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Revision: 1.104
Committed: Sun Dec 20 01:35:55 2015 UTC (8 years, 7 months ago) by root
Branch: MAIN
CVS Tags: EV-rel-4_22, rel-4_22
Changes since 1.103: +7 -4 lines
Log Message:
*** empty log message ***

File Contents

# Content
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132 .rm #[ #] #H #V #F C
133 .\" ========================================================================
134 .\"
135 .IX Title "LIBEV 3"
136 .TH LIBEV 3 "2015-12-20" "libev-4.20" "libev - high performance full featured event loop"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 libev \- a high performance full\-featured event loop written in C
144 .IX Header "SYNOPSIS"
145 .Vb 1
146 \& #include <ev.h>
147 .Ve
148 .SS "\s-1EXAMPLE PROGRAM\s0"
149 .IX Subsection "EXAMPLE PROGRAM"
150 .Vb 2
151 \& // a single header file is required
152 \& #include <ev.h>
153 \&
154 \& #include <stdio.h> // for puts
155 \&
156 \& // every watcher type has its own typedef\*(Aqd struct
157 \& // with the name ev_TYPE
158 \& ev_io stdin_watcher;
159 \& ev_timer timeout_watcher;
160 \&
161 \& // all watcher callbacks have a similar signature
162 \& // this callback is called when data is readable on stdin
163 \& static void
164 \& stdin_cb (EV_P_ ev_io *w, int revents)
165 \& {
166 \& puts ("stdin ready");
167 \& // for one\-shot events, one must manually stop the watcher
168 \& // with its corresponding stop function.
169 \& ev_io_stop (EV_A_ w);
170 \&
171 \& // this causes all nested ev_run\*(Aqs to stop iterating
172 \& ev_break (EV_A_ EVBREAK_ALL);
173 \& }
174 \&
175 \& // another callback, this time for a time\-out
176 \& static void
177 \& timeout_cb (EV_P_ ev_timer *w, int revents)
178 \& {
179 \& puts ("timeout");
180 \& // this causes the innermost ev_run to stop iterating
181 \& ev_break (EV_A_ EVBREAK_ONE);
182 \& }
183 \&
184 \& int
185 \& main (void)
186 \& {
187 \& // use the default event loop unless you have special needs
188 \& struct ev_loop *loop = EV_DEFAULT;
189 \&
190 \& // initialise an io watcher, then start it
191 \& // this one will watch for stdin to become readable
192 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
193 \& ev_io_start (loop, &stdin_watcher);
194 \&
195 \& // initialise a timer watcher, then start it
196 \& // simple non\-repeating 5.5 second timeout
197 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
198 \& ev_timer_start (loop, &timeout_watcher);
199 \&
200 \& // now wait for events to arrive
201 \& ev_run (loop, 0);
202 \&
203 \& // break was called, so exit
204 \& return 0;
205 \& }
206 .Ve
209 This document documents the libev software package.
210 .PP
211 The newest version of this document is also available as an html-formatted
212 web page you might find easier to navigate when reading it for the first
213 time: <>.
214 .PP
215 While this document tries to be as complete as possible in documenting
216 libev, its usage and the rationale behind its design, it is not a tutorial
217 on event-based programming, nor will it introduce event-based programming
218 with libev.
219 .PP
220 Familiarity with event based programming techniques in general is assumed
221 throughout this document.
224 This manual tries to be very detailed, but unfortunately, this also makes
225 it very long. If you just want to know the basics of libev, I suggest
226 reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227 look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228 \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
230 .IX Header "ABOUT LIBEV"
231 Libev is an event loop: you register interest in certain events (such as a
232 file descriptor being readable or a timeout occurring), and it will manage
233 these event sources and provide your program with events.
234 .PP
235 To do this, it must take more or less complete control over your process
236 (or thread) by executing the \fIevent loop\fR handler, and will then
237 communicate events via a callback mechanism.
238 .PP
239 You register interest in certain events by registering so-called \fIevent
240 watchers\fR, which are relatively small C structures you initialise with the
241 details of the event, and then hand it over to libev by \fIstarting\fR the
242 watcher.
243 .SS "\s-1FEATURES\s0"
244 .IX Subsection "FEATURES"
245 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
246 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
247 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
248 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
249 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
250 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
251 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
253 loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
254 \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
256 .PP
257 It also is quite fast (see this
258 benchmark <> comparing it to libevent
259 for example).
260 .SS "\s-1CONVENTIONS\s0"
261 .IX Subsection "CONVENTIONS"
262 Libev is very configurable. In this manual the default (and most common)
263 configuration will be described, which supports multiple event loops. For
264 more info about various configuration options please have a look at
265 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
266 for multiple event loops, then all functions taking an initial argument of
267 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
268 this argument.
271 Libev represents time as a single floating point number, representing
272 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
273 somewhere near the beginning of 1970, details are complicated, don't
274 ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
275 too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
276 any calculations on it, you should treat it as some floating point value.
277 .PP
278 Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279 time differences (e.g. delays) throughout libev.
282 Libev knows three classes of errors: operating system errors, usage errors
283 and internal errors (bugs).
284 .PP
285 When libev catches an operating system error it cannot handle (for example
286 a system call indicating a condition libev cannot fix), it calls the callback
287 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289 ()\*(C'\fR.
290 .PP
291 When libev detects a usage error such as a negative timer interval, then
292 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294 the libev caller and need to be fixed there.
295 .PP
296 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
297 extensive consistency checking code. These do not trigger under normal
298 circumstances, as they indicate either a bug in libev or worse.
301 These functions can be called anytime, even before initialising the
302 library in any way.
303 .IP "ev_tstamp ev_time ()" 4
304 .IX Item "ev_tstamp ev_time ()"
305 Returns the current time as libev would use it. Please note that the
306 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
307 you actually want to know. Also interesting is the combination of
308 \&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
309 .IP "ev_sleep (ev_tstamp interval)" 4
310 .IX Item "ev_sleep (ev_tstamp interval)"
311 Sleep for the given interval: The current thread will be blocked
312 until either it is interrupted or the given time interval has
313 passed (approximately \- it might return a bit earlier even if not
314 interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
315 .Sp
316 Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
317 .Sp
318 The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
319 with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
320 .IP "int ev_version_major ()" 4
321 .IX Item "int ev_version_major ()"
322 .PD 0
323 .IP "int ev_version_minor ()" 4
324 .IX Item "int ev_version_minor ()"
325 .PD
326 You can find out the major and minor \s-1ABI\s0 version numbers of the library
327 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
328 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
329 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
330 version of the library your program was compiled against.
331 .Sp
332 These version numbers refer to the \s-1ABI\s0 version of the library, not the
333 release version.
334 .Sp
335 Usually, it's a good idea to terminate if the major versions mismatch,
336 as this indicates an incompatible change. Minor versions are usually
337 compatible to older versions, so a larger minor version alone is usually
338 not a problem.
339 .Sp
340 Example: Make sure we haven't accidentally been linked against the wrong
341 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
342 such as \s-1LFS\s0 or reentrancy).
343 .Sp
344 .Vb 3
345 \& assert (("libev version mismatch",
346 \& ev_version_major () == EV_VERSION_MAJOR
347 \& && ev_version_minor () >= EV_VERSION_MINOR));
348 .Ve
349 .IP "unsigned int ev_supported_backends ()" 4
350 .IX Item "unsigned int ev_supported_backends ()"
351 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
352 value) compiled into this binary of libev (independent of their
353 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
354 a description of the set values.
355 .Sp
356 Example: make sure we have the epoll method, because yeah this is cool and
357 a must have and can we have a torrent of it please!!!11
358 .Sp
359 .Vb 2
360 \& assert (("sorry, no epoll, no sex",
361 \& ev_supported_backends () & EVBACKEND_EPOLL));
362 .Ve
363 .IP "unsigned int ev_recommended_backends ()" 4
364 .IX Item "unsigned int ev_recommended_backends ()"
365 Return the set of all backends compiled into this binary of libev and
366 also recommended for this platform, meaning it will work for most file
367 descriptor types. This set is often smaller than the one returned by
368 \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
369 and will not be auto-detected unless you explicitly request it (assuming
370 you know what you are doing). This is the set of backends that libev will
371 probe for if you specify no backends explicitly.
372 .IP "unsigned int ev_embeddable_backends ()" 4
373 .IX Item "unsigned int ev_embeddable_backends ()"
374 Returns the set of backends that are embeddable in other event loops. This
375 value is platform-specific but can include backends not available on the
376 current system. To find which embeddable backends might be supported on
377 the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
378 & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
379 .Sp
380 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
381 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
382 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
383 Sets the allocation function to use (the prototype is similar \- the
384 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
385 used to allocate and free memory (no surprises here). If it returns zero
386 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
387 or take some potentially destructive action.
388 .Sp
389 Since some systems (at least OpenBSD and Darwin) fail to implement
390 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
391 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
392 .Sp
393 You could override this function in high-availability programs to, say,
394 free some memory if it cannot allocate memory, to use a special allocator,
395 or even to sleep a while and retry until some memory is available.
396 .Sp
397 Example: Replace the libev allocator with one that waits a bit and then
398 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
399 .Sp
400 .Vb 6
401 \& static void *
402 \& persistent_realloc (void *ptr, size_t size)
403 \& {
404 \& for (;;)
405 \& {
406 \& void *newptr = realloc (ptr, size);
407 \&
408 \& if (newptr)
409 \& return newptr;
410 \&
411 \& sleep (60);
412 \& }
413 \& }
414 \&
415 \& ...
416 \& ev_set_allocator (persistent_realloc);
417 .Ve
418 .IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
419 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
420 Set the callback function to call on a retryable system call error (such
421 as failed select, poll, epoll_wait). The message is a printable string
422 indicating the system call or subsystem causing the problem. If this
423 callback is set, then libev will expect it to remedy the situation, no
424 matter what, when it returns. That is, libev will generally retry the
425 requested operation, or, if the condition doesn't go away, do bad stuff
426 (such as abort).
427 .Sp
428 Example: This is basically the same thing that libev does internally, too.
429 .Sp
430 .Vb 6
431 \& static void
432 \& fatal_error (const char *msg)
433 \& {
434 \& perror (msg);
435 \& abort ();
436 \& }
437 \&
438 \& ...
439 \& ev_set_syserr_cb (fatal_error);
440 .Ve
441 .IP "ev_feed_signal (int signum)" 4
442 .IX Item "ev_feed_signal (int signum)"
443 This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
444 safe to call this function at any time, from any context, including signal
445 handlers or random threads.
446 .Sp
447 Its main use is to customise signal handling in your process, especially
448 in the presence of threads. For example, you could block signals
449 by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
450 creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
451 mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
452 \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
455 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
456 \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
457 libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
458 .PP
459 The library knows two types of such loops, the \fIdefault\fR loop, which
460 supports child process events, and dynamically created event loops which
461 do not.
462 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
463 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
464 This returns the \*(L"default\*(R" event loop object, which is what you should
465 normally use when you just need \*(L"the event loop\*(R". Event loop objects and
466 the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
467 \&\f(CW\*(C`ev_loop_new\*(C'\fR.
468 .Sp
469 If the default loop is already initialised then this function simply
470 returns it (and ignores the flags. If that is troubling you, check
471 \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
472 flags, which should almost always be \f(CW0\fR, unless the caller is also the
473 one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
474 .Sp
475 If you don't know what event loop to use, use the one returned from this
476 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
477 .Sp
478 Note that this function is \fInot\fR thread-safe, so if you want to use it
479 from multiple threads, you have to employ some kind of mutex (note also
480 that this case is unlikely, as loops cannot be shared easily between
481 threads anyway).
482 .Sp
483 The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
484 and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
485 a problem for your application you can either create a dynamic loop with
486 \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
487 \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
488 .Sp
489 Example: This is the most typical usage.
490 .Sp
491 .Vb 2
492 \& if (!ev_default_loop (0))
493 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
494 .Ve
495 .Sp
496 Example: Restrict libev to the select and poll backends, and do not allow
497 environment settings to be taken into account:
498 .Sp
499 .Vb 1
501 .Ve
502 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504 This will create and initialise a new event loop object. If the loop
505 could not be initialised, returns false.
506 .Sp
507 This function is thread-safe, and one common way to use libev with
508 threads is indeed to create one loop per thread, and using the default
509 loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
510 .Sp
511 The flags argument can be used to specify special behaviour or specific
512 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
513 .Sp
514 The following flags are supported:
515 .RS 4
516 .ie n .IP """EVFLAG_AUTO""" 4
517 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
518 .IX Item "EVFLAG_AUTO"
519 The default flags value. Use this if you have no clue (it's the right
520 thing, believe me).
521 .ie n .IP """EVFLAG_NOENV""" 4
522 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
524 If this flag bit is or'ed into the flag value (or the program runs setuid
525 or setgid) then libev will \fInot\fR look at the environment variable
526 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
527 override the flags completely if it is found in the environment. This is
528 useful to try out specific backends to test their performance, to work
529 around bugs, or to make libev threadsafe (accessing environment variables
530 cannot be done in a threadsafe way, but usually it works if no other
531 thread modifies them).
532 .ie n .IP """EVFLAG_FORKCHECK""" 4
533 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
535 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
536 make libev check for a fork in each iteration by enabling this flag.
537 .Sp
538 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
539 and thus this might slow down your event loop if you do a lot of loop
540 iterations and little real work, but is usually not noticeable (on my
541 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
542 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
543 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
544 .Sp
545 The big advantage of this flag is that you can forget about fork (and
546 forget about forgetting to tell libev about forking, although you still
547 have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
548 .Sp
549 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
550 environment variable.
551 .ie n .IP """EVFLAG_NOINOTIFY""" 4
552 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
554 When this flag is specified, then libev will not attempt to use the
555 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
556 testing, this flag can be useful to conserve inotify file descriptors, as
557 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
558 .ie n .IP """EVFLAG_SIGNALFD""" 4
559 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
561 When this flag is specified, then libev will attempt to use the
562 \&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
563 delivers signals synchronously, which makes it both faster and might make
564 it possible to get the queued signal data. It can also simplify signal
565 handling with threads, as long as you properly block signals in your
566 threads that are not interested in handling them.
567 .Sp
568 Signalfd will not be used by default as this changes your signal mask, and
569 there are a lot of shoddy libraries and programs (glib's threadpool for
570 example) that can't properly initialise their signal masks.
571 .ie n .IP """EVFLAG_NOSIGMASK""" 4
572 .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
574 When this flag is specified, then libev will avoid to modify the signal
575 mask. Specifically, this means you have to make sure signals are unblocked
576 when you want to receive them.
577 .Sp
578 This behaviour is useful when you want to do your own signal handling, or
579 want to handle signals only in specific threads and want to avoid libev
580 unblocking the signals.
581 .Sp
582 It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
583 \&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
584 .Sp
585 This flag's behaviour will become the default in future versions of libev.
586 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
587 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
588 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
589 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
590 libev tries to roll its own fd_set with no limits on the number of fds,
591 but if that fails, expect a fairly low limit on the number of fds when
592 using this backend. It doesn't scale too well (O(highest_fd)), but its
593 usually the fastest backend for a low number of (low-numbered :) fds.
594 .Sp
595 To get good performance out of this backend you need a high amount of
596 parallelism (most of the file descriptors should be busy). If you are
597 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
598 connections as possible during one iteration. You might also want to have
599 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
600 readiness notifications you get per iteration.
601 .Sp
602 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
603 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
604 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
605 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
606 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
607 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
608 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
609 than select, but handles sparse fds better and has no artificial
610 limit on the number of fds you can use (except it will slow down
611 considerably with a lot of inactive fds). It scales similarly to select,
612 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
613 performance tips.
614 .Sp
615 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
616 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
617 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
618 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
619 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
620 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
621 kernels).
622 .Sp
623 For few fds, this backend is a bit little slower than poll and select, but
624 it scales phenomenally better. While poll and select usually scale like
625 O(total_fds) where total_fds is the total number of fds (or the highest
626 fd), epoll scales either O(1) or O(active_fds).
627 .Sp
628 The epoll mechanism deserves honorable mention as the most misdesigned
629 of the more advanced event mechanisms: mere annoyances include silently
630 dropping file descriptors, requiring a system call per change per file
631 descriptor (and unnecessary guessing of parameters), problems with dup,
632 returning before the timeout value, resulting in additional iterations
633 (and only giving 5ms accuracy while select on the same platform gives
634 0.1ms) and so on. The biggest issue is fork races, however \- if a program
635 forks then \fIboth\fR parent and child process have to recreate the epoll
636 set, which can take considerable time (one syscall per file descriptor)
637 and is of course hard to detect.
638 .Sp
639 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
640 but of course \fIdoesn't\fR, and epoll just loves to report events for
641 totally \fIdifferent\fR file descriptors (even already closed ones, so
642 one cannot even remove them from the set) than registered in the set
643 (especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
644 notifications by employing an additional generation counter and comparing
645 that against the events to filter out spurious ones, recreating the set
646 when required. Epoll also erroneously rounds down timeouts, but gives you
647 no way to know when and by how much, so sometimes you have to busy-wait
648 because epoll returns immediately despite a nonzero timeout. And last
649 not least, it also refuses to work with some file descriptors which work
650 perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
651 .Sp
652 Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
653 cobbled together in a hurry, no thought to design or interaction with
654 others. Oh, the pain, will it ever stop...
655 .Sp
656 While stopping, setting and starting an I/O watcher in the same iteration
657 will result in some caching, there is still a system call per such
658 incident (because the same \fIfile descriptor\fR could point to a different
659 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
660 file descriptors might not work very well if you register events for both
661 file descriptors.
662 .Sp
663 Best performance from this backend is achieved by not unregistering all
664 watchers for a file descriptor until it has been closed, if possible,
665 i.e. keep at least one watcher active per fd at all times. Stopping and
666 starting a watcher (without re-setting it) also usually doesn't cause
667 extra overhead. A fork can both result in spurious notifications as well
668 as in libev having to destroy and recreate the epoll object, which can
669 take considerable time and thus should be avoided.
670 .Sp
671 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
672 faster than epoll for maybe up to a hundred file descriptors, depending on
673 the usage. So sad.
674 .Sp
675 While nominally embeddable in other event loops, this feature is broken in
676 all kernel versions tested so far.
677 .Sp
678 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
679 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
680 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
681 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
682 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
683 Kqueue deserves special mention, as at the time of this writing, it
684 was broken on all BSDs except NetBSD (usually it doesn't work reliably
685 with anything but sockets and pipes, except on Darwin, where of course
686 it's completely useless). Unlike epoll, however, whose brokenness
687 is by design, these kqueue bugs can (and eventually will) be fixed
688 without \s-1API\s0 changes to existing programs. For this reason it's not being
689 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
690 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
691 system like NetBSD.
692 .Sp
693 You still can embed kqueue into a normal poll or select backend and use it
694 only for sockets (after having made sure that sockets work with kqueue on
695 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
696 .Sp
697 It scales in the same way as the epoll backend, but the interface to the
698 kernel is more efficient (which says nothing about its actual speed, of
699 course). While stopping, setting and starting an I/O watcher does never
700 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
701 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
702 might have to leak fd's on fork, but it's more sane than epoll) and it
703 drops fds silently in similarly hard-to-detect cases.
704 .Sp
705 This backend usually performs well under most conditions.
706 .Sp
707 While nominally embeddable in other event loops, this doesn't work
708 everywhere, so you might need to test for this. And since it is broken
709 almost everywhere, you should only use it when you have a lot of sockets
710 (for which it usually works), by embedding it into another event loop
711 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
712 also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
713 .Sp
714 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
715 \&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
716 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
717 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
718 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
719 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
720 This is not implemented yet (and might never be, unless you send me an
721 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
722 and is not embeddable, which would limit the usefulness of this backend
723 immensely.
724 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
725 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
726 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
727 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
728 it's really slow, but it still scales very well (O(active_fds)).
729 .Sp
730 While this backend scales well, it requires one system call per active
731 file descriptor per loop iteration. For small and medium numbers of file
732 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
733 might perform better.
734 .Sp
735 On the positive side, this backend actually performed fully to
736 specification in all tests and is fully embeddable, which is a rare feat
737 among the OS-specific backends (I vastly prefer correctness over speed
738 hacks).
739 .Sp
740 On the negative side, the interface is \fIbizarre\fR \- so bizarre that
741 even sun itself gets it wrong in their code examples: The event polling
742 function sometimes returns events to the caller even though an error
743 occurred, but with no indication whether it has done so or not (yes, it's
744 even documented that way) \- deadly for edge-triggered interfaces where you
745 absolutely have to know whether an event occurred or not because you have
746 to re-arm the watcher.
747 .Sp
748 Fortunately libev seems to be able to work around these idiocies.
749 .Sp
750 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
751 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
752 .ie n .IP """EVBACKEND_ALL""" 4
753 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
755 Try all backends (even potentially broken ones that wouldn't be tried
756 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
758 .Sp
759 It is definitely not recommended to use this flag, use whatever
760 \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
761 at all.
762 .ie n .IP """EVBACKEND_MASK""" 4
763 .el .IP "\f(CWEVBACKEND_MASK\fR" 4
765 Not a backend at all, but a mask to select all backend bits from a
766 \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
767 value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
768 .RE
769 .RS 4
770 .Sp
771 If one or more of the backend flags are or'ed into the flags value,
772 then only these backends will be tried (in the reverse order as listed
773 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
774 ()\*(C'\fR will be tried.
775 .Sp
776 Example: Try to create a event loop that uses epoll and nothing else.
777 .Sp
778 .Vb 3
779 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
780 \& if (!epoller)
781 \& fatal ("no epoll found here, maybe it hides under your chair");
782 .Ve
783 .Sp
784 Example: Use whatever libev has to offer, but make sure that kqueue is
785 used if available.
786 .Sp
787 .Vb 1
788 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
789 .Ve
790 .RE
791 .IP "ev_loop_destroy (loop)" 4
792 .IX Item "ev_loop_destroy (loop)"
793 Destroys an event loop object (frees all memory and kernel state
794 etc.). None of the active event watchers will be stopped in the normal
795 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
796 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
797 calling this function, or cope with the fact afterwards (which is usually
798 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
799 for example).
800 .Sp
801 Note that certain global state, such as signal state (and installed signal
802 handlers), will not be freed by this function, and related watchers (such
803 as signal and child watchers) would need to be stopped manually.
804 .Sp
805 This function is normally used on loop objects allocated by
806 \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
807 \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
808 .Sp
809 Note that it is not advisable to call this function on the default loop
810 except in the rare occasion where you really need to free its resources.
811 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
812 and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
813 .IP "ev_loop_fork (loop)" 4
814 .IX Item "ev_loop_fork (loop)"
815 This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
816 to reinitialise the kernel state for backends that have one. Despite
817 the name, you can call it anytime you are allowed to start or stop
818 watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
819 sense after forking, in the child process. You \fImust\fR call it (or use
820 \&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
821 .Sp
822 In addition, if you want to reuse a loop (via this function or
823 \&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
824 .Sp
825 Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
826 a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
827 because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
828 during fork.
829 .Sp
830 On the other hand, you only need to call this function in the child
831 process if and only if you want to use the event loop in the child. If
832 you just fork+exec or create a new loop in the child, you don't have to
833 call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
834 difference, but libev will usually detect this case on its own and do a
835 costly reset of the backend).
836 .Sp
837 The function itself is quite fast and it's usually not a problem to call
838 it just in case after a fork.
839 .Sp
840 Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
841 using pthreads.
842 .Sp
843 .Vb 5
844 \& static void
845 \& post_fork_child (void)
846 \& {
847 \& ev_loop_fork (EV_DEFAULT);
848 \& }
849 \&
850 \& ...
851 \& pthread_atfork (0, 0, post_fork_child);
852 .Ve
853 .IP "int ev_is_default_loop (loop)" 4
854 .IX Item "int ev_is_default_loop (loop)"
855 Returns true when the given loop is, in fact, the default loop, and false
856 otherwise.
857 .IP "unsigned int ev_iteration (loop)" 4
858 .IX Item "unsigned int ev_iteration (loop)"
859 Returns the current iteration count for the event loop, which is identical
860 to the number of times libev did poll for new events. It starts at \f(CW0\fR
861 and happily wraps around with enough iterations.
862 .Sp
863 This value can sometimes be useful as a generation counter of sorts (it
864 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
865 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
866 prepare and check phases.
867 .IP "unsigned int ev_depth (loop)" 4
868 .IX Item "unsigned int ev_depth (loop)"
869 Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
870 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
871 .Sp
872 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
873 \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
874 in which case it is higher.
875 .Sp
876 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
877 throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
878 as a hint to avoid such ungentleman-like behaviour unless it's really
879 convenient, in which case it is fully supported.
880 .IP "unsigned int ev_backend (loop)" 4
881 .IX Item "unsigned int ev_backend (loop)"
882 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
883 use.
884 .IP "ev_tstamp ev_now (loop)" 4
885 .IX Item "ev_tstamp ev_now (loop)"
886 Returns the current \*(L"event loop time\*(R", which is the time the event loop
887 received events and started processing them. This timestamp does not
888 change as long as callbacks are being processed, and this is also the base
889 time used for relative timers. You can treat it as the timestamp of the
890 event occurring (or more correctly, libev finding out about it).
891 .IP "ev_now_update (loop)" 4
892 .IX Item "ev_now_update (loop)"
893 Establishes the current time by querying the kernel, updating the time
894 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
895 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
896 .Sp
897 This function is rarely useful, but when some event callback runs for a
898 very long time without entering the event loop, updating libev's idea of
899 the current time is a good idea.
900 .Sp
901 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
902 .IP "ev_suspend (loop)" 4
903 .IX Item "ev_suspend (loop)"
904 .PD 0
905 .IP "ev_resume (loop)" 4
906 .IX Item "ev_resume (loop)"
907 .PD
908 These two functions suspend and resume an event loop, for use when the
909 loop is not used for a while and timeouts should not be processed.
910 .Sp
911 A typical use case would be an interactive program such as a game: When
912 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
913 would be best to handle timeouts as if no time had actually passed while
914 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
915 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
916 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
917 .Sp
918 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
919 between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
920 will be rescheduled (that is, they will lose any events that would have
921 occurred while suspended).
922 .Sp
923 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
924 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
925 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
926 .Sp
927 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
928 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
929 .IP "bool ev_run (loop, int flags)" 4
930 .IX Item "bool ev_run (loop, int flags)"
931 Finally, this is it, the event handler. This function usually is called
932 after you have initialised all your watchers and you want to start
933 handling events. It will ask the operating system for any new events, call
934 the watcher callbacks, and then repeat the whole process indefinitely: This
935 is why event loops are called \fIloops\fR.
936 .Sp
937 If the flags argument is specified as \f(CW0\fR, it will keep handling events
938 until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
939 called.
940 .Sp
941 The return value is false if there are no more active watchers (which
942 usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
943 (which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
944 .Sp
945 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
946 relying on all watchers to be stopped when deciding when a program has
947 finished (especially in interactive programs), but having a program
948 that automatically loops as long as it has to and no longer by virtue
949 of relying on its watchers stopping correctly, that is truly a thing of
950 beauty.
951 .Sp
952 This function is \fImostly\fR exception-safe \- you can break out of a
953 \&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
954 exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
955 will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
956 .Sp
957 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
958 those events and any already outstanding ones, but will not wait and
959 block your process in case there are no events and will return after one
960 iteration of the loop. This is sometimes useful to poll and handle new
961 events while doing lengthy calculations, to keep the program responsive.
962 .Sp
963 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
964 necessary) and will handle those and any already outstanding ones. It
965 will block your process until at least one new event arrives (which could
966 be an event internal to libev itself, so there is no guarantee that a
967 user-registered callback will be called), and will return after one
968 iteration of the loop.
969 .Sp
970 This is useful if you are waiting for some external event in conjunction
971 with something not expressible using other libev watchers (i.e. "roll your
972 own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
973 usually a better approach for this kind of thing.
974 .Sp
975 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
976 understanding, not a guarantee that things will work exactly like this in
977 future versions):
978 .Sp
979 .Vb 10
980 \& \- Increment loop depth.
981 \& \- Reset the ev_break status.
982 \& \- Before the first iteration, call any pending watchers.
983 \& LOOP:
984 \& \- If EVFLAG_FORKCHECK was used, check for a fork.
985 \& \- If a fork was detected (by any means), queue and call all fork watchers.
986 \& \- Queue and call all prepare watchers.
987 \& \- If ev_break was called, goto FINISH.
988 \& \- If we have been forked, detach and recreate the kernel state
989 \& as to not disturb the other process.
990 \& \- Update the kernel state with all outstanding changes.
991 \& \- Update the "event loop time" (ev_now ()).
992 \& \- Calculate for how long to sleep or block, if at all
993 \& (active idle watchers, EVRUN_NOWAIT or not having
994 \& any active watchers at all will result in not sleeping).
995 \& \- Sleep if the I/O and timer collect interval say so.
996 \& \- Increment loop iteration counter.
997 \& \- Block the process, waiting for any events.
998 \& \- Queue all outstanding I/O (fd) events.
999 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
1000 \& \- Queue all expired timers.
1001 \& \- Queue all expired periodics.
1002 \& \- Queue all idle watchers with priority higher than that of pending events.
1003 \& \- Queue all check watchers.
1004 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
1005 \& Signals and child watchers are implemented as I/O watchers, and will
1006 \& be handled here by queueing them when their watcher gets executed.
1007 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
1008 \& were used, or there are no active watchers, goto FINISH, otherwise
1009 \& continue with step LOOP.
1010 \& FINISH:
1011 \& \- Reset the ev_break status iff it was EVBREAK_ONE.
1012 \& \- Decrement the loop depth.
1013 \& \- Return.
1014 .Ve
1015 .Sp
1016 Example: Queue some jobs and then loop until no events are outstanding
1017 anymore.
1018 .Sp
1019 .Vb 4
1020 \& ... queue jobs here, make sure they register event watchers as long
1021 \& ... as they still have work to do (even an idle watcher will do..)
1022 \& ev_run (my_loop, 0);
1023 \& ... jobs done or somebody called break. yeah!
1024 .Ve
1025 .IP "ev_break (loop, how)" 4
1026 .IX Item "ev_break (loop, how)"
1027 Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
1028 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
1029 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
1030 \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1031 .Sp
1032 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1033 .Sp
1034 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1035 which case it will have no effect.
1036 .IP "ev_ref (loop)" 4
1037 .IX Item "ev_ref (loop)"
1038 .PD 0
1039 .IP "ev_unref (loop)" 4
1040 .IX Item "ev_unref (loop)"
1041 .PD
1042 Ref/unref can be used to add or remove a reference count on the event
1043 loop: Every watcher keeps one reference, and as long as the reference
1044 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1045 .Sp
1046 This is useful when you have a watcher that you never intend to
1047 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1048 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1049 before stopping it.
1050 .Sp
1051 As an example, libev itself uses this for its internal signal pipe: It
1052 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1053 exiting if no event watchers registered by it are active. It is also an
1054 excellent way to do this for generic recurring timers or from within
1055 third-party libraries. Just remember to \fIunref after start\fR and \fIref
1056 before stop\fR (but only if the watcher wasn't active before, or was active
1057 before, respectively. Note also that libev might stop watchers itself
1058 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1059 in the callback).
1060 .Sp
1061 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1062 running when nothing else is active.
1063 .Sp
1064 .Vb 4
1065 \& ev_signal exitsig;
1066 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1067 \& ev_signal_start (loop, &exitsig);
1068 \& ev_unref (loop);
1069 .Ve
1070 .Sp
1071 Example: For some weird reason, unregister the above signal handler again.
1072 .Sp
1073 .Vb 2
1074 \& ev_ref (loop);
1075 \& ev_signal_stop (loop, &exitsig);
1076 .Ve
1077 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1078 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1079 .PD 0
1080 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1081 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1082 .PD
1083 These advanced functions influence the time that libev will spend waiting
1084 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1085 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1086 latency.
1087 .Sp
1088 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1089 allows libev to delay invocation of I/O and timer/periodic callbacks
1090 to increase efficiency of loop iterations (or to increase power-saving
1091 opportunities).
1092 .Sp
1093 The idea is that sometimes your program runs just fast enough to handle
1094 one (or very few) event(s) per loop iteration. While this makes the
1095 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1096 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1097 overhead for the actual polling but can deliver many events at once.
1098 .Sp
1099 By setting a higher \fIio collect interval\fR you allow libev to spend more
1100 time collecting I/O events, so you can handle more events per iteration,
1101 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1102 \&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1103 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1104 sleep time ensures that libev will not poll for I/O events more often then
1105 once per this interval, on average (as long as the host time resolution is
1106 good enough).
1107 .Sp
1108 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1109 to spend more time collecting timeouts, at the expense of increased
1110 latency/jitter/inexactness (the watcher callback will be called
1111 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1112 value will not introduce any overhead in libev.
1113 .Sp
1114 Many (busy) programs can usually benefit by setting the I/O collect
1115 interval to a value near \f(CW0.1\fR or so, which is often enough for
1116 interactive servers (of course not for games), likewise for timeouts. It
1117 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1118 as this approaches the timing granularity of most systems. Note that if
1119 you do transactions with the outside world and you can't increase the
1120 parallelity, then this setting will limit your transaction rate (if you
1121 need to poll once per transaction and the I/O collect interval is 0.01,
1122 then you can't do more than 100 transactions per second).
1123 .Sp
1124 Setting the \fItimeout collect interval\fR can improve the opportunity for
1125 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1126 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1127 times the process sleeps and wakes up again. Another useful technique to
1128 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1129 they fire on, say, one-second boundaries only.
1130 .Sp
1131 Example: we only need 0.1s timeout granularity, and we wish not to poll
1132 more often than 100 times per second:
1133 .Sp
1134 .Vb 2
1135 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1136 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1137 .Ve
1138 .IP "ev_invoke_pending (loop)" 4
1139 .IX Item "ev_invoke_pending (loop)"
1140 This call will simply invoke all pending watchers while resetting their
1141 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1142 but when overriding the invoke callback this call comes handy. This
1143 function can be invoked from a watcher \- this can be useful for example
1144 when you want to do some lengthy calculation and want to pass further
1145 event handling to another thread (you still have to make sure only one
1146 thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1147 .IP "int ev_pending_count (loop)" 4
1148 .IX Item "int ev_pending_count (loop)"
1149 Returns the number of pending watchers \- zero indicates that no watchers
1150 are pending.
1151 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1152 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1153 This overrides the invoke pending functionality of the loop: Instead of
1154 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1155 this callback instead. This is useful, for example, when you want to
1156 invoke the actual watchers inside another context (another thread etc.).
1157 .Sp
1158 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1159 callback.
1160 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1161 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1162 Sometimes you want to share the same loop between multiple threads. This
1163 can be done relatively simply by putting mutex_lock/unlock calls around
1164 each call to a libev function.
1165 .Sp
1166 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1167 to wait for it to return. One way around this is to wake up the event
1168 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1169 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1170 .Sp
1171 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1172 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1173 afterwards.
1174 .Sp
1175 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1176 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1177 .Sp
1178 While event loop modifications are allowed between invocations of
1179 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1180 modifications done will affect the event loop, i.e. adding watchers will
1181 have no effect on the set of file descriptors being watched, or the time
1182 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1183 to take note of any changes you made.
1184 .Sp
1185 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1186 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1187 .Sp
1188 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1189 document.
1190 .IP "ev_set_userdata (loop, void *data)" 4
1191 .IX Item "ev_set_userdata (loop, void *data)"
1192 .PD 0
1193 .IP "void *ev_userdata (loop)" 4
1194 .IX Item "void *ev_userdata (loop)"
1195 .PD
1196 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1197 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1198 \&\f(CW0\fR.
1199 .Sp
1200 These two functions can be used to associate arbitrary data with a loop,
1201 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1202 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1203 any other purpose as well.
1204 .IP "ev_verify (loop)" 4
1205 .IX Item "ev_verify (loop)"
1206 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1207 compiled in, which is the default for non-minimal builds. It tries to go
1208 through all internal structures and checks them for validity. If anything
1209 is found to be inconsistent, it will print an error message to standard
1210 error and call \f(CW\*(C`abort ()\*(C'\fR.
1211 .Sp
1212 This can be used to catch bugs inside libev itself: under normal
1213 circumstances, this function will never abort as of course libev keeps its
1214 data structures consistent.
1217 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1218 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1219 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1220 .PP
1221 A watcher is an opaque structure that you allocate and register to record
1222 your interest in some event. To make a concrete example, imagine you want
1223 to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1224 for that:
1225 .PP
1226 .Vb 5
1227 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1228 \& {
1229 \& ev_io_stop (w);
1230 \& ev_break (loop, EVBREAK_ALL);
1231 \& }
1232 \&
1233 \& struct ev_loop *loop = ev_default_loop (0);
1234 \&
1235 \& ev_io stdin_watcher;
1236 \&
1237 \& ev_init (&stdin_watcher, my_cb);
1238 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1239 \& ev_io_start (loop, &stdin_watcher);
1240 \&
1241 \& ev_run (loop, 0);
1242 .Ve
1243 .PP
1244 As you can see, you are responsible for allocating the memory for your
1245 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1246 stack).
1247 .PP
1248 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1249 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1250 .PP
1251 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1252 *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1253 invoked each time the event occurs (or, in the case of I/O watchers, each
1254 time the event loop detects that the file descriptor given is readable
1255 and/or writable).
1256 .PP
1257 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1258 macro to configure it, with arguments specific to the watcher type. There
1259 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1260 .PP
1261 To make the watcher actually watch out for events, you have to start it
1262 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1263 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1264 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1265 .PP
1266 As long as your watcher is active (has been started but not stopped) you
1267 must not touch the values stored in it. Most specifically you must never
1268 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1269 .PP
1270 Each and every callback receives the event loop pointer as first, the
1271 registered watcher structure as second, and a bitset of received events as
1272 third argument.
1273 .PP
1274 The received events usually include a single bit per event type received
1275 (you can receive multiple events at the same time). The possible bit masks
1276 are:
1277 .ie n .IP """EV_READ""" 4
1278 .el .IP "\f(CWEV_READ\fR" 4
1279 .IX Item "EV_READ"
1280 .PD 0
1281 .ie n .IP """EV_WRITE""" 4
1282 .el .IP "\f(CWEV_WRITE\fR" 4
1283 .IX Item "EV_WRITE"
1284 .PD
1285 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1286 writable.
1287 .ie n .IP """EV_TIMER""" 4
1288 .el .IP "\f(CWEV_TIMER\fR" 4
1289 .IX Item "EV_TIMER"
1290 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1291 .ie n .IP """EV_PERIODIC""" 4
1292 .el .IP "\f(CWEV_PERIODIC\fR" 4
1293 .IX Item "EV_PERIODIC"
1294 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1295 .ie n .IP """EV_SIGNAL""" 4
1296 .el .IP "\f(CWEV_SIGNAL\fR" 4
1297 .IX Item "EV_SIGNAL"
1298 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1299 .ie n .IP """EV_CHILD""" 4
1300 .el .IP "\f(CWEV_CHILD\fR" 4
1301 .IX Item "EV_CHILD"
1302 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1303 .ie n .IP """EV_STAT""" 4
1304 .el .IP "\f(CWEV_STAT\fR" 4
1305 .IX Item "EV_STAT"
1306 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1307 .ie n .IP """EV_IDLE""" 4
1308 .el .IP "\f(CWEV_IDLE\fR" 4
1309 .IX Item "EV_IDLE"
1310 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1311 .ie n .IP """EV_PREPARE""" 4
1312 .el .IP "\f(CWEV_PREPARE\fR" 4
1313 .IX Item "EV_PREPARE"
1314 .PD 0
1315 .ie n .IP """EV_CHECK""" 4
1316 .el .IP "\f(CWEV_CHECK\fR" 4
1317 .IX Item "EV_CHECK"
1318 .PD
1319 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
1320 gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
1321 just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1322 for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1323 watchers invoked before the event loop sleeps or polls for new events, and
1324 \&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1325 or lower priority within an event loop iteration.
1326 .Sp
1327 Callbacks of both watcher types can start and stop as many watchers as
1328 they want, and all of them will be taken into account (for example, a
1329 \&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
1330 blocking).
1331 .ie n .IP """EV_EMBED""" 4
1332 .el .IP "\f(CWEV_EMBED\fR" 4
1333 .IX Item "EV_EMBED"
1334 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1335 .ie n .IP """EV_FORK""" 4
1336 .el .IP "\f(CWEV_FORK\fR" 4
1337 .IX Item "EV_FORK"
1338 The event loop has been resumed in the child process after fork (see
1339 \&\f(CW\*(C`ev_fork\*(C'\fR).
1340 .ie n .IP """EV_CLEANUP""" 4
1341 .el .IP "\f(CWEV_CLEANUP\fR" 4
1342 .IX Item "EV_CLEANUP"
1343 The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1344 .ie n .IP """EV_ASYNC""" 4
1345 .el .IP "\f(CWEV_ASYNC\fR" 4
1346 .IX Item "EV_ASYNC"
1347 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1348 .ie n .IP """EV_CUSTOM""" 4
1349 .el .IP "\f(CWEV_CUSTOM\fR" 4
1350 .IX Item "EV_CUSTOM"
1351 Not ever sent (or otherwise used) by libev itself, but can be freely used
1352 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1353 .ie n .IP """EV_ERROR""" 4
1354 .el .IP "\f(CWEV_ERROR\fR" 4
1355 .IX Item "EV_ERROR"
1356 An unspecified error has occurred, the watcher has been stopped. This might
1357 happen because the watcher could not be properly started because libev
1358 ran out of memory, a file descriptor was found to be closed or any other
1359 problem. Libev considers these application bugs.
1360 .Sp
1361 You best act on it by reporting the problem and somehow coping with the
1362 watcher being stopped. Note that well-written programs should not receive
1363 an error ever, so when your watcher receives it, this usually indicates a
1364 bug in your program.
1365 .Sp
1366 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1367 example it might indicate that a fd is readable or writable, and if your
1368 callbacks is well-written it can just attempt the operation and cope with
1369 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1370 programs, though, as the fd could already be closed and reused for another
1371 thing, so beware.
1374 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1375 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1376 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1377 This macro initialises the generic portion of a watcher. The contents
1378 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1379 the generic parts of the watcher are initialised, you \fIneed\fR to call
1380 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1381 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1382 which rolls both calls into one.
1383 .Sp
1384 You can reinitialise a watcher at any time as long as it has been stopped
1385 (or never started) and there are no pending events outstanding.
1386 .Sp
1387 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1388 int revents)\*(C'\fR.
1389 .Sp
1390 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1391 .Sp
1392 .Vb 3
1393 \& ev_io w;
1394 \& ev_init (&w, my_cb);
1395 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1396 .Ve
1397 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1398 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1399 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1400 This macro initialises the type-specific parts of a watcher. You need to
1401 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1402 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1403 macro on a watcher that is active (it can be pending, however, which is a
1404 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1405 .Sp
1406 Although some watcher types do not have type-specific arguments
1407 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1408 .Sp
1409 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1410 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1411 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1412 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1413 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1414 calls into a single call. This is the most convenient method to initialise
1415 a watcher. The same limitations apply, of course.
1416 .Sp
1417 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1418 .Sp
1419 .Vb 1
1420 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1421 .Ve
1422 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1423 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1424 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1425 Starts (activates) the given watcher. Only active watchers will receive
1426 events. If the watcher is already active nothing will happen.
1427 .Sp
1428 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1429 whole section.
1430 .Sp
1431 .Vb 1
1432 \& ev_io_start (EV_DEFAULT_UC, &w);
1433 .Ve
1434 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1435 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1436 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1437 Stops the given watcher if active, and clears the pending status (whether
1438 the watcher was active or not).
1439 .Sp
1440 It is possible that stopped watchers are pending \- for example,
1441 non-repeating timers are being stopped when they become pending \- but
1442 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1443 pending. If you want to free or reuse the memory used by the watcher it is
1444 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1445 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1446 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1447 Returns a true value iff the watcher is active (i.e. it has been started
1448 and not yet been stopped). As long as a watcher is active you must not modify
1449 it.
1450 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1451 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1452 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1453 events but its callback has not yet been invoked). As long as a watcher
1454 is pending (but not active) you must not call an init function on it (but
1455 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1456 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1457 it).
1458 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1459 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1460 Returns the callback currently set on the watcher.
1461 .IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1462 .IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1463 Change the callback. You can change the callback at virtually any time
1464 (modulo threads).
1465 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1466 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1467 .PD 0
1468 .IP "int ev_priority (ev_TYPE *watcher)" 4
1469 .IX Item "int ev_priority (ev_TYPE *watcher)"
1470 .PD
1471 Set and query the priority of the watcher. The priority is a small
1472 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1473 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1474 before watchers with lower priority, but priority will not keep watchers
1475 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1476 .Sp
1477 If you need to suppress invocation when higher priority events are pending
1478 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1479 .Sp
1480 You \fImust not\fR change the priority of a watcher as long as it is active or
1481 pending.
1482 .Sp
1483 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1484 fine, as long as you do not mind that the priority value you query might
1485 or might not have been clamped to the valid range.
1486 .Sp
1487 The default priority used by watchers when no priority has been set is
1488 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1489 .Sp
1490 See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1491 priorities.
1492 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1493 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1494 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
1495 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1496 can deal with that fact, as both are simply passed through to the
1497 callback.
1498 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1499 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1500 If the watcher is pending, this function clears its pending status and
1501 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1502 watcher isn't pending it does nothing and returns \f(CW0\fR.
1503 .Sp
1504 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1505 callback to be invoked, which can be accomplished with this function.
1506 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1507 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1508 Feeds the given event set into the event loop, as if the specified event
1509 had happened for the specified watcher (which must be a pointer to an
1510 initialised but not necessarily started event watcher). Obviously you must
1511 not free the watcher as long as it has pending events.
1512 .Sp
1513 Stopping the watcher, letting libev invoke it, or calling
1514 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1515 not started in the first place.
1516 .Sp
1517 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1518 functions that do not need a watcher.
1519 .PP
1520 See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1521 OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1522 .SS "\s-1WATCHER STATES\s0"
1523 .IX Subsection "WATCHER STATES"
1524 There are various watcher states mentioned throughout this manual \-
1525 active, pending and so on. In this section these states and the rules to
1526 transition between them will be described in more detail \- and while these
1527 rules might look complicated, they usually do \*(L"the right thing\*(R".
1528 .IP "initialised" 4
1529 .IX Item "initialised"
1530 Before a watcher can be registered with the event loop it has to be
1531 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1532 \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1533 .Sp
1534 In this state it is simply some block of memory that is suitable for
1535 use in an event loop. It can be moved around, freed, reused etc. at
1536 will \- as long as you either keep the memory contents intact, or call
1537 \&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1538 .IP "started/running/active" 4
1539 .IX Item "started/running/active"
1540 Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1541 property of the event loop, and is actively waiting for events. While in
1542 this state it cannot be accessed (except in a few documented ways), moved,
1543 freed or anything else \- the only legal thing is to keep a pointer to it,
1544 and call libev functions on it that are documented to work on active watchers.
1545 .IP "pending" 4
1546 .IX Item "pending"
1547 If a watcher is active and libev determines that an event it is interested
1548 in has occurred (such as a timer expiring), it will become pending. It will
1549 stay in this pending state until either it is stopped or its callback is
1550 about to be invoked, so it is not normally pending inside the watcher
1551 callback.
1552 .Sp
1553 The watcher might or might not be active while it is pending (for example,
1554 an expired non-repeating timer can be pending but no longer active). If it
1555 is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1556 but it is still property of the event loop at this time, so cannot be
1557 moved, freed or reused. And if it is active the rules described in the
1558 previous item still apply.
1559 .Sp
1560 It is also possible to feed an event on a watcher that is not active (e.g.
1561 via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1562 active.
1563 .IP "stopped" 4
1564 .IX Item "stopped"
1565 A watcher can be stopped implicitly by libev (in which case it might still
1566 be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1567 latter will clear any pending state the watcher might be in, regardless
1568 of whether it was active or not, so stopping a watcher explicitly before
1569 freeing it is often a good idea.
1570 .Sp
1571 While stopped (and not pending) the watcher is essentially in the
1572 initialised state, that is, it can be reused, moved, modified in any way
1573 you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1574 it again).
1577 Many event loops support \fIwatcher priorities\fR, which are usually small
1578 integers that influence the ordering of event callback invocation
1579 between watchers in some way, all else being equal.
1580 .PP
1581 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1582 description for the more technical details such as the actual priority
1583 range.
1584 .PP
1585 There are two common ways how these these priorities are being interpreted
1586 by event loops:
1587 .PP
1588 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1589 of lower priority watchers, which means as long as higher priority
1590 watchers receive events, lower priority watchers are not being invoked.
1591 .PP
1592 The less common only-for-ordering model uses priorities solely to order
1593 callback invocation within a single event loop iteration: Higher priority
1594 watchers are invoked before lower priority ones, but they all get invoked
1595 before polling for new events.
1596 .PP
1597 Libev uses the second (only-for-ordering) model for all its watchers
1598 except for idle watchers (which use the lock-out model).
1599 .PP
1600 The rationale behind this is that implementing the lock-out model for
1601 watchers is not well supported by most kernel interfaces, and most event
1602 libraries will just poll for the same events again and again as long as
1603 their callbacks have not been executed, which is very inefficient in the
1604 common case of one high-priority watcher locking out a mass of lower
1605 priority ones.
1606 .PP
1607 Static (ordering) priorities are most useful when you have two or more
1608 watchers handling the same resource: a typical usage example is having an
1609 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1610 timeouts. Under load, data might be received while the program handles
1611 other jobs, but since timers normally get invoked first, the timeout
1612 handler will be executed before checking for data. In that case, giving
1613 the timer a lower priority than the I/O watcher ensures that I/O will be
1614 handled first even under adverse conditions (which is usually, but not
1615 always, what you want).
1616 .PP
1617 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1618 will only be executed when no same or higher priority watchers have
1619 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1620 required.
1621 .PP
1622 For example, to emulate how many other event libraries handle priorities,
1623 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1624 the normal watcher callback, you just start the idle watcher. The real
1625 processing is done in the idle watcher callback. This causes libev to
1626 continuously poll and process kernel event data for the watcher, but when
1627 the lock-out case is known to be rare (which in turn is rare :), this is
1628 workable.
1629 .PP
1630 Usually, however, the lock-out model implemented that way will perform
1631 miserably under the type of load it was designed to handle. In that case,
1632 it might be preferable to stop the real watcher before starting the
1633 idle watcher, so the kernel will not have to process the event in case
1634 the actual processing will be delayed for considerable time.
1635 .PP
1636 Here is an example of an I/O watcher that should run at a strictly lower
1637 priority than the default, and which should only process data when no
1638 other events are pending:
1639 .PP
1640 .Vb 2
1641 \& ev_idle idle; // actual processing watcher
1642 \& ev_io io; // actual event watcher
1643 \&
1644 \& static void
1645 \& io_cb (EV_P_ ev_io *w, int revents)
1646 \& {
1647 \& // stop the I/O watcher, we received the event, but
1648 \& // are not yet ready to handle it.
1649 \& ev_io_stop (EV_A_ w);
1650 \&
1651 \& // start the idle watcher to handle the actual event.
1652 \& // it will not be executed as long as other watchers
1653 \& // with the default priority are receiving events.
1654 \& ev_idle_start (EV_A_ &idle);
1655 \& }
1656 \&
1657 \& static void
1658 \& idle_cb (EV_P_ ev_idle *w, int revents)
1659 \& {
1660 \& // actual processing
1661 \& read (STDIN_FILENO, ...);
1662 \&
1663 \& // have to start the I/O watcher again, as
1664 \& // we have handled the event
1665 \& ev_io_start (EV_P_ &io);
1666 \& }
1667 \&
1668 \& // initialisation
1669 \& ev_idle_init (&idle, idle_cb);
1670 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1671 \& ev_io_start (EV_DEFAULT_ &io);
1672 .Ve
1673 .PP
1674 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1675 low-priority connections can not be locked out forever under load. This
1676 enables your program to keep a lower latency for important connections
1677 during short periods of high load, while not completely locking out less
1678 important ones.
1680 .IX Header "WATCHER TYPES"
1681 This section describes each watcher in detail, but will not repeat
1682 information given in the last section. Any initialisation/set macros,
1683 functions and members specific to the watcher type are explained.
1684 .PP
1685 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1686 while the watcher is active, you can look at the member and expect some
1687 sensible content, but you must not modify it (you can modify it while the
1688 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1689 means you can expect it to have some sensible content while the watcher
1690 is active, but you can also modify it. Modifying it may not do something
1691 sensible or take immediate effect (or do anything at all), but libev will
1692 not crash or malfunction in any way.
1693 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1694 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1695 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1696 I/O watchers check whether a file descriptor is readable or writable
1697 in each iteration of the event loop, or, more precisely, when reading
1698 would not block the process and writing would at least be able to write
1699 some data. This behaviour is called level-triggering because you keep
1700 receiving events as long as the condition persists. Remember you can stop
1701 the watcher if you don't want to act on the event and neither want to
1702 receive future events.
1703 .PP
1704 In general you can register as many read and/or write event watchers per
1705 fd as you want (as long as you don't confuse yourself). Setting all file
1706 descriptors to non-blocking mode is also usually a good idea (but not
1707 required if you know what you are doing).
1708 .PP
1709 Another thing you have to watch out for is that it is quite easy to
1710 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1711 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1712 because there is no data. It is very easy to get into this situation even
1713 with a relatively standard program structure. Thus it is best to always
1714 use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1715 preferable to a program hanging until some data arrives.
1716 .PP
1717 If you cannot run the fd in non-blocking mode (for example you should
1718 not play around with an Xlib connection), then you have to separately
1719 re-test whether a file descriptor is really ready with a known-to-be good
1720 interface such as poll (fortunately in the case of Xlib, it already does
1721 this on its own, so its quite safe to use). Some people additionally
1722 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1723 indefinitely.
1724 .PP
1725 But really, best use non-blocking mode.
1726 .PP
1727 \fIThe special problem of disappearing file descriptors\fR
1728 .IX Subsection "The special problem of disappearing file descriptors"
1729 .PP
1730 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1731 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1732 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1733 descriptor, but when it goes away, the operating system will silently drop
1734 this interest. If another file descriptor with the same number then is
1735 registered with libev, there is no efficient way to see that this is, in
1736 fact, a different file descriptor.
1737 .PP
1738 To avoid having to explicitly tell libev about such cases, libev follows
1739 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1740 will assume that this is potentially a new file descriptor, otherwise
1741 it is assumed that the file descriptor stays the same. That means that
1742 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
1743 descriptor even if the file descriptor number itself did not change.
1744 .PP
1745 This is how one would do it normally anyway, the important point is that
1746 the libev application should not optimise around libev but should leave
1747 optimisations to libev.
1748 .PP
1749 \fIThe special problem of dup'ed file descriptors\fR
1750 .IX Subsection "The special problem of dup'ed file descriptors"
1751 .PP
1752 Some backends (e.g. epoll), cannot register events for file descriptors,
1753 but only events for the underlying file descriptions. That means when you
1754 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1755 events for them, only one file descriptor might actually receive events.
1756 .PP
1757 There is no workaround possible except not registering events
1758 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1759 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1760 .PP
1761 \fIThe special problem of files\fR
1762 .IX Subsection "The special problem of files"
1763 .PP
1764 Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1765 representing files, and expect it to become ready when their program
1766 doesn't block on disk accesses (which can take a long time on their own).
1767 .PP
1768 However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1769 notification as soon as the kernel knows whether and how much data is
1770 there, and in the case of open files, that's always the case, so you
1771 always get a readiness notification instantly, and your read (or possibly
1772 write) will still block on the disk I/O.
1773 .PP
1774 Another way to view it is that in the case of sockets, pipes, character
1775 devices and so on, there is another party (the sender) that delivers data
1776 on its own, but in the case of files, there is no such thing: the disk
1777 will not send data on its own, simply because it doesn't know what you
1778 wish to read \- you would first have to request some data.
1779 .PP
1780 Since files are typically not-so-well supported by advanced notification
1781 mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1782 to files, even though you should not use it. The reason for this is
1783 convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1784 usually a tty, often a pipe, but also sometimes files or special devices
1785 (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1786 \&\fI/dev/urandom\fR), and even though the file might better be served with
1787 asynchronous I/O instead of with non-blocking I/O, it is still useful when
1788 it \*(L"just works\*(R" instead of freezing.
1789 .PP
1790 So avoid file descriptors pointing to files when you know it (e.g. use
1791 libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1792 when you rarely read from a file instead of from a socket, and want to
1793 reuse the same code path.
1794 .PP
1795 \fIThe special problem of fork\fR
1796 .IX Subsection "The special problem of fork"
1797 .PP
1798 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1799 useless behaviour. Libev fully supports fork, but needs to be told about
1800 it in the child if you want to continue to use it in the child.
1801 .PP
1802 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1803 ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1804 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1805 .PP
1806 \fIThe special problem of \s-1SIGPIPE\s0\fR
1807 .IX Subsection "The special problem of SIGPIPE"
1808 .PP
1809 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1810 when writing to a pipe whose other end has been closed, your program gets
1811 sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1812 this is sensible behaviour, for daemons, this is usually undesirable.
1813 .PP
1814 So when you encounter spurious, unexplained daemon exits, make sure you
1815 ignore \s-1SIGPIPE \s0(and maybe make sure you log the exit status of your daemon
1816 somewhere, as that would have given you a big clue).
1817 .PP
1818 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1819 .IX Subsection "The special problem of accept()ing when you can't"
1820 .PP
1821 Many implementations of the \s-1POSIX \s0\f(CW\*(C`accept\*(C'\fR function (for example,
1822 found in post\-2004 Linux) have the peculiar behaviour of not removing a
1823 connection from the pending queue in all error cases.
1824 .PP
1825 For example, larger servers often run out of file descriptors (because
1826 of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1827 rejecting the connection, leading to libev signalling readiness on
1828 the next iteration again (the connection still exists after all), and
1829 typically causing the program to loop at 100% \s-1CPU\s0 usage.
1830 .PP
1831 Unfortunately, the set of errors that cause this issue differs between
1832 operating systems, there is usually little the app can do to remedy the
1833 situation, and no known thread-safe method of removing the connection to
1834 cope with overload is known (to me).
1835 .PP
1836 One of the easiest ways to handle this situation is to just ignore it
1837 \&\- when the program encounters an overload, it will just loop until the
1838 situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1839 event-based way to handle this situation, so it's the best one can do.
1840 .PP
1841 A better way to handle the situation is to log any errors other than
1842 \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1843 messages, and continue as usual, which at least gives the user an idea of
1844 what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1845 the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1846 usage.
1847 .PP
1848 If your program is single-threaded, then you could also keep a dummy file
1849 descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1850 when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1851 close that fd, and create a new dummy fd. This will gracefully refuse
1852 clients under typical overload conditions.
1853 .PP
1854 The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1855 is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1856 opportunity for a DoS attack.
1857 .PP
1858 \fIWatcher-Specific Functions\fR
1859 .IX Subsection "Watcher-Specific Functions"
1860 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1861 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1862 .PD 0
1863 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1864 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1865 .PD
1866 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1867 receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1868 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1869 .IP "int fd [read\-only]" 4
1870 .IX Item "int fd [read-only]"
1871 The file descriptor being watched.
1872 .IP "int events [read\-only]" 4
1873 .IX Item "int events [read-only]"
1874 The events being watched.
1875 .PP
1876 \fIExamples\fR
1877 .IX Subsection "Examples"
1878 .PP
1879 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1880 readable, but only once. Since it is likely line-buffered, you could
1881 attempt to read a whole line in the callback.
1882 .PP
1883 .Vb 6
1884 \& static void
1885 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1886 \& {
1887 \& ev_io_stop (loop, w);
1888 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1889 \& }
1890 \&
1891 \& ...
1892 \& struct ev_loop *loop = ev_default_init (0);
1893 \& ev_io stdin_readable;
1894 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1895 \& ev_io_start (loop, &stdin_readable);
1896 \& ev_run (loop, 0);
1897 .Ve
1898 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1899 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1900 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1901 Timer watchers are simple relative timers that generate an event after a
1902 given time, and optionally repeating in regular intervals after that.
1903 .PP
1904 The timers are based on real time, that is, if you register an event that
1905 times out after an hour and you reset your system clock to January last
1906 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1907 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1908 monotonic clock option helps a lot here).
1909 .PP
1910 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1911 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1912 might introduce a small delay, see \*(L"the special problem of being too
1913 early\*(R", below). If multiple timers become ready during the same loop
1914 iteration then the ones with earlier time-out values are invoked before
1915 ones of the same priority with later time-out values (but this is no
1916 longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1917 .PP
1918 \fIBe smart about timeouts\fR
1919 .IX Subsection "Be smart about timeouts"
1920 .PP
1921 Many real-world problems involve some kind of timeout, usually for error
1922 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1923 you want to raise some error after a while.
1924 .PP
1925 What follows are some ways to handle this problem, from obvious and
1926 inefficient to smart and efficient.
1927 .PP
1928 In the following, a 60 second activity timeout is assumed \- a timeout that
1929 gets reset to 60 seconds each time there is activity (e.g. each time some
1930 data or other life sign was received).
1931 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1932 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1933 This is the most obvious, but not the most simple way: In the beginning,
1934 start the watcher:
1935 .Sp
1936 .Vb 2
1937 \& ev_timer_init (timer, callback, 60., 0.);
1938 \& ev_timer_start (loop, timer);
1939 .Ve
1940 .Sp
1941 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1942 and start it again:
1943 .Sp
1944 .Vb 3
1945 \& ev_timer_stop (loop, timer);
1946 \& ev_timer_set (timer, 60., 0.);
1947 \& ev_timer_start (loop, timer);
1948 .Ve
1949 .Sp
1950 This is relatively simple to implement, but means that each time there is
1951 some activity, libev will first have to remove the timer from its internal
1952 data structure and then add it again. Libev tries to be fast, but it's
1953 still not a constant-time operation.
1954 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1955 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1956 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1957 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1958 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1959 .Sp
1960 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1961 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1962 successfully read or write some data. If you go into an idle state where
1963 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1964 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1965 .Sp
1966 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1967 \&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
1968 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1969 .Sp
1970 At start:
1971 .Sp
1972 .Vb 3
1973 \& ev_init (timer, callback);
1974 \& timer\->repeat = 60.;
1975 \& ev_timer_again (loop, timer);
1976 .Ve
1977 .Sp
1978 Each time there is some activity:
1979 .Sp
1980 .Vb 1
1981 \& ev_timer_again (loop, timer);
1982 .Ve
1983 .Sp
1984 It is even possible to change the time-out on the fly, regardless of
1985 whether the watcher is active or not:
1986 .Sp
1987 .Vb 2
1988 \& timer\->repeat = 30.;
1989 \& ev_timer_again (loop, timer);
1990 .Ve
1991 .Sp
1992 This is slightly more efficient then stopping/starting the timer each time
1993 you want to modify its timeout value, as libev does not have to completely
1994 remove and re-insert the timer from/into its internal data structure.
1995 .Sp
1996 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1997 .IP "3. Let the timer time out, but then re-arm it as required." 4
1998 .IX Item "3. Let the timer time out, but then re-arm it as required."
1999 This method is more tricky, but usually most efficient: Most timeouts are
2000 relatively long compared to the intervals between other activity \- in
2001 our example, within 60 seconds, there are usually many I/O events with
2002 associated activity resets.
2003 .Sp
2004 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2005 but remember the time of last activity, and check for a real timeout only
2006 within the callback:
2007 .Sp
2008 .Vb 3
2009 \& ev_tstamp timeout = 60.;
2010 \& ev_tstamp last_activity; // time of last activity
2011 \& ev_timer timer;
2012 \&
2013 \& static void
2014 \& callback (EV_P_ ev_timer *w, int revents)
2015 \& {
2016 \& // calculate when the timeout would happen
2017 \& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2018 \&
2019 \& // if negative, it means we the timeout already occurred
2020 \& if (after < 0.)
2021 \& {
2022 \& // timeout occurred, take action
2023 \& }
2024 \& else
2025 \& {
2026 \& // callback was invoked, but there was some recent
2027 \& // activity. simply restart the timer to time out
2028 \& // after "after" seconds, which is the earliest time
2029 \& // the timeout can occur.
2030 \& ev_timer_set (w, after, 0.);
2031 \& ev_timer_start (EV_A_ w);
2032 \& }
2033 \& }
2034 .Ve
2035 .Sp
2036 To summarise the callback: first calculate in how many seconds the
2037 timeout will occur (by calculating the absolute time when it would occur,
2038 \&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2039 (EV_A)\*(C'\fR from that).
2040 .Sp
2041 If this value is negative, then we are already past the timeout, i.e. we
2042 timed out, and need to do whatever is needed in this case.
2043 .Sp
2044 Otherwise, we now the earliest time at which the timeout would trigger,
2045 and simply start the timer with this timeout value.
2046 .Sp
2047 In other words, each time the callback is invoked it will check whether
2048 the timeout occurred. If not, it will simply reschedule itself to check
2049 again at the earliest time it could time out. Rinse. Repeat.
2050 .Sp
2051 This scheme causes more callback invocations (about one every 60 seconds
2052 minus half the average time between activity), but virtually no calls to
2053 libev to change the timeout.
2054 .Sp
2055 To start the machinery, simply initialise the watcher and set
2056 \&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2057 now), then call the callback, which will \*(L"do the right thing\*(R" and start
2058 the timer:
2059 .Sp
2060 .Vb 3
2061 \& last_activity = ev_now (EV_A);
2062 \& ev_init (&timer, callback);
2063 \& callback (EV_A_ &timer, 0);
2064 .Ve
2065 .Sp
2066 When there is some activity, simply store the current time in
2067 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2068 .Sp
2069 .Vb 2
2070 \& if (activity detected)
2071 \& last_activity = ev_now (EV_A);
2072 .Ve
2073 .Sp
2074 When your timeout value changes, then the timeout can be changed by simply
2075 providing a new value, stopping the timer and calling the callback, which
2076 will again do the right thing (for example, time out immediately :).
2077 .Sp
2078 .Vb 3
2079 \& timeout = new_value;
2080 \& ev_timer_stop (EV_A_ &timer);
2081 \& callback (EV_A_ &timer, 0);
2082 .Ve
2083 .Sp
2084 This technique is slightly more complex, but in most cases where the
2085 time-out is unlikely to be triggered, much more efficient.
2086 .IP "4. Wee, just use a double-linked list for your timeouts." 4
2087 .IX Item "4. Wee, just use a double-linked list for your timeouts."
2088 If there is not one request, but many thousands (millions...), all
2089 employing some kind of timeout with the same timeout value, then one can
2090 do even better:
2091 .Sp
2092 When starting the timeout, calculate the timeout value and put the timeout
2093 at the \fIend\fR of the list.
2094 .Sp
2095 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2096 the list is expected to fire (for example, using the technique #3).
2097 .Sp
2098 When there is some activity, remove the timer from the list, recalculate
2099 the timeout, append it to the end of the list again, and make sure to
2100 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2101 .Sp
2102 This way, one can manage an unlimited number of timeouts in O(1) time for
2103 starting, stopping and updating the timers, at the expense of a major
2104 complication, and having to use a constant timeout. The constant timeout
2105 ensures that the list stays sorted.
2106 .PP
2107 So which method the best?
2108 .PP
2109 Method #2 is a simple no-brain-required solution that is adequate in most
2110 situations. Method #3 requires a bit more thinking, but handles many cases
2111 better, and isn't very complicated either. In most case, choosing either
2112 one is fine, with #3 being better in typical situations.
2113 .PP
2114 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2115 rather complicated, but extremely efficient, something that really pays
2116 off after the first million or so of active timers, i.e. it's usually
2117 overkill :)
2118 .PP
2119 \fIThe special problem of being too early\fR
2120 .IX Subsection "The special problem of being too early"
2121 .PP
2122 If you ask a timer to call your callback after three seconds, then
2123 you expect it to be invoked after three seconds \- but of course, this
2124 cannot be guaranteed to infinite precision. Less obviously, it cannot be
2125 guaranteed to any precision by libev \- imagine somebody suspending the
2126 process with a \s-1STOP\s0 signal for a few hours for example.
2127 .PP
2128 So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2129 delay has occurred, but cannot guarantee this.
2130 .PP
2131 A less obvious failure mode is calling your callback too early: many event
2132 loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2133 this can cause your callback to be invoked much earlier than you would
2134 expect.
2135 .PP
2136 To see why, imagine a system with a clock that only offers full second
2137 resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2138 yourself). If you schedule a one-second timer at the time 500.9, then the
2139 event loop will schedule your timeout to elapse at a system time of 500
2140 (500.9 truncated to the resolution) + 1, or 501.
2141 .PP
2142 If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2143 501\*(R" and invoke the callback 0.1s after it was started, even though a
2144 one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2145 intentions.
2146 .PP
2147 This is the reason why libev will never invoke the callback if the elapsed
2148 delay equals the requested delay, but only when the elapsed delay is
2149 larger than the requested delay. In the example above, libev would only invoke
2150 the callback at system time 502, or 1.1s after the timer was started.
2151 .PP
2152 So, while libev cannot guarantee that your callback will be invoked
2153 exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2154 delay has actually elapsed, or in other words, it always errs on the \*(L"too
2155 late\*(R" side of things.
2156 .PP
2157 \fIThe special problem of time updates\fR
2158 .IX Subsection "The special problem of time updates"
2159 .PP
2160 Establishing the current time is a costly operation (it usually takes
2161 at least one system call): \s-1EV\s0 therefore updates its idea of the current
2162 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2163 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2164 lots of events in one iteration.
2165 .PP
2166 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2167 time. This is usually the right thing as this timestamp refers to the time
2168 of the event triggering whatever timeout you are modifying/starting. If
2169 you suspect event processing to be delayed and you \fIneed\fR to base the
2170 timeout on the current time, use something like the following to adjust
2171 for it:
2172 .PP
2173 .Vb 1
2174 \& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
2175 .Ve
2176 .PP
2177 If the event loop is suspended for a long time, you can also force an
2178 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2179 ()\*(C'\fR, although that will push the event time of all outstanding events
2180 further into the future.
2181 .PP
2182 \fIThe special problem of unsynchronised clocks\fR
2183 .IX Subsection "The special problem of unsynchronised clocks"
2184 .PP
2185 Modern systems have a variety of clocks \- libev itself uses the normal
2186 \&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2187 jumps).
2188 .PP
2189 Neither of these clocks is synchronised with each other or any other clock
2190 on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2191 than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2192 a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2193 than a directly following call to \f(CW\*(C`time\*(C'\fR.
2194 .PP
2195 The moral of this is to only compare libev-related timestamps with
2196 \&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2197 a second or so.
2198 .PP
2199 One more problem arises due to this lack of synchronisation: if libev uses
2200 the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2201 or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2202 invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2203 .PP
2204 This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2205 libev makes sure your callback is not invoked before the delay happened,
2206 \&\fImeasured according to the real time\fR, not the system clock.
2207 .PP
2208 If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2209 connection after 100 seconds\*(R") then this shouldn't bother you as it is
2210 exactly the right behaviour.
2211 .PP
2212 If you want to compare wall clock/system timestamps to your timers, then
2213 you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2214 time, where your comparisons will always generate correct results.
2215 .PP
2216 \fIThe special problems of suspended animation\fR
2217 .IX Subsection "The special problems of suspended animation"
2218 .PP
2219 When you leave the server world it is quite customary to hit machines that
2220 can suspend/hibernate \- what happens to the clocks during such a suspend?
2221 .PP
2222 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2223 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2224 to run until the system is suspended, but they will not advance while the
2225 system is suspended. That means, on resume, it will be as if the program
2226 was frozen for a few seconds, but the suspend time will not be counted
2227 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2228 clock advanced as expected, but if it is used as sole clocksource, then a
2229 long suspend would be detected as a time jump by libev, and timers would
2230 be adjusted accordingly.
2231 .PP
2232 I would not be surprised to see different behaviour in different between
2233 operating systems, \s-1OS\s0 versions or even different hardware.
2234 .PP
2235 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2236 time jump in the monotonic clocks and the realtime clock. If the program
2237 is suspended for a very long time, and monotonic clock sources are in use,
2238 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2239 will be counted towards the timers. When no monotonic clock source is in
2240 use, then libev will again assume a timejump and adjust accordingly.
2241 .PP
2242 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2243 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2244 deterministic behaviour in this case (you can do nothing against
2245 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2246 .PP
2247 \fIWatcher-Specific Functions and Data Members\fR
2248 .IX Subsection "Watcher-Specific Functions and Data Members"
2249 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2250 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2251 .PD 0
2252 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2253 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2254 .PD
2255 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2256 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2257 reached. If it is positive, then the timer will automatically be
2258 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2259 until stopped manually.
2260 .Sp
2261 The timer itself will do a best-effort at avoiding drift, that is, if
2262 you configure a timer to trigger every 10 seconds, then it will normally
2263 trigger at exactly 10 second intervals. If, however, your program cannot
2264 keep up with the timer (because it takes longer than those 10 seconds to
2265 do stuff) the timer will not fire more than once per event loop iteration.
2266 .IP "ev_timer_again (loop, ev_timer *)" 4
2267 .IX Item "ev_timer_again (loop, ev_timer *)"
2268 This will act as if the timer timed out, and restarts it again if it is
2269 repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2270 timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
2271 .Sp
2272 The exact semantics are as in the following rules, all of which will be
2273 applied to the watcher:
2274 .RS 4
2275 .IP "If the timer is pending, the pending status is always cleared." 4
2276 .IX Item "If the timer is pending, the pending status is always cleared."
2277 .PD 0
2278 .IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2279 .IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2280 .ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2281 .el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2282 .IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2283 .RE
2284 .RS 4
2285 .PD
2286 .Sp
2287 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2288 usage example.
2289 .RE
2290 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2291 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2292 Returns the remaining time until a timer fires. If the timer is active,
2293 then this time is relative to the current event loop time, otherwise it's
2294 the timeout value currently configured.
2295 .Sp
2296 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2297 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2298 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2299 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2300 too), and so on.
2301 .IP "ev_tstamp repeat [read\-write]" 4
2302 .IX Item "ev_tstamp repeat [read-write]"
2303 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2304 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2305 which is also when any modifications are taken into account.
2306 .PP
2307 \fIExamples\fR
2308 .IX Subsection "Examples"
2309 .PP
2310 Example: Create a timer that fires after 60 seconds.
2311 .PP
2312 .Vb 5
2313 \& static void
2314 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2315 \& {
2316 \& .. one minute over, w is actually stopped right here
2317 \& }
2318 \&
2319 \& ev_timer mytimer;
2320 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2321 \& ev_timer_start (loop, &mytimer);
2322 .Ve
2323 .PP
2324 Example: Create a timeout timer that times out after 10 seconds of
2325 inactivity.
2326 .PP
2327 .Vb 5
2328 \& static void
2329 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2330 \& {
2331 \& .. ten seconds without any activity
2332 \& }
2333 \&
2334 \& ev_timer mytimer;
2335 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2336 \& ev_timer_again (&mytimer); /* start timer */
2337 \& ev_run (loop, 0);
2338 \&
2339 \& // and in some piece of code that gets executed on any "activity":
2340 \& // reset the timeout to start ticking again at 10 seconds
2341 \& ev_timer_again (&mytimer);
2342 .Ve
2343 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2344 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2345 .IX Subsection "ev_periodic - to cron or not to cron?"
2346 Periodic watchers are also timers of a kind, but they are very versatile
2347 (and unfortunately a bit complex).
2348 .PP
2349 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2350 relative time, the physical time that passes) but on wall clock time
2351 (absolute time, the thing you can read on your calender or clock). The
2352 difference is that wall clock time can run faster or slower than real
2353 time, and time jumps are not uncommon (e.g. when you adjust your
2354 wrist-watch).
2355 .PP
2356 You can tell a periodic watcher to trigger after some specific point
2357 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2358 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2359 not a delay) and then reset your system clock to January of the previous
2360 year, then it will take a year or more to trigger the event (unlike an
2361 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2362 it, as it uses a relative timeout).
2363 .PP
2364 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2365 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2366 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2367 those cannot react to time jumps.
2368 .PP
2369 As with timers, the callback is guaranteed to be invoked only when the
2370 point in time where it is supposed to trigger has passed. If multiple
2371 timers become ready during the same loop iteration then the ones with
2372 earlier time-out values are invoked before ones with later time-out values
2373 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2374 .PP
2375 \fIWatcher-Specific Functions and Data Members\fR
2376 .IX Subsection "Watcher-Specific Functions and Data Members"
2377 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2378 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2379 .PD 0
2380 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2381 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2382 .PD
2383 Lots of arguments, let's sort it out... There are basically three modes of
2384 operation, and we will explain them from simplest to most complex:
2385 .RS 4
2386 .IP "\(bu" 4
2387 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2388 .Sp
2389 In this configuration the watcher triggers an event after the wall clock
2390 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2391 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2392 will be stopped and invoked when the system clock reaches or surpasses
2393 this point in time.
2394 .IP "\(bu" 4
2395 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2396 .Sp
2397 In this mode the watcher will always be scheduled to time out at the next
2398 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2399 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2400 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2401 .Sp
2402 This can be used to create timers that do not drift with respect to the
2403 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2404 hour, on the hour (with respect to \s-1UTC\s0):
2405 .Sp
2406 .Vb 1
2407 \& ev_periodic_set (&periodic, 0., 3600., 0);
2408 .Ve
2409 .Sp
2410 This doesn't mean there will always be 3600 seconds in between triggers,
2411 but only that the callback will be called when the system time shows a
2412 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2413 by 3600.
2414 .Sp
2415 Another way to think about it (for the mathematically inclined) is that
2416 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2417 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2418 .Sp
2419 The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2420 interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2421 microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2422 at most a similar magnitude as the current time (say, within a factor of
2423 ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2424 \&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2425 .Sp
2426 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2427 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2428 will of course deteriorate. Libev itself tries to be exact to be about one
2429 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2430 .IP "\(bu" 4
2431 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2432 .Sp
2433 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2434 ignored. Instead, each time the periodic watcher gets scheduled, the
2435 reschedule callback will be called with the watcher as first, and the
2436 current time as second argument.
2437 .Sp
2438 \&\s-1NOTE: \s0\fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
2439 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2440 allowed by documentation here\fR.
2441 .Sp
2442 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2443 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2444 only event loop modification you are allowed to do).
2445 .Sp
2446 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2447 *w, ev_tstamp now)\*(C'\fR, e.g.:
2448 .Sp
2449 .Vb 5
2450 \& static ev_tstamp
2451 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2452 \& {
2453 \& return now + 60.;
2454 \& }
2455 .Ve
2456 .Sp
2457 It must return the next time to trigger, based on the passed time value
2458 (that is, the lowest time value larger than to the second argument). It
2459 will usually be called just before the callback will be triggered, but
2460 might be called at other times, too.
2461 .Sp
2462 \&\s-1NOTE: \s0\fIThis callback must always return a time that is higher than or
2463 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2464 .Sp
2465 This can be used to create very complex timers, such as a timer that
2466 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2467 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2468 you do this is, again, up to you (but it is not trivial, which is the main
2469 reason I omitted it as an example).
2470 .RE
2471 .RS 4
2472 .RE
2473 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2474 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2475 Simply stops and restarts the periodic watcher again. This is only useful
2476 when you changed some parameters or the reschedule callback would return
2477 a different time than the last time it was called (e.g. in a crond like
2478 program when the crontabs have changed).
2479 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2480 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2481 When active, returns the absolute time that the watcher is supposed
2482 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2483 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2484 rescheduling modes.
2485 .IP "ev_tstamp offset [read\-write]" 4
2486 .IX Item "ev_tstamp offset [read-write]"
2487 When repeating, this contains the offset value, otherwise this is the
2488 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2489 although libev might modify this value for better numerical stability).
2490 .Sp
2491 Can be modified any time, but changes only take effect when the periodic
2492 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2493 .IP "ev_tstamp interval [read\-write]" 4
2494 .IX Item "ev_tstamp interval [read-write]"
2495 The current interval value. Can be modified any time, but changes only
2496 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2497 called.
2498 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2499 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2500 The current reschedule callback, or \f(CW0\fR, if this functionality is
2501 switched off. Can be changed any time, but changes only take effect when
2502 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2503 .PP
2504 \fIExamples\fR
2505 .IX Subsection "Examples"
2506 .PP
2507 Example: Call a callback every hour, or, more precisely, whenever the
2508 system time is divisible by 3600. The callback invocation times have
2509 potentially a lot of jitter, but good long-term stability.
2510 .PP
2511 .Vb 5
2512 \& static void
2513 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2514 \& {
2515 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2516 \& }
2517 \&
2518 \& ev_periodic hourly_tick;
2519 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2520 \& ev_periodic_start (loop, &hourly_tick);
2521 .Ve
2522 .PP
2523 Example: The same as above, but use a reschedule callback to do it:
2524 .PP
2525 .Vb 1
2526 \& #include <math.h>
2527 \&
2528 \& static ev_tstamp
2529 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2530 \& {
2531 \& return now + (3600. \- fmod (now, 3600.));
2532 \& }
2533 \&
2534 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2535 .Ve
2536 .PP
2537 Example: Call a callback every hour, starting now:
2538 .PP
2539 .Vb 4
2540 \& ev_periodic hourly_tick;
2541 \& ev_periodic_init (&hourly_tick, clock_cb,
2542 \& fmod (ev_now (loop), 3600.), 3600., 0);
2543 \& ev_periodic_start (loop, &hourly_tick);
2544 .Ve
2545 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2546 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2547 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2548 Signal watchers will trigger an event when the process receives a specific
2549 signal one or more times. Even though signals are very asynchronous, libev
2550 will try its best to deliver signals synchronously, i.e. as part of the
2551 normal event processing, like any other event.
2552 .PP
2553 If you want signals to be delivered truly asynchronously, just use
2554 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2555 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2556 synchronously wake up an event loop.
2557 .PP
2558 You can configure as many watchers as you like for the same signal, but
2559 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2560 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2561 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2562 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2563 .PP
2564 Only after the first watcher for a signal is started will libev actually
2565 register something with the kernel. It thus coexists with your own signal
2566 handlers as long as you don't register any with libev for the same signal.
2567 .PP
2568 If possible and supported, libev will install its handlers with
2569 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2570 not be unduly interrupted. If you have a problem with system calls getting
2571 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2572 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2573 .PP
2574 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2575 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2576 .PP
2577 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2578 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2579 stopping it again), that is, libev might or might not block the signal,
2580 and might or might not set or restore the installed signal handler (but
2581 see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2582 .PP
2583 While this does not matter for the signal disposition (libev never
2584 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2585 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2586 certain signals to be blocked.
2587 .PP
2588 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2589 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2590 choice usually).
2591 .PP
2592 The simplest way to ensure that the signal mask is reset in the child is
2593 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2594 catch fork calls done by libraries (such as the libc) as well.
2595 .PP
2596 In current versions of libev, the signal will not be blocked indefinitely
2597 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API \s0(\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2598 the window of opportunity for problems, it will not go away, as libev
2599 \&\fIhas\fR to modify the signal mask, at least temporarily.
2600 .PP
2601 So I can't stress this enough: \fIIf you do not reset your signal mask when
2602 you expect it to be empty, you have a race condition in your code\fR. This
2603 is not a libev-specific thing, this is true for most event libraries.
2604 .PP
2605 \fIThe special problem of threads signal handling\fR
2606 .IX Subsection "The special problem of threads signal handling"
2607 .PP
2608 \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2609 a lot of functionality (sigfd, sigwait etc.) only really works if all
2610 threads in a process block signals, which is hard to achieve.
2611 .PP
2612 When you want to use sigwait (or mix libev signal handling with your own
2613 for the same signals), you can tackle this problem by globally blocking
2614 all signals before creating any threads (or creating them with a fully set
2615 sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2616 loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2617 these signals. You can pass on any signals that libev might be interested
2618 in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2619 .PP
2620 \fIWatcher-Specific Functions and Data Members\fR
2621 .IX Subsection "Watcher-Specific Functions and Data Members"
2622 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2623 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2624 .PD 0
2625 .IP "ev_signal_set (ev_signal *, int signum)" 4
2626 .IX Item "ev_signal_set (ev_signal *, int signum)"
2627 .PD
2628 Configures the watcher to trigger on the given signal number (usually one
2629 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2630 .IP "int signum [read\-only]" 4
2631 .IX Item "int signum [read-only]"
2632 The signal the watcher watches out for.
2633 .PP
2634 \fIExamples\fR
2635 .IX Subsection "Examples"
2636 .PP
2637 Example: Try to exit cleanly on \s-1SIGINT.\s0
2638 .PP
2639 .Vb 5
2640 \& static void
2641 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2642 \& {
2643 \& ev_break (loop, EVBREAK_ALL);
2644 \& }
2645 \&
2646 \& ev_signal signal_watcher;
2647 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2648 \& ev_signal_start (loop, &signal_watcher);
2649 .Ve
2650 .ie n .SS """ev_child"" \- watch out for process status changes"
2651 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2652 .IX Subsection "ev_child - watch out for process status changes"
2653 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2654 some child status changes (most typically when a child of yours dies or
2655 exits). It is permissible to install a child watcher \fIafter\fR the child
2656 has been forked (which implies it might have already exited), as long
2657 as the event loop isn't entered (or is continued from a watcher), i.e.,
2658 forking and then immediately registering a watcher for the child is fine,
2659 but forking and registering a watcher a few event loop iterations later or
2660 in the next callback invocation is not.
2661 .PP
2662 Only the default event loop is capable of handling signals, and therefore
2663 you can only register child watchers in the default event loop.
2664 .PP
2665 Due to some design glitches inside libev, child watchers will always be
2666 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2667 libev)
2668 .PP
2669 \fIProcess Interaction\fR
2670 .IX Subsection "Process Interaction"
2671 .PP
2672 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2673 initialised. This is necessary to guarantee proper behaviour even if the
2674 first child watcher is started after the child exits. The occurrence
2675 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2676 synchronously as part of the event loop processing. Libev always reaps all
2677 children, even ones not watched.
2678 .PP
2679 \fIOverriding the Built-In Processing\fR
2680 .IX Subsection "Overriding the Built-In Processing"
2681 .PP
2682 Libev offers no special support for overriding the built-in child
2683 processing, but if your application collides with libev's default child
2684 handler, you can override it easily by installing your own handler for
2685 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2686 default loop never gets destroyed. You are encouraged, however, to use an
2687 event-based approach to child reaping and thus use libev's support for
2688 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2689 .PP
2690 \fIStopping the Child Watcher\fR
2691 .IX Subsection "Stopping the Child Watcher"
2692 .PP
2693 Currently, the child watcher never gets stopped, even when the
2694 child terminates, so normally one needs to stop the watcher in the
2695 callback. Future versions of libev might stop the watcher automatically
2696 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2697 problem).
2698 .PP
2699 \fIWatcher-Specific Functions and Data Members\fR
2700 .IX Subsection "Watcher-Specific Functions and Data Members"
2701 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2702 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2703 .PD 0
2704 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2705 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2706 .PD
2707 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2708 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2709 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2710 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2711 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2712 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2713 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2714 activate the watcher when the process is stopped or continued).
2715 .IP "int pid [read\-only]" 4
2716 .IX Item "int pid [read-only]"
2717 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2718 .IP "int rpid [read\-write]" 4
2719 .IX Item "int rpid [read-write]"
2720 The process id that detected a status change.
2721 .IP "int rstatus [read\-write]" 4
2722 .IX Item "int rstatus [read-write]"
2723 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2724 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2725 .PP
2726 \fIExamples\fR
2727 .IX Subsection "Examples"
2728 .PP
2729 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2730 its completion.
2731 .PP
2732 .Vb 1
2733 \& ev_child cw;
2734 \&
2735 \& static void
2736 \& child_cb (EV_P_ ev_child *w, int revents)
2737 \& {
2738 \& ev_child_stop (EV_A_ w);
2739 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2740 \& }
2741 \&
2742 \& pid_t pid = fork ();
2743 \&
2744 \& if (pid < 0)
2745 \& // error
2746 \& else if (pid == 0)
2747 \& {
2748 \& // the forked child executes here
2749 \& exit (1);
2750 \& }
2751 \& else
2752 \& {
2753 \& ev_child_init (&cw, child_cb, pid, 0);
2754 \& ev_child_start (EV_DEFAULT_ &cw);
2755 \& }
2756 .Ve
2757 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2758 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2759 .IX Subsection "ev_stat - did the file attributes just change?"
2760 This watches a file system path for attribute changes. That is, it calls
2761 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2762 and sees if it changed compared to the last time, invoking the callback
2763 if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2764 happen after the watcher has been started will be reported.
2765 .PP
2766 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2767 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2768 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2769 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2770 least one) and all the other fields of the stat buffer having unspecified
2771 contents.
2772 .PP
2773 The path \fImust not\fR end in a slash or contain special components such as
2774 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2775 your working directory changes, then the behaviour is undefined.
2776 .PP
2777 Since there is no portable change notification interface available, the
2778 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2779 to see if it changed somehow. You can specify a recommended polling
2780 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2781 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2782 (which you can expect to be around five seconds, although this might
2783 change dynamically). Libev will also impose a minimum interval which is
2784 currently around \f(CW0.1\fR, but that's usually overkill.
2785 .PP
2786 This watcher type is not meant for massive numbers of stat watchers,
2787 as even with OS-supported change notifications, this can be
2788 resource-intensive.
2789 .PP
2790 At the time of this writing, the only OS-specific interface implemented
2791 is the Linux inotify interface (implementing kqueue support is left as an
2792 exercise for the reader. Note, however, that the author sees no way of
2793 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2794 .PP
2795 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2796 .IX Subsection "ABI Issues (Largefile Support)"
2797 .PP
2798 Libev by default (unless the user overrides this) uses the default
2799 compilation environment, which means that on systems with large file
2800 support disabled by default, you get the 32 bit version of the stat
2801 structure. When using the library from programs that change the \s-1ABI\s0 to
2802 use 64 bit file offsets the programs will fail. In that case you have to
2803 compile libev with the same flags to get binary compatibility. This is
2804 obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2805 most noticeably displayed with ev_stat and large file support.
2806 .PP
2807 The solution for this is to lobby your distribution maker to make large
2808 file interfaces available by default (as e.g. FreeBSD does) and not
2809 optional. Libev cannot simply switch on large file support because it has
2810 to exchange stat structures with application programs compiled using the
2811 default compilation environment.
2812 .PP
2813 \fIInotify and Kqueue\fR
2814 .IX Subsection "Inotify and Kqueue"
2815 .PP
2816 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2817 runtime, it will be used to speed up change detection where possible. The
2818 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2819 watcher is being started.
2820 .PP
2821 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2822 except that changes might be detected earlier, and in some cases, to avoid
2823 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2824 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2825 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2826 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2827 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2828 xfs are fully working) libev usually gets away without polling.
2829 .PP
2830 There is no support for kqueue, as apparently it cannot be used to
2831 implement this functionality, due to the requirement of having a file
2832 descriptor open on the object at all times, and detecting renames, unlinks
2833 etc. is difficult.
2834 .PP
2835 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2836 .IX Subsection "stat () is a synchronous operation"
2837 .PP
2838 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2839 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2840 ()\*(C'\fR, which is a synchronous operation.
2841 .PP
2842 For local paths, this usually doesn't matter: unless the system is very
2843 busy or the intervals between stat's are large, a stat call will be fast,
2844 as the path data is usually in memory already (except when starting the
2845 watcher).
2846 .PP
2847 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2848 time due to network issues, and even under good conditions, a stat call
2849 often takes multiple milliseconds.
2850 .PP
2851 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2852 paths, although this is fully supported by libev.
2853 .PP
2854 \fIThe special problem of stat time resolution\fR
2855 .IX Subsection "The special problem of stat time resolution"
2856 .PP
2857 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2858 and even on systems where the resolution is higher, most file systems
2859 still only support whole seconds.
2860 .PP
2861 That means that, if the time is the only thing that changes, you can
2862 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2863 calls your callback, which does something. When there is another update
2864 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2865 stat data does change in other ways (e.g. file size).
2866 .PP
2867 The solution to this is to delay acting on a change for slightly more
2868 than a second (or till slightly after the next full second boundary), using
2869 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2870 ev_timer_again (loop, w)\*(C'\fR).
2871 .PP
2872 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2873 of some operating systems (where the second counter of the current time
2874 might be be delayed. One such system is the Linux kernel, where a call to
2875 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2876 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2877 update file times then there will be a small window where the kernel uses
2878 the previous second to update file times but libev might already execute
2879 the timer callback).
2880 .PP
2881 \fIWatcher-Specific Functions and Data Members\fR
2882 .IX Subsection "Watcher-Specific Functions and Data Members"
2883 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2884 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2885 .PD 0
2886 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2887 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2888 .PD
2889 Configures the watcher to wait for status changes of the given
2890 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2891 be detected and should normally be specified as \f(CW0\fR to let libev choose
2892 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2893 path for as long as the watcher is active.
2894 .Sp
2895 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2896 relative to the attributes at the time the watcher was started (or the
2897 last change was detected).
2898 .IP "ev_stat_stat (loop, ev_stat *)" 4
2899 .IX Item "ev_stat_stat (loop, ev_stat *)"
2900 Updates the stat buffer immediately with new values. If you change the
2901 watched path in your callback, you could call this function to avoid
2902 detecting this change (while introducing a race condition if you are not
2903 the only one changing the path). Can also be useful simply to find out the
2904 new values.
2905 .IP "ev_statdata attr [read\-only]" 4
2906 .IX Item "ev_statdata attr [read-only]"
2907 The most-recently detected attributes of the file. Although the type is
2908 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2909 suitable for your system, but you can only rely on the POSIX-standardised
2910 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2911 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2912 .IP "ev_statdata prev [read\-only]" 4
2913 .IX Item "ev_statdata prev [read-only]"
2914 The previous attributes of the file. The callback gets invoked whenever
2915 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2916 differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
2917 \&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
2918 .IP "ev_tstamp interval [read\-only]" 4
2919 .IX Item "ev_tstamp interval [read-only]"
2920 The specified interval.
2921 .IP "const char *path [read\-only]" 4
2922 .IX Item "const char *path [read-only]"
2923 The file system path that is being watched.
2924 .PP
2925 \fIExamples\fR
2926 .IX Subsection "Examples"
2927 .PP
2928 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2929 .PP
2930 .Vb 10
2931 \& static void
2932 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2933 \& {
2934 \& /* /etc/passwd changed in some way */
2935 \& if (w\->attr.st_nlink)
2936 \& {
2937 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2938 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2939 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2940 \& }
2941 \& else
2942 \& /* you shalt not abuse printf for puts */
2943 \& puts ("wow, /etc/passwd is not there, expect problems. "
2944 \& "if this is windows, they already arrived\en");
2945 \& }
2946 \&
2947 \& ...
2948 \& ev_stat passwd;
2949 \&
2950 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2951 \& ev_stat_start (loop, &passwd);
2952 .Ve
2953 .PP
2954 Example: Like above, but additionally use a one-second delay so we do not
2955 miss updates (however, frequent updates will delay processing, too, so
2956 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2957 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2958 .PP
2959 .Vb 2
2960 \& static ev_stat passwd;
2961 \& static ev_timer timer;
2962 \&
2963 \& static void
2964 \& timer_cb (EV_P_ ev_timer *w, int revents)
2965 \& {
2966 \& ev_timer_stop (EV_A_ w);
2967 \&
2968 \& /* now it\*(Aqs one second after the most recent passwd change */
2969 \& }
2970 \&
2971 \& static void
2972 \& stat_cb (EV_P_ ev_stat *w, int revents)
2973 \& {
2974 \& /* reset the one\-second timer */
2975 \& ev_timer_again (EV_A_ &timer);
2976 \& }
2977 \&
2978 \& ...
2979 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2980 \& ev_stat_start (loop, &passwd);
2981 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2982 .Ve
2983 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2984 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2985 .IX Subsection "ev_idle - when you've got nothing better to do..."
2986 Idle watchers trigger events when no other events of the same or higher
2987 priority are pending (prepare, check and other idle watchers do not count
2988 as receiving \*(L"events\*(R").
2989 .PP
2990 That is, as long as your process is busy handling sockets or timeouts
2991 (or even signals, imagine) of the same or higher priority it will not be
2992 triggered. But when your process is idle (or only lower-priority watchers
2993 are pending), the idle watchers are being called once per event loop
2994 iteration \- until stopped, that is, or your process receives more events
2995 and becomes busy again with higher priority stuff.
2996 .PP
2997 The most noteworthy effect is that as long as any idle watchers are
2998 active, the process will not block when waiting for new events.
2999 .PP
3000 Apart from keeping your process non-blocking (which is a useful
3001 effect on its own sometimes), idle watchers are a good place to do
3002 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
3003 event loop has handled all outstanding events.
3004 .PP
3005 \fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3006 .IX Subsection "Abusing an ev_idle watcher for its side-effect"
3007 .PP
3008 As long as there is at least one active idle watcher, libev will never
3009 sleep unnecessarily. Or in other words, it will loop as fast as possible.
3010 For this to work, the idle watcher doesn't need to be invoked at all \- the
3011 lowest priority will do.
3012 .PP
3013 This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3014 to do something on each event loop iteration \- for example to balance load
3015 between different connections.
3016 .PP
3017 See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3018 example.
3019 .PP
3020 \fIWatcher-Specific Functions and Data Members\fR
3021 .IX Subsection "Watcher-Specific Functions and Data Members"
3022 .IP "ev_idle_init (ev_idle *, callback)" 4
3023 .IX Item "ev_idle_init (ev_idle *, callback)"
3024 Initialises and configures the idle watcher \- it has no parameters of any
3025 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
3026 believe me.
3027 .PP
3028 \fIExamples\fR
3029 .IX Subsection "Examples"
3030 .PP
3031 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
3032 callback, free it. Also, use no error checking, as usual.
3033 .PP
3034 .Vb 5
3035 \& static void
3036 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
3037 \& {
3038 \& // stop the watcher
3039 \& ev_idle_stop (loop, w);
3040 \&
3041 \& // now we can free it
3042 \& free (w);
3043 \&
3044 \& // now do something you wanted to do when the program has
3045 \& // no longer anything immediate to do.
3046 \& }
3047 \&
3048 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3049 \& ev_idle_init (idle_watcher, idle_cb);
3050 \& ev_idle_start (loop, idle_watcher);
3051 .Ve
3052 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
3053 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
3054 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
3055 Prepare and check watchers are often (but not always) used in pairs:
3056 prepare watchers get invoked before the process blocks and check watchers
3057 afterwards.
3058 .PP
3059 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3060 current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3061 \&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3062 however. The rationale behind this is that you do not need to check
3063 for recursion in those watchers, i.e. the sequence will always be
3064 \&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3065 kind they will always be called in pairs bracketing the blocking call.
3066 .PP
3067 Their main purpose is to integrate other event mechanisms into libev and
3068 their use is somewhat advanced. They could be used, for example, to track
3069 variable changes, implement your own watchers, integrate net-snmp or a
3070 coroutine library and lots more. They are also occasionally useful if
3071 you cache some data and want to flush it before blocking (for example,
3072 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3073 watcher).
3074 .PP
3075 This is done by examining in each prepare call which file descriptors
3076 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
3077 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
3078 libraries provide exactly this functionality). Then, in the check watcher,
3079 you check for any events that occurred (by checking the pending status
3080 of all watchers and stopping them) and call back into the library. The
3081 I/O and timer callbacks will never actually be called (but must be valid
3082 nevertheless, because you never know, you know?).
3083 .PP
3084 As another example, the Perl Coro module uses these hooks to integrate
3085 coroutines into libev programs, by yielding to other active coroutines
3086 during each prepare and only letting the process block if no coroutines
3087 are ready to run (it's actually more complicated: it only runs coroutines
3088 with priority higher than or equal to the event loop and one coroutine
3089 of lower priority, but only once, using idle watchers to keep the event
3090 loop from blocking if lower-priority coroutines are active, thus mapping
3091 low-priority coroutines to idle/background tasks).
3092 .PP
3093 When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3094 highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3095 any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3096 watchers).
3097 .PP
3098 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3099 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3100 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3101 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3102 loops those other event loops might be in an unusable state until their
3103 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3104 others).
3105 .PP
3106 \fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3107 .IX Subsection "Abusing an ev_check watcher for its side-effect"
3108 .PP
3109 \&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3110 useful because they are called once per event loop iteration. For
3111 example, if you want to handle a large number of connections fairly, you
3112 normally only do a bit of work for each active connection, and if there
3113 is more work to do, you wait for the next event loop iteration, so other
3114 connections have a chance of making progress.
3115 .PP
3116 Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3117 next event loop iteration. However, that isn't as soon as possible \-
3118 without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3119 .PP
3120 This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3121 single global idle watcher that is active as long as you have one active
3122 \&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3123 will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3124 invoked. Neither watcher alone can do that.
3125 .PP
3126 \fIWatcher-Specific Functions and Data Members\fR
3127 .IX Subsection "Watcher-Specific Functions and Data Members"
3128 .IP "ev_prepare_init (ev_prepare *, callback)" 4
3129 .IX Item "ev_prepare_init (ev_prepare *, callback)"
3130 .PD 0
3131 .IP "ev_check_init (ev_check *, callback)" 4
3132 .IX Item "ev_check_init (ev_check *, callback)"
3133 .PD
3134 Initialises and configures the prepare or check watcher \- they have no
3135 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
3136 macros, but using them is utterly, utterly, utterly and completely
3137 pointless.
3138 .PP
3139 \fIExamples\fR
3140 .IX Subsection "Examples"
3141 .PP
3142 There are a number of principal ways to embed other event loops or modules
3143 into libev. Here are some ideas on how to include libadns into libev
3144 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3145 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3146 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3147 Glib event loop).
3148 .PP
3149 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3150 and in a check watcher, destroy them and call into libadns. What follows
3151 is pseudo-code only of course. This requires you to either use a low
3152 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3153 the callbacks for the IO/timeout watchers might not have been called yet.
3154 .PP
3155 .Vb 2
3156 \& static ev_io iow [nfd];
3157 \& static ev_timer tw;
3158 \&
3159 \& static void
3160 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3161 \& {
3162 \& }
3163 \&
3164 \& // create io watchers for each fd and a timer before blocking
3165 \& static void
3166 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3167 \& {
3168 \& int timeout = 3600000;
3169 \& struct pollfd fds [nfd];
3170 \& // actual code will need to loop here and realloc etc.
3171 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3172 \&
3173 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3174 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3175 \& ev_timer_start (loop, &tw);
3176 \&
3177 \& // create one ev_io per pollfd
3178 \& for (int i = 0; i < nfd; ++i)
3179 \& {
3180 \& ev_io_init (iow + i, io_cb, fds [i].fd,
3181 \& ((fds [i].events & POLLIN ? EV_READ : 0)
3182 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3183 \&
3184 \& fds [i].revents = 0;
3185 \& ev_io_start (loop, iow + i);
3186 \& }
3187 \& }
3188 \&
3189 \& // stop all watchers after blocking
3190 \& static void
3191 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3192 \& {
3193 \& ev_timer_stop (loop, &tw);
3194 \&
3195 \& for (int i = 0; i < nfd; ++i)
3196 \& {
3197 \& // set the relevant poll flags
3198 \& // could also call adns_processreadable etc. here
3199 \& struct pollfd *fd = fds + i;
3200 \& int revents = ev_clear_pending (iow + i);
3201 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3202 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3203 \&
3204 \& // now stop the watcher
3205 \& ev_io_stop (loop, iow + i);
3206 \& }
3207 \&
3208 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3209 \& }
3210 .Ve
3211 .PP
3212 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3213 in the prepare watcher and would dispose of the check watcher.
3214 .PP
3215 Method 3: If the module to be embedded supports explicit event
3216 notification (libadns does), you can also make use of the actual watcher
3217 callbacks, and only destroy/create the watchers in the prepare watcher.
3218 .PP
3219 .Vb 5
3220 \& static void
3221 \& timer_cb (EV_P_ ev_timer *w, int revents)
3222 \& {
3223 \& adns_state ads = (adns_state)w\->data;
3224 \& update_now (EV_A);
3225 \&
3226 \& adns_processtimeouts (ads, &tv_now);
3227 \& }
3228 \&
3229 \& static void
3230 \& io_cb (EV_P_ ev_io *w, int revents)
3231 \& {
3232 \& adns_state ads = (adns_state)w\->data;
3233 \& update_now (EV_A);
3234 \&
3235 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3236 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3237 \& }
3238 \&
3239 \& // do not ever call adns_afterpoll
3240 .Ve
3241 .PP
3242 Method 4: Do not use a prepare or check watcher because the module you
3243 want to embed is not flexible enough to support it. Instead, you can
3244 override their poll function. The drawback with this solution is that the
3245 main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3246 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3247 libglib event loop.
3248 .PP
3249 .Vb 4
3250 \& static gint
3251 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3252 \& {
3253 \& int got_events = 0;
3254 \&
3255 \& for (n = 0; n < nfds; ++n)
3256 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3257 \&
3258 \& if (timeout >= 0)
3259 \& // create/start timer
3260 \&
3261 \& // poll
3262 \& ev_run (EV_A_ 0);
3263 \&
3264 \& // stop timer again
3265 \& if (timeout >= 0)
3266 \& ev_timer_stop (EV_A_ &to);
3267 \&
3268 \& // stop io watchers again \- their callbacks should have set
3269 \& for (n = 0; n < nfds; ++n)
3270 \& ev_io_stop (EV_A_ iow [n]);
3271 \&
3272 \& return got_events;
3273 \& }
3274 .Ve
3275 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3276 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3277 .IX Subsection "ev_embed - when one backend isn't enough..."
3278 This is a rather advanced watcher type that lets you embed one event loop
3279 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3280 loop, other types of watchers might be handled in a delayed or incorrect
3281 fashion and must not be used).
3282 .PP
3283 There are primarily two reasons you would want that: work around bugs and
3284 prioritise I/O.
3285 .PP
3286 As an example for a bug workaround, the kqueue backend might only support
3287 sockets on some platform, so it is unusable as generic backend, but you
3288 still want to make use of it because you have many sockets and it scales
3289 so nicely. In this case, you would create a kqueue-based loop and embed
3290 it into your default loop (which might use e.g. poll). Overall operation
3291 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3292 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3293 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3294 .PP
3295 As for prioritising I/O: under rare circumstances you have the case where
3296 some fds have to be watched and handled very quickly (with low latency),
3297 and even priorities and idle watchers might have too much overhead. In
3298 this case you would put all the high priority stuff in one loop and all
3299 the rest in a second one, and embed the second one in the first.
3300 .PP
3301 As long as the watcher is active, the callback will be invoked every
3302 time there might be events pending in the embedded loop. The callback
3303 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3304 sweep and invoke their callbacks (the callback doesn't need to invoke the
3305 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3306 to give the embedded loop strictly lower priority for example).
3307 .PP
3308 You can also set the callback to \f(CW0\fR, in which case the embed watcher
3309 will automatically execute the embedded loop sweep whenever necessary.
3310 .PP
3311 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3312 is active, i.e., the embedded loop will automatically be forked when the
3313 embedding loop forks. In other cases, the user is responsible for calling
3314 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3315 .PP
3316 Unfortunately, not all backends are embeddable: only the ones returned by
3317 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3318 portable one.
3319 .PP
3320 So when you want to use this feature you will always have to be prepared
3321 that you cannot get an embeddable loop. The recommended way to get around
3322 this is to have a separate variables for your embeddable loop, try to
3323 create it, and if that fails, use the normal loop for everything.
3324 .PP
3325 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3326 .IX Subsection "ev_embed and fork"
3327 .PP
3328 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3329 automatically be applied to the embedded loop as well, so no special
3330 fork handling is required in that case. When the watcher is not running,
3331 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3332 as applicable.
3333 .PP
3334 \fIWatcher-Specific Functions and Data Members\fR
3335 .IX Subsection "Watcher-Specific Functions and Data Members"
3336 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3337 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3338 .PD 0
3339 .IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
3340 .IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
3341 .PD
3342 Configures the watcher to embed the given loop, which must be
3343 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3344 invoked automatically, otherwise it is the responsibility of the callback
3345 to invoke it (it will continue to be called until the sweep has been done,
3346 if you do not want that, you need to temporarily stop the embed watcher).
3347 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3348 .IX Item "ev_embed_sweep (loop, ev_embed *)"
3349 Make a single, non-blocking sweep over the embedded loop. This works
3350 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3351 appropriate way for embedded loops.
3352 .IP "struct ev_loop *other [read\-only]" 4
3353 .IX Item "struct ev_loop *other [read-only]"
3354 The embedded event loop.
3355 .PP
3356 \fIExamples\fR
3357 .IX Subsection "Examples"
3358 .PP
3359 Example: Try to get an embeddable event loop and embed it into the default
3360 event loop. If that is not possible, use the default loop. The default
3361 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3362 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3363 used).
3364 .PP
3365 .Vb 3
3366 \& struct ev_loop *loop_hi = ev_default_init (0);
3367 \& struct ev_loop *loop_lo = 0;
3368 \& ev_embed embed;
3369 \&
3370 \& // see if there is a chance of getting one that works
3371 \& // (remember that a flags value of 0 means autodetection)
3372 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3373 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3374 \& : 0;
3375 \&
3376 \& // if we got one, then embed it, otherwise default to loop_hi
3377 \& if (loop_lo)
3378 \& {
3379 \& ev_embed_init (&embed, 0, loop_lo);
3380 \& ev_embed_start (loop_hi, &embed);
3381 \& }
3382 \& else
3383 \& loop_lo = loop_hi;
3384 .Ve
3385 .PP
3386 Example: Check if kqueue is available but not recommended and create
3387 a kqueue backend for use with sockets (which usually work with any
3388 kqueue implementation). Store the kqueue/socket\-only event loop in
3389 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3390 .PP
3391 .Vb 3
3392 \& struct ev_loop *loop = ev_default_init (0);
3393 \& struct ev_loop *loop_socket = 0;
3394 \& ev_embed embed;
3395 \&
3396 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3397 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3398 \& {
3399 \& ev_embed_init (&embed, 0, loop_socket);
3400 \& ev_embed_start (loop, &embed);
3401 \& }
3402 \&
3403 \& if (!loop_socket)
3404 \& loop_socket = loop;
3405 \&
3406 \& // now use loop_socket for all sockets, and loop for everything else
3407 .Ve
3408 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3409 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3410 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3411 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3412 whoever is a good citizen cared to tell libev about it by calling
3413 \&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3414 and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3415 after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3416 and calls it in the wrong process, the fork handlers will be invoked, too,
3417 of course.
3418 .PP
3419 \fIThe special problem of life after fork \- how is it possible?\fR
3420 .IX Subsection "The special problem of life after fork - how is it possible?"
3421 .PP
3422 Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3423 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3424 sequence should be handled by libev without any problems.
3425 .PP
3426 This changes when the application actually wants to do event handling
3427 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3428 fork.
3429 .PP
3430 The default mode of operation (for libev, with application help to detect
3431 forks) is to duplicate all the state in the child, as would be expected
3432 when \fIeither\fR the parent \fIor\fR the child process continues.
3433 .PP
3434 When both processes want to continue using libev, then this is usually the
3435 wrong result. In that case, usually one process (typically the parent) is
3436 supposed to continue with all watchers in place as before, while the other
3437 process typically wants to start fresh, i.e. without any active watchers.
3438 .PP
3439 The cleanest and most efficient way to achieve that with libev is to
3440 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3441 use that for new watchers. This has the advantage of not touching more
3442 memory than necessary, and thus avoiding the copy-on-write, and the
3443 disadvantage of having to use multiple event loops (which do not support
3444 signal watchers).
3445 .PP
3446 When this is not possible, or you want to use the default loop for
3447 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3448 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3449 Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3450 watchers, so you have to be careful not to execute code that modifies
3451 those watchers. Note also that in that case, you have to re-register any
3452 signal watchers.
3453 .PP
3454 \fIWatcher-Specific Functions and Data Members\fR
3455 .IX Subsection "Watcher-Specific Functions and Data Members"
3456 .IP "ev_fork_init (ev_fork *, callback)" 4
3457 .IX Item "ev_fork_init (ev_fork *, callback)"
3458 Initialises and configures the fork watcher \- it has no parameters of any
3459 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3460 really.
3461 .ie n .SS """ev_cleanup"" \- even the best things end"
3462 .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3463 .IX Subsection "ev_cleanup - even the best things end"
3464 Cleanup watchers are called just before the event loop is being destroyed
3465 by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3466 .PP
3467 While there is no guarantee that the event loop gets destroyed, cleanup
3468 watchers provide a convenient method to install cleanup hooks for your
3469 program, worker threads and so on \- you just to make sure to destroy the
3470 loop when you want them to be invoked.
3471 .PP
3472 Cleanup watchers are invoked in the same way as any other watcher. Unlike
3473 all other watchers, they do not keep a reference to the event loop (which
3474 makes a lot of sense if you think about it). Like all other watchers, you
3475 can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3476 .PP
3477 \fIWatcher-Specific Functions and Data Members\fR
3478 .IX Subsection "Watcher-Specific Functions and Data Members"
3479 .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3480 .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3481 Initialises and configures the cleanup watcher \- it has no parameters of
3482 any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3483 pointless, I assure you.
3484 .PP
3485 Example: Register an atexit handler to destroy the default loop, so any
3486 cleanup functions are called.
3487 .PP
3488 .Vb 5
3489 \& static void
3490 \& program_exits (void)
3491 \& {
3492 \& ev_loop_destroy (EV_DEFAULT_UC);
3493 \& }
3494 \&
3495 \& ...
3496 \& atexit (program_exits);
3497 .Ve
3498 .ie n .SS """ev_async"" \- how to wake up an event loop"
3499 .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3500 .IX Subsection "ev_async - how to wake up an event loop"
3501 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3502 asynchronous sources such as signal handlers (as opposed to multiple event
3503 loops \- those are of course safe to use in different threads).
3504 .PP
3505 Sometimes, however, you need to wake up an event loop you do not control,
3506 for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3507 watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3508 it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3509 .PP
3510 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3511 too, are asynchronous in nature, and signals, too, will be compressed
3512 (i.e. the number of callback invocations may be less than the number of
3513 \&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3514 of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3515 signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3516 even without knowing which loop owns the signal.
3517 .PP
3518 \fIQueueing\fR
3519 .IX Subsection "Queueing"
3520 .PP
3521 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3522 is that the author does not know of a simple (or any) algorithm for a
3523 multiple-writer-single-reader queue that works in all cases and doesn't
3524 need elaborate support such as pthreads or unportable memory access
3525 semantics.
3526 .PP
3527 That means that if you want to queue data, you have to provide your own
3528 queue. But at least I can tell you how to implement locking around your
3529 queue:
3530 .IP "queueing from a signal handler context" 4
3531 .IX Item "queueing from a signal handler context"
3532 To implement race-free queueing, you simply add to the queue in the signal
3533 handler but you block the signal handler in the watcher callback. Here is
3534 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3535 .Sp
3536 .Vb 1
3537 \& static ev_async mysig;
3538 \&
3539 \& static void
3540 \& sigusr1_handler (void)
3541 \& {
3542 \& sometype data;
3543 \&
3544 \& // no locking etc.
3545 \& queue_put (data);
3546 \& ev_async_send (EV_DEFAULT_ &mysig);
3547 \& }
3548 \&
3549 \& static void
3550 \& mysig_cb (EV_P_ ev_async *w, int revents)
3551 \& {
3552 \& sometype data;
3553 \& sigset_t block, prev;
3554 \&
3555 \& sigemptyset (&block);
3556 \& sigaddset (&block, SIGUSR1);
3557 \& sigprocmask (SIG_BLOCK, &block, &prev);
3558 \&
3559 \& while (queue_get (&data))
3560 \& process (data);
3561 \&
3562 \& if (sigismember (&prev, SIGUSR1)
3563 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3564 \& }
3565 .Ve
3566 .Sp
3567 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3568 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3569 either...).
3570 .IP "queueing from a thread context" 4
3571 .IX Item "queueing from a thread context"
3572 The strategy for threads is different, as you cannot (easily) block
3573 threads but you can easily preempt them, so to queue safely you need to
3574 employ a traditional mutex lock, such as in this pthread example:
3575 .Sp
3576 .Vb 2
3577 \& static ev_async mysig;
3578 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3579 \&
3580 \& static void
3581 \& otherthread (void)
3582 \& {
3583 \& // only need to lock the actual queueing operation
3584 \& pthread_mutex_lock (&mymutex);
3585 \& queue_put (data);
3586 \& pthread_mutex_unlock (&mymutex);
3587 \&
3588 \& ev_async_send (EV_DEFAULT_ &mysig);
3589 \& }
3590 \&
3591 \& static void
3592 \& mysig_cb (EV_P_ ev_async *w, int revents)
3593 \& {
3594 \& pthread_mutex_lock (&mymutex);
3595 \&
3596 \& while (queue_get (&data))
3597 \& process (data);
3598 \&
3599 \& pthread_mutex_unlock (&mymutex);
3600 \& }
3601 .Ve
3602 .PP
3603 \fIWatcher-Specific Functions and Data Members\fR
3604 .IX Subsection "Watcher-Specific Functions and Data Members"
3605 .IP "ev_async_init (ev_async *, callback)" 4
3606 .IX Item "ev_async_init (ev_async *, callback)"
3607 Initialises and configures the async watcher \- it has no parameters of any
3608 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3609 trust me.
3610 .IP "ev_async_send (loop, ev_async *)" 4
3611 .IX Item "ev_async_send (loop, ev_async *)"
3612 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3613 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3614 returns.
3615 .Sp
3616 Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3617 signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3618 embedding section below on what exactly this means).
3619 .Sp
3620 Note that, as with other watchers in libev, multiple events might get
3621 compressed into a single callback invocation (another way to look at
3622 this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3623 \&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3624 .Sp
3625 This call incurs the overhead of at most one extra system call per event
3626 loop iteration, if the event loop is blocked, and no syscall at all if
3627 the event loop (or your program) is processing events. That means that
3628 repeated calls are basically free (there is no need to avoid calls for
3629 performance reasons) and that the overhead becomes smaller (typically
3630 zero) under load.
3631 .IP "bool = ev_async_pending (ev_async *)" 4
3632 .IX Item "bool = ev_async_pending (ev_async *)"
3633 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3634 watcher but the event has not yet been processed (or even noted) by the
3635 event loop.
3636 .Sp
3637 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3638 the loop iterates next and checks for the watcher to have become active,
3639 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3640 quickly check whether invoking the loop might be a good idea.
3641 .Sp
3642 Not that this does \fInot\fR check whether the watcher itself is pending,
3643 only whether it has been requested to make this watcher pending: there
3644 is a time window between the event loop checking and resetting the async
3645 notification, and the callback being invoked.
3648 There are some other functions of possible interest. Described. Here. Now.
3649 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3650 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3651 This function combines a simple timer and an I/O watcher, calls your
3652 callback on whichever event happens first and automatically stops both
3653 watchers. This is useful if you want to wait for a single event on an fd
3654 or timeout without having to allocate/configure/start/stop/free one or
3655 more watchers yourself.
3656 .Sp
3657 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3658 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3659 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3660 .Sp
3661 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3662 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3663 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3664 .Sp
3665 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3666 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3667 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3668 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3669 a timeout and an io event at the same time \- you probably should give io
3670 events precedence.
3671 .Sp
3672 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
3673 .Sp
3674 .Vb 7
3675 \& static void stdin_ready (int revents, void *arg)
3676 \& {
3677 \& if (revents & EV_READ)
3678 \& /* stdin might have data for us, joy! */;
3679 \& else if (revents & EV_TIMER)
3680 \& /* doh, nothing entered */;
3681 \& }
3682 \&
3683 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3684 .Ve
3685 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3686 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3687 Feed an event on the given fd, as if a file descriptor backend detected
3688 the given events.
3689 .IP "ev_feed_signal_event (loop, int signum)" 4
3690 .IX Item "ev_feed_signal_event (loop, int signum)"
3691 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3692 which is async-safe.
3695 This section explains some common idioms that are not immediately
3696 obvious. Note that examples are sprinkled over the whole manual, and this
3697 section only contains stuff that wouldn't fit anywhere else.
3700 Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3701 or modify at any time: libev will completely ignore it. This can be used
3702 to associate arbitrary data with your watcher. If you need more data and
3703 don't want to allocate memory separately and store a pointer to it in that
3704 data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3705 data:
3706 .PP
3707 .Vb 7
3708 \& struct my_io
3709 \& {
3710 \& ev_io io;
3711 \& int otherfd;
3712 \& void *somedata;
3713 \& struct whatever *mostinteresting;
3714 \& };
3715 \&
3716 \& ...
3717 \& struct my_io w;
3718 \& ev_io_init (&, my_cb, fd, EV_READ);
3719 .Ve
3720 .PP
3721 And since your callback will be called with a pointer to the watcher, you
3722 can cast it back to your own type:
3723 .PP
3724 .Vb 5
3725 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3726 \& {
3727 \& struct my_io *w = (struct my_io *)w_;
3728 \& ...
3729 \& }
3730 .Ve
3731 .PP
3732 More interesting and less C\-conformant ways of casting your callback
3733 function type instead have been omitted.
3736 Another common scenario is to use some data structure with multiple
3737 embedded watchers, in effect creating your own watcher that combines
3738 multiple libev event sources into one \*(L"super-watcher\*(R":
3739 .PP
3740 .Vb 6
3741 \& struct my_biggy
3742 \& {
3743 \& int some_data;
3744 \& ev_timer t1;
3745 \& ev_timer t2;
3746 \& }
3747 .Ve
3748 .PP
3749 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3750 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3751 the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3752 to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3753 real programmers):
3754 .PP
3755 .Vb 1
3756 \& #include <stddef.h>
3757 \&
3758 \& static void
3759 \& t1_cb (EV_P_ ev_timer *w, int revents)
3760 \& {
3761 \& struct my_biggy big = (struct my_biggy *)
3762 \& (((char *)w) \- offsetof (struct my_biggy, t1));
3763 \& }
3764 \&
3765 \& static void
3766 \& t2_cb (EV_P_ ev_timer *w, int revents)
3767 \& {
3768 \& struct my_biggy big = (struct my_biggy *)
3769 \& (((char *)w) \- offsetof (struct my_biggy, t2));
3770 \& }
3771 .Ve
3774 Often you have structures like this in event-based programs:
3775 .PP
3776 .Vb 4
3777 \& callback ()
3778 \& {
3779 \& free (request);
3780 \& }
3781 \&
3782 \& request = start_new_request (..., callback);
3783 .Ve
3784 .PP
3785 The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3786 used to cancel the operation, or do other things with it.
3787 .PP
3788 It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3789 immediately invoke the callback, for example, to report errors. Or you add
3790 some caching layer that finds that it can skip the lengthy aspects of the
3791 operation and simply invoke the callback with the result.
3792 .PP
3793 The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3794 has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3795 .PP
3796 Even if you pass the request by some safer means to the callback, you
3797 might want to do something to the request after starting it, such as
3798 canceling it, which probably isn't working so well when the callback has
3799 already been invoked.
3800 .PP
3801 A common way around all these issues is to make sure that
3802 \&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3803 \&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3804 delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3805 example, or more sneakily, by reusing an existing (stopped) watcher and
3806 pushing it into the pending queue:
3807 .PP
3808 .Vb 2
3809 \& ev_set_cb (watcher, callback);
3810 \& ev_feed_event (EV_A_ watcher, 0);
3811 .Ve
3812 .PP
3813 This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3814 invoked, while not delaying callback invocation too much.
3817 Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3818 \&\fImodal\fR interaction, which is most easily implemented by recursively
3819 invoking \f(CW\*(C`ev_run\*(C'\fR.
3820 .PP
3821 This brings the problem of exiting \- a callback might want to finish the
3822 main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3823 a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3824 and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3825 other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3826 .PP
3827 The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3828 invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3829 triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3830 .PP
3831 .Vb 2
3832 \& // main loop
3833 \& int exit_main_loop = 0;
3834 \&
3835 \& while (!exit_main_loop)
3836 \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3837 \&
3838 \& // in a modal watcher
3839 \& int exit_nested_loop = 0;
3840 \&
3841 \& while (!exit_nested_loop)
3842 \& ev_run (EV_A_ EVRUN_ONCE);
3843 .Ve
3844 .PP
3845 To exit from any of these loops, just set the corresponding exit variable:
3846 .PP
3847 .Vb 2
3848 \& // exit modal loop
3849 \& exit_nested_loop = 1;
3850 \&
3851 \& // exit main program, after modal loop is finished
3852 \& exit_main_loop = 1;
3853 \&
3854 \& // exit both
3855 \& exit_main_loop = exit_nested_loop = 1;
3856 .Ve
3859 Here is a fictitious example of how to run an event loop in a different
3860 thread from where callbacks are being invoked and watchers are
3861 created/added/removed.
3862 .PP
3863 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3864 which uses exactly this technique (which is suited for many high-level
3865 languages).
3866 .PP
3867 The example uses a pthread mutex to protect the loop data, a condition
3868 variable to wait for callback invocations, an async watcher to notify the
3869 event loop thread and an unspecified mechanism to wake up the main thread.
3870 .PP
3871 First, you need to associate some data with the event loop:
3872 .PP
3873 .Vb 6
3874 \& typedef struct {
3875 \& mutex_t lock; /* global loop lock */
3876 \& ev_async async_w;
3877 \& thread_t tid;
3878 \& cond_t invoke_cv;
3879 \& } userdata;
3880 \&
3881 \& void prepare_loop (EV_P)
3882 \& {
3883 \& // for simplicity, we use a static userdata struct.
3884 \& static userdata u;
3885 \&
3886 \& ev_async_init (&u\->async_w, async_cb);
3887 \& ev_async_start (EV_A_ &u\->async_w);
3888 \&
3889 \& pthread_mutex_init (&u\->lock, 0);
3890 \& pthread_cond_init (&u\->invoke_cv, 0);
3891 \&
3892 \& // now associate this with the loop
3893 \& ev_set_userdata (EV_A_ u);
3894 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3895 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3896 \&
3897 \& // then create the thread running ev_run
3898 \& pthread_create (&u\->tid, 0, l_run, EV_A);
3899 \& }
3900 .Ve
3901 .PP
3902 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3903 solely to wake up the event loop so it takes notice of any new watchers
3904 that might have been added:
3905 .PP
3906 .Vb 5
3907 \& static void
3908 \& async_cb (EV_P_ ev_async *w, int revents)
3909 \& {
3910 \& // just used for the side effects
3911 \& }
3912 .Ve
3913 .PP
3914 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3915 protecting the loop data, respectively.
3916 .PP
3917 .Vb 6
3918 \& static void
3919 \& l_release (EV_P)
3920 \& {
3921 \& userdata *u = ev_userdata (EV_A);
3922 \& pthread_mutex_unlock (&u\->lock);
3923 \& }
3924 \&
3925 \& static void
3926 \& l_acquire (EV_P)
3927 \& {
3928 \& userdata *u = ev_userdata (EV_A);
3929 \& pthread_mutex_lock (&u\->lock);
3930 \& }
3931 .Ve
3932 .PP
3933 The event loop thread first acquires the mutex, and then jumps straight
3934 into \f(CW\*(C`ev_run\*(C'\fR:
3935 .PP
3936 .Vb 4
3937 \& void *
3938 \& l_run (void *thr_arg)
3939 \& {
3940 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3941 \&
3942 \& l_acquire (EV_A);
3943 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3944 \& ev_run (EV_A_ 0);
3945 \& l_release (EV_A);
3946 \&
3947 \& return 0;
3948 \& }
3949 .Ve
3950 .PP
3951 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3952 signal the main thread via some unspecified mechanism (signals? pipe
3953 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3954 have been called (in a while loop because a) spurious wakeups are possible
3955 and b) skipping inter-thread-communication when there are no pending
3956 watchers is very beneficial):
3957 .PP
3958 .Vb 4
3959 \& static void
3960 \& l_invoke (EV_P)
3961 \& {
3962 \& userdata *u = ev_userdata (EV_A);
3963 \&
3964 \& while (ev_pending_count (EV_A))
3965 \& {
3966 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3967 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3968 \& }
3969 \& }
3970 .Ve
3971 .PP
3972 Now, whenever the main thread gets told to invoke pending watchers, it
3973 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3974 thread to continue:
3975 .PP
3976 .Vb 4
3977 \& static void
3978 \& real_invoke_pending (EV_P)
3979 \& {
3980 \& userdata *u = ev_userdata (EV_A);
3981 \&
3982 \& pthread_mutex_lock (&u\->lock);
3983 \& ev_invoke_pending (EV_A);
3984 \& pthread_cond_signal (&u\->invoke_cv);
3985 \& pthread_mutex_unlock (&u\->lock);
3986 \& }
3987 .Ve
3988 .PP
3989 Whenever you want to start/stop a watcher or do other modifications to an
3990 event loop, you will now have to lock:
3991 .PP
3992 .Vb 2
3993 \& ev_timer timeout_watcher;
3994 \& userdata *u = ev_userdata (EV_A);
3995 \&
3996 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3997 \&
3998 \& pthread_mutex_lock (&u\->lock);
3999 \& ev_timer_start (EV_A_ &timeout_watcher);
4000 \& ev_async_send (EV_A_ &u\->async_w);
4001 \& pthread_mutex_unlock (&u\->lock);
4002 .Ve
4003 .PP
4004 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4005 an event loop currently blocking in the kernel will have no knowledge
4006 about the newly added timer. By waking up the loop it will pick up any new
4007 watchers in the next event loop iteration.
4010 While the overhead of a callback that e.g. schedules a thread is small, it
4011 is still an overhead. If you embed libev, and your main usage is with some
4012 kind of threads or coroutines, you might want to customise libev so that
4013 doesn't need callbacks anymore.
4014 .PP
4015 Imagine you have coroutines that you can switch to using a function
4016 \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4017 and that due to some magic, the currently active coroutine is stored in a
4018 global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4019 event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4020 the differing \f(CW\*(C`;\*(C'\fR conventions):
4021 .PP
4022 .Vb 2
4023 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4024 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4025 .Ve
4026 .PP
4027 That means instead of having a C callback function, you store the
4028 coroutine to switch to in each watcher, and instead of having libev call
4029 your callback, you instead have it switch to that coroutine.
4030 .PP
4031 A coroutine might now wait for an event with a function called
4032 \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4033 matter when, or whether the watcher is active or not when this function is
4034 called):
4035 .PP
4036 .Vb 6
4037 \& void
4038 \& wait_for_event (ev_watcher *w)
4039 \& {
4040 \& ev_set_cb (w, current_coro);
4041 \& switch_to (libev_coro);
4042 \& }
4043 .Ve
4044 .PP
4045 That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4046 continues the libev coroutine, which, when appropriate, switches back to
4047 this or any other coroutine.
4048 .PP
4049 You can do similar tricks if you have, say, threads with an event queue \-
4050 instead of storing a coroutine, you store the queue object and instead of
4051 switching to a coroutine, you push the watcher onto the queue and notify
4052 any waiters.
4053 .PP
4054 To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4055 files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4056 .PP
4057 .Vb 4
4058 \& // my_ev.h
4059 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4060 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4061 \& #include "../libev/ev.h"
4062 \&
4063 \& // my_ev.c
4064 \& #define EV_H "my_ev.h"
4065 \& #include "../libev/ev.c"
4066 .Ve
4067 .PP
4068 And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4069 \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4070 can even use \fIev.h\fR as header file name directly.
4073 Libev offers a compatibility emulation layer for libevent. It cannot
4074 emulate the internals of libevent, so here are some usage hints:
4075 .IP "\(bu" 4
4076 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4077 .Sp
4078 This was the newest libevent version available when libev was implemented,
4079 and is still mostly unchanged in 2010.
4080 .IP "\(bu" 4
4081 Use it by including <event.h>, as usual.
4082 .IP "\(bu" 4
4083 The following members are fully supported: ev_base, ev_callback,
4084 ev_arg, ev_fd, ev_res, ev_events.
4085 .IP "\(bu" 4
4086 Avoid using ev_flags and the EVLIST_*\-macros, while it is
4087 maintained by libev, it does not work exactly the same way as in libevent (consider
4088 it a private \s-1API\s0).
4089 .IP "\(bu" 4
4090 Priorities are not currently supported. Initialising priorities
4091 will fail and all watchers will have the same priority, even though there
4092 is an ev_pri field.
4093 .IP "\(bu" 4
4094 In libevent, the last base created gets the signals, in libev, the
4095 base that registered the signal gets the signals.
4096 .IP "\(bu" 4
4097 Other members are not supported.
4098 .IP "\(bu" 4
4099 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
4100 to use the libev header file and library.
4101 .SH "\*(C+ SUPPORT"
4102 .IX Header " SUPPORT"
4103 .SS "C \s-1API\s0"
4104 .IX Subsection "C API"
4105 The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4106 libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4107 will work fine.
4108 .PP
4109 Proper exception specifications might have to be added to callbacks passed
4110 to libev: exceptions may be thrown only from watcher callbacks, all
4111 other callbacks (allocator, syserr, loop acquire/release and periodic
4112 reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4113 ()\*(C'\fR specification. If you have code that needs to be compiled as both C
4114 and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4115 .PP
4116 .Vb 6
4117 \& static void
4118 \& fatal_error (const char *msg) EV_THROW
4119 \& {
4120 \& perror (msg);
4121 \& abort ();
4122 \& }
4123 \&
4124 \& ...
4125 \& ev_set_syserr_cb (fatal_error);
4126 .Ve
4127 .PP
4128 The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4129 \&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4130 because it runs cleanup watchers).
4131 .PP
4132 Throwing exceptions in watcher callbacks is only supported if libev itself
4133 is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4134 throwing exceptions through C libraries (most do).
4135 .SS "\*(C+ \s-1API\s0"
4136 .IX Subsection " API"
4137 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4138 you to use some convenience methods to start/stop watchers and also change
4139 the callback model to a model using method callbacks on objects.
4140 .PP
4141 To use it,
4142 .PP
4143 .Vb 1
4144 \& #include <ev++.h>
4145 .Ve
4146 .PP
4147 This automatically includes \fIev.h\fR and puts all of its definitions (many
4148 of them macros) into the global namespace. All \*(C+ specific things are
4149 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4150 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4151 .PP
4152 Care has been taken to keep the overhead low. The only data member the \*(C+
4153 classes add (compared to plain C\-style watchers) is the event loop pointer
4154 that the watcher is associated with (or no additional members at all if
4155 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4156 .PP
4157 Currently, functions, static and non-static member functions and classes
4158 with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4159 to add as long as they only need one additional pointer for context. If
4160 you need support for other types of functors please contact the author
4161 (preferably after implementing it).
4162 .PP
4163 For all this to work, your \*(C+ compiler either has to use the same calling
4164 conventions as your C compiler (for static member functions), or you have
4165 to embed libev and compile libev itself as \*(C+.
4166 .PP
4167 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4168 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4169 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4170 .IX Item "ev::READ, ev::WRITE etc."
4171 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4172 macros from \fIev.h\fR.
4173 .ie n .IP """ev::tstamp"", ""ev::now""" 4
4174 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4175 .IX Item "ev::tstamp, ev::now"
4176 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4177 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4178 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4179 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4180 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4181 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4182 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4183 defined by many implementations.
4184 .Sp
4185 All of those classes have these methods:
4186 .RS 4
4187 .IP "ev::TYPE::TYPE ()" 4
4188 .IX Item "ev::TYPE::TYPE ()"
4189 .PD 0
4190 .IP "ev::TYPE::TYPE (loop)" 4
4191 .IX Item "ev::TYPE::TYPE (loop)"
4192 .IP "ev::TYPE::~TYPE" 4
4193 .IX Item "ev::TYPE::~TYPE"
4194 .PD
4195 The constructor (optionally) takes an event loop to associate the watcher
4196 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4197 .Sp
4198 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4199 \&\f(CW\*(C`set\*(C'\fR method before starting it.
4200 .Sp
4201 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4202 method to set a callback before you can start the watcher.
4203 .Sp
4204 (The reason why you have to use a method is a limitation in \*(C+ which does
4205 not allow explicit template arguments for constructors).
4206 .Sp
4207 The destructor automatically stops the watcher if it is active.
4208 .IP "w\->set<class, &class::method> (object *)" 4
4209 .IX Item "w->set<class, &class::method> (object *)"
4210 This method sets the callback method to call. The method has to have a
4211 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4212 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4213 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4214 .Sp
4215 This method synthesizes efficient thunking code to call your method from
4216 the C callback that libev requires. If your compiler can inline your
4217 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4218 your compiler is good :), then the method will be fully inlined into the
4219 thunking function, making it as fast as a direct C callback.
4220 .Sp
4221 Example: simple class declaration and watcher initialisation
4222 .Sp
4223 .Vb 4
4224 \& struct myclass
4225 \& {
4226 \& void io_cb (ev::io &w, int revents) { }
4227 \& }
4228 \&
4229 \& myclass obj;
4230 \& ev::io iow;
4231 \& iow.set <myclass, &myclass::io_cb> (&obj);
4232 .Ve
4233 .IP "w\->set (object *)" 4
4234 .IX Item "w->set (object *)"
4235 This is a variation of a method callback \- leaving out the method to call
4236 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4237 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4238 the time. Incidentally, you can then also leave out the template argument
4239 list.
4240 .Sp
4241 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4242 int revents)\*(C'\fR.
4243 .Sp
4244 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4245 .Sp
4246 Example: use a functor object as callback.
4247 .Sp
4248 .Vb 7
4249 \& struct myfunctor
4250 \& {
4251 \& void operator() (ev::io &w, int revents)
4252 \& {
4253 \& ...
4254 \& }
4255 \& }
4256 \&
4257 \& myfunctor f;
4258 \&
4259 \& ev::io w;
4260 \& w.set (&f);
4261 .Ve
4262 .IP "w\->set<function> (void *data = 0)" 4
4263 .IX Item "w->set<function> (void *data = 0)"
4264 Also sets a callback, but uses a static method or plain function as
4265 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4266 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4267 .Sp
4268 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4269 .Sp
4270 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4271 .Sp
4272 Example: Use a plain function as callback.
4273 .Sp
4274 .Vb 2
4275 \& static void io_cb (ev::io &w, int revents) { }
4276 \& iow.set <io_cb> ();
4277 .Ve
4278 .IP "w\->set (loop)" 4
4279 .IX Item "w->set (loop)"
4280 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4281 do this when the watcher is inactive (and not pending either).
4282 .IP "w\->set ([arguments])" 4
4283 .IX Item "w->set ([arguments])"
4284 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4285 with the same arguments. Either this method or a suitable start method
4286 must be called at least once. Unlike the C counterpart, an active watcher
4287 gets automatically stopped and restarted when reconfiguring it with this
4288 method.
4289 .Sp
4290 For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4291 clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4292 .IP "w\->start ()" 4
4293 .IX Item "w->start ()"
4294 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4295 constructor already stores the event loop.
4296 .IP "w\->start ([arguments])" 4
4297 .IX Item "w->start ([arguments])"
4298 Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4299 convenient to wrap them in one call. Uses the same type of arguments as
4300 the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4301 .IP "w\->stop ()" 4
4302 .IX Item "w->stop ()"
4303 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4304 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4305 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4306 .IX Item "w->again () (ev::timer, ev::periodic only)"
4307 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4308 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4309 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4310 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4311 .IX Item "w->sweep () (ev::embed only)"
4312 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4313 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4314 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4315 .IX Item "w->update () (ev::stat only)"
4316 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4317 .RE
4318 .RS 4
4319 .RE
4320 .PP
4321 Example: Define a class with two I/O and idle watchers, start the I/O
4322 watchers in the constructor.
4323 .PP
4324 .Vb 5
4325 \& class myclass
4326 \& {
4327 \& ev::io io ; void io_cb (ev::io &w, int revents);
4328 \& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4329 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4330 \&
4331 \& myclass (int fd)
4332 \& {
4333 \& io .set <myclass, &myclass::io_cb > (this);
4334 \& io2 .set <myclass, &myclass::io2_cb > (this);
4335 \& idle.set <myclass, &myclass::idle_cb> (this);
4336 \&
4337 \& io.set (fd, ev::WRITE); // configure the watcher
4338 \& io.start (); // start it whenever convenient
4339 \&
4340 \& io2.start (fd, ev::READ); // set + start in one call
4341 \& }
4342 \& };
4343 .Ve
4346 Libev does not offer other language bindings itself, but bindings for a
4347 number of languages exist in the form of third-party packages. If you know
4348 any interesting language binding in addition to the ones listed here, drop
4349 me a note.
4350 .IP "Perl" 4
4351 .IX Item "Perl"
4352 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4353 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4354 there are additional modules that implement libev-compatible interfaces
4355 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4356 \&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4357 and \f(CW\*(C`EV::Glib\*(C'\fR).
4358 .Sp
4359 It can be found and installed via \s-1CPAN,\s0 its homepage is at
4360 <>.
4361 .IP "Python" 4
4362 .IX Item "Python"
4363 Python bindings can be found at <>. It
4364 seems to be quite complete and well-documented.
4365 .IP "Ruby" 4
4366 .IX Item "Ruby"
4367 Tony Arcieri has written a ruby extension that offers access to a subset
4368 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4369 more on top of it. It can be found via gem servers. Its homepage is at
4370 <>.
4371 .Sp
4372 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4373 makes rev work even on mingw.
4374 .IP "Haskell" 4
4375 .IX Item "Haskell"
4376 A haskell binding to libev is available at
4377 <\-bin/hackage\-scripts/package/hlibev>.
4378 .IP "D" 4
4379 .IX Item "D"
4380 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4381 be found at <>.
4382 .IP "Ocaml" 4
4383 .IX Item "Ocaml"
4384 Erkki Seppala has written Ocaml bindings for libev, to be found at
4385 <\-ev/>.
4386 .IP "Lua" 4
4387 .IX Item "Lua"
4388 Brian Maher has written a partial interface to libev for lua (at the
4389 time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4390 <\-ev>.
4391 .IP "Javascript" 4
4392 .IX Item "Javascript"
4393 Node.js (<>) uses libev as the underlying event library.
4394 .IP "Others" 4
4395 .IX Item "Others"
4396 There are others, and I stopped counting.
4398 .IX Header "MACRO MAGIC"
4399 Libev can be compiled with a variety of options, the most fundamental
4400 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4401 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4402 .PP
4403 To make it easier to write programs that cope with either variant, the
4404 following macros are defined:
4405 .ie n .IP """EV_A"", ""EV_A_""" 4
4406 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4407 .IX Item "EV_A, EV_A_"
4408 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4409 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4410 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4411 .Sp
4412 .Vb 3
4413 \& ev_unref (EV_A);
4414 \& ev_timer_add (EV_A_ watcher);
4415 \& ev_run (EV_A_ 0);
4416 .Ve
4417 .Sp
4418 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4419 which is often provided by the following macro.
4420 .ie n .IP """EV_P"", ""EV_P_""" 4
4421 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4422 .IX Item "EV_P, EV_P_"
4423 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4424 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4425 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4426 .Sp
4427 .Vb 2
4428 \& // this is how ev_unref is being declared
4429 \& static void ev_unref (EV_P);
4430 \&
4431 \& // this is how you can declare your typical callback
4432 \& static void cb (EV_P_ ev_timer *w, int revents)
4433 .Ve
4434 .Sp
4435 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4436 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4437 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4438 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4440 Similar to the other two macros, this gives you the value of the default
4441 loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4442 will be initialised if it isn't already initialised.
4443 .Sp
4444 For non-multiplicity builds, these macros do nothing, so you always have
4445 to initialise the loop somewhere.
4446 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4447 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4449 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4450 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4451 is undefined when the default loop has not been initialised by a previous
4452 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.
4453 .Sp
4454 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4455 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4456 .PP
4457 Example: Declare and initialise a check watcher, utilising the above
4458 macros so it will work regardless of whether multiple loops are supported
4459 or not.
4460 .PP
4461 .Vb 5
4462 \& static void
4463 \& check_cb (EV_P_ ev_timer *w, int revents)
4464 \& {
4465 \& ev_check_stop (EV_A_ w);
4466 \& }
4467 \&
4468 \& ev_check check;
4469 \& ev_check_init (&check, check_cb);
4470 \& ev_check_start (EV_DEFAULT_ &check);
4471 \& ev_run (EV_DEFAULT_ 0);
4472 .Ve
4474 .IX Header "EMBEDDING"
4475 Libev can (and often is) directly embedded into host
4476 applications. Examples of applications that embed it include the Deliantra
4477 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4478 and rxvt-unicode.
4479 .PP
4480 The goal is to enable you to just copy the necessary files into your
4481 source directory without having to change even a single line in them, so
4482 you can easily upgrade by simply copying (or having a checked-out copy of
4483 libev somewhere in your source tree).
4484 .SS "\s-1FILESETS\s0"
4485 .IX Subsection "FILESETS"
4486 Depending on what features you need you need to include one or more sets of files
4487 in your application.
4488 .PP
4489 \fI\s-1CORE EVENT LOOP\s0\fR
4490 .IX Subsection "CORE EVENT LOOP"
4491 .PP
4492 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4493 configuration (no autoconf):
4494 .PP
4495 .Vb 2
4496 \& #define EV_STANDALONE 1
4497 \& #include "ev.c"
4498 .Ve
4499 .PP
4500 This will automatically include \fIev.h\fR, too, and should be done in a
4501 single C source file only to provide the function implementations. To use
4502 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API \s0(best
4503 done by writing a wrapper around \fIev.h\fR that you can include instead and
4504 where you can put other configuration options):
4505 .PP
4506 .Vb 2
4507 \& #define EV_STANDALONE 1
4508 \& #include "ev.h"
4509 .Ve
4510 .PP
4511 Both header files and implementation files can be compiled with a \*(C+
4512 compiler (at least, that's a stated goal, and breakage will be treated
4513 as a bug).
4514 .PP
4515 You need the following files in your source tree, or in a directory
4516 in your include path (e.g. in libev/ when using \-Ilibev):
4517 .PP
4518 .Vb 4
4519 \& ev.h
4520 \& ev.c
4521 \& ev_vars.h
4522 \& ev_wrap.h
4523 \&
4524 \& ev_win32.c required on win32 platforms only
4525 \&
4526 \& ev_select.c only when select backend is enabled (which is enabled by default)
4527 \& ev_poll.c only when poll backend is enabled (disabled by default)
4528 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4529 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4530 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4531 .Ve
4532 .PP
4533 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4534 to compile this single file.
4535 .PP
4538 .PP
4539 To include the libevent compatibility \s-1API,\s0 also include:
4540 .PP
4541 .Vb 1
4542 \& #include "event.c"
4543 .Ve
4544 .PP
4545 in the file including \fIev.c\fR, and:
4546 .PP
4547 .Vb 1
4548 \& #include "event.h"
4549 .Ve
4550 .PP
4551 in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4552 .PP
4553 You need the following additional files for this:
4554 .PP
4555 .Vb 2
4556 \& event.h
4557 \& event.c
4558 .Ve
4559 .PP
4560 \fI\s-1AUTOCONF SUPPORT\s0\fR
4561 .IX Subsection "AUTOCONF SUPPORT"
4562 .PP
4563 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4564 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4565 \&\\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4566 include \fIconfig.h\fR and configure itself accordingly.
4567 .PP
4568 For this of course you need the m4 file:
4569 .PP
4570 .Vb 1
4571 \& libev.m4
4572 .Ve
4575 Libev can be configured via a variety of preprocessor symbols you have to
4576 define before including (or compiling) any of its files. The default in
4577 the absence of autoconf is documented for every option.
4578 .PP
4579 Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4580 values when compiling libev vs. including \fIev.h\fR, so it is permissible
4581 to redefine them before including \fIev.h\fR without breaking compatibility
4582 to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4583 users of libev and the libev code itself must be compiled with compatible
4584 settings.
4585 .IP "\s-1EV_COMPAT3 \s0(h)" 4
4586 .IX Item "EV_COMPAT3 (h)"
4587 Backwards compatibility is a major concern for libev. This is why this
4588 release of libev comes with wrappers for the functions and symbols that
4589 have been renamed between libev version 3 and 4.
4590 .Sp
4591 You can disable these wrappers (to test compatibility with future
4592 versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4593 sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4594 from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4595 typedef in that case.
4596 .Sp
4597 In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4598 and in some even more future version the compatibility code will be
4599 removed completely.
4600 .IP "\s-1EV_STANDALONE \s0(h)" 4
4601 .IX Item "EV_STANDALONE (h)"
4602 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4603 keeps libev from including \fIconfig.h\fR, and it also defines dummy
4604 implementations for some libevent functions (such as logging, which is not
4605 supported). It will also not define any of the structs usually found in
4606 \&\fIevent.h\fR that are not directly supported by the libev core alone.
4607 .Sp
4608 In standalone mode, libev will still try to automatically deduce the
4609 configuration, but has to be more conservative.
4610 .IP "\s-1EV_USE_FLOOR\s0" 4
4611 .IX Item "EV_USE_FLOOR"
4612 If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4613 periodic reschedule calculations, otherwise libev will fall back on a
4614 portable (slower) implementation. If you enable this, you usually have to
4615 link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4616 function is not available will fail, so the safe default is to not enable
4617 this.
4618 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4620 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4621 monotonic clock option at both compile time and runtime. Otherwise no
4622 use of the monotonic clock option will be attempted. If you enable this,
4623 you usually have to link against librt or something similar. Enabling it
4624 when the functionality isn't available is safe, though, although you have
4625 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4626 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4627 .IP "\s-1EV_USE_REALTIME\s0" 4
4629 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4630 real-time clock option at compile time (and assume its availability
4631 at runtime if successful). Otherwise no use of the real-time clock
4632 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4633 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4634 correctness. See the note about libraries in the description of
4635 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4636 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4637 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4639 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4640 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4641 exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4642 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4643 programs needlessly. Using a direct syscall is slightly slower (in
4644 theory), because no optimised vdso implementation can be used, but avoids
4645 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4646 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4647 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4649 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4650 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4651 .IP "\s-1EV_USE_EVENTFD\s0" 4
4652 .IX Item "EV_USE_EVENTFD"
4653 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4654 available and will probe for kernel support at runtime. This will improve
4655 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4656 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4657 2.7 or newer, otherwise disabled.
4658 .IP "\s-1EV_USE_SELECT\s0" 4
4659 .IX Item "EV_USE_SELECT"
4660 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4661 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4662 other method takes over, select will be it. Otherwise the select backend
4663 will not be compiled in.
4664 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4666 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4667 structure. This is useful if libev doesn't compile due to a missing
4668 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4669 on exotic systems. This usually limits the range of file descriptors to
4670 some low limit such as 1024 or might have other limitations (winsocket
4671 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4672 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4673 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4675 When defined to \f(CW1\fR, the select backend will assume that
4676 select/socket/connect etc. don't understand file descriptors but
4677 wants osf handles on win32 (this is the case when the select to
4678 be used is the winsock select). This means that it will call
4679 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4680 it is assumed that all these functions actually work on fds, even
4681 on win32. Should not be defined on non\-win32 platforms.
4682 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4683 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4684 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4685 file descriptors to socket handles. When not defining this symbol (the
4686 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4687 correct. In some cases, programs use their own file descriptor management,
4688 in which case they can provide this function to map fds to socket handles.
4689 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4690 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4691 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4692 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4693 their own fd to handle mapping, overwriting this function makes it easier
4694 to do so. This can be done by defining this macro to an appropriate value.
4695 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4696 .IX Item "EV_WIN32_CLOSE_FD(fd)"
4697 If programs implement their own fd to handle mapping on win32, then this
4698 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4699 file descriptors again. Note that the replacement function has to close
4700 the underlying \s-1OS\s0 handle.
4701 .IP "\s-1EV_USE_WSASOCKET\s0" 4
4703 If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4704 communication socket, which works better in some environments. Otherwise,
4705 the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4706 environments.
4707 .IP "\s-1EV_USE_POLL\s0" 4
4708 .IX Item "EV_USE_POLL"
4709 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4710 backend. Otherwise it will be enabled on non\-win32 platforms. It
4711 takes precedence over select.
4712 .IP "\s-1EV_USE_EPOLL\s0" 4
4713 .IX Item "EV_USE_EPOLL"
4714 If defined to be \f(CW1\fR, libev will compile in support for the Linux
4715 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4716 otherwise another method will be used as fallback. This is the preferred
4717 backend for GNU/Linux systems. If undefined, it will be enabled if the
4718 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4719 .IP "\s-1EV_USE_KQUEUE\s0" 4
4720 .IX Item "EV_USE_KQUEUE"
4721 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4722 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4723 otherwise another method will be used as fallback. This is the preferred
4724 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4725 supports some types of fds correctly (the only platform we found that
4726 supports ptys for example was NetBSD), so kqueue might be compiled in, but
4727 not be used unless explicitly requested. The best way to use it is to find
4728 out whether kqueue supports your type of fd properly and use an embedded
4729 kqueue loop.
4730 .IP "\s-1EV_USE_PORT\s0" 4
4731 .IX Item "EV_USE_PORT"
4732 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4733 10 port style backend. Its availability will be detected at runtime,
4734 otherwise another method will be used as fallback. This is the preferred
4735 backend for Solaris 10 systems.
4736 .IP "\s-1EV_USE_DEVPOLL\s0" 4
4737 .IX Item "EV_USE_DEVPOLL"
4738 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4739 .IP "\s-1EV_USE_INOTIFY\s0" 4
4740 .IX Item "EV_USE_INOTIFY"
4741 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4742 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4743 be detected at runtime. If undefined, it will be enabled if the headers
4744 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4745 .IP "\s-1EV_NO_SMP\s0" 4
4746 .IX Item "EV_NO_SMP"
4747 If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4748 between threads, that is, threads can be used, but threads never run on
4749 different cpus (or different cpu cores). This reduces dependencies
4750 and makes libev faster.
4751 .IP "\s-1EV_NO_THREADS\s0" 4
4752 .IX Item "EV_NO_THREADS"
4753 If defined to be \f(CW1\fR, libev will assume that it will never be called from
4754 different threads (that includes signal handlers), which is a stronger
4755 assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4756 libev faster.
4757 .IP "\s-1EV_ATOMIC_T\s0" 4
4758 .IX Item "EV_ATOMIC_T"
4759 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4760 access is atomic with respect to other threads or signal contexts. No
4761 such type is easily found in the C language, so you can provide your own
4762 type that you know is safe for your purposes. It is used both for signal
4763 handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4764 watchers.
4765 .Sp
4766 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4767 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4768 .IP "\s-1EV_H \s0(h)" 4
4769 .IX Item "EV_H (h)"
4770 The name of the \fIev.h\fR header file used to include it. The default if
4771 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4772 used to virtually rename the \fIev.h\fR header file in case of conflicts.