ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev.3
Revision: 1.102
Committed: Fri Sep 5 16:00:17 2014 UTC (9 years, 10 months ago) by root
Branch: MAIN
CVS Tags: rel-4_18, rel-4_19
Changes since 1.101: +24 -21 lines
Log Message:
*** empty log message ***

File Contents

# Content
1 .\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.28)
2 .\"
3 .\" Standard preamble:
4 .\" ========================================================================
5 .de Sp \" Vertical space (when we can't use .PP)
6 .if t .sp .5v
7 .if n .sp
8 ..
9 .de Vb \" Begin verbatim text
10 .ft CW
11 .nf
12 .ne \\$1
13 ..
14 .de Ve \" End verbatim text
15 .ft R
16 .fi
17 ..
18 .\" Set up some character translations and predefined strings. \*(-- will
19 .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
20 .\" double quote, and \*(R" will give a right double quote. \*(C+ will
21 .\" give a nicer C++. Capital omega is used to do unbreakable dashes and
22 .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
23 .\" nothing in troff, for use with C<>.
24 .tr \(*W-
25 .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
26 .ie n \{\
27 . ds -- \(*W-
28 . ds PI pi
29 . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
30 . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
31 . ds L" ""
32 . ds R" ""
33 . ds C` ""
34 . ds C' ""
35 'br\}
36 .el\{\
37 . ds -- \|\(em\|
38 . ds PI \(*p
39 . ds L" ``
40 . ds R" ''
41 . ds C`
42 . ds C'
43 'br\}
44 .\"
45 .\" Escape single quotes in literal strings from groff's Unicode transform.
46 .ie \n(.g .ds Aq \(aq
47 .el .ds Aq '
48 .\"
49 .\" If the F register is turned on, we'll generate index entries on stderr for
50 .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
51 .\" entries marked with X<> in POD. Of course, you'll have to process the
52 .\" output yourself in some meaningful fashion.
53 .\"
54 .\" Avoid warning from groff about undefined register 'F'.
55 .de IX
56 ..
57 .nr rF 0
58 .if \n(.g .if rF .nr rF 1
59 .if (\n(rF:(\n(.g==0)) \{
60 . if \nF \{
61 . de IX
62 . tm Index:\\$1\t\\n%\t"\\$2"
63 ..
64 . if !\nF==2 \{
65 . nr % 0
66 . nr F 2
67 . \}
68 . \}
69 .\}
70 .rr rF
71 .\"
72 .\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
73 .\" Fear. Run. Save yourself. No user-serviceable parts.
74 . \" fudge factors for nroff and troff
75 .if n \{\
76 . ds #H 0
77 . ds #V .8m
78 . ds #F .3m
79 . ds #[ \f1
80 . ds #] \fP
81 .\}
82 .if t \{\
83 . ds #H ((1u-(\\\\n(.fu%2u))*.13m)
84 . ds #V .6m
85 . ds #F 0
86 . ds #[ \&
87 . ds #] \&
88 .\}
89 . \" simple accents for nroff and troff
90 .if n \{\
91 . ds ' \&
92 . ds ` \&
93 . ds ^ \&
94 . ds , \&
95 . ds ~ ~
96 . ds /
97 .\}
98 .if t \{\
99 . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
100 . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
101 . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
102 . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
103 . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
104 . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
105 .\}
106 . \" troff and (daisy-wheel) nroff accents
107 .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
108 .ds 8 \h'\*(#H'\(*b\h'-\*(#H'
109 .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
110 .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
111 .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
112 .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
113 .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
114 .ds ae a\h'-(\w'a'u*4/10)'e
115 .ds Ae A\h'-(\w'A'u*4/10)'E
116 . \" corrections for vroff
117 .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
118 .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
119 . \" for low resolution devices (crt and lpr)
120 .if \n(.H>23 .if \n(.V>19 \
121 \{\
122 . ds : e
123 . ds 8 ss
124 . ds o a
125 . ds d- d\h'-1'\(ga
126 . ds D- D\h'-1'\(hy
127 . ds th \o'bp'
128 . ds Th \o'LP'
129 . ds ae ae
130 . ds Ae AE
131 .\}
132 .rm #[ #] #H #V #F C
133 .\" ========================================================================
134 .\"
135 .IX Title "LIBEV 3"
136 .TH LIBEV 3 "2014-09-05" "libev-4.15" "libev - high performance full featured event loop"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 libev \- a high performance full\-featured event loop written in C
143 .SH "SYNOPSIS"
144 .IX Header "SYNOPSIS"
145 .Vb 1
146 \& #include <ev.h>
147 .Ve
148 .SS "\s-1EXAMPLE PROGRAM\s0"
149 .IX Subsection "EXAMPLE PROGRAM"
150 .Vb 2
151 \& // a single header file is required
152 \& #include <ev.h>
153 \&
154 \& #include <stdio.h> // for puts
155 \&
156 \& // every watcher type has its own typedef\*(Aqd struct
157 \& // with the name ev_TYPE
158 \& ev_io stdin_watcher;
159 \& ev_timer timeout_watcher;
160 \&
161 \& // all watcher callbacks have a similar signature
162 \& // this callback is called when data is readable on stdin
163 \& static void
164 \& stdin_cb (EV_P_ ev_io *w, int revents)
165 \& {
166 \& puts ("stdin ready");
167 \& // for one\-shot events, one must manually stop the watcher
168 \& // with its corresponding stop function.
169 \& ev_io_stop (EV_A_ w);
170 \&
171 \& // this causes all nested ev_run\*(Aqs to stop iterating
172 \& ev_break (EV_A_ EVBREAK_ALL);
173 \& }
174 \&
175 \& // another callback, this time for a time\-out
176 \& static void
177 \& timeout_cb (EV_P_ ev_timer *w, int revents)
178 \& {
179 \& puts ("timeout");
180 \& // this causes the innermost ev_run to stop iterating
181 \& ev_break (EV_A_ EVBREAK_ONE);
182 \& }
183 \&
184 \& int
185 \& main (void)
186 \& {
187 \& // use the default event loop unless you have special needs
188 \& struct ev_loop *loop = EV_DEFAULT;
189 \&
190 \& // initialise an io watcher, then start it
191 \& // this one will watch for stdin to become readable
192 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
193 \& ev_io_start (loop, &stdin_watcher);
194 \&
195 \& // initialise a timer watcher, then start it
196 \& // simple non\-repeating 5.5 second timeout
197 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
198 \& ev_timer_start (loop, &timeout_watcher);
199 \&
200 \& // now wait for events to arrive
201 \& ev_run (loop, 0);
202 \&
203 \& // break was called, so exit
204 \& return 0;
205 \& }
206 .Ve
207 .SH "ABOUT THIS DOCUMENT"
208 .IX Header "ABOUT THIS DOCUMENT"
209 This document documents the libev software package.
210 .PP
211 The newest version of this document is also available as an html-formatted
212 web page you might find easier to navigate when reading it for the first
213 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
214 .PP
215 While this document tries to be as complete as possible in documenting
216 libev, its usage and the rationale behind its design, it is not a tutorial
217 on event-based programming, nor will it introduce event-based programming
218 with libev.
219 .PP
220 Familiarity with event based programming techniques in general is assumed
221 throughout this document.
222 .SH "WHAT TO READ WHEN IN A HURRY"
223 .IX Header "WHAT TO READ WHEN IN A HURRY"
224 This manual tries to be very detailed, but unfortunately, this also makes
225 it very long. If you just want to know the basics of libev, I suggest
226 reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227 look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228 \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229 .SH "ABOUT LIBEV"
230 .IX Header "ABOUT LIBEV"
231 Libev is an event loop: you register interest in certain events (such as a
232 file descriptor being readable or a timeout occurring), and it will manage
233 these event sources and provide your program with events.
234 .PP
235 To do this, it must take more or less complete control over your process
236 (or thread) by executing the \fIevent loop\fR handler, and will then
237 communicate events via a callback mechanism.
238 .PP
239 You register interest in certain events by registering so-called \fIevent
240 watchers\fR, which are relatively small C structures you initialise with the
241 details of the event, and then hand it over to libev by \fIstarting\fR the
242 watcher.
243 .SS "\s-1FEATURES\s0"
244 .IX Subsection "FEATURES"
245 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
246 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
247 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
248 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
249 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
250 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
251 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
253 loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
254 \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
256 .PP
257 It also is quite fast (see this
258 benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
259 for example).
260 .SS "\s-1CONVENTIONS\s0"
261 .IX Subsection "CONVENTIONS"
262 Libev is very configurable. In this manual the default (and most common)
263 configuration will be described, which supports multiple event loops. For
264 more info about various configuration options please have a look at
265 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
266 for multiple event loops, then all functions taking an initial argument of
267 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
268 this argument.
269 .SS "\s-1TIME REPRESENTATION\s0"
270 .IX Subsection "TIME REPRESENTATION"
271 Libev represents time as a single floating point number, representing
272 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
273 somewhere near the beginning of 1970, details are complicated, don't
274 ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
275 too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
276 any calculations on it, you should treat it as some floating point value.
277 .PP
278 Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279 time differences (e.g. delays) throughout libev.
280 .SH "ERROR HANDLING"
281 .IX Header "ERROR HANDLING"
282 Libev knows three classes of errors: operating system errors, usage errors
283 and internal errors (bugs).
284 .PP
285 When libev catches an operating system error it cannot handle (for example
286 a system call indicating a condition libev cannot fix), it calls the callback
287 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289 ()\*(C'\fR.
290 .PP
291 When libev detects a usage error such as a negative timer interval, then
292 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294 the libev caller and need to be fixed there.
295 .PP
296 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
297 extensive consistency checking code. These do not trigger under normal
298 circumstances, as they indicate either a bug in libev or worse.
299 .SH "GLOBAL FUNCTIONS"
300 .IX Header "GLOBAL FUNCTIONS"
301 These functions can be called anytime, even before initialising the
302 library in any way.
303 .IP "ev_tstamp ev_time ()" 4
304 .IX Item "ev_tstamp ev_time ()"
305 Returns the current time as libev would use it. Please note that the
306 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
307 you actually want to know. Also interesting is the combination of
308 \&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
309 .IP "ev_sleep (ev_tstamp interval)" 4
310 .IX Item "ev_sleep (ev_tstamp interval)"
311 Sleep for the given interval: The current thread will be blocked
312 until either it is interrupted or the given time interval has
313 passed (approximately \- it might return a bit earlier even if not
314 interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
315 .Sp
316 Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
317 .Sp
318 The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
319 with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
320 .IP "int ev_version_major ()" 4
321 .IX Item "int ev_version_major ()"
322 .PD 0
323 .IP "int ev_version_minor ()" 4
324 .IX Item "int ev_version_minor ()"
325 .PD
326 You can find out the major and minor \s-1ABI\s0 version numbers of the library
327 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
328 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
329 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
330 version of the library your program was compiled against.
331 .Sp
332 These version numbers refer to the \s-1ABI\s0 version of the library, not the
333 release version.
334 .Sp
335 Usually, it's a good idea to terminate if the major versions mismatch,
336 as this indicates an incompatible change. Minor versions are usually
337 compatible to older versions, so a larger minor version alone is usually
338 not a problem.
339 .Sp
340 Example: Make sure we haven't accidentally been linked against the wrong
341 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
342 such as \s-1LFS\s0 or reentrancy).
343 .Sp
344 .Vb 3
345 \& assert (("libev version mismatch",
346 \& ev_version_major () == EV_VERSION_MAJOR
347 \& && ev_version_minor () >= EV_VERSION_MINOR));
348 .Ve
349 .IP "unsigned int ev_supported_backends ()" 4
350 .IX Item "unsigned int ev_supported_backends ()"
351 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
352 value) compiled into this binary of libev (independent of their
353 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
354 a description of the set values.
355 .Sp
356 Example: make sure we have the epoll method, because yeah this is cool and
357 a must have and can we have a torrent of it please!!!11
358 .Sp
359 .Vb 2
360 \& assert (("sorry, no epoll, no sex",
361 \& ev_supported_backends () & EVBACKEND_EPOLL));
362 .Ve
363 .IP "unsigned int ev_recommended_backends ()" 4
364 .IX Item "unsigned int ev_recommended_backends ()"
365 Return the set of all backends compiled into this binary of libev and
366 also recommended for this platform, meaning it will work for most file
367 descriptor types. This set is often smaller than the one returned by
368 \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
369 and will not be auto-detected unless you explicitly request it (assuming
370 you know what you are doing). This is the set of backends that libev will
371 probe for if you specify no backends explicitly.
372 .IP "unsigned int ev_embeddable_backends ()" 4
373 .IX Item "unsigned int ev_embeddable_backends ()"
374 Returns the set of backends that are embeddable in other event loops. This
375 value is platform-specific but can include backends not available on the
376 current system. To find which embeddable backends might be supported on
377 the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
378 & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
379 .Sp
380 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
381 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
382 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
383 Sets the allocation function to use (the prototype is similar \- the
384 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
385 used to allocate and free memory (no surprises here). If it returns zero
386 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
387 or take some potentially destructive action.
388 .Sp
389 Since some systems (at least OpenBSD and Darwin) fail to implement
390 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
391 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
392 .Sp
393 You could override this function in high-availability programs to, say,
394 free some memory if it cannot allocate memory, to use a special allocator,
395 or even to sleep a while and retry until some memory is available.
396 .Sp
397 Example: Replace the libev allocator with one that waits a bit and then
398 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
399 .Sp
400 .Vb 6
401 \& static void *
402 \& persistent_realloc (void *ptr, size_t size)
403 \& {
404 \& for (;;)
405 \& {
406 \& void *newptr = realloc (ptr, size);
407 \&
408 \& if (newptr)
409 \& return newptr;
410 \&
411 \& sleep (60);
412 \& }
413 \& }
414 \&
415 \& ...
416 \& ev_set_allocator (persistent_realloc);
417 .Ve
418 .IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
419 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
420 Set the callback function to call on a retryable system call error (such
421 as failed select, poll, epoll_wait). The message is a printable string
422 indicating the system call or subsystem causing the problem. If this
423 callback is set, then libev will expect it to remedy the situation, no
424 matter what, when it returns. That is, libev will generally retry the
425 requested operation, or, if the condition doesn't go away, do bad stuff
426 (such as abort).
427 .Sp
428 Example: This is basically the same thing that libev does internally, too.
429 .Sp
430 .Vb 6
431 \& static void
432 \& fatal_error (const char *msg)
433 \& {
434 \& perror (msg);
435 \& abort ();
436 \& }
437 \&
438 \& ...
439 \& ev_set_syserr_cb (fatal_error);
440 .Ve
441 .IP "ev_feed_signal (int signum)" 4
442 .IX Item "ev_feed_signal (int signum)"
443 This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
444 safe to call this function at any time, from any context, including signal
445 handlers or random threads.
446 .Sp
447 Its main use is to customise signal handling in your process, especially
448 in the presence of threads. For example, you could block signals
449 by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
450 creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
451 mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
452 \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
453 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
454 .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
455 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
456 \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
457 libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
458 .PP
459 The library knows two types of such loops, the \fIdefault\fR loop, which
460 supports child process events, and dynamically created event loops which
461 do not.
462 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
463 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
464 This returns the \*(L"default\*(R" event loop object, which is what you should
465 normally use when you just need \*(L"the event loop\*(R". Event loop objects and
466 the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
467 \&\f(CW\*(C`ev_loop_new\*(C'\fR.
468 .Sp
469 If the default loop is already initialised then this function simply
470 returns it (and ignores the flags. If that is troubling you, check
471 \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
472 flags, which should almost always be \f(CW0\fR, unless the caller is also the
473 one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
474 .Sp
475 If you don't know what event loop to use, use the one returned from this
476 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
477 .Sp
478 Note that this function is \fInot\fR thread-safe, so if you want to use it
479 from multiple threads, you have to employ some kind of mutex (note also
480 that this case is unlikely, as loops cannot be shared easily between
481 threads anyway).
482 .Sp
483 The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
484 and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
485 a problem for your application you can either create a dynamic loop with
486 \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
487 \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
488 .Sp
489 Example: This is the most typical usage.
490 .Sp
491 .Vb 2
492 \& if (!ev_default_loop (0))
493 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
494 .Ve
495 .Sp
496 Example: Restrict libev to the select and poll backends, and do not allow
497 environment settings to be taken into account:
498 .Sp
499 .Vb 1
500 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
501 .Ve
502 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504 This will create and initialise a new event loop object. If the loop
505 could not be initialised, returns false.
506 .Sp
507 This function is thread-safe, and one common way to use libev with
508 threads is indeed to create one loop per thread, and using the default
509 loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
510 .Sp
511 The flags argument can be used to specify special behaviour or specific
512 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
513 .Sp
514 The following flags are supported:
515 .RS 4
516 .ie n .IP """EVFLAG_AUTO""" 4
517 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
518 .IX Item "EVFLAG_AUTO"
519 The default flags value. Use this if you have no clue (it's the right
520 thing, believe me).
521 .ie n .IP """EVFLAG_NOENV""" 4
522 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
523 .IX Item "EVFLAG_NOENV"
524 If this flag bit is or'ed into the flag value (or the program runs setuid
525 or setgid) then libev will \fInot\fR look at the environment variable
526 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
527 override the flags completely if it is found in the environment. This is
528 useful to try out specific backends to test their performance, to work
529 around bugs, or to make libev threadsafe (accessing environment variables
530 cannot be done in a threadsafe way, but usually it works if no other
531 thread modifies them).
532 .ie n .IP """EVFLAG_FORKCHECK""" 4
533 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
534 .IX Item "EVFLAG_FORKCHECK"
535 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
536 make libev check for a fork in each iteration by enabling this flag.
537 .Sp
538 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
539 and thus this might slow down your event loop if you do a lot of loop
540 iterations and little real work, but is usually not noticeable (on my
541 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
542 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
543 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
544 .Sp
545 The big advantage of this flag is that you can forget about fork (and
546 forget about forgetting to tell libev about forking) when you use this
547 flag.
548 .Sp
549 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
550 environment variable.
551 .ie n .IP """EVFLAG_NOINOTIFY""" 4
552 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
553 .IX Item "EVFLAG_NOINOTIFY"
554 When this flag is specified, then libev will not attempt to use the
555 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
556 testing, this flag can be useful to conserve inotify file descriptors, as
557 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
558 .ie n .IP """EVFLAG_SIGNALFD""" 4
559 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
560 .IX Item "EVFLAG_SIGNALFD"
561 When this flag is specified, then libev will attempt to use the
562 \&\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
563 delivers signals synchronously, which makes it both faster and might make
564 it possible to get the queued signal data. It can also simplify signal
565 handling with threads, as long as you properly block signals in your
566 threads that are not interested in handling them.
567 .Sp
568 Signalfd will not be used by default as this changes your signal mask, and
569 there are a lot of shoddy libraries and programs (glib's threadpool for
570 example) that can't properly initialise their signal masks.
571 .ie n .IP """EVFLAG_NOSIGMASK""" 4
572 .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
573 .IX Item "EVFLAG_NOSIGMASK"
574 When this flag is specified, then libev will avoid to modify the signal
575 mask. Specifically, this means you have to make sure signals are unblocked
576 when you want to receive them.
577 .Sp
578 This behaviour is useful when you want to do your own signal handling, or
579 want to handle signals only in specific threads and want to avoid libev
580 unblocking the signals.
581 .Sp
582 It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
583 \&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
584 .Sp
585 This flag's behaviour will become the default in future versions of libev.
586 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
587 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
588 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
589 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
590 libev tries to roll its own fd_set with no limits on the number of fds,
591 but if that fails, expect a fairly low limit on the number of fds when
592 using this backend. It doesn't scale too well (O(highest_fd)), but its
593 usually the fastest backend for a low number of (low-numbered :) fds.
594 .Sp
595 To get good performance out of this backend you need a high amount of
596 parallelism (most of the file descriptors should be busy). If you are
597 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
598 connections as possible during one iteration. You might also want to have
599 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
600 readiness notifications you get per iteration.
601 .Sp
602 This 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
603 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
604 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
605 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
606 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
607 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
608 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
609 than select, but handles sparse fds better and has no artificial
610 limit on the number of fds you can use (except it will slow down
611 considerably with a lot of inactive fds). It scales similarly to select,
612 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
613 performance tips.
614 .Sp
615 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
616 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
617 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
618 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
619 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
620 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
621 kernels).
622 .Sp
623 For few fds, this backend is a bit little slower than poll and select, but
624 it scales phenomenally better. While poll and select usually scale like
625 O(total_fds) where total_fds is the total number of fds (or the highest
626 fd), epoll scales either O(1) or O(active_fds).
627 .Sp
628 The epoll mechanism deserves honorable mention as the most misdesigned
629 of the more advanced event mechanisms: mere annoyances include silently
630 dropping file descriptors, requiring a system call per change per file
631 descriptor (and unnecessary guessing of parameters), problems with dup,
632 returning before the timeout value, resulting in additional iterations
633 (and only giving 5ms accuracy while select on the same platform gives
634 0.1ms) and so on. The biggest issue is fork races, however \- if a program
635 forks then \fIboth\fR parent and child process have to recreate the epoll
636 set, which can take considerable time (one syscall per file descriptor)
637 and is of course hard to detect.
638 .Sp
639 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
640 but of course \fIdoesn't\fR, and epoll just loves to report events for
641 totally \fIdifferent\fR file descriptors (even already closed ones, so
642 one cannot even remove them from the set) than registered in the set
643 (especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
644 notifications by employing an additional generation counter and comparing
645 that against the events to filter out spurious ones, recreating the set
646 when required. Epoll also erroneously rounds down timeouts, but gives you
647 no way to know when and by how much, so sometimes you have to busy-wait
648 because epoll returns immediately despite a nonzero timeout. And last
649 not least, it also refuses to work with some file descriptors which work
650 perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
651 .Sp
652 Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
653 cobbled together in a hurry, no thought to design or interaction with
654 others. Oh, the pain, will it ever stop...
655 .Sp
656 While stopping, setting and starting an I/O watcher in the same iteration
657 will result in some caching, there is still a system call per such
658 incident (because the same \fIfile descriptor\fR could point to a different
659 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
660 file descriptors might not work very well if you register events for both
661 file descriptors.
662 .Sp
663 Best performance from this backend is achieved by not unregistering all
664 watchers for a file descriptor until it has been closed, if possible,
665 i.e. keep at least one watcher active per fd at all times. Stopping and
666 starting a watcher (without re-setting it) also usually doesn't cause
667 extra overhead. A fork can both result in spurious notifications as well
668 as in libev having to destroy and recreate the epoll object, which can
669 take considerable time and thus should be avoided.
670 .Sp
671 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
672 faster than epoll for maybe up to a hundred file descriptors, depending on
673 the usage. So sad.
674 .Sp
675 While nominally embeddable in other event loops, this feature is broken in
676 all kernel versions tested so far.
677 .Sp
678 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
679 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
680 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
681 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
682 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
683 Kqueue deserves special mention, as at the time of this writing, it
684 was broken on all BSDs except NetBSD (usually it doesn't work reliably
685 with anything but sockets and pipes, except on Darwin, where of course
686 it's completely useless). Unlike epoll, however, whose brokenness
687 is by design, these kqueue bugs can (and eventually will) be fixed
688 without \s-1API\s0 changes to existing programs. For this reason it's not being
689 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
690 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
691 system like NetBSD.
692 .Sp
693 You still can embed kqueue into a normal poll or select backend and use it
694 only for sockets (after having made sure that sockets work with kqueue on
695 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
696 .Sp
697 It scales in the same way as the epoll backend, but the interface to the
698 kernel is more efficient (which says nothing about its actual speed, of
699 course). While stopping, setting and starting an I/O watcher does never
700 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
701 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
702 might have to leak fd's on fork, but it's more sane than epoll) and it
703 drops fds silently in similarly hard-to-detect cases.
704 .Sp
705 This backend usually performs well under most conditions.
706 .Sp
707 While nominally embeddable in other event loops, this doesn't work
708 everywhere, so you might need to test for this. And since it is broken
709 almost everywhere, you should only use it when you have a lot of sockets
710 (for which it usually works), by embedding it into another event loop
711 (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
712 also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
713 .Sp
714 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
715 \&\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
716 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
717 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
718 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
719 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
720 This is not implemented yet (and might never be, unless you send me an
721 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
722 and is not embeddable, which would limit the usefulness of this backend
723 immensely.
724 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
725 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
726 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
727 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
728 it's really slow, but it still scales very well (O(active_fds)).
729 .Sp
730 While this backend scales well, it requires one system call per active
731 file descriptor per loop iteration. For small and medium numbers of file
732 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
733 might perform better.
734 .Sp
735 On the positive side, this backend actually performed fully to
736 specification in all tests and is fully embeddable, which is a rare feat
737 among the OS-specific backends (I vastly prefer correctness over speed
738 hacks).
739 .Sp
740 On the negative side, the interface is \fIbizarre\fR \- so bizarre that
741 even sun itself gets it wrong in their code examples: The event polling
742 function sometimes returns events to the caller even though an error
743 occurred, but with no indication whether it has done so or not (yes, it's
744 even documented that way) \- deadly for edge-triggered interfaces where you
745 absolutely have to know whether an event occurred or not because you have
746 to re-arm the watcher.
747 .Sp
748 Fortunately libev seems to be able to work around these idiocies.
749 .Sp
750 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
751 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
752 .ie n .IP """EVBACKEND_ALL""" 4
753 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
754 .IX Item "EVBACKEND_ALL"
755 Try all backends (even potentially broken ones that wouldn't be tried
756 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
757 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
758 .Sp
759 It is definitely not recommended to use this flag, use whatever
760 \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
761 at all.
762 .ie n .IP """EVBACKEND_MASK""" 4
763 .el .IP "\f(CWEVBACKEND_MASK\fR" 4
764 .IX Item "EVBACKEND_MASK"
765 Not a backend at all, but a mask to select all backend bits from a
766 \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
767 value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
768 .RE
769 .RS 4
770 .Sp
771 If one or more of the backend flags are or'ed into the flags value,
772 then only these backends will be tried (in the reverse order as listed
773 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
774 ()\*(C'\fR will be tried.
775 .Sp
776 Example: Try to create a event loop that uses epoll and nothing else.
777 .Sp
778 .Vb 3
779 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
780 \& if (!epoller)
781 \& fatal ("no epoll found here, maybe it hides under your chair");
782 .Ve
783 .Sp
784 Example: Use whatever libev has to offer, but make sure that kqueue is
785 used if available.
786 .Sp
787 .Vb 1
788 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
789 .Ve
790 .RE
791 .IP "ev_loop_destroy (loop)" 4
792 .IX Item "ev_loop_destroy (loop)"
793 Destroys an event loop object (frees all memory and kernel state
794 etc.). None of the active event watchers will be stopped in the normal
795 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
796 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
797 calling this function, or cope with the fact afterwards (which is usually
798 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
799 for example).
800 .Sp
801 Note that certain global state, such as signal state (and installed signal
802 handlers), will not be freed by this function, and related watchers (such
803 as signal and child watchers) would need to be stopped manually.
804 .Sp
805 This function is normally used on loop objects allocated by
806 \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
807 \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
808 .Sp
809 Note that it is not advisable to call this function on the default loop
810 except in the rare occasion where you really need to free its resources.
811 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
812 and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
813 .IP "ev_loop_fork (loop)" 4
814 .IX Item "ev_loop_fork (loop)"
815 This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
816 to reinitialise the kernel state for backends that have one. Despite
817 the name, you can call it anytime you are allowed to start or stop
818 watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
819 sense after forking, in the child process. You \fImust\fR call it (or use
820 \&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
821 .Sp
822 Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
823 a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
824 because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
825 during fork.
826 .Sp
827 On the other hand, you only need to call this function in the child
828 process if and only if you want to use the event loop in the child. If
829 you just fork+exec or create a new loop in the child, you don't have to
830 call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
831 difference, but libev will usually detect this case on its own and do a
832 costly reset of the backend).
833 .Sp
834 The function itself is quite fast and it's usually not a problem to call
835 it just in case after a fork.
836 .Sp
837 Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
838 using pthreads.
839 .Sp
840 .Vb 5
841 \& static void
842 \& post_fork_child (void)
843 \& {
844 \& ev_loop_fork (EV_DEFAULT);
845 \& }
846 \&
847 \& ...
848 \& pthread_atfork (0, 0, post_fork_child);
849 .Ve
850 .IP "int ev_is_default_loop (loop)" 4
851 .IX Item "int ev_is_default_loop (loop)"
852 Returns true when the given loop is, in fact, the default loop, and false
853 otherwise.
854 .IP "unsigned int ev_iteration (loop)" 4
855 .IX Item "unsigned int ev_iteration (loop)"
856 Returns the current iteration count for the event loop, which is identical
857 to the number of times libev did poll for new events. It starts at \f(CW0\fR
858 and happily wraps around with enough iterations.
859 .Sp
860 This value can sometimes be useful as a generation counter of sorts (it
861 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
862 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
863 prepare and check phases.
864 .IP "unsigned int ev_depth (loop)" 4
865 .IX Item "unsigned int ev_depth (loop)"
866 Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
867 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
868 .Sp
869 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
870 \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
871 in which case it is higher.
872 .Sp
873 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
874 throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
875 as a hint to avoid such ungentleman-like behaviour unless it's really
876 convenient, in which case it is fully supported.
877 .IP "unsigned int ev_backend (loop)" 4
878 .IX Item "unsigned int ev_backend (loop)"
879 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
880 use.
881 .IP "ev_tstamp ev_now (loop)" 4
882 .IX Item "ev_tstamp ev_now (loop)"
883 Returns the current \*(L"event loop time\*(R", which is the time the event loop
884 received events and started processing them. This timestamp does not
885 change as long as callbacks are being processed, and this is also the base
886 time used for relative timers. You can treat it as the timestamp of the
887 event occurring (or more correctly, libev finding out about it).
888 .IP "ev_now_update (loop)" 4
889 .IX Item "ev_now_update (loop)"
890 Establishes the current time by querying the kernel, updating the time
891 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
892 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
893 .Sp
894 This function is rarely useful, but when some event callback runs for a
895 very long time without entering the event loop, updating libev's idea of
896 the current time is a good idea.
897 .Sp
898 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
899 .IP "ev_suspend (loop)" 4
900 .IX Item "ev_suspend (loop)"
901 .PD 0
902 .IP "ev_resume (loop)" 4
903 .IX Item "ev_resume (loop)"
904 .PD
905 These two functions suspend and resume an event loop, for use when the
906 loop is not used for a while and timeouts should not be processed.
907 .Sp
908 A typical use case would be an interactive program such as a game: When
909 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
910 would be best to handle timeouts as if no time had actually passed while
911 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
912 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
913 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
914 .Sp
915 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
916 between \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
917 will be rescheduled (that is, they will lose any events that would have
918 occurred while suspended).
919 .Sp
920 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
921 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
922 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
923 .Sp
924 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
925 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
926 .IP "bool ev_run (loop, int flags)" 4
927 .IX Item "bool ev_run (loop, int flags)"
928 Finally, this is it, the event handler. This function usually is called
929 after you have initialised all your watchers and you want to start
930 handling events. It will ask the operating system for any new events, call
931 the watcher callbacks, and then repeat the whole process indefinitely: This
932 is why event loops are called \fIloops\fR.
933 .Sp
934 If the flags argument is specified as \f(CW0\fR, it will keep handling events
935 until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
936 called.
937 .Sp
938 The return value is false if there are no more active watchers (which
939 usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
940 (which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
941 .Sp
942 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
943 relying on all watchers to be stopped when deciding when a program has
944 finished (especially in interactive programs), but having a program
945 that automatically loops as long as it has to and no longer by virtue
946 of relying on its watchers stopping correctly, that is truly a thing of
947 beauty.
948 .Sp
949 This function is \fImostly\fR exception-safe \- you can break out of a
950 \&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
951 exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
952 will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
953 .Sp
954 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
955 those events and any already outstanding ones, but will not wait and
956 block your process in case there are no events and will return after one
957 iteration of the loop. This is sometimes useful to poll and handle new
958 events while doing lengthy calculations, to keep the program responsive.
959 .Sp
960 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
961 necessary) and will handle those and any already outstanding ones. It
962 will block your process until at least one new event arrives (which could
963 be an event internal to libev itself, so there is no guarantee that a
964 user-registered callback will be called), and will return after one
965 iteration of the loop.
966 .Sp
967 This is useful if you are waiting for some external event in conjunction
968 with something not expressible using other libev watchers (i.e. "roll your
969 own \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
970 usually a better approach for this kind of thing.
971 .Sp
972 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
973 understanding, not a guarantee that things will work exactly like this in
974 future versions):
975 .Sp
976 .Vb 10
977 \& \- Increment loop depth.
978 \& \- Reset the ev_break status.
979 \& \- Before the first iteration, call any pending watchers.
980 \& LOOP:
981 \& \- If EVFLAG_FORKCHECK was used, check for a fork.
982 \& \- If a fork was detected (by any means), queue and call all fork watchers.
983 \& \- Queue and call all prepare watchers.
984 \& \- If ev_break was called, goto FINISH.
985 \& \- If we have been forked, detach and recreate the kernel state
986 \& as to not disturb the other process.
987 \& \- Update the kernel state with all outstanding changes.
988 \& \- Update the "event loop time" (ev_now ()).
989 \& \- Calculate for how long to sleep or block, if at all
990 \& (active idle watchers, EVRUN_NOWAIT or not having
991 \& any active watchers at all will result in not sleeping).
992 \& \- Sleep if the I/O and timer collect interval say so.
993 \& \- Increment loop iteration counter.
994 \& \- Block the process, waiting for any events.
995 \& \- Queue all outstanding I/O (fd) events.
996 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
997 \& \- Queue all expired timers.
998 \& \- Queue all expired periodics.
999 \& \- Queue all idle watchers with priority higher than that of pending events.
1000 \& \- Queue all check watchers.
1001 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
1002 \& Signals and child watchers are implemented as I/O watchers, and will
1003 \& be handled here by queueing them when their watcher gets executed.
1004 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
1005 \& were used, or there are no active watchers, goto FINISH, otherwise
1006 \& continue with step LOOP.
1007 \& FINISH:
1008 \& \- Reset the ev_break status iff it was EVBREAK_ONE.
1009 \& \- Decrement the loop depth.
1010 \& \- Return.
1011 .Ve
1012 .Sp
1013 Example: Queue some jobs and then loop until no events are outstanding
1014 anymore.
1015 .Sp
1016 .Vb 4
1017 \& ... queue jobs here, make sure they register event watchers as long
1018 \& ... as they still have work to do (even an idle watcher will do..)
1019 \& ev_run (my_loop, 0);
1020 \& ... jobs done or somebody called break. yeah!
1021 .Ve
1022 .IP "ev_break (loop, how)" 4
1023 .IX Item "ev_break (loop, how)"
1024 Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
1025 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
1026 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
1027 \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1028 .Sp
1029 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1030 .Sp
1031 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1032 which case it will have no effect.
1033 .IP "ev_ref (loop)" 4
1034 .IX Item "ev_ref (loop)"
1035 .PD 0
1036 .IP "ev_unref (loop)" 4
1037 .IX Item "ev_unref (loop)"
1038 .PD
1039 Ref/unref can be used to add or remove a reference count on the event
1040 loop: Every watcher keeps one reference, and as long as the reference
1041 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1042 .Sp
1043 This is useful when you have a watcher that you never intend to
1044 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1045 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1046 before stopping it.
1047 .Sp
1048 As an example, libev itself uses this for its internal signal pipe: It
1049 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1050 exiting if no event watchers registered by it are active. It is also an
1051 excellent way to do this for generic recurring timers or from within
1052 third-party libraries. Just remember to \fIunref after start\fR and \fIref
1053 before stop\fR (but only if the watcher wasn't active before, or was active
1054 before, respectively. Note also that libev might stop watchers itself
1055 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1056 in the callback).
1057 .Sp
1058 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1059 running when nothing else is active.
1060 .Sp
1061 .Vb 4
1062 \& ev_signal exitsig;
1063 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1064 \& ev_signal_start (loop, &exitsig);
1065 \& ev_unref (loop);
1066 .Ve
1067 .Sp
1068 Example: For some weird reason, unregister the above signal handler again.
1069 .Sp
1070 .Vb 2
1071 \& ev_ref (loop);
1072 \& ev_signal_stop (loop, &exitsig);
1073 .Ve
1074 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1075 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1076 .PD 0
1077 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1078 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1079 .PD
1080 These advanced functions influence the time that libev will spend waiting
1081 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1082 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1083 latency.
1084 .Sp
1085 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1086 allows libev to delay invocation of I/O and timer/periodic callbacks
1087 to increase efficiency of loop iterations (or to increase power-saving
1088 opportunities).
1089 .Sp
1090 The idea is that sometimes your program runs just fast enough to handle
1091 one (or very few) event(s) per loop iteration. While this makes the
1092 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1093 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1094 overhead for the actual polling but can deliver many events at once.
1095 .Sp
1096 By setting a higher \fIio collect interval\fR you allow libev to spend more
1097 time collecting I/O events, so you can handle more events per iteration,
1098 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1099 \&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1100 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1101 sleep time ensures that libev will not poll for I/O events more often then
1102 once per this interval, on average (as long as the host time resolution is
1103 good enough).
1104 .Sp
1105 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1106 to spend more time collecting timeouts, at the expense of increased
1107 latency/jitter/inexactness (the watcher callback will be called
1108 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1109 value will not introduce any overhead in libev.
1110 .Sp
1111 Many (busy) programs can usually benefit by setting the I/O collect
1112 interval to a value near \f(CW0.1\fR or so, which is often enough for
1113 interactive servers (of course not for games), likewise for timeouts. It
1114 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1115 as this approaches the timing granularity of most systems. Note that if
1116 you do transactions with the outside world and you can't increase the
1117 parallelity, then this setting will limit your transaction rate (if you
1118 need to poll once per transaction and the I/O collect interval is 0.01,
1119 then you can't do more than 100 transactions per second).
1120 .Sp
1121 Setting the \fItimeout collect interval\fR can improve the opportunity for
1122 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1123 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1124 times the process sleeps and wakes up again. Another useful technique to
1125 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1126 they fire on, say, one-second boundaries only.
1127 .Sp
1128 Example: we only need 0.1s timeout granularity, and we wish not to poll
1129 more often than 100 times per second:
1130 .Sp
1131 .Vb 2
1132 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1133 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1134 .Ve
1135 .IP "ev_invoke_pending (loop)" 4
1136 .IX Item "ev_invoke_pending (loop)"
1137 This call will simply invoke all pending watchers while resetting their
1138 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1139 but when overriding the invoke callback this call comes handy. This
1140 function can be invoked from a watcher \- this can be useful for example
1141 when you want to do some lengthy calculation and want to pass further
1142 event handling to another thread (you still have to make sure only one
1143 thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1144 .IP "int ev_pending_count (loop)" 4
1145 .IX Item "int ev_pending_count (loop)"
1146 Returns the number of pending watchers \- zero indicates that no watchers
1147 are pending.
1148 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1149 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1150 This overrides the invoke pending functionality of the loop: Instead of
1151 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1152 this callback instead. This is useful, for example, when you want to
1153 invoke the actual watchers inside another context (another thread etc.).
1154 .Sp
1155 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1156 callback.
1157 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1158 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1159 Sometimes you want to share the same loop between multiple threads. This
1160 can be done relatively simply by putting mutex_lock/unlock calls around
1161 each call to a libev function.
1162 .Sp
1163 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1164 to wait for it to return. One way around this is to wake up the event
1165 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1166 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1167 .Sp
1168 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1169 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1170 afterwards.
1171 .Sp
1172 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1173 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1174 .Sp
1175 While event loop modifications are allowed between invocations of
1176 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1177 modifications done will affect the event loop, i.e. adding watchers will
1178 have no effect on the set of file descriptors being watched, or the time
1179 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1180 to take note of any changes you made.
1181 .Sp
1182 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1183 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1184 .Sp
1185 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1186 document.
1187 .IP "ev_set_userdata (loop, void *data)" 4
1188 .IX Item "ev_set_userdata (loop, void *data)"
1189 .PD 0
1190 .IP "void *ev_userdata (loop)" 4
1191 .IX Item "void *ev_userdata (loop)"
1192 .PD
1193 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1194 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1195 \&\f(CW0\fR.
1196 .Sp
1197 These two functions can be used to associate arbitrary data with a loop,
1198 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1199 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1200 any other purpose as well.
1201 .IP "ev_verify (loop)" 4
1202 .IX Item "ev_verify (loop)"
1203 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1204 compiled in, which is the default for non-minimal builds. It tries to go
1205 through all internal structures and checks them for validity. If anything
1206 is found to be inconsistent, it will print an error message to standard
1207 error and call \f(CW\*(C`abort ()\*(C'\fR.
1208 .Sp
1209 This can be used to catch bugs inside libev itself: under normal
1210 circumstances, this function will never abort as of course libev keeps its
1211 data structures consistent.
1212 .SH "ANATOMY OF A WATCHER"
1213 .IX Header "ANATOMY OF A WATCHER"
1214 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1215 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1216 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1217 .PP
1218 A watcher is an opaque structure that you allocate and register to record
1219 your interest in some event. To make a concrete example, imagine you want
1220 to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1221 for that:
1222 .PP
1223 .Vb 5
1224 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1225 \& {
1226 \& ev_io_stop (w);
1227 \& ev_break (loop, EVBREAK_ALL);
1228 \& }
1229 \&
1230 \& struct ev_loop *loop = ev_default_loop (0);
1231 \&
1232 \& ev_io stdin_watcher;
1233 \&
1234 \& ev_init (&stdin_watcher, my_cb);
1235 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1236 \& ev_io_start (loop, &stdin_watcher);
1237 \&
1238 \& ev_run (loop, 0);
1239 .Ve
1240 .PP
1241 As you can see, you are responsible for allocating the memory for your
1242 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1243 stack).
1244 .PP
1245 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1246 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1247 .PP
1248 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1249 *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1250 invoked each time the event occurs (or, in the case of I/O watchers, each
1251 time the event loop detects that the file descriptor given is readable
1252 and/or writable).
1253 .PP
1254 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1255 macro to configure it, with arguments specific to the watcher type. There
1256 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1257 .PP
1258 To make the watcher actually watch out for events, you have to start it
1259 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1260 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1261 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1262 .PP
1263 As long as your watcher is active (has been started but not stopped) you
1264 must not touch the values stored in it. Most specifically you must never
1265 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1266 .PP
1267 Each and every callback receives the event loop pointer as first, the
1268 registered watcher structure as second, and a bitset of received events as
1269 third argument.
1270 .PP
1271 The received events usually include a single bit per event type received
1272 (you can receive multiple events at the same time). The possible bit masks
1273 are:
1274 .ie n .IP """EV_READ""" 4
1275 .el .IP "\f(CWEV_READ\fR" 4
1276 .IX Item "EV_READ"
1277 .PD 0
1278 .ie n .IP """EV_WRITE""" 4
1279 .el .IP "\f(CWEV_WRITE\fR" 4
1280 .IX Item "EV_WRITE"
1281 .PD
1282 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1283 writable.
1284 .ie n .IP """EV_TIMER""" 4
1285 .el .IP "\f(CWEV_TIMER\fR" 4
1286 .IX Item "EV_TIMER"
1287 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1288 .ie n .IP """EV_PERIODIC""" 4
1289 .el .IP "\f(CWEV_PERIODIC\fR" 4
1290 .IX Item "EV_PERIODIC"
1291 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1292 .ie n .IP """EV_SIGNAL""" 4
1293 .el .IP "\f(CWEV_SIGNAL\fR" 4
1294 .IX Item "EV_SIGNAL"
1295 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1296 .ie n .IP """EV_CHILD""" 4
1297 .el .IP "\f(CWEV_CHILD\fR" 4
1298 .IX Item "EV_CHILD"
1299 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1300 .ie n .IP """EV_STAT""" 4
1301 .el .IP "\f(CWEV_STAT\fR" 4
1302 .IX Item "EV_STAT"
1303 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1304 .ie n .IP """EV_IDLE""" 4
1305 .el .IP "\f(CWEV_IDLE\fR" 4
1306 .IX Item "EV_IDLE"
1307 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1308 .ie n .IP """EV_PREPARE""" 4
1309 .el .IP "\f(CWEV_PREPARE\fR" 4
1310 .IX Item "EV_PREPARE"
1311 .PD 0
1312 .ie n .IP """EV_CHECK""" 4
1313 .el .IP "\f(CWEV_CHECK\fR" 4
1314 .IX Item "EV_CHECK"
1315 .PD
1316 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
1317 gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
1318 just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1319 for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1320 watchers invoked before the event loop sleeps or polls for new events, and
1321 \&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1322 or lower priority within an event loop iteration.
1323 .Sp
1324 Callbacks of both watcher types can start and stop as many watchers as
1325 they want, and all of them will be taken into account (for example, a
1326 \&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
1327 blocking).
1328 .ie n .IP """EV_EMBED""" 4
1329 .el .IP "\f(CWEV_EMBED\fR" 4
1330 .IX Item "EV_EMBED"
1331 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1332 .ie n .IP """EV_FORK""" 4
1333 .el .IP "\f(CWEV_FORK\fR" 4
1334 .IX Item "EV_FORK"
1335 The event loop has been resumed in the child process after fork (see
1336 \&\f(CW\*(C`ev_fork\*(C'\fR).
1337 .ie n .IP """EV_CLEANUP""" 4
1338 .el .IP "\f(CWEV_CLEANUP\fR" 4
1339 .IX Item "EV_CLEANUP"
1340 The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1341 .ie n .IP """EV_ASYNC""" 4
1342 .el .IP "\f(CWEV_ASYNC\fR" 4
1343 .IX Item "EV_ASYNC"
1344 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1345 .ie n .IP """EV_CUSTOM""" 4
1346 .el .IP "\f(CWEV_CUSTOM\fR" 4
1347 .IX Item "EV_CUSTOM"
1348 Not ever sent (or otherwise used) by libev itself, but can be freely used
1349 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1350 .ie n .IP """EV_ERROR""" 4
1351 .el .IP "\f(CWEV_ERROR\fR" 4
1352 .IX Item "EV_ERROR"
1353 An unspecified error has occurred, the watcher has been stopped. This might
1354 happen because the watcher could not be properly started because libev
1355 ran out of memory, a file descriptor was found to be closed or any other
1356 problem. Libev considers these application bugs.
1357 .Sp
1358 You best act on it by reporting the problem and somehow coping with the
1359 watcher being stopped. Note that well-written programs should not receive
1360 an error ever, so when your watcher receives it, this usually indicates a
1361 bug in your program.
1362 .Sp
1363 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1364 example it might indicate that a fd is readable or writable, and if your
1365 callbacks is well-written it can just attempt the operation and cope with
1366 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1367 programs, though, as the fd could already be closed and reused for another
1368 thing, so beware.
1369 .SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
1370 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1371 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1372 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1373 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1374 This macro initialises the generic portion of a watcher. The contents
1375 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1376 the generic parts of the watcher are initialised, you \fIneed\fR to call
1377 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1378 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1379 which rolls both calls into one.
1380 .Sp
1381 You can reinitialise a watcher at any time as long as it has been stopped
1382 (or never started) and there are no pending events outstanding.
1383 .Sp
1384 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1385 int revents)\*(C'\fR.
1386 .Sp
1387 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1388 .Sp
1389 .Vb 3
1390 \& ev_io w;
1391 \& ev_init (&w, my_cb);
1392 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1393 .Ve
1394 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1395 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1396 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1397 This macro initialises the type-specific parts of a watcher. You need to
1398 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1399 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1400 macro on a watcher that is active (it can be pending, however, which is a
1401 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1402 .Sp
1403 Although some watcher types do not have type-specific arguments
1404 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1405 .Sp
1406 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1407 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1408 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1409 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1410 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1411 calls into a single call. This is the most convenient method to initialise
1412 a watcher. The same limitations apply, of course.
1413 .Sp
1414 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1415 .Sp
1416 .Vb 1
1417 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1418 .Ve
1419 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1420 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1421 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1422 Starts (activates) the given watcher. Only active watchers will receive
1423 events. If the watcher is already active nothing will happen.
1424 .Sp
1425 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1426 whole section.
1427 .Sp
1428 .Vb 1
1429 \& ev_io_start (EV_DEFAULT_UC, &w);
1430 .Ve
1431 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1432 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1433 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1434 Stops the given watcher if active, and clears the pending status (whether
1435 the watcher was active or not).
1436 .Sp
1437 It is possible that stopped watchers are pending \- for example,
1438 non-repeating timers are being stopped when they become pending \- but
1439 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1440 pending. If you want to free or reuse the memory used by the watcher it is
1441 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1442 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1443 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1444 Returns a true value iff the watcher is active (i.e. it has been started
1445 and not yet been stopped). As long as a watcher is active you must not modify
1446 it.
1447 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1448 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1449 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1450 events but its callback has not yet been invoked). As long as a watcher
1451 is pending (but not active) you must not call an init function on it (but
1452 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1453 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1454 it).
1455 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1456 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1457 Returns the callback currently set on the watcher.
1458 .IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1459 .IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1460 Change the callback. You can change the callback at virtually any time
1461 (modulo threads).
1462 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1463 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1464 .PD 0
1465 .IP "int ev_priority (ev_TYPE *watcher)" 4
1466 .IX Item "int ev_priority (ev_TYPE *watcher)"
1467 .PD
1468 Set and query the priority of the watcher. The priority is a small
1469 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1470 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1471 before watchers with lower priority, but priority will not keep watchers
1472 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1473 .Sp
1474 If you need to suppress invocation when higher priority events are pending
1475 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1476 .Sp
1477 You \fImust not\fR change the priority of a watcher as long as it is active or
1478 pending.
1479 .Sp
1480 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1481 fine, as long as you do not mind that the priority value you query might
1482 or might not have been clamped to the valid range.
1483 .Sp
1484 The default priority used by watchers when no priority has been set is
1485 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1486 .Sp
1487 See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1488 priorities.
1489 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1490 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1491 Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1492 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1493 can deal with that fact, as both are simply passed through to the
1494 callback.
1495 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1496 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1497 If the watcher is pending, this function clears its pending status and
1498 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1499 watcher isn't pending it does nothing and returns \f(CW0\fR.
1500 .Sp
1501 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1502 callback to be invoked, which can be accomplished with this function.
1503 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1504 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1505 Feeds the given event set into the event loop, as if the specified event
1506 had happened for the specified watcher (which must be a pointer to an
1507 initialised but not necessarily started event watcher). Obviously you must
1508 not free the watcher as long as it has pending events.
1509 .Sp
1510 Stopping the watcher, letting libev invoke it, or calling
1511 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1512 not started in the first place.
1513 .Sp
1514 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1515 functions that do not need a watcher.
1516 .PP
1517 See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1518 OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1519 .SS "\s-1WATCHER STATES\s0"
1520 .IX Subsection "WATCHER STATES"
1521 There are various watcher states mentioned throughout this manual \-
1522 active, pending and so on. In this section these states and the rules to
1523 transition between them will be described in more detail \- and while these
1524 rules might look complicated, they usually do \*(L"the right thing\*(R".
1525 .IP "initialised" 4
1526 .IX Item "initialised"
1527 Before a watcher can be registered with the event loop it has to be
1528 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1529 \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1530 .Sp
1531 In this state it is simply some block of memory that is suitable for
1532 use in an event loop. It can be moved around, freed, reused etc. at
1533 will \- as long as you either keep the memory contents intact, or call
1534 \&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1535 .IP "started/running/active" 4
1536 .IX Item "started/running/active"
1537 Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1538 property of the event loop, and is actively waiting for events. While in
1539 this state it cannot be accessed (except in a few documented ways), moved,
1540 freed or anything else \- the only legal thing is to keep a pointer to it,
1541 and call libev functions on it that are documented to work on active watchers.
1542 .IP "pending" 4
1543 .IX Item "pending"
1544 If a watcher is active and libev determines that an event it is interested
1545 in has occurred (such as a timer expiring), it will become pending. It will
1546 stay in this pending state until either it is stopped or its callback is
1547 about to be invoked, so it is not normally pending inside the watcher
1548 callback.
1549 .Sp
1550 The watcher might or might not be active while it is pending (for example,
1551 an expired non-repeating timer can be pending but no longer active). If it
1552 is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1553 but it is still property of the event loop at this time, so cannot be
1554 moved, freed or reused. And if it is active the rules described in the
1555 previous item still apply.
1556 .Sp
1557 It is also possible to feed an event on a watcher that is not active (e.g.
1558 via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1559 active.
1560 .IP "stopped" 4
1561 .IX Item "stopped"
1562 A watcher can be stopped implicitly by libev (in which case it might still
1563 be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1564 latter will clear any pending state the watcher might be in, regardless
1565 of whether it was active or not, so stopping a watcher explicitly before
1566 freeing it is often a good idea.
1567 .Sp
1568 While stopped (and not pending) the watcher is essentially in the
1569 initialised state, that is, it can be reused, moved, modified in any way
1570 you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1571 it again).
1572 .SS "\s-1WATCHER PRIORITY MODELS\s0"
1573 .IX Subsection "WATCHER PRIORITY MODELS"
1574 Many event loops support \fIwatcher priorities\fR, which are usually small
1575 integers that influence the ordering of event callback invocation
1576 between watchers in some way, all else being equal.
1577 .PP
1578 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1579 description for the more technical details such as the actual priority
1580 range.
1581 .PP
1582 There are two common ways how these these priorities are being interpreted
1583 by event loops:
1584 .PP
1585 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1586 of lower priority watchers, which means as long as higher priority
1587 watchers receive events, lower priority watchers are not being invoked.
1588 .PP
1589 The less common only-for-ordering model uses priorities solely to order
1590 callback invocation within a single event loop iteration: Higher priority
1591 watchers are invoked before lower priority ones, but they all get invoked
1592 before polling for new events.
1593 .PP
1594 Libev uses the second (only-for-ordering) model for all its watchers
1595 except for idle watchers (which use the lock-out model).
1596 .PP
1597 The rationale behind this is that implementing the lock-out model for
1598 watchers is not well supported by most kernel interfaces, and most event
1599 libraries will just poll for the same events again and again as long as
1600 their callbacks have not been executed, which is very inefficient in the
1601 common case of one high-priority watcher locking out a mass of lower
1602 priority ones.
1603 .PP
1604 Static (ordering) priorities are most useful when you have two or more
1605 watchers handling the same resource: a typical usage example is having an
1606 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1607 timeouts. Under load, data might be received while the program handles
1608 other jobs, but since timers normally get invoked first, the timeout
1609 handler will be executed before checking for data. In that case, giving
1610 the timer a lower priority than the I/O watcher ensures that I/O will be
1611 handled first even under adverse conditions (which is usually, but not
1612 always, what you want).
1613 .PP
1614 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1615 will only be executed when no same or higher priority watchers have
1616 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1617 required.
1618 .PP
1619 For example, to emulate how many other event libraries handle priorities,
1620 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1621 the normal watcher callback, you just start the idle watcher. The real
1622 processing is done in the idle watcher callback. This causes libev to
1623 continuously poll and process kernel event data for the watcher, but when
1624 the lock-out case is known to be rare (which in turn is rare :), this is
1625 workable.
1626 .PP
1627 Usually, however, the lock-out model implemented that way will perform
1628 miserably under the type of load it was designed to handle. In that case,
1629 it might be preferable to stop the real watcher before starting the
1630 idle watcher, so the kernel will not have to process the event in case
1631 the actual processing will be delayed for considerable time.
1632 .PP
1633 Here is an example of an I/O watcher that should run at a strictly lower
1634 priority than the default, and which should only process data when no
1635 other events are pending:
1636 .PP
1637 .Vb 2
1638 \& ev_idle idle; // actual processing watcher
1639 \& ev_io io; // actual event watcher
1640 \&
1641 \& static void
1642 \& io_cb (EV_P_ ev_io *w, int revents)
1643 \& {
1644 \& // stop the I/O watcher, we received the event, but
1645 \& // are not yet ready to handle it.
1646 \& ev_io_stop (EV_A_ w);
1647 \&
1648 \& // start the idle watcher to handle the actual event.
1649 \& // it will not be executed as long as other watchers
1650 \& // with the default priority are receiving events.
1651 \& ev_idle_start (EV_A_ &idle);
1652 \& }
1653 \&
1654 \& static void
1655 \& idle_cb (EV_P_ ev_idle *w, int revents)
1656 \& {
1657 \& // actual processing
1658 \& read (STDIN_FILENO, ...);
1659 \&
1660 \& // have to start the I/O watcher again, as
1661 \& // we have handled the event
1662 \& ev_io_start (EV_P_ &io);
1663 \& }
1664 \&
1665 \& // initialisation
1666 \& ev_idle_init (&idle, idle_cb);
1667 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1668 \& ev_io_start (EV_DEFAULT_ &io);
1669 .Ve
1670 .PP
1671 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1672 low-priority connections can not be locked out forever under load. This
1673 enables your program to keep a lower latency for important connections
1674 during short periods of high load, while not completely locking out less
1675 important ones.
1676 .SH "WATCHER TYPES"
1677 .IX Header "WATCHER TYPES"
1678 This section describes each watcher in detail, but will not repeat
1679 information given in the last section. Any initialisation/set macros,
1680 functions and members specific to the watcher type are explained.
1681 .PP
1682 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1683 while the watcher is active, you can look at the member and expect some
1684 sensible content, but you must not modify it (you can modify it while the
1685 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1686 means you can expect it to have some sensible content while the watcher
1687 is active, but you can also modify it. Modifying it may not do something
1688 sensible or take immediate effect (or do anything at all), but libev will
1689 not crash or malfunction in any way.
1690 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1691 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1692 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1693 I/O watchers check whether a file descriptor is readable or writable
1694 in each iteration of the event loop, or, more precisely, when reading
1695 would not block the process and writing would at least be able to write
1696 some data. This behaviour is called level-triggering because you keep
1697 receiving events as long as the condition persists. Remember you can stop
1698 the watcher if you don't want to act on the event and neither want to
1699 receive future events.
1700 .PP
1701 In general you can register as many read and/or write event watchers per
1702 fd as you want (as long as you don't confuse yourself). Setting all file
1703 descriptors to non-blocking mode is also usually a good idea (but not
1704 required if you know what you are doing).
1705 .PP
1706 Another thing you have to watch out for is that it is quite easy to
1707 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1708 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1709 because there is no data. It is very easy to get into this situation even
1710 with a relatively standard program structure. Thus it is best to always
1711 use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1712 preferable to a program hanging until some data arrives.
1713 .PP
1714 If you cannot run the fd in non-blocking mode (for example you should
1715 not play around with an Xlib connection), then you have to separately
1716 re-test whether a file descriptor is really ready with a known-to-be good
1717 interface such as poll (fortunately in the case of Xlib, it already does
1718 this on its own, so its quite safe to use). Some people additionally
1719 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1720 indefinitely.
1721 .PP
1722 But really, best use non-blocking mode.
1723 .PP
1724 \fIThe special problem of disappearing file descriptors\fR
1725 .IX Subsection "The special problem of disappearing file descriptors"
1726 .PP
1727 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1728 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1729 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1730 descriptor, but when it goes away, the operating system will silently drop
1731 this interest. If another file descriptor with the same number then is
1732 registered with libev, there is no efficient way to see that this is, in
1733 fact, a different file descriptor.
1734 .PP
1735 To avoid having to explicitly tell libev about such cases, libev follows
1736 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1737 will assume that this is potentially a new file descriptor, otherwise
1738 it is assumed that the file descriptor stays the same. That means that
1739 you \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
1740 descriptor even if the file descriptor number itself did not change.
1741 .PP
1742 This is how one would do it normally anyway, the important point is that
1743 the libev application should not optimise around libev but should leave
1744 optimisations to libev.
1745 .PP
1746 \fIThe special problem of dup'ed file descriptors\fR
1747 .IX Subsection "The special problem of dup'ed file descriptors"
1748 .PP
1749 Some backends (e.g. epoll), cannot register events for file descriptors,
1750 but only events for the underlying file descriptions. That means when you
1751 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1752 events for them, only one file descriptor might actually receive events.
1753 .PP
1754 There is no workaround possible except not registering events
1755 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1756 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1757 .PP
1758 \fIThe special problem of files\fR
1759 .IX Subsection "The special problem of files"
1760 .PP
1761 Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1762 representing files, and expect it to become ready when their program
1763 doesn't block on disk accesses (which can take a long time on their own).
1764 .PP
1765 However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1766 notification as soon as the kernel knows whether and how much data is
1767 there, and in the case of open files, that's always the case, so you
1768 always get a readiness notification instantly, and your read (or possibly
1769 write) will still block on the disk I/O.
1770 .PP
1771 Another way to view it is that in the case of sockets, pipes, character
1772 devices and so on, there is another party (the sender) that delivers data
1773 on its own, but in the case of files, there is no such thing: the disk
1774 will not send data on its own, simply because it doesn't know what you
1775 wish to read \- you would first have to request some data.
1776 .PP
1777 Since files are typically not-so-well supported by advanced notification
1778 mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1779 to files, even though you should not use it. The reason for this is
1780 convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1781 usually a tty, often a pipe, but also sometimes files or special devices
1782 (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1783 \&\fI/dev/urandom\fR), and even though the file might better be served with
1784 asynchronous I/O instead of with non-blocking I/O, it is still useful when
1785 it \*(L"just works\*(R" instead of freezing.
1786 .PP
1787 So avoid file descriptors pointing to files when you know it (e.g. use
1788 libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1789 when you rarely read from a file instead of from a socket, and want to
1790 reuse the same code path.
1791 .PP
1792 \fIThe special problem of fork\fR
1793 .IX Subsection "The special problem of fork"
1794 .PP
1795 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1796 useless behaviour. Libev fully supports fork, but needs to be told about
1797 it in the child if you want to continue to use it in the child.
1798 .PP
1799 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1800 ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1801 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1802 .PP
1803 \fIThe special problem of \s-1SIGPIPE\s0\fR
1804 .IX Subsection "The special problem of SIGPIPE"
1805 .PP
1806 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1807 when writing to a pipe whose other end has been closed, your program gets
1808 sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1809 this is sensible behaviour, for daemons, this is usually undesirable.
1810 .PP
1811 So when you encounter spurious, unexplained daemon exits, make sure you
1812 ignore \s-1SIGPIPE \s0(and maybe make sure you log the exit status of your daemon
1813 somewhere, as that would have given you a big clue).
1814 .PP
1815 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1816 .IX Subsection "The special problem of accept()ing when you can't"
1817 .PP
1818 Many implementations of the \s-1POSIX \s0\f(CW\*(C`accept\*(C'\fR function (for example,
1819 found in post\-2004 Linux) have the peculiar behaviour of not removing a
1820 connection from the pending queue in all error cases.
1821 .PP
1822 For example, larger servers often run out of file descriptors (because
1823 of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1824 rejecting the connection, leading to libev signalling readiness on
1825 the next iteration again (the connection still exists after all), and
1826 typically causing the program to loop at 100% \s-1CPU\s0 usage.
1827 .PP
1828 Unfortunately, the set of errors that cause this issue differs between
1829 operating systems, there is usually little the app can do to remedy the
1830 situation, and no known thread-safe method of removing the connection to
1831 cope with overload is known (to me).
1832 .PP
1833 One of the easiest ways to handle this situation is to just ignore it
1834 \&\- when the program encounters an overload, it will just loop until the
1835 situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1836 event-based way to handle this situation, so it's the best one can do.
1837 .PP
1838 A better way to handle the situation is to log any errors other than
1839 \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1840 messages, and continue as usual, which at least gives the user an idea of
1841 what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1842 the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1843 usage.
1844 .PP
1845 If your program is single-threaded, then you could also keep a dummy file
1846 descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1847 when 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,
1848 close that fd, and create a new dummy fd. This will gracefully refuse
1849 clients under typical overload conditions.
1850 .PP
1851 The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1852 is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1853 opportunity for a DoS attack.
1854 .PP
1855 \fIWatcher-Specific Functions\fR
1856 .IX Subsection "Watcher-Specific Functions"
1857 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1858 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1859 .PD 0
1860 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1861 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1862 .PD
1863 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1864 receive 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
1865 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1866 .IP "int fd [read\-only]" 4
1867 .IX Item "int fd [read-only]"
1868 The file descriptor being watched.
1869 .IP "int events [read\-only]" 4
1870 .IX Item "int events [read-only]"
1871 The events being watched.
1872 .PP
1873 \fIExamples\fR
1874 .IX Subsection "Examples"
1875 .PP
1876 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1877 readable, but only once. Since it is likely line-buffered, you could
1878 attempt to read a whole line in the callback.
1879 .PP
1880 .Vb 6
1881 \& static void
1882 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1883 \& {
1884 \& ev_io_stop (loop, w);
1885 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1886 \& }
1887 \&
1888 \& ...
1889 \& struct ev_loop *loop = ev_default_init (0);
1890 \& ev_io stdin_readable;
1891 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1892 \& ev_io_start (loop, &stdin_readable);
1893 \& ev_run (loop, 0);
1894 .Ve
1895 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1896 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1897 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1898 Timer watchers are simple relative timers that generate an event after a
1899 given time, and optionally repeating in regular intervals after that.
1900 .PP
1901 The timers are based on real time, that is, if you register an event that
1902 times out after an hour and you reset your system clock to January last
1903 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1904 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1905 monotonic clock option helps a lot here).
1906 .PP
1907 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1908 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1909 might introduce a small delay, see \*(L"the special problem of being too
1910 early\*(R", below). If multiple timers become ready during the same loop
1911 iteration then the ones with earlier time-out values are invoked before
1912 ones of the same priority with later time-out values (but this is no
1913 longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1914 .PP
1915 \fIBe smart about timeouts\fR
1916 .IX Subsection "Be smart about timeouts"
1917 .PP
1918 Many real-world problems involve some kind of timeout, usually for error
1919 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1920 you want to raise some error after a while.
1921 .PP
1922 What follows are some ways to handle this problem, from obvious and
1923 inefficient to smart and efficient.
1924 .PP
1925 In the following, a 60 second activity timeout is assumed \- a timeout that
1926 gets reset to 60 seconds each time there is activity (e.g. each time some
1927 data or other life sign was received).
1928 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1929 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1930 This is the most obvious, but not the most simple way: In the beginning,
1931 start the watcher:
1932 .Sp
1933 .Vb 2
1934 \& ev_timer_init (timer, callback, 60., 0.);
1935 \& ev_timer_start (loop, timer);
1936 .Ve
1937 .Sp
1938 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1939 and start it again:
1940 .Sp
1941 .Vb 3
1942 \& ev_timer_stop (loop, timer);
1943 \& ev_timer_set (timer, 60., 0.);
1944 \& ev_timer_start (loop, timer);
1945 .Ve
1946 .Sp
1947 This is relatively simple to implement, but means that each time there is
1948 some activity, libev will first have to remove the timer from its internal
1949 data structure and then add it again. Libev tries to be fast, but it's
1950 still not a constant-time operation.
1951 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1952 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1953 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1954 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1955 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1956 .Sp
1957 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1958 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1959 successfully read or write some data. If you go into an idle state where
1960 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1961 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1962 .Sp
1963 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1964 \&\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
1965 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1966 .Sp
1967 At start:
1968 .Sp
1969 .Vb 3
1970 \& ev_init (timer, callback);
1971 \& timer\->repeat = 60.;
1972 \& ev_timer_again (loop, timer);
1973 .Ve
1974 .Sp
1975 Each time there is some activity:
1976 .Sp
1977 .Vb 1
1978 \& ev_timer_again (loop, timer);
1979 .Ve
1980 .Sp
1981 It is even possible to change the time-out on the fly, regardless of
1982 whether the watcher is active or not:
1983 .Sp
1984 .Vb 2
1985 \& timer\->repeat = 30.;
1986 \& ev_timer_again (loop, timer);
1987 .Ve
1988 .Sp
1989 This is slightly more efficient then stopping/starting the timer each time
1990 you want to modify its timeout value, as libev does not have to completely
1991 remove and re-insert the timer from/into its internal data structure.
1992 .Sp
1993 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1994 .IP "3. Let the timer time out, but then re-arm it as required." 4
1995 .IX Item "3. Let the timer time out, but then re-arm it as required."
1996 This method is more tricky, but usually most efficient: Most timeouts are
1997 relatively long compared to the intervals between other activity \- in
1998 our example, within 60 seconds, there are usually many I/O events with
1999 associated activity resets.
2000 .Sp
2001 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2002 but remember the time of last activity, and check for a real timeout only
2003 within the callback:
2004 .Sp
2005 .Vb 3
2006 \& ev_tstamp timeout = 60.;
2007 \& ev_tstamp last_activity; // time of last activity
2008 \& ev_timer timer;
2009 \&
2010 \& static void
2011 \& callback (EV_P_ ev_timer *w, int revents)
2012 \& {
2013 \& // calculate when the timeout would happen
2014 \& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2015 \&
2016 \& // if negative, it means we the timeout already occurred
2017 \& if (after < 0.)
2018 \& {
2019 \& // timeout occurred, take action
2020 \& }
2021 \& else
2022 \& {
2023 \& // callback was invoked, but there was some recent
2024 \& // activity. simply restart the timer to time out
2025 \& // after "after" seconds, which is the earliest time
2026 \& // the timeout can occur.
2027 \& ev_timer_set (w, after, 0.);
2028 \& ev_timer_start (EV_A_ w);
2029 \& }
2030 \& }
2031 .Ve
2032 .Sp
2033 To summarise the callback: first calculate in how many seconds the
2034 timeout will occur (by calculating the absolute time when it would occur,
2035 \&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2036 (EV_A)\*(C'\fR from that).
2037 .Sp
2038 If this value is negative, then we are already past the timeout, i.e. we
2039 timed out, and need to do whatever is needed in this case.
2040 .Sp
2041 Otherwise, we now the earliest time at which the timeout would trigger,
2042 and simply start the timer with this timeout value.
2043 .Sp
2044 In other words, each time the callback is invoked it will check whether
2045 the timeout occurred. If not, it will simply reschedule itself to check
2046 again at the earliest time it could time out. Rinse. Repeat.
2047 .Sp
2048 This scheme causes more callback invocations (about one every 60 seconds
2049 minus half the average time between activity), but virtually no calls to
2050 libev to change the timeout.
2051 .Sp
2052 To start the machinery, simply initialise the watcher and set
2053 \&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2054 now), then call the callback, which will \*(L"do the right thing\*(R" and start
2055 the timer:
2056 .Sp
2057 .Vb 3
2058 \& last_activity = ev_now (EV_A);
2059 \& ev_init (&timer, callback);
2060 \& callback (EV_A_ &timer, 0);
2061 .Ve
2062 .Sp
2063 When there is some activity, simply store the current time in
2064 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2065 .Sp
2066 .Vb 2
2067 \& if (activity detected)
2068 \& last_activity = ev_now (EV_A);
2069 .Ve
2070 .Sp
2071 When your timeout value changes, then the timeout can be changed by simply
2072 providing a new value, stopping the timer and calling the callback, which
2073 will again do the right thing (for example, time out immediately :).
2074 .Sp
2075 .Vb 3
2076 \& timeout = new_value;
2077 \& ev_timer_stop (EV_A_ &timer);
2078 \& callback (EV_A_ &timer, 0);
2079 .Ve
2080 .Sp
2081 This technique is slightly more complex, but in most cases where the
2082 time-out is unlikely to be triggered, much more efficient.
2083 .IP "4. Wee, just use a double-linked list for your timeouts." 4
2084 .IX Item "4. Wee, just use a double-linked list for your timeouts."
2085 If there is not one request, but many thousands (millions...), all
2086 employing some kind of timeout with the same timeout value, then one can
2087 do even better:
2088 .Sp
2089 When starting the timeout, calculate the timeout value and put the timeout
2090 at the \fIend\fR of the list.
2091 .Sp
2092 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2093 the list is expected to fire (for example, using the technique #3).
2094 .Sp
2095 When there is some activity, remove the timer from the list, recalculate
2096 the timeout, append it to the end of the list again, and make sure to
2097 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2098 .Sp
2099 This way, one can manage an unlimited number of timeouts in O(1) time for
2100 starting, stopping and updating the timers, at the expense of a major
2101 complication, and having to use a constant timeout. The constant timeout
2102 ensures that the list stays sorted.
2103 .PP
2104 So which method the best?
2105 .PP
2106 Method #2 is a simple no-brain-required solution that is adequate in most
2107 situations. Method #3 requires a bit more thinking, but handles many cases
2108 better, and isn't very complicated either. In most case, choosing either
2109 one is fine, with #3 being better in typical situations.
2110 .PP
2111 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2112 rather complicated, but extremely efficient, something that really pays
2113 off after the first million or so of active timers, i.e. it's usually
2114 overkill :)
2115 .PP
2116 \fIThe special problem of being too early\fR
2117 .IX Subsection "The special problem of being too early"
2118 .PP
2119 If you ask a timer to call your callback after three seconds, then
2120 you expect it to be invoked after three seconds \- but of course, this
2121 cannot be guaranteed to infinite precision. Less obviously, it cannot be
2122 guaranteed to any precision by libev \- imagine somebody suspending the
2123 process with a \s-1STOP\s0 signal for a few hours for example.
2124 .PP
2125 So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2126 delay has occurred, but cannot guarantee this.
2127 .PP
2128 A less obvious failure mode is calling your callback too early: many event
2129 loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2130 this can cause your callback to be invoked much earlier than you would
2131 expect.
2132 .PP
2133 To see why, imagine a system with a clock that only offers full second
2134 resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2135 yourself). If you schedule a one-second timer at the time 500.9, then the
2136 event loop will schedule your timeout to elapse at a system time of 500
2137 (500.9 truncated to the resolution) + 1, or 501.
2138 .PP
2139 If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2140 501\*(R" and invoke the callback 0.1s after it was started, even though a
2141 one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2142 intentions.
2143 .PP
2144 This is the reason why libev will never invoke the callback if the elapsed
2145 delay equals the requested delay, but only when the elapsed delay is
2146 larger than the requested delay. In the example above, libev would only invoke
2147 the callback at system time 502, or 1.1s after the timer was started.
2148 .PP
2149 So, while libev cannot guarantee that your callback will be invoked
2150 exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2151 delay has actually elapsed, or in other words, it always errs on the \*(L"too
2152 late\*(R" side of things.
2153 .PP
2154 \fIThe special problem of time updates\fR
2155 .IX Subsection "The special problem of time updates"
2156 .PP
2157 Establishing the current time is a costly operation (it usually takes
2158 at least one system call): \s-1EV\s0 therefore updates its idea of the current
2159 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2160 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2161 lots of events in one iteration.
2162 .PP
2163 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2164 time. This is usually the right thing as this timestamp refers to the time
2165 of the event triggering whatever timeout you are modifying/starting. If
2166 you suspect event processing to be delayed and you \fIneed\fR to base the
2167 timeout on the current time, use something like the following to adjust
2168 for it:
2169 .PP
2170 .Vb 1
2171 \& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
2172 .Ve
2173 .PP
2174 If the event loop is suspended for a long time, you can also force an
2175 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2176 ()\*(C'\fR, although that will push the event time of all outstanding events
2177 further into the future.
2178 .PP
2179 \fIThe special problem of unsynchronised clocks\fR
2180 .IX Subsection "The special problem of unsynchronised clocks"
2181 .PP
2182 Modern systems have a variety of clocks \- libev itself uses the normal
2183 \&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2184 jumps).
2185 .PP
2186 Neither of these clocks is synchronised with each other or any other clock
2187 on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2188 than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2189 a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2190 than a directly following call to \f(CW\*(C`time\*(C'\fR.
2191 .PP
2192 The moral of this is to only compare libev-related timestamps with
2193 \&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2194 a second or so.
2195 .PP
2196 One more problem arises due to this lack of synchronisation: if libev uses
2197 the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2198 or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2199 invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2200 .PP
2201 This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2202 libev makes sure your callback is not invoked before the delay happened,
2203 \&\fImeasured according to the real time\fR, not the system clock.
2204 .PP
2205 If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2206 connection after 100 seconds\*(R") then this shouldn't bother you as it is
2207 exactly the right behaviour.
2208 .PP
2209 If you want to compare wall clock/system timestamps to your timers, then
2210 you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2211 time, where your comparisons will always generate correct results.
2212 .PP
2213 \fIThe special problems of suspended animation\fR
2214 .IX Subsection "The special problems of suspended animation"
2215 .PP
2216 When you leave the server world it is quite customary to hit machines that
2217 can suspend/hibernate \- what happens to the clocks during such a suspend?
2218 .PP
2219 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2220 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2221 to run until the system is suspended, but they will not advance while the
2222 system is suspended. That means, on resume, it will be as if the program
2223 was frozen for a few seconds, but the suspend time will not be counted
2224 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2225 clock advanced as expected, but if it is used as sole clocksource, then a
2226 long suspend would be detected as a time jump by libev, and timers would
2227 be adjusted accordingly.
2228 .PP
2229 I would not be surprised to see different behaviour in different between
2230 operating systems, \s-1OS\s0 versions or even different hardware.
2231 .PP
2232 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2233 time jump in the monotonic clocks and the realtime clock. If the program
2234 is suspended for a very long time, and monotonic clock sources are in use,
2235 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2236 will be counted towards the timers. When no monotonic clock source is in
2237 use, then libev will again assume a timejump and adjust accordingly.
2238 .PP
2239 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2240 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2241 deterministic behaviour in this case (you can do nothing against
2242 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2243 .PP
2244 \fIWatcher-Specific Functions and Data Members\fR
2245 .IX Subsection "Watcher-Specific Functions and Data Members"
2246 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2247 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2248 .PD 0
2249 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2250 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2251 .PD
2252 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2253 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2254 reached. If it is positive, then the timer will automatically be
2255 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2256 until stopped manually.
2257 .Sp
2258 The timer itself will do a best-effort at avoiding drift, that is, if
2259 you configure a timer to trigger every 10 seconds, then it will normally
2260 trigger at exactly 10 second intervals. If, however, your program cannot
2261 keep up with the timer (because it takes longer than those 10 seconds to
2262 do stuff) the timer will not fire more than once per event loop iteration.
2263 .IP "ev_timer_again (loop, ev_timer *)" 4
2264 .IX Item "ev_timer_again (loop, ev_timer *)"
2265 This will act as if the timer timed out, and restarts it again if it is
2266 repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2267 timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
2268 .Sp
2269 The exact semantics are as in the following rules, all of which will be
2270 applied to the watcher:
2271 .RS 4
2272 .IP "If the timer is pending, the pending status is always cleared." 4
2273 .IX Item "If the timer is pending, the pending status is always cleared."
2274 .PD 0
2275 .IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2276 .IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2277 .ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2278 .el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2279 .IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2280 .RE
2281 .RS 4
2282 .PD
2283 .Sp
2284 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2285 usage example.
2286 .RE
2287 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2288 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2289 Returns the remaining time until a timer fires. If the timer is active,
2290 then this time is relative to the current event loop time, otherwise it's
2291 the timeout value currently configured.
2292 .Sp
2293 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2294 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2295 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2296 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2297 too), and so on.
2298 .IP "ev_tstamp repeat [read\-write]" 4
2299 .IX Item "ev_tstamp repeat [read-write]"
2300 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2301 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2302 which is also when any modifications are taken into account.
2303 .PP
2304 \fIExamples\fR
2305 .IX Subsection "Examples"
2306 .PP
2307 Example: Create a timer that fires after 60 seconds.
2308 .PP
2309 .Vb 5
2310 \& static void
2311 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2312 \& {
2313 \& .. one minute over, w is actually stopped right here
2314 \& }
2315 \&
2316 \& ev_timer mytimer;
2317 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2318 \& ev_timer_start (loop, &mytimer);
2319 .Ve
2320 .PP
2321 Example: Create a timeout timer that times out after 10 seconds of
2322 inactivity.
2323 .PP
2324 .Vb 5
2325 \& static void
2326 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2327 \& {
2328 \& .. ten seconds without any activity
2329 \& }
2330 \&
2331 \& ev_timer mytimer;
2332 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2333 \& ev_timer_again (&mytimer); /* start timer */
2334 \& ev_run (loop, 0);
2335 \&
2336 \& // and in some piece of code that gets executed on any "activity":
2337 \& // reset the timeout to start ticking again at 10 seconds
2338 \& ev_timer_again (&mytimer);
2339 .Ve
2340 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2341 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2342 .IX Subsection "ev_periodic - to cron or not to cron?"
2343 Periodic watchers are also timers of a kind, but they are very versatile
2344 (and unfortunately a bit complex).
2345 .PP
2346 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2347 relative time, the physical time that passes) but on wall clock time
2348 (absolute time, the thing you can read on your calender or clock). The
2349 difference is that wall clock time can run faster or slower than real
2350 time, and time jumps are not uncommon (e.g. when you adjust your
2351 wrist-watch).
2352 .PP
2353 You can tell a periodic watcher to trigger after some specific point
2354 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2355 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2356 not a delay) and then reset your system clock to January of the previous
2357 year, then it will take a year or more to trigger the event (unlike an
2358 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2359 it, as it uses a relative timeout).
2360 .PP
2361 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2362 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2363 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2364 those cannot react to time jumps.
2365 .PP
2366 As with timers, the callback is guaranteed to be invoked only when the
2367 point in time where it is supposed to trigger has passed. If multiple
2368 timers become ready during the same loop iteration then the ones with
2369 earlier time-out values are invoked before ones with later time-out values
2370 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2371 .PP
2372 \fIWatcher-Specific Functions and Data Members\fR
2373 .IX Subsection "Watcher-Specific Functions and Data Members"
2374 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2375 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2376 .PD 0
2377 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2378 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2379 .PD
2380 Lots of arguments, let's sort it out... There are basically three modes of
2381 operation, and we will explain them from simplest to most complex:
2382 .RS 4
2383 .IP "\(bu" 4
2384 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2385 .Sp
2386 In this configuration the watcher triggers an event after the wall clock
2387 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2388 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2389 will be stopped and invoked when the system clock reaches or surpasses
2390 this point in time.
2391 .IP "\(bu" 4
2392 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2393 .Sp
2394 In this mode the watcher will always be scheduled to time out at the next
2395 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2396 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2397 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2398 .Sp
2399 This can be used to create timers that do not drift with respect to the
2400 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2401 hour, on the hour (with respect to \s-1UTC\s0):
2402 .Sp
2403 .Vb 1
2404 \& ev_periodic_set (&periodic, 0., 3600., 0);
2405 .Ve
2406 .Sp
2407 This doesn't mean there will always be 3600 seconds in between triggers,
2408 but only that the callback will be called when the system time shows a
2409 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2410 by 3600.
2411 .Sp
2412 Another way to think about it (for the mathematically inclined) is that
2413 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2414 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2415 .Sp
2416 The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2417 interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2418 microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2419 at most a similar magnitude as the current time (say, within a factor of
2420 ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2421 \&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2422 .Sp
2423 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2424 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2425 will of course deteriorate. Libev itself tries to be exact to be about one
2426 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2427 .IP "\(bu" 4
2428 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2429 .Sp
2430 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2431 ignored. Instead, each time the periodic watcher gets scheduled, the
2432 reschedule callback will be called with the watcher as first, and the
2433 current time as second argument.
2434 .Sp
2435 \&\s-1NOTE: \s0\fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
2436 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2437 allowed by documentation here\fR.
2438 .Sp
2439 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2440 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2441 only event loop modification you are allowed to do).
2442 .Sp
2443 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2444 *w, ev_tstamp now)\*(C'\fR, e.g.:
2445 .Sp
2446 .Vb 5
2447 \& static ev_tstamp
2448 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2449 \& {
2450 \& return now + 60.;
2451 \& }
2452 .Ve
2453 .Sp
2454 It must return the next time to trigger, based on the passed time value
2455 (that is, the lowest time value larger than to the second argument). It
2456 will usually be called just before the callback will be triggered, but
2457 might be called at other times, too.
2458 .Sp
2459 \&\s-1NOTE: \s0\fIThis callback must always return a time that is higher than or
2460 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2461 .Sp
2462 This can be used to create very complex timers, such as a timer that
2463 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2464 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2465 you do this is, again, up to you (but it is not trivial, which is the main
2466 reason I omitted it as an example).
2467 .RE
2468 .RS 4
2469 .RE
2470 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2471 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2472 Simply stops and restarts the periodic watcher again. This is only useful
2473 when you changed some parameters or the reschedule callback would return
2474 a different time than the last time it was called (e.g. in a crond like
2475 program when the crontabs have changed).
2476 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2477 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2478 When active, returns the absolute time that the watcher is supposed
2479 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2480 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2481 rescheduling modes.
2482 .IP "ev_tstamp offset [read\-write]" 4
2483 .IX Item "ev_tstamp offset [read-write]"
2484 When repeating, this contains the offset value, otherwise this is the
2485 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2486 although libev might modify this value for better numerical stability).
2487 .Sp
2488 Can be modified any time, but changes only take effect when the periodic
2489 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2490 .IP "ev_tstamp interval [read\-write]" 4
2491 .IX Item "ev_tstamp interval [read-write]"
2492 The current interval value. Can be modified any time, but changes only
2493 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2494 called.
2495 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2496 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2497 The current reschedule callback, or \f(CW0\fR, if this functionality is
2498 switched off. Can be changed any time, but changes only take effect when
2499 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2500 .PP
2501 \fIExamples\fR
2502 .IX Subsection "Examples"
2503 .PP
2504 Example: Call a callback every hour, or, more precisely, whenever the
2505 system time is divisible by 3600. The callback invocation times have
2506 potentially a lot of jitter, but good long-term stability.
2507 .PP
2508 .Vb 5
2509 \& static void
2510 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2511 \& {
2512 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2513 \& }
2514 \&
2515 \& ev_periodic hourly_tick;
2516 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2517 \& ev_periodic_start (loop, &hourly_tick);
2518 .Ve
2519 .PP
2520 Example: The same as above, but use a reschedule callback to do it:
2521 .PP
2522 .Vb 1
2523 \& #include <math.h>
2524 \&
2525 \& static ev_tstamp
2526 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2527 \& {
2528 \& return now + (3600. \- fmod (now, 3600.));
2529 \& }
2530 \&
2531 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2532 .Ve
2533 .PP
2534 Example: Call a callback every hour, starting now:
2535 .PP
2536 .Vb 4
2537 \& ev_periodic hourly_tick;
2538 \& ev_periodic_init (&hourly_tick, clock_cb,
2539 \& fmod (ev_now (loop), 3600.), 3600., 0);
2540 \& ev_periodic_start (loop, &hourly_tick);
2541 .Ve
2542 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2543 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2544 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2545 Signal watchers will trigger an event when the process receives a specific
2546 signal one or more times. Even though signals are very asynchronous, libev
2547 will try its best to deliver signals synchronously, i.e. as part of the
2548 normal event processing, like any other event.
2549 .PP
2550 If you want signals to be delivered truly asynchronously, just use
2551 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2552 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2553 synchronously wake up an event loop.
2554 .PP
2555 You can configure as many watchers as you like for the same signal, but
2556 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2557 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2558 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2559 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2560 .PP
2561 Only after the first watcher for a signal is started will libev actually
2562 register something with the kernel. It thus coexists with your own signal
2563 handlers as long as you don't register any with libev for the same signal.
2564 .PP
2565 If possible and supported, libev will install its handlers with
2566 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2567 not be unduly interrupted. If you have a problem with system calls getting
2568 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2569 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2570 .PP
2571 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2572 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2573 .PP
2574 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2575 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2576 stopping it again), that is, libev might or might not block the signal,
2577 and might or might not set or restore the installed signal handler (but
2578 see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2579 .PP
2580 While this does not matter for the signal disposition (libev never
2581 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2582 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2583 certain signals to be blocked.
2584 .PP
2585 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2586 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2587 choice usually).
2588 .PP
2589 The simplest way to ensure that the signal mask is reset in the child is
2590 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2591 catch fork calls done by libraries (such as the libc) as well.
2592 .PP
2593 In current versions of libev, the signal will not be blocked indefinitely
2594 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API \s0(\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2595 the window of opportunity for problems, it will not go away, as libev
2596 \&\fIhas\fR to modify the signal mask, at least temporarily.
2597 .PP
2598 So I can't stress this enough: \fIIf you do not reset your signal mask when
2599 you expect it to be empty, you have a race condition in your code\fR. This
2600 is not a libev-specific thing, this is true for most event libraries.
2601 .PP
2602 \fIThe special problem of threads signal handling\fR
2603 .IX Subsection "The special problem of threads signal handling"
2604 .PP
2605 \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2606 a lot of functionality (sigfd, sigwait etc.) only really works if all
2607 threads in a process block signals, which is hard to achieve.
2608 .PP
2609 When you want to use sigwait (or mix libev signal handling with your own
2610 for the same signals), you can tackle this problem by globally blocking
2611 all signals before creating any threads (or creating them with a fully set
2612 sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2613 loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2614 these signals. You can pass on any signals that libev might be interested
2615 in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2616 .PP
2617 \fIWatcher-Specific Functions and Data Members\fR
2618 .IX Subsection "Watcher-Specific Functions and Data Members"
2619 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2620 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2621 .PD 0
2622 .IP "ev_signal_set (ev_signal *, int signum)" 4
2623 .IX Item "ev_signal_set (ev_signal *, int signum)"
2624 .PD
2625 Configures the watcher to trigger on the given signal number (usually one
2626 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2627 .IP "int signum [read\-only]" 4
2628 .IX Item "int signum [read-only]"
2629 The signal the watcher watches out for.
2630 .PP
2631 \fIExamples\fR
2632 .IX Subsection "Examples"
2633 .PP
2634 Example: Try to exit cleanly on \s-1SIGINT.\s0
2635 .PP
2636 .Vb 5
2637 \& static void
2638 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2639 \& {
2640 \& ev_break (loop, EVBREAK_ALL);
2641 \& }
2642 \&
2643 \& ev_signal signal_watcher;
2644 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2645 \& ev_signal_start (loop, &signal_watcher);
2646 .Ve
2647 .ie n .SS """ev_child"" \- watch out for process status changes"
2648 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2649 .IX Subsection "ev_child - watch out for process status changes"
2650 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2651 some child status changes (most typically when a child of yours dies or
2652 exits). It is permissible to install a child watcher \fIafter\fR the child
2653 has been forked (which implies it might have already exited), as long
2654 as the event loop isn't entered (or is continued from a watcher), i.e.,
2655 forking and then immediately registering a watcher for the child is fine,
2656 but forking and registering a watcher a few event loop iterations later or
2657 in the next callback invocation is not.
2658 .PP
2659 Only the default event loop is capable of handling signals, and therefore
2660 you can only register child watchers in the default event loop.
2661 .PP
2662 Due to some design glitches inside libev, child watchers will always be
2663 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2664 libev)
2665 .PP
2666 \fIProcess Interaction\fR
2667 .IX Subsection "Process Interaction"
2668 .PP
2669 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2670 initialised. This is necessary to guarantee proper behaviour even if the
2671 first child watcher is started after the child exits. The occurrence
2672 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2673 synchronously as part of the event loop processing. Libev always reaps all
2674 children, even ones not watched.
2675 .PP
2676 \fIOverriding the Built-In Processing\fR
2677 .IX Subsection "Overriding the Built-In Processing"
2678 .PP
2679 Libev offers no special support for overriding the built-in child
2680 processing, but if your application collides with libev's default child
2681 handler, you can override it easily by installing your own handler for
2682 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2683 default loop never gets destroyed. You are encouraged, however, to use an
2684 event-based approach to child reaping and thus use libev's support for
2685 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2686 .PP
2687 \fIStopping the Child Watcher\fR
2688 .IX Subsection "Stopping the Child Watcher"
2689 .PP
2690 Currently, the child watcher never gets stopped, even when the
2691 child terminates, so normally one needs to stop the watcher in the
2692 callback. Future versions of libev might stop the watcher automatically
2693 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2694 problem).
2695 .PP
2696 \fIWatcher-Specific Functions and Data Members\fR
2697 .IX Subsection "Watcher-Specific Functions and Data Members"
2698 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2699 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2700 .PD 0
2701 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2702 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2703 .PD
2704 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2705 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2706 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2707 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2708 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2709 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2710 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2711 activate the watcher when the process is stopped or continued).
2712 .IP "int pid [read\-only]" 4
2713 .IX Item "int pid [read-only]"
2714 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2715 .IP "int rpid [read\-write]" 4
2716 .IX Item "int rpid [read-write]"
2717 The process id that detected a status change.
2718 .IP "int rstatus [read\-write]" 4
2719 .IX Item "int rstatus [read-write]"
2720 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2721 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2722 .PP
2723 \fIExamples\fR
2724 .IX Subsection "Examples"
2725 .PP
2726 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2727 its completion.
2728 .PP
2729 .Vb 1
2730 \& ev_child cw;
2731 \&
2732 \& static void
2733 \& child_cb (EV_P_ ev_child *w, int revents)
2734 \& {
2735 \& ev_child_stop (EV_A_ w);
2736 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2737 \& }
2738 \&
2739 \& pid_t pid = fork ();
2740 \&
2741 \& if (pid < 0)
2742 \& // error
2743 \& else if (pid == 0)
2744 \& {
2745 \& // the forked child executes here
2746 \& exit (1);
2747 \& }
2748 \& else
2749 \& {
2750 \& ev_child_init (&cw, child_cb, pid, 0);
2751 \& ev_child_start (EV_DEFAULT_ &cw);
2752 \& }
2753 .Ve
2754 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2755 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2756 .IX Subsection "ev_stat - did the file attributes just change?"
2757 This watches a file system path for attribute changes. That is, it calls
2758 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2759 and sees if it changed compared to the last time, invoking the callback
2760 if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2761 happen after the watcher has been started will be reported.
2762 .PP
2763 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2764 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2765 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2766 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2767 least one) and all the other fields of the stat buffer having unspecified
2768 contents.
2769 .PP
2770 The path \fImust not\fR end in a slash or contain special components such as
2771 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2772 your working directory changes, then the behaviour is undefined.
2773 .PP
2774 Since there is no portable change notification interface available, the
2775 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2776 to see if it changed somehow. You can specify a recommended polling
2777 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2778 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2779 (which you can expect to be around five seconds, although this might
2780 change dynamically). Libev will also impose a minimum interval which is
2781 currently around \f(CW0.1\fR, but that's usually overkill.
2782 .PP
2783 This watcher type is not meant for massive numbers of stat watchers,
2784 as even with OS-supported change notifications, this can be
2785 resource-intensive.
2786 .PP
2787 At the time of this writing, the only OS-specific interface implemented
2788 is the Linux inotify interface (implementing kqueue support is left as an
2789 exercise for the reader. Note, however, that the author sees no way of
2790 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2791 .PP
2792 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2793 .IX Subsection "ABI Issues (Largefile Support)"
2794 .PP
2795 Libev by default (unless the user overrides this) uses the default
2796 compilation environment, which means that on systems with large file
2797 support disabled by default, you get the 32 bit version of the stat
2798 structure. When using the library from programs that change the \s-1ABI\s0 to
2799 use 64 bit file offsets the programs will fail. In that case you have to
2800 compile libev with the same flags to get binary compatibility. This is
2801 obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2802 most noticeably displayed with ev_stat and large file support.
2803 .PP
2804 The solution for this is to lobby your distribution maker to make large
2805 file interfaces available by default (as e.g. FreeBSD does) and not
2806 optional. Libev cannot simply switch on large file support because it has
2807 to exchange stat structures with application programs compiled using the
2808 default compilation environment.
2809 .PP
2810 \fIInotify and Kqueue\fR
2811 .IX Subsection "Inotify and Kqueue"
2812 .PP
2813 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2814 runtime, it will be used to speed up change detection where possible. The
2815 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2816 watcher is being started.
2817 .PP
2818 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2819 except that changes might be detected earlier, and in some cases, to avoid
2820 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2821 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2822 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2823 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2824 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2825 xfs are fully working) libev usually gets away without polling.
2826 .PP
2827 There is no support for kqueue, as apparently it cannot be used to
2828 implement this functionality, due to the requirement of having a file
2829 descriptor open on the object at all times, and detecting renames, unlinks
2830 etc. is difficult.
2831 .PP
2832 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2833 .IX Subsection "stat () is a synchronous operation"
2834 .PP
2835 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2836 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2837 ()\*(C'\fR, which is a synchronous operation.
2838 .PP
2839 For local paths, this usually doesn't matter: unless the system is very
2840 busy or the intervals between stat's are large, a stat call will be fast,
2841 as the path data is usually in memory already (except when starting the
2842 watcher).
2843 .PP
2844 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2845 time due to network issues, and even under good conditions, a stat call
2846 often takes multiple milliseconds.
2847 .PP
2848 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2849 paths, although this is fully supported by libev.
2850 .PP
2851 \fIThe special problem of stat time resolution\fR
2852 .IX Subsection "The special problem of stat time resolution"
2853 .PP
2854 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2855 and even on systems where the resolution is higher, most file systems
2856 still only support whole seconds.
2857 .PP
2858 That means that, if the time is the only thing that changes, you can
2859 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2860 calls your callback, which does something. When there is another update
2861 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2862 stat data does change in other ways (e.g. file size).
2863 .PP
2864 The solution to this is to delay acting on a change for slightly more
2865 than a second (or till slightly after the next full second boundary), using
2866 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2867 ev_timer_again (loop, w)\*(C'\fR).
2868 .PP
2869 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2870 of some operating systems (where the second counter of the current time
2871 might be be delayed. One such system is the Linux kernel, where a call to
2872 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2873 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2874 update file times then there will be a small window where the kernel uses
2875 the previous second to update file times but libev might already execute
2876 the timer callback).
2877 .PP
2878 \fIWatcher-Specific Functions and Data Members\fR
2879 .IX Subsection "Watcher-Specific Functions and Data Members"
2880 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2881 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2882 .PD 0
2883 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2884 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2885 .PD
2886 Configures the watcher to wait for status changes of the given
2887 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2888 be detected and should normally be specified as \f(CW0\fR to let libev choose
2889 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2890 path for as long as the watcher is active.
2891 .Sp
2892 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2893 relative to the attributes at the time the watcher was started (or the
2894 last change was detected).
2895 .IP "ev_stat_stat (loop, ev_stat *)" 4
2896 .IX Item "ev_stat_stat (loop, ev_stat *)"
2897 Updates the stat buffer immediately with new values. If you change the
2898 watched path in your callback, you could call this function to avoid
2899 detecting this change (while introducing a race condition if you are not
2900 the only one changing the path). Can also be useful simply to find out the
2901 new values.
2902 .IP "ev_statdata attr [read\-only]" 4
2903 .IX Item "ev_statdata attr [read-only]"
2904 The most-recently detected attributes of the file. Although the type is
2905 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2906 suitable for your system, but you can only rely on the POSIX-standardised
2907 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2908 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2909 .IP "ev_statdata prev [read\-only]" 4
2910 .IX Item "ev_statdata prev [read-only]"
2911 The previous attributes of the file. The callback gets invoked whenever
2912 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2913 differ: \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,
2914 \&\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.
2915 .IP "ev_tstamp interval [read\-only]" 4
2916 .IX Item "ev_tstamp interval [read-only]"
2917 The specified interval.
2918 .IP "const char *path [read\-only]" 4
2919 .IX Item "const char *path [read-only]"
2920 The file system path that is being watched.
2921 .PP
2922 \fIExamples\fR
2923 .IX Subsection "Examples"
2924 .PP
2925 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2926 .PP
2927 .Vb 10
2928 \& static void
2929 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2930 \& {
2931 \& /* /etc/passwd changed in some way */
2932 \& if (w\->attr.st_nlink)
2933 \& {
2934 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2935 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2936 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2937 \& }
2938 \& else
2939 \& /* you shalt not abuse printf for puts */
2940 \& puts ("wow, /etc/passwd is not there, expect problems. "
2941 \& "if this is windows, they already arrived\en");
2942 \& }
2943 \&
2944 \& ...
2945 \& ev_stat passwd;
2946 \&
2947 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2948 \& ev_stat_start (loop, &passwd);
2949 .Ve
2950 .PP
2951 Example: Like above, but additionally use a one-second delay so we do not
2952 miss updates (however, frequent updates will delay processing, too, so
2953 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2954 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2955 .PP
2956 .Vb 2
2957 \& static ev_stat passwd;
2958 \& static ev_timer timer;
2959 \&
2960 \& static void
2961 \& timer_cb (EV_P_ ev_timer *w, int revents)
2962 \& {
2963 \& ev_timer_stop (EV_A_ w);
2964 \&
2965 \& /* now it\*(Aqs one second after the most recent passwd change */
2966 \& }
2967 \&
2968 \& static void
2969 \& stat_cb (EV_P_ ev_stat *w, int revents)
2970 \& {
2971 \& /* reset the one\-second timer */
2972 \& ev_timer_again (EV_A_ &timer);
2973 \& }
2974 \&
2975 \& ...
2976 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2977 \& ev_stat_start (loop, &passwd);
2978 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2979 .Ve
2980 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2981 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2982 .IX Subsection "ev_idle - when you've got nothing better to do..."
2983 Idle watchers trigger events when no other events of the same or higher
2984 priority are pending (prepare, check and other idle watchers do not count
2985 as receiving \*(L"events\*(R").
2986 .PP
2987 That is, as long as your process is busy handling sockets or timeouts
2988 (or even signals, imagine) of the same or higher priority it will not be
2989 triggered. But when your process is idle (or only lower-priority watchers
2990 are pending), the idle watchers are being called once per event loop
2991 iteration \- until stopped, that is, or your process receives more events
2992 and becomes busy again with higher priority stuff.
2993 .PP
2994 The most noteworthy effect is that as long as any idle watchers are
2995 active, the process will not block when waiting for new events.
2996 .PP
2997 Apart from keeping your process non-blocking (which is a useful
2998 effect on its own sometimes), idle watchers are a good place to do
2999 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
3000 event loop has handled all outstanding events.
3001 .PP
3002 \fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3003 .IX Subsection "Abusing an ev_idle watcher for its side-effect"
3004 .PP
3005 As long as there is at least one active idle watcher, libev will never
3006 sleep unnecessarily. Or in other words, it will loop as fast as possible.
3007 For this to work, the idle watcher doesn't need to be invoked at all \- the
3008 lowest priority will do.
3009 .PP
3010 This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3011 to do something on each event loop iteration \- for example to balance load
3012 between different connections.
3013 .PP
3014 See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3015 example.
3016 .PP
3017 \fIWatcher-Specific Functions and Data Members\fR
3018 .IX Subsection "Watcher-Specific Functions and Data Members"
3019 .IP "ev_idle_init (ev_idle *, callback)" 4
3020 .IX Item "ev_idle_init (ev_idle *, callback)"
3021 Initialises and configures the idle watcher \- it has no parameters of any
3022 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
3023 believe me.
3024 .PP
3025 \fIExamples\fR
3026 .IX Subsection "Examples"
3027 .PP
3028 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
3029 callback, free it. Also, use no error checking, as usual.
3030 .PP
3031 .Vb 5
3032 \& static void
3033 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
3034 \& {
3035 \& // stop the watcher
3036 \& ev_idle_stop (loop, w);
3037 \&
3038 \& // now we can free it
3039 \& free (w);
3040 \&
3041 \& // now do something you wanted to do when the program has
3042 \& // no longer anything immediate to do.
3043 \& }
3044 \&
3045 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3046 \& ev_idle_init (idle_watcher, idle_cb);
3047 \& ev_idle_start (loop, idle_watcher);
3048 .Ve
3049 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
3050 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
3051 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
3052 Prepare and check watchers are often (but not always) used in pairs:
3053 prepare watchers get invoked before the process blocks and check watchers
3054 afterwards.
3055 .PP
3056 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3057 current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3058 \&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3059 however. The rationale behind this is that you do not need to check
3060 for recursion in those watchers, i.e. the sequence will always be
3061 \&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3062 kind they will always be called in pairs bracketing the blocking call.
3063 .PP
3064 Their main purpose is to integrate other event mechanisms into libev and
3065 their use is somewhat advanced. They could be used, for example, to track
3066 variable changes, implement your own watchers, integrate net-snmp or a
3067 coroutine library and lots more. They are also occasionally useful if
3068 you cache some data and want to flush it before blocking (for example,
3069 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3070 watcher).
3071 .PP
3072 This is done by examining in each prepare call which file descriptors
3073 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
3074 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
3075 libraries provide exactly this functionality). Then, in the check watcher,
3076 you check for any events that occurred (by checking the pending status
3077 of all watchers and stopping them) and call back into the library. The
3078 I/O and timer callbacks will never actually be called (but must be valid
3079 nevertheless, because you never know, you know?).
3080 .PP
3081 As another example, the Perl Coro module uses these hooks to integrate
3082 coroutines into libev programs, by yielding to other active coroutines
3083 during each prepare and only letting the process block if no coroutines
3084 are ready to run (it's actually more complicated: it only runs coroutines
3085 with priority higher than or equal to the event loop and one coroutine
3086 of lower priority, but only once, using idle watchers to keep the event
3087 loop from blocking if lower-priority coroutines are active, thus mapping
3088 low-priority coroutines to idle/background tasks).
3089 .PP
3090 When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3091 highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3092 any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3093 watchers).
3094 .PP
3095 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3096 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3097 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3098 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3099 loops those other event loops might be in an unusable state until their
3100 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3101 others).
3102 .PP
3103 \fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3104 .IX Subsection "Abusing an ev_check watcher for its side-effect"
3105 .PP
3106 \&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3107 useful because they are called once per event loop iteration. For
3108 example, if you want to handle a large number of connections fairly, you
3109 normally only do a bit of work for each active connection, and if there
3110 is more work to do, you wait for the next event loop iteration, so other
3111 connections have a chance of making progress.
3112 .PP
3113 Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3114 next event loop iteration. However, that isn't as soon as possible \-
3115 without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3116 .PP
3117 This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3118 single global idle watcher that is active as long as you have one active
3119 \&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3120 will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3121 invoked. Neither watcher alone can do that.
3122 .PP
3123 \fIWatcher-Specific Functions and Data Members\fR
3124 .IX Subsection "Watcher-Specific Functions and Data Members"
3125 .IP "ev_prepare_init (ev_prepare *, callback)" 4
3126 .IX Item "ev_prepare_init (ev_prepare *, callback)"
3127 .PD 0
3128 .IP "ev_check_init (ev_check *, callback)" 4
3129 .IX Item "ev_check_init (ev_check *, callback)"
3130 .PD
3131 Initialises and configures the prepare or check watcher \- they have no
3132 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
3133 macros, but using them is utterly, utterly, utterly and completely
3134 pointless.
3135 .PP
3136 \fIExamples\fR
3137 .IX Subsection "Examples"
3138 .PP
3139 There are a number of principal ways to embed other event loops or modules
3140 into libev. Here are some ideas on how to include libadns into libev
3141 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3142 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3143 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3144 Glib event loop).
3145 .PP
3146 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3147 and in a check watcher, destroy them and call into libadns. What follows
3148 is pseudo-code only of course. This requires you to either use a low
3149 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3150 the callbacks for the IO/timeout watchers might not have been called yet.
3151 .PP
3152 .Vb 2
3153 \& static ev_io iow [nfd];
3154 \& static ev_timer tw;
3155 \&
3156 \& static void
3157 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3158 \& {
3159 \& }
3160 \&
3161 \& // create io watchers for each fd and a timer before blocking
3162 \& static void
3163 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3164 \& {
3165 \& int timeout = 3600000;
3166 \& struct pollfd fds [nfd];
3167 \& // actual code will need to loop here and realloc etc.
3168 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3169 \&
3170 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3171 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3172 \& ev_timer_start (loop, &tw);
3173 \&
3174 \& // create one ev_io per pollfd
3175 \& for (int i = 0; i < nfd; ++i)
3176 \& {
3177 \& ev_io_init (iow + i, io_cb, fds [i].fd,
3178 \& ((fds [i].events & POLLIN ? EV_READ : 0)
3179 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3180 \&
3181 \& fds [i].revents = 0;
3182 \& ev_io_start (loop, iow + i);
3183 \& }
3184 \& }
3185 \&
3186 \& // stop all watchers after blocking
3187 \& static void
3188 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3189 \& {
3190 \& ev_timer_stop (loop, &tw);
3191 \&
3192 \& for (int i = 0; i < nfd; ++i)
3193 \& {
3194 \& // set the relevant poll flags
3195 \& // could also call adns_processreadable etc. here
3196 \& struct pollfd *fd = fds + i;
3197 \& int revents = ev_clear_pending (iow + i);
3198 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3199 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3200 \&
3201 \& // now stop the watcher
3202 \& ev_io_stop (loop, iow + i);
3203 \& }
3204 \&
3205 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3206 \& }
3207 .Ve
3208 .PP
3209 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3210 in the prepare watcher and would dispose of the check watcher.
3211 .PP
3212 Method 3: If the module to be embedded supports explicit event
3213 notification (libadns does), you can also make use of the actual watcher
3214 callbacks, and only destroy/create the watchers in the prepare watcher.
3215 .PP
3216 .Vb 5
3217 \& static void
3218 \& timer_cb (EV_P_ ev_timer *w, int revents)
3219 \& {
3220 \& adns_state ads = (adns_state)w\->data;
3221 \& update_now (EV_A);
3222 \&
3223 \& adns_processtimeouts (ads, &tv_now);
3224 \& }
3225 \&
3226 \& static void
3227 \& io_cb (EV_P_ ev_io *w, int revents)
3228 \& {
3229 \& adns_state ads = (adns_state)w\->data;
3230 \& update_now (EV_A);
3231 \&
3232 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3233 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3234 \& }
3235 \&
3236 \& // do not ever call adns_afterpoll
3237 .Ve
3238 .PP
3239 Method 4: Do not use a prepare or check watcher because the module you
3240 want to embed is not flexible enough to support it. Instead, you can
3241 override their poll function. The drawback with this solution is that the
3242 main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3243 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3244 libglib event loop.
3245 .PP
3246 .Vb 4
3247 \& static gint
3248 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3249 \& {
3250 \& int got_events = 0;
3251 \&
3252 \& for (n = 0; n < nfds; ++n)
3253 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3254 \&
3255 \& if (timeout >= 0)
3256 \& // create/start timer
3257 \&
3258 \& // poll
3259 \& ev_run (EV_A_ 0);
3260 \&
3261 \& // stop timer again
3262 \& if (timeout >= 0)
3263 \& ev_timer_stop (EV_A_ &to);
3264 \&
3265 \& // stop io watchers again \- their callbacks should have set
3266 \& for (n = 0; n < nfds; ++n)
3267 \& ev_io_stop (EV_A_ iow [n]);
3268 \&
3269 \& return got_events;
3270 \& }
3271 .Ve
3272 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3273 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3274 .IX Subsection "ev_embed - when one backend isn't enough..."
3275 This is a rather advanced watcher type that lets you embed one event loop
3276 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3277 loop, other types of watchers might be handled in a delayed or incorrect
3278 fashion and must not be used).
3279 .PP
3280 There are primarily two reasons you would want that: work around bugs and
3281 prioritise I/O.
3282 .PP
3283 As an example for a bug workaround, the kqueue backend might only support
3284 sockets on some platform, so it is unusable as generic backend, but you
3285 still want to make use of it because you have many sockets and it scales
3286 so nicely. In this case, you would create a kqueue-based loop and embed
3287 it into your default loop (which might use e.g. poll). Overall operation
3288 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3289 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3290 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3291 .PP
3292 As for prioritising I/O: under rare circumstances you have the case where
3293 some fds have to be watched and handled very quickly (with low latency),
3294 and even priorities and idle watchers might have too much overhead. In
3295 this case you would put all the high priority stuff in one loop and all
3296 the rest in a second one, and embed the second one in the first.
3297 .PP
3298 As long as the watcher is active, the callback will be invoked every
3299 time there might be events pending in the embedded loop. The callback
3300 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3301 sweep and invoke their callbacks (the callback doesn't need to invoke the
3302 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3303 to give the embedded loop strictly lower priority for example).
3304 .PP
3305 You can also set the callback to \f(CW0\fR, in which case the embed watcher
3306 will automatically execute the embedded loop sweep whenever necessary.
3307 .PP
3308 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3309 is active, i.e., the embedded loop will automatically be forked when the
3310 embedding loop forks. In other cases, the user is responsible for calling
3311 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3312 .PP
3313 Unfortunately, not all backends are embeddable: only the ones returned by
3314 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3315 portable one.
3316 .PP
3317 So when you want to use this feature you will always have to be prepared
3318 that you cannot get an embeddable loop. The recommended way to get around
3319 this is to have a separate variables for your embeddable loop, try to
3320 create it, and if that fails, use the normal loop for everything.
3321 .PP
3322 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3323 .IX Subsection "ev_embed and fork"
3324 .PP
3325 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3326 automatically be applied to the embedded loop as well, so no special
3327 fork handling is required in that case. When the watcher is not running,
3328 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3329 as applicable.
3330 .PP
3331 \fIWatcher-Specific Functions and Data Members\fR
3332 .IX Subsection "Watcher-Specific Functions and Data Members"
3333 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3334 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3335 .PD 0
3336 .IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
3337 .IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
3338 .PD
3339 Configures the watcher to embed the given loop, which must be
3340 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3341 invoked automatically, otherwise it is the responsibility of the callback
3342 to invoke it (it will continue to be called until the sweep has been done,
3343 if you do not want that, you need to temporarily stop the embed watcher).
3344 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3345 .IX Item "ev_embed_sweep (loop, ev_embed *)"
3346 Make a single, non-blocking sweep over the embedded loop. This works
3347 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3348 appropriate way for embedded loops.
3349 .IP "struct ev_loop *other [read\-only]" 4
3350 .IX Item "struct ev_loop *other [read-only]"
3351 The embedded event loop.
3352 .PP
3353 \fIExamples\fR
3354 .IX Subsection "Examples"
3355 .PP
3356 Example: Try to get an embeddable event loop and embed it into the default
3357 event loop. If that is not possible, use the default loop. The default
3358 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3359 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3360 used).
3361 .PP
3362 .Vb 3
3363 \& struct ev_loop *loop_hi = ev_default_init (0);
3364 \& struct ev_loop *loop_lo = 0;
3365 \& ev_embed embed;
3366 \&
3367 \& // see if there is a chance of getting one that works
3368 \& // (remember that a flags value of 0 means autodetection)
3369 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3370 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3371 \& : 0;
3372 \&
3373 \& // if we got one, then embed it, otherwise default to loop_hi
3374 \& if (loop_lo)
3375 \& {
3376 \& ev_embed_init (&embed, 0, loop_lo);
3377 \& ev_embed_start (loop_hi, &embed);
3378 \& }
3379 \& else
3380 \& loop_lo = loop_hi;
3381 .Ve
3382 .PP
3383 Example: Check if kqueue is available but not recommended and create
3384 a kqueue backend for use with sockets (which usually work with any
3385 kqueue implementation). Store the kqueue/socket\-only event loop in
3386 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3387 .PP
3388 .Vb 3
3389 \& struct ev_loop *loop = ev_default_init (0);
3390 \& struct ev_loop *loop_socket = 0;
3391 \& ev_embed embed;
3392 \&
3393 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3394 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3395 \& {
3396 \& ev_embed_init (&embed, 0, loop_socket);
3397 \& ev_embed_start (loop, &embed);
3398 \& }
3399 \&
3400 \& if (!loop_socket)
3401 \& loop_socket = loop;
3402 \&
3403 \& // now use loop_socket for all sockets, and loop for everything else
3404 .Ve
3405 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3406 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3407 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3408 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3409 whoever is a good citizen cared to tell libev about it by calling
3410 \&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3411 and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3412 after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3413 and calls it in the wrong process, the fork handlers will be invoked, too,
3414 of course.
3415 .PP
3416 \fIThe special problem of life after fork \- how is it possible?\fR
3417 .IX Subsection "The special problem of life after fork - how is it possible?"
3418 .PP
3419 Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3420 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3421 sequence should be handled by libev without any problems.
3422 .PP
3423 This changes when the application actually wants to do event handling
3424 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3425 fork.
3426 .PP
3427 The default mode of operation (for libev, with application help to detect
3428 forks) is to duplicate all the state in the child, as would be expected
3429 when \fIeither\fR the parent \fIor\fR the child process continues.
3430 .PP
3431 When both processes want to continue using libev, then this is usually the
3432 wrong result. In that case, usually one process (typically the parent) is
3433 supposed to continue with all watchers in place as before, while the other
3434 process typically wants to start fresh, i.e. without any active watchers.
3435 .PP
3436 The cleanest and most efficient way to achieve that with libev is to
3437 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3438 use that for new watchers. This has the advantage of not touching more
3439 memory than necessary, and thus avoiding the copy-on-write, and the
3440 disadvantage of having to use multiple event loops (which do not support
3441 signal watchers).
3442 .PP
3443 When this is not possible, or you want to use the default loop for
3444 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3445 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3446 Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3447 watchers, so you have to be careful not to execute code that modifies
3448 those watchers. Note also that in that case, you have to re-register any
3449 signal watchers.
3450 .PP
3451 \fIWatcher-Specific Functions and Data Members\fR
3452 .IX Subsection "Watcher-Specific Functions and Data Members"
3453 .IP "ev_fork_init (ev_fork *, callback)" 4
3454 .IX Item "ev_fork_init (ev_fork *, callback)"
3455 Initialises and configures the fork watcher \- it has no parameters of any
3456 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3457 really.
3458 .ie n .SS """ev_cleanup"" \- even the best things end"
3459 .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3460 .IX Subsection "ev_cleanup - even the best things end"
3461 Cleanup watchers are called just before the event loop is being destroyed
3462 by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3463 .PP
3464 While there is no guarantee that the event loop gets destroyed, cleanup
3465 watchers provide a convenient method to install cleanup hooks for your
3466 program, worker threads and so on \- you just to make sure to destroy the
3467 loop when you want them to be invoked.
3468 .PP
3469 Cleanup watchers are invoked in the same way as any other watcher. Unlike
3470 all other watchers, they do not keep a reference to the event loop (which
3471 makes a lot of sense if you think about it). Like all other watchers, you
3472 can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3473 .PP
3474 \fIWatcher-Specific Functions and Data Members\fR
3475 .IX Subsection "Watcher-Specific Functions and Data Members"
3476 .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3477 .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3478 Initialises and configures the cleanup watcher \- it has no parameters of
3479 any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3480 pointless, I assure you.
3481 .PP
3482 Example: Register an atexit handler to destroy the default loop, so any
3483 cleanup functions are called.
3484 .PP
3485 .Vb 5
3486 \& static void
3487 \& program_exits (void)
3488 \& {
3489 \& ev_loop_destroy (EV_DEFAULT_UC);
3490 \& }
3491 \&
3492 \& ...
3493 \& atexit (program_exits);
3494 .Ve
3495 .ie n .SS """ev_async"" \- how to wake up an event loop"
3496 .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3497 .IX Subsection "ev_async - how to wake up an event loop"
3498 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3499 asynchronous sources such as signal handlers (as opposed to multiple event
3500 loops \- those are of course safe to use in different threads).
3501 .PP
3502 Sometimes, however, you need to wake up an event loop you do not control,
3503 for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3504 watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3505 it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3506 .PP
3507 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3508 too, are asynchronous in nature, and signals, too, will be compressed
3509 (i.e. the number of callback invocations may be less than the number of
3510 \&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3511 of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3512 signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3513 even without knowing which loop owns the signal.
3514 .PP
3515 \fIQueueing\fR
3516 .IX Subsection "Queueing"
3517 .PP
3518 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3519 is that the author does not know of a simple (or any) algorithm for a
3520 multiple-writer-single-reader queue that works in all cases and doesn't
3521 need elaborate support such as pthreads or unportable memory access
3522 semantics.
3523 .PP
3524 That means that if you want to queue data, you have to provide your own
3525 queue. But at least I can tell you how to implement locking around your
3526 queue:
3527 .IP "queueing from a signal handler context" 4
3528 .IX Item "queueing from a signal handler context"
3529 To implement race-free queueing, you simply add to the queue in the signal
3530 handler but you block the signal handler in the watcher callback. Here is
3531 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3532 .Sp
3533 .Vb 1
3534 \& static ev_async mysig;
3535 \&
3536 \& static void
3537 \& sigusr1_handler (void)
3538 \& {
3539 \& sometype data;
3540 \&
3541 \& // no locking etc.
3542 \& queue_put (data);
3543 \& ev_async_send (EV_DEFAULT_ &mysig);
3544 \& }
3545 \&
3546 \& static void
3547 \& mysig_cb (EV_P_ ev_async *w, int revents)
3548 \& {
3549 \& sometype data;
3550 \& sigset_t block, prev;
3551 \&
3552 \& sigemptyset (&block);
3553 \& sigaddset (&block, SIGUSR1);
3554 \& sigprocmask (SIG_BLOCK, &block, &prev);
3555 \&
3556 \& while (queue_get (&data))
3557 \& process (data);
3558 \&
3559 \& if (sigismember (&prev, SIGUSR1)
3560 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3561 \& }
3562 .Ve
3563 .Sp
3564 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3565 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3566 either...).
3567 .IP "queueing from a thread context" 4
3568 .IX Item "queueing from a thread context"
3569 The strategy for threads is different, as you cannot (easily) block
3570 threads but you can easily preempt them, so to queue safely you need to
3571 employ a traditional mutex lock, such as in this pthread example:
3572 .Sp
3573 .Vb 2
3574 \& static ev_async mysig;
3575 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3576 \&
3577 \& static void
3578 \& otherthread (void)
3579 \& {
3580 \& // only need to lock the actual queueing operation
3581 \& pthread_mutex_lock (&mymutex);
3582 \& queue_put (data);
3583 \& pthread_mutex_unlock (&mymutex);
3584 \&
3585 \& ev_async_send (EV_DEFAULT_ &mysig);
3586 \& }
3587 \&
3588 \& static void
3589 \& mysig_cb (EV_P_ ev_async *w, int revents)
3590 \& {
3591 \& pthread_mutex_lock (&mymutex);
3592 \&
3593 \& while (queue_get (&data))
3594 \& process (data);
3595 \&
3596 \& pthread_mutex_unlock (&mymutex);
3597 \& }
3598 .Ve
3599 .PP
3600 \fIWatcher-Specific Functions and Data Members\fR
3601 .IX Subsection "Watcher-Specific Functions and Data Members"
3602 .IP "ev_async_init (ev_async *, callback)" 4
3603 .IX Item "ev_async_init (ev_async *, callback)"
3604 Initialises and configures the async watcher \- it has no parameters of any
3605 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3606 trust me.
3607 .IP "ev_async_send (loop, ev_async *)" 4
3608 .IX Item "ev_async_send (loop, ev_async *)"
3609 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3610 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3611 returns.
3612 .Sp
3613 Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3614 signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3615 embedding section below on what exactly this means).
3616 .Sp
3617 Note that, as with other watchers in libev, multiple events might get
3618 compressed into a single callback invocation (another way to look at
3619 this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3620 \&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3621 .Sp
3622 This call incurs the overhead of at most one extra system call per event
3623 loop iteration, if the event loop is blocked, and no syscall at all if
3624 the event loop (or your program) is processing events. That means that
3625 repeated calls are basically free (there is no need to avoid calls for
3626 performance reasons) and that the overhead becomes smaller (typically
3627 zero) under load.
3628 .IP "bool = ev_async_pending (ev_async *)" 4
3629 .IX Item "bool = ev_async_pending (ev_async *)"
3630 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3631 watcher but the event has not yet been processed (or even noted) by the
3632 event loop.
3633 .Sp
3634 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3635 the loop iterates next and checks for the watcher to have become active,
3636 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3637 quickly check whether invoking the loop might be a good idea.
3638 .Sp
3639 Not that this does \fInot\fR check whether the watcher itself is pending,
3640 only whether it has been requested to make this watcher pending: there
3641 is a time window between the event loop checking and resetting the async
3642 notification, and the callback being invoked.
3643 .SH "OTHER FUNCTIONS"
3644 .IX Header "OTHER FUNCTIONS"
3645 There are some other functions of possible interest. Described. Here. Now.
3646 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3647 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3648 This function combines a simple timer and an I/O watcher, calls your
3649 callback on whichever event happens first and automatically stops both
3650 watchers. This is useful if you want to wait for a single event on an fd
3651 or timeout without having to allocate/configure/start/stop/free one or
3652 more watchers yourself.
3653 .Sp
3654 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3655 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3656 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3657 .Sp
3658 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3659 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3660 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3661 .Sp
3662 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3663 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3664 \&\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
3665 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3666 a timeout and an io event at the same time \- you probably should give io
3667 events precedence.
3668 .Sp
3669 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
3670 .Sp
3671 .Vb 7
3672 \& static void stdin_ready (int revents, void *arg)
3673 \& {
3674 \& if (revents & EV_READ)
3675 \& /* stdin might have data for us, joy! */;
3676 \& else if (revents & EV_TIMER)
3677 \& /* doh, nothing entered */;
3678 \& }
3679 \&
3680 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3681 .Ve
3682 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3683 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3684 Feed an event on the given fd, as if a file descriptor backend detected
3685 the given events.
3686 .IP "ev_feed_signal_event (loop, int signum)" 4
3687 .IX Item "ev_feed_signal_event (loop, int signum)"
3688 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3689 which is async-safe.
3690 .SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3691 .IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3692 This section explains some common idioms that are not immediately
3693 obvious. Note that examples are sprinkled over the whole manual, and this
3694 section only contains stuff that wouldn't fit anywhere else.
3695 .SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3696 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3697 Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3698 or modify at any time: libev will completely ignore it. This can be used
3699 to associate arbitrary data with your watcher. If you need more data and
3700 don't want to allocate memory separately and store a pointer to it in that
3701 data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3702 data:
3703 .PP
3704 .Vb 7
3705 \& struct my_io
3706 \& {
3707 \& ev_io io;
3708 \& int otherfd;
3709 \& void *somedata;
3710 \& struct whatever *mostinteresting;
3711 \& };
3712 \&
3713 \& ...
3714 \& struct my_io w;
3715 \& ev_io_init (&w.io, my_cb, fd, EV_READ);
3716 .Ve
3717 .PP
3718 And since your callback will be called with a pointer to the watcher, you
3719 can cast it back to your own type:
3720 .PP
3721 .Vb 5
3722 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3723 \& {
3724 \& struct my_io *w = (struct my_io *)w_;
3725 \& ...
3726 \& }
3727 .Ve
3728 .PP
3729 More interesting and less C\-conformant ways of casting your callback
3730 function type instead have been omitted.
3731 .SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3732 .IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3733 Another common scenario is to use some data structure with multiple
3734 embedded watchers, in effect creating your own watcher that combines
3735 multiple libev event sources into one \*(L"super-watcher\*(R":
3736 .PP
3737 .Vb 6
3738 \& struct my_biggy
3739 \& {
3740 \& int some_data;
3741 \& ev_timer t1;
3742 \& ev_timer t2;
3743 \& }
3744 .Ve
3745 .PP
3746 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3747 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3748 the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3749 to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3750 real programmers):
3751 .PP
3752 .Vb 1
3753 \& #include <stddef.h>
3754 \&
3755 \& static void
3756 \& t1_cb (EV_P_ ev_timer *w, int revents)
3757 \& {
3758 \& struct my_biggy big = (struct my_biggy *)
3759 \& (((char *)w) \- offsetof (struct my_biggy, t1));
3760 \& }
3761 \&
3762 \& static void
3763 \& t2_cb (EV_P_ ev_timer *w, int revents)
3764 \& {
3765 \& struct my_biggy big = (struct my_biggy *)
3766 \& (((char *)w) \- offsetof (struct my_biggy, t2));
3767 \& }
3768 .Ve
3769 .SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3770 .IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3771 Often you have structures like this in event-based programs:
3772 .PP
3773 .Vb 4
3774 \& callback ()
3775 \& {
3776 \& free (request);
3777 \& }
3778 \&
3779 \& request = start_new_request (..., callback);
3780 .Ve
3781 .PP
3782 The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3783 used to cancel the operation, or do other things with it.
3784 .PP
3785 It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3786 immediately invoke the callback, for example, to report errors. Or you add
3787 some caching layer that finds that it can skip the lengthy aspects of the
3788 operation and simply invoke the callback with the result.
3789 .PP
3790 The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3791 has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3792 .PP
3793 Even if you pass the request by some safer means to the callback, you
3794 might want to do something to the request after starting it, such as
3795 canceling it, which probably isn't working so well when the callback has
3796 already been invoked.
3797 .PP
3798 A common way around all these issues is to make sure that
3799 \&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3800 \&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3801 delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3802 example, or more sneakily, by reusing an existing (stopped) watcher and
3803 pushing it into the pending queue:
3804 .PP
3805 .Vb 2
3806 \& ev_set_cb (watcher, callback);
3807 \& ev_feed_event (EV_A_ watcher, 0);
3808 .Ve
3809 .PP
3810 This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3811 invoked, while not delaying callback invocation too much.
3812 .SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
3813 .IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3814 Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3815 \&\fImodal\fR interaction, which is most easily implemented by recursively
3816 invoking \f(CW\*(C`ev_run\*(C'\fR.
3817 .PP
3818 This brings the problem of exiting \- a callback might want to finish the
3819 main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3820 a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3821 and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3822 other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3823 .PP
3824 The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3825 invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3826 triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3827 .PP
3828 .Vb 2
3829 \& // main loop
3830 \& int exit_main_loop = 0;
3831 \&
3832 \& while (!exit_main_loop)
3833 \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3834 \&
3835 \& // in a modal watcher
3836 \& int exit_nested_loop = 0;
3837 \&
3838 \& while (!exit_nested_loop)
3839 \& ev_run (EV_A_ EVRUN_ONCE);
3840 .Ve
3841 .PP
3842 To exit from any of these loops, just set the corresponding exit variable:
3843 .PP
3844 .Vb 2
3845 \& // exit modal loop
3846 \& exit_nested_loop = 1;
3847 \&
3848 \& // exit main program, after modal loop is finished
3849 \& exit_main_loop = 1;
3850 \&
3851 \& // exit both
3852 \& exit_main_loop = exit_nested_loop = 1;
3853 .Ve
3854 .SS "\s-1THREAD LOCKING EXAMPLE\s0"
3855 .IX Subsection "THREAD LOCKING EXAMPLE"
3856 Here is a fictitious example of how to run an event loop in a different
3857 thread from where callbacks are being invoked and watchers are
3858 created/added/removed.
3859 .PP
3860 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3861 which uses exactly this technique (which is suited for many high-level
3862 languages).
3863 .PP
3864 The example uses a pthread mutex to protect the loop data, a condition
3865 variable to wait for callback invocations, an async watcher to notify the
3866 event loop thread and an unspecified mechanism to wake up the main thread.
3867 .PP
3868 First, you need to associate some data with the event loop:
3869 .PP
3870 .Vb 6
3871 \& typedef struct {
3872 \& mutex_t lock; /* global loop lock */
3873 \& ev_async async_w;
3874 \& thread_t tid;
3875 \& cond_t invoke_cv;
3876 \& } userdata;
3877 \&
3878 \& void prepare_loop (EV_P)
3879 \& {
3880 \& // for simplicity, we use a static userdata struct.
3881 \& static userdata u;
3882 \&
3883 \& ev_async_init (&u\->async_w, async_cb);
3884 \& ev_async_start (EV_A_ &u\->async_w);
3885 \&
3886 \& pthread_mutex_init (&u\->lock, 0);
3887 \& pthread_cond_init (&u\->invoke_cv, 0);
3888 \&
3889 \& // now associate this with the loop
3890 \& ev_set_userdata (EV_A_ u);
3891 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3892 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3893 \&
3894 \& // then create the thread running ev_run
3895 \& pthread_create (&u\->tid, 0, l_run, EV_A);
3896 \& }
3897 .Ve
3898 .PP
3899 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3900 solely to wake up the event loop so it takes notice of any new watchers
3901 that might have been added:
3902 .PP
3903 .Vb 5
3904 \& static void
3905 \& async_cb (EV_P_ ev_async *w, int revents)
3906 \& {
3907 \& // just used for the side effects
3908 \& }
3909 .Ve
3910 .PP
3911 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3912 protecting the loop data, respectively.
3913 .PP
3914 .Vb 6
3915 \& static void
3916 \& l_release (EV_P)
3917 \& {
3918 \& userdata *u = ev_userdata (EV_A);
3919 \& pthread_mutex_unlock (&u\->lock);
3920 \& }
3921 \&
3922 \& static void
3923 \& l_acquire (EV_P)
3924 \& {
3925 \& userdata *u = ev_userdata (EV_A);
3926 \& pthread_mutex_lock (&u\->lock);
3927 \& }
3928 .Ve
3929 .PP
3930 The event loop thread first acquires the mutex, and then jumps straight
3931 into \f(CW\*(C`ev_run\*(C'\fR:
3932 .PP
3933 .Vb 4
3934 \& void *
3935 \& l_run (void *thr_arg)
3936 \& {
3937 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3938 \&
3939 \& l_acquire (EV_A);
3940 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3941 \& ev_run (EV_A_ 0);
3942 \& l_release (EV_A);
3943 \&
3944 \& return 0;
3945 \& }
3946 .Ve
3947 .PP
3948 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3949 signal the main thread via some unspecified mechanism (signals? pipe
3950 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3951 have been called (in a while loop because a) spurious wakeups are possible
3952 and b) skipping inter-thread-communication when there are no pending
3953 watchers is very beneficial):
3954 .PP
3955 .Vb 4
3956 \& static void
3957 \& l_invoke (EV_P)
3958 \& {
3959 \& userdata *u = ev_userdata (EV_A);
3960 \&
3961 \& while (ev_pending_count (EV_A))
3962 \& {
3963 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3964 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3965 \& }
3966 \& }
3967 .Ve
3968 .PP
3969 Now, whenever the main thread gets told to invoke pending watchers, it
3970 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3971 thread to continue:
3972 .PP
3973 .Vb 4
3974 \& static void
3975 \& real_invoke_pending (EV_P)
3976 \& {
3977 \& userdata *u = ev_userdata (EV_A);
3978 \&
3979 \& pthread_mutex_lock (&u\->lock);
3980 \& ev_invoke_pending (EV_A);
3981 \& pthread_cond_signal (&u\->invoke_cv);
3982 \& pthread_mutex_unlock (&u\->lock);
3983 \& }
3984 .Ve
3985 .PP
3986 Whenever you want to start/stop a watcher or do other modifications to an
3987 event loop, you will now have to lock:
3988 .PP
3989 .Vb 2
3990 \& ev_timer timeout_watcher;
3991 \& userdata *u = ev_userdata (EV_A);
3992 \&
3993 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3994 \&
3995 \& pthread_mutex_lock (&u\->lock);
3996 \& ev_timer_start (EV_A_ &timeout_watcher);
3997 \& ev_async_send (EV_A_ &u\->async_w);
3998 \& pthread_mutex_unlock (&u\->lock);
3999 .Ve
4000 .PP
4001 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4002 an event loop currently blocking in the kernel will have no knowledge
4003 about the newly added timer. By waking up the loop it will pick up any new
4004 watchers in the next event loop iteration.
4005 .SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4006 .IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4007 While the overhead of a callback that e.g. schedules a thread is small, it
4008 is still an overhead. If you embed libev, and your main usage is with some
4009 kind of threads or coroutines, you might want to customise libev so that
4010 doesn't need callbacks anymore.
4011 .PP
4012 Imagine you have coroutines that you can switch to using a function
4013 \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4014 and that due to some magic, the currently active coroutine is stored in a
4015 global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4016 event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4017 the differing \f(CW\*(C`;\*(C'\fR conventions):
4018 .PP
4019 .Vb 2
4020 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4021 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4022 .Ve
4023 .PP
4024 That means instead of having a C callback function, you store the
4025 coroutine to switch to in each watcher, and instead of having libev call
4026 your callback, you instead have it switch to that coroutine.
4027 .PP
4028 A coroutine might now wait for an event with a function called
4029 \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4030 matter when, or whether the watcher is active or not when this function is
4031 called):
4032 .PP
4033 .Vb 6
4034 \& void
4035 \& wait_for_event (ev_watcher *w)
4036 \& {
4037 \& ev_set_cb (w, current_coro);
4038 \& switch_to (libev_coro);
4039 \& }
4040 .Ve
4041 .PP
4042 That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4043 continues the libev coroutine, which, when appropriate, switches back to
4044 this or any other coroutine.
4045 .PP
4046 You can do similar tricks if you have, say, threads with an event queue \-
4047 instead of storing a coroutine, you store the queue object and instead of
4048 switching to a coroutine, you push the watcher onto the queue and notify
4049 any waiters.
4050 .PP
4051 To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4052 files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4053 .PP
4054 .Vb 4
4055 \& // my_ev.h
4056 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4057 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
4058 \& #include "../libev/ev.h"
4059 \&
4060 \& // my_ev.c
4061 \& #define EV_H "my_ev.h"
4062 \& #include "../libev/ev.c"
4063 .Ve
4064 .PP
4065 And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4066 \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4067 can even use \fIev.h\fR as header file name directly.
4068 .SH "LIBEVENT EMULATION"
4069 .IX Header "LIBEVENT EMULATION"
4070 Libev offers a compatibility emulation layer for libevent. It cannot
4071 emulate the internals of libevent, so here are some usage hints:
4072 .IP "\(bu" 4
4073 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4074 .Sp
4075 This was the newest libevent version available when libev was implemented,
4076 and is still mostly unchanged in 2010.
4077 .IP "\(bu" 4
4078 Use it by including <event.h>, as usual.
4079 .IP "\(bu" 4
4080 The following members are fully supported: ev_base, ev_callback,
4081 ev_arg, ev_fd, ev_res, ev_events.
4082 .IP "\(bu" 4
4083 Avoid using ev_flags and the EVLIST_*\-macros, while it is
4084 maintained by libev, it does not work exactly the same way as in libevent (consider
4085 it a private \s-1API\s0).
4086 .IP "\(bu" 4
4087 Priorities are not currently supported. Initialising priorities
4088 will fail and all watchers will have the same priority, even though there
4089 is an ev_pri field.
4090 .IP "\(bu" 4
4091 In libevent, the last base created gets the signals, in libev, the
4092 base that registered the signal gets the signals.
4093 .IP "\(bu" 4
4094 Other members are not supported.
4095 .IP "\(bu" 4
4096 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
4097 to use the libev header file and library.
4098 .SH "\*(C+ SUPPORT"
4099 .IX Header " SUPPORT"
4100 .SS "C \s-1API\s0"
4101 .IX Subsection "C API"
4102 The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4103 libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4104 will work fine.
4105 .PP
4106 Proper exception specifications might have to be added to callbacks passed
4107 to libev: exceptions may be thrown only from watcher callbacks, all
4108 other callbacks (allocator, syserr, loop acquire/release and periodic
4109 reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4110 ()\*(C'\fR specification. If you have code that needs to be compiled as both C
4111 and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4112 .PP
4113 .Vb 6
4114 \& static void
4115 \& fatal_error (const char *msg) EV_THROW
4116 \& {
4117 \& perror (msg);
4118 \& abort ();
4119 \& }
4120 \&
4121 \& ...
4122 \& ev_set_syserr_cb (fatal_error);
4123 .Ve
4124 .PP
4125 The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4126 \&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4127 because it runs cleanup watchers).
4128 .PP
4129 Throwing exceptions in watcher callbacks is only supported if libev itself
4130 is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4131 throwing exceptions through C libraries (most do).
4132 .SS "\*(C+ \s-1API\s0"
4133 .IX Subsection " API"
4134 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4135 you to use some convenience methods to start/stop watchers and also change
4136 the callback model to a model using method callbacks on objects.
4137 .PP
4138 To use it,
4139 .PP
4140 .Vb 1
4141 \& #include <ev++.h>
4142 .Ve
4143 .PP
4144 This automatically includes \fIev.h\fR and puts all of its definitions (many
4145 of them macros) into the global namespace. All \*(C+ specific things are
4146 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4147 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4148 .PP
4149 Care has been taken to keep the overhead low. The only data member the \*(C+
4150 classes add (compared to plain C\-style watchers) is the event loop pointer
4151 that the watcher is associated with (or no additional members at all if
4152 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4153 .PP
4154 Currently, functions, static and non-static member functions and classes
4155 with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4156 to add as long as they only need one additional pointer for context. If
4157 you need support for other types of functors please contact the author
4158 (preferably after implementing it).
4159 .PP
4160 For all this to work, your \*(C+ compiler either has to use the same calling
4161 conventions as your C compiler (for static member functions), or you have
4162 to embed libev and compile libev itself as \*(C+.
4163 .PP
4164 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4165 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4166 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4167 .IX Item "ev::READ, ev::WRITE etc."
4168 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4169 macros from \fIev.h\fR.
4170 .ie n .IP """ev::tstamp"", ""ev::now""" 4
4171 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4172 .IX Item "ev::tstamp, ev::now"
4173 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4174 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4175 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4176 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4177 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4178 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4179 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4180 defined by many implementations.
4181 .Sp
4182 All of those classes have these methods:
4183 .RS 4
4184 .IP "ev::TYPE::TYPE ()" 4
4185 .IX Item "ev::TYPE::TYPE ()"
4186 .PD 0
4187 .IP "ev::TYPE::TYPE (loop)" 4
4188 .IX Item "ev::TYPE::TYPE (loop)"
4189 .IP "ev::TYPE::~TYPE" 4
4190 .IX Item "ev::TYPE::~TYPE"
4191 .PD
4192 The constructor (optionally) takes an event loop to associate the watcher
4193 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4194 .Sp
4195 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4196 \&\f(CW\*(C`set\*(C'\fR method before starting it.
4197 .Sp
4198 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4199 method to set a callback before you can start the watcher.
4200 .Sp
4201 (The reason why you have to use a method is a limitation in \*(C+ which does
4202 not allow explicit template arguments for constructors).
4203 .Sp
4204 The destructor automatically stops the watcher if it is active.
4205 .IP "w\->set<class, &class::method> (object *)" 4
4206 .IX Item "w->set<class, &class::method> (object *)"
4207 This method sets the callback method to call. The method has to have a
4208 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4209 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4210 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4211 .Sp
4212 This method synthesizes efficient thunking code to call your method from
4213 the C callback that libev requires. If your compiler can inline your
4214 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4215 your compiler is good :), then the method will be fully inlined into the
4216 thunking function, making it as fast as a direct C callback.
4217 .Sp
4218 Example: simple class declaration and watcher initialisation
4219 .Sp
4220 .Vb 4
4221 \& struct myclass
4222 \& {
4223 \& void io_cb (ev::io &w, int revents) { }
4224 \& }
4225 \&
4226 \& myclass obj;
4227 \& ev::io iow;
4228 \& iow.set <myclass, &myclass::io_cb> (&obj);
4229 .Ve
4230 .IP "w\->set (object *)" 4
4231 .IX Item "w->set (object *)"
4232 This is a variation of a method callback \- leaving out the method to call
4233 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4234 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4235 the time. Incidentally, you can then also leave out the template argument
4236 list.
4237 .Sp
4238 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4239 int revents)\*(C'\fR.
4240 .Sp
4241 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4242 .Sp
4243 Example: use a functor object as callback.
4244 .Sp
4245 .Vb 7
4246 \& struct myfunctor
4247 \& {
4248 \& void operator() (ev::io &w, int revents)
4249 \& {
4250 \& ...
4251 \& }
4252 \& }
4253 \&
4254 \& myfunctor f;
4255 \&
4256 \& ev::io w;
4257 \& w.set (&f);
4258 .Ve
4259 .IP "w\->set<function> (void *data = 0)" 4
4260 .IX Item "w->set<function> (void *data = 0)"
4261 Also sets a callback, but uses a static method or plain function as
4262 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4263 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4264 .Sp
4265 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4266 .Sp
4267 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4268 .Sp
4269 Example: Use a plain function as callback.
4270 .Sp
4271 .Vb 2
4272 \& static void io_cb (ev::io &w, int revents) { }
4273 \& iow.set <io_cb> ();
4274 .Ve
4275 .IP "w\->set (loop)" 4
4276 .IX Item "w->set (loop)"
4277 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4278 do this when the watcher is inactive (and not pending either).
4279 .IP "w\->set ([arguments])" 4
4280 .IX Item "w->set ([arguments])"
4281 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4282 with the same arguments. Either this method or a suitable start method
4283 must be called at least once. Unlike the C counterpart, an active watcher
4284 gets automatically stopped and restarted when reconfiguring it with this
4285 method.
4286 .Sp
4287 For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4288 clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4289 .IP "w\->start ()" 4
4290 .IX Item "w->start ()"
4291 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4292 constructor already stores the event loop.
4293 .IP "w\->start ([arguments])" 4
4294 .IX Item "w->start ([arguments])"
4295 Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4296 convenient to wrap them in one call. Uses the same type of arguments as
4297 the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4298 .IP "w\->stop ()" 4
4299 .IX Item "w->stop ()"
4300 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4301 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4302 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4303 .IX Item "w->again () (ev::timer, ev::periodic only)"
4304 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4305 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4306 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4307 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4308 .IX Item "w->sweep () (ev::embed only)"
4309 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4310 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4311 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4312 .IX Item "w->update () (ev::stat only)"
4313 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4314 .RE
4315 .RS 4
4316 .RE
4317 .PP
4318 Example: Define a class with two I/O and idle watchers, start the I/O
4319 watchers in the constructor.
4320 .PP
4321 .Vb 5
4322 \& class myclass
4323 \& {
4324 \& ev::io io ; void io_cb (ev::io &w, int revents);
4325 \& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4326 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4327 \&
4328 \& myclass (int fd)
4329 \& {
4330 \& io .set <myclass, &myclass::io_cb > (this);
4331 \& io2 .set <myclass, &myclass::io2_cb > (this);
4332 \& idle.set <myclass, &myclass::idle_cb> (this);
4333 \&
4334 \& io.set (fd, ev::WRITE); // configure the watcher
4335 \& io.start (); // start it whenever convenient
4336 \&
4337 \& io2.start (fd, ev::READ); // set + start in one call
4338 \& }
4339 \& };
4340 .Ve
4341 .SH "OTHER LANGUAGE BINDINGS"
4342 .IX Header "OTHER LANGUAGE BINDINGS"
4343 Libev does not offer other language bindings itself, but bindings for a
4344 number of languages exist in the form of third-party packages. If you know
4345 any interesting language binding in addition to the ones listed here, drop
4346 me a note.
4347 .IP "Perl" 4
4348 .IX Item "Perl"
4349 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4350 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4351 there are additional modules that implement libev-compatible interfaces
4352 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4353 \&\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
4354 and \f(CW\*(C`EV::Glib\*(C'\fR).
4355 .Sp
4356 It can be found and installed via \s-1CPAN,\s0 its homepage is at
4357 <http://software.schmorp.de/pkg/EV>.
4358 .IP "Python" 4
4359 .IX Item "Python"
4360 Python bindings can be found at <http://code.google.com/p/pyev/>. It
4361 seems to be quite complete and well-documented.
4362 .IP "Ruby" 4
4363 .IX Item "Ruby"
4364 Tony Arcieri has written a ruby extension that offers access to a subset
4365 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4366 more on top of it. It can be found via gem servers. Its homepage is at
4367 <http://rev.rubyforge.org/>.
4368 .Sp
4369 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4370 makes rev work even on mingw.
4371 .IP "Haskell" 4
4372 .IX Item "Haskell"
4373 A haskell binding to libev is available at
4374 <http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4375 .IP "D" 4
4376 .IX Item "D"
4377 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4378 be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4379 .IP "Ocaml" 4
4380 .IX Item "Ocaml"
4381 Erkki Seppala has written Ocaml bindings for libev, to be found at
4382 <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4383 .IP "Lua" 4
4384 .IX Item "Lua"
4385 Brian Maher has written a partial interface to libev for lua (at the
4386 time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4387 <http://github.com/brimworks/lua\-ev>.
4388 .IP "Javascript" 4
4389 .IX Item "Javascript"
4390 Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4391 .IP "Others" 4
4392 .IX Item "Others"
4393 There are others, and I stopped counting.
4394 .SH "MACRO MAGIC"
4395 .IX Header "MACRO MAGIC"
4396 Libev can be compiled with a variety of options, the most fundamental
4397 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4398 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4399 .PP
4400 To make it easier to write programs that cope with either variant, the
4401 following macros are defined:
4402 .ie n .IP """EV_A"", ""EV_A_""" 4
4403 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4404 .IX Item "EV_A, EV_A_"
4405 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4406 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4407 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4408 .Sp
4409 .Vb 3
4410 \& ev_unref (EV_A);
4411 \& ev_timer_add (EV_A_ watcher);
4412 \& ev_run (EV_A_ 0);
4413 .Ve
4414 .Sp
4415 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4416 which is often provided by the following macro.
4417 .ie n .IP """EV_P"", ""EV_P_""" 4
4418 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4419 .IX Item "EV_P, EV_P_"
4420 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4421 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4422 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4423 .Sp
4424 .Vb 2
4425 \& // this is how ev_unref is being declared
4426 \& static void ev_unref (EV_P);
4427 \&
4428 \& // this is how you can declare your typical callback
4429 \& static void cb (EV_P_ ev_timer *w, int revents)
4430 .Ve
4431 .Sp
4432 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4433 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4434 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4435 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4436 .IX Item "EV_DEFAULT, EV_DEFAULT_"
4437 Similar to the other two macros, this gives you the value of the default
4438 loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4439 will be initialised if it isn't already initialised.
4440 .Sp
4441 For non-multiplicity builds, these macros do nothing, so you always have
4442 to initialise the loop somewhere.
4443 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4444 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4445 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4446 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4447 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4448 is undefined when the default loop has not been initialised by a previous
4449 execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4450 .Sp
4451 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4452 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4453 .PP
4454 Example: Declare and initialise a check watcher, utilising the above
4455 macros so it will work regardless of whether multiple loops are supported
4456 or not.
4457 .PP
4458 .Vb 5
4459 \& static void
4460 \& check_cb (EV_P_ ev_timer *w, int revents)
4461 \& {
4462 \& ev_check_stop (EV_A_ w);
4463 \& }
4464 \&
4465 \& ev_check check;
4466 \& ev_check_init (&check, check_cb);
4467 \& ev_check_start (EV_DEFAULT_ &check);
4468 \& ev_run (EV_DEFAULT_ 0);
4469 .Ve
4470 .SH "EMBEDDING"
4471 .IX Header "EMBEDDING"
4472 Libev can (and often is) directly embedded into host
4473 applications. Examples of applications that embed it include the Deliantra
4474 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4475 and rxvt-unicode.
4476 .PP
4477 The goal is to enable you to just copy the necessary files into your
4478 source directory without having to change even a single line in them, so
4479 you can easily upgrade by simply copying (or having a checked-out copy of
4480 libev somewhere in your source tree).
4481 .SS "\s-1FILESETS\s0"
4482 .IX Subsection "FILESETS"
4483 Depending on what features you need you need to include one or more sets of files
4484 in your application.
4485 .PP
4486 \fI\s-1CORE EVENT LOOP\s0\fR
4487 .IX Subsection "CORE EVENT LOOP"
4488 .PP
4489 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4490 configuration (no autoconf):
4491 .PP
4492 .Vb 2
4493 \& #define EV_STANDALONE 1
4494 \& #include "ev.c"
4495 .Ve
4496 .PP
4497 This will automatically include \fIev.h\fR, too, and should be done in a
4498 single C source file only to provide the function implementations. To use
4499 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API \s0(best
4500 done by writing a wrapper around \fIev.h\fR that you can include instead and
4501 where you can put other configuration options):
4502 .PP
4503 .Vb 2
4504 \& #define EV_STANDALONE 1
4505 \& #include "ev.h"
4506 .Ve
4507 .PP
4508 Both header files and implementation files can be compiled with a \*(C+
4509 compiler (at least, that's a stated goal, and breakage will be treated
4510 as a bug).
4511 .PP
4512 You need the following files in your source tree, or in a directory
4513 in your include path (e.g. in libev/ when using \-Ilibev):
4514 .PP
4515 .Vb 4
4516 \& ev.h
4517 \& ev.c
4518 \& ev_vars.h
4519 \& ev_wrap.h
4520 \&
4521 \& ev_win32.c required on win32 platforms only
4522 \&
4523 \& ev_select.c only when select backend is enabled (which is enabled by default)
4524 \& ev_poll.c only when poll backend is enabled (disabled by default)
4525 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4526 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4527 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4528 .Ve
4529 .PP
4530 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4531 to compile this single file.
4532 .PP
4533 \fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
4534 .IX Subsection "LIBEVENT COMPATIBILITY API"
4535 .PP
4536 To include the libevent compatibility \s-1API,\s0 also include:
4537 .PP
4538 .Vb 1
4539 \& #include "event.c"
4540 .Ve
4541 .PP
4542 in the file including \fIev.c\fR, and:
4543 .PP
4544 .Vb 1
4545 \& #include "event.h"
4546 .Ve
4547 .PP
4548 in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4549 .PP
4550 You need the following additional files for this:
4551 .PP
4552 .Vb 2
4553 \& event.h
4554 \& event.c
4555 .Ve
4556 .PP
4557 \fI\s-1AUTOCONF SUPPORT\s0\fR
4558 .IX Subsection "AUTOCONF SUPPORT"
4559 .PP
4560 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4561 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4562 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4563 include \fIconfig.h\fR and configure itself accordingly.
4564 .PP
4565 For this of course you need the m4 file:
4566 .PP
4567 .Vb 1
4568 \& libev.m4
4569 .Ve
4570 .SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
4571 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4572 Libev can be configured via a variety of preprocessor symbols you have to
4573 define before including (or compiling) any of its files. The default in
4574 the absence of autoconf is documented for every option.
4575 .PP
4576 Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4577 values when compiling libev vs. including \fIev.h\fR, so it is permissible
4578 to redefine them before including \fIev.h\fR without breaking compatibility
4579 to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4580 users of libev and the libev code itself must be compiled with compatible
4581 settings.
4582 .IP "\s-1EV_COMPAT3 \s0(h)" 4
4583 .IX Item "EV_COMPAT3 (h)"
4584 Backwards compatibility is a major concern for libev. This is why this
4585 release of libev comes with wrappers for the functions and symbols that
4586 have been renamed between libev version 3 and 4.
4587 .Sp
4588 You can disable these wrappers (to test compatibility with future
4589 versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4590 sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4591 from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4592 typedef in that case.
4593 .Sp
4594 In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4595 and in some even more future version the compatibility code will be
4596 removed completely.
4597 .IP "\s-1EV_STANDALONE \s0(h)" 4
4598 .IX Item "EV_STANDALONE (h)"
4599 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4600 keeps libev from including \fIconfig.h\fR, and it also defines dummy
4601 implementations for some libevent functions (such as logging, which is not
4602 supported). It will also not define any of the structs usually found in
4603 \&\fIevent.h\fR that are not directly supported by the libev core alone.
4604 .Sp
4605 In standalone mode, libev will still try to automatically deduce the
4606 configuration, but has to be more conservative.
4607 .IP "\s-1EV_USE_FLOOR\s0" 4
4608 .IX Item "EV_USE_FLOOR"
4609 If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4610 periodic reschedule calculations, otherwise libev will fall back on a
4611 portable (slower) implementation. If you enable this, you usually have to
4612 link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4613 function is not available will fail, so the safe default is to not enable
4614 this.
4615 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4616 .IX Item "EV_USE_MONOTONIC"
4617 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4618 monotonic clock option at both compile time and runtime. Otherwise no
4619 use of the monotonic clock option will be attempted. If you enable this,
4620 you usually have to link against librt or something similar. Enabling it
4621 when the functionality isn't available is safe, though, although you have
4622 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4623 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4624 .IP "\s-1EV_USE_REALTIME\s0" 4
4625 .IX Item "EV_USE_REALTIME"
4626 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4627 real-time clock option at compile time (and assume its availability
4628 at runtime if successful). Otherwise no use of the real-time clock
4629 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4630 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4631 correctness. See the note about libraries in the description of
4632 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4633 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4634 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4635 .IX Item "EV_USE_CLOCK_SYSCALL"
4636 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4637 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4638 exists 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
4639 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4640 programs needlessly. Using a direct syscall is slightly slower (in
4641 theory), because no optimised vdso implementation can be used, but avoids
4642 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4643 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4644 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4645 .IX Item "EV_USE_NANOSLEEP"
4646 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4647 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4648 .IP "\s-1EV_USE_EVENTFD\s0" 4
4649 .IX Item "EV_USE_EVENTFD"
4650 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4651 available and will probe for kernel support at runtime. This will improve
4652 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4653 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4654 2.7 or newer, otherwise disabled.
4655 .IP "\s-1EV_USE_SELECT\s0" 4
4656 .IX Item "EV_USE_SELECT"
4657 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4658 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4659 other method takes over, select will be it. Otherwise the select backend
4660 will not be compiled in.
4661 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4662 .IX Item "EV_SELECT_USE_FD_SET"
4663 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4664 structure. This is useful if libev doesn't compile due to a missing
4665 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4666 on exotic systems. This usually limits the range of file descriptors to
4667 some low limit such as 1024 or might have other limitations (winsocket
4668 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4669 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4670 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4671 .IX Item "EV_SELECT_IS_WINSOCKET"
4672 When defined to \f(CW1\fR, the select backend will assume that
4673 select/socket/connect etc. don't understand file descriptors but
4674 wants osf handles on win32 (this is the case when the select to
4675 be used is the winsock select). This means that it will call
4676 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4677 it is assumed that all these functions actually work on fds, even
4678 on win32. Should not be defined on non\-win32 platforms.
4679 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4680 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4681 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4682 file descriptors to socket handles. When not defining this symbol (the
4683 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4684 correct. In some cases, programs use their own file descriptor management,
4685 in which case they can provide this function to map fds to socket handles.
4686 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4687 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4688 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4689 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4690 their own fd to handle mapping, overwriting this function makes it easier
4691 to do so. This can be done by defining this macro to an appropriate value.
4692 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4693 .IX Item "EV_WIN32_CLOSE_FD(fd)"
4694 If programs implement their own fd to handle mapping on win32, then this
4695 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4696 file descriptors again. Note that the replacement function has to close
4697 the underlying \s-1OS\s0 handle.
4698 .IP "\s-1EV_USE_WSASOCKET\s0" 4
4699 .IX Item "EV_USE_WSASOCKET"
4700 If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4701 communication socket, which works better in some environments. Otherwise,
4702 the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4703 environments.
4704 .IP "\s-1EV_USE_POLL\s0" 4
4705 .IX Item "EV_USE_POLL"
4706 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4707 backend. Otherwise it will be enabled on non\-win32 platforms. It
4708 takes precedence over select.
4709 .IP "\s-1EV_USE_EPOLL\s0" 4
4710 .IX Item "EV_USE_EPOLL"
4711 If defined to be \f(CW1\fR, libev will compile in support for the Linux
4712 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4713 otherwise another method will be used as fallback. This is the preferred
4714 backend for GNU/Linux systems. If undefined, it will be enabled if the
4715 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4716 .IP "\s-1EV_USE_KQUEUE\s0" 4
4717 .IX Item "EV_USE_KQUEUE"
4718 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4719 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4720 otherwise another method will be used as fallback. This is the preferred
4721 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4722 supports some types of fds correctly (the only platform we found that
4723 supports ptys for example was NetBSD), so kqueue might be compiled in, but
4724 not be used unless explicitly requested. The best way to use it is to find
4725 out whether kqueue supports your type of fd properly and use an embedded
4726 kqueue loop.
4727 .IP "\s-1EV_USE_PORT\s0" 4
4728 .IX Item "EV_USE_PORT"
4729 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4730 10 port style backend. Its availability will be detected at runtime,
4731 otherwise another method will be used as fallback. This is the preferred
4732 backend for Solaris 10 systems.
4733 .IP "\s-1EV_USE_DEVPOLL\s0" 4
4734 .IX Item "EV_USE_DEVPOLL"
4735 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4736 .IP "\s-1EV_USE_INOTIFY\s0" 4
4737 .IX Item "EV_USE_INOTIFY"
4738 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4739 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4740 be detected at runtime. If undefined, it will be enabled if the headers
4741 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4742 .IP "\s-1EV_NO_SMP\s0" 4
4743 .IX Item "EV_NO_SMP"
4744 If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4745 between threads, that is, threads can be used, but threads never run on
4746 different cpus (or different cpu cores). This reduces dependencies
4747 and makes libev faster.
4748 .IP "\s-1EV_NO_THREADS\s0" 4
4749 .IX Item "EV_NO_THREADS"
4750 If defined to be \f(CW1\fR, libev will assume that it will never be called from
4751 different threads (that includes signal handlers), which is a stronger
4752 assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4753 libev faster.
4754 .IP "\s-1EV_ATOMIC_T\s0" 4
4755 .IX Item "EV_ATOMIC_T"
4756 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4757 access is atomic with respect to other threads or signal contexts. No
4758 such type is easily found in the C language, so you can provide your own
4759 type that you know is safe for your purposes. It is used both for signal
4760 handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4761 watchers.
4762 .Sp
4763 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4764 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4765 .IP "\s-1EV_H \s0(h)" 4
4766 .IX Item "EV_H (h)"
4767 The name of the \fIev.h\fR header file used to include it. The default if
4768 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4769 used to virtually rename the \fIev.h\fR header file in case of conflicts.
4770 .IP "\s-1EV_CONFIG_H \s0(h)" 4
4771 .IX Item "EV_CONFIG_H (h)"
4772 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4773 \&\fIev.c\fR's idea of where to find the \fIconfig.h