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

Comparing libev/ev.3 (file contents):
Revision 1.15 by root, Sat Nov 24 10:15:16 2007 UTC vs.
Revision 1.84 by root, Fri Nov 5 22:28:54 2010 UTC

1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
2.\" 2.\"
3.\" Standard preamble: 3.\" Standard preamble:
4.\" ======================================================================== 4.\" ========================================================================
5.de Sh \" Subsection heading
6.br
7.if t .Sp
8.ne 5
9.PP
10\fB\\$1\fR
11.PP
12..
13.de Sp \" Vertical space (when we can't use .PP) 5.de Sp \" Vertical space (when we can't use .PP)
14.if t .sp .5v 6.if t .sp .5v
15.if n .sp 7.if n .sp
16.. 8..
17.de Vb \" Begin verbatim text 9.de Vb \" Begin verbatim text
… …
23.ft R 15.ft R
24.fi 16.fi
25.. 17..
26.\" Set up some character translations and predefined strings. \*(-- will 18.\" Set up some character translations and predefined strings. \*(-- will
27.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left 19.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
28.\" double quote, and \*(R" will give a right double quote. | will give a 20.\" double quote, and \*(R" will give a right double quote. \*(C+ will
29.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to 21.\" give a nicer C++. Capital omega is used to do unbreakable dashes and
30.\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' 22.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
31.\" expand to `' in nroff, nothing in troff, for use with C<>. 23.\" nothing in troff, for use with C<>.
32.tr \(*W-|\(bv\*(Tr 24.tr \(*W-
33.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' 25.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
34.ie n \{\ 26.ie n \{\
35. ds -- \(*W- 27. ds -- \(*W-
36. ds PI pi 28. ds PI pi
37. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch 29. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
… …
46. ds PI \(*p 38. ds PI \(*p
47. ds L" `` 39. ds L" ``
48. ds R" '' 40. ds R" ''
49'br\} 41'br\}
50.\" 42.\"
43.\" Escape single quotes in literal strings from groff's Unicode transform.
44.ie \n(.g .ds Aq \(aq
45.el .ds Aq '
46.\"
51.\" If the F register is turned on, we'll generate index entries on stderr for 47.\" If the F register is turned on, we'll generate index entries on stderr for
52.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index 48.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
53.\" entries marked with X<> in POD. Of course, you'll have to process the 49.\" entries marked with X<> in POD. Of course, you'll have to process the
54.\" output yourself in some meaningful fashion. 50.\" output yourself in some meaningful fashion.
55.if \nF \{\ 51.ie \nF \{\
56. de IX 52. de IX
57. tm Index:\\$1\t\\n%\t"\\$2" 53. tm Index:\\$1\t\\n%\t"\\$2"
58.. 54..
59. nr % 0 55. nr % 0
60. rr F 56. rr F
61.\} 57.\}
62.\" 58.el \{\
63.\" For nroff, turn off justification. Always turn off hyphenation; it makes 59. de IX
64.\" way too many mistakes in technical documents. 60..
65.hy 0 61.\}
66.if n .na
67.\" 62.\"
68.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). 63.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
69.\" Fear. Run. Save yourself. No user-serviceable parts. 64.\" Fear. Run. Save yourself. No user-serviceable parts.
70. \" fudge factors for nroff and troff 65. \" fudge factors for nroff and troff
71.if n \{\ 66.if n \{\
… …
126. ds Ae AE 121. ds Ae AE
127.\} 122.\}
128.rm #[ #] #H #V #F C 123.rm #[ #] #H #V #F C
129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2010-11-03" "libev-4.01" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& ev_io stdin_watcher;
150\& ev_timer timeout_watcher;
151\&
152\& // all watcher callbacks have a similar signature
153\& // this callback is called when data is readable on stdin
154\& static void
155\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
157\& puts ("stdin ready");
158\& // for one\-shot events, one must manually stop the watcher
159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = EV_DEFAULT;
180\&
181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184\& ev_io_start (loop, &stdin_watcher);
185\&
186\& // initialise a timer watcher, then start it
187\& // simple non\-repeating 5.5 second timeout
188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189\& ev_timer_start (loop, &timeout_watcher);
190\&
191\& // now wait for events to arrive
192\& ev_run (loop, 0);
193\&
194\& // unloop was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 222Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 224these event sources and provide your program with events.
145.PP 225.PP
146To do this, it must take more or less complete control over your process 226To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 227(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 228communicate events via a callback mechanism.
149.PP 229.PP
150You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 232details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 233watcher.
154.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 235.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249<benchmark> comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 259this argument.
172.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
179it, you should treat it as such. 267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
183library in any way. 293library in any way.
184.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 296Returns the current time as libev would use it. Please note that the
187\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked until
303either it is interrupted or the given time interval has passed. Basically
304this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
189.IP "int ev_version_major ()" 4 305.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 306.IX Item "int ev_version_major ()"
191.PD 0 307.PD 0
192.IP "int ev_version_minor ()" 4 308.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 309.IX Item "int ev_version_minor ()"
194.PD 310.PD
195You can find out the major and minor version numbers of the library 311You can find out the major and minor \s-1ABI\s0 version numbers of the library
196you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 312you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 313\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 314symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199version of the library your program was compiled against. 315version of the library your program was compiled against.
200.Sp 316.Sp
317These version numbers refer to the \s-1ABI\s0 version of the library, not the
318release version.
319.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 320Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 321as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 322compatible to older versions, so a larger minor version alone is usually
204not a problem. 323not a problem.
205.Sp 324.Sp
206Example: make sure we haven't accidentally been linked against the wrong 325Example: Make sure we haven't accidentally been linked against the wrong
207version: 326version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327such as \s-1LFS\s0 or reentrancy).
208.Sp 328.Sp
209.Vb 3 329.Vb 3
210\& assert (("libev version mismatch", 330\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 331\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 332\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 333.Ve
214.IP "unsigned int ev_supported_backends ()" 4 334.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 335.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 336Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
217value) compiled into this binary of libev (independent of their 337value) compiled into this binary of libev (independent of their
… …
220.Sp 340.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 341Example: make sure we have the epoll method, because yeah this is cool and
222a must have and can we have a torrent of it please!!!11 342a must have and can we have a torrent of it please!!!11
223.Sp 343.Sp
224.Vb 2 344.Vb 2
225\& assert (("sorry, no epoll, no sex", 345\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 346\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 347.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 348.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 349.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 350Return the set of all backends compiled into this binary of libev and
231recommended for this platform. This set is often smaller than the one 351also recommended for this platform, meaning it will work for most file
352descriptor types. This set is often smaller than the one returned by
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 353\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
233most BSDs and will not be autodetected unless you explicitly request it 354and will not be auto-detected unless you explicitly request it (assuming
234(assuming you know what you are doing). This is the set of backends that 355you know what you are doing). This is the set of backends that libev will
235libev will probe for if you specify no backends explicitly. 356probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4 357.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()" 358.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This 359Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends 360value is platform-specific but can include backends not available on the
240might be supported on the current system, you would need to look at 361current system. To find which embeddable backends might be supported on
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 362the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
242recommended ones. 363& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
243.Sp 364.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 365See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
245.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 366.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 367.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
247Sets the allocation function to use (the prototype is similar to the 368Sets the allocation function to use (the prototype is similar \- the
248realloc C function, the semantics are identical). It is used to allocate 369semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249and free memory (no surprises here). If it returns zero when memory 370used to allocate and free memory (no surprises here). If it returns zero
250needs to be allocated, the library might abort or take some potentially 371when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251destructive action. The default is your system realloc function. 372or take some potentially destructive action.
373.Sp
374Since some systems (at least OpenBSD and Darwin) fail to implement
375correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
252.Sp 377.Sp
253You could override this function in high-availability programs to, say, 378You could override this function in high-availability programs to, say,
254free some memory if it cannot allocate memory, to use a special allocator, 379free some memory if it cannot allocate memory, to use a special allocator,
255or even to sleep a while and retry until some memory is available. 380or even to sleep a while and retry until some memory is available.
256.Sp 381.Sp
257Example: replace the libev allocator with one that waits a bit and then 382Example: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 383retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
259.Sp 384.Sp
260.Vb 6 385.Vb 6
261\& static void * 386\& static void *
262\& persistent_realloc (void *ptr, long size) 387\& persistent_realloc (void *ptr, size_t size)
263\& { 388\& {
264\& for (;;) 389\& for (;;)
265\& { 390\& {
266\& void *newptr = realloc (ptr, size); 391\& void *newptr = realloc (ptr, size);
267.Ve 392\&
268.Sp
269.Vb 2
270\& if (newptr) 393\& if (newptr)
271\& return newptr; 394\& return newptr;
272.Ve 395\&
273.Sp
274.Vb 3
275\& sleep (60); 396\& sleep (60);
276\& } 397\& }
277\& } 398\& }
278.Ve 399\&
279.Sp
280.Vb 2
281\& ... 400\& ...
282\& ev_set_allocator (persistent_realloc); 401\& ev_set_allocator (persistent_realloc);
283.Ve 402.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 403.IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 404.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
286Set the callback function to call on a retryable syscall error (such 405Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 406as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 407indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 408callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 409matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 410requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 411(such as abort).
293.Sp 412.Sp
294Example: do the same thing as libev does internally: 413Example: This is basically the same thing that libev does internally, too.
295.Sp 414.Sp
296.Vb 6 415.Vb 6
297\& static void 416\& static void
298\& fatal_error (const char *msg) 417\& fatal_error (const char *msg)
299\& { 418\& {
300\& perror (msg); 419\& perror (msg);
301\& abort (); 420\& abort ();
302\& } 421\& }
303.Ve 422\&
304.Sp
305.Vb 2
306\& ... 423\& ...
307\& ev_set_syserr_cb (fatal_error); 424\& ev_set_syserr_cb (fatal_error);
308.Ve 425.Ve
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 426.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 427.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
311An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 428An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
312types of such loops, the \fIdefault\fR loop, which supports signals and child 429\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
313events, and dynamically created loops which do not. 430libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
314.PP 431.PP
315If you use threads, a common model is to run the default event loop 432The library knows two types of such loops, the \fIdefault\fR loop, which
316in your main thread (or in a separate thread) and for each thread you 433supports child process events, and dynamically created event loops which
317create, you also create another event loop. Libev itself does no locking 434do not.
318whatsoever, so if you mix calls to the same event loop in different
319threads, make sure you lock (this is usually a bad idea, though, even if
320done correctly, because it's hideous and inefficient).
321.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 435.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 436.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 437This returns the \*(L"default\*(R" event loop object, which is what you should
324yet and return it. If the default loop could not be initialised, returns 438normally use when you just need \*(L"the event loop\*(R". Event loop objects and
325false. If it already was initialised it simply returns it (and ignores the 439the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
326flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 440\&\f(CW\*(C`ev_loop_new\*(C'\fR.
441.Sp
442If the default loop is already initialised then this function simply
443returns it (and ignores the flags. If that is troubling you, check
444\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
445flags, which should almost always be \f(CW0\fR, unless the caller is also the
446one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
327.Sp 447.Sp
328If you don't know what event loop to use, use the one returned from this 448If you don't know what event loop to use, use the one returned from this
329function. 449function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
450.Sp
451Note that this function is \fInot\fR thread-safe, so if you want to use it
452from multiple threads, you have to employ some kind of mutex (note also
453that this case is unlikely, as loops cannot be shared easily between
454threads anyway).
455.Sp
456The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
457and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
458a problem for your application you can either create a dynamic loop with
459\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
460\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
461.Sp
462Example: This is the most typical usage.
463.Sp
464.Vb 2
465\& if (!ev_default_loop (0))
466\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
467.Ve
468.Sp
469Example: Restrict libev to the select and poll backends, and do not allow
470environment settings to be taken into account:
471.Sp
472.Vb 1
473\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
474.Ve
475.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
476.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
477This will create and initialise a new event loop object. If the loop
478could not be initialised, returns false.
479.Sp
480Note that this function \fIis\fR thread-safe, and one common way to use
481libev with threads is indeed to create one loop per thread, and using the
482default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
330.Sp 483.Sp
331The flags argument can be used to specify special behaviour or specific 484The flags argument can be used to specify special behaviour or specific
332backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 485backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 486.Sp
334The following flags are supported: 487The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 492The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 493thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 494.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 495.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 496.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 497If this flag bit is or'ed into the flag value (or the program runs setuid
345or setgid) then libev will \fInot\fR look at the environment variable 498or setgid) then libev will \fInot\fR look at the environment variable
346\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 499\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
347override the flags completely if it is found in the environment. This is 500override the flags completely if it is found in the environment. This is
348useful to try out specific backends to test their performance, or to work 501useful to try out specific backends to test their performance, or to work
349around bugs. 502around bugs.
503.ie n .IP """EVFLAG_FORKCHECK""" 4
504.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
505.IX Item "EVFLAG_FORKCHECK"
506Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
507make libev check for a fork in each iteration by enabling this flag.
508.Sp
509This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
510and thus this might slow down your event loop if you do a lot of loop
511iterations and little real work, but is usually not noticeable (on my
512GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
513without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
514\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
515.Sp
516The big advantage of this flag is that you can forget about fork (and
517forget about forgetting to tell libev about forking) when you use this
518flag.
519.Sp
520This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
521environment variable.
522.ie n .IP """EVFLAG_NOINOTIFY""" 4
523.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
524.IX Item "EVFLAG_NOINOTIFY"
525When this flag is specified, then libev will not attempt to use the
526\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
527testing, this flag can be useful to conserve inotify file descriptors, as
528otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
529.ie n .IP """EVFLAG_SIGNALFD""" 4
530.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
531.IX Item "EVFLAG_SIGNALFD"
532When this flag is specified, then libev will attempt to use the
533\&\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
534delivers signals synchronously, which makes it both faster and might make
535it possible to get the queued signal data. It can also simplify signal
536handling with threads, as long as you properly block signals in your
537threads that are not interested in handling them.
538.Sp
539Signalfd will not be used by default as this changes your signal mask, and
540there are a lot of shoddy libraries and programs (glib's threadpool for
541example) that can't properly initialise their signal masks.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 542.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 543.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 544.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 545This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354libev tries to roll its own fd_set with no limits on the number of fds, 546libev tries to roll its own fd_set with no limits on the number of fds,
355but if that fails, expect a fairly low limit on the number of fds when 547but if that fails, expect a fairly low limit on the number of fds when
356using this backend. It doesn't scale too well (O(highest_fd)), but its usually 548using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 549usually the fastest backend for a low number of (low-numbered :) fds.
550.Sp
551To get good performance out of this backend you need a high amount of
552parallelism (most of the file descriptors should be busy). If you are
553writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
554connections as possible during one iteration. You might also want to have
555a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
556readiness notifications you get per iteration.
557.Sp
558This 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
559\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
560\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
358.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 561.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
359.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 562.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
360.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 563.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
361And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 564And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
362select, but handles sparse fds better and has no artificial limit on the 565than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 566limit on the number of fds you can use (except it will slow down
364lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 567considerably with a lot of inactive fds). It scales similarly to select,
568i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
569performance tips.
570.Sp
571This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
572\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
365.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 573.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 574.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 575.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
576Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
577kernels).
578.Sp
368For few fds, this backend is a bit little slower than poll and select, 579For few fds, this backend is a bit little slower than poll and select,
369but it scales phenomenally better. While poll and select usually scale like 580but it scales phenomenally better. While poll and select usually scale
370O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 581like O(total_fds) where n is the total number of fds (or the highest fd),
371either O(1) or O(active_fds). 582epoll scales either O(1) or O(active_fds).
372.Sp 583.Sp
584The epoll mechanism deserves honorable mention as the most misdesigned
585of the more advanced event mechanisms: mere annoyances include silently
586dropping file descriptors, requiring a system call per change per file
587descriptor (and unnecessary guessing of parameters), problems with dup,
588returning before the timeout value, resulting in additional iterations
589(and only giving 5ms accuracy while select on the same platform gives
5900.1ms) and so on. The biggest issue is fork races, however \- if a program
591forks then \fIboth\fR parent and child process have to recreate the epoll
592set, which can take considerable time (one syscall per file descriptor)
593and is of course hard to detect.
594.Sp
595Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
596of course \fIdoesn't\fR, and epoll just loves to report events for totally
597\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
598even remove them from the set) than registered in the set (especially
599on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
600employing an additional generation counter and comparing that against the
601events to filter out spurious ones, recreating the set when required. Last
602not least, it also refuses to work with some file descriptors which work
603perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
604.Sp
605Epoll is truly the train wreck analog among event poll mechanisms.
606.Sp
373While stopping and starting an I/O watcher in the same iteration will 607While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 608will result in some caching, there is still a system call per such
375(because the fd could point to a different file description now), so its 609incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 610\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
377well if you register events for both fds. 611file descriptors might not work very well if you register events for both
612file descriptors.
378.Sp 613.Sp
379Please note that epoll sometimes generates spurious notifications, so you 614Best performance from this backend is achieved by not unregistering all
380need to use non-blocking I/O or other means to avoid blocking when no data 615watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 616i.e. keep at least one watcher active per fd at all times. Stopping and
617starting a watcher (without re-setting it) also usually doesn't cause
618extra overhead. A fork can both result in spurious notifications as well
619as in libev having to destroy and recreate the epoll object, which can
620take considerable time and thus should be avoided.
621.Sp
622All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
623faster than epoll for maybe up to a hundred file descriptors, depending on
624the usage. So sad.
625.Sp
626While nominally embeddable in other event loops, this feature is broken in
627all kernel versions tested so far.
628.Sp
629This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
630\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 631.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
383.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 632.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 633.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 634Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 635was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 636with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 637it's completely useless). Unlike epoll, however, whose brokenness
638is by design, these kqueue bugs can (and eventually will) be fixed
639without \s-1API\s0 changes to existing programs. For this reason it's not being
389unless you explicitly specify it explicitly in the flags (i.e. using 640\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 641\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
642system like NetBSD.
643.Sp
644You still can embed kqueue into a normal poll or select backend and use it
645only for sockets (after having made sure that sockets work with kqueue on
646the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 647.Sp
392It scales in the same way as the epoll backend, but the interface to the 648It scales in the same way as the epoll backend, but the interface to the
393kernel is more efficient (which says nothing about its actual speed, of 649kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 650course). While stopping, setting and starting an I/O watcher does never
395extra syscall as with epoll, it still adds up to four event changes per 651cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
396incident, so its best to avoid that. 652two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
653sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
654cases
655.Sp
656This backend usually performs well under most conditions.
657.Sp
658While nominally embeddable in other event loops, this doesn't work
659everywhere, so you might need to test for this. And since it is broken
660almost everywhere, you should only use it when you have a lot of sockets
661(for which it usually works), by embedding it into another event loop
662(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
663also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
664.Sp
665This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
666\&\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
667\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 668.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 669.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 670.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 671This is not implemented yet (and might never be, unless you send me an
672implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
673and is not embeddable, which would limit the usefulness of this backend
674immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 675.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 676.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 677.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 678This uses the Solaris 10 event port mechanism. As with everything on Solaris,
405it's really slow, but it still scales very well (O(active_fds)). 679it's really slow, but it still scales very well (O(active_fds)).
406.Sp 680.Sp
407Please note that solaris ports can result in a lot of spurious 681Please note that Solaris event ports can deliver a lot of spurious
408notifications, so you need to use non-blocking I/O or other means to avoid 682notifications, so you need to use non-blocking I/O or other means to avoid
409blocking when no data (or space) is available. 683blocking when no data (or space) is available.
684.Sp
685While this backend scales well, it requires one system call per active
686file descriptor per loop iteration. For small and medium numbers of file
687descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
688might perform better.
689.Sp
690On the positive side, with the exception of the spurious readiness
691notifications, this backend actually performed fully to specification
692in all tests and is fully embeddable, which is a rare feat among the
693OS-specific backends (I vastly prefer correctness over speed hacks).
694.Sp
695This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
696\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 697.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 698.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 699.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 700Try all backends (even potentially broken ones that wouldn't be tried
414with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 701with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
415\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 702\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
703.Sp
704It is definitely not recommended to use this flag.
416.RE 705.RE
417.RS 4 706.RS 4
418.Sp 707.Sp
419If one or more of these are ored into the flags value, then only these 708If one or more of the backend flags are or'ed into the flags value,
420backends will be tried (in the reverse order as given here). If none are 709then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 710here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 711()\*(C'\fR will be tried.
423.Sp 712.Sp
424The most typical usage is like this: 713Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 714.Sp
426.Vb 2 715.Vb 3
427\& if (!ev_default_loop (0)) 716\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 717\& if (!epoller)
718\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 719.Ve
430.Sp 720.Sp
431Restrict libev to the select and poll backends, and do not allow 721Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 722used if available.
433.Sp 723.Sp
434.Vb 1 724.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
436.Ve
437.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if
439available (warning, breaks stuff, best use only with your own private
440event loop and only if you know the \s-1OS\s0 supports your types of fds):
441.Sp
442.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 725\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
444.Ve 726.Ve
445.RE 727.RE
446.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449always distinct from the default loop. Unlike the default loop, it cannot
450handle signal and child watchers, and attempts to do so will be greeted by
451undefined behaviour (or a failed assertion if assertions are enabled).
452.Sp
453Example: try to create a event loop that uses epoll and nothing else.
454.Sp
455.Vb 3
456\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
457\& if (!epoller)
458\& fatal ("no epoll found here, maybe it hides under your chair");
459.Ve
460.IP "ev_default_destroy ()" 4 728.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 729.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 730Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 731etc.). None of the active event watchers will be stopped in the normal
464sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 732sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
465responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 733responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 734calling this function, or cope with the fact afterwards (which is usually
467the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 735the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 736for example).
469.IP "ev_loop_destroy (loop)" 4
470.IX Item "ev_loop_destroy (loop)"
471Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
472earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
473.IP "ev_default_fork ()" 4
474.IX Item "ev_default_fork ()"
475This function reinitialises the kernel state for backends that have
476one. Despite the name, you can call it anytime, but it makes most sense
477after forking, in either the parent or child process (or both, but that
478again makes little sense).
479.Sp 737.Sp
480You \fImust\fR call this function in the child process after forking if and 738Note that certain global state, such as signal state (and installed signal
481only if you want to use the event library in both processes. If you just 739handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 740as signal and child watchers) would need to be stopped manually.
483.Sp 741.Sp
484The function itself is quite fast and it's usually not a problem to call 742This function is normally used on loop objects allocated by
485it just in case after a fork. To make this easy, the function will fit in 743\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
486quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 744\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 745.Sp
488.Vb 1 746Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 747except in the rare occasion where you really need to free its resources.
490.Ve 748If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 749and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
492At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
493without calling this function, so if you force one of those backends you
494do not need to care.
495.IP "ev_loop_fork (loop)" 4 750.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 751.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 752This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
498\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 753reinitialise the kernel state for backends that have one. Despite the
499after fork, and how you do this is entirely your own problem. 754name, you can call it anytime, but it makes most sense after forking, in
755the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
756child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
757.Sp
758Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
759a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
760because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
761during fork.
762.Sp
763On the other hand, you only need to call this function in the child
764process if and only if you want to use the event loop in the child. If
765you just fork+exec or create a new loop in the child, you don't have to
766call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
767difference, but libev will usually detect this case on its own and do a
768costly reset of the backend).
769.Sp
770The function itself is quite fast and it's usually not a problem to call
771it just in case after a fork.
772.Sp
773Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
774using pthreads.
775.Sp
776.Vb 5
777\& static void
778\& post_fork_child (void)
779\& {
780\& ev_loop_fork (EV_DEFAULT);
781\& }
782\&
783\& ...
784\& pthread_atfork (0, 0, post_fork_child);
785.Ve
786.IP "int ev_is_default_loop (loop)" 4
787.IX Item "int ev_is_default_loop (loop)"
788Returns true when the given loop is, in fact, the default loop, and false
789otherwise.
790.IP "unsigned int ev_iteration (loop)" 4
791.IX Item "unsigned int ev_iteration (loop)"
792Returns the current iteration count for the event loop, which is identical
793to the number of times libev did poll for new events. It starts at \f(CW0\fR
794and happily wraps around with enough iterations.
795.Sp
796This value can sometimes be useful as a generation counter of sorts (it
797\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
798\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
799prepare and check phases.
800.IP "unsigned int ev_depth (loop)" 4
801.IX Item "unsigned int ev_depth (loop)"
802Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
803times \f(CW\*(C`ev_run\*(C'\fR was exited, in other words, the recursion depth.
804.Sp
805Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
806\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
807in which case it is higher.
808.Sp
809Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
810etc.), doesn't count as \*(L"exit\*(R" \- consider this as a hint to avoid such
811ungentleman-like behaviour unless it's really convenient.
500.IP "unsigned int ev_backend (loop)" 4 812.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 813.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 814Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 815use.
504.IP "ev_tstamp ev_now (loop)" 4 816.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 817.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 818Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 819received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 820change as long as callbacks are being processed, and this is also the base
509time used for relative timers. You can treat it as the timestamp of the 821time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 822event occurring (or more correctly, libev finding out about it).
823.IP "ev_now_update (loop)" 4
824.IX Item "ev_now_update (loop)"
825Establishes the current time by querying the kernel, updating the time
826returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
827is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
828.Sp
829This function is rarely useful, but when some event callback runs for a
830very long time without entering the event loop, updating libev's idea of
831the current time is a good idea.
832.Sp
833See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
834.IP "ev_suspend (loop)" 4
835.IX Item "ev_suspend (loop)"
836.PD 0
837.IP "ev_resume (loop)" 4
838.IX Item "ev_resume (loop)"
839.PD
840These two functions suspend and resume an event loop, for use when the
841loop is not used for a while and timeouts should not be processed.
842.Sp
843A typical use case would be an interactive program such as a game: When
844the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
845would be best to handle timeouts as if no time had actually passed while
846the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
847in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
848\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
849.Sp
850Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
851between \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
852will be rescheduled (that is, they will lose any events that would have
853occurred while suspended).
854.Sp
855After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
856given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
857without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
858.Sp
859Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
860event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 861.IP "ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 862.IX Item "ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 863Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 864after you have initialised all your watchers and you want to start
515events. 865handling events. It will ask the operating system for any new events, call
866the watcher callbacks, an then repeat the whole process indefinitely: This
867is why event loops are called \fIloops\fR.
516.Sp 868.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 869If the flags argument is specified as \f(CW0\fR, it will keep handling events
518either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 870until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
871called.
519.Sp 872.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 873Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
521relying on all watchers to be stopped when deciding when a program has 874relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 875finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 876that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 877of relying on its watchers stopping correctly, that is truly a thing of
878beauty.
525.Sp 879.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 880A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
527those events and any outstanding ones, but will not block your process in 881those events and any already outstanding ones, but will not wait and
528case there are no events and will return after one iteration of the loop. 882block your process in case there are no events and will return after one
883iteration of the loop. This is sometimes useful to poll and handle new
884events while doing lengthy calculations, to keep the program responsive.
529.Sp 885.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 886A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
531neccessary) and will handle those and any outstanding ones. It will block 887necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 888will block your process until at least one new event arrives (which could
533one iteration of the loop. This is useful if you are waiting for some 889be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 890user-registered callback will be called), and will return after one
891iteration of the loop.
892.Sp
893This is useful if you are waiting for some external event in conjunction
894with something not expressible using other libev watchers (i.e. "roll your
535libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 895own \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
536usually a better approach for this kind of thing. 896usually a better approach for this kind of thing.
537.Sp 897.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 898Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
539.Sp 899.Sp
540.Vb 18 900.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 901\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 902\& \- Reset the ev_break status.
903\& \- Before the first iteration, call any pending watchers.
904\& LOOP:
905\& \- If EVFLAG_FORKCHECK was used, check for a fork.
906\& \- If a fork was detected (by any means), queue and call all fork watchers.
907\& \- Queue and call all prepare watchers.
908\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 909\& \- If we have been forked, detach and recreate the kernel state
910\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 911\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 912\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 913\& \- Calculate for how long to sleep or block, if at all
914\& (active idle watchers, EVRUN_NOWAIT or not having
915\& any active watchers at all will result in not sleeping).
916\& \- Sleep if the I/O and timer collect interval say so.
917\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 918\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 919\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 920\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 921\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 922\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 923\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 924\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 925\& \- Call all queued watchers in reverse order (i.e. check watchers first).
555\& Signals and child watchers are implemented as I/O watchers, and will 926\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 927\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 928\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 929\& were used, or there are no active watchers, goto FINISH, otherwise
930\& continue with step LOOP.
931\& FINISH:
932\& \- Reset the ev_break status iff it was EVBREAK_ONE.
933\& \- Decrement the loop depth.
934\& \- Return.
559.Ve 935.Ve
560.Sp 936.Sp
561Example: queue some jobs and then loop until no events are outsanding 937Example: Queue some jobs and then loop until no events are outstanding
562anymore. 938anymore.
563.Sp 939.Sp
564.Vb 4 940.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 941\& ... queue jobs here, make sure they register event watchers as long
566\& ... as they still have work to do (even an idle watcher will do..) 942\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 943\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 944\& ... jobs done or somebody called unloop. yeah!
569.Ve 945.Ve
570.IP "ev_unloop (loop, how)" 4 946.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 947.IX Item "ev_break (loop, how)"
572Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 948Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
573has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 949has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
574\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 950\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
575\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 951\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
952.Sp
953This \*(L"break state\*(R" will be cleared when entering \f(CW\*(C`ev_run\*(C'\fR again.
954.Sp
955It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too.
576.IP "ev_ref (loop)" 4 956.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 957.IX Item "ev_ref (loop)"
578.PD 0 958.PD 0
579.IP "ev_unref (loop)" 4 959.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 960.IX Item "ev_unref (loop)"
581.PD 961.PD
582Ref/unref can be used to add or remove a reference count on the event 962Ref/unref can be used to add or remove a reference count on the event
583loop: Every watcher keeps one reference, and as long as the reference 963loop: Every watcher keeps one reference, and as long as the reference
584count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 964count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
585a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 965.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 966This is useful when you have a watcher that you never intend to
967unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
968returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
969before stopping it.
970.Sp
587example, libev itself uses this for its internal signal pipe: It is not 971As an example, libev itself uses this for its internal signal pipe: It
588visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 972is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
589no event watchers registered by it are active. It is also an excellent 973exiting if no event watchers registered by it are active. It is also an
590way to do this for generic recurring timers or from within third-party 974excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 975third-party libraries. Just remember to \fIunref after start\fR and \fIref
976before stop\fR (but only if the watcher wasn't active before, or was active
977before, respectively. Note also that libev might stop watchers itself
978(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
979in the callback).
592.Sp 980.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 981Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 982running when nothing else is active.
595.Sp 983.Sp
596.Vb 4 984.Vb 4
597\& struct dv_signal exitsig; 985\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 986\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 987\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 988\& evf_unref (loop);
601.Ve 989.Ve
602.Sp 990.Sp
603Example: for some weird reason, unregister the above signal handler again. 991Example: For some weird reason, unregister the above signal handler again.
604.Sp 992.Sp
605.Vb 2 993.Vb 2
606\& ev_ref (myloop); 994\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 995\& ev_signal_stop (loop, &exitsig);
608.Ve 996.Ve
997.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
998.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
999.PD 0
1000.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1001.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1002.PD
1003These advanced functions influence the time that libev will spend waiting
1004for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1005will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1006latency.
1007.Sp
1008Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1009allows libev to delay invocation of I/O and timer/periodic callbacks
1010to increase efficiency of loop iterations (or to increase power-saving
1011opportunities).
1012.Sp
1013The idea is that sometimes your program runs just fast enough to handle
1014one (or very few) event(s) per loop iteration. While this makes the
1015program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1016events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1017overhead for the actual polling but can deliver many events at once.
1018.Sp
1019By setting a higher \fIio collect interval\fR you allow libev to spend more
1020time collecting I/O events, so you can handle more events per iteration,
1021at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1022\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1023introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1024sleep time ensures that libev will not poll for I/O events more often then
1025once per this interval, on average.
1026.Sp
1027Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1028to spend more time collecting timeouts, at the expense of increased
1029latency/jitter/inexactness (the watcher callback will be called
1030later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1031value will not introduce any overhead in libev.
1032.Sp
1033Many (busy) programs can usually benefit by setting the I/O collect
1034interval to a value near \f(CW0.1\fR or so, which is often enough for
1035interactive servers (of course not for games), likewise for timeouts. It
1036usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1037as this approaches the timing granularity of most systems. Note that if
1038you do transactions with the outside world and you can't increase the
1039parallelity, then this setting will limit your transaction rate (if you
1040need to poll once per transaction and the I/O collect interval is 0.01,
1041then you can't do more than 100 transactions per second).
1042.Sp
1043Setting the \fItimeout collect interval\fR can improve the opportunity for
1044saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1045are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1046times the process sleeps and wakes up again. Another useful technique to
1047reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1048they fire on, say, one-second boundaries only.
1049.Sp
1050Example: we only need 0.1s timeout granularity, and we wish not to poll
1051more often than 100 times per second:
1052.Sp
1053.Vb 2
1054\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1055\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1056.Ve
1057.IP "ev_invoke_pending (loop)" 4
1058.IX Item "ev_invoke_pending (loop)"
1059This call will simply invoke all pending watchers while resetting their
1060pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1061but when overriding the invoke callback this call comes handy. This
1062function can be invoked from a watcher \- this can be useful for example
1063when you want to do some lengthy calculation and want to pass further
1064event handling to another thread (you still have to make sure only one
1065thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1066.IP "int ev_pending_count (loop)" 4
1067.IX Item "int ev_pending_count (loop)"
1068Returns the number of pending watchers \- zero indicates that no watchers
1069are pending.
1070.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1071.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1072This overrides the invoke pending functionality of the loop: Instead of
1073invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1074this callback instead. This is useful, for example, when you want to
1075invoke the actual watchers inside another context (another thread etc.).
1076.Sp
1077If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1078callback.
1079.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1080.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1081Sometimes you want to share the same loop between multiple threads. This
1082can be done relatively simply by putting mutex_lock/unlock calls around
1083each call to a libev function.
1084.Sp
1085However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1086to wait for it to return. One way around this is to wake up the event
1087loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1088\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1089.Sp
1090When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1091suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1092afterwards.
1093.Sp
1094Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1095\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1096.Sp
1097While event loop modifications are allowed between invocations of
1098\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1099modifications done will affect the event loop, i.e. adding watchers will
1100have no effect on the set of file descriptors being watched, or the time
1101waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1102to take note of any changes you made.
1103.Sp
1104In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1105invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1106.Sp
1107See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1108document.
1109.IP "ev_set_userdata (loop, void *data)" 4
1110.IX Item "ev_set_userdata (loop, void *data)"
1111.PD 0
1112.IP "ev_userdata (loop)" 4
1113.IX Item "ev_userdata (loop)"
1114.PD
1115Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1116\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1117\&\f(CW0.\fR
1118.Sp
1119These two functions can be used to associate arbitrary data with a loop,
1120and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1121\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1122any other purpose as well.
1123.IP "ev_verify (loop)" 4
1124.IX Item "ev_verify (loop)"
1125This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1126compiled in, which is the default for non-minimal builds. It tries to go
1127through all internal structures and checks them for validity. If anything
1128is found to be inconsistent, it will print an error message to standard
1129error and call \f(CW\*(C`abort ()\*(C'\fR.
1130.Sp
1131This can be used to catch bugs inside libev itself: under normal
1132circumstances, this function will never abort as of course libev keeps its
1133data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1134.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1135.IX Header "ANATOMY OF A WATCHER"
1136In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1137watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1138watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1139.PP
611A watcher is a structure that you create and register to record your 1140A watcher is an opaque structure that you allocate and register to record
612interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1141your interest in some event. To make a concrete example, imagine you want
613become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1142to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1143for that:
614.PP 1144.PP
615.Vb 5 1145.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1146\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1147\& {
618\& ev_io_stop (w); 1148\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1149\& ev_break (loop, EVBREAK_ALL);
620\& } 1150\& }
621.Ve 1151\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1152\& struct ev_loop *loop = ev_default_loop (0);
1153\&
625\& struct ev_io stdin_watcher; 1154\& ev_io stdin_watcher;
1155\&
626\& ev_init (&stdin_watcher, my_cb); 1156\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1157\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1158\& ev_io_start (loop, &stdin_watcher);
1159\&
629\& ev_loop (loop, 0); 1160\& ev_run (loop, 0);
630.Ve 1161.Ve
631.PP 1162.PP
632As you can see, you are responsible for allocating the memory for your 1163As you can see, you are responsible for allocating the memory for your
633watcher structures (and it is usually a bad idea to do this on the stack, 1164watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1165stack).
635.PP 1166.PP
1167Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1168or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1169.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1170Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
637(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1171*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
638callback gets invoked each time the event occurs (or, in the case of io 1172invoked each time the event occurs (or, in the case of I/O watchers, each
639watchers, each time the event loop detects that the file descriptor given 1173time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1174and/or writable).
641.PP 1175.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1176Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
643with arguments specific to this watcher type. There is also a macro 1177macro to configure it, with arguments specific to the watcher type. There
644to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1178is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
645(watcher *, callback, ...)\*(C'\fR.
646.PP 1179.PP
647To make the watcher actually watch out for events, you have to start it 1180To make the watcher actually watch out for events, you have to start it
648with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1181with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
649*)\*(C'\fR), and you can stop watching for events at any time by calling the 1182*)\*(C'\fR), and you can stop watching for events at any time by calling the
650corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1183corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1184.PP
652As long as your watcher is active (has been started but not stopped) you 1185As long as your watcher is active (has been started but not stopped) you
653must not touch the values stored in it. Most specifically you must never 1186must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1187reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1188.PP
656Each and every callback receives the event loop pointer as first, the 1189Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1190registered watcher structure as second, and a bitset of received events as
658third argument. 1191third argument.
659.PP 1192.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1201.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1202.IX Item "EV_WRITE"
670.PD 1203.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1204The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1205writable.
673.ie n .IP """EV_TIMEOUT""" 4 1206.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1207.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1208.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1209The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1210.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1211.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1212.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1213The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
684The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1217The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
685.ie n .IP """EV_CHILD""" 4 1218.ie n .IP """EV_CHILD""" 4
686.el .IP "\f(CWEV_CHILD\fR" 4 1219.el .IP "\f(CWEV_CHILD\fR" 4
687.IX Item "EV_CHILD" 1220.IX Item "EV_CHILD"
688The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1221The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1222.ie n .IP """EV_STAT""" 4
1223.el .IP "\f(CWEV_STAT\fR" 4
1224.IX Item "EV_STAT"
1225The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
689.ie n .IP """EV_IDLE""" 4 1226.ie n .IP """EV_IDLE""" 4
690.el .IP "\f(CWEV_IDLE\fR" 4 1227.el .IP "\f(CWEV_IDLE\fR" 4
691.IX Item "EV_IDLE" 1228.IX Item "EV_IDLE"
692The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1229The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
693.ie n .IP """EV_PREPARE""" 4 1230.ie n .IP """EV_PREPARE""" 4
… …
696.PD 0 1233.PD 0
697.ie n .IP """EV_CHECK""" 4 1234.ie n .IP """EV_CHECK""" 4
698.el .IP "\f(CWEV_CHECK\fR" 4 1235.el .IP "\f(CWEV_CHECK\fR" 4
699.IX Item "EV_CHECK" 1236.IX Item "EV_CHECK"
700.PD 1237.PD
701All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1238All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
702to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1239to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
703\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1240\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
704received events. Callbacks of both watcher types can start and stop as 1241received events. Callbacks of both watcher types can start and stop as
705many watchers as they want, and all of them will be taken into account 1242many watchers as they want, and all of them will be taken into account
706(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1243(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
707\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1244\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1245.ie n .IP """EV_EMBED""" 4
1246.el .IP "\f(CWEV_EMBED\fR" 4
1247.IX Item "EV_EMBED"
1248The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1249.ie n .IP """EV_FORK""" 4
1250.el .IP "\f(CWEV_FORK\fR" 4
1251.IX Item "EV_FORK"
1252The event loop has been resumed in the child process after fork (see
1253\&\f(CW\*(C`ev_fork\*(C'\fR).
1254.ie n .IP """EV_CLEANUP""" 4
1255.el .IP "\f(CWEV_CLEANUP\fR" 4
1256.IX Item "EV_CLEANUP"
1257The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1258.ie n .IP """EV_ASYNC""" 4
1259.el .IP "\f(CWEV_ASYNC\fR" 4
1260.IX Item "EV_ASYNC"
1261The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1262.ie n .IP """EV_CUSTOM""" 4
1263.el .IP "\f(CWEV_CUSTOM\fR" 4
1264.IX Item "EV_CUSTOM"
1265Not ever sent (or otherwise used) by libev itself, but can be freely used
1266by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
708.ie n .IP """EV_ERROR""" 4 1267.ie n .IP """EV_ERROR""" 4
709.el .IP "\f(CWEV_ERROR\fR" 4 1268.el .IP "\f(CWEV_ERROR\fR" 4
710.IX Item "EV_ERROR" 1269.IX Item "EV_ERROR"
711An unspecified error has occured, the watcher has been stopped. This might 1270An unspecified error has occurred, the watcher has been stopped. This might
712happen because the watcher could not be properly started because libev 1271happen because the watcher could not be properly started because libev
713ran out of memory, a file descriptor was found to be closed or any other 1272ran out of memory, a file descriptor was found to be closed or any other
1273problem. Libev considers these application bugs.
1274.Sp
714problem. You best act on it by reporting the problem and somehow coping 1275You best act on it by reporting the problem and somehow coping with the
715with the watcher being stopped. 1276watcher being stopped. Note that well-written programs should not receive
1277an error ever, so when your watcher receives it, this usually indicates a
1278bug in your program.
716.Sp 1279.Sp
717Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1280Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
718for example it might indicate that a fd is readable or writable, and if 1281example it might indicate that a fd is readable or writable, and if your
719your callbacks is well-written it can just attempt the operation and cope 1282callbacks is well-written it can just attempt the operation and cope with
720with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1283the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
721programs, though, so beware. 1284programs, though, as the fd could already be closed and reused for another
1285thing, so beware.
722.Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1286.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
723.IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS" 1287.IX Subsection "GENERIC WATCHER FUNCTIONS"
724In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
725e.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.
726.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1288.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
727.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1289.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
728.IX Item "ev_init (ev_TYPE *watcher, callback)" 1290.IX Item "ev_init (ev_TYPE *watcher, callback)"
729This macro initialises the generic portion of a watcher. The contents 1291This macro initialises the generic portion of a watcher. The contents
730of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1292of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
734which rolls both calls into one. 1296which rolls both calls into one.
735.Sp 1297.Sp
736You can reinitialise a watcher at any time as long as it has been stopped 1298You can reinitialise a watcher at any time as long as it has been stopped
737(or never started) and there are no pending events outstanding. 1299(or never started) and there are no pending events outstanding.
738.Sp 1300.Sp
739The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1301The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
740int revents)\*(C'\fR. 1302int revents)\*(C'\fR.
1303.Sp
1304Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1305.Sp
1306.Vb 3
1307\& ev_io w;
1308\& ev_init (&w, my_cb);
1309\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1310.Ve
741.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1311.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
742.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1312.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
743.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1313.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
744This macro initialises the type-specific parts of a watcher. You need to 1314This macro initialises the type-specific parts of a watcher. You need to
745call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1315call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
746call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1316call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
747macro on a watcher that is active (it can be pending, however, which is a 1317macro on a watcher that is active (it can be pending, however, which is a
748difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1318difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
749.Sp 1319.Sp
750Although some watcher types do not have type-specific arguments 1320Although some watcher types do not have type-specific arguments
751(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1321(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1322.Sp
1323See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
752.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1324.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
753.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1325.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
754.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1326.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
755This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1327This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
756calls into a single call. This is the most convinient method to initialise 1328calls into a single call. This is the most convenient method to initialise
757a watcher. The same limitations apply, of course. 1329a watcher. The same limitations apply, of course.
1330.Sp
1331Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1332.Sp
1333.Vb 1
1334\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1335.Ve
758.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1336.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
759.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1337.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
760.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1338.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
761Starts (activates) the given watcher. Only active watchers will receive 1339Starts (activates) the given watcher. Only active watchers will receive
762events. If the watcher is already active nothing will happen. 1340events. If the watcher is already active nothing will happen.
1341.Sp
1342Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1343whole section.
1344.Sp
1345.Vb 1
1346\& ev_io_start (EV_DEFAULT_UC, &w);
1347.Ve
763.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1348.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
764.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1349.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
765.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1350.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
766Stops the given watcher again (if active) and clears the pending 1351Stops the given watcher if active, and clears the pending status (whether
1352the watcher was active or not).
1353.Sp
767status. It is possible that stopped watchers are pending (for example, 1354It is possible that stopped watchers are pending \- for example,
768non-repeating timers are being stopped when they become pending), but 1355non-repeating timers are being stopped when they become pending \- but
769\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1356calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
770you want to free or reuse the memory used by the watcher it is therefore a 1357pending. If you want to free or reuse the memory used by the watcher it is
771good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1358therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
772.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1359.IP "bool ev_is_active (ev_TYPE *watcher)" 4
773.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1360.IX Item "bool ev_is_active (ev_TYPE *watcher)"
774Returns a true value iff the watcher is active (i.e. it has been started 1361Returns a true value iff the watcher is active (i.e. it has been started
775and not yet been stopped). As long as a watcher is active you must not modify 1362and not yet been stopped). As long as a watcher is active you must not modify
776it. 1363it.
777.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1364.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
778.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1365.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
779Returns a true value iff the watcher is pending, (i.e. it has outstanding 1366Returns a true value iff the watcher is pending, (i.e. it has outstanding
780events but its callback has not yet been invoked). As long as a watcher 1367events but its callback has not yet been invoked). As long as a watcher
781is pending (but not active) you must not call an init function on it (but 1368is pending (but not active) you must not call an init function on it (but
782\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1369\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
783libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1370make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1371it).
784.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1372.IP "callback ev_cb (ev_TYPE *watcher)" 4
785.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1373.IX Item "callback ev_cb (ev_TYPE *watcher)"
786Returns the callback currently set on the watcher. 1374Returns the callback currently set on the watcher.
787.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1375.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
788.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1376.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
789Change the callback. You can change the callback at virtually any time 1377Change the callback. You can change the callback at virtually any time
790(modulo threads). 1378(modulo threads).
1379.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1380.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1381.PD 0
1382.IP "int ev_priority (ev_TYPE *watcher)" 4
1383.IX Item "int ev_priority (ev_TYPE *watcher)"
1384.PD
1385Set and query the priority of the watcher. The priority is a small
1386integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1387(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1388before watchers with lower priority, but priority will not keep watchers
1389from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1390.Sp
1391If you need to suppress invocation when higher priority events are pending
1392you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1393.Sp
1394You \fImust not\fR change the priority of a watcher as long as it is active or
1395pending.
1396.Sp
1397Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1398fine, as long as you do not mind that the priority value you query might
1399or might not have been clamped to the valid range.
1400.Sp
1401The default priority used by watchers when no priority has been set is
1402always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1403.Sp
1404See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1405priorities.
1406.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1407.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1408Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1409\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1410can deal with that fact, as both are simply passed through to the
1411callback.
1412.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1413.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1414If the watcher is pending, this function clears its pending status and
1415returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1416watcher isn't pending it does nothing and returns \f(CW0\fR.
1417.Sp
1418Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1419callback to be invoked, which can be accomplished with this function.
1420.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1421.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1422Feeds the given event set into the event loop, as if the specified event
1423had happened for the specified watcher (which must be a pointer to an
1424initialised but not necessarily started event watcher). Obviously you must
1425not free the watcher as long as it has pending events.
1426.Sp
1427Stopping the watcher, letting libev invoke it, or calling
1428\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1429not started in the first place.
1430.Sp
1431See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1432functions that do not need a watcher.
791.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1433.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
792.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1434.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
793Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1435Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
794and read at any time, libev will completely ignore it. This can be used 1436and read at any time: libev will completely ignore it. This can be used
795to associate arbitrary data with your watcher. If you need more data and 1437to associate arbitrary data with your watcher. If you need more data and
796don't want to allocate memory and store a pointer to it in that data 1438don't want to allocate memory and store a pointer to it in that data
797member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1439member, you can also \*(L"subclass\*(R" the watcher type and provide your own
798data: 1440data:
799.PP 1441.PP
800.Vb 7 1442.Vb 7
801\& struct my_io 1443\& struct my_io
802\& { 1444\& {
803\& struct ev_io io; 1445\& ev_io io;
804\& int otherfd; 1446\& int otherfd;
805\& void *somedata; 1447\& void *somedata;
806\& struct whatever *mostinteresting; 1448\& struct whatever *mostinteresting;
807\& } 1449\& };
1450\&
1451\& ...
1452\& struct my_io w;
1453\& ev_io_init (&w.io, my_cb, fd, EV_READ);
808.Ve 1454.Ve
809.PP 1455.PP
810And since your callback will be called with a pointer to the watcher, you 1456And since your callback will be called with a pointer to the watcher, you
811can cast it back to your own type: 1457can cast it back to your own type:
812.PP 1458.PP
813.Vb 5 1459.Vb 5
814\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1460\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
815\& { 1461\& {
816\& struct my_io *w = (struct my_io *)w_; 1462\& struct my_io *w = (struct my_io *)w_;
817\& ... 1463\& ...
818\& } 1464\& }
819.Ve 1465.Ve
820.PP 1466.PP
821More interesting and less C\-conformant ways of catsing your callback type 1467More interesting and less C\-conformant ways of casting your callback type
822have been omitted.... 1468instead have been omitted.
1469.PP
1470Another common scenario is to use some data structure with multiple
1471embedded watchers:
1472.PP
1473.Vb 6
1474\& struct my_biggy
1475\& {
1476\& int some_data;
1477\& ev_timer t1;
1478\& ev_timer t2;
1479\& }
1480.Ve
1481.PP
1482In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1483complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1484in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1485some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1486programmers):
1487.PP
1488.Vb 1
1489\& #include <stddef.h>
1490\&
1491\& static void
1492\& t1_cb (EV_P_ ev_timer *w, int revents)
1493\& {
1494\& struct my_biggy big = (struct my_biggy *)
1495\& (((char *)w) \- offsetof (struct my_biggy, t1));
1496\& }
1497\&
1498\& static void
1499\& t2_cb (EV_P_ ev_timer *w, int revents)
1500\& {
1501\& struct my_biggy big = (struct my_biggy *)
1502\& (((char *)w) \- offsetof (struct my_biggy, t2));
1503\& }
1504.Ve
1505.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1506.IX Subsection "WATCHER STATES"
1507There are various watcher states mentioned throughout this manual \-
1508active, pending and so on. In this section these states and the rules to
1509transition between them will be described in more detail \- and while these
1510rules might look complicated, they usually do \*(L"the right thing\*(R".
1511.IP "initialiased" 4
1512.IX Item "initialiased"
1513Before a watcher can be registered with the event looop it has to be
1514initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1515\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1516.Sp
1517In this state it is simply some block of memory that is suitable for use
1518in an event loop. It can be moved around, freed, reused etc. at will.
1519.IP "started/running/active" 4
1520.IX Item "started/running/active"
1521Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1522property of the event loop, and is actively waiting for events. While in
1523this state it cannot be accessed (except in a few documented ways), moved,
1524freed or anything else \- the only legal thing is to keep a pointer to it,
1525and call libev functions on it that are documented to work on active watchers.
1526.IP "pending" 4
1527.IX Item "pending"
1528If a watcher is active and libev determines that an event it is interested
1529in has occurred (such as a timer expiring), it will become pending. It will
1530stay in this pending state until either it is stopped or its callback is
1531about to be invoked, so it is not normally pending inside the watcher
1532callback.
1533.Sp
1534The watcher might or might not be active while it is pending (for example,
1535an expired non-repeating timer can be pending but no longer active). If it
1536is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1537but it is still property of the event loop at this time, so cannot be
1538moved, freed or reused. And if it is active the rules described in the
1539previous item still apply.
1540.Sp
1541It is also possible to feed an event on a watcher that is not active (e.g.
1542via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1543active.
1544.IP "stopped" 4
1545.IX Item "stopped"
1546A watcher can be stopped implicitly by libev (in which case it might still
1547be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1548latter will clear any pending state the watcher might be in, regardless
1549of whether it was active or not, so stopping a watcher explicitly before
1550freeing it is often a good idea.
1551.Sp
1552While stopped (and not pending) the watcher is essentially in the
1553initialised state, that is it can be reused, moved, modified in any way
1554you wish.
1555.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1556.IX Subsection "WATCHER PRIORITY MODELS"
1557Many event loops support \fIwatcher priorities\fR, which are usually small
1558integers that influence the ordering of event callback invocation
1559between watchers in some way, all else being equal.
1560.PP
1561In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1562description for the more technical details such as the actual priority
1563range.
1564.PP
1565There are two common ways how these these priorities are being interpreted
1566by event loops:
1567.PP
1568In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1569of lower priority watchers, which means as long as higher priority
1570watchers receive events, lower priority watchers are not being invoked.
1571.PP
1572The less common only-for-ordering model uses priorities solely to order
1573callback invocation within a single event loop iteration: Higher priority
1574watchers are invoked before lower priority ones, but they all get invoked
1575before polling for new events.
1576.PP
1577Libev uses the second (only-for-ordering) model for all its watchers
1578except for idle watchers (which use the lock-out model).
1579.PP
1580The rationale behind this is that implementing the lock-out model for
1581watchers is not well supported by most kernel interfaces, and most event
1582libraries will just poll for the same events again and again as long as
1583their callbacks have not been executed, which is very inefficient in the
1584common case of one high-priority watcher locking out a mass of lower
1585priority ones.
1586.PP
1587Static (ordering) priorities are most useful when you have two or more
1588watchers handling the same resource: a typical usage example is having an
1589\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1590timeouts. Under load, data might be received while the program handles
1591other jobs, but since timers normally get invoked first, the timeout
1592handler will be executed before checking for data. In that case, giving
1593the timer a lower priority than the I/O watcher ensures that I/O will be
1594handled first even under adverse conditions (which is usually, but not
1595always, what you want).
1596.PP
1597Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1598will only be executed when no same or higher priority watchers have
1599received events, they can be used to implement the \*(L"lock-out\*(R" model when
1600required.
1601.PP
1602For example, to emulate how many other event libraries handle priorities,
1603you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1604the normal watcher callback, you just start the idle watcher. The real
1605processing is done in the idle watcher callback. This causes libev to
1606continuously poll and process kernel event data for the watcher, but when
1607the lock-out case is known to be rare (which in turn is rare :), this is
1608workable.
1609.PP
1610Usually, however, the lock-out model implemented that way will perform
1611miserably under the type of load it was designed to handle. In that case,
1612it might be preferable to stop the real watcher before starting the
1613idle watcher, so the kernel will not have to process the event in case
1614the actual processing will be delayed for considerable time.
1615.PP
1616Here is an example of an I/O watcher that should run at a strictly lower
1617priority than the default, and which should only process data when no
1618other events are pending:
1619.PP
1620.Vb 2
1621\& ev_idle idle; // actual processing watcher
1622\& ev_io io; // actual event watcher
1623\&
1624\& static void
1625\& io_cb (EV_P_ ev_io *w, int revents)
1626\& {
1627\& // stop the I/O watcher, we received the event, but
1628\& // are not yet ready to handle it.
1629\& ev_io_stop (EV_A_ w);
1630\&
1631\& // start the idle watcher to handle the actual event.
1632\& // it will not be executed as long as other watchers
1633\& // with the default priority are receiving events.
1634\& ev_idle_start (EV_A_ &idle);
1635\& }
1636\&
1637\& static void
1638\& idle_cb (EV_P_ ev_idle *w, int revents)
1639\& {
1640\& // actual processing
1641\& read (STDIN_FILENO, ...);
1642\&
1643\& // have to start the I/O watcher again, as
1644\& // we have handled the event
1645\& ev_io_start (EV_P_ &io);
1646\& }
1647\&
1648\& // initialisation
1649\& ev_idle_init (&idle, idle_cb);
1650\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1651\& ev_io_start (EV_DEFAULT_ &io);
1652.Ve
1653.PP
1654In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1655low-priority connections can not be locked out forever under load. This
1656enables your program to keep a lower latency for important connections
1657during short periods of high load, while not completely locking out less
1658important ones.
823.SH "WATCHER TYPES" 1659.SH "WATCHER TYPES"
824.IX Header "WATCHER TYPES" 1660.IX Header "WATCHER TYPES"
825This section describes each watcher in detail, but will not repeat 1661This section describes each watcher in detail, but will not repeat
826information given in the last section. 1662information given in the last section. Any initialisation/set macros,
1663functions and members specific to the watcher type are explained.
1664.PP
1665Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1666while the watcher is active, you can look at the member and expect some
1667sensible content, but you must not modify it (you can modify it while the
1668watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1669means you can expect it to have some sensible content while the watcher
1670is active, but you can also modify it. Modifying it may not do something
1671sensible or take immediate effect (or do anything at all), but libev will
1672not crash or malfunction in any way.
827.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1673.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
828.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1674.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
829.IX Subsection "ev_io - is this file descriptor readable or writable" 1675.IX Subsection "ev_io - is this file descriptor readable or writable?"
830I/O watchers check whether a file descriptor is readable or writable 1676I/O watchers check whether a file descriptor is readable or writable
831in each iteration of the event loop (This behaviour is called 1677in each iteration of the event loop, or, more precisely, when reading
832level-triggering because you keep receiving events as long as the 1678would not block the process and writing would at least be able to write
833condition persists. Remember you can stop the watcher if you don't want to 1679some data. This behaviour is called level-triggering because you keep
834act on the event and neither want to receive future events). 1680receiving events as long as the condition persists. Remember you can stop
1681the watcher if you don't want to act on the event and neither want to
1682receive future events.
835.PP 1683.PP
836In general you can register as many read and/or write event watchers per 1684In general you can register as many read and/or write event watchers per
837fd as you want (as long as you don't confuse yourself). Setting all file 1685fd as you want (as long as you don't confuse yourself). Setting all file
838descriptors to non-blocking mode is also usually a good idea (but not 1686descriptors to non-blocking mode is also usually a good idea (but not
839required if you know what you are doing). 1687required if you know what you are doing).
840.PP 1688.PP
841You have to be careful with dup'ed file descriptors, though. Some backends 1689If you cannot use non-blocking mode, then force the use of a
842(the linux epoll backend is a notable example) cannot handle dup'ed file 1690known-to-be-good backend (at the time of this writing, this includes only
843descriptors correctly if you register interest in two or more fds pointing 1691\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
844to the same underlying file/socket etc. description (that is, they share 1692descriptors for which non-blocking operation makes no sense (such as
845the same underlying \*(L"file open\*(R"). 1693files) \- libev doesn't guarantee any specific behaviour in that case.
846.PP 1694.PP
847If you must do this, then force the use of a known-to-be-good backend 1695Another thing you have to watch out for is that it is quite easy to
848(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1696receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1697be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1698because there is no data. Not only are some backends known to create a
1699lot of those (for example Solaris ports), it is very easy to get into
1700this situation even with a relatively standard program structure. Thus
1701it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1702\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1703.PP
1704If you cannot run the fd in non-blocking mode (for example you should
1705not play around with an Xlib connection), then you have to separately
1706re-test whether a file descriptor is really ready with a known-to-be good
1707interface such as poll (fortunately in our Xlib example, Xlib already
1708does this on its own, so its quite safe to use). Some people additionally
1709use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1710indefinitely.
1711.PP
1712But really, best use non-blocking mode.
1713.PP
1714\fIThe special problem of disappearing file descriptors\fR
1715.IX Subsection "The special problem of disappearing file descriptors"
1716.PP
1717Some backends (e.g. kqueue, epoll) need to be told about closing a file
1718descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1719such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1720descriptor, but when it goes away, the operating system will silently drop
1721this interest. If another file descriptor with the same number then is
1722registered with libev, there is no efficient way to see that this is, in
1723fact, a different file descriptor.
1724.PP
1725To avoid having to explicitly tell libev about such cases, libev follows
1726the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1727will assume that this is potentially a new file descriptor, otherwise
1728it is assumed that the file descriptor stays the same. That means that
1729you \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
1730descriptor even if the file descriptor number itself did not change.
1731.PP
1732This is how one would do it normally anyway, the important point is that
1733the libev application should not optimise around libev but should leave
1734optimisations to libev.
1735.PP
1736\fIThe special problem of dup'ed file descriptors\fR
1737.IX Subsection "The special problem of dup'ed file descriptors"
1738.PP
1739Some backends (e.g. epoll), cannot register events for file descriptors,
1740but only events for the underlying file descriptions. That means when you
1741have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1742events for them, only one file descriptor might actually receive events.
1743.PP
1744There is no workaround possible except not registering events
1745for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1746\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1747.PP
1748\fIThe special problem of fork\fR
1749.IX Subsection "The special problem of fork"
1750.PP
1751Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1752useless behaviour. Libev fully supports fork, but needs to be told about
1753it in the child.
1754.PP
1755To support fork in your programs, you either have to call
1756\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1757enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
849\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1758\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1759.PP
1760\fIThe special problem of \s-1SIGPIPE\s0\fR
1761.IX Subsection "The special problem of SIGPIPE"
1762.PP
1763While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1764when writing to a pipe whose other end has been closed, your program gets
1765sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1766this is sensible behaviour, for daemons, this is usually undesirable.
1767.PP
1768So when you encounter spurious, unexplained daemon exits, make sure you
1769ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1770somewhere, as that would have given you a big clue).
1771.PP
1772\fIThe special problem of \fIaccept()\fIing when you can't\fR
1773.IX Subsection "The special problem of accept()ing when you can't"
1774.PP
1775Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1776found in post\-2004 Linux) have the peculiar behaviour of not removing a
1777connection from the pending queue in all error cases.
1778.PP
1779For example, larger servers often run out of file descriptors (because
1780of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1781rejecting the connection, leading to libev signalling readiness on
1782the next iteration again (the connection still exists after all), and
1783typically causing the program to loop at 100% \s-1CPU\s0 usage.
1784.PP
1785Unfortunately, the set of errors that cause this issue differs between
1786operating systems, there is usually little the app can do to remedy the
1787situation, and no known thread-safe method of removing the connection to
1788cope with overload is known (to me).
1789.PP
1790One of the easiest ways to handle this situation is to just ignore it
1791\&\- when the program encounters an overload, it will just loop until the
1792situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1793event-based way to handle this situation, so it's the best one can do.
1794.PP
1795A better way to handle the situation is to log any errors other than
1796\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1797messages, and continue as usual, which at least gives the user an idea of
1798what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1799the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1800usage.
1801.PP
1802If your program is single-threaded, then you could also keep a dummy file
1803descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1804when 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,
1805close that fd, and create a new dummy fd. This will gracefully refuse
1806clients under typical overload conditions.
1807.PP
1808The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1809is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1810opportunity for a DoS attack.
1811.PP
1812\fIWatcher-Specific Functions\fR
1813.IX Subsection "Watcher-Specific Functions"
850.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1814.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
851.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1815.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
852.PD 0 1816.PD 0
853.IP "ev_io_set (ev_io *, int fd, int events)" 4 1817.IP "ev_io_set (ev_io *, int fd, int events)" 4
854.IX Item "ev_io_set (ev_io *, int fd, int events)" 1818.IX Item "ev_io_set (ev_io *, int fd, int events)"
855.PD 1819.PD
856Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1820Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
857events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1821receive 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
858EV_WRITE\*(C'\fR to receive the given events. 1822\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
859.Sp 1823.IP "int fd [read\-only]" 4
860Please note that most of the more scalable backend mechanisms (for example 1824.IX Item "int fd [read-only]"
861epoll and solaris ports) can result in spurious readyness notifications 1825The file descriptor being watched.
862for file descriptors, so you practically need to use non-blocking I/O (and 1826.IP "int events [read\-only]" 4
863treat callback invocation as hint only), or retest separately with a safe 1827.IX Item "int events [read-only]"
864interface before doing I/O (XLib can do this), or force the use of either 1828The events being watched.
865\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
866problem. Also note that it is quite easy to have your callback invoked
867when the readyness condition is no longer valid even when employing
868typical ways of handling events, so its a good idea to use non-blocking
869I/O unconditionally.
870.PP 1829.PP
1830\fIExamples\fR
1831.IX Subsection "Examples"
1832.PP
871Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1833Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
872readable, but only once. Since it is likely line\-buffered, you could 1834readable, but only once. Since it is likely line-buffered, you could
873attempt to read a whole line in the callback: 1835attempt to read a whole line in the callback.
874.PP 1836.PP
875.Vb 6 1837.Vb 6
876\& static void 1838\& static void
877\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1839\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
878\& { 1840\& {
879\& ev_io_stop (loop, w); 1841\& ev_io_stop (loop, w);
880\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1842\& .. read from stdin here (or from w\->fd) and handle any I/O errors
881\& } 1843\& }
882.Ve 1844\&
883.PP
884.Vb 6
885\& ... 1845\& ...
886\& struct ev_loop *loop = ev_default_init (0); 1846\& struct ev_loop *loop = ev_default_init (0);
887\& struct ev_io stdin_readable; 1847\& ev_io stdin_readable;
888\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1848\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
889\& ev_io_start (loop, &stdin_readable); 1849\& ev_io_start (loop, &stdin_readable);
890\& ev_loop (loop, 0); 1850\& ev_run (loop, 0);
891.Ve 1851.Ve
892.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1852.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
893.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1853.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
894.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1854.IX Subsection "ev_timer - relative and optionally repeating timeouts"
895Timer watchers are simple relative timers that generate an event after a 1855Timer watchers are simple relative timers that generate an event after a
896given time, and optionally repeating in regular intervals after that. 1856given time, and optionally repeating in regular intervals after that.
897.PP 1857.PP
898The timers are based on real time, that is, if you register an event that 1858The timers are based on real time, that is, if you register an event that
899times out after an hour and you reset your system clock to last years 1859times out after an hour and you reset your system clock to January last
900time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1860year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
901detecting time jumps is hard, and some inaccuracies are unavoidable (the 1861detecting time jumps is hard, and some inaccuracies are unavoidable (the
902monotonic clock option helps a lot here). 1862monotonic clock option helps a lot here).
1863.PP
1864The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1865passed (not \fIat\fR, so on systems with very low-resolution clocks this
1866might introduce a small delay). If multiple timers become ready during the
1867same loop iteration then the ones with earlier time-out values are invoked
1868before ones of the same priority with later time-out values (but this is
1869no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1870.PP
1871\fIBe smart about timeouts\fR
1872.IX Subsection "Be smart about timeouts"
1873.PP
1874Many real-world problems involve some kind of timeout, usually for error
1875recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1876you want to raise some error after a while.
1877.PP
1878What follows are some ways to handle this problem, from obvious and
1879inefficient to smart and efficient.
1880.PP
1881In the following, a 60 second activity timeout is assumed \- a timeout that
1882gets reset to 60 seconds each time there is activity (e.g. each time some
1883data or other life sign was received).
1884.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1885.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1886This is the most obvious, but not the most simple way: In the beginning,
1887start the watcher:
1888.Sp
1889.Vb 2
1890\& ev_timer_init (timer, callback, 60., 0.);
1891\& ev_timer_start (loop, timer);
1892.Ve
1893.Sp
1894Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1895and start it again:
1896.Sp
1897.Vb 3
1898\& ev_timer_stop (loop, timer);
1899\& ev_timer_set (timer, 60., 0.);
1900\& ev_timer_start (loop, timer);
1901.Ve
1902.Sp
1903This is relatively simple to implement, but means that each time there is
1904some activity, libev will first have to remove the timer from its internal
1905data structure and then add it again. Libev tries to be fast, but it's
1906still not a constant-time operation.
1907.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1908.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1909.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1910This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1911\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1912.Sp
1913To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1914of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1915successfully read or write some data. If you go into an idle state where
1916you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1917the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1918.Sp
1919That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1920\&\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
1921member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1922.Sp
1923At start:
1924.Sp
1925.Vb 3
1926\& ev_init (timer, callback);
1927\& timer\->repeat = 60.;
1928\& ev_timer_again (loop, timer);
1929.Ve
1930.Sp
1931Each time there is some activity:
1932.Sp
1933.Vb 1
1934\& ev_timer_again (loop, timer);
1935.Ve
1936.Sp
1937It is even possible to change the time-out on the fly, regardless of
1938whether the watcher is active or not:
1939.Sp
1940.Vb 2
1941\& timer\->repeat = 30.;
1942\& ev_timer_again (loop, timer);
1943.Ve
1944.Sp
1945This is slightly more efficient then stopping/starting the timer each time
1946you want to modify its timeout value, as libev does not have to completely
1947remove and re-insert the timer from/into its internal data structure.
1948.Sp
1949It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1950.IP "3. Let the timer time out, but then re-arm it as required." 4
1951.IX Item "3. Let the timer time out, but then re-arm it as required."
1952This method is more tricky, but usually most efficient: Most timeouts are
1953relatively long compared to the intervals between other activity \- in
1954our example, within 60 seconds, there are usually many I/O events with
1955associated activity resets.
1956.Sp
1957In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1958but remember the time of last activity, and check for a real timeout only
1959within the callback:
1960.Sp
1961.Vb 1
1962\& ev_tstamp last_activity; // time of last activity
1963\&
1964\& static void
1965\& callback (EV_P_ ev_timer *w, int revents)
1966\& {
1967\& ev_tstamp now = ev_now (EV_A);
1968\& ev_tstamp timeout = last_activity + 60.;
1969\&
1970\& // if last_activity + 60. is older than now, we did time out
1971\& if (timeout < now)
1972\& {
1973\& // timeout occurred, take action
1974\& }
1975\& else
1976\& {
1977\& // callback was invoked, but there was some activity, re\-arm
1978\& // the watcher to fire in last_activity + 60, which is
1979\& // guaranteed to be in the future, so "again" is positive:
1980\& w\->repeat = timeout \- now;
1981\& ev_timer_again (EV_A_ w);
1982\& }
1983\& }
1984.Ve
1985.Sp
1986To summarise the callback: first calculate the real timeout (defined
1987as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1988been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1989the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1990re-schedule the timer to fire at that future time, to see if maybe we have
1991a timeout then.
1992.Sp
1993Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1994\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1995.Sp
1996This scheme causes more callback invocations (about one every 60 seconds
1997minus half the average time between activity), but virtually no calls to
1998libev to change the timeout.
1999.Sp
2000To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
2001to the current time (meaning we just have some activity :), then call the
2002callback, which will \*(L"do the right thing\*(R" and start the timer:
2003.Sp
2004.Vb 3
2005\& ev_init (timer, callback);
2006\& last_activity = ev_now (loop);
2007\& callback (loop, timer, EV_TIMER);
2008.Ve
2009.Sp
2010And when there is some activity, simply store the current time in
2011\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2012.Sp
2013.Vb 1
2014\& last_activity = ev_now (loop);
2015.Ve
2016.Sp
2017This technique is slightly more complex, but in most cases where the
2018time-out is unlikely to be triggered, much more efficient.
2019.Sp
2020Changing the timeout is trivial as well (if it isn't hard-coded in the
2021callback :) \- just change the timeout and invoke the callback, which will
2022fix things for you.
2023.IP "4. Wee, just use a double-linked list for your timeouts." 4
2024.IX Item "4. Wee, just use a double-linked list for your timeouts."
2025If there is not one request, but many thousands (millions...), all
2026employing some kind of timeout with the same timeout value, then one can
2027do even better:
2028.Sp
2029When starting the timeout, calculate the timeout value and put the timeout
2030at the \fIend\fR of the list.
2031.Sp
2032Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2033the list is expected to fire (for example, using the technique #3).
2034.Sp
2035When there is some activity, remove the timer from the list, recalculate
2036the timeout, append it to the end of the list again, and make sure to
2037update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2038.Sp
2039This way, one can manage an unlimited number of timeouts in O(1) time for
2040starting, stopping and updating the timers, at the expense of a major
2041complication, and having to use a constant timeout. The constant timeout
2042ensures that the list stays sorted.
2043.PP
2044So which method the best?
2045.PP
2046Method #2 is a simple no-brain-required solution that is adequate in most
2047situations. Method #3 requires a bit more thinking, but handles many cases
2048better, and isn't very complicated either. In most case, choosing either
2049one is fine, with #3 being better in typical situations.
2050.PP
2051Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2052rather complicated, but extremely efficient, something that really pays
2053off after the first million or so of active timers, i.e. it's usually
2054overkill :)
2055.PP
2056\fIThe special problem of time updates\fR
2057.IX Subsection "The special problem of time updates"
2058.PP
2059Establishing the current time is a costly operation (it usually takes at
2060least two system calls): \s-1EV\s0 therefore updates its idea of the current
2061time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2062growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2063lots of events in one iteration.
903.PP 2064.PP
904The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2065The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
905time. This is usually the right thing as this timestamp refers to the time 2066time. This is usually the right thing as this timestamp refers to the time
906of the event triggering whatever timeout you are modifying/starting. If 2067of the event triggering whatever timeout you are modifying/starting. If
907you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2068you suspect event processing to be delayed and you \fIneed\fR to base the
908on the current time, use something like this to adjust for this: 2069timeout on the current time, use something like this to adjust for this:
909.PP 2070.PP
910.Vb 1 2071.Vb 1
911\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2072\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
912.Ve 2073.Ve
913.PP 2074.PP
914The callback is guarenteed to be invoked only when its timeout has passed, 2075If the event loop is suspended for a long time, you can also force an
915but if multiple timers become ready during the same loop iteration then 2076update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
916order of execution is undefined. 2077()\*(C'\fR.
2078.PP
2079\fIThe special problems of suspended animation\fR
2080.IX Subsection "The special problems of suspended animation"
2081.PP
2082When you leave the server world it is quite customary to hit machines that
2083can suspend/hibernate \- what happens to the clocks during such a suspend?
2084.PP
2085Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2086all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2087to run until the system is suspended, but they will not advance while the
2088system is suspended. That means, on resume, it will be as if the program
2089was frozen for a few seconds, but the suspend time will not be counted
2090towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2091clock advanced as expected, but if it is used as sole clocksource, then a
2092long suspend would be detected as a time jump by libev, and timers would
2093be adjusted accordingly.
2094.PP
2095I would not be surprised to see different behaviour in different between
2096operating systems, \s-1OS\s0 versions or even different hardware.
2097.PP
2098The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2099time jump in the monotonic clocks and the realtime clock. If the program
2100is suspended for a very long time, and monotonic clock sources are in use,
2101then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2102will be counted towards the timers. When no monotonic clock source is in
2103use, then libev will again assume a timejump and adjust accordingly.
2104.PP
2105It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2106and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2107deterministic behaviour in this case (you can do nothing against
2108\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2109.PP
2110\fIWatcher-Specific Functions and Data Members\fR
2111.IX Subsection "Watcher-Specific Functions and Data Members"
917.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2112.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
918.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2113.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
919.PD 0 2114.PD 0
920.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2115.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
921.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2116.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
922.PD 2117.PD
923Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2118Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
924\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2119is \f(CW0.\fR, then it will automatically be stopped once the timeout is
925timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2120reached. If it is positive, then the timer will automatically be
926later, again, and again, until stopped manually. 2121configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2122until stopped manually.
927.Sp 2123.Sp
928The timer itself will do a best-effort at avoiding drift, that is, if you 2124The timer itself will do a best-effort at avoiding drift, that is, if
929configure a timer to trigger every 10 seconds, then it will trigger at 2125you configure a timer to trigger every 10 seconds, then it will normally
930exactly 10 second intervals. If, however, your program cannot keep up with 2126trigger at exactly 10 second intervals. If, however, your program cannot
931the timer (because it takes longer than those 10 seconds to do stuff) the 2127keep up with the timer (because it takes longer than those 10 seconds to
932timer will not fire more than once per event loop iteration. 2128do stuff) the timer will not fire more than once per event loop iteration.
933.IP "ev_timer_again (loop)" 4 2129.IP "ev_timer_again (loop, ev_timer *)" 4
934.IX Item "ev_timer_again (loop)" 2130.IX Item "ev_timer_again (loop, ev_timer *)"
935This will act as if the timer timed out and restart it again if it is 2131This will act as if the timer timed out and restart it again if it is
936repeating. The exact semantics are: 2132repeating. The exact semantics are:
937.Sp 2133.Sp
2134If the timer is pending, its pending status is cleared.
2135.Sp
938If the timer is started but nonrepeating, stop it. 2136If the timer is started but non-repeating, stop it (as if it timed out).
939.Sp 2137.Sp
940If the timer is repeating, either start it if necessary (with the repeat 2138If the timer is repeating, either start it if necessary (with the
941value), or reset the running timer to the repeat value. 2139\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
942.Sp 2140.Sp
943This sounds a bit complicated, but here is a useful and typical 2141This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
944example: Imagine you have a tcp connection and you want a so-called idle 2142usage example.
945timeout, that is, you want to be called when there have been, say, 60 2143.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
946seconds of inactivity on the socket. The easiest way to do this is to 2144.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
947configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2145Returns the remaining time until a timer fires. If the timer is active,
948time you successfully read or write some data. If you go into an idle 2146then this time is relative to the current event loop time, otherwise it's
949state where you do not expect data to travel on the socket, you can stop 2147the timeout value currently configured.
950the timer, and again will automatically restart it if need be. 2148.Sp
2149That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2150\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2151will return \f(CW4\fR. When the timer expires and is restarted, it will return
2152roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2153too), and so on.
2154.IP "ev_tstamp repeat [read\-write]" 4
2155.IX Item "ev_tstamp repeat [read-write]"
2156The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2157or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2158which is also when any modifications are taken into account.
951.PP 2159.PP
2160\fIExamples\fR
2161.IX Subsection "Examples"
2162.PP
952Example: create a timer that fires after 60 seconds. 2163Example: Create a timer that fires after 60 seconds.
953.PP 2164.PP
954.Vb 5 2165.Vb 5
955\& static void 2166\& static void
956\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2167\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
957\& { 2168\& {
958\& .. one minute over, w is actually stopped right here 2169\& .. one minute over, w is actually stopped right here
959\& } 2170\& }
960.Ve 2171\&
961.PP
962.Vb 3
963\& struct ev_timer mytimer; 2172\& ev_timer mytimer;
964\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2173\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
965\& ev_timer_start (loop, &mytimer); 2174\& ev_timer_start (loop, &mytimer);
966.Ve 2175.Ve
967.PP 2176.PP
968Example: create a timeout timer that times out after 10 seconds of 2177Example: Create a timeout timer that times out after 10 seconds of
969inactivity. 2178inactivity.
970.PP 2179.PP
971.Vb 5 2180.Vb 5
972\& static void 2181\& static void
973\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2182\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974\& { 2183\& {
975\& .. ten seconds without any activity 2184\& .. ten seconds without any activity
976\& } 2185\& }
977.Ve 2186\&
978.PP
979.Vb 4
980\& struct ev_timer mytimer; 2187\& ev_timer mytimer;
981\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2188\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982\& ev_timer_again (&mytimer); /* start timer */ 2189\& ev_timer_again (&mytimer); /* start timer */
983\& ev_loop (loop, 0); 2190\& ev_run (loop, 0);
984.Ve 2191\&
985.PP
986.Vb 3
987\& // and in some piece of code that gets executed on any "activity": 2192\& // and in some piece of code that gets executed on any "activity":
988\& // reset the timeout to start ticking again at 10 seconds 2193\& // reset the timeout to start ticking again at 10 seconds
989\& ev_timer_again (&mytimer); 2194\& ev_timer_again (&mytimer);
990.Ve 2195.Ve
991.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2196.ie n .SS """ev_periodic"" \- to cron or not to cron?"
992.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2197.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
993.IX Subsection "ev_periodic - to cron or not to cron" 2198.IX Subsection "ev_periodic - to cron or not to cron?"
994Periodic watchers are also timers of a kind, but they are very versatile 2199Periodic watchers are also timers of a kind, but they are very versatile
995(and unfortunately a bit complex). 2200(and unfortunately a bit complex).
996.PP 2201.PP
997Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2202Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
998but on wallclock time (absolute time). You can tell a periodic watcher 2203relative time, the physical time that passes) but on wall clock time
999to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2204(absolute time, the thing you can read on your calender or clock). The
1000periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2205difference is that wall clock time can run faster or slower than real
1001+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2206time, and time jumps are not uncommon (e.g. when you adjust your
1002take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2207wrist-watch).
1003roughly 10 seconds later and of course not if you reset your system time
1004again).
1005.PP 2208.PP
1006They can also be used to implement vastly more complex timers, such as 2209You can tell a periodic watcher to trigger after some specific point
1007triggering an event on eahc midnight, local time. 2210in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2211seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2212not a delay) and then reset your system clock to January of the previous
2213year, then it will take a year or more to trigger the event (unlike an
2214\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2215it, as it uses a relative timeout).
1008.PP 2216.PP
2217\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2218timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2219other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2220those cannot react to time jumps.
2221.PP
1009As with timers, the callback is guarenteed to be invoked only when the 2222As with timers, the callback is guaranteed to be invoked only when the
1010time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2223point in time where it is supposed to trigger has passed. If multiple
1011during the same loop iteration then order of execution is undefined. 2224timers become ready during the same loop iteration then the ones with
2225earlier time-out values are invoked before ones with later time-out values
2226(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2227.PP
2228\fIWatcher-Specific Functions and Data Members\fR
2229.IX Subsection "Watcher-Specific Functions and Data Members"
1012.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2230.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1013.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2231.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1014.PD 0 2232.PD 0
1015.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2233.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1016.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2234.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1017.PD 2235.PD
1018Lots of arguments, lets sort it out... There are basically three modes of 2236Lots of arguments, let's sort it out... There are basically three modes of
1019operation, and we will explain them from simplest to complex: 2237operation, and we will explain them from simplest to most complex:
1020.RS 4 2238.RS 4
1021.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2239.IP "\(bu" 4
1022.IX Item "absolute timer (interval = reschedule_cb = 0)" 2240absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2241.Sp
1023In this configuration the watcher triggers an event at the wallclock time 2242In this configuration the watcher triggers an event after the wall clock
1024\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2243time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1025that is, if it is to be run at January 1st 2011 then it will run when the 2244time jump occurs, that is, if it is to be run at January 1st 2011 then it
1026system time reaches or surpasses this time. 2245will be stopped and invoked when the system clock reaches or surpasses
1027.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2246this point in time.
1028.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2247.IP "\(bu" 4
2248repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2249.Sp
1029In this mode the watcher will always be scheduled to time out at the next 2250In this mode the watcher will always be scheduled to time out at the next
1030\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2251\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1031of any time jumps. 2252negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2253argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1032.Sp 2254.Sp
1033This can be used to create timers that do not drift with respect to system 2255This can be used to create timers that do not drift with respect to the
1034time: 2256system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2257hour, on the hour (with respect to \s-1UTC\s0):
1035.Sp 2258.Sp
1036.Vb 1 2259.Vb 1
1037\& ev_periodic_set (&periodic, 0., 3600., 0); 2260\& ev_periodic_set (&periodic, 0., 3600., 0);
1038.Ve 2261.Ve
1039.Sp 2262.Sp
1040This doesn't mean there will always be 3600 seconds in between triggers, 2263This doesn't mean there will always be 3600 seconds in between triggers,
1041but only that the the callback will be called when the system time shows a 2264but only that the callback will be called when the system time shows a
1042full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2265full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1043by 3600. 2266by 3600.
1044.Sp 2267.Sp
1045Another way to think about it (for the mathematically inclined) is that 2268Another way to think about it (for the mathematically inclined) is that
1046\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2269\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1047time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2270time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1048.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2271.Sp
1049.IX Item "manual reschedule mode (reschedule_cb = callback)" 2272For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2273\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2274this value, and in fact is often specified as zero.
2275.Sp
2276Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2277speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2278will of course deteriorate. Libev itself tries to be exact to be about one
2279millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2280.IP "\(bu" 4
2281manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2282.Sp
1050In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2283In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1051ignored. Instead, each time the periodic watcher gets scheduled, the 2284ignored. Instead, each time the periodic watcher gets scheduled, the
1052reschedule callback will be called with the watcher as first, and the 2285reschedule callback will be called with the watcher as first, and the
1053current time as second argument. 2286current time as second argument.
1054.Sp 2287.Sp
1055\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2288\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1056ever, or make any event loop modifications\fR. If you need to stop it, 2289or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1057return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2290allowed by documentation here\fR.
1058starting a prepare watcher).
1059.Sp 2291.Sp
2292If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2293it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2294only event loop modification you are allowed to do).
2295.Sp
1060Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2296The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1061ev_tstamp now)\*(C'\fR, e.g.: 2297*w, ev_tstamp now)\*(C'\fR, e.g.:
1062.Sp 2298.Sp
1063.Vb 4 2299.Vb 5
2300\& static ev_tstamp
1064\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2301\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1065\& { 2302\& {
1066\& return now + 60.; 2303\& return now + 60.;
1067\& } 2304\& }
1068.Ve 2305.Ve
1069.Sp 2306.Sp
1070It must return the next time to trigger, based on the passed time value 2307It must return the next time to trigger, based on the passed time value
1071(that is, the lowest time value larger than to the second argument). It 2308(that is, the lowest time value larger than to the second argument). It
1072will usually be called just before the callback will be triggered, but 2309will usually be called just before the callback will be triggered, but
1073might be called at other times, too. 2310might be called at other times, too.
1074.Sp 2311.Sp
1075\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2312\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1076passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2313equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1077.Sp 2314.Sp
1078This can be used to create very complex timers, such as a timer that 2315This can be used to create very complex timers, such as a timer that
1079triggers on each midnight, local time. To do this, you would calculate the 2316triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1080next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2317next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1081you do this is, again, up to you (but it is not trivial, which is the main 2318you do this is, again, up to you (but it is not trivial, which is the main
1082reason I omitted it as an example). 2319reason I omitted it as an example).
1083.RE 2320.RE
1084.RS 4 2321.RS 4
… …
1087.IX Item "ev_periodic_again (loop, ev_periodic *)" 2324.IX Item "ev_periodic_again (loop, ev_periodic *)"
1088Simply stops and restarts the periodic watcher again. This is only useful 2325Simply stops and restarts the periodic watcher again. This is only useful
1089when you changed some parameters or the reschedule callback would return 2326when you changed some parameters or the reschedule callback would return
1090a different time than the last time it was called (e.g. in a crond like 2327a different time than the last time it was called (e.g. in a crond like
1091program when the crontabs have changed). 2328program when the crontabs have changed).
2329.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2330.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2331When active, returns the absolute time that the watcher is supposed
2332to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2333\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2334rescheduling modes.
2335.IP "ev_tstamp offset [read\-write]" 4
2336.IX Item "ev_tstamp offset [read-write]"
2337When repeating, this contains the offset value, otherwise this is the
2338absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2339although libev might modify this value for better numerical stability).
2340.Sp
2341Can be modified any time, but changes only take effect when the periodic
2342timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2343.IP "ev_tstamp interval [read\-write]" 4
2344.IX Item "ev_tstamp interval [read-write]"
2345The current interval value. Can be modified any time, but changes only
2346take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2347called.
2348.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2349.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2350The current reschedule callback, or \f(CW0\fR, if this functionality is
2351switched off. Can be changed any time, but changes only take effect when
2352the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1092.PP 2353.PP
2354\fIExamples\fR
2355.IX Subsection "Examples"
2356.PP
1093Example: call a callback every hour, or, more precisely, whenever the 2357Example: Call a callback every hour, or, more precisely, whenever the
1094system clock is divisible by 3600. The callback invocation times have 2358system time is divisible by 3600. The callback invocation times have
1095potentially a lot of jittering, but good long-term stability. 2359potentially a lot of jitter, but good long-term stability.
1096.PP 2360.PP
1097.Vb 5 2361.Vb 5
1098\& static void 2362\& static void
1099\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2363\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1100\& { 2364\& {
1101\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2365\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1102\& } 2366\& }
1103.Ve 2367\&
1104.PP
1105.Vb 3
1106\& struct ev_periodic hourly_tick; 2368\& ev_periodic hourly_tick;
1107\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2369\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1108\& ev_periodic_start (loop, &hourly_tick); 2370\& ev_periodic_start (loop, &hourly_tick);
1109.Ve 2371.Ve
1110.PP 2372.PP
1111Example: the same as above, but use a reschedule callback to do it: 2373Example: The same as above, but use a reschedule callback to do it:
1112.PP 2374.PP
1113.Vb 1 2375.Vb 1
1114\& #include <math.h> 2376\& #include <math.h>
1115.Ve 2377\&
1116.PP
1117.Vb 5
1118\& static ev_tstamp 2378\& static ev_tstamp
1119\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2379\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1120\& { 2380\& {
1121\& return fmod (now, 3600.) + 3600.; 2381\& return now + (3600. \- fmod (now, 3600.));
1122\& } 2382\& }
1123.Ve 2383\&
1124.PP
1125.Vb 1
1126\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2384\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1127.Ve 2385.Ve
1128.PP 2386.PP
1129Example: call a callback every hour, starting now: 2387Example: Call a callback every hour, starting now:
1130.PP 2388.PP
1131.Vb 4 2389.Vb 4
1132\& struct ev_periodic hourly_tick; 2390\& ev_periodic hourly_tick;
1133\& ev_periodic_init (&hourly_tick, clock_cb, 2391\& ev_periodic_init (&hourly_tick, clock_cb,
1134\& fmod (ev_now (loop), 3600.), 3600., 0); 2392\& fmod (ev_now (loop), 3600.), 3600., 0);
1135\& ev_periodic_start (loop, &hourly_tick); 2393\& ev_periodic_start (loop, &hourly_tick);
1136.Ve 2394.Ve
1137.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2395.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1138.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2396.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1139.IX Subsection "ev_signal - signal me when a signal gets signalled" 2397.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1140Signal watchers will trigger an event when the process receives a specific 2398Signal watchers will trigger an event when the process receives a specific
1141signal one or more times. Even though signals are very asynchronous, libev 2399signal one or more times. Even though signals are very asynchronous, libev
1142will try it's best to deliver signals synchronously, i.e. as part of the 2400will try its best to deliver signals synchronously, i.e. as part of the
1143normal event processing, like any other event. 2401normal event processing, like any other event.
1144.PP 2402.PP
2403If you want signals to be delivered truly asynchronously, just use
2404\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2405the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2406synchronously wake up an event loop.
2407.PP
1145You can configure as many watchers as you like per signal. Only when the 2408You can configure as many watchers as you like for the same signal, but
2409only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2410default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2411\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2412the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2413.PP
1146first watcher gets started will libev actually register a signal watcher 2414When the first watcher gets started will libev actually register something
1147with the kernel (thus it coexists with your own signal handlers as long 2415with the kernel (thus it coexists with your own signal handlers as long as
1148as you don't register any with libev). Similarly, when the last signal 2416you don't register any with libev for the same signal).
1149watcher for a signal is stopped libev will reset the signal handler to 2417.PP
1150\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2418If possible and supported, libev will install its handlers with
2419\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2420not be unduly interrupted. If you have a problem with system calls getting
2421interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2422and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2423.PP
2424\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2425.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2426.PP
2427Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2428(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2429stopping it again), that is, libev might or might not block the signal,
2430and might or might not set or restore the installed signal handler.
2431.PP
2432While this does not matter for the signal disposition (libev never
2433sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2434\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2435certain signals to be blocked.
2436.PP
2437This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2438the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2439choice usually).
2440.PP
2441The simplest way to ensure that the signal mask is reset in the child is
2442to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2443catch fork calls done by libraries (such as the libc) as well.
2444.PP
2445In current versions of libev, the signal will not be blocked indefinitely
2446unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2447the window of opportunity for problems, it will not go away, as libev
2448\&\fIhas\fR to modify the signal mask, at least temporarily.
2449.PP
2450So I can't stress this enough: \fIIf you do not reset your signal mask when
2451you expect it to be empty, you have a race condition in your code\fR. This
2452is not a libev-specific thing, this is true for most event libraries.
2453.PP
2454\fIWatcher-Specific Functions and Data Members\fR
2455.IX Subsection "Watcher-Specific Functions and Data Members"
1151.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2456.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1152.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2457.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1153.PD 0 2458.PD 0
1154.IP "ev_signal_set (ev_signal *, int signum)" 4 2459.IP "ev_signal_set (ev_signal *, int signum)" 4
1155.IX Item "ev_signal_set (ev_signal *, int signum)" 2460.IX Item "ev_signal_set (ev_signal *, int signum)"
1156.PD 2461.PD
1157Configures the watcher to trigger on the given signal number (usually one 2462Configures the watcher to trigger on the given signal number (usually one
1158of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2463of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2464.IP "int signum [read\-only]" 4
2465.IX Item "int signum [read-only]"
2466The signal the watcher watches out for.
2467.PP
2468\fIExamples\fR
2469.IX Subsection "Examples"
2470.PP
2471Example: Try to exit cleanly on \s-1SIGINT\s0.
2472.PP
2473.Vb 5
2474\& static void
2475\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2476\& {
2477\& ev_break (loop, EVBREAK_ALL);
2478\& }
2479\&
2480\& ev_signal signal_watcher;
2481\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2482\& ev_signal_start (loop, &signal_watcher);
2483.Ve
1159.ie n .Sh """ev_child"" \- wait for pid status changes" 2484.ie n .SS """ev_child"" \- watch out for process status changes"
1160.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2485.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1161.IX Subsection "ev_child - wait for pid status changes" 2486.IX Subsection "ev_child - watch out for process status changes"
1162Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2487Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1163some child status changes (most typically when a child of yours dies). 2488some child status changes (most typically when a child of yours dies or
2489exits). It is permissible to install a child watcher \fIafter\fR the child
2490has been forked (which implies it might have already exited), as long
2491as the event loop isn't entered (or is continued from a watcher), i.e.,
2492forking and then immediately registering a watcher for the child is fine,
2493but forking and registering a watcher a few event loop iterations later or
2494in the next callback invocation is not.
2495.PP
2496Only the default event loop is capable of handling signals, and therefore
2497you can only register child watchers in the default event loop.
2498.PP
2499Due to some design glitches inside libev, child watchers will always be
2500handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2501libev)
2502.PP
2503\fIProcess Interaction\fR
2504.IX Subsection "Process Interaction"
2505.PP
2506Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2507initialised. This is necessary to guarantee proper behaviour even if the
2508first child watcher is started after the child exits. The occurrence
2509of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2510synchronously as part of the event loop processing. Libev always reaps all
2511children, even ones not watched.
2512.PP
2513\fIOverriding the Built-In Processing\fR
2514.IX Subsection "Overriding the Built-In Processing"
2515.PP
2516Libev offers no special support for overriding the built-in child
2517processing, but if your application collides with libev's default child
2518handler, you can override it easily by installing your own handler for
2519\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2520default loop never gets destroyed. You are encouraged, however, to use an
2521event-based approach to child reaping and thus use libev's support for
2522that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2523.PP
2524\fIStopping the Child Watcher\fR
2525.IX Subsection "Stopping the Child Watcher"
2526.PP
2527Currently, the child watcher never gets stopped, even when the
2528child terminates, so normally one needs to stop the watcher in the
2529callback. Future versions of libev might stop the watcher automatically
2530when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2531problem).
2532.PP
2533\fIWatcher-Specific Functions and Data Members\fR
2534.IX Subsection "Watcher-Specific Functions and Data Members"
1164.IP "ev_child_init (ev_child *, callback, int pid)" 4 2535.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1165.IX Item "ev_child_init (ev_child *, callback, int pid)" 2536.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1166.PD 0 2537.PD 0
1167.IP "ev_child_set (ev_child *, int pid)" 4 2538.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1168.IX Item "ev_child_set (ev_child *, int pid)" 2539.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1169.PD 2540.PD
1170Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2541Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1171\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2542\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1172at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2543at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1173the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2544the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1174\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2545\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1175process causing the status change. 2546process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2547activate the watcher when the process terminates) or \f(CW1\fR (additionally
2548activate the watcher when the process is stopped or continued).
2549.IP "int pid [read\-only]" 4
2550.IX Item "int pid [read-only]"
2551The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2552.IP "int rpid [read\-write]" 4
2553.IX Item "int rpid [read-write]"
2554The process id that detected a status change.
2555.IP "int rstatus [read\-write]" 4
2556.IX Item "int rstatus [read-write]"
2557The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2558\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1176.PP 2559.PP
1177Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2560\fIExamples\fR
2561.IX Subsection "Examples"
1178.PP 2562.PP
2563Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2564its completion.
2565.PP
1179.Vb 5 2566.Vb 1
2567\& ev_child cw;
2568\&
1180\& static void 2569\& static void
1181\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2570\& child_cb (EV_P_ ev_child *w, int revents)
1182\& { 2571\& {
1183\& ev_unloop (loop, EVUNLOOP_ALL); 2572\& ev_child_stop (EV_A_ w);
2573\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1184\& } 2574\& }
2575\&
2576\& pid_t pid = fork ();
2577\&
2578\& if (pid < 0)
2579\& // error
2580\& else if (pid == 0)
2581\& {
2582\& // the forked child executes here
2583\& exit (1);
2584\& }
2585\& else
2586\& {
2587\& ev_child_init (&cw, child_cb, pid, 0);
2588\& ev_child_start (EV_DEFAULT_ &cw);
2589\& }
1185.Ve 2590.Ve
2591.ie n .SS """ev_stat"" \- did the file attributes just change?"
2592.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2593.IX Subsection "ev_stat - did the file attributes just change?"
2594This watches a file system path for attribute changes. That is, it calls
2595\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2596and sees if it changed compared to the last time, invoking the callback if
2597it did.
1186.PP 2598.PP
2599The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2600not exist\*(R" is a status change like any other. The condition \*(L"path does not
2601exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2602\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2603least one) and all the other fields of the stat buffer having unspecified
2604contents.
2605.PP
2606The path \fImust not\fR end in a slash or contain special components such as
2607\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2608your working directory changes, then the behaviour is undefined.
2609.PP
2610Since there is no portable change notification interface available, the
2611portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2612to see if it changed somehow. You can specify a recommended polling
2613interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2614recommended!) then a \fIsuitable, unspecified default\fR value will be used
2615(which you can expect to be around five seconds, although this might
2616change dynamically). Libev will also impose a minimum interval which is
2617currently around \f(CW0.1\fR, but that's usually overkill.
2618.PP
2619This watcher type is not meant for massive numbers of stat watchers,
2620as even with OS-supported change notifications, this can be
2621resource-intensive.
2622.PP
2623At the time of this writing, the only OS-specific interface implemented
2624is the Linux inotify interface (implementing kqueue support is left as an
2625exercise for the reader. Note, however, that the author sees no way of
2626implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2627.PP
2628\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2629.IX Subsection "ABI Issues (Largefile Support)"
2630.PP
2631Libev by default (unless the user overrides this) uses the default
2632compilation environment, which means that on systems with large file
2633support disabled by default, you get the 32 bit version of the stat
2634structure. When using the library from programs that change the \s-1ABI\s0 to
2635use 64 bit file offsets the programs will fail. In that case you have to
2636compile libev with the same flags to get binary compatibility. This is
2637obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2638most noticeably displayed with ev_stat and large file support.
2639.PP
2640The solution for this is to lobby your distribution maker to make large
2641file interfaces available by default (as e.g. FreeBSD does) and not
2642optional. Libev cannot simply switch on large file support because it has
2643to exchange stat structures with application programs compiled using the
2644default compilation environment.
2645.PP
2646\fIInotify and Kqueue\fR
2647.IX Subsection "Inotify and Kqueue"
2648.PP
2649When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2650runtime, it will be used to speed up change detection where possible. The
2651inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2652watcher is being started.
2653.PP
2654Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2655except that changes might be detected earlier, and in some cases, to avoid
2656making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2657there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2658but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2659many bugs), the path exists (i.e. stat succeeds), and the path resides on
2660a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2661xfs are fully working) libev usually gets away without polling.
2662.PP
2663There is no support for kqueue, as apparently it cannot be used to
2664implement this functionality, due to the requirement of having a file
2665descriptor open on the object at all times, and detecting renames, unlinks
2666etc. is difficult.
2667.PP
2668\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2669.IX Subsection "stat () is a synchronous operation"
2670.PP
2671Libev doesn't normally do any kind of I/O itself, and so is not blocking
2672the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2673()\*(C'\fR, which is a synchronous operation.
2674.PP
2675For local paths, this usually doesn't matter: unless the system is very
2676busy or the intervals between stat's are large, a stat call will be fast,
2677as the path data is usually in memory already (except when starting the
2678watcher).
2679.PP
2680For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2681time due to network issues, and even under good conditions, a stat call
2682often takes multiple milliseconds.
2683.PP
2684Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2685paths, although this is fully supported by libev.
2686.PP
2687\fIThe special problem of stat time resolution\fR
2688.IX Subsection "The special problem of stat time resolution"
2689.PP
2690The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2691and even on systems where the resolution is higher, most file systems
2692still only support whole seconds.
2693.PP
2694That means that, if the time is the only thing that changes, you can
2695easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2696calls your callback, which does something. When there is another update
2697within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2698stat data does change in other ways (e.g. file size).
2699.PP
2700The solution to this is to delay acting on a change for slightly more
2701than a second (or till slightly after the next full second boundary), using
2702a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2703ev_timer_again (loop, w)\*(C'\fR).
2704.PP
2705The \f(CW.02\fR offset is added to work around small timing inconsistencies
2706of some operating systems (where the second counter of the current time
2707might be be delayed. One such system is the Linux kernel, where a call to
2708\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2709a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2710update file times then there will be a small window where the kernel uses
2711the previous second to update file times but libev might already execute
2712the timer callback).
2713.PP
2714\fIWatcher-Specific Functions and Data Members\fR
2715.IX Subsection "Watcher-Specific Functions and Data Members"
2716.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2717.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2718.PD 0
2719.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2720.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2721.PD
2722Configures the watcher to wait for status changes of the given
2723\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2724be detected and should normally be specified as \f(CW0\fR to let libev choose
2725a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2726path for as long as the watcher is active.
2727.Sp
2728The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2729relative to the attributes at the time the watcher was started (or the
2730last change was detected).
2731.IP "ev_stat_stat (loop, ev_stat *)" 4
2732.IX Item "ev_stat_stat (loop, ev_stat *)"
2733Updates the stat buffer immediately with new values. If you change the
2734watched path in your callback, you could call this function to avoid
2735detecting this change (while introducing a race condition if you are not
2736the only one changing the path). Can also be useful simply to find out the
2737new values.
2738.IP "ev_statdata attr [read\-only]" 4
2739.IX Item "ev_statdata attr [read-only]"
2740The most-recently detected attributes of the file. Although the type is
2741\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2742suitable for your system, but you can only rely on the POSIX-standardised
2743members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2744some error while \f(CW\*(C`stat\*(C'\fRing the file.
2745.IP "ev_statdata prev [read\-only]" 4
2746.IX Item "ev_statdata prev [read-only]"
2747The previous attributes of the file. The callback gets invoked whenever
2748\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2749differ: \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,
2750\&\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.
2751.IP "ev_tstamp interval [read\-only]" 4
2752.IX Item "ev_tstamp interval [read-only]"
2753The specified interval.
2754.IP "const char *path [read\-only]" 4
2755.IX Item "const char *path [read-only]"
2756The file system path that is being watched.
2757.PP
2758\fIExamples\fR
2759.IX Subsection "Examples"
2760.PP
2761Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2762.PP
2763.Vb 10
2764\& static void
2765\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2766\& {
2767\& /* /etc/passwd changed in some way */
2768\& if (w\->attr.st_nlink)
2769\& {
2770\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2771\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2772\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2773\& }
2774\& else
2775\& /* you shalt not abuse printf for puts */
2776\& puts ("wow, /etc/passwd is not there, expect problems. "
2777\& "if this is windows, they already arrived\en");
2778\& }
2779\&
2780\& ...
2781\& ev_stat passwd;
2782\&
2783\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2784\& ev_stat_start (loop, &passwd);
2785.Ve
2786.PP
2787Example: Like above, but additionally use a one-second delay so we do not
2788miss updates (however, frequent updates will delay processing, too, so
2789one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2790\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2791.PP
1187.Vb 3 2792.Vb 2
1188\& struct ev_signal signal_watcher; 2793\& static ev_stat passwd;
1189\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2794\& static ev_timer timer;
1190\& ev_signal_start (loop, &sigint_cb); 2795\&
2796\& static void
2797\& timer_cb (EV_P_ ev_timer *w, int revents)
2798\& {
2799\& ev_timer_stop (EV_A_ w);
2800\&
2801\& /* now it\*(Aqs one second after the most recent passwd change */
2802\& }
2803\&
2804\& static void
2805\& stat_cb (EV_P_ ev_stat *w, int revents)
2806\& {
2807\& /* reset the one\-second timer */
2808\& ev_timer_again (EV_A_ &timer);
2809\& }
2810\&
2811\& ...
2812\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2813\& ev_stat_start (loop, &passwd);
2814\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1191.Ve 2815.Ve
1192.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2816.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1193.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2817.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1194.IX Subsection "ev_idle - when you've got nothing better to do" 2818.IX Subsection "ev_idle - when you've got nothing better to do..."
1195Idle watchers trigger events when there are no other events are pending 2819Idle watchers trigger events when no other events of the same or higher
1196(prepare, check and other idle watchers do not count). That is, as long 2820priority are pending (prepare, check and other idle watchers do not count
1197as your process is busy handling sockets or timeouts (or even signals, 2821as receiving \*(L"events\*(R").
1198imagine) it will not be triggered. But when your process is idle all idle 2822.PP
1199watchers are being called again and again, once per event loop iteration \- 2823That is, as long as your process is busy handling sockets or timeouts
2824(or even signals, imagine) of the same or higher priority it will not be
2825triggered. But when your process is idle (or only lower-priority watchers
2826are pending), the idle watchers are being called once per event loop
1200until stopped, that is, or your process receives more events and becomes 2827iteration \- until stopped, that is, or your process receives more events
1201busy. 2828and becomes busy again with higher priority stuff.
1202.PP 2829.PP
1203The most noteworthy effect is that as long as any idle watchers are 2830The most noteworthy effect is that as long as any idle watchers are
1204active, the process will not block when waiting for new events. 2831active, the process will not block when waiting for new events.
1205.PP 2832.PP
1206Apart from keeping your process non-blocking (which is a useful 2833Apart from keeping your process non-blocking (which is a useful
1207effect on its own sometimes), idle watchers are a good place to do 2834effect on its own sometimes), idle watchers are a good place to do
1208\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2835\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1209event loop has handled all outstanding events. 2836event loop has handled all outstanding events.
2837.PP
2838\fIWatcher-Specific Functions and Data Members\fR
2839.IX Subsection "Watcher-Specific Functions and Data Members"
1210.IP "ev_idle_init (ev_signal *, callback)" 4 2840.IP "ev_idle_init (ev_idle *, callback)" 4
1211.IX Item "ev_idle_init (ev_signal *, callback)" 2841.IX Item "ev_idle_init (ev_idle *, callback)"
1212Initialises and configures the idle watcher \- it has no parameters of any 2842Initialises and configures the idle watcher \- it has no parameters of any
1213kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2843kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1214believe me. 2844believe me.
1215.PP 2845.PP
2846\fIExamples\fR
2847.IX Subsection "Examples"
2848.PP
1216Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 2849Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1217callback, free it. Alos, use no error checking, as usual. 2850callback, free it. Also, use no error checking, as usual.
1218.PP 2851.PP
1219.Vb 7 2852.Vb 7
1220\& static void 2853\& static void
1221\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2854\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1222\& { 2855\& {
1223\& free (w); 2856\& free (w);
1224\& // now do something you wanted to do when the program has 2857\& // now do something you wanted to do when the program has
1225\& // no longer asnything immediate to do. 2858\& // no longer anything immediate to do.
1226\& } 2859\& }
1227.Ve 2860\&
1228.PP
1229.Vb 3
1230\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 2861\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1231\& ev_idle_init (idle_watcher, idle_cb); 2862\& ev_idle_init (idle_watcher, idle_cb);
1232\& ev_idle_start (loop, idle_cb); 2863\& ev_idle_start (loop, idle_watcher);
1233.Ve 2864.Ve
1234.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2865.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1235.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2866.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1236.IX Subsection "ev_prepare and ev_check - customise your event loop" 2867.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1237Prepare and check watchers are usually (but not always) used in tandem: 2868Prepare and check watchers are usually (but not always) used in pairs:
1238prepare watchers get invoked before the process blocks and check watchers 2869prepare watchers get invoked before the process blocks and check watchers
1239afterwards. 2870afterwards.
1240.PP 2871.PP
2872You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2873the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2874watchers. Other loops than the current one are fine, however. The
2875rationale behind this is that you do not need to check for recursion in
2876those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2877\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2878called in pairs bracketing the blocking call.
2879.PP
1241Their main purpose is to integrate other event mechanisms into libev and 2880Their main purpose is to integrate other event mechanisms into libev and
1242their use is somewhat advanced. This could be used, for example, to track 2881their use is somewhat advanced. They could be used, for example, to track
1243variable changes, implement your own watchers, integrate net-snmp or a 2882variable changes, implement your own watchers, integrate net-snmp or a
1244coroutine library and lots more. 2883coroutine library and lots more. They are also occasionally useful if
2884you cache some data and want to flush it before blocking (for example,
2885in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2886watcher).
1245.PP 2887.PP
1246This is done by examining in each prepare call which file descriptors need 2888This is done by examining in each prepare call which file descriptors
1247to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2889need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1248them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2890for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1249provide just this functionality). Then, in the check watcher you check for 2891libraries provide exactly this functionality). Then, in the check watcher,
1250any events that occured (by checking the pending status of all watchers 2892you check for any events that occurred (by checking the pending status
1251and stopping them) and call back into the library. The I/O and timer 2893of all watchers and stopping them) and call back into the library. The
1252callbacks will never actually be called (but must be valid nevertheless, 2894I/O and timer callbacks will never actually be called (but must be valid
1253because you never know, you know?). 2895nevertheless, because you never know, you know?).
1254.PP 2896.PP
1255As another example, the Perl Coro module uses these hooks to integrate 2897As another example, the Perl Coro module uses these hooks to integrate
1256coroutines into libev programs, by yielding to other active coroutines 2898coroutines into libev programs, by yielding to other active coroutines
1257during each prepare and only letting the process block if no coroutines 2899during each prepare and only letting the process block if no coroutines
1258are ready to run (it's actually more complicated: it only runs coroutines 2900are ready to run (it's actually more complicated: it only runs coroutines
1259with priority higher than or equal to the event loop and one coroutine 2901with priority higher than or equal to the event loop and one coroutine
1260of lower priority, but only once, using idle watchers to keep the event 2902of lower priority, but only once, using idle watchers to keep the event
1261loop from blocking if lower-priority coroutines are active, thus mapping 2903loop from blocking if lower-priority coroutines are active, thus mapping
1262low-priority coroutines to idle/background tasks). 2904low-priority coroutines to idle/background tasks).
2905.PP
2906It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2907priority, to ensure that they are being run before any other watchers
2908after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2909.PP
2910Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2911activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2912might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2913\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2914loops those other event loops might be in an unusable state until their
2915\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2916others).
2917.PP
2918\fIWatcher-Specific Functions and Data Members\fR
2919.IX Subsection "Watcher-Specific Functions and Data Members"
1263.IP "ev_prepare_init (ev_prepare *, callback)" 4 2920.IP "ev_prepare_init (ev_prepare *, callback)" 4
1264.IX Item "ev_prepare_init (ev_prepare *, callback)" 2921.IX Item "ev_prepare_init (ev_prepare *, callback)"
1265.PD 0 2922.PD 0
1266.IP "ev_check_init (ev_check *, callback)" 4 2923.IP "ev_check_init (ev_check *, callback)" 4
1267.IX Item "ev_check_init (ev_check *, callback)" 2924.IX Item "ev_check_init (ev_check *, callback)"
1268.PD 2925.PD
1269Initialises and configures the prepare or check watcher \- they have no 2926Initialises and configures the prepare or check watcher \- they have no
1270parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2927parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1271macros, but using them is utterly, utterly and completely pointless. 2928macros, but using them is utterly, utterly, utterly and completely
2929pointless.
1272.PP 2930.PP
1273Example: *TODO*. 2931\fIExamples\fR
2932.IX Subsection "Examples"
2933.PP
2934There are a number of principal ways to embed other event loops or modules
2935into libev. Here are some ideas on how to include libadns into libev
2936(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2937use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2938Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2939Glib event loop).
2940.PP
2941Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2942and in a check watcher, destroy them and call into libadns. What follows
2943is pseudo-code only of course. This requires you to either use a low
2944priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2945the callbacks for the IO/timeout watchers might not have been called yet.
2946.PP
2947.Vb 2
2948\& static ev_io iow [nfd];
2949\& static ev_timer tw;
2950\&
2951\& static void
2952\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2953\& {
2954\& }
2955\&
2956\& // create io watchers for each fd and a timer before blocking
2957\& static void
2958\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2959\& {
2960\& int timeout = 3600000;
2961\& struct pollfd fds [nfd];
2962\& // actual code will need to loop here and realloc etc.
2963\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2964\&
2965\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2966\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2967\& ev_timer_start (loop, &tw);
2968\&
2969\& // create one ev_io per pollfd
2970\& for (int i = 0; i < nfd; ++i)
2971\& {
2972\& ev_io_init (iow + i, io_cb, fds [i].fd,
2973\& ((fds [i].events & POLLIN ? EV_READ : 0)
2974\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2975\&
2976\& fds [i].revents = 0;
2977\& ev_io_start (loop, iow + i);
2978\& }
2979\& }
2980\&
2981\& // stop all watchers after blocking
2982\& static void
2983\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2984\& {
2985\& ev_timer_stop (loop, &tw);
2986\&
2987\& for (int i = 0; i < nfd; ++i)
2988\& {
2989\& // set the relevant poll flags
2990\& // could also call adns_processreadable etc. here
2991\& struct pollfd *fd = fds + i;
2992\& int revents = ev_clear_pending (iow + i);
2993\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2994\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2995\&
2996\& // now stop the watcher
2997\& ev_io_stop (loop, iow + i);
2998\& }
2999\&
3000\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3001\& }
3002.Ve
3003.PP
3004Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3005in the prepare watcher and would dispose of the check watcher.
3006.PP
3007Method 3: If the module to be embedded supports explicit event
3008notification (libadns does), you can also make use of the actual watcher
3009callbacks, and only destroy/create the watchers in the prepare watcher.
3010.PP
3011.Vb 5
3012\& static void
3013\& timer_cb (EV_P_ ev_timer *w, int revents)
3014\& {
3015\& adns_state ads = (adns_state)w\->data;
3016\& update_now (EV_A);
3017\&
3018\& adns_processtimeouts (ads, &tv_now);
3019\& }
3020\&
3021\& static void
3022\& io_cb (EV_P_ ev_io *w, int revents)
3023\& {
3024\& adns_state ads = (adns_state)w\->data;
3025\& update_now (EV_A);
3026\&
3027\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3028\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3029\& }
3030\&
3031\& // do not ever call adns_afterpoll
3032.Ve
3033.PP
3034Method 4: Do not use a prepare or check watcher because the module you
3035want to embed is not flexible enough to support it. Instead, you can
3036override their poll function. The drawback with this solution is that the
3037main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3038this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3039libglib event loop.
3040.PP
3041.Vb 4
3042\& static gint
3043\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3044\& {
3045\& int got_events = 0;
3046\&
3047\& for (n = 0; n < nfds; ++n)
3048\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3049\&
3050\& if (timeout >= 0)
3051\& // create/start timer
3052\&
3053\& // poll
3054\& ev_run (EV_A_ 0);
3055\&
3056\& // stop timer again
3057\& if (timeout >= 0)
3058\& ev_timer_stop (EV_A_ &to);
3059\&
3060\& // stop io watchers again \- their callbacks should have set
3061\& for (n = 0; n < nfds; ++n)
3062\& ev_io_stop (EV_A_ iow [n]);
3063\&
3064\& return got_events;
3065\& }
3066.Ve
1274.ie n .Sh """ev_embed"" \- when one backend isn't enough" 3067.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1275.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough" 3068.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1276.IX Subsection "ev_embed - when one backend isn't enough" 3069.IX Subsection "ev_embed - when one backend isn't enough..."
1277This is a rather advanced watcher type that lets you embed one event loop 3070This is a rather advanced watcher type that lets you embed one event loop
1278into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3071into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1279loop, other types of watchers might be handled in a delayed or incorrect 3072loop, other types of watchers might be handled in a delayed or incorrect
1280fashion and must not be used). 3073fashion and must not be used).
1281.PP 3074.PP
… …
1283prioritise I/O. 3076prioritise I/O.
1284.PP 3077.PP
1285As an example for a bug workaround, the kqueue backend might only support 3078As an example for a bug workaround, the kqueue backend might only support
1286sockets on some platform, so it is unusable as generic backend, but you 3079sockets on some platform, so it is unusable as generic backend, but you
1287still want to make use of it because you have many sockets and it scales 3080still want to make use of it because you have many sockets and it scales
1288so nicely. In this case, you would create a kqueue-based loop and embed it 3081so nicely. In this case, you would create a kqueue-based loop and embed
1289into your default loop (which might use e.g. poll). Overall operation will 3082it into your default loop (which might use e.g. poll). Overall operation
1290be a bit slower because first libev has to poll and then call kevent, but 3083will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1291at least you can use both at what they are best. 3084\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3085best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1292.PP 3086.PP
1293As for prioritising I/O: rarely you have the case where some fds have 3087As for prioritising I/O: under rare circumstances you have the case where
1294to be watched and handled very quickly (with low latency), and even 3088some fds have to be watched and handled very quickly (with low latency),
1295priorities and idle watchers might have too much overhead. In this case 3089and even priorities and idle watchers might have too much overhead. In
1296you would put all the high priority stuff in one loop and all the rest in 3090this case you would put all the high priority stuff in one loop and all
1297a second one, and embed the second one in the first. 3091the rest in a second one, and embed the second one in the first.
1298.PP 3092.PP
1299As long as the watcher is active, the callback will be invoked every time 3093As long as the watcher is active, the callback will be invoked every
1300there might be events pending in the embedded loop. The callback must then 3094time there might be events pending in the embedded loop. The callback
1301call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3095must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1302their callbacks (you could also start an idle watcher to give the embedded 3096sweep and invoke their callbacks (the callback doesn't need to invoke the
1303loop strictly lower priority for example). You can also set the callback 3097\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1304to \f(CW0\fR, in which case the embed watcher will automatically execute the 3098to give the embedded loop strictly lower priority for example).
1305embedded loop sweep.
1306.PP 3099.PP
1307As long as the watcher is started it will automatically handle events. The 3100You can also set the callback to \f(CW0\fR, in which case the embed watcher
1308callback will be invoked whenever some events have been handled. You can 3101will automatically execute the embedded loop sweep whenever necessary.
1309set the callback to \f(CW0\fR to avoid having to specify one if you are not
1310interested in that.
1311.PP 3102.PP
1312Also, there have not currently been made special provisions for forking: 3103Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1313when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3104is active, i.e., the embedded loop will automatically be forked when the
1314but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3105embedding loop forks. In other cases, the user is responsible for calling
1315yourself. 3106\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1316.PP 3107.PP
1317Unfortunately, not all backends are embeddable, only the ones returned by 3108Unfortunately, not all backends are embeddable: only the ones returned by
1318\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3109\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1319portable one. 3110portable one.
1320.PP 3111.PP
1321So when you want to use this feature you will always have to be prepared 3112So when you want to use this feature you will always have to be prepared
1322that you cannot get an embeddable loop. The recommended way to get around 3113that you cannot get an embeddable loop. The recommended way to get around
1323this is to have a separate variables for your embeddable loop, try to 3114this is to have a separate variables for your embeddable loop, try to
1324create it, and if that fails, use the normal loop for everything: 3115create it, and if that fails, use the normal loop for everything.
1325.PP 3116.PP
1326.Vb 3 3117\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1327\& struct ev_loop *loop_hi = ev_default_init (0); 3118.IX Subsection "ev_embed and fork"
1328\& struct ev_loop *loop_lo = 0;
1329\& struct ev_embed embed;
1330.Ve
1331.PP 3119.PP
1332.Vb 5 3120While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1333\& // see if there is a chance of getting one that works 3121automatically be applied to the embedded loop as well, so no special
1334\& // (remember that a flags value of 0 means autodetection) 3122fork handling is required in that case. When the watcher is not running,
1335\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3123however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1336\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3124as applicable.
1337\& : 0;
1338.Ve
1339.PP 3125.PP
1340.Vb 8 3126\fIWatcher-Specific Functions and Data Members\fR
1341\& // if we got one, then embed it, otherwise default to loop_hi 3127.IX Subsection "Watcher-Specific Functions and Data Members"
1342\& if (loop_lo)
1343\& {
1344\& ev_embed_init (&embed, 0, loop_lo);
1345\& ev_embed_start (loop_hi, &embed);
1346\& }
1347\& else
1348\& loop_lo = loop_hi;
1349.Ve
1350.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3128.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1351.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3129.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1352.PD 0 3130.PD 0
1353.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3131.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1354.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3132.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1355.PD 3133.PD
1356Configures the watcher to embed the given loop, which must be 3134Configures the watcher to embed the given loop, which must be
1357embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3135embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1358invoked automatically, otherwise it is the responsibility of the callback 3136invoked automatically, otherwise it is the responsibility of the callback
1359to invoke it (it will continue to be called until the sweep has been done, 3137to invoke it (it will continue to be called until the sweep has been done,
1360if you do not want thta, you need to temporarily stop the embed watcher). 3138if you do not want that, you need to temporarily stop the embed watcher).
1361.IP "ev_embed_sweep (loop, ev_embed *)" 4 3139.IP "ev_embed_sweep (loop, ev_embed *)" 4
1362.IX Item "ev_embed_sweep (loop, ev_embed *)" 3140.IX Item "ev_embed_sweep (loop, ev_embed *)"
1363Make a single, non-blocking sweep over the embedded loop. This works 3141Make a single, non-blocking sweep over the embedded loop. This works
1364similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3142similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1365apropriate way for embedded loops. 3143appropriate way for embedded loops.
3144.IP "struct ev_loop *other [read\-only]" 4
3145.IX Item "struct ev_loop *other [read-only]"
3146The embedded event loop.
3147.PP
3148\fIExamples\fR
3149.IX Subsection "Examples"
3150.PP
3151Example: Try to get an embeddable event loop and embed it into the default
3152event loop. If that is not possible, use the default loop. The default
3153loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3154\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3155used).
3156.PP
3157.Vb 3
3158\& struct ev_loop *loop_hi = ev_default_init (0);
3159\& struct ev_loop *loop_lo = 0;
3160\& ev_embed embed;
3161\&
3162\& // see if there is a chance of getting one that works
3163\& // (remember that a flags value of 0 means autodetection)
3164\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3165\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3166\& : 0;
3167\&
3168\& // if we got one, then embed it, otherwise default to loop_hi
3169\& if (loop_lo)
3170\& {
3171\& ev_embed_init (&embed, 0, loop_lo);
3172\& ev_embed_start (loop_hi, &embed);
3173\& }
3174\& else
3175\& loop_lo = loop_hi;
3176.Ve
3177.PP
3178Example: Check if kqueue is available but not recommended and create
3179a kqueue backend for use with sockets (which usually work with any
3180kqueue implementation). Store the kqueue/socket\-only event loop in
3181\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3182.PP
3183.Vb 3
3184\& struct ev_loop *loop = ev_default_init (0);
3185\& struct ev_loop *loop_socket = 0;
3186\& ev_embed embed;
3187\&
3188\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3189\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3190\& {
3191\& ev_embed_init (&embed, 0, loop_socket);
3192\& ev_embed_start (loop, &embed);
3193\& }
3194\&
3195\& if (!loop_socket)
3196\& loop_socket = loop;
3197\&
3198\& // now use loop_socket for all sockets, and loop for everything else
3199.Ve
3200.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3201.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3202.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3203Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3204whoever is a good citizen cared to tell libev about it by calling
3205\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3206event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3207and only in the child after the fork. If whoever good citizen calling
3208\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3209handlers will be invoked, too, of course.
3210.PP
3211\fIThe special problem of life after fork \- how is it possible?\fR
3212.IX Subsection "The special problem of life after fork - how is it possible?"
3213.PP
3214Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3215up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3216sequence should be handled by libev without any problems.
3217.PP
3218This changes when the application actually wants to do event handling
3219in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3220fork.
3221.PP
3222The default mode of operation (for libev, with application help to detect
3223forks) is to duplicate all the state in the child, as would be expected
3224when \fIeither\fR the parent \fIor\fR the child process continues.
3225.PP
3226When both processes want to continue using libev, then this is usually the
3227wrong result. In that case, usually one process (typically the parent) is
3228supposed to continue with all watchers in place as before, while the other
3229process typically wants to start fresh, i.e. without any active watchers.
3230.PP
3231The cleanest and most efficient way to achieve that with libev is to
3232simply create a new event loop, which of course will be \*(L"empty\*(R", and
3233use that for new watchers. This has the advantage of not touching more
3234memory than necessary, and thus avoiding the copy-on-write, and the
3235disadvantage of having to use multiple event loops (which do not support
3236signal watchers).
3237.PP
3238When this is not possible, or you want to use the default loop for
3239other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3240\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3241Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3242watchers, so you have to be careful not to execute code that modifies
3243those watchers. Note also that in that case, you have to re-register any
3244signal watchers.
3245.PP
3246\fIWatcher-Specific Functions and Data Members\fR
3247.IX Subsection "Watcher-Specific Functions and Data Members"
3248.IP "ev_fork_init (ev_fork *, callback)" 4
3249.IX Item "ev_fork_init (ev_fork *, callback)"
3250Initialises and configures the fork watcher \- it has no parameters of any
3251kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3252really.
3253.ie n .SS """ev_cleanup"" \- even the best things end"
3254.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3255.IX Subsection "ev_cleanup - even the best things end"
3256Cleanup watchers are called just before the event loop is being destroyed
3257by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3258.PP
3259While there is no guarantee that the event loop gets destroyed, cleanup
3260watchers provide a convenient method to install cleanup hooks for your
3261program, worker threads and so on \- you just to make sure to destroy the
3262loop when you want them to be invoked.
3263.PP
3264Cleanup watchers are invoked in the same way as any other watcher. Unlike
3265all other watchers, they do not keep a reference to the event loop (which
3266makes a lot of sense if you think about it). Like all other watchers, you
3267can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3268.PP
3269\fIWatcher-Specific Functions and Data Members\fR
3270.IX Subsection "Watcher-Specific Functions and Data Members"
3271.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3272.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3273Initialises and configures the cleanup watcher \- it has no parameters of
3274any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3275pointless, I assure you.
3276.PP
3277Example: Register an atexit handler to destroy the default loop, so any
3278cleanup functions are called.
3279.PP
3280.Vb 5
3281\& static void
3282\& program_exits (void)
3283\& {
3284\& ev_loop_destroy (EV_DEFAULT_UC);
3285\& }
3286\&
3287\& ...
3288\& atexit (program_exits);
3289.Ve
3290.ie n .SS """ev_async"" \- how to wake up an event loop"
3291.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3292.IX Subsection "ev_async - how to wake up an event loop"
3293In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3294asynchronous sources such as signal handlers (as opposed to multiple event
3295loops \- those are of course safe to use in different threads).
3296.PP
3297Sometimes, however, you need to wake up an event loop you do not control,
3298for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3299watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3300it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3301.PP
3302This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3303too, are asynchronous in nature, and signals, too, will be compressed
3304(i.e. the number of callback invocations may be less than the number of
3305\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3306.PP
3307Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3308just the default loop.
3309.PP
3310\fIQueueing\fR
3311.IX Subsection "Queueing"
3312.PP
3313\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3314is that the author does not know of a simple (or any) algorithm for a
3315multiple-writer-single-reader queue that works in all cases and doesn't
3316need elaborate support such as pthreads or unportable memory access
3317semantics.
3318.PP
3319That means that if you want to queue data, you have to provide your own
3320queue. But at least I can tell you how to implement locking around your
3321queue:
3322.IP "queueing from a signal handler context" 4
3323.IX Item "queueing from a signal handler context"
3324To implement race-free queueing, you simply add to the queue in the signal
3325handler but you block the signal handler in the watcher callback. Here is
3326an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3327.Sp
3328.Vb 1
3329\& static ev_async mysig;
3330\&
3331\& static void
3332\& sigusr1_handler (void)
3333\& {
3334\& sometype data;
3335\&
3336\& // no locking etc.
3337\& queue_put (data);
3338\& ev_async_send (EV_DEFAULT_ &mysig);
3339\& }
3340\&
3341\& static void
3342\& mysig_cb (EV_P_ ev_async *w, int revents)
3343\& {
3344\& sometype data;
3345\& sigset_t block, prev;
3346\&
3347\& sigemptyset (&block);
3348\& sigaddset (&block, SIGUSR1);
3349\& sigprocmask (SIG_BLOCK, &block, &prev);
3350\&
3351\& while (queue_get (&data))
3352\& process (data);
3353\&
3354\& if (sigismember (&prev, SIGUSR1)
3355\& sigprocmask (SIG_UNBLOCK, &block, 0);
3356\& }
3357.Ve
3358.Sp
3359(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3360instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3361either...).
3362.IP "queueing from a thread context" 4
3363.IX Item "queueing from a thread context"
3364The strategy for threads is different, as you cannot (easily) block
3365threads but you can easily preempt them, so to queue safely you need to
3366employ a traditional mutex lock, such as in this pthread example:
3367.Sp
3368.Vb 2
3369\& static ev_async mysig;
3370\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3371\&
3372\& static void
3373\& otherthread (void)
3374\& {
3375\& // only need to lock the actual queueing operation
3376\& pthread_mutex_lock (&mymutex);
3377\& queue_put (data);
3378\& pthread_mutex_unlock (&mymutex);
3379\&
3380\& ev_async_send (EV_DEFAULT_ &mysig);
3381\& }
3382\&
3383\& static void
3384\& mysig_cb (EV_P_ ev_async *w, int revents)
3385\& {
3386\& pthread_mutex_lock (&mymutex);
3387\&
3388\& while (queue_get (&data))
3389\& process (data);
3390\&
3391\& pthread_mutex_unlock (&mymutex);
3392\& }
3393.Ve
3394.PP
3395\fIWatcher-Specific Functions and Data Members\fR
3396.IX Subsection "Watcher-Specific Functions and Data Members"
3397.IP "ev_async_init (ev_async *, callback)" 4
3398.IX Item "ev_async_init (ev_async *, callback)"
3399Initialises and configures the async watcher \- it has no parameters of any
3400kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3401trust me.
3402.IP "ev_async_send (loop, ev_async *)" 4
3403.IX Item "ev_async_send (loop, ev_async *)"
3404Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3405an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3406\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3407similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3408section below on what exactly this means).
3409.Sp
3410Note that, as with other watchers in libev, multiple events might get
3411compressed into a single callback invocation (another way to look at this
3412is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3413reset when the event loop detects that).
3414.Sp
3415This call incurs the overhead of a system call only once per event loop
3416iteration, so while the overhead might be noticeable, it doesn't apply to
3417repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3418.IP "bool = ev_async_pending (ev_async *)" 4
3419.IX Item "bool = ev_async_pending (ev_async *)"
3420Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3421watcher but the event has not yet been processed (or even noted) by the
3422event loop.
3423.Sp
3424\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3425the loop iterates next and checks for the watcher to have become active,
3426it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3427quickly check whether invoking the loop might be a good idea.
3428.Sp
3429Not that this does \fInot\fR check whether the watcher itself is pending,
3430only whether it has been requested to make this watcher pending: there
3431is a time window between the event loop checking and resetting the async
3432notification, and the callback being invoked.
1366.SH "OTHER FUNCTIONS" 3433.SH "OTHER FUNCTIONS"
1367.IX Header "OTHER FUNCTIONS" 3434.IX Header "OTHER FUNCTIONS"
1368There are some other functions of possible interest. Described. Here. Now. 3435There are some other functions of possible interest. Described. Here. Now.
1369.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3436.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1370.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3437.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1371This function combines a simple timer and an I/O watcher, calls your 3438This function combines a simple timer and an I/O watcher, calls your
1372callback on whichever event happens first and automatically stop both 3439callback on whichever event happens first and automatically stops both
1373watchers. This is useful if you want to wait for a single event on an fd 3440watchers. This is useful if you want to wait for a single event on an fd
1374or timeout without having to allocate/configure/start/stop/free one or 3441or timeout without having to allocate/configure/start/stop/free one or
1375more watchers yourself. 3442more watchers yourself.
1376.Sp 3443.Sp
1377If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3444If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1378is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3445\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1379\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3446the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1380.Sp 3447.Sp
1381If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3448If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1382started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3449started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1383repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3450repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1384dubious value.
1385.Sp 3451.Sp
1386The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3452The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1387passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3453passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1388\&\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 3454\&\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
1389value passed to \f(CW\*(C`ev_once\*(C'\fR: 3455value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3456a timeout and an io event at the same time \- you probably should give io
3457events precedence.
3458.Sp
3459Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
1390.Sp 3460.Sp
1391.Vb 7 3461.Vb 7
1392\& static void stdin_ready (int revents, void *arg) 3462\& static void stdin_ready (int revents, void *arg)
1393\& { 3463\& {
1394\& if (revents & EV_TIMEOUT)
1395\& /* doh, nothing entered */;
1396\& else if (revents & EV_READ) 3464\& if (revents & EV_READ)
1397\& /* stdin might have data for us, joy! */; 3465\& /* stdin might have data for us, joy! */;
3466\& else if (revents & EV_TIMER)
3467\& /* doh, nothing entered */;
1398\& } 3468\& }
1399.Ve 3469\&
1400.Sp
1401.Vb 1
1402\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3470\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1403.Ve 3471.Ve
1404.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1405.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1406Feeds the given event set into the event loop, as if the specified event
1407had happened for the specified watcher (which must be a pointer to an
1408initialised but not necessarily started event watcher).
1409.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3472.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
1410.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3473.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
1411Feed an event on the given fd, as if a file descriptor backend detected 3474Feed an event on the given fd, as if a file descriptor backend detected
1412the given events it. 3475the given events it.
1413.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3476.IP "ev_feed_signal_event (loop, int signum)" 4
1414.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3477.IX Item "ev_feed_signal_event (loop, int signum)"
1415Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3478Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
1416loop!). 3479loop!).
1417.SH "LIBEVENT EMULATION" 3480.SH "LIBEVENT EMULATION"
1418.IX Header "LIBEVENT EMULATION" 3481.IX Header "LIBEVENT EMULATION"
1419Libev offers a compatibility emulation layer for libevent. It cannot 3482Libev offers a compatibility emulation layer for libevent. It cannot
1420emulate the internals of libevent, so here are some usage hints: 3483emulate the internals of libevent, so here are some usage hints:
3484.IP "\(bu" 4
1421.IP "* Use it by including <event.h>, as usual." 4 3485Use it by including <event.h>, as usual.
1422.IX Item "Use it by including <event.h>, as usual." 3486.IP "\(bu" 4
1423.PD 0 3487The following members are fully supported: ev_base, ev_callback,
1424.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3488ev_arg, ev_fd, ev_res, ev_events.
1425.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3489.IP "\(bu" 4
1426.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 3490Avoid using ev_flags and the EVLIST_*\-macros, while it is
1427.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)." 3491maintained by libev, it does not work exactly the same way as in libevent (consider
1428.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 3492it a private \s-1API\s0).
1429.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." 3493.IP "\(bu" 4
3494Priorities are not currently supported. Initialising priorities
3495will fail and all watchers will have the same priority, even though there
3496is an ev_pri field.
3497.IP "\(bu" 4
3498In libevent, the last base created gets the signals, in libev, the
3499first base created (== the default loop) gets the signals.
3500.IP "\(bu" 4
1430.IP "* Other members are not supported." 4 3501Other members are not supported.
1431.IX Item "Other members are not supported." 3502.IP "\(bu" 4
1432.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3503The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1433.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3504to use the libev header file and library.
1434.PD
1435.SH "\*(C+ SUPPORT" 3505.SH "\*(C+ SUPPORT"
1436.IX Header " SUPPORT" 3506.IX Header " SUPPORT"
1437Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 3507Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1438you to use some convinience methods to start/stop watchers and also change 3508you to use some convenience methods to start/stop watchers and also change
1439the callback model to a model using method callbacks on objects. 3509the callback model to a model using method callbacks on objects.
1440.PP 3510.PP
1441To use it, 3511To use it,
1442.PP 3512.PP
1443.Vb 1 3513.Vb 1
1444\& #include <ev++.h> 3514\& #include <ev++.h>
1445.Ve 3515.Ve
1446.PP 3516.PP
1447(it is not installed by default). This automatically includes \fIev.h\fR 3517This automatically includes \fIev.h\fR and puts all of its definitions (many
1448and puts all of its definitions (many of them macros) into the global 3518of them macros) into the global namespace. All \*(C+ specific things are
1449namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 3519put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3520options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1450.PP 3521.PP
1451It should support all the same embedding options as \fIev.h\fR, most notably 3522Care has been taken to keep the overhead low. The only data member the \*(C+
1452\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 3523classes add (compared to plain C\-style watchers) is the event loop pointer
3524that the watcher is associated with (or no additional members at all if
3525you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3526.PP
3527Currently, functions, and static and non-static member functions can be
3528used as callbacks. Other types should be easy to add as long as they only
3529need one additional pointer for context. If you need support for other
3530types of functors please contact the author (preferably after implementing
3531it).
1453.PP 3532.PP
1454Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 3533Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1455.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 3534.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1456.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 3535.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1457.IX Item "ev::READ, ev::WRITE etc." 3536.IX Item "ev::READ, ev::WRITE etc."
1458These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 3537These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1459macros from \fIev.h\fR. 3538macros from \fIev.h\fR.
1460.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 3539.ie n .IP """ev::tstamp"", ""ev::now""" 4
1461.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 3540.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1462.IX Item "ev::tstamp, ev::now" 3541.IX Item "ev::tstamp, ev::now"
1463Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 3542Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1464.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 3543.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1465.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 3544.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1466.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 3545.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1467For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 3546For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1468the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 3547the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1469which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 3548which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1470defines by many implementations. 3549defines by many implementations.
1471.Sp 3550.Sp
1472All of those classes have these methods: 3551All of those classes have these methods:
1473.RS 4 3552.RS 4
1474.IP "ev::TYPE::TYPE (object *, object::method *)" 4 3553.IP "ev::TYPE::TYPE ()" 4
1475.IX Item "ev::TYPE::TYPE (object *, object::method *)" 3554.IX Item "ev::TYPE::TYPE ()"
1476.PD 0 3555.PD 0
1477.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 3556.IP "ev::TYPE::TYPE (loop)" 4
1478.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 3557.IX Item "ev::TYPE::TYPE (loop)"
1479.IP "ev::TYPE::~TYPE" 4 3558.IP "ev::TYPE::~TYPE" 4
1480.IX Item "ev::TYPE::~TYPE" 3559.IX Item "ev::TYPE::~TYPE"
1481.PD 3560.PD
1482The constructor takes a pointer to an object and a method pointer to 3561The constructor (optionally) takes an event loop to associate the watcher
1483the event handler callback to call in this class. The constructor calls 3562with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1484\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 3563.Sp
1485before starting it. If you do not specify a loop then the constructor 3564The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1486automatically associates the default loop with this watcher. 3565\&\f(CW\*(C`set\*(C'\fR method before starting it.
3566.Sp
3567It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3568method to set a callback before you can start the watcher.
3569.Sp
3570(The reason why you have to use a method is a limitation in \*(C+ which does
3571not allow explicit template arguments for constructors).
1487.Sp 3572.Sp
1488The destructor automatically stops the watcher if it is active. 3573The destructor automatically stops the watcher if it is active.
3574.IP "w\->set<class, &class::method> (object *)" 4
3575.IX Item "w->set<class, &class::method> (object *)"
3576This method sets the callback method to call. The method has to have a
3577signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3578first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3579parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3580.Sp
3581This method synthesizes efficient thunking code to call your method from
3582the C callback that libev requires. If your compiler can inline your
3583callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3584your compiler is good :), then the method will be fully inlined into the
3585thunking function, making it as fast as a direct C callback.
3586.Sp
3587Example: simple class declaration and watcher initialisation
3588.Sp
3589.Vb 4
3590\& struct myclass
3591\& {
3592\& void io_cb (ev::io &w, int revents) { }
3593\& }
3594\&
3595\& myclass obj;
3596\& ev::io iow;
3597\& iow.set <myclass, &myclass::io_cb> (&obj);
3598.Ve
3599.IP "w\->set (object *)" 4
3600.IX Item "w->set (object *)"
3601This is a variation of a method callback \- leaving out the method to call
3602will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3603functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3604the time. Incidentally, you can then also leave out the template argument
3605list.
3606.Sp
3607The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3608int revents)\*(C'\fR.
3609.Sp
3610See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3611.Sp
3612Example: use a functor object as callback.
3613.Sp
3614.Vb 7
3615\& struct myfunctor
3616\& {
3617\& void operator() (ev::io &w, int revents)
3618\& {
3619\& ...
3620\& }
3621\& }
3622\&
3623\& myfunctor f;
3624\&
3625\& ev::io w;
3626\& w.set (&f);
3627.Ve
3628.IP "w\->set<function> (void *data = 0)" 4
3629.IX Item "w->set<function> (void *data = 0)"
3630Also sets a callback, but uses a static method or plain function as
3631callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3632\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3633.Sp
3634The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3635.Sp
3636See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3637.Sp
3638Example: Use a plain function as callback.
3639.Sp
3640.Vb 2
3641\& static void io_cb (ev::io &w, int revents) { }
3642\& iow.set <io_cb> ();
3643.Ve
1489.IP "w\->set (struct ev_loop *)" 4 3644.IP "w\->set (loop)" 4
1490.IX Item "w->set (struct ev_loop *)" 3645.IX Item "w->set (loop)"
1491Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 3646Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1492do this when the watcher is inactive (and not pending either). 3647do this when the watcher is inactive (and not pending either).
1493.IP "w\->set ([args])" 4 3648.IP "w\->set ([arguments])" 4
1494.IX Item "w->set ([args])" 3649.IX Item "w->set ([arguments])"
1495Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 3650Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
1496called at least once. Unlike the C counterpart, an active watcher gets 3651method or a suitable start method must be called at least once. Unlike the
1497automatically stopped and restarted. 3652C counterpart, an active watcher gets automatically stopped and restarted
3653when reconfiguring it with this method.
1498.IP "w\->start ()" 4 3654.IP "w\->start ()" 4
1499.IX Item "w->start ()" 3655.IX Item "w->start ()"
1500Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 3656Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1501constructor already takes the loop. 3657constructor already stores the event loop.
3658.IP "w\->start ([arguments])" 4
3659.IX Item "w->start ([arguments])"
3660Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
3661convenient to wrap them in one call. Uses the same type of arguments as
3662the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1502.IP "w\->stop ()" 4 3663.IP "w\->stop ()" 4
1503.IX Item "w->stop ()" 3664.IX Item "w->stop ()"
1504Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 3665Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1505.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 3666.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1506.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 3667.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1507.IX Item "w->again () ev::timer, ev::periodic only" 3668.IX Item "w->again () (ev::timer, ev::periodic only)"
1508For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 3669For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1509\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 3670\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1510.ie n .IP "w\->sweep () ""ev::embed"" only" 4 3671.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1511.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 3672.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1512.IX Item "w->sweep () ev::embed only" 3673.IX Item "w->sweep () (ev::embed only)"
1513Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 3674Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3675.ie n .IP "w\->update () (""ev::stat"" only)" 4
3676.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3677.IX Item "w->update () (ev::stat only)"
3678Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1514.RE 3679.RE
1515.RS 4 3680.RS 4
1516.RE 3681.RE
1517.PP 3682.PP
1518Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 3683Example: Define a class with two I/O and idle watchers, start the I/O
1519the constructor. 3684watchers in the constructor.
1520.PP 3685.PP
1521.Vb 4 3686.Vb 5
1522\& class myclass 3687\& class myclass
1523\& { 3688\& {
1524\& ev_io io; void io_cb (ev::io &w, int revents); 3689\& ev::io io ; void io_cb (ev::io &w, int revents);
3690\& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1525\& ev_idle idle void idle_cb (ev::idle &w, int revents); 3691\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3692\&
3693\& myclass (int fd)
3694\& {
3695\& io .set <myclass, &myclass::io_cb > (this);
3696\& io2 .set <myclass, &myclass::io2_cb > (this);
3697\& idle.set <myclass, &myclass::idle_cb> (this);
3698\&
3699\& io.set (fd, ev::WRITE); // configure the watcher
3700\& io.start (); // start it whenever convenient
3701\&
3702\& io2.start (fd, ev::READ); // set + start in one call
3703\& }
3704\& };
1526.Ve 3705.Ve
3706.SH "OTHER LANGUAGE BINDINGS"
3707.IX Header "OTHER LANGUAGE BINDINGS"
3708Libev does not offer other language bindings itself, but bindings for a
3709number of languages exist in the form of third-party packages. If you know
3710any interesting language binding in addition to the ones listed here, drop
3711me a note.
3712.IP "Perl" 4
3713.IX Item "Perl"
3714The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3715libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3716there are additional modules that implement libev-compatible interfaces
3717to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
3718\&\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
3719and \f(CW\*(C`EV::Glib\*(C'\fR).
3720.Sp
3721It can be found and installed via \s-1CPAN\s0, its homepage is at
3722<http://software.schmorp.de/pkg/EV>.
3723.IP "Python" 4
3724.IX Item "Python"
3725Python bindings can be found at <http://code.google.com/p/pyev/>. It
3726seems to be quite complete and well-documented.
3727.IP "Ruby" 4
3728.IX Item "Ruby"
3729Tony Arcieri has written a ruby extension that offers access to a subset
3730of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3731more on top of it. It can be found via gem servers. Its homepage is at
3732<http://rev.rubyforge.org/>.
3733.Sp
3734Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3735makes rev work even on mingw.
3736.IP "Haskell" 4
3737.IX Item "Haskell"
3738A haskell binding to libev is available at
3739<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3740.IP "D" 4
3741.IX Item "D"
3742Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3743be found at <http://proj.llucax.com.ar/wiki/evd>.
3744.IP "Ocaml" 4
3745.IX Item "Ocaml"
3746Erkki Seppala has written Ocaml bindings for libev, to be found at
3747<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3748.IP "Lua" 4
3749.IX Item "Lua"
3750Brian Maher has written a partial interface to libev for lua (at the
3751time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
3752<http://github.com/brimworks/lua\-ev>.
3753.SH "MACRO MAGIC"
3754.IX Header "MACRO MAGIC"
3755Libev can be compiled with a variety of options, the most fundamental
3756of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3757functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1527.PP 3758.PP
3759To make it easier to write programs that cope with either variant, the
3760following macros are defined:
3761.ie n .IP """EV_A"", ""EV_A_""" 4
3762.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3763.IX Item "EV_A, EV_A_"
3764This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3765loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3766\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3767.Sp
3768.Vb 3
3769\& ev_unref (EV_A);
3770\& ev_timer_add (EV_A_ watcher);
3771\& ev_run (EV_A_ 0);
3772.Ve
3773.Sp
3774It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3775which is often provided by the following macro.
3776.ie n .IP """EV_P"", ""EV_P_""" 4
3777.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3778.IX Item "EV_P, EV_P_"
3779This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3780loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3781\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3782.Sp
1528.Vb 2 3783.Vb 2
1529\& myclass (); 3784\& // this is how ev_unref is being declared
1530\& } 3785\& static void ev_unref (EV_P);
3786\&
3787\& // this is how you can declare your typical callback
3788\& static void cb (EV_P_ ev_timer *w, int revents)
1531.Ve 3789.Ve
3790.Sp
3791It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3792suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3793.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3794.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3795.IX Item "EV_DEFAULT, EV_DEFAULT_"
3796Similar to the other two macros, this gives you the value of the default
3797loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3798.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3799.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3800.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3801Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3802default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3803is undefined when the default loop has not been initialised by a previous
3804execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
3805.Sp
3806It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3807watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1532.PP 3808.PP
3809Example: Declare and initialise a check watcher, utilising the above
3810macros so it will work regardless of whether multiple loops are supported
3811or not.
3812.PP
1533.Vb 6 3813.Vb 5
1534\& myclass::myclass (int fd) 3814\& static void
1535\& : io (this, &myclass::io_cb), 3815\& check_cb (EV_P_ ev_timer *w, int revents)
1536\& idle (this, &myclass::idle_cb)
1537\& { 3816\& {
1538\& io.start (fd, ev::READ); 3817\& ev_check_stop (EV_A_ w);
1539\& } 3818\& }
3819\&
3820\& ev_check check;
3821\& ev_check_init (&check, check_cb);
3822\& ev_check_start (EV_DEFAULT_ &check);
3823\& ev_run (EV_DEFAULT_ 0);
1540.Ve 3824.Ve
1541.SH "EMBEDDING" 3825.SH "EMBEDDING"
1542.IX Header "EMBEDDING" 3826.IX Header "EMBEDDING"
1543Libev can (and often is) directly embedded into host 3827Libev can (and often is) directly embedded into host
1544applications. Examples of applications that embed it include the Deliantra 3828applications. Examples of applications that embed it include the Deliantra
1545Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 3829Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1546and rxvt\-unicode. 3830and rxvt-unicode.
1547.PP 3831.PP
1548The goal is to enable you to just copy the neecssary files into your 3832The goal is to enable you to just copy the necessary files into your
1549source directory without having to change even a single line in them, so 3833source directory without having to change even a single line in them, so
1550you can easily upgrade by simply copying (or having a checked-out copy of 3834you can easily upgrade by simply copying (or having a checked-out copy of
1551libev somewhere in your source tree). 3835libev somewhere in your source tree).
1552.Sh "\s-1FILESETS\s0" 3836.SS "\s-1FILESETS\s0"
1553.IX Subsection "FILESETS" 3837.IX Subsection "FILESETS"
1554Depending on what features you need you need to include one or more sets of files 3838Depending on what features you need you need to include one or more sets of files
1555in your app. 3839in your application.
1556.PP 3840.PP
1557\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 3841\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
1558.IX Subsection "CORE EVENT LOOP" 3842.IX Subsection "CORE EVENT LOOP"
1559.PP 3843.PP
1560To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 3844To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1561configuration (no autoconf): 3845configuration (no autoconf):
1562.PP 3846.PP
1563.Vb 2 3847.Vb 2
1564\& #define EV_STANDALONE 1 3848\& #define EV_STANDALONE 1
1565\& #include "ev.c" 3849\& #include "ev.c"
1566.Ve 3850.Ve
1567.PP 3851.PP
1568This will automatically include \fIev.h\fR, too, and should be done in a 3852This will automatically include \fIev.h\fR, too, and should be done in a
1569single C source file only to provide the function implementations. To use 3853single C source file only to provide the function implementations. To use
1570it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 3854it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1571done by writing a wrapper around \fIev.h\fR that you can include instead and 3855done by writing a wrapper around \fIev.h\fR that you can include instead and
1572where you can put other configuration options): 3856where you can put other configuration options):
1573.PP 3857.PP
1574.Vb 2 3858.Vb 2
1575\& #define EV_STANDALONE 1 3859\& #define EV_STANDALONE 1
1576\& #include "ev.h" 3860\& #include "ev.h"
1577.Ve 3861.Ve
1578.PP 3862.PP
1579Both header files and implementation files can be compiled with a \*(C+ 3863Both header files and implementation files can be compiled with a \*(C+
1580compiler (at least, thats a stated goal, and breakage will be treated 3864compiler (at least, that's a stated goal, and breakage will be treated
1581as a bug). 3865as a bug).
1582.PP 3866.PP
1583You need the following files in your source tree, or in a directory 3867You need the following files in your source tree, or in a directory
1584in your include path (e.g. in libev/ when using \-Ilibev): 3868in your include path (e.g. in libev/ when using \-Ilibev):
1585.PP 3869.PP
1586.Vb 4 3870.Vb 4
1587\& ev.h 3871\& ev.h
1588\& ev.c 3872\& ev.c
1589\& ev_vars.h 3873\& ev_vars.h
1590\& ev_wrap.h 3874\& ev_wrap.h
1591.Ve 3875\&
1592.PP
1593.Vb 1
1594\& ev_win32.c required on win32 platforms only 3876\& ev_win32.c required on win32 platforms only
1595.Ve 3877\&
1596.PP
1597.Vb 5
1598\& ev_select.c only when select backend is enabled (which is is by default) 3878\& ev_select.c only when select backend is enabled (which is enabled by default)
1599\& ev_poll.c only when poll backend is enabled (disabled by default) 3879\& ev_poll.c only when poll backend is enabled (disabled by default)
1600\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 3880\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
1601\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 3881\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1602\& ev_port.c only when the solaris port backend is enabled (disabled by default) 3882\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1603.Ve 3883.Ve
1604.PP 3884.PP
1605\&\fIev.c\fR includes the backend files directly when enabled, so you only need 3885\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1606to compile a single file. 3886to compile this single file.
1607.PP 3887.PP
1608\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 3888\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
1609.IX Subsection "LIBEVENT COMPATIBILITY API" 3889.IX Subsection "LIBEVENT COMPATIBILITY API"
1610.PP 3890.PP
1611To include the libevent compatibility \s-1API\s0, also include: 3891To include the libevent compatibility \s-1API\s0, also include:
1612.PP 3892.PP
1613.Vb 1 3893.Vb 1
1614\& #include "event.c" 3894\& #include "event.c"
1615.Ve 3895.Ve
1616.PP 3896.PP
1617in the file including \fIev.c\fR, and: 3897in the file including \fIev.c\fR, and:
1618.PP 3898.PP
1619.Vb 1 3899.Vb 1
1620\& #include "event.h" 3900\& #include "event.h"
1621.Ve 3901.Ve
1622.PP 3902.PP
1623in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 3903in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
1624.PP 3904.PP
1625You need the following additional files for this: 3905You need the following additional files for this:
1626.PP 3906.PP
1627.Vb 2 3907.Vb 2
1628\& event.h 3908\& event.h
1629\& event.c 3909\& event.c
1630.Ve 3910.Ve
1631.PP 3911.PP
1632\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 3912\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
1633.IX Subsection "AUTOCONF SUPPORT" 3913.IX Subsection "AUTOCONF SUPPORT"
1634.PP 3914.PP
1635Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 3915Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
1636whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 3916whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1637\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR off. \fIev.c\fR will then include 3917\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
1638\&\fIconfig.h\fR and configure itself accordingly. 3918include \fIconfig.h\fR and configure itself accordingly.
1639.PP 3919.PP
1640For this of course you need the m4 file: 3920For this of course you need the m4 file:
1641.PP 3921.PP
1642.Vb 1 3922.Vb 1
1643\& libev.m4 3923\& libev.m4
1644.Ve 3924.Ve
1645.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 3925.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
1646.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 3926.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1647Libev can be configured via a variety of preprocessor symbols you have to define 3927Libev can be configured via a variety of preprocessor symbols you have to
1648before including any of its files. The default is not to build for multiplicity 3928define before including (or compiling) any of its files. The default in
1649and only include the select backend. 3929the absence of autoconf is documented for every option.
3930.PP
3931Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
3932values when compiling libev vs. including \fIev.h\fR, so it is permissible
3933to redefine them before including \fIev.h\fR without breaking compatibility
3934to a compiled library. All other symbols change the \s-1ABI\s0, which means all
3935users of libev and the libev code itself must be compiled with compatible
3936settings.
3937.IP "\s-1EV_COMPAT3\s0 (h)" 4
3938.IX Item "EV_COMPAT3 (h)"
3939Backwards compatibility is a major concern for libev. This is why this
3940release of libev comes with wrappers for the functions and symbols that
3941have been renamed between libev version 3 and 4.
3942.Sp
3943You can disable these wrappers (to test compatibility with future
3944versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
3945sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
3946from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
3947typedef in that case.
3948.Sp
3949In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
3950and in some even more future version the compatibility code will be
3951removed completely.
1650.IP "\s-1EV_STANDALONE\s0" 4 3952.IP "\s-1EV_STANDALONE\s0 (h)" 4
1651.IX Item "EV_STANDALONE" 3953.IX Item "EV_STANDALONE (h)"
1652Must always be \f(CW1\fR if you do not use autoconf configuration, which 3954Must always be \f(CW1\fR if you do not use autoconf configuration, which
1653keeps libev from including \fIconfig.h\fR, and it also defines dummy 3955keeps libev from including \fIconfig.h\fR, and it also defines dummy
1654implementations for some libevent functions (such as logging, which is not 3956implementations for some libevent functions (such as logging, which is not
1655supported). It will also not define any of the structs usually found in 3957supported). It will also not define any of the structs usually found in
1656\&\fIevent.h\fR that are not directly supported by the libev core alone. 3958\&\fIevent.h\fR that are not directly supported by the libev core alone.
3959.Sp
3960In standalone mode, libev will still try to automatically deduce the
3961configuration, but has to be more conservative.
1657.IP "\s-1EV_USE_MONOTONIC\s0" 4 3962.IP "\s-1EV_USE_MONOTONIC\s0" 4
1658.IX Item "EV_USE_MONOTONIC" 3963.IX Item "EV_USE_MONOTONIC"
1659If defined to be \f(CW1\fR, libev will try to detect the availability of the 3964If defined to be \f(CW1\fR, libev will try to detect the availability of the
1660monotonic clock option at both compiletime and runtime. Otherwise no use 3965monotonic clock option at both compile time and runtime. Otherwise no
1661of the monotonic clock option will be attempted. If you enable this, you 3966use of the monotonic clock option will be attempted. If you enable this,
1662usually have to link against librt or something similar. Enabling it when 3967you usually have to link against librt or something similar. Enabling it
1663the functionality isn't available is safe, though, althoguh you have 3968when the functionality isn't available is safe, though, although you have
1664to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 3969to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
1665function is hiding in (often \fI\-lrt\fR). 3970function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
1666.IP "\s-1EV_USE_REALTIME\s0" 4 3971.IP "\s-1EV_USE_REALTIME\s0" 4
1667.IX Item "EV_USE_REALTIME" 3972.IX Item "EV_USE_REALTIME"
1668If defined to be \f(CW1\fR, libev will try to detect the availability of the 3973If defined to be \f(CW1\fR, libev will try to detect the availability of the
1669realtime clock option at compiletime (and assume its availability at 3974real-time clock option at compile time (and assume its availability
1670runtime if successful). Otherwise no use of the realtime clock option will 3975at runtime if successful). Otherwise no use of the real-time clock
1671be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 3976option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
1672(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 3977by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
1673in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 3978correctness. See the note about libraries in the description of
3979\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3980\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3981.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3982.IX Item "EV_USE_CLOCK_SYSCALL"
3983If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3984of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3985exists 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
3986unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3987programs needlessly. Using a direct syscall is slightly slower (in
3988theory), because no optimised vdso implementation can be used, but avoids
3989the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3990higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3991.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3992.IX Item "EV_USE_NANOSLEEP"
3993If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3994and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3995.IP "\s-1EV_USE_EVENTFD\s0" 4
3996.IX Item "EV_USE_EVENTFD"
3997If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3998available and will probe for kernel support at runtime. This will improve
3999\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4000If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
40012.7 or newer, otherwise disabled.
1674.IP "\s-1EV_USE_SELECT\s0" 4 4002.IP "\s-1EV_USE_SELECT\s0" 4
1675.IX Item "EV_USE_SELECT" 4003.IX Item "EV_USE_SELECT"
1676If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4004If undefined or defined to be \f(CW1\fR, libev will compile in support for the
1677\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4005\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
1678other method takes over, select will be it. Otherwise the select backend 4006other method takes over, select will be it. Otherwise the select backend
1679will not be compiled in. 4007will not be compiled in.
1680.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4008.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
1681.IX Item "EV_SELECT_USE_FD_SET" 4009.IX Item "EV_SELECT_USE_FD_SET"
1682If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4010If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
1683structure. This is useful if libev doesn't compile due to a missing 4011structure. This is useful if libev doesn't compile due to a missing
1684\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4012\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
1685exotic systems. This usually limits the range of file descriptors to some 4013on exotic systems. This usually limits the range of file descriptors to
1686low limit such as 1024 or might have other limitations (winsocket only 4014some low limit such as 1024 or might have other limitations (winsocket
1687allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4015only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
1688influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4016configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
1689.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4017.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
1690.IX Item "EV_SELECT_IS_WINSOCKET" 4018.IX Item "EV_SELECT_IS_WINSOCKET"
1691When defined to \f(CW1\fR, the select backend will assume that 4019When defined to \f(CW1\fR, the select backend will assume that
1692select/socket/connect etc. don't understand file descriptors but 4020select/socket/connect etc. don't understand file descriptors but
1693wants osf handles on win32 (this is the case when the select to 4021wants osf handles on win32 (this is the case when the select to
1694be used is the winsock select). This means that it will call 4022be used is the winsock select). This means that it will call
1695\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4023\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
1696it is assumed that all these functions actually work on fds, even 4024it is assumed that all these functions actually work on fds, even
1697on win32. Should not be defined on non\-win32 platforms. 4025on win32. Should not be defined on non\-win32 platforms.
4026.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4027.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4028If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4029file descriptors to socket handles. When not defining this symbol (the
4030default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4031correct. In some cases, programs use their own file descriptor management,
4032in which case they can provide this function to map fds to socket handles.
4033.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4034.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4035If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4036using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4037their own fd to handle mapping, overwriting this function makes it easier
4038to do so. This can be done by defining this macro to an appropriate value.
4039.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4040.IX Item "EV_WIN32_CLOSE_FD(fd)"
4041If programs implement their own fd to handle mapping on win32, then this
4042macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4043file descriptors again. Note that the replacement function has to close
4044the underlying \s-1OS\s0 handle.
1698.IP "\s-1EV_USE_POLL\s0" 4 4045.IP "\s-1EV_USE_POLL\s0" 4
1699.IX Item "EV_USE_POLL" 4046.IX Item "EV_USE_POLL"
1700If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4047If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
1701backend. Otherwise it will be enabled on non\-win32 platforms. It 4048backend. Otherwise it will be enabled on non\-win32 platforms. It
1702takes precedence over select. 4049takes precedence over select.
1703.IP "\s-1EV_USE_EPOLL\s0" 4 4050.IP "\s-1EV_USE_EPOLL\s0" 4
1704.IX Item "EV_USE_EPOLL" 4051.IX Item "EV_USE_EPOLL"
1705If defined to be \f(CW1\fR, libev will compile in support for the Linux 4052If defined to be \f(CW1\fR, libev will compile in support for the Linux
1706\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4053\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
1707otherwise another method will be used as fallback. This is the 4054otherwise another method will be used as fallback. This is the preferred
1708preferred backend for GNU/Linux systems. 4055backend for GNU/Linux systems. If undefined, it will be enabled if the
4056headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1709.IP "\s-1EV_USE_KQUEUE\s0" 4 4057.IP "\s-1EV_USE_KQUEUE\s0" 4
1710.IX Item "EV_USE_KQUEUE" 4058.IX Item "EV_USE_KQUEUE"
1711If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4059If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
1712\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4060\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
1713otherwise another method will be used as fallback. This is the preferred 4061otherwise another method will be used as fallback. This is the preferred
1714backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only 4062backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
1715supports some types of fds correctly (the only platform we found that 4063supports some types of fds correctly (the only platform we found that
1716supports ptys for example was NetBSD), so kqueue might be compiled in, but 4064supports ptys for example was NetBSD), so kqueue might be compiled in, but
1717not be used unless explicitly requested. The best way to use it is to find 4065not be used unless explicitly requested. The best way to use it is to find
1718out wether kqueue supports your type of fd properly and use an embedded 4066out whether kqueue supports your type of fd properly and use an embedded
1719kqueue loop. 4067kqueue loop.
1720.IP "\s-1EV_USE_PORT\s0" 4 4068.IP "\s-1EV_USE_PORT\s0" 4
1721.IX Item "EV_USE_PORT" 4069.IX Item "EV_USE_PORT"
1722If defined to be \f(CW1\fR, libev will compile in support for the Solaris 4070If defined to be \f(CW1\fR, libev will compile in support for the Solaris
172310 port style backend. Its availability will be detected at runtime, 407110 port style backend. Its availability will be detected at runtime,
1724otherwise another method will be used as fallback. This is the preferred 4072otherwise another method will be used as fallback. This is the preferred
1725backend for Solaris 10 systems. 4073backend for Solaris 10 systems.
1726.IP "\s-1EV_USE_DEVPOLL\s0" 4 4074.IP "\s-1EV_USE_DEVPOLL\s0" 4
1727.IX Item "EV_USE_DEVPOLL" 4075.IX Item "EV_USE_DEVPOLL"
1728reserved for future expansion, works like the \s-1USE\s0 symbols above. 4076Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4077.IP "\s-1EV_USE_INOTIFY\s0" 4
4078.IX Item "EV_USE_INOTIFY"
4079If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4080interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4081be detected at runtime. If undefined, it will be enabled if the headers
4082indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4083.IP "\s-1EV_ATOMIC_T\s0" 4
4084.IX Item "EV_ATOMIC_T"
4085Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4086access is atomic with respect to other threads or signal contexts. No such
4087type is easily found in the C language, so you can provide your own type
4088that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4089as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4090.Sp
4091In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4092(from \fIsignal.h\fR), which is usually good enough on most platforms.
1729.IP "\s-1EV_H\s0" 4 4093.IP "\s-1EV_H\s0 (h)" 4
1730.IX Item "EV_H" 4094.IX Item "EV_H (h)"
1731The name of the \fIev.h\fR header file used to include it. The default if 4095The name of the \fIev.h\fR header file used to include it. The default if
1732undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4096undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
1733can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4097used to virtually rename the \fIev.h\fR header file in case of conflicts.
1734.IP "\s-1EV_CONFIG_H\s0" 4 4098.IP "\s-1EV_CONFIG_H\s0 (h)" 4
1735.IX Item "EV_CONFIG_H" 4099.IX Item "EV_CONFIG_H (h)"
1736If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4100If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
1737\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4101\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
1738\&\f(CW\*(C`EV_H\*(C'\fR, above. 4102\&\f(CW\*(C`EV_H\*(C'\fR, above.
1739.IP "\s-1EV_EVENT_H\s0" 4 4103.IP "\s-1EV_EVENT_H\s0 (h)" 4
1740.IX Item "EV_EVENT_H" 4104.IX Item "EV_EVENT_H (h)"
1741Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4105Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
1742of how the \fIevent.h\fR header can be found. 4106of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
1743.IP "\s-1EV_PROTOTYPES\s0" 4 4107.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
1744.IX Item "EV_PROTOTYPES" 4108.IX Item "EV_PROTOTYPES (h)"
1745If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4109If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
1746prototypes, but still define all the structs and other symbols. This is 4110prototypes, but still define all the structs and other symbols. This is
1747occasionally useful if you want to provide your own wrapper functions 4111occasionally useful if you want to provide your own wrapper functions
1748around libev functions. 4112around libev functions.
1749.IP "\s-1EV_MULTIPLICITY\s0" 4 4113.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
1751If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4115If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
1752will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4116will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
1753additional independent event loops. Otherwise there will be no support 4117additional independent event loops. Otherwise there will be no support
1754for multiple event loops and there is no first event loop pointer 4118for multiple event loops and there is no first event loop pointer
1755argument. Instead, all functions act on the single default loop. 4119argument. Instead, all functions act on the single default loop.
1756.IP "\s-1EV_PERIODICS\s0" 4 4120.IP "\s-1EV_MINPRI\s0" 4
1757.IX Item "EV_PERIODICS" 4121.IX Item "EV_MINPRI"
1758If undefined or defined to be \f(CW1\fR, then periodic timers are supported, 4122.PD 0
1759otherwise not. This saves a few kb of code. 4123.IP "\s-1EV_MAXPRI\s0" 4
4124.IX Item "EV_MAXPRI"
4125.PD
4126The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4127\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4128provide for more priorities by overriding those symbols (usually defined
4129to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4130.Sp
4131When doing priority-based operations, libev usually has to linearly search
4132all the priorities, so having many of them (hundreds) uses a lot of space
4133and time, so using the defaults of five priorities (\-2 .. +2) is usually
4134fine.
4135.Sp
4136If your embedding application does not need any priorities, defining these
4137both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4138.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4139.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."
4140If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4141the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4142is not. Disabling watcher types mainly saves code size.
4143.IP "\s-1EV_FEATURES\s0" 4
4144.IX Item "EV_FEATURES"
4145If you need to shave off some kilobytes of code at the expense of some
4146speed (but with the full \s-1API\s0), you can define this symbol to request
4147certain subsets of functionality. The default is to enable all features
4148that can be enabled on the platform.
4149.Sp
4150A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4151with some broad features you want) and then selectively re-enable
4152additional parts you want, for example if you want everything minimal,
4153but multiple event loop support, async and child watchers and the poll
4154backend, use this:
4155.Sp
4156.Vb 5
4157\& #define EV_FEATURES 0
4158\& #define EV_MULTIPLICITY 1
4159\& #define EV_USE_POLL 1
4160\& #define EV_CHILD_ENABLE 1
4161\& #define EV_ASYNC_ENABLE 1
4162.Ve
4163.Sp
4164The actual value is a bitset, it can be a combination of the following
4165values:
4166.RS 4
4167.ie n .IP "1 \- faster/larger code" 4
4168.el .IP "\f(CW1\fR \- faster/larger code" 4
4169.IX Item "1 - faster/larger code"
4170Use larger code to speed up some operations.
4171.Sp
4172Currently this is used to override some inlining decisions (enlarging the
4173code size by roughly 30% on amd64).
4174.Sp
4175When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4176gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4177assertions.
4178.ie n .IP "2 \- faster/larger data structures" 4
4179.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4180.IX Item "2 - faster/larger data structures"
4181Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4182hash table sizes and so on. This will usually further increase code size
4183and can additionally have an effect on the size of data structures at
4184runtime.
4185.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4186.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4187.IX Item "4 - full API configuration"
4188This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4189enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4190.ie n .IP "8 \- full \s-1API\s0" 4
4191.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4192.IX Item "8 - full API"
4193This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4194details on which parts of the \s-1API\s0 are still available without this
4195feature, and do not complain if this subset changes over time.
4196.ie n .IP "16 \- enable all optional watcher types" 4
4197.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4198.IX Item "16 - enable all optional watcher types"
4199Enables all optional watcher types. If you want to selectively enable
4200only some watcher types other than I/O and timers (e.g. prepare,
4201embed, async, child...) you can enable them manually by defining
4202\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4203.ie n .IP "32 \- enable all backends" 4
4204.el .IP "\f(CW32\fR \- enable all backends" 4
4205.IX Item "32 - enable all backends"
4206This enables all backends \- without this feature, you need to enable at
4207least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4208.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4209.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4210.IX Item "64 - enable OS-specific helper APIs"
4211Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4212default.
4213.RE
4214.RS 4
4215.Sp
4216Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4217reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4218code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4219watchers, timers and monotonic clock support.
4220.Sp
4221With an intelligent-enough linker (gcc+binutils are intelligent enough
4222when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4223your program might be left out as well \- a binary starting a timer and an
4224I/O watcher then might come out at only 5Kb.
4225.RE
4226.IP "\s-1EV_AVOID_STDIO\s0" 4
4227.IX Item "EV_AVOID_STDIO"
4228If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4229functions (printf, scanf, perror etc.). This will increase the code size
4230somewhat, but if your program doesn't otherwise depend on stdio and your
4231libc allows it, this avoids linking in the stdio library which is quite
4232big.
4233.Sp
4234Note that error messages might become less precise when this option is
4235enabled.
4236.IP "\s-1EV_NSIG\s0" 4
4237.IX Item "EV_NSIG"
4238The highest supported signal number, +1 (or, the number of
4239signals): Normally, libev tries to deduce the maximum number of signals
4240automatically, but sometimes this fails, in which case it can be
4241specified. Also, using a lower number than detected (\f(CW32\fR should be
4242good for about any system in existence) can save some memory, as libev
4243statically allocates some 12\-24 bytes per signal number.
4244.IP "\s-1EV_PID_HASHSIZE\s0" 4
4245.IX Item "EV_PID_HASHSIZE"
4246\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4247pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4248usually more than enough. If you need to manage thousands of children you
4249might want to increase this value (\fImust\fR be a power of two).
4250.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4251.IX Item "EV_INOTIFY_HASHSIZE"
4252\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4253inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4254disabled), usually more than enough. If you need to manage thousands of
4255\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4256power of two).
4257.IP "\s-1EV_USE_4HEAP\s0" 4
4258.IX Item "EV_USE_4HEAP"
4259Heaps are not very cache-efficient. To improve the cache-efficiency of the
4260timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4261to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4262faster performance with many (thousands) of watchers.
4263.Sp
4264The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4265will be \f(CW0\fR.
4266.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4267.IX Item "EV_HEAP_CACHE_AT"
4268Heaps are not very cache-efficient. To improve the cache-efficiency of the
4269timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4270the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4271which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4272but avoids random read accesses on heap changes. This improves performance
4273noticeably with many (hundreds) of watchers.
4274.Sp
4275The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4276will be \f(CW0\fR.
4277.IP "\s-1EV_VERIFY\s0" 4
4278.IX Item "EV_VERIFY"
4279Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4280be done: If set to \f(CW0\fR, no internal verification code will be compiled
4281in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4282called. If set to \f(CW2\fR, then the internal verification code will be
4283called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4284verification code will be called very frequently, which will slow down
4285libev considerably.
4286.Sp
4287The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4288will be \f(CW0\fR.
1760.IP "\s-1EV_COMMON\s0" 4 4289.IP "\s-1EV_COMMON\s0" 4
1761.IX Item "EV_COMMON" 4290.IX Item "EV_COMMON"
1762By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4291By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
1763this macro to a something else you can include more and other types of 4292this macro to something else you can include more and other types of
1764members. You have to define it each time you include one of the files, 4293members. You have to define it each time you include one of the files,
1765though, and it must be identical each time. 4294though, and it must be identical each time.
1766.Sp 4295.Sp
1767For example, the perl \s-1EV\s0 module uses something like this: 4296For example, the perl \s-1EV\s0 module uses something like this:
1768.Sp 4297.Sp
1769.Vb 3 4298.Vb 3
1770\& #define EV_COMMON \e 4299\& #define EV_COMMON \e
1771\& SV *self; /* contains this struct */ \e 4300\& SV *self; /* contains this struct */ \e
1772\& SV *cb_sv, *fh /* note no trailing ";" */ 4301\& SV *cb_sv, *fh /* note no trailing ";" */
1773.Ve 4302.Ve
1774.IP "\s-1EV_CB_DECLARE\s0(type)" 4 4303.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
1775.IX Item "EV_CB_DECLARE(type)" 4304.IX Item "EV_CB_DECLARE (type)"
1776.PD 0 4305.PD 0
1777.IP "\s-1EV_CB_INVOKE\s0(watcher,revents)" 4 4306.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
1778.IX Item "EV_CB_INVOKE(watcher,revents)" 4307.IX Item "EV_CB_INVOKE (watcher, revents)"
1779.IP "ev_set_cb(ev,cb)" 4 4308.IP "ev_set_cb (ev, cb)" 4
1780.IX Item "ev_set_cb(ev,cb)" 4309.IX Item "ev_set_cb (ev, cb)"
1781.PD 4310.PD
1782Can be used to change the callback member declaration in each watcher, 4311Can be used to change the callback member declaration in each watcher,
1783and the way callbacks are invoked and set. Must expand to a struct member 4312and the way callbacks are invoked and set. Must expand to a struct member
1784definition and a statement, respectively. See the \fIev.v\fR header file for 4313definition and a statement, respectively. See the \fIev.h\fR header file for
1785their default definitions. One possible use for overriding these is to 4314their default definitions. One possible use for overriding these is to
1786avoid the ev_loop pointer as first argument in all cases, or to use method 4315avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
1787calls instead of plain function calls in \*(C+. 4316method calls instead of plain function calls in \*(C+.
4317.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4318.IX Subsection "EXPORTED API SYMBOLS"
4319If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4320exported symbols, you can use the provided \fISymbol.*\fR files which list
4321all public symbols, one per line:
4322.PP
4323.Vb 2
4324\& Symbols.ev for libev proper
4325\& Symbols.event for the libevent emulation
4326.Ve
4327.PP
4328This can also be used to rename all public symbols to avoid clashes with
4329multiple versions of libev linked together (which is obviously bad in
4330itself, but sometimes it is inconvenient to avoid this).
4331.PP
4332A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4333include before including \fIev.h\fR:
4334.PP
4335.Vb 1
4336\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4337.Ve
4338.PP
4339This would create a file \fIwrap.h\fR which essentially looks like this:
4340.PP
4341.Vb 4
4342\& #define ev_backend myprefix_ev_backend
4343\& #define ev_check_start myprefix_ev_check_start
4344\& #define ev_check_stop myprefix_ev_check_stop
4345\& ...
4346.Ve
1788.Sh "\s-1EXAMPLES\s0" 4347.SS "\s-1EXAMPLES\s0"
1789.IX Subsection "EXAMPLES" 4348.IX Subsection "EXAMPLES"
1790For a real-world example of a program the includes libev 4349For a real-world example of a program the includes libev
1791verbatim, you can have a look at the \s-1EV\s0 perl module 4350verbatim, you can have a look at the \s-1EV\s0 perl module
1792(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 4351(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
1793the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 4352the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
1794interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 4353interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
1795will be compiled. It is pretty complex because it provides its own header 4354will be compiled. It is pretty complex because it provides its own header
1796file. 4355file.
1797.Sp 4356.PP
1798The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 4357The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
1799that everybody includes and which overrides some autoconf choices: 4358that everybody includes and which overrides some configure choices:
4359.PP
4360.Vb 8
4361\& #define EV_FEATURES 8
4362\& #define EV_USE_SELECT 1
4363\& #define EV_PREPARE_ENABLE 1
4364\& #define EV_IDLE_ENABLE 1
4365\& #define EV_SIGNAL_ENABLE 1
4366\& #define EV_CHILD_ENABLE 1
4367\& #define EV_USE_STDEXCEPT 0
4368\& #define EV_CONFIG_H <config.h>
4369\&
4370\& #include "ev++.h"
4371.Ve
4372.PP
4373And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4374.PP
4375.Vb 2
4376\& #include "ev_cpp.h"
4377\& #include "ev.c"
4378.Ve
4379.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4380.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4381.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4382.IX Subsection "THREADS AND COROUTINES"
4383\fI\s-1THREADS\s0\fR
4384.IX Subsection "THREADS"
4385.PP
4386All libev functions are reentrant and thread-safe unless explicitly
4387documented otherwise, but libev implements no locking itself. This means
4388that you can use as many loops as you want in parallel, as long as there
4389are no concurrent calls into any libev function with the same loop
4390parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4391of course): libev guarantees that different event loops share no data
4392structures that need any locking.
4393.PP
4394Or to put it differently: calls with different loop parameters can be done
4395concurrently from multiple threads, calls with the same loop parameter
4396must be done serially (but can be done from different threads, as long as
4397only one thread ever is inside a call at any point in time, e.g. by using
4398a mutex per loop).
4399.PP
4400Specifically to support threads (and signal handlers), libev implements
4401so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4402concurrency on the same event loop, namely waking it up \*(L"from the
4403outside\*(R".
4404.PP
4405If you want to know which design (one loop, locking, or multiple loops
4406without or something else still) is best for your problem, then I cannot
4407help you, but here is some generic advice:
4408.IP "\(bu" 4
4409most applications have a main thread: use the default libev loop
4410in that thread, or create a separate thread running only the default loop.
1800.Sp 4411.Sp
4412This helps integrating other libraries or software modules that use libev
4413themselves and don't care/know about threading.
4414.IP "\(bu" 4
4415one loop per thread is usually a good model.
4416.Sp
4417Doing this is almost never wrong, sometimes a better-performance model
4418exists, but it is always a good start.
4419.IP "\(bu" 4
4420other models exist, such as the leader/follower pattern, where one
4421loop is handed through multiple threads in a kind of round-robin fashion.
4422.Sp
4423Choosing a model is hard \- look around, learn, know that usually you can do
4424better than you currently do :\-)
4425.IP "\(bu" 4
4426often you need to talk to some other thread which blocks in the
4427event loop.
4428.Sp
4429\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4430(or from signal contexts...).
4431.Sp
4432An example use would be to communicate signals or other events that only
4433work in the default loop by registering the signal watcher with the
4434default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4435watcher callback into the event loop interested in the signal.
4436.PP
4437\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4438.IX Subsection "THREAD LOCKING EXAMPLE"
4439.PP
4440Here is a fictitious example of how to run an event loop in a different
4441thread than where callbacks are being invoked and watchers are
4442created/added/removed.
4443.PP
4444For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4445which uses exactly this technique (which is suited for many high-level
4446languages).
4447.PP
4448The example uses a pthread mutex to protect the loop data, a condition
4449variable to wait for callback invocations, an async watcher to notify the
4450event loop thread and an unspecified mechanism to wake up the main thread.
4451.PP
4452First, you need to associate some data with the event loop:
4453.PP
4454.Vb 6
4455\& typedef struct {
4456\& mutex_t lock; /* global loop lock */
4457\& ev_async async_w;
4458\& thread_t tid;
4459\& cond_t invoke_cv;
4460\& } userdata;
4461\&
4462\& void prepare_loop (EV_P)
4463\& {
4464\& // for simplicity, we use a static userdata struct.
4465\& static userdata u;
4466\&
4467\& ev_async_init (&u\->async_w, async_cb);
4468\& ev_async_start (EV_A_ &u\->async_w);
4469\&
4470\& pthread_mutex_init (&u\->lock, 0);
4471\& pthread_cond_init (&u\->invoke_cv, 0);
4472\&
4473\& // now associate this with the loop
4474\& ev_set_userdata (EV_A_ u);
4475\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4476\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4477\&
4478\& // then create the thread running ev_loop
4479\& pthread_create (&u\->tid, 0, l_run, EV_A);
4480\& }
4481.Ve
4482.PP
4483The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4484solely to wake up the event loop so it takes notice of any new watchers
4485that might have been added:
4486.PP
4487.Vb 5
4488\& static void
4489\& async_cb (EV_P_ ev_async *w, int revents)
4490\& {
4491\& // just used for the side effects
4492\& }
4493.Ve
4494.PP
4495The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4496protecting the loop data, respectively.
4497.PP
4498.Vb 6
4499\& static void
4500\& l_release (EV_P)
4501\& {
4502\& userdata *u = ev_userdata (EV_A);
4503\& pthread_mutex_unlock (&u\->lock);
4504\& }
4505\&
4506\& static void
4507\& l_acquire (EV_P)
4508\& {
4509\& userdata *u = ev_userdata (EV_A);
4510\& pthread_mutex_lock (&u\->lock);
4511\& }
4512.Ve
4513.PP
4514The event loop thread first acquires the mutex, and then jumps straight
4515into \f(CW\*(C`ev_run\*(C'\fR:
4516.PP
1801.Vb 4 4517.Vb 4
1802\& #define EV_USE_POLL 0 4518\& void *
1803\& #define EV_MULTIPLICITY 0 4519\& l_run (void *thr_arg)
1804\& #define EV_PERIODICS 0 4520\& {
1805\& #define EV_CONFIG_H <config.h> 4521\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4522\&
4523\& l_acquire (EV_A);
4524\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4525\& ev_run (EV_A_ 0);
4526\& l_release (EV_A);
4527\&
4528\& return 0;
4529\& }
1806.Ve 4530.Ve
1807.Sp 4531.PP
4532Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4533signal the main thread via some unspecified mechanism (signals? pipe
4534writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4535have been called (in a while loop because a) spurious wakeups are possible
4536and b) skipping inter-thread-communication when there are no pending
4537watchers is very beneficial):
4538.PP
1808.Vb 1 4539.Vb 4
1809\& #include "ev++.h" 4540\& static void
4541\& l_invoke (EV_P)
4542\& {
4543\& userdata *u = ev_userdata (EV_A);
4544\&
4545\& while (ev_pending_count (EV_A))
4546\& {
4547\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4548\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4549\& }
4550\& }
1810.Ve 4551.Ve
1811.Sp 4552.PP
1812And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 4553Now, whenever the main thread gets told to invoke pending watchers, it
1813.Sp 4554will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4555thread to continue:
4556.PP
4557.Vb 4
4558\& static void
4559\& real_invoke_pending (EV_P)
4560\& {
4561\& userdata *u = ev_userdata (EV_A);
4562\&
4563\& pthread_mutex_lock (&u\->lock);
4564\& ev_invoke_pending (EV_A);
4565\& pthread_cond_signal (&u\->invoke_cv);
4566\& pthread_mutex_unlock (&u\->lock);
4567\& }
4568.Ve
4569.PP
4570Whenever you want to start/stop a watcher or do other modifications to an
4571event loop, you will now have to lock:
4572.PP
1814.Vb 2 4573.Vb 2
4574\& ev_timer timeout_watcher;
4575\& userdata *u = ev_userdata (EV_A);
4576\&
4577\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4578\&
4579\& pthread_mutex_lock (&u\->lock);
4580\& ev_timer_start (EV_A_ &timeout_watcher);
4581\& ev_async_send (EV_A_ &u\->async_w);
4582\& pthread_mutex_unlock (&u\->lock);
4583.Ve
4584.PP
4585Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4586an event loop currently blocking in the kernel will have no knowledge
4587about the newly added timer. By waking up the loop it will pick up any new
4588watchers in the next event loop iteration.
4589.PP
4590\fI\s-1COROUTINES\s0\fR
4591.IX Subsection "COROUTINES"
4592.PP
4593Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4594libev fully supports nesting calls to its functions from different
4595coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4596different coroutines, and switch freely between both coroutines running
4597the loop, as long as you don't confuse yourself). The only exception is
4598that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4599.PP
4600Care has been taken to ensure that libev does not keep local state inside
4601\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4602they do not call any callbacks.
4603.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4604.IX Subsection "COMPILER WARNINGS"
4605Depending on your compiler and compiler settings, you might get no or a
4606lot of warnings when compiling libev code. Some people are apparently
4607scared by this.
4608.PP
4609However, these are unavoidable for many reasons. For one, each compiler
4610has different warnings, and each user has different tastes regarding
4611warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4612targeting a specific compiler and compiler-version.
4613.PP
4614Another reason is that some compiler warnings require elaborate
4615workarounds, or other changes to the code that make it less clear and less
4616maintainable.
4617.PP
4618And of course, some compiler warnings are just plain stupid, or simply
4619wrong (because they don't actually warn about the condition their message
4620seems to warn about). For example, certain older gcc versions had some
4621warnings that resulted in an extreme number of false positives. These have
4622been fixed, but some people still insist on making code warn-free with
4623such buggy versions.
4624.PP
4625While libev is written to generate as few warnings as possible,
4626\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4627with any compiler warnings enabled unless you are prepared to cope with
4628them (e.g. by ignoring them). Remember that warnings are just that:
4629warnings, not errors, or proof of bugs.
4630.SS "\s-1VALGRIND\s0"
4631.IX Subsection "VALGRIND"
4632Valgrind has a special section here because it is a popular tool that is
4633highly useful. Unfortunately, valgrind reports are very hard to interpret.
4634.PP
4635If you think you found a bug (memory leak, uninitialised data access etc.)
4636in libev, then check twice: If valgrind reports something like:
4637.PP
4638.Vb 3
4639\& ==2274== definitely lost: 0 bytes in 0 blocks.
4640\& ==2274== possibly lost: 0 bytes in 0 blocks.
4641\& ==2274== still reachable: 256 bytes in 1 blocks.
4642.Ve
4643.PP
4644Then there is no memory leak, just as memory accounted to global variables
4645is not a memleak \- the memory is still being referenced, and didn't leak.
4646.PP
4647Similarly, under some circumstances, valgrind might report kernel bugs
4648as if it were a bug in libev (e.g. in realloc or in the poll backend,
4649although an acceptable workaround has been found here), or it might be
4650confused.
4651.PP
4652Keep in mind that valgrind is a very good tool, but only a tool. Don't
4653make it into some kind of religion.
4654.PP
4655If you are unsure about something, feel free to contact the mailing list
4656with the full valgrind report and an explanation on why you think this
4657is a bug in libev (best check the archives, too :). However, don't be
4658annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4659of learning how to interpret valgrind properly.
4660.PP
4661If you need, for some reason, empty reports from valgrind for your project
4662I suggest using suppression lists.
4663.SH "PORTABILITY NOTES"
4664.IX Header "PORTABILITY NOTES"
4665.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4666.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4667GNU/Linux is the only common platform that supports 64 bit file/large file
4668interfaces but \fIdisables\fR them by default.
4669.PP
4670That means that libev compiled in the default environment doesn't support
4671files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4672.PP
4673Unfortunately, many programs try to work around this GNU/Linux issue
4674by enabling the large file \s-1API\s0, which makes them incompatible with the
4675standard libev compiled for their system.
4676.PP
4677Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4678suddenly make it incompatible to the default compile time environment,
4679i.e. all programs not using special compile switches.
4680.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4681.IX Subsection "OS/X AND DARWIN BUGS"
4682The whole thing is a bug if you ask me \- basically any system interface
4683you touch is broken, whether it is locales, poll, kqueue or even the
4684OpenGL drivers.
4685.PP
4686\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4687.IX Subsection "kqueue is buggy"
4688.PP
4689The kqueue syscall is broken in all known versions \- most versions support
4690only sockets, many support pipes.
4691.PP
4692Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4693rotten platform, but of course you can still ask for it when creating a
4694loop \- embedding a socket-only kqueue loop into a select-based one is
4695probably going to work well.
4696.PP
4697\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4698.IX Subsection "poll is buggy"
4699.PP
4700Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4701implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4702release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4703.PP
4704Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4705this rotten platform, but of course you can still ask for it when creating
4706a loop.
4707.PP
4708\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4709.IX Subsection "select is buggy"
4710.PP
4711All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4712one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4713descriptors you can pass in to 1024 \- your program suddenly crashes when
4714you use more.
4715.PP
4716There is an undocumented \*(L"workaround\*(R" for this \- defining
4717\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4718work on \s-1OS/X\s0.
4719.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4720.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4721\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4722.IX Subsection "errno reentrancy"
4723.PP
4724The default compile environment on Solaris is unfortunately so
4725thread-unsafe that you can't even use components/libraries compiled
4726without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4727defined by default. A valid, if stupid, implementation choice.
4728.PP
4729If you want to use libev in threaded environments you have to make sure
4730it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4731.PP
4732\fIEvent port backend\fR
4733.IX Subsection "Event port backend"
4734.PP
4735The scalable event interface for Solaris is called \*(L"event
4736ports\*(R". Unfortunately, this mechanism is very buggy in all major
4737releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4738a large number of spurious wakeups, make sure you have all the relevant
4739and latest kernel patches applied. No, I don't know which ones, but there
4740are multiple ones to apply, and afterwards, event ports actually work
4741great.
4742.PP
4743If you can't get it to work, you can try running the program by setting
4744the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4745\&\f(CW\*(C`select\*(C'\fR backends.
4746.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4747.IX Subsection "AIX POLL BUG"
4748\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4749this by trying to avoid the poll backend altogether (i.e. it's not even
4750compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4751with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4752.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4753.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4754\fIGeneral issues\fR
4755.IX Subsection "General issues"
4756.PP
4757Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4758requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4759model. Libev still offers limited functionality on this platform in
4760the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4761descriptors. This only applies when using Win32 natively, not when using
4762e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4763as every compielr comes with a slightly differently broken/incompatible
4764environment.
4765.PP
4766Lifting these limitations would basically require the full
4767re-implementation of the I/O system. If you are into this kind of thing,
4768then note that glib does exactly that for you in a very portable way (note
4769also that glib is the slowest event library known to man).
4770.PP
4771There is no supported compilation method available on windows except
4772embedding it into other applications.
4773.PP
4774Sensible signal handling is officially unsupported by Microsoft \- libev
4775tries its best, but under most conditions, signals will simply not work.
4776.PP
4777Not a libev limitation but worth mentioning: windows apparently doesn't
4778accept large writes: instead of resulting in a partial write, windows will
4779either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4780so make sure you only write small amounts into your sockets (less than a
4781megabyte seems safe, but this apparently depends on the amount of memory
4782available).
4783.PP
4784Due to the many, low, and arbitrary limits on the win32 platform and
4785the abysmal performance of winsockets, using a large number of sockets
4786is not recommended (and not reasonable). If your program needs to use
4787more than a hundred or so sockets, then likely it needs to use a totally
4788different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4789notification model, which cannot be implemented efficiently on windows
4790(due to Microsoft monopoly games).
4791.PP
4792A typical way to use libev under windows is to embed it (see the embedding
4793section for details) and use the following \fIevwrap.h\fR header file instead
4794of \fIev.h\fR:
4795.PP
4796.Vb 2
4797\& #define EV_STANDALONE /* keeps ev from requiring config.h */
4798\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4799\&
1815\& #include "ev_cpp.h" 4800\& #include "ev.h"
4801.Ve
4802.PP
4803And compile the following \fIevwrap.c\fR file into your project (make sure
4804you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4805.PP
4806.Vb 2
4807\& #include "evwrap.h"
1816\& #include "ev.c" 4808\& #include "ev.c"
1817.Ve 4809.Ve
4810.PP
4811\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
4812.IX Subsection "The winsocket select function"
4813.PP
4814The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4815requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4816also extremely buggy). This makes select very inefficient, and also
4817requires a mapping from file descriptors to socket handles (the Microsoft
4818C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4819discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4820\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4821.PP
4822The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4823libraries and raw winsocket select is:
4824.PP
4825.Vb 2
4826\& #define EV_USE_SELECT 1
4827\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4828.Ve
4829.PP
4830Note that winsockets handling of fd sets is O(n), so you can easily get a
4831complexity in the O(nA\*^X) range when using win32.
4832.PP
4833\fILimited number of file descriptors\fR
4834.IX Subsection "Limited number of file descriptors"
4835.PP
4836Windows has numerous arbitrary (and low) limits on things.
4837.PP
4838Early versions of winsocket's select only supported waiting for a maximum
4839of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4840can only wait for \f(CW64\fR things at the same time internally; Microsoft
4841recommends spawning a chain of threads and wait for 63 handles and the
4842previous thread in each. Sounds great!).
4843.PP
4844Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4845to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4846call (which might be in libev or elsewhere, for example, perl and many
4847other interpreters do their own select emulation on windows).
4848.PP
4849Another limit is the number of file descriptors in the Microsoft runtime
4850libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4851fetish or something like this inside Microsoft). You can increase this
4852by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4853(another arbitrary limit), but is broken in many versions of the Microsoft
4854runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4855(depending on windows version and/or the phase of the moon). To get more,
4856you need to wrap all I/O functions and provide your own fd management, but
4857the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4858.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4859.IX Subsection "PORTABILITY REQUIREMENTS"
4860In addition to a working ISO-C implementation and of course the
4861backend-specific APIs, libev relies on a few additional extensions:
4862.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4863.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4864.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4865Libev assumes not only that all watcher pointers have the same internal
4866structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4867assumes that the same (machine) code can be used to call any watcher
4868callback: The watcher callbacks have different type signatures, but libev
4869calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4870.IP "pointer accesses must be thread-atomic" 4
4871.IX Item "pointer accesses must be thread-atomic"
4872Accessing a pointer value must be atomic, it must both be readable and
4873writable in one piece \- this is the case on all current architectures.
4874.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4875.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4876.IX Item "sig_atomic_t volatile must be thread-atomic as well"
4877The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4878\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4879threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4880believed to be sufficiently portable.
4881.ie n .IP """sigprocmask"" must work in a threaded environment" 4
4882.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4883.IX Item "sigprocmask must work in a threaded environment"
4884Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4885allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4886pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4887thread\*(R" or will block signals process-wide, both behaviours would
4888be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4889\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4890.Sp
4891The most portable way to handle signals is to block signals in all threads
4892except the initial one, and run the default loop in the initial thread as
4893well.
4894.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4895.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4896.IX Item "long must be large enough for common memory allocation sizes"
4897To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4898instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4899systems (Microsoft...) this might be unexpectedly low, but is still at
4900least 31 bits everywhere, which is enough for hundreds of millions of
4901watchers.
4902.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4903.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4904.IX Item "double must hold a time value in seconds with enough accuracy"
4905The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4906have at least 51 bits of mantissa (and 9 bits of exponent), which is
4907good enough for at least into the year 4000 with millisecond accuracy
4908(the design goal for libev). This requirement is overfulfilled by
4909implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
4910\&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
4911.PP
4912If you know of other additional requirements drop me a note.
4913.SH "ALGORITHMIC COMPLEXITIES"
4914.IX Header "ALGORITHMIC COMPLEXITIES"
4915In this section the complexities of (many of) the algorithms used inside
4916libev will be documented. For complexity discussions about backends see
4917the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4918.PP
4919All of the following are about amortised time: If an array needs to be
4920extended, libev needs to realloc and move the whole array, but this
4921happens asymptotically rarer with higher number of elements, so O(1) might
4922mean that libev does a lengthy realloc operation in rare cases, but on
4923average it is much faster and asymptotically approaches constant time.
4924.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4925.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4926This means that, when you have a watcher that triggers in one hour and
4927there are 100 watchers that would trigger before that, then inserting will
4928have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4929.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4930.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4931That means that changing a timer costs less than removing/adding them,
4932as only the relative motion in the event queue has to be paid for.
4933.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4934.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4935These just add the watcher into an array or at the head of a list.
4936.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4937.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4938.PD 0
4939.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4940.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4941.PD
4942These watchers are stored in lists, so they need to be walked to find the
4943correct watcher to remove. The lists are usually short (you don't usually
4944have many watchers waiting for the same fd or signal: one is typical, two
4945is rare).
4946.IP "Finding the next timer in each loop iteration: O(1)" 4
4947.IX Item "Finding the next timer in each loop iteration: O(1)"
4948By virtue of using a binary or 4\-heap, the next timer is always found at a
4949fixed position in the storage array.
4950.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4951.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4952A change means an I/O watcher gets started or stopped, which requires
4953libev to recalculate its status (and possibly tell the kernel, depending
4954on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4955.IP "Activating one watcher (putting it into the pending state): O(1)" 4
4956.IX Item "Activating one watcher (putting it into the pending state): O(1)"
4957.PD 0
4958.IP "Priority handling: O(number_of_priorities)" 4
4959.IX Item "Priority handling: O(number_of_priorities)"
4960.PD
4961Priorities are implemented by allocating some space for each
4962priority. When doing priority-based operations, libev usually has to
4963linearly search all the priorities, but starting/stopping and activating
4964watchers becomes O(1) with respect to priority handling.
4965.IP "Sending an ev_async: O(1)" 4
4966.IX Item "Sending an ev_async: O(1)"
4967.PD 0
4968.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4969.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4970.IP "Processing signals: O(max_signal_number)" 4
4971.IX Item "Processing signals: O(max_signal_number)"
4972.PD
4973Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4974calls in the current loop iteration. Checking for async and signal events
4975involves iterating over all running async watchers or all signal numbers.
4976.SH "PORTING FROM LIBEV 3.X TO 4.X"
4977.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
4978The major version 4 introduced some incompatible changes to the \s-1API\s0.
4979.PP
4980At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
4981for all changes, so most programs should still compile. The compatibility
4982layer might be removed in later versions of libev, so better update to the
4983new \s-1API\s0 early than late.
4984.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
4985.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
4986.IX Item "EV_COMPAT3 backwards compatibility mechanism"
4987The backward compatibility mechanism can be controlled by
4988\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
4989section.
4990.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
4991.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
4992.IX Item "ev_default_destroy and ev_default_fork have been removed"
4993These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
4994.Sp
4995.Vb 2
4996\& ev_loop_destroy (EV_DEFAULT_UC);
4997\& ev_loop_fork (EV_DEFAULT);
4998.Ve
4999.IP "function/symbol renames" 4
5000.IX Item "function/symbol renames"
5001A number of functions and symbols have been renamed:
5002.Sp
5003.Vb 3
5004\& ev_loop => ev_run
5005\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5006\& EVLOOP_ONESHOT => EVRUN_ONCE
5007\&
5008\& ev_unloop => ev_break
5009\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5010\& EVUNLOOP_ONE => EVBREAK_ONE
5011\& EVUNLOOP_ALL => EVBREAK_ALL
5012\&
5013\& EV_TIMEOUT => EV_TIMER
5014\&
5015\& ev_loop_count => ev_iteration
5016\& ev_loop_depth => ev_depth
5017\& ev_loop_verify => ev_verify
5018.Ve
5019.Sp
5020Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5021\&\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
5022associated constants have been renamed to not collide with the \f(CW\*(C`struct
5023ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5024as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5025\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5026typedef.
5027.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5028.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5029.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5030The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5031mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5032and work, but the library code will of course be larger.
5033.SH "GLOSSARY"
5034.IX Header "GLOSSARY"
5035.IP "active" 4
5036.IX Item "active"
5037A watcher is active as long as it has been started and not yet stopped.
5038See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5039.IP "application" 4
5040.IX Item "application"
5041In this document, an application is whatever is using libev.
5042.IP "backend" 4
5043.IX Item "backend"
5044The part of the code dealing with the operating system interfaces.
5045.IP "callback" 4
5046.IX Item "callback"
5047The address of a function that is called when some event has been
5048detected. Callbacks are being passed the event loop, the watcher that
5049received the event, and the actual event bitset.
5050.IP "callback/watcher invocation" 4
5051.IX Item "callback/watcher invocation"
5052The act of calling the callback associated with a watcher.
5053.IP "event" 4
5054.IX Item "event"
5055A change of state of some external event, such as data now being available
5056for reading on a file descriptor, time having passed or simply not having
5057any other events happening anymore.
5058.Sp
5059In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5060\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5061.IP "event library" 4
5062.IX Item "event library"
5063A software package implementing an event model and loop.
5064.IP "event loop" 4
5065.IX Item "event loop"
5066An entity that handles and processes external events and converts them
5067into callback invocations.
5068.IP "event model" 4
5069.IX Item "event model"
5070The model used to describe how an event loop handles and processes
5071watchers and events.
5072.IP "pending" 4
5073.IX Item "pending"
5074A watcher is pending as soon as the corresponding event has been
5075detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5076.IP "real time" 4
5077.IX Item "real time"
5078The physical time that is observed. It is apparently strictly monotonic :)
5079.IP "wall-clock time" 4
5080.IX Item "wall-clock time"
5081The time and date as shown on clocks. Unlike real time, it can actually
5082be wrong and jump forwards and backwards, e.g. when the you adjust your
5083clock.
5084.IP "watcher" 4
5085.IX Item "watcher"
5086A data structure that describes interest in certain events. Watchers need
5087to be started (attached to an event loop) before they can receive events.
1818.SH "AUTHOR" 5088.SH "AUTHOR"
1819.IX Header "AUTHOR" 5089.IX Header "AUTHOR"
1820Marc Lehmann <libev@schmorp.de>. 5090Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5091Magnusson and Emanuele Giaquinta.

Diff Legend

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