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Revision: 1.60
Committed: Mon Jan 28 12:23:02 2008 UTC (16 years, 5 months ago) by root
Branch: MAIN
CVS Tags: rel-3_0
Changes since 1.59: +365 -335 lines
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File Contents

# Content
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132 .\" ========================================================================
133 .\"
134 .IX Title "EV 1"
135 .TH EV 1 "2008-01-28" "perl v5.10.0" "User Contributed Perl Documentation"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137 .\" way too many mistakes in technical documents.
138 .if n .ad l
139 .nh
140 .SH "NAME"
141 libev \- a high performance full\-featured event loop written in C
143 .IX Header "SYNOPSIS"
144 .Vb 1
145 \& #include <ev.h>
146 .Ve
147 .Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
148 .IX Subsection "EXAMPLE PROGRAM"
149 .Vb 1
150 \& #include <ev.h>
151 \&
152 \& ev_io stdin_watcher;
153 \& ev_timer timeout_watcher;
154 \&
155 \& /* called when data readable on stdin */
156 \& static void
157 \& stdin_cb (EV_P_ struct ev_io *w, int revents)
158 \& {
159 \& /* puts ("stdin ready"); */
160 \& ev_io_stop (EV_A_ w); /* just a syntax example */
161 \& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
162 \& }
163 \&
164 \& static void
165 \& timeout_cb (EV_P_ struct ev_timer *w, int revents)
166 \& {
167 \& /* puts ("timeout"); */
168 \& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
169 \& }
170 \&
171 \& int
172 \& main (void)
173 \& {
174 \& struct ev_loop *loop = ev_default_loop (0);
175 \&
176 \& /* initialise an io watcher, then start it */
177 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
178 \& ev_io_start (loop, &stdin_watcher);
179 \&
180 \& /* simple non\-repeating 5.5 second timeout */
181 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
182 \& ev_timer_start (loop, &timeout_watcher);
183 \&
184 \& /* loop till timeout or data ready */
185 \& ev_loop (loop, 0);
186 \&
187 \& return 0;
188 \& }
189 .Ve
191 .IX Header "DESCRIPTION"
192 The newest version of this document is also available as a html-formatted
193 web page you might find easier to navigate when reading it for the first
194 time: <>.
195 .PP
196 Libev is an event loop: you register interest in certain events (such as a
197 file descriptor being readable or a timeout occurring), and it will manage
198 these event sources and provide your program with events.
199 .PP
200 To do this, it must take more or less complete control over your process
201 (or thread) by executing the \fIevent loop\fR handler, and will then
202 communicate events via a callback mechanism.
203 .PP
204 You register interest in certain events by registering so-called \fIevent
205 watchers\fR, which are relatively small C structures you initialise with the
206 details of the event, and then hand it over to libev by \fIstarting\fR the
207 watcher.
208 .Sh "\s-1FEATURES\s0"
209 .IX Subsection "FEATURES"
210 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
211 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
212 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
213 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
214 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
215 (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
216 watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
217 \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
218 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
219 (\f(CW\*(C`ev_fork\*(C'\fR).
220 .PP
221 It also is quite fast (see this
222 benchmark comparing it to libevent
223 for example).
224 .Sh "\s-1CONVENTIONS\s0"
225 .IX Subsection "CONVENTIONS"
226 Libev is very configurable. In this manual the default configuration will
227 be described, which supports multiple event loops. For more info about
228 various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
229 this manual. If libev was configured without support for multiple event
230 loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
231 (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
232 .Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
234 Libev represents time as a single floating point number, representing the
235 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
236 the beginning of 1970, details are complicated, don't ask). This type is
237 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
238 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
239 it, you should treat it as some floatingpoint value. Unlike the name
240 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
241 throughout libev.
244 These functions can be called anytime, even before initialising the
245 library in any way.
246 .IP "ev_tstamp ev_time ()" 4
247 .IX Item "ev_tstamp ev_time ()"
248 Returns the current time as libev would use it. Please note that the
249 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
250 you actually want to know.
251 .IP "ev_sleep (ev_tstamp interval)" 4
252 .IX Item "ev_sleep (ev_tstamp interval)"
253 Sleep for the given interval: The current thread will be blocked until
254 either it is interrupted or the given time interval has passed. Basically
255 this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
256 .IP "int ev_version_major ()" 4
257 .IX Item "int ev_version_major ()"
258 .PD 0
259 .IP "int ev_version_minor ()" 4
260 .IX Item "int ev_version_minor ()"
261 .PD
262 You can find out the major and minor \s-1ABI\s0 version numbers of the library
263 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
264 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
265 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
266 version of the library your program was compiled against.
267 .Sp
268 These version numbers refer to the \s-1ABI\s0 version of the library, not the
269 release version.
270 .Sp
271 Usually, it's a good idea to terminate if the major versions mismatch,
272 as this indicates an incompatible change. Minor versions are usually
273 compatible to older versions, so a larger minor version alone is usually
274 not a problem.
275 .Sp
276 Example: Make sure we haven't accidentally been linked against the wrong
277 version.
278 .Sp
279 .Vb 3
280 \& assert (("libev version mismatch",
281 \& ev_version_major () == EV_VERSION_MAJOR
282 \& && ev_version_minor () >= EV_VERSION_MINOR));
283 .Ve
284 .IP "unsigned int ev_supported_backends ()" 4
285 .IX Item "unsigned int ev_supported_backends ()"
286 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
287 value) compiled into this binary of libev (independent of their
288 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
289 a description of the set values.
290 .Sp
291 Example: make sure we have the epoll method, because yeah this is cool and
292 a must have and can we have a torrent of it please!!!11
293 .Sp
294 .Vb 2
295 \& assert (("sorry, no epoll, no sex",
296 \& ev_supported_backends () & EVBACKEND_EPOLL));
297 .Ve
298 .IP "unsigned int ev_recommended_backends ()" 4
299 .IX Item "unsigned int ev_recommended_backends ()"
300 Return the set of all backends compiled into this binary of libev and also
301 recommended for this platform. This set is often smaller than the one
302 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
303 most BSDs and will not be autodetected unless you explicitly request it
304 (assuming you know what you are doing). This is the set of backends that
305 libev will probe for if you specify no backends explicitly.
306 .IP "unsigned int ev_embeddable_backends ()" 4
307 .IX Item "unsigned int ev_embeddable_backends ()"
308 Returns the set of backends that are embeddable in other event loops. This
309 is the theoretical, all-platform, value. To find which backends
310 might be supported on the current system, you would need to look at
311 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
312 recommended ones.
313 .Sp
314 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
315 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
316 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
317 Sets the allocation function to use (the prototype is similar \- the
318 semantics is identical \- to the realloc C function). It is used to
319 allocate and free memory (no surprises here). If it returns zero when
320 memory needs to be allocated, the library might abort or take some
321 potentially destructive action. The default is your system realloc
322 function.
323 .Sp
324 You could override this function in high-availability programs to, say,
325 free some memory if it cannot allocate memory, to use a special allocator,
326 or even to sleep a while and retry until some memory is available.
327 .Sp
328 Example: Replace the libev allocator with one that waits a bit and then
329 retries).
330 .Sp
331 .Vb 6
332 \& static void *
333 \& persistent_realloc (void *ptr, size_t size)
334 \& {
335 \& for (;;)
336 \& {
337 \& void *newptr = realloc (ptr, size);
338 \&
339 \& if (newptr)
340 \& return newptr;
341 \&
342 \& sleep (60);
343 \& }
344 \& }
345 \&
346 \& ...
347 \& ev_set_allocator (persistent_realloc);
348 .Ve
349 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
350 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
351 Set the callback function to call on a retryable syscall error (such
352 as failed select, poll, epoll_wait). The message is a printable string
353 indicating the system call or subsystem causing the problem. If this
354 callback is set, then libev will expect it to remedy the sitution, no
355 matter what, when it returns. That is, libev will generally retry the
356 requested operation, or, if the condition doesn't go away, do bad stuff
357 (such as abort).
358 .Sp
359 Example: This is basically the same thing that libev does internally, too.
360 .Sp
361 .Vb 6
362 \& static void
363 \& fatal_error (const char *msg)
364 \& {
365 \& perror (msg);
366 \& abort ();
367 \& }
368 \&
369 \& ...
370 \& ev_set_syserr_cb (fatal_error);
371 .Ve
374 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
375 types of such loops, the \fIdefault\fR loop, which supports signals and child
376 events, and dynamically created loops which do not.
377 .PP
378 If you use threads, a common model is to run the default event loop
379 in your main thread (or in a separate thread) and for each thread you
380 create, you also create another event loop. Libev itself does no locking
381 whatsoever, so if you mix calls to the same event loop in different
382 threads, make sure you lock (this is usually a bad idea, though, even if
383 done correctly, because it's hideous and inefficient).
384 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
385 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
386 This will initialise the default event loop if it hasn't been initialised
387 yet and return it. If the default loop could not be initialised, returns
388 false. If it already was initialised it simply returns it (and ignores the
389 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
390 .Sp
391 If you don't know what event loop to use, use the one returned from this
392 function.
393 .Sp
394 The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
395 \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
396 for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either
397 create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
398 can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
399 \&\f(CW\*(C`ev_default_init\*(C'\fR.
400 .Sp
401 The flags argument can be used to specify special behaviour or specific
402 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
403 .Sp
404 The following flags are supported:
405 .RS 4
406 .ie n .IP """EVFLAG_AUTO""" 4
407 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
408 .IX Item "EVFLAG_AUTO"
409 The default flags value. Use this if you have no clue (it's the right
410 thing, believe me).
411 .ie n .IP """EVFLAG_NOENV""" 4
412 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
414 If this flag bit is ored into the flag value (or the program runs setuid
415 or setgid) then libev will \fInot\fR look at the environment variable
416 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
417 override the flags completely if it is found in the environment. This is
418 useful to try out specific backends to test their performance, or to work
419 around bugs.
420 .ie n .IP """EVFLAG_FORKCHECK""" 4
421 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
423 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
424 a fork, you can also make libev check for a fork in each iteration by
425 enabling this flag.
426 .Sp
427 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
428 and thus this might slow down your event loop if you do a lot of loop
429 iterations and little real work, but is usually not noticeable (on my
430 Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
431 without a syscall and thus \fIvery\fR fast, but my Linux system also has
432 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
433 .Sp
434 The big advantage of this flag is that you can forget about fork (and
435 forget about forgetting to tell libev about forking) when you use this
436 flag.
437 .Sp
438 This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
439 environment variable.
440 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
441 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
442 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
443 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
444 libev tries to roll its own fd_set with no limits on the number of fds,
445 but if that fails, expect a fairly low limit on the number of fds when
446 using this backend. It doesn't scale too well (O(highest_fd)), but its
447 usually the fastest backend for a low number of (low-numbered :) fds.
448 .Sp
449 To get good performance out of this backend you need a high amount of
450 parallelity (most of the file descriptors should be busy). If you are
451 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
452 connections as possible during one iteration. You might also want to have
453 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
454 readyness notifications you get per iteration.
455 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
456 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
457 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
458 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
459 than select, but handles sparse fds better and has no artificial
460 limit on the number of fds you can use (except it will slow down
461 considerably with a lot of inactive fds). It scales similarly to select,
462 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
463 performance tips.
464 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
465 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
466 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
467 For few fds, this backend is a bit little slower than poll and select,
468 but it scales phenomenally better. While poll and select usually scale
469 like O(total_fds) where n is the total number of fds (or the highest fd),
470 epoll scales either O(1) or O(active_fds). The epoll design has a number
471 of shortcomings, such as silently dropping events in some hard-to-detect
472 cases and rewiring a syscall per fd change, no fork support and bad
473 support for dup.
474 .Sp
475 While stopping, setting and starting an I/O watcher in the same iteration
476 will result in some caching, there is still a syscall per such incident
477 (because the fd could point to a different file description now), so its
478 best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
479 very well if you register events for both fds.
480 .Sp
481 Please note that epoll sometimes generates spurious notifications, so you
482 need to use non-blocking I/O or other means to avoid blocking when no data
483 (or space) is available.
484 .Sp
485 Best performance from this backend is achieved by not unregistering all
486 watchers for a file descriptor until it has been closed, if possible, i.e.
487 keep at least one watcher active per fd at all times.
488 .Sp
489 While nominally embeddeble in other event loops, this feature is broken in
490 all kernel versions tested so far.
491 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
492 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
493 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
494 Kqueue deserves special mention, as at the time of this writing, it
495 was broken on all BSDs except NetBSD (usually it doesn't work reliably
496 with anything but sockets and pipes, except on Darwin, where of course
497 it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
498 unless you explicitly specify it explicitly in the flags (i.e. using
499 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
500 system like NetBSD.
501 .Sp
502 You still can embed kqueue into a normal poll or select backend and use it
503 only for sockets (after having made sure that sockets work with kqueue on
504 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
505 .Sp
506 It scales in the same way as the epoll backend, but the interface to the
507 kernel is more efficient (which says nothing about its actual speed, of
508 course). While stopping, setting and starting an I/O watcher does never
509 cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
510 two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
511 drops fds silently in similarly hard-to-detect cases.
512 .Sp
513 This backend usually performs well under most conditions.
514 .Sp
515 While nominally embeddable in other event loops, this doesn't work
516 everywhere, so you might need to test for this. And since it is broken
517 almost everywhere, you should only use it when you have a lot of sockets
518 (for which it usually works), by embedding it into another event loop
519 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
520 sockets.
521 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
522 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
523 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
524 This is not implemented yet (and might never be, unless you send me an
525 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
526 and is not embeddable, which would limit the usefulness of this backend
527 immensely.
528 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
529 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
530 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
531 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
532 it's really slow, but it still scales very well (O(active_fds)).
533 .Sp
534 Please note that solaris event ports can deliver a lot of spurious
535 notifications, so you need to use non-blocking I/O or other means to avoid
536 blocking when no data (or space) is available.
537 .Sp
538 While this backend scales well, it requires one system call per active
539 file descriptor per loop iteration. For small and medium numbers of file
540 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
541 might perform better.
542 .Sp
543 On the positive side, ignoring the spurious readyness notifications, this
544 backend actually performed to specification in all tests and is fully
545 embeddable, which is a rare feat among the OS-specific backends.
546 .ie n .IP """EVBACKEND_ALL""" 4
547 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
549 Try all backends (even potentially broken ones that wouldn't be tried
550 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
552 .Sp
553 It is definitely not recommended to use this flag.
554 .RE
555 .RS 4
556 .Sp
557 If one or more of these are ored into the flags value, then only these
558 backends will be tried (in the reverse order as listed here). If none are
559 specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
560 .Sp
561 The most typical usage is like this:
562 .Sp
563 .Vb 2
564 \& if (!ev_default_loop (0))
565 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
566 .Ve
567 .Sp
568 Restrict libev to the select and poll backends, and do not allow
569 environment settings to be taken into account:
570 .Sp
571 .Vb 1
573 .Ve
574 .Sp
575 Use whatever libev has to offer, but make sure that kqueue is used if
576 available (warning, breaks stuff, best use only with your own private
577 event loop and only if you know the \s-1OS\s0 supports your types of fds):
578 .Sp
579 .Vb 1
580 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
581 .Ve
582 .RE
583 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
584 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
585 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
586 always distinct from the default loop. Unlike the default loop, it cannot
587 handle signal and child watchers, and attempts to do so will be greeted by
588 undefined behaviour (or a failed assertion if assertions are enabled).
589 .Sp
590 Example: Try to create a event loop that uses epoll and nothing else.
591 .Sp
592 .Vb 3
593 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
594 \& if (!epoller)
595 \& fatal ("no epoll found here, maybe it hides under your chair");
596 .Ve
597 .IP "ev_default_destroy ()" 4
598 .IX Item "ev_default_destroy ()"
599 Destroys the default loop again (frees all memory and kernel state
600 etc.). None of the active event watchers will be stopped in the normal
601 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
602 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
603 calling this function, or cope with the fact afterwards (which is usually
604 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
605 for example).
606 .Sp
607 Note that certain global state, such as signal state, will not be freed by
608 this function, and related watchers (such as signal and child watchers)
609 would need to be stopped manually.
610 .Sp
611 In general it is not advisable to call this function except in the
612 rare occasion where you really need to free e.g. the signal handling
613 pipe fds. If you need dynamically allocated loops it is better to use
614 \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
615 .IP "ev_loop_destroy (loop)" 4
616 .IX Item "ev_loop_destroy (loop)"
617 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
618 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
619 .IP "ev_default_fork ()" 4
620 .IX Item "ev_default_fork ()"
621 This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
622 to reinitialise the kernel state for backends that have one. Despite the
623 name, you can call it anytime, but it makes most sense after forking, in
624 the child process (or both child and parent, but that again makes little
625 sense). You \fImust\fR call it in the child before using any of the libev
626 functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
627 .Sp
628 On the other hand, you only need to call this function in the child
629 process if and only if you want to use the event library in the child. If
630 you just fork+exec, you don't have to call it at all.
631 .Sp
632 The function itself is quite fast and it's usually not a problem to call
633 it just in case after a fork. To make this easy, the function will fit in
634 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
635 .Sp
636 .Vb 1
637 \& pthread_atfork (0, 0, ev_default_fork);
638 .Ve
639 .IP "ev_loop_fork (loop)" 4
640 .IX Item "ev_loop_fork (loop)"
641 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
642 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
643 after fork, and how you do this is entirely your own problem.
644 .IP "unsigned int ev_loop_count (loop)" 4
645 .IX Item "unsigned int ev_loop_count (loop)"
646 Returns the count of loop iterations for the loop, which is identical to
647 the number of times libev did poll for new events. It starts at \f(CW0\fR and
648 happily wraps around with enough iterations.
649 .Sp
650 This value can sometimes be useful as a generation counter of sorts (it
651 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
652 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
653 .IP "unsigned int ev_backend (loop)" 4
654 .IX Item "unsigned int ev_backend (loop)"
655 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
656 use.
657 .IP "ev_tstamp ev_now (loop)" 4
658 .IX Item "ev_tstamp ev_now (loop)"
659 Returns the current \*(L"event loop time\*(R", which is the time the event loop
660 received events and started processing them. This timestamp does not
661 change as long as callbacks are being processed, and this is also the base
662 time used for relative timers. You can treat it as the timestamp of the
663 event occurring (or more correctly, libev finding out about it).
664 .IP "ev_loop (loop, int flags)" 4
665 .IX Item "ev_loop (loop, int flags)"
666 Finally, this is it, the event handler. This function usually is called
667 after you initialised all your watchers and you want to start handling
668 events.
669 .Sp
670 If the flags argument is specified as \f(CW0\fR, it will not return until
671 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
672 .Sp
673 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
674 relying on all watchers to be stopped when deciding when a program has
675 finished (especially in interactive programs), but having a program that
676 automatically loops as long as it has to and no longer by virtue of
677 relying on its watchers stopping correctly is a thing of beauty.
678 .Sp
679 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
680 those events and any outstanding ones, but will not block your process in
681 case there are no events and will return after one iteration of the loop.
682 .Sp
683 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
684 neccessary) and will handle those and any outstanding ones. It will block
685 your process until at least one new event arrives, and will return after
686 one iteration of the loop. This is useful if you are waiting for some
687 external event in conjunction with something not expressible using other
688 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
689 usually a better approach for this kind of thing.
690 .Sp
691 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
692 .Sp
693 .Vb 10
694 \& \- Before the first iteration, call any pending watchers.
695 \& * If EVFLAG_FORKCHECK was used, check for a fork.
696 \& \- If a fork was detected, queue and call all fork watchers.
697 \& \- Queue and call all prepare watchers.
698 \& \- If we have been forked, recreate the kernel state.
699 \& \- Update the kernel state with all outstanding changes.
700 \& \- Update the "event loop time".
701 \& \- Calculate for how long to sleep or block, if at all
702 \& (active idle watchers, EVLOOP_NONBLOCK or not having
703 \& any active watchers at all will result in not sleeping).
704 \& \- Sleep if the I/O and timer collect interval say so.
705 \& \- Block the process, waiting for any events.
706 \& \- Queue all outstanding I/O (fd) events.
707 \& \- Update the "event loop time" and do time jump handling.
708 \& \- Queue all outstanding timers.
709 \& \- Queue all outstanding periodics.
710 \& \- If no events are pending now, queue all idle watchers.
711 \& \- Queue all check watchers.
712 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
713 \& Signals and child watchers are implemented as I/O watchers, and will
714 \& be handled here by queueing them when their watcher gets executed.
715 \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
716 \& were used, or there are no active watchers, return, otherwise
717 \& continue with step *.
718 .Ve
719 .Sp
720 Example: Queue some jobs and then loop until no events are outstanding
721 anymore.
722 .Sp
723 .Vb 4
724 \& ... queue jobs here, make sure they register event watchers as long
725 \& ... as they still have work to do (even an idle watcher will do..)
726 \& ev_loop (my_loop, 0);
727 \& ... jobs done. yeah!
728 .Ve
729 .IP "ev_unloop (loop, how)" 4
730 .IX Item "ev_unloop (loop, how)"
731 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
732 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
733 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
734 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
735 .Sp
736 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
737 .IP "ev_ref (loop)" 4
738 .IX Item "ev_ref (loop)"
739 .PD 0
740 .IP "ev_unref (loop)" 4
741 .IX Item "ev_unref (loop)"
742 .PD
743 Ref/unref can be used to add or remove a reference count on the event
744 loop: Every watcher keeps one reference, and as long as the reference
745 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
746 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
747 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
748 example, libev itself uses this for its internal signal pipe: It is not
749 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
750 no event watchers registered by it are active. It is also an excellent
751 way to do this for generic recurring timers or from within third-party
752 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
753 (but only if the watcher wasn't active before, or was active before,
754 respectively).
755 .Sp
756 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
757 running when nothing else is active.
758 .Sp
759 .Vb 4
760 \& struct ev_signal exitsig;
761 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
762 \& ev_signal_start (loop, &exitsig);
763 \& evf_unref (loop);
764 .Ve
765 .Sp
766 Example: For some weird reason, unregister the above signal handler again.
767 .Sp
768 .Vb 2
769 \& ev_ref (loop);
770 \& ev_signal_stop (loop, &exitsig);
771 .Ve
772 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
773 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
774 .PD 0
775 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
776 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
777 .PD
778 These advanced functions influence the time that libev will spend waiting
779 for events. Both are by default \f(CW0\fR, meaning that libev will try to
780 invoke timer/periodic callbacks and I/O callbacks with minimum latency.
781 .Sp
782 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
783 allows libev to delay invocation of I/O and timer/periodic callbacks to
784 increase efficiency of loop iterations.
785 .Sp
786 The background is that sometimes your program runs just fast enough to
787 handle one (or very few) event(s) per loop iteration. While this makes
788 the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
789 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
790 overhead for the actual polling but can deliver many events at once.
791 .Sp
792 By setting a higher \fIio collect interval\fR you allow libev to spend more
793 time collecting I/O events, so you can handle more events per iteration,
794 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
795 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
796 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
797 .Sp
798 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
799 to spend more time collecting timeouts, at the expense of increased
800 latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
801 will not be affected. Setting this to a non-null value will not introduce
802 any overhead in libev.
803 .Sp
804 Many (busy) programs can usually benefit by setting the io collect
805 interval to a value near \f(CW0.1\fR or so, which is often enough for
806 interactive servers (of course not for games), likewise for timeouts. It
807 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
808 as this approsaches the timing granularity of most systems.
811 A watcher is a structure that you create and register to record your
812 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
813 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
814 .PP
815 .Vb 5
816 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
817 \& {
818 \& ev_io_stop (w);
819 \& ev_unloop (loop, EVUNLOOP_ALL);
820 \& }
821 \&
822 \& struct ev_loop *loop = ev_default_loop (0);
823 \& struct ev_io stdin_watcher;
824 \& ev_init (&stdin_watcher, my_cb);
825 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
826 \& ev_io_start (loop, &stdin_watcher);
827 \& ev_loop (loop, 0);
828 .Ve
829 .PP
830 As you can see, you are responsible for allocating the memory for your
831 watcher structures (and it is usually a bad idea to do this on the stack,
832 although this can sometimes be quite valid).
833 .PP
834 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
835 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
836 callback gets invoked each time the event occurs (or, in the case of io
837 watchers, each time the event loop detects that the file descriptor given
838 is readable and/or writable).
839 .PP
840 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
841 with arguments specific to this watcher type. There is also a macro
842 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
843 (watcher *, callback, ...)\*(C'\fR.
844 .PP
845 To make the watcher actually watch out for events, you have to start it
846 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
847 *)\*(C'\fR), and you can stop watching for events at any time by calling the
848 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
849 .PP
850 As long as your watcher is active (has been started but not stopped) you
851 must not touch the values stored in it. Most specifically you must never
852 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
853 .PP
854 Each and every callback receives the event loop pointer as first, the
855 registered watcher structure as second, and a bitset of received events as
856 third argument.
857 .PP
858 The received events usually include a single bit per event type received
859 (you can receive multiple events at the same time). The possible bit masks
860 are:
861 .ie n .IP """EV_READ""" 4
862 .el .IP "\f(CWEV_READ\fR" 4
863 .IX Item "EV_READ"
864 .PD 0
865 .ie n .IP """EV_WRITE""" 4
866 .el .IP "\f(CWEV_WRITE\fR" 4
867 .IX Item "EV_WRITE"
868 .PD
869 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
870 writable.
871 .ie n .IP """EV_TIMEOUT""" 4
872 .el .IP "\f(CWEV_TIMEOUT\fR" 4
873 .IX Item "EV_TIMEOUT"
874 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
875 .ie n .IP """EV_PERIODIC""" 4
876 .el .IP "\f(CWEV_PERIODIC\fR" 4
877 .IX Item "EV_PERIODIC"
878 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
879 .ie n .IP """EV_SIGNAL""" 4
880 .el .IP "\f(CWEV_SIGNAL\fR" 4
881 .IX Item "EV_SIGNAL"
882 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
883 .ie n .IP """EV_CHILD""" 4
884 .el .IP "\f(CWEV_CHILD\fR" 4
885 .IX Item "EV_CHILD"
886 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
887 .ie n .IP """EV_STAT""" 4
888 .el .IP "\f(CWEV_STAT\fR" 4
889 .IX Item "EV_STAT"
890 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
891 .ie n .IP """EV_IDLE""" 4
892 .el .IP "\f(CWEV_IDLE\fR" 4
893 .IX Item "EV_IDLE"
894 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
895 .ie n .IP """EV_PREPARE""" 4
896 .el .IP "\f(CWEV_PREPARE\fR" 4
897 .IX Item "EV_PREPARE"
898 .PD 0
899 .ie n .IP """EV_CHECK""" 4
900 .el .IP "\f(CWEV_CHECK\fR" 4
901 .IX Item "EV_CHECK"
902 .PD
903 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
904 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
905 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
906 received events. Callbacks of both watcher types can start and stop as
907 many watchers as they want, and all of them will be taken into account
908 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
909 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
910 .ie n .IP """EV_EMBED""" 4
911 .el .IP "\f(CWEV_EMBED\fR" 4
912 .IX Item "EV_EMBED"
913 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
914 .ie n .IP """EV_FORK""" 4
915 .el .IP "\f(CWEV_FORK\fR" 4
916 .IX Item "EV_FORK"
917 The event loop has been resumed in the child process after fork (see
918 \&\f(CW\*(C`ev_fork\*(C'\fR).
919 .ie n .IP """EV_ERROR""" 4
920 .el .IP "\f(CWEV_ERROR\fR" 4
921 .IX Item "EV_ERROR"
922 An unspecified error has occured, the watcher has been stopped. This might
923 happen because the watcher could not be properly started because libev
924 ran out of memory, a file descriptor was found to be closed or any other
925 problem. You best act on it by reporting the problem and somehow coping
926 with the watcher being stopped.
927 .Sp
928 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
929 for example it might indicate that a fd is readable or writable, and if
930 your callbacks is well-written it can just attempt the operation and cope
931 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
932 programs, though, so beware.
933 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
935 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
936 e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
937 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
938 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
939 .IX Item "ev_init (ev_TYPE *watcher, callback)"
940 This macro initialises the generic portion of a watcher. The contents
941 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
942 the generic parts of the watcher are initialised, you \fIneed\fR to call
943 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
944 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
945 which rolls both calls into one.
946 .Sp
947 You can reinitialise a watcher at any time as long as it has been stopped
948 (or never started) and there are no pending events outstanding.
949 .Sp
950 The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
951 int revents)\*(C'\fR.
952 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
953 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
954 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
955 This macro initialises the type-specific parts of a watcher. You need to
956 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
957 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
958 macro on a watcher that is active (it can be pending, however, which is a
959 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
960 .Sp
961 Although some watcher types do not have type-specific arguments
962 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
963 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
964 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
965 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
966 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
967 calls into a single call. This is the most convinient method to initialise
968 a watcher. The same limitations apply, of course.
969 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
970 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
971 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
972 Starts (activates) the given watcher. Only active watchers will receive
973 events. If the watcher is already active nothing will happen.
974 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
975 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
976 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
977 Stops the given watcher again (if active) and clears the pending
978 status. It is possible that stopped watchers are pending (for example,
979 non-repeating timers are being stopped when they become pending), but
980 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
981 you want to free or reuse the memory used by the watcher it is therefore a
982 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
983 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
984 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
985 Returns a true value iff the watcher is active (i.e. it has been started
986 and not yet been stopped). As long as a watcher is active you must not modify
987 it.
988 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
989 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
990 Returns a true value iff the watcher is pending, (i.e. it has outstanding
991 events but its callback has not yet been invoked). As long as a watcher
992 is pending (but not active) you must not call an init function on it (but
993 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
994 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
995 it).
996 .IP "callback ev_cb (ev_TYPE *watcher)" 4
997 .IX Item "callback ev_cb (ev_TYPE *watcher)"
998 Returns the callback currently set on the watcher.
999 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1000 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1001 Change the callback. You can change the callback at virtually any time
1002 (modulo threads).
1003 .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1004 .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1005 .PD 0
1006 .IP "int ev_priority (ev_TYPE *watcher)" 4
1007 .IX Item "int ev_priority (ev_TYPE *watcher)"
1008 .PD
1009 Set and query the priority of the watcher. The priority is a small
1010 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1011 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1012 before watchers with lower priority, but priority will not keep watchers
1013 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1014 .Sp
1015 This means that priorities are \fIonly\fR used for ordering callback
1016 invocation after new events have been received. This is useful, for
1017 example, to reduce latency after idling, or more often, to bind two
1018 watchers on the same event and make sure one is called first.
1019 .Sp
1020 If you need to suppress invocation when higher priority events are pending
1021 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1022 .Sp
1023 You \fImust not\fR change the priority of a watcher as long as it is active or
1024 pending.
1025 .Sp
1026 The default priority used by watchers when no priority has been set is
1027 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1028 .Sp
1029 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1030 fine, as long as you do not mind that the priority value you query might
1031 or might not have been adjusted to be within valid range.
1032 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1033 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1034 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
1035 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1036 can deal with that fact.
1037 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1038 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1039 If the watcher is pending, this function returns clears its pending status
1040 and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1041 watcher isn't pending it does nothing and returns \f(CW0\fR.
1042 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1044 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1045 and read at any time, libev will completely ignore it. This can be used
1046 to associate arbitrary data with your watcher. If you need more data and
1047 don't want to allocate memory and store a pointer to it in that data
1048 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1049 data:
1050 .PP
1051 .Vb 7
1052 \& struct my_io
1053 \& {
1054 \& struct ev_io io;
1055 \& int otherfd;
1056 \& void *somedata;
1057 \& struct whatever *mostinteresting;
1058 \& }
1059 .Ve
1060 .PP
1061 And since your callback will be called with a pointer to the watcher, you
1062 can cast it back to your own type:
1063 .PP
1064 .Vb 5
1065 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1066 \& {
1067 \& struct my_io *w = (struct my_io *)w_;
1068 \& ...
1069 \& }
1070 .Ve
1071 .PP
1072 More interesting and less C\-conformant ways of casting your callback type
1073 instead have been omitted.
1074 .PP
1075 Another common scenario is having some data structure with multiple
1076 watchers:
1077 .PP
1078 .Vb 6
1079 \& struct my_biggy
1080 \& {
1081 \& int some_data;
1082 \& ev_timer t1;
1083 \& ev_timer t2;
1084 \& }
1085 .Ve
1086 .PP
1087 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1088 you need to use \f(CW\*(C`offsetof\*(C'\fR:
1089 .PP
1090 .Vb 1
1091 \& #include <stddef.h>
1092 \&
1093 \& static void
1094 \& t1_cb (EV_P_ struct ev_timer *w, int revents)
1095 \& {
1096 \& struct my_biggy big = (struct my_biggy *
1097 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1098 \& }
1099 \&
1100 \& static void
1101 \& t2_cb (EV_P_ struct ev_timer *w, int revents)
1102 \& {
1103 \& struct my_biggy big = (struct my_biggy *
1104 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1105 \& }
1106 .Ve
1108 .IX Header "WATCHER TYPES"
1109 This section describes each watcher in detail, but will not repeat
1110 information given in the last section. Any initialisation/set macros,
1111 functions and members specific to the watcher type are explained.
1112 .PP
1113 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1114 while the watcher is active, you can look at the member and expect some
1115 sensible content, but you must not modify it (you can modify it while the
1116 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1117 means you can expect it to have some sensible content while the watcher
1118 is active, but you can also modify it. Modifying it may not do something
1119 sensible or take immediate effect (or do anything at all), but libev will
1120 not crash or malfunction in any way.
1121 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1122 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1123 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1124 I/O watchers check whether a file descriptor is readable or writable
1125 in each iteration of the event loop, or, more precisely, when reading
1126 would not block the process and writing would at least be able to write
1127 some data. This behaviour is called level-triggering because you keep
1128 receiving events as long as the condition persists. Remember you can stop
1129 the watcher if you don't want to act on the event and neither want to
1130 receive future events.
1131 .PP
1132 In general you can register as many read and/or write event watchers per
1133 fd as you want (as long as you don't confuse yourself). Setting all file
1134 descriptors to non-blocking mode is also usually a good idea (but not
1135 required if you know what you are doing).
1136 .PP
1137 If you must do this, then force the use of a known-to-be-good backend
1138 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1139 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1140 .PP
1141 Another thing you have to watch out for is that it is quite easy to
1142 receive \*(L"spurious\*(R" readyness notifications, that is your callback might
1143 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1144 because there is no data. Not only are some backends known to create a
1145 lot of those (for example solaris ports), it is very easy to get into
1146 this situation even with a relatively standard program structure. Thus
1147 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1148 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1149 .PP
1150 If you cannot run the fd in non-blocking mode (for example you should not
1151 play around with an Xlib connection), then you have to seperately re-test
1152 whether a file descriptor is really ready with a known-to-be good interface
1153 such as poll (fortunately in our Xlib example, Xlib already does this on
1154 its own, so its quite safe to use).
1155 .PP
1156 \fIThe special problem of disappearing file descriptors\fR
1157 .IX Subsection "The special problem of disappearing file descriptors"
1158 .PP
1159 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1160 descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
1161 such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file
1162 descriptor, but when it goes away, the operating system will silently drop
1163 this interest. If another file descriptor with the same number then is
1164 registered with libev, there is no efficient way to see that this is, in
1165 fact, a different file descriptor.
1166 .PP
1167 To avoid having to explicitly tell libev about such cases, libev follows
1168 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1169 will assume that this is potentially a new file descriptor, otherwise
1170 it is assumed that the file descriptor stays the same. That means that
1171 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
1172 descriptor even if the file descriptor number itself did not change.
1173 .PP
1174 This is how one would do it normally anyway, the important point is that
1175 the libev application should not optimise around libev but should leave
1176 optimisations to libev.
1177 .PP
1178 \fIThe special problem of dup'ed file descriptors\fR
1179 .IX Subsection "The special problem of dup'ed file descriptors"
1180 .PP
1181 Some backends (e.g. epoll), cannot register events for file descriptors,
1182 but only events for the underlying file descriptions. That means when you
1183 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1184 events for them, only one file descriptor might actually receive events.
1185 .PP
1186 There is no workaround possible except not registering events
1187 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1188 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1189 .PP
1190 \fIThe special problem of fork\fR
1191 .IX Subsection "The special problem of fork"
1192 .PP
1193 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1194 useless behaviour. Libev fully supports fork, but needs to be told about
1195 it in the child.
1196 .PP
1197 To support fork in your programs, you either have to call
1198 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1199 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1200 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1201 .PP
1202 \fIWatcher-Specific Functions\fR
1203 .IX Subsection "Watcher-Specific Functions"
1204 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1205 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1206 .PD 0
1207 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1208 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1209 .PD
1210 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1211 rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1212 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1213 .IP "int fd [read\-only]" 4
1214 .IX Item "int fd [read-only]"
1215 The file descriptor being watched.
1216 .IP "int events [read\-only]" 4
1217 .IX Item "int events [read-only]"
1218 The events being watched.
1219 .PP
1220 \fIExamples\fR
1221 .IX Subsection "Examples"
1222 .PP
1223 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1224 readable, but only once. Since it is likely line-buffered, you could
1225 attempt to read a whole line in the callback.
1226 .PP
1227 .Vb 6
1228 \& static void
1229 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1230 \& {
1231 \& ev_io_stop (loop, w);
1232 \& .. read from stdin here (or from w\->fd) and haqndle any I/O errors
1233 \& }
1234 \&
1235 \& ...
1236 \& struct ev_loop *loop = ev_default_init (0);
1237 \& struct ev_io stdin_readable;
1238 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1239 \& ev_io_start (loop, &stdin_readable);
1240 \& ev_loop (loop, 0);
1241 .Ve
1242 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1243 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1244 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1245 Timer watchers are simple relative timers that generate an event after a
1246 given time, and optionally repeating in regular intervals after that.
1247 .PP
1248 The timers are based on real time, that is, if you register an event that
1249 times out after an hour and you reset your system clock to last years
1250 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
1251 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1252 monotonic clock option helps a lot here).
1253 .PP
1254 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1255 time. This is usually the right thing as this timestamp refers to the time
1256 of the event triggering whatever timeout you are modifying/starting. If
1257 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
1258 on the current time, use something like this to adjust for this:
1259 .PP
1260 .Vb 1
1261 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1262 .Ve
1263 .PP
1264 The callback is guarenteed to be invoked only when its timeout has passed,
1265 but if multiple timers become ready during the same loop iteration then
1266 order of execution is undefined.
1267 .PP
1268 \fIWatcher-Specific Functions and Data Members\fR
1269 .IX Subsection "Watcher-Specific Functions and Data Members"
1270 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1271 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1272 .PD 0
1273 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1274 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1275 .PD
1276 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
1277 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
1278 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
1279 later, again, and again, until stopped manually.
1280 .Sp
1281 The timer itself will do a best-effort at avoiding drift, that is, if you
1282 configure a timer to trigger every 10 seconds, then it will trigger at
1283 exactly 10 second intervals. If, however, your program cannot keep up with
1284 the timer (because it takes longer than those 10 seconds to do stuff) the
1285 timer will not fire more than once per event loop iteration.
1286 .IP "ev_timer_again (loop)" 4
1287 .IX Item "ev_timer_again (loop)"
1288 This will act as if the timer timed out and restart it again if it is
1289 repeating. The exact semantics are:
1290 .Sp
1291 If the timer is pending, its pending status is cleared.
1292 .Sp
1293 If the timer is started but nonrepeating, stop it (as if it timed out).
1294 .Sp
1295 If the timer is repeating, either start it if necessary (with the
1296 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1297 .Sp
1298 This sounds a bit complicated, but here is a useful and typical
1299 example: Imagine you have a tcp connection and you want a so-called idle
1300 timeout, that is, you want to be called when there have been, say, 60
1301 seconds of inactivity on the socket. The easiest way to do this is to
1302 configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
1303 \&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1304 you go into an idle state where you do not expect data to travel on the
1305 socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1306 automatically restart it if need be.
1307 .Sp
1308 That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1309 altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1310 .Sp
1311 .Vb 8
1312 \& ev_timer_init (timer, callback, 0., 5.);
1313 \& ev_timer_again (loop, timer);
1314 \& ...
1315 \& timer\->again = 17.;
1316 \& ev_timer_again (loop, timer);
1317 \& ...
1318 \& timer\->again = 10.;
1319 \& ev_timer_again (loop, timer);
1320 .Ve
1321 .Sp
1322 This is more slightly efficient then stopping/starting the timer each time
1323 you want to modify its timeout value.
1324 .IP "ev_tstamp repeat [read\-write]" 4
1325 .IX Item "ev_tstamp repeat [read-write]"
1326 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1327 or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1328 which is also when any modifications are taken into account.
1329 .PP
1330 \fIExamples\fR
1331 .IX Subsection "Examples"
1332 .PP
1333 Example: Create a timer that fires after 60 seconds.
1334 .PP
1335 .Vb 5
1336 \& static void
1337 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1338 \& {
1339 \& .. one minute over, w is actually stopped right here
1340 \& }
1341 \&
1342 \& struct ev_timer mytimer;
1343 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1344 \& ev_timer_start (loop, &mytimer);
1345 .Ve
1346 .PP
1347 Example: Create a timeout timer that times out after 10 seconds of
1348 inactivity.
1349 .PP
1350 .Vb 5
1351 \& static void
1352 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1353 \& {
1354 \& .. ten seconds without any activity
1355 \& }
1356 \&
1357 \& struct ev_timer mytimer;
1358 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1359 \& ev_timer_again (&mytimer); /* start timer */
1360 \& ev_loop (loop, 0);
1361 \&
1362 \& // and in some piece of code that gets executed on any "activity":
1363 \& // reset the timeout to start ticking again at 10 seconds
1364 \& ev_timer_again (&mytimer);
1365 .Ve
1366 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1367 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1368 .IX Subsection "ev_periodic - to cron or not to cron?"
1369 Periodic watchers are also timers of a kind, but they are very versatile
1370 (and unfortunately a bit complex).
1371 .PP
1372 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1373 but on wallclock time (absolute time). You can tell a periodic watcher
1374 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1375 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1376 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1377 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1378 roughly 10 seconds later).
1379 .PP
1380 They can also be used to implement vastly more complex timers, such as
1381 triggering an event on each midnight, local time or other, complicated,
1382 rules.
1383 .PP
1384 As with timers, the callback is guarenteed to be invoked only when the
1385 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1386 during the same loop iteration then order of execution is undefined.
1387 .PP
1388 \fIWatcher-Specific Functions and Data Members\fR
1389 .IX Subsection "Watcher-Specific Functions and Data Members"
1390 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1391 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1392 .PD 0
1393 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1394 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1395 .PD
1396 Lots of arguments, lets sort it out... There are basically three modes of
1397 operation, and we will explain them from simplest to complex:
1398 .RS 4
1399 .IP "\(bu" 4
1400 absolute timer (at = time, interval = reschedule_cb = 0)
1401 .Sp
1402 In this configuration the watcher triggers an event at the wallclock time
1403 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1404 that is, if it is to be run at January 1st 2011 then it will run when the
1405 system time reaches or surpasses this time.
1406 .IP "\(bu" 4
1407 non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1408 .Sp
1409 In this mode the watcher will always be scheduled to time out at the next
1410 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
1411 and then repeat, regardless of any time jumps.
1412 .Sp
1413 This can be used to create timers that do not drift with respect to system
1414 time:
1415 .Sp
1416 .Vb 1
1417 \& ev_periodic_set (&periodic, 0., 3600., 0);
1418 .Ve
1419 .Sp
1420 This doesn't mean there will always be 3600 seconds in between triggers,
1421 but only that the the callback will be called when the system time shows a
1422 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1423 by 3600.
1424 .Sp
1425 Another way to think about it (for the mathematically inclined) is that
1426 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1427 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1428 .Sp
1429 For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1430 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1431 this value.
1432 .IP "\(bu" 4
1433 manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1434 .Sp
1435 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1436 ignored. Instead, each time the periodic watcher gets scheduled, the
1437 reschedule callback will be called with the watcher as first, and the
1438 current time as second argument.
1439 .Sp
1440 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1441 ever, or make any event loop modifications\fR. If you need to stop it,
1442 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1443 starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).
1444 .Sp
1445 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1446 ev_tstamp now)\*(C'\fR, e.g.:
1447 .Sp
1448 .Vb 4
1449 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1450 \& {
1451 \& return now + 60.;
1452 \& }
1453 .Ve
1454 .Sp
1455 It must return the next time to trigger, based on the passed time value
1456 (that is, the lowest time value larger than to the second argument). It
1457 will usually be called just before the callback will be triggered, but
1458 might be called at other times, too.
1459 .Sp
1460 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1461 passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
1462 .Sp
1463 This can be used to create very complex timers, such as a timer that
1464 triggers on each midnight, local time. To do this, you would calculate the
1465 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1466 you do this is, again, up to you (but it is not trivial, which is the main
1467 reason I omitted it as an example).
1468 .RE
1469 .RS 4
1470 .RE
1471 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1472 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1473 Simply stops and restarts the periodic watcher again. This is only useful
1474 when you changed some parameters or the reschedule callback would return
1475 a different time than the last time it was called (e.g. in a crond like
1476 program when the crontabs have changed).
1477 .IP "ev_tstamp offset [read\-write]" 4
1478 .IX Item "ev_tstamp offset [read-write]"
1479 When repeating, this contains the offset value, otherwise this is the
1480 absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1481 .Sp
1482 Can be modified any time, but changes only take effect when the periodic
1483 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1484 .IP "ev_tstamp interval [read\-write]" 4
1485 .IX Item "ev_tstamp interval [read-write]"
1486 The current interval value. Can be modified any time, but changes only
1487 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1488 called.
1489 .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1490 .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1491 The current reschedule callback, or \f(CW0\fR, if this functionality is
1492 switched off. Can be changed any time, but changes only take effect when
1493 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1494 .IP "ev_tstamp at [read\-only]" 4
1495 .IX Item "ev_tstamp at [read-only]"
1496 When active, contains the absolute time that the watcher is supposed to
1497 trigger next.
1498 .PP
1499 \fIExamples\fR
1500 .IX Subsection "Examples"
1501 .PP
1502 Example: Call a callback every hour, or, more precisely, whenever the
1503 system clock is divisible by 3600. The callback invocation times have
1504 potentially a lot of jittering, but good long-term stability.
1505 .PP
1506 .Vb 5
1507 \& static void
1508 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1509 \& {
1510 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1511 \& }
1512 \&
1513 \& struct ev_periodic hourly_tick;
1514 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1515 \& ev_periodic_start (loop, &hourly_tick);
1516 .Ve
1517 .PP
1518 Example: The same as above, but use a reschedule callback to do it:
1519 .PP
1520 .Vb 1
1521 \& #include <math.h>
1522 \&
1523 \& static ev_tstamp
1524 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1525 \& {
1526 \& return fmod (now, 3600.) + 3600.;
1527 \& }
1528 \&
1529 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530 .Ve
1531 .PP
1532 Example: Call a callback every hour, starting now:
1533 .PP
1534 .Vb 4
1535 \& struct ev_periodic hourly_tick;
1536 \& ev_periodic_init (&hourly_tick, clock_cb,
1537 \& fmod (ev_now (loop), 3600.), 3600., 0);
1538 \& ev_periodic_start (loop, &hourly_tick);
1539 .Ve
1540 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1541 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1542 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1543 Signal watchers will trigger an event when the process receives a specific
1544 signal one or more times. Even though signals are very asynchronous, libev
1545 will try it's best to deliver signals synchronously, i.e. as part of the
1546 normal event processing, like any other event.
1547 .PP
1548 You can configure as many watchers as you like per signal. Only when the
1549 first watcher gets started will libev actually register a signal watcher
1550 with the kernel (thus it coexists with your own signal handlers as long
1551 as you don't register any with libev). Similarly, when the last signal
1552 watcher for a signal is stopped libev will reset the signal handler to
1553 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1554 .PP
1555 \fIWatcher-Specific Functions and Data Members\fR
1556 .IX Subsection "Watcher-Specific Functions and Data Members"
1557 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1558 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1559 .PD 0
1560 .IP "ev_signal_set (ev_signal *, int signum)" 4
1561 .IX Item "ev_signal_set (ev_signal *, int signum)"
1562 .PD
1563 Configures the watcher to trigger on the given signal number (usually one
1564 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1565 .IP "int signum [read\-only]" 4
1566 .IX Item "int signum [read-only]"
1567 The signal the watcher watches out for.
1568 .ie n .Sh """ev_child"" \- watch out for process status changes"
1569 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1570 .IX Subsection "ev_child - watch out for process status changes"
1571 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1572 some child status changes (most typically when a child of yours dies).
1573 .PP
1574 \fIWatcher-Specific Functions and Data Members\fR
1575 .IX Subsection "Watcher-Specific Functions and Data Members"
1576 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1577 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1578 .PD 0
1579 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
1580 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
1581 .PD
1582 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1583 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1584 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1585 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1586 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1587 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1588 activate the watcher when the process terminates) or \f(CW1\fR (additionally
1589 activate the watcher when the process is stopped or continued).
1590 .IP "int pid [read\-only]" 4
1591 .IX Item "int pid [read-only]"
1592 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1593 .IP "int rpid [read\-write]" 4
1594 .IX Item "int rpid [read-write]"
1595 The process id that detected a status change.
1596 .IP "int rstatus [read\-write]" 4
1597 .IX Item "int rstatus [read-write]"
1598 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1599 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1600 .PP
1601 \fIExamples\fR
1602 .IX Subsection "Examples"
1603 .PP
1604 Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1605 .PP
1606 .Vb 5
1607 \& static void
1608 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1609 \& {
1610 \& ev_unloop (loop, EVUNLOOP_ALL);
1611 \& }
1612 \&
1613 \& struct ev_signal signal_watcher;
1614 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1615 \& ev_signal_start (loop, &sigint_cb);
1616 .Ve
1617 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
1618 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1619 .IX Subsection "ev_stat - did the file attributes just change?"
1620 This watches a filesystem path for attribute changes. That is, it calls
1621 \&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1622 compared to the last time, invoking the callback if it did.
1623 .PP
1624 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1625 not exist\*(R" is a status change like any other. The condition \*(L"path does
1626 not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1627 otherwise always forced to be at least one) and all the other fields of
1628 the stat buffer having unspecified contents.
1629 .PP
1630 The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1631 relative and your working directory changes, the behaviour is undefined.
1632 .PP
1633 Since there is no standard to do this, the portable implementation simply
1634 calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1635 can specify a recommended polling interval for this case. If you specify
1636 a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1637 unspecified default\fR value will be used (which you can expect to be around
1638 five seconds, although this might change dynamically). Libev will also
1639 impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1640 usually overkill.
1641 .PP
1642 This watcher type is not meant for massive numbers of stat watchers,
1643 as even with OS-supported change notifications, this can be
1644 resource-intensive.
1645 .PP
1646 At the time of this writing, only the Linux inotify interface is
1647 implemented (implementing kqueue support is left as an exercise for the
1648 reader). Inotify will be used to give hints only and should not change the
1649 semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs
1650 to fall back to regular polling again even with inotify, but changes are
1651 usually detected immediately, and if the file exists there will be no
1652 polling.
1653 .PP
1654 \fIInotify\fR
1655 .IX Subsection "Inotify"
1656 .PP
1657 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1658 available on Linux) and present at runtime, it will be used to speed up
1659 change detection where possible. The inotify descriptor will be created lazily
1660 when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1661 .PP
1662 Inotify presense does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1663 except that changes might be detected earlier, and in some cases, to avoid
1664 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presense of inotify support
1665 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1666 .PP
1667 (There is no support for kqueue, as apparently it cannot be used to
1668 implement this functionality, due to the requirement of having a file
1669 descriptor open on the object at all times).
1670 .PP
1671 \fIThe special problem of stat time resolution\fR
1672 .IX Subsection "The special problem of stat time resolution"
1673 .PP
1674 The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1675 even on systems where the resolution is higher, many filesystems still
1676 only support whole seconds.
1677 .PP
1678 That means that, if the time is the only thing that changes, you might
1679 miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and calls
1680 your callback, which does something. When there is another update within
1681 the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it.
1682 .PP
1683 The solution to this is to delay acting on a change for a second (or till
1684 the next second boundary), using a roughly one-second delay \f(CW\*(C`ev_timer\*(C'\fR
1685 (\f(CW\*(C`ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)\*(C'\fR). The \f(CW.01\fR
1686 is added to work around small timing inconsistencies of some operating
1687 systems.
1688 .PP
1689 \fIWatcher-Specific Functions and Data Members\fR
1690 .IX Subsection "Watcher-Specific Functions and Data Members"
1691 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1692 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1693 .PD 0
1694 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1695 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1696 .PD
1697 Configures the watcher to wait for status changes of the given
1698 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1699 be detected and should normally be specified as \f(CW0\fR to let libev choose
1700 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1701 path for as long as the watcher is active.
1702 .Sp
1703 The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected,
1704 relative to the attributes at the time the watcher was started (or the
1705 last change was detected).
1706 .IP "ev_stat_stat (ev_stat *)" 4
1707 .IX Item "ev_stat_stat (ev_stat *)"
1708 Updates the stat buffer immediately with new values. If you change the
1709 watched path in your callback, you could call this fucntion to avoid
1710 detecting this change (while introducing a race condition). Can also be
1711 useful simply to find out the new values.
1712 .IP "ev_statdata attr [read\-only]" 4
1713 .IX Item "ev_statdata attr [read-only]"
1714 The most-recently detected attributes of the file. Although the type is of
1715 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1716 suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there
1717 was some error while \f(CW\*(C`stat\*(C'\fRing the file.
1718 .IP "ev_statdata prev [read\-only]" 4
1719 .IX Item "ev_statdata prev [read-only]"
1720 The previous attributes of the file. The callback gets invoked whenever
1721 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR.
1722 .IP "ev_tstamp interval [read\-only]" 4
1723 .IX Item "ev_tstamp interval [read-only]"
1724 The specified interval.
1725 .IP "const char *path [read\-only]" 4
1726 .IX Item "const char *path [read-only]"
1727 The filesystem path that is being watched.
1728 .PP
1729 \fIExamples\fR
1730 .IX Subsection "Examples"
1731 .PP
1732 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1733 .PP
1734 .Vb 10
1735 \& static void
1736 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1737 \& {
1738 \& /* /etc/passwd changed in some way */
1739 \& if (w\->attr.st_nlink)
1740 \& {
1741 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1742 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1743 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1744 \& }
1745 \& else
1746 \& /* you shalt not abuse printf for puts */
1747 \& puts ("wow, /etc/passwd is not there, expect problems. "
1748 \& "if this is windows, they already arrived\en");
1749 \& }
1750 \&
1751 \& ...
1752 \& ev_stat passwd;
1753 \&
1754 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1755 \& ev_stat_start (loop, &passwd);
1756 .Ve
1757 .PP
1758 Example: Like above, but additionally use a one-second delay so we do not
1759 miss updates (however, frequent updates will delay processing, too, so
1760 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1761 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1762 .PP
1763 .Vb 2
1764 \& static ev_stat passwd;
1765 \& static ev_timer timer;
1766 \&
1767 \& static void
1768 \& timer_cb (EV_P_ ev_timer *w, int revents)
1769 \& {
1770 \& ev_timer_stop (EV_A_ w);
1771 \&
1772 \& /* now it\*(Aqs one second after the most recent passwd change */
1773 \& }
1774 \&
1775 \& static void
1776 \& stat_cb (EV_P_ ev_stat *w, int revents)
1777 \& {
1778 \& /* reset the one\-second timer */
1779 \& ev_timer_again (EV_A_ &timer);
1780 \& }
1781 \&
1782 \& ...
1783 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1784 \& ev_stat_start (loop, &passwd);
1785 \& ev_timer_init (&timer, timer_cb, 0., 1.01);
1786 .Ve
1787 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1788 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1789 .IX Subsection "ev_idle - when you've got nothing better to do..."
1790 Idle watchers trigger events when no other events of the same or higher
1791 priority are pending (prepare, check and other idle watchers do not
1792 count).
1793 .PP
1794 That is, as long as your process is busy handling sockets or timeouts
1795 (or even signals, imagine) of the same or higher priority it will not be
1796 triggered. But when your process is idle (or only lower-priority watchers
1797 are pending), the idle watchers are being called once per event loop
1798 iteration \- until stopped, that is, or your process receives more events
1799 and becomes busy again with higher priority stuff.
1800 .PP
1801 The most noteworthy effect is that as long as any idle watchers are
1802 active, the process will not block when waiting for new events.
1803 .PP
1804 Apart from keeping your process non-blocking (which is a useful
1805 effect on its own sometimes), idle watchers are a good place to do
1806 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1807 event loop has handled all outstanding events.
1808 .PP
1809 \fIWatcher-Specific Functions and Data Members\fR
1810 .IX Subsection "Watcher-Specific Functions and Data Members"
1811 .IP "ev_idle_init (ev_signal *, callback)" 4
1812 .IX Item "ev_idle_init (ev_signal *, callback)"
1813 Initialises and configures the idle watcher \- it has no parameters of any
1814 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1815 believe me.
1816 .PP
1817 \fIExamples\fR
1818 .IX Subsection "Examples"
1819 .PP
1820 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1821 callback, free it. Also, use no error checking, as usual.
1822 .PP
1823 .Vb 7
1824 \& static void
1825 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1826 \& {
1827 \& free (w);
1828 \& // now do something you wanted to do when the program has
1829 \& // no longer anything immediate to do.
1830 \& }
1831 \&
1832 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1833 \& ev_idle_init (idle_watcher, idle_cb);
1834 \& ev_idle_start (loop, idle_cb);
1835 .Ve
1836 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1837 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1838 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
1839 Prepare and check watchers are usually (but not always) used in tandem:
1840 prepare watchers get invoked before the process blocks and check watchers
1841 afterwards.
1842 .PP
1843 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1844 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1845 watchers. Other loops than the current one are fine, however. The
1846 rationale behind this is that you do not need to check for recursion in
1847 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1848 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1849 called in pairs bracketing the blocking call.
1850 .PP
1851 Their main purpose is to integrate other event mechanisms into libev and
1852 their use is somewhat advanced. This could be used, for example, to track
1853 variable changes, implement your own watchers, integrate net-snmp or a
1854 coroutine library and lots more. They are also occasionally useful if
1855 you cache some data and want to flush it before blocking (for example,
1856 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1857 watcher).
1858 .PP
1859 This is done by examining in each prepare call which file descriptors need
1860 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1861 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1862 provide just this functionality). Then, in the check watcher you check for
1863 any events that occured (by checking the pending status of all watchers
1864 and stopping them) and call back into the library. The I/O and timer
1865 callbacks will never actually be called (but must be valid nevertheless,
1866 because you never know, you know?).
1867 .PP
1868 As another example, the Perl Coro module uses these hooks to integrate
1869 coroutines into libev programs, by yielding to other active coroutines
1870 during each prepare and only letting the process block if no coroutines
1871 are ready to run (it's actually more complicated: it only runs coroutines
1872 with priority higher than or equal to the event loop and one coroutine
1873 of lower priority, but only once, using idle watchers to keep the event
1874 loop from blocking if lower-priority coroutines are active, thus mapping
1875 low-priority coroutines to idle/background tasks).
1876 .PP
1877 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
1878 priority, to ensure that they are being run before any other watchers
1879 after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
1880 too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
1881 supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers
1882 did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
1883 (non-libev) event loops those other event loops might be in an unusable
1884 state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
1885 coexist peacefully with others).
1886 .PP
1887 \fIWatcher-Specific Functions and Data Members\fR
1888 .IX Subsection "Watcher-Specific Functions and Data Members"
1889 .IP "ev_prepare_init (ev_prepare *, callback)" 4
1890 .IX Item "ev_prepare_init (ev_prepare *, callback)"
1891 .PD 0
1892 .IP "ev_check_init (ev_check *, callback)" 4
1893 .IX Item "ev_check_init (ev_check *, callback)"
1894 .PD
1895 Initialises and configures the prepare or check watcher \- they have no
1896 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1897 macros, but using them is utterly, utterly and completely pointless.
1898 .PP
1899 \fIExamples\fR
1900 .IX Subsection "Examples"
1901 .PP
1902 There are a number of principal ways to embed other event loops or modules
1903 into libev. Here are some ideas on how to include libadns into libev
1904 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1905 use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR
1906 embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0
1907 into the Glib event loop).
1908 .PP
1909 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1910 and in a check watcher, destroy them and call into libadns. What follows
1911 is pseudo-code only of course. This requires you to either use a low
1912 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1913 the callbacks for the IO/timeout watchers might not have been called yet.
1914 .PP
1915 .Vb 2
1916 \& static ev_io iow [nfd];
1917 \& static ev_timer tw;
1918 \&
1919 \& static void
1920 \& io_cb (ev_loop *loop, ev_io *w, int revents)
1921 \& {
1922 \& }
1923 \&
1924 \& // create io watchers for each fd and a timer before blocking
1925 \& static void
1926 \& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1927 \& {
1928 \& int timeout = 3600000;
1929 \& struct pollfd fds [nfd];
1930 \& // actual code will need to loop here and realloc etc.
1931 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1932 \&
1933 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1934 \& ev_timer_init (&tw, 0, timeout * 1e\-3);
1935 \& ev_timer_start (loop, &tw);
1936 \&
1937 \& // create one ev_io per pollfd
1938 \& for (int i = 0; i < nfd; ++i)
1939 \& {
1940 \& ev_io_init (iow + i, io_cb, fds [i].fd,
1941 \& ((fds [i].events & POLLIN ? EV_READ : 0)
1942 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1943 \&
1944 \& fds [i].revents = 0;
1945 \& ev_io_start (loop, iow + i);
1946 \& }
1947 \& }
1948 \&
1949 \& // stop all watchers after blocking
1950 \& static void
1951 \& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1952 \& {
1953 \& ev_timer_stop (loop, &tw);
1954 \&
1955 \& for (int i = 0; i < nfd; ++i)
1956 \& {
1957 \& // set the relevant poll flags
1958 \& // could also call adns_processreadable etc. here
1959 \& struct pollfd *fd = fds + i;
1960 \& int revents = ev_clear_pending (iow + i);
1961 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1962 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1963 \&
1964 \& // now stop the watcher
1965 \& ev_io_stop (loop, iow + i);
1966 \& }
1967 \&
1968 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1969 \& }
1970 .Ve
1971 .PP
1972 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
1973 in the prepare watcher and would dispose of the check watcher.
1974 .PP
1975 Method 3: If the module to be embedded supports explicit event
1976 notification (adns does), you can also make use of the actual watcher
1977 callbacks, and only destroy/create the watchers in the prepare watcher.
1978 .PP
1979 .Vb 5
1980 \& static void
1981 \& timer_cb (EV_P_ ev_timer *w, int revents)
1982 \& {
1983 \& adns_state ads = (adns_state)w\->data;
1984 \& update_now (EV_A);
1985 \&
1986 \& adns_processtimeouts (ads, &tv_now);
1987 \& }
1988 \&
1989 \& static void
1990 \& io_cb (EV_P_ ev_io *w, int revents)
1991 \& {
1992 \& adns_state ads = (adns_state)w\->data;
1993 \& update_now (EV_A);
1994 \&
1995 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
1996 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
1997 \& }
1998 \&
1999 \& // do not ever call adns_afterpoll
2000 .Ve
2001 .PP
2002 Method 4: Do not use a prepare or check watcher because the module you
2003 want to embed is too inflexible to support it. Instead, youc na override
2004 their poll function. The drawback with this solution is that the main
2005 loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
2006 this.
2007 .PP
2008 .Vb 4
2009 \& static gint
2010 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2011 \& {
2012 \& int got_events = 0;
2013 \&
2014 \& for (n = 0; n < nfds; ++n)
2015 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2016 \&
2017 \& if (timeout >= 0)
2018 \& // create/start timer
2019 \&
2020 \& // poll
2021 \& ev_loop (EV_A_ 0);
2022 \&
2023 \& // stop timer again
2024 \& if (timeout >= 0)
2025 \& ev_timer_stop (EV_A_ &to);
2026 \&
2027 \& // stop io watchers again \- their callbacks should have set
2028 \& for (n = 0; n < nfds; ++n)
2029 \& ev_io_stop (EV_A_ iow [n]);
2030 \&
2031 \& return got_events;
2032 \& }
2033 .Ve
2034 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2035 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2036 .IX Subsection "ev_embed - when one backend isn't enough..."
2037 This is a rather advanced watcher type that lets you embed one event loop
2038 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2039 loop, other types of watchers might be handled in a delayed or incorrect
2040 fashion and must not be used).
2041 .PP
2042 There are primarily two reasons you would want that: work around bugs and
2043 prioritise I/O.
2044 .PP
2045 As an example for a bug workaround, the kqueue backend might only support
2046 sockets on some platform, so it is unusable as generic backend, but you
2047 still want to make use of it because you have many sockets and it scales
2048 so nicely. In this case, you would create a kqueue-based loop and embed it
2049 into your default loop (which might use e.g. poll). Overall operation will
2050 be a bit slower because first libev has to poll and then call kevent, but
2051 at least you can use both at what they are best.
2052 .PP
2053 As for prioritising I/O: rarely you have the case where some fds have
2054 to be watched and handled very quickly (with low latency), and even
2055 priorities and idle watchers might have too much overhead. In this case
2056 you would put all the high priority stuff in one loop and all the rest in
2057 a second one, and embed the second one in the first.
2058 .PP
2059 As long as the watcher is active, the callback will be invoked every time
2060 there might be events pending in the embedded loop. The callback must then
2061 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2062 their callbacks (you could also start an idle watcher to give the embedded
2063 loop strictly lower priority for example). You can also set the callback
2064 to \f(CW0\fR, in which case the embed watcher will automatically execute the
2065 embedded loop sweep.
2066 .PP
2067 As long as the watcher is started it will automatically handle events. The
2068 callback will be invoked whenever some events have been handled. You can
2069 set the callback to \f(CW0\fR to avoid having to specify one if you are not
2070 interested in that.
2071 .PP
2072 Also, there have not currently been made special provisions for forking:
2073 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2074 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2075 yourself.
2076 .PP
2077 Unfortunately, not all backends are embeddable, only the ones returned by
2078 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2079 portable one.
2080 .PP
2081 So when you want to use this feature you will always have to be prepared
2082 that you cannot get an embeddable loop. The recommended way to get around
2083 this is to have a separate variables for your embeddable loop, try to
2084 create it, and if that fails, use the normal loop for everything.
2085 .PP
2086 \fIWatcher-Specific Functions and Data Members\fR
2087 .IX Subsection "Watcher-Specific Functions and Data Members"
2088 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2089 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2090 .PD 0
2091 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2092 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2093 .PD
2094 Configures the watcher to embed the given loop, which must be
2095 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2096 invoked automatically, otherwise it is the responsibility of the callback
2097 to invoke it (it will continue to be called until the sweep has been done,
2098 if you do not want thta, you need to temporarily stop the embed watcher).
2099 .IP "ev_embed_sweep (loop, ev_embed *)" 4
2100 .IX Item "ev_embed_sweep (loop, ev_embed *)"
2101 Make a single, non-blocking sweep over the embedded loop. This works
2102 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2103 apropriate way for embedded loops.
2104 .IP "struct ev_loop *other [read\-only]" 4
2105 .IX Item "struct ev_loop *other [read-only]"
2106 The embedded event loop.
2107 .PP
2108 \fIExamples\fR
2109 .IX Subsection "Examples"
2110 .PP
2111 Example: Try to get an embeddable event loop and embed it into the default
2112 event loop. If that is not possible, use the default loop. The default
2113 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in
2114 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be
2115 used).
2116 .PP
2117 .Vb 3
2118 \& struct ev_loop *loop_hi = ev_default_init (0);
2119 \& struct ev_loop *loop_lo = 0;
2120 \& struct ev_embed embed;
2121 \&
2122 \& // see if there is a chance of getting one that works
2123 \& // (remember that a flags value of 0 means autodetection)
2124 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2125 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2126 \& : 0;
2127 \&
2128 \& // if we got one, then embed it, otherwise default to loop_hi
2129 \& if (loop_lo)
2130 \& {
2131 \& ev_embed_init (&embed, 0, loop_lo);
2132 \& ev_embed_start (loop_hi, &embed);
2133 \& }
2134 \& else
2135 \& loop_lo = loop_hi;
2136 .Ve
2137 .PP
2138 Example: Check if kqueue is available but not recommended and create
2139 a kqueue backend for use with sockets (which usually work with any
2140 kqueue implementation). Store the kqueue/socket\-only event loop in
2141 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2142 .PP
2143 .Vb 3
2144 \& struct ev_loop *loop = ev_default_init (0);
2145 \& struct ev_loop *loop_socket = 0;
2146 \& struct ev_embed embed;
2147 \&
2148 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2149 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2150 \& {
2151 \& ev_embed_init (&embed, 0, loop_socket);
2152 \& ev_embed_start (loop, &embed);
2153 \& }
2154 \&
2155 \& if (!loop_socket)
2156 \& loop_socket = loop;
2157 \&
2158 \& // now use loop_socket for all sockets, and loop for everything else
2159 .Ve
2160 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2161 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2162 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2163 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2164 whoever is a good citizen cared to tell libev about it by calling
2165 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2166 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2167 and only in the child after the fork. If whoever good citizen calling
2168 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2169 handlers will be invoked, too, of course.
2170 .PP
2171 \fIWatcher-Specific Functions and Data Members\fR
2172 .IX Subsection "Watcher-Specific Functions and Data Members"
2173 .IP "ev_fork_init (ev_signal *, callback)" 4
2174 .IX Item "ev_fork_init (ev_signal *, callback)"
2175 Initialises and configures the fork watcher \- it has no parameters of any
2176 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2177 believe me.
2180 There are some other functions of possible interest. Described. Here. Now.
2181 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2182 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2183 This function combines a simple timer and an I/O watcher, calls your
2184 callback on whichever event happens first and automatically stop both
2185 watchers. This is useful if you want to wait for a single event on an fd
2186 or timeout without having to allocate/configure/start/stop/free one or
2187 more watchers yourself.
2188 .Sp
2189 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
2190 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
2191 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
2192 .Sp
2193 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2194 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2195 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
2196 dubious value.
2197 .Sp
2198 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
2199 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2200 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
2201 value passed to \f(CW\*(C`ev_once\*(C'\fR:
2202 .Sp
2203 .Vb 7
2204 \& static void stdin_ready (int revents, void *arg)
2205 \& {
2206 \& if (revents & EV_TIMEOUT)
2207 \& /* doh, nothing entered */;
2208 \& else if (revents & EV_READ)
2209 \& /* stdin might have data for us, joy! */;
2210 \& }
2211 \&
2212 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2213 .Ve
2214 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
2215 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
2216 Feeds the given event set into the event loop, as if the specified event
2217 had happened for the specified watcher (which must be a pointer to an
2218 initialised but not necessarily started event watcher).
2219 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
2220 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
2221 Feed an event on the given fd, as if a file descriptor backend detected
2222 the given events it.
2223 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
2224 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
2225 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
2226 loop!).
2229 Libev offers a compatibility emulation layer for libevent. It cannot
2230 emulate the internals of libevent, so here are some usage hints:
2231 .IP "\(bu" 4
2232 Use it by including <event.h>, as usual.
2233 .IP "\(bu" 4
2234 The following members are fully supported: ev_base, ev_callback,
2235 ev_arg, ev_fd, ev_res, ev_events.
2236 .IP "\(bu" 4
2237 Avoid using ev_flags and the EVLIST_*\-macros, while it is
2238 maintained by libev, it does not work exactly the same way as in libevent (consider
2239 it a private \s-1API\s0).
2240 .IP "\(bu" 4
2241 Priorities are not currently supported. Initialising priorities
2242 will fail and all watchers will have the same priority, even though there
2243 is an ev_pri field.
2244 .IP "\(bu" 4
2245 Other members are not supported.
2246 .IP "\(bu" 4
2247 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2248 to use the libev header file and library.
2249 .SH "\*(C+ SUPPORT"
2250 .IX Header " SUPPORT"
2251 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2252 you to use some convinience methods to start/stop watchers and also change
2253 the callback model to a model using method callbacks on objects.
2254 .PP
2255 To use it,
2256 .PP
2257 .Vb 1
2258 \& #include <ev++.h>
2259 .Ve
2260 .PP
2261 This automatically includes \fIev.h\fR and puts all of its definitions (many
2262 of them macros) into the global namespace. All \*(C+ specific things are
2263 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2264 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2265 .PP
2266 Care has been taken to keep the overhead low. The only data member the \*(C+
2267 classes add (compared to plain C\-style watchers) is the event loop pointer
2268 that the watcher is associated with (or no additional members at all if
2269 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2270 .PP
2271 Currently, functions, and static and non-static member functions can be
2272 used as callbacks. Other types should be easy to add as long as they only
2273 need one additional pointer for context. If you need support for other
2274 types of functors please contact the author (preferably after implementing
2275 it).
2276 .PP
2277 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2278 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2279 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2280 .IX Item "ev::READ, ev::WRITE etc."
2281 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2282 macros from \fIev.h\fR.
2283 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2284 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2285 .IX Item "ev::tstamp, ev::now"
2286 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2287 .ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
2288 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2289 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2290 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2291 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2292 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2293 defines by many implementations.
2294 .Sp
2295 All of those classes have these methods:
2296 .RS 4
2297 .IP "ev::TYPE::TYPE ()" 4
2298 .IX Item "ev::TYPE::TYPE ()"
2299 .PD 0
2300 .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2301 .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2302 .IP "ev::TYPE::~TYPE" 4
2303 .IX Item "ev::TYPE::~TYPE"
2304 .PD
2305 The constructor (optionally) takes an event loop to associate the watcher
2306 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2307 .Sp
2308 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2309 \&\f(CW\*(C`set\*(C'\fR method before starting it.
2310 .Sp
2311 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2312 method to set a callback before you can start the watcher.
2313 .Sp
2314 (The reason why you have to use a method is a limitation in \*(C+ which does
2315 not allow explicit template arguments for constructors).
2316 .Sp
2317 The destructor automatically stops the watcher if it is active.
2318 .IP "w\->set<class, &class::method> (object *)" 4
2319 .IX Item "w->set<class, &class::method> (object *)"
2320 This method sets the callback method to call. The method has to have a
2321 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2322 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2323 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2324 .Sp
2325 This method synthesizes efficient thunking code to call your method from
2326 the C callback that libev requires. If your compiler can inline your
2327 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2328 your compiler is good :), then the method will be fully inlined into the
2329 thunking function, making it as fast as a direct C callback.
2330 .Sp
2331 Example: simple class declaration and watcher initialisation
2332 .Sp
2333 .Vb 4
2334 \& struct myclass
2335 \& {
2336 \& void io_cb (ev::io &w, int revents) { }
2337 \& }
2338 \&
2339 \& myclass obj;
2340 \& ev::io iow;
2341 \& iow.set <myclass, &myclass::io_cb> (&obj);
2342 .Ve
2343 .IP "w\->set<function> (void *data = 0)" 4
2344 .IX Item "w->set<function> (void *data = 0)"
2345 Also sets a callback, but uses a static method or plain function as
2346 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2347 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2348 .Sp
2349 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2350 .Sp
2351 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2352 .Sp
2353 Example:
2354 .Sp
2355 .Vb 2
2356 \& static void io_cb (ev::io &w, int revents) { }
2357 \& iow.set <io_cb> ();
2358 .Ve
2359 .IP "w\->set (struct ev_loop *)" 4
2360 .IX Item "w->set (struct ev_loop *)"
2361 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2362 do this when the watcher is inactive (and not pending either).
2363 .IP "w\->set ([args])" 4
2364 .IX Item "w->set ([args])"
2365 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2366 called at least once. Unlike the C counterpart, an active watcher gets
2367 automatically stopped and restarted when reconfiguring it with this
2368 method.
2369 .IP "w\->start ()" 4
2370 .IX Item "w->start ()"
2371 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2372 constructor already stores the event loop.
2373 .IP "w\->stop ()" 4
2374 .IX Item "w->stop ()"
2375 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2376 .ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2377 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2378 .IX Item "w->again () (ev::timer, ev::periodic only)"
2379 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2380 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2381 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2382 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2383 .IX Item "w->sweep () (ev::embed only)"
2384 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2385 .ie n .IP "w\->update () (""ev::stat"" only)" 4
2386 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2387 .IX Item "w->update () (ev::stat only)"
2388 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2389 .RE
2390 .RS 4
2391 .RE
2392 .PP
2393 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2394 the constructor.
2395 .PP
2396 .Vb 4
2397 \& class myclass
2398 \& {
2399 \& ev::io io; void io_cb (ev::io &w, int revents);
2400 \& ev:idle idle void idle_cb (ev::idle &w, int revents);
2401 \&
2402 \& myclass (int fd)
2403 \& {
2404 \& io .set <myclass, &myclass::io_cb > (this);
2405 \& idle.set <myclass, &myclass::idle_cb> (this);
2406 \&
2407 \& io.start (fd, ev::READ);
2408 \& }
2409 \& };
2410 .Ve
2412 .IX Header "MACRO MAGIC"
2413 Libev can be compiled with a variety of options, the most fundamantal
2414 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2415 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2416 .PP
2417 To make it easier to write programs that cope with either variant, the
2418 following macros are defined:
2419 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2420 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2421 .IX Item "EV_A, EV_A_"
2422 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2423 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2424 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2425 .Sp
2426 .Vb 3
2427 \& ev_unref (EV_A);
2428 \& ev_timer_add (EV_A_ watcher);
2429 \& ev_loop (EV_A_ 0);
2430 .Ve
2431 .Sp
2432 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2433 which is often provided by the following macro.
2434 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2435 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2436 .IX Item "EV_P, EV_P_"
2437 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2438 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2439 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2440 .Sp
2441 .Vb 2
2442 \& // this is how ev_unref is being declared
2443 \& static void ev_unref (EV_P);
2444 \&
2445 \& // this is how you can declare your typical callback
2446 \& static void cb (EV_P_ ev_timer *w, int revents)
2447 .Ve
2448 .Sp
2449 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2450 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2451 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2452 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2454 Similar to the other two macros, this gives you the value of the default
2455 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2456 .PP
2457 Example: Declare and initialise a check watcher, utilising the above
2458 macros so it will work regardless of whether multiple loops are supported
2459 or not.
2460 .PP
2461 .Vb 5
2462 \& static void
2463 \& check_cb (EV_P_ ev_timer *w, int revents)
2464 \& {
2465 \& ev_check_stop (EV_A_ w);
2466 \& }
2467 \&
2468 \& ev_check check;
2469 \& ev_check_init (&check, check_cb);
2470 \& ev_check_start (EV_DEFAULT_ &check);
2471 \& ev_loop (EV_DEFAULT_ 0);
2472 .Ve
2474 .IX Header "EMBEDDING"
2475 Libev can (and often is) directly embedded into host
2476 applications. Examples of applications that embed it include the Deliantra
2477 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2478 and rxvt-unicode.
2479 .PP
2480 The goal is to enable you to just copy the necessary files into your
2481 source directory without having to change even a single line in them, so
2482 you can easily upgrade by simply copying (or having a checked-out copy of
2483 libev somewhere in your source tree).
2484 .Sh "\s-1FILESETS\s0"
2485 .IX Subsection "FILESETS"
2486 Depending on what features you need you need to include one or more sets of files
2487 in your app.
2488 .PP
2489 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2490 .IX Subsection "CORE EVENT LOOP"
2491 .PP
2492 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2493 configuration (no autoconf):
2494 .PP
2495 .Vb 2
2496 \& #define EV_STANDALONE 1
2497 \& #include "ev.c"
2498 .Ve
2499 .PP
2500 This will automatically include \fIev.h\fR, too, and should be done in a
2501 single C source file only to provide the function implementations. To use
2502 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2503 done by writing a wrapper around \fIev.h\fR that you can include instead and
2504 where you can put other configuration options):
2505 .PP
2506 .Vb 2
2507 \& #define EV_STANDALONE 1
2508 \& #include "ev.h"
2509 .Ve
2510 .PP
2511 Both header files and implementation files can be compiled with a \*(C+
2512 compiler (at least, thats a stated goal, and breakage will be treated
2513 as a bug).
2514 .PP
2515 You need the following files in your source tree, or in a directory
2516 in your include path (e.g. in libev/ when using \-Ilibev):
2517 .PP
2518 .Vb 4
2519 \& ev.h
2520 \& ev.c
2521 \& ev_vars.h
2522 \& ev_wrap.h
2523 \&
2524 \& ev_win32.c required on win32 platforms only
2525 \&
2526 \& ev_select.c only when select backend is enabled (which is enabled by default)
2527 \& ev_poll.c only when poll backend is enabled (disabled by default)
2528 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2529 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2530 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
2531 .Ve
2532 .PP
2533 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
2534 to compile this single file.
2535 .PP
2536 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2538 .PP
2539 To include the libevent compatibility \s-1API\s0, also include:
2540 .PP
2541 .Vb 1
2542 \& #include "event.c"
2543 .Ve
2544 .PP
2545 in the file including \fIev.c\fR, and:
2546 .PP
2547 .Vb 1
2548 \& #include "event.h"
2549 .Ve
2550 .PP
2551 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2552 .PP
2553 You need the following additional files for this:
2554 .PP
2555 .Vb 2
2556 \& event.h
2557 \& event.c
2558 .Ve
2559 .PP
2560 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2561 .IX Subsection "AUTOCONF SUPPORT"
2562 .PP
2563 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2564 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2565 \&\\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2566 include \fIconfig.h\fR and configure itself accordingly.
2567 .PP
2568 For this of course you need the m4 file:
2569 .PP
2570 .Vb 1
2571 \& libev.m4
2572 .Ve
2573 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2575 Libev can be configured via a variety of preprocessor symbols you have to define
2576 before including any of its files. The default is not to build for multiplicity
2577 and only include the select backend.
2578 .IP "\s-1EV_STANDALONE\s0" 4
2580 Must always be \f(CW1\fR if you do not use autoconf configuration, which
2581 keeps libev from including \fIconfig.h\fR, and it also defines dummy
2582 implementations for some libevent functions (such as logging, which is not
2583 supported). It will also not define any of the structs usually found in
2584 \&\fIevent.h\fR that are not directly supported by the libev core alone.
2585 .IP "\s-1EV_USE_MONOTONIC\s0" 4
2587 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2588 monotonic clock option at both compiletime and runtime. Otherwise no use
2589 of the monotonic clock option will be attempted. If you enable this, you
2590 usually have to link against librt or something similar. Enabling it when
2591 the functionality isn't available is safe, though, although you have
2592 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2593 function is hiding in (often \fI\-lrt\fR).
2594 .IP "\s-1EV_USE_REALTIME\s0" 4
2596 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2597 realtime clock option at compiletime (and assume its availability at
2598 runtime if successful). Otherwise no use of the realtime clock option will
2599 be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2600 (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
2601 note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2602 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
2604 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2605 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
2606 .IP "\s-1EV_USE_SELECT\s0" 4
2607 .IX Item "EV_USE_SELECT"
2608 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2609 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2610 other method takes over, select will be it. Otherwise the select backend
2611 will not be compiled in.
2612 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2614 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2615 structure. This is useful if libev doesn't compile due to a missing
2616 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2617 exotic systems. This usually limits the range of file descriptors to some
2618 low limit such as 1024 or might have other limitations (winsocket only
2619 allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2620 influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2621 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2623 When defined to \f(CW1\fR, the select backend will assume that
2624 select/socket/connect etc. don't understand file descriptors but
2625 wants osf handles on win32 (this is the case when the select to
2626 be used is the winsock select). This means that it will call
2627 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2628 it is assumed that all these functions actually work on fds, even
2629 on win32. Should not be defined on non\-win32 platforms.
2630 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
2631 .IX Item "EV_FD_TO_WIN32_HANDLE"
2632 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
2633 file descriptors to socket handles. When not defining this symbol (the
2634 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
2635 correct. In some cases, programs use their own file descriptor management,
2636 in which case they can provide this function to map fds to socket handles.
2637 .IP "\s-1EV_USE_POLL\s0" 4
2638 .IX Item "EV_USE_POLL"
2639 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2640 backend. Otherwise it will be enabled on non\-win32 platforms. It
2641 takes precedence over select.
2642 .IP "\s-1EV_USE_EPOLL\s0" 4
2643 .IX Item "EV_USE_EPOLL"
2644 If defined to be \f(CW1\fR, libev will compile in support for the Linux
2645 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2646 otherwise another method will be used as fallback. This is the
2647 preferred backend for GNU/Linux systems.
2648 .IP "\s-1EV_USE_KQUEUE\s0" 4
2649 .IX Item "EV_USE_KQUEUE"
2650 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2651 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2652 otherwise another method will be used as fallback. This is the preferred
2653 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2654 supports some types of fds correctly (the only platform we found that
2655 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2656 not be used unless explicitly requested. The best way to use it is to find
2657 out whether kqueue supports your type of fd properly and use an embedded
2658 kqueue loop.
2659 .IP "\s-1EV_USE_PORT\s0" 4
2660 .IX Item "EV_USE_PORT"
2661 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
2662 10 port style backend. Its availability will be detected at runtime,
2663 otherwise another method will be used as fallback. This is the preferred
2664 backend for Solaris 10 systems.
2665 .IP "\s-1EV_USE_DEVPOLL\s0" 4
2666 .IX Item "EV_USE_DEVPOLL"
2667 reserved for future expansion, works like the \s-1USE\s0 symbols above.
2668 .IP "\s-1EV_USE_INOTIFY\s0" 4
2669 .IX Item "EV_USE_INOTIFY"
2670 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2671 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2672 be detected at runtime.
2673 .IP "\s-1EV_H\s0" 4
2674 .IX Item "EV_H"
2675 The name of the \fIev.h\fR header file used to include it. The default if
2676 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2677 used to virtually rename the \fIev.h\fR header file in case of conflicts.
2678 .IP "\s-1EV_CONFIG_H\s0" 4
2679 .IX Item "EV_CONFIG_H"
2680 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2681 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2682 \&\f(CW\*(C`EV_H\*(C'\fR, above.
2683 .IP "\s-1EV_EVENT_H\s0" 4
2684 .IX Item "EV_EVENT_H"
2685 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2686 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2687 .IP "\s-1EV_PROTOTYPES\s0" 4
2689 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2690 prototypes, but still define all the structs and other symbols. This is
2691 occasionally useful if you want to provide your own wrapper functions
2692 around libev functions.
2693 .IP "\s-1EV_MULTIPLICITY\s0" 4
2695 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2696 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2697 additional independent event loops. Otherwise there will be no support
2698 for multiple event loops and there is no first event loop pointer
2699 argument. Instead, all functions act on the single default loop.
2700 .IP "\s-1EV_MINPRI\s0" 4
2701 .IX Item "EV_MINPRI"
2702 .PD 0
2703 .IP "\s-1EV_MAXPRI\s0" 4
2704 .IX Item "EV_MAXPRI"
2705 .PD
2706 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
2707 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
2708 provide for more priorities by overriding those symbols (usually defined
2709 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
2710 .Sp
2711 When doing priority-based operations, libev usually has to linearly search
2712 all the priorities, so having many of them (hundreds) uses a lot of space
2713 and time, so using the defaults of five priorities (\-2 .. +2) is usually
2714 fine.
2715 .Sp
2716 If your embedding app does not need any priorities, defining these both to
2717 \&\f(CW0\fR will save some memory and cpu.
2718 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
2720 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
2721 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2722 code.
2723 .IP "\s-1EV_IDLE_ENABLE\s0" 4
2724 .IX Item "EV_IDLE_ENABLE"
2725 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2726 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2727 code.
2728 .IP "\s-1EV_EMBED_ENABLE\s0" 4
2730 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2731 defined to be \f(CW0\fR, then they are not.
2732 .IP "\s-1EV_STAT_ENABLE\s0" 4
2733 .IX Item "EV_STAT_ENABLE"
2734 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2735 defined to be \f(CW0\fR, then they are not.
2736 .IP "\s-1EV_FORK_ENABLE\s0" 4
2737 .IX Item "EV_FORK_ENABLE"
2738 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2739 defined to be \f(CW0\fR, then they are not.
2740 .IP "\s-1EV_MINIMAL\s0" 4
2741 .IX Item "EV_MINIMAL"
2742 If you need to shave off some kilobytes of code at the expense of some
2743 speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override
2744 some inlining decisions, saves roughly 30% codesize of amd64.
2745 .IP "\s-1EV_PID_HASHSIZE\s0" 4
2747 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2748 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
2749 than enough. If you need to manage thousands of children you might want to
2750 increase this value (\fImust\fR be a power of two).
2751 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2753 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2754 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
2755 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
2756 watchers you might want to increase this value (\fImust\fR be a power of
2757 two).
2758 .IP "\s-1EV_COMMON\s0" 4
2759 .IX Item "EV_COMMON"
2760 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2761 this macro to a something else you can include more and other types of
2762 members. You have to define it each time you include one of the files,
2763 though, and it must be identical each time.
2764 .Sp
2765 For example, the perl \s-1EV\s0 module uses something like this:
2766 .Sp
2767 .Vb 3
2768 \& #define EV_COMMON \e
2769 \& SV *self; /* contains this struct */ \e
2770 \& SV *cb_sv, *fh /* note no trailing ";" */
2771 .Ve
2772 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2773 .IX Item "EV_CB_DECLARE (type)"
2774 .PD 0
2775 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
2776 .IX Item "EV_CB_INVOKE (watcher, revents)"
2777 .IP "ev_set_cb (ev, cb)" 4
2778 .IX Item "ev_set_cb (ev, cb)"
2779 .PD
2780 Can be used to change the callback member declaration in each watcher,
2781 and the way callbacks are invoked and set. Must expand to a struct member
2782 definition and a statement, respectively. See the \fIev.h\fR header file for
2783 their default definitions. One possible use for overriding these is to
2784 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2785 method calls instead of plain function calls in \*(C+.
2786 .Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
2787 .IX Subsection "EXPORTED API SYMBOLS"
2788 If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
2789 exported symbols, you can use the provided \fISymbol.*\fR files which list
2790 all public symbols, one per line:
2791 .PP
2792 .Vb 2
2793 \& Symbols.ev for libev proper
2794 \& Symbols.event for the libevent emulation
2795 .Ve
2796 .PP
2797 This can also be used to rename all public symbols to avoid clashes with
2798 multiple versions of libev linked together (which is obviously bad in
2799 itself, but sometimes it is inconvinient to avoid this).
2800 .PP
2801 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
2802 include before including \fIev.h\fR:
2803 .PP
2804 .Vb 1
2805 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
2806 .Ve
2807 .PP
2808 This would create a file \fIwrap.h\fR which essentially looks like this:
2809 .PP
2810 .Vb 4
2811 \& #define ev_backend myprefix_ev_backend
2812 \& #define ev_check_start myprefix_ev_check_start
2813 \& #define ev_check_stop myprefix_ev_check_stop
2814 \& ...
2815 .Ve
2816 .Sh "\s-1EXAMPLES\s0"
2817 .IX Subsection "EXAMPLES"
2818 For a real-world example of a program the includes libev
2819 verbatim, you can have a look at the \s-1EV\s0 perl module
2820 (<>). It has the libev files in
2821 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2822 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2823 will be compiled. It is pretty complex because it provides its own header
2824 file.
2825 .PP
2826 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2827 that everybody includes and which overrides some configure choices:
2828 .PP
2829 .Vb 9
2830 \& #define EV_MINIMAL 1
2831 \& #define EV_USE_POLL 0
2832 \& #define EV_MULTIPLICITY 0
2833 \& #define EV_PERIODIC_ENABLE 0
2834 \& #define EV_STAT_ENABLE 0
2835 \& #define EV_FORK_ENABLE 0
2836 \& #define EV_CONFIG_H <config.h>
2837 \& #define EV_MINPRI 0
2838 \& #define EV_MAXPRI 0
2839 \&
2840 \& #include "ev++.h"
2841 .Ve
2842 .PP
2843 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2844 .PP
2845 .Vb 2
2846 \& #include "ev_cpp.h"
2847 \& #include "ev.c"
2848 .Ve
2850 .IX Header "COMPLEXITIES"
2851 In this section the complexities of (many of) the algorithms used inside
2852 libev will be explained. For complexity discussions about backends see the
2853 documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2854 .PP
2855 All of the following are about amortised time: If an array needs to be
2856 extended, libev needs to realloc and move the whole array, but this
2857 happens asymptotically never with higher number of elements, so O(1) might
2858 mean it might do a lengthy realloc operation in rare cases, but on average
2859 it is much faster and asymptotically approaches constant time.
2860 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2861 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2862 This means that, when you have a watcher that triggers in one hour and
2863 there are 100 watchers that would trigger before that then inserting will
2864 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2865 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2866 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2867 That means that changing a timer costs less than removing/adding them
2868 as only the relative motion in the event queue has to be paid for.
2869 .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2870 .IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2871 These just add the watcher into an array or at the head of a list.
2872 .IP "Stopping check/prepare/idle watchers: O(1)" 4
2873 .IX Item "Stopping check/prepare/idle watchers: O(1)"
2874 .PD 0
2875 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2876 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
2877 .PD
2878 These watchers are stored in lists then need to be walked to find the
2879 correct watcher to remove. The lists are usually short (you don't usually
2880 have many watchers waiting for the same fd or signal).
2881 .IP "Finding the next timer in each loop iteration: O(1)" 4
2882 .IX Item "Finding the next timer in each loop iteration: O(1)"
2883 By virtue of using a binary heap, the next timer is always found at the
2884 beginning of the storage array.
2885 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2886 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2887 A change means an I/O watcher gets started or stopped, which requires
2888 libev to recalculate its status (and possibly tell the kernel, depending
2889 on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2890 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
2891 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
2892 .PD 0
2893 .IP "Priority handling: O(number_of_priorities)" 4
2894 .IX Item "Priority handling: O(number_of_priorities)"
2895 .PD
2896 Priorities are implemented by allocating some space for each
2897 priority. When doing priority-based operations, libev usually has to
2898 linearly search all the priorities, but starting/stopping and activating
2899 watchers becomes O(1) w.r.t. prioritiy handling.
2900 .SH "Win32 platform limitations and workarounds"
2901 .IX Header "Win32 platform limitations and workarounds"
2902 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
2903 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
2904 model. Libev still offers limited functionality on this platform in
2905 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
2906 descriptors. This only applies when using Win32 natively, not when using
2907 e.g. cygwin.
2908 .PP
2909 There is no supported compilation method available on windows except
2910 embedding it into other applications.
2911 .PP
2912 Due to the many, low, and arbitrary limits on the win32 platform and the
2913 abysmal performance of winsockets, using a large number of sockets is not
2914 recommended (and not reasonable). If your program needs to use more than
2915 a hundred or so sockets, then likely it needs to use a totally different
2916 implementation for windows, as libev offers the \s-1POSIX\s0 model, which cannot
2917 be implemented efficiently on windows (microsoft monopoly games).
2918 .IP "The winsocket select function" 4
2919 .IX Item "The winsocket select function"
2920 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it requires
2921 socket \fIhandles\fR and not socket \fIfile descriptors\fR. This makes select
2922 very inefficient, and also requires a mapping from file descriptors
2923 to socket handles. See the discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR,
2924 \&\f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and \f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor
2925 symbols for more info.
2926 .Sp
2927 The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime
2928 libraries and raw winsocket select is:
2929 .Sp
2930 .Vb 2
2931 \& #define EV_USE_SELECT 1
2932 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2933 .Ve
2934 .Sp
2935 Note that winsockets handling of fd sets is O(n), so you can easily get a
2936 complexity in the O(nA\*^X) range when using win32.
2937 .IP "Limited number of file descriptors" 4
2938 .IX Item "Limited number of file descriptors"
2939 Windows has numerous arbitrary (and low) limits on things. Early versions
2940 of winsocket's select only supported waiting for a max. of \f(CW64\fR handles
2941 (probably owning to the fact that all windows kernels can only wait for
2942 \&\f(CW64\fR things at the same time internally; microsoft recommends spawning a
2943 chain of threads and wait for 63 handles and the previous thread in each).
2944 .Sp
2945 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
2946 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
2947 call (which might be in libev or elsewhere, for example, perl does its own
2948 select emulation on windows).
2949 .Sp
2950 Another limit is the number of file descriptors in the microsoft runtime
2951 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
2952 or something like this inside microsoft). You can increase this by calling
2953 \&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
2954 arbitrary limit), but is broken in many versions of the microsoft runtime
2955 libraries.
2956 .Sp
2957 This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
2958 windows version and/or the phase of the moon). To get more, you need to
2959 wrap all I/O functions and provide your own fd management, but the cost of
2960 calling select (O(nA\*^X)) will likely make this unworkable.
2961 .SH "AUTHOR"
2962 .IX Header "AUTHOR"
2963 Marc Lehmann <>.
2965 .IX Header "POD ERRORS"
2966 Hey! \fBThe above document had some coding errors, which are explained below:\fR
2967 .IP "Around line 2686:" 4
2968 .IX Item "Around line 2686:"
2969 You forgot a '=back' before '=head2'