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Revision: 1.81
Committed: Thu Dec 31 07:04:33 2009 UTC (14 years, 6 months ago) by root
Branch: MAIN
CVS Tags: rel-3_9
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# Content
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123 .rm #[ #] #H #V #F C
124 .\" ========================================================================
125 .\"
126 .IX Title "LIBEV 3"
127 .TH LIBEV 3 "2009-12-31" "libev-3.9" "libev - high performance full featured event loop"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
129 .\" way too many mistakes in technical documents.
130 .if n .ad l
131 .nh
132 .SH "NAME"
133 libev \- a high performance full\-featured event loop written in C
135 .IX Header "SYNOPSIS"
136 .Vb 1
137 \& #include <ev.h>
138 .Ve
139 .SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140 .IX Subsection "EXAMPLE PROGRAM"
141 .Vb 2
142 \& // a single header file is required
143 \& #include <ev.h>
144 \&
145 \& #include <stdio.h> // for puts
146 \&
147 \& // every watcher type has its own typedef\*(Aqd struct
148 \& // with the name ev_TYPE
149 \& ev_io stdin_watcher;
150 \& ev_timer timeout_watcher;
151 \&
152 \& // all watcher callbacks have a similar signature
153 \& // this callback is called when data is readable on stdin
154 \& static void
155 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 \& {
157 \& puts ("stdin ready");
158 \& // for one\-shot events, one must manually stop the watcher
159 \& // with its corresponding stop function.
160 \& ev_io_stop (EV_A_ w);
161 \&
162 \& // this causes all nested ev_loop\*(Aqs to stop iterating
163 \& ev_unloop (EV_A_ EVUNLOOP_ALL);
164 \& }
165 \&
166 \& // another callback, this time for a time\-out
167 \& static void
168 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 \& {
170 \& puts ("timeout");
171 \& // this causes the innermost ev_loop to stop iterating
172 \& ev_unloop (EV_A_ EVUNLOOP_ONE);
173 \& }
174 \&
175 \& int
176 \& main (void)
177 \& {
178 \& // use the default event loop unless you have special needs
179 \& struct ev_loop *loop = ev_default_loop (0);
180 \&
181 \& // initialise an io watcher, then start it
182 \& // this one will watch for stdin to become readable
183 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184 \& ev_io_start (loop, &stdin_watcher);
185 \&
186 \& // initialise a timer watcher, then start it
187 \& // simple non\-repeating 5.5 second timeout
188 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189 \& ev_timer_start (loop, &timeout_watcher);
190 \&
191 \& // now wait for events to arrive
192 \& ev_loop (loop, 0);
193 \&
194 \& // unloop was called, so exit
195 \& return 0;
196 \& }
197 .Ve
200 This document documents the libev software package.
201 .PP
202 The newest version of this document is also available as an html-formatted
203 web page you might find easier to navigate when reading it for the first
204 time: <>.
205 .PP
206 While this document tries to be as complete as possible in documenting
207 libev, its usage and the rationale behind its design, it is not a tutorial
208 on event-based programming, nor will it introduce event-based programming
209 with libev.
210 .PP
211 Familarity with event based programming techniques in general is assumed
212 throughout this document.
214 .IX Header "ABOUT LIBEV"
215 Libev is an event loop: you register interest in certain events (such as a
216 file descriptor being readable or a timeout occurring), and it will manage
217 these event sources and provide your program with events.
218 .PP
219 To do this, it must take more or less complete control over your process
220 (or thread) by executing the \fIevent loop\fR handler, and will then
221 communicate events via a callback mechanism.
222 .PP
223 You register interest in certain events by registering so-called \fIevent
224 watchers\fR, which are relatively small C structures you initialise with the
225 details of the event, and then hand it over to libev by \fIstarting\fR the
226 watcher.
227 .SS "\s-1FEATURES\s0"
228 .IX Subsection "FEATURES"
229 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
230 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
231 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
232 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
233 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
234 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
235 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
236 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
237 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
238 \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
239 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
240 .PP
241 It also is quite fast (see this
242 <benchmark> comparing it to libevent
243 for example).
244 .SS "\s-1CONVENTIONS\s0"
245 .IX Subsection "CONVENTIONS"
246 Libev is very configurable. In this manual the default (and most common)
247 configuration will be described, which supports multiple event loops. For
248 more info about various configuration options please have a look at
249 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
250 for multiple event loops, then all functions taking an initial argument of
251 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
252 this argument.
253 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
255 Libev represents time as a single floating point number, representing
256 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
257 near the beginning of 1970, details are complicated, don't ask). This
258 type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually
259 aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do any calculations
260 on it, you should treat it as some floating point value. Unlike the name
261 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
262 throughout libev.
265 Libev knows three classes of errors: operating system errors, usage errors
266 and internal errors (bugs).
267 .PP
268 When libev catches an operating system error it cannot handle (for example
269 a system call indicating a condition libev cannot fix), it calls the callback
270 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
271 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
272 ()\*(C'\fR.
273 .PP
274 When libev detects a usage error such as a negative timer interval, then
275 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
276 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
277 the libev caller and need to be fixed there.
278 .PP
279 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
280 extensive consistency checking code. These do not trigger under normal
281 circumstances, as they indicate either a bug in libev or worse.
284 These functions can be called anytime, even before initialising the
285 library in any way.
286 .IP "ev_tstamp ev_time ()" 4
287 .IX Item "ev_tstamp ev_time ()"
288 Returns the current time as libev would use it. Please note that the
289 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
290 you actually want to know.
291 .IP "ev_sleep (ev_tstamp interval)" 4
292 .IX Item "ev_sleep (ev_tstamp interval)"
293 Sleep for the given interval: The current thread will be blocked until
294 either it is interrupted or the given time interval has passed. Basically
295 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
296 .IP "int ev_version_major ()" 4
297 .IX Item "int ev_version_major ()"
298 .PD 0
299 .IP "int ev_version_minor ()" 4
300 .IX Item "int ev_version_minor ()"
301 .PD
302 You can find out the major and minor \s-1ABI\s0 version numbers of the library
303 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
304 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
305 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
306 version of the library your program was compiled against.
307 .Sp
308 These version numbers refer to the \s-1ABI\s0 version of the library, not the
309 release version.
310 .Sp
311 Usually, it's a good idea to terminate if the major versions mismatch,
312 as this indicates an incompatible change. Minor versions are usually
313 compatible to older versions, so a larger minor version alone is usually
314 not a problem.
315 .Sp
316 Example: Make sure we haven't accidentally been linked against the wrong
317 version.
318 .Sp
319 .Vb 3
320 \& assert (("libev version mismatch",
321 \& ev_version_major () == EV_VERSION_MAJOR
322 \& && ev_version_minor () >= EV_VERSION_MINOR));
323 .Ve
324 .IP "unsigned int ev_supported_backends ()" 4
325 .IX Item "unsigned int ev_supported_backends ()"
326 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
327 value) compiled into this binary of libev (independent of their
328 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
329 a description of the set values.
330 .Sp
331 Example: make sure we have the epoll method, because yeah this is cool and
332 a must have and can we have a torrent of it please!!!11
333 .Sp
334 .Vb 2
335 \& assert (("sorry, no epoll, no sex",
336 \& ev_supported_backends () & EVBACKEND_EPOLL));
337 .Ve
338 .IP "unsigned int ev_recommended_backends ()" 4
339 .IX Item "unsigned int ev_recommended_backends ()"
340 Return the set of all backends compiled into this binary of libev and also
341 recommended for this platform. This set is often smaller than the one
342 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
343 most BSDs and will not be auto-detected unless you explicitly request it
344 (assuming you know what you are doing). This is the set of backends that
345 libev will probe for if you specify no backends explicitly.
346 .IP "unsigned int ev_embeddable_backends ()" 4
347 .IX Item "unsigned int ev_embeddable_backends ()"
348 Returns the set of backends that are embeddable in other event loops. This
349 is the theoretical, all-platform, value. To find which backends
350 might be supported on the current system, you would need to look at
351 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
352 recommended ones.
353 .Sp
354 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
355 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
356 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
357 Sets the allocation function to use (the prototype is similar \- the
358 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
359 used to allocate and free memory (no surprises here). If it returns zero
360 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
361 or take some potentially destructive action.
362 .Sp
363 Since some systems (at least OpenBSD and Darwin) fail to implement
364 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
365 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
366 .Sp
367 You could override this function in high-availability programs to, say,
368 free some memory if it cannot allocate memory, to use a special allocator,
369 or even to sleep a while and retry until some memory is available.
370 .Sp
371 Example: Replace the libev allocator with one that waits a bit and then
372 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
373 .Sp
374 .Vb 6
375 \& static void *
376 \& persistent_realloc (void *ptr, size_t size)
377 \& {
378 \& for (;;)
379 \& {
380 \& void *newptr = realloc (ptr, size);
381 \&
382 \& if (newptr)
383 \& return newptr;
384 \&
385 \& sleep (60);
386 \& }
387 \& }
388 \&
389 \& ...
390 \& ev_set_allocator (persistent_realloc);
391 .Ve
392 .IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
393 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
394 Set the callback function to call on a retryable system call error (such
395 as failed select, poll, epoll_wait). The message is a printable string
396 indicating the system call or subsystem causing the problem. If this
397 callback is set, then libev will expect it to remedy the situation, no
398 matter what, when it returns. That is, libev will generally retry the
399 requested operation, or, if the condition doesn't go away, do bad stuff
400 (such as abort).
401 .Sp
402 Example: This is basically the same thing that libev does internally, too.
403 .Sp
404 .Vb 6
405 \& static void
406 \& fatal_error (const char *msg)
407 \& {
408 \& perror (msg);
409 \& abort ();
410 \& }
411 \&
412 \& ...
413 \& ev_set_syserr_cb (fatal_error);
414 .Ve
417 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
418 is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
419 \&\fIfunction\fR).
420 .PP
421 The library knows two types of such loops, the \fIdefault\fR loop, which
422 supports signals and child events, and dynamically created loops which do
423 not.
424 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
425 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
426 This will initialise the default event loop if it hasn't been initialised
427 yet and return it. If the default loop could not be initialised, returns
428 false. If it already was initialised it simply returns it (and ignores the
429 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
430 .Sp
431 If you don't know what event loop to use, use the one returned from this
432 function.
433 .Sp
434 Note that this function is \fInot\fR thread-safe, so if you want to use it
435 from multiple threads, you have to lock (note also that this is unlikely,
436 as loops cannot be shared easily between threads anyway).
437 .Sp
438 The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
439 \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
440 for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
441 create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
442 can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
443 \&\f(CW\*(C`ev_default_init\*(C'\fR.
444 .Sp
445 The flags argument can be used to specify special behaviour or specific
446 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
447 .Sp
448 The following flags are supported:
449 .RS 4
450 .ie n .IP """EVFLAG_AUTO""" 4
451 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
452 .IX Item "EVFLAG_AUTO"
453 The default flags value. Use this if you have no clue (it's the right
454 thing, believe me).
455 .ie n .IP """EVFLAG_NOENV""" 4
456 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
458 If this flag bit is or'ed into the flag value (or the program runs setuid
459 or setgid) then libev will \fInot\fR look at the environment variable
460 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
461 override the flags completely if it is found in the environment. This is
462 useful to try out specific backends to test their performance, or to work
463 around bugs.
464 .ie n .IP """EVFLAG_FORKCHECK""" 4
465 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
467 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
468 a fork, you can also make libev check for a fork in each iteration by
469 enabling this flag.
470 .Sp
471 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
472 and thus this might slow down your event loop if you do a lot of loop
473 iterations and little real work, but is usually not noticeable (on my
474 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
475 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
476 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
477 .Sp
478 The big advantage of this flag is that you can forget about fork (and
479 forget about forgetting to tell libev about forking) when you use this
480 flag.
481 .Sp
482 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
483 environment variable.
484 .ie n .IP """EVFLAG_NOINOTIFY""" 4
485 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
487 When this flag is specified, then libev will not attempt to use the
488 \&\fIinotify\fR \s-1API\s0 for it's \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
489 testing, this flag can be useful to conserve inotify file descriptors, as
490 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
491 .ie n .IP """EVFLAG_SIGNALFD""" 4
492 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
494 When this flag is specified, then libev will attempt to use the
495 \&\fIsignalfd\fR \s-1API\s0 for it's \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
496 delivers signals synchronously, which makes it both faster and might make
497 it possible to get the queued signal data. It can also simplify signal
498 handling with threads, as long as you properly block signals in your
499 threads that are not interested in handling them.
500 .Sp
501 Signalfd will not be used by default as this changes your signal mask, and
502 there are a lot of shoddy libraries and programs (glib's threadpool for
503 example) that can't properly initialise their signal masks.
504 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
505 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
506 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
507 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
508 libev tries to roll its own fd_set with no limits on the number of fds,
509 but if that fails, expect a fairly low limit on the number of fds when
510 using this backend. It doesn't scale too well (O(highest_fd)), but its
511 usually the fastest backend for a low number of (low-numbered :) fds.
512 .Sp
513 To get good performance out of this backend you need a high amount of
514 parallelism (most of the file descriptors should be busy). If you are
515 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
516 connections as possible during one iteration. You might also want to have
517 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
518 readiness notifications you get per iteration.
519 .Sp
520 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
521 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
522 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
523 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
524 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
525 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
526 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
527 than select, but handles sparse fds better and has no artificial
528 limit on the number of fds you can use (except it will slow down
529 considerably with a lot of inactive fds). It scales similarly to select,
530 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
531 performance tips.
532 .Sp
533 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
534 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
535 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
536 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
537 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
538 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
539 kernels).
540 .Sp
541 For few fds, this backend is a bit little slower than poll and select,
542 but it scales phenomenally better. While poll and select usually scale
543 like O(total_fds) where n is the total number of fds (or the highest fd),
544 epoll scales either O(1) or O(active_fds).
545 .Sp
546 The epoll mechanism deserves honorable mention as the most misdesigned
547 of the more advanced event mechanisms: mere annoyances include silently
548 dropping file descriptors, requiring a system call per change per file
549 descriptor (and unnecessary guessing of parameters), problems with dup and
550 so on. The biggest issue is fork races, however \- if a program forks then
551 \&\fIboth\fR parent and child process have to recreate the epoll set, which can
552 take considerable time (one syscall per file descriptor) and is of course
553 hard to detect.
554 .Sp
555 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
556 of course \fIdoesn't\fR, and epoll just loves to report events for totally
557 \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
558 even remove them from the set) than registered in the set (especially
559 on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
560 employing an additional generation counter and comparing that against the
561 events to filter out spurious ones, recreating the set when required.
562 .Sp
563 While stopping, setting and starting an I/O watcher in the same iteration
564 will result in some caching, there is still a system call per such
565 incident (because the same \fIfile descriptor\fR could point to a different
566 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
567 file descriptors might not work very well if you register events for both
568 file descriptors.
569 .Sp
570 Best performance from this backend is achieved by not unregistering all
571 watchers for a file descriptor until it has been closed, if possible,
572 i.e. keep at least one watcher active per fd at all times. Stopping and
573 starting a watcher (without re-setting it) also usually doesn't cause
574 extra overhead. A fork can both result in spurious notifications as well
575 as in libev having to destroy and recreate the epoll object, which can
576 take considerable time and thus should be avoided.
577 .Sp
578 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
579 faster than epoll for maybe up to a hundred file descriptors, depending on
580 the usage. So sad.
581 .Sp
582 While nominally embeddable in other event loops, this feature is broken in
583 all kernel versions tested so far.
584 .Sp
585 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
586 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
587 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
588 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
589 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
590 Kqueue deserves special mention, as at the time of this writing, it
591 was broken on all BSDs except NetBSD (usually it doesn't work reliably
592 with anything but sockets and pipes, except on Darwin, where of course
593 it's completely useless). Unlike epoll, however, whose brokenness
594 is by design, these kqueue bugs can (and eventually will) be fixed
595 without \s-1API\s0 changes to existing programs. For this reason it's not being
596 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
597 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
598 system like NetBSD.
599 .Sp
600 You still can embed kqueue into a normal poll or select backend and use it
601 only for sockets (after having made sure that sockets work with kqueue on
602 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
603 .Sp
604 It scales in the same way as the epoll backend, but the interface to the
605 kernel is more efficient (which says nothing about its actual speed, of
606 course). While stopping, setting and starting an I/O watcher does never
607 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
608 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
609 sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
610 cases
611 .Sp
612 This backend usually performs well under most conditions.
613 .Sp
614 While nominally embeddable in other event loops, this doesn't work
615 everywhere, so you might need to test for this. And since it is broken
616 almost everywhere, you should only use it when you have a lot of sockets
617 (for which it usually works), by embedding it into another event loop
618 (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
619 also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
620 .Sp
621 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
622 \&\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
623 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
624 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
625 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
626 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
627 This is not implemented yet (and might never be, unless you send me an
628 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
629 and is not embeddable, which would limit the usefulness of this backend
630 immensely.
631 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
632 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
633 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
634 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
635 it's really slow, but it still scales very well (O(active_fds)).
636 .Sp
637 Please note that Solaris event ports can deliver a lot of spurious
638 notifications, so you need to use non-blocking I/O or other means to avoid
639 blocking when no data (or space) is available.
640 .Sp
641 While this backend scales well, it requires one system call per active
642 file descriptor per loop iteration. For small and medium numbers of file
643 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
644 might perform better.
645 .Sp
646 On the positive side, with the exception of the spurious readiness
647 notifications, this backend actually performed fully to specification
648 in all tests and is fully embeddable, which is a rare feat among the
649 OS-specific backends (I vastly prefer correctness over speed hacks).
650 .Sp
651 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
652 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
653 .ie n .IP """EVBACKEND_ALL""" 4
654 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
656 Try all backends (even potentially broken ones that wouldn't be tried
657 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
659 .Sp
660 It is definitely not recommended to use this flag.
661 .RE
662 .RS 4
663 .Sp
664 If one or more of the backend flags are or'ed into the flags value,
665 then only these backends will be tried (in the reverse order as listed
666 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
667 ()\*(C'\fR will be tried.
668 .Sp
669 Example: This is the most typical usage.
670 .Sp
671 .Vb 2
672 \& if (!ev_default_loop (0))
673 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
674 .Ve
675 .Sp
676 Example: Restrict libev to the select and poll backends, and do not allow
677 environment settings to be taken into account:
678 .Sp
679 .Vb 1
681 .Ve
682 .Sp
683 Example: Use whatever libev has to offer, but make sure that kqueue is
684 used if available (warning, breaks stuff, best use only with your own
685 private event loop and only if you know the \s-1OS\s0 supports your types of
686 fds):
687 .Sp
688 .Vb 1
689 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
690 .Ve
691 .RE
692 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
693 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
694 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
695 always distinct from the default loop. Unlike the default loop, it cannot
696 handle signal and child watchers, and attempts to do so will be greeted by
697 undefined behaviour (or a failed assertion if assertions are enabled).
698 .Sp
699 Note that this function \fIis\fR thread-safe, and the recommended way to use
700 libev with threads is indeed to create one loop per thread, and using the
701 default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
702 .Sp
703 Example: Try to create a event loop that uses epoll and nothing else.
704 .Sp
705 .Vb 3
706 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
707 \& if (!epoller)
708 \& fatal ("no epoll found here, maybe it hides under your chair");
709 .Ve
710 .IP "ev_default_destroy ()" 4
711 .IX Item "ev_default_destroy ()"
712 Destroys the default loop again (frees all memory and kernel state
713 etc.). None of the active event watchers will be stopped in the normal
714 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
715 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
716 calling this function, or cope with the fact afterwards (which is usually
717 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
718 for example).
719 .Sp
720 Note that certain global state, such as signal state (and installed signal
721 handlers), will not be freed by this function, and related watchers (such
722 as signal and child watchers) would need to be stopped manually.
723 .Sp
724 In general it is not advisable to call this function except in the
725 rare occasion where you really need to free e.g. the signal handling
726 pipe fds. If you need dynamically allocated loops it is better to use
727 \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
728 .IP "ev_loop_destroy (loop)" 4
729 .IX Item "ev_loop_destroy (loop)"
730 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
731 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
732 .IP "ev_default_fork ()" 4
733 .IX Item "ev_default_fork ()"
734 This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
735 to reinitialise the kernel state for backends that have one. Despite the
736 name, you can call it anytime, but it makes most sense after forking, in
737 the child process (or both child and parent, but that again makes little
738 sense). You \fImust\fR call it in the child before using any of the libev
739 functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
740 .Sp
741 On the other hand, you only need to call this function in the child
742 process if and only if you want to use the event library in the child. If
743 you just fork+exec, you don't have to call it at all.
744 .Sp
745 The function itself is quite fast and it's usually not a problem to call
746 it just in case after a fork. To make this easy, the function will fit in
747 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
748 .Sp
749 .Vb 1
750 \& pthread_atfork (0, 0, ev_default_fork);
751 .Ve
752 .IP "ev_loop_fork (loop)" 4
753 .IX Item "ev_loop_fork (loop)"
754 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
755 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
756 after fork that you want to re-use in the child, and how you do this is
757 entirely your own problem.
758 .IP "int ev_is_default_loop (loop)" 4
759 .IX Item "int ev_is_default_loop (loop)"
760 Returns true when the given loop is, in fact, the default loop, and false
761 otherwise.
762 .IP "unsigned int ev_loop_count (loop)" 4
763 .IX Item "unsigned int ev_loop_count (loop)"
764 Returns the count of loop iterations for the loop, which is identical to
765 the number of times libev did poll for new events. It starts at \f(CW0\fR and
766 happily wraps around with enough iterations.
767 .Sp
768 This value can sometimes be useful as a generation counter of sorts (it
769 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
770 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
771 .IP "unsigned int ev_loop_depth (loop)" 4
772 .IX Item "unsigned int ev_loop_depth (loop)"
773 Returns the number of times \f(CW\*(C`ev_loop\*(C'\fR was entered minus the number of
774 times \f(CW\*(C`ev_loop\*(C'\fR was exited, in other words, the recursion depth.
775 .Sp
776 Outside \f(CW\*(C`ev_loop\*(C'\fR, this number is zero. In a callback, this number is
777 \&\f(CW1\fR, unless \f(CW\*(C`ev_loop\*(C'\fR was invoked recursively (or from another thread),
778 in which case it is higher.
779 .Sp
780 Leaving \f(CW\*(C`ev_loop\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
781 etc.), doesn't count as exit.
782 .IP "unsigned int ev_backend (loop)" 4
783 .IX Item "unsigned int ev_backend (loop)"
784 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
785 use.
786 .IP "ev_tstamp ev_now (loop)" 4
787 .IX Item "ev_tstamp ev_now (loop)"
788 Returns the current \*(L"event loop time\*(R", which is the time the event loop
789 received events and started processing them. This timestamp does not
790 change as long as callbacks are being processed, and this is also the base
791 time used for relative timers. You can treat it as the timestamp of the
792 event occurring (or more correctly, libev finding out about it).
793 .IP "ev_now_update (loop)" 4
794 .IX Item "ev_now_update (loop)"
795 Establishes the current time by querying the kernel, updating the time
796 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
797 is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
798 .Sp
799 This function is rarely useful, but when some event callback runs for a
800 very long time without entering the event loop, updating libev's idea of
801 the current time is a good idea.
802 .Sp
803 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
804 .IP "ev_suspend (loop)" 4
805 .IX Item "ev_suspend (loop)"
806 .PD 0
807 .IP "ev_resume (loop)" 4
808 .IX Item "ev_resume (loop)"
809 .PD
810 These two functions suspend and resume a loop, for use when the loop is
811 not used for a while and timeouts should not be processed.
812 .Sp
813 A typical use case would be an interactive program such as a game: When
814 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
815 would be best to handle timeouts as if no time had actually passed while
816 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
817 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
818 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
819 .Sp
820 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
821 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
822 will be rescheduled (that is, they will lose any events that would have
823 occured while suspended).
824 .Sp
825 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
826 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
827 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
828 .Sp
829 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
830 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
831 .IP "ev_loop (loop, int flags)" 4
832 .IX Item "ev_loop (loop, int flags)"
833 Finally, this is it, the event handler. This function usually is called
834 after you have initialised all your watchers and you want to start
835 handling events.
836 .Sp
837 If the flags argument is specified as \f(CW0\fR, it will not return until
838 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
839 .Sp
840 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
841 relying on all watchers to be stopped when deciding when a program has
842 finished (especially in interactive programs), but having a program
843 that automatically loops as long as it has to and no longer by virtue
844 of relying on its watchers stopping correctly, that is truly a thing of
845 beauty.
846 .Sp
847 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
848 those events and any already outstanding ones, but will not block your
849 process in case there are no events and will return after one iteration of
850 the loop.
851 .Sp
852 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
853 necessary) and will handle those and any already outstanding ones. It
854 will block your process until at least one new event arrives (which could
855 be an event internal to libev itself, so there is no guarantee that a
856 user-registered callback will be called), and will return after one
857 iteration of the loop.
858 .Sp
859 This is useful if you are waiting for some external event in conjunction
860 with something not expressible using other libev watchers (i.e. "roll your
861 own \f(CW\*(C`ev_loop\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
862 usually a better approach for this kind of thing.
863 .Sp
864 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
865 .Sp
866 .Vb 10
867 \& \- Before the first iteration, call any pending watchers.
868 \& * If EVFLAG_FORKCHECK was used, check for a fork.
869 \& \- If a fork was detected (by any means), queue and call all fork watchers.
870 \& \- Queue and call all prepare watchers.
871 \& \- If we have been forked, detach and recreate the kernel state
872 \& as to not disturb the other process.
873 \& \- Update the kernel state with all outstanding changes.
874 \& \- Update the "event loop time" (ev_now ()).
875 \& \- Calculate for how long to sleep or block, if at all
876 \& (active idle watchers, EVLOOP_NONBLOCK or not having
877 \& any active watchers at all will result in not sleeping).
878 \& \- Sleep if the I/O and timer collect interval say so.
879 \& \- Block the process, waiting for any events.
880 \& \- Queue all outstanding I/O (fd) events.
881 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
882 \& \- Queue all expired timers.
883 \& \- Queue all expired periodics.
884 \& \- Unless any events are pending now, queue all idle watchers.
885 \& \- Queue all check watchers.
886 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
887 \& Signals and child watchers are implemented as I/O watchers, and will
888 \& be handled here by queueing them when their watcher gets executed.
889 \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
890 \& were used, or there are no active watchers, return, otherwise
891 \& continue with step *.
892 .Ve
893 .Sp
894 Example: Queue some jobs and then loop until no events are outstanding
895 anymore.
896 .Sp
897 .Vb 4
898 \& ... queue jobs here, make sure they register event watchers as long
899 \& ... as they still have work to do (even an idle watcher will do..)
900 \& ev_loop (my_loop, 0);
901 \& ... jobs done or somebody called unloop. yeah!
902 .Ve
903 .IP "ev_unloop (loop, how)" 4
904 .IX Item "ev_unloop (loop, how)"
905 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
906 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
907 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
908 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
909 .Sp
910 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
911 .Sp
912 It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
913 .IP "ev_ref (loop)" 4
914 .IX Item "ev_ref (loop)"
915 .PD 0
916 .IP "ev_unref (loop)" 4
917 .IX Item "ev_unref (loop)"
918 .PD
919 Ref/unref can be used to add or remove a reference count on the event
920 loop: Every watcher keeps one reference, and as long as the reference
921 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
922 .Sp
923 This is useful when you have a watcher that you never intend to
924 unregister, but that nevertheless should not keep \f(CW\*(C`ev_loop\*(C'\fR from
925 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
926 before stopping it.
927 .Sp
928 As an example, libev itself uses this for its internal signal pipe: It
929 is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
930 exiting if no event watchers registered by it are active. It is also an
931 excellent way to do this for generic recurring timers or from within
932 third-party libraries. Just remember to \fIunref after start\fR and \fIref
933 before stop\fR (but only if the watcher wasn't active before, or was active
934 before, respectively. Note also that libev might stop watchers itself
935 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
936 in the callback).
937 .Sp
938 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
939 running when nothing else is active.
940 .Sp
941 .Vb 4
942 \& ev_signal exitsig;
943 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
944 \& ev_signal_start (loop, &exitsig);
945 \& evf_unref (loop);
946 .Ve
947 .Sp
948 Example: For some weird reason, unregister the above signal handler again.
949 .Sp
950 .Vb 2
951 \& ev_ref (loop);
952 \& ev_signal_stop (loop, &exitsig);
953 .Ve
954 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
955 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
956 .PD 0
957 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
958 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
959 .PD
960 These advanced functions influence the time that libev will spend waiting
961 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
962 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
963 latency.
964 .Sp
965 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
966 allows libev to delay invocation of I/O and timer/periodic callbacks
967 to increase efficiency of loop iterations (or to increase power-saving
968 opportunities).
969 .Sp
970 The idea is that sometimes your program runs just fast enough to handle
971 one (or very few) event(s) per loop iteration. While this makes the
972 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
973 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
974 overhead for the actual polling but can deliver many events at once.
975 .Sp
976 By setting a higher \fIio collect interval\fR you allow libev to spend more
977 time collecting I/O events, so you can handle more events per iteration,
978 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
979 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
980 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
981 sleep time ensures that libev will not poll for I/O events more often then
982 once per this interval, on average.
983 .Sp
984 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
985 to spend more time collecting timeouts, at the expense of increased
986 latency/jitter/inexactness (the watcher callback will be called
987 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
988 value will not introduce any overhead in libev.
989 .Sp
990 Many (busy) programs can usually benefit by setting the I/O collect
991 interval to a value near \f(CW0.1\fR or so, which is often enough for
992 interactive servers (of course not for games), likewise for timeouts. It
993 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
994 as this approaches the timing granularity of most systems. Note that if
995 you do transactions with the outside world and you can't increase the
996 parallelity, then this setting will limit your transaction rate (if you
997 need to poll once per transaction and the I/O collect interval is 0.01,
998 then you can't do more than 100 transations per second).
999 .Sp
1000 Setting the \fItimeout collect interval\fR can improve the opportunity for
1001 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1002 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1003 times the process sleeps and wakes up again. Another useful technique to
1004 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1005 they fire on, say, one-second boundaries only.
1006 .Sp
1007 Example: we only need 0.1s timeout granularity, and we wish not to poll
1008 more often than 100 times per second:
1009 .Sp
1010 .Vb 2
1011 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1012 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1013 .Ve
1014 .IP "ev_invoke_pending (loop)" 4
1015 .IX Item "ev_invoke_pending (loop)"
1016 This call will simply invoke all pending watchers while resetting their
1017 pending state. Normally, \f(CW\*(C`ev_loop\*(C'\fR does this automatically when required,
1018 but when overriding the invoke callback this call comes handy.
1019 .IP "int ev_pending_count (loop)" 4
1020 .IX Item "int ev_pending_count (loop)"
1021 Returns the number of pending watchers \- zero indicates that no watchers
1022 are pending.
1023 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1024 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1025 This overrides the invoke pending functionality of the loop: Instead of
1026 invoking all pending watchers when there are any, \f(CW\*(C`ev_loop\*(C'\fR will call
1027 this callback instead. This is useful, for example, when you want to
1028 invoke the actual watchers inside another context (another thread etc.).
1029 .Sp
1030 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1031 callback.
1032 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1033 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1034 Sometimes you want to share the same loop between multiple threads. This
1035 can be done relatively simply by putting mutex_lock/unlock calls around
1036 each call to a libev function.
1037 .Sp
1038 However, \f(CW\*(C`ev_loop\*(C'\fR can run an indefinite time, so it is not feasible to
1039 wait for it to return. One way around this is to wake up the loop via
1040 \&\f(CW\*(C`ev_unloop\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these \fIrelease\fR
1041 and \fIacquire\fR callbacks on the loop.
1042 .Sp
1043 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1044 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1045 afterwards.
1046 .Sp
1047 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1048 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1049 .Sp
1050 While event loop modifications are allowed between invocations of
1051 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1052 modifications done will affect the event loop, i.e. adding watchers will
1053 have no effect on the set of file descriptors being watched, or the time
1054 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_loop\*(C'\fR when you want it
1055 to take note of any changes you made.
1056 .Sp
1057 In theory, threads executing \f(CW\*(C`ev_loop\*(C'\fR will be async-cancel safe between
1058 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1059 .Sp
1060 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1061 document.
1062 .IP "ev_set_userdata (loop, void *data)" 4
1063 .IX Item "ev_set_userdata (loop, void *data)"
1064 .PD 0
1065 .IP "ev_userdata (loop)" 4
1066 .IX Item "ev_userdata (loop)"
1067 .PD
1068 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1069 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1070 \&\f(CW0.\fR
1071 .Sp
1072 These two functions can be used to associate arbitrary data with a loop,
1073 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1074 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1075 any other purpose as well.
1076 .IP "ev_loop_verify (loop)" 4
1077 .IX Item "ev_loop_verify (loop)"
1078 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1079 compiled in, which is the default for non-minimal builds. It tries to go
1080 through all internal structures and checks them for validity. If anything
1081 is found to be inconsistent, it will print an error message to standard
1082 error and call \f(CW\*(C`abort ()\*(C'\fR.
1083 .Sp
1084 This can be used to catch bugs inside libev itself: under normal
1085 circumstances, this function will never abort as of course libev keeps its
1086 data structures consistent.
1089 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1090 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1091 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1092 .PP
1093 A watcher is a structure that you create and register to record your
1094 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
1095 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
1096 .PP
1097 .Vb 5
1098 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1099 \& {
1100 \& ev_io_stop (w);
1101 \& ev_unloop (loop, EVUNLOOP_ALL);
1102 \& }
1103 \&
1104 \& struct ev_loop *loop = ev_default_loop (0);
1105 \&
1106 \& ev_io stdin_watcher;
1107 \&
1108 \& ev_init (&stdin_watcher, my_cb);
1109 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1110 \& ev_io_start (loop, &stdin_watcher);
1111 \&
1112 \& ev_loop (loop, 0);
1113 .Ve
1114 .PP
1115 As you can see, you are responsible for allocating the memory for your
1116 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1117 stack).
1118 .PP
1119 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1120 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1121 .PP
1122 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
1123 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
1124 callback gets invoked each time the event occurs (or, in the case of I/O
1125 watchers, each time the event loop detects that the file descriptor given
1126 is readable and/or writable).
1127 .PP
1128 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1129 macro to configure it, with arguments specific to the watcher type. There
1130 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1131 .PP
1132 To make the watcher actually watch out for events, you have to start it
1133 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1134 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1135 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1136 .PP
1137 As long as your watcher is active (has been started but not stopped) you
1138 must not touch the values stored in it. Most specifically you must never
1139 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1140 .PP
1141 Each and every callback receives the event loop pointer as first, the
1142 registered watcher structure as second, and a bitset of received events as
1143 third argument.
1144 .PP
1145 The received events usually include a single bit per event type received
1146 (you can receive multiple events at the same time). The possible bit masks
1147 are:
1148 .ie n .IP """EV_READ""" 4
1149 .el .IP "\f(CWEV_READ\fR" 4
1150 .IX Item "EV_READ"
1151 .PD 0
1152 .ie n .IP """EV_WRITE""" 4
1153 .el .IP "\f(CWEV_WRITE\fR" 4
1154 .IX Item "EV_WRITE"
1155 .PD
1156 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1157 writable.
1158 .ie n .IP """EV_TIMEOUT""" 4
1159 .el .IP "\f(CWEV_TIMEOUT\fR" 4
1160 .IX Item "EV_TIMEOUT"
1161 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1162 .ie n .IP """EV_PERIODIC""" 4
1163 .el .IP "\f(CWEV_PERIODIC\fR" 4
1164 .IX Item "EV_PERIODIC"
1165 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1166 .ie n .IP """EV_SIGNAL""" 4
1167 .el .IP "\f(CWEV_SIGNAL\fR" 4
1168 .IX Item "EV_SIGNAL"
1169 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1170 .ie n .IP """EV_CHILD""" 4
1171 .el .IP "\f(CWEV_CHILD\fR" 4
1172 .IX Item "EV_CHILD"
1173 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1174 .ie n .IP """EV_STAT""" 4
1175 .el .IP "\f(CWEV_STAT\fR" 4
1176 .IX Item "EV_STAT"
1177 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1178 .ie n .IP """EV_IDLE""" 4
1179 .el .IP "\f(CWEV_IDLE\fR" 4
1180 .IX Item "EV_IDLE"
1181 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1182 .ie n .IP """EV_PREPARE""" 4
1183 .el .IP "\f(CWEV_PREPARE\fR" 4
1184 .IX Item "EV_PREPARE"
1185 .PD 0
1186 .ie n .IP """EV_CHECK""" 4
1187 .el .IP "\f(CWEV_CHECK\fR" 4
1188 .IX Item "EV_CHECK"
1189 .PD
1190 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
1191 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1192 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
1193 received events. Callbacks of both watcher types can start and stop as
1194 many watchers as they want, and all of them will be taken into account
1195 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1196 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1197 .ie n .IP """EV_EMBED""" 4
1198 .el .IP "\f(CWEV_EMBED\fR" 4
1199 .IX Item "EV_EMBED"
1200 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1201 .ie n .IP """EV_FORK""" 4
1202 .el .IP "\f(CWEV_FORK\fR" 4
1203 .IX Item "EV_FORK"
1204 The event loop has been resumed in the child process after fork (see
1205 \&\f(CW\*(C`ev_fork\*(C'\fR).
1206 .ie n .IP """EV_ASYNC""" 4
1207 .el .IP "\f(CWEV_ASYNC\fR" 4
1208 .IX Item "EV_ASYNC"
1209 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1210 .ie n .IP """EV_CUSTOM""" 4
1211 .el .IP "\f(CWEV_CUSTOM\fR" 4
1212 .IX Item "EV_CUSTOM"
1213 Not ever sent (or otherwise used) by libev itself, but can be freely used
1214 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1215 .ie n .IP """EV_ERROR""" 4
1216 .el .IP "\f(CWEV_ERROR\fR" 4
1217 .IX Item "EV_ERROR"
1218 An unspecified error has occurred, the watcher has been stopped. This might
1219 happen because the watcher could not be properly started because libev
1220 ran out of memory, a file descriptor was found to be closed or any other
1221 problem. Libev considers these application bugs.
1222 .Sp
1223 You best act on it by reporting the problem and somehow coping with the
1224 watcher being stopped. Note that well-written programs should not receive
1225 an error ever, so when your watcher receives it, this usually indicates a
1226 bug in your program.
1227 .Sp
1228 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1229 example it might indicate that a fd is readable or writable, and if your
1230 callbacks is well-written it can just attempt the operation and cope with
1231 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1232 programs, though, as the fd could already be closed and reused for another
1233 thing, so beware.
1234 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1236 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1237 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1238 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1239 This macro initialises the generic portion of a watcher. The contents
1240 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1241 the generic parts of the watcher are initialised, you \fIneed\fR to call
1242 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1243 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1244 which rolls both calls into one.
1245 .Sp
1246 You can reinitialise a watcher at any time as long as it has been stopped
1247 (or never started) and there are no pending events outstanding.
1248 .Sp
1249 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1250 int revents)\*(C'\fR.
1251 .Sp
1252 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1253 .Sp
1254 .Vb 3
1255 \& ev_io w;
1256 \& ev_init (&w, my_cb);
1257 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1258 .Ve
1259 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1260 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1261 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1262 This macro initialises the type-specific parts of a watcher. You need to
1263 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1264 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1265 macro on a watcher that is active (it can be pending, however, which is a
1266 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1267 .Sp
1268 Although some watcher types do not have type-specific arguments
1269 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1270 .Sp
1271 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1272 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1273 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1274 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1275 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1276 calls into a single call. This is the most convenient method to initialise
1277 a watcher. The same limitations apply, of course.
1278 .Sp
1279 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1280 .Sp
1281 .Vb 1
1282 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1283 .Ve
1284 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1285 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1286 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1287 Starts (activates) the given watcher. Only active watchers will receive
1288 events. If the watcher is already active nothing will happen.
1289 .Sp
1290 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1291 whole section.
1292 .Sp
1293 .Vb 1
1294 \& ev_io_start (EV_DEFAULT_UC, &w);
1295 .Ve
1296 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1297 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1298 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1299 Stops the given watcher if active, and clears the pending status (whether
1300 the watcher was active or not).
1301 .Sp
1302 It is possible that stopped watchers are pending \- for example,
1303 non-repeating timers are being stopped when they become pending \- but
1304 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1305 pending. If you want to free or reuse the memory used by the watcher it is
1306 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1307 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1308 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1309 Returns a true value iff the watcher is active (i.e. it has been started
1310 and not yet been stopped). As long as a watcher is active you must not modify
1311 it.
1312 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1313 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1314 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1315 events but its callback has not yet been invoked). As long as a watcher
1316 is pending (but not active) you must not call an init function on it (but
1317 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1318 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1319 it).
1320 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1321 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1322 Returns the callback currently set on the watcher.
1323 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1324 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1325 Change the callback. You can change the callback at virtually any time
1326 (modulo threads).
1327 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1328 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1329 .PD 0
1330 .IP "int ev_priority (ev_TYPE *watcher)" 4
1331 .IX Item "int ev_priority (ev_TYPE *watcher)"
1332 .PD
1333 Set and query the priority of the watcher. The priority is a small
1334 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1335 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1336 before watchers with lower priority, but priority will not keep watchers
1337 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1338 .Sp
1339 If you need to suppress invocation when higher priority events are pending
1340 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1341 .Sp
1342 You \fImust not\fR change the priority of a watcher as long as it is active or
1343 pending.
1344 .Sp
1345 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1346 fine, as long as you do not mind that the priority value you query might
1347 or might not have been clamped to the valid range.
1348 .Sp
1349 The default priority used by watchers when no priority has been set is
1350 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1351 .Sp
1352 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1353 priorities.
1354 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1355 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1356 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
1357 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1358 can deal with that fact, as both are simply passed through to the
1359 callback.
1360 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1361 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1362 If the watcher is pending, this function clears its pending status and
1363 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1364 watcher isn't pending it does nothing and returns \f(CW0\fR.
1365 .Sp
1366 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1367 callback to be invoked, which can be accomplished with this function.
1368 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1369 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1370 Feeds the given event set into the event loop, as if the specified event
1371 had happened for the specified watcher (which must be a pointer to an
1372 initialised but not necessarily started event watcher). Obviously you must
1373 not free the watcher as long as it has pending events.
1374 .Sp
1375 Stopping the watcher, letting libev invoke it, or calling
1376 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1377 not started in the first place.
1378 .Sp
1379 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1380 functions that do not need a watcher.
1381 .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1383 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1384 and read at any time: libev will completely ignore it. This can be used
1385 to associate arbitrary data with your watcher. If you need more data and
1386 don't want to allocate memory and store a pointer to it in that data
1387 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1388 data:
1389 .PP
1390 .Vb 7
1391 \& struct my_io
1392 \& {
1393 \& ev_io io;
1394 \& int otherfd;
1395 \& void *somedata;
1396 \& struct whatever *mostinteresting;
1397 \& };
1398 \&
1399 \& ...
1400 \& struct my_io w;
1401 \& ev_io_init (&, my_cb, fd, EV_READ);
1402 .Ve
1403 .PP
1404 And since your callback will be called with a pointer to the watcher, you
1405 can cast it back to your own type:
1406 .PP
1407 .Vb 5
1408 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1409 \& {
1410 \& struct my_io *w = (struct my_io *)w_;
1411 \& ...
1412 \& }
1413 .Ve
1414 .PP
1415 More interesting and less C\-conformant ways of casting your callback type
1416 instead have been omitted.
1417 .PP
1418 Another common scenario is to use some data structure with multiple
1419 embedded watchers:
1420 .PP
1421 .Vb 6
1422 \& struct my_biggy
1423 \& {
1424 \& int some_data;
1425 \& ev_timer t1;
1426 \& ev_timer t2;
1427 \& }
1428 .Ve
1429 .PP
1430 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1431 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1432 in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1433 some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1434 programmers):
1435 .PP
1436 .Vb 1
1437 \& #include <stddef.h>
1438 \&
1439 \& static void
1440 \& t1_cb (EV_P_ ev_timer *w, int revents)
1441 \& {
1442 \& struct my_biggy big = (struct my_biggy *)
1443 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1444 \& }
1445 \&
1446 \& static void
1447 \& t2_cb (EV_P_ ev_timer *w, int revents)
1448 \& {
1449 \& struct my_biggy big = (struct my_biggy *)
1450 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1451 \& }
1452 .Ve
1453 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1455 Many event loops support \fIwatcher priorities\fR, which are usually small
1456 integers that influence the ordering of event callback invocation
1457 between watchers in some way, all else being equal.
1458 .PP
1459 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1460 description for the more technical details such as the actual priority
1461 range.
1462 .PP
1463 There are two common ways how these these priorities are being interpreted
1464 by event loops:
1465 .PP
1466 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1467 of lower priority watchers, which means as long as higher priority
1468 watchers receive events, lower priority watchers are not being invoked.
1469 .PP
1470 The less common only-for-ordering model uses priorities solely to order
1471 callback invocation within a single event loop iteration: Higher priority
1472 watchers are invoked before lower priority ones, but they all get invoked
1473 before polling for new events.
1474 .PP
1475 Libev uses the second (only-for-ordering) model for all its watchers
1476 except for idle watchers (which use the lock-out model).
1477 .PP
1478 The rationale behind this is that implementing the lock-out model for
1479 watchers is not well supported by most kernel interfaces, and most event
1480 libraries will just poll for the same events again and again as long as
1481 their callbacks have not been executed, which is very inefficient in the
1482 common case of one high-priority watcher locking out a mass of lower
1483 priority ones.
1484 .PP
1485 Static (ordering) priorities are most useful when you have two or more
1486 watchers handling the same resource: a typical usage example is having an
1487 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1488 timeouts. Under load, data might be received while the program handles
1489 other jobs, but since timers normally get invoked first, the timeout
1490 handler will be executed before checking for data. In that case, giving
1491 the timer a lower priority than the I/O watcher ensures that I/O will be
1492 handled first even under adverse conditions (which is usually, but not
1493 always, what you want).
1494 .PP
1495 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1496 will only be executed when no same or higher priority watchers have
1497 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1498 required.
1499 .PP
1500 For example, to emulate how many other event libraries handle priorities,
1501 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1502 the normal watcher callback, you just start the idle watcher. The real
1503 processing is done in the idle watcher callback. This causes libev to
1504 continously poll and process kernel event data for the watcher, but when
1505 the lock-out case is known to be rare (which in turn is rare :), this is
1506 workable.
1507 .PP
1508 Usually, however, the lock-out model implemented that way will perform
1509 miserably under the type of load it was designed to handle. In that case,
1510 it might be preferable to stop the real watcher before starting the
1511 idle watcher, so the kernel will not have to process the event in case
1512 the actual processing will be delayed for considerable time.
1513 .PP
1514 Here is an example of an I/O watcher that should run at a strictly lower
1515 priority than the default, and which should only process data when no
1516 other events are pending:
1517 .PP
1518 .Vb 2
1519 \& ev_idle idle; // actual processing watcher
1520 \& ev_io io; // actual event watcher
1521 \&
1522 \& static void
1523 \& io_cb (EV_P_ ev_io *w, int revents)
1524 \& {
1525 \& // stop the I/O watcher, we received the event, but
1526 \& // are not yet ready to handle it.
1527 \& ev_io_stop (EV_A_ w);
1528 \&
1529 \& // start the idle watcher to ahndle the actual event.
1530 \& // it will not be executed as long as other watchers
1531 \& // with the default priority are receiving events.
1532 \& ev_idle_start (EV_A_ &idle);
1533 \& }
1534 \&
1535 \& static void
1536 \& idle_cb (EV_P_ ev_idle *w, int revents)
1537 \& {
1538 \& // actual processing
1539 \& read (STDIN_FILENO, ...);
1540 \&
1541 \& // have to start the I/O watcher again, as
1542 \& // we have handled the event
1543 \& ev_io_start (EV_P_ &io);
1544 \& }
1545 \&
1546 \& // initialisation
1547 \& ev_idle_init (&idle, idle_cb);
1548 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1549 \& ev_io_start (EV_DEFAULT_ &io);
1550 .Ve
1551 .PP
1552 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1553 low-priority connections can not be locked out forever under load. This
1554 enables your program to keep a lower latency for important connections
1555 during short periods of high load, while not completely locking out less
1556 important ones.
1558 .IX Header "WATCHER TYPES"
1559 This section describes each watcher in detail, but will not repeat
1560 information given in the last section. Any initialisation/set macros,
1561 functions and members specific to the watcher type are explained.
1562 .PP
1563 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1564 while the watcher is active, you can look at the member and expect some
1565 sensible content, but you must not modify it (you can modify it while the
1566 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1567 means you can expect it to have some sensible content while the watcher
1568 is active, but you can also modify it. Modifying it may not do something
1569 sensible or take immediate effect (or do anything at all), but libev will
1570 not crash or malfunction in any way.
1571 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1572 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1573 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1574 I/O watchers check whether a file descriptor is readable or writable
1575 in each iteration of the event loop, or, more precisely, when reading
1576 would not block the process and writing would at least be able to write
1577 some data. This behaviour is called level-triggering because you keep
1578 receiving events as long as the condition persists. Remember you can stop
1579 the watcher if you don't want to act on the event and neither want to
1580 receive future events.
1581 .PP
1582 In general you can register as many read and/or write event watchers per
1583 fd as you want (as long as you don't confuse yourself). Setting all file
1584 descriptors to non-blocking mode is also usually a good idea (but not
1585 required if you know what you are doing).
1586 .PP
1587 If you cannot use non-blocking mode, then force the use of a
1588 known-to-be-good backend (at the time of this writing, this includes only
1589 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
1590 descriptors for which non-blocking operation makes no sense (such as
1591 files) \- libev doesn't guarentee any specific behaviour in that case.
1592 .PP
1593 Another thing you have to watch out for is that it is quite easy to
1594 receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1595 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1596 because there is no data. Not only are some backends known to create a
1597 lot of those (for example Solaris ports), it is very easy to get into
1598 this situation even with a relatively standard program structure. Thus
1599 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1600 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1601 .PP
1602 If you cannot run the fd in non-blocking mode (for example you should
1603 not play around with an Xlib connection), then you have to separately
1604 re-test whether a file descriptor is really ready with a known-to-be good
1605 interface such as poll (fortunately in our Xlib example, Xlib already
1606 does this on its own, so its quite safe to use). Some people additionally
1607 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1608 indefinitely.
1609 .PP
1610 But really, best use non-blocking mode.
1611 .PP
1612 \fIThe special problem of disappearing file descriptors\fR
1613 .IX Subsection "The special problem of disappearing file descriptors"
1614 .PP
1615 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1616 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1617 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1618 descriptor, but when it goes away, the operating system will silently drop
1619 this interest. If another file descriptor with the same number then is
1620 registered with libev, there is no efficient way to see that this is, in
1621 fact, a different file descriptor.
1622 .PP
1623 To avoid having to explicitly tell libev about such cases, libev follows
1624 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1625 will assume that this is potentially a new file descriptor, otherwise
1626 it is assumed that the file descriptor stays the same. That means that
1627 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
1628 descriptor even if the file descriptor number itself did not change.
1629 .PP
1630 This is how one would do it normally anyway, the important point is that
1631 the libev application should not optimise around libev but should leave
1632 optimisations to libev.
1633 .PP
1634 \fIThe special problem of dup'ed file descriptors\fR
1635 .IX Subsection "The special problem of dup'ed file descriptors"
1636 .PP
1637 Some backends (e.g. epoll), cannot register events for file descriptors,
1638 but only events for the underlying file descriptions. That means when you
1639 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1640 events for them, only one file descriptor might actually receive events.
1641 .PP
1642 There is no workaround possible except not registering events
1643 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1644 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1645 .PP
1646 \fIThe special problem of fork\fR
1647 .IX Subsection "The special problem of fork"
1648 .PP
1649 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1650 useless behaviour. Libev fully supports fork, but needs to be told about
1651 it in the child.
1652 .PP
1653 To support fork in your programs, you either have to call
1654 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1655 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1656 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1657 .PP
1658 \fIThe special problem of \s-1SIGPIPE\s0\fR
1659 .IX Subsection "The special problem of SIGPIPE"
1660 .PP
1661 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1662 when writing to a pipe whose other end has been closed, your program gets
1663 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1664 this is sensible behaviour, for daemons, this is usually undesirable.
1665 .PP
1666 So when you encounter spurious, unexplained daemon exits, make sure you
1667 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1668 somewhere, as that would have given you a big clue).
1669 .PP
1670 \fIWatcher-Specific Functions\fR
1671 .IX Subsection "Watcher-Specific Functions"
1672 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1673 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1674 .PD 0
1675 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1676 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1677 .PD
1678 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1679 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
1680 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1681 .IP "int fd [read\-only]" 4
1682 .IX Item "int fd [read-only]"
1683 The file descriptor being watched.
1684 .IP "int events [read\-only]" 4
1685 .IX Item "int events [read-only]"
1686 The events being watched.
1687 .PP
1688 \fIExamples\fR
1689 .IX Subsection "Examples"
1690 .PP
1691 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1692 readable, but only once. Since it is likely line-buffered, you could
1693 attempt to read a whole line in the callback.
1694 .PP
1695 .Vb 6
1696 \& static void
1697 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1698 \& {
1699 \& ev_io_stop (loop, w);
1700 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1701 \& }
1702 \&
1703 \& ...
1704 \& struct ev_loop *loop = ev_default_init (0);
1705 \& ev_io stdin_readable;
1706 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1707 \& ev_io_start (loop, &stdin_readable);
1708 \& ev_loop (loop, 0);
1709 .Ve
1710 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1711 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1712 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1713 Timer watchers are simple relative timers that generate an event after a
1714 given time, and optionally repeating in regular intervals after that.
1715 .PP
1716 The timers are based on real time, that is, if you register an event that
1717 times out after an hour and you reset your system clock to January last
1718 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1719 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1720 monotonic clock option helps a lot here).
1721 .PP
1722 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1723 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1724 might introduce a small delay). If multiple timers become ready during the
1725 same loop iteration then the ones with earlier time-out values are invoked
1726 before ones of the same priority with later time-out values (but this is
1727 no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1728 .PP
1729 \fIBe smart about timeouts\fR
1730 .IX Subsection "Be smart about timeouts"
1731 .PP
1732 Many real-world problems involve some kind of timeout, usually for error
1733 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1734 you want to raise some error after a while.
1735 .PP
1736 What follows are some ways to handle this problem, from obvious and
1737 inefficient to smart and efficient.
1738 .PP
1739 In the following, a 60 second activity timeout is assumed \- a timeout that
1740 gets reset to 60 seconds each time there is activity (e.g. each time some
1741 data or other life sign was received).
1742 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1743 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1744 This is the most obvious, but not the most simple way: In the beginning,
1745 start the watcher:
1746 .Sp
1747 .Vb 2
1748 \& ev_timer_init (timer, callback, 60., 0.);
1749 \& ev_timer_start (loop, timer);
1750 .Ve
1751 .Sp
1752 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1753 and start it again:
1754 .Sp
1755 .Vb 3
1756 \& ev_timer_stop (loop, timer);
1757 \& ev_timer_set (timer, 60., 0.);
1758 \& ev_timer_start (loop, timer);
1759 .Ve
1760 .Sp
1761 This is relatively simple to implement, but means that each time there is
1762 some activity, libev will first have to remove the timer from its internal
1763 data structure and then add it again. Libev tries to be fast, but it's
1764 still not a constant-time operation.
1765 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1766 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1767 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1768 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1769 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1770 .Sp
1771 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1772 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1773 successfully read or write some data. If you go into an idle state where
1774 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1775 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1776 .Sp
1777 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1778 \&\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
1779 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1780 .Sp
1781 At start:
1782 .Sp
1783 .Vb 3
1784 \& ev_init (timer, callback);
1785 \& timer\->repeat = 60.;
1786 \& ev_timer_again (loop, timer);
1787 .Ve
1788 .Sp
1789 Each time there is some activity:
1790 .Sp
1791 .Vb 1
1792 \& ev_timer_again (loop, timer);
1793 .Ve
1794 .Sp
1795 It is even possible to change the time-out on the fly, regardless of
1796 whether the watcher is active or not:
1797 .Sp
1798 .Vb 2
1799 \& timer\->repeat = 30.;
1800 \& ev_timer_again (loop, timer);
1801 .Ve
1802 .Sp
1803 This is slightly more efficient then stopping/starting the timer each time
1804 you want to modify its timeout value, as libev does not have to completely
1805 remove and re-insert the timer from/into its internal data structure.
1806 .Sp
1807 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1808 .IP "3. Let the timer time out, but then re-arm it as required." 4
1809 .IX Item "3. Let the timer time out, but then re-arm it as required."
1810 This method is more tricky, but usually most efficient: Most timeouts are
1811 relatively long compared to the intervals between other activity \- in
1812 our example, within 60 seconds, there are usually many I/O events with
1813 associated activity resets.
1814 .Sp
1815 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1816 but remember the time of last activity, and check for a real timeout only
1817 within the callback:
1818 .Sp
1819 .Vb 1
1820 \& ev_tstamp last_activity; // time of last activity
1821 \&
1822 \& static void
1823 \& callback (EV_P_ ev_timer *w, int revents)
1824 \& {
1825 \& ev_tstamp now = ev_now (EV_A);
1826 \& ev_tstamp timeout = last_activity + 60.;
1827 \&
1828 \& // if last_activity + 60. is older than now, we did time out
1829 \& if (timeout < now)
1830 \& {
1831 \& // timeout occured, take action
1832 \& }
1833 \& else
1834 \& {
1835 \& // callback was invoked, but there was some activity, re\-arm
1836 \& // the watcher to fire in last_activity + 60, which is
1837 \& // guaranteed to be in the future, so "again" is positive:
1838 \& w\->repeat = timeout \- now;
1839 \& ev_timer_again (EV_A_ w);
1840 \& }
1841 \& }
1842 .Ve
1843 .Sp
1844 To summarise the callback: first calculate the real timeout (defined
1845 as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1846 been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1847 the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1848 re-schedule the timer to fire at that future time, to see if maybe we have
1849 a timeout then.
1850 .Sp
1851 Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1852 \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1853 .Sp
1854 This scheme causes more callback invocations (about one every 60 seconds
1855 minus half the average time between activity), but virtually no calls to
1856 libev to change the timeout.
1857 .Sp
1858 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1859 to the current time (meaning we just have some activity :), then call the
1860 callback, which will \*(L"do the right thing\*(R" and start the timer:
1861 .Sp
1862 .Vb 3
1863 \& ev_init (timer, callback);
1864 \& last_activity = ev_now (loop);
1865 \& callback (loop, timer, EV_TIMEOUT);
1866 .Ve
1867 .Sp
1868 And when there is some activity, simply store the current time in
1869 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1870 .Sp
1871 .Vb 1
1872 \& last_actiivty = ev_now (loop);
1873 .Ve
1874 .Sp
1875 This technique is slightly more complex, but in most cases where the
1876 time-out is unlikely to be triggered, much more efficient.
1877 .Sp
1878 Changing the timeout is trivial as well (if it isn't hard-coded in the
1879 callback :) \- just change the timeout and invoke the callback, which will
1880 fix things for you.
1881 .IP "4. Wee, just use a double-linked list for your timeouts." 4
1882 .IX Item "4. Wee, just use a double-linked list for your timeouts."
1883 If there is not one request, but many thousands (millions...), all
1884 employing some kind of timeout with the same timeout value, then one can
1885 do even better:
1886 .Sp
1887 When starting the timeout, calculate the timeout value and put the timeout
1888 at the \fIend\fR of the list.
1889 .Sp
1890 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1891 the list is expected to fire (for example, using the technique #3).
1892 .Sp
1893 When there is some activity, remove the timer from the list, recalculate
1894 the timeout, append it to the end of the list again, and make sure to
1895 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1896 .Sp
1897 This way, one can manage an unlimited number of timeouts in O(1) time for
1898 starting, stopping and updating the timers, at the expense of a major
1899 complication, and having to use a constant timeout. The constant timeout
1900 ensures that the list stays sorted.
1901 .PP
1902 So which method the best?
1903 .PP
1904 Method #2 is a simple no-brain-required solution that is adequate in most
1905 situations. Method #3 requires a bit more thinking, but handles many cases
1906 better, and isn't very complicated either. In most case, choosing either
1907 one is fine, with #3 being better in typical situations.
1908 .PP
1909 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1910 rather complicated, but extremely efficient, something that really pays
1911 off after the first million or so of active timers, i.e. it's usually
1912 overkill :)
1913 .PP
1914 \fIThe special problem of time updates\fR
1915 .IX Subsection "The special problem of time updates"
1916 .PP
1917 Establishing the current time is a costly operation (it usually takes at
1918 least two system calls): \s-1EV\s0 therefore updates its idea of the current
1919 time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1920 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1921 lots of events in one iteration.
1922 .PP
1923 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1924 time. This is usually the right thing as this timestamp refers to the time
1925 of the event triggering whatever timeout you are modifying/starting. If
1926 you suspect event processing to be delayed and you \fIneed\fR to base the
1927 timeout on the current time, use something like this to adjust for this:
1928 .PP
1929 .Vb 1
1930 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1931 .Ve
1932 .PP
1933 If the event loop is suspended for a long time, you can also force an
1934 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1935 ()\*(C'\fR.
1936 .PP
1937 \fIThe special problems of suspended animation\fR
1938 .IX Subsection "The special problems of suspended animation"
1939 .PP
1940 When you leave the server world it is quite customary to hit machines that
1941 can suspend/hibernate \- what happens to the clocks during such a suspend?
1942 .PP
1943 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
1944 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
1945 to run until the system is suspended, but they will not advance while the
1946 system is suspended. That means, on resume, it will be as if the program
1947 was frozen for a few seconds, but the suspend time will not be counted
1948 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
1949 clock advanced as expected, but if it is used as sole clocksource, then a
1950 long suspend would be detected as a time jump by libev, and timers would
1951 be adjusted accordingly.
1952 .PP
1953 I would not be surprised to see different behaviour in different between
1954 operating systems, \s-1OS\s0 versions or even different hardware.
1955 .PP
1956 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
1957 time jump in the monotonic clocks and the realtime clock. If the program
1958 is suspended for a very long time, and monotonic clock sources are in use,
1959 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
1960 will be counted towards the timers. When no monotonic clock source is in
1961 use, then libev will again assume a timejump and adjust accordingly.
1962 .PP
1963 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
1964 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
1965 deterministic behaviour in this case (you can do nothing against
1966 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
1967 .PP
1968 \fIWatcher-Specific Functions and Data Members\fR
1969 .IX Subsection "Watcher-Specific Functions and Data Members"
1970 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1971 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1972 .PD 0
1973 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1974 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1975 .PD
1976 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1977 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1978 reached. If it is positive, then the timer will automatically be
1979 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1980 until stopped manually.
1981 .Sp
1982 The timer itself will do a best-effort at avoiding drift, that is, if
1983 you configure a timer to trigger every 10 seconds, then it will normally
1984 trigger at exactly 10 second intervals. If, however, your program cannot
1985 keep up with the timer (because it takes longer than those 10 seconds to
1986 do stuff) the timer will not fire more than once per event loop iteration.
1987 .IP "ev_timer_again (loop, ev_timer *)" 4
1988 .IX Item "ev_timer_again (loop, ev_timer *)"
1989 This will act as if the timer timed out and restart it again if it is
1990 repeating. The exact semantics are:
1991 .Sp
1992 If the timer is pending, its pending status is cleared.
1993 .Sp
1994 If the timer is started but non-repeating, stop it (as if it timed out).
1995 .Sp
1996 If the timer is repeating, either start it if necessary (with the
1997 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1998 .Sp
1999 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2000 usage example.
2001 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2002 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2003 Returns the remaining time until a timer fires. If the timer is active,
2004 then this time is relative to the current event loop time, otherwise it's
2005 the timeout value currently configured.
2006 .Sp
2007 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2008 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remain\*(C'\fR
2009 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2010 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2011 too), and so on.
2012 .IP "ev_tstamp repeat [read\-write]" 4
2013 .IX Item "ev_tstamp repeat [read-write]"
2014 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2015 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2016 which is also when any modifications are taken into account.
2017 .PP
2018 \fIExamples\fR
2019 .IX Subsection "Examples"
2020 .PP
2021 Example: Create a timer that fires after 60 seconds.
2022 .PP
2023 .Vb 5
2024 \& static void
2025 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2026 \& {
2027 \& .. one minute over, w is actually stopped right here
2028 \& }
2029 \&
2030 \& ev_timer mytimer;
2031 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2032 \& ev_timer_start (loop, &mytimer);
2033 .Ve
2034 .PP
2035 Example: Create a timeout timer that times out after 10 seconds of
2036 inactivity.
2037 .PP
2038 .Vb 5
2039 \& static void
2040 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2041 \& {
2042 \& .. ten seconds without any activity
2043 \& }
2044 \&
2045 \& ev_timer mytimer;
2046 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2047 \& ev_timer_again (&mytimer); /* start timer */
2048 \& ev_loop (loop, 0);
2049 \&
2050 \& // and in some piece of code that gets executed on any "activity":
2051 \& // reset the timeout to start ticking again at 10 seconds
2052 \& ev_timer_again (&mytimer);
2053 .Ve
2054 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2055 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2056 .IX Subsection "ev_periodic - to cron or not to cron?"
2057 Periodic watchers are also timers of a kind, but they are very versatile
2058 (and unfortunately a bit complex).
2059 .PP
2060 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2061 relative time, the physical time that passes) but on wall clock time
2062 (absolute time, the thing you can read on your calender or clock). The
2063 difference is that wall clock time can run faster or slower than real
2064 time, and time jumps are not uncommon (e.g. when you adjust your
2065 wrist-watch).
2066 .PP
2067 You can tell a periodic watcher to trigger after some specific point
2068 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2069 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2070 not a delay) and then reset your system clock to January of the previous
2071 year, then it will take a year or more to trigger the event (unlike an
2072 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2073 it, as it uses a relative timeout).
2074 .PP
2075 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2076 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2077 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2078 those cannot react to time jumps.
2079 .PP
2080 As with timers, the callback is guaranteed to be invoked only when the
2081 point in time where it is supposed to trigger has passed. If multiple
2082 timers become ready during the same loop iteration then the ones with
2083 earlier time-out values are invoked before ones with later time-out values
2084 (but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
2085 .PP
2086 \fIWatcher-Specific Functions and Data Members\fR
2087 .IX Subsection "Watcher-Specific Functions and Data Members"
2088 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2089 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2090 .PD 0
2091 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2092 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2093 .PD
2094 Lots of arguments, let's sort it out... There are basically three modes of
2095 operation, and we will explain them from simplest to most complex:
2096 .RS 4
2097 .IP "\(bu" 4
2098 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2099 .Sp
2100 In this configuration the watcher triggers an event after the wall clock
2101 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2102 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2103 will be stopped and invoked when the system clock reaches or surpasses
2104 this point in time.
2105 .IP "\(bu" 4
2106 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2107 .Sp
2108 In this mode the watcher will always be scheduled to time out at the next
2109 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2110 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2111 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2112 .Sp
2113 This can be used to create timers that do not drift with respect to the
2114 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2115 hour, on the hour (with respect to \s-1UTC\s0):
2116 .Sp
2117 .Vb 1
2118 \& ev_periodic_set (&periodic, 0., 3600., 0);
2119 .Ve
2120 .Sp
2121 This doesn't mean there will always be 3600 seconds in between triggers,
2122 but only that the callback will be called when the system time shows a
2123 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2124 by 3600.
2125 .Sp
2126 Another way to think about it (for the mathematically inclined) is that
2127 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2128 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2129 .Sp
2130 For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2131 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2132 this value, and in fact is often specified as zero.
2133 .Sp
2134 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2135 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2136 will of course deteriorate. Libev itself tries to be exact to be about one
2137 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2138 .IP "\(bu" 4
2139 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2140 .Sp
2141 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2142 ignored. Instead, each time the periodic watcher gets scheduled, the
2143 reschedule callback will be called with the watcher as first, and the
2144 current time as second argument.
2145 .Sp
2146 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2147 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2148 allowed by documentation here\fR.
2149 .Sp
2150 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2151 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2152 only event loop modification you are allowed to do).
2153 .Sp
2154 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2155 *w, ev_tstamp now)\*(C'\fR, e.g.:
2156 .Sp
2157 .Vb 5
2158 \& static ev_tstamp
2159 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2160 \& {
2161 \& return now + 60.;
2162 \& }
2163 .Ve
2164 .Sp
2165 It must return the next time to trigger, based on the passed time value
2166 (that is, the lowest time value larger than to the second argument). It
2167 will usually be called just before the callback will be triggered, but
2168 might be called at other times, too.
2169 .Sp
2170 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2171 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2172 .Sp
2173 This can be used to create very complex timers, such as a timer that
2174 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2175 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2176 you do this is, again, up to you (but it is not trivial, which is the main
2177 reason I omitted it as an example).
2178 .RE
2179 .RS 4
2180 .RE
2181 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2182 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2183 Simply stops and restarts the periodic watcher again. This is only useful
2184 when you changed some parameters or the reschedule callback would return
2185 a different time than the last time it was called (e.g. in a crond like
2186 program when the crontabs have changed).
2187 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2188 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2189 When active, returns the absolute time that the watcher is supposed
2190 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2191 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2192 rescheduling modes.
2193 .IP "ev_tstamp offset [read\-write]" 4
2194 .IX Item "ev_tstamp offset [read-write]"
2195 When repeating, this contains the offset value, otherwise this is the
2196 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2197 although libev might modify this value for better numerical stability).
2198 .Sp
2199 Can be modified any time, but changes only take effect when the periodic
2200 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2201 .IP "ev_tstamp interval [read\-write]" 4
2202 .IX Item "ev_tstamp interval [read-write]"
2203 The current interval value. Can be modified any time, but changes only
2204 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2205 called.
2206 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2207 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2208 The current reschedule callback, or \f(CW0\fR, if this functionality is
2209 switched off. Can be changed any time, but changes only take effect when
2210 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2211 .PP
2212 \fIExamples\fR
2213 .IX Subsection "Examples"
2214 .PP
2215 Example: Call a callback every hour, or, more precisely, whenever the
2216 system time is divisible by 3600. The callback invocation times have
2217 potentially a lot of jitter, but good long-term stability.
2218 .PP
2219 .Vb 5
2220 \& static void
2221 \& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
2222 \& {
2223 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2224 \& }
2225 \&
2226 \& ev_periodic hourly_tick;
2227 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2228 \& ev_periodic_start (loop, &hourly_tick);
2229 .Ve
2230 .PP
2231 Example: The same as above, but use a reschedule callback to do it:
2232 .PP
2233 .Vb 1
2234 \& #include <math.h>
2235 \&
2236 \& static ev_tstamp
2237 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2238 \& {
2239 \& return now + (3600. \- fmod (now, 3600.));
2240 \& }
2241 \&
2242 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2243 .Ve
2244 .PP
2245 Example: Call a callback every hour, starting now:
2246 .PP
2247 .Vb 4
2248 \& ev_periodic hourly_tick;
2249 \& ev_periodic_init (&hourly_tick, clock_cb,
2250 \& fmod (ev_now (loop), 3600.), 3600., 0);
2251 \& ev_periodic_start (loop, &hourly_tick);
2252 .Ve
2253 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2254 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2255 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2256 Signal watchers will trigger an event when the process receives a specific
2257 signal one or more times. Even though signals are very asynchronous, libev
2258 will try it's best to deliver signals synchronously, i.e. as part of the
2259 normal event processing, like any other event.
2260 .PP
2261 If you want signals to be delivered truly asynchronously, just use
2262 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2263 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2264 synchronously wake up an event loop.
2265 .PP
2266 You can configure as many watchers as you like for the same signal, but
2267 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2268 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2269 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2270 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2271 .PP
2272 When the first watcher gets started will libev actually register something
2273 with the kernel (thus it coexists with your own signal handlers as long as
2274 you don't register any with libev for the same signal).
2275 .PP
2276 If possible and supported, libev will install its handlers with
2277 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2278 not be unduly interrupted. If you have a problem with system calls getting
2279 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2280 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2281 .PP
2282 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2283 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2284 .PP
2285 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2286 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2287 stopping it again), that is, libev might or might not block the signal,
2288 and might or might not set or restore the installed signal handler.
2289 .PP
2290 While this does not matter for the signal disposition (libev never
2291 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2292 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2293 certain signals to be blocked.
2294 .PP
2295 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2296 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2297 choice usually).
2298 .PP
2299 The simplest way to ensure that the signal mask is reset in the child is
2300 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2301 catch fork calls done by libraries (such as the libc) as well.
2302 .PP
2303 In current versions of libev, the signal will not be blocked indefinitely
2304 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2305 the window of opportunity for problems, it will not go away, as libev
2306 \&\fIhas\fR to modify the signal mask, at least temporarily.
2307 .PP
2308 So I can't stress this enough: \fIIf you do not reset your signal mask when
2309 you expect it to be empty, you have a race condition in your code\fR. This
2310 is not a libev-specific thing, this is true for most event libraries.
2311 .PP
2312 \fIWatcher-Specific Functions and Data Members\fR
2313 .IX Subsection "Watcher-Specific Functions and Data Members"
2314 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2315 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2316 .PD 0
2317 .IP "ev_signal_set (ev_signal *, int signum)" 4
2318 .IX Item "ev_signal_set (ev_signal *, int signum)"
2319 .PD
2320 Configures the watcher to trigger on the given signal number (usually one
2321 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2322 .IP "int signum [read\-only]" 4
2323 .IX Item "int signum [read-only]"
2324 The signal the watcher watches out for.
2325 .PP
2326 \fIExamples\fR
2327 .IX Subsection "Examples"
2328 .PP
2329 Example: Try to exit cleanly on \s-1SIGINT\s0.
2330 .PP
2331 .Vb 5
2332 \& static void
2333 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2334 \& {
2335 \& ev_unloop (loop, EVUNLOOP_ALL);
2336 \& }
2337 \&
2338 \& ev_signal signal_watcher;
2339 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2340 \& ev_signal_start (loop, &signal_watcher);
2341 .Ve
2342 .ie n .SS """ev_child"" \- watch out for process status changes"
2343 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2344 .IX Subsection "ev_child - watch out for process status changes"
2345 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2346 some child status changes (most typically when a child of yours dies or
2347 exits). It is permissible to install a child watcher \fIafter\fR the child
2348 has been forked (which implies it might have already exited), as long
2349 as the event loop isn't entered (or is continued from a watcher), i.e.,
2350 forking and then immediately registering a watcher for the child is fine,
2351 but forking and registering a watcher a few event loop iterations later or
2352 in the next callback invocation is not.
2353 .PP
2354 Only the default event loop is capable of handling signals, and therefore
2355 you can only register child watchers in the default event loop.
2356 .PP
2357 Due to some design glitches inside libev, child watchers will always be
2358 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2359 libev)
2360 .PP
2361 \fIProcess Interaction\fR
2362 .IX Subsection "Process Interaction"
2363 .PP
2364 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2365 initialised. This is necessary to guarantee proper behaviour even if the
2366 first child watcher is started after the child exits. The occurrence
2367 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2368 synchronously as part of the event loop processing. Libev always reaps all
2369 children, even ones not watched.
2370 .PP
2371 \fIOverriding the Built-In Processing\fR
2372 .IX Subsection "Overriding the Built-In Processing"
2373 .PP
2374 Libev offers no special support for overriding the built-in child
2375 processing, but if your application collides with libev's default child
2376 handler, you can override it easily by installing your own handler for
2377 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2378 default loop never gets destroyed. You are encouraged, however, to use an
2379 event-based approach to child reaping and thus use libev's support for
2380 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2381 .PP
2382 \fIStopping the Child Watcher\fR
2383 .IX Subsection "Stopping the Child Watcher"
2384 .PP
2385 Currently, the child watcher never gets stopped, even when the
2386 child terminates, so normally one needs to stop the watcher in the
2387 callback. Future versions of libev might stop the watcher automatically
2388 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2389 problem).
2390 .PP
2391 \fIWatcher-Specific Functions and Data Members\fR
2392 .IX Subsection "Watcher-Specific Functions and Data Members"
2393 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2394 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2395 .PD 0
2396 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2397 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2398 .PD
2399 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2400 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2401 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2402 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2403 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2404 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2405 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2406 activate the watcher when the process is stopped or continued).
2407 .IP "int pid [read\-only]" 4
2408 .IX Item "int pid [read-only]"
2409 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2410 .IP "int rpid [read\-write]" 4
2411 .IX Item "int rpid [read-write]"
2412 The process id that detected a status change.
2413 .IP "int rstatus [read\-write]" 4
2414 .IX Item "int rstatus [read-write]"
2415 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2416 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2417 .PP
2418 \fIExamples\fR
2419 .IX Subsection "Examples"
2420 .PP
2421 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2422 its completion.
2423 .PP
2424 .Vb 1
2425 \& ev_child cw;
2426 \&
2427 \& static void
2428 \& child_cb (EV_P_ ev_child *w, int revents)
2429 \& {
2430 \& ev_child_stop (EV_A_ w);
2431 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2432 \& }
2433 \&
2434 \& pid_t pid = fork ();
2435 \&
2436 \& if (pid < 0)
2437 \& // error
2438 \& else if (pid == 0)
2439 \& {
2440 \& // the forked child executes here
2441 \& exit (1);
2442 \& }
2443 \& else
2444 \& {
2445 \& ev_child_init (&cw, child_cb, pid, 0);
2446 \& ev_child_start (EV_DEFAULT_ &cw);
2447 \& }
2448 .Ve
2449 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2450 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2451 .IX Subsection "ev_stat - did the file attributes just change?"
2452 This watches a file system path for attribute changes. That is, it calls
2453 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2454 and sees if it changed compared to the last time, invoking the callback if
2455 it did.
2456 .PP
2457 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2458 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2459 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2460 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2461 least one) and all the other fields of the stat buffer having unspecified
2462 contents.
2463 .PP
2464 The path \fImust not\fR end in a slash or contain special components such as
2465 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2466 your working directory changes, then the behaviour is undefined.
2467 .PP
2468 Since there is no portable change notification interface available, the
2469 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2470 to see if it changed somehow. You can specify a recommended polling
2471 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2472 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2473 (which you can expect to be around five seconds, although this might
2474 change dynamically). Libev will also impose a minimum interval which is
2475 currently around \f(CW0.1\fR, but that's usually overkill.
2476 .PP
2477 This watcher type is not meant for massive numbers of stat watchers,
2478 as even with OS-supported change notifications, this can be
2479 resource-intensive.
2480 .PP
2481 At the time of this writing, the only OS-specific interface implemented
2482 is the Linux inotify interface (implementing kqueue support is left as an
2483 exercise for the reader. Note, however, that the author sees no way of
2484 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2485 .PP
2486 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2487 .IX Subsection "ABI Issues (Largefile Support)"
2488 .PP
2489 Libev by default (unless the user overrides this) uses the default
2490 compilation environment, which means that on systems with large file
2491 support disabled by default, you get the 32 bit version of the stat
2492 structure. When using the library from programs that change the \s-1ABI\s0 to
2493 use 64 bit file offsets the programs will fail. In that case you have to
2494 compile libev with the same flags to get binary compatibility. This is
2495 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2496 most noticeably displayed with ev_stat and large file support.
2497 .PP
2498 The solution for this is to lobby your distribution maker to make large
2499 file interfaces available by default (as e.g. FreeBSD does) and not
2500 optional. Libev cannot simply switch on large file support because it has
2501 to exchange stat structures with application programs compiled using the
2502 default compilation environment.
2503 .PP
2504 \fIInotify and Kqueue\fR
2505 .IX Subsection "Inotify and Kqueue"
2506 .PP
2507 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2508 runtime, it will be used to speed up change detection where possible. The
2509 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2510 watcher is being started.
2511 .PP
2512 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2513 except that changes might be detected earlier, and in some cases, to avoid
2514 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2515 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2516 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2517 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2518 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2519 xfs are fully working) libev usually gets away without polling.
2520 .PP
2521 There is no support for kqueue, as apparently it cannot be used to
2522 implement this functionality, due to the requirement of having a file
2523 descriptor open on the object at all times, and detecting renames, unlinks
2524 etc. is difficult.
2525 .PP
2526 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2527 .IX Subsection "stat () is a synchronous operation"
2528 .PP
2529 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2530 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2531 ()\*(C'\fR, which is a synchronous operation.
2532 .PP
2533 For local paths, this usually doesn't matter: unless the system is very
2534 busy or the intervals between stat's are large, a stat call will be fast,
2535 as the path data is usually in memory already (except when starting the
2536 watcher).
2537 .PP
2538 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2539 time due to network issues, and even under good conditions, a stat call
2540 often takes multiple milliseconds.
2541 .PP
2542 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2543 paths, although this is fully supported by libev.
2544 .PP
2545 \fIThe special problem of stat time resolution\fR
2546 .IX Subsection "The special problem of stat time resolution"
2547 .PP
2548 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2549 and even on systems where the resolution is higher, most file systems
2550 still only support whole seconds.
2551 .PP
2552 That means that, if the time is the only thing that changes, you can
2553 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2554 calls your callback, which does something. When there is another update
2555 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2556 stat data does change in other ways (e.g. file size).
2557 .PP
2558 The solution to this is to delay acting on a change for slightly more
2559 than a second (or till slightly after the next full second boundary), using
2560 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2561 ev_timer_again (loop, w)\*(C'\fR).
2562 .PP
2563 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2564 of some operating systems (where the second counter of the current time
2565 might be be delayed. One such system is the Linux kernel, where a call to
2566 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2567 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2568 update file times then there will be a small window where the kernel uses
2569 the previous second to update file times but libev might already execute
2570 the timer callback).
2571 .PP
2572 \fIWatcher-Specific Functions and Data Members\fR
2573 .IX Subsection "Watcher-Specific Functions and Data Members"
2574 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2575 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2576 .PD 0
2577 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2578 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2579 .PD
2580 Configures the watcher to wait for status changes of the given
2581 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2582 be detected and should normally be specified as \f(CW0\fR to let libev choose
2583 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2584 path for as long as the watcher is active.
2585 .Sp
2586 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2587 relative to the attributes at the time the watcher was started (or the
2588 last change was detected).
2589 .IP "ev_stat_stat (loop, ev_stat *)" 4
2590 .IX Item "ev_stat_stat (loop, ev_stat *)"
2591 Updates the stat buffer immediately with new values. If you change the
2592 watched path in your callback, you could call this function to avoid
2593 detecting this change (while introducing a race condition if you are not
2594 the only one changing the path). Can also be useful simply to find out the
2595 new values.
2596 .IP "ev_statdata attr [read\-only]" 4
2597 .IX Item "ev_statdata attr [read-only]"
2598 The most-recently detected attributes of the file. Although the type is
2599 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2600 suitable for your system, but you can only rely on the POSIX-standardised
2601 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2602 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2603 .IP "ev_statdata prev [read\-only]" 4
2604 .IX Item "ev_statdata prev [read-only]"
2605 The previous attributes of the file. The callback gets invoked whenever
2606 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2607 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,
2608 \&\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.
2609 .IP "ev_tstamp interval [read\-only]" 4
2610 .IX Item "ev_tstamp interval [read-only]"
2611 The specified interval.
2612 .IP "const char *path [read\-only]" 4
2613 .IX Item "const char *path [read-only]"
2614 The file system path that is being watched.
2615 .PP
2616 \fIExamples\fR
2617 .IX Subsection "Examples"
2618 .PP
2619 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2620 .PP
2621 .Vb 10
2622 \& static void
2623 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2624 \& {
2625 \& /* /etc/passwd changed in some way */
2626 \& if (w\->attr.st_nlink)
2627 \& {
2628 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2629 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2630 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2631 \& }
2632 \& else
2633 \& /* you shalt not abuse printf for puts */
2634 \& puts ("wow, /etc/passwd is not there, expect problems. "
2635 \& "if this is windows, they already arrived\en");
2636 \& }
2637 \&
2638 \& ...
2639 \& ev_stat passwd;
2640 \&
2641 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2642 \& ev_stat_start (loop, &passwd);
2643 .Ve
2644 .PP
2645 Example: Like above, but additionally use a one-second delay so we do not
2646 miss updates (however, frequent updates will delay processing, too, so
2647 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2648 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2649 .PP
2650 .Vb 2
2651 \& static ev_stat passwd;
2652 \& static ev_timer timer;
2653 \&
2654 \& static void
2655 \& timer_cb (EV_P_ ev_timer *w, int revents)
2656 \& {
2657 \& ev_timer_stop (EV_A_ w);
2658 \&
2659 \& /* now it\*(Aqs one second after the most recent passwd change */
2660 \& }
2661 \&
2662 \& static void
2663 \& stat_cb (EV_P_ ev_stat *w, int revents)
2664 \& {
2665 \& /* reset the one\-second timer */
2666 \& ev_timer_again (EV_A_ &timer);
2667 \& }
2668 \&
2669 \& ...
2670 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2671 \& ev_stat_start (loop, &passwd);
2672 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2673 .Ve
2674 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2675 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2676 .IX Subsection "ev_idle - when you've got nothing better to do..."
2677 Idle watchers trigger events when no other events of the same or higher
2678 priority are pending (prepare, check and other idle watchers do not count
2679 as receiving \*(L"events\*(R").
2680 .PP
2681 That is, as long as your process is busy handling sockets or timeouts
2682 (or even signals, imagine) of the same or higher priority it will not be
2683 triggered. But when your process is idle (or only lower-priority watchers
2684 are pending), the idle watchers are being called once per event loop
2685 iteration \- until stopped, that is, or your process receives more events
2686 and becomes busy again with higher priority stuff.
2687 .PP
2688 The most noteworthy effect is that as long as any idle watchers are
2689 active, the process will not block when waiting for new events.
2690 .PP
2691 Apart from keeping your process non-blocking (which is a useful
2692 effect on its own sometimes), idle watchers are a good place to do
2693 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2694 event loop has handled all outstanding events.
2695 .PP
2696 \fIWatcher-Specific Functions and Data Members\fR
2697 .IX Subsection "Watcher-Specific Functions and Data Members"
2698 .IP "ev_idle_init (ev_idle *, callback)" 4
2699 .IX Item "ev_idle_init (ev_idle *, callback)"
2700 Initialises and configures the idle watcher \- it has no parameters of any
2701 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2702 believe me.
2703 .PP
2704 \fIExamples\fR
2705 .IX Subsection "Examples"
2706 .PP
2707 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2708 callback, free it. Also, use no error checking, as usual.
2709 .PP
2710 .Vb 7
2711 \& static void
2712 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2713 \& {
2714 \& free (w);
2715 \& // now do something you wanted to do when the program has
2716 \& // no longer anything immediate to do.
2717 \& }
2718 \&
2719 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2720 \& ev_idle_init (idle_watcher, idle_cb);
2721 \& ev_idle_start (loop, idle_watcher);
2722 .Ve
2723 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
2724 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2725 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2726 Prepare and check watchers are usually (but not always) used in pairs:
2727 prepare watchers get invoked before the process blocks and check watchers
2728 afterwards.
2729 .PP
2730 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2731 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2732 watchers. Other loops than the current one are fine, however. The
2733 rationale behind this is that you do not need to check for recursion in
2734 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2735 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2736 called in pairs bracketing the blocking call.
2737 .PP
2738 Their main purpose is to integrate other event mechanisms into libev and
2739 their use is somewhat advanced. They could be used, for example, to track
2740 variable changes, implement your own watchers, integrate net-snmp or a
2741 coroutine library and lots more. They are also occasionally useful if
2742 you cache some data and want to flush it before blocking (for example,
2743 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2744 watcher).
2745 .PP
2746 This is done by examining in each prepare call which file descriptors
2747 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2748 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2749 libraries provide exactly this functionality). Then, in the check watcher,
2750 you check for any events that occurred (by checking the pending status
2751 of all watchers and stopping them) and call back into the library. The
2752 I/O and timer callbacks will never actually be called (but must be valid
2753 nevertheless, because you never know, you know?).
2754 .PP
2755 As another example, the Perl Coro module uses these hooks to integrate
2756 coroutines into libev programs, by yielding to other active coroutines
2757 during each prepare and only letting the process block if no coroutines
2758 are ready to run (it's actually more complicated: it only runs coroutines
2759 with priority higher than or equal to the event loop and one coroutine
2760 of lower priority, but only once, using idle watchers to keep the event
2761 loop from blocking if lower-priority coroutines are active, thus mapping
2762 low-priority coroutines to idle/background tasks).
2763 .PP
2764 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2765 priority, to ensure that they are being run before any other watchers
2766 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2767 .PP
2768 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2769 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2770 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2771 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2772 loops those other event loops might be in an unusable state until their
2773 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2774 others).
2775 .PP
2776 \fIWatcher-Specific Functions and Data Members\fR
2777 .IX Subsection "Watcher-Specific Functions and Data Members"
2778 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2779 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2780 .PD 0
2781 .IP "ev_check_init (ev_check *, callback)" 4
2782 .IX Item "ev_check_init (ev_check *, callback)"
2783 .PD
2784 Initialises and configures the prepare or check watcher \- they have no
2785 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2786 macros, but using them is utterly, utterly, utterly and completely
2787 pointless.
2788 .PP
2789 \fIExamples\fR
2790 .IX Subsection "Examples"
2791 .PP
2792 There are a number of principal ways to embed other event loops or modules
2793 into libev. Here are some ideas on how to include libadns into libev
2794 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2795 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2796 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2797 Glib event loop).
2798 .PP
2799 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2800 and in a check watcher, destroy them and call into libadns. What follows
2801 is pseudo-code only of course. This requires you to either use a low
2802 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2803 the callbacks for the IO/timeout watchers might not have been called yet.
2804 .PP
2805 .Vb 2
2806 \& static ev_io iow [nfd];
2807 \& static ev_timer tw;
2808 \&
2809 \& static void
2810 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2811 \& {
2812 \& }
2813 \&
2814 \& // create io watchers for each fd and a timer before blocking
2815 \& static void
2816 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2817 \& {
2818 \& int timeout = 3600000;
2819 \& struct pollfd fds [nfd];
2820 \& // actual code will need to loop here and realloc etc.
2821 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2822 \&
2823 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2824 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2825 \& ev_timer_start (loop, &tw);
2826 \&
2827 \& // create one ev_io per pollfd
2828 \& for (int i = 0; i < nfd; ++i)
2829 \& {
2830 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2831 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2832 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2833 \&
2834 \& fds [i].revents = 0;
2835 \& ev_io_start (loop, iow + i);
2836 \& }
2837 \& }
2838 \&
2839 \& // stop all watchers after blocking
2840 \& static void
2841 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2842 \& {
2843 \& ev_timer_stop (loop, &tw);
2844 \&
2845 \& for (int i = 0; i < nfd; ++i)
2846 \& {
2847 \& // set the relevant poll flags
2848 \& // could also call adns_processreadable etc. here
2849 \& struct pollfd *fd = fds + i;
2850 \& int revents = ev_clear_pending (iow + i);
2851 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2852 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2853 \&
2854 \& // now stop the watcher
2855 \& ev_io_stop (loop, iow + i);
2856 \& }
2857 \&
2858 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2859 \& }
2860 .Ve
2861 .PP
2862 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2863 in the prepare watcher and would dispose of the check watcher.
2864 .PP
2865 Method 3: If the module to be embedded supports explicit event
2866 notification (libadns does), you can also make use of the actual watcher
2867 callbacks, and only destroy/create the watchers in the prepare watcher.
2868 .PP
2869 .Vb 5
2870 \& static void
2871 \& timer_cb (EV_P_ ev_timer *w, int revents)
2872 \& {
2873 \& adns_state ads = (adns_state)w\->data;
2874 \& update_now (EV_A);
2875 \&
2876 \& adns_processtimeouts (ads, &tv_now);
2877 \& }
2878 \&
2879 \& static void
2880 \& io_cb (EV_P_ ev_io *w, int revents)
2881 \& {
2882 \& adns_state ads = (adns_state)w\->data;
2883 \& update_now (EV_A);
2884 \&
2885 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2886 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2887 \& }
2888 \&
2889 \& // do not ever call adns_afterpoll
2890 .Ve
2891 .PP
2892 Method 4: Do not use a prepare or check watcher because the module you
2893 want to embed is not flexible enough to support it. Instead, you can
2894 override their poll function. The drawback with this solution is that the
2895 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2896 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2897 libglib event loop.
2898 .PP
2899 .Vb 4
2900 \& static gint
2901 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2902 \& {
2903 \& int got_events = 0;
2904 \&
2905 \& for (n = 0; n < nfds; ++n)
2906 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2907 \&
2908 \& if (timeout >= 0)
2909 \& // create/start timer
2910 \&
2911 \& // poll
2912 \& ev_loop (EV_A_ 0);
2913 \&
2914 \& // stop timer again
2915 \& if (timeout >= 0)
2916 \& ev_timer_stop (EV_A_ &to);
2917 \&
2918 \& // stop io watchers again \- their callbacks should have set
2919 \& for (n = 0; n < nfds; ++n)
2920 \& ev_io_stop (EV_A_ iow [n]);
2921 \&
2922 \& return got_events;
2923 \& }
2924 .Ve
2925 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
2926 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
2927 .IX Subsection "ev_embed - when one backend isn't enough..."
2928 This is a rather advanced watcher type that lets you embed one event loop
2929 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2930 loop, other types of watchers might be handled in a delayed or incorrect
2931 fashion and must not be used).
2932 .PP
2933 There are primarily two reasons you would want that: work around bugs and
2934 prioritise I/O.
2935 .PP
2936 As an example for a bug workaround, the kqueue backend might only support
2937 sockets on some platform, so it is unusable as generic backend, but you
2938 still want to make use of it because you have many sockets and it scales
2939 so nicely. In this case, you would create a kqueue-based loop and embed
2940 it into your default loop (which might use e.g. poll). Overall operation
2941 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2942 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2943 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2944 .PP
2945 As for prioritising I/O: under rare circumstances you have the case where
2946 some fds have to be watched and handled very quickly (with low latency),
2947 and even priorities and idle watchers might have too much overhead. In
2948 this case you would put all the high priority stuff in one loop and all
2949 the rest in a second one, and embed the second one in the first.
2950 .PP
2951 As long as the watcher is active, the callback will be invoked every
2952 time there might be events pending in the embedded loop. The callback
2953 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2954 sweep and invoke their callbacks (the callback doesn't need to invoke the
2955 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2956 to give the embedded loop strictly lower priority for example).
2957 .PP
2958 You can also set the callback to \f(CW0\fR, in which case the embed watcher
2959 will automatically execute the embedded loop sweep whenever necessary.
2960 .PP
2961 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2962 is active, i.e., the embedded loop will automatically be forked when the
2963 embedding loop forks. In other cases, the user is responsible for calling
2964 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2965 .PP
2966 Unfortunately, not all backends are embeddable: only the ones returned by
2967 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2968 portable one.
2969 .PP
2970 So when you want to use this feature you will always have to be prepared
2971 that you cannot get an embeddable loop. The recommended way to get around
2972 this is to have a separate variables for your embeddable loop, try to
2973 create it, and if that fails, use the normal loop for everything.
2974 .PP
2975 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2976 .IX Subsection "ev_embed and fork"
2977 .PP
2978 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2979 automatically be applied to the embedded loop as well, so no special
2980 fork handling is required in that case. When the watcher is not running,
2981 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2982 as applicable.
2983 .PP
2984 \fIWatcher-Specific Functions and Data Members\fR
2985 .IX Subsection "Watcher-Specific Functions and Data Members"
2986 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2987 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2988 .PD 0
2989 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2990 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2991 .PD
2992 Configures the watcher to embed the given loop, which must be
2993 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2994 invoked automatically, otherwise it is the responsibility of the callback
2995 to invoke it (it will continue to be called until the sweep has been done,
2996 if you do not want that, you need to temporarily stop the embed watcher).
2997 .IP "ev_embed_sweep (loop, ev_embed *)" 4
2998 .IX Item "ev_embed_sweep (loop, ev_embed *)"
2999 Make a single, non-blocking sweep over the embedded loop. This works
3000 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
3001 appropriate way for embedded loops.
3002 .IP "struct ev_loop *other [read\-only]" 4
3003 .IX Item "struct ev_loop *other [read-only]"
3004 The embedded event loop.
3005 .PP
3006 \fIExamples\fR
3007 .IX Subsection "Examples"
3008 .PP
3009 Example: Try to get an embeddable event loop and embed it into the default
3010 event loop. If that is not possible, use the default loop. The default
3011 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3012 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3013 used).
3014 .PP
3015 .Vb 3
3016 \& struct ev_loop *loop_hi = ev_default_init (0);
3017 \& struct ev_loop *loop_lo = 0;
3018 \& ev_embed embed;
3019 \&
3020 \& // see if there is a chance of getting one that works
3021 \& // (remember that a flags value of 0 means autodetection)
3022 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3023 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3024 \& : 0;
3025 \&
3026 \& // if we got one, then embed it, otherwise default to loop_hi
3027 \& if (loop_lo)
3028 \& {
3029 \& ev_embed_init (&embed, 0, loop_lo);
3030 \& ev_embed_start (loop_hi, &embed);
3031 \& }
3032 \& else
3033 \& loop_lo = loop_hi;
3034 .Ve
3035 .PP
3036 Example: Check if kqueue is available but not recommended and create
3037 a kqueue backend for use with sockets (which usually work with any
3038 kqueue implementation). Store the kqueue/socket\-only event loop in
3039 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3040 .PP
3041 .Vb 3
3042 \& struct ev_loop *loop = ev_default_init (0);
3043 \& struct ev_loop *loop_socket = 0;
3044 \& ev_embed embed;
3045 \&
3046 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048 \& {
3049 \& ev_embed_init (&embed, 0, loop_socket);
3050 \& ev_embed_start (loop, &embed);
3051 \& }
3052 \&
3053 \& if (!loop_socket)
3054 \& loop_socket = loop;
3055 \&
3056 \& // now use loop_socket for all sockets, and loop for everything else
3057 .Ve
3058 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3059 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3060 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3061 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3062 whoever is a good citizen cared to tell libev about it by calling
3063 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3064 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3065 and only in the child after the fork. If whoever good citizen calling
3066 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3067 handlers will be invoked, too, of course.
3068 .PP
3069 \fIThe special problem of life after fork \- how is it possible?\fR
3070 .IX Subsection "The special problem of life after fork - how is it possible?"
3071 .PP
3072 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
3073 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3074 sequence should be handled by libev without any problems.
3075 .PP
3076 This changes when the application actually wants to do event handling
3077 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3078 fork.
3079 .PP
3080 The default mode of operation (for libev, with application help to detect
3081 forks) is to duplicate all the state in the child, as would be expected
3082 when \fIeither\fR the parent \fIor\fR the child process continues.
3083 .PP
3084 When both processes want to continue using libev, then this is usually the
3085 wrong result. In that case, usually one process (typically the parent) is
3086 supposed to continue with all watchers in place as before, while the other
3087 process typically wants to start fresh, i.e. without any active watchers.
3088 .PP
3089 The cleanest and most efficient way to achieve that with libev is to
3090 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3091 use that for new watchers. This has the advantage of not touching more
3092 memory than necessary, and thus avoiding the copy-on-write, and the
3093 disadvantage of having to use multiple event loops (which do not support
3094 signal watchers).
3095 .PP
3096 When this is not possible, or you want to use the default loop for
3097 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3098 \&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
3099 the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
3100 have to be careful not to execute code that modifies those watchers. Note
3101 also that in that case, you have to re-register any signal watchers.
3102 .PP
3103 \fIWatcher-Specific Functions and Data Members\fR
3104 .IX Subsection "Watcher-Specific Functions and Data Members"
3105 .IP "ev_fork_init (ev_signal *, callback)" 4
3106 .IX Item "ev_fork_init (ev_signal *, callback)"
3107 Initialises and configures the fork watcher \- it has no parameters of any
3108 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3109 believe me.
3110 .ie n .SS """ev_async"" \- how to wake up another event loop"
3111 .el .SS "\f(CWev_async\fP \- how to wake up another event loop"
3112 .IX Subsection "ev_async - how to wake up another event loop"
3113 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3114 asynchronous sources such as signal handlers (as opposed to multiple event
3115 loops \- those are of course safe to use in different threads).
3116 .PP
3117 Sometimes, however, you need to wake up another event loop you do not
3118 control, for example because it belongs to another thread. This is what
3119 \&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
3120 can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
3121 safe.
3122 .PP
3123 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3124 too, are asynchronous in nature, and signals, too, will be compressed
3125 (i.e. the number of callback invocations may be less than the number of
3126 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3127 .PP
3128 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3129 just the default loop.
3130 .PP
3131 \fIQueueing\fR
3132 .IX Subsection "Queueing"
3133 .PP
3134 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3135 is that the author does not know of a simple (or any) algorithm for a
3136 multiple-writer-single-reader queue that works in all cases and doesn't
3137 need elaborate support such as pthreads or unportable memory access
3138 semantics.
3139 .PP
3140 That means that if you want to queue data, you have to provide your own
3141 queue. But at least I can tell you how to implement locking around your
3142 queue:
3143 .IP "queueing from a signal handler context" 4
3144 .IX Item "queueing from a signal handler context"
3145 To implement race-free queueing, you simply add to the queue in the signal
3146 handler but you block the signal handler in the watcher callback. Here is
3147 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3148 .Sp
3149 .Vb 1
3150 \& static ev_async mysig;
3151 \&
3152 \& static void
3153 \& sigusr1_handler (void)
3154 \& {
3155 \& sometype data;
3156 \&
3157 \& // no locking etc.
3158 \& queue_put (data);
3159 \& ev_async_send (EV_DEFAULT_ &mysig);
3160 \& }
3161 \&
3162 \& static void
3163 \& mysig_cb (EV_P_ ev_async *w, int revents)
3164 \& {
3165 \& sometype data;
3166 \& sigset_t block, prev;
3167 \&
3168 \& sigemptyset (&block);
3169 \& sigaddset (&block, SIGUSR1);
3170 \& sigprocmask (SIG_BLOCK, &block, &prev);
3171 \&
3172 \& while (queue_get (&data))
3173 \& process (data);
3174 \&
3175 \& if (sigismember (&prev, SIGUSR1)
3176 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3177 \& }
3178 .Ve
3179 .Sp
3180 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3181 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3182 either...).
3183 .IP "queueing from a thread context" 4
3184 .IX Item "queueing from a thread context"
3185 The strategy for threads is different, as you cannot (easily) block
3186 threads but you can easily preempt them, so to queue safely you need to
3187 employ a traditional mutex lock, such as in this pthread example:
3188 .Sp
3189 .Vb 2
3190 \& static ev_async mysig;
3191 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3192 \&
3193 \& static void
3194 \& otherthread (void)
3195 \& {
3196 \& // only need to lock the actual queueing operation
3197 \& pthread_mutex_lock (&mymutex);
3198 \& queue_put (data);
3199 \& pthread_mutex_unlock (&mymutex);
3200 \&
3201 \& ev_async_send (EV_DEFAULT_ &mysig);
3202 \& }
3203 \&
3204 \& static void
3205 \& mysig_cb (EV_P_ ev_async *w, int revents)
3206 \& {
3207 \& pthread_mutex_lock (&mymutex);
3208 \&
3209 \& while (queue_get (&data))
3210 \& process (data);
3211 \&
3212 \& pthread_mutex_unlock (&mymutex);
3213 \& }
3214 .Ve
3215 .PP
3216 \fIWatcher-Specific Functions and Data Members\fR
3217 .IX Subsection "Watcher-Specific Functions and Data Members"
3218 .IP "ev_async_init (ev_async *, callback)" 4
3219 .IX Item "ev_async_init (ev_async *, callback)"
3220 Initialises and configures the async watcher \- it has no parameters of any
3221 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3222 trust me.
3223 .IP "ev_async_send (loop, ev_async *)" 4
3224 .IX Item "ev_async_send (loop, ev_async *)"
3225 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3226 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3227 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3228 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3229 section below on what exactly this means).
3230 .Sp
3231 Note that, as with other watchers in libev, multiple events might get
3232 compressed into a single callback invocation (another way to look at this
3233 is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3234 reset when the event loop detects that).
3235 .Sp
3236 This call incurs the overhead of a system call only once per event loop
3237 iteration, so while the overhead might be noticeable, it doesn't apply to
3238 repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3239 .IP "bool = ev_async_pending (ev_async *)" 4
3240 .IX Item "bool = ev_async_pending (ev_async *)"
3241 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3242 watcher but the event has not yet been processed (or even noted) by the
3243 event loop.
3244 .Sp
3245 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3246 the loop iterates next and checks for the watcher to have become active,
3247 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3248 quickly check whether invoking the loop might be a good idea.
3249 .Sp
3250 Not that this does \fInot\fR check whether the watcher itself is pending,
3251 only whether it has been requested to make this watcher pending: there
3252 is a time window between the event loop checking and resetting the async
3253 notification, and the callback being invoked.
3256 There are some other functions of possible interest. Described. Here. Now.
3257 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3258 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3259 This function combines a simple timer and an I/O watcher, calls your
3260 callback on whichever event happens first and automatically stops both
3261 watchers. This is useful if you want to wait for a single event on an fd
3262 or timeout without having to allocate/configure/start/stop/free one or
3263 more watchers yourself.
3264 .Sp
3265 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3266 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3267 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3268 .Sp
3269 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3270 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3271 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3272 .Sp
3273 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
3274 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3275 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3276 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3277 a timeout and an io event at the same time \- you probably should give io
3278 events precedence.
3279 .Sp
3280 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3281 .Sp
3282 .Vb 7
3283 \& static void stdin_ready (int revents, void *arg)
3284 \& {
3285 \& if (revents & EV_READ)
3286 \& /* stdin might have data for us, joy! */;
3287 \& else if (revents & EV_TIMEOUT)
3288 \& /* doh, nothing entered */;
3289 \& }
3290 \&
3291 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3292 .Ve
3293 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3294 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3295 Feed an event on the given fd, as if a file descriptor backend detected
3296 the given events it.
3297 .IP "ev_feed_signal_event (loop, int signum)" 4
3298 .IX Item "ev_feed_signal_event (loop, int signum)"
3299 Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3300 loop!).
3303 Libev offers a compatibility emulation layer for libevent. It cannot
3304 emulate the internals of libevent, so here are some usage hints:
3305 .IP "\(bu" 4
3306 Use it by including <event.h>, as usual.
3307 .IP "\(bu" 4
3308 The following members are fully supported: ev_base, ev_callback,
3309 ev_arg, ev_fd, ev_res, ev_events.
3310 .IP "\(bu" 4
3311 Avoid using ev_flags and the EVLIST_*\-macros, while it is
3312 maintained by libev, it does not work exactly the same way as in libevent (consider
3313 it a private \s-1API\s0).
3314 .IP "\(bu" 4
3315 Priorities are not currently supported. Initialising priorities
3316 will fail and all watchers will have the same priority, even though there
3317 is an ev_pri field.
3318 .IP "\(bu" 4
3319 In libevent, the last base created gets the signals, in libev, the
3320 first base created (== the default loop) gets the signals.
3321 .IP "\(bu" 4
3322 Other members are not supported.
3323 .IP "\(bu" 4
3324 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
3325 to use the libev header file and library.
3326 .SH "\*(C+ SUPPORT"
3327 .IX Header " SUPPORT"
3328 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3329 you to use some convenience methods to start/stop watchers and also change
3330 the callback model to a model using method callbacks on objects.
3331 .PP
3332 To use it,
3333 .PP
3334 .Vb 1
3335 \& #include <ev++.h>
3336 .Ve
3337 .PP
3338 This automatically includes \fIev.h\fR and puts all of its definitions (many
3339 of them macros) into the global namespace. All \*(C+ specific things are
3340 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3341 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3342 .PP
3343 Care has been taken to keep the overhead low. The only data member the \*(C+
3344 classes add (compared to plain C\-style watchers) is the event loop pointer
3345 that the watcher is associated with (or no additional members at all if
3346 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3347 .PP
3348 Currently, functions, and static and non-static member functions can be
3349 used as callbacks. Other types should be easy to add as long as they only
3350 need one additional pointer for context. If you need support for other
3351 types of functors please contact the author (preferably after implementing
3352 it).
3353 .PP
3354 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3355 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3356 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3357 .IX Item "ev::READ, ev::WRITE etc."
3358 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3359 macros from \fIev.h\fR.
3360 .ie n .IP """ev::tstamp"", ""ev::now""" 4
3361 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3362 .IX Item "ev::tstamp, ev::now"
3363 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3364 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3365 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3366 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3367 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3368 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3369 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3370 defines by many implementations.
3371 .Sp
3372 All of those classes have these methods:
3373 .RS 4
3374 .IP "ev::TYPE::TYPE ()" 4
3375 .IX Item "ev::TYPE::TYPE ()"
3376 .PD 0
3377 .IP "ev::TYPE::TYPE (loop)" 4
3378 .IX Item "ev::TYPE::TYPE (loop)"
3379 .IP "ev::TYPE::~TYPE" 4
3380 .IX Item "ev::TYPE::~TYPE"
3381 .PD
3382 The constructor (optionally) takes an event loop to associate the watcher
3383 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3384 .Sp
3385 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3386 \&\f(CW\*(C`set\*(C'\fR method before starting it.
3387 .Sp
3388 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3389 method to set a callback before you can start the watcher.
3390 .Sp
3391 (The reason why you have to use a method is a limitation in \*(C+ which does
3392 not allow explicit template arguments for constructors).
3393 .Sp
3394 The destructor automatically stops the watcher if it is active.
3395 .IP "w\->set<class, &class::method> (object *)" 4
3396 .IX Item "w->set<class, &class::method> (object *)"
3397 This method sets the callback method to call. The method has to have a
3398 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3399 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3400 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3401 .Sp
3402 This method synthesizes efficient thunking code to call your method from
3403 the C callback that libev requires. If your compiler can inline your
3404 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3405 your compiler is good :), then the method will be fully inlined into the
3406 thunking function, making it as fast as a direct C callback.
3407 .Sp
3408 Example: simple class declaration and watcher initialisation
3409 .Sp
3410 .Vb 4
3411 \& struct myclass
3412 \& {
3413 \& void io_cb (ev::io &w, int revents) { }
3414 \& }
3415 \&
3416 \& myclass obj;
3417 \& ev::io iow;
3418 \& iow.set <myclass, &myclass::io_cb> (&obj);
3419 .Ve
3420 .IP "w\->set (object *)" 4
3421 .IX Item "w->set (object *)"
3422 This is an \fBexperimental\fR feature that might go away in a future version.
3423 .Sp
3424 This is a variation of a method callback \- leaving out the method to call
3425 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3426 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3427 the time. Incidentally, you can then also leave out the template argument
3428 list.
3429 .Sp
3430 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3431 int revents)\*(C'\fR.
3432 .Sp
3433 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3434 .Sp
3435 Example: use a functor object as callback.
3436 .Sp
3437 .Vb 7
3438 \& struct myfunctor
3439 \& {
3440 \& void operator() (ev::io &w, int revents)
3441 \& {
3442 \& ...
3443 \& }
3444 \& }
3445 \&
3446 \& myfunctor f;
3447 \&
3448 \& ev::io w;
3449 \& w.set (&f);
3450 .Ve
3451 .IP "w\->set<function> (void *data = 0)" 4
3452 .IX Item "w->set<function> (void *data = 0)"
3453 Also sets a callback, but uses a static method or plain function as
3454 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3455 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3456 .Sp
3457 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3458 .Sp
3459 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3460 .Sp
3461 Example: Use a plain function as callback.
3462 .Sp
3463 .Vb 2
3464 \& static void io_cb (ev::io &w, int revents) { }
3465 \& iow.set <io_cb> ();
3466 .Ve
3467 .IP "w\->set (loop)" 4
3468 .IX Item "w->set (loop)"
3469 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3470 do this when the watcher is inactive (and not pending either).
3471 .IP "w\->set ([arguments])" 4
3472 .IX Item "w->set ([arguments])"
3473 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3474 called at least once. Unlike the C counterpart, an active watcher gets
3475 automatically stopped and restarted when reconfiguring it with this
3476 method.
3477 .IP "w\->start ()" 4
3478 .IX Item "w->start ()"
3479 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3480 constructor already stores the event loop.
3481 .IP "w\->stop ()" 4
3482 .IX Item "w->stop ()"
3483 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3484 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
3485 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3486 .IX Item "w->again () (ev::timer, ev::periodic only)"
3487 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3488 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3489 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3490 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3491 .IX Item "w->sweep () (ev::embed only)"
3492 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3493 .ie n .IP "w\->update () (""ev::stat"" only)" 4
3494 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3495 .IX Item "w->update () (ev::stat only)"
3496 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3497 .RE
3498 .RS 4
3499 .RE
3500 .PP
3501 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3502 the constructor.
3503 .PP
3504 .Vb 4
3505 \& class myclass
3506 \& {
3507 \& ev::io io ; void io_cb (ev::io &w, int revents);
3508 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3509 \&
3510 \& myclass (int fd)
3511 \& {
3512 \& io .set <myclass, &myclass::io_cb > (this);
3513 \& idle.set <myclass, &myclass::idle_cb> (this);
3514 \&
3515 \& io.start (fd, ev::READ);
3516 \& }
3517 \& };
3518 .Ve
3521 Libev does not offer other language bindings itself, but bindings for a
3522 number of languages exist in the form of third-party packages. If you know
3523 any interesting language binding in addition to the ones listed here, drop
3524 me a note.
3525 .IP "Perl" 4
3526 .IX Item "Perl"
3527 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3528 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3529 there are additional modules that implement libev-compatible interfaces
3530 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),
3531 \&\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
3532 and \f(CW\*(C`EV::Glib\*(C'\fR).
3533 .Sp
3534 It can be found and installed via \s-1CPAN\s0, its homepage is at
3535 <>.
3536 .IP "Python" 4
3537 .IX Item "Python"
3538 Python bindings can be found at <>. It
3539 seems to be quite complete and well-documented.
3540 .IP "Ruby" 4
3541 .IX Item "Ruby"
3542 Tony Arcieri has written a ruby extension that offers access to a subset
3543 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3544 more on top of it. It can be found via gem servers. Its homepage is at
3545 <>.
3546 .Sp
3547 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3548 makes rev work even on mingw.
3549 .IP "Haskell" 4
3550 .IX Item "Haskell"
3551 A haskell binding to libev is available at
3552 <\-bin/hackage\-scripts/package/hlibev>.
3553 .IP "D" 4
3554 .IX Item "D"
3555 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3556 be found at <>.
3557 .IP "Ocaml" 4
3558 .IX Item "Ocaml"
3559 Erkki Seppala has written Ocaml bindings for libev, to be found at
3560 <\-ev/>.
3561 .IP "Lua" 4
3562 .IX Item "Lua"
3563 Brian Maher has written a partial interface to libev
3564 for lua (only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
3565 <\-ev>.
3567 .IX Header "MACRO MAGIC"
3568 Libev can be compiled with a variety of options, the most fundamental
3569 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3570 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3571 .PP
3572 To make it easier to write programs that cope with either variant, the
3573 following macros are defined:
3574 .ie n .IP """EV_A"", ""EV_A_""" 4
3575 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3576 .IX Item "EV_A, EV_A_"
3577 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3578 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3579 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3580 .Sp
3581 .Vb 3
3582 \& ev_unref (EV_A);
3583 \& ev_timer_add (EV_A_ watcher);
3584 \& ev_loop (EV_A_ 0);
3585 .Ve
3586 .Sp
3587 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3588 which is often provided by the following macro.
3589 .ie n .IP """EV_P"", ""EV_P_""" 4
3590 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3591 .IX Item "EV_P, EV_P_"
3592 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3593 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3594 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3595 .Sp
3596 .Vb 2
3597 \& // this is how ev_unref is being declared
3598 \& static void ev_unref (EV_P);
3599 \&
3600 \& // this is how you can declare your typical callback
3601 \& static void cb (EV_P_ ev_timer *w, int revents)
3602 .Ve
3603 .Sp
3604 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3605 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3606 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3607 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3609 Similar to the other two macros, this gives you the value of the default
3610 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3611 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3612 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3614 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3615 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3616 is undefined when the default loop has not been initialised by a previous
3617 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.
3618 .Sp
3619 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3620 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3621 .PP
3622 Example: Declare and initialise a check watcher, utilising the above
3623 macros so it will work regardless of whether multiple loops are supported
3624 or not.
3625 .PP
3626 .Vb 5
3627 \& static void
3628 \& check_cb (EV_P_ ev_timer *w, int revents)
3629 \& {
3630 \& ev_check_stop (EV_A_ w);
3631 \& }
3632 \&
3633 \& ev_check check;
3634 \& ev_check_init (&check, check_cb);
3635 \& ev_check_start (EV_DEFAULT_ &check);
3636 \& ev_loop (EV_DEFAULT_ 0);
3637 .Ve
3639 .IX Header "EMBEDDING"
3640 Libev can (and often is) directly embedded into host
3641 applications. Examples of applications that embed it include the Deliantra
3642 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3643 and rxvt-unicode.
3644 .PP
3645 The goal is to enable you to just copy the necessary files into your
3646 source directory without having to change even a single line in them, so
3647 you can easily upgrade by simply copying (or having a checked-out copy of
3648 libev somewhere in your source tree).
3649 .SS "\s-1FILESETS\s0"
3650 .IX Subsection "FILESETS"
3651 Depending on what features you need you need to include one or more sets of files
3652 in your application.
3653 .PP
3654 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3655 .IX Subsection "CORE EVENT LOOP"
3656 .PP
3657 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3658 configuration (no autoconf):
3659 .PP
3660 .Vb 2
3661 \& #define EV_STANDALONE 1
3662 \& #include "ev.c"
3663 .Ve
3664 .PP
3665 This will automatically include \fIev.h\fR, too, and should be done in a
3666 single C source file only to provide the function implementations. To use
3667 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3668 done by writing a wrapper around \fIev.h\fR that you can include instead and
3669 where you can put other configuration options):
3670 .PP
3671 .Vb 2
3672 \& #define EV_STANDALONE 1
3673 \& #include "ev.h"
3674 .Ve
3675 .PP
3676 Both header files and implementation files can be compiled with a \*(C+
3677 compiler (at least, that's a stated goal, and breakage will be treated
3678 as a bug).
3679 .PP
3680 You need the following files in your source tree, or in a directory
3681 in your include path (e.g. in libev/ when using \-Ilibev):
3682 .PP
3683 .Vb 4
3684 \& ev.h
3685 \& ev.c
3686 \& ev_vars.h
3687 \& ev_wrap.h
3688 \&
3689 \& ev_win32.c required on win32 platforms only
3690 \&
3691 \& ev_select.c only when select backend is enabled (which is enabled by default)
3692 \& ev_poll.c only when poll backend is enabled (disabled by default)
3693 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3694 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3695 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
3696 .Ve
3697 .PP
3698 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
3699 to compile this single file.
3700 .PP
3701 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3703 .PP
3704 To include the libevent compatibility \s-1API\s0, also include:
3705 .PP
3706 .Vb 1
3707 \& #include "event.c"
3708 .Ve
3709 .PP
3710 in the file including \fIev.c\fR, and:
3711 .PP
3712 .Vb 1
3713 \& #include "event.h"
3714 .Ve
3715 .PP
3716 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3717 .PP
3718 You need the following additional files for this:
3719 .PP
3720 .Vb 2
3721 \& event.h
3722 \& event.c
3723 .Ve
3724 .PP
3725 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3726 .IX Subsection "AUTOCONF SUPPORT"
3727 .PP
3728 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3729 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3730 \&\\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3731 include \fIconfig.h\fR and configure itself accordingly.
3732 .PP
3733 For this of course you need the m4 file:
3734 .PP
3735 .Vb 1
3736 \& libev.m4
3737 .Ve
3740 Libev can be configured via a variety of preprocessor symbols you have to
3741 define before including any of its files. The default in the absence of
3742 autoconf is documented for every option.
3743 .IP "\s-1EV_STANDALONE\s0" 4
3745 Must always be \f(CW1\fR if you do not use autoconf configuration, which
3746 keeps libev from including \fIconfig.h\fR, and it also defines dummy
3747 implementations for some libevent functions (such as logging, which is not
3748 supported). It will also not define any of the structs usually found in
3749 \&\fIevent.h\fR that are not directly supported by the libev core alone.
3750 .Sp
3751 In standalone mode, libev will still try to automatically deduce the
3752 configuration, but has to be more conservative.
3753 .IP "\s-1EV_USE_MONOTONIC\s0" 4
3755 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3756 monotonic clock option at both compile time and runtime. Otherwise no
3757 use of the monotonic clock option will be attempted. If you enable this,
3758 you usually have to link against librt or something similar. Enabling it
3759 when the functionality isn't available is safe, though, although you have
3760 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3761 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3762 .IP "\s-1EV_USE_REALTIME\s0" 4
3764 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3765 real-time clock option at compile time (and assume its availability
3766 at runtime if successful). Otherwise no use of the real-time clock
3767 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3768 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3769 correctness. See the note about libraries in the description of
3770 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3771 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3772 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3774 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3775 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3776 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
3777 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3778 programs needlessly. Using a direct syscall is slightly slower (in
3779 theory), because no optimised vdso implementation can be used, but avoids
3780 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3781 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3782 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
3784 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3785 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3786 .IP "\s-1EV_USE_EVENTFD\s0" 4
3787 .IX Item "EV_USE_EVENTFD"
3788 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3789 available and will probe for kernel support at runtime. This will improve
3790 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3791 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3792 2.7 or newer, otherwise disabled.
3793 .IP "\s-1EV_USE_SELECT\s0" 4
3794 .IX Item "EV_USE_SELECT"
3795 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3796 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3797 other method takes over, select will be it. Otherwise the select backend
3798 will not be compiled in.
3799 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3801 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3802 structure. This is useful if libev doesn't compile due to a missing
3803 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
3804 on exotic systems. This usually limits the range of file descriptors to
3805 some low limit such as 1024 or might have other limitations (winsocket
3806 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
3807 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
3808 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3810 When defined to \f(CW1\fR, the select backend will assume that
3811 select/socket/connect etc. don't understand file descriptors but
3812 wants osf handles on win32 (this is the case when the select to
3813 be used is the winsock select). This means that it will call
3814 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3815 it is assumed that all these functions actually work on fds, even
3816 on win32. Should not be defined on non\-win32 platforms.
3817 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
3818 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
3819 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3820 file descriptors to socket handles. When not defining this symbol (the
3821 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3822 correct. In some cases, programs use their own file descriptor management,
3823 in which case they can provide this function to map fds to socket handles.
3824 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
3825 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
3826 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
3827 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
3828 their own fd to handle mapping, overwriting this function makes it easier
3829 to do so. This can be done by defining this macro to an appropriate value.
3830 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
3831 .IX Item "EV_WIN32_CLOSE_FD(fd)"
3832 If programs implement their own fd to handle mapping on win32, then this
3833 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
3834 file descriptors again. Note that the replacement function has to close
3835 the underlying \s-1OS\s0 handle.
3836 .IP "\s-1EV_USE_POLL\s0" 4
3837 .IX Item "EV_USE_POLL"
3838 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3839 backend. Otherwise it will be enabled on non\-win32 platforms. It
3840 takes precedence over select.
3841 .IP "\s-1EV_USE_EPOLL\s0" 4
3842 .IX Item "EV_USE_EPOLL"
3843 If defined to be \f(CW1\fR, libev will compile in support for the Linux
3844 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3845 otherwise another method will be used as fallback. This is the preferred
3846 backend for GNU/Linux systems. If undefined, it will be enabled if the
3847 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3848 .IP "\s-1EV_USE_KQUEUE\s0" 4
3849 .IX Item "EV_USE_KQUEUE"
3850 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3851 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3852 otherwise another method will be used as fallback. This is the preferred
3853 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3854 supports some types of fds correctly (the only platform we found that
3855 supports ptys for example was NetBSD), so kqueue might be compiled in, but
3856 not be used unless explicitly requested. The best way to use it is to find
3857 out whether kqueue supports your type of fd properly and use an embedded
3858 kqueue loop.
3859 .IP "\s-1EV_USE_PORT\s0" 4
3860 .IX Item "EV_USE_PORT"
3861 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
3862 10 port style backend. Its availability will be detected at runtime,
3863 otherwise another method will be used as fallback. This is the preferred
3864 backend for Solaris 10 systems.
3865 .IP "\s-1EV_USE_DEVPOLL\s0" 4
3866 .IX Item "EV_USE_DEVPOLL"
3867 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3868 .IP "\s-1EV_USE_INOTIFY\s0" 4
3869 .IX Item "EV_USE_INOTIFY"
3870 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3871 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3872 be detected at runtime. If undefined, it will be enabled if the headers
3873 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3874 .IP "\s-1EV_ATOMIC_T\s0" 4
3875 .IX Item "EV_ATOMIC_T"
3876 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3877 access is atomic with respect to other threads or signal contexts. No such
3878 type is easily found in the C language, so you can provide your own type
3879 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3880 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3881 .Sp
3882 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3883 (from \fIsignal.h\fR), which is usually good enough on most platforms.
3884 .IP "\s-1EV_H\s0" 4
3885 .IX Item "EV_H"
3886 The name of the \fIev.h\fR header file used to include it. The default if
3887 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3888 used to virtually rename the \fIev.h\fR header file in case of conflicts.
3889 .IP "\s-1EV_CONFIG_H\s0" 4
3890 .IX Item "EV_CONFIG_H"
3891 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3892 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3893 \&\f(CW\*(C`EV_H\*(C'\fR, above.
3894 .IP "\s-1EV_EVENT_H\s0" 4
3895 .IX Item "EV_EVENT_H"
3896 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3897 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3898 .IP "\s-1EV_PROTOTYPES\s0" 4
3900 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3901 prototypes, but still define all the structs and other symbols. This is
3902 occasionally useful if you want to provide your own wrapper functions
3903 around libev functions.
3904 .IP "\s-1EV_MULTIPLICITY\s0" 4
3906 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3907 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3908 additional independent event loops. Otherwise there will be no support
3909 for multiple event loops and there is no first event loop pointer
3910 argument. Instead, all functions act on the single default loop.
3911 .IP "\s-1EV_MINPRI\s0" 4
3912 .IX Item "EV_MINPRI"
3913 .PD 0
3914 .IP "\s-1EV_MAXPRI\s0" 4
3915 .IX Item "EV_MAXPRI"
3916 .PD
3917 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3918 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3919 provide for more priorities by overriding those symbols (usually defined
3920 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3921 .Sp
3922 When doing priority-based operations, libev usually has to linearly search
3923 all the priorities, so having many of them (hundreds) uses a lot of space
3924 and time, so using the defaults of five priorities (\-2 .. +2) is usually
3925 fine.
3926 .Sp
3927 If your embedding application does not need any priorities, defining these
3928 both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3929 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3931 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3932 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3933 code.
3934 .IP "\s-1EV_IDLE_ENABLE\s0" 4
3935 .IX Item "EV_IDLE_ENABLE"
3936 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3937 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3938 code.
3939 .IP "\s-1EV_EMBED_ENABLE\s0" 4
3941 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3942 defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3943 watcher types, which therefore must not be disabled.
3944 .IP "\s-1EV_STAT_ENABLE\s0" 4
3945 .IX Item "EV_STAT_ENABLE"
3946 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3947 defined to be \f(CW0\fR, then they are not.
3948 .IP "\s-1EV_FORK_ENABLE\s0" 4
3949 .IX Item "EV_FORK_ENABLE"
3950 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3951 defined to be \f(CW0\fR, then they are not.
3952 .IP "\s-1EV_ASYNC_ENABLE\s0" 4
3954 If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3955 defined to be \f(CW0\fR, then they are not.
3956 .IP "\s-1EV_MINIMAL\s0" 4
3957 .IX Item "EV_MINIMAL"
3958 If you need to shave off some kilobytes of code at the expense of some
3959 speed (but with the full \s-1API\s0), define this symbol to \f(CW1\fR. Currently this
3960 is used to override some inlining decisions, saves roughly 30% code size
3961 on amd64. It also selects a much smaller 2\-heap for timer management over
3962 the default 4\-heap.
3963 .Sp
3964 You can save even more by disabling watcher types you do not need
3965 and setting \f(CW\*(C`EV_MAXPRI\*(C'\fR == \f(CW\*(C`EV_MINPRI\*(C'\fR. Also, disabling \f(CW\*(C`assert\*(C'\fR
3966 (\f(CW\*(C`\-DNDEBUG\*(C'\fR) will usually reduce code size a lot.
3967 .Sp
3968 Defining \f(CW\*(C`EV_MINIMAL\*(C'\fR to \f(CW2\fR will additionally reduce the core \s-1API\s0 to
3969 provide a bare-bones event library. See \f(CW\*(C`ev.h\*(C'\fR for details on what parts
3970 of the \s-1API\s0 are still available, and do not complain if this subset changes
3971 over time.
3972 .IP "\s-1EV_NSIG\s0" 4
3973 .IX Item "EV_NSIG"
3974 The highest supported signal number, +1 (or, the number of
3975 signals): Normally, libev tries to deduce the maximum number of signals
3976 automatically, but sometimes this fails, in which case it can be
3977 specified. Also, using a lower number than detected (\f(CW32\fR should be
3978 good for about any system in existance) can save some memory, as libev
3979 statically allocates some 12\-24 bytes per signal number.
3980 .IP "\s-1EV_PID_HASHSIZE\s0" 4
3982 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3983 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3984 than enough. If you need to manage thousands of children you might want to
3985 increase this value (\fImust\fR be a power of two).
3986 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3988 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3989 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3990 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3991 watchers you might want to increase this value (\fImust\fR be a power of
3992 two).
3993 .IP "\s-1EV_USE_4HEAP\s0" 4
3994 .IX Item "EV_USE_4HEAP"
3995 Heaps are not very cache-efficient. To improve the cache-efficiency of the
3996 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3997 to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3998 faster performance with many (thousands) of watchers.
3999 .Sp
4000 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
4001 (disabled).
4002 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4003 .IX Item "EV_HEAP_CACHE_AT"
4004 Heaps are not very cache-efficient. To improve the cache-efficiency of the
4005 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4006 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4007 which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4008 but avoids random read accesses on heap changes. This improves performance
4009 noticeably with many (hundreds) of watchers.
4010 .Sp
4011 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
4012 (disabled).
4013 .IP "\s-1EV_VERIFY\s0" 4
4014 .IX Item "EV_VERIFY"
4015 Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
4016 be done: If set to \f(CW0\fR, no internal verification code will be compiled
4017 in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4018 called. If set to \f(CW2\fR, then the internal verification code will be
4019 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4020 verification code will be called very frequently, which will slow down
4021 libev considerably.
4022 .Sp
4023 The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
4024 \&\f(CW0\fR.
4025 .IP "\s-1EV_COMMON\s0" 4
4026 .IX Item "EV_COMMON"
4027 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4028 this macro to a something else you can include more and other types of
4029 members. You have to define it each time you include one of the files,
4030 though, and it must be identical each time.
4031 .Sp
4032 For example, the perl \s-1EV\s0 module uses something like this:
4033 .Sp
4034 .Vb 3
4035 \& #define EV_COMMON \e
4036 \& SV *self; /* contains this struct */ \e
4037 \& SV *cb_sv, *fh /* note no trailing ";" */
4038 .Ve
4039 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4040 .IX Item "EV_CB_DECLARE (type)"
4041 .PD 0
4042 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4043 .IX Item "EV_CB_INVOKE (watcher, revents)"
4044 .IP "ev_set_cb (ev, cb)" 4
4045 .IX Item "ev_set_cb (ev, cb)"
4046 .PD
4047 Can be used to change the callback member declaration in each watcher,
4048 and the way callbacks are invoked and set. Must expand to a struct member
4049 definition and a statement, respectively. See the \fIev.h\fR header file for
4050 their default definitions. One possible use for overriding these is to
4051 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4052 method calls instead of plain function calls in \*(C+.
4053 .SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4054 .IX Subsection "EXPORTED API SYMBOLS"
4055 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4056 exported symbols, you can use the provided \fISymbol.*\fR files which list
4057 all public symbols, one per line:
4058 .PP
4059 .Vb 2
4060 \& Symbols.ev for libev proper
4061 \& Symbols.event for the libevent emulation
4062 .Ve
4063 .PP
4064 This can also be used to rename all public symbols to avoid clashes with
4065 multiple versions of libev linked together (which is obviously bad in
4066 itself, but sometimes it is inconvenient to avoid this).
4067 .PP
4068 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4069 include before including \fIev.h\fR:
4070 .PP
4071 .Vb 1
4072 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4073 .Ve
4074 .PP
4075 This would create a file \fIwrap.h\fR which essentially looks like this:
4076 .PP
4077 .Vb 4
4078 \& #define ev_backend myprefix_ev_backend
4079 \& #define ev_check_start myprefix_ev_check_start
4080 \& #define ev_check_stop myprefix_ev_check_stop
4081 \& ...
4082 .Ve
4083 .SS "\s-1EXAMPLES\s0"
4084 .IX Subsection "EXAMPLES"
4085 For a real-world example of a program the includes libev
4086 verbatim, you can have a look at the \s-1EV\s0 perl module
4087 (<>). It has the libev files in
4088 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4089 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4090 will be compiled. It is pretty complex because it provides its own header
4091 file.
4092 .PP
4093 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4094 that everybody includes and which overrides some configure choices:
4095 .PP
4096 .Vb 9
4097 \& #define EV_MINIMAL 1
4098 \& #define EV_USE_POLL 0
4099 \& #define EV_MULTIPLICITY 0
4100 \& #define EV_PERIODIC_ENABLE 0
4101 \& #define EV_STAT_ENABLE 0
4102 \& #define EV_FORK_ENABLE 0
4103 \& #define EV_CONFIG_H <config.h>
4104 \& #define EV_MINPRI 0
4105 \& #define EV_MAXPRI 0
4106 \&
4107 \& #include "ev++.h"
4108 .Ve
4109 .PP
4110 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4111 .PP
4112 .Vb 2
4113 \& #include "ev_cpp.h"
4114 \& #include "ev.c"
4115 .Ve
4118 .SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4120 \fI\s-1THREADS\s0\fR
4121 .IX Subsection "THREADS"
4122 .PP
4123 All libev functions are reentrant and thread-safe unless explicitly
4124 documented otherwise, but libev implements no locking itself. This means
4125 that you can use as many loops as you want in parallel, as long as there
4126 are no concurrent calls into any libev function with the same loop
4127 parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4128 of course): libev guarantees that different event loops share no data
4129 structures that need any locking.
4130 .PP
4131 Or to put it differently: calls with different loop parameters can be done
4132 concurrently from multiple threads, calls with the same loop parameter
4133 must be done serially (but can be done from different threads, as long as
4134 only one thread ever is inside a call at any point in time, e.g. by using
4135 a mutex per loop).
4136 .PP
4137 Specifically to support threads (and signal handlers), libev implements
4138 so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4139 concurrency on the same event loop, namely waking it up \*(L"from the
4140 outside\*(R".
4141 .PP
4142 If you want to know which design (one loop, locking, or multiple loops
4143 without or something else still) is best for your problem, then I cannot
4144 help you, but here is some generic advice:
4145 .IP "\(bu" 4
4146 most applications have a main thread: use the default libev loop
4147 in that thread, or create a separate thread running only the default loop.
4148 .Sp
4149 This helps integrating other libraries or software modules that use libev
4150 themselves and don't care/know about threading.
4151 .IP "\(bu" 4
4152 one loop per thread is usually a good model.
4153 .Sp
4154 Doing this is almost never wrong, sometimes a better-performance model
4155 exists, but it is always a good start.
4156 .IP "\(bu" 4
4157 other models exist, such as the leader/follower pattern, where one
4158 loop is handed through multiple threads in a kind of round-robin fashion.
4159 .Sp
4160 Choosing a model is hard \- look around, learn, know that usually you can do
4161 better than you currently do :\-)
4162 .IP "\(bu" 4
4163 often you need to talk to some other thread which blocks in the
4164 event loop.
4165 .Sp
4166 \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4167 (or from signal contexts...).
4168 .Sp
4169 An example use would be to communicate signals or other events that only
4170 work in the default loop by registering the signal watcher with the
4171 default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4172 watcher callback into the event loop interested in the signal.
4173 .PP
4174 \s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4176 .PP
4177 Here is a fictitious example of how to run an event loop in a different
4178 thread than where callbacks are being invoked and watchers are
4179 created/added/removed.
4180 .PP
4181 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4182 which uses exactly this technique (which is suited for many high-level
4183 languages).
4184 .PP
4185 The example uses a pthread mutex to protect the loop data, a condition
4186 variable to wait for callback invocations, an async watcher to notify the
4187 event loop thread and an unspecified mechanism to wake up the main thread.
4188 .PP
4189 First, you need to associate some data with the event loop:
4190 .PP
4191 .Vb 6
4192 \& typedef struct {
4193 \& mutex_t lock; /* global loop lock */
4194 \& ev_async async_w;
4195 \& thread_t tid;
4196 \& cond_t invoke_cv;
4197 \& } userdata;
4198 \&
4199 \& void prepare_loop (EV_P)
4200 \& {
4201 \& // for simplicity, we use a static userdata struct.
4202 \& static userdata u;
4203 \&
4204 \& ev_async_init (&u\->async_w, async_cb);
4205 \& ev_async_start (EV_A_ &u\->async_w);
4206 \&
4207 \& pthread_mutex_init (&u\->lock, 0);
4208 \& pthread_cond_init (&u\->invoke_cv, 0);
4209 \&
4210 \& // now associate this with the loop
4211 \& ev_set_userdata (EV_A_ u);
4212 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4213 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4214 \&
4215 \& // then create the thread running ev_loop
4216 \& pthread_create (&u\->tid, 0, l_run, EV_A);
4217 \& }
4218 .Ve
4219 .PP
4220 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4221 solely to wake up the event loop so it takes notice of any new watchers
4222 that might have been added:
4223 .PP
4224 .Vb 5
4225 \& static void
4226 \& async_cb (EV_P_ ev_async *w, int revents)
4227 \& {
4228 \& // just used for the side effects
4229 \& }
4230 .Ve
4231 .PP
4232 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4233 protecting the loop data, respectively.
4234 .PP
4235 .Vb 6
4236 \& static void
4237 \& l_release (EV_P)
4238 \& {
4239 \& userdata *u = ev_userdata (EV_A);
4240 \& pthread_mutex_unlock (&u\->lock);
4241 \& }
4242 \&
4243 \& static void
4244 \& l_acquire (EV_P)
4245 \& {
4246 \& userdata *u = ev_userdata (EV_A);
4247 \& pthread_mutex_lock (&u\->lock);
4248 \& }
4249 .Ve
4250 .PP
4251 The event loop thread first acquires the mutex, and then jumps straight
4252 into \f(CW\*(C`ev_loop\*(C'\fR:
4253 .PP
4254 .Vb 4
4255 \& void *
4256 \& l_run (void *thr_arg)
4257 \& {
4258 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4259 \&
4260 \& l_acquire (EV_A);
4261 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4262 \& ev_loop (EV_A_ 0);
4263 \& l_release (EV_A);
4264 \&
4265 \& return 0;
4266 \& }
4267 .Ve
4268 .PP
4269 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4270 signal the main thread via some unspecified mechanism (signals? pipe
4271 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4272 have been called (in a while loop because a) spurious wakeups are possible
4273 and b) skipping inter-thread-communication when there are no pending
4274 watchers is very beneficial):
4275 .PP
4276 .Vb 4
4277 \& static void
4278 \& l_invoke (EV_P)
4279 \& {
4280 \& userdata *u = ev_userdata (EV_A);
4281 \&
4282 \& while (ev_pending_count (EV_A))
4283 \& {
4284 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4285 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4286 \& }
4287 \& }
4288 .Ve
4289 .PP
4290 Now, whenever the main thread gets told to invoke pending watchers, it
4291 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4292 thread to continue:
4293 .PP
4294 .Vb 4
4295 \& static void
4296 \& real_invoke_pending (EV_P)
4297 \& {
4298 \& userdata *u = ev_userdata (EV_A);
4299 \&
4300 \& pthread_mutex_lock (&u\->lock);
4301 \& ev_invoke_pending (EV_A);
4302 \& pthread_cond_signal (&u\->invoke_cv);
4303 \& pthread_mutex_unlock (&u\->lock);
4304 \& }
4305 .Ve
4306 .PP
4307 Whenever you want to start/stop a watcher or do other modifications to an
4308 event loop, you will now have to lock:
4309 .PP
4310 .Vb 2
4311 \& ev_timer timeout_watcher;
4312 \& userdata *u = ev_userdata (EV_A);
4313 \&
4314 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4315 \&
4316 \& pthread_mutex_lock (&u\->lock);
4317 \& ev_timer_start (EV_A_ &timeout_watcher);
4318 \& ev_async_send (EV_A_ &u\->async_w);
4319 \& pthread_mutex_unlock (&u\->lock);
4320 .Ve
4321 .PP
4322 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4323 an event loop currently blocking in the kernel will have no knowledge
4324 about the newly added timer. By waking up the loop it will pick up any new
4325 watchers in the next event loop iteration.
4326 .PP
4327 \fI\s-1COROUTINES\s0\fR
4328 .IX Subsection "COROUTINES"
4329 .PP
4330 Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4331 libev fully supports nesting calls to its functions from different
4332 coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
4333 different coroutines, and switch freely between both coroutines running
4334 the loop, as long as you don't confuse yourself). The only exception is
4335 that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4336 .PP
4337 Care has been taken to ensure that libev does not keep local state inside
4338 \&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
4339 they do not call any callbacks.
4340 .SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4341 .IX Subsection "COMPILER WARNINGS"
4342 Depending on your compiler and compiler settings, you might get no or a
4343 lot of warnings when compiling libev code. Some people are apparently
4344 scared by this.
4345 .PP
4346 However, these are unavoidable for many reasons. For one, each compiler
4347 has different warnings, and each user has different tastes regarding
4348 warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4349 targeting a specific compiler and compiler-version.
4350 .PP
4351 Another reason is that some compiler warnings require elaborate
4352 workarounds, or other changes to the code that make it less clear and less
4353 maintainable.
4354 .PP
4355 And of course, some compiler warnings are just plain stupid, or simply
4356 wrong (because they don't actually warn about the condition their message
4357 seems to warn about). For example, certain older gcc versions had some
4358 warnings that resulted an extreme number of false positives. These have
4359 been fixed, but some people still insist on making code warn-free with
4360 such buggy versions.
4361 .PP
4362 While libev is written to generate as few warnings as possible,
4363 \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4364 with any compiler warnings enabled unless you are prepared to cope with
4365 them (e.g. by ignoring them). Remember that warnings are just that:
4366 warnings, not errors, or proof of bugs.
4367 .SS "\s-1VALGRIND\s0"
4368 .IX Subsection "VALGRIND"
4369 Valgrind has a special section here because it is a popular tool that is
4370 highly useful. Unfortunately, valgrind reports are very hard to interpret.
4371 .PP
4372 If you think you found a bug (memory leak, uninitialised data access etc.)
4373 in libev, then check twice: If valgrind reports something like:
4374 .PP
4375 .Vb 3
4376 \& ==2274== definitely lost: 0 bytes in 0 blocks.
4377 \& ==2274== possibly lost: 0 bytes in 0 blocks.
4378 \& ==2274== still reachable: 256 bytes in 1 blocks.
4379 .Ve
4380 .PP
4381 Then there is no memory leak, just as memory accounted to global variables
4382 is not a memleak \- the memory is still being referenced, and didn't leak.
4383 .PP
4384 Similarly, under some circumstances, valgrind might report kernel bugs
4385 as if it were a bug in libev (e.g. in realloc or in the poll backend,
4386 although an acceptable workaround has been found here), or it might be
4387 confused.
4388 .PP
4389 Keep in mind that valgrind is a very good tool, but only a tool. Don't
4390 make it into some kind of religion.
4391 .PP
4392 If you are unsure about something, feel free to contact the mailing list
4393 with the full valgrind report and an explanation on why you think this
4394 is a bug in libev (best check the archives, too :). However, don't be
4395 annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4396 of learning how to interpret valgrind properly.
4397 .PP
4398 If you need, for some reason, empty reports from valgrind for your project
4399 I suggest using suppression lists.
4402 .SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4404 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4405 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4406 model. Libev still offers limited functionality on this platform in
4407 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4408 descriptors. This only applies when using Win32 natively, not when using
4409 e.g. cygwin.
4410 .PP
4411 Lifting these limitations would basically require the full
4412 re-implementation of the I/O system. If you are into these kinds of
4413 things, then note that glib does exactly that for you in a very portable
4414 way (note also that glib is the slowest event library known to man).
4415 .PP
4416 There is no supported compilation method available on windows except
4417 embedding it into other applications.
4418 .PP
4419 Sensible signal handling is officially unsupported by Microsoft \- libev
4420 tries its best, but under most conditions, signals will simply not work.
4421 .PP
4422 Not a libev limitation but worth mentioning: windows apparently doesn't
4423 accept large writes: instead of resulting in a partial write, windows will
4424 either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4425 so make sure you only write small amounts into your sockets (less than a
4426 megabyte seems safe, but this apparently depends on the amount of memory
4427 available).
4428 .PP
4429 Due to the many, low, and arbitrary limits on the win32 platform and
4430 the abysmal performance of winsockets, using a large number of sockets
4431 is not recommended (and not reasonable). If your program needs to use
4432 more than a hundred or so sockets, then likely it needs to use a totally
4433 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4434 notification model, which cannot be implemented efficiently on windows
4435 (due to Microsoft monopoly games).
4436 .PP
4437 A typical way to use libev under windows is to embed it (see the embedding
4438 section for details) and use the following \fIevwrap.h\fR header file instead
4439 of \fIev.h\fR:
4440 .PP
4441 .Vb 2
4442 \& #define EV_STANDALONE /* keeps ev from requiring config.h */
4443 \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4444 \&
4445 \& #include "ev.h"
4446 .Ve
4447 .PP
4448 And compile the following \fIevwrap.c\fR file into your project (make sure
4449 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4450 .PP
4451 .Vb 2
4452 \& #include "evwrap.h"
4453 \& #include "ev.c"
4454 .Ve
4455 .IP "The winsocket select function" 4
4456 .IX Item "The winsocket select function"
4457 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4458 requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4459 also extremely buggy). This makes select very inefficient, and also
4460 requires a mapping from file descriptors to socket handles (the Microsoft
4461 C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4462 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4463 \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4464 .Sp
4465 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4466 libraries and raw winsocket select is:
4467 .Sp
4468 .Vb 2
4469 \& #define EV_USE_SELECT 1
4470 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4471 .Ve
4472 .Sp
4473 Note that winsockets handling of fd sets is O(n), so you can easily get a
4474 complexity in the O(nA\*^X) range when using win32.
4475 .IP "Limited number of file descriptors" 4
4476 .IX Item "Limited number of file descriptors"
4477 Windows has numerous arbitrary (and low) limits on things.
4478 .Sp
4479 Early versions of winsocket's select only supported waiting for a maximum
4480 of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4481 can only wait for \f(CW64\fR things at the same time internally; Microsoft
4482 recommends spawning a chain of threads and wait for 63 handles and the
4483 previous thread in each. Sounds great!).
4484 .Sp
4485 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4486 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4487 call (which might be in libev or elsewhere, for example, perl and many
4488 other interpreters do their own select emulation on windows).
4489 .Sp
4490 Another limit is the number of file descriptors in the Microsoft runtime
4491 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4492 fetish or something like this inside Microsoft). You can increase this
4493 by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4494 (another arbitrary limit), but is broken in many versions of the Microsoft
4495 runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4496 (depending on windows version and/or the phase of the moon). To get more,
4497 you need to wrap all I/O functions and provide your own fd management, but
4498 the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4501 In addition to a working ISO-C implementation and of course the
4502 backend-specific APIs, libev relies on a few additional extensions:
4503 .ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4504 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4505 .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4506 Libev assumes not only that all watcher pointers have the same internal
4507 structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4508 assumes that the same (machine) code can be used to call any watcher
4509 callback: The watcher callbacks have different type signatures, but libev
4510 calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4511 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4512 .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4513 .IX Item "sig_atomic_t volatile must be thread-atomic as well"
4514 The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4515 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4516 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4517 believed to be sufficiently portable.
4518 .ie n .IP """sigprocmask"" must work in a threaded environment" 4
4519 .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4520 .IX Item "sigprocmask must work in a threaded environment"
4521 Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4522 allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4523 pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4524 thread\*(R" or will block signals process-wide, both behaviours would
4525 be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4526 \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4527 .Sp
4528 The most portable way to handle signals is to block signals in all threads
4529 except the initial one, and run the default loop in the initial thread as
4530 well.
4531 .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4532 .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4533 .IX Item "long must be large enough for common memory allocation sizes"
4534 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4535 instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4536 systems (Microsoft...) this might be unexpectedly low, but is still at
4537 least 31 bits everywhere, which is enough for hundreds of millions of
4538 watchers.
4539 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4540 .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4541 .IX Item "double must hold a time value in seconds with enough accuracy"
4542 The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4543 have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4544 enough for at least into the year 4000. This requirement is fulfilled by
4545 implementations implementing \s-1IEEE\s0 754, which is basically all existing
4546 ones. With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least
4547 2200.
4548 .PP
4549 If you know of other additional requirements drop me a note.
4552 In this section the complexities of (many of) the algorithms used inside
4553 libev will be documented. For complexity discussions about backends see
4554 the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4555 .PP
4556 All of the following are about amortised time: If an array needs to be
4557 extended, libev needs to realloc and move the whole array, but this
4558 happens asymptotically rarer with higher number of elements, so O(1) might
4559 mean that libev does a lengthy realloc operation in rare cases, but on
4560 average it is much faster and asymptotically approaches constant time.
4561 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4562 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4563 This means that, when you have a watcher that triggers in one hour and
4564 there are 100 watchers that would trigger before that, then inserting will
4565 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4566 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4567 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4568 That means that changing a timer costs less than removing/adding them,
4569 as only the relative motion in the event queue has to be paid for.
4570 .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4571 .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4572 These just add the watcher into an array or at the head of a list.
4573 .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4574 .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4575 .PD 0
4576 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4577 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4578 .PD
4579 These watchers are stored in lists, so they need to be walked to find the
4580 correct watcher to remove. The lists are usually short (you don't usually
4581 have many watchers waiting for the same fd or signal: one is typical, two
4582 is rare).
4583 .IP "Finding the next timer in each loop iteration: O(1)" 4
4584 .IX Item "Finding the next timer in each loop iteration: O(1)"
4585 By virtue of using a binary or 4\-heap, the next timer is always found at a
4586 fixed position in the storage array.
4587 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4588 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4589 A change means an I/O watcher gets started or stopped, which requires
4590 libev to recalculate its status (and possibly tell the kernel, depending
4591 on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4592 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
4593 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
4594 .PD 0
4595 .IP "Priority handling: O(number_of_priorities)" 4
4596 .IX Item "Priority handling: O(number_of_priorities)"
4597 .PD
4598 Priorities are implemented by allocating some space for each
4599 priority. When doing priority-based operations, libev usually has to
4600 linearly search all the priorities, but starting/stopping and activating
4601 watchers becomes O(1) with respect to priority handling.
4602 .IP "Sending an ev_async: O(1)" 4
4603 .IX Item "Sending an ev_async: O(1)"
4604 .PD 0
4605 .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4606 .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4607 .IP "Processing signals: O(max_signal_number)" 4
4608 .IX Item "Processing signals: O(max_signal_number)"
4609 .PD
4610 Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4611 calls in the current loop iteration. Checking for async and signal events
4612 involves iterating over all running async watchers or all signal numbers.
4614 .IX Header "GLOSSARY"
4615 .IP "active" 4
4616 .IX Item "active"
4617 A watcher is active as long as it has been started (has been attached to
4618 an event loop) but not yet stopped (disassociated from the event loop).
4619 .IP "application" 4
4620 .IX Item "application"
4621 In this document, an application is whatever is using libev.
4622 .IP "callback" 4
4623 .IX Item "callback"
4624 The address of a function that is called when some event has been
4625 detected. Callbacks are being passed the event loop, the watcher that
4626 received the event, and the actual event bitset.
4627 .IP "callback invocation" 4
4628 .IX Item "callback invocation"
4629 The act of calling the callback associated with a watcher.
4630 .IP "event" 4
4631 .IX Item "event"
4632 A change of state of some external event, such as data now being available
4633 for reading on a file descriptor, time having passed or simply not having
4634 any other events happening anymore.
4635 .Sp
4636 In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
4637 \&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
4638 .IP "event library" 4
4639 .IX Item "event library"
4640 A software package implementing an event model and loop.
4641 .IP "event loop" 4
4642 .IX Item "event loop"
4643 An entity that handles and processes external events and converts them
4644 into callback invocations.
4645 .IP "event model" 4
4646 .IX Item "event model"
4647 The model used to describe how an event loop handles and processes
4648 watchers and events.
4649 .IP "pending" 4
4650 .IX Item "pending"
4651 A watcher is pending as soon as the corresponding event has been detected,
4652 and stops being pending as soon as the watcher will be invoked or its
4653 pending status is explicitly cleared by the application.
4654 .Sp
4655 A watcher can be pending, but not active. Stopping a watcher also clears
4656 its pending status.
4657 .IP "real time" 4
4658 .IX Item "real time"
4659 The physical time that is observed. It is apparently strictly monotonic :)
4660 .IP "wall-clock time" 4
4661 .IX Item "wall-clock time"
4662 The time and date as shown on clocks. Unlike real time, it can actually
4663 be wrong and jump forwards and backwards, e.g. when the you adjust your
4664 clock.
4665 .IP "watcher" 4
4666 .IX Item "watcher"
4667 A data structure that describes interest in certain events. Watchers need
4668 to be started (attached to an event loop) before they can receive events.
4669 .IP "watcher invocation" 4
4670 .IX Item "watcher invocation"
4671 The act of calling the callback associated with a watcher.
4672 .SH "AUTHOR"
4673 .IX Header "AUTHOR"
4674 Marc Lehmann <>, with repeated corrections by Mikael Magnusson.