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

Comparing libev/ev.3 (file contents):
Revision 1.34 by root, Thu Nov 29 12:21:21 2007 UTC vs.
Revision 1.116 by root, Sun Jul 7 06:00:32 2019 UTC

1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35)
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
… …
44.el\{\ 36.el\{\
45. ds -- \|\(em\| 37. ds -- \|\(em\|
46. ds PI \(*p 38. ds PI \(*p
47. ds L" `` 39. ds L" ``
48. ds R" '' 40. ds R" ''
41. ds C`
42. ds C'
49'br\} 43'br\}
50.\" 44.\"
45.\" Escape single quotes in literal strings from groff's Unicode transform.
46.ie \n(.g .ds Aq \(aq
47.el .ds Aq '
48.\"
51.\" If the F register is turned on, we'll generate index entries on stderr for 49.\" If the F register is >0, we'll generate index entries on stderr for
52.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index 50.\" 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 51.\" entries marked with X<> in POD. Of course, you'll have to process the
54.\" output yourself in some meaningful fashion. 52.\" output yourself in some meaningful fashion.
55.if \nF \{\ 53.\"
54.\" Avoid warning from groff about undefined register 'F'.
56. de IX 55.de IX
57. tm Index:\\$1\t\\n%\t"\\$2"
58.. 56..
59. nr % 0 57.nr rF 0
60. rr F 58.if \n(.g .if rF .nr rF 1
59.if (\n(rF:(\n(.g==0)) \{\
60. if \nF \{\
61. de IX
62. tm Index:\\$1\t\\n%\t"\\$2"
63..
64. if !\nF==2 \{\
65. nr % 0
66. nr F 2
67. \}
68. \}
61.\} 69.\}
62.\" 70.rr rF
63.\" For nroff, turn off justification. Always turn off hyphenation; it makes
64.\" way too many mistakes in technical documents.
65.hy 0
66.if n .na
67.\" 71.\"
68.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). 72.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
69.\" Fear. Run. Save yourself. No user-serviceable parts. 73.\" Fear. Run. Save yourself. No user-serviceable parts.
70. \" fudge factors for nroff and troff 74. \" fudge factors for nroff and troff
71.if n \{\ 75.if n \{\
… …
126. ds Ae AE 130. ds Ae AE
127.\} 131.\}
128.rm #[ #] #H #V #F C 132.rm #[ #] #H #V #F C
129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-29" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2019-07-07" "libev-4.27" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "EXAMPLE PROGRAM" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "EXAMPLE PROGRAM" 149.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1
143\& #include <ev.h>
144.Ve
145.PP
146.Vb 2 150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
147\& ev_io stdin_watcher; 158\& ev_io stdin_watcher;
148\& ev_timer timeout_watcher; 159\& ev_timer timeout_watcher;
149.Ve 160\&
150.PP 161\& // all watcher callbacks have a similar signature
151.Vb 8
152\& /* called when data readable on stdin */ 162\& // this callback is called when data is readable on stdin
153\& static void 163\& static void
154\& stdin_cb (EV_P_ struct ev_io *w, int revents) 164\& stdin_cb (EV_P_ ev_io *w, int revents)
155\& { 165\& {
156\& /* puts ("stdin ready"); */ 166\& puts ("stdin ready");
157\& ev_io_stop (EV_A_ w); /* just a syntax example */ 167\& // for one\-shot events, one must manually stop the watcher
158\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
159\& } 173\& }
160.Ve 174\&
161.PP 175\& // another callback, this time for a time\-out
162.Vb 6
163\& static void 176\& static void
164\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 177\& timeout_cb (EV_P_ ev_timer *w, int revents)
165\& { 178\& {
166\& /* puts ("timeout"); */ 179\& puts ("timeout");
167\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
168\& } 182\& }
169.Ve 183\&
170.PP
171.Vb 4
172\& int 184\& int
173\& main (void) 185\& main (void)
174\& { 186\& {
175\& struct ev_loop *loop = ev_default_loop (0); 187\& // use the default event loop unless you have special needs
176.Ve 188\& struct ev_loop *loop = EV_DEFAULT;
177.PP 189\&
178.Vb 3
179\& /* initialise an io watcher, then start it */ 190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
180\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181\& ev_io_start (loop, &stdin_watcher); 193\& ev_io_start (loop, &stdin_watcher);
182.Ve 194\&
183.PP 195\& // initialise a timer watcher, then start it
184.Vb 3
185\& /* simple non-repeating 5.5 second timeout */ 196\& // simple non\-repeating 5.5 second timeout
186\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187\& ev_timer_start (loop, &timeout_watcher); 198\& ev_timer_start (loop, &timeout_watcher);
188.Ve 199\&
189.PP 200\& // now wait for events to arrive
190.Vb 2
191\& /* loop till timeout or data ready */
192\& ev_loop (loop, 0); 201\& ev_run (loop, 0);
193.Ve 202\&
194.PP 203\& // break was called, so exit
195.Vb 2
196\& return 0; 204\& return 0;
197\& } 205\& }
198.Ve 206.Ve
199.SH "DESCRIPTION" 207.SH "ABOUT THIS DOCUMENT"
200.IX Header "DESCRIPTION" 208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
211The newest version of this document is also available as an html-formatted
212web page you might find easier to navigate when reading it for the first
213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
201Libev is an event loop: you register interest in certain events (such as a 231Libev is an event loop: you register interest in certain events (such as a
202file descriptor being readable or a timeout occuring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
203these event sources and provide your program with events. 233these event sources and provide your program with events.
204.PP 234.PP
205To do this, it must take more or less complete control over your process 235To do this, it must take more or less complete control over your process
206(or thread) by executing the \fIevent loop\fR handler, and will then 236(or thread) by executing the \fIevent loop\fR handler, and will then
207communicate events via a callback mechanism. 237communicate events via a callback mechanism.
208.PP 238.PP
209You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
210watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
211details of the event, and then hand it over to libev by \fIstarting\fR the 241details of the event, and then hand it over to libev by \fIstarting\fR the
212watcher. 242watcher.
213.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
214.IX Header "FEATURES" 244.IX Subsection "FEATURES"
215Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the 245Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR
216BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms 246interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
217for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface 247mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
218(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers 248interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
219with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
220(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
221watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
222\&\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 252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
223file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events 253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
224(\f(CW\*(C`ev_fork\*(C'\fR). 254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
225.PP 256.PP
226It also is quite fast (see this 257It also is quite fast (see this
227benchmark comparing it to libevent 258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
228for example). 259for example).
229.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
230.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
231Libev is very configurable. In this manual the default configuration will 262Libev is very configurable. In this manual the default (and most common)
232be described, which supports multiple event loops. For more info about 263configuration will be described, which supports multiple event loops. For
233various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 264more info about various configuration options please have a look at
234this manual. If libev was configured without support for multiple event 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
235loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR 266for multiple event loops, then all functions taking an initial argument of
236(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument. 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
268this argument.
237.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
238.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
239Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
240(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
241the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
242called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
243to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
244it, you should treat it as such. 276any calculations on it, you should treat it as some floating point value.
277.PP
278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR macro you can compile in and/or enable extensive
297consistency checking code inside libev that can be used to check for
298internal inconsistencies, suually caused by application bugs.
299.PP
300Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. These do not
301trigger under normal circumstances, as they indicate either a bug in libev
302or worse.
245.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
246.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
247These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
248library in any way. 306library in any way.
249.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
250.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
251Returns the current time as libev would use it. Please note that the 309Returns the current time as libev would use it. Please note that the
252\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 310\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
253you actually want to know. 311you actually want to know. Also interesting is the combination of
312\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
313.IP "ev_sleep (ev_tstamp interval)" 4
314.IX Item "ev_sleep (ev_tstamp interval)"
315Sleep for the given interval: The current thread will be blocked
316until either it is interrupted or the given time interval has
317passed (approximately \- it might return a bit earlier even if not
318interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
319.Sp
320Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
321.Sp
322The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
323with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
254.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
255.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
256.PD 0 326.PD 0
257.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
258.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
259.PD 329.PD
260You can find out the major and minor version numbers of the library 330You can find out the major and minor \s-1ABI\s0 version numbers of the library
261you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 331you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
262\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 332\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
263symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 333symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
264version of the library your program was compiled against. 334version of the library your program was compiled against.
265.Sp 335.Sp
336These version numbers refer to the \s-1ABI\s0 version of the library, not the
337release version.
338.Sp
266Usually, it's a good idea to terminate if the major versions mismatch, 339Usually, it's a good idea to terminate if the major versions mismatch,
267as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
268compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
269not a problem. 342not a problem.
270.Sp 343.Sp
271Example: Make sure we haven't accidentally been linked against the wrong 344Example: Make sure we haven't accidentally been linked against the wrong
272version. 345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
273.Sp 347.Sp
274.Vb 3 348.Vb 3
275\& assert (("libev version mismatch", 349\& assert (("libev version mismatch",
276\& ev_version_major () == EV_VERSION_MAJOR 350\& ev_version_major () == EV_VERSION_MAJOR
277\& && ev_version_minor () >= EV_VERSION_MINOR)); 351\& && ev_version_minor () >= EV_VERSION_MINOR));
278.Ve 352.Ve
279.IP "unsigned int ev_supported_backends ()" 4 353.IP "unsigned int ev_supported_backends ()" 4
280.IX Item "unsigned int ev_supported_backends ()" 354.IX Item "unsigned int ev_supported_backends ()"
281Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 355Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
282value) compiled into this binary of libev (independent of their 356value) compiled into this binary of libev (independent of their
… …
285.Sp 359.Sp
286Example: make sure we have the epoll method, because yeah this is cool and 360Example: make sure we have the epoll method, because yeah this is cool and
287a must have and can we have a torrent of it please!!!11 361a must have and can we have a torrent of it please!!!11
288.Sp 362.Sp
289.Vb 2 363.Vb 2
290\& assert (("sorry, no epoll, no sex", 364\& assert (("sorry, no epoll, no sex",
291\& ev_supported_backends () & EVBACKEND_EPOLL)); 365\& ev_supported_backends () & EVBACKEND_EPOLL));
292.Ve 366.Ve
293.IP "unsigned int ev_recommended_backends ()" 4 367.IP "unsigned int ev_recommended_backends ()" 4
294.IX Item "unsigned int ev_recommended_backends ()" 368.IX Item "unsigned int ev_recommended_backends ()"
295Return the set of all backends compiled into this binary of libev and also 369Return the set of all backends compiled into this binary of libev and
296recommended for this platform. This set is often smaller than the one 370also recommended for this platform, meaning it will work for most file
371descriptor types. This set is often smaller than the one returned by
297returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 372\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
298most BSDs and will not be autodetected unless you explicitly request it 373and will not be auto-detected unless you explicitly request it (assuming
299(assuming you know what you are doing). This is the set of backends that 374you know what you are doing). This is the set of backends that libev will
300libev will probe for if you specify no backends explicitly. 375probe for if you specify no backends explicitly.
301.IP "unsigned int ev_embeddable_backends ()" 4 376.IP "unsigned int ev_embeddable_backends ()" 4
302.IX Item "unsigned int ev_embeddable_backends ()" 377.IX Item "unsigned int ev_embeddable_backends ()"
303Returns the set of backends that are embeddable in other event loops. This 378Returns the set of backends that are embeddable in other event loops. This
304is the theoretical, all\-platform, value. To find which backends 379value is platform-specific but can include backends not available on the
305might be supported on the current system, you would need to look at 380current system. To find which embeddable backends might be supported on
306\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 381the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
307recommended ones. 382& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
308.Sp 383.Sp
309See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 384See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
310.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
311.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
312Sets the allocation function to use (the prototype is similar \- the 387Sets the allocation function to use (the prototype is similar \- the
313semantics is identical \- to the realloc C function). It is used to 388semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
314allocate and free memory (no surprises here). If it returns zero when 389used to allocate and free memory (no surprises here). If it returns zero
315memory needs to be allocated, the library might abort or take some 390when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
316potentially destructive action. The default is your system realloc 391or take some potentially destructive action.
317function. 392.Sp
393Since some systems (at least OpenBSD and Darwin) fail to implement
394correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
395\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
318.Sp 396.Sp
319You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
320free some memory if it cannot allocate memory, to use a special allocator, 398free some memory if it cannot allocate memory, to use a special allocator,
321or even to sleep a while and retry until some memory is available. 399or even to sleep a while and retry until some memory is available.
322.Sp 400.Sp
401Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
402which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and
403is probably a good basis for your own implementation.
404.Sp
405.Vb 5
406\& static void *
407\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
408\& {
409\& if (size)
410\& return realloc (ptr, size);
411\&
412\& free (ptr);
413\& return 0;
414\& }
415.Ve
416.Sp
323Example: Replace the libev allocator with one that waits a bit and then 417Example: Replace the libev allocator with one that waits a bit and then
324retries). 418retries.
325.Sp 419.Sp
326.Vb 6 420.Vb 8
327\& static void * 421\& static void *
328\& persistent_realloc (void *ptr, size_t size) 422\& persistent_realloc (void *ptr, size_t size)
329\& { 423\& {
424\& if (!size)
425\& {
426\& free (ptr);
427\& return 0;
428\& }
429\&
330\& for (;;) 430\& for (;;)
331\& { 431\& {
332\& void *newptr = realloc (ptr, size); 432\& void *newptr = realloc (ptr, size);
333.Ve 433\&
334.Sp
335.Vb 2
336\& if (newptr) 434\& if (newptr)
337\& return newptr; 435\& return newptr;
338.Ve 436\&
339.Sp
340.Vb 3
341\& sleep (60); 437\& sleep (60);
342\& } 438\& }
343\& } 439\& }
344.Ve 440\&
345.Sp
346.Vb 2
347\& ... 441\& ...
348\& ev_set_allocator (persistent_realloc); 442\& ev_set_allocator (persistent_realloc);
349.Ve 443.Ve
350.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
351.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
352Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
353as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
354indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
355callback is set, then libev will expect it to remedy the sitution, no 449callback is set, then libev will expect it to remedy the situation, no
356matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
357requested operation, or, if the condition doesn't go away, do bad stuff 451requested operation, or, if the condition doesn't go away, do bad stuff
358(such as abort). 452(such as abort).
359.Sp 453.Sp
360Example: This is basically the same thing that libev does internally, too. 454Example: This is basically the same thing that libev does internally, too.
… …
364\& fatal_error (const char *msg) 458\& fatal_error (const char *msg)
365\& { 459\& {
366\& perror (msg); 460\& perror (msg);
367\& abort (); 461\& abort ();
368\& } 462\& }
369.Ve 463\&
370.Sp
371.Vb 2
372\& ... 464\& ...
373\& ev_set_syserr_cb (fatal_error); 465\& ev_set_syserr_cb (fatal_error);
374.Ve 466.Ve
467.IP "ev_feed_signal (int signum)" 4
468.IX Item "ev_feed_signal (int signum)"
469This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
470safe to call this function at any time, from any context, including signal
471handlers or random threads.
472.Sp
473Its main use is to customise signal handling in your process, especially
474in the presence of threads. For example, you could block signals
475by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
476creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
477mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
478\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
375.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
376.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
377An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 481An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
378types of such loops, the \fIdefault\fR loop, which supports signals and child 482\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
379events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
380.PP 484.PP
381If you use threads, a common model is to run the default event loop 485The library knows two types of such loops, the \fIdefault\fR loop, which
382in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
383create, you also create another event loop. Libev itself does no locking 487do not.
384whatsoever, so if you mix calls to the same event loop in different
385threads, make sure you lock (this is usually a bad idea, though, even if
386done correctly, because it's hideous and inefficient).
387.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
388.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
389This will initialise the default event loop if it hasn't been initialised 490This returns the \*(L"default\*(R" event loop object, which is what you should
390yet and return it. If the default loop could not be initialised, returns 491normally use when you just need \*(L"the event loop\*(R". Event loop objects and
391false. If it already was initialised it simply returns it (and ignores the 492the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
392flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 493\&\f(CW\*(C`ev_loop_new\*(C'\fR.
494.Sp
495If the default loop is already initialised then this function simply
496returns it (and ignores the flags. If that is troubling you, check
497\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
498flags, which should almost always be \f(CW0\fR, unless the caller is also the
499one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
393.Sp 500.Sp
394If you don't know what event loop to use, use the one returned from this 501If you don't know what event loop to use, use the one returned from this
395function. 502function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
503.Sp
504Note that this function is \fInot\fR thread-safe, so if you want to use it
505from multiple threads, you have to employ some kind of mutex (note also
506that this case is unlikely, as loops cannot be shared easily between
507threads anyway).
508.Sp
509The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
510and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
511a problem for your application you can either create a dynamic loop with
512\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
513\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
514.Sp
515Example: This is the most typical usage.
516.Sp
517.Vb 2
518\& if (!ev_default_loop (0))
519\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
520.Ve
521.Sp
522Example: Restrict libev to the select and poll backends, and do not allow
523environment settings to be taken into account:
524.Sp
525.Vb 1
526\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
527.Ve
528.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
529.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
530This will create and initialise a new event loop object. If the loop
531could not be initialised, returns false.
532.Sp
533This function is thread-safe, and one common way to use libev with
534threads is indeed to create one loop per thread, and using the default
535loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
396.Sp 536.Sp
397The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
398backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 538backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
399.Sp 539.Sp
400The following flags are supported: 540The following flags are supported:
… …
405The default flags value. Use this if you have no clue (it's the right 545The default flags value. Use this if you have no clue (it's the right
406thing, believe me). 546thing, believe me).
407.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
408.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
409.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
410If this flag bit is ored into the flag value (or the program runs setuid 550If this flag bit is or'ed into the flag value (or the program runs setuid
411or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
412\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 552\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
413override the flags completely if it is found in the environment. This is 553override the flags completely if it is found in the environment. This is
414useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
415around bugs. 555around bugs, or to make libev threadsafe (accessing environment variables
556cannot be done in a threadsafe way, but usually it works if no other
557thread modifies them).
558.ie n .IP """EVFLAG_FORKCHECK""" 4
559.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
560.IX Item "EVFLAG_FORKCHECK"
561Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
562make libev check for a fork in each iteration by enabling this flag.
563.Sp
564This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
565and thus this might slow down your event loop if you do a lot of loop
566iterations and little real work, but is usually not noticeable (on my
567GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
568sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
569system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc
570versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again).
571.Sp
572The big advantage of this flag is that you can forget about fork (and
573forget about forgetting to tell libev about forking, although you still
574have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
575.Sp
576This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
577environment variable.
578.ie n .IP """EVFLAG_NOINOTIFY""" 4
579.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
580.IX Item "EVFLAG_NOINOTIFY"
581When this flag is specified, then libev will not attempt to use the
582\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
583testing, this flag can be useful to conserve inotify file descriptors, as
584otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
585.ie n .IP """EVFLAG_SIGNALFD""" 4
586.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
587.IX Item "EVFLAG_SIGNALFD"
588When this flag is specified, then libev will attempt to use the
589\&\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
590delivers signals synchronously, which makes it both faster and might make
591it possible to get the queued signal data. It can also simplify signal
592handling with threads, as long as you properly block signals in your
593threads that are not interested in handling them.
594.Sp
595Signalfd will not be used by default as this changes your signal mask, and
596there are a lot of shoddy libraries and programs (glib's threadpool for
597example) that can't properly initialise their signal masks.
598.ie n .IP """EVFLAG_NOSIGMASK""" 4
599.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
600.IX Item "EVFLAG_NOSIGMASK"
601When this flag is specified, then libev will avoid to modify the signal
602mask. Specifically, this means you have to make sure signals are unblocked
603when you want to receive them.
604.Sp
605This behaviour is useful when you want to do your own signal handling, or
606want to handle signals only in specific threads and want to avoid libev
607unblocking the signals.
608.Sp
609It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
610\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
611.Sp
612This flag's behaviour will become the default in future versions of libev.
416.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 613.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
417.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 614.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
418.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 615.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
419This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 616This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
420libev tries to roll its own fd_set with no limits on the number of fds, 617libev tries to roll its own fd_set with no limits on the number of fds,
421but if that fails, expect a fairly low limit on the number of fds when 618but if that fails, expect a fairly low limit on the number of fds when
422using this backend. It doesn't scale too well (O(highest_fd)), but its usually 619using this backend. It doesn't scale too well (O(highest_fd)), but its
423the fastest backend for a low number of fds. 620usually the fastest backend for a low number of (low-numbered :) fds.
621.Sp
622To get good performance out of this backend you need a high amount of
623parallelism (most of the file descriptors should be busy). If you are
624writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
625connections as possible during one iteration. You might also want to have
626a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
627readiness notifications you get per iteration.
628.Sp
629This 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
630\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
631\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
424.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 632.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
425.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 633.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
426.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 634.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
427And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 635And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
428select, but handles sparse fds better and has no artificial limit on the 636than select, but handles sparse fds better and has no artificial
429number of fds you can use (except it will slow down considerably with a 637limit on the number of fds you can use (except it will slow down
430lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 638considerably with a lot of inactive fds). It scales similarly to select,
639i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
640performance tips.
641.Sp
642This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
643\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
431.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 644.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
432.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 645.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
433.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 646.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
647Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
648kernels).
649.Sp
434For few fds, this backend is a bit little slower than poll and select, 650For few fds, this backend is a bit little slower than poll and select, but
435but it scales phenomenally better. While poll and select usually scale like 651it scales phenomenally better. While poll and select usually scale like
436O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 652O(total_fds) where total_fds is the total number of fds (or the highest
437either O(1) or O(active_fds). 653fd), epoll scales either O(1) or O(active_fds).
438.Sp 654.Sp
655The epoll mechanism deserves honorable mention as the most misdesigned
656of the more advanced event mechanisms: mere annoyances include silently
657dropping file descriptors, requiring a system call per change per file
658descriptor (and unnecessary guessing of parameters), problems with dup,
659returning before the timeout value, resulting in additional iterations
660(and only giving 5ms accuracy while select on the same platform gives
6610.1ms) and so on. The biggest issue is fork races, however \- if a program
662forks then \fIboth\fR parent and child process have to recreate the epoll
663set, which can take considerable time (one syscall per file descriptor)
664and is of course hard to detect.
665.Sp
666Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
667but of course \fIdoesn't\fR, and epoll just loves to report events for
668totally \fIdifferent\fR file descriptors (even already closed ones, so
669one cannot even remove them from the set) than registered in the set
670(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
671notifications by employing an additional generation counter and comparing
672that against the events to filter out spurious ones, recreating the set
673when required. Epoll also erroneously rounds down timeouts, but gives you
674no way to know when and by how much, so sometimes you have to busy-wait
675because epoll returns immediately despite a nonzero timeout. And last
676not least, it also refuses to work with some file descriptors which work
677perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
678.Sp
679Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
680cobbled together in a hurry, no thought to design or interaction with
681others. Oh, the pain, will it ever stop...
682.Sp
439While stopping and starting an I/O watcher in the same iteration will 683While stopping, setting and starting an I/O watcher in the same iteration
440result in some caching, there is still a syscall per such incident 684will result in some caching, there is still a system call per such
441(because the fd could point to a different file description now), so its 685incident (because the same \fIfile descriptor\fR could point to a different
442best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 686\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
443well if you register events for both fds. 687file descriptors might not work very well if you register events for both
688file descriptors.
444.Sp 689.Sp
445Please note that epoll sometimes generates spurious notifications, so you 690Best performance from this backend is achieved by not unregistering all
446need to use non-blocking I/O or other means to avoid blocking when no data 691watchers for a file descriptor until it has been closed, if possible,
447(or space) is available. 692i.e. keep at least one watcher active per fd at all times. Stopping and
693starting a watcher (without re-setting it) also usually doesn't cause
694extra overhead. A fork can both result in spurious notifications as well
695as in libev having to destroy and recreate the epoll object, which can
696take considerable time and thus should be avoided.
697.Sp
698All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
699faster than epoll for maybe up to a hundred file descriptors, depending on
700the usage. So sad.
701.Sp
702While nominally embeddable in other event loops, this feature is broken in
703a lot of kernel revisions, but probably(!) works in current versions.
704.Sp
705This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
706\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
707.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
708.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
709.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
710Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
711only tries to use it in 4.19+).
712.Sp
713This is another Linux train wreck of an event interface.
714.Sp
715If this backend works for you (as of this writing, it was very
716experimental), it is the best event interface available on Linux and might
717be well worth enabling it \- if it isn't available in your kernel this will
718be detected and this backend will be skipped.
719.Sp
720This backend can batch oneshot requests and supports a user-space ring
721buffer to receive events. It also doesn't suffer from most of the design
722problems of epoll (such as not being able to remove event sources from
723the epoll set), and generally sounds too good to be true. Because, this
724being the Linux kernel, of course it suffers from a whole new set of
725limitations, forcing you to fall back to epoll, inheriting all its design
726issues.
727.Sp
728For one, it is not easily embeddable (but probably could be done using
729an event fd at some extra overhead). It also is subject to a system wide
730limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
731requests are left, this backend will be skipped during initialisation, and
732will switch to epoll when the loop is active.
733.Sp
734Most problematic in practice, however, is that not all file descriptors
735work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
736files, \fI/dev/null\fR and many others are supported, but ttys do not work
737properly (a known bug that the kernel developers don't care about, see
738<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
739(yet?) a generic event polling interface.
740.Sp
741Overall, it seems the Linux developers just don't want it to have a
742generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
743.Sp
744To work around all these problem, the current version of libev uses its
745epoll backend as a fallback for file descriptor types that do not work. Or
746falls back completely to epoll if the kernel acts up.
747.Sp
748This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
749\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
448.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 750.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
449.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 751.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
450.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 752.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
451Kqueue deserves special mention, as at the time of this writing, it 753Kqueue deserves special mention, as at the time this backend was
452was broken on all BSDs except NetBSD (usually it doesn't work with 754implemented, it was broken on all BSDs except NetBSD (usually it doesn't
453anything but sockets and pipes, except on Darwin, where of course its 755work reliably with anything but sockets and pipes, except on Darwin,
454completely useless). For this reason its not being \*(L"autodetected\*(R" 756where of course it's completely useless). Unlike epoll, however, whose
455unless you explicitly specify it explicitly in the flags (i.e. using 757brokenness is by design, these kqueue bugs can be (and mostly have been)
456\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 758fixed without \s-1API\s0 changes to existing programs. For this reason it's not
759being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
760in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
761known-to-be-good (\-enough) system like NetBSD.
762.Sp
763You still can embed kqueue into a normal poll or select backend and use it
764only for sockets (after having made sure that sockets work with kqueue on
765the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
457.Sp 766.Sp
458It scales in the same way as the epoll backend, but the interface to the 767It scales in the same way as the epoll backend, but the interface to the
459kernel is more efficient (which says nothing about its actual speed, of 768kernel is more efficient (which says nothing about its actual speed, of
460course). While starting and stopping an I/O watcher does not cause an 769course). While stopping, setting and starting an I/O watcher does never
461extra syscall as with epoll, it still adds up to four event changes per 770cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
462incident, so its best to avoid that. 771two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
772might have to leak fds on fork, but it's more sane than epoll) and it
773drops fds silently in similarly hard-to-detect cases.
774.Sp
775This backend usually performs well under most conditions.
776.Sp
777While nominally embeddable in other event loops, this doesn't work
778everywhere, so you might need to test for this. And since it is broken
779almost everywhere, you should only use it when you have a lot of sockets
780(for which it usually works), by embedding it into another event loop
781(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
782also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
783.Sp
784This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
785\&\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
786\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
463.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 787.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
464.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 788.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
465.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 789.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
466This is not implemented yet (and might never be). 790This is not implemented yet (and might never be, unless you send me an
791implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
792and is not embeddable, which would limit the usefulness of this backend
793immensely.
467.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 794.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
468.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 795.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
469.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 796.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
470This uses the Solaris 10 port mechanism. As with everything on Solaris, 797This uses the Solaris 10 event port mechanism. As with everything on Solaris,
471it's really slow, but it still scales very well (O(active_fds)). 798it's really slow, but it still scales very well (O(active_fds)).
472.Sp 799.Sp
473Please note that solaris ports can result in a lot of spurious 800While this backend scales well, it requires one system call per active
474notifications, so you need to use non-blocking I/O or other means to avoid 801file descriptor per loop iteration. For small and medium numbers of file
475blocking when no data (or space) is available. 802descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
803might perform better.
804.Sp
805On the positive side, this backend actually performed fully to
806specification in all tests and is fully embeddable, which is a rare feat
807among the OS-specific backends (I vastly prefer correctness over speed
808hacks).
809.Sp
810On the negative side, the interface is \fIbizarre\fR \- so bizarre that
811even sun itself gets it wrong in their code examples: The event polling
812function sometimes returns events to the caller even though an error
813occurred, but with no indication whether it has done so or not (yes, it's
814even documented that way) \- deadly for edge-triggered interfaces where you
815absolutely have to know whether an event occurred or not because you have
816to re-arm the watcher.
817.Sp
818Fortunately libev seems to be able to work around these idiocies.
819.Sp
820This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
821\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
476.ie n .IP """EVBACKEND_ALL""" 4 822.ie n .IP """EVBACKEND_ALL""" 4
477.el .IP "\f(CWEVBACKEND_ALL\fR" 4 823.el .IP "\f(CWEVBACKEND_ALL\fR" 4
478.IX Item "EVBACKEND_ALL" 824.IX Item "EVBACKEND_ALL"
479Try all backends (even potentially broken ones that wouldn't be tried 825Try all backends (even potentially broken ones that wouldn't be tried
480with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 826with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
481\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 827\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
828.Sp
829It is definitely not recommended to use this flag, use whatever
830\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
831at all.
832.ie n .IP """EVBACKEND_MASK""" 4
833.el .IP "\f(CWEVBACKEND_MASK\fR" 4
834.IX Item "EVBACKEND_MASK"
835Not a backend at all, but a mask to select all backend bits from a
836\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
837value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
482.RE 838.RE
483.RS 4 839.RS 4
484.Sp 840.Sp
485If one or more of these are ored into the flags value, then only these 841If one or more of the backend flags are or'ed into the flags value,
486backends will be tried (in the reverse order as given here). If none are 842then only these backends will be tried (in the reverse order as listed
487specified, most compiled-in backend will be tried, usually in reverse 843here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
488order of their flag values :) 844()\*(C'\fR will be tried.
489.Sp 845.Sp
490The most typical usage is like this: 846Example: Try to create a event loop that uses epoll and nothing else.
491.Sp 847.Sp
492.Vb 2 848.Vb 3
493\& if (!ev_default_loop (0)) 849\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
494\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 850\& if (!epoller)
851\& fatal ("no epoll found here, maybe it hides under your chair");
495.Ve 852.Ve
496.Sp 853.Sp
497Restrict libev to the select and poll backends, and do not allow 854Example: Use whatever libev has to offer, but make sure that kqueue is
498environment settings to be taken into account: 855used if available.
499.Sp 856.Sp
500.Vb 1 857.Vb 1
501\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 858\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
502.Ve 859.Ve
503.Sp 860.Sp
504Use whatever libev has to offer, but make sure that kqueue is used if 861Example: Similarly, on linux, you mgiht want to take advantage of the
505available (warning, breaks stuff, best use only with your own private 862linux aio backend if possible, but fall back to something else if that
506event loop and only if you know the \s-1OS\s0 supports your types of fds): 863isn't available.
507.Sp 864.Sp
508.Vb 1 865.Vb 1
509\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 866\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
510.Ve 867.Ve
511.RE 868.RE
512.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
513.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
514Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
515always distinct from the default loop. Unlike the default loop, it cannot
516handle signal and child watchers, and attempts to do so will be greeted by
517undefined behaviour (or a failed assertion if assertions are enabled).
518.Sp
519Example: Try to create a event loop that uses epoll and nothing else.
520.Sp
521.Vb 3
522\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
523\& if (!epoller)
524\& fatal ("no epoll found here, maybe it hides under your chair");
525.Ve
526.IP "ev_default_destroy ()" 4 869.IP "ev_loop_destroy (loop)" 4
527.IX Item "ev_default_destroy ()" 870.IX Item "ev_loop_destroy (loop)"
528Destroys the default loop again (frees all memory and kernel state 871Destroys an event loop object (frees all memory and kernel state
529etc.). None of the active event watchers will be stopped in the normal 872etc.). None of the active event watchers will be stopped in the normal
530sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 873sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
531responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 874responsibility to either stop all watchers cleanly yourself \fIbefore\fR
532calling this function, or cope with the fact afterwards (which is usually 875calling this function, or cope with the fact afterwards (which is usually
533the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 876the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
534for example). 877for example).
535.IP "ev_loop_destroy (loop)" 4
536.IX Item "ev_loop_destroy (loop)"
537Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
538earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
539.IP "ev_default_fork ()" 4
540.IX Item "ev_default_fork ()"
541This function reinitialises the kernel state for backends that have
542one. Despite the name, you can call it anytime, but it makes most sense
543after forking, in either the parent or child process (or both, but that
544again makes little sense).
545.Sp 878.Sp
546You \fImust\fR call this function in the child process after forking if and 879Note that certain global state, such as signal state (and installed signal
547only if you want to use the event library in both processes. If you just 880handlers), will not be freed by this function, and related watchers (such
548fork+exec, you don't have to call it. 881as signal and child watchers) would need to be stopped manually.
549.Sp 882.Sp
550The function itself is quite fast and it's usually not a problem to call 883This function is normally used on loop objects allocated by
551it just in case after a fork. To make this easy, the function will fit in 884\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
552quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 885\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
553.Sp 886.Sp
554.Vb 1 887Note that it is not advisable to call this function on the default loop
555\& pthread_atfork (0, 0, ev_default_fork); 888except in the rare occasion where you really need to free its resources.
556.Ve 889If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
557.Sp 890and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
558At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
559without calling this function, so if you force one of those backends you
560do not need to care.
561.IP "ev_loop_fork (loop)" 4 891.IP "ev_loop_fork (loop)" 4
562.IX Item "ev_loop_fork (loop)" 892.IX Item "ev_loop_fork (loop)"
563Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 893This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
564\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 894to reinitialise the kernel state for backends that have one. Despite
565after fork, and how you do this is entirely your own problem. 895the name, you can call it anytime you are allowed to start or stop
896watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
897sense after forking, in the child process. You \fImust\fR call it (or use
898\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
899.Sp
900In addition, if you want to reuse a loop (via this function or
901\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
902.Sp
903Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
904a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
905because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
906during fork.
907.Sp
908On the other hand, you only need to call this function in the child
909process if and only if you want to use the event loop in the child. If
910you just fork+exec or create a new loop in the child, you don't have to
911call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
912difference, but libev will usually detect this case on its own and do a
913costly reset of the backend).
914.Sp
915The function itself is quite fast and it's usually not a problem to call
916it just in case after a fork.
917.Sp
918Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
919using pthreads.
920.Sp
921.Vb 5
922\& static void
923\& post_fork_child (void)
924\& {
925\& ev_loop_fork (EV_DEFAULT);
926\& }
927\&
928\& ...
929\& pthread_atfork (0, 0, post_fork_child);
930.Ve
931.IP "int ev_is_default_loop (loop)" 4
932.IX Item "int ev_is_default_loop (loop)"
933Returns true when the given loop is, in fact, the default loop, and false
934otherwise.
935.IP "unsigned int ev_iteration (loop)" 4
936.IX Item "unsigned int ev_iteration (loop)"
937Returns the current iteration count for the event loop, which is identical
938to the number of times libev did poll for new events. It starts at \f(CW0\fR
939and happily wraps around with enough iterations.
940.Sp
941This value can sometimes be useful as a generation counter of sorts (it
942\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
943\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
944prepare and check phases.
945.IP "unsigned int ev_depth (loop)" 4
946.IX Item "unsigned int ev_depth (loop)"
947Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
948times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
949.Sp
950Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
951\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
952in which case it is higher.
953.Sp
954Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
955throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
956as a hint to avoid such ungentleman-like behaviour unless it's really
957convenient, in which case it is fully supported.
566.IP "unsigned int ev_backend (loop)" 4 958.IP "unsigned int ev_backend (loop)" 4
567.IX Item "unsigned int ev_backend (loop)" 959.IX Item "unsigned int ev_backend (loop)"
568Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 960Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
569use. 961use.
570.IP "ev_tstamp ev_now (loop)" 4 962.IP "ev_tstamp ev_now (loop)" 4
571.IX Item "ev_tstamp ev_now (loop)" 963.IX Item "ev_tstamp ev_now (loop)"
572Returns the current \*(L"event loop time\*(R", which is the time the event loop 964Returns the current \*(L"event loop time\*(R", which is the time the event loop
573received events and started processing them. This timestamp does not 965received events and started processing them. This timestamp does not
574change as long as callbacks are being processed, and this is also the base 966change as long as callbacks are being processed, and this is also the base
575time used for relative timers. You can treat it as the timestamp of the 967time used for relative timers. You can treat it as the timestamp of the
576event occuring (or more correctly, libev finding out about it). 968event occurring (or more correctly, libev finding out about it).
969.IP "ev_now_update (loop)" 4
970.IX Item "ev_now_update (loop)"
971Establishes the current time by querying the kernel, updating the time
972returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
973is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
974.Sp
975This function is rarely useful, but when some event callback runs for a
976very long time without entering the event loop, updating libev's idea of
977the current time is a good idea.
978.Sp
979See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
980.IP "ev_suspend (loop)" 4
981.IX Item "ev_suspend (loop)"
982.PD 0
983.IP "ev_resume (loop)" 4
984.IX Item "ev_resume (loop)"
985.PD
986These two functions suspend and resume an event loop, for use when the
987loop is not used for a while and timeouts should not be processed.
988.Sp
989A typical use case would be an interactive program such as a game: When
990the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
991would be best to handle timeouts as if no time had actually passed while
992the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
993in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
994\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
995.Sp
996Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
997between \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
998will be rescheduled (that is, they will lose any events that would have
999occurred while suspended).
1000.Sp
1001After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
1002given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
1003without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
1004.Sp
1005Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
1006event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
577.IP "ev_loop (loop, int flags)" 4 1007.IP "bool ev_run (loop, int flags)" 4
578.IX Item "ev_loop (loop, int flags)" 1008.IX Item "bool ev_run (loop, int flags)"
579Finally, this is it, the event handler. This function usually is called 1009Finally, this is it, the event handler. This function usually is called
580after you initialised all your watchers and you want to start handling 1010after you have initialised all your watchers and you want to start
581events. 1011handling events. It will ask the operating system for any new events, call
1012the watcher callbacks, and then repeat the whole process indefinitely: This
1013is why event loops are called \fIloops\fR.
582.Sp 1014.Sp
583If the flags argument is specified as \f(CW0\fR, it will not return until 1015If the flags argument is specified as \f(CW0\fR, it will keep handling events
584either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 1016until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1017called.
585.Sp 1018.Sp
1019The return value is false if there are no more active watchers (which
1020usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1021(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1022.Sp
586Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1023Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
587relying on all watchers to be stopped when deciding when a program has 1024relying on all watchers to be stopped when deciding when a program has
588finished (especially in interactive programs), but having a program that 1025finished (especially in interactive programs), but having a program
589automatically loops as long as it has to and no longer by virtue of 1026that automatically loops as long as it has to and no longer by virtue
590relying on its watchers stopping correctly is a thing of beauty. 1027of relying on its watchers stopping correctly, that is truly a thing of
1028beauty.
591.Sp 1029.Sp
1030This function is \fImostly\fR exception-safe \- you can break out of a
1031\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1032exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1033will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1034.Sp
592A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1035A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
593those events and any outstanding ones, but will not block your process in 1036those events and any already outstanding ones, but will not wait and
594case there are no events and will return after one iteration of the loop. 1037block your process in case there are no events and will return after one
1038iteration of the loop. This is sometimes useful to poll and handle new
1039events while doing lengthy calculations, to keep the program responsive.
595.Sp 1040.Sp
596A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1041A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
597neccessary) and will handle those and any outstanding ones. It will block 1042necessary) and will handle those and any already outstanding ones. It
598your process until at least one new event arrives, and will return after 1043will block your process until at least one new event arrives (which could
599one iteration of the loop. This is useful if you are waiting for some 1044be an event internal to libev itself, so there is no guarantee that a
600external event in conjunction with something not expressible using other 1045user-registered callback will be called), and will return after one
1046iteration of the loop.
1047.Sp
1048This is useful if you are waiting for some external event in conjunction
1049with something not expressible using other libev watchers (i.e. "roll your
601libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 1050own \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
602usually a better approach for this kind of thing. 1051usually a better approach for this kind of thing.
603.Sp 1052.Sp
604Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1053Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1054understanding, not a guarantee that things will work exactly like this in
1055future versions):
605.Sp 1056.Sp
606.Vb 18 1057.Vb 10
607\& * If there are no active watchers (reference count is zero), return. 1058\& \- Increment loop depth.
608\& - Queue prepare watchers and then call all outstanding watchers. 1059\& \- Reset the ev_break status.
1060\& \- Before the first iteration, call any pending watchers.
1061\& LOOP:
1062\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1063\& \- If a fork was detected (by any means), queue and call all fork watchers.
1064\& \- Queue and call all prepare watchers.
1065\& \- If ev_break was called, goto FINISH.
609\& - If we have been forked, recreate the kernel state. 1066\& \- If we have been forked, detach and recreate the kernel state
1067\& as to not disturb the other process.
610\& - Update the kernel state with all outstanding changes. 1068\& \- Update the kernel state with all outstanding changes.
611\& - Update the "event loop time". 1069\& \- Update the "event loop time" (ev_now ()).
612\& - Calculate for how long to block. 1070\& \- Calculate for how long to sleep or block, if at all
1071\& (active idle watchers, EVRUN_NOWAIT or not having
1072\& any active watchers at all will result in not sleeping).
1073\& \- Sleep if the I/O and timer collect interval say so.
1074\& \- Increment loop iteration counter.
613\& - Block the process, waiting for any events. 1075\& \- Block the process, waiting for any events.
614\& - Queue all outstanding I/O (fd) events. 1076\& \- Queue all outstanding I/O (fd) events.
615\& - Update the "event loop time" and do time jump handling. 1077\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
616\& - Queue all outstanding timers. 1078\& \- Queue all expired timers.
617\& - Queue all outstanding periodics. 1079\& \- Queue all expired periodics.
618\& - If no events are pending now, queue all idle watchers. 1080\& \- Queue all idle watchers with priority higher than that of pending events.
619\& - Queue all check watchers. 1081\& \- Queue all check watchers.
620\& - Call all queued watchers in reverse order (i.e. check watchers first). 1082\& \- Call all queued watchers in reverse order (i.e. check watchers first).
621\& Signals and child watchers are implemented as I/O watchers, and will 1083\& Signals and child watchers are implemented as I/O watchers, and will
622\& be handled here by queueing them when their watcher gets executed. 1084\& be handled here by queueing them when their watcher gets executed.
623\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1085\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
624\& were used, return, otherwise continue with step *. 1086\& were used, or there are no active watchers, goto FINISH, otherwise
1087\& continue with step LOOP.
1088\& FINISH:
1089\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1090\& \- Decrement the loop depth.
1091\& \- Return.
625.Ve 1092.Ve
626.Sp 1093.Sp
627Example: Queue some jobs and then loop until no events are outsanding 1094Example: Queue some jobs and then loop until no events are outstanding
628anymore. 1095anymore.
629.Sp 1096.Sp
630.Vb 4 1097.Vb 4
631\& ... queue jobs here, make sure they register event watchers as long 1098\& ... queue jobs here, make sure they register event watchers as long
632\& ... as they still have work to do (even an idle watcher will do..) 1099\& ... as they still have work to do (even an idle watcher will do..)
633\& ev_loop (my_loop, 0); 1100\& ev_run (my_loop, 0);
634\& ... jobs done. yeah! 1101\& ... jobs done or somebody called break. yeah!
635.Ve 1102.Ve
636.IP "ev_unloop (loop, how)" 4 1103.IP "ev_break (loop, how)" 4
637.IX Item "ev_unloop (loop, how)" 1104.IX Item "ev_break (loop, how)"
638Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1105Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
639has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1106has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
640\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1107\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
641\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1108\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1109.Sp
1110This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1111.Sp
1112It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1113which case it will have no effect.
642.IP "ev_ref (loop)" 4 1114.IP "ev_ref (loop)" 4
643.IX Item "ev_ref (loop)" 1115.IX Item "ev_ref (loop)"
644.PD 0 1116.PD 0
645.IP "ev_unref (loop)" 4 1117.IP "ev_unref (loop)" 4
646.IX Item "ev_unref (loop)" 1118.IX Item "ev_unref (loop)"
647.PD 1119.PD
648Ref/unref can be used to add or remove a reference count on the event 1120Ref/unref can be used to add or remove a reference count on the event
649loop: Every watcher keeps one reference, and as long as the reference 1121loop: Every watcher keeps one reference, and as long as the reference
650count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1122count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
651a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1123.Sp
652returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1124This is useful when you have a watcher that you never intend to
1125unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1126returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1127before stopping it.
1128.Sp
653example, libev itself uses this for its internal signal pipe: It is not 1129As an example, libev itself uses this for its internal signal pipe: It
654visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1130is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
655no event watchers registered by it are active. It is also an excellent 1131exiting if no event watchers registered by it are active. It is also an
656way to do this for generic recurring timers or from within third-party 1132excellent way to do this for generic recurring timers or from within
657libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1133third-party libraries. Just remember to \fIunref after start\fR and \fIref
1134before stop\fR (but only if the watcher wasn't active before, or was active
1135before, respectively. Note also that libev might stop watchers itself
1136(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1137in the callback).
658.Sp 1138.Sp
659Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1139Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
660running when nothing else is active. 1140running when nothing else is active.
661.Sp 1141.Sp
662.Vb 4 1142.Vb 4
663\& struct ev_signal exitsig; 1143\& ev_signal exitsig;
664\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1144\& ev_signal_init (&exitsig, sig_cb, SIGINT);
665\& ev_signal_start (loop, &exitsig); 1145\& ev_signal_start (loop, &exitsig);
666\& evf_unref (loop); 1146\& ev_unref (loop);
667.Ve 1147.Ve
668.Sp 1148.Sp
669Example: For some weird reason, unregister the above signal handler again. 1149Example: For some weird reason, unregister the above signal handler again.
670.Sp 1150.Sp
671.Vb 2 1151.Vb 2
672\& ev_ref (loop); 1152\& ev_ref (loop);
673\& ev_signal_stop (loop, &exitsig); 1153\& ev_signal_stop (loop, &exitsig);
674.Ve 1154.Ve
1155.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1156.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1157.PD 0
1158.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1159.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1160.PD
1161These advanced functions influence the time that libev will spend waiting
1162for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1163will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1164latency.
1165.Sp
1166Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1167allows libev to delay invocation of I/O and timer/periodic callbacks
1168to increase efficiency of loop iterations (or to increase power-saving
1169opportunities).
1170.Sp
1171The idea is that sometimes your program runs just fast enough to handle
1172one (or very few) event(s) per loop iteration. While this makes the
1173program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1174events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1175overhead for the actual polling but can deliver many events at once.
1176.Sp
1177By setting a higher \fIio collect interval\fR you allow libev to spend more
1178time collecting I/O events, so you can handle more events per iteration,
1179at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1180\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1181introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1182sleep time ensures that libev will not poll for I/O events more often then
1183once per this interval, on average (as long as the host time resolution is
1184good enough).
1185.Sp
1186Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1187to spend more time collecting timeouts, at the expense of increased
1188latency/jitter/inexactness (the watcher callback will be called
1189later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1190value will not introduce any overhead in libev.
1191.Sp
1192Many (busy) programs can usually benefit by setting the I/O collect
1193interval to a value near \f(CW0.1\fR or so, which is often enough for
1194interactive servers (of course not for games), likewise for timeouts. It
1195usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1196as this approaches the timing granularity of most systems. Note that if
1197you do transactions with the outside world and you can't increase the
1198parallelity, then this setting will limit your transaction rate (if you
1199need to poll once per transaction and the I/O collect interval is 0.01,
1200then you can't do more than 100 transactions per second).
1201.Sp
1202Setting the \fItimeout collect interval\fR can improve the opportunity for
1203saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1204are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1205times the process sleeps and wakes up again. Another useful technique to
1206reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1207they fire on, say, one-second boundaries only.
1208.Sp
1209Example: we only need 0.1s timeout granularity, and we wish not to poll
1210more often than 100 times per second:
1211.Sp
1212.Vb 2
1213\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1214\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1215.Ve
1216.IP "ev_invoke_pending (loop)" 4
1217.IX Item "ev_invoke_pending (loop)"
1218This call will simply invoke all pending watchers while resetting their
1219pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1220but when overriding the invoke callback this call comes handy. This
1221function can be invoked from a watcher \- this can be useful for example
1222when you want to do some lengthy calculation and want to pass further
1223event handling to another thread (you still have to make sure only one
1224thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1225.IP "int ev_pending_count (loop)" 4
1226.IX Item "int ev_pending_count (loop)"
1227Returns the number of pending watchers \- zero indicates that no watchers
1228are pending.
1229.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1230.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1231This overrides the invoke pending functionality of the loop: Instead of
1232invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1233this callback instead. This is useful, for example, when you want to
1234invoke the actual watchers inside another context (another thread etc.).
1235.Sp
1236If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1237callback.
1238.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1239.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1240Sometimes you want to share the same loop between multiple threads. This
1241can be done relatively simply by putting mutex_lock/unlock calls around
1242each call to a libev function.
1243.Sp
1244However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1245to wait for it to return. One way around this is to wake up the event
1246loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1247\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1248.Sp
1249When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1250suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1251afterwards.
1252.Sp
1253Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1254\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1255.Sp
1256While event loop modifications are allowed between invocations of
1257\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1258modifications done will affect the event loop, i.e. adding watchers will
1259have no effect on the set of file descriptors being watched, or the time
1260waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1261to take note of any changes you made.
1262.Sp
1263In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1264invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1265.Sp
1266See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1267document.
1268.IP "ev_set_userdata (loop, void *data)" 4
1269.IX Item "ev_set_userdata (loop, void *data)"
1270.PD 0
1271.IP "void *ev_userdata (loop)" 4
1272.IX Item "void *ev_userdata (loop)"
1273.PD
1274Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1275\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1276\&\f(CW0\fR.
1277.Sp
1278These two functions can be used to associate arbitrary data with a loop,
1279and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1280\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1281any other purpose as well.
1282.IP "ev_verify (loop)" 4
1283.IX Item "ev_verify (loop)"
1284This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1285compiled in, which is the default for non-minimal builds. It tries to go
1286through all internal structures and checks them for validity. If anything
1287is found to be inconsistent, it will print an error message to standard
1288error and call \f(CW\*(C`abort ()\*(C'\fR.
1289.Sp
1290This can be used to catch bugs inside libev itself: under normal
1291circumstances, this function will never abort as of course libev keeps its
1292data structures consistent.
675.SH "ANATOMY OF A WATCHER" 1293.SH "ANATOMY OF A WATCHER"
676.IX Header "ANATOMY OF A WATCHER" 1294.IX Header "ANATOMY OF A WATCHER"
1295In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1296watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1297watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1298.PP
677A watcher is a structure that you create and register to record your 1299A watcher is an opaque structure that you allocate and register to record
678interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1300your interest in some event. To make a concrete example, imagine you want
679become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1301to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1302for that:
680.PP 1303.PP
681.Vb 5 1304.Vb 5
682\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1305\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
683\& { 1306\& {
684\& ev_io_stop (w); 1307\& ev_io_stop (w);
685\& ev_unloop (loop, EVUNLOOP_ALL); 1308\& ev_break (loop, EVBREAK_ALL);
686\& } 1309\& }
687.Ve 1310\&
688.PP
689.Vb 6
690\& struct ev_loop *loop = ev_default_loop (0); 1311\& struct ev_loop *loop = ev_default_loop (0);
1312\&
691\& struct ev_io stdin_watcher; 1313\& ev_io stdin_watcher;
1314\&
692\& ev_init (&stdin_watcher, my_cb); 1315\& ev_init (&stdin_watcher, my_cb);
693\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1316\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
694\& ev_io_start (loop, &stdin_watcher); 1317\& ev_io_start (loop, &stdin_watcher);
1318\&
695\& ev_loop (loop, 0); 1319\& ev_run (loop, 0);
696.Ve 1320.Ve
697.PP 1321.PP
698As you can see, you are responsible for allocating the memory for your 1322As you can see, you are responsible for allocating the memory for your
699watcher structures (and it is usually a bad idea to do this on the stack, 1323watcher structures (and it is \fIusually\fR a bad idea to do this on the
700although this can sometimes be quite valid). 1324stack).
701.PP 1325.PP
1326Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1327or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1328.PP
702Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1329Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
703(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1330*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
704callback gets invoked each time the event occurs (or, in the case of io 1331invoked each time the event occurs (or, in the case of I/O watchers, each
705watchers, each time the event loop detects that the file descriptor given 1332time the event loop detects that the file descriptor given is readable
706is readable and/or writable). 1333and/or writable).
707.PP 1334.PP
708Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1335Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
709with arguments specific to this watcher type. There is also a macro 1336macro to configure it, with arguments specific to the watcher type. There
710to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1337is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
711(watcher *, callback, ...)\*(C'\fR.
712.PP 1338.PP
713To make the watcher actually watch out for events, you have to start it 1339To make the watcher actually watch out for events, you have to start it
714with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1340with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
715*)\*(C'\fR), and you can stop watching for events at any time by calling the 1341*)\*(C'\fR), and you can stop watching for events at any time by calling the
716corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1342corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
717.PP 1343.PP
718As long as your watcher is active (has been started but not stopped) you 1344As long as your watcher is active (has been started but not stopped) you
719must not touch the values stored in it. Most specifically you must never 1345must not touch the values stored in it. Most specifically you must never
720reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1346reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
721.PP 1347.PP
722Each and every callback receives the event loop pointer as first, the 1348Each and every callback receives the event loop pointer as first, the
723registered watcher structure as second, and a bitset of received events as 1349registered watcher structure as second, and a bitset of received events as
724third argument. 1350third argument.
725.PP 1351.PP
… …
734.el .IP "\f(CWEV_WRITE\fR" 4 1360.el .IP "\f(CWEV_WRITE\fR" 4
735.IX Item "EV_WRITE" 1361.IX Item "EV_WRITE"
736.PD 1362.PD
737The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1363The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
738writable. 1364writable.
739.ie n .IP """EV_TIMEOUT""" 4 1365.ie n .IP """EV_TIMER""" 4
740.el .IP "\f(CWEV_TIMEOUT\fR" 4 1366.el .IP "\f(CWEV_TIMER\fR" 4
741.IX Item "EV_TIMEOUT" 1367.IX Item "EV_TIMER"
742The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1368The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
743.ie n .IP """EV_PERIODIC""" 4 1369.ie n .IP """EV_PERIODIC""" 4
744.el .IP "\f(CWEV_PERIODIC\fR" 4 1370.el .IP "\f(CWEV_PERIODIC\fR" 4
745.IX Item "EV_PERIODIC" 1371.IX Item "EV_PERIODIC"
746The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1372The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
766.PD 0 1392.PD 0
767.ie n .IP """EV_CHECK""" 4 1393.ie n .IP """EV_CHECK""" 4
768.el .IP "\f(CWEV_CHECK\fR" 4 1394.el .IP "\f(CWEV_CHECK\fR" 4
769.IX Item "EV_CHECK" 1395.IX Item "EV_CHECK"
770.PD 1396.PD
771All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1397All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
772to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1398gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
773\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1399just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1400for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1401watchers invoked before the event loop sleeps or polls for new events, and
1402\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1403or lower priority within an event loop iteration.
1404.Sp
774received events. Callbacks of both watcher types can start and stop as 1405Callbacks of both watcher types can start and stop as many watchers as
775many watchers as they want, and all of them will be taken into account 1406they want, and all of them will be taken into account (for example, a
776(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1407\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
777\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1408blocking).
778.ie n .IP """EV_EMBED""" 4 1409.ie n .IP """EV_EMBED""" 4
779.el .IP "\f(CWEV_EMBED\fR" 4 1410.el .IP "\f(CWEV_EMBED\fR" 4
780.IX Item "EV_EMBED" 1411.IX Item "EV_EMBED"
781The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1412The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
782.ie n .IP """EV_FORK""" 4 1413.ie n .IP """EV_FORK""" 4
783.el .IP "\f(CWEV_FORK\fR" 4 1414.el .IP "\f(CWEV_FORK\fR" 4
784.IX Item "EV_FORK" 1415.IX Item "EV_FORK"
785The event loop has been resumed in the child process after fork (see 1416The event loop has been resumed in the child process after fork (see
786\&\f(CW\*(C`ev_fork\*(C'\fR). 1417\&\f(CW\*(C`ev_fork\*(C'\fR).
1418.ie n .IP """EV_CLEANUP""" 4
1419.el .IP "\f(CWEV_CLEANUP\fR" 4
1420.IX Item "EV_CLEANUP"
1421The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1422.ie n .IP """EV_ASYNC""" 4
1423.el .IP "\f(CWEV_ASYNC\fR" 4
1424.IX Item "EV_ASYNC"
1425The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1426.ie n .IP """EV_CUSTOM""" 4
1427.el .IP "\f(CWEV_CUSTOM\fR" 4
1428.IX Item "EV_CUSTOM"
1429Not ever sent (or otherwise used) by libev itself, but can be freely used
1430by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
787.ie n .IP """EV_ERROR""" 4 1431.ie n .IP """EV_ERROR""" 4
788.el .IP "\f(CWEV_ERROR\fR" 4 1432.el .IP "\f(CWEV_ERROR\fR" 4
789.IX Item "EV_ERROR" 1433.IX Item "EV_ERROR"
790An unspecified error has occured, the watcher has been stopped. This might 1434An unspecified error has occurred, the watcher has been stopped. This might
791happen because the watcher could not be properly started because libev 1435happen because the watcher could not be properly started because libev
792ran out of memory, a file descriptor was found to be closed or any other 1436ran out of memory, a file descriptor was found to be closed or any other
1437problem. Libev considers these application bugs.
1438.Sp
793problem. You best act on it by reporting the problem and somehow coping 1439You best act on it by reporting the problem and somehow coping with the
794with the watcher being stopped. 1440watcher being stopped. Note that well-written programs should not receive
1441an error ever, so when your watcher receives it, this usually indicates a
1442bug in your program.
795.Sp 1443.Sp
796Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1444Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
797for example it might indicate that a fd is readable or writable, and if 1445example it might indicate that a fd is readable or writable, and if your
798your callbacks is well-written it can just attempt the operation and cope 1446callbacks is well-written it can just attempt the operation and cope with
799with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1447the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
800programs, though, so beware. 1448programs, though, as the fd could already be closed and reused for another
1449thing, so beware.
801.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1450.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
802.IX Subsection "GENERIC WATCHER FUNCTIONS" 1451.IX Subsection "GENERIC WATCHER FUNCTIONS"
803In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
804e.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.
805.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1452.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
806.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1453.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
807.IX Item "ev_init (ev_TYPE *watcher, callback)" 1454.IX Item "ev_init (ev_TYPE *watcher, callback)"
808This macro initialises the generic portion of a watcher. The contents 1455This macro initialises the generic portion of a watcher. The contents
809of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1456of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
813which rolls both calls into one. 1460which rolls both calls into one.
814.Sp 1461.Sp
815You can reinitialise a watcher at any time as long as it has been stopped 1462You can reinitialise a watcher at any time as long as it has been stopped
816(or never started) and there are no pending events outstanding. 1463(or never started) and there are no pending events outstanding.
817.Sp 1464.Sp
818The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1465The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
819int revents)\*(C'\fR. 1466int revents)\*(C'\fR.
1467.Sp
1468Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1469.Sp
1470.Vb 3
1471\& ev_io w;
1472\& ev_init (&w, my_cb);
1473\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1474.Ve
820.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1475.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
821.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1476.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
822.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1477.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
823This macro initialises the type-specific parts of a watcher. You need to 1478This macro initialises the type-specific parts of a watcher. You need to
824call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1479call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
825call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1480call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
826macro on a watcher that is active (it can be pending, however, which is a 1481macro on a watcher that is active (it can be pending, however, which is a
827difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1482difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
828.Sp 1483.Sp
829Although some watcher types do not have type-specific arguments 1484Although some watcher types do not have type-specific arguments
830(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1485(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1486.Sp
1487See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
831.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1488.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
832.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1489.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
833.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1490.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
834This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1491This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
835calls into a single call. This is the most convinient method to initialise 1492calls into a single call. This is the most convenient method to initialise
836a watcher. The same limitations apply, of course. 1493a watcher. The same limitations apply, of course.
1494.Sp
1495Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1496.Sp
1497.Vb 1
1498\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1499.Ve
837.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1500.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
838.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1501.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
839.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1502.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
840Starts (activates) the given watcher. Only active watchers will receive 1503Starts (activates) the given watcher. Only active watchers will receive
841events. If the watcher is already active nothing will happen. 1504events. If the watcher is already active nothing will happen.
1505.Sp
1506Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1507whole section.
1508.Sp
1509.Vb 1
1510\& ev_io_start (EV_DEFAULT_UC, &w);
1511.Ve
842.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1512.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
843.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1513.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
844.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1514.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
845Stops the given watcher again (if active) and clears the pending 1515Stops the given watcher if active, and clears the pending status (whether
1516the watcher was active or not).
1517.Sp
846status. It is possible that stopped watchers are pending (for example, 1518It is possible that stopped watchers are pending \- for example,
847non-repeating timers are being stopped when they become pending), but 1519non-repeating timers are being stopped when they become pending \- but
848\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1520calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
849you want to free or reuse the memory used by the watcher it is therefore a 1521pending. If you want to free or reuse the memory used by the watcher it is
850good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1522therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
851.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1523.IP "bool ev_is_active (ev_TYPE *watcher)" 4
852.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1524.IX Item "bool ev_is_active (ev_TYPE *watcher)"
853Returns a true value iff the watcher is active (i.e. it has been started 1525Returns a true value iff the watcher is active (i.e. it has been started
854and not yet been stopped). As long as a watcher is active you must not modify 1526and not yet been stopped). As long as a watcher is active you must not modify
855it. 1527it.
856.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1528.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
857.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1529.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
858Returns a true value iff the watcher is pending, (i.e. it has outstanding 1530Returns a true value iff the watcher is pending, (i.e. it has outstanding
859events but its callback has not yet been invoked). As long as a watcher 1531events but its callback has not yet been invoked). As long as a watcher
860is pending (but not active) you must not call an init function on it (but 1532is pending (but not active) you must not call an init function on it (but
861\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1533\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
862libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1534make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1535it).
863.IP "callback ev_cb (ev_TYPE *watcher)" 4 1536.IP "callback ev_cb (ev_TYPE *watcher)" 4
864.IX Item "callback ev_cb (ev_TYPE *watcher)" 1537.IX Item "callback ev_cb (ev_TYPE *watcher)"
865Returns the callback currently set on the watcher. 1538Returns the callback currently set on the watcher.
866.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1539.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
867.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1540.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
868Change the callback. You can change the callback at virtually any time 1541Change the callback. You can change the callback at virtually any time
869(modulo threads). 1542(modulo threads).
870.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1543.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
871.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1544.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
872Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1545.PD 0
873and read at any time, libev will completely ignore it. This can be used 1546.IP "int ev_priority (ev_TYPE *watcher)" 4
874to associate arbitrary data with your watcher. If you need more data and 1547.IX Item "int ev_priority (ev_TYPE *watcher)"
875don't want to allocate memory and store a pointer to it in that data 1548.PD
876member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1549Set and query the priority of the watcher. The priority is a small
877data: 1550integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1551(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1552before watchers with lower priority, but priority will not keep watchers
1553from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1554.Sp
1555If you need to suppress invocation when higher priority events are pending
1556you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1557.Sp
1558You \fImust not\fR change the priority of a watcher as long as it is active or
1559pending.
1560.Sp
1561Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1562fine, as long as you do not mind that the priority value you query might
1563or might not have been clamped to the valid range.
1564.Sp
1565The default priority used by watchers when no priority has been set is
1566always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1567.Sp
1568See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1569priorities.
1570.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1571.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1572Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1573\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1574can deal with that fact, as both are simply passed through to the
1575callback.
1576.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1577.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1578If the watcher is pending, this function clears its pending status and
1579returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1580watcher isn't pending it does nothing and returns \f(CW0\fR.
1581.Sp
1582Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1583callback to be invoked, which can be accomplished with this function.
1584.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1585.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1586Feeds the given event set into the event loop, as if the specified event
1587had happened for the specified watcher (which must be a pointer to an
1588initialised but not necessarily started event watcher). Obviously you must
1589not free the watcher as long as it has pending events.
1590.Sp
1591Stopping the watcher, letting libev invoke it, or calling
1592\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1593not started in the first place.
1594.Sp
1595See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1596functions that do not need a watcher.
878.PP 1597.PP
1598See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1599OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1600.SS "\s-1WATCHER STATES\s0"
1601.IX Subsection "WATCHER STATES"
1602There are various watcher states mentioned throughout this manual \-
1603active, pending and so on. In this section these states and the rules to
1604transition between them will be described in more detail \- and while these
1605rules might look complicated, they usually do \*(L"the right thing\*(R".
1606.IP "initialised" 4
1607.IX Item "initialised"
1608Before a watcher can be registered with the event loop it has to be
1609initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1610\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1611.Sp
1612In this state it is simply some block of memory that is suitable for
1613use in an event loop. It can be moved around, freed, reused etc. at
1614will \- as long as you either keep the memory contents intact, or call
1615\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1616.IP "started/running/active" 4
1617.IX Item "started/running/active"
1618Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1619property of the event loop, and is actively waiting for events. While in
1620this state it cannot be accessed (except in a few documented ways), moved,
1621freed or anything else \- the only legal thing is to keep a pointer to it,
1622and call libev functions on it that are documented to work on active watchers.
1623.IP "pending" 4
1624.IX Item "pending"
1625If a watcher is active and libev determines that an event it is interested
1626in has occurred (such as a timer expiring), it will become pending. It will
1627stay in this pending state until either it is stopped or its callback is
1628about to be invoked, so it is not normally pending inside the watcher
1629callback.
1630.Sp
1631The watcher might or might not be active while it is pending (for example,
1632an expired non-repeating timer can be pending but no longer active). If it
1633is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1634but it is still property of the event loop at this time, so cannot be
1635moved, freed or reused. And if it is active the rules described in the
1636previous item still apply.
1637.Sp
1638It is also possible to feed an event on a watcher that is not active (e.g.
1639via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1640active.
1641.IP "stopped" 4
1642.IX Item "stopped"
1643A watcher can be stopped implicitly by libev (in which case it might still
1644be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1645latter will clear any pending state the watcher might be in, regardless
1646of whether it was active or not, so stopping a watcher explicitly before
1647freeing it is often a good idea.
1648.Sp
1649While stopped (and not pending) the watcher is essentially in the
1650initialised state, that is, it can be reused, moved, modified in any way
1651you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1652it again).
1653.SS "\s-1WATCHER PRIORITY MODELS\s0"
1654.IX Subsection "WATCHER PRIORITY MODELS"
1655Many event loops support \fIwatcher priorities\fR, which are usually small
1656integers that influence the ordering of event callback invocation
1657between watchers in some way, all else being equal.
1658.PP
1659In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1660description for the more technical details such as the actual priority
1661range.
1662.PP
1663There are two common ways how these these priorities are being interpreted
1664by event loops:
1665.PP
1666In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1667of lower priority watchers, which means as long as higher priority
1668watchers receive events, lower priority watchers are not being invoked.
1669.PP
1670The less common only-for-ordering model uses priorities solely to order
1671callback invocation within a single event loop iteration: Higher priority
1672watchers are invoked before lower priority ones, but they all get invoked
1673before polling for new events.
1674.PP
1675Libev uses the second (only-for-ordering) model for all its watchers
1676except for idle watchers (which use the lock-out model).
1677.PP
1678The rationale behind this is that implementing the lock-out model for
1679watchers is not well supported by most kernel interfaces, and most event
1680libraries will just poll for the same events again and again as long as
1681their callbacks have not been executed, which is very inefficient in the
1682common case of one high-priority watcher locking out a mass of lower
1683priority ones.
1684.PP
1685Static (ordering) priorities are most useful when you have two or more
1686watchers handling the same resource: a typical usage example is having an
1687\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1688timeouts. Under load, data might be received while the program handles
1689other jobs, but since timers normally get invoked first, the timeout
1690handler will be executed before checking for data. In that case, giving
1691the timer a lower priority than the I/O watcher ensures that I/O will be
1692handled first even under adverse conditions (which is usually, but not
1693always, what you want).
1694.PP
1695Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1696will only be executed when no same or higher priority watchers have
1697received events, they can be used to implement the \*(L"lock-out\*(R" model when
1698required.
1699.PP
1700For example, to emulate how many other event libraries handle priorities,
1701you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1702the normal watcher callback, you just start the idle watcher. The real
1703processing is done in the idle watcher callback. This causes libev to
1704continuously poll and process kernel event data for the watcher, but when
1705the lock-out case is known to be rare (which in turn is rare :), this is
1706workable.
1707.PP
1708Usually, however, the lock-out model implemented that way will perform
1709miserably under the type of load it was designed to handle. In that case,
1710it might be preferable to stop the real watcher before starting the
1711idle watcher, so the kernel will not have to process the event in case
1712the actual processing will be delayed for considerable time.
1713.PP
1714Here is an example of an I/O watcher that should run at a strictly lower
1715priority than the default, and which should only process data when no
1716other events are pending:
1717.PP
879.Vb 7 1718.Vb 2
880\& struct my_io 1719\& ev_idle idle; // actual processing watcher
881\& { 1720\& ev_io io; // actual event watcher
882\& struct ev_io io; 1721\&
883\& int otherfd;
884\& void *somedata;
885\& struct whatever *mostinteresting;
886\& }
887.Ve
888.PP
889And since your callback will be called with a pointer to the watcher, you
890can cast it back to your own type:
891.PP
892.Vb 5
893\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
894\& {
895\& struct my_io *w = (struct my_io *)w_;
896\& ...
897\& }
898.Ve
899.PP
900More interesting and less C\-conformant ways of casting your callback type
901instead have been omitted.
902.PP
903Another common scenario is having some data structure with multiple
904watchers:
905.PP
906.Vb 6
907\& struct my_biggy
908\& {
909\& int some_data;
910\& ev_timer t1;
911\& ev_timer t2;
912\& }
913.Ve
914.PP
915In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
916you need to use \f(CW\*(C`offsetof\*(C'\fR:
917.PP
918.Vb 1
919\& #include <stddef.h>
920.Ve
921.PP
922.Vb 6
923\& static void 1722\& static void
924\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1723\& io_cb (EV_P_ ev_io *w, int revents)
925\& { 1724\& {
926\& struct my_biggy big = (struct my_biggy * 1725\& // stop the I/O watcher, we received the event, but
927\& (((char *)w) - offsetof (struct my_biggy, t1)); 1726\& // are not yet ready to handle it.
1727\& ev_io_stop (EV_A_ w);
1728\&
1729\& // start the idle watcher to handle the actual event.
1730\& // it will not be executed as long as other watchers
1731\& // with the default priority are receiving events.
1732\& ev_idle_start (EV_A_ &idle);
928\& } 1733\& }
929.Ve 1734\&
930.PP
931.Vb 6
932\& static void 1735\& static void
933\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1736\& idle_cb (EV_P_ ev_idle *w, int revents)
934\& { 1737\& {
935\& struct my_biggy big = (struct my_biggy * 1738\& // actual processing
936\& (((char *)w) - offsetof (struct my_biggy, t2)); 1739\& read (STDIN_FILENO, ...);
1740\&
1741\& // have to start the I/O watcher again, as
1742\& // we have handled the event
1743\& ev_io_start (EV_P_ &io);
937\& } 1744\& }
1745\&
1746\& // initialisation
1747\& ev_idle_init (&idle, idle_cb);
1748\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1749\& ev_io_start (EV_DEFAULT_ &io);
938.Ve 1750.Ve
1751.PP
1752In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1753low-priority connections can not be locked out forever under load. This
1754enables your program to keep a lower latency for important connections
1755during short periods of high load, while not completely locking out less
1756important ones.
939.SH "WATCHER TYPES" 1757.SH "WATCHER TYPES"
940.IX Header "WATCHER TYPES" 1758.IX Header "WATCHER TYPES"
941This section describes each watcher in detail, but will not repeat 1759This section describes each watcher in detail, but will not repeat
942information given in the last section. Any initialisation/set macros, 1760information given in the last section. Any initialisation/set macros,
943functions and members specific to the watcher type are explained. 1761functions and members specific to the watcher type are explained.
… …
948watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1766watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
949means you can expect it to have some sensible content while the watcher 1767means you can expect it to have some sensible content while the watcher
950is active, but you can also modify it. Modifying it may not do something 1768is active, but you can also modify it. Modifying it may not do something
951sensible or take immediate effect (or do anything at all), but libev will 1769sensible or take immediate effect (or do anything at all), but libev will
952not crash or malfunction in any way. 1770not crash or malfunction in any way.
953.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1771.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
954.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1772.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
955.IX Subsection "ev_io - is this file descriptor readable or writable?" 1773.IX Subsection "ev_io - is this file descriptor readable or writable?"
956I/O watchers check whether a file descriptor is readable or writable 1774I/O watchers check whether a file descriptor is readable or writable
957in each iteration of the event loop, or, more precisely, when reading 1775in each iteration of the event loop, or, more precisely, when reading
958would not block the process and writing would at least be able to write 1776would not block the process and writing would at least be able to write
959some data. This behaviour is called level-triggering because you keep 1777some data. This behaviour is called level-triggering because you keep
… …
964In general you can register as many read and/or write event watchers per 1782In general you can register as many read and/or write event watchers per
965fd as you want (as long as you don't confuse yourself). Setting all file 1783fd as you want (as long as you don't confuse yourself). Setting all file
966descriptors to non-blocking mode is also usually a good idea (but not 1784descriptors to non-blocking mode is also usually a good idea (but not
967required if you know what you are doing). 1785required if you know what you are doing).
968.PP 1786.PP
969You have to be careful with dup'ed file descriptors, though. Some backends
970(the linux epoll backend is a notable example) cannot handle dup'ed file
971descriptors correctly if you register interest in two or more fds pointing
972to the same underlying file/socket/etc. description (that is, they share
973the same underlying \*(L"file open\*(R").
974.PP
975If you must do this, then force the use of a known-to-be-good backend
976(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
977\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
978.PP
979Another thing you have to watch out for is that it is quite easy to 1787Another thing you have to watch out for is that it is quite easy to
980receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1788receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
981be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1789be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
982because there is no data. Not only are some backends known to create a 1790because there is no data. It is very easy to get into this situation even
983lot of those (for example solaris ports), it is very easy to get into 1791with a relatively standard program structure. Thus it is best to always
984this situation even with a relatively standard program structure. Thus 1792use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
985it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
986\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1793preferable to a program hanging until some data arrives.
987.PP 1794.PP
988If you cannot run the fd in non-blocking mode (for example you should not 1795If you cannot run the fd in non-blocking mode (for example you should
989play around with an Xlib connection), then you have to seperately re-test 1796not play around with an Xlib connection), then you have to separately
990wether a file descriptor is really ready with a known-to-be good interface 1797re-test whether a file descriptor is really ready with a known-to-be good
991such as poll (fortunately in our Xlib example, Xlib already does this on 1798interface such as poll (fortunately in the case of Xlib, it already does
992its own, so its quite safe to use). 1799this on its own, so its quite safe to use). Some people additionally
1800use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1801indefinitely.
1802.PP
1803But really, best use non-blocking mode.
1804.PP
1805\fIThe special problem of disappearing file descriptors\fR
1806.IX Subsection "The special problem of disappearing file descriptors"
1807.PP
1808Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1809a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1810means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1811file descriptor, but when it goes away, the operating system will silently
1812drop this interest. If another file descriptor with the same number then
1813is registered with libev, there is no efficient way to see that this is,
1814in fact, a different file descriptor.
1815.PP
1816To avoid having to explicitly tell libev about such cases, libev follows
1817the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1818will assume that this is potentially a new file descriptor, otherwise
1819it is assumed that the file descriptor stays the same. That means that
1820you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
1821descriptor even if the file descriptor number itself did not change.
1822.PP
1823This is how one would do it normally anyway, the important point is that
1824the libev application should not optimise around libev but should leave
1825optimisations to libev.
1826.PP
1827\fIThe special problem of dup'ed file descriptors\fR
1828.IX Subsection "The special problem of dup'ed file descriptors"
1829.PP
1830Some backends (e.g. epoll), cannot register events for file descriptors,
1831but only events for the underlying file descriptions. That means when you
1832have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1833events for them, only one file descriptor might actually receive events.
1834.PP
1835There is no workaround possible except not registering events
1836for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1837\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1838.PP
1839\fIThe special problem of files\fR
1840.IX Subsection "The special problem of files"
1841.PP
1842Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1843representing files, and expect it to become ready when their program
1844doesn't block on disk accesses (which can take a long time on their own).
1845.PP
1846However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1847notification as soon as the kernel knows whether and how much data is
1848there, and in the case of open files, that's always the case, so you
1849always get a readiness notification instantly, and your read (or possibly
1850write) will still block on the disk I/O.
1851.PP
1852Another way to view it is that in the case of sockets, pipes, character
1853devices and so on, there is another party (the sender) that delivers data
1854on its own, but in the case of files, there is no such thing: the disk
1855will not send data on its own, simply because it doesn't know what you
1856wish to read \- you would first have to request some data.
1857.PP
1858Since files are typically not-so-well supported by advanced notification
1859mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1860to files, even though you should not use it. The reason for this is
1861convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1862usually a tty, often a pipe, but also sometimes files or special devices
1863(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1864\&\fI/dev/urandom\fR), and even though the file might better be served with
1865asynchronous I/O instead of with non-blocking I/O, it is still useful when
1866it \*(L"just works\*(R" instead of freezing.
1867.PP
1868So avoid file descriptors pointing to files when you know it (e.g. use
1869libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1870when you rarely read from a file instead of from a socket, and want to
1871reuse the same code path.
1872.PP
1873\fIThe special problem of fork\fR
1874.IX Subsection "The special problem of fork"
1875.PP
1876Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1877at all or exhibit useless behaviour. Libev fully supports fork, but needs
1878to be told about it in the child if you want to continue to use it in the
1879child.
1880.PP
1881To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1882()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1883\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1884.PP
1885\fIThe special problem of \s-1SIGPIPE\s0\fR
1886.IX Subsection "The special problem of SIGPIPE"
1887.PP
1888While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1889when writing to a pipe whose other end has been closed, your program gets
1890sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1891this is sensible behaviour, for daemons, this is usually undesirable.
1892.PP
1893So when you encounter spurious, unexplained daemon exits, make sure you
1894ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1895somewhere, as that would have given you a big clue).
1896.PP
1897\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1898.IX Subsection "The special problem of accept()ing when you can't"
1899.PP
1900Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1901found in post\-2004 Linux) have the peculiar behaviour of not removing a
1902connection from the pending queue in all error cases.
1903.PP
1904For example, larger servers often run out of file descriptors (because
1905of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1906rejecting the connection, leading to libev signalling readiness on
1907the next iteration again (the connection still exists after all), and
1908typically causing the program to loop at 100% \s-1CPU\s0 usage.
1909.PP
1910Unfortunately, the set of errors that cause this issue differs between
1911operating systems, there is usually little the app can do to remedy the
1912situation, and no known thread-safe method of removing the connection to
1913cope with overload is known (to me).
1914.PP
1915One of the easiest ways to handle this situation is to just ignore it
1916\&\- when the program encounters an overload, it will just loop until the
1917situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1918event-based way to handle this situation, so it's the best one can do.
1919.PP
1920A better way to handle the situation is to log any errors other than
1921\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1922messages, and continue as usual, which at least gives the user an idea of
1923what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1924the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1925usage.
1926.PP
1927If your program is single-threaded, then you could also keep a dummy file
1928descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1929when 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,
1930close that fd, and create a new dummy fd. This will gracefully refuse
1931clients under typical overload conditions.
1932.PP
1933The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1934is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1935opportunity for a DoS attack.
1936.PP
1937\fIWatcher-Specific Functions\fR
1938.IX Subsection "Watcher-Specific Functions"
993.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1939.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
994.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1940.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
995.PD 0 1941.PD 0
996.IP "ev_io_set (ev_io *, int fd, int events)" 4 1942.IP "ev_io_set (ev_io *, int fd, int events)" 4
997.IX Item "ev_io_set (ev_io *, int fd, int events)" 1943.IX Item "ev_io_set (ev_io *, int fd, int events)"
998.PD 1944.PD
999Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1945Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1000rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1946receive 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
1001\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1947\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1002.IP "int fd [read\-only]" 4 1948.IP "int fd [read\-only]" 4
1003.IX Item "int fd [read-only]" 1949.IX Item "int fd [read-only]"
1004The file descriptor being watched. 1950The file descriptor being watched.
1005.IP "int events [read\-only]" 4 1951.IP "int events [read\-only]" 4
1006.IX Item "int events [read-only]" 1952.IX Item "int events [read-only]"
1007The events being watched. 1953The events being watched.
1008.PP 1954.PP
1955\fIExamples\fR
1956.IX Subsection "Examples"
1957.PP
1009Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1958Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1010readable, but only once. Since it is likely line\-buffered, you could 1959readable, but only once. Since it is likely line-buffered, you could
1011attempt to read a whole line in the callback. 1960attempt to read a whole line in the callback.
1012.PP 1961.PP
1013.Vb 6 1962.Vb 6
1014\& static void 1963\& static void
1015\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1964\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1016\& { 1965\& {
1017\& ev_io_stop (loop, w); 1966\& ev_io_stop (loop, w);
1018\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1967\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1019\& } 1968\& }
1020.Ve 1969\&
1021.PP
1022.Vb 6
1023\& ... 1970\& ...
1024\& struct ev_loop *loop = ev_default_init (0); 1971\& struct ev_loop *loop = ev_default_init (0);
1025\& struct ev_io stdin_readable; 1972\& ev_io stdin_readable;
1026\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1973\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1027\& ev_io_start (loop, &stdin_readable); 1974\& ev_io_start (loop, &stdin_readable);
1028\& ev_loop (loop, 0); 1975\& ev_run (loop, 0);
1029.Ve 1976.Ve
1030.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1977.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1031.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1978.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1032.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1979.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1033Timer watchers are simple relative timers that generate an event after a 1980Timer watchers are simple relative timers that generate an event after a
1034given time, and optionally repeating in regular intervals after that. 1981given time, and optionally repeating in regular intervals after that.
1035.PP 1982.PP
1036The timers are based on real time, that is, if you register an event that 1983The timers are based on real time, that is, if you register an event that
1037times out after an hour and you reset your system clock to last years 1984times out after an hour and you reset your system clock to January last
1038time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1985year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1039detecting time jumps is hard, and some inaccuracies are unavoidable (the 1986detecting time jumps is hard, and some inaccuracies are unavoidable (the
1040monotonic clock option helps a lot here). 1987monotonic clock option helps a lot here).
1988.PP
1989The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1990passed (not \fIat\fR, so on systems with very low-resolution clocks this
1991might introduce a small delay, see \*(L"the special problem of being too
1992early\*(R", below). If multiple timers become ready during the same loop
1993iteration then the ones with earlier time-out values are invoked before
1994ones of the same priority with later time-out values (but this is no
1995longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1996.PP
1997\fIBe smart about timeouts\fR
1998.IX Subsection "Be smart about timeouts"
1999.PP
2000Many real-world problems involve some kind of timeout, usually for error
2001recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2002you want to raise some error after a while.
2003.PP
2004What follows are some ways to handle this problem, from obvious and
2005inefficient to smart and efficient.
2006.PP
2007In the following, a 60 second activity timeout is assumed \- a timeout that
2008gets reset to 60 seconds each time there is activity (e.g. each time some
2009data or other life sign was received).
2010.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2011.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2012This is the most obvious, but not the most simple way: In the beginning,
2013start the watcher:
2014.Sp
2015.Vb 2
2016\& ev_timer_init (timer, callback, 60., 0.);
2017\& ev_timer_start (loop, timer);
2018.Ve
2019.Sp
2020Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2021and start it again:
2022.Sp
2023.Vb 3
2024\& ev_timer_stop (loop, timer);
2025\& ev_timer_set (timer, 60., 0.);
2026\& ev_timer_start (loop, timer);
2027.Ve
2028.Sp
2029This is relatively simple to implement, but means that each time there is
2030some activity, libev will first have to remove the timer from its internal
2031data structure and then add it again. Libev tries to be fast, but it's
2032still not a constant-time operation.
2033.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2034.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2035.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2036This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2037\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2038.Sp
2039To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2040of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2041successfully read or write some data. If you go into an idle state where
2042you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2043the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2044.Sp
2045That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2046\&\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
2047member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2048.Sp
2049At start:
2050.Sp
2051.Vb 3
2052\& ev_init (timer, callback);
2053\& timer\->repeat = 60.;
2054\& ev_timer_again (loop, timer);
2055.Ve
2056.Sp
2057Each time there is some activity:
2058.Sp
2059.Vb 1
2060\& ev_timer_again (loop, timer);
2061.Ve
2062.Sp
2063It is even possible to change the time-out on the fly, regardless of
2064whether the watcher is active or not:
2065.Sp
2066.Vb 2
2067\& timer\->repeat = 30.;
2068\& ev_timer_again (loop, timer);
2069.Ve
2070.Sp
2071This is slightly more efficient then stopping/starting the timer each time
2072you want to modify its timeout value, as libev does not have to completely
2073remove and re-insert the timer from/into its internal data structure.
2074.Sp
2075It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2076.IP "3. Let the timer time out, but then re-arm it as required." 4
2077.IX Item "3. Let the timer time out, but then re-arm it as required."
2078This method is more tricky, but usually most efficient: Most timeouts are
2079relatively long compared to the intervals between other activity \- in
2080our example, within 60 seconds, there are usually many I/O events with
2081associated activity resets.
2082.Sp
2083In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2084but remember the time of last activity, and check for a real timeout only
2085within the callback:
2086.Sp
2087.Vb 3
2088\& ev_tstamp timeout = 60.;
2089\& ev_tstamp last_activity; // time of last activity
2090\& ev_timer timer;
2091\&
2092\& static void
2093\& callback (EV_P_ ev_timer *w, int revents)
2094\& {
2095\& // calculate when the timeout would happen
2096\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2097\&
2098\& // if negative, it means we the timeout already occurred
2099\& if (after < 0.)
2100\& {
2101\& // timeout occurred, take action
2102\& }
2103\& else
2104\& {
2105\& // callback was invoked, but there was some recent
2106\& // activity. simply restart the timer to time out
2107\& // after "after" seconds, which is the earliest time
2108\& // the timeout can occur.
2109\& ev_timer_set (w, after, 0.);
2110\& ev_timer_start (EV_A_ w);
2111\& }
2112\& }
2113.Ve
2114.Sp
2115To summarise the callback: first calculate in how many seconds the
2116timeout will occur (by calculating the absolute time when it would occur,
2117\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2118(EV_A)\*(C'\fR from that).
2119.Sp
2120If this value is negative, then we are already past the timeout, i.e. we
2121timed out, and need to do whatever is needed in this case.
2122.Sp
2123Otherwise, we now the earliest time at which the timeout would trigger,
2124and simply start the timer with this timeout value.
2125.Sp
2126In other words, each time the callback is invoked it will check whether
2127the timeout occurred. If not, it will simply reschedule itself to check
2128again at the earliest time it could time out. Rinse. Repeat.
2129.Sp
2130This scheme causes more callback invocations (about one every 60 seconds
2131minus half the average time between activity), but virtually no calls to
2132libev to change the timeout.
2133.Sp
2134To start the machinery, simply initialise the watcher and set
2135\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2136now), then call the callback, which will \*(L"do the right thing\*(R" and start
2137the timer:
2138.Sp
2139.Vb 3
2140\& last_activity = ev_now (EV_A);
2141\& ev_init (&timer, callback);
2142\& callback (EV_A_ &timer, 0);
2143.Ve
2144.Sp
2145When there is some activity, simply store the current time in
2146\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2147.Sp
2148.Vb 2
2149\& if (activity detected)
2150\& last_activity = ev_now (EV_A);
2151.Ve
2152.Sp
2153When your timeout value changes, then the timeout can be changed by simply
2154providing a new value, stopping the timer and calling the callback, which
2155will again do the right thing (for example, time out immediately :).
2156.Sp
2157.Vb 3
2158\& timeout = new_value;
2159\& ev_timer_stop (EV_A_ &timer);
2160\& callback (EV_A_ &timer, 0);
2161.Ve
2162.Sp
2163This technique is slightly more complex, but in most cases where the
2164time-out is unlikely to be triggered, much more efficient.
2165.IP "4. Wee, just use a double-linked list for your timeouts." 4
2166.IX Item "4. Wee, just use a double-linked list for your timeouts."
2167If there is not one request, but many thousands (millions...), all
2168employing some kind of timeout with the same timeout value, then one can
2169do even better:
2170.Sp
2171When starting the timeout, calculate the timeout value and put the timeout
2172at the \fIend\fR of the list.
2173.Sp
2174Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2175the list is expected to fire (for example, using the technique #3).
2176.Sp
2177When there is some activity, remove the timer from the list, recalculate
2178the timeout, append it to the end of the list again, and make sure to
2179update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2180.Sp
2181This way, one can manage an unlimited number of timeouts in O(1) time for
2182starting, stopping and updating the timers, at the expense of a major
2183complication, and having to use a constant timeout. The constant timeout
2184ensures that the list stays sorted.
2185.PP
2186So which method the best?
2187.PP
2188Method #2 is a simple no-brain-required solution that is adequate in most
2189situations. Method #3 requires a bit more thinking, but handles many cases
2190better, and isn't very complicated either. In most case, choosing either
2191one is fine, with #3 being better in typical situations.
2192.PP
2193Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2194rather complicated, but extremely efficient, something that really pays
2195off after the first million or so of active timers, i.e. it's usually
2196overkill :)
2197.PP
2198\fIThe special problem of being too early\fR
2199.IX Subsection "The special problem of being too early"
2200.PP
2201If you ask a timer to call your callback after three seconds, then
2202you expect it to be invoked after three seconds \- but of course, this
2203cannot be guaranteed to infinite precision. Less obviously, it cannot be
2204guaranteed to any precision by libev \- imagine somebody suspending the
2205process with a \s-1STOP\s0 signal for a few hours for example.
2206.PP
2207So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2208delay has occurred, but cannot guarantee this.
2209.PP
2210A less obvious failure mode is calling your callback too early: many event
2211loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2212this can cause your callback to be invoked much earlier than you would
2213expect.
2214.PP
2215To see why, imagine a system with a clock that only offers full second
2216resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2217yourself). If you schedule a one-second timer at the time 500.9, then the
2218event loop will schedule your timeout to elapse at a system time of 500
2219(500.9 truncated to the resolution) + 1, or 501.
2220.PP
2221If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2222501\*(R" and invoke the callback 0.1s after it was started, even though a
2223one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2224intentions.
2225.PP
2226This is the reason why libev will never invoke the callback if the elapsed
2227delay equals the requested delay, but only when the elapsed delay is
2228larger than the requested delay. In the example above, libev would only invoke
2229the callback at system time 502, or 1.1s after the timer was started.
2230.PP
2231So, while libev cannot guarantee that your callback will be invoked
2232exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2233delay has actually elapsed, or in other words, it always errs on the \*(L"too
2234late\*(R" side of things.
2235.PP
2236\fIThe special problem of time updates\fR
2237.IX Subsection "The special problem of time updates"
2238.PP
2239Establishing the current time is a costly operation (it usually takes
2240at least one system call): \s-1EV\s0 therefore updates its idea of the current
2241time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2242growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2243lots of events in one iteration.
1041.PP 2244.PP
1042The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2245The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1043time. This is usually the right thing as this timestamp refers to the time 2246time. This is usually the right thing as this timestamp refers to the time
1044of the event triggering whatever timeout you are modifying/starting. If 2247of the event triggering whatever timeout you are modifying/starting. If
1045you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2248you suspect event processing to be delayed and you \fIneed\fR to base the
1046on the current time, use something like this to adjust for this: 2249timeout on the current time, use something like the following to adjust
2250for it:
1047.PP 2251.PP
1048.Vb 1 2252.Vb 1
1049\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2253\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
1050.Ve 2254.Ve
1051.PP 2255.PP
1052The callback is guarenteed to be invoked only when its timeout has passed, 2256If the event loop is suspended for a long time, you can also force an
1053but if multiple timers become ready during the same loop iteration then 2257update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1054order of execution is undefined. 2258()\*(C'\fR, although that will push the event time of all outstanding events
2259further into the future.
2260.PP
2261\fIThe special problem of unsynchronised clocks\fR
2262.IX Subsection "The special problem of unsynchronised clocks"
2263.PP
2264Modern systems have a variety of clocks \- libev itself uses the normal
2265\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2266jumps).
2267.PP
2268Neither of these clocks is synchronised with each other or any other clock
2269on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2270than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2271a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2272than a directly following call to \f(CW\*(C`time\*(C'\fR.
2273.PP
2274The moral of this is to only compare libev-related timestamps with
2275\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2276a second or so.
2277.PP
2278One more problem arises due to this lack of synchronisation: if libev uses
2279the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2280or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2281invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2282.PP
2283This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2284libev makes sure your callback is not invoked before the delay happened,
2285\&\fImeasured according to the real time\fR, not the system clock.
2286.PP
2287If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2288connection after 100 seconds\*(R") then this shouldn't bother you as it is
2289exactly the right behaviour.
2290.PP
2291If you want to compare wall clock/system timestamps to your timers, then
2292you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2293time, where your comparisons will always generate correct results.
2294.PP
2295\fIThe special problems of suspended animation\fR
2296.IX Subsection "The special problems of suspended animation"
2297.PP
2298When you leave the server world it is quite customary to hit machines that
2299can suspend/hibernate \- what happens to the clocks during such a suspend?
2300.PP
2301Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2302all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2303to run until the system is suspended, but they will not advance while the
2304system is suspended. That means, on resume, it will be as if the program
2305was frozen for a few seconds, but the suspend time will not be counted
2306towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2307clock advanced as expected, but if it is used as sole clocksource, then a
2308long suspend would be detected as a time jump by libev, and timers would
2309be adjusted accordingly.
2310.PP
2311I would not be surprised to see different behaviour in different between
2312operating systems, \s-1OS\s0 versions or even different hardware.
2313.PP
2314The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2315time jump in the monotonic clocks and the realtime clock. If the program
2316is suspended for a very long time, and monotonic clock sources are in use,
2317then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2318will be counted towards the timers. When no monotonic clock source is in
2319use, then libev will again assume a timejump and adjust accordingly.
2320.PP
2321It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2322and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2323deterministic behaviour in this case (you can do nothing against
2324\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2325.PP
2326\fIWatcher-Specific Functions and Data Members\fR
2327.IX Subsection "Watcher-Specific Functions and Data Members"
1055.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2328.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1056.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2329.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1057.PD 0 2330.PD 0
1058.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2331.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1059.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2332.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1060.PD 2333.PD
1061Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2334Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
1062\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2335negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2336automatically be stopped once the timeout is reached. If it is positive,
1063timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2337then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
1064later, again, and again, until stopped manually. 2338seconds later, again, and again, until stopped manually.
1065.Sp 2339.Sp
1066The timer itself will do a best-effort at avoiding drift, that is, if you 2340The timer itself will do a best-effort at avoiding drift, that is, if
1067configure a timer to trigger every 10 seconds, then it will trigger at 2341you configure a timer to trigger every 10 seconds, then it will normally
1068exactly 10 second intervals. If, however, your program cannot keep up with 2342trigger at exactly 10 second intervals. If, however, your program cannot
1069the timer (because it takes longer than those 10 seconds to do stuff) the 2343keep up with the timer (because it takes longer than those 10 seconds to
1070timer will not fire more than once per event loop iteration. 2344do stuff) the timer will not fire more than once per event loop iteration.
1071.IP "ev_timer_again (loop)" 4 2345.IP "ev_timer_again (loop, ev_timer *)" 4
1072.IX Item "ev_timer_again (loop)" 2346.IX Item "ev_timer_again (loop, ev_timer *)"
1073This will act as if the timer timed out and restart it again if it is 2347This will act as if the timer timed out, and restarts it again if it is
1074repeating. The exact semantics are: 2348repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2349timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1075.Sp 2350.Sp
2351The exact semantics are as in the following rules, all of which will be
2352applied to the watcher:
2353.RS 4
1076If the timer is pending, its pending status is cleared. 2354.IP "If the timer is pending, the pending status is always cleared." 4
1077.Sp 2355.IX Item "If the timer is pending, the pending status is always cleared."
2356.PD 0
1078If the timer is started but nonrepeating, stop it (as if it timed out). 2357.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2358.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2359.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2360.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2361.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2362.RE
2363.RS 4
2364.PD
1079.Sp 2365.Sp
1080If the timer is repeating, either start it if necessary (with the 2366This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1081\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. 2367usage example.
2368.RE
2369.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2370.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2371Returns the remaining time until a timer fires. If the timer is active,
2372then this time is relative to the current event loop time, otherwise it's
2373the timeout value currently configured.
1082.Sp 2374.Sp
1083This sounds a bit complicated, but here is a useful and typical 2375That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1084example: Imagine you have a tcp connection and you want a so-called idle 2376\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1085timeout, that is, you want to be called when there have been, say, 60 2377will return \f(CW4\fR. When the timer expires and is restarted, it will return
1086seconds of inactivity on the socket. The easiest way to do this is to 2378roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1087configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call 2379too), and so on.
1088\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1089you go into an idle state where you do not expect data to travel on the
1090socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1091automatically restart it if need be.
1092.Sp
1093That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1094altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1095.Sp
1096.Vb 8
1097\& ev_timer_init (timer, callback, 0., 5.);
1098\& ev_timer_again (loop, timer);
1099\& ...
1100\& timer->again = 17.;
1101\& ev_timer_again (loop, timer);
1102\& ...
1103\& timer->again = 10.;
1104\& ev_timer_again (loop, timer);
1105.Ve
1106.Sp
1107This is more slightly efficient then stopping/starting the timer each time
1108you want to modify its timeout value.
1109.IP "ev_tstamp repeat [read\-write]" 4 2380.IP "ev_tstamp repeat [read\-write]" 4
1110.IX Item "ev_tstamp repeat [read-write]" 2381.IX Item "ev_tstamp repeat [read-write]"
1111The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2382The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1112or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2383or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1113which is also when any modifications are taken into account. 2384which is also when any modifications are taken into account.
1114.PP 2385.PP
2386\fIExamples\fR
2387.IX Subsection "Examples"
2388.PP
1115Example: Create a timer that fires after 60 seconds. 2389Example: Create a timer that fires after 60 seconds.
1116.PP 2390.PP
1117.Vb 5 2391.Vb 5
1118\& static void 2392\& static void
1119\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2393\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1120\& { 2394\& {
1121\& .. one minute over, w is actually stopped right here 2395\& .. one minute over, w is actually stopped right here
1122\& } 2396\& }
1123.Ve 2397\&
1124.PP
1125.Vb 3
1126\& struct ev_timer mytimer; 2398\& ev_timer mytimer;
1127\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2399\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1128\& ev_timer_start (loop, &mytimer); 2400\& ev_timer_start (loop, &mytimer);
1129.Ve 2401.Ve
1130.PP 2402.PP
1131Example: Create a timeout timer that times out after 10 seconds of 2403Example: Create a timeout timer that times out after 10 seconds of
1132inactivity. 2404inactivity.
1133.PP 2405.PP
1134.Vb 5 2406.Vb 5
1135\& static void 2407\& static void
1136\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2408\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1137\& { 2409\& {
1138\& .. ten seconds without any activity 2410\& .. ten seconds without any activity
1139\& } 2411\& }
1140.Ve 2412\&
1141.PP
1142.Vb 4
1143\& struct ev_timer mytimer; 2413\& ev_timer mytimer;
1144\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2414\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1145\& ev_timer_again (&mytimer); /* start timer */ 2415\& ev_timer_again (&mytimer); /* start timer */
1146\& ev_loop (loop, 0); 2416\& ev_run (loop, 0);
1147.Ve 2417\&
1148.PP
1149.Vb 3
1150\& // and in some piece of code that gets executed on any "activity": 2418\& // and in some piece of code that gets executed on any "activity":
1151\& // reset the timeout to start ticking again at 10 seconds 2419\& // reset the timeout to start ticking again at 10 seconds
1152\& ev_timer_again (&mytimer); 2420\& ev_timer_again (&mytimer);
1153.Ve 2421.Ve
1154.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2422.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1155.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2423.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1156.IX Subsection "ev_periodic - to cron or not to cron?" 2424.IX Subsection "ev_periodic - to cron or not to cron?"
1157Periodic watchers are also timers of a kind, but they are very versatile 2425Periodic watchers are also timers of a kind, but they are very versatile
1158(and unfortunately a bit complex). 2426(and unfortunately a bit complex).
1159.PP 2427.PP
1160Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2428Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1161but on wallclock time (absolute time). You can tell a periodic watcher 2429relative time, the physical time that passes) but on wall clock time
1162to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2430(absolute time, the thing you can read on your calendar or clock). The
1163periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2431difference is that wall clock time can run faster or slower than real
1164+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2432time, and time jumps are not uncommon (e.g. when you adjust your
1165take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2433wrist-watch).
1166roughly 10 seconds later and of course not if you reset your system time
1167again).
1168.PP 2434.PP
1169They can also be used to implement vastly more complex timers, such as 2435You can tell a periodic watcher to trigger after some specific point
1170triggering an event on eahc midnight, local time. 2436in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2437seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2438not a delay) and then reset your system clock to January of the previous
2439year, then it will take a year or more to trigger the event (unlike an
2440\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2441it, as it uses a relative timeout).
1171.PP 2442.PP
2443\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2444timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2445other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2446watchers, as those cannot react to time jumps.
2447.PP
1172As with timers, the callback is guarenteed to be invoked only when the 2448As with timers, the callback is guaranteed to be invoked only when the
1173time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2449point in time where it is supposed to trigger has passed. If multiple
1174during the same loop iteration then order of execution is undefined. 2450timers become ready during the same loop iteration then the ones with
2451earlier time-out values are invoked before ones with later time-out values
2452(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2453.PP
2454\fIWatcher-Specific Functions and Data Members\fR
2455.IX Subsection "Watcher-Specific Functions and Data Members"
1175.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2456.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1176.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2457.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1177.PD 0 2458.PD 0
1178.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2459.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1179.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2460.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1180.PD 2461.PD
1181Lots of arguments, lets sort it out... There are basically three modes of 2462Lots of arguments, let's sort it out... There are basically three modes of
1182operation, and we will explain them from simplest to complex: 2463operation, and we will explain them from simplest to most complex:
1183.RS 4 2464.RS 4
1184.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2465.IP "\(bu" 4
1185.IX Item "absolute timer (interval = reschedule_cb = 0)" 2466absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2467.Sp
1186In this configuration the watcher triggers an event at the wallclock time 2468In this configuration the watcher triggers an event after the wall clock
1187\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2469time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1188that is, if it is to be run at January 1st 2011 then it will run when the 2470time jump occurs, that is, if it is to be run at January 1st 2011 then it
1189system time reaches or surpasses this time. 2471will be stopped and invoked when the system clock reaches or surpasses
1190.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2472this point in time.
1191.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2473.IP "\(bu" 4
2474repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2475.Sp
1192In this mode the watcher will always be scheduled to time out at the next 2476In this mode the watcher will always be scheduled to time out at the next
1193\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2477\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1194of any time jumps. 2478negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2479argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1195.Sp 2480.Sp
1196This can be used to create timers that do not drift with respect to system 2481This can be used to create timers that do not drift with respect to the
1197time: 2482system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2483hour, on the hour (with respect to \s-1UTC\s0):
1198.Sp 2484.Sp
1199.Vb 1 2485.Vb 1
1200\& ev_periodic_set (&periodic, 0., 3600., 0); 2486\& ev_periodic_set (&periodic, 0., 3600., 0);
1201.Ve 2487.Ve
1202.Sp 2488.Sp
1203This doesn't mean there will always be 3600 seconds in between triggers, 2489This doesn't mean there will always be 3600 seconds in between triggers,
1204but only that the the callback will be called when the system time shows a 2490but only that the callback will be called when the system time shows a
1205full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2491full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1206by 3600. 2492by 3600.
1207.Sp 2493.Sp
1208Another way to think about it (for the mathematically inclined) is that 2494Another way to think about it (for the mathematically inclined) is that
1209\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2495\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1210time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2496time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1211.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2497.Sp
1212.IX Item "manual reschedule mode (reschedule_cb = callback)" 2498The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2499interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2500microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2501at most a similar magnitude as the current time (say, within a factor of
2502ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2503\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2504.Sp
2505Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2506speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2507will of course deteriorate. Libev itself tries to be exact to be about one
2508millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2509.IP "\(bu" 4
2510manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2511.Sp
1213In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2512In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1214ignored. Instead, each time the periodic watcher gets scheduled, the 2513ignored. Instead, each time the periodic watcher gets scheduled, the
1215reschedule callback will be called with the watcher as first, and the 2514reschedule callback will be called with the watcher as first, and the
1216current time as second argument. 2515current time as second argument.
1217.Sp 2516.Sp
1218\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2517\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1219ever, or make any event loop modifications\fR. If you need to stop it, 2518or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1220return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2519allowed by documentation here\fR.
1221starting a prepare watcher).
1222.Sp 2520.Sp
2521If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2522it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2523only event loop modification you are allowed to do).
2524.Sp
1223Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2525The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1224ev_tstamp now)\*(C'\fR, e.g.: 2526*w, ev_tstamp now)\*(C'\fR, e.g.:
1225.Sp 2527.Sp
1226.Vb 4 2528.Vb 5
2529\& static ev_tstamp
1227\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2530\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1228\& { 2531\& {
1229\& return now + 60.; 2532\& return now + 60.;
1230\& } 2533\& }
1231.Ve 2534.Ve
1232.Sp 2535.Sp
1233It must return the next time to trigger, based on the passed time value 2536It must return the next time to trigger, based on the passed time value
1234(that is, the lowest time value larger than to the second argument). It 2537(that is, the lowest time value larger than to the second argument). It
1235will usually be called just before the callback will be triggered, but 2538will usually be called just before the callback will be triggered, but
1236might be called at other times, too. 2539might be called at other times, too.
1237.Sp 2540.Sp
1238\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2541\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1239passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2542equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1240.Sp 2543.Sp
1241This can be used to create very complex timers, such as a timer that 2544This can be used to create very complex timers, such as a timer that
1242triggers on each midnight, local time. To do this, you would calculate the 2545triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1243next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2546the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1244you do this is, again, up to you (but it is not trivial, which is the main 2547this. Here is a (completely untested, no error checking) example on how to
1245reason I omitted it as an example). 2548do this:
2549.Sp
2550.Vb 1
2551\& #include <time.h>
2552\&
2553\& static ev_tstamp
2554\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2555\& {
2556\& time_t tnow = (time_t)now;
2557\& struct tm tm;
2558\& localtime_r (&tnow, &tm);
2559\&
2560\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2561\& ++tm.tm_mday; // midnight next day
2562\&
2563\& return mktime (&tm);
2564\& }
2565.Ve
2566.Sp
2567Note: this code might run into trouble on days that have more then two
2568midnights (beginning and end).
1246.RE 2569.RE
1247.RS 4 2570.RS 4
1248.RE 2571.RE
1249.IP "ev_periodic_again (loop, ev_periodic *)" 4 2572.IP "ev_periodic_again (loop, ev_periodic *)" 4
1250.IX Item "ev_periodic_again (loop, ev_periodic *)" 2573.IX Item "ev_periodic_again (loop, ev_periodic *)"
1251Simply stops and restarts the periodic watcher again. This is only useful 2574Simply stops and restarts the periodic watcher again. This is only useful
1252when you changed some parameters or the reschedule callback would return 2575when you changed some parameters or the reschedule callback would return
1253a different time than the last time it was called (e.g. in a crond like 2576a different time than the last time it was called (e.g. in a crond like
1254program when the crontabs have changed). 2577program when the crontabs have changed).
2578.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2579.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2580When active, returns the absolute time that the watcher is supposed
2581to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2582\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2583rescheduling modes.
2584.IP "ev_tstamp offset [read\-write]" 4
2585.IX Item "ev_tstamp offset [read-write]"
2586When repeating, this contains the offset value, otherwise this is the
2587absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2588although libev might modify this value for better numerical stability).
2589.Sp
2590Can be modified any time, but changes only take effect when the periodic
2591timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1255.IP "ev_tstamp interval [read\-write]" 4 2592.IP "ev_tstamp interval [read\-write]" 4
1256.IX Item "ev_tstamp interval [read-write]" 2593.IX Item "ev_tstamp interval [read-write]"
1257The current interval value. Can be modified any time, but changes only 2594The current interval value. Can be modified any time, but changes only
1258take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2595take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1259called. 2596called.
1260.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2597.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1261.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2598.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1262The current reschedule callback, or \f(CW0\fR, if this functionality is 2599The current reschedule callback, or \f(CW0\fR, if this functionality is
1263switched off. Can be changed any time, but changes only take effect when 2600switched off. Can be changed any time, but changes only take effect when
1264the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2601the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1265.PP 2602.PP
2603\fIExamples\fR
2604.IX Subsection "Examples"
2605.PP
1266Example: Call a callback every hour, or, more precisely, whenever the 2606Example: Call a callback every hour, or, more precisely, whenever the
1267system clock is divisible by 3600. The callback invocation times have 2607system time is divisible by 3600. The callback invocation times have
1268potentially a lot of jittering, but good long-term stability. 2608potentially a lot of jitter, but good long-term stability.
1269.PP 2609.PP
1270.Vb 5 2610.Vb 5
1271\& static void 2611\& static void
1272\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2612\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1273\& { 2613\& {
1274\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2614\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1275\& } 2615\& }
1276.Ve 2616\&
1277.PP
1278.Vb 3
1279\& struct ev_periodic hourly_tick; 2617\& ev_periodic hourly_tick;
1280\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2618\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1281\& ev_periodic_start (loop, &hourly_tick); 2619\& ev_periodic_start (loop, &hourly_tick);
1282.Ve 2620.Ve
1283.PP 2621.PP
1284Example: The same as above, but use a reschedule callback to do it: 2622Example: The same as above, but use a reschedule callback to do it:
1285.PP 2623.PP
1286.Vb 1 2624.Vb 1
1287\& #include <math.h> 2625\& #include <math.h>
1288.Ve 2626\&
1289.PP
1290.Vb 5
1291\& static ev_tstamp 2627\& static ev_tstamp
1292\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2628\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1293\& { 2629\& {
1294\& return fmod (now, 3600.) + 3600.; 2630\& return now + (3600. \- fmod (now, 3600.));
1295\& } 2631\& }
1296.Ve 2632\&
1297.PP
1298.Vb 1
1299\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2633\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1300.Ve 2634.Ve
1301.PP 2635.PP
1302Example: Call a callback every hour, starting now: 2636Example: Call a callback every hour, starting now:
1303.PP 2637.PP
1304.Vb 4 2638.Vb 4
1305\& struct ev_periodic hourly_tick; 2639\& ev_periodic hourly_tick;
1306\& ev_periodic_init (&hourly_tick, clock_cb, 2640\& ev_periodic_init (&hourly_tick, clock_cb,
1307\& fmod (ev_now (loop), 3600.), 3600., 0); 2641\& fmod (ev_now (loop), 3600.), 3600., 0);
1308\& ev_periodic_start (loop, &hourly_tick); 2642\& ev_periodic_start (loop, &hourly_tick);
1309.Ve 2643.Ve
1310.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2644.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1311.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2645.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1312.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2646.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1313Signal watchers will trigger an event when the process receives a specific 2647Signal watchers will trigger an event when the process receives a specific
1314signal one or more times. Even though signals are very asynchronous, libev 2648signal one or more times. Even though signals are very asynchronous, libev
1315will try it's best to deliver signals synchronously, i.e. as part of the 2649will try its best to deliver signals synchronously, i.e. as part of the
1316normal event processing, like any other event. 2650normal event processing, like any other event.
1317.PP 2651.PP
2652If you want signals to be delivered truly asynchronously, just use
2653\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2654the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2655synchronously wake up an event loop.
2656.PP
1318You can configure as many watchers as you like per signal. Only when the 2657You can configure as many watchers as you like for the same signal, but
1319first watcher gets started will libev actually register a signal watcher 2658only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1320with the kernel (thus it coexists with your own signal handlers as long 2659default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1321as you don't register any with libev). Similarly, when the last signal 2660\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1322watcher for a signal is stopped libev will reset the signal handler to 2661the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1323\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2662.PP
2663Only after the first watcher for a signal is started will libev actually
2664register something with the kernel. It thus coexists with your own signal
2665handlers as long as you don't register any with libev for the same signal.
2666.PP
2667If possible and supported, libev will install its handlers with
2668\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2669not be unduly interrupted. If you have a problem with system calls getting
2670interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2671and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2672.PP
2673\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2674.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2675.PP
2676Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2677(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2678stopping it again), that is, libev might or might not block the signal,
2679and might or might not set or restore the installed signal handler (but
2680see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2681.PP
2682While this does not matter for the signal disposition (libev never
2683sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2684\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2685certain signals to be blocked.
2686.PP
2687This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2688the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2689choice usually).
2690.PP
2691The simplest way to ensure that the signal mask is reset in the child is
2692to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2693catch fork calls done by libraries (such as the libc) as well.
2694.PP
2695In current versions of libev, the signal will not be blocked indefinitely
2696unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2697the window of opportunity for problems, it will not go away, as libev
2698\&\fIhas\fR to modify the signal mask, at least temporarily.
2699.PP
2700So I can't stress this enough: \fIIf you do not reset your signal mask when
2701you expect it to be empty, you have a race condition in your code\fR. This
2702is not a libev-specific thing, this is true for most event libraries.
2703.PP
2704\fIThe special problem of threads signal handling\fR
2705.IX Subsection "The special problem of threads signal handling"
2706.PP
2707\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2708a lot of functionality (sigfd, sigwait etc.) only really works if all
2709threads in a process block signals, which is hard to achieve.
2710.PP
2711When you want to use sigwait (or mix libev signal handling with your own
2712for the same signals), you can tackle this problem by globally blocking
2713all signals before creating any threads (or creating them with a fully set
2714sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2715loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2716these signals. You can pass on any signals that libev might be interested
2717in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2718.PP
2719\fIWatcher-Specific Functions and Data Members\fR
2720.IX Subsection "Watcher-Specific Functions and Data Members"
1324.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2721.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1325.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2722.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1326.PD 0 2723.PD 0
1327.IP "ev_signal_set (ev_signal *, int signum)" 4 2724.IP "ev_signal_set (ev_signal *, int signum)" 4
1328.IX Item "ev_signal_set (ev_signal *, int signum)" 2725.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1330Configures the watcher to trigger on the given signal number (usually one 2727Configures the watcher to trigger on the given signal number (usually one
1331of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2728of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1332.IP "int signum [read\-only]" 4 2729.IP "int signum [read\-only]" 4
1333.IX Item "int signum [read-only]" 2730.IX Item "int signum [read-only]"
1334The signal the watcher watches out for. 2731The signal the watcher watches out for.
2732.PP
2733\fIExamples\fR
2734.IX Subsection "Examples"
2735.PP
2736Example: Try to exit cleanly on \s-1SIGINT.\s0
2737.PP
2738.Vb 5
2739\& static void
2740\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2741\& {
2742\& ev_break (loop, EVBREAK_ALL);
2743\& }
2744\&
2745\& ev_signal signal_watcher;
2746\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2747\& ev_signal_start (loop, &signal_watcher);
2748.Ve
1335.ie n .Sh """ev_child"" \- watch out for process status changes" 2749.ie n .SS """ev_child"" \- watch out for process status changes"
1336.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2750.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1337.IX Subsection "ev_child - watch out for process status changes" 2751.IX Subsection "ev_child - watch out for process status changes"
1338Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2752Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1339some child status changes (most typically when a child of yours dies). 2753some child status changes (most typically when a child of yours dies or
2754exits). It is permissible to install a child watcher \fIafter\fR the child
2755has been forked (which implies it might have already exited), as long
2756as the event loop isn't entered (or is continued from a watcher), i.e.,
2757forking and then immediately registering a watcher for the child is fine,
2758but forking and registering a watcher a few event loop iterations later or
2759in the next callback invocation is not.
2760.PP
2761Only the default event loop is capable of handling signals, and therefore
2762you can only register child watchers in the default event loop.
2763.PP
2764Due to some design glitches inside libev, child watchers will always be
2765handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2766libev)
2767.PP
2768\fIProcess Interaction\fR
2769.IX Subsection "Process Interaction"
2770.PP
2771Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2772initialised. This is necessary to guarantee proper behaviour even if the
2773first child watcher is started after the child exits. The occurrence
2774of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2775synchronously as part of the event loop processing. Libev always reaps all
2776children, even ones not watched.
2777.PP
2778\fIOverriding the Built-In Processing\fR
2779.IX Subsection "Overriding the Built-In Processing"
2780.PP
2781Libev offers no special support for overriding the built-in child
2782processing, but if your application collides with libev's default child
2783handler, you can override it easily by installing your own handler for
2784\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2785default loop never gets destroyed. You are encouraged, however, to use an
2786event-based approach to child reaping and thus use libev's support for
2787that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2788.PP
2789\fIStopping the Child Watcher\fR
2790.IX Subsection "Stopping the Child Watcher"
2791.PP
2792Currently, the child watcher never gets stopped, even when the
2793child terminates, so normally one needs to stop the watcher in the
2794callback. Future versions of libev might stop the watcher automatically
2795when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2796problem).
2797.PP
2798\fIWatcher-Specific Functions and Data Members\fR
2799.IX Subsection "Watcher-Specific Functions and Data Members"
1340.IP "ev_child_init (ev_child *, callback, int pid)" 4 2800.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1341.IX Item "ev_child_init (ev_child *, callback, int pid)" 2801.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1342.PD 0 2802.PD 0
1343.IP "ev_child_set (ev_child *, int pid)" 4 2803.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1344.IX Item "ev_child_set (ev_child *, int pid)" 2804.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1345.PD 2805.PD
1346Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2806Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1347\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2807\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1348at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2808at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1349the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2809the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1350\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2810\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1351process causing the status change. 2811process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2812activate the watcher when the process terminates) or \f(CW1\fR (additionally
2813activate the watcher when the process is stopped or continued).
1352.IP "int pid [read\-only]" 4 2814.IP "int pid [read\-only]" 4
1353.IX Item "int pid [read-only]" 2815.IX Item "int pid [read-only]"
1354The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2816The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1355.IP "int rpid [read\-write]" 4 2817.IP "int rpid [read\-write]" 4
1356.IX Item "int rpid [read-write]" 2818.IX Item "int rpid [read-write]"
… …
1358.IP "int rstatus [read\-write]" 4 2820.IP "int rstatus [read\-write]" 4
1359.IX Item "int rstatus [read-write]" 2821.IX Item "int rstatus [read-write]"
1360The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2822The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1361\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2823\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1362.PP 2824.PP
1363Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2825\fIExamples\fR
2826.IX Subsection "Examples"
1364.PP 2827.PP
2828Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2829its completion.
2830.PP
1365.Vb 5 2831.Vb 1
2832\& ev_child cw;
2833\&
1366\& static void 2834\& static void
1367\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2835\& child_cb (EV_P_ ev_child *w, int revents)
1368\& { 2836\& {
1369\& ev_unloop (loop, EVUNLOOP_ALL); 2837\& ev_child_stop (EV_A_ w);
2838\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1370\& } 2839\& }
2840\&
2841\& pid_t pid = fork ();
2842\&
2843\& if (pid < 0)
2844\& // error
2845\& else if (pid == 0)
2846\& {
2847\& // the forked child executes here
2848\& exit (1);
2849\& }
2850\& else
2851\& {
2852\& ev_child_init (&cw, child_cb, pid, 0);
2853\& ev_child_start (EV_DEFAULT_ &cw);
2854\& }
1371.Ve 2855.Ve
1372.PP
1373.Vb 3
1374\& struct ev_signal signal_watcher;
1375\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1376\& ev_signal_start (loop, &sigint_cb);
1377.Ve
1378.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2856.ie n .SS """ev_stat"" \- did the file attributes just change?"
1379.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2857.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1380.IX Subsection "ev_stat - did the file attributes just change?" 2858.IX Subsection "ev_stat - did the file attributes just change?"
1381This watches a filesystem path for attribute changes. That is, it calls 2859This watches a file system path for attribute changes. That is, it calls
1382\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2860\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1383compared to the last time, invoking the callback if it did. 2861and sees if it changed compared to the last time, invoking the callback
2862if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2863happen after the watcher has been started will be reported.
1384.PP 2864.PP
1385The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2865The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1386not exist\*(R" is a status change like any other. The condition \*(L"path does 2866not exist\*(R" is a status change like any other. The condition \*(L"path does not
1387not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2867exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1388otherwise always forced to be at least one) and all the other fields of 2868\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1389the stat buffer having unspecified contents. 2869least one) and all the other fields of the stat buffer having unspecified
2870contents.
1390.PP 2871.PP
1391The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2872The path \fImust not\fR end in a slash or contain special components such as
2873\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1392relative and your working directory changes, the behaviour is undefined. 2874your working directory changes, then the behaviour is undefined.
1393.PP 2875.PP
1394Since there is no standard to do this, the portable implementation simply 2876Since there is no portable change notification interface available, the
1395calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You 2877portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1396can specify a recommended polling interval for this case. If you specify 2878to see if it changed somehow. You can specify a recommended polling
1397a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2879interval for this case. If you specify a polling interval of \f(CW0\fR (highly
1398unspecified default\fR value will be used (which you can expect to be around 2880recommended!) then a \fIsuitable, unspecified default\fR value will be used
1399five seconds, although this might change dynamically). Libev will also 2881(which you can expect to be around five seconds, although this might
1400impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2882change dynamically). Libev will also impose a minimum interval which is
1401usually overkill. 2883currently around \f(CW0.1\fR, but that's usually overkill.
1402.PP 2884.PP
1403This watcher type is not meant for massive numbers of stat watchers, 2885This watcher type is not meant for massive numbers of stat watchers,
1404as even with OS-supported change notifications, this can be 2886as even with OS-supported change notifications, this can be
1405resource\-intensive. 2887resource-intensive.
1406.PP 2888.PP
1407At the time of this writing, only the Linux inotify interface is 2889At the time of this writing, the only OS-specific interface implemented
1408implemented (implementing kqueue support is left as an exercise for the 2890is the Linux inotify interface (implementing kqueue support is left as an
1409reader). Inotify will be used to give hints only and should not change the 2891exercise for the reader. Note, however, that the author sees no way of
1410semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 2892implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
1411to fall back to regular polling again even with inotify, but changes are 2893.PP
1412usually detected immediately, and if the file exists there will be no 2894\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1413polling. 2895.IX Subsection "ABI Issues (Largefile Support)"
2896.PP
2897Libev by default (unless the user overrides this) uses the default
2898compilation environment, which means that on systems with large file
2899support disabled by default, you get the 32 bit version of the stat
2900structure. When using the library from programs that change the \s-1ABI\s0 to
2901use 64 bit file offsets the programs will fail. In that case you have to
2902compile libev with the same flags to get binary compatibility. This is
2903obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2904most noticeably displayed with ev_stat and large file support.
2905.PP
2906The solution for this is to lobby your distribution maker to make large
2907file interfaces available by default (as e.g. FreeBSD does) and not
2908optional. Libev cannot simply switch on large file support because it has
2909to exchange stat structures with application programs compiled using the
2910default compilation environment.
2911.PP
2912\fIInotify and Kqueue\fR
2913.IX Subsection "Inotify and Kqueue"
2914.PP
2915When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2916runtime, it will be used to speed up change detection where possible. The
2917inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2918watcher is being started.
2919.PP
2920Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2921except that changes might be detected earlier, and in some cases, to avoid
2922making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2923there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2924but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2925many bugs), the path exists (i.e. stat succeeds), and the path resides on
2926a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2927xfs are fully working) libev usually gets away without polling.
2928.PP
2929There is no support for kqueue, as apparently it cannot be used to
2930implement this functionality, due to the requirement of having a file
2931descriptor open on the object at all times, and detecting renames, unlinks
2932etc. is difficult.
2933.PP
2934\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2935.IX Subsection "stat () is a synchronous operation"
2936.PP
2937Libev doesn't normally do any kind of I/O itself, and so is not blocking
2938the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2939()\*(C'\fR, which is a synchronous operation.
2940.PP
2941For local paths, this usually doesn't matter: unless the system is very
2942busy or the intervals between stat's are large, a stat call will be fast,
2943as the path data is usually in memory already (except when starting the
2944watcher).
2945.PP
2946For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2947time due to network issues, and even under good conditions, a stat call
2948often takes multiple milliseconds.
2949.PP
2950Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2951paths, although this is fully supported by libev.
2952.PP
2953\fIThe special problem of stat time resolution\fR
2954.IX Subsection "The special problem of stat time resolution"
2955.PP
2956The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2957and even on systems where the resolution is higher, most file systems
2958still only support whole seconds.
2959.PP
2960That means that, if the time is the only thing that changes, you can
2961easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2962calls your callback, which does something. When there is another update
2963within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2964stat data does change in other ways (e.g. file size).
2965.PP
2966The solution to this is to delay acting on a change for slightly more
2967than a second (or till slightly after the next full second boundary), using
2968a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2969ev_timer_again (loop, w)\*(C'\fR).
2970.PP
2971The \f(CW.02\fR offset is added to work around small timing inconsistencies
2972of some operating systems (where the second counter of the current time
2973might be be delayed. One such system is the Linux kernel, where a call to
2974\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2975a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2976update file times then there will be a small window where the kernel uses
2977the previous second to update file times but libev might already execute
2978the timer callback).
2979.PP
2980\fIWatcher-Specific Functions and Data Members\fR
2981.IX Subsection "Watcher-Specific Functions and Data Members"
1414.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2982.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1415.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2983.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1416.PD 0 2984.PD 0
1417.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 2985.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1418.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 2986.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1421\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2989\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1422be detected and should normally be specified as \f(CW0\fR to let libev choose 2990be detected and should normally be specified as \f(CW0\fR to let libev choose
1423a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2991a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1424path for as long as the watcher is active. 2992path for as long as the watcher is active.
1425.Sp 2993.Sp
1426The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2994The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1427relative to the attributes at the time the watcher was started (or the 2995relative to the attributes at the time the watcher was started (or the
1428last change was detected). 2996last change was detected).
1429.IP "ev_stat_stat (ev_stat *)" 4 2997.IP "ev_stat_stat (loop, ev_stat *)" 4
1430.IX Item "ev_stat_stat (ev_stat *)" 2998.IX Item "ev_stat_stat (loop, ev_stat *)"
1431Updates the stat buffer immediately with new values. If you change the 2999Updates the stat buffer immediately with new values. If you change the
1432watched path in your callback, you could call this fucntion to avoid 3000watched path in your callback, you could call this function to avoid
1433detecting this change (while introducing a race condition). Can also be 3001detecting this change (while introducing a race condition if you are not
1434useful simply to find out the new values. 3002the only one changing the path). Can also be useful simply to find out the
3003new values.
1435.IP "ev_statdata attr [read\-only]" 4 3004.IP "ev_statdata attr [read\-only]" 4
1436.IX Item "ev_statdata attr [read-only]" 3005.IX Item "ev_statdata attr [read-only]"
1437The most-recently detected attributes of the file. Although the type is of 3006The most-recently detected attributes of the file. Although the type is
1438\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 3007\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3008suitable for your system, but you can only rely on the POSIX-standardised
1439suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 3009members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1440was some error while \f(CW\*(C`stat\*(C'\fRing the file. 3010some error while \f(CW\*(C`stat\*(C'\fRing the file.
1441.IP "ev_statdata prev [read\-only]" 4 3011.IP "ev_statdata prev [read\-only]" 4
1442.IX Item "ev_statdata prev [read-only]" 3012.IX Item "ev_statdata prev [read-only]"
1443The previous attributes of the file. The callback gets invoked whenever 3013The previous attributes of the file. The callback gets invoked whenever
1444\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3014\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3015differ: \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,
3016\&\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.
1445.IP "ev_tstamp interval [read\-only]" 4 3017.IP "ev_tstamp interval [read\-only]" 4
1446.IX Item "ev_tstamp interval [read-only]" 3018.IX Item "ev_tstamp interval [read-only]"
1447The specified interval. 3019The specified interval.
1448.IP "const char *path [read\-only]" 4 3020.IP "const char *path [read\-only]" 4
1449.IX Item "const char *path [read-only]" 3021.IX Item "const char *path [read-only]"
1450The filesystem path that is being watched. 3022The file system path that is being watched.
3023.PP
3024\fIExamples\fR
3025.IX Subsection "Examples"
1451.PP 3026.PP
1452Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3027Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1453.PP 3028.PP
1454.Vb 15 3029.Vb 10
1455\& static void 3030\& static void
1456\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3031\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1457\& { 3032\& {
1458\& /* /etc/passwd changed in some way */ 3033\& /* /etc/passwd changed in some way */
1459\& if (w->attr.st_nlink) 3034\& if (w\->attr.st_nlink)
1460\& { 3035\& {
1461\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3036\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1462\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3037\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1463\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3038\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1464\& } 3039\& }
1465\& else 3040\& else
1466\& /* you shalt not abuse printf for puts */ 3041\& /* you shalt not abuse printf for puts */
1467\& puts ("wow, /etc/passwd is not there, expect problems. " 3042\& puts ("wow, /etc/passwd is not there, expect problems. "
1468\& "if this is windows, they already arrived\en"); 3043\& "if this is windows, they already arrived\en");
1469\& } 3044\& }
3045\&
3046\& ...
3047\& ev_stat passwd;
3048\&
3049\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3050\& ev_stat_start (loop, &passwd);
1470.Ve 3051.Ve
3052.PP
3053Example: Like above, but additionally use a one-second delay so we do not
3054miss updates (however, frequent updates will delay processing, too, so
3055one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3056\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1471.PP 3057.PP
1472.Vb 2 3058.Vb 2
3059\& static ev_stat passwd;
3060\& static ev_timer timer;
3061\&
3062\& static void
3063\& timer_cb (EV_P_ ev_timer *w, int revents)
3064\& {
3065\& ev_timer_stop (EV_A_ w);
3066\&
3067\& /* now it\*(Aqs one second after the most recent passwd change */
3068\& }
3069\&
3070\& static void
3071\& stat_cb (EV_P_ ev_stat *w, int revents)
3072\& {
3073\& /* reset the one\-second timer */
3074\& ev_timer_again (EV_A_ &timer);
3075\& }
3076\&
1473\& ... 3077\& ...
1474\& ev_stat passwd;
1475.Ve
1476.PP
1477.Vb 2
1478\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3078\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1479\& ev_stat_start (loop, &passwd); 3079\& ev_stat_start (loop, &passwd);
3080\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1480.Ve 3081.Ve
1481.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3082.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1482.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3083.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1483.IX Subsection "ev_idle - when you've got nothing better to do..." 3084.IX Subsection "ev_idle - when you've got nothing better to do..."
1484Idle watchers trigger events when there are no other events are pending 3085Idle watchers trigger events when no other events of the same or higher
1485(prepare, check and other idle watchers do not count). That is, as long 3086priority are pending (prepare, check and other idle watchers do not count
1486as your process is busy handling sockets or timeouts (or even signals, 3087as receiving \*(L"events\*(R").
1487imagine) it will not be triggered. But when your process is idle all idle 3088.PP
1488watchers are being called again and again, once per event loop iteration \- 3089That is, as long as your process is busy handling sockets or timeouts
3090(or even signals, imagine) of the same or higher priority it will not be
3091triggered. But when your process is idle (or only lower-priority watchers
3092are pending), the idle watchers are being called once per event loop
1489until stopped, that is, or your process receives more events and becomes 3093iteration \- until stopped, that is, or your process receives more events
1490busy. 3094and becomes busy again with higher priority stuff.
1491.PP 3095.PP
1492The most noteworthy effect is that as long as any idle watchers are 3096The most noteworthy effect is that as long as any idle watchers are
1493active, the process will not block when waiting for new events. 3097active, the process will not block when waiting for new events.
1494.PP 3098.PP
1495Apart from keeping your process non-blocking (which is a useful 3099Apart from keeping your process non-blocking (which is a useful
1496effect on its own sometimes), idle watchers are a good place to do 3100effect on its own sometimes), idle watchers are a good place to do
1497\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3101\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1498event loop has handled all outstanding events. 3102event loop has handled all outstanding events.
3103.PP
3104\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3105.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3106.PP
3107As long as there is at least one active idle watcher, libev will never
3108sleep unnecessarily. Or in other words, it will loop as fast as possible.
3109For this to work, the idle watcher doesn't need to be invoked at all \- the
3110lowest priority will do.
3111.PP
3112This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3113to do something on each event loop iteration \- for example to balance load
3114between different connections.
3115.PP
3116See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3117example.
3118.PP
3119\fIWatcher-Specific Functions and Data Members\fR
3120.IX Subsection "Watcher-Specific Functions and Data Members"
1499.IP "ev_idle_init (ev_signal *, callback)" 4 3121.IP "ev_idle_init (ev_idle *, callback)" 4
1500.IX Item "ev_idle_init (ev_signal *, callback)" 3122.IX Item "ev_idle_init (ev_idle *, callback)"
1501Initialises and configures the idle watcher \- it has no parameters of any 3123Initialises and configures the idle watcher \- it has no parameters of any
1502kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3124kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1503believe me. 3125believe me.
1504.PP 3126.PP
3127\fIExamples\fR
3128.IX Subsection "Examples"
3129.PP
1505Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 3130Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1506callback, free it. Also, use no error checking, as usual. 3131callback, free it. Also, use no error checking, as usual.
1507.PP 3132.PP
1508.Vb 7 3133.Vb 5
1509\& static void 3134\& static void
1510\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3135\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1511\& { 3136\& {
3137\& // stop the watcher
3138\& ev_idle_stop (loop, w);
3139\&
3140\& // now we can free it
1512\& free (w); 3141\& free (w);
3142\&
1513\& // now do something you wanted to do when the program has 3143\& // now do something you wanted to do when the program has
1514\& // no longer asnything immediate to do. 3144\& // no longer anything immediate to do.
1515\& } 3145\& }
1516.Ve 3146\&
1517.PP
1518.Vb 3
1519\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3147\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1520\& ev_idle_init (idle_watcher, idle_cb); 3148\& ev_idle_init (idle_watcher, idle_cb);
1521\& ev_idle_start (loop, idle_cb); 3149\& ev_idle_start (loop, idle_watcher);
1522.Ve 3150.Ve
1523.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3151.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1524.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3152.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1525.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3153.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1526Prepare and check watchers are usually (but not always) used in tandem: 3154Prepare and check watchers are often (but not always) used in pairs:
1527prepare watchers get invoked before the process blocks and check watchers 3155prepare watchers get invoked before the process blocks and check watchers
1528afterwards. 3156afterwards.
1529.PP 3157.PP
1530You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3158You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1531the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3159current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1532watchers. Other loops than the current one are fine, however. The 3160\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1533rationale behind this is that you do not need to check for recursion in 3161however. The rationale behind this is that you do not need to check
1534those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3162for recursion in those watchers, i.e. the sequence will always be
1535\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3163\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1536called in pairs bracketing the blocking call. 3164kind they will always be called in pairs bracketing the blocking call.
1537.PP 3165.PP
1538Their main purpose is to integrate other event mechanisms into libev and 3166Their main purpose is to integrate other event mechanisms into libev and
1539their use is somewhat advanced. This could be used, for example, to track 3167their use is somewhat advanced. They could be used, for example, to track
1540variable changes, implement your own watchers, integrate net-snmp or a 3168variable changes, implement your own watchers, integrate net-snmp or a
1541coroutine library and lots more. They are also occasionally useful if 3169coroutine library and lots more. They are also occasionally useful if
1542you cache some data and want to flush it before blocking (for example, 3170you cache some data and want to flush it before blocking (for example,
1543in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3171in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1544watcher). 3172watcher).
1545.PP 3173.PP
1546This is done by examining in each prepare call which file descriptors need 3174This is done by examining in each prepare call which file descriptors
1547to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3175need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1548them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3176for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1549provide just this functionality). Then, in the check watcher you check for 3177libraries provide exactly this functionality). Then, in the check watcher,
1550any events that occured (by checking the pending status of all watchers 3178you check for any events that occurred (by checking the pending status
1551and stopping them) and call back into the library. The I/O and timer 3179of all watchers and stopping them) and call back into the library. The
1552callbacks will never actually be called (but must be valid nevertheless, 3180I/O and timer callbacks will never actually be called (but must be valid
1553because you never know, you know?). 3181nevertheless, because you never know, you know?).
1554.PP 3182.PP
1555As another example, the Perl Coro module uses these hooks to integrate 3183As another example, the Perl Coro module uses these hooks to integrate
1556coroutines into libev programs, by yielding to other active coroutines 3184coroutines into libev programs, by yielding to other active coroutines
1557during each prepare and only letting the process block if no coroutines 3185during each prepare and only letting the process block if no coroutines
1558are ready to run (it's actually more complicated: it only runs coroutines 3186are ready to run (it's actually more complicated: it only runs coroutines
1559with priority higher than or equal to the event loop and one coroutine 3187with priority higher than or equal to the event loop and one coroutine
1560of lower priority, but only once, using idle watchers to keep the event 3188of lower priority, but only once, using idle watchers to keep the event
1561loop from blocking if lower-priority coroutines are active, thus mapping 3189loop from blocking if lower-priority coroutines are active, thus mapping
1562low-priority coroutines to idle/background tasks). 3190low-priority coroutines to idle/background tasks).
3191.PP
3192When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3193highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3194any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3195watchers).
3196.PP
3197Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3198activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3199might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3200\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3201loops those other event loops might be in an unusable state until their
3202\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3203others).
3204.PP
3205\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3206.IX Subsection "Abusing an ev_check watcher for its side-effect"
3207.PP
3208\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3209useful because they are called once per event loop iteration. For
3210example, if you want to handle a large number of connections fairly, you
3211normally only do a bit of work for each active connection, and if there
3212is more work to do, you wait for the next event loop iteration, so other
3213connections have a chance of making progress.
3214.PP
3215Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3216next event loop iteration. However, that isn't as soon as possible \-
3217without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3218.PP
3219This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3220single global idle watcher that is active as long as you have one active
3221\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3222will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3223invoked. Neither watcher alone can do that.
3224.PP
3225\fIWatcher-Specific Functions and Data Members\fR
3226.IX Subsection "Watcher-Specific Functions and Data Members"
1563.IP "ev_prepare_init (ev_prepare *, callback)" 4 3227.IP "ev_prepare_init (ev_prepare *, callback)" 4
1564.IX Item "ev_prepare_init (ev_prepare *, callback)" 3228.IX Item "ev_prepare_init (ev_prepare *, callback)"
1565.PD 0 3229.PD 0
1566.IP "ev_check_init (ev_check *, callback)" 4 3230.IP "ev_check_init (ev_check *, callback)" 4
1567.IX Item "ev_check_init (ev_check *, callback)" 3231.IX Item "ev_check_init (ev_check *, callback)"
1568.PD 3232.PD
1569Initialises and configures the prepare or check watcher \- they have no 3233Initialises and configures the prepare or check watcher \- they have no
1570parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3234parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1571macros, but using them is utterly, utterly and completely pointless. 3235macros, but using them is utterly, utterly, utterly and completely
3236pointless.
1572.PP 3237.PP
1573Example: To include a library such as adns, you would add \s-1IO\s0 watchers 3238\fIExamples\fR
1574and a timeout watcher in a prepare handler, as required by libadns, and 3239.IX Subsection "Examples"
3240.PP
3241There are a number of principal ways to embed other event loops or modules
3242into libev. Here are some ideas on how to include libadns into libev
3243(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3244use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3245Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3246Glib event loop).
3247.PP
3248Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1575in a check watcher, destroy them and call into libadns. What follows is 3249and in a check watcher, destroy them and call into libadns. What follows
1576pseudo-code only of course: 3250is pseudo-code only of course. This requires you to either use a low
3251priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3252the callbacks for the IO/timeout watchers might not have been called yet.
1577.PP 3253.PP
1578.Vb 2 3254.Vb 2
1579\& static ev_io iow [nfd]; 3255\& static ev_io iow [nfd];
1580\& static ev_timer tw; 3256\& static ev_timer tw;
1581.Ve 3257\&
1582.PP
1583.Vb 9
1584\& static void 3258\& static void
1585\& io_cb (ev_loop *loop, ev_io *w, int revents) 3259\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1586\& { 3260\& {
1587\& // set the relevant poll flags
1588\& // could also call adns_processreadable etc. here
1589\& struct pollfd *fd = (struct pollfd *)w->data;
1590\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1591\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1592\& } 3261\& }
1593.Ve 3262\&
1594.PP
1595.Vb 7
1596\& // create io watchers for each fd and a timer before blocking 3263\& // create io watchers for each fd and a timer before blocking
1597\& static void 3264\& static void
1598\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3265\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1599\& { 3266\& {
1600\& int timeout = 3600000;truct pollfd fds [nfd]; 3267\& int timeout = 3600000;
3268\& struct pollfd fds [nfd];
1601\& // actual code will need to loop here and realloc etc. 3269\& // actual code will need to loop here and realloc etc.
1602\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3270\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1603.Ve 3271\&
1604.PP
1605.Vb 3
1606\& /* the callback is illegal, but won't be called as we stop during check */ 3272\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1607\& ev_timer_init (&tw, 0, timeout * 1e-3); 3273\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1608\& ev_timer_start (loop, &tw); 3274\& ev_timer_start (loop, &tw);
1609.Ve 3275\&
1610.PP
1611.Vb 6
1612\& // create on ev_io per pollfd 3276\& // create one ev_io per pollfd
1613\& for (int i = 0; i < nfd; ++i) 3277\& for (int i = 0; i < nfd; ++i)
1614\& { 3278\& {
1615\& ev_io_init (iow + i, io_cb, fds [i].fd, 3279\& ev_io_init (iow + i, io_cb, fds [i].fd,
1616\& ((fds [i].events & POLLIN ? EV_READ : 0) 3280\& ((fds [i].events & POLLIN ? EV_READ : 0)
1617\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3281\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3282\&
3283\& fds [i].revents = 0;
3284\& ev_io_start (loop, iow + i);
3285\& }
3286\& }
3287\&
3288\& // stop all watchers after blocking
3289\& static void
3290\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3291\& {
3292\& ev_timer_stop (loop, &tw);
3293\&
3294\& for (int i = 0; i < nfd; ++i)
3295\& {
3296\& // set the relevant poll flags
3297\& // could also call adns_processreadable etc. here
3298\& struct pollfd *fd = fds + i;
3299\& int revents = ev_clear_pending (iow + i);
3300\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3301\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3302\&
3303\& // now stop the watcher
3304\& ev_io_stop (loop, iow + i);
3305\& }
3306\&
3307\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3308\& }
1618.Ve 3309.Ve
3310.PP
3311Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3312in the prepare watcher and would dispose of the check watcher.
3313.PP
3314Method 3: If the module to be embedded supports explicit event
3315notification (libadns does), you can also make use of the actual watcher
3316callbacks, and only destroy/create the watchers in the prepare watcher.
1619.PP 3317.PP
1620.Vb 5 3318.Vb 5
1621\& fds [i].revents = 0;
1622\& iow [i].data = fds + i;
1623\& ev_io_start (loop, iow + i);
1624\& }
1625\& }
1626.Ve
1627.PP
1628.Vb 5
1629\& // stop all watchers after blocking
1630\& static void 3319\& static void
1631\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3320\& timer_cb (EV_P_ ev_timer *w, int revents)
1632\& { 3321\& {
1633\& ev_timer_stop (loop, &tw); 3322\& adns_state ads = (adns_state)w\->data;
1634.Ve 3323\& update_now (EV_A);
1635.PP 3324\&
1636.Vb 2 3325\& adns_processtimeouts (ads, &tv_now);
1637\& for (int i = 0; i < nfd; ++i)
1638\& ev_io_stop (loop, iow + i);
1639.Ve
1640.PP
1641.Vb 2
1642\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1643\& } 3326\& }
3327\&
3328\& static void
3329\& io_cb (EV_P_ ev_io *w, int revents)
3330\& {
3331\& adns_state ads = (adns_state)w\->data;
3332\& update_now (EV_A);
3333\&
3334\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3335\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3336\& }
3337\&
3338\& // do not ever call adns_afterpoll
1644.Ve 3339.Ve
3340.PP
3341Method 4: Do not use a prepare or check watcher because the module you
3342want to embed is not flexible enough to support it. Instead, you can
3343override their poll function. The drawback with this solution is that the
3344main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3345this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3346libglib event loop.
3347.PP
3348.Vb 4
3349\& static gint
3350\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3351\& {
3352\& int got_events = 0;
3353\&
3354\& for (n = 0; n < nfds; ++n)
3355\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3356\&
3357\& if (timeout >= 0)
3358\& // create/start timer
3359\&
3360\& // poll
3361\& ev_run (EV_A_ 0);
3362\&
3363\& // stop timer again
3364\& if (timeout >= 0)
3365\& ev_timer_stop (EV_A_ &to);
3366\&
3367\& // stop io watchers again \- their callbacks should have set
3368\& for (n = 0; n < nfds; ++n)
3369\& ev_io_stop (EV_A_ iow [n]);
3370\&
3371\& return got_events;
3372\& }
3373.Ve
1645.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3374.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1646.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3375.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1647.IX Subsection "ev_embed - when one backend isn't enough..." 3376.IX Subsection "ev_embed - when one backend isn't enough..."
1648This is a rather advanced watcher type that lets you embed one event loop 3377This is a rather advanced watcher type that lets you embed one event loop
1649into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3378into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1650loop, other types of watchers might be handled in a delayed or incorrect 3379loop, other types of watchers might be handled in a delayed or incorrect
1651fashion and must not be used). 3380fashion and must not be used).
… …
1654prioritise I/O. 3383prioritise I/O.
1655.PP 3384.PP
1656As an example for a bug workaround, the kqueue backend might only support 3385As an example for a bug workaround, the kqueue backend might only support
1657sockets on some platform, so it is unusable as generic backend, but you 3386sockets on some platform, so it is unusable as generic backend, but you
1658still want to make use of it because you have many sockets and it scales 3387still want to make use of it because you have many sockets and it scales
1659so nicely. In this case, you would create a kqueue-based loop and embed it 3388so nicely. In this case, you would create a kqueue-based loop and embed
1660into your default loop (which might use e.g. poll). Overall operation will 3389it into your default loop (which might use e.g. poll). Overall operation
1661be a bit slower because first libev has to poll and then call kevent, but 3390will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1662at least you can use both at what they are best. 3391\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3392best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1663.PP 3393.PP
1664As for prioritising I/O: rarely you have the case where some fds have 3394As for prioritising I/O: under rare circumstances you have the case where
1665to be watched and handled very quickly (with low latency), and even 3395some fds have to be watched and handled very quickly (with low latency),
1666priorities and idle watchers might have too much overhead. In this case 3396and even priorities and idle watchers might have too much overhead. In
1667you would put all the high priority stuff in one loop and all the rest in 3397this case you would put all the high priority stuff in one loop and all
1668a second one, and embed the second one in the first. 3398the rest in a second one, and embed the second one in the first.
1669.PP 3399.PP
1670As long as the watcher is active, the callback will be invoked every time 3400As long as the watcher is active, the callback will be invoked every
1671there might be events pending in the embedded loop. The callback must then 3401time there might be events pending in the embedded loop. The callback
1672call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3402must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1673their callbacks (you could also start an idle watcher to give the embedded 3403sweep and invoke their callbacks (the callback doesn't need to invoke the
1674loop strictly lower priority for example). You can also set the callback 3404\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1675to \f(CW0\fR, in which case the embed watcher will automatically execute the 3405to give the embedded loop strictly lower priority for example).
1676embedded loop sweep.
1677.PP 3406.PP
1678As long as the watcher is started it will automatically handle events. The 3407You can also set the callback to \f(CW0\fR, in which case the embed watcher
1679callback will be invoked whenever some events have been handled. You can 3408will automatically execute the embedded loop sweep whenever necessary.
1680set the callback to \f(CW0\fR to avoid having to specify one if you are not
1681interested in that.
1682.PP 3409.PP
1683Also, there have not currently been made special provisions for forking: 3410Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1684when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3411is active, i.e., the embedded loop will automatically be forked when the
1685but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3412embedding loop forks. In other cases, the user is responsible for calling
1686yourself. 3413\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1687.PP 3414.PP
1688Unfortunately, not all backends are embeddable, only the ones returned by 3415Unfortunately, not all backends are embeddable: only the ones returned by
1689\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3416\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1690portable one. 3417portable one.
1691.PP 3418.PP
1692So when you want to use this feature you will always have to be prepared 3419So when you want to use this feature you will always have to be prepared
1693that you cannot get an embeddable loop. The recommended way to get around 3420that you cannot get an embeddable loop. The recommended way to get around
1694this is to have a separate variables for your embeddable loop, try to 3421this is to have a separate variables for your embeddable loop, try to
1695create it, and if that fails, use the normal loop for everything: 3422create it, and if that fails, use the normal loop for everything.
1696.PP 3423.PP
1697.Vb 3 3424\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1698\& struct ev_loop *loop_hi = ev_default_init (0); 3425.IX Subsection "ev_embed and fork"
1699\& struct ev_loop *loop_lo = 0;
1700\& struct ev_embed embed;
1701.Ve
1702.PP 3426.PP
1703.Vb 5 3427While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1704\& // see if there is a chance of getting one that works 3428automatically be applied to the embedded loop as well, so no special
1705\& // (remember that a flags value of 0 means autodetection) 3429fork handling is required in that case. When the watcher is not running,
1706\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3430however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1707\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3431as applicable.
1708\& : 0;
1709.Ve
1710.PP 3432.PP
1711.Vb 8 3433\fIWatcher-Specific Functions and Data Members\fR
1712\& // if we got one, then embed it, otherwise default to loop_hi 3434.IX Subsection "Watcher-Specific Functions and Data Members"
1713\& if (loop_lo)
1714\& {
1715\& ev_embed_init (&embed, 0, loop_lo);
1716\& ev_embed_start (loop_hi, &embed);
1717\& }
1718\& else
1719\& loop_lo = loop_hi;
1720.Ve
1721.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3435.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1722.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3436.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1723.PD 0 3437.PD 0
1724.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3438.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1725.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3439.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1726.PD 3440.PD
1727Configures the watcher to embed the given loop, which must be 3441Configures the watcher to embed the given loop, which must be
1728embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3442embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1729invoked automatically, otherwise it is the responsibility of the callback 3443invoked automatically, otherwise it is the responsibility of the callback
1730to invoke it (it will continue to be called until the sweep has been done, 3444to invoke it (it will continue to be called until the sweep has been done,
1731if you do not want thta, you need to temporarily stop the embed watcher). 3445if you do not want that, you need to temporarily stop the embed watcher).
1732.IP "ev_embed_sweep (loop, ev_embed *)" 4 3446.IP "ev_embed_sweep (loop, ev_embed *)" 4
1733.IX Item "ev_embed_sweep (loop, ev_embed *)" 3447.IX Item "ev_embed_sweep (loop, ev_embed *)"
1734Make a single, non-blocking sweep over the embedded loop. This works 3448Make a single, non-blocking sweep over the embedded loop. This works
1735similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3449similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1736apropriate way for embedded loops. 3450appropriate way for embedded loops.
1737.IP "struct ev_loop *loop [read\-only]" 4 3451.IP "struct ev_loop *other [read\-only]" 4
1738.IX Item "struct ev_loop *loop [read-only]" 3452.IX Item "struct ev_loop *other [read-only]"
1739The embedded event loop. 3453The embedded event loop.
3454.PP
3455\fIExamples\fR
3456.IX Subsection "Examples"
3457.PP
3458Example: Try to get an embeddable event loop and embed it into the default
3459event loop. If that is not possible, use the default loop. The default
3460loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3461\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3462used).
3463.PP
3464.Vb 3
3465\& struct ev_loop *loop_hi = ev_default_init (0);
3466\& struct ev_loop *loop_lo = 0;
3467\& ev_embed embed;
3468\&
3469\& // see if there is a chance of getting one that works
3470\& // (remember that a flags value of 0 means autodetection)
3471\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3472\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3473\& : 0;
3474\&
3475\& // if we got one, then embed it, otherwise default to loop_hi
3476\& if (loop_lo)
3477\& {
3478\& ev_embed_init (&embed, 0, loop_lo);
3479\& ev_embed_start (loop_hi, &embed);
3480\& }
3481\& else
3482\& loop_lo = loop_hi;
3483.Ve
3484.PP
3485Example: Check if kqueue is available but not recommended and create
3486a kqueue backend for use with sockets (which usually work with any
3487kqueue implementation). Store the kqueue/socket\-only event loop in
3488\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3489.PP
3490.Vb 3
3491\& struct ev_loop *loop = ev_default_init (0);
3492\& struct ev_loop *loop_socket = 0;
3493\& ev_embed embed;
3494\&
3495\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3496\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3497\& {
3498\& ev_embed_init (&embed, 0, loop_socket);
3499\& ev_embed_start (loop, &embed);
3500\& }
3501\&
3502\& if (!loop_socket)
3503\& loop_socket = loop;
3504\&
3505\& // now use loop_socket for all sockets, and loop for everything else
3506.Ve
1740.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3507.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
1741.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3508.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1742.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3509.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1743Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3510Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1744whoever is a good citizen cared to tell libev about it by calling 3511whoever is a good citizen cared to tell libev about it by calling
1745\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3512\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
1746event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3513and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
1747and only in the child after the fork. If whoever good citizen calling 3514after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
1748\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3515and calls it in the wrong process, the fork handlers will be invoked, too,
1749handlers will be invoked, too, of course. 3516of course.
3517.PP
3518\fIThe special problem of life after fork \- how is it possible?\fR
3519.IX Subsection "The special problem of life after fork - how is it possible?"
3520.PP
3521Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3522up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3523sequence should be handled by libev without any problems.
3524.PP
3525This changes when the application actually wants to do event handling
3526in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3527fork.
3528.PP
3529The default mode of operation (for libev, with application help to detect
3530forks) is to duplicate all the state in the child, as would be expected
3531when \fIeither\fR the parent \fIor\fR the child process continues.
3532.PP
3533When both processes want to continue using libev, then this is usually the
3534wrong result. In that case, usually one process (typically the parent) is
3535supposed to continue with all watchers in place as before, while the other
3536process typically wants to start fresh, i.e. without any active watchers.
3537.PP
3538The cleanest and most efficient way to achieve that with libev is to
3539simply create a new event loop, which of course will be \*(L"empty\*(R", and
3540use that for new watchers. This has the advantage of not touching more
3541memory than necessary, and thus avoiding the copy-on-write, and the
3542disadvantage of having to use multiple event loops (which do not support
3543signal watchers).
3544.PP
3545When this is not possible, or you want to use the default loop for
3546other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3547\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3548Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3549watchers, so you have to be careful not to execute code that modifies
3550those watchers. Note also that in that case, you have to re-register any
3551signal watchers.
3552.PP
3553\fIWatcher-Specific Functions and Data Members\fR
3554.IX Subsection "Watcher-Specific Functions and Data Members"
1750.IP "ev_fork_init (ev_signal *, callback)" 4 3555.IP "ev_fork_init (ev_fork *, callback)" 4
1751.IX Item "ev_fork_init (ev_signal *, callback)" 3556.IX Item "ev_fork_init (ev_fork *, callback)"
1752Initialises and configures the fork watcher \- it has no parameters of any 3557Initialises and configures the fork watcher \- it has no parameters of any
1753kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3558kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1754believe me. 3559really.
3560.ie n .SS """ev_cleanup"" \- even the best things end"
3561.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3562.IX Subsection "ev_cleanup - even the best things end"
3563Cleanup watchers are called just before the event loop is being destroyed
3564by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3565.PP
3566While there is no guarantee that the event loop gets destroyed, cleanup
3567watchers provide a convenient method to install cleanup hooks for your
3568program, worker threads and so on \- you just to make sure to destroy the
3569loop when you want them to be invoked.
3570.PP
3571Cleanup watchers are invoked in the same way as any other watcher. Unlike
3572all other watchers, they do not keep a reference to the event loop (which
3573makes a lot of sense if you think about it). Like all other watchers, you
3574can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3575.PP
3576\fIWatcher-Specific Functions and Data Members\fR
3577.IX Subsection "Watcher-Specific Functions and Data Members"
3578.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3579.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3580Initialises and configures the cleanup watcher \- it has no parameters of
3581any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3582pointless, I assure you.
3583.PP
3584Example: Register an atexit handler to destroy the default loop, so any
3585cleanup functions are called.
3586.PP
3587.Vb 5
3588\& static void
3589\& program_exits (void)
3590\& {
3591\& ev_loop_destroy (EV_DEFAULT_UC);
3592\& }
3593\&
3594\& ...
3595\& atexit (program_exits);
3596.Ve
3597.ie n .SS """ev_async"" \- how to wake up an event loop"
3598.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3599.IX Subsection "ev_async - how to wake up an event loop"
3600In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3601asynchronous sources such as signal handlers (as opposed to multiple event
3602loops \- those are of course safe to use in different threads).
3603.PP
3604Sometimes, however, you need to wake up an event loop you do not control,
3605for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3606watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3607it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3608.PP
3609This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3610too, are asynchronous in nature, and signals, too, will be compressed
3611(i.e. the number of callback invocations may be less than the number of
3612\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3613of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3614signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3615even without knowing which loop owns the signal.
3616.PP
3617\fIQueueing\fR
3618.IX Subsection "Queueing"
3619.PP
3620\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3621is that the author does not know of a simple (or any) algorithm for a
3622multiple-writer-single-reader queue that works in all cases and doesn't
3623need elaborate support such as pthreads or unportable memory access
3624semantics.
3625.PP
3626That means that if you want to queue data, you have to provide your own
3627queue. But at least I can tell you how to implement locking around your
3628queue:
3629.IP "queueing from a signal handler context" 4
3630.IX Item "queueing from a signal handler context"
3631To implement race-free queueing, you simply add to the queue in the signal
3632handler but you block the signal handler in the watcher callback. Here is
3633an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3634.Sp
3635.Vb 1
3636\& static ev_async mysig;
3637\&
3638\& static void
3639\& sigusr1_handler (void)
3640\& {
3641\& sometype data;
3642\&
3643\& // no locking etc.
3644\& queue_put (data);
3645\& ev_async_send (EV_DEFAULT_ &mysig);
3646\& }
3647\&
3648\& static void
3649\& mysig_cb (EV_P_ ev_async *w, int revents)
3650\& {
3651\& sometype data;
3652\& sigset_t block, prev;
3653\&
3654\& sigemptyset (&block);
3655\& sigaddset (&block, SIGUSR1);
3656\& sigprocmask (SIG_BLOCK, &block, &prev);
3657\&
3658\& while (queue_get (&data))
3659\& process (data);
3660\&
3661\& if (sigismember (&prev, SIGUSR1)
3662\& sigprocmask (SIG_UNBLOCK, &block, 0);
3663\& }
3664.Ve
3665.Sp
3666(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3667instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3668either...).
3669.IP "queueing from a thread context" 4
3670.IX Item "queueing from a thread context"
3671The strategy for threads is different, as you cannot (easily) block
3672threads but you can easily preempt them, so to queue safely you need to
3673employ a traditional mutex lock, such as in this pthread example:
3674.Sp
3675.Vb 2
3676\& static ev_async mysig;
3677\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3678\&
3679\& static void
3680\& otherthread (void)
3681\& {
3682\& // only need to lock the actual queueing operation
3683\& pthread_mutex_lock (&mymutex);
3684\& queue_put (data);
3685\& pthread_mutex_unlock (&mymutex);
3686\&
3687\& ev_async_send (EV_DEFAULT_ &mysig);
3688\& }
3689\&
3690\& static void
3691\& mysig_cb (EV_P_ ev_async *w, int revents)
3692\& {
3693\& pthread_mutex_lock (&mymutex);
3694\&
3695\& while (queue_get (&data))
3696\& process (data);
3697\&
3698\& pthread_mutex_unlock (&mymutex);
3699\& }
3700.Ve
3701.PP
3702\fIWatcher-Specific Functions and Data Members\fR
3703.IX Subsection "Watcher-Specific Functions and Data Members"
3704.IP "ev_async_init (ev_async *, callback)" 4
3705.IX Item "ev_async_init (ev_async *, callback)"
3706Initialises and configures the async watcher \- it has no parameters of any
3707kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3708trust me.
3709.IP "ev_async_send (loop, ev_async *)" 4
3710.IX Item "ev_async_send (loop, ev_async *)"
3711Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3712an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3713returns.
3714.Sp
3715Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3716signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3717embedding section below on what exactly this means).
3718.Sp
3719Note that, as with other watchers in libev, multiple events might get
3720compressed into a single callback invocation (another way to look at
3721this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3722\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3723.Sp
3724This call incurs the overhead of at most one extra system call per event
3725loop iteration, if the event loop is blocked, and no syscall at all if
3726the event loop (or your program) is processing events. That means that
3727repeated calls are basically free (there is no need to avoid calls for
3728performance reasons) and that the overhead becomes smaller (typically
3729zero) under load.
3730.IP "bool = ev_async_pending (ev_async *)" 4
3731.IX Item "bool = ev_async_pending (ev_async *)"
3732Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3733watcher but the event has not yet been processed (or even noted) by the
3734event loop.
3735.Sp
3736\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3737the loop iterates next and checks for the watcher to have become active,
3738it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3739quickly check whether invoking the loop might be a good idea.
3740.Sp
3741Not that this does \fInot\fR check whether the watcher itself is pending,
3742only whether it has been requested to make this watcher pending: there
3743is a time window between the event loop checking and resetting the async
3744notification, and the callback being invoked.
1755.SH "OTHER FUNCTIONS" 3745.SH "OTHER FUNCTIONS"
1756.IX Header "OTHER FUNCTIONS" 3746.IX Header "OTHER FUNCTIONS"
1757There are some other functions of possible interest. Described. Here. Now. 3747There are some other functions of possible interest. Described. Here. Now.
1758.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3748.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1759.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3749.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1760This function combines a simple timer and an I/O watcher, calls your 3750This function combines a simple timer and an I/O watcher, calls your
1761callback on whichever event happens first and automatically stop both 3751callback on whichever event happens first and automatically stops both
1762watchers. This is useful if you want to wait for a single event on an fd 3752watchers. This is useful if you want to wait for a single event on an fd
1763or timeout without having to allocate/configure/start/stop/free one or 3753or timeout without having to allocate/configure/start/stop/free one or
1764more watchers yourself. 3754more watchers yourself.
1765.Sp 3755.Sp
1766If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3756If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1767is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3757\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1768\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3758the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1769.Sp 3759.Sp
1770If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3760If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1771started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3761started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1772repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3762repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1773dubious value.
1774.Sp 3763.Sp
1775The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3764The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1776passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3765passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1777\&\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 3766\&\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
1778value passed to \f(CW\*(C`ev_once\*(C'\fR: 3767value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3768a timeout and an io event at the same time \- you probably should give io
3769events precedence.
3770.Sp
3771Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1779.Sp 3772.Sp
1780.Vb 7 3773.Vb 7
1781\& static void stdin_ready (int revents, void *arg) 3774\& static void stdin_ready (int revents, void *arg)
3775\& {
3776\& if (revents & EV_READ)
3777\& /* stdin might have data for us, joy! */;
3778\& else if (revents & EV_TIMER)
3779\& /* doh, nothing entered */;
3780\& }
3781\&
3782\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3783.Ve
3784.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3785.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3786Feed an event on the given fd, as if a file descriptor backend detected
3787the given events.
3788.IP "ev_feed_signal_event (loop, int signum)" 4
3789.IX Item "ev_feed_signal_event (loop, int signum)"
3790Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3791which is async-safe.
3792.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3793.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3794This section explains some common idioms that are not immediately
3795obvious. Note that examples are sprinkled over the whole manual, and this
3796section only contains stuff that wouldn't fit anywhere else.
3797.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3798.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3799Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3800or modify at any time: libev will completely ignore it. This can be used
3801to associate arbitrary data with your watcher. If you need more data and
3802don't want to allocate memory separately and store a pointer to it in that
3803data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3804data:
3805.PP
3806.Vb 7
3807\& struct my_io
3808\& {
3809\& ev_io io;
3810\& int otherfd;
3811\& void *somedata;
3812\& struct whatever *mostinteresting;
3813\& };
3814\&
3815\& ...
3816\& struct my_io w;
3817\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3818.Ve
3819.PP
3820And since your callback will be called with a pointer to the watcher, you
3821can cast it back to your own type:
3822.PP
3823.Vb 5
3824\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3825\& {
3826\& struct my_io *w = (struct my_io *)w_;
3827\& ...
3828\& }
3829.Ve
3830.PP
3831More interesting and less C\-conformant ways of casting your callback
3832function type instead have been omitted.
3833.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3834.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3835Another common scenario is to use some data structure with multiple
3836embedded watchers, in effect creating your own watcher that combines
3837multiple libev event sources into one \*(L"super-watcher\*(R":
3838.PP
3839.Vb 6
3840\& struct my_biggy
3841\& {
3842\& int some_data;
3843\& ev_timer t1;
3844\& ev_timer t2;
3845\& }
3846.Ve
3847.PP
3848In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3849complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3850the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3851to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3852real programmers):
3853.PP
3854.Vb 1
3855\& #include <stddef.h>
3856\&
3857\& static void
3858\& t1_cb (EV_P_ ev_timer *w, int revents)
3859\& {
3860\& struct my_biggy big = (struct my_biggy *)
3861\& (((char *)w) \- offsetof (struct my_biggy, t1));
3862\& }
3863\&
3864\& static void
3865\& t2_cb (EV_P_ ev_timer *w, int revents)
3866\& {
3867\& struct my_biggy big = (struct my_biggy *)
3868\& (((char *)w) \- offsetof (struct my_biggy, t2));
3869\& }
3870.Ve
3871.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3872.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3873Often you have structures like this in event-based programs:
3874.PP
3875.Vb 4
3876\& callback ()
1782\& { 3877\& {
1783\& if (revents & EV_TIMEOUT) 3878\& free (request);
1784\& /* doh, nothing entered */;
1785\& else if (revents & EV_READ)
1786\& /* stdin might have data for us, joy! */;
1787\& } 3879\& }
3880\&
3881\& request = start_new_request (..., callback);
1788.Ve 3882.Ve
1789.Sp 3883.PP
3884The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3885used to cancel the operation, or do other things with it.
3886.PP
3887It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3888immediately invoke the callback, for example, to report errors. Or you add
3889some caching layer that finds that it can skip the lengthy aspects of the
3890operation and simply invoke the callback with the result.
3891.PP
3892The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3893has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3894.PP
3895Even if you pass the request by some safer means to the callback, you
3896might want to do something to the request after starting it, such as
3897canceling it, which probably isn't working so well when the callback has
3898already been invoked.
3899.PP
3900A common way around all these issues is to make sure that
3901\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3902\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3903delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3904example, or more sneakily, by reusing an existing (stopped) watcher and
3905pushing it into the pending queue:
3906.PP
1790.Vb 1 3907.Vb 2
1791\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3908\& ev_set_cb (watcher, callback);
3909\& ev_feed_event (EV_A_ watcher, 0);
1792.Ve 3910.Ve
1793.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3911.PP
1794.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3912This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1795Feeds the given event set into the event loop, as if the specified event 3913invoked, while not delaying callback invocation too much.
1796had happened for the specified watcher (which must be a pointer to an 3914.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1797initialised but not necessarily started event watcher). 3915.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1798.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3916Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1799.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3917\&\fImodal\fR interaction, which is most easily implemented by recursively
1800Feed an event on the given fd, as if a file descriptor backend detected 3918invoking \f(CW\*(C`ev_run\*(C'\fR.
1801the given events it. 3919.PP
1802.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3920This brings the problem of exiting \- a callback might want to finish the
1803.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3921main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1804Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3922a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1805loop!). 3923and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3924other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3925.PP
3926The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3927invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3928triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3929.PP
3930.Vb 2
3931\& // main loop
3932\& int exit_main_loop = 0;
3933\&
3934\& while (!exit_main_loop)
3935\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3936\&
3937\& // in a modal watcher
3938\& int exit_nested_loop = 0;
3939\&
3940\& while (!exit_nested_loop)
3941\& ev_run (EV_A_ EVRUN_ONCE);
3942.Ve
3943.PP
3944To exit from any of these loops, just set the corresponding exit variable:
3945.PP
3946.Vb 2
3947\& // exit modal loop
3948\& exit_nested_loop = 1;
3949\&
3950\& // exit main program, after modal loop is finished
3951\& exit_main_loop = 1;
3952\&
3953\& // exit both
3954\& exit_main_loop = exit_nested_loop = 1;
3955.Ve
3956.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3957.IX Subsection "THREAD LOCKING EXAMPLE"
3958Here is a fictitious example of how to run an event loop in a different
3959thread from where callbacks are being invoked and watchers are
3960created/added/removed.
3961.PP
3962For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3963which uses exactly this technique (which is suited for many high-level
3964languages).
3965.PP
3966The example uses a pthread mutex to protect the loop data, a condition
3967variable to wait for callback invocations, an async watcher to notify the
3968event loop thread and an unspecified mechanism to wake up the main thread.
3969.PP
3970First, you need to associate some data with the event loop:
3971.PP
3972.Vb 6
3973\& typedef struct {
3974\& mutex_t lock; /* global loop lock */
3975\& ev_async async_w;
3976\& thread_t tid;
3977\& cond_t invoke_cv;
3978\& } userdata;
3979\&
3980\& void prepare_loop (EV_P)
3981\& {
3982\& // for simplicity, we use a static userdata struct.
3983\& static userdata u;
3984\&
3985\& ev_async_init (&u\->async_w, async_cb);
3986\& ev_async_start (EV_A_ &u\->async_w);
3987\&
3988\& pthread_mutex_init (&u\->lock, 0);
3989\& pthread_cond_init (&u\->invoke_cv, 0);
3990\&
3991\& // now associate this with the loop
3992\& ev_set_userdata (EV_A_ u);
3993\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3994\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3995\&
3996\& // then create the thread running ev_run
3997\& pthread_create (&u\->tid, 0, l_run, EV_A);
3998\& }
3999.Ve
4000.PP
4001The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4002solely to wake up the event loop so it takes notice of any new watchers
4003that might have been added:
4004.PP
4005.Vb 5
4006\& static void
4007\& async_cb (EV_P_ ev_async *w, int revents)
4008\& {
4009\& // just used for the side effects
4010\& }
4011.Ve
4012.PP
4013The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4014protecting the loop data, respectively.
4015.PP
4016.Vb 6
4017\& static void
4018\& l_release (EV_P)
4019\& {
4020\& userdata *u = ev_userdata (EV_A);
4021\& pthread_mutex_unlock (&u\->lock);
4022\& }
4023\&
4024\& static void
4025\& l_acquire (EV_P)
4026\& {
4027\& userdata *u = ev_userdata (EV_A);
4028\& pthread_mutex_lock (&u\->lock);
4029\& }
4030.Ve
4031.PP
4032The event loop thread first acquires the mutex, and then jumps straight
4033into \f(CW\*(C`ev_run\*(C'\fR:
4034.PP
4035.Vb 4
4036\& void *
4037\& l_run (void *thr_arg)
4038\& {
4039\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4040\&
4041\& l_acquire (EV_A);
4042\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4043\& ev_run (EV_A_ 0);
4044\& l_release (EV_A);
4045\&
4046\& return 0;
4047\& }
4048.Ve
4049.PP
4050Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4051signal the main thread via some unspecified mechanism (signals? pipe
4052writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4053have been called (in a while loop because a) spurious wakeups are possible
4054and b) skipping inter-thread-communication when there are no pending
4055watchers is very beneficial):
4056.PP
4057.Vb 4
4058\& static void
4059\& l_invoke (EV_P)
4060\& {
4061\& userdata *u = ev_userdata (EV_A);
4062\&
4063\& while (ev_pending_count (EV_A))
4064\& {
4065\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4066\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4067\& }
4068\& }
4069.Ve
4070.PP
4071Now, whenever the main thread gets told to invoke pending watchers, it
4072will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4073thread to continue:
4074.PP
4075.Vb 4
4076\& static void
4077\& real_invoke_pending (EV_P)
4078\& {
4079\& userdata *u = ev_userdata (EV_A);
4080\&
4081\& pthread_mutex_lock (&u\->lock);
4082\& ev_invoke_pending (EV_A);
4083\& pthread_cond_signal (&u\->invoke_cv);
4084\& pthread_mutex_unlock (&u\->lock);
4085\& }
4086.Ve
4087.PP
4088Whenever you want to start/stop a watcher or do other modifications to an
4089event loop, you will now have to lock:
4090.PP
4091.Vb 2
4092\& ev_timer timeout_watcher;
4093\& userdata *u = ev_userdata (EV_A);
4094\&
4095\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4096\&
4097\& pthread_mutex_lock (&u\->lock);
4098\& ev_timer_start (EV_A_ &timeout_watcher);
4099\& ev_async_send (EV_A_ &u\->async_w);
4100\& pthread_mutex_unlock (&u\->lock);
4101.Ve
4102.PP
4103Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4104an event loop currently blocking in the kernel will have no knowledge
4105about the newly added timer. By waking up the loop it will pick up any new
4106watchers in the next event loop iteration.
4107.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4108.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4109While the overhead of a callback that e.g. schedules a thread is small, it
4110is still an overhead. If you embed libev, and your main usage is with some
4111kind of threads or coroutines, you might want to customise libev so that
4112doesn't need callbacks anymore.
4113.PP
4114Imagine you have coroutines that you can switch to using a function
4115\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4116and that due to some magic, the currently active coroutine is stored in a
4117global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4118event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4119the differing \f(CW\*(C`;\*(C'\fR conventions):
4120.PP
4121.Vb 2
4122\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4123\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4124.Ve
4125.PP
4126That means instead of having a C callback function, you store the
4127coroutine to switch to in each watcher, and instead of having libev call
4128your callback, you instead have it switch to that coroutine.
4129.PP
4130A coroutine might now wait for an event with a function called
4131\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4132matter when, or whether the watcher is active or not when this function is
4133called):
4134.PP
4135.Vb 6
4136\& void
4137\& wait_for_event (ev_watcher *w)
4138\& {
4139\& ev_set_cb (w, current_coro);
4140\& switch_to (libev_coro);
4141\& }
4142.Ve
4143.PP
4144That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4145continues the libev coroutine, which, when appropriate, switches back to
4146this or any other coroutine.
4147.PP
4148You can do similar tricks if you have, say, threads with an event queue \-
4149instead of storing a coroutine, you store the queue object and instead of
4150switching to a coroutine, you push the watcher onto the queue and notify
4151any waiters.
4152.PP
4153To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4154files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4155.PP
4156.Vb 4
4157\& // my_ev.h
4158\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4159\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4160\& #include "../libev/ev.h"
4161\&
4162\& // my_ev.c
4163\& #define EV_H "my_ev.h"
4164\& #include "../libev/ev.c"
4165.Ve
4166.PP
4167And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4168\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4169can even use \fIev.h\fR as header file name directly.
1806.SH "LIBEVENT EMULATION" 4170.SH "LIBEVENT EMULATION"
1807.IX Header "LIBEVENT EMULATION" 4171.IX Header "LIBEVENT EMULATION"
1808Libev offers a compatibility emulation layer for libevent. It cannot 4172Libev offers a compatibility emulation layer for libevent. It cannot
1809emulate the internals of libevent, so here are some usage hints: 4173emulate the internals of libevent, so here are some usage hints:
4174.IP "\(bu" 4
4175Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4176.Sp
4177This was the newest libevent version available when libev was implemented,
4178and is still mostly unchanged in 2010.
4179.IP "\(bu" 4
1810.IP "* Use it by including <event.h>, as usual." 4 4180Use it by including <event.h>, as usual.
1811.IX Item "Use it by including <event.h>, as usual." 4181.IP "\(bu" 4
1812.PD 0 4182The following members are fully supported: ev_base, ev_callback,
1813.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4183ev_arg, ev_fd, ev_res, ev_events.
1814.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4184.IP "\(bu" 4
1815.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 4185Avoid using ev_flags and the EVLIST_*\-macros, while it is
1816.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)." 4186maintained by libev, it does not work exactly the same way as in libevent (consider
1817.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 4187it a private \s-1API\s0).
1818.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." 4188.IP "\(bu" 4
4189Priorities are not currently supported. Initialising priorities
4190will fail and all watchers will have the same priority, even though there
4191is an ev_pri field.
4192.IP "\(bu" 4
4193In libevent, the last base created gets the signals, in libev, the
4194base that registered the signal gets the signals.
4195.IP "\(bu" 4
1819.IP "* Other members are not supported." 4 4196Other members are not supported.
1820.IX Item "Other members are not supported." 4197.IP "\(bu" 4
1821.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4198The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1822.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4199to use the libev header file and library.
1823.PD
1824.SH "\*(C+ SUPPORT" 4200.SH "\*(C+ SUPPORT"
1825.IX Header " SUPPORT" 4201.IX Header " SUPPORT"
4202.SS "C \s-1API\s0"
4203.IX Subsection "C API"
4204The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4205libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4206will work fine.
4207.PP
4208Proper exception specifications might have to be added to callbacks passed
4209to libev: exceptions may be thrown only from watcher callbacks, all other
4210callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4211callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4212specification. If you have code that needs to be compiled as both C and
4213\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4214.PP
4215.Vb 6
4216\& static void
4217\& fatal_error (const char *msg) EV_NOEXCEPT
4218\& {
4219\& perror (msg);
4220\& abort ();
4221\& }
4222\&
4223\& ...
4224\& ev_set_syserr_cb (fatal_error);
4225.Ve
4226.PP
4227The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4228\&\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
4229because it runs cleanup watchers).
4230.PP
4231Throwing exceptions in watcher callbacks is only supported if libev itself
4232is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4233throwing exceptions through C libraries (most do).
4234.SS "\*(C+ \s-1API\s0"
4235.IX Subsection " API"
1826Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4236Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1827you to use some convinience methods to start/stop watchers and also change 4237you to use some convenience methods to start/stop watchers and also change
1828the callback model to a model using method callbacks on objects. 4238the callback model to a model using method callbacks on objects.
1829.PP 4239.PP
1830To use it, 4240To use it,
1831.PP 4241.PP
1832.Vb 1 4242.Vb 1
1833\& #include <ev++.h> 4243\& #include <ev++.h>
1834.Ve 4244.Ve
1835.PP 4245.PP
1836(it is not installed by default). This automatically includes \fIev.h\fR 4246This automatically includes \fIev.h\fR and puts all of its definitions (many
1837and puts all of its definitions (many of them macros) into the global 4247of them macros) into the global namespace. All \*(C+ specific things are
1838namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4248put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4249options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1839.PP 4250.PP
1840It should support all the same embedding options as \fIev.h\fR, most notably 4251Care has been taken to keep the overhead low. The only data member the \*(C+
1841\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4252classes add (compared to plain C\-style watchers) is the event loop pointer
4253that the watcher is associated with (or no additional members at all if
4254you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4255.PP
4256Currently, functions, static and non-static member functions and classes
4257with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4258to add as long as they only need one additional pointer for context. If
4259you need support for other types of functors please contact the author
4260(preferably after implementing it).
4261.PP
4262For all this to work, your \*(C+ compiler either has to use the same calling
4263conventions as your C compiler (for static member functions), or you have
4264to embed libev and compile libev itself as \*(C+.
1842.PP 4265.PP
1843Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4266Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1844.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4267.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1845.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4268.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1846.IX Item "ev::READ, ev::WRITE etc." 4269.IX Item "ev::READ, ev::WRITE etc."
1847These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4270These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1848macros from \fIev.h\fR. 4271macros from \fIev.h\fR.
1849.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4272.ie n .IP """ev::tstamp"", ""ev::now""" 4
1850.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4273.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1851.IX Item "ev::tstamp, ev::now" 4274.IX Item "ev::tstamp, ev::now"
1852Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4275Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1853.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 4276.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1854.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4277.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1855.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4278.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1856For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4279For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1857the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4280the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1858which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4281which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1859defines by many implementations. 4282defined by many implementations.
1860.Sp 4283.Sp
1861All of those classes have these methods: 4284All of those classes have these methods:
1862.RS 4 4285.RS 4
1863.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4286.IP "ev::TYPE::TYPE ()" 4
1864.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4287.IX Item "ev::TYPE::TYPE ()"
1865.PD 0 4288.PD 0
1866.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4289.IP "ev::TYPE::TYPE (loop)" 4
1867.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4290.IX Item "ev::TYPE::TYPE (loop)"
1868.IP "ev::TYPE::~TYPE" 4 4291.IP "ev::TYPE::~TYPE" 4
1869.IX Item "ev::TYPE::~TYPE" 4292.IX Item "ev::TYPE::~TYPE"
1870.PD 4293.PD
1871The constructor takes a pointer to an object and a method pointer to 4294The constructor (optionally) takes an event loop to associate the watcher
1872the event handler callback to call in this class. The constructor calls 4295with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1873\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4296.Sp
1874before starting it. If you do not specify a loop then the constructor 4297The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1875automatically associates the default loop with this watcher. 4298\&\f(CW\*(C`set\*(C'\fR method before starting it.
4299.Sp
4300It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4301method to set a callback before you can start the watcher.
4302.Sp
4303(The reason why you have to use a method is a limitation in \*(C+ which does
4304not allow explicit template arguments for constructors).
1876.Sp 4305.Sp
1877The destructor automatically stops the watcher if it is active. 4306The destructor automatically stops the watcher if it is active.
4307.IP "w\->set<class, &class::method> (object *)" 4
4308.IX Item "w->set<class, &class::method> (object *)"
4309This method sets the callback method to call. The method has to have a
4310signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4311first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4312parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4313.Sp
4314This method synthesizes efficient thunking code to call your method from
4315the C callback that libev requires. If your compiler can inline your
4316callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4317your compiler is good :), then the method will be fully inlined into the
4318thunking function, making it as fast as a direct C callback.
4319.Sp
4320Example: simple class declaration and watcher initialisation
4321.Sp
4322.Vb 4
4323\& struct myclass
4324\& {
4325\& void io_cb (ev::io &w, int revents) { }
4326\& }
4327\&
4328\& myclass obj;
4329\& ev::io iow;
4330\& iow.set <myclass, &myclass::io_cb> (&obj);
4331.Ve
4332.IP "w\->set (object *)" 4
4333.IX Item "w->set (object *)"
4334This is a variation of a method callback \- leaving out the method to call
4335will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4336functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4337the time. Incidentally, you can then also leave out the template argument
4338list.
4339.Sp
4340The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4341int revents)\*(C'\fR.
4342.Sp
4343See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4344.Sp
4345Example: use a functor object as callback.
4346.Sp
4347.Vb 7
4348\& struct myfunctor
4349\& {
4350\& void operator() (ev::io &w, int revents)
4351\& {
4352\& ...
4353\& }
4354\& }
4355\&
4356\& myfunctor f;
4357\&
4358\& ev::io w;
4359\& w.set (&f);
4360.Ve
4361.IP "w\->set<function> (void *data = 0)" 4
4362.IX Item "w->set<function> (void *data = 0)"
4363Also sets a callback, but uses a static method or plain function as
4364callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4365\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4366.Sp
4367The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4368.Sp
4369See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4370.Sp
4371Example: Use a plain function as callback.
4372.Sp
4373.Vb 2
4374\& static void io_cb (ev::io &w, int revents) { }
4375\& iow.set <io_cb> ();
4376.Ve
1878.IP "w\->set (struct ev_loop *)" 4 4377.IP "w\->set (loop)" 4
1879.IX Item "w->set (struct ev_loop *)" 4378.IX Item "w->set (loop)"
1880Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4379Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1881do this when the watcher is inactive (and not pending either). 4380do this when the watcher is inactive (and not pending either).
1882.IP "w\->set ([args])" 4 4381.IP "w\->set ([arguments])" 4
1883.IX Item "w->set ([args])" 4382.IX Item "w->set ([arguments])"
1884Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4383Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4384with the same arguments. Either this method or a suitable start method
1885called at least once. Unlike the C counterpart, an active watcher gets 4385must be called at least once. Unlike the C counterpart, an active watcher
1886automatically stopped and restarted. 4386gets automatically stopped and restarted when reconfiguring it with this
4387method.
4388.Sp
4389For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4390clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1887.IP "w\->start ()" 4 4391.IP "w\->start ()" 4
1888.IX Item "w->start ()" 4392.IX Item "w->start ()"
1889Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4393Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1890constructor already takes the loop. 4394constructor already stores the event loop.
4395.IP "w\->start ([arguments])" 4
4396.IX Item "w->start ([arguments])"
4397Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4398convenient to wrap them in one call. Uses the same type of arguments as
4399the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1891.IP "w\->stop ()" 4 4400.IP "w\->stop ()" 4
1892.IX Item "w->stop ()" 4401.IX Item "w->stop ()"
1893Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4402Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1894.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4403.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1895.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4404.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1896.IX Item "w->again () ev::timer, ev::periodic only" 4405.IX Item "w->again () (ev::timer, ev::periodic only)"
1897For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4406For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1898\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4407\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1899.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4408.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1900.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4409.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1901.IX Item "w->sweep () ev::embed only" 4410.IX Item "w->sweep () (ev::embed only)"
1902Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4411Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1903.ie n .IP "w\->update () ""ev::stat"" only" 4 4412.ie n .IP "w\->update () (""ev::stat"" only)" 4
1904.el .IP "w\->update () \f(CWev::stat\fR only" 4 4413.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
1905.IX Item "w->update () ev::stat only" 4414.IX Item "w->update () (ev::stat only)"
1906Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4415Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1907.RE 4416.RE
1908.RS 4 4417.RS 4
1909.RE 4418.RE
1910.PP 4419.PP
1911Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4420Example: Define a class with two I/O and idle watchers, start the I/O
1912the constructor. 4421watchers in the constructor.
1913.PP 4422.PP
1914.Vb 4 4423.Vb 5
1915\& class myclass 4424\& class myclass
1916\& { 4425\& {
1917\& ev_io io; void io_cb (ev::io &w, int revents); 4426\& ev::io io ; void io_cb (ev::io &w, int revents);
4427\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1918\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4428\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
1919.Ve 4429\&
1920.PP
1921.Vb 2
1922\& myclass (); 4430\& myclass (int fd)
4431\& {
4432\& io .set <myclass, &myclass::io_cb > (this);
4433\& io2 .set <myclass, &myclass::io2_cb > (this);
4434\& idle.set <myclass, &myclass::idle_cb> (this);
4435\&
4436\& io.set (fd, ev::WRITE); // configure the watcher
4437\& io.start (); // start it whenever convenient
4438\&
4439\& io2.start (fd, ev::READ); // set + start in one call
4440\& }
1923\& } 4441\& };
1924.Ve 4442.Ve
1925.PP 4443.SH "OTHER LANGUAGE BINDINGS"
1926.Vb 6 4444.IX Header "OTHER LANGUAGE BINDINGS"
1927\& myclass::myclass (int fd) 4445Libev does not offer other language bindings itself, but bindings for a
1928\& : io (this, &myclass::io_cb), 4446number of languages exist in the form of third-party packages. If you know
1929\& idle (this, &myclass::idle_cb) 4447any interesting language binding in addition to the ones listed here, drop
1930\& { 4448me a note.
1931\& io.start (fd, ev::READ); 4449.IP "Perl" 4
1932\& } 4450.IX Item "Perl"
1933.Ve 4451The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4452libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4453there are additional modules that implement libev-compatible interfaces
4454to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4455\&\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
4456and \f(CW\*(C`EV::Glib\*(C'\fR).
4457.Sp
4458It can be found and installed via \s-1CPAN,\s0 its homepage is at
4459<http://software.schmorp.de/pkg/EV>.
4460.IP "Python" 4
4461.IX Item "Python"
4462Python bindings can be found at <http://code.google.com/p/pyev/>. It
4463seems to be quite complete and well-documented.
4464.IP "Ruby" 4
4465.IX Item "Ruby"
4466Tony Arcieri has written a ruby extension that offers access to a subset
4467of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4468more on top of it. It can be found via gem servers. Its homepage is at
4469<http://rev.rubyforge.org/>.
4470.Sp
4471Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4472makes rev work even on mingw.
4473.IP "Haskell" 4
4474.IX Item "Haskell"
4475A haskell binding to libev is available at
4476<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4477.IP "D" 4
4478.IX Item "D"
4479Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4480be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4481.IP "Ocaml" 4
4482.IX Item "Ocaml"
4483Erkki Seppala has written Ocaml bindings for libev, to be found at
4484<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4485.IP "Lua" 4
4486.IX Item "Lua"
4487Brian Maher has written a partial interface to libev for lua (at the
4488time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4489<http://github.com/brimworks/lua\-ev>.
4490.IP "Javascript" 4
4491.IX Item "Javascript"
4492Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4493.IP "Others" 4
4494.IX Item "Others"
4495There are others, and I stopped counting.
1934.SH "MACRO MAGIC" 4496.SH "MACRO MAGIC"
1935.IX Header "MACRO MAGIC" 4497.IX Header "MACRO MAGIC"
1936Libev can be compiled with a variety of options, the most fundemantal is 4498Libev can be compiled with a variety of options, the most fundamental
1937\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and 4499of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
1938callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4500functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1939.PP 4501.PP
1940To make it easier to write programs that cope with either variant, the 4502To make it easier to write programs that cope with either variant, the
1941following macros are defined: 4503following macros are defined:
1942.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4504.ie n .IP """EV_A"", ""EV_A_""" 4
1943.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4505.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
1944.IX Item "EV_A, EV_A_" 4506.IX Item "EV_A, EV_A_"
1945This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4507This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
1946loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4508loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
1947\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4509\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
1948.Sp 4510.Sp
1949.Vb 3 4511.Vb 3
1950\& ev_unref (EV_A); 4512\& ev_unref (EV_A);
1951\& ev_timer_add (EV_A_ watcher); 4513\& ev_timer_add (EV_A_ watcher);
1952\& ev_loop (EV_A_ 0); 4514\& ev_run (EV_A_ 0);
1953.Ve 4515.Ve
1954.Sp 4516.Sp
1955It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4517It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
1956which is often provided by the following macro. 4518which is often provided by the following macro.
1957.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4519.ie n .IP """EV_P"", ""EV_P_""" 4
1958.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4520.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
1959.IX Item "EV_P, EV_P_" 4521.IX Item "EV_P, EV_P_"
1960This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4522This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
1961loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4523loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
1962\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4524\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
1963.Sp 4525.Sp
1964.Vb 2 4526.Vb 2
1965\& // this is how ev_unref is being declared 4527\& // this is how ev_unref is being declared
1966\& static void ev_unref (EV_P); 4528\& static void ev_unref (EV_P);
1967.Ve 4529\&
1968.Sp
1969.Vb 2
1970\& // this is how you can declare your typical callback 4530\& // this is how you can declare your typical callback
1971\& static void cb (EV_P_ ev_timer *w, int revents) 4531\& static void cb (EV_P_ ev_timer *w, int revents)
1972.Ve 4532.Ve
1973.Sp 4533.Sp
1974It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4534It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
1975suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4535suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
1976.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4536.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
1977.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4537.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
1978.IX Item "EV_DEFAULT, EV_DEFAULT_" 4538.IX Item "EV_DEFAULT, EV_DEFAULT_"
1979Similar to the other two macros, this gives you the value of the default 4539Similar to the other two macros, this gives you the value of the default
1980loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4540loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4541will be initialised if it isn't already initialised.
4542.Sp
4543For non-multiplicity builds, these macros do nothing, so you always have
4544to initialise the loop somewhere.
4545.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4546.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4547.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4548Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4549default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4550is undefined when the default loop has not been initialised by a previous
4551execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4552.Sp
4553It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4554watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1981.PP 4555.PP
1982Example: Declare and initialise a check watcher, working regardless of 4556Example: Declare and initialise a check watcher, utilising the above
1983wether multiple loops are supported or not. 4557macros so it will work regardless of whether multiple loops are supported
4558or not.
1984.PP 4559.PP
1985.Vb 5 4560.Vb 5
1986\& static void 4561\& static void
1987\& check_cb (EV_P_ ev_timer *w, int revents) 4562\& check_cb (EV_P_ ev_timer *w, int revents)
1988\& { 4563\& {
1989\& ev_check_stop (EV_A_ w); 4564\& ev_check_stop (EV_A_ w);
1990\& } 4565\& }
1991.Ve 4566\&
1992.PP
1993.Vb 4
1994\& ev_check check; 4567\& ev_check check;
1995\& ev_check_init (&check, check_cb); 4568\& ev_check_init (&check, check_cb);
1996\& ev_check_start (EV_DEFAULT_ &check); 4569\& ev_check_start (EV_DEFAULT_ &check);
1997\& ev_loop (EV_DEFAULT_ 0); 4570\& ev_run (EV_DEFAULT_ 0);
1998.Ve 4571.Ve
1999.SH "EMBEDDING" 4572.SH "EMBEDDING"
2000.IX Header "EMBEDDING" 4573.IX Header "EMBEDDING"
2001Libev can (and often is) directly embedded into host 4574Libev can (and often is) directly embedded into host
2002applications. Examples of applications that embed it include the Deliantra 4575applications. Examples of applications that embed it include the Deliantra
2003Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4576Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2004and rxvt\-unicode. 4577and rxvt-unicode.
2005.PP 4578.PP
2006The goal is to enable you to just copy the neecssary files into your 4579The goal is to enable you to just copy the necessary files into your
2007source directory without having to change even a single line in them, so 4580source directory without having to change even a single line in them, so
2008you can easily upgrade by simply copying (or having a checked-out copy of 4581you can easily upgrade by simply copying (or having a checked-out copy of
2009libev somewhere in your source tree). 4582libev somewhere in your source tree).
2010.Sh "\s-1FILESETS\s0" 4583.SS "\s-1FILESETS\s0"
2011.IX Subsection "FILESETS" 4584.IX Subsection "FILESETS"
2012Depending on what features you need you need to include one or more sets of files 4585Depending on what features you need you need to include one or more sets of files
2013in your app. 4586in your application.
2014.PP 4587.PP
2015\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4588\fI\s-1CORE EVENT LOOP\s0\fR
2016.IX Subsection "CORE EVENT LOOP" 4589.IX Subsection "CORE EVENT LOOP"
2017.PP 4590.PP
2018To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4591To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2019configuration (no autoconf): 4592configuration (no autoconf):
2020.PP 4593.PP
2021.Vb 2 4594.Vb 2
2022\& #define EV_STANDALONE 1 4595\& #define EV_STANDALONE 1
2023\& #include "ev.c" 4596\& #include "ev.c"
2024.Ve 4597.Ve
2025.PP 4598.PP
2026This will automatically include \fIev.h\fR, too, and should be done in a 4599This will automatically include \fIev.h\fR, too, and should be done in a
2027single C source file only to provide the function implementations. To use 4600single C source file only to provide the function implementations. To use
2028it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4601it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2029done by writing a wrapper around \fIev.h\fR that you can include instead and 4602done by writing a wrapper around \fIev.h\fR that you can include instead and
2030where you can put other configuration options): 4603where you can put other configuration options):
2031.PP 4604.PP
2032.Vb 2 4605.Vb 2
2033\& #define EV_STANDALONE 1 4606\& #define EV_STANDALONE 1
2034\& #include "ev.h" 4607\& #include "ev.h"
2035.Ve 4608.Ve
2036.PP 4609.PP
2037Both header files and implementation files can be compiled with a \*(C+ 4610Both header files and implementation files can be compiled with a \*(C+
2038compiler (at least, thats a stated goal, and breakage will be treated 4611compiler (at least, that's a stated goal, and breakage will be treated
2039as a bug). 4612as a bug).
2040.PP 4613.PP
2041You need the following files in your source tree, or in a directory 4614You need the following files in your source tree, or in a directory
2042in your include path (e.g. in libev/ when using \-Ilibev): 4615in your include path (e.g. in libev/ when using \-Ilibev):
2043.PP 4616.PP
2044.Vb 4 4617.Vb 4
2045\& ev.h 4618\& ev.h
2046\& ev.c 4619\& ev.c
2047\& ev_vars.h 4620\& ev_vars.h
2048\& ev_wrap.h 4621\& ev_wrap.h
2049.Ve 4622\&
2050.PP
2051.Vb 1
2052\& ev_win32.c required on win32 platforms only 4623\& ev_win32.c required on win32 platforms only
2053.Ve 4624\&
2054.PP
2055.Vb 5
2056\& ev_select.c only when select backend is enabled (which is by default) 4625\& ev_select.c only when select backend is enabled
2057\& ev_poll.c only when poll backend is enabled (disabled by default) 4626\& ev_poll.c only when poll backend is enabled
2058\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4627\& ev_epoll.c only when the epoll backend is enabled
4628\& ev_linuxaio.c only when the linux aio backend is enabled
4629\& ev_iouring.c only when the linux io_uring backend is enabled
2059\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4630\& ev_kqueue.c only when the kqueue backend is enabled
2060\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4631\& ev_port.c only when the solaris port backend is enabled
2061.Ve 4632.Ve
2062.PP 4633.PP
2063\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4634\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2064to compile this single file. 4635to compile this single file.
2065.PP 4636.PP
2066\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4637\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
2067.IX Subsection "LIBEVENT COMPATIBILITY API" 4638.IX Subsection "LIBEVENT COMPATIBILITY API"
2068.PP 4639.PP
2069To include the libevent compatibility \s-1API\s0, also include: 4640To include the libevent compatibility \s-1API,\s0 also include:
2070.PP 4641.PP
2071.Vb 1 4642.Vb 1
2072\& #include "event.c" 4643\& #include "event.c"
2073.Ve 4644.Ve
2074.PP 4645.PP
2075in the file including \fIev.c\fR, and: 4646in the file including \fIev.c\fR, and:
2076.PP 4647.PP
2077.Vb 1 4648.Vb 1
2078\& #include "event.h" 4649\& #include "event.h"
2079.Ve 4650.Ve
2080.PP 4651.PP
2081in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4652in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
2082.PP 4653.PP
2083You need the following additional files for this: 4654You need the following additional files for this:
2084.PP 4655.PP
2085.Vb 2 4656.Vb 2
2086\& event.h 4657\& event.h
2087\& event.c 4658\& event.c
2088.Ve 4659.Ve
2089.PP 4660.PP
2090\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4661\fI\s-1AUTOCONF SUPPORT\s0\fR
2091.IX Subsection "AUTOCONF SUPPORT" 4662.IX Subsection "AUTOCONF SUPPORT"
2092.PP 4663.PP
2093Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4664Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2094whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4665whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2095\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4666\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2096include \fIconfig.h\fR and configure itself accordingly. 4667include \fIconfig.h\fR and configure itself accordingly.
2097.PP 4668.PP
2098For this of course you need the m4 file: 4669For this of course you need the m4 file:
2099.PP 4670.PP
2100.Vb 1 4671.Vb 1
2101\& libev.m4 4672\& libev.m4
2102.Ve 4673.Ve
2103.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4674.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
2104.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4675.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2105Libev can be configured via a variety of preprocessor symbols you have to define 4676Libev can be configured via a variety of preprocessor symbols you have to
2106before including any of its files. The default is not to build for multiplicity 4677define before including (or compiling) any of its files. The default in
2107and only include the select backend. 4678the absence of autoconf is documented for every option.
4679.PP
4680Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4681values when compiling libev vs. including \fIev.h\fR, so it is permissible
4682to redefine them before including \fIev.h\fR without breaking compatibility
4683to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4684users of libev and the libev code itself must be compiled with compatible
4685settings.
4686.IP "\s-1EV_COMPAT3\s0 (h)" 4
4687.IX Item "EV_COMPAT3 (h)"
4688Backwards compatibility is a major concern for libev. This is why this
4689release of libev comes with wrappers for the functions and symbols that
4690have been renamed between libev version 3 and 4.
4691.Sp
4692You can disable these wrappers (to test compatibility with future
4693versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4694sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4695from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4696typedef in that case.
4697.Sp
4698In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4699and in some even more future version the compatibility code will be
4700removed completely.
2108.IP "\s-1EV_STANDALONE\s0" 4 4701.IP "\s-1EV_STANDALONE\s0 (h)" 4
2109.IX Item "EV_STANDALONE" 4702.IX Item "EV_STANDALONE (h)"
2110Must always be \f(CW1\fR if you do not use autoconf configuration, which 4703Must always be \f(CW1\fR if you do not use autoconf configuration, which
2111keeps libev from including \fIconfig.h\fR, and it also defines dummy 4704keeps libev from including \fIconfig.h\fR, and it also defines dummy
2112implementations for some libevent functions (such as logging, which is not 4705implementations for some libevent functions (such as logging, which is not
2113supported). It will also not define any of the structs usually found in 4706supported). It will also not define any of the structs usually found in
2114\&\fIevent.h\fR that are not directly supported by the libev core alone. 4707\&\fIevent.h\fR that are not directly supported by the libev core alone.
4708.Sp
4709In standalone mode, libev will still try to automatically deduce the
4710configuration, but has to be more conservative.
4711.IP "\s-1EV_USE_FLOOR\s0" 4
4712.IX Item "EV_USE_FLOOR"
4713If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4714periodic reschedule calculations, otherwise libev will fall back on a
4715portable (slower) implementation. If you enable this, you usually have to
4716link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4717function is not available will fail, so the safe default is to not enable
4718this.
2115.IP "\s-1EV_USE_MONOTONIC\s0" 4 4719.IP "\s-1EV_USE_MONOTONIC\s0" 4
2116.IX Item "EV_USE_MONOTONIC" 4720.IX Item "EV_USE_MONOTONIC"
2117If defined to be \f(CW1\fR, libev will try to detect the availability of the 4721If defined to be \f(CW1\fR, libev will try to detect the availability of the
2118monotonic clock option at both compiletime and runtime. Otherwise no use 4722monotonic clock option at both compile time and runtime. Otherwise no
2119of the monotonic clock option will be attempted. If you enable this, you 4723use of the monotonic clock option will be attempted. If you enable this,
2120usually have to link against librt or something similar. Enabling it when 4724you usually have to link against librt or something similar. Enabling it
2121the functionality isn't available is safe, though, althoguh you have 4725when the functionality isn't available is safe, though, although you have
2122to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4726to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2123function is hiding in (often \fI\-lrt\fR). 4727function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2124.IP "\s-1EV_USE_REALTIME\s0" 4 4728.IP "\s-1EV_USE_REALTIME\s0" 4
2125.IX Item "EV_USE_REALTIME" 4729.IX Item "EV_USE_REALTIME"
2126If defined to be \f(CW1\fR, libev will try to detect the availability of the 4730If defined to be \f(CW1\fR, libev will try to detect the availability of the
2127realtime clock option at compiletime (and assume its availability at 4731real-time clock option at compile time (and assume its availability
2128runtime if successful). Otherwise no use of the realtime clock option will 4732at runtime if successful). Otherwise no use of the real-time clock
2129be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4733option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2130(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4734by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2131in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4735correctness. See the note about libraries in the description of
4736\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4737\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4738.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4739.IX Item "EV_USE_CLOCK_SYSCALL"
4740If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4741of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4742exists 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
4743unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4744programs needlessly. Using a direct syscall is slightly slower (in
4745theory), because no optimised vdso implementation can be used, but avoids
4746the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4747higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4748.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4749.IX Item "EV_USE_NANOSLEEP"
4750If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4751and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4752.IP "\s-1EV_USE_EVENTFD\s0" 4
4753.IX Item "EV_USE_EVENTFD"
4754If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4755available and will probe for kernel support at runtime. This will improve
4756\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4757If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47582.7 or newer, otherwise disabled.
2132.IP "\s-1EV_USE_SELECT\s0" 4 4759.IP "\s-1EV_USE_SELECT\s0" 4
2133.IX Item "EV_USE_SELECT" 4760.IX Item "EV_USE_SELECT"
2134If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4761If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2135\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4762\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2136other method takes over, select will be it. Otherwise the select backend 4763other method takes over, select will be it. Otherwise the select backend
2137will not be compiled in. 4764will not be compiled in.
2138.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4765.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2139.IX Item "EV_SELECT_USE_FD_SET" 4766.IX Item "EV_SELECT_USE_FD_SET"
2140If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4767If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2141structure. This is useful if libev doesn't compile due to a missing 4768structure. This is useful if libev doesn't compile due to a missing
2142\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4769\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2143exotic systems. This usually limits the range of file descriptors to some 4770on exotic systems. This usually limits the range of file descriptors to
2144low limit such as 1024 or might have other limitations (winsocket only 4771some low limit such as 1024 or might have other limitations (winsocket
2145allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4772only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2146influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4773configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2147.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4774.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2148.IX Item "EV_SELECT_IS_WINSOCKET" 4775.IX Item "EV_SELECT_IS_WINSOCKET"
2149When defined to \f(CW1\fR, the select backend will assume that 4776When defined to \f(CW1\fR, the select backend will assume that
2150select/socket/connect etc. don't understand file descriptors but 4777select/socket/connect etc. don't understand file descriptors but
2151wants osf handles on win32 (this is the case when the select to 4778wants osf handles on win32 (this is the case when the select to
2152be used is the winsock select). This means that it will call 4779be used is the winsock select). This means that it will call
2153\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4780\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2154it is assumed that all these functions actually work on fds, even 4781it is assumed that all these functions actually work on fds, even
2155on win32. Should not be defined on non\-win32 platforms. 4782on win32. Should not be defined on non\-win32 platforms.
4783.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4784.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4785If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4786file descriptors to socket handles. When not defining this symbol (the
4787default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4788correct. In some cases, programs use their own file descriptor management,
4789in which case they can provide this function to map fds to socket handles.
4790.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4791.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4792If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4793using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4794their own fd to handle mapping, overwriting this function makes it easier
4795to do so. This can be done by defining this macro to an appropriate value.
4796.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4797.IX Item "EV_WIN32_CLOSE_FD(fd)"
4798If programs implement their own fd to handle mapping on win32, then this
4799macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4800file descriptors again. Note that the replacement function has to close
4801the underlying \s-1OS\s0 handle.
4802.IP "\s-1EV_USE_WSASOCKET\s0" 4
4803.IX Item "EV_USE_WSASOCKET"
4804If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4805communication socket, which works better in some environments. Otherwise,
4806the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4807environments.
2156.IP "\s-1EV_USE_POLL\s0" 4 4808.IP "\s-1EV_USE_POLL\s0" 4
2157.IX Item "EV_USE_POLL" 4809.IX Item "EV_USE_POLL"
2158If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4810If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2159backend. Otherwise it will be enabled on non\-win32 platforms. It 4811backend. Otherwise it will be enabled on non\-win32 platforms. It
2160takes precedence over select. 4812takes precedence over select.
2161.IP "\s-1EV_USE_EPOLL\s0" 4 4813.IP "\s-1EV_USE_EPOLL\s0" 4
2162.IX Item "EV_USE_EPOLL" 4814.IX Item "EV_USE_EPOLL"
2163If defined to be \f(CW1\fR, libev will compile in support for the Linux 4815If defined to be \f(CW1\fR, libev will compile in support for the Linux
2164\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4816\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2165otherwise another method will be used as fallback. This is the 4817otherwise another method will be used as fallback. This is the preferred
2166preferred backend for GNU/Linux systems. 4818backend for GNU/Linux systems. If undefined, it will be enabled if the
4819headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4820.IP "\s-1EV_USE_LINUXAIO\s0" 4
4821.IX Item "EV_USE_LINUXAIO"
4822If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4823backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4824enabled on linux, otherwise disabled.
4825.IP "\s-1EV_USE_IOURING\s0" 4
4826.IX Item "EV_USE_IOURING"
4827If defined to be \f(CW1\fR, libev will compile in support for the Linux
4828io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4829current limitations it has to be requested explicitly. If undefined, it
4830will be enabled on linux, otherwise disabled.
2167.IP "\s-1EV_USE_KQUEUE\s0" 4 4831.IP "\s-1EV_USE_KQUEUE\s0" 4
2168.IX Item "EV_USE_KQUEUE" 4832.IX Item "EV_USE_KQUEUE"
2169If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4833If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2170\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4834\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2171otherwise another method will be used as fallback. This is the preferred 4835otherwise another method will be used as fallback. This is the preferred
… …
218110 port style backend. Its availability will be detected at runtime, 484510 port style backend. Its availability will be detected at runtime,
2182otherwise another method will be used as fallback. This is the preferred 4846otherwise another method will be used as fallback. This is the preferred
2183backend for Solaris 10 systems. 4847backend for Solaris 10 systems.
2184.IP "\s-1EV_USE_DEVPOLL\s0" 4 4848.IP "\s-1EV_USE_DEVPOLL\s0" 4
2185.IX Item "EV_USE_DEVPOLL" 4849.IX Item "EV_USE_DEVPOLL"
2186reserved for future expansion, works like the \s-1USE\s0 symbols above. 4850Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2187.IP "\s-1EV_USE_INOTIFY\s0" 4 4851.IP "\s-1EV_USE_INOTIFY\s0" 4
2188.IX Item "EV_USE_INOTIFY" 4852.IX Item "EV_USE_INOTIFY"
2189If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4853If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2190interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 4854interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2191be detected at runtime. 4855be detected at runtime. If undefined, it will be enabled if the headers
4856indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4857.IP "\s-1EV_NO_SMP\s0" 4
4858.IX Item "EV_NO_SMP"
4859If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4860between threads, that is, threads can be used, but threads never run on
4861different cpus (or different cpu cores). This reduces dependencies
4862and makes libev faster.
4863.IP "\s-1EV_NO_THREADS\s0" 4
4864.IX Item "EV_NO_THREADS"
4865If defined to be \f(CW1\fR, libev will assume that it will never be called from
4866different threads (that includes signal handlers), which is a stronger
4867assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4868libev faster.
4869.IP "\s-1EV_ATOMIC_T\s0" 4
4870.IX Item "EV_ATOMIC_T"
4871Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4872access is atomic with respect to other threads or signal contexts. No
4873such type is easily found in the C language, so you can provide your own
4874type that you know is safe for your purposes. It is used both for signal
4875handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4876watchers.
4877.Sp
4878In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4879(from \fIsignal.h\fR), which is usually good enough on most platforms.
2192.IP "\s-1EV_H\s0" 4 4880.IP "\s-1EV_H\s0 (h)" 4
2193.IX Item "EV_H" 4881.IX Item "EV_H (h)"
2194The name of the \fIev.h\fR header file used to include it. The default if 4882The name of the \fIev.h\fR header file used to include it. The default if
2195undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4883undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2196can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4884used to virtually rename the \fIev.h\fR header file in case of conflicts.
2197.IP "\s-1EV_CONFIG_H\s0" 4 4885.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2198.IX Item "EV_CONFIG_H" 4886.IX Item "EV_CONFIG_H (h)"
2199If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4887If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2200\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4888\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2201\&\f(CW\*(C`EV_H\*(C'\fR, above. 4889\&\f(CW\*(C`EV_H\*(C'\fR, above.
2202.IP "\s-1EV_EVENT_H\s0" 4 4890.IP "\s-1EV_EVENT_H\s0 (h)" 4
2203.IX Item "EV_EVENT_H" 4891.IX Item "EV_EVENT_H (h)"
2204Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4892Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2205of how the \fIevent.h\fR header can be found. 4893of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2206.IP "\s-1EV_PROTOTYPES\s0" 4 4894.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2207.IX Item "EV_PROTOTYPES" 4895.IX Item "EV_PROTOTYPES (h)"
2208If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4896If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2209prototypes, but still define all the structs and other symbols. This is 4897prototypes, but still define all the structs and other symbols. This is
2210occasionally useful if you want to provide your own wrapper functions 4898occasionally useful if you want to provide your own wrapper functions
2211around libev functions. 4899around libev functions.
2212.IP "\s-1EV_MULTIPLICITY\s0" 4 4900.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2214If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4902If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2215will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4903will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2216additional independent event loops. Otherwise there will be no support 4904additional independent event loops. Otherwise there will be no support
2217for multiple event loops and there is no first event loop pointer 4905for multiple event loops and there is no first event loop pointer
2218argument. Instead, all functions act on the single default loop. 4906argument. Instead, all functions act on the single default loop.
2219.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4907.Sp
2220.IX Item "EV_PERIODIC_ENABLE" 4908Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
2221If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4909default loop when multiplicity is switched off \- you always have to
2222defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4910initialise the loop manually in this case.
2223code.
2224.IP "\s-1EV_EMBED_ENABLE\s0" 4
2225.IX Item "EV_EMBED_ENABLE"
2226If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2227defined to be \f(CW0\fR, then they are not.
2228.IP "\s-1EV_STAT_ENABLE\s0" 4
2229.IX Item "EV_STAT_ENABLE"
2230If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2231defined to be \f(CW0\fR, then they are not.
2232.IP "\s-1EV_FORK_ENABLE\s0" 4
2233.IX Item "EV_FORK_ENABLE"
2234If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2235defined to be \f(CW0\fR, then they are not.
2236.IP "\s-1EV_MINIMAL\s0" 4 4911.IP "\s-1EV_MINPRI\s0" 4
2237.IX Item "EV_MINIMAL" 4912.IX Item "EV_MINPRI"
4913.PD 0
4914.IP "\s-1EV_MAXPRI\s0" 4
4915.IX Item "EV_MAXPRI"
4916.PD
4917The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4918\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4919provide for more priorities by overriding those symbols (usually defined
4920to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4921.Sp
4922When doing priority-based operations, libev usually has to linearly search
4923all the priorities, so having many of them (hundreds) uses a lot of space
4924and time, so using the defaults of five priorities (\-2 .. +2) is usually
4925fine.
4926.Sp
4927If your embedding application does not need any priorities, defining these
4928both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4929.IP "\s-1EV_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.\s0" 4
4930.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."
4931If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4932the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4933is not. Disabling watcher types mainly saves code size.
4934.IP "\s-1EV_FEATURES\s0" 4
4935.IX Item "EV_FEATURES"
2238If you need to shave off some kilobytes of code at the expense of some 4936If you need to shave off some kilobytes of code at the expense of some
2239speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4937speed (but with the full \s-1API\s0), you can define this symbol to request
2240some inlining decisions, saves roughly 30% codesize of amd64. 4938certain subsets of functionality. The default is to enable all features
4939that can be enabled on the platform.
4940.Sp
4941A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4942with some broad features you want) and then selectively re-enable
4943additional parts you want, for example if you want everything minimal,
4944but multiple event loop support, async and child watchers and the poll
4945backend, use this:
4946.Sp
4947.Vb 5
4948\& #define EV_FEATURES 0
4949\& #define EV_MULTIPLICITY 1
4950\& #define EV_USE_POLL 1
4951\& #define EV_CHILD_ENABLE 1
4952\& #define EV_ASYNC_ENABLE 1
4953.Ve
4954.Sp
4955The actual value is a bitset, it can be a combination of the following
4956values (by default, all of these are enabled):
4957.RS 4
4958.ie n .IP "1 \- faster/larger code" 4
4959.el .IP "\f(CW1\fR \- faster/larger code" 4
4960.IX Item "1 - faster/larger code"
4961Use larger code to speed up some operations.
4962.Sp
4963Currently this is used to override some inlining decisions (enlarging the
4964code size by roughly 30% on amd64).
4965.Sp
4966When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4967gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4968assertions.
4969.Sp
4970The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4971(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4972.ie n .IP "2 \- faster/larger data structures" 4
4973.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4974.IX Item "2 - faster/larger data structures"
4975Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4976hash table sizes and so on. This will usually further increase code size
4977and can additionally have an effect on the size of data structures at
4978runtime.
4979.Sp
4980The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4981(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4982.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4983.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4984.IX Item "4 - full API configuration"
4985This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4986enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4987.ie n .IP "8 \- full \s-1API\s0" 4
4988.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4989.IX Item "8 - full API"
4990This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4991details on which parts of the \s-1API\s0 are still available without this
4992feature, and do not complain if this subset changes over time.
4993.ie n .IP "16 \- enable all optional watcher types" 4
4994.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4995.IX Item "16 - enable all optional watcher types"
4996Enables all optional watcher types. If you want to selectively enable
4997only some watcher types other than I/O and timers (e.g. prepare,
4998embed, async, child...) you can enable them manually by defining
4999\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5000.ie n .IP "32 \- enable all backends" 4
5001.el .IP "\f(CW32\fR \- enable all backends" 4
5002.IX Item "32 - enable all backends"
5003This enables all backends \- without this feature, you need to enable at
5004least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5005.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5006.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5007.IX Item "64 - enable OS-specific helper APIs"
5008Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5009default.
5010.RE
5011.RS 4
5012.Sp
5013Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5014reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5015code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5016watchers, timers and monotonic clock support.
5017.Sp
5018With an intelligent-enough linker (gcc+binutils are intelligent enough
5019when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5020your program might be left out as well \- a binary starting a timer and an
5021I/O watcher then might come out at only 5Kb.
5022.RE
5023.IP "\s-1EV_API_STATIC\s0" 4
5024.IX Item "EV_API_STATIC"
5025If this symbol is defined (by default it is not), then all identifiers
5026will have static linkage. This means that libev will not export any
5027identifiers, and you cannot link against libev anymore. This can be useful
5028when you embed libev, only want to use libev functions in a single file,
5029and do not want its identifiers to be visible.
5030.Sp
5031To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5032wants to use libev.
5033.Sp
5034This option only works when libev is compiled with a C compiler, as \*(C+
5035doesn't support the required declaration syntax.
5036.IP "\s-1EV_AVOID_STDIO\s0" 4
5037.IX Item "EV_AVOID_STDIO"
5038If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5039functions (printf, scanf, perror etc.). This will increase the code size
5040somewhat, but if your program doesn't otherwise depend on stdio and your
5041libc allows it, this avoids linking in the stdio library which is quite
5042big.
5043.Sp
5044Note that error messages might become less precise when this option is
5045enabled.
5046.IP "\s-1EV_NSIG\s0" 4
5047.IX Item "EV_NSIG"
5048The highest supported signal number, +1 (or, the number of
5049signals): Normally, libev tries to deduce the maximum number of signals
5050automatically, but sometimes this fails, in which case it can be
5051specified. Also, using a lower number than detected (\f(CW32\fR should be
5052good for about any system in existence) can save some memory, as libev
5053statically allocates some 12\-24 bytes per signal number.
2241.IP "\s-1EV_PID_HASHSIZE\s0" 4 5054.IP "\s-1EV_PID_HASHSIZE\s0" 4
2242.IX Item "EV_PID_HASHSIZE" 5055.IX Item "EV_PID_HASHSIZE"
2243\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 5056\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2244pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 5057pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2245than enough. If you need to manage thousands of children you might want to 5058usually more than enough. If you need to manage thousands of children you
2246increase this value (\fImust\fR be a power of two). 5059might want to increase this value (\fImust\fR be a power of two).
2247.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 5060.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2248.IX Item "EV_INOTIFY_HASHSIZE" 5061.IX Item "EV_INOTIFY_HASHSIZE"
2249\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 5062\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2250inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 5063inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
2251usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 5064disabled), usually more than enough. If you need to manage thousands of
2252watchers you might want to increase this value (\fImust\fR be a power of 5065\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2253two). 5066power of two).
5067.IP "\s-1EV_USE_4HEAP\s0" 4
5068.IX Item "EV_USE_4HEAP"
5069Heaps are not very cache-efficient. To improve the cache-efficiency of the
5070timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5071to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5072faster performance with many (thousands) of watchers.
5073.Sp
5074The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5075will be \f(CW0\fR.
5076.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5077.IX Item "EV_HEAP_CACHE_AT"
5078Heaps are not very cache-efficient. To improve the cache-efficiency of the
5079timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5080the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5081which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5082but avoids random read accesses on heap changes. This improves performance
5083noticeably with many (hundreds) of watchers.
5084.Sp
5085The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5086will be \f(CW0\fR.
5087.IP "\s-1EV_VERIFY\s0" 4
5088.IX Item "EV_VERIFY"
5089Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5090be done: If set to \f(CW0\fR, no internal verification code will be compiled
5091in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5092called. If set to \f(CW2\fR, then the internal verification code will be
5093called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5094verification code will be called very frequently, which will slow down
5095libev considerably.
5096.Sp
5097Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5098disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5099.Sp
5100The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5101will be \f(CW0\fR.
2254.IP "\s-1EV_COMMON\s0" 4 5102.IP "\s-1EV_COMMON\s0" 4
2255.IX Item "EV_COMMON" 5103.IX Item "EV_COMMON"
2256By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5104By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2257this macro to a something else you can include more and other types of 5105this macro to something else you can include more and other types of
2258members. You have to define it each time you include one of the files, 5106members. You have to define it each time you include one of the files,
2259though, and it must be identical each time. 5107though, and it must be identical each time.
2260.Sp 5108.Sp
2261For example, the perl \s-1EV\s0 module uses something like this: 5109For example, the perl \s-1EV\s0 module uses something like this:
2262.Sp 5110.Sp
2263.Vb 3 5111.Vb 3
2264\& #define EV_COMMON \e 5112\& #define EV_COMMON \e
2265\& SV *self; /* contains this struct */ \e 5113\& SV *self; /* contains this struct */ \e
2266\& SV *cb_sv, *fh /* note no trailing ";" */ 5114\& SV *cb_sv, *fh /* note no trailing ";" */
2267.Ve 5115.Ve
2268.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5116.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2269.IX Item "EV_CB_DECLARE (type)" 5117.IX Item "EV_CB_DECLARE (type)"
2270.PD 0 5118.PD 0
2271.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5119.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2273.IP "ev_set_cb (ev, cb)" 4 5121.IP "ev_set_cb (ev, cb)" 4
2274.IX Item "ev_set_cb (ev, cb)" 5122.IX Item "ev_set_cb (ev, cb)"
2275.PD 5123.PD
2276Can be used to change the callback member declaration in each watcher, 5124Can be used to change the callback member declaration in each watcher,
2277and the way callbacks are invoked and set. Must expand to a struct member 5125and the way callbacks are invoked and set. Must expand to a struct member
2278definition and a statement, respectively. See the \fIev.v\fR header file for 5126definition and a statement, respectively. See the \fIev.h\fR header file for
2279their default definitions. One possible use for overriding these is to 5127their default definitions. One possible use for overriding these is to
2280avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5128avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2281method calls instead of plain function calls in \*(C+. 5129method calls instead of plain function calls in \*(C+.
5130.SS "\s-1EXPORTED API SYMBOLS\s0"
5131.IX Subsection "EXPORTED API SYMBOLS"
5132If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5133exported symbols, you can use the provided \fISymbol.*\fR files which list
5134all public symbols, one per line:
5135.PP
5136.Vb 2
5137\& Symbols.ev for libev proper
5138\& Symbols.event for the libevent emulation
5139.Ve
5140.PP
5141This can also be used to rename all public symbols to avoid clashes with
5142multiple versions of libev linked together (which is obviously bad in
5143itself, but sometimes it is inconvenient to avoid this).
5144.PP
5145A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5146include before including \fIev.h\fR:
5147.PP
5148.Vb 1
5149\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5150.Ve
5151.PP
5152This would create a file \fIwrap.h\fR which essentially looks like this:
5153.PP
5154.Vb 4
5155\& #define ev_backend myprefix_ev_backend
5156\& #define ev_check_start myprefix_ev_check_start
5157\& #define ev_check_stop myprefix_ev_check_stop
5158\& ...
5159.Ve
2282.Sh "\s-1EXAMPLES\s0" 5160.SS "\s-1EXAMPLES\s0"
2283.IX Subsection "EXAMPLES" 5161.IX Subsection "EXAMPLES"
2284For a real-world example of a program the includes libev 5162For a real-world example of a program the includes libev
2285verbatim, you can have a look at the \s-1EV\s0 perl module 5163verbatim, you can have a look at the \s-1EV\s0 perl module
2286(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5164(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2287the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5165the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2288interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5166interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2289will be compiled. It is pretty complex because it provides its own header 5167will be compiled. It is pretty complex because it provides its own header
2290file. 5168file.
2291.Sp 5169.PP
2292The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5170The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2293that everybody includes and which overrides some autoconf choices: 5171that everybody includes and which overrides some configure choices:
2294.Sp 5172.PP
2295.Vb 4 5173.Vb 8
5174\& #define EV_FEATURES 8
5175\& #define EV_USE_SELECT 1
5176\& #define EV_PREPARE_ENABLE 1
5177\& #define EV_IDLE_ENABLE 1
5178\& #define EV_SIGNAL_ENABLE 1
5179\& #define EV_CHILD_ENABLE 1
2296\& #define EV_USE_POLL 0 5180\& #define EV_USE_STDEXCEPT 0
2297\& #define EV_MULTIPLICITY 0
2298\& #define EV_PERIODICS 0
2299\& #define EV_CONFIG_H <config.h> 5181\& #define EV_CONFIG_H <config.h>
2300.Ve 5182\&
2301.Sp
2302.Vb 1
2303\& #include "ev++.h" 5183\& #include "ev++.h"
2304.Ve 5184.Ve
2305.Sp 5185.PP
2306And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5186And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2307.Sp 5187.PP
2308.Vb 2 5188.Vb 2
2309\& #include "ev_cpp.h" 5189\& #include "ev_cpp.h"
2310\& #include "ev.c" 5190\& #include "ev.c"
2311.Ve 5191.Ve
5192.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5193.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5194.SS "\s-1THREADS AND COROUTINES\s0"
5195.IX Subsection "THREADS AND COROUTINES"
5196\fI\s-1THREADS\s0\fR
5197.IX Subsection "THREADS"
5198.PP
5199All libev functions are reentrant and thread-safe unless explicitly
5200documented otherwise, but libev implements no locking itself. This means
5201that you can use as many loops as you want in parallel, as long as there
5202are no concurrent calls into any libev function with the same loop
5203parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5204of course): libev guarantees that different event loops share no data
5205structures that need any locking.
5206.PP
5207Or to put it differently: calls with different loop parameters can be done
5208concurrently from multiple threads, calls with the same loop parameter
5209must be done serially (but can be done from different threads, as long as
5210only one thread ever is inside a call at any point in time, e.g. by using
5211a mutex per loop).
5212.PP
5213Specifically to support threads (and signal handlers), libev implements
5214so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5215concurrency on the same event loop, namely waking it up \*(L"from the
5216outside\*(R".
5217.PP
5218If you want to know which design (one loop, locking, or multiple loops
5219without or something else still) is best for your problem, then I cannot
5220help you, but here is some generic advice:
5221.IP "\(bu" 4
5222most applications have a main thread: use the default libev loop
5223in that thread, or create a separate thread running only the default loop.
5224.Sp
5225This helps integrating other libraries or software modules that use libev
5226themselves and don't care/know about threading.
5227.IP "\(bu" 4
5228one loop per thread is usually a good model.
5229.Sp
5230Doing this is almost never wrong, sometimes a better-performance model
5231exists, but it is always a good start.
5232.IP "\(bu" 4
5233other models exist, such as the leader/follower pattern, where one
5234loop is handed through multiple threads in a kind of round-robin fashion.
5235.Sp
5236Choosing a model is hard \- look around, learn, know that usually you can do
5237better than you currently do :\-)
5238.IP "\(bu" 4
5239often you need to talk to some other thread which blocks in the
5240event loop.
5241.Sp
5242\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5243(or from signal contexts...).
5244.Sp
5245An example use would be to communicate signals or other events that only
5246work in the default loop by registering the signal watcher with the
5247default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5248watcher callback into the event loop interested in the signal.
5249.PP
5250See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5251.PP
5252\fI\s-1COROUTINES\s0\fR
5253.IX Subsection "COROUTINES"
5254.PP
5255Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5256libev fully supports nesting calls to its functions from different
5257coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5258different coroutines, and switch freely between both coroutines running
5259the loop, as long as you don't confuse yourself). The only exception is
5260that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5261.PP
5262Care has been taken to ensure that libev does not keep local state inside
5263\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5264they do not call any callbacks.
5265.SS "\s-1COMPILER WARNINGS\s0"
5266.IX Subsection "COMPILER WARNINGS"
5267Depending on your compiler and compiler settings, you might get no or a
5268lot of warnings when compiling libev code. Some people are apparently
5269scared by this.
5270.PP
5271However, these are unavoidable for many reasons. For one, each compiler
5272has different warnings, and each user has different tastes regarding
5273warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5274targeting a specific compiler and compiler-version.
5275.PP
5276Another reason is that some compiler warnings require elaborate
5277workarounds, or other changes to the code that make it less clear and less
5278maintainable.
5279.PP
5280And of course, some compiler warnings are just plain stupid, or simply
5281wrong (because they don't actually warn about the condition their message
5282seems to warn about). For example, certain older gcc versions had some
5283warnings that resulted in an extreme number of false positives. These have
5284been fixed, but some people still insist on making code warn-free with
5285such buggy versions.
5286.PP
5287While libev is written to generate as few warnings as possible,
5288\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5289with any compiler warnings enabled unless you are prepared to cope with
5290them (e.g. by ignoring them). Remember that warnings are just that:
5291warnings, not errors, or proof of bugs.
5292.SS "\s-1VALGRIND\s0"
5293.IX Subsection "VALGRIND"
5294Valgrind has a special section here because it is a popular tool that is
5295highly useful. Unfortunately, valgrind reports are very hard to interpret.
5296.PP
5297If you think you found a bug (memory leak, uninitialised data access etc.)
5298in libev, then check twice: If valgrind reports something like:
5299.PP
5300.Vb 3
5301\& ==2274== definitely lost: 0 bytes in 0 blocks.
5302\& ==2274== possibly lost: 0 bytes in 0 blocks.
5303\& ==2274== still reachable: 256 bytes in 1 blocks.
5304.Ve
5305.PP
5306Then there is no memory leak, just as memory accounted to global variables
5307is not a memleak \- the memory is still being referenced, and didn't leak.
5308.PP
5309Similarly, under some circumstances, valgrind might report kernel bugs
5310as if it were a bug in libev (e.g. in realloc or in the poll backend,
5311although an acceptable workaround has been found here), or it might be
5312confused.
5313.PP
5314Keep in mind that valgrind is a very good tool, but only a tool. Don't
5315make it into some kind of religion.
5316.PP
5317If you are unsure about something, feel free to contact the mailing list
5318with the full valgrind report and an explanation on why you think this
5319is a bug in libev (best check the archives, too :). However, don't be
5320annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5321of learning how to interpret valgrind properly.
5322.PP
5323If you need, for some reason, empty reports from valgrind for your project
5324I suggest using suppression lists.
5325.SH "PORTABILITY NOTES"
5326.IX Header "PORTABILITY NOTES"
5327.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5328.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5329GNU/Linux is the only common platform that supports 64 bit file/large file
5330interfaces but \fIdisables\fR them by default.
5331.PP
5332That means that libev compiled in the default environment doesn't support
5333files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5334.PP
5335Unfortunately, many programs try to work around this GNU/Linux issue
5336by enabling the large file \s-1API,\s0 which makes them incompatible with the
5337standard libev compiled for their system.
5338.PP
5339Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5340suddenly make it incompatible to the default compile time environment,
5341i.e. all programs not using special compile switches.
5342.SS "\s-1OS/X AND DARWIN BUGS\s0"
5343.IX Subsection "OS/X AND DARWIN BUGS"
5344The whole thing is a bug if you ask me \- basically any system interface
5345you touch is broken, whether it is locales, poll, kqueue or even the
5346OpenGL drivers.
5347.PP
5348\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5349.IX Subsection "kqueue is buggy"
5350.PP
5351The kqueue syscall is broken in all known versions \- most versions support
5352only sockets, many support pipes.
5353.PP
5354Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5355rotten platform, but of course you can still ask for it when creating a
5356loop \- embedding a socket-only kqueue loop into a select-based one is
5357probably going to work well.
5358.PP
5359\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5360.IX Subsection "poll is buggy"
5361.PP
5362Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5363implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5364release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5365.PP
5366Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5367this rotten platform, but of course you can still ask for it when creating
5368a loop.
5369.PP
5370\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5371.IX Subsection "select is buggy"
5372.PP
5373All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5374one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5375descriptors you can pass in to 1024 \- your program suddenly crashes when
5376you use more.
5377.PP
5378There is an undocumented \*(L"workaround\*(R" for this \- defining
5379\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5380work on \s-1OS/X.\s0
5381.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5382.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5383\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5384.IX Subsection "errno reentrancy"
5385.PP
5386The default compile environment on Solaris is unfortunately so
5387thread-unsafe that you can't even use components/libraries compiled
5388without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5389defined by default. A valid, if stupid, implementation choice.
5390.PP
5391If you want to use libev in threaded environments you have to make sure
5392it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5393.PP
5394\fIEvent port backend\fR
5395.IX Subsection "Event port backend"
5396.PP
5397The scalable event interface for Solaris is called \*(L"event
5398ports\*(R". Unfortunately, this mechanism is very buggy in all major
5399releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5400a large number of spurious wakeups, make sure you have all the relevant
5401and latest kernel patches applied. No, I don't know which ones, but there
5402are multiple ones to apply, and afterwards, event ports actually work
5403great.
5404.PP
5405If you can't get it to work, you can try running the program by setting
5406the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5407\&\f(CW\*(C`select\*(C'\fR backends.
5408.SS "\s-1AIX POLL BUG\s0"
5409.IX Subsection "AIX POLL BUG"
5410\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5411this by trying to avoid the poll backend altogether (i.e. it's not even
5412compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5413with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5414.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5415.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5416\fIGeneral issues\fR
5417.IX Subsection "General issues"
5418.PP
5419Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5420requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5421model. Libev still offers limited functionality on this platform in
5422the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5423descriptors. This only applies when using Win32 natively, not when using
5424e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5425as every compiler comes with a slightly differently broken/incompatible
5426environment.
5427.PP
5428Lifting these limitations would basically require the full
5429re-implementation of the I/O system. If you are into this kind of thing,
5430then note that glib does exactly that for you in a very portable way (note
5431also that glib is the slowest event library known to man).
5432.PP
5433There is no supported compilation method available on windows except
5434embedding it into other applications.
5435.PP
5436Sensible signal handling is officially unsupported by Microsoft \- libev
5437tries its best, but under most conditions, signals will simply not work.
5438.PP
5439Not a libev limitation but worth mentioning: windows apparently doesn't
5440accept large writes: instead of resulting in a partial write, windows will
5441either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5442so make sure you only write small amounts into your sockets (less than a
5443megabyte seems safe, but this apparently depends on the amount of memory
5444available).
5445.PP
5446Due to the many, low, and arbitrary limits on the win32 platform and
5447the abysmal performance of winsockets, using a large number of sockets
5448is not recommended (and not reasonable). If your program needs to use
5449more than a hundred or so sockets, then likely it needs to use a totally
5450different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5451notification model, which cannot be implemented efficiently on windows
5452(due to Microsoft monopoly games).
5453.PP
5454A typical way to use libev under windows is to embed it (see the embedding
5455section for details) and use the following \fIevwrap.h\fR header file instead
5456of \fIev.h\fR:
5457.PP
5458.Vb 2
5459\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5460\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5461\&
5462\& #include "ev.h"
5463.Ve
5464.PP
5465And compile the following \fIevwrap.c\fR file into your project (make sure
5466you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5467.PP
5468.Vb 2
5469\& #include "evwrap.h"
5470\& #include "ev.c"
5471.Ve
5472.PP
5473\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5474.IX Subsection "The winsocket select function"
5475.PP
5476The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5477requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5478also extremely buggy). This makes select very inefficient, and also
5479requires a mapping from file descriptors to socket handles (the Microsoft
5480C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5481discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5482\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5483.PP
5484The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5485libraries and raw winsocket select is:
5486.PP
5487.Vb 2
5488\& #define EV_USE_SELECT 1
5489\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5490.Ve
5491.PP
5492Note that winsockets handling of fd sets is O(n), so you can easily get a
5493complexity in the O(nX) range when using win32.
5494.PP
5495\fILimited number of file descriptors\fR
5496.IX Subsection "Limited number of file descriptors"
5497.PP
5498Windows has numerous arbitrary (and low) limits on things.
5499.PP
5500Early versions of winsocket's select only supported waiting for a maximum
5501of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5502can only wait for \f(CW64\fR things at the same time internally; Microsoft
5503recommends spawning a chain of threads and wait for 63 handles and the
5504previous thread in each. Sounds great!).
5505.PP
5506Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5507to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5508call (which might be in libev or elsewhere, for example, perl and many
5509other interpreters do their own select emulation on windows).
5510.PP
5511Another limit is the number of file descriptors in the Microsoft runtime
5512libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5513fetish or something like this inside Microsoft). You can increase this
5514by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5515(another arbitrary limit), but is broken in many versions of the Microsoft
5516runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5517(depending on windows version and/or the phase of the moon). To get more,
5518you need to wrap all I/O functions and provide your own fd management, but
5519the cost of calling select (O(nX)) will likely make this unworkable.
5520.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5521.IX Subsection "PORTABILITY REQUIREMENTS"
5522In addition to a working ISO-C implementation and of course the
5523backend-specific APIs, libev relies on a few additional extensions:
5524.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5525.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5526.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5527Libev assumes not only that all watcher pointers have the same internal
5528structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5529assumes that the same (machine) code can be used to call any watcher
5530callback: The watcher callbacks have different type signatures, but libev
5531calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5532.IP "null pointers and integer zero are represented by 0 bytes" 4
5533.IX Item "null pointers and integer zero are represented by 0 bytes"
5534Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5535relies on this setting pointers and integers to null.
5536.IP "pointer accesses must be thread-atomic" 4
5537.IX Item "pointer accesses must be thread-atomic"
5538Accessing a pointer value must be atomic, it must both be readable and
5539writable in one piece \- this is the case on all current architectures.
5540.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5541.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5542.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5543The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5544\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5545threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5546believed to be sufficiently portable.
5547.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5548.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5549.IX Item "sigprocmask must work in a threaded environment"
5550Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5551allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5552pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5553thread\*(R" or will block signals process-wide, both behaviours would
5554be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5555\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5556.Sp
5557The most portable way to handle signals is to block signals in all threads
5558except the initial one, and run the signal handling loop in the initial
5559thread as well.
5560.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5561.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5562.IX Item "long must be large enough for common memory allocation sizes"
5563To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5564instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5565systems (Microsoft...) this might be unexpectedly low, but is still at
5566least 31 bits everywhere, which is enough for hundreds of millions of
5567watchers.
5568.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5569.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5570.IX Item "double must hold a time value in seconds with enough accuracy"
5571The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5572have at least 51 bits of mantissa (and 9 bits of exponent), which is
5573good enough for at least into the year 4000 with millisecond accuracy
5574(the design goal for libev). This requirement is overfulfilled by
5575implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5576.Sp
5577With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5578year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5579is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5580something like that, just kidding).
5581.PP
5582If you know of other additional requirements drop me a note.
2312.SH "COMPLEXITIES" 5583.SH "ALGORITHMIC COMPLEXITIES"
2313.IX Header "COMPLEXITIES" 5584.IX Header "ALGORITHMIC COMPLEXITIES"
2314In this section the complexities of (many of) the algorithms used inside 5585In this section the complexities of (many of) the algorithms used inside
2315libev will be explained. For complexity discussions about backends see the 5586libev will be documented. For complexity discussions about backends see
2316documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5587the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2317.RS 4 5588.PP
5589All of the following are about amortised time: If an array needs to be
5590extended, libev needs to realloc and move the whole array, but this
5591happens asymptotically rarer with higher number of elements, so O(1) might
5592mean that libev does a lengthy realloc operation in rare cases, but on
5593average it is much faster and asymptotically approaches constant time.
2318.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5594.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2319.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5595.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5596This means that, when you have a watcher that triggers in one hour and
5597there are 100 watchers that would trigger before that, then inserting will
5598have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5599.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5600.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5601That means that changing a timer costs less than removing/adding them,
5602as only the relative motion in the event queue has to be paid for.
5603.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5604.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5605These just add the watcher into an array or at the head of a list.
5606.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5607.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2320.PD 0 5608.PD 0
2321.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2322.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2323.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2324.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2325.IP "Stopping check/prepare/idle watchers: O(1)" 4
2326.IX Item "Stopping check/prepare/idle watchers: O(1)"
2327.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5609.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2328.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5610.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5611.PD
5612These watchers are stored in lists, so they need to be walked to find the
5613correct watcher to remove. The lists are usually short (you don't usually
5614have many watchers waiting for the same fd or signal: one is typical, two
5615is rare).
2329.IP "Finding the next timer per loop iteration: O(1)" 4 5616.IP "Finding the next timer in each loop iteration: O(1)" 4
2330.IX Item "Finding the next timer per loop iteration: O(1)" 5617.IX Item "Finding the next timer in each loop iteration: O(1)"
5618By virtue of using a binary or 4\-heap, the next timer is always found at a
5619fixed position in the storage array.
2331.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5620.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2332.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5621.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2333.IP "Activating one watcher: O(1)" 4 5622A change means an I/O watcher gets started or stopped, which requires
2334.IX Item "Activating one watcher: O(1)" 5623libev to recalculate its status (and possibly tell the kernel, depending
2335.RE 5624on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2336.RS 4 5625.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5626.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5627.PD 0
5628.IP "Priority handling: O(number_of_priorities)" 4
5629.IX Item "Priority handling: O(number_of_priorities)"
2337.PD 5630.PD
5631Priorities are implemented by allocating some space for each
5632priority. When doing priority-based operations, libev usually has to
5633linearly search all the priorities, but starting/stopping and activating
5634watchers becomes O(1) with respect to priority handling.
5635.IP "Sending an ev_async: O(1)" 4
5636.IX Item "Sending an ev_async: O(1)"
5637.PD 0
5638.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5639.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5640.IP "Processing signals: O(max_signal_number)" 4
5641.IX Item "Processing signals: O(max_signal_number)"
5642.PD
5643Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5644calls in the current loop iteration and the loop is currently
5645blocked. Checking for async and signal events involves iterating over all
5646running async watchers or all signal numbers.
5647.SH "PORTING FROM LIBEV 3.X TO 4.X"
5648.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5649The major version 4 introduced some incompatible changes to the \s-1API.\s0
5650.PP
5651At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5652for all changes, so most programs should still compile. The compatibility
5653layer might be removed in later versions of libev, so better update to the
5654new \s-1API\s0 early than late.
5655.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5656.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5657.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5658The backward compatibility mechanism can be controlled by
5659\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5660section.
5661.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5662.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5663.IX Item "ev_default_destroy and ev_default_fork have been removed"
5664These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5665.Sp
5666.Vb 2
5667\& ev_loop_destroy (EV_DEFAULT_UC);
5668\& ev_loop_fork (EV_DEFAULT);
5669.Ve
5670.IP "function/symbol renames" 4
5671.IX Item "function/symbol renames"
5672A number of functions and symbols have been renamed:
5673.Sp
5674.Vb 3
5675\& ev_loop => ev_run
5676\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5677\& EVLOOP_ONESHOT => EVRUN_ONCE
5678\&
5679\& ev_unloop => ev_break
5680\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5681\& EVUNLOOP_ONE => EVBREAK_ONE
5682\& EVUNLOOP_ALL => EVBREAK_ALL
5683\&
5684\& EV_TIMEOUT => EV_TIMER
5685\&
5686\& ev_loop_count => ev_iteration
5687\& ev_loop_depth => ev_depth
5688\& ev_loop_verify => ev_verify
5689.Ve
5690.Sp
5691Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5692\&\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
5693associated constants have been renamed to not collide with the \f(CW\*(C`struct
5694ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5695as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5696\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5697typedef.
5698.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5699.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5700.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5701The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5702mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5703and work, but the library code will of course be larger.
5704.SH "GLOSSARY"
5705.IX Header "GLOSSARY"
5706.IP "active" 4
5707.IX Item "active"
5708A watcher is active as long as it has been started and not yet stopped.
5709See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5710.IP "application" 4
5711.IX Item "application"
5712In this document, an application is whatever is using libev.
5713.IP "backend" 4
5714.IX Item "backend"
5715The part of the code dealing with the operating system interfaces.
5716.IP "callback" 4
5717.IX Item "callback"
5718The address of a function that is called when some event has been
5719detected. Callbacks are being passed the event loop, the watcher that
5720received the event, and the actual event bitset.
5721.IP "callback/watcher invocation" 4
5722.IX Item "callback/watcher invocation"
5723The act of calling the callback associated with a watcher.
5724.IP "event" 4
5725.IX Item "event"
5726A change of state of some external event, such as data now being available
5727for reading on a file descriptor, time having passed or simply not having
5728any other events happening anymore.
5729.Sp
5730In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5731\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5732.IP "event library" 4
5733.IX Item "event library"
5734A software package implementing an event model and loop.
5735.IP "event loop" 4
5736.IX Item "event loop"
5737An entity that handles and processes external events and converts them
5738into callback invocations.
5739.IP "event model" 4
5740.IX Item "event model"
5741The model used to describe how an event loop handles and processes
5742watchers and events.
5743.IP "pending" 4
5744.IX Item "pending"
5745A watcher is pending as soon as the corresponding event has been
5746detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5747.IP "real time" 4
5748.IX Item "real time"
5749The physical time that is observed. It is apparently strictly monotonic :)
5750.IP "wall-clock time" 4
5751.IX Item "wall-clock time"
5752The time and date as shown on clocks. Unlike real time, it can actually
5753be wrong and jump forwards and backwards, e.g. when you adjust your
5754clock.
5755.IP "watcher" 4
5756.IX Item "watcher"
5757A data structure that describes interest in certain events. Watchers need
5758to be started (attached to an event loop) before they can receive events.
2338.SH "AUTHOR" 5759.SH "AUTHOR"
2339.IX Header "AUTHOR" 5760.IX Header "AUTHOR"
2340Marc Lehmann <libev@schmorp.de>. 5761Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5762Magnusson and Emanuele Giaquinta, and minor corrections by many others.

Diff Legend

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