic backend, but you 3270sockets on some platform, so it is unusable as generic backend, but you
2098still want to make use of it because you have many sockets and it scales 3271still want to make use of it because you have many sockets and it scales
2099so nicely. In this case, you would create a kqueue-based loop and embed it 3272so nicely. In this case, you would create a kqueue-based loop and embed
2100into your default loop (which might use e.g. poll). Overall operation will 3273it into your default loop (which might use e.g. poll). Overall operation
2101be a bit slower because first libev has to poll and then call kevent, but 3274will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2102at least you can use both at what they are best. 3275\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3276best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2103.PP 3277.PP
2104As for prioritising I/O: rarely you have the case where some fds have 3278As for prioritising I/O: under rare circumstances you have the case where
2105to be watched and handled very quickly (with low latency), and even 3279some fds have to be watched and handled very quickly (with low latency),
2106priorities and idle watchers might have too much overhead. In this case 3280and even priorities and idle watchers might have too much overhead. In
2107you would put all the high priority stuff in one loop and all the rest in 3281this case you would put all the high priority stuff in one loop and all
2108a second one, and embed the second one in the first. 3282the rest in a second one, and embed the second one in the first.
2109.PP 3283.PP
2110As long as the watcher is active, the callback will be invoked every time 3284As long as the watcher is active, the callback will be invoked every
2111there might be events pending in the embedded loop. The callback must then 3285time there might be events pending in the embedded loop. The callback
2112call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3286must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2113their callbacks (you could also start an idle watcher to give the embedded 3287sweep and invoke their callbacks (the callback doesn't need to invoke the
2114loop strictly lower priority for example). You can also set the callback 3288\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2115to \f(CW0\fR, in which case the embed watcher will automatically execute the 3289to give the embedded loop strictly lower priority for example).
2116embedded loop sweep.
2117.PP 3290.PP
2118As long as the watcher is started it will automatically handle events. The 3291You can also set the callback to \f(CW0\fR, in which case the embed watcher
2119callback will be invoked whenever some events have been handled. You can 3292will automatically execute the embedded loop sweep whenever necessary.
2120set the callback to \f(CW0\fR to avoid having to specify one if you are not
2121interested in that.
2122.PP 3293.PP
2123Also, there have not currently been made special provisions for forking: 3294Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2124when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3295is active, i.e., the embedded loop will automatically be forked when the
2125but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3296embedding loop forks. In other cases, the user is responsible for calling
2126yourself. 3297\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2127.PP 3298.PP
2128Unfortunately, not all backends are embeddable, only the ones returned by 3299Unfortunately, not all backends are embeddable: only the ones returned by
2129\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3300\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2130portable one. 3301portable one.
2131.PP 3302.PP
2132So when you want to use this feature you will always have to be prepared 3303So when you want to use this feature you will always have to be prepared
2133that you cannot get an embeddable loop. The recommended way to get around 3304that you cannot get an embeddable loop. The recommended way to get around
2134this is to have a separate variables for your embeddable loop, try to 3305this is to have a separate variables for your embeddable loop, try to
2135create it, and if that fails, use the normal loop for everything: 3306create it, and if that fails, use the normal loop for everything.
2136.PP 3307.PP
2137.Vb 3 3308\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2138\& struct ev_loop *loop_hi = ev_default_init (0); 3309.IX Subsection "ev_embed and fork"
2139\& struct ev_loop *loop_lo = 0;
2140\& struct ev_embed embed;
2141.Ve
2142.PP 3310.PP
2143.Vb 5 3311While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2144\& // see if there is a chance of getting one that works 3312automatically be applied to the embedded loop as well, so no special
2145\& // (remember that a flags value of 0 means autodetection) 3313fork handling is required in that case. When the watcher is not running,
2146\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3314however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2147\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3315as applicable.
2148\& : 0;
2149.Ve
2150.PP
2151.Vb 8
2152\& // if we got one, then embed it, otherwise default to loop_hi
2153\& if (loop_lo)
2154\& {
2155\& ev_embed_init (&embed, 0, loop_lo);
2156\& ev_embed_start (loop_hi, &embed);
2157\& }
2158\& else
2159\& loop_lo = loop_hi;
2160.Ve
2161.PP 3316.PP
2162\fIWatcher-Specific Functions and Data Members\fR 3317\fIWatcher-Specific Functions and Data Members\fR
2163.IX Subsection "Watcher-Specific Functions and Data Members" 3318.IX Subsection "Watcher-Specific Functions and Data Members"
2164.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3319.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2165.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3320.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2166.PD 0 3321.PD 0
2167.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3322.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
2168.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3323.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
2169.PD 3324.PD
2170Configures the watcher to embed the given loop, which must be 3325Configures the watcher to embed the given loop, which must be
2171embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3326embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2172invoked automatically, otherwise it is the responsibility of the callback 3327invoked automatically, otherwise it is the responsibility of the callback
2173to invoke it (it will continue to be called until the sweep has been done, 3328to invoke it (it will continue to be called until the sweep has been done,
2174if you do not want thta, you need to temporarily stop the embed watcher). 3329if you do not want that, you need to temporarily stop the embed watcher).
2175.IP "ev_embed_sweep (loop, ev_embed *)" 4 3330.IP "ev_embed_sweep (loop, ev_embed *)" 4
2176.IX Item "ev_embed_sweep (loop, ev_embed *)" 3331.IX Item "ev_embed_sweep (loop, ev_embed *)"
2177Make a single, non-blocking sweep over the embedded loop. This works 3332Make a single, non-blocking sweep over the embedded loop. This works
2178similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3333similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
2179apropriate way for embedded loops. 3334appropriate way for embedded loops.
2180.IP "struct ev_loop *other [read\-only]" 4 3335.IP "struct ev_loop *other [read\-only]" 4
2181.IX Item "struct ev_loop *other [read-only]" 3336.IX Item "struct ev_loop *other [read-only]"
2182The embedded event loop. 3337The embedded event loop.
3338.PP
3339\fIExamples\fR
3340.IX Subsection "Examples"
3341.PP
3342Example: Try to get an embeddable event loop and embed it into the default
3343event loop. If that is not possible, use the default loop. The default
3344loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3345\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3346used).
3347.PP
3348.Vb 3
3349\& struct ev_loop *loop_hi = ev_default_init (0);
3350\& struct ev_loop *loop_lo = 0;
3351\& ev_embed embed;
3352\&
3353\& // see if there is a chance of getting one that works
3354\& // (remember that a flags value of 0 means autodetection)
3355\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3356\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3357\& : 0;
3358\&
3359\& // if we got one, then embed it, otherwise default to loop_hi
3360\& if (loop_lo)
3361\& {
3362\& ev_embed_init (&embed, 0, loop_lo);
3363\& ev_embed_start (loop_hi, &embed);
3364\& }
3365\& else
3366\& loop_lo = loop_hi;
3367.Ve
3368.PP
3369Example: Check if kqueue is available but not recommended and create
3370a kqueue backend for use with sockets (which usually work with any
3371kqueue implementation). Store the kqueue/socket\-only event loop in
3372\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3373.PP
3374.Vb 3
3375\& struct ev_loop *loop = ev_default_init (0);
3376\& struct ev_loop *loop_socket = 0;
3377\& ev_embed embed;
3378\&
3379\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3380\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3381\& {
3382\& ev_embed_init (&embed, 0, loop_socket);
3383\& ev_embed_start (loop, &embed);
3384\& }
3385\&
3386\& if (!loop_socket)
3387\& loop_socket = loop;
3388\&
3389\& // now use loop_socket for all sockets, and loop for everything else
3390.Ve
2183.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3391.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
2184.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3392.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2185.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3393.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2186Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3394Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2187whoever is a good citizen cared to tell libev about it by calling 3395whoever is a good citizen cared to tell libev about it by calling
2188\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3396\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
2189event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3397and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
2190and only in the child after the fork. If whoever good citizen calling 3398after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
2191\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3399and calls it in the wrong process, the fork handlers will be invoked, too,
2192handlers will be invoked, too, of course. 3400of course.
3401.PP
3402\fIThe special problem of life after fork \- how is it possible?\fR
3403.IX Subsection "The special problem of life after fork - how is it possible?"
3404.PP
3405Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3406up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3407sequence should be handled by libev without any problems.
3408.PP
3409This changes when the application actually wants to do event handling
3410in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3411fork.
3412.PP
3413The default mode of operation (for libev, with application help to detect
3414forks) is to duplicate all the state in the child, as would be expected
3415when \fIeither\fR the parent \fIor\fR the child process continues.
3416.PP
3417When both processes want to continue using libev, then this is usually the
3418wrong result. In that case, usually one process (typically the parent) is
3419supposed to continue with all watchers in place as before, while the other
3420process typically wants to start fresh, i.e. without any active watchers.
3421.PP
3422The cleanest and most efficient way to achieve that with libev is to
3423simply create a new event loop, which of course will be \*(L"empty\*(R", and
3424use that for new watchers. This has the advantage of not touching more
3425memory than necessary, and thus avoiding the copy-on-write, and the
3426disadvantage of having to use multiple event loops (which do not support
3427signal watchers).
3428.PP
3429When this is not possible, or you want to use the default loop for
3430other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3431\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3432Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3433watchers, so you have to be careful not to execute code that modifies
3434those watchers. Note also that in that case, you have to re-register any
3435signal watchers.
2193.PP 3436.PP
2194\fIWatcher-Specific Functions and Data Members\fR 3437\fIWatcher-Specific Functions and Data Members\fR
2195.IX Subsection "Watcher-Specific Functions and Data Members" 3438.IX Subsection "Watcher-Specific Functions and Data Members"
2196.IP "ev_fork_init (ev_signal *, callback)" 4 3439.IP "ev_fork_init (ev_fork *, callback)" 4
2197.IX Item "ev_fork_init (ev_signal *, callback)" 3440.IX Item "ev_fork_init (ev_fork *, callback)"
2198Initialises and configures the fork watcher \- it has no parameters of any 3441Initialises and configures the fork watcher \- it has no parameters of any
2199kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3442kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2200believe me. 3443really.
3444.ie n .SS """ev_cleanup"" \- even the best things end"
3445.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3446.IX Subsection "ev_cleanup - even the best things end"
3447Cleanup watchers are called just before the event loop is being destroyed
3448by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3449.PP
3450While there is no guarantee that the event loop gets destroyed, cleanup
3451watchers provide a convenient method to install cleanup hooks for your
3452program, worker threads and so on \- you just to make sure to destroy the
3453loop when you want them to be invoked.
3454.PP
3455Cleanup watchers are invoked in the same way as any other watcher. Unlike
3456all other watchers, they do not keep a reference to the event loop (which
3457makes a lot of sense if you think about it). Like all other watchers, you
3458can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3459.PP
3460\fIWatcher-Specific Functions and Data Members\fR
3461.IX Subsection "Watcher-Specific Functions and Data Members"
3462.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3463.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3464Initialises and configures the cleanup watcher \- it has no parameters of
3465any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3466pointless, I assure you.
3467.PP
3468Example: Register an atexit handler to destroy the default loop, so any
3469cleanup functions are called.
3470.PP
3471.Vb 5
3472\& static void
3473\& program_exits (void)
3474\& {
3475\& ev_loop_destroy (EV_DEFAULT_UC);
3476\& }
3477\&
3478\& ...
3479\& atexit (program_exits);
3480.Ve
3481.ie n .SS """ev_async"" \- how to wake up an event loop"
3482.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3483.IX Subsection "ev_async - how to wake up an event loop"
3484In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3485asynchronous sources such as signal handlers (as opposed to multiple event
3486loops \- those are of course safe to use in different threads).
3487.PP
3488Sometimes, however, you need to wake up an event loop you do not control,
3489for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3490watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3491it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3492.PP
3493This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3494too, are asynchronous in nature, and signals, too, will be compressed
3495(i.e. the number of callback invocations may be less than the number of
3496\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3497of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3498signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3499even without knowing which loop owns the signal.
3500.PP
3501\fIQueueing\fR
3502.IX Subsection "Queueing"
3503.PP
3504\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3505is that the author does not know of a simple (or any) algorithm for a
3506multiple-writer-single-reader queue that works in all cases and doesn't
3507need elaborate support such as pthreads or unportable memory access
3508semantics.
3509.PP
3510That means that if you want to queue data, you have to provide your own
3511queue. But at least I can tell you how to implement locking around your
3512queue:
3513.IP "queueing from a signal handler context" 4
3514.IX Item "queueing from a signal handler context"
3515To implement race-free queueing, you simply add to the queue in the signal
3516handler but you block the signal handler in the watcher callback. Here is
3517an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3518.Sp
3519.Vb 1
3520\& static ev_async mysig;
3521\&
3522\& static void
3523\& sigusr1_handler (void)
3524\& {
3525\& sometype data;
3526\&
3527\& // no locking etc.
3528\& queue_put (data);
3529\& ev_async_send (EV_DEFAULT_ &mysig);
3530\& }
3531\&
3532\& static void
3533\& mysig_cb (EV_P_ ev_async *w, int revents)
3534\& {
3535\& sometype data;
3536\& sigset_t block, prev;
3537\&
3538\& sigemptyset (&block);
3539\& sigaddset (&block, SIGUSR1);
3540\& sigprocmask (SIG_BLOCK, &block, &prev);
3541\&
3542\& while (queue_get (&data))
3543\& process (data);
3544\&
3545\& if (sigismember (&prev, SIGUSR1)
3546\& sigprocmask (SIG_UNBLOCK, &block, 0);
3547\& }
3548.Ve
3549.Sp
3550(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3551instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3552either...).
3553.IP "queueing from a thread context" 4
3554.IX Item "queueing from a thread context"
3555The strategy for threads is different, as you cannot (easily) block
3556threads but you can easily preempt them, so to queue safely you need to
3557employ a traditional mutex lock, such as in this pthread example:
3558.Sp
3559.Vb 2
3560\& static ev_async mysig;
3561\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3562\&
3563\& static void
3564\& otherthread (void)
3565\& {
3566\& // only need to lock the actual queueing operation
3567\& pthread_mutex_lock (&mymutex);
3568\& queue_put (data);
3569\& pthread_mutex_unlock (&mymutex);
3570\&
3571\& ev_async_send (EV_DEFAULT_ &mysig);
3572\& }
3573\&
3574\& static void
3575\& mysig_cb (EV_P_ ev_async *w, int revents)
3576\& {
3577\& pthread_mutex_lock (&mymutex);
3578\&
3579\& while (queue_get (&data))
3580\& process (data);
3581\&
3582\& pthread_mutex_unlock (&mymutex);
3583\& }
3584.Ve
3585.PP
3586\fIWatcher-Specific Functions and Data Members\fR
3587.IX Subsection "Watcher-Specific Functions and Data Members"
3588.IP "ev_async_init (ev_async *, callback)" 4
3589.IX Item "ev_async_init (ev_async *, callback)"
3590Initialises and configures the async watcher \- it has no parameters of any
3591kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3592trust me.
3593.IP "ev_async_send (loop, ev_async *)" 4
3594.IX Item "ev_async_send (loop, ev_async *)"
3595Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3596an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3597returns.
3598.Sp
3599Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3600signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3601embedding section below on what exactly this means).
3602.Sp
3603Note that, as with other watchers in libev, multiple events might get
3604compressed into a single callback invocation (another way to look at
3605this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3606\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3607.Sp
3608This call incurs the overhead of at most one extra system call per event
3609loop iteration, if the event loop is blocked, and no syscall at all if
3610the event loop (or your program) is processing events. That means that
3611repeated calls are basically free (there is no need to avoid calls for
3612performance reasons) and that the overhead becomes smaller (typically
3613zero) under load.
3614.IP "bool = ev_async_pending (ev_async *)" 4
3615.IX Item "bool = ev_async_pending (ev_async *)"
3616Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3617watcher but the event has not yet been processed (or even noted) by the
3618event loop.
3619.Sp
3620\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3621the loop iterates next and checks for the watcher to have become active,
3622it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3623quickly check whether invoking the loop might be a good idea.
3624.Sp
3625Not that this does \fInot\fR check whether the watcher itself is pending,
3626only whether it has been requested to make this watcher pending: there
3627is a time window between the event loop checking and resetting the async
3628notification, and the callback being invoked.
2201.SH "OTHER FUNCTIONS" 3629.SH "OTHER FUNCTIONS"
2202.IX Header "OTHER FUNCTIONS" 3630.IX Header "OTHER FUNCTIONS"
2203There are some other functions of possible interest. Described. Here. Now. 3631There are some other functions of possible interest. Described. Here. Now.
2204.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3632.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2205.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3633.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2206This function combines a simple timer and an I/O watcher, calls your 3634This function combines a simple timer and an I/O watcher, calls your
2207callback on whichever event happens first and automatically stop both 3635callback on whichever event happens first and automatically stops both
2208watchers. This is useful if you want to wait for a single event on an fd 3636watchers. This is useful if you want to wait for a single event on an fd
2209or timeout without having to allocate/configure/start/stop/free one or 3637or timeout without having to allocate/configure/start/stop/free one or
2210more watchers yourself. 3638more watchers yourself.
2211.Sp 3639.Sp
2212If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3640If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
2213is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3641\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
2214\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3642the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
2215.Sp 3643.Sp
2216If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3644If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2217started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3645started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2218repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3646repeat = 0) will be started. \f(CW0\fR is a valid timeout.
2219dubious value.
2220.Sp 3647.Sp
2221The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3648The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
2222passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3649passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2223\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3650\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
2224value passed to \f(CW\*(C`ev_once\*(C'\fR: 3651value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3652a timeout and an io event at the same time \- you probably should give io
3653events precedence.
3654.Sp
3655Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
2225.Sp 3656.Sp
2226.Vb 7 3657.Vb 7
2227\& static void stdin_ready (int revents, void *arg) 3658\& static void stdin_ready (int revents, void *arg)
3659\& {
3660\& if (revents & EV_READ)
3661\& /* stdin might have data for us, joy! */;
3662\& else if (revents & EV_TIMER)
3663\& /* doh, nothing entered */;
3664\& }
3665\&
3666\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3667.Ve
3668.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3669.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3670Feed an event on the given fd, as if a file descriptor backend detected
3671the given events.
3672.IP "ev_feed_signal_event (loop, int signum)" 4
3673.IX Item "ev_feed_signal_event (loop, int signum)"
3674Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3675which is async-safe.
3676.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3677.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3678This section explains some common idioms that are not immediately
3679obvious. Note that examples are sprinkled over the whole manual, and this
3680section only contains stuff that wouldn't fit anywhere else.
3681.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3682.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3683Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3684or modify at any time: libev will completely ignore it. This can be used
3685to associate arbitrary data with your watcher. If you need more data and
3686don't want to allocate memory separately and store a pointer to it in that
3687data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3688data:
3689.PP
3690.Vb 7
3691\& struct my_io
3692\& {
3693\& ev_io io;
3694\& int otherfd;
3695\& void *somedata;
3696\& struct whatever *mostinteresting;
3697\& };
3698\&
3699\& ...
3700\& struct my_io w;
3701\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3702.Ve
3703.PP
3704And since your callback will be called with a pointer to the watcher, you
3705can cast it back to your own type:
3706.PP
3707.Vb 5
3708\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3709\& {
3710\& struct my_io *w = (struct my_io *)w_;
3711\& ...
3712\& }
3713.Ve
3714.PP
3715More interesting and less C\-conformant ways of casting your callback
3716function type instead have been omitted.
3717.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3718.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3719Another common scenario is to use some data structure with multiple
3720embedded watchers, in effect creating your own watcher that combines
3721multiple libev event sources into one \*(L"super-watcher\*(R":
3722.PP
3723.Vb 6
3724\& struct my_biggy
3725\& {
3726\& int some_data;
3727\& ev_timer t1;
3728\& ev_timer t2;
3729\& }
3730.Ve
3731.PP
3732In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3733complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3734the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3735to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3736real programmers):
3737.PP
3738.Vb 1
3739\& #include <stddef.h>
3740\&
3741\& static void
3742\& t1_cb (EV_P_ ev_timer *w, int revents)
3743\& {
3744\& struct my_biggy big = (struct my_biggy *)
3745\& (((char *)w) \- offsetof (struct my_biggy, t1));
3746\& }
3747\&
3748\& static void
3749\& t2_cb (EV_P_ ev_timer *w, int revents)
3750\& {
3751\& struct my_biggy big = (struct my_biggy *)
3752\& (((char *)w) \- offsetof (struct my_biggy, t2));
3753\& }
3754.Ve
3755.SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3756.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3757Often you have structures like this in event-based programs:
3758.PP
3759.Vb 4
3760\& callback ()
2228\& { 3761\& {
2229\& if (revents & EV_TIMEOUT) 3762\& free (request);
2230\& /* doh, nothing entered */;
2231\& else if (revents & EV_READ)
2232\& /* stdin might have data for us, joy! */;
2233\& } 3763\& }
3764\&
3765\& request = start_new_request (..., callback);
2234.Ve 3766.Ve
2235.Sp 3767.PP
3768The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3769used to cancel the operation, or do other things with it.
3770.PP
3771It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3772immediately invoke the callback, for example, to report errors. Or you add
3773some caching layer that finds that it can skip the lengthy aspects of the
3774operation and simply invoke the callback with the result.
3775.PP
3776The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3777has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3778.PP
3779Even if you pass the request by some safer means to the callback, you
3780might want to do something to the request after starting it, such as
3781canceling it, which probably isn't working so well when the callback has
3782already been invoked.
3783.PP
3784A common way around all these issues is to make sure that
3785\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3786\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3787delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3788example, or more sneakily, by reusing an existing (stopped) watcher and
3789pushing it into the pending queue:
3790.PP
2236.Vb 1 3791.Vb 2
2237\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3792\& ev_set_cb (watcher, callback);
3793\& ev_feed_event (EV_A_ watcher, 0);
2238.Ve 3794.Ve
2239.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3795.PP
2240.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3796This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
2241Feeds the given event set into the event loop, as if the specified event 3797invoked, while not delaying callback invocation too much.
2242had happened for the specified watcher (which must be a pointer to an 3798.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
2243initialised but not necessarily started event watcher). 3799.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
2244.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3800Often (especially in \s-1GUI\s0 toolkits) there are places where you have
2245.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3801\&\fImodal\fR interaction, which is most easily implemented by recursively
2246Feed an event on the given fd, as if a file descriptor backend detected 3802invoking \f(CW\*(C`ev_run\*(C'\fR.
2247the given events it. 3803.PP
2248.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3804This brings the problem of exiting \- a callback might want to finish the
2249.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3805main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
2250Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3806a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
2251loop!). 3807and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3808other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3809.PP
3810The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3811invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3812triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3813.PP
3814.Vb 2
3815\& // main loop
3816\& int exit_main_loop = 0;
3817\&
3818\& while (!exit_main_loop)
3819\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3820\&
3821\& // in a modal watcher
3822\& int exit_nested_loop = 0;
3823\&
3824\& while (!exit_nested_loop)
3825\& ev_run (EV_A_ EVRUN_ONCE);
3826.Ve
3827.PP
3828To exit from any of these loops, just set the corresponding exit variable:
3829.PP
3830.Vb 2
3831\& // exit modal loop
3832\& exit_nested_loop = 1;
3833\&
3834\& // exit main program, after modal loop is finished
3835\& exit_main_loop = 1;
3836\&
3837\& // exit both
3838\& exit_main_loop = exit_nested_loop = 1;
3839.Ve
3840.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3841.IX Subsection "THREAD LOCKING EXAMPLE"
3842Here is a fictitious example of how to run an event loop in a different
3843thread from where callbacks are being invoked and watchers are
3844created/added/removed.
3845.PP
3846For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3847which uses exactly this technique (which is suited for many high-level
3848languages).
3849.PP
3850The example uses a pthread mutex to protect the loop data, a condition
3851variable to wait for callback invocations, an async watcher to notify the
3852event loop thread and an unspecified mechanism to wake up the main thread.
3853.PP
3854First, you need to associate some data with the event loop:
3855.PP
3856.Vb 6
3857\& typedef struct {
3858\& mutex_t lock; /* global loop lock */
3859\& ev_async async_w;
3860\& thread_t tid;
3861\& cond_t invoke_cv;
3862\& } userdata;
3863\&
3864\& void prepare_loop (EV_P)
3865\& {
3866\& // for simplicity, we use a static userdata struct.
3867\& static userdata u;
3868\&
3869\& ev_async_init (&u\->async_w, async_cb);
3870\& ev_async_start (EV_A_ &u\->async_w);
3871\&
3872\& pthread_mutex_init (&u\->lock, 0);
3873\& pthread_cond_init (&u\->invoke_cv, 0);
3874\&
3875\& // now associate this with the loop
3876\& ev_set_userdata (EV_A_ u);
3877\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3878\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3879\&
3880\& // then create the thread running ev_run
3881\& pthread_create (&u\->tid, 0, l_run, EV_A);
3882\& }
3883.Ve
3884.PP
3885The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3886solely to wake up the event loop so it takes notice of any new watchers
3887that might have been added:
3888.PP
3889.Vb 5
3890\& static void
3891\& async_cb (EV_P_ ev_async *w, int revents)
3892\& {
3893\& // just used for the side effects
3894\& }
3895.Ve
3896.PP
3897The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3898protecting the loop data, respectively.
3899.PP
3900.Vb 6
3901\& static void
3902\& l_release (EV_P)
3903\& {
3904\& userdata *u = ev_userdata (EV_A);
3905\& pthread_mutex_unlock (&u\->lock);
3906\& }
3907\&
3908\& static void
3909\& l_acquire (EV_P)
3910\& {
3911\& userdata *u = ev_userdata (EV_A);
3912\& pthread_mutex_lock (&u\->lock);
3913\& }
3914.Ve
3915.PP
3916The event loop thread first acquires the mutex, and then jumps straight
3917into \f(CW\*(C`ev_run\*(C'\fR:
3918.PP
3919.Vb 4
3920\& void *
3921\& l_run (void *thr_arg)
3922\& {
3923\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3924\&
3925\& l_acquire (EV_A);
3926\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3927\& ev_run (EV_A_ 0);
3928\& l_release (EV_A);
3929\&
3930\& return 0;
3931\& }
3932.Ve
3933.PP
3934Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3935signal the main thread via some unspecified mechanism (signals? pipe
3936writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3937have been called (in a while loop because a) spurious wakeups are possible
3938and b) skipping inter-thread-communication when there are no pending
3939watchers is very beneficial):
3940.PP
3941.Vb 4
3942\& static void
3943\& l_invoke (EV_P)
3944\& {
3945\& userdata *u = ev_userdata (EV_A);
3946\&
3947\& while (ev_pending_count (EV_A))
3948\& {
3949\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3950\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3951\& }
3952\& }
3953.Ve
3954.PP
3955Now, whenever the main thread gets told to invoke pending watchers, it
3956will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3957thread to continue:
3958.PP
3959.Vb 4
3960\& static void
3961\& real_invoke_pending (EV_P)
3962\& {
3963\& userdata *u = ev_userdata (EV_A);
3964\&
3965\& pthread_mutex_lock (&u\->lock);
3966\& ev_invoke_pending (EV_A);
3967\& pthread_cond_signal (&u\->invoke_cv);
3968\& pthread_mutex_unlock (&u\->lock);
3969\& }
3970.Ve
3971.PP
3972Whenever you want to start/stop a watcher or do other modifications to an
3973event loop, you will now have to lock:
3974.PP
3975.Vb 2
3976\& ev_timer timeout_watcher;
3977\& userdata *u = ev_userdata (EV_A);
3978\&
3979\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3980\&
3981\& pthread_mutex_lock (&u\->lock);
3982\& ev_timer_start (EV_A_ &timeout_watcher);
3983\& ev_async_send (EV_A_ &u\->async_w);
3984\& pthread_mutex_unlock (&u\->lock);
3985.Ve
3986.PP
3987Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3988an event loop currently blocking in the kernel will have no knowledge
3989about the newly added timer. By waking up the loop it will pick up any new
3990watchers in the next event loop iteration.
3991.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3992.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3993While the overhead of a callback that e.g. schedules a thread is small, it
3994is still an overhead. If you embed libev, and your main usage is with some
3995kind of threads or coroutines, you might want to customise libev so that
3996doesn't need callbacks anymore.
3997.PP
3998Imagine you have coroutines that you can switch to using a function
3999\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4000and that due to some magic, the currently active coroutine is stored in a
4001global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4002event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4003the differing \f(CW\*(C`;\*(C'\fR conventions):
4004.PP
4005.Vb 2
4006\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4007\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4008.Ve
4009.PP
4010That means instead of having a C callback function, you store the
4011coroutine to switch to in each watcher, and instead of having libev call
4012your callback, you instead have it switch to that coroutine.
4013.PP
4014A coroutine might now wait for an event with a function called
4015\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4016matter when, or whether the watcher is active or not when this function is
4017called):
4018.PP
4019.Vb 6
4020\& void
4021\& wait_for_event (ev_watcher *w)
4022\& {
4023\& ev_set_cb (w, current_coro);
4024\& switch_to (libev_coro);
4025\& }
4026.Ve
4027.PP
4028That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4029continues the libev coroutine, which, when appropriate, switches back to
4030this or any other coroutine.
4031.PP
4032You can do similar tricks if you have, say, threads with an event queue \-
4033instead of storing a coroutine, you store the queue object and instead of
4034switching to a coroutine, you push the watcher onto the queue and notify
4035any waiters.
4036.PP
4037To embed libev, see \*(L"\s-1EMBEDDING\s0\*(R", but in short, it's easiest to create two
4038files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4039.PP
4040.Vb 4
4041\& // my_ev.h
4042\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4043\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
4044\& #include "../libev/ev.h"
4045\&
4046\& // my_ev.c
4047\& #define EV_H "my_ev.h"
4048\& #include "../libev/ev.c"
4049.Ve
4050.PP
4051And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4052\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4053can even use \fIev.h\fR as header file name directly.
2252.SH "LIBEVENT EMULATION" 4054.SH "LIBEVENT EMULATION"
2253.IX Header "LIBEVENT EMULATION" 4055.IX Header "LIBEVENT EMULATION"
2254Libev offers a compatibility emulation layer for libevent. It cannot 4056Libev offers a compatibility emulation layer for libevent. It cannot
2255emulate the internals of libevent, so here are some usage hints: 4057emulate the internals of libevent, so here are some usage hints:
4058.IP "\(bu" 4
4059Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4060.Sp
4061This was the newest libevent version available when libev was implemented,
4062and is still mostly unchanged in 2010.
4063.IP "\(bu" 4
2256.IP "* Use it by including <event.h>, as usual." 4 4064Use it by including <event.h>, as usual.
2257.IX Item "Use it by including <event.h>, as usual." 4065.IP "\(bu" 4
2258.PD 0 4066The following members are fully supported: ev_base, ev_callback,
2259.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4067ev_arg, ev_fd, ev_res, ev_events.
2260.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4068.IP "\(bu" 4
2261.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 4069Avoid using ev_flags and the EVLIST_*\-macros, while it is
2262.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 4070maintained by libev, it does not work exactly the same way as in libevent (consider
2263.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 4071it a private \s-1API\s0).
2264.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4072.IP "\(bu" 4
4073Priorities are not currently supported. Initialising priorities
4074will fail and all watchers will have the same priority, even though there
4075is an ev_pri field.
4076.IP "\(bu" 4
4077In libevent, the last base created gets the signals, in libev, the
4078base that registered the signal gets the signals.
4079.IP "\(bu" 4
2265.IP "* Other members are not supported." 4 4080Other members are not supported.
2266.IX Item "Other members are not supported." 4081.IP "\(bu" 4
2267.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4082The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2268.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4083to use the libev header file and library.
2269.PD
2270.SH "\*(C+ SUPPORT" 4084.SH "\*(C+ SUPPORT"
2271.IX Header " SUPPORT" 4085.IX Header " SUPPORT"
4086.SS "C \s-1API\s0"
4087.IX Subsection "C API"
4088The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4089libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4090will work fine.
4091.PP
4092Proper exception specifications might have to be added to callbacks passed
4093to libev: exceptions may be thrown only from watcher callbacks, all
4094other callbacks (allocator, syserr, loop acquire/release and periodic
4095reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4096()\*(C'\fR specification. If you have code that needs to be compiled as both C
4097and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4098.PP
4099.Vb 6
4100\& static void
4101\& fatal_error (const char *msg) EV_THROW
4102\& {
4103\& perror (msg);
4104\& abort ();
4105\& }
4106\&
4107\& ...
4108\& ev_set_syserr_cb (fatal_error);
4109.Ve
4110.PP
4111The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4112\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4113because it runs cleanup watchers).
4114.PP
4115Throwing exceptions in watcher callbacks is only supported if libev itself
4116is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4117throwing exceptions through C libraries (most do).
4118.SS "\*(C+ \s-1API\s0"
4119.IX Subsection " API"
2272Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4120Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2273you to use some convinience methods to start/stop watchers and also change 4121you to use some convenience methods to start/stop watchers and also change
2274the callback model to a model using method callbacks on objects. 4122the callback model to a model using method callbacks on objects.
2275.PP 4123.PP
2276To use it, 4124To use it,
2277.PP 4125.PP
2278.Vb 1 4126.Vb 1
2279\& #include <ev++.h> 4127\& #include <ev++.h>
2280.Ve 4128.Ve
2281.PP 4129.PP
2282This automatically includes \fIev.h\fR and puts all of its definitions (many 4130This automatically includes \fIev.h\fR and puts all of its definitions (many
2283of them macros) into the global namespace. All \*(C+ specific things are 4131of them macros) into the global namespace. All \*(C+ specific things are
2284put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding 4132put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
… …
2287Care has been taken to keep the overhead low. The only data member the \*(C+ 4135Care has been taken to keep the overhead low. The only data member the \*(C+
2288classes add (compared to plain C\-style watchers) is the event loop pointer 4136classes add (compared to plain C\-style watchers) is the event loop pointer
2289that the watcher is associated with (or no additional members at all if 4137that the watcher is associated with (or no additional members at all if
2290you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). 4138you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2291.PP 4139.PP
2292Currently, functions, and static and non-static member functions can be 4140Currently, functions, static and non-static member functions and classes
2293used as callbacks. Other types should be easy to add as long as they only 4141with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
2294need one additional pointer for context. If you need support for other 4142to add as long as they only need one additional pointer for context. If
2295types of functors please contact the author (preferably after implementing 4143you need support for other types of functors please contact the author
2296it). 4144(preferably after implementing it).
4145.PP
4146For all this to work, your \*(C+ compiler either has to use the same calling
4147conventions as your C compiler (for static member functions), or you have
4148to embed libev and compile libev itself as \*(C+.
2297.PP 4149.PP
2298Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4150Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2299.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4151.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
2300.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4152.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2301.IX Item "ev::READ, ev::WRITE etc." 4153.IX Item "ev::READ, ev::WRITE etc."
2302These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4154These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2303macros from \fIev.h\fR. 4155macros from \fIev.h\fR.
2304.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4156.ie n .IP """ev::tstamp"", ""ev::now""" 4
2305.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4157.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2306.IX Item "ev::tstamp, ev::now" 4158.IX Item "ev::tstamp, ev::now"
2307Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4159Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2308.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 4160.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
2309.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4161.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2310.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4162.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2311For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4163For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2312the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4164the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2313which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4165which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2314defines by many implementations. 4166defined by many implementations.
2315.Sp 4167.Sp
2316All of those classes have these methods: 4168All of those classes have these methods:
2317.RS 4 4169.RS 4
2318.IP "ev::TYPE::TYPE ()" 4 4170.IP "ev::TYPE::TYPE ()" 4
2319.IX Item "ev::TYPE::TYPE ()" 4171.IX Item "ev::TYPE::TYPE ()"
2320.PD 0 4172.PD 0
2321.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 4173.IP "ev::TYPE::TYPE (loop)" 4
2322.IX Item "ev::TYPE::TYPE (struct ev_loop *)" 4174.IX Item "ev::TYPE::TYPE (loop)"
2323.IP "ev::TYPE::~TYPE" 4 4175.IP "ev::TYPE::~TYPE" 4
2324.IX Item "ev::TYPE::~TYPE" 4176.IX Item "ev::TYPE::~TYPE"
2325.PD 4177.PD
2326The constructor (optionally) takes an event loop to associate the watcher 4178The constructor (optionally) takes an event loop to associate the watcher
2327with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. 4179with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
… …
2350thunking function, making it as fast as a direct C callback. 4202thunking function, making it as fast as a direct C callback.
2351.Sp 4203.Sp
2352Example: simple class declaration and watcher initialisation 4204Example: simple class declaration and watcher initialisation
2353.Sp 4205.Sp
2354.Vb 4 4206.Vb 4
2355\& struct myclass 4207\& struct myclass
2356\& { 4208\& {
2357\& void io_cb (ev::io &w, int revents) { } 4209\& void io_cb (ev::io &w, int revents) { }
2358\& } 4210\& }
2359.Ve 4211\&
2360.Sp
2361.Vb 3
2362\& myclass obj; 4212\& myclass obj;
2363\& ev::io iow; 4213\& ev::io iow;
2364\& iow.set <myclass, &myclass::io_cb> (&obj); 4214\& iow.set <myclass, &myclass::io_cb> (&obj);
4215.Ve
4216.IP "w\->set (object *)" 4
4217.IX Item "w->set (object *)"
4218This is a variation of a method callback \- leaving out the method to call
4219will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4220functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4221the time. Incidentally, you can then also leave out the template argument
4222list.
4223.Sp
4224The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4225int revents)\*(C'\fR.
4226.Sp
4227See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4228.Sp
4229Example: use a functor object as callback.
4230.Sp
4231.Vb 7
4232\& struct myfunctor
4233\& {
4234\& void operator() (ev::io &w, int revents)
4235\& {
4236\& ...
4237\& }
4238\& }
4239\&
4240\& myfunctor f;
4241\&
4242\& ev::io w;
4243\& w.set (&f);
2365.Ve 4244.Ve
2366.IP "w\->set<function> (void *data = 0)" 4 4245.IP "w\->set<function> (void *data = 0)" 4
2367.IX Item "w->set<function> (void *data = 0)" 4246.IX Item "w->set<function> (void *data = 0)"
2368Also sets a callback, but uses a static method or plain function as 4247Also sets a callback, but uses a static method or plain function as
2369callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's 4248callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
… …
2371.Sp 4250.Sp
2372The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. 4251The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2373.Sp 4252.Sp
2374See the method\-\f(CW\*(C`set\*(C'\fR above for more details. 4253See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2375.Sp 4254.Sp
2376Example: 4255Example: Use a plain function as callback.
2377.Sp 4256.Sp
2378.Vb 2 4257.Vb 2
2379\& static void io_cb (ev::io &w, int revents) { } 4258\& static void io_cb (ev::io &w, int revents) { }
2380\& iow.set <io_cb> (); 4259\& iow.set <io_cb> ();
2381.Ve 4260.Ve
2382.IP "w\->set (struct ev_loop *)" 4 4261.IP "w\->set (loop)" 4
2383.IX Item "w->set (struct ev_loop *)" 4262.IX Item "w->set (loop)"
2384Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4263Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2385do this when the watcher is inactive (and not pending either). 4264do this when the watcher is inactive (and not pending either).
2386.IP "w\->set ([args])" 4 4265.IP "w\->set ([arguments])" 4
2387.IX Item "w->set ([args])" 4266.IX Item "w->set ([arguments])"
2388Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4267Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4268with the same arguments. Either this method or a suitable start method
2389called at least once. Unlike the C counterpart, an active watcher gets 4269must be called at least once. Unlike the C counterpart, an active watcher
2390automatically stopped and restarted when reconfiguring it with this 4270gets automatically stopped and restarted when reconfiguring it with this
2391method. 4271method.
4272.Sp
4273For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4274clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
2392.IP "w\->start ()" 4 4275.IP "w\->start ()" 4
2393.IX Item "w->start ()" 4276.IX Item "w->start ()"
2394Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the 4277Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2395constructor already stores the event loop. 4278constructor already stores the event loop.
4279.IP "w\->start ([arguments])" 4
4280.IX Item "w->start ([arguments])"
4281Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4282convenient to wrap them in one call. Uses the same type of arguments as
4283the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
2396.IP "w\->stop ()" 4 4284.IP "w\->stop ()" 4
2397.IX Item "w->stop ()" 4285.IX Item "w->stop ()"
2398Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4286Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2399.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4 4287.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
2400.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4 4288.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2401.IX Item "w->again () (ev::timer, ev::periodic only)" 4289.IX Item "w->again () (ev::timer, ev::periodic only)"
2402For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4290For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2403\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4291\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2404.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 4292.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
… …
2411Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4299Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2412.RE 4300.RE
2413.RS 4 4301.RS 4
2414.RE 4302.RE
2415.PP 4303.PP
2416Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4304Example: Define a class with two I/O and idle watchers, start the I/O
2417the constructor. 4305watchers in the constructor.
2418.PP 4306.PP
2419.Vb 4 4307.Vb 5
2420\& class myclass 4308\& class myclass
2421\& { 4309\& {
2422\& ev_io io; void io_cb (ev::io &w, int revents); 4310\& ev::io io ; void io_cb (ev::io &w, int revents);
4311\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
2423\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4312\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2424.Ve 4313\&
2425.PP
2426.Vb 2
2427\& myclass (); 4314\& myclass (int fd)
2428\& }
2429.Ve
2430.PP
2431.Vb 4
2432\& myclass::myclass (int fd)
2433\& { 4315\& {
2434\& io .set <myclass, &myclass::io_cb > (this); 4316\& io .set <myclass, &myclass::io_cb > (this);
4317\& io2 .set <myclass, &myclass::io2_cb > (this);
2435\& idle.set <myclass, &myclass::idle_cb> (this); 4318\& idle.set <myclass, &myclass::idle_cb> (this);
2436.Ve 4319\&
2437.PP 4320\& io.set (fd, ev::WRITE); // configure the watcher
2438.Vb 2 4321\& io.start (); // start it whenever convenient
2439\& io.start (fd, ev::READ); 4322\&
4323\& io2.start (fd, ev::READ); // set + start in one call
4324\& }
2440\& } 4325\& };
2441.Ve 4326.Ve
4327.SH "OTHER LANGUAGE BINDINGS"
4328.IX Header "OTHER LANGUAGE BINDINGS"
4329Libev does not offer other language bindings itself, but bindings for a
4330number of languages exist in the form of third-party packages. If you know
4331any interesting language binding in addition to the ones listed here, drop
4332me a note.
4333.IP "Perl" 4
4334.IX Item "Perl"
4335The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4336libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4337there are additional modules that implement libev-compatible interfaces
4338to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4339\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4340and \f(CW\*(C`EV::Glib\*(C'\fR).
4341.Sp
4342It can be found and installed via \s-1CPAN\s0, its homepage is at
4343<http://software.schmorp.de/pkg/EV>.
4344.IP "Python" 4
4345.IX Item "Python"
4346Python bindings can be found at <http://code.google.com/p/pyev/>. It
4347seems to be quite complete and well-documented.
4348.IP "Ruby" 4
4349.IX Item "Ruby"
4350Tony Arcieri has written a ruby extension that offers access to a subset
4351of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4352more on top of it. It can be found via gem servers. Its homepage is at
4353<http://rev.rubyforge.org/>.
4354.Sp
4355Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4356makes rev work even on mingw.
4357.IP "Haskell" 4
4358.IX Item "Haskell"
4359A haskell binding to libev is available at
4360http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4361.IP "D" 4
4362.IX Item "D"
4363Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4364be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4365.IP "Ocaml" 4
4366.IX Item "Ocaml"
4367Erkki Seppala has written Ocaml bindings for libev, to be found at
4368http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4369.IP "Lua" 4
4370.IX Item "Lua"
4371Brian Maher has written a partial interface to libev for lua (at the
4372time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4373http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
4374.IP "Javascript" 4
4375.IX Item "Javascript"
4376Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4377.IP "Others" 4
4378.IX Item "Others"
4379There are others, and I stopped counting.
2442.SH "MACRO MAGIC" 4380.SH "MACRO MAGIC"
2443.IX Header "MACRO MAGIC" 4381.IX Header "MACRO MAGIC"
2444Libev can be compiled with a variety of options, the most fundamantal 4382Libev can be compiled with a variety of options, the most fundamental
2445of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) 4383of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2446functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4384functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2447.PP 4385.PP
2448To make it easier to write programs that cope with either variant, the 4386To make it easier to write programs that cope with either variant, the
2449following macros are defined: 4387following macros are defined:
2450.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4388.ie n .IP """EV_A"", ""EV_A_""" 4
2451.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4389.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2452.IX Item "EV_A, EV_A_" 4390.IX Item "EV_A, EV_A_"
2453This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4391This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2454loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4392loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2455\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4393\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2456.Sp 4394.Sp
2457.Vb 3 4395.Vb 3
2458\& ev_unref (EV_A); 4396\& ev_unref (EV_A);
2459\& ev_timer_add (EV_A_ watcher); 4397\& ev_timer_add (EV_A_ watcher);
2460\& ev_loop (EV_A_ 0); 4398\& ev_run (EV_A_ 0);
2461.Ve 4399.Ve
2462.Sp 4400.Sp
2463It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4401It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2464which is often provided by the following macro. 4402which is often provided by the following macro.
2465.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4403.ie n .IP """EV_P"", ""EV_P_""" 4
2466.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4404.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2467.IX Item "EV_P, EV_P_" 4405.IX Item "EV_P, EV_P_"
2468This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4406This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2469loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4407loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2470\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4408\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2471.Sp 4409.Sp
2472.Vb 2 4410.Vb 2
2473\& // this is how ev_unref is being declared 4411\& // this is how ev_unref is being declared
2474\& static void ev_unref (EV_P); 4412\& static void ev_unref (EV_P);
2475.Ve 4413\&
2476.Sp
2477.Vb 2
2478\& // this is how you can declare your typical callback 4414\& // this is how you can declare your typical callback
2479\& static void cb (EV_P_ ev_timer *w, int revents) 4415\& static void cb (EV_P_ ev_timer *w, int revents)
2480.Ve 4416.Ve
2481.Sp 4417.Sp
2482It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4418It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2483suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4419suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2484.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4420.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
2485.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4421.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2486.IX Item "EV_DEFAULT, EV_DEFAULT_" 4422.IX Item "EV_DEFAULT, EV_DEFAULT_"
2487Similar to the other two macros, this gives you the value of the default 4423Similar to the other two macros, this gives you the value of the default
2488loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4424loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4425will be initialised if it isn't already initialised.
4426.Sp
4427For non-multiplicity builds, these macros do nothing, so you always have
4428to initialise the loop somewhere.
4429.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4430.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4431.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4432Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4433default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4434is undefined when the default loop has not been initialised by a previous
4435execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4436.Sp
4437It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4438watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2489.PP 4439.PP
2490Example: Declare and initialise a check watcher, utilising the above 4440Example: Declare and initialise a check watcher, utilising the above
2491macros so it will work regardless of whether multiple loops are supported 4441macros so it will work regardless of whether multiple loops are supported
2492or not. 4442or not.
2493.PP 4443.PP
2494.Vb 5 4444.Vb 5
2495\& static void 4445\& static void
2496\& check_cb (EV_P_ ev_timer *w, int revents) 4446\& check_cb (EV_P_ ev_timer *w, int revents)
2497\& { 4447\& {
2498\& ev_check_stop (EV_A_ w); 4448\& ev_check_stop (EV_A_ w);
2499\& } 4449\& }
2500.Ve 4450\&
2501.PP
2502.Vb 4
2503\& ev_check check; 4451\& ev_check check;
2504\& ev_check_init (&check, check_cb); 4452\& ev_check_init (&check, check_cb);
2505\& ev_check_start (EV_DEFAULT_ &check); 4453\& ev_check_start (EV_DEFAULT_ &check);
2506\& ev_loop (EV_DEFAULT_ 0); 4454\& ev_run (EV_DEFAULT_ 0);
2507.Ve 4455.Ve
2508.SH "EMBEDDING" 4456.SH "EMBEDDING"
2509.IX Header "EMBEDDING" 4457.IX Header "EMBEDDING"
2510Libev can (and often is) directly embedded into host 4458Libev can (and often is) directly embedded into host
2511applications. Examples of applications that embed it include the Deliantra 4459applications. Examples of applications that embed it include the Deliantra
2512Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4460Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2513and rxvt\-unicode. 4461and rxvt-unicode.
2514.PP 4462.PP
2515The goal is to enable you to just copy the necessary files into your 4463The goal is to enable you to just copy the necessary files into your
2516source directory without having to change even a single line in them, so 4464source directory without having to change even a single line in them, so
2517you can easily upgrade by simply copying (or having a checked-out copy of 4465you can easily upgrade by simply copying (or having a checked-out copy of
2518libev somewhere in your source tree). 4466libev somewhere in your source tree).
2519.Sh "\s-1FILESETS\s0" 4467.SS "\s-1FILESETS\s0"
2520.IX Subsection "FILESETS" 4468.IX Subsection "FILESETS"
2521Depending on what features you need you need to include one or more sets of files 4469Depending on what features you need you need to include one or more sets of files
2522in your app. 4470in your application.
2523.PP 4471.PP
2524\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4472\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2525.IX Subsection "CORE EVENT LOOP" 4473.IX Subsection "CORE EVENT LOOP"
2526.PP 4474.PP
2527To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4475To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2528configuration (no autoconf): 4476configuration (no autoconf):
2529.PP 4477.PP
2530.Vb 2 4478.Vb 2
2531\& #define EV_STANDALONE 1 4479\& #define EV_STANDALONE 1
2532\& #include "ev.c" 4480\& #include "ev.c"
2533.Ve 4481.Ve
2534.PP 4482.PP
2535This will automatically include \fIev.h\fR, too, and should be done in a 4483This will automatically include \fIev.h\fR, too, and should be done in a
2536single C source file only to provide the function implementations. To use 4484single C source file only to provide the function implementations. To use
2537it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4485it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2538done by writing a wrapper around \fIev.h\fR that you can include instead and 4486done by writing a wrapper around \fIev.h\fR that you can include instead and
2539where you can put other configuration options): 4487where you can put other configuration options):
2540.PP 4488.PP
2541.Vb 2 4489.Vb 2
2542\& #define EV_STANDALONE 1 4490\& #define EV_STANDALONE 1
2543\& #include "ev.h" 4491\& #include "ev.h"
2544.Ve 4492.Ve
2545.PP 4493.PP
2546Both header files and implementation files can be compiled with a \*(C+ 4494Both header files and implementation files can be compiled with a \*(C+
2547compiler (at least, thats a stated goal, and breakage will be treated 4495compiler (at least, that's a stated goal, and breakage will be treated
2548as a bug). 4496as a bug).
2549.PP 4497.PP
2550You need the following files in your source tree, or in a directory 4498You need the following files in your source tree, or in a directory
2551in your include path (e.g. in libev/ when using \-Ilibev): 4499in your include path (e.g. in libev/ when using \-Ilibev):
2552.PP 4500.PP
2553.Vb 4 4501.Vb 4
2554\& ev.h 4502\& ev.h
2555\& ev.c 4503\& ev.c
2556\& ev_vars.h 4504\& ev_vars.h
2557\& ev_wrap.h 4505\& ev_wrap.h
2558.Ve 4506\&
2559.PP
2560.Vb 1
2561\& ev_win32.c required on win32 platforms only 4507\& ev_win32.c required on win32 platforms only
2562.Ve 4508\&
2563.PP
2564.Vb 5
2565\& ev_select.c only when select backend is enabled (which is enabled by default) 4509\& ev_select.c only when select backend is enabled (which is enabled by default)
2566\& ev_poll.c only when poll backend is enabled (disabled by default) 4510\& ev_poll.c only when poll backend is enabled (disabled by default)
2567\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4511\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2568\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4512\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2569\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4513\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2570.Ve 4514.Ve
2571.PP 4515.PP
2572\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4516\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2573to compile this single file. 4517to compile this single file.
2574.PP 4518.PP
… …
2576.IX Subsection "LIBEVENT COMPATIBILITY API" 4520.IX Subsection "LIBEVENT COMPATIBILITY API"
2577.PP 4521.PP
2578To include the libevent compatibility \s-1API\s0, also include: 4522To include the libevent compatibility \s-1API\s0, also include:
2579.PP 4523.PP
2580.Vb 1 4524.Vb 1
2581\& #include "event.c" 4525\& #include "event.c"
2582.Ve 4526.Ve
2583.PP 4527.PP
2584in the file including \fIev.c\fR, and: 4528in the file including \fIev.c\fR, and:
2585.PP 4529.PP
2586.Vb 1 4530.Vb 1
2587\& #include "event.h" 4531\& #include "event.h"
2588.Ve 4532.Ve
2589.PP 4533.PP
2590in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4534in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2591.PP 4535.PP
2592You need the following additional files for this: 4536You need the following additional files for this:
2593.PP 4537.PP
2594.Vb 2 4538.Vb 2
2595\& event.h 4539\& event.h
2596\& event.c 4540\& event.c
2597.Ve 4541.Ve
2598.PP 4542.PP
2599\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4543\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2600.IX Subsection "AUTOCONF SUPPORT" 4544.IX Subsection "AUTOCONF SUPPORT"
2601.PP 4545.PP
2602Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4546Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2603whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4547whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2604\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4548\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2605include \fIconfig.h\fR and configure itself accordingly. 4549include \fIconfig.h\fR and configure itself accordingly.
2606.PP 4550.PP
2607For this of course you need the m4 file: 4551For this of course you need the m4 file:
2608.PP 4552.PP
2609.Vb 1 4553.Vb 1
2610\& libev.m4 4554\& libev.m4
2611.Ve 4555.Ve
2612.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4556.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2613.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4557.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2614Libev can be configured via a variety of preprocessor symbols you have to define 4558Libev can be configured via a variety of preprocessor symbols you have to
2615before including any of its files. The default is not to build for multiplicity 4559define before including (or compiling) any of its files. The default in
2616and only include the select backend. 4560the absence of autoconf is documented for every option.
4561.PP
4562Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4563values when compiling libev vs. including \fIev.h\fR, so it is permissible
4564to redefine them before including \fIev.h\fR without breaking compatibility
4565to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4566users of libev and the libev code itself must be compiled with compatible
4567settings.
4568.IP "\s-1EV_COMPAT3\s0 (h)" 4
4569.IX Item "EV_COMPAT3 (h)"
4570Backwards compatibility is a major concern for libev. This is why this
4571release of libev comes with wrappers for the functions and symbols that
4572have been renamed between libev version 3 and 4.
4573.Sp
4574You can disable these wrappers (to test compatibility with future
4575versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4576sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4577from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4578typedef in that case.
4579.Sp
4580In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4581and in some even more future version the compatibility code will be
4582removed completely.
2617.IP "\s-1EV_STANDALONE\s0" 4 4583.IP "\s-1EV_STANDALONE\s0 (h)" 4
2618.IX Item "EV_STANDALONE" 4584.IX Item "EV_STANDALONE (h)"
2619Must always be \f(CW1\fR if you do not use autoconf configuration, which 4585Must always be \f(CW1\fR if you do not use autoconf configuration, which
2620keeps libev from including \fIconfig.h\fR, and it also defines dummy 4586keeps libev from including \fIconfig.h\fR, and it also defines dummy
2621implementations for some libevent functions (such as logging, which is not 4587implementations for some libevent functions (such as logging, which is not
2622supported). It will also not define any of the structs usually found in 4588supported). It will also not define any of the structs usually found in
2623\&\fIevent.h\fR that are not directly supported by the libev core alone. 4589\&\fIevent.h\fR that are not directly supported by the libev core alone.
4590.Sp
4591In standalone mode, libev will still try to automatically deduce the
4592configuration, but has to be more conservative.
4593.IP "\s-1EV_USE_FLOOR\s0" 4
4594.IX Item "EV_USE_FLOOR"
4595If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4596periodic reschedule calculations, otherwise libev will fall back on a
4597portable (slower) implementation. If you enable this, you usually have to
4598link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4599function is not available will fail, so the safe default is to not enable
4600this.
2624.IP "\s-1EV_USE_MONOTONIC\s0" 4 4601.IP "\s-1EV_USE_MONOTONIC\s0" 4
2625.IX Item "EV_USE_MONOTONIC" 4602.IX Item "EV_USE_MONOTONIC"
2626If defined to be \f(CW1\fR, libev will try to detect the availability of the 4603If defined to be \f(CW1\fR, libev will try to detect the availability of the
2627monotonic clock option at both compiletime and runtime. Otherwise no use 4604monotonic clock option at both compile time and runtime. Otherwise no
2628of the monotonic clock option will be attempted. If you enable this, you 4605use of the monotonic clock option will be attempted. If you enable this,
2629usually have to link against librt or something similar. Enabling it when 4606you usually have to link against librt or something similar. Enabling it
2630the functionality isn't available is safe, though, although you have 4607when the functionality isn't available is safe, though, although you have
2631to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4608to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2632function is hiding in (often \fI\-lrt\fR). 4609function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2633.IP "\s-1EV_USE_REALTIME\s0" 4 4610.IP "\s-1EV_USE_REALTIME\s0" 4
2634.IX Item "EV_USE_REALTIME" 4611.IX Item "EV_USE_REALTIME"
2635If defined to be \f(CW1\fR, libev will try to detect the availability of the 4612If defined to be \f(CW1\fR, libev will try to detect the availability of the
2636realtime clock option at compiletime (and assume its availability at 4613real-time clock option at compile time (and assume its availability
2637runtime if successful). Otherwise no use of the realtime clock option will 4614at runtime if successful). Otherwise no use of the real-time clock
2638be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4615option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2639(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the 4616by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2640note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4617correctness. See the note about libraries in the description of
4618\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4619\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4620.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4621.IX Item "EV_USE_CLOCK_SYSCALL"
4622If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4623of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4624exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4625unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4626programs needlessly. Using a direct syscall is slightly slower (in
4627theory), because no optimised vdso implementation can be used, but avoids
4628the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4629higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
2641.IP "\s-1EV_USE_NANOSLEEP\s0" 4 4630.IP "\s-1EV_USE_NANOSLEEP\s0" 4
2642.IX Item "EV_USE_NANOSLEEP" 4631.IX Item "EV_USE_NANOSLEEP"
2643If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available 4632If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2644and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR. 4633and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4634.IP "\s-1EV_USE_EVENTFD\s0" 4
4635.IX Item "EV_USE_EVENTFD"
4636If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4637available and will probe for kernel support at runtime. This will improve
4638\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4639If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
46402.7 or newer, otherwise disabled.
2645.IP "\s-1EV_USE_SELECT\s0" 4 4641.IP "\s-1EV_USE_SELECT\s0" 4
2646.IX Item "EV_USE_SELECT" 4642.IX Item "EV_USE_SELECT"
2647If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4643If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2648\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4644\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2649other method takes over, select will be it. Otherwise the select backend 4645other method takes over, select will be it. Otherwise the select backend
2650will not be compiled in. 4646will not be compiled in.
2651.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4647.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2652.IX Item "EV_SELECT_USE_FD_SET" 4648.IX Item "EV_SELECT_USE_FD_SET"
2653If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4649If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2654structure. This is useful if libev doesn't compile due to a missing 4650structure. This is useful if libev doesn't compile due to a missing
2655\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4651\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2656exotic systems. This usually limits the range of file descriptors to some 4652on exotic systems. This usually limits the range of file descriptors to
2657low limit such as 1024 or might have other limitations (winsocket only 4653some low limit such as 1024 or might have other limitations (winsocket
2658allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4654only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2659influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4655configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2660.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4656.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2661.IX Item "EV_SELECT_IS_WINSOCKET" 4657.IX Item "EV_SELECT_IS_WINSOCKET"
2662When defined to \f(CW1\fR, the select backend will assume that 4658When defined to \f(CW1\fR, the select backend will assume that
2663select/socket/connect etc. don't understand file descriptors but 4659select/socket/connect etc. don't understand file descriptors but
2664wants osf handles on win32 (this is the case when the select to 4660wants osf handles on win32 (this is the case when the select to
2665be used is the winsock select). This means that it will call 4661be used is the winsock select). This means that it will call
2666\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4662\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2667it is assumed that all these functions actually work on fds, even 4663it is assumed that all these functions actually work on fds, even
2668on win32. Should not be defined on non\-win32 platforms. 4664on win32. Should not be defined on non\-win32 platforms.
4665.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4666.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4667If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4668file descriptors to socket handles. When not defining this symbol (the
4669default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4670correct. In some cases, programs use their own file descriptor management,
4671in which case they can provide this function to map fds to socket handles.
4672.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4673.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4674If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4675using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4676their own fd to handle mapping, overwriting this function makes it easier
4677to do so. This can be done by defining this macro to an appropriate value.
4678.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4679.IX Item "EV_WIN32_CLOSE_FD(fd)"
4680If programs implement their own fd to handle mapping on win32, then this
4681macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4682file descriptors again. Note that the replacement function has to close
4683the underlying \s-1OS\s0 handle.
4684.IP "\s-1EV_USE_WSASOCKET\s0" 4
4685.IX Item "EV_USE_WSASOCKET"
4686If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4687communication socket, which works better in some environments. Otherwise,
4688the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4689environments.
2669.IP "\s-1EV_USE_POLL\s0" 4 4690.IP "\s-1EV_USE_POLL\s0" 4
2670.IX Item "EV_USE_POLL" 4691.IX Item "EV_USE_POLL"
2671If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4692If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2672backend. Otherwise it will be enabled on non\-win32 platforms. It 4693backend. Otherwise it will be enabled on non\-win32 platforms. It
2673takes precedence over select. 4694takes precedence over select.
2674.IP "\s-1EV_USE_EPOLL\s0" 4 4695.IP "\s-1EV_USE_EPOLL\s0" 4
2675.IX Item "EV_USE_EPOLL" 4696.IX Item "EV_USE_EPOLL"
2676If defined to be \f(CW1\fR, libev will compile in support for the Linux 4697If defined to be \f(CW1\fR, libev will compile in support for the Linux
2677\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4698\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2678otherwise another method will be used as fallback. This is the 4699otherwise another method will be used as fallback. This is the preferred
2679preferred backend for GNU/Linux systems. 4700backend for GNU/Linux systems. If undefined, it will be enabled if the
4701headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2680.IP "\s-1EV_USE_KQUEUE\s0" 4 4702.IP "\s-1EV_USE_KQUEUE\s0" 4
2681.IX Item "EV_USE_KQUEUE" 4703.IX Item "EV_USE_KQUEUE"
2682If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4704If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2683\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4705\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2684otherwise another method will be used as fallback. This is the preferred 4706otherwise another method will be used as fallback. This is the preferred
… …
269410 port style backend. Its availability will be detected at runtime, 471610 port style backend. Its availability will be detected at runtime,
2695otherwise another method will be used as fallback. This is the preferred 4717otherwise another method will be used as fallback. This is the preferred
2696backend for Solaris 10 systems. 4718backend for Solaris 10 systems.
2697.IP "\s-1EV_USE_DEVPOLL\s0" 4 4719.IP "\s-1EV_USE_DEVPOLL\s0" 4
2698.IX Item "EV_USE_DEVPOLL" 4720.IX Item "EV_USE_DEVPOLL"
2699reserved for future expansion, works like the \s-1USE\s0 symbols above. 4721Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2700.IP "\s-1EV_USE_INOTIFY\s0" 4 4722.IP "\s-1EV_USE_INOTIFY\s0" 4
2701.IX Item "EV_USE_INOTIFY" 4723.IX Item "EV_USE_INOTIFY"
2702If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4724If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2703interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 4725interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2704be detected at runtime. 4726be detected at runtime. If undefined, it will be enabled if the headers
4727indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4728.IP "\s-1EV_NO_SMP\s0" 4
4729.IX Item "EV_NO_SMP"
4730If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4731between threads, that is, threads can be used, but threads never run on
4732different cpus (or different cpu cores). This reduces dependencies
4733and makes libev faster.
4734.IP "\s-1EV_NO_THREADS\s0" 4
4735.IX Item "EV_NO_THREADS"
4736If defined to be \f(CW1\fR, libev will assume that it will never be called from
4737different threads (that includes signal handlers), which is a stronger
4738assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4739libev faster.
4740.IP "\s-1EV_ATOMIC_T\s0" 4
4741.IX Item "EV_ATOMIC_T"
4742Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4743access is atomic with respect to other threads or signal contexts. No
4744such type is easily found in the C language, so you can provide your own
4745type that you know is safe for your purposes. It is used both for signal
4746handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4747watchers.
4748.Sp
4749In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4750(from \fIsignal.h\fR), which is usually good enough on most platforms.
2705.IP "\s-1EV_H\s0" 4 4751.IP "\s-1EV_H\s0 (h)" 4
2706.IX Item "EV_H" 4752.IX Item "EV_H (h)"
2707The name of the \fIev.h\fR header file used to include it. The default if 4753The name of the \fIev.h\fR header file used to include it. The default if
2708undefined is \f(CW"ev.h"\fR in \fIevent.h\fR and \fIev.c\fR. This can be used to 4754undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2709virtually rename the \fIev.h\fR header file in case of conflicts. 4755used to virtually rename the \fIev.h\fR header file in case of conflicts.
2710.IP "\s-1EV_CONFIG_H\s0" 4 4756.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2711.IX Item "EV_CONFIG_H" 4757.IX Item "EV_CONFIG_H (h)"
2712If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4758If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2713\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4759\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2714\&\f(CW\*(C`EV_H\*(C'\fR, above. 4760\&\f(CW\*(C`EV_H\*(C'\fR, above.
2715.IP "\s-1EV_EVENT_H\s0" 4 4761.IP "\s-1EV_EVENT_H\s0 (h)" 4
2716.IX Item "EV_EVENT_H" 4762.IX Item "EV_EVENT_H (h)"
2717Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4763Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2718of how the \fIevent.h\fR header can be found, the dfeault is \f(CW"event.h"\fR. 4764of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2719.IP "\s-1EV_PROTOTYPES\s0" 4 4765.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2720.IX Item "EV_PROTOTYPES" 4766.IX Item "EV_PROTOTYPES (h)"
2721If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4767If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2722prototypes, but still define all the structs and other symbols. This is 4768prototypes, but still define all the structs and other symbols. This is
2723occasionally useful if you want to provide your own wrapper functions 4769occasionally useful if you want to provide your own wrapper functions
2724around libev functions. 4770around libev functions.
2725.IP "\s-1EV_MULTIPLICITY\s0" 4 4771.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2727If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4773If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2728will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4774will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2729additional independent event loops. Otherwise there will be no support 4775additional independent event loops. Otherwise there will be no support
2730for multiple event loops and there is no first event loop pointer 4776for multiple event loops and there is no first event loop pointer
2731argument. Instead, all functions act on the single default loop. 4777argument. Instead, all functions act on the single default loop.
4778.Sp
4779Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4780default loop when multiplicity is switched off \- you always have to
4781initialise the loop manually in this case.
2732.IP "\s-1EV_MINPRI\s0" 4 4782.IP "\s-1EV_MINPRI\s0" 4
2733.IX Item "EV_MINPRI" 4783.IX Item "EV_MINPRI"
2734.PD 0 4784.PD 0
2735.IP "\s-1EV_MAXPRI\s0" 4 4785.IP "\s-1EV_MAXPRI\s0" 4
2736.IX Item "EV_MAXPRI" 4786.IX Item "EV_MAXPRI"
… …
2743When doing priority-based operations, libev usually has to linearly search 4793When doing priority-based operations, libev usually has to linearly search
2744all the priorities, so having many of them (hundreds) uses a lot of space 4794all the priorities, so having many of them (hundreds) uses a lot of space
2745and time, so using the defaults of five priorities (\-2 .. +2) is usually 4795and time, so using the defaults of five priorities (\-2 .. +2) is usually
2746fine. 4796fine.
2747.Sp 4797.Sp
2748If your embedding app does not need any priorities, defining these both to 4798If your embedding application does not need any priorities, defining these
2749\&\f(CW0\fR will save some memory and cpu. 4799both to \f(CW0\fR will save some memory and \s-1CPU\s0.
2750.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4800.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
2751.IX Item "EV_PERIODIC_ENABLE" 4801.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
2752If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4802If undefined or defined to be \f(CW1\fR (and the platform supports it), then
2753defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4803the respective watcher type is supported. If defined to be \f(CW0\fR, then it
2754code. 4804is not. Disabling watcher types mainly saves code size.
2755.IP "\s-1EV_IDLE_ENABLE\s0" 4
2756.IX Item "EV_IDLE_ENABLE"
2757If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2758defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2759code.
2760.IP "\s-1EV_EMBED_ENABLE\s0" 4
2761.IX Item "EV_EMBED_ENABLE"
2762If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2763defined to be \f(CW0\fR, then they are not.
2764.IP "\s-1EV_STAT_ENABLE\s0" 4 4805.IP "\s-1EV_FEATURES\s0" 4
2765.IX Item "EV_STAT_ENABLE" 4806.IX Item "EV_FEATURES"
2766If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2767defined to be \f(CW0\fR, then they are not.
2768.IP "\s-1EV_FORK_ENABLE\s0" 4
2769.IX Item "EV_FORK_ENABLE"
2770If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2771defined to be \f(CW0\fR, then they are not.
2772.IP "\s-1EV_MINIMAL\s0" 4
2773.IX Item "EV_MINIMAL"
2774If you need to shave off some kilobytes of code at the expense of some 4807If you need to shave off some kilobytes of code at the expense of some
2775speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4808speed (but with the full \s-1API\s0), you can define this symbol to request
2776some inlining decisions, saves roughly 30% codesize of amd64. 4809certain subsets of functionality. The default is to enable all features
4810that can be enabled on the platform.
4811.Sp
4812A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4813with some broad features you want) and then selectively re-enable
4814additional parts you want, for example if you want everything minimal,
4815but multiple event loop support, async and child watchers and the poll
4816backend, use this:
4817.Sp
4818.Vb 5
4819\& #define EV_FEATURES 0
4820\& #define EV_MULTIPLICITY 1
4821\& #define EV_USE_POLL 1
4822\& #define EV_CHILD_ENABLE 1
4823\& #define EV_ASYNC_ENABLE 1
4824.Ve
4825.Sp
4826The actual value is a bitset, it can be a combination of the following
4827values (by default, all of these are enabled):
4828.RS 4
4829.ie n .IP "1 \- faster/larger code" 4
4830.el .IP "\f(CW1\fR \- faster/larger code" 4
4831.IX Item "1 - faster/larger code"
4832Use larger code to speed up some operations.
4833.Sp
4834Currently this is used to override some inlining decisions (enlarging the
4835code size by roughly 30% on amd64).
4836.Sp
4837When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4838gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4839assertions.
4840.Sp
4841The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4842(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4843.ie n .IP "2 \- faster/larger data structures" 4
4844.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4845.IX Item "2 - faster/larger data structures"
4846Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4847hash table sizes and so on. This will usually further increase code size
4848and can additionally have an effect on the size of data structures at
4849runtime.
4850.Sp
4851The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4852(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4853.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4854.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4855.IX Item "4 - full API configuration"
4856This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4857enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4858.ie n .IP "8 \- full \s-1API\s0" 4
4859.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4860.IX Item "8 - full API"
4861This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4862details on which parts of the \s-1API\s0 are still available without this
4863feature, and do not complain if this subset changes over time.
4864.ie n .IP "16 \- enable all optional watcher types" 4
4865.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4866.IX Item "16 - enable all optional watcher types"
4867Enables all optional watcher types. If you want to selectively enable
4868only some watcher types other than I/O and timers (e.g. prepare,
4869embed, async, child...) you can enable them manually by defining
4870\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4871.ie n .IP "32 \- enable all backends" 4
4872.el .IP "\f(CW32\fR \- enable all backends" 4
4873.IX Item "32 - enable all backends"
4874This enables all backends \- without this feature, you need to enable at
4875least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4876.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4877.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4878.IX Item "64 - enable OS-specific helper APIs"
4879Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4880default.
4881.RE
4882.RS 4
4883.Sp
4884Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4885reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4886code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4887watchers, timers and monotonic clock support.
4888.Sp
4889With an intelligent-enough linker (gcc+binutils are intelligent enough
4890when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4891your program might be left out as well \- a binary starting a timer and an
4892I/O watcher then might come out at only 5Kb.
4893.RE
4894.IP "\s-1EV_API_STATIC\s0" 4
4895.IX Item "EV_API_STATIC"
4896If this symbol is defined (by default it is not), then all identifiers
4897will have static linkage. This means that libev will not export any
4898identifiers, and you cannot link against libev anymore. This can be useful
4899when you embed libev, only want to use libev functions in a single file,
4900and do not want its identifiers to be visible.
4901.Sp
4902To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4903wants to use libev.
4904.Sp
4905This option only works when libev is compiled with a C compiler, as \*(C+
4906doesn't support the required declaration syntax.
4907.IP "\s-1EV_AVOID_STDIO\s0" 4
4908.IX Item "EV_AVOID_STDIO"
4909If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4910functions (printf, scanf, perror etc.). This will increase the code size
4911somewhat, but if your program doesn't otherwise depend on stdio and your
4912libc allows it, this avoids linking in the stdio library which is quite
4913big.
4914.Sp
4915Note that error messages might become less precise when this option is
4916enabled.
4917.IP "\s-1EV_NSIG\s0" 4
4918.IX Item "EV_NSIG"
4919The highest supported signal number, +1 (or, the number of
4920signals): Normally, libev tries to deduce the maximum number of signals
4921automatically, but sometimes this fails, in which case it can be
4922specified. Also, using a lower number than detected (\f(CW32\fR should be
4923good for about any system in existence) can save some memory, as libev
4924statically allocates some 12\-24 bytes per signal number.
2777.IP "\s-1EV_PID_HASHSIZE\s0" 4 4925.IP "\s-1EV_PID_HASHSIZE\s0" 4
2778.IX Item "EV_PID_HASHSIZE" 4926.IX Item "EV_PID_HASHSIZE"
2779\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 4927\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2780pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 4928pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2781than enough. If you need to manage thousands of children you might want to 4929usually more than enough. If you need to manage thousands of children you
2782increase this value (\fImust\fR be a power of two). 4930might want to increase this value (\fImust\fR be a power of two).
2783.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 4931.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2784.IX Item "EV_INOTIFY_HASHSIZE" 4932.IX Item "EV_INOTIFY_HASHSIZE"
2785\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by 4933\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2786inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 4934inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
2787usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 4935disabled), usually more than enough. If you need to manage thousands of
2788watchers you might want to increase this value (\fImust\fR be a power of 4936\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2789two). 4937power of two).
4938.IP "\s-1EV_USE_4HEAP\s0" 4
4939.IX Item "EV_USE_4HEAP"
4940Heaps are not very cache-efficient. To improve the cache-efficiency of the
4941timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4942to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4943faster performance with many (thousands) of watchers.
4944.Sp
4945The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4946will be \f(CW0\fR.
4947.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4948.IX Item "EV_HEAP_CACHE_AT"
4949Heaps are not very cache-efficient. To improve the cache-efficiency of the
4950timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4951the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4952which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4953but avoids random read accesses on heap changes. This improves performance
4954noticeably with many (hundreds) of watchers.
4955.Sp
4956The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4957will be \f(CW0\fR.
4958.IP "\s-1EV_VERIFY\s0" 4
4959.IX Item "EV_VERIFY"
4960Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4961be done: If set to \f(CW0\fR, no internal verification code will be compiled
4962in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4963called. If set to \f(CW2\fR, then the internal verification code will be
4964called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4965verification code will be called very frequently, which will slow down
4966libev considerably.
4967.Sp
4968The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4969will be \f(CW0\fR.
2790.IP "\s-1EV_COMMON\s0" 4 4970.IP "\s-1EV_COMMON\s0" 4
2791.IX Item "EV_COMMON" 4971.IX Item "EV_COMMON"
2792By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4972By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2793this macro to a something else you can include more and other types of 4973this macro to something else you can include more and other types of
2794members. You have to define it each time you include one of the files, 4974members. You have to define it each time you include one of the files,
2795though, and it must be identical each time. 4975though, and it must be identical each time.
2796.Sp 4976.Sp
2797For example, the perl \s-1EV\s0 module uses something like this: 4977For example, the perl \s-1EV\s0 module uses something like this:
2798.Sp 4978.Sp
2799.Vb 3 4979.Vb 3
2800\& #define EV_COMMON \e 4980\& #define EV_COMMON \e
2801\& SV *self; /* contains this struct */ \e 4981\& SV *self; /* contains this struct */ \e
2802\& SV *cb_sv, *fh /* note no trailing ";" */ 4982\& SV *cb_sv, *fh /* note no trailing ";" */
2803.Ve 4983.Ve
2804.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 4984.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2805.IX Item "EV_CB_DECLARE (type)" 4985.IX Item "EV_CB_DECLARE (type)"
2806.PD 0 4986.PD 0
2807.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 4987.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2813and the way callbacks are invoked and set. Must expand to a struct member 4993and the way callbacks are invoked and set. Must expand to a struct member
2814definition and a statement, respectively. See the \fIev.h\fR header file for 4994definition and a statement, respectively. See the \fIev.h\fR header file for
2815their default definitions. One possible use for overriding these is to 4995their default definitions. One possible use for overriding these is to
2816avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 4996avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2817method calls instead of plain function calls in \*(C+. 4997method calls instead of plain function calls in \*(C+.
2818.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0" 4998.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
2819.IX Subsection "EXPORTED API SYMBOLS" 4999.IX Subsection "EXPORTED API SYMBOLS"
2820If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of 5000If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
2821exported symbols, you can use the provided \fISymbol.*\fR files which list 5001exported symbols, you can use the provided \fISymbol.*\fR files which list
2822all public symbols, one per line: 5002all public symbols, one per line:
2823.Sp 5003.PP
2824.Vb 2 5004.Vb 2
2825\& Symbols.ev for libev proper 5005\& Symbols.ev for libev proper
2826\& Symbols.event for the libevent emulation 5006\& Symbols.event for the libevent emulation
2827.Ve 5007.Ve
2828.Sp 5008.PP
2829This can also be used to rename all public symbols to avoid clashes with 5009This can also be used to rename all public symbols to avoid clashes with
2830multiple versions of libev linked together (which is obviously bad in 5010multiple versions of libev linked together (which is obviously bad in
2831itself, but sometimes it is inconvinient to avoid this). 5011itself, but sometimes it is inconvenient to avoid this).
2832.Sp 5012.PP
2833A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to 5013A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
2834include before including \fIev.h\fR: 5014include before including \fIev.h\fR:
2835.Sp 5015.PP
2836.Vb 1 5016.Vb 1
2837\& <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h 5017\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
2838.Ve 5018.Ve
2839.Sp 5019.PP
2840This would create a file \fIwrap.h\fR which essentially looks like this: 5020This would create a file \fIwrap.h\fR which essentially looks like this:
2841.Sp 5021.PP
2842.Vb 4 5022.Vb 4
2843\& #define ev_backend myprefix_ev_backend 5023\& #define ev_backend myprefix_ev_backend
2844\& #define ev_check_start myprefix_ev_check_start 5024\& #define ev_check_start myprefix_ev_check_start
2845\& #define ev_check_stop myprefix_ev_check_stop 5025\& #define ev_check_stop myprefix_ev_check_stop
2846\& ... 5026\& ...
2847.Ve 5027.Ve
2848.Sh "\s-1EXAMPLES\s0" 5028.SS "\s-1EXAMPLES\s0"
2849.IX Subsection "EXAMPLES" 5029.IX Subsection "EXAMPLES"
2850For a real-world example of a program the includes libev 5030For a real-world example of a program the includes libev
2851verbatim, you can have a look at the \s-1EV\s0 perl module 5031verbatim, you can have a look at the \s-1EV\s0 perl module
2852(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5032(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2853the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5033the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2854interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5034interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2855will be compiled. It is pretty complex because it provides its own header 5035will be compiled. It is pretty complex because it provides its own header
2856file. 5036file.
2857.Sp 5037.PP
2858The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5038The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2859that everybody includes and which overrides some configure choices: 5039that everybody includes and which overrides some configure choices:
2860.Sp 5040.PP
2861.Vb 9 5041.Vb 8
2862\& #define EV_MINIMAL 1 5042\& #define EV_FEATURES 8
2863\& #define EV_USE_POLL 0 5043\& #define EV_USE_SELECT 1
2864\& #define EV_MULTIPLICITY 0
2865\& #define EV_PERIODIC_ENABLE 0 5044\& #define EV_PREPARE_ENABLE 1
5045\& #define EV_IDLE_ENABLE 1
2866\& #define EV_STAT_ENABLE 0 5046\& #define EV_SIGNAL_ENABLE 1
2867\& #define EV_FORK_ENABLE 0 5047\& #define EV_CHILD_ENABLE 1
5048\& #define EV_USE_STDEXCEPT 0
2868\& #define EV_CONFIG_H <config.h> 5049\& #define EV_CONFIG_H <config.h>
2869\& #define EV_MINPRI 0 5050\&
2870\& #define EV_MAXPRI 0
2871.Ve
2872.Sp
2873.Vb 1
2874\& #include "ev++.h" 5051\& #include "ev++.h"
2875.Ve 5052.Ve
2876.Sp 5053.PP
2877And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5054And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2878.Sp 5055.PP
2879.Vb 2 5056.Vb 2
2880\& #include "ev_cpp.h" 5057\& #include "ev_cpp.h"
2881\& #include "ev.c" 5058\& #include "ev.c"
2882.Ve 5059.Ve
5060.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5061.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5062.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
5063.IX Subsection "THREADS AND COROUTINES"
5064\fI\s-1THREADS\s0\fR
5065.IX Subsection "THREADS"
5066.PP
5067All libev functions are reentrant and thread-safe unless explicitly
5068documented otherwise, but libev implements no locking itself. This means
5069that you can use as many loops as you want in parallel, as long as there
5070are no concurrent calls into any libev function with the same loop
5071parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5072of course): libev guarantees that different event loops share no data
5073structures that need any locking.
5074.PP
5075Or to put it differently: calls with different loop parameters can be done
5076concurrently from multiple threads, calls with the same loop parameter
5077must be done serially (but can be done from different threads, as long as
5078only one thread ever is inside a call at any point in time, e.g. by using
5079a mutex per loop).
5080.PP
5081Specifically to support threads (and signal handlers), libev implements
5082so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5083concurrency on the same event loop, namely waking it up \*(L"from the
5084outside\*(R".
5085.PP
5086If you want to know which design (one loop, locking, or multiple loops
5087without or something else still) is best for your problem, then I cannot
5088help you, but here is some generic advice:
5089.IP "\(bu" 4
5090most applications have a main thread: use the default libev loop
5091in that thread, or create a separate thread running only the default loop.
5092.Sp
5093This helps integrating other libraries or software modules that use libev
5094themselves and don't care/know about threading.
5095.IP "\(bu" 4
5096one loop per thread is usually a good model.
5097.Sp
5098Doing this is almost never wrong, sometimes a better-performance model
5099exists, but it is always a good start.
5100.IP "\(bu" 4
5101other models exist, such as the leader/follower pattern, where one
5102loop is handed through multiple threads in a kind of round-robin fashion.
5103.Sp
5104Choosing a model is hard \- look around, learn, know that usually you can do
5105better than you currently do :\-)
5106.IP "\(bu" 4
5107often you need to talk to some other thread which blocks in the
5108event loop.
5109.Sp
5110\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5111(or from signal contexts...).
5112.Sp
5113An example use would be to communicate signals or other events that only
5114work in the default loop by registering the signal watcher with the
5115default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5116watcher callback into the event loop interested in the signal.
5117.PP
5118See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
5119.PP
5120\fI\s-1COROUTINES\s0\fR
5121.IX Subsection "COROUTINES"
5122.PP
5123Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5124libev fully supports nesting calls to its functions from different
5125coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5126different coroutines, and switch freely between both coroutines running
5127the loop, as long as you don't confuse yourself). The only exception is
5128that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5129.PP
5130Care has been taken to ensure that libev does not keep local state inside
5131\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5132they do not call any callbacks.
5133.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
5134.IX Subsection "COMPILER WARNINGS"
5135Depending on your compiler and compiler settings, you might get no or a
5136lot of warnings when compiling libev code. Some people are apparently
5137scared by this.
5138.PP
5139However, these are unavoidable for many reasons. For one, each compiler
5140has different warnings, and each user has different tastes regarding
5141warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5142targeting a specific compiler and compiler-version.
5143.PP
5144Another reason is that some compiler warnings require elaborate
5145workarounds, or other changes to the code that make it less clear and less
5146maintainable.
5147.PP
5148And of course, some compiler warnings are just plain stupid, or simply
5149wrong (because they don't actually warn about the condition their message
5150seems to warn about). For example, certain older gcc versions had some
5151warnings that resulted in an extreme number of false positives. These have
5152been fixed, but some people still insist on making code warn-free with
5153such buggy versions.
5154.PP
5155While libev is written to generate as few warnings as possible,
5156\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5157with any compiler warnings enabled unless you are prepared to cope with
5158them (e.g. by ignoring them). Remember that warnings are just that:
5159warnings, not errors, or proof of bugs.
5160.SS "\s-1VALGRIND\s0"
5161.IX Subsection "VALGRIND"
5162Valgrind has a special section here because it is a popular tool that is
5163highly useful. Unfortunately, valgrind reports are very hard to interpret.
5164.PP
5165If you think you found a bug (memory leak, uninitialised data access etc.)
5166in libev, then check twice: If valgrind reports something like:
5167.PP
5168.Vb 3
5169\& ==2274== definitely lost: 0 bytes in 0 blocks.
5170\& ==2274== possibly lost: 0 bytes in 0 blocks.
5171\& ==2274== still reachable: 256 bytes in 1 blocks.
5172.Ve
5173.PP
5174Then there is no memory leak, just as memory accounted to global variables
5175is not a memleak \- the memory is still being referenced, and didn't leak.
5176.PP
5177Similarly, under some circumstances, valgrind might report kernel bugs
5178as if it were a bug in libev (e.g. in realloc or in the poll backend,
5179although an acceptable workaround has been found here), or it might be
5180confused.
5181.PP
5182Keep in mind that valgrind is a very good tool, but only a tool. Don't
5183make it into some kind of religion.
5184.PP
5185If you are unsure about something, feel free to contact the mailing list
5186with the full valgrind report and an explanation on why you think this
5187is a bug in libev (best check the archives, too :). However, don't be
5188annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5189of learning how to interpret valgrind properly.
5190.PP
5191If you need, for some reason, empty reports from valgrind for your project
5192I suggest using suppression lists.
5193.SH "PORTABILITY NOTES"
5194.IX Header "PORTABILITY NOTES"
5195.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
5196.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5197GNU/Linux is the only common platform that supports 64 bit file/large file
5198interfaces but \fIdisables\fR them by default.
5199.PP
5200That means that libev compiled in the default environment doesn't support
5201files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5202.PP
5203Unfortunately, many programs try to work around this GNU/Linux issue
5204by enabling the large file \s-1API\s0, which makes them incompatible with the
5205standard libev compiled for their system.
5206.PP
5207Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5208suddenly make it incompatible to the default compile time environment,
5209i.e. all programs not using special compile switches.
5210.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
5211.IX Subsection "OS/X AND DARWIN BUGS"
5212The whole thing is a bug if you ask me \- basically any system interface
5213you touch is broken, whether it is locales, poll, kqueue or even the
5214OpenGL drivers.
5215.PP
5216\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5217.IX Subsection "kqueue is buggy"
5218.PP
5219The kqueue syscall is broken in all known versions \- most versions support
5220only sockets, many support pipes.
5221.PP
5222Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5223rotten platform, but of course you can still ask for it when creating a
5224loop \- embedding a socket-only kqueue loop into a select-based one is
5225probably going to work well.
5226.PP
5227\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5228.IX Subsection "poll is buggy"
5229.PP
5230Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5231implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5232release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5233.PP
5234Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5235this rotten platform, but of course you can still ask for it when creating
5236a loop.
5237.PP
5238\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5239.IX Subsection "select is buggy"
5240.PP
5241All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5242one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
5243descriptors you can pass in to 1024 \- your program suddenly crashes when
5244you use more.
5245.PP
5246There is an undocumented \*(L"workaround\*(R" for this \- defining
5247\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5248work on \s-1OS/X\s0.
5249.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5250.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5251\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5252.IX Subsection "errno reentrancy"
5253.PP
5254The default compile environment on Solaris is unfortunately so
5255thread-unsafe that you can't even use components/libraries compiled
5256without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5257defined by default. A valid, if stupid, implementation choice.
5258.PP
5259If you want to use libev in threaded environments you have to make sure
5260it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5261.PP
5262\fIEvent port backend\fR
5263.IX Subsection "Event port backend"
5264.PP
5265The scalable event interface for Solaris is called \*(L"event
5266ports\*(R". Unfortunately, this mechanism is very buggy in all major
5267releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5268a large number of spurious wakeups, make sure you have all the relevant
5269and latest kernel patches applied. No, I don't know which ones, but there
5270are multiple ones to apply, and afterwards, event ports actually work
5271great.
5272.PP
5273If you can't get it to work, you can try running the program by setting
5274the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5275\&\f(CW\*(C`select\*(C'\fR backends.
5276.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
5277.IX Subsection "AIX POLL BUG"
5278\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5279this by trying to avoid the poll backend altogether (i.e. it's not even
5280compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5281with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
5282.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5283.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5284\fIGeneral issues\fR
5285.IX Subsection "General issues"
5286.PP
5287Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5288requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5289model. Libev still offers limited functionality on this platform in
5290the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5291descriptors. This only applies when using Win32 natively, not when using
5292e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5293as every compiler comes with a slightly differently broken/incompatible
5294environment.
5295.PP
5296Lifting these limitations would basically require the full
5297re-implementation of the I/O system. If you are into this kind of thing,
5298then note that glib does exactly that for you in a very portable way (note
5299also that glib is the slowest event library known to man).
5300.PP
5301There is no supported compilation method available on windows except
5302embedding it into other applications.
5303.PP
5304Sensible signal handling is officially unsupported by Microsoft \- libev
5305tries its best, but under most conditions, signals will simply not work.
5306.PP
5307Not a libev limitation but worth mentioning: windows apparently doesn't
5308accept large writes: instead of resulting in a partial write, windows will
5309either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5310so make sure you only write small amounts into your sockets (less than a
5311megabyte seems safe, but this apparently depends on the amount of memory
5312available).
5313.PP
5314Due to the many, low, and arbitrary limits on the win32 platform and
5315the abysmal performance of winsockets, using a large number of sockets
5316is not recommended (and not reasonable). If your program needs to use
5317more than a hundred or so sockets, then likely it needs to use a totally
5318different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5319notification model, which cannot be implemented efficiently on windows
5320(due to Microsoft monopoly games).
5321.PP
5322A typical way to use libev under windows is to embed it (see the embedding
5323section for details) and use the following \fIevwrap.h\fR header file instead
5324of \fIev.h\fR:
5325.PP
5326.Vb 2
5327\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5328\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5329\&
5330\& #include "ev.h"
5331.Ve
5332.PP
5333And compile the following \fIevwrap.c\fR file into your project (make sure
5334you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5335.PP
5336.Vb 2
5337\& #include "evwrap.h"
5338\& #include "ev.c"
5339.Ve
5340.PP
5341\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5342.IX Subsection "The winsocket select function"
5343.PP
5344The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5345requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5346also extremely buggy). This makes select very inefficient, and also
5347requires a mapping from file descriptors to socket handles (the Microsoft
5348C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5349discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5350\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5351.PP
5352The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5353libraries and raw winsocket select is:
5354.PP
5355.Vb 2
5356\& #define EV_USE_SELECT 1
5357\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5358.Ve
5359.PP
5360Note that winsockets handling of fd sets is O(n), so you can easily get a
5361complexity in the O(nA\*^X) range when using win32.
5362.PP
5363\fILimited number of file descriptors\fR
5364.IX Subsection "Limited number of file descriptors"
5365.PP
5366Windows has numerous arbitrary (and low) limits on things.
5367.PP
5368Early versions of winsocket's select only supported waiting for a maximum
5369of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5370can only wait for \f(CW64\fR things at the same time internally; Microsoft
5371recommends spawning a chain of threads and wait for 63 handles and the
5372previous thread in each. Sounds great!).
5373.PP
5374Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5375to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5376call (which might be in libev or elsewhere, for example, perl and many
5377other interpreters do their own select emulation on windows).
5378.PP
5379Another limit is the number of file descriptors in the Microsoft runtime
5380libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5381fetish or something like this inside Microsoft). You can increase this
5382by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5383(another arbitrary limit), but is broken in many versions of the Microsoft
5384runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5385(depending on windows version and/or the phase of the moon). To get more,
5386you need to wrap all I/O functions and provide your own fd management, but
5387the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5388.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5389.IX Subsection "PORTABILITY REQUIREMENTS"
5390In addition to a working ISO-C implementation and of course the
5391backend-specific APIs, libev relies on a few additional extensions:
5392.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5393.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5394.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5395Libev assumes not only that all watcher pointers have the same internal
5396structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5397assumes that the same (machine) code can be used to call any watcher
5398callback: The watcher callbacks have different type signatures, but libev
5399calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5400.IP "pointer accesses must be thread-atomic" 4
5401.IX Item "pointer accesses must be thread-atomic"
5402Accessing a pointer value must be atomic, it must both be readable and
5403writable in one piece \- this is the case on all current architectures.
5404.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5405.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5406.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5407The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5408\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5409threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5410believed to be sufficiently portable.
5411.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5412.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5413.IX Item "sigprocmask must work in a threaded environment"
5414Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5415allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5416pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5417thread\*(R" or will block signals process-wide, both behaviours would
5418be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5419\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5420.Sp
5421The most portable way to handle signals is to block signals in all threads
5422except the initial one, and run the signal handling loop in the initial
5423thread as well.
5424.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5425.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5426.IX Item "long must be large enough for common memory allocation sizes"
5427To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5428instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5429systems (Microsoft...) this might be unexpectedly low, but is still at
5430least 31 bits everywhere, which is enough for hundreds of millions of
5431watchers.
5432.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5433.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5434.IX Item "double must hold a time value in seconds with enough accuracy"
5435The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5436have at least 51 bits of mantissa (and 9 bits of exponent), which is
5437good enough for at least into the year 4000 with millisecond accuracy
5438(the design goal for libev). This requirement is overfulfilled by
5439implementations using \s-1IEEE\s0 754, which is basically all existing ones.
5440.Sp
5441With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
5442year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5443is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5444something like that, just kidding).
5445.PP
5446If you know of other additional requirements drop me a note.
2883.SH "COMPLEXITIES" 5447.SH "ALGORITHMIC COMPLEXITIES"
2884.IX Header "COMPLEXITIES" 5448.IX Header "ALGORITHMIC COMPLEXITIES"
2885In this section the complexities of (many of) the algorithms used inside 5449In this section the complexities of (many of) the algorithms used inside
2886libev will be explained. For complexity discussions about backends see the 5450libev will be documented. For complexity discussions about backends see
2887documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5451the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2888.Sp 5452.PP
2889All of the following are about amortised time: If an array needs to be 5453All of the following are about amortised time: If an array needs to be
2890extended, libev needs to realloc and move the whole array, but this 5454extended, libev needs to realloc and move the whole array, but this
2891happens asymptotically never with higher number of elements, so O(1) might 5455happens asymptotically rarer with higher number of elements, so O(1) might
2892mean it might do a lengthy realloc operation in rare cases, but on average 5456mean that libev does a lengthy realloc operation in rare cases, but on
2893it is much faster and asymptotically approaches constant time. 5457average it is much faster and asymptotically approaches constant time.
2894.RS 4
2895.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5458.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2896.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5459.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2897This means that, when you have a watcher that triggers in one hour and 5460This means that, when you have a watcher that triggers in one hour and
2898there are 100 watchers that would trigger before that then inserting will 5461there are 100 watchers that would trigger before that, then inserting will
2899have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers. 5462have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2900.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4 5463.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2901.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 5464.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2902That means that changing a timer costs less than removing/adding them 5465That means that changing a timer costs less than removing/adding them,
2903as only the relative motion in the event queue has to be paid for. 5466as only the relative motion in the event queue has to be paid for.
2904.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 5467.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
2905.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 5468.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
2906These just add the watcher into an array or at the head of a list. 5469These just add the watcher into an array or at the head of a list.
2907.IP "Stopping check/prepare/idle watchers: O(1)" 4 5470.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
2908.IX Item "Stopping check/prepare/idle watchers: O(1)" 5471.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2909.PD 0 5472.PD 0
2910.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5473.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2911.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5474.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
2912.PD 5475.PD
2913These watchers are stored in lists then need to be walked to find the 5476These watchers are stored in lists, so they need to be walked to find the
2914correct watcher to remove. The lists are usually short (you don't usually 5477correct watcher to remove. The lists are usually short (you don't usually
2915have many watchers waiting for the same fd or signal). 5478have many watchers waiting for the same fd or signal: one is typical, two
5479is rare).
2916.IP "Finding the next timer in each loop iteration: O(1)" 4 5480.IP "Finding the next timer in each loop iteration: O(1)" 4
2917.IX Item "Finding the next timer in each loop iteration: O(1)" 5481.IX Item "Finding the next timer in each loop iteration: O(1)"
2918By virtue of using a binary heap, the next timer is always found at the 5482By virtue of using a binary or 4\-heap, the next timer is always found at a
2919beginning of the storage array. 5483fixed position in the storage array.
2920.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5484.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2921.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5485.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2922A change means an I/O watcher gets started or stopped, which requires 5486A change means an I/O watcher gets started or stopped, which requires
2923libev to recalculate its status (and possibly tell the kernel, depending 5487libev to recalculate its status (and possibly tell the kernel, depending
2924on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used). 5488on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2925.IP "Activating one watcher (putting it into the pending state): O(1)" 4 5489.IP "Activating one watcher (putting it into the pending state): O(1)" 4
2926.IX Item "Activating one watcher (putting it into the pending state): O(1)" 5490.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2927.PD 0 5491.PD 0
2928.IP "Priority handling: O(number_of_priorities)" 4 5492.IP "Priority handling: O(number_of_priorities)" 4
2929.IX Item "Priority handling: O(number_of_priorities)" 5493.IX Item "Priority handling: O(number_of_priorities)"
2930.PD 5494.PD
2931Priorities are implemented by allocating some space for each 5495Priorities are implemented by allocating some space for each
2932priority. When doing priority-based operations, libev usually has to 5496priority. When doing priority-based operations, libev usually has to
2933linearly search all the priorities, but starting/stopping and activating 5497linearly search all the priorities, but starting/stopping and activating
2934watchers becomes O(1) w.r.t. prioritiy handling. 5498watchers becomes O(1) with respect to priority handling.
2935.RE 5499.IP "Sending an ev_async: O(1)" 4
2936.RS 4 5500.IX Item "Sending an ev_async: O(1)"
5501.PD 0
5502.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5503.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5504.IP "Processing signals: O(max_signal_number)" 4
5505.IX Item "Processing signals: O(max_signal_number)"
5506.PD
5507Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5508calls in the current loop iteration and the loop is currently
5509blocked. Checking for async and signal events involves iterating over all
5510running async watchers or all signal numbers.
5511.SH "PORTING FROM LIBEV 3.X TO 4.X"
5512.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5513The major version 4 introduced some incompatible changes to the \s-1API\s0.
5514.PP
5515At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5516for all changes, so most programs should still compile. The compatibility
5517layer might be removed in later versions of libev, so better update to the
5518new \s-1API\s0 early than late.
5519.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5520.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5521.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5522The backward compatibility mechanism can be controlled by
5523\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0\*(R" in the \*(L"\s-1EMBEDDING\s0\*(R"
5524section.
5525.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5526.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5527.IX Item "ev_default_destroy and ev_default_fork have been removed"
5528These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5529.Sp
5530.Vb 2
5531\& ev_loop_destroy (EV_DEFAULT_UC);
5532\& ev_loop_fork (EV_DEFAULT);
5533.Ve
5534.IP "function/symbol renames" 4
5535.IX Item "function/symbol renames"
5536A number of functions and symbols have been renamed:
5537.Sp
5538.Vb 3
5539\& ev_loop => ev_run
5540\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5541\& EVLOOP_ONESHOT => EVRUN_ONCE
5542\&
5543\& ev_unloop => ev_break
5544\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5545\& EVUNLOOP_ONE => EVBREAK_ONE
5546\& EVUNLOOP_ALL => EVBREAK_ALL
5547\&
5548\& EV_TIMEOUT => EV_TIMER
5549\&
5550\& ev_loop_count => ev_iteration
5551\& ev_loop_depth => ev_depth
5552\& ev_loop_verify => ev_verify
5553.Ve
5554.Sp
5555Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5556\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5557associated constants have been renamed to not collide with the \f(CW\*(C`struct
5558ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5559as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5560\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5561typedef.
5562.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5563.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5564.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5565The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5566mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5567and work, but the library code will of course be larger.
5568.SH "GLOSSARY"
5569.IX Header "GLOSSARY"
5570.IP "active" 4
5571.IX Item "active"
5572A watcher is active as long as it has been started and not yet stopped.
5573See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5574.IP "application" 4
5575.IX Item "application"
5576In this document, an application is whatever is using libev.
5577.IP "backend" 4
5578.IX Item "backend"
5579The part of the code dealing with the operating system interfaces.
5580.IP "callback" 4
5581.IX Item "callback"
5582The address of a function that is called when some event has been
5583detected. Callbacks are being passed the event loop, the watcher that
5584received the event, and the actual event bitset.
5585.IP "callback/watcher invocation" 4
5586.IX Item "callback/watcher invocation"
5587The act of calling the callback associated with a watcher.
5588.IP "event" 4
5589.IX Item "event"
5590A change of state of some external event, such as data now being available
5591for reading on a file descriptor, time having passed or simply not having
5592any other events happening anymore.
5593.Sp
5594In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5595\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5596.IP "event library" 4
5597.IX Item "event library"
5598A software package implementing an event model and loop.
5599.IP "event loop" 4
5600.IX Item "event loop"
5601An entity that handles and processes external events and converts them
5602into callback invocations.
5603.IP "event model" 4
5604.IX Item "event model"
5605The model used to describe how an event loop handles and processes
5606watchers and events.
5607.IP "pending" 4
5608.IX Item "pending"
5609A watcher is pending as soon as the corresponding event has been
5610detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5611.IP "real time" 4
5612.IX Item "real time"
5613The physical time that is observed. It is apparently strictly monotonic :)
5614.IP "wall-clock time" 4
5615.IX Item "wall-clock time"
5616The time and date as shown on clocks. Unlike real time, it can actually
5617be wrong and jump forwards and backwards, e.g. when you adjust your
5618clock.
5619.IP "watcher" 4
5620.IX Item "watcher"
5621A data structure that describes interest in certain events. Watchers need
5622to be started (attached to an event loop) before they can receive events.
2937.SH "AUTHOR" 5623.SH "AUTHOR"
2938.IX Header "AUTHOR" 5624.IX Header "AUTHOR"
2939Marc Lehmann <libev@schmorp.de>. 5625Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5626Magnusson and Emanuele Giaquinta, and minor corrections by many others.

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines