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Revision: 1.64
Committed: Wed Apr 16 17:08:29 2008 UTC (16 years, 3 months ago) by root
Branch: MAIN
CVS Tags: rel-3_31, rel-3_3
Changes since 1.63: +91 -23 lines
Log Message:
*** empty log message ***

File Contents

# Content
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132 .\" ========================================================================
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134 .IX Title "EV 1"
135 .TH EV 1 "2008-04-11" "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 2
150 \& // a single header file is required
151 \& #include <ev.h>
152 \&
153 \& // every watcher type has its own typedef\*(Aqd struct
154 \& // with the name ev_<type>
155 \& ev_io stdin_watcher;
156 \& ev_timer timeout_watcher;
157 \&
158 \& // all watcher callbacks have a similar signature
159 \& // this callback is called when data is readable on stdin
160 \& static void
161 \& stdin_cb (EV_P_ struct ev_io *w, int revents)
162 \& {
163 \& puts ("stdin ready");
164 \& // for one\-shot events, one must manually stop the watcher
165 \& // with its corresponding stop function.
166 \& ev_io_stop (EV_A_ w);
167 \&
168 \& // this causes all nested ev_loop\*(Aqs to stop iterating
169 \& ev_unloop (EV_A_ EVUNLOOP_ALL);
170 \& }
171 \&
172 \& // another callback, this time for a time\-out
173 \& static void
174 \& timeout_cb (EV_P_ struct ev_timer *w, int revents)
175 \& {
176 \& puts ("timeout");
177 \& // this causes the innermost ev_loop to stop iterating
178 \& ev_unloop (EV_A_ EVUNLOOP_ONE);
179 \& }
180 \&
181 \& int
182 \& main (void)
183 \& {
184 \& // use the default event loop unless you have special needs
185 \& struct ev_loop *loop = ev_default_loop (0);
186 \&
187 \& // initialise an io watcher, then start it
188 \& // this one will watch for stdin to become readable
189 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
190 \& ev_io_start (loop, &stdin_watcher);
191 \&
192 \& // initialise a timer watcher, then start it
193 \& // simple non\-repeating 5.5 second timeout
194 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
195 \& ev_timer_start (loop, &timeout_watcher);
196 \&
197 \& // now wait for events to arrive
198 \& ev_loop (loop, 0);
199 \&
200 \& // unloop was called, so exit
201 \& return 0;
202 \& }
203 .Ve
205 .IX Header "DESCRIPTION"
206 The newest version of this document is also available as an html-formatted
207 web page you might find easier to navigate when reading it for the first
208 time: <>.
209 .PP
210 Libev is an event loop: you register interest in certain events (such as a
211 file descriptor being readable or a timeout occurring), and it will manage
212 these event sources and provide your program with events.
213 .PP
214 To do this, it must take more or less complete control over your process
215 (or thread) by executing the \fIevent loop\fR handler, and will then
216 communicate events via a callback mechanism.
217 .PP
218 You register interest in certain events by registering so-called \fIevent
219 watchers\fR, which are relatively small C structures you initialise with the
220 details of the event, and then hand it over to libev by \fIstarting\fR the
221 watcher.
222 .Sh "\s-1FEATURES\s0"
223 .IX Subsection "FEATURES"
224 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
225 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
226 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
227 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
228 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
229 (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
230 watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
231 \&\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
232 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
233 (\f(CW\*(C`ev_fork\*(C'\fR).
234 .PP
235 It also is quite fast (see this
236 benchmark comparing it to libevent
237 for example).
238 .Sh "\s-1CONVENTIONS\s0"
239 .IX Subsection "CONVENTIONS"
240 Libev is very configurable. In this manual the default (and most common)
241 configuration will be described, which supports multiple event loops. For
242 more info about various configuration options please have a look at
243 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
244 for multiple event loops, then all functions taking an initial argument of
245 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
246 this argument.
247 .Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
249 Libev represents time as a single floating point number, representing the
250 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
251 the beginning of 1970, details are complicated, don't ask). This type is
252 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
253 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
254 it, you should treat it as some floatingpoint value. Unlike the name
255 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
256 throughout libev.
259 These functions can be called anytime, even before initialising the
260 library in any way.
261 .IP "ev_tstamp ev_time ()" 4
262 .IX Item "ev_tstamp ev_time ()"
263 Returns the current time as libev would use it. Please note that the
264 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
265 you actually want to know.
266 .IP "ev_sleep (ev_tstamp interval)" 4
267 .IX Item "ev_sleep (ev_tstamp interval)"
268 Sleep for the given interval: The current thread will be blocked until
269 either it is interrupted or the given time interval has passed. Basically
270 this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
271 .IP "int ev_version_major ()" 4
272 .IX Item "int ev_version_major ()"
273 .PD 0
274 .IP "int ev_version_minor ()" 4
275 .IX Item "int ev_version_minor ()"
276 .PD
277 You can find out the major and minor \s-1ABI\s0 version numbers of the library
278 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
279 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
280 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
281 version of the library your program was compiled against.
282 .Sp
283 These version numbers refer to the \s-1ABI\s0 version of the library, not the
284 release version.
285 .Sp
286 Usually, it's a good idea to terminate if the major versions mismatch,
287 as this indicates an incompatible change. Minor versions are usually
288 compatible to older versions, so a larger minor version alone is usually
289 not a problem.
290 .Sp
291 Example: Make sure we haven't accidentally been linked against the wrong
292 version.
293 .Sp
294 .Vb 3
295 \& assert (("libev version mismatch",
296 \& ev_version_major () == EV_VERSION_MAJOR
297 \& && ev_version_minor () >= EV_VERSION_MINOR));
298 .Ve
299 .IP "unsigned int ev_supported_backends ()" 4
300 .IX Item "unsigned int ev_supported_backends ()"
301 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
302 value) compiled into this binary of libev (independent of their
303 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
304 a description of the set values.
305 .Sp
306 Example: make sure we have the epoll method, because yeah this is cool and
307 a must have and can we have a torrent of it please!!!11
308 .Sp
309 .Vb 2
310 \& assert (("sorry, no epoll, no sex",
311 \& ev_supported_backends () & EVBACKEND_EPOLL));
312 .Ve
313 .IP "unsigned int ev_recommended_backends ()" 4
314 .IX Item "unsigned int ev_recommended_backends ()"
315 Return the set of all backends compiled into this binary of libev and also
316 recommended for this platform. This set is often smaller than the one
317 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
318 most BSDs and will not be autodetected unless you explicitly request it
319 (assuming you know what you are doing). This is the set of backends that
320 libev will probe for if you specify no backends explicitly.
321 .IP "unsigned int ev_embeddable_backends ()" 4
322 .IX Item "unsigned int ev_embeddable_backends ()"
323 Returns the set of backends that are embeddable in other event loops. This
324 is the theoretical, all-platform, value. To find which backends
325 might be supported on the current system, you would need to look at
326 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
327 recommended ones.
328 .Sp
329 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
330 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
331 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
332 Sets the allocation function to use (the prototype is similar \- the
333 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
334 used to allocate and free memory (no surprises here). If it returns zero
335 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
336 or take some potentially destructive action.
337 .Sp
338 Since some systems (at least OpenBSD and Darwin) fail to implement
339 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
340 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
341 .Sp
342 You could override this function in high-availability programs to, say,
343 free some memory if it cannot allocate memory, to use a special allocator,
344 or even to sleep a while and retry until some memory is available.
345 .Sp
346 Example: Replace the libev allocator with one that waits a bit and then
347 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
348 .Sp
349 .Vb 6
350 \& static void *
351 \& persistent_realloc (void *ptr, size_t size)
352 \& {
353 \& for (;;)
354 \& {
355 \& void *newptr = realloc (ptr, size);
356 \&
357 \& if (newptr)
358 \& return newptr;
359 \&
360 \& sleep (60);
361 \& }
362 \& }
363 \&
364 \& ...
365 \& ev_set_allocator (persistent_realloc);
366 .Ve
367 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
368 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
369 Set the callback function to call on a retryable syscall error (such
370 as failed select, poll, epoll_wait). The message is a printable string
371 indicating the system call or subsystem causing the problem. If this
372 callback is set, then libev will expect it to remedy the sitution, no
373 matter what, when it returns. That is, libev will generally retry the
374 requested operation, or, if the condition doesn't go away, do bad stuff
375 (such as abort).
376 .Sp
377 Example: This is basically the same thing that libev does internally, too.
378 .Sp
379 .Vb 6
380 \& static void
381 \& fatal_error (const char *msg)
382 \& {
383 \& perror (msg);
384 \& abort ();
385 \& }
386 \&
387 \& ...
388 \& ev_set_syserr_cb (fatal_error);
389 .Ve
392 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
393 types of such loops, the \fIdefault\fR loop, which supports signals and child
394 events, and dynamically created loops which do not.
395 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
396 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
397 This will initialise the default event loop if it hasn't been initialised
398 yet and return it. If the default loop could not be initialised, returns
399 false. If it already was initialised it simply returns it (and ignores the
400 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
401 .Sp
402 If you don't know what event loop to use, use the one returned from this
403 function.
404 .Sp
405 Note that this function is \fInot\fR thread-safe, so if you want to use it
406 from multiple threads, you have to lock (note also that this is unlikely,
407 as loops cannot bes hared easily between threads anyway).
408 .Sp
409 The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
410 \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
411 for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either
412 create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
413 can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
414 \&\f(CW\*(C`ev_default_init\*(C'\fR.
415 .Sp
416 The flags argument can be used to specify special behaviour or specific
417 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
418 .Sp
419 The following flags are supported:
420 .RS 4
421 .ie n .IP """EVFLAG_AUTO""" 4
422 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
423 .IX Item "EVFLAG_AUTO"
424 The default flags value. Use this if you have no clue (it's the right
425 thing, believe me).
426 .ie n .IP """EVFLAG_NOENV""" 4
427 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
429 If this flag bit is ored into the flag value (or the program runs setuid
430 or setgid) then libev will \fInot\fR look at the environment variable
431 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
432 override the flags completely if it is found in the environment. This is
433 useful to try out specific backends to test their performance, or to work
434 around bugs.
435 .ie n .IP """EVFLAG_FORKCHECK""" 4
436 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
438 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
439 a fork, you can also make libev check for a fork in each iteration by
440 enabling this flag.
441 .Sp
442 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
443 and thus this might slow down your event loop if you do a lot of loop
444 iterations and little real work, but is usually not noticeable (on my
445 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
446 without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has
447 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
448 .Sp
449 The big advantage of this flag is that you can forget about fork (and
450 forget about forgetting to tell libev about forking) when you use this
451 flag.
452 .Sp
453 This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
454 environment variable.
455 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
456 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
457 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
458 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
459 libev tries to roll its own fd_set with no limits on the number of fds,
460 but if that fails, expect a fairly low limit on the number of fds when
461 using this backend. It doesn't scale too well (O(highest_fd)), but its
462 usually the fastest backend for a low number of (low-numbered :) fds.
463 .Sp
464 To get good performance out of this backend you need a high amount of
465 parallelity (most of the file descriptors should be busy). If you are
466 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
467 connections as possible during one iteration. You might also want to have
468 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
469 readyness notifications you get per iteration.
470 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
471 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
472 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
473 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
474 than select, but handles sparse fds better and has no artificial
475 limit on the number of fds you can use (except it will slow down
476 considerably with a lot of inactive fds). It scales similarly to select,
477 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
478 performance tips.
479 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
480 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
481 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
482 For few fds, this backend is a bit little slower than poll and select,
483 but it scales phenomenally better. While poll and select usually scale
484 like O(total_fds) where n is the total number of fds (or the highest fd),
485 epoll scales either O(1) or O(active_fds). The epoll design has a number
486 of shortcomings, such as silently dropping events in some hard-to-detect
487 cases and requiring a syscall per fd change, no fork support and bad
488 support for dup.
489 .Sp
490 While stopping, setting and starting an I/O watcher in the same iteration
491 will result in some caching, there is still a syscall per such incident
492 (because the fd could point to a different file description now), so its
493 best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
494 very well if you register events for both fds.
495 .Sp
496 Please note that epoll sometimes generates spurious notifications, so you
497 need to use non-blocking I/O or other means to avoid blocking when no data
498 (or space) is available.
499 .Sp
500 Best performance from this backend is achieved by not unregistering all
501 watchers for a file descriptor until it has been closed, if possible, i.e.
502 keep at least one watcher active per fd at all times.
503 .Sp
504 While nominally embeddeble in other event loops, this feature is broken in
505 all kernel versions tested so far.
506 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
507 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
508 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
509 Kqueue deserves special mention, as at the time of this writing, it
510 was broken on all BSDs except NetBSD (usually it doesn't work reliably
511 with anything but sockets and pipes, except on Darwin, where of course
512 it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
513 unless you explicitly specify it explicitly in the flags (i.e. using
514 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
515 system like NetBSD.
516 .Sp
517 You still can embed kqueue into a normal poll or select backend and use it
518 only for sockets (after having made sure that sockets work with kqueue on
519 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
520 .Sp
521 It scales in the same way as the epoll backend, but the interface to the
522 kernel is more efficient (which says nothing about its actual speed, of
523 course). While stopping, setting and starting an I/O watcher does never
524 cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
525 two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
526 drops fds silently in similarly hard-to-detect cases.
527 .Sp
528 This backend usually performs well under most conditions.
529 .Sp
530 While nominally embeddable in other event loops, this doesn't work
531 everywhere, so you might need to test for this. And since it is broken
532 almost everywhere, you should only use it when you have a lot of sockets
533 (for which it usually works), by embedding it into another event loop
534 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
535 sockets.
536 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
537 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
538 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
539 This is not implemented yet (and might never be, unless you send me an
540 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
541 and is not embeddable, which would limit the usefulness of this backend
542 immensely.
543 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
544 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
545 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
546 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
547 it's really slow, but it still scales very well (O(active_fds)).
548 .Sp
549 Please note that solaris event ports can deliver a lot of spurious
550 notifications, so you need to use non-blocking I/O or other means to avoid
551 blocking when no data (or space) is available.
552 .Sp
553 While this backend scales well, it requires one system call per active
554 file descriptor per loop iteration. For small and medium numbers of file
555 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
556 might perform better.
557 .Sp
558 On the positive side, ignoring the spurious readyness notifications, this
559 backend actually performed to specification in all tests and is fully
560 embeddable, which is a rare feat among the OS-specific backends.
561 .ie n .IP """EVBACKEND_ALL""" 4
562 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
564 Try all backends (even potentially broken ones that wouldn't be tried
565 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
567 .Sp
568 It is definitely not recommended to use this flag.
569 .RE
570 .RS 4
571 .Sp
572 If one or more of these are ored into the flags value, then only these
573 backends will be tried (in the reverse order as listed here). If none are
574 specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
575 .Sp
576 The most typical usage is like this:
577 .Sp
578 .Vb 2
579 \& if (!ev_default_loop (0))
580 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
581 .Ve
582 .Sp
583 Restrict libev to the select and poll backends, and do not allow
584 environment settings to be taken into account:
585 .Sp
586 .Vb 1
588 .Ve
589 .Sp
590 Use whatever libev has to offer, but make sure that kqueue is used if
591 available (warning, breaks stuff, best use only with your own private
592 event loop and only if you know the \s-1OS\s0 supports your types of fds):
593 .Sp
594 .Vb 1
595 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
596 .Ve
597 .RE
598 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
599 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
600 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
601 always distinct from the default loop. Unlike the default loop, it cannot
602 handle signal and child watchers, and attempts to do so will be greeted by
603 undefined behaviour (or a failed assertion if assertions are enabled).
604 .Sp
605 Note that this function \fIis\fR thread-safe, and the recommended way to use
606 libev with threads is indeed to create one loop per thread, and using the
607 default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
608 .Sp
609 Example: Try to create a event loop that uses epoll and nothing else.
610 .Sp
611 .Vb 3
612 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
613 \& if (!epoller)
614 \& fatal ("no epoll found here, maybe it hides under your chair");
615 .Ve
616 .IP "ev_default_destroy ()" 4
617 .IX Item "ev_default_destroy ()"
618 Destroys the default loop again (frees all memory and kernel state
619 etc.). None of the active event watchers will be stopped in the normal
620 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
621 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
622 calling this function, or cope with the fact afterwards (which is usually
623 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
624 for example).
625 .Sp
626 Note that certain global state, such as signal state, will not be freed by
627 this function, and related watchers (such as signal and child watchers)
628 would need to be stopped manually.
629 .Sp
630 In general it is not advisable to call this function except in the
631 rare occasion where you really need to free e.g. the signal handling
632 pipe fds. If you need dynamically allocated loops it is better to use
633 \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
634 .IP "ev_loop_destroy (loop)" 4
635 .IX Item "ev_loop_destroy (loop)"
636 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
637 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
638 .IP "ev_default_fork ()" 4
639 .IX Item "ev_default_fork ()"
640 This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
641 to reinitialise the kernel state for backends that have one. Despite the
642 name, you can call it anytime, but it makes most sense after forking, in
643 the child process (or both child and parent, but that again makes little
644 sense). You \fImust\fR call it in the child before using any of the libev
645 functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
646 .Sp
647 On the other hand, you only need to call this function in the child
648 process if and only if you want to use the event library in the child. If
649 you just fork+exec, you don't have to call it at all.
650 .Sp
651 The function itself is quite fast and it's usually not a problem to call
652 it just in case after a fork. To make this easy, the function will fit in
653 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
654 .Sp
655 .Vb 1
656 \& pthread_atfork (0, 0, ev_default_fork);
657 .Ve
658 .IP "ev_loop_fork (loop)" 4
659 .IX Item "ev_loop_fork (loop)"
660 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
661 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
662 after fork, and how you do this is entirely your own problem.
663 .IP "int ev_is_default_loop (loop)" 4
664 .IX Item "int ev_is_default_loop (loop)"
665 Returns true when the given loop actually is the default loop, false otherwise.
666 .IP "unsigned int ev_loop_count (loop)" 4
667 .IX Item "unsigned int ev_loop_count (loop)"
668 Returns the count of loop iterations for the loop, which is identical to
669 the number of times libev did poll for new events. It starts at \f(CW0\fR and
670 happily wraps around with enough iterations.
671 .Sp
672 This value can sometimes be useful as a generation counter of sorts (it
673 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
674 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
675 .IP "unsigned int ev_backend (loop)" 4
676 .IX Item "unsigned int ev_backend (loop)"
677 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
678 use.
679 .IP "ev_tstamp ev_now (loop)" 4
680 .IX Item "ev_tstamp ev_now (loop)"
681 Returns the current \*(L"event loop time\*(R", which is the time the event loop
682 received events and started processing them. This timestamp does not
683 change as long as callbacks are being processed, and this is also the base
684 time used for relative timers. You can treat it as the timestamp of the
685 event occurring (or more correctly, libev finding out about it).
686 .IP "ev_loop (loop, int flags)" 4
687 .IX Item "ev_loop (loop, int flags)"
688 Finally, this is it, the event handler. This function usually is called
689 after you initialised all your watchers and you want to start handling
690 events.
691 .Sp
692 If the flags argument is specified as \f(CW0\fR, it will not return until
693 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
694 .Sp
695 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
696 relying on all watchers to be stopped when deciding when a program has
697 finished (especially in interactive programs), but having a program that
698 automatically loops as long as it has to and no longer by virtue of
699 relying on its watchers stopping correctly is a thing of beauty.
700 .Sp
701 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
702 those events and any outstanding ones, but will not block your process in
703 case there are no events and will return after one iteration of the loop.
704 .Sp
705 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
706 neccessary) and will handle those and any outstanding ones. It will block
707 your process until at least one new event arrives, and will return after
708 one iteration of the loop. This is useful if you are waiting for some
709 external event in conjunction with something not expressible using other
710 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
711 usually a better approach for this kind of thing.
712 .Sp
713 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
714 .Sp
715 .Vb 10
716 \& \- Before the first iteration, call any pending watchers.
717 \& * If EVFLAG_FORKCHECK was used, check for a fork.
718 \& \- If a fork was detected, queue and call all fork watchers.
719 \& \- Queue and call all prepare watchers.
720 \& \- If we have been forked, recreate the kernel state.
721 \& \- Update the kernel state with all outstanding changes.
722 \& \- Update the "event loop time".
723 \& \- Calculate for how long to sleep or block, if at all
724 \& (active idle watchers, EVLOOP_NONBLOCK or not having
725 \& any active watchers at all will result in not sleeping).
726 \& \- Sleep if the I/O and timer collect interval say so.
727 \& \- Block the process, waiting for any events.
728 \& \- Queue all outstanding I/O (fd) events.
729 \& \- Update the "event loop time" and do time jump handling.
730 \& \- Queue all outstanding timers.
731 \& \- Queue all outstanding periodics.
732 \& \- If no events are pending now, queue all idle watchers.
733 \& \- Queue all check watchers.
734 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
735 \& Signals and child watchers are implemented as I/O watchers, and will
736 \& be handled here by queueing them when their watcher gets executed.
737 \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
738 \& were used, or there are no active watchers, return, otherwise
739 \& continue with step *.
740 .Ve
741 .Sp
742 Example: Queue some jobs and then loop until no events are outstanding
743 anymore.
744 .Sp
745 .Vb 4
746 \& ... queue jobs here, make sure they register event watchers as long
747 \& ... as they still have work to do (even an idle watcher will do..)
748 \& ev_loop (my_loop, 0);
749 \& ... jobs done. yeah!
750 .Ve
751 .IP "ev_unloop (loop, how)" 4
752 .IX Item "ev_unloop (loop, how)"
753 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
754 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
755 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
756 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
757 .Sp
758 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
759 .IP "ev_ref (loop)" 4
760 .IX Item "ev_ref (loop)"
761 .PD 0
762 .IP "ev_unref (loop)" 4
763 .IX Item "ev_unref (loop)"
764 .PD
765 Ref/unref can be used to add or remove a reference count on the event
766 loop: Every watcher keeps one reference, and as long as the reference
767 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
768 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
769 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
770 example, libev itself uses this for its internal signal pipe: It is not
771 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
772 no event watchers registered by it are active. It is also an excellent
773 way to do this for generic recurring timers or from within third-party
774 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
775 (but only if the watcher wasn't active before, or was active before,
776 respectively).
777 .Sp
778 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
779 running when nothing else is active.
780 .Sp
781 .Vb 4
782 \& struct ev_signal exitsig;
783 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
784 \& ev_signal_start (loop, &exitsig);
785 \& evf_unref (loop);
786 .Ve
787 .Sp
788 Example: For some weird reason, unregister the above signal handler again.
789 .Sp
790 .Vb 2
791 \& ev_ref (loop);
792 \& ev_signal_stop (loop, &exitsig);
793 .Ve
794 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
795 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
796 .PD 0
797 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
798 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
799 .PD
800 These advanced functions influence the time that libev will spend waiting
801 for events. Both are by default \f(CW0\fR, meaning that libev will try to
802 invoke timer/periodic callbacks and I/O callbacks with minimum latency.
803 .Sp
804 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
805 allows libev to delay invocation of I/O and timer/periodic callbacks to
806 increase efficiency of loop iterations.
807 .Sp
808 The background is that sometimes your program runs just fast enough to
809 handle one (or very few) event(s) per loop iteration. While this makes
810 the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
811 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
812 overhead for the actual polling but can deliver many events at once.
813 .Sp
814 By setting a higher \fIio collect interval\fR you allow libev to spend more
815 time collecting I/O events, so you can handle more events per iteration,
816 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
817 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
818 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
819 .Sp
820 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
821 to spend more time collecting timeouts, at the expense of increased
822 latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
823 will not be affected. Setting this to a non-null value will not introduce
824 any overhead in libev.
825 .Sp
826 Many (busy) programs can usually benefit by setting the io collect
827 interval to a value near \f(CW0.1\fR or so, which is often enough for
828 interactive servers (of course not for games), likewise for timeouts. It
829 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
830 as this approsaches the timing granularity of most systems.
833 A watcher is a structure that you create and register to record your
834 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
835 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
836 .PP
837 .Vb 5
838 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
839 \& {
840 \& ev_io_stop (w);
841 \& ev_unloop (loop, EVUNLOOP_ALL);
842 \& }
843 \&
844 \& struct ev_loop *loop = ev_default_loop (0);
845 \& struct ev_io stdin_watcher;
846 \& ev_init (&stdin_watcher, my_cb);
847 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
848 \& ev_io_start (loop, &stdin_watcher);
849 \& ev_loop (loop, 0);
850 .Ve
851 .PP
852 As you can see, you are responsible for allocating the memory for your
853 watcher structures (and it is usually a bad idea to do this on the stack,
854 although this can sometimes be quite valid).
855 .PP
856 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
857 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
858 callback gets invoked each time the event occurs (or, in the case of io
859 watchers, each time the event loop detects that the file descriptor given
860 is readable and/or writable).
861 .PP
862 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
863 with arguments specific to this watcher type. There is also a macro
864 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
865 (watcher *, callback, ...)\*(C'\fR.
866 .PP
867 To make the watcher actually watch out for events, you have to start it
868 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
869 *)\*(C'\fR), and you can stop watching for events at any time by calling the
870 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
871 .PP
872 As long as your watcher is active (has been started but not stopped) you
873 must not touch the values stored in it. Most specifically you must never
874 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
875 .PP
876 Each and every callback receives the event loop pointer as first, the
877 registered watcher structure as second, and a bitset of received events as
878 third argument.
879 .PP
880 The received events usually include a single bit per event type received
881 (you can receive multiple events at the same time). The possible bit masks
882 are:
883 .ie n .IP """EV_READ""" 4
884 .el .IP "\f(CWEV_READ\fR" 4
885 .IX Item "EV_READ"
886 .PD 0
887 .ie n .IP """EV_WRITE""" 4
888 .el .IP "\f(CWEV_WRITE\fR" 4
889 .IX Item "EV_WRITE"
890 .PD
891 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
892 writable.
893 .ie n .IP """EV_TIMEOUT""" 4
894 .el .IP "\f(CWEV_TIMEOUT\fR" 4
895 .IX Item "EV_TIMEOUT"
896 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
897 .ie n .IP """EV_PERIODIC""" 4
898 .el .IP "\f(CWEV_PERIODIC\fR" 4
899 .IX Item "EV_PERIODIC"
900 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
901 .ie n .IP """EV_SIGNAL""" 4
902 .el .IP "\f(CWEV_SIGNAL\fR" 4
903 .IX Item "EV_SIGNAL"
904 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
905 .ie n .IP """EV_CHILD""" 4
906 .el .IP "\f(CWEV_CHILD\fR" 4
907 .IX Item "EV_CHILD"
908 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
909 .ie n .IP """EV_STAT""" 4
910 .el .IP "\f(CWEV_STAT\fR" 4
911 .IX Item "EV_STAT"
912 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
913 .ie n .IP """EV_IDLE""" 4
914 .el .IP "\f(CWEV_IDLE\fR" 4
915 .IX Item "EV_IDLE"
916 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
917 .ie n .IP """EV_PREPARE""" 4
918 .el .IP "\f(CWEV_PREPARE\fR" 4
919 .IX Item "EV_PREPARE"
920 .PD 0
921 .ie n .IP """EV_CHECK""" 4
922 .el .IP "\f(CWEV_CHECK\fR" 4
923 .IX Item "EV_CHECK"
924 .PD
925 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
926 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
927 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
928 received events. Callbacks of both watcher types can start and stop as
929 many watchers as they want, and all of them will be taken into account
930 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
931 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
932 .ie n .IP """EV_EMBED""" 4
933 .el .IP "\f(CWEV_EMBED\fR" 4
934 .IX Item "EV_EMBED"
935 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
936 .ie n .IP """EV_FORK""" 4
937 .el .IP "\f(CWEV_FORK\fR" 4
938 .IX Item "EV_FORK"
939 The event loop has been resumed in the child process after fork (see
940 \&\f(CW\*(C`ev_fork\*(C'\fR).
941 .ie n .IP """EV_ASYNC""" 4
942 .el .IP "\f(CWEV_ASYNC\fR" 4
943 .IX Item "EV_ASYNC"
944 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
945 .ie n .IP """EV_ERROR""" 4
946 .el .IP "\f(CWEV_ERROR\fR" 4
947 .IX Item "EV_ERROR"
948 An unspecified error has occured, the watcher has been stopped. This might
949 happen because the watcher could not be properly started because libev
950 ran out of memory, a file descriptor was found to be closed or any other
951 problem. You best act on it by reporting the problem and somehow coping
952 with the watcher being stopped.
953 .Sp
954 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
955 for example it might indicate that a fd is readable or writable, and if
956 your callbacks is well-written it can just attempt the operation and cope
957 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
958 programs, though, so beware.
959 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
961 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
962 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.
963 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
964 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
965 .IX Item "ev_init (ev_TYPE *watcher, callback)"
966 This macro initialises the generic portion of a watcher. The contents
967 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
968 the generic parts of the watcher are initialised, you \fIneed\fR to call
969 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
970 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
971 which rolls both calls into one.
972 .Sp
973 You can reinitialise a watcher at any time as long as it has been stopped
974 (or never started) and there are no pending events outstanding.
975 .Sp
976 The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
977 int revents)\*(C'\fR.
978 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
979 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
980 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
981 This macro initialises the type-specific parts of a watcher. You need to
982 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
983 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
984 macro on a watcher that is active (it can be pending, however, which is a
985 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
986 .Sp
987 Although some watcher types do not have type-specific arguments
988 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
989 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
990 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
991 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
992 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
993 calls into a single call. This is the most convinient method to initialise
994 a watcher. The same limitations apply, of course.
995 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
996 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
997 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
998 Starts (activates) the given watcher. Only active watchers will receive
999 events. If the watcher is already active nothing will happen.
1000 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1001 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1002 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1003 Stops the given watcher again (if active) and clears the pending
1004 status. It is possible that stopped watchers are pending (for example,
1005 non-repeating timers are being stopped when they become pending), but
1006 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
1007 you want to free or reuse the memory used by the watcher it is therefore a
1008 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1009 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1010 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1011 Returns a true value iff the watcher is active (i.e. it has been started
1012 and not yet been stopped). As long as a watcher is active you must not modify
1013 it.
1014 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1015 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1016 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1017 events but its callback has not yet been invoked). As long as a watcher
1018 is pending (but not active) you must not call an init function on it (but
1019 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1020 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1021 it).
1022 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1023 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1024 Returns the callback currently set on the watcher.
1025 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1026 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1027 Change the callback. You can change the callback at virtually any time
1028 (modulo threads).
1029 .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1030 .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1031 .PD 0
1032 .IP "int ev_priority (ev_TYPE *watcher)" 4
1033 .IX Item "int ev_priority (ev_TYPE *watcher)"
1034 .PD
1035 Set and query the priority of the watcher. The priority is a small
1036 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1037 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1038 before watchers with lower priority, but priority will not keep watchers
1039 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1040 .Sp
1041 This means that priorities are \fIonly\fR used for ordering callback
1042 invocation after new events have been received. This is useful, for
1043 example, to reduce latency after idling, or more often, to bind two
1044 watchers on the same event and make sure one is called first.
1045 .Sp
1046 If you need to suppress invocation when higher priority events are pending
1047 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1048 .Sp
1049 You \fImust not\fR change the priority of a watcher as long as it is active or
1050 pending.
1051 .Sp
1052 The default priority used by watchers when no priority has been set is
1053 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1054 .Sp
1055 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1056 fine, as long as you do not mind that the priority value you query might
1057 or might not have been adjusted to be within valid range.
1058 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1059 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1060 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
1061 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1062 can deal with that fact.
1063 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1064 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1065 If the watcher is pending, this function returns clears its pending status
1066 and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1067 watcher isn't pending it does nothing and returns \f(CW0\fR.
1068 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1070 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1071 and read at any time, libev will completely ignore it. This can be used
1072 to associate arbitrary data with your watcher. If you need more data and
1073 don't want to allocate memory and store a pointer to it in that data
1074 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1075 data:
1076 .PP
1077 .Vb 7
1078 \& struct my_io
1079 \& {
1080 \& struct ev_io io;
1081 \& int otherfd;
1082 \& void *somedata;
1083 \& struct whatever *mostinteresting;
1084 \& }
1085 .Ve
1086 .PP
1087 And since your callback will be called with a pointer to the watcher, you
1088 can cast it back to your own type:
1089 .PP
1090 .Vb 5
1091 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1092 \& {
1093 \& struct my_io *w = (struct my_io *)w_;
1094 \& ...
1095 \& }
1096 .Ve
1097 .PP
1098 More interesting and less C\-conformant ways of casting your callback type
1099 instead have been omitted.
1100 .PP
1101 Another common scenario is having some data structure with multiple
1102 watchers:
1103 .PP
1104 .Vb 6
1105 \& struct my_biggy
1106 \& {
1107 \& int some_data;
1108 \& ev_timer t1;
1109 \& ev_timer t2;
1110 \& }
1111 .Ve
1112 .PP
1113 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1114 you need to use \f(CW\*(C`offsetof\*(C'\fR:
1115 .PP
1116 .Vb 1
1117 \& #include <stddef.h>
1118 \&
1119 \& static void
1120 \& t1_cb (EV_P_ struct ev_timer *w, int revents)
1121 \& {
1122 \& struct my_biggy big = (struct my_biggy *
1123 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1124 \& }
1125 \&
1126 \& static void
1127 \& t2_cb (EV_P_ struct ev_timer *w, int revents)
1128 \& {
1129 \& struct my_biggy big = (struct my_biggy *
1130 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1131 \& }
1132 .Ve
1134 .IX Header "WATCHER TYPES"
1135 This section describes each watcher in detail, but will not repeat
1136 information given in the last section. Any initialisation/set macros,
1137 functions and members specific to the watcher type are explained.
1138 .PP
1139 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1140 while the watcher is active, you can look at the member and expect some
1141 sensible content, but you must not modify it (you can modify it while the
1142 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1143 means you can expect it to have some sensible content while the watcher
1144 is active, but you can also modify it. Modifying it may not do something
1145 sensible or take immediate effect (or do anything at all), but libev will
1146 not crash or malfunction in any way.
1147 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1148 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1149 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1150 I/O watchers check whether a file descriptor is readable or writable
1151 in each iteration of the event loop, or, more precisely, when reading
1152 would not block the process and writing would at least be able to write
1153 some data. This behaviour is called level-triggering because you keep
1154 receiving events as long as the condition persists. Remember you can stop
1155 the watcher if you don't want to act on the event and neither want to
1156 receive future events.
1157 .PP
1158 In general you can register as many read and/or write event watchers per
1159 fd as you want (as long as you don't confuse yourself). Setting all file
1160 descriptors to non-blocking mode is also usually a good idea (but not
1161 required if you know what you are doing).
1162 .PP
1163 If you must do this, then force the use of a known-to-be-good backend
1164 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1165 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1166 .PP
1167 Another thing you have to watch out for is that it is quite easy to
1168 receive \*(L"spurious\*(R" readyness notifications, that is your callback might
1169 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1170 because there is no data. Not only are some backends known to create a
1171 lot of those (for example solaris ports), it is very easy to get into
1172 this situation even with a relatively standard program structure. Thus
1173 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1174 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1175 .PP
1176 If you cannot run the fd in non-blocking mode (for example you should not
1177 play around with an Xlib connection), then you have to seperately re-test
1178 whether a file descriptor is really ready with a known-to-be good interface
1179 such as poll (fortunately in our Xlib example, Xlib already does this on
1180 its own, so its quite safe to use).
1181 .PP
1182 \fIThe special problem of disappearing file descriptors\fR
1183 .IX Subsection "The special problem of disappearing file descriptors"
1184 .PP
1185 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1186 descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
1187 such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file
1188 descriptor, but when it goes away, the operating system will silently drop
1189 this interest. If another file descriptor with the same number then is
1190 registered with libev, there is no efficient way to see that this is, in
1191 fact, a different file descriptor.
1192 .PP
1193 To avoid having to explicitly tell libev about such cases, libev follows
1194 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1195 will assume that this is potentially a new file descriptor, otherwise
1196 it is assumed that the file descriptor stays the same. That means that
1197 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
1198 descriptor even if the file descriptor number itself did not change.
1199 .PP
1200 This is how one would do it normally anyway, the important point is that
1201 the libev application should not optimise around libev but should leave
1202 optimisations to libev.
1203 .PP
1204 \fIThe special problem of dup'ed file descriptors\fR
1205 .IX Subsection "The special problem of dup'ed file descriptors"
1206 .PP
1207 Some backends (e.g. epoll), cannot register events for file descriptors,
1208 but only events for the underlying file descriptions. That means when you
1209 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1210 events for them, only one file descriptor might actually receive events.
1211 .PP
1212 There is no workaround possible except not registering events
1213 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1214 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1215 .PP
1216 \fIThe special problem of fork\fR
1217 .IX Subsection "The special problem of fork"
1218 .PP
1219 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1220 useless behaviour. Libev fully supports fork, but needs to be told about
1221 it in the child.
1222 .PP
1223 To support fork in your programs, you either have to call
1224 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1225 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1226 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1227 .PP
1228 \fIThe special problem of \s-1SIGPIPE\s0\fR
1229 .IX Subsection "The special problem of SIGPIPE"
1230 .PP
1231 While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0
1232 when reading from a pipe whose other end has been closed, your program
1233 gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most
1234 programs this is sensible behaviour, for daemons, this is usually
1235 undesirable.
1236 .PP
1237 So when you encounter spurious, unexplained daemon exits, make sure you
1238 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1239 somewhere, as that would have given you a big clue).
1240 .PP
1241 \fIWatcher-Specific Functions\fR
1242 .IX Subsection "Watcher-Specific Functions"
1243 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1244 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1245 .PD 0
1246 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1247 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1248 .PD
1249 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1250 rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1251 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1252 .IP "int fd [read\-only]" 4
1253 .IX Item "int fd [read-only]"
1254 The file descriptor being watched.
1255 .IP "int events [read\-only]" 4
1256 .IX Item "int events [read-only]"
1257 The events being watched.
1258 .PP
1259 \fIExamples\fR
1260 .IX Subsection "Examples"
1261 .PP
1262 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1263 readable, but only once. Since it is likely line-buffered, you could
1264 attempt to read a whole line in the callback.
1265 .PP
1266 .Vb 6
1267 \& static void
1268 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1269 \& {
1270 \& ev_io_stop (loop, w);
1271 \& .. read from stdin here (or from w\->fd) and haqndle any I/O errors
1272 \& }
1273 \&
1274 \& ...
1275 \& struct ev_loop *loop = ev_default_init (0);
1276 \& struct ev_io stdin_readable;
1277 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1278 \& ev_io_start (loop, &stdin_readable);
1279 \& ev_loop (loop, 0);
1280 .Ve
1281 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1282 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1283 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1284 Timer watchers are simple relative timers that generate an event after a
1285 given time, and optionally repeating in regular intervals after that.
1286 .PP
1287 The timers are based on real time, that is, if you register an event that
1288 times out after an hour and you reset your system clock to last years
1289 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
1290 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1291 monotonic clock option helps a lot here).
1292 .PP
1293 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1294 time. This is usually the right thing as this timestamp refers to the time
1295 of the event triggering whatever timeout you are modifying/starting. If
1296 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
1297 on the current time, use something like this to adjust for this:
1298 .PP
1299 .Vb 1
1300 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1301 .Ve
1302 .PP
1303 The callback is guarenteed to be invoked only when its timeout has passed,
1304 but if multiple timers become ready during the same loop iteration then
1305 order of execution is undefined.
1306 .PP
1307 \fIWatcher-Specific Functions and Data Members\fR
1308 .IX Subsection "Watcher-Specific Functions and Data Members"
1309 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1310 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1311 .PD 0
1312 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1313 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1314 .PD
1315 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
1316 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
1317 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
1318 later, again, and again, until stopped manually.
1319 .Sp
1320 The timer itself will do a best-effort at avoiding drift, that is, if you
1321 configure a timer to trigger every 10 seconds, then it will trigger at
1322 exactly 10 second intervals. If, however, your program cannot keep up with
1323 the timer (because it takes longer than those 10 seconds to do stuff) the
1324 timer will not fire more than once per event loop iteration.
1325 .IP "ev_timer_again (loop, ev_timer *)" 4
1326 .IX Item "ev_timer_again (loop, ev_timer *)"
1327 This will act as if the timer timed out and restart it again if it is
1328 repeating. The exact semantics are:
1329 .Sp
1330 If the timer is pending, its pending status is cleared.
1331 .Sp
1332 If the timer is started but nonrepeating, stop it (as if it timed out).
1333 .Sp
1334 If the timer is repeating, either start it if necessary (with the
1335 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1336 .Sp
1337 This sounds a bit complicated, but here is a useful and typical
1338 example: Imagine you have a tcp connection and you want a so-called idle
1339 timeout, that is, you want to be called when there have been, say, 60
1340 seconds of inactivity on the socket. The easiest way to do this is to
1341 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
1342 \&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1343 you go into an idle state where you do not expect data to travel on the
1344 socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1345 automatically restart it if need be.
1346 .Sp
1347 That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1348 altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1349 .Sp
1350 .Vb 8
1351 \& ev_timer_init (timer, callback, 0., 5.);
1352 \& ev_timer_again (loop, timer);
1353 \& ...
1354 \& timer\->again = 17.;
1355 \& ev_timer_again (loop, timer);
1356 \& ...
1357 \& timer\->again = 10.;
1358 \& ev_timer_again (loop, timer);
1359 .Ve
1360 .Sp
1361 This is more slightly efficient then stopping/starting the timer each time
1362 you want to modify its timeout value.
1363 .IP "ev_tstamp repeat [read\-write]" 4
1364 .IX Item "ev_tstamp repeat [read-write]"
1365 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1366 or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1367 which is also when any modifications are taken into account.
1368 .PP
1369 \fIExamples\fR
1370 .IX Subsection "Examples"
1371 .PP
1372 Example: Create a timer that fires after 60 seconds.
1373 .PP
1374 .Vb 5
1375 \& static void
1376 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1377 \& {
1378 \& .. one minute over, w is actually stopped right here
1379 \& }
1380 \&
1381 \& struct ev_timer mytimer;
1382 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1383 \& ev_timer_start (loop, &mytimer);
1384 .Ve
1385 .PP
1386 Example: Create a timeout timer that times out after 10 seconds of
1387 inactivity.
1388 .PP
1389 .Vb 5
1390 \& static void
1391 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1392 \& {
1393 \& .. ten seconds without any activity
1394 \& }
1395 \&
1396 \& struct ev_timer mytimer;
1397 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1398 \& ev_timer_again (&mytimer); /* start timer */
1399 \& ev_loop (loop, 0);
1400 \&
1401 \& // and in some piece of code that gets executed on any "activity":
1402 \& // reset the timeout to start ticking again at 10 seconds
1403 \& ev_timer_again (&mytimer);
1404 .Ve
1405 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1406 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1407 .IX Subsection "ev_periodic - to cron or not to cron?"
1408 Periodic watchers are also timers of a kind, but they are very versatile
1409 (and unfortunately a bit complex).
1410 .PP
1411 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1412 but on wallclock time (absolute time). You can tell a periodic watcher
1413 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1414 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1415 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1416 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1417 roughly 10 seconds later).
1418 .PP
1419 They can also be used to implement vastly more complex timers, such as
1420 triggering an event on each midnight, local time or other, complicated,
1421 rules.
1422 .PP
1423 As with timers, the callback is guarenteed to be invoked only when the
1424 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1425 during the same loop iteration then order of execution is undefined.
1426 .PP
1427 \fIWatcher-Specific Functions and Data Members\fR
1428 .IX Subsection "Watcher-Specific Functions and Data Members"
1429 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1430 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1431 .PD 0
1432 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1433 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1434 .PD
1435 Lots of arguments, lets sort it out... There are basically three modes of
1436 operation, and we will explain them from simplest to complex:
1437 .RS 4
1438 .IP "\(bu" 4
1439 absolute timer (at = time, interval = reschedule_cb = 0)
1440 .Sp
1441 In this configuration the watcher triggers an event at the wallclock time
1442 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1443 that is, if it is to be run at January 1st 2011 then it will run when the
1444 system time reaches or surpasses this time.
1445 .IP "\(bu" 4
1446 repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1447 .Sp
1448 In this mode the watcher will always be scheduled to time out at the next
1449 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
1450 and then repeat, regardless of any time jumps.
1451 .Sp
1452 This can be used to create timers that do not drift with respect to system
1453 time:
1454 .Sp
1455 .Vb 1
1456 \& ev_periodic_set (&periodic, 0., 3600., 0);
1457 .Ve
1458 .Sp
1459 This doesn't mean there will always be 3600 seconds in between triggers,
1460 but only that the the callback will be called when the system time shows a
1461 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1462 by 3600.
1463 .Sp
1464 Another way to think about it (for the mathematically inclined) is that
1465 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1466 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1467 .Sp
1468 For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1469 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1470 this value.
1471 .IP "\(bu" 4
1472 manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1473 .Sp
1474 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1475 ignored. Instead, each time the periodic watcher gets scheduled, the
1476 reschedule callback will be called with the watcher as first, and the
1477 current time as second argument.
1478 .Sp
1479 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1480 ever, or make any event loop modifications\fR. If you need to stop it,
1481 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1482 starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).
1483 .Sp
1484 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1485 ev_tstamp now)\*(C'\fR, e.g.:
1486 .Sp
1487 .Vb 4
1488 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1489 \& {
1490 \& return now + 60.;
1491 \& }
1492 .Ve
1493 .Sp
1494 It must return the next time to trigger, based on the passed time value
1495 (that is, the lowest time value larger than to the second argument). It
1496 will usually be called just before the callback will be triggered, but
1497 might be called at other times, too.
1498 .Sp
1499 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1500 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.
1501 .Sp
1502 This can be used to create very complex timers, such as a timer that
1503 triggers on each midnight, local time. To do this, you would calculate the
1504 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1505 you do this is, again, up to you (but it is not trivial, which is the main
1506 reason I omitted it as an example).
1507 .RE
1508 .RS 4
1509 .RE
1510 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1511 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1512 Simply stops and restarts the periodic watcher again. This is only useful
1513 when you changed some parameters or the reschedule callback would return
1514 a different time than the last time it was called (e.g. in a crond like
1515 program when the crontabs have changed).
1516 .IP "ev_tstamp offset [read\-write]" 4
1517 .IX Item "ev_tstamp offset [read-write]"
1518 When repeating, this contains the offset value, otherwise this is the
1519 absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1520 .Sp
1521 Can be modified any time, but changes only take effect when the periodic
1522 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1523 .IP "ev_tstamp interval [read\-write]" 4
1524 .IX Item "ev_tstamp interval [read-write]"
1525 The current interval value. Can be modified any time, but changes only
1526 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1527 called.
1528 .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1529 .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1530 The current reschedule callback, or \f(CW0\fR, if this functionality is
1531 switched off. Can be changed any time, but changes only take effect when
1532 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1533 .IP "ev_tstamp at [read\-only]" 4
1534 .IX Item "ev_tstamp at [read-only]"
1535 When active, contains the absolute time that the watcher is supposed to
1536 trigger next.
1537 .PP
1538 \fIExamples\fR
1539 .IX Subsection "Examples"
1540 .PP
1541 Example: Call a callback every hour, or, more precisely, whenever the
1542 system clock is divisible by 3600. The callback invocation times have
1543 potentially a lot of jittering, but good long-term stability.
1544 .PP
1545 .Vb 5
1546 \& static void
1547 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1548 \& {
1549 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1550 \& }
1551 \&
1552 \& struct ev_periodic hourly_tick;
1553 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1554 \& ev_periodic_start (loop, &hourly_tick);
1555 .Ve
1556 .PP
1557 Example: The same as above, but use a reschedule callback to do it:
1558 .PP
1559 .Vb 1
1560 \& #include <math.h>
1561 \&
1562 \& static ev_tstamp
1563 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1564 \& {
1565 \& return fmod (now, 3600.) + 3600.;
1566 \& }
1567 \&
1568 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1569 .Ve
1570 .PP
1571 Example: Call a callback every hour, starting now:
1572 .PP
1573 .Vb 4
1574 \& struct ev_periodic hourly_tick;
1575 \& ev_periodic_init (&hourly_tick, clock_cb,
1576 \& fmod (ev_now (loop), 3600.), 3600., 0);
1577 \& ev_periodic_start (loop, &hourly_tick);
1578 .Ve
1579 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1580 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1581 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1582 Signal watchers will trigger an event when the process receives a specific
1583 signal one or more times. Even though signals are very asynchronous, libev
1584 will try it's best to deliver signals synchronously, i.e. as part of the
1585 normal event processing, like any other event.
1586 .PP
1587 You can configure as many watchers as you like per signal. Only when the
1588 first watcher gets started will libev actually register a signal watcher
1589 with the kernel (thus it coexists with your own signal handlers as long
1590 as you don't register any with libev). Similarly, when the last signal
1591 watcher for a signal is stopped libev will reset the signal handler to
1592 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1593 .PP
1594 If possible and supported, libev will install its handlers with
1595 \&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly
1596 interrupted. If you have a problem with syscalls getting interrupted by
1597 signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1598 them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1599 .PP
1600 \fIWatcher-Specific Functions and Data Members\fR
1601 .IX Subsection "Watcher-Specific Functions and Data Members"
1602 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1603 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1604 .PD 0
1605 .IP "ev_signal_set (ev_signal *, int signum)" 4
1606 .IX Item "ev_signal_set (ev_signal *, int signum)"
1607 .PD
1608 Configures the watcher to trigger on the given signal number (usually one
1609 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1610 .IP "int signum [read\-only]" 4
1611 .IX Item "int signum [read-only]"
1612 The signal the watcher watches out for.
1613 .PP
1614 \fIExamples\fR
1615 .IX Subsection "Examples"
1616 .PP
1617 Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1618 .PP
1619 .Vb 5
1620 \& static void
1621 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1622 \& {
1623 \& ev_unloop (loop, EVUNLOOP_ALL);
1624 \& }
1625 \&
1626 \& struct ev_signal signal_watcher;
1627 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1628 \& ev_signal_start (loop, &sigint_cb);
1629 .Ve
1630 .ie n .Sh """ev_child"" \- watch out for process status changes"
1631 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1632 .IX Subsection "ev_child - watch out for process status changes"
1633 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1634 some child status changes (most typically when a child of yours dies). It
1635 is permissible to install a child watcher \fIafter\fR the child has been
1636 forked (which implies it might have already exited), as long as the event
1637 loop isn't entered (or is continued from a watcher).
1638 .PP
1639 Only the default event loop is capable of handling signals, and therefore
1640 you can only rgeister child watchers in the default event loop.
1641 .PP
1642 \fIProcess Interaction\fR
1643 .IX Subsection "Process Interaction"
1644 .PP
1645 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
1646 initialised. This is necessary to guarantee proper behaviour even if
1647 the first child watcher is started after the child exits. The occurance
1648 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
1649 synchronously as part of the event loop processing. Libev always reaps all
1650 children, even ones not watched.
1651 .PP
1652 \fIOverriding the Built-In Processing\fR
1653 .IX Subsection "Overriding the Built-In Processing"
1654 .PP
1655 Libev offers no special support for overriding the built-in child
1656 processing, but if your application collides with libev's default child
1657 handler, you can override it easily by installing your own handler for
1658 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
1659 default loop never gets destroyed. You are encouraged, however, to use an
1660 event-based approach to child reaping and thus use libev's support for
1661 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
1662 .PP
1663 \fIWatcher-Specific Functions and Data Members\fR
1664 .IX Subsection "Watcher-Specific Functions and Data Members"
1665 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1666 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1667 .PD 0
1668 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
1669 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
1670 .PD
1671 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1672 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1673 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1674 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1675 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1676 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1677 activate the watcher when the process terminates) or \f(CW1\fR (additionally
1678 activate the watcher when the process is stopped or continued).
1679 .IP "int pid [read\-only]" 4
1680 .IX Item "int pid [read-only]"
1681 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1682 .IP "int rpid [read\-write]" 4
1683 .IX Item "int rpid [read-write]"
1684 The process id that detected a status change.
1685 .IP "int rstatus [read\-write]" 4
1686 .IX Item "int rstatus [read-write]"
1687 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1688 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1689 .PP
1690 \fIExamples\fR
1691 .IX Subsection "Examples"
1692 .PP
1693 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
1694 its completion.
1695 .PP
1696 .Vb 1
1697 \& ev_child cw;
1698 \&
1699 \& static void
1700 \& child_cb (EV_P_ struct ev_child *w, int revents)
1701 \& {
1702 \& ev_child_stop (EV_A_ w);
1703 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1704 \& }
1705 \&
1706 \& pid_t pid = fork ();
1707 \&
1708 \& if (pid < 0)
1709 \& // error
1710 \& else if (pid == 0)
1711 \& {
1712 \& // the forked child executes here
1713 \& exit (1);
1714 \& }
1715 \& else
1716 \& {
1717 \& ev_child_init (&cw, child_cb, pid, 0);
1718 \& ev_child_start (EV_DEFAULT_ &cw);
1719 \& }
1720 .Ve
1721 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
1722 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1723 .IX Subsection "ev_stat - did the file attributes just change?"
1724 This watches a filesystem path for attribute changes. That is, it calls
1725 \&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1726 compared to the last time, invoking the callback if it did.
1727 .PP
1728 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1729 not exist\*(R" is a status change like any other. The condition \*(L"path does
1730 not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1731 otherwise always forced to be at least one) and all the other fields of
1732 the stat buffer having unspecified contents.
1733 .PP
1734 The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1735 relative and your working directory changes, the behaviour is undefined.
1736 .PP
1737 Since there is no standard to do this, the portable implementation simply
1738 calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1739 can specify a recommended polling interval for this case. If you specify
1740 a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1741 unspecified default\fR value will be used (which you can expect to be around
1742 five seconds, although this might change dynamically). Libev will also
1743 impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1744 usually overkill.
1745 .PP
1746 This watcher type is not meant for massive numbers of stat watchers,
1747 as even with OS-supported change notifications, this can be
1748 resource-intensive.
1749 .PP
1750 At the time of this writing, only the Linux inotify interface is
1751 implemented (implementing kqueue support is left as an exercise for the
1752 reader). Inotify will be used to give hints only and should not change the
1753 semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs
1754 to fall back to regular polling again even with inotify, but changes are
1755 usually detected immediately, and if the file exists there will be no
1756 polling.
1757 .PP
1758 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
1759 .IX Subsection "ABI Issues (Largefile Support)"
1760 .PP
1761 Libev by default (unless the user overrides this) uses the default
1762 compilation environment, which means that on systems with optionally
1763 disabled large file support, you get the 32 bit version of the stat
1764 structure. When using the library from programs that change the \s-1ABI\s0 to
1765 use 64 bit file offsets the programs will fail. In that case you have to
1766 compile libev with the same flags to get binary compatibility. This is
1767 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
1768 most noticably with ev_stat and largefile support.
1769 .PP
1770 \fIInotify\fR
1771 .IX Subsection "Inotify"
1772 .PP
1773 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1774 available on Linux) and present at runtime, it will be used to speed up
1775 change detection where possible. The inotify descriptor will be created lazily
1776 when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1777 .PP
1778 Inotify presense does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1779 except that changes might be detected earlier, and in some cases, to avoid
1780 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presense of inotify support
1781 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1782 .PP
1783 (There is no support for kqueue, as apparently it cannot be used to
1784 implement this functionality, due to the requirement of having a file
1785 descriptor open on the object at all times).
1786 .PP
1787 \fIThe special problem of stat time resolution\fR
1788 .IX Subsection "The special problem of stat time resolution"
1789 .PP
1790 The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1791 even on systems where the resolution is higher, many filesystems still
1792 only support whole seconds.
1793 .PP
1794 That means that, if the time is the only thing that changes, you might
1795 miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and calls
1796 your callback, which does something. When there is another update within
1797 the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it.
1798 .PP
1799 The solution to this is to delay acting on a change for a second (or till
1800 the next second boundary), using a roughly one-second delay \f(CW\*(C`ev_timer\*(C'\fR
1801 (\f(CW\*(C`ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)\*(C'\fR). The \f(CW.01\fR
1802 is added to work around small timing inconsistencies of some operating
1803 systems.
1804 .PP
1805 \fIWatcher-Specific Functions and Data Members\fR
1806 .IX Subsection "Watcher-Specific Functions and Data Members"
1807 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1808 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1809 .PD 0
1810 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1811 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1812 .PD
1813 Configures the watcher to wait for status changes of the given
1814 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1815 be detected and should normally be specified as \f(CW0\fR to let libev choose
1816 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1817 path for as long as the watcher is active.
1818 .Sp
1819 The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected,
1820 relative to the attributes at the time the watcher was started (or the
1821 last change was detected).
1822 .IP "ev_stat_stat (loop, ev_stat *)" 4
1823 .IX Item "ev_stat_stat (loop, ev_stat *)"
1824 Updates the stat buffer immediately with new values. If you change the
1825 watched path in your callback, you could call this fucntion to avoid
1826 detecting this change (while introducing a race condition). Can also be
1827 useful simply to find out the new values.
1828 .IP "ev_statdata attr [read\-only]" 4
1829 .IX Item "ev_statdata attr [read-only]"
1830 The most-recently detected attributes of the file. Although the type is of
1831 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1832 suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there
1833 was some error while \f(CW\*(C`stat\*(C'\fRing the file.
1834 .IP "ev_statdata prev [read\-only]" 4
1835 .IX Item "ev_statdata prev [read-only]"
1836 The previous attributes of the file. The callback gets invoked whenever
1837 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR.
1838 .IP "ev_tstamp interval [read\-only]" 4
1839 .IX Item "ev_tstamp interval [read-only]"
1840 The specified interval.
1841 .IP "const char *path [read\-only]" 4
1842 .IX Item "const char *path [read-only]"
1843 The filesystem path that is being watched.
1844 .PP
1845 \fIExamples\fR
1846 .IX Subsection "Examples"
1847 .PP
1848 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1849 .PP
1850 .Vb 10
1851 \& static void
1852 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1853 \& {
1854 \& /* /etc/passwd changed in some way */
1855 \& if (w\->attr.st_nlink)
1856 \& {
1857 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1858 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1859 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1860 \& }
1861 \& else
1862 \& /* you shalt not abuse printf for puts */
1863 \& puts ("wow, /etc/passwd is not there, expect problems. "
1864 \& "if this is windows, they already arrived\en");
1865 \& }
1866 \&
1867 \& ...
1868 \& ev_stat passwd;
1869 \&
1870 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1871 \& ev_stat_start (loop, &passwd);
1872 .Ve
1873 .PP
1874 Example: Like above, but additionally use a one-second delay so we do not
1875 miss updates (however, frequent updates will delay processing, too, so
1876 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1877 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1878 .PP
1879 .Vb 2
1880 \& static ev_stat passwd;
1881 \& static ev_timer timer;
1882 \&
1883 \& static void
1884 \& timer_cb (EV_P_ ev_timer *w, int revents)
1885 \& {
1886 \& ev_timer_stop (EV_A_ w);
1887 \&
1888 \& /* now it\*(Aqs one second after the most recent passwd change */
1889 \& }
1890 \&
1891 \& static void
1892 \& stat_cb (EV_P_ ev_stat *w, int revents)
1893 \& {
1894 \& /* reset the one\-second timer */
1895 \& ev_timer_again (EV_A_ &timer);
1896 \& }
1897 \&
1898 \& ...
1899 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1900 \& ev_stat_start (loop, &passwd);
1901 \& ev_timer_init (&timer, timer_cb, 0., 1.01);
1902 .Ve
1903 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1904 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1905 .IX Subsection "ev_idle - when you've got nothing better to do..."
1906 Idle watchers trigger events when no other events of the same or higher
1907 priority are pending (prepare, check and other idle watchers do not
1908 count).
1909 .PP
1910 That is, as long as your process is busy handling sockets or timeouts
1911 (or even signals, imagine) of the same or higher priority it will not be
1912 triggered. But when your process is idle (or only lower-priority watchers
1913 are pending), the idle watchers are being called once per event loop
1914 iteration \- until stopped, that is, or your process receives more events
1915 and becomes busy again with higher priority stuff.
1916 .PP
1917 The most noteworthy effect is that as long as any idle watchers are
1918 active, the process will not block when waiting for new events.
1919 .PP
1920 Apart from keeping your process non-blocking (which is a useful
1921 effect on its own sometimes), idle watchers are a good place to do
1922 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1923 event loop has handled all outstanding events.
1924 .PP
1925 \fIWatcher-Specific Functions and Data Members\fR
1926 .IX Subsection "Watcher-Specific Functions and Data Members"
1927 .IP "ev_idle_init (ev_signal *, callback)" 4
1928 .IX Item "ev_idle_init (ev_signal *, callback)"
1929 Initialises and configures the idle watcher \- it has no parameters of any
1930 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1931 believe me.
1932 .PP
1933 \fIExamples\fR
1934 .IX Subsection "Examples"
1935 .PP
1936 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1937 callback, free it. Also, use no error checking, as usual.
1938 .PP
1939 .Vb 7
1940 \& static void
1941 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1942 \& {
1943 \& free (w);
1944 \& // now do something you wanted to do when the program has
1945 \& // no longer anything immediate to do.
1946 \& }
1947 \&
1948 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1949 \& ev_idle_init (idle_watcher, idle_cb);
1950 \& ev_idle_start (loop, idle_cb);
1951 .Ve
1952 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1953 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1954 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
1955 Prepare and check watchers are usually (but not always) used in tandem:
1956 prepare watchers get invoked before the process blocks and check watchers
1957 afterwards.
1958 .PP
1959 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1960 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1961 watchers. Other loops than the current one are fine, however. The
1962 rationale behind this is that you do not need to check for recursion in
1963 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1964 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1965 called in pairs bracketing the blocking call.
1966 .PP
1967 Their main purpose is to integrate other event mechanisms into libev and
1968 their use is somewhat advanced. This could be used, for example, to track
1969 variable changes, implement your own watchers, integrate net-snmp or a
1970 coroutine library and lots more. They are also occasionally useful if
1971 you cache some data and want to flush it before blocking (for example,
1972 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1973 watcher).
1974 .PP
1975 This is done by examining in each prepare call which file descriptors need
1976 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1977 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1978 provide just this functionality). Then, in the check watcher you check for
1979 any events that occured (by checking the pending status of all watchers
1980 and stopping them) and call back into the library. The I/O and timer
1981 callbacks will never actually be called (but must be valid nevertheless,
1982 because you never know, you know?).
1983 .PP
1984 As another example, the Perl Coro module uses these hooks to integrate
1985 coroutines into libev programs, by yielding to other active coroutines
1986 during each prepare and only letting the process block if no coroutines
1987 are ready to run (it's actually more complicated: it only runs coroutines
1988 with priority higher than or equal to the event loop and one coroutine
1989 of lower priority, but only once, using idle watchers to keep the event
1990 loop from blocking if lower-priority coroutines are active, thus mapping
1991 low-priority coroutines to idle/background tasks).
1992 .PP
1993 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
1994 priority, to ensure that they are being run before any other watchers
1995 after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
1996 too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
1997 supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers
1998 did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
1999 (non-libev) event loops those other event loops might be in an unusable
2000 state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
2001 coexist peacefully with others).
2002 .PP
2003 \fIWatcher-Specific Functions and Data Members\fR
2004 .IX Subsection "Watcher-Specific Functions and Data Members"
2005 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2006 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2007 .PD 0
2008 .IP "ev_check_init (ev_check *, callback)" 4
2009 .IX Item "ev_check_init (ev_check *, callback)"
2010 .PD
2011 Initialises and configures the prepare or check watcher \- they have no
2012 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2013 macros, but using them is utterly, utterly and completely pointless.
2014 .PP
2015 \fIExamples\fR
2016 .IX Subsection "Examples"
2017 .PP
2018 There are a number of principal ways to embed other event loops or modules
2019 into libev. Here are some ideas on how to include libadns into libev
2020 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2021 use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR
2022 embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0
2023 into the Glib event loop).
2024 .PP
2025 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2026 and in a check watcher, destroy them and call into libadns. What follows
2027 is pseudo-code only of course. This requires you to either use a low
2028 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2029 the callbacks for the IO/timeout watchers might not have been called yet.
2030 .PP
2031 .Vb 2
2032 \& static ev_io iow [nfd];
2033 \& static ev_timer tw;
2034 \&
2035 \& static void
2036 \& io_cb (ev_loop *loop, ev_io *w, int revents)
2037 \& {
2038 \& }
2039 \&
2040 \& // create io watchers for each fd and a timer before blocking
2041 \& static void
2042 \& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
2043 \& {
2044 \& int timeout = 3600000;
2045 \& struct pollfd fds [nfd];
2046 \& // actual code will need to loop here and realloc etc.
2047 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2048 \&
2049 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2050 \& ev_timer_init (&tw, 0, timeout * 1e\-3);
2051 \& ev_timer_start (loop, &tw);
2052 \&
2053 \& // create one ev_io per pollfd
2054 \& for (int i = 0; i < nfd; ++i)
2055 \& {
2056 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2057 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2058 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2059 \&
2060 \& fds [i].revents = 0;
2061 \& ev_io_start (loop, iow + i);
2062 \& }
2063 \& }
2064 \&
2065 \& // stop all watchers after blocking
2066 \& static void
2067 \& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
2068 \& {
2069 \& ev_timer_stop (loop, &tw);
2070 \&
2071 \& for (int i = 0; i < nfd; ++i)
2072 \& {
2073 \& // set the relevant poll flags
2074 \& // could also call adns_processreadable etc. here
2075 \& struct pollfd *fd = fds + i;
2076 \& int revents = ev_clear_pending (iow + i);
2077 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2078 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2079 \&
2080 \& // now stop the watcher
2081 \& ev_io_stop (loop, iow + i);
2082 \& }
2083 \&
2084 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2085 \& }
2086 .Ve
2087 .PP
2088 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2089 in the prepare watcher and would dispose of the check watcher.
2090 .PP
2091 Method 3: If the module to be embedded supports explicit event
2092 notification (adns does), you can also make use of the actual watcher
2093 callbacks, and only destroy/create the watchers in the prepare watcher.
2094 .PP
2095 .Vb 5
2096 \& static void
2097 \& timer_cb (EV_P_ ev_timer *w, int revents)
2098 \& {
2099 \& adns_state ads = (adns_state)w\->data;
2100 \& update_now (EV_A);
2101 \&
2102 \& adns_processtimeouts (ads, &tv_now);
2103 \& }
2104 \&
2105 \& static void
2106 \& io_cb (EV_P_ ev_io *w, int revents)
2107 \& {
2108 \& adns_state ads = (adns_state)w\->data;
2109 \& update_now (EV_A);
2110 \&
2111 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2112 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2113 \& }
2114 \&
2115 \& // do not ever call adns_afterpoll
2116 .Ve
2117 .PP
2118 Method 4: Do not use a prepare or check watcher because the module you
2119 want to embed is too inflexible to support it. Instead, youc na override
2120 their poll function. The drawback with this solution is that the main
2121 loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
2122 this.
2123 .PP
2124 .Vb 4
2125 \& static gint
2126 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2127 \& {
2128 \& int got_events = 0;
2129 \&
2130 \& for (n = 0; n < nfds; ++n)
2131 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2132 \&
2133 \& if (timeout >= 0)
2134 \& // create/start timer
2135 \&
2136 \& // poll
2137 \& ev_loop (EV_A_ 0);
2138 \&
2139 \& // stop timer again
2140 \& if (timeout >= 0)
2141 \& ev_timer_stop (EV_A_ &to);
2142 \&
2143 \& // stop io watchers again \- their callbacks should have set
2144 \& for (n = 0; n < nfds; ++n)
2145 \& ev_io_stop (EV_A_ iow [n]);
2146 \&
2147 \& return got_events;
2148 \& }
2149 .Ve
2150 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2151 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2152 .IX Subsection "ev_embed - when one backend isn't enough..."
2153 This is a rather advanced watcher type that lets you embed one event loop
2154 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2155 loop, other types of watchers might be handled in a delayed or incorrect
2156 fashion and must not be used).
2157 .PP
2158 There are primarily two reasons you would want that: work around bugs and
2159 prioritise I/O.
2160 .PP
2161 As an example for a bug workaround, the kqueue backend might only support
2162 sockets on some platform, so it is unusable as generic backend, but you
2163 still want to make use of it because you have many sockets and it scales
2164 so nicely. In this case, you would create a kqueue-based loop and embed it
2165 into your default loop (which might use e.g. poll). Overall operation will
2166 be a bit slower because first libev has to poll and then call kevent, but
2167 at least you can use both at what they are best.
2168 .PP
2169 As for prioritising I/O: rarely you have the case where some fds have
2170 to be watched and handled very quickly (with low latency), and even
2171 priorities and idle watchers might have too much overhead. In this case
2172 you would put all the high priority stuff in one loop and all the rest in
2173 a second one, and embed the second one in the first.
2174 .PP
2175 As long as the watcher is active, the callback will be invoked every time
2176 there might be events pending in the embedded loop. The callback must then
2177 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2178 their callbacks (you could also start an idle watcher to give the embedded
2179 loop strictly lower priority for example). You can also set the callback
2180 to \f(CW0\fR, in which case the embed watcher will automatically execute the
2181 embedded loop sweep.
2182 .PP
2183 As long as the watcher is started it will automatically handle events. The
2184 callback will be invoked whenever some events have been handled. You can
2185 set the callback to \f(CW0\fR to avoid having to specify one if you are not
2186 interested in that.
2187 .PP
2188 Also, there have not currently been made special provisions for forking:
2189 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2190 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2191 yourself.
2192 .PP
2193 Unfortunately, not all backends are embeddable, only the ones returned by
2194 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2195 portable one.
2196 .PP
2197 So when you want to use this feature you will always have to be prepared
2198 that you cannot get an embeddable loop. The recommended way to get around
2199 this is to have a separate variables for your embeddable loop, try to
2200 create it, and if that fails, use the normal loop for everything.
2201 .PP
2202 \fIWatcher-Specific Functions and Data Members\fR
2203 .IX Subsection "Watcher-Specific Functions and Data Members"
2204 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2205 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2206 .PD 0
2207 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2208 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2209 .PD
2210 Configures the watcher to embed the given loop, which must be
2211 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2212 invoked automatically, otherwise it is the responsibility of the callback
2213 to invoke it (it will continue to be called until the sweep has been done,
2214 if you do not want thta, you need to temporarily stop the embed watcher).
2215 .IP "ev_embed_sweep (loop, ev_embed *)" 4
2216 .IX Item "ev_embed_sweep (loop, ev_embed *)"
2217 Make a single, non-blocking sweep over the embedded loop. This works
2218 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2219 apropriate way for embedded loops.
2220 .IP "struct ev_loop *other [read\-only]" 4
2221 .IX Item "struct ev_loop *other [read-only]"
2222 The embedded event loop.
2223 .PP
2224 \fIExamples\fR
2225 .IX Subsection "Examples"
2226 .PP
2227 Example: Try to get an embeddable event loop and embed it into the default
2228 event loop. If that is not possible, use the default loop. The default
2229 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in
2230 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be
2231 used).
2232 .PP
2233 .Vb 3
2234 \& struct ev_loop *loop_hi = ev_default_init (0);
2235 \& struct ev_loop *loop_lo = 0;
2236 \& struct ev_embed embed;
2237 \&
2238 \& // see if there is a chance of getting one that works
2239 \& // (remember that a flags value of 0 means autodetection)
2240 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2241 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2242 \& : 0;
2243 \&
2244 \& // if we got one, then embed it, otherwise default to loop_hi
2245 \& if (loop_lo)
2246 \& {
2247 \& ev_embed_init (&embed, 0, loop_lo);
2248 \& ev_embed_start (loop_hi, &embed);
2249 \& }
2250 \& else
2251 \& loop_lo = loop_hi;
2252 .Ve
2253 .PP
2254 Example: Check if kqueue is available but not recommended and create
2255 a kqueue backend for use with sockets (which usually work with any
2256 kqueue implementation). Store the kqueue/socket\-only event loop in
2257 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2258 .PP
2259 .Vb 3
2260 \& struct ev_loop *loop = ev_default_init (0);
2261 \& struct ev_loop *loop_socket = 0;
2262 \& struct ev_embed embed;
2263 \&
2264 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2265 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2266 \& {
2267 \& ev_embed_init (&embed, 0, loop_socket);
2268 \& ev_embed_start (loop, &embed);
2269 \& }
2270 \&
2271 \& if (!loop_socket)
2272 \& loop_socket = loop;
2273 \&
2274 \& // now use loop_socket for all sockets, and loop for everything else
2275 .Ve
2276 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2277 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2278 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2279 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2280 whoever is a good citizen cared to tell libev about it by calling
2281 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2282 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2283 and only in the child after the fork. If whoever good citizen calling
2284 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2285 handlers will be invoked, too, of course.
2286 .PP
2287 \fIWatcher-Specific Functions and Data Members\fR
2288 .IX Subsection "Watcher-Specific Functions and Data Members"
2289 .IP "ev_fork_init (ev_signal *, callback)" 4
2290 .IX Item "ev_fork_init (ev_signal *, callback)"
2291 Initialises and configures the fork watcher \- it has no parameters of any
2292 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2293 believe me.
2294 .ie n .Sh """ev_async"" \- how to wake up another event loop"
2295 .el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2296 .IX Subsection "ev_async - how to wake up another event loop"
2297 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2298 asynchronous sources such as signal handlers (as opposed to multiple event
2299 loops \- those are of course safe to use in different threads).
2300 .PP
2301 Sometimes, however, you need to wake up another event loop you do not
2302 control, for example because it belongs to another thread. This is what
2303 \&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2304 can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2305 safe.
2306 .PP
2307 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2308 too, are asynchronous in nature, and signals, too, will be compressed
2309 (i.e. the number of callback invocations may be less than the number of
2310 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2311 .PP
2312 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2313 just the default loop.
2314 .PP
2315 \fIQueueing\fR
2316 .IX Subsection "Queueing"
2317 .PP
2318 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2319 is that the author does not know of a simple (or any) algorithm for a
2320 multiple-writer-single-reader queue that works in all cases and doesn't
2321 need elaborate support such as pthreads.
2322 .PP
2323 That means that if you want to queue data, you have to provide your own
2324 queue. But at least I can tell you would implement locking around your
2325 queue:
2326 .IP "queueing from a signal handler context" 4
2327 .IX Item "queueing from a signal handler context"
2328 To implement race-free queueing, you simply add to the queue in the signal
2329 handler but you block the signal handler in the watcher callback. Here is an example that does that for
2330 some fictitiuous \s-1SIGUSR1\s0 handler:
2331 .Sp
2332 .Vb 1
2333 \& static ev_async mysig;
2334 \&
2335 \& static void
2336 \& sigusr1_handler (void)
2337 \& {
2338 \& sometype data;
2339 \&
2340 \& // no locking etc.
2341 \& queue_put (data);
2342 \& ev_async_send (EV_DEFAULT_ &mysig);
2343 \& }
2344 \&
2345 \& static void
2346 \& mysig_cb (EV_P_ ev_async *w, int revents)
2347 \& {
2348 \& sometype data;
2349 \& sigset_t block, prev;
2350 \&
2351 \& sigemptyset (&block);
2352 \& sigaddset (&block, SIGUSR1);
2353 \& sigprocmask (SIG_BLOCK, &block, &prev);
2354 \&
2355 \& while (queue_get (&data))
2356 \& process (data);
2357 \&
2358 \& if (sigismember (&prev, SIGUSR1)
2359 \& sigprocmask (SIG_UNBLOCK, &block, 0);
2360 \& }
2361 .Ve
2362 .Sp
2363 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2364 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2365 either...).
2366 .IP "queueing from a thread context" 4
2367 .IX Item "queueing from a thread context"
2368 The strategy for threads is different, as you cannot (easily) block
2369 threads but you can easily preempt them, so to queue safely you need to
2370 employ a traditional mutex lock, such as in this pthread example:
2371 .Sp
2372 .Vb 2
2373 \& static ev_async mysig;
2374 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2375 \&
2376 \& static void
2377 \& otherthread (void)
2378 \& {
2379 \& // only need to lock the actual queueing operation
2380 \& pthread_mutex_lock (&mymutex);
2381 \& queue_put (data);
2382 \& pthread_mutex_unlock (&mymutex);
2383 \&
2384 \& ev_async_send (EV_DEFAULT_ &mysig);
2385 \& }
2386 \&
2387 \& static void
2388 \& mysig_cb (EV_P_ ev_async *w, int revents)
2389 \& {
2390 \& pthread_mutex_lock (&mymutex);
2391 \&
2392 \& while (queue_get (&data))
2393 \& process (data);
2394 \&
2395 \& pthread_mutex_unlock (&mymutex);
2396 \& }
2397 .Ve
2398 .PP
2399 \fIWatcher-Specific Functions and Data Members\fR
2400 .IX Subsection "Watcher-Specific Functions and Data Members"
2401 .IP "ev_async_init (ev_async *, callback)" 4
2402 .IX Item "ev_async_init (ev_async *, callback)"
2403 Initialises and configures the async watcher \- it has no parameters of any
2404 kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
2405 believe me.
2406 .IP "ev_async_send (loop, ev_async *)" 4
2407 .IX Item "ev_async_send (loop, ev_async *)"
2408 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2409 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2410 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or
2411 similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2412 section below on what exactly this means).
2413 .Sp
2414 This call incurs the overhead of a syscall only once per loop iteration,
2415 so while the overhead might be noticable, it doesn't apply to repeated
2416 calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2417 .IP "bool = ev_async_pending (ev_async *)" 4
2418 .IX Item "bool = ev_async_pending (ev_async *)"
2419 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2420 watcher but the event has not yet been processed (or even noted) by the
2421 event loop.
2422 .Sp
2423 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2424 the loop iterates next and checks for the watcher to have become active,
2425 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2426 quickly check wether invoking the loop might be a good idea.
2427 .Sp
2428 Not that this does \fInot\fR check wether the watcher itself is pending, only
2429 wether it has been requested to make this watcher pending.
2432 There are some other functions of possible interest. Described. Here. Now.
2433 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2434 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2435 This function combines a simple timer and an I/O watcher, calls your
2436 callback on whichever event happens first and automatically stop both
2437 watchers. This is useful if you want to wait for a single event on an fd
2438 or timeout without having to allocate/configure/start/stop/free one or
2439 more watchers yourself.
2440 .Sp
2441 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
2442 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
2443 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
2444 .Sp
2445 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2446 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2447 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
2448 dubious value.
2449 .Sp
2450 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
2451 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2452 \&\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
2453 value passed to \f(CW\*(C`ev_once\*(C'\fR:
2454 .Sp
2455 .Vb 7
2456 \& static void stdin_ready (int revents, void *arg)
2457 \& {
2458 \& if (revents & EV_TIMEOUT)
2459 \& /* doh, nothing entered */;
2460 \& else if (revents & EV_READ)
2461 \& /* stdin might have data for us, joy! */;
2462 \& }
2463 \&
2464 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2465 .Ve
2466 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
2467 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
2468 Feeds the given event set into the event loop, as if the specified event
2469 had happened for the specified watcher (which must be a pointer to an
2470 initialised but not necessarily started event watcher).
2471 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
2472 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
2473 Feed an event on the given fd, as if a file descriptor backend detected
2474 the given events it.
2475 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
2476 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
2477 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
2478 loop!).
2481 Libev offers a compatibility emulation layer for libevent. It cannot
2482 emulate the internals of libevent, so here are some usage hints:
2483 .IP "\(bu" 4
2484 Use it by including <event.h>, as usual.
2485 .IP "\(bu" 4
2486 The following members are fully supported: ev_base, ev_callback,
2487 ev_arg, ev_fd, ev_res, ev_events.
2488 .IP "\(bu" 4
2489 Avoid using ev_flags and the EVLIST_*\-macros, while it is
2490 maintained by libev, it does not work exactly the same way as in libevent (consider
2491 it a private \s-1API\s0).
2492 .IP "\(bu" 4
2493 Priorities are not currently supported. Initialising priorities
2494 will fail and all watchers will have the same priority, even though there
2495 is an ev_pri field.
2496 .IP "\(bu" 4
2497 In libevent, the last base created gets the signals, in libev, the
2498 first base created (== the default loop) gets the signals.
2499 .IP "\(bu" 4
2500 Other members are not supported.
2501 .IP "\(bu" 4
2502 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2503 to use the libev header file and library.
2504 .SH "\*(C+ SUPPORT"
2505 .IX Header " SUPPORT"
2506 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2507 you to use some convinience methods to start/stop watchers and also change
2508 the callback model to a model using method callbacks on objects.
2509 .PP
2510 To use it,
2511 .PP
2512 .Vb 1
2513 \& #include <ev++.h>
2514 .Ve
2515 .PP
2516 This automatically includes \fIev.h\fR and puts all of its definitions (many
2517 of them macros) into the global namespace. All \*(C+ specific things are
2518 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2519 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2520 .PP
2521 Care has been taken to keep the overhead low. The only data member the \*(C+
2522 classes add (compared to plain C\-style watchers) is the event loop pointer
2523 that the watcher is associated with (or no additional members at all if
2524 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2525 .PP
2526 Currently, functions, and static and non-static member functions can be
2527 used as callbacks. Other types should be easy to add as long as they only
2528 need one additional pointer for context. If you need support for other
2529 types of functors please contact the author (preferably after implementing
2530 it).
2531 .PP
2532 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2533 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2534 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2535 .IX Item "ev::READ, ev::WRITE etc."
2536 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2537 macros from \fIev.h\fR.
2538 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2539 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2540 .IX Item "ev::tstamp, ev::now"
2541 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2542 .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
2543 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2544 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2545 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2546 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2547 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2548 defines by many implementations.
2549 .Sp
2550 All of those classes have these methods:
2551 .RS 4
2552 .IP "ev::TYPE::TYPE ()" 4
2553 .IX Item "ev::TYPE::TYPE ()"
2554 .PD 0
2555 .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2556 .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2557 .IP "ev::TYPE::~TYPE" 4
2558 .IX Item "ev::TYPE::~TYPE"
2559 .PD
2560 The constructor (optionally) takes an event loop to associate the watcher
2561 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2562 .Sp
2563 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2564 \&\f(CW\*(C`set\*(C'\fR method before starting it.
2565 .Sp
2566 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2567 method to set a callback before you can start the watcher.
2568 .Sp
2569 (The reason why you have to use a method is a limitation in \*(C+ which does
2570 not allow explicit template arguments for constructors).
2571 .Sp
2572 The destructor automatically stops the watcher if it is active.
2573 .IP "w\->set<class, &class::method> (object *)" 4
2574 .IX Item "w->set<class, &class::method> (object *)"
2575 This method sets the callback method to call. The method has to have a
2576 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2577 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2578 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2579 .Sp
2580 This method synthesizes efficient thunking code to call your method from
2581 the C callback that libev requires. If your compiler can inline your
2582 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2583 your compiler is good :), then the method will be fully inlined into the
2584 thunking function, making it as fast as a direct C callback.
2585 .Sp
2586 Example: simple class declaration and watcher initialisation
2587 .Sp
2588 .Vb 4
2589 \& struct myclass
2590 \& {
2591 \& void io_cb (ev::io &w, int revents) { }
2592 \& }
2593 \&
2594 \& myclass obj;
2595 \& ev::io iow;
2596 \& iow.set <myclass, &myclass::io_cb> (&obj);
2597 .Ve
2598 .IP "w\->set<function> (void *data = 0)" 4
2599 .IX Item "w->set<function> (void *data = 0)"
2600 Also sets a callback, but uses a static method or plain function as
2601 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2602 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2603 .Sp
2604 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2605 .Sp
2606 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2607 .Sp
2608 Example:
2609 .Sp
2610 .Vb 2
2611 \& static void io_cb (ev::io &w, int revents) { }
2612 \& iow.set <io_cb> ();
2613 .Ve
2614 .IP "w\->set (struct ev_loop *)" 4
2615 .IX Item "w->set (struct ev_loop *)"
2616 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2617 do this when the watcher is inactive (and not pending either).
2618 .IP "w\->set ([args])" 4
2619 .IX Item "w->set ([args])"
2620 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2621 called at least once. Unlike the C counterpart, an active watcher gets
2622 automatically stopped and restarted when reconfiguring it with this
2623 method.
2624 .IP "w\->start ()" 4
2625 .IX Item "w->start ()"
2626 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2627 constructor already stores the event loop.
2628 .IP "w\->stop ()" 4
2629 .IX Item "w->stop ()"
2630 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2631 .ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2632 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2633 .IX Item "w->again () (ev::timer, ev::periodic only)"
2634 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2635 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2636 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2637 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2638 .IX Item "w->sweep () (ev::embed only)"
2639 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2640 .ie n .IP "w\->update () (""ev::stat"" only)" 4
2641 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2642 .IX Item "w->update () (ev::stat only)"
2643 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2644 .RE
2645 .RS 4
2646 .RE
2647 .PP
2648 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2649 the constructor.
2650 .PP
2651 .Vb 4
2652 \& class myclass
2653 \& {
2654 \& ev::io io; void io_cb (ev::io &w, int revents);
2655 \& ev:idle idle void idle_cb (ev::idle &w, int revents);
2656 \&
2657 \& myclass (int fd)
2658 \& {
2659 \& io .set <myclass, &myclass::io_cb > (this);
2660 \& idle.set <myclass, &myclass::idle_cb> (this);
2661 \&
2662 \& io.start (fd, ev::READ);
2663 \& }
2664 \& };
2665 .Ve
2668 Libev does not offer other language bindings itself, but bindings for a
2669 numbe rof languages exist in the form of third-party packages. If you know
2670 any interesting language binding in addition to the ones listed here, drop
2671 me a note.
2672 .IP "Perl" 4
2673 .IX Item "Perl"
2674 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
2675 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
2676 there are additional modules that implement libev-compatible interfaces
2677 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR), \f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the
2678 \&\f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR and \f(CW\*(C`EV::Glib\*(C'\fR).
2679 .Sp
2680 It can be found and installed via \s-1CPAN\s0, its homepage is found at
2681 <>.
2682 .IP "Ruby" 4
2683 .IX Item "Ruby"
2684 Tony Arcieri has written a ruby extension that offers access to a subset
2685 of the libev \s-1API\s0 and adds filehandle abstractions, asynchronous \s-1DNS\s0 and
2686 more on top of it. It can be found via gem servers. Its homepage is at
2687 <>.
2688 .IP "D" 4
2689 .IX Item "D"
2690 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
2691 be found at <;a=summary>.
2693 .IX Header "MACRO MAGIC"
2694 Libev can be compiled with a variety of options, the most fundamantal
2695 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2696 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2697 .PP
2698 To make it easier to write programs that cope with either variant, the
2699 following macros are defined:
2700 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2701 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2702 .IX Item "EV_A, EV_A_"
2703 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2704 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2705 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2706 .Sp
2707 .Vb 3
2708 \& ev_unref (EV_A);
2709 \& ev_timer_add (EV_A_ watcher);
2710 \& ev_loop (EV_A_ 0);
2711 .Ve
2712 .Sp
2713 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2714 which is often provided by the following macro.
2715 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2716 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2717 .IX Item "EV_P, EV_P_"
2718 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2719 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2720 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2721 .Sp
2722 .Vb 2
2723 \& // this is how ev_unref is being declared
2724 \& static void ev_unref (EV_P);
2725 \&
2726 \& // this is how you can declare your typical callback
2727 \& static void cb (EV_P_ ev_timer *w, int revents)
2728 .Ve
2729 .Sp
2730 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2731 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2732 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2733 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2735 Similar to the other two macros, this gives you the value of the default
2736 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2737 .ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
2738 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
2740 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
2741 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
2742 is undefined when the default loop has not been initialised by a previous
2743 execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
2744 .Sp
2745 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
2746 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2747 .PP
2748 Example: Declare and initialise a check watcher, utilising the above
2749 macros so it will work regardless of whether multiple loops are supported
2750 or not.
2751 .PP
2752 .Vb 5
2753 \& static void
2754 \& check_cb (EV_P_ ev_timer *w, int revents)
2755 \& {
2756 \& ev_check_stop (EV_A_ w);
2757 \& }
2758 \&
2759 \& ev_check check;
2760 \& ev_check_init (&check, check_cb);
2761 \& ev_check_start (EV_DEFAULT_ &check);
2762 \& ev_loop (EV_DEFAULT_ 0);
2763 .Ve
2765 .IX Header "EMBEDDING"
2766 Libev can (and often is) directly embedded into host
2767 applications. Examples of applications that embed it include the Deliantra
2768 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2769 and rxvt-unicode.
2770 .PP
2771 The goal is to enable you to just copy the necessary files into your
2772 source directory without having to change even a single line in them, so
2773 you can easily upgrade by simply copying (or having a checked-out copy of
2774 libev somewhere in your source tree).
2775 .Sh "\s-1FILESETS\s0"
2776 .IX Subsection "FILESETS"
2777 Depending on what features you need you need to include one or more sets of files
2778 in your app.
2779 .PP
2780 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2781 .IX Subsection "CORE EVENT LOOP"
2782 .PP
2783 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2784 configuration (no autoconf):
2785 .PP
2786 .Vb 2
2787 \& #define EV_STANDALONE 1
2788 \& #include "ev.c"
2789 .Ve
2790 .PP
2791 This will automatically include \fIev.h\fR, too, and should be done in a
2792 single C source file only to provide the function implementations. To use
2793 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2794 done by writing a wrapper around \fIev.h\fR that you can include instead and
2795 where you can put other configuration options):
2796 .PP
2797 .Vb 2
2798 \& #define EV_STANDALONE 1
2799 \& #include "ev.h"
2800 .Ve
2801 .PP
2802 Both header files and implementation files can be compiled with a \*(C+
2803 compiler (at least, thats a stated goal, and breakage will be treated
2804 as a bug).
2805 .PP
2806 You need the following files in your source tree, or in a directory
2807 in your include path (e.g. in libev/ when using \-Ilibev):
2808 .PP
2809 .Vb 4
2810 \& ev.h
2811 \& ev.c
2812 \& ev_vars.h
2813 \& ev_wrap.h
2814 \&
2815 \& ev_win32.c required on win32 platforms only
2816 \&
2817 \& ev_select.c only when select backend is enabled (which is enabled by default)
2818 \& ev_poll.c only when poll backend is enabled (disabled by default)
2819 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2820 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2821 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
2822 .Ve
2823 .PP
2824 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
2825 to compile this single file.
2826 .PP
2827 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2829 .PP
2830 To include the libevent compatibility \s-1API\s0, also include:
2831 .PP
2832 .Vb 1
2833 \& #include "event.c"
2834 .Ve
2835 .PP
2836 in the file including \fIev.c\fR, and:
2837 .PP
2838 .Vb 1
2839 \& #include "event.h"
2840 .Ve
2841 .PP
2842 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2843 .PP
2844 You need the following additional files for this:
2845 .PP
2846 .Vb 2
2847 \& event.h
2848 \& event.c
2849 .Ve
2850 .PP
2851 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2852 .IX Subsection "AUTOCONF SUPPORT"
2853 .PP
2854 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2855 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2856 \&\\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2857 include \fIconfig.h\fR and configure itself accordingly.
2858 .PP
2859 For this of course you need the m4 file:
2860 .PP
2861 .Vb 1
2862 \& libev.m4
2863 .Ve
2864 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2866 Libev can be configured via a variety of preprocessor symbols you have to
2867 define before including any of its files. The default in the absense of
2868 autoconf is noted for every option.
2869 .IP "\s-1EV_STANDALONE\s0" 4
2871 Must always be \f(CW1\fR if you do not use autoconf configuration, which
2872 keeps libev from including \fIconfig.h\fR, and it also defines dummy
2873 implementations for some libevent functions (such as logging, which is not
2874 supported). It will also not define any of the structs usually found in
2875 \&\fIevent.h\fR that are not directly supported by the libev core alone.
2876 .IP "\s-1EV_USE_MONOTONIC\s0" 4
2878 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2879 monotonic clock option at both compiletime and runtime. Otherwise no use
2880 of the monotonic clock option will be attempted. If you enable this, you
2881 usually have to link against librt or something similar. Enabling it when
2882 the functionality isn't available is safe, though, although you have
2883 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2884 function is hiding in (often \fI\-lrt\fR).
2885 .IP "\s-1EV_USE_REALTIME\s0" 4
2887 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2888 realtime clock option at compiletime (and assume its availability at
2889 runtime if successful). Otherwise no use of the realtime clock option will
2890 be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2891 (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
2892 note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2893 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
2895 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2896 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
2897 .IP "\s-1EV_USE_EVENTFD\s0" 4
2898 .IX Item "EV_USE_EVENTFD"
2899 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
2900 available and will probe for kernel support at runtime. This will improve
2901 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
2902 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
2903 2.7 or newer, otherwise disabled.
2904 .IP "\s-1EV_USE_SELECT\s0" 4
2905 .IX Item "EV_USE_SELECT"
2906 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2907 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2908 other method takes over, select will be it. Otherwise the select backend
2909 will not be compiled in.
2910 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2912 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2913 structure. This is useful if libev doesn't compile due to a missing
2914 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2915 exotic systems. This usually limits the range of file descriptors to some
2916 low limit such as 1024 or might have other limitations (winsocket only
2917 allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2918 influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2919 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2921 When defined to \f(CW1\fR, the select backend will assume that
2922 select/socket/connect etc. don't understand file descriptors but
2923 wants osf handles on win32 (this is the case when the select to
2924 be used is the winsock select). This means that it will call
2925 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2926 it is assumed that all these functions actually work on fds, even
2927 on win32. Should not be defined on non\-win32 platforms.
2928 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
2929 .IX Item "EV_FD_TO_WIN32_HANDLE"
2930 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
2931 file descriptors to socket handles. When not defining this symbol (the
2932 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
2933 correct. In some cases, programs use their own file descriptor management,
2934 in which case they can provide this function to map fds to socket handles.
2935 .IP "\s-1EV_USE_POLL\s0" 4
2936 .IX Item "EV_USE_POLL"
2937 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2938 backend. Otherwise it will be enabled on non\-win32 platforms. It
2939 takes precedence over select.
2940 .IP "\s-1EV_USE_EPOLL\s0" 4
2941 .IX Item "EV_USE_EPOLL"
2942 If defined to be \f(CW1\fR, libev will compile in support for the Linux
2943 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2944 otherwise another method will be used as fallback. This is the preferred
2945 backend for GNU/Linux systems. If undefined, it will be enabled if the
2946 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2947 .IP "\s-1EV_USE_KQUEUE\s0" 4
2948 .IX Item "EV_USE_KQUEUE"
2949 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2950 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2951 otherwise another method will be used as fallback. This is the preferred
2952 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2953 supports some types of fds correctly (the only platform we found that
2954 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2955 not be used unless explicitly requested. The best way to use it is to find
2956 out whether kqueue supports your type of fd properly and use an embedded
2957 kqueue loop.
2958 .IP "\s-1EV_USE_PORT\s0" 4
2959 .IX Item "EV_USE_PORT"
2960 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
2961 10 port style backend. Its availability will be detected at runtime,
2962 otherwise another method will be used as fallback. This is the preferred
2963 backend for Solaris 10 systems.
2964 .IP "\s-1EV_USE_DEVPOLL\s0" 4
2965 .IX Item "EV_USE_DEVPOLL"
2966 reserved for future expansion, works like the \s-1USE\s0 symbols above.
2967 .IP "\s-1EV_USE_INOTIFY\s0" 4
2968 .IX Item "EV_USE_INOTIFY"
2969 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2970 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2971 be detected at runtime. If undefined, it will be enabled if the headers
2972 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2973 .IP "\s-1EV_ATOMIC_T\s0" 4
2974 .IX Item "EV_ATOMIC_T"
2975 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
2976 access is atomic with respect to other threads or signal contexts. No such
2977 type is easily found in the C language, so you can provide your own type
2978 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
2979 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
2980 .Sp
2981 In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
2982 (from \fIsignal.h\fR), which is usually good enough on most platforms.
2983 .IP "\s-1EV_H\s0" 4
2984 .IX Item "EV_H"
2985 The name of the \fIev.h\fR header file used to include it. The default if
2986 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2987 used to virtually rename the \fIev.h\fR header file in case of conflicts.
2988 .IP "\s-1EV_CONFIG_H\s0" 4
2989 .IX Item "EV_CONFIG_H"
2990 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2991 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2992 \&\f(CW\*(C`EV_H\*(C'\fR, above.
2993 .IP "\s-1EV_EVENT_H\s0" 4
2994 .IX Item "EV_EVENT_H"
2995 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2996 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2997 .IP "\s-1EV_PROTOTYPES\s0" 4
2999 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3000 prototypes, but still define all the structs and other symbols. This is
3001 occasionally useful if you want to provide your own wrapper functions
3002 around libev functions.
3003 .IP "\s-1EV_MULTIPLICITY\s0" 4
3005 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3006 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3007 additional independent event loops. Otherwise there will be no support
3008 for multiple event loops and there is no first event loop pointer
3009 argument. Instead, all functions act on the single default loop.
3010 .IP "\s-1EV_MINPRI\s0" 4
3011 .IX Item "EV_MINPRI"
3012 .PD 0
3013 .IP "\s-1EV_MAXPRI\s0" 4
3014 .IX Item "EV_MAXPRI"
3015 .PD
3016 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3017 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3018 provide for more priorities by overriding those symbols (usually defined
3019 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3020 .Sp
3021 When doing priority-based operations, libev usually has to linearly search
3022 all the priorities, so having many of them (hundreds) uses a lot of space
3023 and time, so using the defaults of five priorities (\-2 .. +2) is usually
3024 fine.
3025 .Sp
3026 If your embedding app does not need any priorities, defining these both to
3027 \&\f(CW0\fR will save some memory and cpu.
3028 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3030 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3031 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3032 code.
3033 .IP "\s-1EV_IDLE_ENABLE\s0" 4
3034 .IX Item "EV_IDLE_ENABLE"
3035 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3036 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3037 code.
3038 .IP "\s-1EV_EMBED_ENABLE\s0" 4
3040 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3041 defined to be \f(CW0\fR, then they are not.
3042 .IP "\s-1EV_STAT_ENABLE\s0" 4
3043 .IX Item "EV_STAT_ENABLE"
3044 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3045 defined to be \f(CW0\fR, then they are not.
3046 .IP "\s-1EV_FORK_ENABLE\s0" 4
3047 .IX Item "EV_FORK_ENABLE"
3048 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3049 defined to be \f(CW0\fR, then they are not.
3050 .IP "\s-1EV_ASYNC_ENABLE\s0" 4
3052 If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3053 defined to be \f(CW0\fR, then they are not.
3054 .IP "\s-1EV_MINIMAL\s0" 4
3055 .IX Item "EV_MINIMAL"
3056 If you need to shave off some kilobytes of code at the expense of some
3057 speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override
3058 some inlining decisions, saves roughly 30% codesize of amd64.
3059 .IP "\s-1EV_PID_HASHSIZE\s0" 4
3061 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3062 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3063 than enough. If you need to manage thousands of children you might want to
3064 increase this value (\fImust\fR be a power of two).
3065 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3067 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3068 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3069 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3070 watchers you might want to increase this value (\fImust\fR be a power of
3071 two).
3072 .IP "\s-1EV_COMMON\s0" 4
3073 .IX Item "EV_COMMON"
3074 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3075 this macro to a something else you can include more and other types of
3076 members. You have to define it each time you include one of the files,
3077 though, and it must be identical each time.
3078 .Sp
3079 For example, the perl \s-1EV\s0 module uses something like this:
3080 .Sp
3081 .Vb 3
3082 \& #define EV_COMMON \e
3083 \& SV *self; /* contains this struct */ \e
3084 \& SV *cb_sv, *fh /* note no trailing ";" */
3085 .Ve
3086 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3087 .IX Item "EV_CB_DECLARE (type)"
3088 .PD 0
3089 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3090 .IX Item "EV_CB_INVOKE (watcher, revents)"
3091 .IP "ev_set_cb (ev, cb)" 4
3092 .IX Item "ev_set_cb (ev, cb)"
3093 .PD
3094 Can be used to change the callback member declaration in each watcher,
3095 and the way callbacks are invoked and set. Must expand to a struct member
3096 definition and a statement, respectively. See the \fIev.h\fR header file for
3097 their default definitions. One possible use for overriding these is to
3098 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3099 method calls instead of plain function calls in \*(C+.
3100 .Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3101 .IX Subsection "EXPORTED API SYMBOLS"
3102 If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
3103 exported symbols, you can use the provided \fISymbol.*\fR files which list
3104 all public symbols, one per line:
3105 .PP
3106 .Vb 2
3107 \& Symbols.ev for libev proper
3108 \& Symbols.event for the libevent emulation
3109 .Ve
3110 .PP
3111 This can also be used to rename all public symbols to avoid clashes with
3112 multiple versions of libev linked together (which is obviously bad in
3113 itself, but sometimes it is inconvinient to avoid this).
3114 .PP
3115 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3116 include before including \fIev.h\fR:
3117 .PP
3118 .Vb 1
3119 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3120 .Ve
3121 .PP
3122 This would create a file \fIwrap.h\fR which essentially looks like this:
3123 .PP
3124 .Vb 4
3125 \& #define ev_backend myprefix_ev_backend
3126 \& #define ev_check_start myprefix_ev_check_start
3127 \& #define ev_check_stop myprefix_ev_check_stop
3128 \& ...
3129 .Ve
3130 .Sh "\s-1EXAMPLES\s0"
3131 .IX Subsection "EXAMPLES"
3132 For a real-world example of a program the includes libev
3133 verbatim, you can have a look at the \s-1EV\s0 perl module
3134 (<>). It has the libev files in
3135 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3136 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3137 will be compiled. It is pretty complex because it provides its own header
3138 file.
3139 .PP
3140 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3141 that everybody includes and which overrides some configure choices:
3142 .PP
3143 .Vb 9
3144 \& #define EV_MINIMAL 1
3145 \& #define EV_USE_POLL 0
3146 \& #define EV_MULTIPLICITY 0
3147 \& #define EV_PERIODIC_ENABLE 0
3148 \& #define EV_STAT_ENABLE 0
3149 \& #define EV_FORK_ENABLE 0
3150 \& #define EV_CONFIG_H <config.h>
3151 \& #define EV_MINPRI 0
3152 \& #define EV_MAXPRI 0
3153 \&
3154 \& #include "ev++.h"
3155 .Ve
3156 .PP
3157 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3158 .PP
3159 .Vb 2
3160 \& #include "ev_cpp.h"
3161 \& #include "ev.c"
3162 .Ve
3165 .Sh "\s-1THREADS\s0"
3166 .IX Subsection "THREADS"
3167 Libev itself is completely threadsafe, but it uses no locking. This
3168 means that you can use as many loops as you want in parallel, as long as
3169 only one thread ever calls into one libev function with the same loop
3170 parameter.
3171 .PP
3172 Or put differently: calls with different loop parameters can be done in
3173 parallel from multiple threads, calls with the same loop parameter must be
3174 done serially (but can be done from different threads, as long as only one
3175 thread ever is inside a call at any point in time, e.g. by using a mutex
3176 per loop).
3177 .PP
3178 If you want to know which design is best for your problem, then I cannot
3179 help you but by giving some generic advice:
3180 .IP "\(bu" 4
3181 most applications have a main thread: use the default libev loop
3182 in that thread, or create a seperate thread running only the default loop.
3183 .Sp
3184 This helps integrating other libraries or software modules that use libev
3185 themselves and don't care/know about threading.
3186 .IP "\(bu" 4
3187 one loop per thread is usually a good model.
3188 .Sp
3189 Doing this is almost never wrong, sometimes a better-performance model
3190 exists, but it is always a good start.
3191 .IP "\(bu" 4
3192 other models exist, such as the leader/follower pattern, where one
3193 loop is handed through multiple threads in a kind of round-robbin fashion.
3194 .Sp
3195 Chosing a model is hard \- look around, learn, know that usually you cna do
3196 better than you currently do :\-)
3197 .IP "\(bu" 4
3198 often you need to talk to some other thread which blocks in the
3199 event loop \- \f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other
3200 threads safely (or from signal contexts...).
3201 .Sh "\s-1COROUTINES\s0"
3202 .IX Subsection "COROUTINES"
3203 Libev is much more accomodating to coroutines (\*(L"cooperative threads\*(R"):
3204 libev fully supports nesting calls to it's functions from different
3205 coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3206 different coroutines and switch freely between both coroutines running the
3207 loop, as long as you don't confuse yourself). The only exception is that
3208 you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3209 .PP
3210 Care has been invested into making sure that libev does not keep local
3211 state inside \f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow coroutine
3212 switches.
3214 .IX Header "COMPLEXITIES"
3215 In this section the complexities of (many of) the algorithms used inside
3216 libev will be explained. For complexity discussions about backends see the
3217 documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
3218 .PP
3219 All of the following are about amortised time: If an array needs to be
3220 extended, libev needs to realloc and move the whole array, but this
3221 happens asymptotically never with higher number of elements, so O(1) might
3222 mean it might do a lengthy realloc operation in rare cases, but on average
3223 it is much faster and asymptotically approaches constant time.
3224 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
3225 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
3226 This means that, when you have a watcher that triggers in one hour and
3227 there are 100 watchers that would trigger before that then inserting will
3228 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
3229 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
3230 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
3231 That means that changing a timer costs less than removing/adding them
3232 as only the relative motion in the event queue has to be paid for.
3233 .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
3234 .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
3235 These just add the watcher into an array or at the head of a list.
3236 .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
3237 .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
3238 .PD 0
3239 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
3240 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
3241 .PD
3242 These watchers are stored in lists then need to be walked to find the
3243 correct watcher to remove. The lists are usually short (you don't usually
3244 have many watchers waiting for the same fd or signal).
3245 .IP "Finding the next timer in each loop iteration: O(1)" 4
3246 .IX Item "Finding the next timer in each loop iteration: O(1)"
3247 By virtue of using a binary heap, the next timer is always found at the
3248 beginning of the storage array.
3249 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
3250 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
3251 A change means an I/O watcher gets started or stopped, which requires
3252 libev to recalculate its status (and possibly tell the kernel, depending
3253 on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
3254 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
3255 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
3256 .PD 0
3257 .IP "Priority handling: O(number_of_priorities)" 4
3258 .IX Item "Priority handling: O(number_of_priorities)"
3259 .PD
3260 Priorities are implemented by allocating some space for each
3261 priority. When doing priority-based operations, libev usually has to
3262 linearly search all the priorities, but starting/stopping and activating
3263 watchers becomes O(1) w.r.t. priority handling.
3264 .IP "Sending an ev_async: O(1)" 4
3265 .IX Item "Sending an ev_async: O(1)"
3266 .PD 0
3267 .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
3268 .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
3269 .IP "Processing signals: O(max_signal_number)" 4
3270 .IX Item "Processing signals: O(max_signal_number)"
3271 .PD
3272 Sending involves a syscall \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
3273 calls in the current loop iteration. Checking for async and signal events
3274 involves iterating over all running async watchers or all signal numbers.
3275 .SH "Win32 platform limitations and workarounds"
3276 .IX Header "Win32 platform limitations and workarounds"
3277 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
3278 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
3279 model. Libev still offers limited functionality on this platform in
3280 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
3281 descriptors. This only applies when using Win32 natively, not when using
3282 e.g. cygwin.
3283 .PP
3284 There is no supported compilation method available on windows except
3285 embedding it into other applications.
3286 .PP
3287 Due to the many, low, and arbitrary limits on the win32 platform and the
3288 abysmal performance of winsockets, using a large number of sockets is not
3289 recommended (and not reasonable). If your program needs to use more than
3290 a hundred or so sockets, then likely it needs to use a totally different
3291 implementation for windows, as libev offers the \s-1POSIX\s0 model, which cannot
3292 be implemented efficiently on windows (microsoft monopoly games).
3293 .IP "The winsocket select function" 4
3294 .IX Item "The winsocket select function"
3295 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it requires
3296 socket \fIhandles\fR and not socket \fIfile descriptors\fR. This makes select
3297 very inefficient, and also requires a mapping from file descriptors
3298 to socket handles. See the discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR,
3299 \&\f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and \f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor
3300 symbols for more info.
3301 .Sp
3302 The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime
3303 libraries and raw winsocket select is:
3304 .Sp
3305 .Vb 2
3306 \& #define EV_USE_SELECT 1
3307 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3308 .Ve
3309 .Sp
3310 Note that winsockets handling of fd sets is O(n), so you can easily get a
3311 complexity in the O(nA\*^X) range when using win32.
3312 .IP "Limited number of file descriptors" 4
3313 .IX Item "Limited number of file descriptors"
3314 Windows has numerous arbitrary (and low) limits on things. Early versions
3315 of winsocket's select only supported waiting for a max. of \f(CW64\fR handles
3316 (probably owning to the fact that all windows kernels can only wait for
3317 \&\f(CW64\fR things at the same time internally; microsoft recommends spawning a
3318 chain of threads and wait for 63 handles and the previous thread in each).
3319 .Sp
3320 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
3321 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
3322 call (which might be in libev or elsewhere, for example, perl does its own
3323 select emulation on windows).
3324 .Sp
3325 Another limit is the number of file descriptors in the microsoft runtime
3326 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
3327 or something like this inside microsoft). You can increase this by calling
3328 \&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
3329 arbitrary limit), but is broken in many versions of the microsoft runtime
3330 libraries.
3331 .Sp
3332 This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
3333 windows version and/or the phase of the moon). To get more, you need to
3334 wrap all I/O functions and provide your own fd management, but the cost of
3335 calling select (O(nA\*^X)) will likely make this unworkable.
3336 .SH "AUTHOR"
3337 .IX Header "AUTHOR"
3338 Marc Lehmann <>.
3340 .IX Header "POD ERRORS"
3341 Hey! \fBThe above document had some coding errors, which are explained below:\fR
3342 .IP "Around line 3015:" 4
3343 .IX Item "Around line 3015:"
3344 You forgot a '=back' before '=head2'