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Revision: 1.74
Committed: Wed Nov 19 10:33:32 2008 UTC (15 years, 8 months ago) by root
Branch: MAIN
CVS Tags: rel-3_49
Changes since 1.73: +43 -15 lines
Log Message:
3.49

File Contents

# Content
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131 .rm #[ #] #H #V #F C
132 .\" ========================================================================
133 .\"
134 .IX Title "LIBEV 3"
135 .TH LIBEV 3 "2008-11-17" "libev-3.49" "libev - high performance full featured event loop"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137 .\" way too many mistakes in technical documents.
138 .if n .ad l
139 .nh
140 .SH "NAME"
141 libev \- a high performance full\-featured event loop written in C
142 .SH "SYNOPSIS"
143 .IX Header "SYNOPSIS"
144 .Vb 1
145 \& #include <ev.h>
146 .Ve
147 .Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
148 .IX Subsection "EXAMPLE PROGRAM"
149 .Vb 2
150 \& // a single header file is required
151 \& #include <ev.h>
152 \&
153 \& #include <stdio.h> // for puts
154 \&
155 \& // every watcher type has its own typedef\*(Aqd struct
156 \& // with the name ev_TYPE
157 \& ev_io stdin_watcher;
158 \& ev_timer timeout_watcher;
159 \&
160 \& // all watcher callbacks have a similar signature
161 \& // this callback is called when data is readable on stdin
162 \& static void
163 \& stdin_cb (EV_P_ ev_io *w, int revents)
164 \& {
165 \& puts ("stdin ready");
166 \& // for one\-shot events, one must manually stop the watcher
167 \& // with its corresponding stop function.
168 \& ev_io_stop (EV_A_ w);
169 \&
170 \& // this causes all nested ev_loop\*(Aqs to stop iterating
171 \& ev_unloop (EV_A_ EVUNLOOP_ALL);
172 \& }
173 \&
174 \& // another callback, this time for a time\-out
175 \& static void
176 \& timeout_cb (EV_P_ ev_timer *w, int revents)
177 \& {
178 \& puts ("timeout");
179 \& // this causes the innermost ev_loop to stop iterating
180 \& ev_unloop (EV_A_ EVUNLOOP_ONE);
181 \& }
182 \&
183 \& int
184 \& main (void)
185 \& {
186 \& // use the default event loop unless you have special needs
187 \& ev_loop *loop = ev_default_loop (0);
188 \&
189 \& // initialise an io watcher, then start it
190 \& // this one will watch for stdin to become readable
191 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
192 \& ev_io_start (loop, &stdin_watcher);
193 \&
194 \& // initialise a timer watcher, then start it
195 \& // simple non\-repeating 5.5 second timeout
196 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
197 \& ev_timer_start (loop, &timeout_watcher);
198 \&
199 \& // now wait for events to arrive
200 \& ev_loop (loop, 0);
201 \&
202 \& // unloop was called, so exit
203 \& return 0;
204 \& }
205 .Ve
206 .SH "DESCRIPTION"
207 .IX Header "DESCRIPTION"
208 The newest version of this document is also available as an html-formatted
209 web page you might find easier to navigate when reading it for the first
210 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
211 .PP
212 Libev is an event loop: you register interest in certain events (such as a
213 file descriptor being readable or a timeout occurring), and it will manage
214 these event sources and provide your program with events.
215 .PP
216 To do this, it must take more or less complete control over your process
217 (or thread) by executing the \fIevent loop\fR handler, and will then
218 communicate events via a callback mechanism.
219 .PP
220 You register interest in certain events by registering so-called \fIevent
221 watchers\fR, which are relatively small C structures you initialise with the
222 details of the event, and then hand it over to libev by \fIstarting\fR the
223 watcher.
224 .Sh "\s-1FEATURES\s0"
225 .IX Subsection "FEATURES"
226 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
227 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
228 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
229 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
230 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
231 (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
232 watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
233 \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
234 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
235 (\f(CW\*(C`ev_fork\*(C'\fR).
236 .PP
237 It also is quite fast (see this
238 benchmark comparing it to libevent
239 for example).
240 .Sh "\s-1CONVENTIONS\s0"
241 .IX Subsection "CONVENTIONS"
242 Libev is very configurable. In this manual the default (and most common)
243 configuration will be described, which supports multiple event loops. For
244 more info about various configuration options please have a look at
245 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
246 for multiple event loops, then all functions taking an initial argument of
247 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`ev_loop *\*(C'\fR) will not have
248 this argument.
249 .Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
250 .IX Subsection "TIME REPRESENTATION"
251 Libev represents time as a single floating point number, representing the
252 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
253 the beginning of 1970, details are complicated, don't ask). This type is
254 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
255 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
256 it, you should treat it as some floating point value. Unlike the name
257 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
258 throughout libev.
259 .SH "ERROR HANDLING"
260 .IX Header "ERROR HANDLING"
261 Libev knows three classes of errors: operating system errors, usage errors
262 and internal errors (bugs).
263 .PP
264 When libev catches an operating system error it cannot handle (for example
265 a system call indicating a condition libev cannot fix), it calls the callback
266 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
267 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
268 ()\*(C'\fR.
269 .PP
270 When libev detects a usage error such as a negative timer interval, then
271 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
272 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
273 the libev caller and need to be fixed there.
274 .PP
275 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
276 extensive consistency checking code. These do not trigger under normal
277 circumstances, as they indicate either a bug in libev or worse.
278 .SH "GLOBAL FUNCTIONS"
279 .IX Header "GLOBAL FUNCTIONS"
280 These functions can be called anytime, even before initialising the
281 library in any way.
282 .IP "ev_tstamp ev_time ()" 4
283 .IX Item "ev_tstamp ev_time ()"
284 Returns the current time as libev would use it. Please note that the
285 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
286 you actually want to know.
287 .IP "ev_sleep (ev_tstamp interval)" 4
288 .IX Item "ev_sleep (ev_tstamp interval)"
289 Sleep for the given interval: The current thread will be blocked until
290 either it is interrupted or the given time interval has passed. Basically
291 this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
292 .IP "int ev_version_major ()" 4
293 .IX Item "int ev_version_major ()"
294 .PD 0
295 .IP "int ev_version_minor ()" 4
296 .IX Item "int ev_version_minor ()"
297 .PD
298 You can find out the major and minor \s-1ABI\s0 version numbers of the library
299 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
300 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
301 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
302 version of the library your program was compiled against.
303 .Sp
304 These version numbers refer to the \s-1ABI\s0 version of the library, not the
305 release version.
306 .Sp
307 Usually, it's a good idea to terminate if the major versions mismatch,
308 as this indicates an incompatible change. Minor versions are usually
309 compatible to older versions, so a larger minor version alone is usually
310 not a problem.
311 .Sp
312 Example: Make sure we haven't accidentally been linked against the wrong
313 version.
314 .Sp
315 .Vb 3
316 \& assert (("libev version mismatch",
317 \& ev_version_major () == EV_VERSION_MAJOR
318 \& && ev_version_minor () >= EV_VERSION_MINOR));
319 .Ve
320 .IP "unsigned int ev_supported_backends ()" 4
321 .IX Item "unsigned int ev_supported_backends ()"
322 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
323 value) compiled into this binary of libev (independent of their
324 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
325 a description of the set values.
326 .Sp
327 Example: make sure we have the epoll method, because yeah this is cool and
328 a must have and can we have a torrent of it please!!!11
329 .Sp
330 .Vb 2
331 \& assert (("sorry, no epoll, no sex",
332 \& ev_supported_backends () & EVBACKEND_EPOLL));
333 .Ve
334 .IP "unsigned int ev_recommended_backends ()" 4
335 .IX Item "unsigned int ev_recommended_backends ()"
336 Return the set of all backends compiled into this binary of libev and also
337 recommended for this platform. This set is often smaller than the one
338 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
339 most BSDs and will not be auto-detected unless you explicitly request it
340 (assuming you know what you are doing). This is the set of backends that
341 libev will probe for if you specify no backends explicitly.
342 .IP "unsigned int ev_embeddable_backends ()" 4
343 .IX Item "unsigned int ev_embeddable_backends ()"
344 Returns the set of backends that are embeddable in other event loops. This
345 is the theoretical, all-platform, value. To find which backends
346 might be supported on the current system, you would need to look at
347 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
348 recommended ones.
349 .Sp
350 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
351 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
352 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
353 Sets the allocation function to use (the prototype is similar \- the
354 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
355 used to allocate and free memory (no surprises here). If it returns zero
356 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
357 or take some potentially destructive action.
358 .Sp
359 Since some systems (at least OpenBSD and Darwin) fail to implement
360 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
361 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
362 .Sp
363 You could override this function in high-availability programs to, say,
364 free some memory if it cannot allocate memory, to use a special allocator,
365 or even to sleep a while and retry until some memory is available.
366 .Sp
367 Example: Replace the libev allocator with one that waits a bit and then
368 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
369 .Sp
370 .Vb 6
371 \& static void *
372 \& persistent_realloc (void *ptr, size_t size)
373 \& {
374 \& for (;;)
375 \& {
376 \& void *newptr = realloc (ptr, size);
377 \&
378 \& if (newptr)
379 \& return newptr;
380 \&
381 \& sleep (60);
382 \& }
383 \& }
384 \&
385 \& ...
386 \& ev_set_allocator (persistent_realloc);
387 .Ve
388 .IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
389 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
390 Set the callback function to call on a retryable system call error (such
391 as failed select, poll, epoll_wait). The message is a printable string
392 indicating the system call or subsystem causing the problem. If this
393 callback is set, then libev will expect it to remedy the situation, no
394 matter what, when it returns. That is, libev will generally retry the
395 requested operation, or, if the condition doesn't go away, do bad stuff
396 (such as abort).
397 .Sp
398 Example: This is basically the same thing that libev does internally, too.
399 .Sp
400 .Vb 6
401 \& static void
402 \& fatal_error (const char *msg)
403 \& {
404 \& perror (msg);
405 \& abort ();
406 \& }
407 \&
408 \& ...
409 \& ev_set_syserr_cb (fatal_error);
410 .Ve
411 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
412 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
413 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
414 is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
415 \&\fIfunction\fR).
416 .PP
417 The library knows two types of such loops, the \fIdefault\fR loop, which
418 supports signals and child events, and dynamically created loops which do
419 not.
420 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
421 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
422 This will initialise the default event loop if it hasn't been initialised
423 yet and return it. If the default loop could not be initialised, returns
424 false. If it already was initialised it simply returns it (and ignores the
425 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
426 .Sp
427 If you don't know what event loop to use, use the one returned from this
428 function.
429 .Sp
430 Note that this function is \fInot\fR thread-safe, so if you want to use it
431 from multiple threads, you have to lock (note also that this is unlikely,
432 as loops cannot be shared easily between threads anyway).
433 .Sp
434 The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
435 \&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
436 for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
437 create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
438 can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
439 \&\f(CW\*(C`ev_default_init\*(C'\fR.
440 .Sp
441 The flags argument can be used to specify special behaviour or specific
442 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
443 .Sp
444 The following flags are supported:
445 .RS 4
446 .ie n .IP """EVFLAG_AUTO""" 4
447 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
448 .IX Item "EVFLAG_AUTO"
449 The default flags value. Use this if you have no clue (it's the right
450 thing, believe me).
451 .ie n .IP """EVFLAG_NOENV""" 4
452 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
453 .IX Item "EVFLAG_NOENV"
454 If this flag bit is or'ed into the flag value (or the program runs setuid
455 or setgid) then libev will \fInot\fR look at the environment variable
456 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
457 override the flags completely if it is found in the environment. This is
458 useful to try out specific backends to test their performance, or to work
459 around bugs.
460 .ie n .IP """EVFLAG_FORKCHECK""" 4
461 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
462 .IX Item "EVFLAG_FORKCHECK"
463 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
464 a fork, you can also make libev check for a fork in each iteration by
465 enabling this flag.
466 .Sp
467 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
468 and thus this might slow down your event loop if you do a lot of loop
469 iterations and little real work, but is usually not noticeable (on my
470 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
471 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
472 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
473 .Sp
474 The big advantage of this flag is that you can forget about fork (and
475 forget about forgetting to tell libev about forking) when you use this
476 flag.
477 .Sp
478 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
479 environment variable.
480 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
481 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
482 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
483 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
484 libev tries to roll its own fd_set with no limits on the number of fds,
485 but if that fails, expect a fairly low limit on the number of fds when
486 using this backend. It doesn't scale too well (O(highest_fd)), but its
487 usually the fastest backend for a low number of (low-numbered :) fds.
488 .Sp
489 To get good performance out of this backend you need a high amount of
490 parallelism (most of the file descriptors should be busy). If you are
491 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
492 connections as possible during one iteration. You might also want to have
493 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
494 readiness notifications you get per iteration.
495 .Sp
496 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
497 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
498 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
499 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
500 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
501 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
502 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
503 than select, but handles sparse fds better and has no artificial
504 limit on the number of fds you can use (except it will slow down
505 considerably with a lot of inactive fds). It scales similarly to select,
506 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
507 performance tips.
508 .Sp
509 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
510 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
511 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
512 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
513 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
514 For few fds, this backend is a bit little slower than poll and select,
515 but it scales phenomenally better. While poll and select usually scale
516 like O(total_fds) where n is the total number of fds (or the highest fd),
517 epoll scales either O(1) or O(active_fds).
518 .Sp
519 The epoll mechanism deserves honorable mention as the most misdesigned
520 of the more advanced event mechanisms: mere annoyances include silently
521 dropping file descriptors, requiring a system call per change per file
522 descriptor (and unnecessary guessing of parameters), problems with dup and
523 so on. The biggest issue is fork races, however \- if a program forks then
524 \&\fIboth\fR parent and child process have to recreate the epoll set, which can
525 take considerable time (one syscall per file descriptor) and is of course
526 hard to detect.
527 .Sp
528 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
529 of course \fIdoesn't\fR, and epoll just loves to report events for totally
530 \&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
531 even remove them from the set) than registered in the set (especially
532 on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
533 employing an additional generation counter and comparing that against the
534 events to filter out spurious ones, recreating the set when required.
535 .Sp
536 While stopping, setting and starting an I/O watcher in the same iteration
537 will result in some caching, there is still a system call per such
538 incident (because the same \fIfile descriptor\fR could point to a different
539 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
540 file descriptors might not work very well if you register events for both
541 file descriptors.
542 .Sp
543 Best performance from this backend is achieved by not unregistering all
544 watchers for a file descriptor until it has been closed, if possible,
545 i.e. keep at least one watcher active per fd at all times. Stopping and
546 starting a watcher (without re-setting it) also usually doesn't cause
547 extra overhead. A fork can both result in spurious notifications as well
548 as in libev having to destroy and recreate the epoll object, which can
549 take considerable time and thus should be avoided.
550 .Sp
551 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
552 faster than epoll for maybe up to a hundred file descriptors, depending on
553 the usage. So sad.
554 .Sp
555 While nominally embeddable in other event loops, this feature is broken in
556 all kernel versions tested so far.
557 .Sp
558 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
559 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
560 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
561 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
562 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
563 Kqueue deserves special mention, as at the time of this writing, it
564 was broken on all BSDs except NetBSD (usually it doesn't work reliably
565 with anything but sockets and pipes, except on Darwin, where of course
566 it's completely useless). Unlike epoll, however, whose brokenness
567 is by design, these kqueue bugs can (and eventually will) be fixed
568 without \s-1API\s0 changes to existing programs. For this reason it's not being
569 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
570 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
571 system like NetBSD.
572 .Sp
573 You still can embed kqueue into a normal poll or select backend and use it
574 only for sockets (after having made sure that sockets work with kqueue on
575 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
576 .Sp
577 It scales in the same way as the epoll backend, but the interface to the
578 kernel is more efficient (which says nothing about its actual speed, of
579 course). While stopping, setting and starting an I/O watcher does never
580 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
581 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
582 sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
583 cases
584 .Sp
585 This backend usually performs well under most conditions.
586 .Sp
587 While nominally embeddable in other event loops, this doesn't work
588 everywhere, so you might need to test for this. And since it is broken
589 almost everywhere, you should only use it when you have a lot of sockets
590 (for which it usually works), by embedding it into another event loop
591 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and, did I mention it,
592 using it only for sockets.
593 .Sp
594 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
595 \&\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
596 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
597 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
598 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
599 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
600 This is not implemented yet (and might never be, unless you send me an
601 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
602 and is not embeddable, which would limit the usefulness of this backend
603 immensely.
604 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
605 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
606 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
607 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
608 it's really slow, but it still scales very well (O(active_fds)).
609 .Sp
610 Please note that Solaris event ports can deliver a lot of spurious
611 notifications, so you need to use non-blocking I/O or other means to avoid
612 blocking when no data (or space) is available.
613 .Sp
614 While this backend scales well, it requires one system call per active
615 file descriptor per loop iteration. For small and medium numbers of file
616 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
617 might perform better.
618 .Sp
619 On the positive side, with the exception of the spurious readiness
620 notifications, this backend actually performed fully to specification
621 in all tests and is fully embeddable, which is a rare feat among the
622 OS-specific backends (I vastly prefer correctness over speed hacks).
623 .Sp
624 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
625 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
626 .ie n .IP """EVBACKEND_ALL""" 4
627 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
628 .IX Item "EVBACKEND_ALL"
629 Try all backends (even potentially broken ones that wouldn't be tried
630 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
631 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
632 .Sp
633 It is definitely not recommended to use this flag.
634 .RE
635 .RS 4
636 .Sp
637 If one or more of these are or'ed into the flags value, then only these
638 backends will be tried (in the reverse order as listed here). If none are
639 specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
640 .Sp
641 Example: This is the most typical usage.
642 .Sp
643 .Vb 2
644 \& if (!ev_default_loop (0))
645 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
646 .Ve
647 .Sp
648 Example: Restrict libev to the select and poll backends, and do not allow
649 environment settings to be taken into account:
650 .Sp
651 .Vb 1
652 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
653 .Ve
654 .Sp
655 Example: Use whatever libev has to offer, but make sure that kqueue is
656 used if available (warning, breaks stuff, best use only with your own
657 private event loop and only if you know the \s-1OS\s0 supports your types of
658 fds):
659 .Sp
660 .Vb 1
661 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
662 .Ve
663 .RE
664 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
665 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
666 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
667 always distinct from the default loop. Unlike the default loop, it cannot
668 handle signal and child watchers, and attempts to do so will be greeted by
669 undefined behaviour (or a failed assertion if assertions are enabled).
670 .Sp
671 Note that this function \fIis\fR thread-safe, and the recommended way to use
672 libev with threads is indeed to create one loop per thread, and using the
673 default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
674 .Sp
675 Example: Try to create a event loop that uses epoll and nothing else.
676 .Sp
677 .Vb 3
678 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
679 \& if (!epoller)
680 \& fatal ("no epoll found here, maybe it hides under your chair");
681 .Ve
682 .IP "ev_default_destroy ()" 4
683 .IX Item "ev_default_destroy ()"
684 Destroys the default loop again (frees all memory and kernel state
685 etc.). None of the active event watchers will be stopped in the normal
686 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
687 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
688 calling this function, or cope with the fact afterwards (which is usually
689 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
690 for example).
691 .Sp
692 Note that certain global state, such as signal state (and installed signal
693 handlers), will not be freed by this function, and related watchers (such
694 as signal and child watchers) would need to be stopped manually.
695 .Sp
696 In general it is not advisable to call this function except in the
697 rare occasion where you really need to free e.g. the signal handling
698 pipe fds. If you need dynamically allocated loops it is better to use
699 \&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
700 .IP "ev_loop_destroy (loop)" 4
701 .IX Item "ev_loop_destroy (loop)"
702 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
703 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
704 .IP "ev_default_fork ()" 4
705 .IX Item "ev_default_fork ()"
706 This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
707 to reinitialise the kernel state for backends that have one. Despite the
708 name, you can call it anytime, but it makes most sense after forking, in
709 the child process (or both child and parent, but that again makes little
710 sense). You \fImust\fR call it in the child before using any of the libev
711 functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
712 .Sp
713 On the other hand, you only need to call this function in the child
714 process if and only if you want to use the event library in the child. If
715 you just fork+exec, you don't have to call it at all.
716 .Sp
717 The function itself is quite fast and it's usually not a problem to call
718 it just in case after a fork. To make this easy, the function will fit in
719 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
720 .Sp
721 .Vb 1
722 \& pthread_atfork (0, 0, ev_default_fork);
723 .Ve
724 .IP "ev_loop_fork (loop)" 4
725 .IX Item "ev_loop_fork (loop)"
726 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
727 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
728 after fork that you want to re-use in the child, and how you do this is
729 entirely your own problem.
730 .IP "int ev_is_default_loop (loop)" 4
731 .IX Item "int ev_is_default_loop (loop)"
732 Returns true when the given loop is, in fact, the default loop, and false
733 otherwise.
734 .IP "unsigned int ev_loop_count (loop)" 4
735 .IX Item "unsigned int ev_loop_count (loop)"
736 Returns the count of loop iterations for the loop, which is identical to
737 the number of times libev did poll for new events. It starts at \f(CW0\fR and
738 happily wraps around with enough iterations.
739 .Sp
740 This value can sometimes be useful as a generation counter of sorts (it
741 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
742 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
743 .IP "unsigned int ev_backend (loop)" 4
744 .IX Item "unsigned int ev_backend (loop)"
745 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
746 use.
747 .IP "ev_tstamp ev_now (loop)" 4
748 .IX Item "ev_tstamp ev_now (loop)"
749 Returns the current \*(L"event loop time\*(R", which is the time the event loop
750 received events and started processing them. This timestamp does not
751 change as long as callbacks are being processed, and this is also the base
752 time used for relative timers. You can treat it as the timestamp of the
753 event occurring (or more correctly, libev finding out about it).
754 .IP "ev_now_update (loop)" 4
755 .IX Item "ev_now_update (loop)"
756 Establishes the current time by querying the kernel, updating the time
757 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
758 is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
759 .Sp
760 This function is rarely useful, but when some event callback runs for a
761 very long time without entering the event loop, updating libev's idea of
762 the current time is a good idea.
763 .Sp
764 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
765 .IP "ev_loop (loop, int flags)" 4
766 .IX Item "ev_loop (loop, int flags)"
767 Finally, this is it, the event handler. This function usually is called
768 after you initialised all your watchers and you want to start handling
769 events.
770 .Sp
771 If the flags argument is specified as \f(CW0\fR, it will not return until
772 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
773 .Sp
774 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
775 relying on all watchers to be stopped when deciding when a program has
776 finished (especially in interactive programs), but having a program
777 that automatically loops as long as it has to and no longer by virtue
778 of relying on its watchers stopping correctly, that is truly a thing of
779 beauty.
780 .Sp
781 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
782 those events and any already outstanding ones, but will not block your
783 process in case there are no events and will return after one iteration of
784 the loop.
785 .Sp
786 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
787 necessary) and will handle those and any already outstanding ones. It
788 will block your process until at least one new event arrives (which could
789 be an event internal to libev itself, so there is no guarantee that a
790 user-registered callback will be called), and will return after one
791 iteration of the loop.
792 .Sp
793 This is useful if you are waiting for some external event in conjunction
794 with something not expressible using other libev watchers (i.e. "roll your
795 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
796 usually a better approach for this kind of thing.
797 .Sp
798 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
799 .Sp
800 .Vb 10
801 \& \- Before the first iteration, call any pending watchers.
802 \& * If EVFLAG_FORKCHECK was used, check for a fork.
803 \& \- If a fork was detected (by any means), queue and call all fork watchers.
804 \& \- Queue and call all prepare watchers.
805 \& \- If we have been forked, detach and recreate the kernel state
806 \& as to not disturb the other process.
807 \& \- Update the kernel state with all outstanding changes.
808 \& \- Update the "event loop time" (ev_now ()).
809 \& \- Calculate for how long to sleep or block, if at all
810 \& (active idle watchers, EVLOOP_NONBLOCK or not having
811 \& any active watchers at all will result in not sleeping).
812 \& \- Sleep if the I/O and timer collect interval say so.
813 \& \- Block the process, waiting for any events.
814 \& \- Queue all outstanding I/O (fd) events.
815 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
816 \& \- Queue all expired timers.
817 \& \- Queue all expired periodics.
818 \& \- Unless any events are pending now, queue all idle watchers.
819 \& \- Queue all check watchers.
820 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
821 \& Signals and child watchers are implemented as I/O watchers, and will
822 \& be handled here by queueing them when their watcher gets executed.
823 \& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
824 \& were used, or there are no active watchers, return, otherwise
825 \& continue with step *.
826 .Ve
827 .Sp
828 Example: Queue some jobs and then loop until no events are outstanding
829 anymore.
830 .Sp
831 .Vb 4
832 \& ... queue jobs here, make sure they register event watchers as long
833 \& ... as they still have work to do (even an idle watcher will do..)
834 \& ev_loop (my_loop, 0);
835 \& ... jobs done or somebody called unloop. yeah!
836 .Ve
837 .IP "ev_unloop (loop, how)" 4
838 .IX Item "ev_unloop (loop, how)"
839 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
840 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
841 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
842 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
843 .Sp
844 This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
845 .Sp
846 It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
847 .IP "ev_ref (loop)" 4
848 .IX Item "ev_ref (loop)"
849 .PD 0
850 .IP "ev_unref (loop)" 4
851 .IX Item "ev_unref (loop)"
852 .PD
853 Ref/unref can be used to add or remove a reference count on the event
854 loop: Every watcher keeps one reference, and as long as the reference
855 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
856 .Sp
857 If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
858 from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
859 stopping it.
860 .Sp
861 As an example, libev itself uses this for its internal signal pipe: It is
862 not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting
863 if no event watchers registered by it are active. It is also an excellent
864 way to do this for generic recurring timers or from within third-party
865 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
866 (but only if the watcher wasn't active before, or was active before,
867 respectively).
868 .Sp
869 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
870 running when nothing else is active.
871 .Sp
872 .Vb 4
873 \& ev_signal exitsig;
874 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
875 \& ev_signal_start (loop, &exitsig);
876 \& evf_unref (loop);
877 .Ve
878 .Sp
879 Example: For some weird reason, unregister the above signal handler again.
880 .Sp
881 .Vb 2
882 \& ev_ref (loop);
883 \& ev_signal_stop (loop, &exitsig);
884 .Ve
885 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
886 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
887 .PD 0
888 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
889 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
890 .PD
891 These advanced functions influence the time that libev will spend waiting
892 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
893 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
894 latency.
895 .Sp
896 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
897 allows libev to delay invocation of I/O and timer/periodic callbacks
898 to increase efficiency of loop iterations (or to increase power-saving
899 opportunities).
900 .Sp
901 The idea is that sometimes your program runs just fast enough to handle
902 one (or very few) event(s) per loop iteration. While this makes the
903 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
904 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
905 overhead for the actual polling but can deliver many events at once.
906 .Sp
907 By setting a higher \fIio collect interval\fR you allow libev to spend more
908 time collecting I/O events, so you can handle more events per iteration,
909 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
910 \&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
911 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
912 .Sp
913 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
914 to spend more time collecting timeouts, at the expense of increased
915 latency/jitter/inexactness (the watcher callback will be called
916 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
917 value will not introduce any overhead in libev.
918 .Sp
919 Many (busy) programs can usually benefit by setting the I/O collect
920 interval to a value near \f(CW0.1\fR or so, which is often enough for
921 interactive servers (of course not for games), likewise for timeouts. It
922 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
923 as this approaches the timing granularity of most systems.
924 .Sp
925 Setting the \fItimeout collect interval\fR can improve the opportunity for
926 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
927 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
928 times the process sleeps and wakes up again. Another useful technique to
929 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
930 they fire on, say, one-second boundaries only.
931 .IP "ev_loop_verify (loop)" 4
932 .IX Item "ev_loop_verify (loop)"
933 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
934 compiled in, which is the default for non-minimal builds. It tries to go
935 through all internal structures and checks them for validity. If anything
936 is found to be inconsistent, it will print an error message to standard
937 error and call \f(CW\*(C`abort ()\*(C'\fR.
938 .Sp
939 This can be used to catch bugs inside libev itself: under normal
940 circumstances, this function will never abort as of course libev keeps its
941 data structures consistent.
942 .SH "ANATOMY OF A WATCHER"
943 .IX Header "ANATOMY OF A WATCHER"
944 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
945 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
946 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
947 .PP
948 A watcher is a structure that you create and register to record your
949 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
950 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
951 .PP
952 .Vb 5
953 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
954 \& {
955 \& ev_io_stop (w);
956 \& ev_unloop (loop, EVUNLOOP_ALL);
957 \& }
958 \&
959 \& struct ev_loop *loop = ev_default_loop (0);
960 \&
961 \& ev_io stdin_watcher;
962 \&
963 \& ev_init (&stdin_watcher, my_cb);
964 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
965 \& ev_io_start (loop, &stdin_watcher);
966 \&
967 \& ev_loop (loop, 0);
968 .Ve
969 .PP
970 As you can see, you are responsible for allocating the memory for your
971 watcher structures (and it is \fIusually\fR a bad idea to do this on the
972 stack).
973 .PP
974 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
975 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
976 .PP
977 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
978 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
979 callback gets invoked each time the event occurs (or, in the case of I/O
980 watchers, each time the event loop detects that the file descriptor given
981 is readable and/or writable).
982 .PP
983 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
984 macro to configure it, with arguments specific to the watcher type. There
985 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
986 .PP
987 To make the watcher actually watch out for events, you have to start it
988 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
989 *)\*(C'\fR), and you can stop watching for events at any time by calling the
990 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
991 .PP
992 As long as your watcher is active (has been started but not stopped) you
993 must not touch the values stored in it. Most specifically you must never
994 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
995 .PP
996 Each and every callback receives the event loop pointer as first, the
997 registered watcher structure as second, and a bitset of received events as
998 third argument.
999 .PP
1000 The received events usually include a single bit per event type received
1001 (you can receive multiple events at the same time). The possible bit masks
1002 are:
1003 .ie n .IP """EV_READ""" 4
1004 .el .IP "\f(CWEV_READ\fR" 4
1005 .IX Item "EV_READ"
1006 .PD 0
1007 .ie n .IP """EV_WRITE""" 4
1008 .el .IP "\f(CWEV_WRITE\fR" 4
1009 .IX Item "EV_WRITE"
1010 .PD
1011 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1012 writable.
1013 .ie n .IP """EV_TIMEOUT""" 4
1014 .el .IP "\f(CWEV_TIMEOUT\fR" 4
1015 .IX Item "EV_TIMEOUT"
1016 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1017 .ie n .IP """EV_PERIODIC""" 4
1018 .el .IP "\f(CWEV_PERIODIC\fR" 4
1019 .IX Item "EV_PERIODIC"
1020 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1021 .ie n .IP """EV_SIGNAL""" 4
1022 .el .IP "\f(CWEV_SIGNAL\fR" 4
1023 .IX Item "EV_SIGNAL"
1024 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1025 .ie n .IP """EV_CHILD""" 4
1026 .el .IP "\f(CWEV_CHILD\fR" 4
1027 .IX Item "EV_CHILD"
1028 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1029 .ie n .IP """EV_STAT""" 4
1030 .el .IP "\f(CWEV_STAT\fR" 4
1031 .IX Item "EV_STAT"
1032 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1033 .ie n .IP """EV_IDLE""" 4
1034 .el .IP "\f(CWEV_IDLE\fR" 4
1035 .IX Item "EV_IDLE"
1036 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1037 .ie n .IP """EV_PREPARE""" 4
1038 .el .IP "\f(CWEV_PREPARE\fR" 4
1039 .IX Item "EV_PREPARE"
1040 .PD 0
1041 .ie n .IP """EV_CHECK""" 4
1042 .el .IP "\f(CWEV_CHECK\fR" 4
1043 .IX Item "EV_CHECK"
1044 .PD
1045 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
1046 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1047 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
1048 received events. Callbacks of both watcher types can start and stop as
1049 many watchers as they want, and all of them will be taken into account
1050 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1051 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1052 .ie n .IP """EV_EMBED""" 4
1053 .el .IP "\f(CWEV_EMBED\fR" 4
1054 .IX Item "EV_EMBED"
1055 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1056 .ie n .IP """EV_FORK""" 4
1057 .el .IP "\f(CWEV_FORK\fR" 4
1058 .IX Item "EV_FORK"
1059 The event loop has been resumed in the child process after fork (see
1060 \&\f(CW\*(C`ev_fork\*(C'\fR).
1061 .ie n .IP """EV_ASYNC""" 4
1062 .el .IP "\f(CWEV_ASYNC\fR" 4
1063 .IX Item "EV_ASYNC"
1064 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1065 .ie n .IP """EV_ERROR""" 4
1066 .el .IP "\f(CWEV_ERROR\fR" 4
1067 .IX Item "EV_ERROR"
1068 An unspecified error has occurred, the watcher has been stopped. This might
1069 happen because the watcher could not be properly started because libev
1070 ran out of memory, a file descriptor was found to be closed or any other
1071 problem. Libev considers these application bugs.
1072 .Sp
1073 You best act on it by reporting the problem and somehow coping with the
1074 watcher being stopped. Note that well-written programs should not receive
1075 an error ever, so when your watcher receives it, this usually indicates a
1076 bug in your program.
1077 .Sp
1078 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1079 example it might indicate that a fd is readable or writable, and if your
1080 callbacks is well-written it can just attempt the operation and cope with
1081 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1082 programs, though, as the fd could already be closed and reused for another
1083 thing, so beware.
1084 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1085 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1086 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1087 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1088 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1089 This macro initialises the generic portion of a watcher. The contents
1090 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1091 the generic parts of the watcher are initialised, you \fIneed\fR to call
1092 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1093 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1094 which rolls both calls into one.
1095 .Sp
1096 You can reinitialise a watcher at any time as long as it has been stopped
1097 (or never started) and there are no pending events outstanding.
1098 .Sp
1099 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1100 int revents)\*(C'\fR.
1101 .Sp
1102 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1103 .Sp
1104 .Vb 3
1105 \& ev_io w;
1106 \& ev_init (&w, my_cb);
1107 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1108 .Ve
1109 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1110 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1111 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1112 This macro initialises the type-specific parts of a watcher. You need to
1113 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1114 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1115 macro on a watcher that is active (it can be pending, however, which is a
1116 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1117 .Sp
1118 Although some watcher types do not have type-specific arguments
1119 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1120 .Sp
1121 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1122 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1123 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1124 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1125 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1126 calls into a single call. This is the most convenient method to initialise
1127 a watcher. The same limitations apply, of course.
1128 .Sp
1129 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1130 .Sp
1131 .Vb 1
1132 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1133 .Ve
1134 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1135 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1136 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1137 Starts (activates) the given watcher. Only active watchers will receive
1138 events. If the watcher is already active nothing will happen.
1139 .Sp
1140 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1141 whole section.
1142 .Sp
1143 .Vb 1
1144 \& ev_io_start (EV_DEFAULT_UC, &w);
1145 .Ve
1146 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1147 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1148 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1149 Stops the given watcher if active, and clears the pending status (whether
1150 the watcher was active or not).
1151 .Sp
1152 It is possible that stopped watchers are pending \- for example,
1153 non-repeating timers are being stopped when they become pending \- but
1154 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1155 pending. If you want to free or reuse the memory used by the watcher it is
1156 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1157 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1158 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1159 Returns a true value iff the watcher is active (i.e. it has been started
1160 and not yet been stopped). As long as a watcher is active you must not modify
1161 it.
1162 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1163 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1164 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1165 events but its callback has not yet been invoked). As long as a watcher
1166 is pending (but not active) you must not call an init function on it (but
1167 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1168 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1169 it).
1170 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1171 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1172 Returns the callback currently set on the watcher.
1173 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1174 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1175 Change the callback. You can change the callback at virtually any time
1176 (modulo threads).
1177 .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1178 .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1179 .PD 0
1180 .IP "int ev_priority (ev_TYPE *watcher)" 4
1181 .IX Item "int ev_priority (ev_TYPE *watcher)"
1182 .PD
1183 Set and query the priority of the watcher. The priority is a small
1184 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1185 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1186 before watchers with lower priority, but priority will not keep watchers
1187 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1188 .Sp
1189 This means that priorities are \fIonly\fR used for ordering callback
1190 invocation after new events have been received. This is useful, for
1191 example, to reduce latency after idling, or more often, to bind two
1192 watchers on the same event and make sure one is called first.
1193 .Sp
1194 If you need to suppress invocation when higher priority events are pending
1195 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1196 .Sp
1197 You \fImust not\fR change the priority of a watcher as long as it is active or
1198 pending.
1199 .Sp
1200 The default priority used by watchers when no priority has been set is
1201 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1202 .Sp
1203 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1204 fine, as long as you do not mind that the priority value you query might
1205 or might not have been clamped to the valid range.
1206 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1207 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1208 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
1209 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1210 can deal with that fact, as both are simply passed through to the
1211 callback.
1212 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1213 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1214 If the watcher is pending, this function clears its pending status and
1215 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1216 watcher isn't pending it does nothing and returns \f(CW0\fR.
1217 .Sp
1218 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1219 callback to be invoked, which can be accomplished with this function.
1220 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
1221 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
1222 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
1223 and read at any time: libev will completely ignore it. This can be used
1224 to associate arbitrary data with your watcher. If you need more data and
1225 don't want to allocate memory and store a pointer to it in that data
1226 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
1227 data:
1228 .PP
1229 .Vb 7
1230 \& struct my_io
1231 \& {
1232 \& ev_io io;
1233 \& int otherfd;
1234 \& void *somedata;
1235 \& struct whatever *mostinteresting;
1236 \& };
1237 \&
1238 \& ...
1239 \& struct my_io w;
1240 \& ev_io_init (&w.io, my_cb, fd, EV_READ);
1241 .Ve
1242 .PP
1243 And since your callback will be called with a pointer to the watcher, you
1244 can cast it back to your own type:
1245 .PP
1246 .Vb 5
1247 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1248 \& {
1249 \& struct my_io *w = (struct my_io *)w_;
1250 \& ...
1251 \& }
1252 .Ve
1253 .PP
1254 More interesting and less C\-conformant ways of casting your callback type
1255 instead have been omitted.
1256 .PP
1257 Another common scenario is to use some data structure with multiple
1258 embedded watchers:
1259 .PP
1260 .Vb 6
1261 \& struct my_biggy
1262 \& {
1263 \& int some_data;
1264 \& ev_timer t1;
1265 \& ev_timer t2;
1266 \& }
1267 .Ve
1268 .PP
1269 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1270 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1271 in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1272 some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1273 programmers):
1274 .PP
1275 .Vb 1
1276 \& #include <stddef.h>
1277 \&
1278 \& static void
1279 \& t1_cb (EV_P_ ev_timer *w, int revents)
1280 \& {
1281 \& struct my_biggy big = (struct my_biggy *
1282 \& (((char *)w) \- offsetof (struct my_biggy, t1));
1283 \& }
1284 \&
1285 \& static void
1286 \& t2_cb (EV_P_ ev_timer *w, int revents)
1287 \& {
1288 \& struct my_biggy big = (struct my_biggy *
1289 \& (((char *)w) \- offsetof (struct my_biggy, t2));
1290 \& }
1291 .Ve
1292 .SH "WATCHER TYPES"
1293 .IX Header "WATCHER TYPES"
1294 This section describes each watcher in detail, but will not repeat
1295 information given in the last section. Any initialisation/set macros,
1296 functions and members specific to the watcher type are explained.
1297 .PP
1298 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1299 while the watcher is active, you can look at the member and expect some
1300 sensible content, but you must not modify it (you can modify it while the
1301 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1302 means you can expect it to have some sensible content while the watcher
1303 is active, but you can also modify it. Modifying it may not do something
1304 sensible or take immediate effect (or do anything at all), but libev will
1305 not crash or malfunction in any way.
1306 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1307 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1308 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1309 I/O watchers check whether a file descriptor is readable or writable
1310 in each iteration of the event loop, or, more precisely, when reading
1311 would not block the process and writing would at least be able to write
1312 some data. This behaviour is called level-triggering because you keep
1313 receiving events as long as the condition persists. Remember you can stop
1314 the watcher if you don't want to act on the event and neither want to
1315 receive future events.
1316 .PP
1317 In general you can register as many read and/or write event watchers per
1318 fd as you want (as long as you don't confuse yourself). Setting all file
1319 descriptors to non-blocking mode is also usually a good idea (but not
1320 required if you know what you are doing).
1321 .PP
1322 If you cannot use non-blocking mode, then force the use of a
1323 known-to-be-good backend (at the time of this writing, this includes only
1324 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1325 .PP
1326 Another thing you have to watch out for is that it is quite easy to
1327 receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1328 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1329 because there is no data. Not only are some backends known to create a
1330 lot of those (for example Solaris ports), it is very easy to get into
1331 this situation even with a relatively standard program structure. Thus
1332 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1333 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1334 .PP
1335 If you cannot run the fd in non-blocking mode (for example you should
1336 not play around with an Xlib connection), then you have to separately
1337 re-test whether a file descriptor is really ready with a known-to-be good
1338 interface such as poll (fortunately in our Xlib example, Xlib already
1339 does this on its own, so its quite safe to use). Some people additionally
1340 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1341 indefinitely.
1342 .PP
1343 But really, best use non-blocking mode.
1344 .PP
1345 \fIThe special problem of disappearing file descriptors\fR
1346 .IX Subsection "The special problem of disappearing file descriptors"
1347 .PP
1348 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1349 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1350 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1351 descriptor, but when it goes away, the operating system will silently drop
1352 this interest. If another file descriptor with the same number then is
1353 registered with libev, there is no efficient way to see that this is, in
1354 fact, a different file descriptor.
1355 .PP
1356 To avoid having to explicitly tell libev about such cases, libev follows
1357 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1358 will assume that this is potentially a new file descriptor, otherwise
1359 it is assumed that the file descriptor stays the same. That means that
1360 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
1361 descriptor even if the file descriptor number itself did not change.
1362 .PP
1363 This is how one would do it normally anyway, the important point is that
1364 the libev application should not optimise around libev but should leave
1365 optimisations to libev.
1366 .PP
1367 \fIThe special problem of dup'ed file descriptors\fR
1368 .IX Subsection "The special problem of dup'ed file descriptors"
1369 .PP
1370 Some backends (e.g. epoll), cannot register events for file descriptors,
1371 but only events for the underlying file descriptions. That means when you
1372 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1373 events for them, only one file descriptor might actually receive events.
1374 .PP
1375 There is no workaround possible except not registering events
1376 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1377 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1378 .PP
1379 \fIThe special problem of fork\fR
1380 .IX Subsection "The special problem of fork"
1381 .PP
1382 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1383 useless behaviour. Libev fully supports fork, but needs to be told about
1384 it in the child.
1385 .PP
1386 To support fork in your programs, you either have to call
1387 \&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1388 enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1389 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1390 .PP
1391 \fIThe special problem of \s-1SIGPIPE\s0\fR
1392 .IX Subsection "The special problem of SIGPIPE"
1393 .PP
1394 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1395 when writing to a pipe whose other end has been closed, your program gets
1396 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1397 this is sensible behaviour, for daemons, this is usually undesirable.
1398 .PP
1399 So when you encounter spurious, unexplained daemon exits, make sure you
1400 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1401 somewhere, as that would have given you a big clue).
1402 .PP
1403 \fIWatcher-Specific Functions\fR
1404 .IX Subsection "Watcher-Specific Functions"
1405 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1406 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1407 .PD 0
1408 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1409 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1410 .PD
1411 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1412 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
1413 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1414 .IP "int fd [read\-only]" 4
1415 .IX Item "int fd [read-only]"
1416 The file descriptor being watched.
1417 .IP "int events [read\-only]" 4
1418 .IX Item "int events [read-only]"
1419 The events being watched.
1420 .PP
1421 \fIExamples\fR
1422 .IX Subsection "Examples"
1423 .PP
1424 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1425 readable, but only once. Since it is likely line-buffered, you could
1426 attempt to read a whole line in the callback.
1427 .PP
1428 .Vb 6
1429 \& static void
1430 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1431 \& {
1432 \& ev_io_stop (loop, w);
1433 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1434 \& }
1435 \&
1436 \& ...
1437 \& struct ev_loop *loop = ev_default_init (0);
1438 \& ev_io stdin_readable;
1439 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1440 \& ev_io_start (loop, &stdin_readable);
1441 \& ev_loop (loop, 0);
1442 .Ve
1443 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1444 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1445 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1446 Timer watchers are simple relative timers that generate an event after a
1447 given time, and optionally repeating in regular intervals after that.
1448 .PP
1449 The timers are based on real time, that is, if you register an event that
1450 times out after an hour and you reset your system clock to January last
1451 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1452 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1453 monotonic clock option helps a lot here).
1454 .PP
1455 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1456 passed, but if multiple timers become ready during the same loop iteration
1457 then order of execution is undefined.
1458 .PP
1459 \fIBe smart about timeouts\fR
1460 .IX Subsection "Be smart about timeouts"
1461 .PP
1462 Many real-world problems involve some kind of timeout, usually for error
1463 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1464 you want to raise some error after a while.
1465 .PP
1466 What follows are some ways to handle this problem, from obvious and
1467 inefficient to smart and efficient.
1468 .PP
1469 In the following, a 60 second activity timeout is assumed \- a timeout that
1470 gets reset to 60 seconds each time there is activity (e.g. each time some
1471 data or other life sign was received).
1472 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1473 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1474 This is the most obvious, but not the most simple way: In the beginning,
1475 start the watcher:
1476 .Sp
1477 .Vb 2
1478 \& ev_timer_init (timer, callback, 60., 0.);
1479 \& ev_timer_start (loop, timer);
1480 .Ve
1481 .Sp
1482 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1483 and start it again:
1484 .Sp
1485 .Vb 3
1486 \& ev_timer_stop (loop, timer);
1487 \& ev_timer_set (timer, 60., 0.);
1488 \& ev_timer_start (loop, timer);
1489 .Ve
1490 .Sp
1491 This is relatively simple to implement, but means that each time there is
1492 some activity, libev will first have to remove the timer from its internal
1493 data structure and then add it again. Libev tries to be fast, but it's
1494 still not a constant-time operation.
1495 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1496 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1497 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1498 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1499 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1500 .Sp
1501 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1502 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1503 successfully read or write some data. If you go into an idle state where
1504 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1505 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1506 .Sp
1507 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1508 \&\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
1509 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1510 .Sp
1511 At start:
1512 .Sp
1513 .Vb 3
1514 \& ev_timer_init (timer, callback);
1515 \& timer\->repeat = 60.;
1516 \& ev_timer_again (loop, timer);
1517 .Ve
1518 .Sp
1519 Each time there is some activity:
1520 .Sp
1521 .Vb 1
1522 \& ev_timer_again (loop, timer);
1523 .Ve
1524 .Sp
1525 It is even possible to change the time-out on the fly, regardless of
1526 whether the watcher is active or not:
1527 .Sp
1528 .Vb 2
1529 \& timer\->repeat = 30.;
1530 \& ev_timer_again (loop, timer);
1531 .Ve
1532 .Sp
1533 This is slightly more efficient then stopping/starting the timer each time
1534 you want to modify its timeout value, as libev does not have to completely
1535 remove and re-insert the timer from/into its internal data structure.
1536 .Sp
1537 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1538 .IP "3. Let the timer time out, but then re-arm it as required." 4
1539 .IX Item "3. Let the timer time out, but then re-arm it as required."
1540 This method is more tricky, but usually most efficient: Most timeouts are
1541 relatively long compared to the intervals between other activity \- in
1542 our example, within 60 seconds, there are usually many I/O events with
1543 associated activity resets.
1544 .Sp
1545 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1546 but remember the time of last activity, and check for a real timeout only
1547 within the callback:
1548 .Sp
1549 .Vb 1
1550 \& ev_tstamp last_activity; // time of last activity
1551 \&
1552 \& static void
1553 \& callback (EV_P_ ev_timer *w, int revents)
1554 \& {
1555 \& ev_tstamp now = ev_now (EV_A);
1556 \& ev_tstamp timeout = last_activity + 60.;
1557 \&
1558 \& // if last_activity + 60. is older than now, we did time out
1559 \& if (timeout < now)
1560 \& {
1561 \& // timeout occured, take action
1562 \& }
1563 \& else
1564 \& {
1565 \& // callback was invoked, but there was some activity, re\-arm
1566 \& // the watcher to fire in last_activity + 60, which is
1567 \& // guaranteed to be in the future, so "again" is positive:
1568 \& w\->repeat = timeout \- now;
1569 \& ev_timer_again (EV_A_ w);
1570 \& }
1571 \& }
1572 .Ve
1573 .Sp
1574 To summarise the callback: first calculate the real timeout (defined
1575 as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1576 been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1577 the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1578 re-schedule the timer to fire at that future time, to see if maybe we have
1579 a timeout then.
1580 .Sp
1581 Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1582 \&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1583 .Sp
1584 This scheme causes more callback invocations (about one every 60 seconds
1585 minus half the average time between activity), but virtually no calls to
1586 libev to change the timeout.
1587 .Sp
1588 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1589 to the current time (meaning we just have some activity :), then call the
1590 callback, which will \*(L"do the right thing\*(R" and start the timer:
1591 .Sp
1592 .Vb 3
1593 \& ev_timer_init (timer, callback);
1594 \& last_activity = ev_now (loop);
1595 \& callback (loop, timer, EV_TIMEOUT);
1596 .Ve
1597 .Sp
1598 And when there is some activity, simply store the current time in
1599 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1600 .Sp
1601 .Vb 1
1602 \& last_actiivty = ev_now (loop);
1603 .Ve
1604 .Sp
1605 This technique is slightly more complex, but in most cases where the
1606 time-out is unlikely to be triggered, much more efficient.
1607 .Sp
1608 Changing the timeout is trivial as well (if it isn't hard-coded in the
1609 callback :) \- just change the timeout and invoke the callback, which will
1610 fix things for you.
1611 .IP "4. Wee, just use a double-linked list for your timeouts." 4
1612 .IX Item "4. Wee, just use a double-linked list for your timeouts."
1613 If there is not one request, but many thousands (millions...), all
1614 employing some kind of timeout with the same timeout value, then one can
1615 do even better:
1616 .Sp
1617 When starting the timeout, calculate the timeout value and put the timeout
1618 at the \fIend\fR of the list.
1619 .Sp
1620 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1621 the list is expected to fire (for example, using the technique #3).
1622 .Sp
1623 When there is some activity, remove the timer from the list, recalculate
1624 the timeout, append it to the end of the list again, and make sure to
1625 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1626 .Sp
1627 This way, one can manage an unlimited number of timeouts in O(1) time for
1628 starting, stopping and updating the timers, at the expense of a major
1629 complication, and having to use a constant timeout. The constant timeout
1630 ensures that the list stays sorted.
1631 .PP
1632 So which method the best?
1633 .PP
1634 Method #2 is a simple no-brain-required solution that is adequate in most
1635 situations. Method #3 requires a bit more thinking, but handles many cases
1636 better, and isn't very complicated either. In most case, choosing either
1637 one is fine, with #3 being better in typical situations.
1638 .PP
1639 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1640 rather complicated, but extremely efficient, something that really pays
1641 off after the first million or so of active timers, i.e. it's usually
1642 overkill :)
1643 .PP
1644 \fIThe special problem of time updates\fR
1645 .IX Subsection "The special problem of time updates"
1646 .PP
1647 Establishing the current time is a costly operation (it usually takes at
1648 least two system calls): \s-1EV\s0 therefore updates its idea of the current
1649 time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1650 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1651 lots of events in one iteration.
1652 .PP
1653 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1654 time. This is usually the right thing as this timestamp refers to the time
1655 of the event triggering whatever timeout you are modifying/starting. If
1656 you suspect event processing to be delayed and you \fIneed\fR to base the
1657 timeout on the current time, use something like this to adjust for this:
1658 .PP
1659 .Vb 1
1660 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
1661 .Ve
1662 .PP
1663 If the event loop is suspended for a long time, you can also force an
1664 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1665 ()\*(C'\fR.
1666 .PP
1667 \fIWatcher-Specific Functions and Data Members\fR
1668 .IX Subsection "Watcher-Specific Functions and Data Members"
1669 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1670 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1671 .PD 0
1672 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1673 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1674 .PD
1675 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
1676 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
1677 reached. If it is positive, then the timer will automatically be
1678 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1679 until stopped manually.
1680 .Sp
1681 The timer itself will do a best-effort at avoiding drift, that is, if
1682 you configure a timer to trigger every 10 seconds, then it will normally
1683 trigger at exactly 10 second intervals. If, however, your program cannot
1684 keep up with the timer (because it takes longer than those 10 seconds to
1685 do stuff) the timer will not fire more than once per event loop iteration.
1686 .IP "ev_timer_again (loop, ev_timer *)" 4
1687 .IX Item "ev_timer_again (loop, ev_timer *)"
1688 This will act as if the timer timed out and restart it again if it is
1689 repeating. The exact semantics are:
1690 .Sp
1691 If the timer is pending, its pending status is cleared.
1692 .Sp
1693 If the timer is started but non-repeating, stop it (as if it timed out).
1694 .Sp
1695 If the timer is repeating, either start it if necessary (with the
1696 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1697 .Sp
1698 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1699 usage example.
1700 .IP "ev_tstamp repeat [read\-write]" 4
1701 .IX Item "ev_tstamp repeat [read-write]"
1702 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1703 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1704 which is also when any modifications are taken into account.
1705 .PP
1706 \fIExamples\fR
1707 .IX Subsection "Examples"
1708 .PP
1709 Example: Create a timer that fires after 60 seconds.
1710 .PP
1711 .Vb 5
1712 \& static void
1713 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1714 \& {
1715 \& .. one minute over, w is actually stopped right here
1716 \& }
1717 \&
1718 \& ev_timer mytimer;
1719 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1720 \& ev_timer_start (loop, &mytimer);
1721 .Ve
1722 .PP
1723 Example: Create a timeout timer that times out after 10 seconds of
1724 inactivity.
1725 .PP
1726 .Vb 5
1727 \& static void
1728 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1729 \& {
1730 \& .. ten seconds without any activity
1731 \& }
1732 \&
1733 \& ev_timer mytimer;
1734 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1735 \& ev_timer_again (&mytimer); /* start timer */
1736 \& ev_loop (loop, 0);
1737 \&
1738 \& // and in some piece of code that gets executed on any "activity":
1739 \& // reset the timeout to start ticking again at 10 seconds
1740 \& ev_timer_again (&mytimer);
1741 .Ve
1742 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1743 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1744 .IX Subsection "ev_periodic - to cron or not to cron?"
1745 Periodic watchers are also timers of a kind, but they are very versatile
1746 (and unfortunately a bit complex).
1747 .PP
1748 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1749 but on wall clock time (absolute time). You can tell a periodic watcher
1750 to trigger after some specific point in time. For example, if you tell a
1751 periodic watcher to trigger in 10 seconds (by specifying e.g. \f(CW\*(C`ev_now ()
1752 + 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system
1753 clock to January of the previous year, then it will take more than year
1754 to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would still trigger
1755 roughly 10 seconds later as it uses a relative timeout).
1756 .PP
1757 \&\f(CW\*(C`ev_periodic\*(C'\fRs can also be used to implement vastly more complex timers,
1758 such as triggering an event on each \*(L"midnight, local time\*(R", or other
1759 complicated rules.
1760 .PP
1761 As with timers, the callback is guaranteed to be invoked only when the
1762 time (\f(CW\*(C`at\*(C'\fR) has passed, but if multiple periodic timers become ready
1763 during the same loop iteration, then order of execution is undefined.
1764 .PP
1765 \fIWatcher-Specific Functions and Data Members\fR
1766 .IX Subsection "Watcher-Specific Functions and Data Members"
1767 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1768 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1769 .PD 0
1770 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1771 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1772 .PD
1773 Lots of arguments, lets sort it out... There are basically three modes of
1774 operation, and we will explain them from simplest to most complex:
1775 .RS 4
1776 .IP "\(bu" 4
1777 absolute timer (at = time, interval = reschedule_cb = 0)
1778 .Sp
1779 In this configuration the watcher triggers an event after the wall clock
1780 time \f(CW\*(C`at\*(C'\fR has passed. It will not repeat and will not adjust when a time
1781 jump occurs, that is, if it is to be run at January 1st 2011 then it will
1782 only run when the system clock reaches or surpasses this time.
1783 .IP "\(bu" 4
1784 repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1785 .Sp
1786 In this mode the watcher will always be scheduled to time out at the next
1787 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
1788 and then repeat, regardless of any time jumps.
1789 .Sp
1790 This can be used to create timers that do not drift with respect to the
1791 system clock, for example, here is a \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
1792 hour, on the hour:
1793 .Sp
1794 .Vb 1
1795 \& ev_periodic_set (&periodic, 0., 3600., 0);
1796 .Ve
1797 .Sp
1798 This doesn't mean there will always be 3600 seconds in between triggers,
1799 but only that the callback will be called when the system time shows a
1800 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1801 by 3600.
1802 .Sp
1803 Another way to think about it (for the mathematically inclined) is that
1804 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1805 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1806 .Sp
1807 For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1808 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1809 this value, and in fact is often specified as zero.
1810 .Sp
1811 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
1812 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
1813 will of course deteriorate. Libev itself tries to be exact to be about one
1814 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
1815 .IP "\(bu" 4
1816 manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1817 .Sp
1818 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1819 ignored. Instead, each time the periodic watcher gets scheduled, the
1820 reschedule callback will be called with the watcher as first, and the
1821 current time as second argument.
1822 .Sp
1823 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1824 ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR.
1825 .Sp
1826 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1827 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
1828 only event loop modification you are allowed to do).
1829 .Sp
1830 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1831 *w, ev_tstamp now)\*(C'\fR, e.g.:
1832 .Sp
1833 .Vb 5
1834 \& static ev_tstamp
1835 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
1836 \& {
1837 \& return now + 60.;
1838 \& }
1839 .Ve
1840 .Sp
1841 It must return the next time to trigger, based on the passed time value
1842 (that is, the lowest time value larger than to the second argument). It
1843 will usually be called just before the callback will be triggered, but
1844 might be called at other times, too.
1845 .Sp
1846 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1847 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1848 .Sp
1849 This can be used to create very complex timers, such as a timer that
1850 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1851 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1852 you do this is, again, up to you (but it is not trivial, which is the main
1853 reason I omitted it as an example).
1854 .RE
1855 .RS 4
1856 .RE
1857 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1858 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1859 Simply stops and restarts the periodic watcher again. This is only useful
1860 when you changed some parameters or the reschedule callback would return
1861 a different time than the last time it was called (e.g. in a crond like
1862 program when the crontabs have changed).
1863 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
1864 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
1865 When active, returns the absolute time that the watcher is supposed to
1866 trigger next.
1867 .IP "ev_tstamp offset [read\-write]" 4
1868 .IX Item "ev_tstamp offset [read-write]"
1869 When repeating, this contains the offset value, otherwise this is the
1870 absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1871 .Sp
1872 Can be modified any time, but changes only take effect when the periodic
1873 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1874 .IP "ev_tstamp interval [read\-write]" 4
1875 .IX Item "ev_tstamp interval [read-write]"
1876 The current interval value. Can be modified any time, but changes only
1877 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1878 called.
1879 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1880 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1881 The current reschedule callback, or \f(CW0\fR, if this functionality is
1882 switched off. Can be changed any time, but changes only take effect when
1883 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1884 .PP
1885 \fIExamples\fR
1886 .IX Subsection "Examples"
1887 .PP
1888 Example: Call a callback every hour, or, more precisely, whenever the
1889 system time is divisible by 3600. The callback invocation times have
1890 potentially a lot of jitter, but good long-term stability.
1891 .PP
1892 .Vb 5
1893 \& static void
1894 \& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1895 \& {
1896 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1897 \& }
1898 \&
1899 \& ev_periodic hourly_tick;
1900 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1901 \& ev_periodic_start (loop, &hourly_tick);
1902 .Ve
1903 .PP
1904 Example: The same as above, but use a reschedule callback to do it:
1905 .PP
1906 .Vb 1
1907 \& #include <math.h>
1908 \&
1909 \& static ev_tstamp
1910 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1911 \& {
1912 \& return now + (3600. \- fmod (now, 3600.));
1913 \& }
1914 \&
1915 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1916 .Ve
1917 .PP
1918 Example: Call a callback every hour, starting now:
1919 .PP
1920 .Vb 4
1921 \& ev_periodic hourly_tick;
1922 \& ev_periodic_init (&hourly_tick, clock_cb,
1923 \& fmod (ev_now (loop), 3600.), 3600., 0);
1924 \& ev_periodic_start (loop, &hourly_tick);
1925 .Ve
1926 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1927 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1928 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1929 Signal watchers will trigger an event when the process receives a specific
1930 signal one or more times. Even though signals are very asynchronous, libev
1931 will try it's best to deliver signals synchronously, i.e. as part of the
1932 normal event processing, like any other event.
1933 .PP
1934 If you want signals asynchronously, just use \f(CW\*(C`sigaction\*(C'\fR as you would
1935 do without libev and forget about sharing the signal. You can even use
1936 \&\f(CW\*(C`ev_async\*(C'\fR from a signal handler to synchronously wake up an event loop.
1937 .PP
1938 You can configure as many watchers as you like per signal. Only when the
1939 first watcher gets started will libev actually register a signal handler
1940 with the kernel (thus it coexists with your own signal handlers as long as
1941 you don't register any with libev for the same signal). Similarly, when
1942 the last signal watcher for a signal is stopped, libev will reset the
1943 signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
1944 .PP
1945 If possible and supported, libev will install its handlers with
1946 \&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so system calls should not be unduly
1947 interrupted. If you have a problem with system calls getting interrupted by
1948 signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1949 them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1950 .PP
1951 \fIWatcher-Specific Functions and Data Members\fR
1952 .IX Subsection "Watcher-Specific Functions and Data Members"
1953 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1954 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1955 .PD 0
1956 .IP "ev_signal_set (ev_signal *, int signum)" 4
1957 .IX Item "ev_signal_set (ev_signal *, int signum)"
1958 .PD
1959 Configures the watcher to trigger on the given signal number (usually one
1960 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1961 .IP "int signum [read\-only]" 4
1962 .IX Item "int signum [read-only]"
1963 The signal the watcher watches out for.
1964 .PP
1965 \fIExamples\fR
1966 .IX Subsection "Examples"
1967 .PP
1968 Example: Try to exit cleanly on \s-1SIGINT\s0.
1969 .PP
1970 .Vb 5
1971 \& static void
1972 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1973 \& {
1974 \& ev_unloop (loop, EVUNLOOP_ALL);
1975 \& }
1976 \&
1977 \& ev_signal signal_watcher;
1978 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1979 \& ev_signal_start (loop, &signal_watcher);
1980 .Ve
1981 .ie n .Sh """ev_child"" \- watch out for process status changes"
1982 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1983 .IX Subsection "ev_child - watch out for process status changes"
1984 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1985 some child status changes (most typically when a child of yours dies or
1986 exits). It is permissible to install a child watcher \fIafter\fR the child
1987 has been forked (which implies it might have already exited), as long
1988 as the event loop isn't entered (or is continued from a watcher), i.e.,
1989 forking and then immediately registering a watcher for the child is fine,
1990 but forking and registering a watcher a few event loop iterations later is
1991 not.
1992 .PP
1993 Only the default event loop is capable of handling signals, and therefore
1994 you can only register child watchers in the default event loop.
1995 .PP
1996 \fIProcess Interaction\fR
1997 .IX Subsection "Process Interaction"
1998 .PP
1999 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2000 initialised. This is necessary to guarantee proper behaviour even if
2001 the first child watcher is started after the child exits. The occurrence
2002 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2003 synchronously as part of the event loop processing. Libev always reaps all
2004 children, even ones not watched.
2005 .PP
2006 \fIOverriding the Built-In Processing\fR
2007 .IX Subsection "Overriding the Built-In Processing"
2008 .PP
2009 Libev offers no special support for overriding the built-in child
2010 processing, but if your application collides with libev's default child
2011 handler, you can override it easily by installing your own handler for
2012 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2013 default loop never gets destroyed. You are encouraged, however, to use an
2014 event-based approach to child reaping and thus use libev's support for
2015 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2016 .PP
2017 \fIStopping the Child Watcher\fR
2018 .IX Subsection "Stopping the Child Watcher"
2019 .PP
2020 Currently, the child watcher never gets stopped, even when the
2021 child terminates, so normally one needs to stop the watcher in the
2022 callback. Future versions of libev might stop the watcher automatically
2023 when a child exit is detected.
2024 .PP
2025 \fIWatcher-Specific Functions and Data Members\fR
2026 .IX Subsection "Watcher-Specific Functions and Data Members"
2027 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2028 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2029 .PD 0
2030 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2031 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2032 .PD
2033 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2034 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2035 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2036 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2037 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2038 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2039 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2040 activate the watcher when the process is stopped or continued).
2041 .IP "int pid [read\-only]" 4
2042 .IX Item "int pid [read-only]"
2043 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2044 .IP "int rpid [read\-write]" 4
2045 .IX Item "int rpid [read-write]"
2046 The process id that detected a status change.
2047 .IP "int rstatus [read\-write]" 4
2048 .IX Item "int rstatus [read-write]"
2049 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2050 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2051 .PP
2052 \fIExamples\fR
2053 .IX Subsection "Examples"
2054 .PP
2055 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2056 its completion.
2057 .PP
2058 .Vb 1
2059 \& ev_child cw;
2060 \&
2061 \& static void
2062 \& child_cb (EV_P_ ev_child *w, int revents)
2063 \& {
2064 \& ev_child_stop (EV_A_ w);
2065 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2066 \& }
2067 \&
2068 \& pid_t pid = fork ();
2069 \&
2070 \& if (pid < 0)
2071 \& // error
2072 \& else if (pid == 0)
2073 \& {
2074 \& // the forked child executes here
2075 \& exit (1);
2076 \& }
2077 \& else
2078 \& {
2079 \& ev_child_init (&cw, child_cb, pid, 0);
2080 \& ev_child_start (EV_DEFAULT_ &cw);
2081 \& }
2082 .Ve
2083 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
2084 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
2085 .IX Subsection "ev_stat - did the file attributes just change?"
2086 This watches a file system path for attribute changes. That is, it calls
2087 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2088 and sees if it changed compared to the last time, invoking the callback if
2089 it did.
2090 .PP
2091 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2092 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2093 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2094 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2095 least one) and all the other fields of the stat buffer having unspecified
2096 contents.
2097 .PP
2098 The path \fImust not\fR end in a slash or contain special components such as
2099 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2100 your working directory changes, then the behaviour is undefined.
2101 .PP
2102 Since there is no portable change notification interface available, the
2103 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2104 to see if it changed somehow. You can specify a recommended polling
2105 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2106 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2107 (which you can expect to be around five seconds, although this might
2108 change dynamically). Libev will also impose a minimum interval which is
2109 currently around \f(CW0.1\fR, but that's usually overkill.
2110 .PP
2111 This watcher type is not meant for massive numbers of stat watchers,
2112 as even with OS-supported change notifications, this can be
2113 resource-intensive.
2114 .PP
2115 At the time of this writing, the only OS-specific interface implemented
2116 is the Linux inotify interface (implementing kqueue support is left as an
2117 exercise for the reader. Note, however, that the author sees no way of
2118 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2119 .PP
2120 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2121 .IX Subsection "ABI Issues (Largefile Support)"
2122 .PP
2123 Libev by default (unless the user overrides this) uses the default
2124 compilation environment, which means that on systems with large file
2125 support disabled by default, you get the 32 bit version of the stat
2126 structure. When using the library from programs that change the \s-1ABI\s0 to
2127 use 64 bit file offsets the programs will fail. In that case you have to
2128 compile libev with the same flags to get binary compatibility. This is
2129 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2130 most noticeably displayed with ev_stat and large file support.
2131 .PP
2132 The solution for this is to lobby your distribution maker to make large
2133 file interfaces available by default (as e.g. FreeBSD does) and not
2134 optional. Libev cannot simply switch on large file support because it has
2135 to exchange stat structures with application programs compiled using the
2136 default compilation environment.
2137 .PP
2138 \fIInotify and Kqueue\fR
2139 .IX Subsection "Inotify and Kqueue"
2140 .PP
2141 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2142 runtime, it will be used to speed up change detection where possible. The
2143 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2144 watcher is being started.
2145 .PP
2146 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2147 except that changes might be detected earlier, and in some cases, to avoid
2148 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2149 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2150 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2151 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2152 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2153 xfs are fully working) libev usually gets away without polling.
2154 .PP
2155 There is no support for kqueue, as apparently it cannot be used to
2156 implement this functionality, due to the requirement of having a file
2157 descriptor open on the object at all times, and detecting renames, unlinks
2158 etc. is difficult.
2159 .PP
2160 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2161 .IX Subsection "stat () is a synchronous operation"
2162 .PP
2163 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2164 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2165 ()\*(C'\fR, which is a synchronous operation.
2166 .PP
2167 For local paths, this usually doesn't matter: unless the system is very
2168 busy or the intervals between stat's are large, a stat call will be fast,
2169 as the path data is suually in memory already (except when starting the
2170 watcher).
2171 .PP
2172 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2173 time due to network issues, and even under good conditions, a stat call
2174 often takes multiple milliseconds.
2175 .PP
2176 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2177 paths, although this is fully supported by libev.
2178 .PP
2179 \fIThe special problem of stat time resolution\fR
2180 .IX Subsection "The special problem of stat time resolution"
2181 .PP
2182 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2183 and even on systems where the resolution is higher, most file systems
2184 still only support whole seconds.
2185 .PP
2186 That means that, if the time is the only thing that changes, you can
2187 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2188 calls your callback, which does something. When there is another update
2189 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2190 stat data does change in other ways (e.g. file size).
2191 .PP
2192 The solution to this is to delay acting on a change for slightly more
2193 than a second (or till slightly after the next full second boundary), using
2194 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2195 ev_timer_again (loop, w)\*(C'\fR).
2196 .PP
2197 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2198 of some operating systems (where the second counter of the current time
2199 might be be delayed. One such system is the Linux kernel, where a call to
2200 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2201 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2202 update file times then there will be a small window where the kernel uses
2203 the previous second to update file times but libev might already execute
2204 the timer callback).
2205 .PP
2206 \fIWatcher-Specific Functions and Data Members\fR
2207 .IX Subsection "Watcher-Specific Functions and Data Members"
2208 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2209 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2210 .PD 0
2211 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2212 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2213 .PD
2214 Configures the watcher to wait for status changes of the given
2215 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2216 be detected and should normally be specified as \f(CW0\fR to let libev choose
2217 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2218 path for as long as the watcher is active.
2219 .Sp
2220 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2221 relative to the attributes at the time the watcher was started (or the
2222 last change was detected).
2223 .IP "ev_stat_stat (loop, ev_stat *)" 4
2224 .IX Item "ev_stat_stat (loop, ev_stat *)"
2225 Updates the stat buffer immediately with new values. If you change the
2226 watched path in your callback, you could call this function to avoid
2227 detecting this change (while introducing a race condition if you are not
2228 the only one changing the path). Can also be useful simply to find out the
2229 new values.
2230 .IP "ev_statdata attr [read\-only]" 4
2231 .IX Item "ev_statdata attr [read-only]"
2232 The most-recently detected attributes of the file. Although the type is
2233 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2234 suitable for your system, but you can only rely on the POSIX-standardised
2235 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2236 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2237 .IP "ev_statdata prev [read\-only]" 4
2238 .IX Item "ev_statdata prev [read-only]"
2239 The previous attributes of the file. The callback gets invoked whenever
2240 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2241 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,
2242 \&\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.
2243 .IP "ev_tstamp interval [read\-only]" 4
2244 .IX Item "ev_tstamp interval [read-only]"
2245 The specified interval.
2246 .IP "const char *path [read\-only]" 4
2247 .IX Item "const char *path [read-only]"
2248 The file system path that is being watched.
2249 .PP
2250 \fIExamples\fR
2251 .IX Subsection "Examples"
2252 .PP
2253 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2254 .PP
2255 .Vb 10
2256 \& static void
2257 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2258 \& {
2259 \& /* /etc/passwd changed in some way */
2260 \& if (w\->attr.st_nlink)
2261 \& {
2262 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2263 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2264 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2265 \& }
2266 \& else
2267 \& /* you shalt not abuse printf for puts */
2268 \& puts ("wow, /etc/passwd is not there, expect problems. "
2269 \& "if this is windows, they already arrived\en");
2270 \& }
2271 \&
2272 \& ...
2273 \& ev_stat passwd;
2274 \&
2275 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2276 \& ev_stat_start (loop, &passwd);
2277 .Ve
2278 .PP
2279 Example: Like above, but additionally use a one-second delay so we do not
2280 miss updates (however, frequent updates will delay processing, too, so
2281 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2282 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2283 .PP
2284 .Vb 2
2285 \& static ev_stat passwd;
2286 \& static ev_timer timer;
2287 \&
2288 \& static void
2289 \& timer_cb (EV_P_ ev_timer *w, int revents)
2290 \& {
2291 \& ev_timer_stop (EV_A_ w);
2292 \&
2293 \& /* now it\*(Aqs one second after the most recent passwd change */
2294 \& }
2295 \&
2296 \& static void
2297 \& stat_cb (EV_P_ ev_stat *w, int revents)
2298 \& {
2299 \& /* reset the one\-second timer */
2300 \& ev_timer_again (EV_A_ &timer);
2301 \& }
2302 \&
2303 \& ...
2304 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2305 \& ev_stat_start (loop, &passwd);
2306 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2307 .Ve
2308 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
2309 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
2310 .IX Subsection "ev_idle - when you've got nothing better to do..."
2311 Idle watchers trigger events when no other events of the same or higher
2312 priority are pending (prepare, check and other idle watchers do not count
2313 as receiving \*(L"events\*(R").
2314 .PP
2315 That is, as long as your process is busy handling sockets or timeouts
2316 (or even signals, imagine) of the same or higher priority it will not be
2317 triggered. But when your process is idle (or only lower-priority watchers
2318 are pending), the idle watchers are being called once per event loop
2319 iteration \- until stopped, that is, or your process receives more events
2320 and becomes busy again with higher priority stuff.
2321 .PP
2322 The most noteworthy effect is that as long as any idle watchers are
2323 active, the process will not block when waiting for new events.
2324 .PP
2325 Apart from keeping your process non-blocking (which is a useful
2326 effect on its own sometimes), idle watchers are a good place to do
2327 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2328 event loop has handled all outstanding events.
2329 .PP
2330 \fIWatcher-Specific Functions and Data Members\fR
2331 .IX Subsection "Watcher-Specific Functions and Data Members"
2332 .IP "ev_idle_init (ev_signal *, callback)" 4
2333 .IX Item "ev_idle_init (ev_signal *, callback)"
2334 Initialises and configures the idle watcher \- it has no parameters of any
2335 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2336 believe me.
2337 .PP
2338 \fIExamples\fR
2339 .IX Subsection "Examples"
2340 .PP
2341 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2342 callback, free it. Also, use no error checking, as usual.
2343 .PP
2344 .Vb 7
2345 \& static void
2346 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2347 \& {
2348 \& free (w);
2349 \& // now do something you wanted to do when the program has
2350 \& // no longer anything immediate to do.
2351 \& }
2352 \&
2353 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2354 \& ev_idle_init (idle_watcher, idle_cb);
2355 \& ev_idle_start (loop, idle_cb);
2356 .Ve
2357 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
2358 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
2359 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
2360 Prepare and check watchers are usually (but not always) used in pairs:
2361 prepare watchers get invoked before the process blocks and check watchers
2362 afterwards.
2363 .PP
2364 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2365 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2366 watchers. Other loops than the current one are fine, however. The
2367 rationale behind this is that you do not need to check for recursion in
2368 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2369 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2370 called in pairs bracketing the blocking call.
2371 .PP
2372 Their main purpose is to integrate other event mechanisms into libev and
2373 their use is somewhat advanced. They could be used, for example, to track
2374 variable changes, implement your own watchers, integrate net-snmp or a
2375 coroutine library and lots more. They are also occasionally useful if
2376 you cache some data and want to flush it before blocking (for example,
2377 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2378 watcher).
2379 .PP
2380 This is done by examining in each prepare call which file descriptors
2381 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
2382 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
2383 libraries provide exactly this functionality). Then, in the check watcher,
2384 you check for any events that occurred (by checking the pending status
2385 of all watchers and stopping them) and call back into the library. The
2386 I/O and timer callbacks will never actually be called (but must be valid
2387 nevertheless, because you never know, you know?).
2388 .PP
2389 As another example, the Perl Coro module uses these hooks to integrate
2390 coroutines into libev programs, by yielding to other active coroutines
2391 during each prepare and only letting the process block if no coroutines
2392 are ready to run (it's actually more complicated: it only runs coroutines
2393 with priority higher than or equal to the event loop and one coroutine
2394 of lower priority, but only once, using idle watchers to keep the event
2395 loop from blocking if lower-priority coroutines are active, thus mapping
2396 low-priority coroutines to idle/background tasks).
2397 .PP
2398 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2399 priority, to ensure that they are being run before any other watchers
2400 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2401 .PP
2402 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2403 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2404 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2405 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2406 loops those other event loops might be in an unusable state until their
2407 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2408 others).
2409 .PP
2410 \fIWatcher-Specific Functions and Data Members\fR
2411 .IX Subsection "Watcher-Specific Functions and Data Members"
2412 .IP "ev_prepare_init (ev_prepare *, callback)" 4
2413 .IX Item "ev_prepare_init (ev_prepare *, callback)"
2414 .PD 0
2415 .IP "ev_check_init (ev_check *, callback)" 4
2416 .IX Item "ev_check_init (ev_check *, callback)"
2417 .PD
2418 Initialises and configures the prepare or check watcher \- they have no
2419 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
2420 macros, but using them is utterly, utterly, utterly and completely
2421 pointless.
2422 .PP
2423 \fIExamples\fR
2424 .IX Subsection "Examples"
2425 .PP
2426 There are a number of principal ways to embed other event loops or modules
2427 into libev. Here are some ideas on how to include libadns into libev
2428 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2429 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2430 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2431 Glib event loop).
2432 .PP
2433 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2434 and in a check watcher, destroy them and call into libadns. What follows
2435 is pseudo-code only of course. This requires you to either use a low
2436 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2437 the callbacks for the IO/timeout watchers might not have been called yet.
2438 .PP
2439 .Vb 2
2440 \& static ev_io iow [nfd];
2441 \& static ev_timer tw;
2442 \&
2443 \& static void
2444 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2445 \& {
2446 \& }
2447 \&
2448 \& // create io watchers for each fd and a timer before blocking
2449 \& static void
2450 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2451 \& {
2452 \& int timeout = 3600000;
2453 \& struct pollfd fds [nfd];
2454 \& // actual code will need to loop here and realloc etc.
2455 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2456 \&
2457 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2458 \& ev_timer_init (&tw, 0, timeout * 1e\-3);
2459 \& ev_timer_start (loop, &tw);
2460 \&
2461 \& // create one ev_io per pollfd
2462 \& for (int i = 0; i < nfd; ++i)
2463 \& {
2464 \& ev_io_init (iow + i, io_cb, fds [i].fd,
2465 \& ((fds [i].events & POLLIN ? EV_READ : 0)
2466 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2467 \&
2468 \& fds [i].revents = 0;
2469 \& ev_io_start (loop, iow + i);
2470 \& }
2471 \& }
2472 \&
2473 \& // stop all watchers after blocking
2474 \& static void
2475 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2476 \& {
2477 \& ev_timer_stop (loop, &tw);
2478 \&
2479 \& for (int i = 0; i < nfd; ++i)
2480 \& {
2481 \& // set the relevant poll flags
2482 \& // could also call adns_processreadable etc. here
2483 \& struct pollfd *fd = fds + i;
2484 \& int revents = ev_clear_pending (iow + i);
2485 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2486 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2487 \&
2488 \& // now stop the watcher
2489 \& ev_io_stop (loop, iow + i);
2490 \& }
2491 \&
2492 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2493 \& }
2494 .Ve
2495 .PP
2496 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2497 in the prepare watcher and would dispose of the check watcher.
2498 .PP
2499 Method 3: If the module to be embedded supports explicit event
2500 notification (libadns does), you can also make use of the actual watcher
2501 callbacks, and only destroy/create the watchers in the prepare watcher.
2502 .PP
2503 .Vb 5
2504 \& static void
2505 \& timer_cb (EV_P_ ev_timer *w, int revents)
2506 \& {
2507 \& adns_state ads = (adns_state)w\->data;
2508 \& update_now (EV_A);
2509 \&
2510 \& adns_processtimeouts (ads, &tv_now);
2511 \& }
2512 \&
2513 \& static void
2514 \& io_cb (EV_P_ ev_io *w, int revents)
2515 \& {
2516 \& adns_state ads = (adns_state)w\->data;
2517 \& update_now (EV_A);
2518 \&
2519 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2520 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2521 \& }
2522 \&
2523 \& // do not ever call adns_afterpoll
2524 .Ve
2525 .PP
2526 Method 4: Do not use a prepare or check watcher because the module you
2527 want to embed is not flexible enough to support it. Instead, you can
2528 override their poll function. The drawback with this solution is that the
2529 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2530 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2531 libglib event loop.
2532 .PP
2533 .Vb 4
2534 \& static gint
2535 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2536 \& {
2537 \& int got_events = 0;
2538 \&
2539 \& for (n = 0; n < nfds; ++n)
2540 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2541 \&
2542 \& if (timeout >= 0)
2543 \& // create/start timer
2544 \&
2545 \& // poll
2546 \& ev_loop (EV_A_ 0);
2547 \&
2548 \& // stop timer again
2549 \& if (timeout >= 0)
2550 \& ev_timer_stop (EV_A_ &to);
2551 \&
2552 \& // stop io watchers again \- their callbacks should have set
2553 \& for (n = 0; n < nfds; ++n)
2554 \& ev_io_stop (EV_A_ iow [n]);
2555 \&
2556 \& return got_events;
2557 \& }
2558 .Ve
2559 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2560 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2561 .IX Subsection "ev_embed - when one backend isn't enough..."
2562 This is a rather advanced watcher type that lets you embed one event loop
2563 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2564 loop, other types of watchers might be handled in a delayed or incorrect
2565 fashion and must not be used).
2566 .PP
2567 There are primarily two reasons you would want that: work around bugs and
2568 prioritise I/O.
2569 .PP
2570 As an example for a bug workaround, the kqueue backend might only support
2571 sockets on some platform, so it is unusable as generic backend, but you
2572 still want to make use of it because you have many sockets and it scales
2573 so nicely. In this case, you would create a kqueue-based loop and embed
2574 it into your default loop (which might use e.g. poll). Overall operation
2575 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2576 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2577 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2578 .PP
2579 As for prioritising I/O: under rare circumstances you have the case where
2580 some fds have to be watched and handled very quickly (with low latency),
2581 and even priorities and idle watchers might have too much overhead. In
2582 this case you would put all the high priority stuff in one loop and all
2583 the rest in a second one, and embed the second one in the first.
2584 .PP
2585 As long as the watcher is active, the callback will be invoked every time
2586 there might be events pending in the embedded loop. The callback must then
2587 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2588 their callbacks (you could also start an idle watcher to give the embedded
2589 loop strictly lower priority for example). You can also set the callback
2590 to \f(CW0\fR, in which case the embed watcher will automatically execute the
2591 embedded loop sweep.
2592 .PP
2593 As long as the watcher is started it will automatically handle events. The
2594 callback will be invoked whenever some events have been handled. You can
2595 set the callback to \f(CW0\fR to avoid having to specify one if you are not
2596 interested in that.
2597 .PP
2598 Also, there have not currently been made special provisions for forking:
2599 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2600 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2601 yourself \- but you can use a fork watcher to handle this automatically,
2602 and future versions of libev might do just that.
2603 .PP
2604 Unfortunately, not all backends are embeddable: only the ones returned by
2605 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2606 portable one.
2607 .PP
2608 So when you want to use this feature you will always have to be prepared
2609 that you cannot get an embeddable loop. The recommended way to get around
2610 this is to have a separate variables for your embeddable loop, try to
2611 create it, and if that fails, use the normal loop for everything.
2612 .PP
2613 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2614 .IX Subsection "ev_embed and fork"
2615 .PP
2616 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2617 automatically be applied to the embedded loop as well, so no special
2618 fork handling is required in that case. When the watcher is not running,
2619 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2620 as applicable.
2621 .PP
2622 \fIWatcher-Specific Functions and Data Members\fR
2623 .IX Subsection "Watcher-Specific Functions and Data Members"
2624 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2625 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2626 .PD 0
2627 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2628 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2629 .PD
2630 Configures the watcher to embed the given loop, which must be
2631 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2632 invoked automatically, otherwise it is the responsibility of the callback
2633 to invoke it (it will continue to be called until the sweep has been done,
2634 if you do not want that, you need to temporarily stop the embed watcher).
2635 .IP "ev_embed_sweep (loop, ev_embed *)" 4
2636 .IX Item "ev_embed_sweep (loop, ev_embed *)"
2637 Make a single, non-blocking sweep over the embedded loop. This works
2638 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2639 appropriate way for embedded loops.
2640 .IP "struct ev_loop *other [read\-only]" 4
2641 .IX Item "struct ev_loop *other [read-only]"
2642 The embedded event loop.
2643 .PP
2644 \fIExamples\fR
2645 .IX Subsection "Examples"
2646 .PP
2647 Example: Try to get an embeddable event loop and embed it into the default
2648 event loop. If that is not possible, use the default loop. The default
2649 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
2650 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
2651 used).
2652 .PP
2653 .Vb 3
2654 \& struct ev_loop *loop_hi = ev_default_init (0);
2655 \& struct ev_loop *loop_lo = 0;
2656 \& ev_embed embed;
2657 \&
2658 \& // see if there is a chance of getting one that works
2659 \& // (remember that a flags value of 0 means autodetection)
2660 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2661 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2662 \& : 0;
2663 \&
2664 \& // if we got one, then embed it, otherwise default to loop_hi
2665 \& if (loop_lo)
2666 \& {
2667 \& ev_embed_init (&embed, 0, loop_lo);
2668 \& ev_embed_start (loop_hi, &embed);
2669 \& }
2670 \& else
2671 \& loop_lo = loop_hi;
2672 .Ve
2673 .PP
2674 Example: Check if kqueue is available but not recommended and create
2675 a kqueue backend for use with sockets (which usually work with any
2676 kqueue implementation). Store the kqueue/socket\-only event loop in
2677 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2678 .PP
2679 .Vb 3
2680 \& struct ev_loop *loop = ev_default_init (0);
2681 \& struct ev_loop *loop_socket = 0;
2682 \& ev_embed embed;
2683 \&
2684 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2685 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2686 \& {
2687 \& ev_embed_init (&embed, 0, loop_socket);
2688 \& ev_embed_start (loop, &embed);
2689 \& }
2690 \&
2691 \& if (!loop_socket)
2692 \& loop_socket = loop;
2693 \&
2694 \& // now use loop_socket for all sockets, and loop for everything else
2695 .Ve
2696 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2697 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2698 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2699 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2700 whoever is a good citizen cared to tell libev about it by calling
2701 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2702 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2703 and only in the child after the fork. If whoever good citizen calling
2704 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2705 handlers will be invoked, too, of course.
2706 .PP
2707 \fIWatcher-Specific Functions and Data Members\fR
2708 .IX Subsection "Watcher-Specific Functions and Data Members"
2709 .IP "ev_fork_init (ev_signal *, callback)" 4
2710 .IX Item "ev_fork_init (ev_signal *, callback)"
2711 Initialises and configures the fork watcher \- it has no parameters of any
2712 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2713 believe me.
2714 .ie n .Sh """ev_async"" \- how to wake up another event loop"
2715 .el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2716 .IX Subsection "ev_async - how to wake up another event loop"
2717 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2718 asynchronous sources such as signal handlers (as opposed to multiple event
2719 loops \- those are of course safe to use in different threads).
2720 .PP
2721 Sometimes, however, you need to wake up another event loop you do not
2722 control, for example because it belongs to another thread. This is what
2723 \&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2724 can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2725 safe.
2726 .PP
2727 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2728 too, are asynchronous in nature, and signals, too, will be compressed
2729 (i.e. the number of callback invocations may be less than the number of
2730 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2731 .PP
2732 Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2733 just the default loop.
2734 .PP
2735 \fIQueueing\fR
2736 .IX Subsection "Queueing"
2737 .PP
2738 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2739 is that the author does not know of a simple (or any) algorithm for a
2740 multiple-writer-single-reader queue that works in all cases and doesn't
2741 need elaborate support such as pthreads.
2742 .PP
2743 That means that if you want to queue data, you have to provide your own
2744 queue. But at least I can tell you how to implement locking around your
2745 queue:
2746 .IP "queueing from a signal handler context" 4
2747 .IX Item "queueing from a signal handler context"
2748 To implement race-free queueing, you simply add to the queue in the signal
2749 handler but you block the signal handler in the watcher callback. Here is
2750 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
2751 .Sp
2752 .Vb 1
2753 \& static ev_async mysig;
2754 \&
2755 \& static void
2756 \& sigusr1_handler (void)
2757 \& {
2758 \& sometype data;
2759 \&
2760 \& // no locking etc.
2761 \& queue_put (data);
2762 \& ev_async_send (EV_DEFAULT_ &mysig);
2763 \& }
2764 \&
2765 \& static void
2766 \& mysig_cb (EV_P_ ev_async *w, int revents)
2767 \& {
2768 \& sometype data;
2769 \& sigset_t block, prev;
2770 \&
2771 \& sigemptyset (&block);
2772 \& sigaddset (&block, SIGUSR1);
2773 \& sigprocmask (SIG_BLOCK, &block, &prev);
2774 \&
2775 \& while (queue_get (&data))
2776 \& process (data);
2777 \&
2778 \& if (sigismember (&prev, SIGUSR1)
2779 \& sigprocmask (SIG_UNBLOCK, &block, 0);
2780 \& }
2781 .Ve
2782 .Sp
2783 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2784 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2785 either...).
2786 .IP "queueing from a thread context" 4
2787 .IX Item "queueing from a thread context"
2788 The strategy for threads is different, as you cannot (easily) block
2789 threads but you can easily preempt them, so to queue safely you need to
2790 employ a traditional mutex lock, such as in this pthread example:
2791 .Sp
2792 .Vb 2
2793 \& static ev_async mysig;
2794 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2795 \&
2796 \& static void
2797 \& otherthread (void)
2798 \& {
2799 \& // only need to lock the actual queueing operation
2800 \& pthread_mutex_lock (&mymutex);
2801 \& queue_put (data);
2802 \& pthread_mutex_unlock (&mymutex);
2803 \&
2804 \& ev_async_send (EV_DEFAULT_ &mysig);
2805 \& }
2806 \&
2807 \& static void
2808 \& mysig_cb (EV_P_ ev_async *w, int revents)
2809 \& {
2810 \& pthread_mutex_lock (&mymutex);
2811 \&
2812 \& while (queue_get (&data))
2813 \& process (data);
2814 \&
2815 \& pthread_mutex_unlock (&mymutex);
2816 \& }
2817 .Ve
2818 .PP
2819 \fIWatcher-Specific Functions and Data Members\fR
2820 .IX Subsection "Watcher-Specific Functions and Data Members"
2821 .IP "ev_async_init (ev_async *, callback)" 4
2822 .IX Item "ev_async_init (ev_async *, callback)"
2823 Initialises and configures the async watcher \- it has no parameters of any
2824 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
2825 trust me.
2826 .IP "ev_async_send (loop, ev_async *)" 4
2827 .IX Item "ev_async_send (loop, ev_async *)"
2828 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2829 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2830 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
2831 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2832 section below on what exactly this means).
2833 .Sp
2834 This call incurs the overhead of a system call only once per loop iteration,
2835 so while the overhead might be noticeable, it doesn't apply to repeated
2836 calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2837 .IP "bool = ev_async_pending (ev_async *)" 4
2838 .IX Item "bool = ev_async_pending (ev_async *)"
2839 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2840 watcher but the event has not yet been processed (or even noted) by the
2841 event loop.
2842 .Sp
2843 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2844 the loop iterates next and checks for the watcher to have become active,
2845 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2846 quickly check whether invoking the loop might be a good idea.
2847 .Sp
2848 Not that this does \fInot\fR check whether the watcher itself is pending, only
2849 whether it has been requested to make this watcher pending.
2850 .SH "OTHER FUNCTIONS"
2851 .IX Header "OTHER FUNCTIONS"
2852 There are some other functions of possible interest. Described. Here. Now.
2853 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
2854 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
2855 This function combines a simple timer and an I/O watcher, calls your
2856 callback on whichever event happens first and automatically stops both
2857 watchers. This is useful if you want to wait for a single event on an fd
2858 or timeout without having to allocate/configure/start/stop/free one or
2859 more watchers yourself.
2860 .Sp
2861 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
2862 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
2863 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
2864 .Sp
2865 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2866 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2867 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
2868 .Sp
2869 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
2870 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2871 \&\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
2872 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
2873 a timeout and an io event at the same time \- you probably should give io
2874 events precedence.
2875 .Sp
2876 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
2877 .Sp
2878 .Vb 7
2879 \& static void stdin_ready (int revents, void *arg)
2880 \& {
2881 \& if (revents & EV_READ)
2882 \& /* stdin might have data for us, joy! */;
2883 \& else if (revents & EV_TIMEOUT)
2884 \& /* doh, nothing entered */;
2885 \& }
2886 \&
2887 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2888 .Ve
2889 .IP "ev_feed_event (struct ev_loop *, watcher *, int revents)" 4
2890 .IX Item "ev_feed_event (struct ev_loop *, watcher *, int revents)"
2891 Feeds the given event set into the event loop, as if the specified event
2892 had happened for the specified watcher (which must be a pointer to an
2893 initialised but not necessarily started event watcher).
2894 .IP "ev_feed_fd_event (struct ev_loop *, int fd, int revents)" 4
2895 .IX Item "ev_feed_fd_event (struct ev_loop *, int fd, int revents)"
2896 Feed an event on the given fd, as if a file descriptor backend detected
2897 the given events it.
2898 .IP "ev_feed_signal_event (struct ev_loop *loop, int signum)" 4
2899 .IX Item "ev_feed_signal_event (struct ev_loop *loop, int signum)"
2900 Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
2901 loop!).
2902 .SH "LIBEVENT EMULATION"
2903 .IX Header "LIBEVENT EMULATION"
2904 Libev offers a compatibility emulation layer for libevent. It cannot
2905 emulate the internals of libevent, so here are some usage hints:
2906 .IP "\(bu" 4
2907 Use it by including <event.h>, as usual.
2908 .IP "\(bu" 4
2909 The following members are fully supported: ev_base, ev_callback,
2910 ev_arg, ev_fd, ev_res, ev_events.
2911 .IP "\(bu" 4
2912 Avoid using ev_flags and the EVLIST_*\-macros, while it is
2913 maintained by libev, it does not work exactly the same way as in libevent (consider
2914 it a private \s-1API\s0).
2915 .IP "\(bu" 4
2916 Priorities are not currently supported. Initialising priorities
2917 will fail and all watchers will have the same priority, even though there
2918 is an ev_pri field.
2919 .IP "\(bu" 4
2920 In libevent, the last base created gets the signals, in libev, the
2921 first base created (== the default loop) gets the signals.
2922 .IP "\(bu" 4
2923 Other members are not supported.
2924 .IP "\(bu" 4
2925 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2926 to use the libev header file and library.
2927 .SH "\*(C+ SUPPORT"
2928 .IX Header " SUPPORT"
2929 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2930 you to use some convenience methods to start/stop watchers and also change
2931 the callback model to a model using method callbacks on objects.
2932 .PP
2933 To use it,
2934 .PP
2935 .Vb 1
2936 \& #include <ev++.h>
2937 .Ve
2938 .PP
2939 This automatically includes \fIev.h\fR and puts all of its definitions (many
2940 of them macros) into the global namespace. All \*(C+ specific things are
2941 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2942 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2943 .PP
2944 Care has been taken to keep the overhead low. The only data member the \*(C+
2945 classes add (compared to plain C\-style watchers) is the event loop pointer
2946 that the watcher is associated with (or no additional members at all if
2947 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2948 .PP
2949 Currently, functions, and static and non-static member functions can be
2950 used as callbacks. Other types should be easy to add as long as they only
2951 need one additional pointer for context. If you need support for other
2952 types of functors please contact the author (preferably after implementing
2953 it).
2954 .PP
2955 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2956 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2957 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2958 .IX Item "ev::READ, ev::WRITE etc."
2959 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2960 macros from \fIev.h\fR.
2961 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2962 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2963 .IX Item "ev::tstamp, ev::now"
2964 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2965 .ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
2966 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2967 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2968 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2969 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2970 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2971 defines by many implementations.
2972 .Sp
2973 All of those classes have these methods:
2974 .RS 4
2975 .IP "ev::TYPE::TYPE ()" 4
2976 .IX Item "ev::TYPE::TYPE ()"
2977 .PD 0
2978 .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2979 .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2980 .IP "ev::TYPE::~TYPE" 4
2981 .IX Item "ev::TYPE::~TYPE"
2982 .PD
2983 The constructor (optionally) takes an event loop to associate the watcher
2984 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2985 .Sp
2986 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2987 \&\f(CW\*(C`set\*(C'\fR method before starting it.
2988 .Sp
2989 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2990 method to set a callback before you can start the watcher.
2991 .Sp
2992 (The reason why you have to use a method is a limitation in \*(C+ which does
2993 not allow explicit template arguments for constructors).
2994 .Sp
2995 The destructor automatically stops the watcher if it is active.
2996 .IP "w\->set<class, &class::method> (object *)" 4
2997 .IX Item "w->set<class, &class::method> (object *)"
2998 This method sets the callback method to call. The method has to have a
2999 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3000 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3001 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3002 .Sp
3003 This method synthesizes efficient thunking code to call your method from
3004 the C callback that libev requires. If your compiler can inline your
3005 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3006 your compiler is good :), then the method will be fully inlined into the
3007 thunking function, making it as fast as a direct C callback.
3008 .Sp
3009 Example: simple class declaration and watcher initialisation
3010 .Sp
3011 .Vb 4
3012 \& struct myclass
3013 \& {
3014 \& void io_cb (ev::io &w, int revents) { }
3015 \& }
3016 \&
3017 \& myclass obj;
3018 \& ev::io iow;
3019 \& iow.set <myclass, &myclass::io_cb> (&obj);
3020 .Ve
3021 .IP "w\->set<function> (void *data = 0)" 4
3022 .IX Item "w->set<function> (void *data = 0)"
3023 Also sets a callback, but uses a static method or plain function as
3024 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3025 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3026 .Sp
3027 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3028 .Sp
3029 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3030 .Sp
3031 Example: Use a plain function as callback.
3032 .Sp
3033 .Vb 2
3034 \& static void io_cb (ev::io &w, int revents) { }
3035 \& iow.set <io_cb> ();
3036 .Ve
3037 .IP "w\->set (struct ev_loop *)" 4
3038 .IX Item "w->set (struct ev_loop *)"
3039 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3040 do this when the watcher is inactive (and not pending either).
3041 .IP "w\->set ([arguments])" 4
3042 .IX Item "w->set ([arguments])"
3043 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3044 called at least once. Unlike the C counterpart, an active watcher gets
3045 automatically stopped and restarted when reconfiguring it with this
3046 method.
3047 .IP "w\->start ()" 4
3048 .IX Item "w->start ()"
3049 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3050 constructor already stores the event loop.
3051 .IP "w\->stop ()" 4
3052 .IX Item "w->stop ()"
3053 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3054 .ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
3055 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3056 .IX Item "w->again () (ev::timer, ev::periodic only)"
3057 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3058 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3059 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3060 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3061 .IX Item "w->sweep () (ev::embed only)"
3062 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3063 .ie n .IP "w\->update () (""ev::stat"" only)" 4
3064 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3065 .IX Item "w->update () (ev::stat only)"
3066 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3067 .RE
3068 .RS 4
3069 .RE
3070 .PP
3071 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3072 the constructor.
3073 .PP
3074 .Vb 4
3075 \& class myclass
3076 \& {
3077 \& ev::io io ; void io_cb (ev::io &w, int revents);
3078 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3079 \&
3080 \& myclass (int fd)
3081 \& {
3082 \& io .set <myclass, &myclass::io_cb > (this);
3083 \& idle.set <myclass, &myclass::idle_cb> (this);
3084 \&
3085 \& io.start (fd, ev::READ);
3086 \& }
3087 \& };
3088 .Ve
3089 .SH "OTHER LANGUAGE BINDINGS"
3090 .IX Header "OTHER LANGUAGE BINDINGS"
3091 Libev does not offer other language bindings itself, but bindings for a
3092 number of languages exist in the form of third-party packages. If you know
3093 any interesting language binding in addition to the ones listed here, drop
3094 me a note.
3095 .IP "Perl" 4
3096 .IX Item "Perl"
3097 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3098 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3099 there are additional modules that implement libev-compatible interfaces
3100 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),
3101 \&\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
3102 and \f(CW\*(C`EV::Glib\*(C'\fR).
3103 .Sp
3104 It can be found and installed via \s-1CPAN\s0, its homepage is at
3105 <http://software.schmorp.de/pkg/EV>.
3106 .IP "Python" 4
3107 .IX Item "Python"
3108 Python bindings can be found at <http://code.google.com/p/pyev/>. It
3109 seems to be quite complete and well-documented. Note, however, that the
3110 patch they require for libev is outright dangerous as it breaks the \s-1ABI\s0
3111 for everybody else, and therefore, should never be applied in an installed
3112 libev (if python requires an incompatible \s-1ABI\s0 then it needs to embed
3113 libev).
3114 .IP "Ruby" 4
3115 .IX Item "Ruby"
3116 Tony Arcieri has written a ruby extension that offers access to a subset
3117 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3118 more on top of it. It can be found via gem servers. Its homepage is at
3119 <http://rev.rubyforge.org/>.
3120 .IP "D" 4
3121 .IX Item "D"
3122 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3123 be found at <http://proj.llucax.com.ar/wiki/evd>.
3124 .IP "Ocaml" 4
3125 .IX Item "Ocaml"
3126 Erkki Seppala has written Ocaml bindings for libev, to be found at
3127 <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3128 .SH "MACRO MAGIC"
3129 .IX Header "MACRO MAGIC"
3130 Libev can be compiled with a variety of options, the most fundamental
3131 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3132 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3133 .PP
3134 To make it easier to write programs that cope with either variant, the
3135 following macros are defined:
3136 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
3137 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3138 .IX Item "EV_A, EV_A_"
3139 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3140 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3141 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3142 .Sp
3143 .Vb 3
3144 \& ev_unref (EV_A);
3145 \& ev_timer_add (EV_A_ watcher);
3146 \& ev_loop (EV_A_ 0);
3147 .Ve
3148 .Sp
3149 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3150 which is often provided by the following macro.
3151 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
3152 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3153 .IX Item "EV_P, EV_P_"
3154 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3155 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3156 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3157 .Sp
3158 .Vb 2
3159 \& // this is how ev_unref is being declared
3160 \& static void ev_unref (EV_P);
3161 \&
3162 \& // this is how you can declare your typical callback
3163 \& static void cb (EV_P_ ev_timer *w, int revents)
3164 .Ve
3165 .Sp
3166 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3167 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3168 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
3169 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3170 .IX Item "EV_DEFAULT, EV_DEFAULT_"
3171 Similar to the other two macros, this gives you the value of the default
3172 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3173 .ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
3174 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3175 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3176 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3177 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3178 is undefined when the default loop has not been initialised by a previous
3179 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.
3180 .Sp
3181 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3182 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3183 .PP
3184 Example: Declare and initialise a check watcher, utilising the above
3185 macros so it will work regardless of whether multiple loops are supported
3186 or not.
3187 .PP
3188 .Vb 5
3189 \& static void
3190 \& check_cb (EV_P_ ev_timer *w, int revents)
3191 \& {
3192 \& ev_check_stop (EV_A_ w);
3193 \& }
3194 \&
3195 \& ev_check check;
3196 \& ev_check_init (&check, check_cb);
3197 \& ev_check_start (EV_DEFAULT_ &check);
3198 \& ev_loop (EV_DEFAULT_ 0);
3199 .Ve
3200 .SH "EMBEDDING"
3201 .IX Header "EMBEDDING"
3202 Libev can (and often is) directly embedded into host
3203 applications. Examples of applications that embed it include the Deliantra
3204 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3205 and rxvt-unicode.
3206 .PP
3207 The goal is to enable you to just copy the necessary files into your
3208 source directory without having to change even a single line in them, so
3209 you can easily upgrade by simply copying (or having a checked-out copy of
3210 libev somewhere in your source tree).
3211 .Sh "\s-1FILESETS\s0"
3212 .IX Subsection "FILESETS"
3213 Depending on what features you need you need to include one or more sets of files
3214 in your application.
3215 .PP
3216 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3217 .IX Subsection "CORE EVENT LOOP"
3218 .PP
3219 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3220 configuration (no autoconf):
3221 .PP
3222 .Vb 2
3223 \& #define EV_STANDALONE 1
3224 \& #include "ev.c"
3225 .Ve
3226 .PP
3227 This will automatically include \fIev.h\fR, too, and should be done in a
3228 single C source file only to provide the function implementations. To use
3229 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3230 done by writing a wrapper around \fIev.h\fR that you can include instead and
3231 where you can put other configuration options):
3232 .PP
3233 .Vb 2
3234 \& #define EV_STANDALONE 1
3235 \& #include "ev.h"
3236 .Ve
3237 .PP
3238 Both header files and implementation files can be compiled with a \*(C+
3239 compiler (at least, that's a stated goal, and breakage will be treated
3240 as a bug).
3241 .PP
3242 You need the following files in your source tree, or in a directory
3243 in your include path (e.g. in libev/ when using \-Ilibev):
3244 .PP
3245 .Vb 4
3246 \& ev.h
3247 \& ev.c
3248 \& ev_vars.h
3249 \& ev_wrap.h
3250 \&
3251 \& ev_win32.c required on win32 platforms only
3252 \&
3253 \& ev_select.c only when select backend is enabled (which is enabled by default)
3254 \& ev_poll.c only when poll backend is enabled (disabled by default)
3255 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3256 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3257 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
3258 .Ve
3259 .PP
3260 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
3261 to compile this single file.
3262 .PP
3263 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3264 .IX Subsection "LIBEVENT COMPATIBILITY API"
3265 .PP
3266 To include the libevent compatibility \s-1API\s0, also include:
3267 .PP
3268 .Vb 1
3269 \& #include "event.c"
3270 .Ve
3271 .PP
3272 in the file including \fIev.c\fR, and:
3273 .PP
3274 .Vb 1
3275 \& #include "event.h"
3276 .Ve
3277 .PP
3278 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3279 .PP
3280 You need the following additional files for this:
3281 .PP
3282 .Vb 2
3283 \& event.h
3284 \& event.c
3285 .Ve
3286 .PP
3287 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3288 .IX Subsection "AUTOCONF SUPPORT"
3289 .PP
3290 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3291 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3292 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3293 include \fIconfig.h\fR and configure itself accordingly.
3294 .PP
3295 For this of course you need the m4 file:
3296 .PP
3297 .Vb 1
3298 \& libev.m4
3299 .Ve
3300 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3301 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3302 Libev can be configured via a variety of preprocessor symbols you have to
3303 define before including any of its files. The default in the absence of
3304 autoconf is documented for every option.
3305 .IP "\s-1EV_STANDALONE\s0" 4
3306 .IX Item "EV_STANDALONE"
3307 Must always be \f(CW1\fR if you do not use autoconf configuration, which
3308 keeps libev from including \fIconfig.h\fR, and it also defines dummy
3309 implementations for some libevent functions (such as logging, which is not
3310 supported). It will also not define any of the structs usually found in
3311 \&\fIevent.h\fR that are not directly supported by the libev core alone.
3312 .IP "\s-1EV_USE_MONOTONIC\s0" 4
3313 .IX Item "EV_USE_MONOTONIC"
3314 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3315 monotonic clock option at both compile time and runtime. Otherwise no use
3316 of the monotonic clock option will be attempted. If you enable this, you
3317 usually have to link against librt or something similar. Enabling it when
3318 the functionality isn't available is safe, though, although you have
3319 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3320 function is hiding in (often \fI\-lrt\fR).
3321 .IP "\s-1EV_USE_REALTIME\s0" 4
3322 .IX Item "EV_USE_REALTIME"
3323 If defined to be \f(CW1\fR, libev will try to detect the availability of the
3324 real-time clock option at compile time (and assume its availability at
3325 runtime if successful). Otherwise no use of the real-time clock option will
3326 be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
3327 (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
3328 note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
3329 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
3330 .IX Item "EV_USE_NANOSLEEP"
3331 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3332 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3333 .IP "\s-1EV_USE_EVENTFD\s0" 4
3334 .IX Item "EV_USE_EVENTFD"
3335 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3336 available and will probe for kernel support at runtime. This will improve
3337 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3338 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3339 2.7 or newer, otherwise disabled.
3340 .IP "\s-1EV_USE_SELECT\s0" 4
3341 .IX Item "EV_USE_SELECT"
3342 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3343 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3344 other method takes over, select will be it. Otherwise the select backend
3345 will not be compiled in.
3346 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3347 .IX Item "EV_SELECT_USE_FD_SET"
3348 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3349 structure. This is useful if libev doesn't compile due to a missing
3350 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout on
3351 exotic systems. This usually limits the range of file descriptors to some
3352 low limit such as 1024 or might have other limitations (winsocket only
3353 allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
3354 influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
3355 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3356 .IX Item "EV_SELECT_IS_WINSOCKET"
3357 When defined to \f(CW1\fR, the select backend will assume that
3358 select/socket/connect etc. don't understand file descriptors but
3359 wants osf handles on win32 (this is the case when the select to
3360 be used is the winsock select). This means that it will call
3361 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3362 it is assumed that all these functions actually work on fds, even
3363 on win32. Should not be defined on non\-win32 platforms.
3364 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
3365 .IX Item "EV_FD_TO_WIN32_HANDLE"
3366 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3367 file descriptors to socket handles. When not defining this symbol (the
3368 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3369 correct. In some cases, programs use their own file descriptor management,
3370 in which case they can provide this function to map fds to socket handles.
3371 .IP "\s-1EV_USE_POLL\s0" 4
3372 .IX Item "EV_USE_POLL"
3373 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3374 backend. Otherwise it will be enabled on non\-win32 platforms. It
3375 takes precedence over select.
3376 .IP "\s-1EV_USE_EPOLL\s0" 4
3377 .IX Item "EV_USE_EPOLL"
3378 If defined to be \f(CW1\fR, libev will compile in support for the Linux
3379 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3380 otherwise another method will be used as fallback. This is the preferred
3381 backend for GNU/Linux systems. If undefined, it will be enabled if the
3382 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3383 .IP "\s-1EV_USE_KQUEUE\s0" 4
3384 .IX Item "EV_USE_KQUEUE"
3385 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3386 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3387 otherwise another method will be used as fallback. This is the preferred
3388 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3389 supports some types of fds correctly (the only platform we found that
3390 supports ptys for example was NetBSD), so kqueue might be compiled in, but
3391 not be used unless explicitly requested. The best way to use it is to find
3392 out whether kqueue supports your type of fd properly and use an embedded
3393 kqueue loop.
3394 .IP "\s-1EV_USE_PORT\s0" 4
3395 .IX Item "EV_USE_PORT"
3396 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
3397 10 port style backend. Its availability will be detected at runtime,
3398 otherwise another method will be used as fallback. This is the preferred
3399 backend for Solaris 10 systems.
3400 .IP "\s-1EV_USE_DEVPOLL\s0" 4
3401 .IX Item "EV_USE_DEVPOLL"
3402 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3403 .IP "\s-1EV_USE_INOTIFY\s0" 4
3404 .IX Item "EV_USE_INOTIFY"
3405 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3406 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3407 be detected at runtime. If undefined, it will be enabled if the headers
3408 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3409 .IP "\s-1EV_ATOMIC_T\s0" 4
3410 .IX Item "EV_ATOMIC_T"
3411 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3412 access is atomic with respect to other threads or signal contexts. No such
3413 type is easily found in the C language, so you can provide your own type
3414 that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3415 as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3416 .Sp
3417 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3418 (from \fIsignal.h\fR), which is usually good enough on most platforms.
3419 .IP "\s-1EV_H\s0" 4
3420 .IX Item "EV_H"
3421 The name of the \fIev.h\fR header file used to include it. The default if
3422 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3423 used to virtually rename the \fIev.h\fR header file in case of conflicts.
3424 .IP "\s-1EV_CONFIG_H\s0" 4
3425 .IX Item "EV_CONFIG_H"
3426 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3427 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3428 \&\f(CW\*(C`EV_H\*(C'\fR, above.
3429 .IP "\s-1EV_EVENT_H\s0" 4
3430 .IX Item "EV_EVENT_H"
3431 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3432 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3433 .IP "\s-1EV_PROTOTYPES\s0" 4
3434 .IX Item "EV_PROTOTYPES"
3435 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3436 prototypes, but still define all the structs and other symbols. This is
3437 occasionally useful if you want to provide your own wrapper functions
3438 around libev functions.
3439 .IP "\s-1EV_MULTIPLICITY\s0" 4
3440 .IX Item "EV_MULTIPLICITY"
3441 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3442 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3443 additional independent event loops. Otherwise there will be no support
3444 for multiple event loops and there is no first event loop pointer
3445 argument. Instead, all functions act on the single default loop.
3446 .IP "\s-1EV_MINPRI\s0" 4
3447 .IX Item "EV_MINPRI"
3448 .PD 0
3449 .IP "\s-1EV_MAXPRI\s0" 4
3450 .IX Item "EV_MAXPRI"
3451 .PD
3452 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3453 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3454 provide for more priorities by overriding those symbols (usually defined
3455 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3456 .Sp
3457 When doing priority-based operations, libev usually has to linearly search
3458 all the priorities, so having many of them (hundreds) uses a lot of space
3459 and time, so using the defaults of five priorities (\-2 .. +2) is usually
3460 fine.
3461 .Sp
3462 If your embedding application does not need any priorities, defining these
3463 both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3464 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3465 .IX Item "EV_PERIODIC_ENABLE"
3466 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3467 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3468 code.
3469 .IP "\s-1EV_IDLE_ENABLE\s0" 4
3470 .IX Item "EV_IDLE_ENABLE"
3471 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3472 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3473 code.
3474 .IP "\s-1EV_EMBED_ENABLE\s0" 4
3475 .IX Item "EV_EMBED_ENABLE"
3476 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3477 defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3478 watcher types, which therefore must not be disabled.
3479 .IP "\s-1EV_STAT_ENABLE\s0" 4
3480 .IX Item "EV_STAT_ENABLE"
3481 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3482 defined to be \f(CW0\fR, then they are not.
3483 .IP "\s-1EV_FORK_ENABLE\s0" 4
3484 .IX Item "EV_FORK_ENABLE"
3485 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3486 defined to be \f(CW0\fR, then they are not.
3487 .IP "\s-1EV_ASYNC_ENABLE\s0" 4
3488 .IX Item "EV_ASYNC_ENABLE"
3489 If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3490 defined to be \f(CW0\fR, then they are not.
3491 .IP "\s-1EV_MINIMAL\s0" 4
3492 .IX Item "EV_MINIMAL"
3493 If you need to shave off some kilobytes of code at the expense of some
3494 speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3495 inlining decisions, saves roughly 30% code size on amd64. It also selects a
3496 much smaller 2\-heap for timer management over the default 4\-heap.
3497 .IP "\s-1EV_PID_HASHSIZE\s0" 4
3498 .IX Item "EV_PID_HASHSIZE"
3499 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3500 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3501 than enough. If you need to manage thousands of children you might want to
3502 increase this value (\fImust\fR be a power of two).
3503 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3504 .IX Item "EV_INOTIFY_HASHSIZE"
3505 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3506 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3507 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3508 watchers you might want to increase this value (\fImust\fR be a power of
3509 two).
3510 .IP "\s-1EV_USE_4HEAP\s0" 4
3511 .IX Item "EV_USE_4HEAP"
3512 Heaps are not very cache-efficient. To improve the cache-efficiency of the
3513 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3514 to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3515 faster performance with many (thousands) of watchers.
3516 .Sp
3517 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3518 (disabled).
3519 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3520 .IX Item "EV_HEAP_CACHE_AT"
3521 Heaps are not very cache-efficient. To improve the cache-efficiency of the
3522 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
3523 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3524 which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3525 but avoids random read accesses on heap changes. This improves performance
3526 noticeably with many (hundreds) of watchers.
3527 .Sp
3528 The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3529 (disabled).
3530 .IP "\s-1EV_VERIFY\s0" 4
3531 .IX Item "EV_VERIFY"
3532 Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3533 be done: If set to \f(CW0\fR, no internal verification code will be compiled
3534 in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3535 called. If set to \f(CW2\fR, then the internal verification code will be
3536 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3537 verification code will be called very frequently, which will slow down
3538 libev considerably.
3539 .Sp
3540 The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3541 \&\f(CW0\fR.
3542 .IP "\s-1EV_COMMON\s0" 4
3543 .IX Item "EV_COMMON"
3544 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3545 this macro to a something else you can include more and other types of
3546 members. You have to define it each time you include one of the files,
3547 though, and it must be identical each time.
3548 .Sp
3549 For example, the perl \s-1EV\s0 module uses something like this:
3550 .Sp
3551 .Vb 3
3552 \& #define EV_COMMON \e
3553 \& SV *self; /* contains this struct */ \e
3554 \& SV *cb_sv, *fh /* note no trailing ";" */
3555 .Ve
3556 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3557 .IX Item "EV_CB_DECLARE (type)"
3558 .PD 0
3559 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3560 .IX Item "EV_CB_INVOKE (watcher, revents)"
3561 .IP "ev_set_cb (ev, cb)" 4
3562 .IX Item "ev_set_cb (ev, cb)"
3563 .PD
3564 Can be used to change the callback member declaration in each watcher,
3565 and the way callbacks are invoked and set. Must expand to a struct member
3566 definition and a statement, respectively. See the \fIev.h\fR header file for
3567 their default definitions. One possible use for overriding these is to
3568 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3569 method calls instead of plain function calls in \*(C+.
3570 .Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3571 .IX Subsection "EXPORTED API SYMBOLS"
3572 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
3573 exported symbols, you can use the provided \fISymbol.*\fR files which list
3574 all public symbols, one per line:
3575 .PP
3576 .Vb 2
3577 \& Symbols.ev for libev proper
3578 \& Symbols.event for the libevent emulation
3579 .Ve
3580 .PP
3581 This can also be used to rename all public symbols to avoid clashes with
3582 multiple versions of libev linked together (which is obviously bad in
3583 itself, but sometimes it is inconvenient to avoid this).
3584 .PP
3585 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3586 include before including \fIev.h\fR:
3587 .PP
3588 .Vb 1
3589 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3590 .Ve
3591 .PP
3592 This would create a file \fIwrap.h\fR which essentially looks like this:
3593 .PP
3594 .Vb 4
3595 \& #define ev_backend myprefix_ev_backend
3596 \& #define ev_check_start myprefix_ev_check_start
3597 \& #define ev_check_stop myprefix_ev_check_stop
3598 \& ...
3599 .Ve
3600 .Sh "\s-1EXAMPLES\s0"
3601 .IX Subsection "EXAMPLES"
3602 For a real-world example of a program the includes libev
3603 verbatim, you can have a look at the \s-1EV\s0 perl module
3604 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3605 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3606 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3607 will be compiled. It is pretty complex because it provides its own header
3608 file.
3609 .PP
3610 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3611 that everybody includes and which overrides some configure choices:
3612 .PP
3613 .Vb 9
3614 \& #define EV_MINIMAL 1
3615 \& #define EV_USE_POLL 0
3616 \& #define EV_MULTIPLICITY 0
3617 \& #define EV_PERIODIC_ENABLE 0
3618 \& #define EV_STAT_ENABLE 0
3619 \& #define EV_FORK_ENABLE 0
3620 \& #define EV_CONFIG_H <config.h>
3621 \& #define EV_MINPRI 0
3622 \& #define EV_MAXPRI 0
3623 \&
3624 \& #include "ev++.h"
3625 .Ve
3626 .PP
3627 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3628 .PP
3629 .Vb 2
3630 \& #include "ev_cpp.h"
3631 \& #include "ev.c"
3632 .Ve
3633 .SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
3634 .IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
3635 .Sh "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
3636 .IX Subsection "THREADS AND COROUTINES"
3637 \fI\s-1THREADS\s0\fR
3638 .IX Subsection "THREADS"
3639 .PP
3640 All libev functions are reentrant and thread-safe unless explicitly
3641 documented otherwise, but libev implements no locking itself. This means
3642 that you can use as many loops as you want in parallel, as long as there
3643 are no concurrent calls into any libev function with the same loop
3644 parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
3645 of course): libev guarantees that different event loops share no data
3646 structures that need any locking.
3647 .PP
3648 Or to put it differently: calls with different loop parameters can be done
3649 concurrently from multiple threads, calls with the same loop parameter
3650 must be done serially (but can be done from different threads, as long as
3651 only one thread ever is inside a call at any point in time, e.g. by using
3652 a mutex per loop).
3653 .PP
3654 Specifically to support threads (and signal handlers), libev implements
3655 so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
3656 concurrency on the same event loop, namely waking it up \*(L"from the
3657 outside\*(R".
3658 .PP
3659 If you want to know which design (one loop, locking, or multiple loops
3660 without or something else still) is best for your problem, then I cannot
3661 help you, but here is some generic advice:
3662 .IP "\(bu" 4
3663 most applications have a main thread: use the default libev loop
3664 in that thread, or create a separate thread running only the default loop.
3665 .Sp
3666 This helps integrating other libraries or software modules that use libev
3667 themselves and don't care/know about threading.
3668 .IP "\(bu" 4
3669 one loop per thread is usually a good model.
3670 .Sp
3671 Doing this is almost never wrong, sometimes a better-performance model
3672 exists, but it is always a good start.
3673 .IP "\(bu" 4
3674 other models exist, such as the leader/follower pattern, where one
3675 loop is handed through multiple threads in a kind of round-robin fashion.
3676 .Sp
3677 Choosing a model is hard \- look around, learn, know that usually you can do
3678 better than you currently do :\-)
3679 .IP "\(bu" 4
3680 often you need to talk to some other thread which blocks in the
3681 event loop.
3682 .Sp
3683 \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
3684 (or from signal contexts...).
3685 .Sp
3686 An example use would be to communicate signals or other events that only
3687 work in the default loop by registering the signal watcher with the
3688 default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
3689 watcher callback into the event loop interested in the signal.
3690 .PP
3691 \fI\s-1COROUTINES\s0\fR
3692 .IX Subsection "COROUTINES"
3693 .PP
3694 Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
3695 libev fully supports nesting calls to its functions from different
3696 coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3697 different coroutines, and switch freely between both coroutines running the
3698 loop, as long as you don't confuse yourself). The only exception is that
3699 you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3700 .PP
3701 Care has been taken to ensure that libev does not keep local state inside
3702 \&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
3703 they do not call any callbacks.
3704 .Sh "\s-1COMPILER\s0 \s-1WARNINGS\s0"
3705 .IX Subsection "COMPILER WARNINGS"
3706 Depending on your compiler and compiler settings, you might get no or a
3707 lot of warnings when compiling libev code. Some people are apparently
3708 scared by this.
3709 .PP
3710 However, these are unavoidable for many reasons. For one, each compiler
3711 has different warnings, and each user has different tastes regarding
3712 warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
3713 targeting a specific compiler and compiler-version.
3714 .PP
3715 Another reason is that some compiler warnings require elaborate
3716 workarounds, or other changes to the code that make it less clear and less
3717 maintainable.
3718 .PP
3719 And of course, some compiler warnings are just plain stupid, or simply
3720 wrong (because they don't actually warn about the condition their message
3721 seems to warn about). For example, certain older gcc versions had some
3722 warnings that resulted an extreme number of false positives. These have
3723 been fixed, but some people still insist on making code warn-free with
3724 such buggy versions.
3725 .PP
3726 While libev is written to generate as few warnings as possible,
3727 \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
3728 with any compiler warnings enabled unless you are prepared to cope with
3729 them (e.g. by ignoring them). Remember that warnings are just that:
3730 warnings, not errors, or proof of bugs.
3731 .Sh "\s-1VALGRIND\s0"
3732 .IX Subsection "VALGRIND"
3733 Valgrind has a special section here because it is a popular tool that is
3734 highly useful. Unfortunately, valgrind reports are very hard to interpret.
3735 .PP
3736 If you think you found a bug (memory leak, uninitialised data access etc.)
3737 in libev, then check twice: If valgrind reports something like:
3738 .PP
3739 .Vb 3
3740 \& ==2274== definitely lost: 0 bytes in 0 blocks.
3741 \& ==2274== possibly lost: 0 bytes in 0 blocks.
3742 \& ==2274== still reachable: 256 bytes in 1 blocks.
3743 .Ve
3744 .PP
3745 Then there is no memory leak, just as memory accounted to global variables
3746 is not a memleak \- the memory is still being referenced, and didn't leak.
3747 .PP
3748 Similarly, under some circumstances, valgrind might report kernel bugs
3749 as if it were a bug in libev (e.g. in realloc or in the poll backend,
3750 although an acceptable workaround has been found here), or it might be
3751 confused.
3752 .PP
3753 Keep in mind that valgrind is a very good tool, but only a tool. Don't
3754 make it into some kind of religion.
3755 .PP
3756 If you are unsure about something, feel free to contact the mailing list
3757 with the full valgrind report and an explanation on why you think this
3758 is a bug in libev (best check the archives, too :). However, don't be
3759 annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
3760 of learning how to interpret valgrind properly.
3761 .PP
3762 If you need, for some reason, empty reports from valgrind for your project
3763 I suggest using suppression lists.
3764 .SH "PORTABILITY NOTES"
3765 .IX Header "PORTABILITY NOTES"
3766 .Sh "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
3767 .IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
3768 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
3769 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
3770 model. Libev still offers limited functionality on this platform in
3771 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
3772 descriptors. This only applies when using Win32 natively, not when using
3773 e.g. cygwin.
3774 .PP
3775 Lifting these limitations would basically require the full
3776 re-implementation of the I/O system. If you are into these kinds of
3777 things, then note that glib does exactly that for you in a very portable
3778 way (note also that glib is the slowest event library known to man).
3779 .PP
3780 There is no supported compilation method available on windows except
3781 embedding it into other applications.
3782 .PP
3783 Not a libev limitation but worth mentioning: windows apparently doesn't
3784 accept large writes: instead of resulting in a partial write, windows will
3785 either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
3786 so make sure you only write small amounts into your sockets (less than a
3787 megabyte seems safe, but this apparently depends on the amount of memory
3788 available).
3789 .PP
3790 Due to the many, low, and arbitrary limits on the win32 platform and
3791 the abysmal performance of winsockets, using a large number of sockets
3792 is not recommended (and not reasonable). If your program needs to use
3793 more than a hundred or so sockets, then likely it needs to use a totally
3794 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
3795 notification model, which cannot be implemented efficiently on windows
3796 (Microsoft monopoly games).
3797 .PP
3798 A typical way to use libev under windows is to embed it (see the embedding
3799 section for details) and use the following \fIevwrap.h\fR header file instead
3800 of \fIev.h\fR:
3801 .PP
3802 .Vb 2
3803 \& #define EV_STANDALONE /* keeps ev from requiring config.h */
3804 \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3805 \&
3806 \& #include "ev.h"
3807 .Ve
3808 .PP
3809 And compile the following \fIevwrap.c\fR file into your project (make sure
3810 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
3811 .PP
3812 .Vb 2
3813 \& #include "evwrap.h"
3814 \& #include "ev.c"
3815 .Ve
3816 .IP "The winsocket select function" 4
3817 .IX Item "The winsocket select function"
3818 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
3819 requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
3820 also extremely buggy). This makes select very inefficient, and also
3821 requires a mapping from file descriptors to socket handles (the Microsoft
3822 C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
3823 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
3824 \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
3825 .Sp
3826 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
3827 libraries and raw winsocket select is:
3828 .Sp
3829 .Vb 2
3830 \& #define EV_USE_SELECT 1
3831 \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3832 .Ve
3833 .Sp
3834 Note that winsockets handling of fd sets is O(n), so you can easily get a
3835 complexity in the O(nA\*^X) range when using win32.
3836 .IP "Limited number of file descriptors" 4
3837 .IX Item "Limited number of file descriptors"
3838 Windows has numerous arbitrary (and low) limits on things.
3839 .Sp
3840 Early versions of winsocket's select only supported waiting for a maximum
3841 of \f(CW64\fR handles (probably owning to the fact that all windows kernels
3842 can only wait for \f(CW64\fR things at the same time internally; Microsoft
3843 recommends spawning a chain of threads and wait for 63 handles and the
3844 previous thread in each. Great).
3845 .Sp
3846 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
3847 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
3848 call (which might be in libev or elsewhere, for example, perl does its own
3849 select emulation on windows).
3850 .Sp
3851 Another limit is the number of file descriptors in the Microsoft runtime
3852 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
3853 or something like this inside Microsoft). You can increase this by calling
3854 \&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
3855 arbitrary limit), but is broken in many versions of the Microsoft runtime
3856 libraries.
3857 .Sp
3858 This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
3859 windows version and/or the phase of the moon). To get more, you need to
3860 wrap all I/O functions and provide your own fd management, but the cost of
3861 calling select (O(nA\*^X)) will likely make this unworkable.
3862 .Sh "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
3863 .IX Subsection "PORTABILITY REQUIREMENTS"
3864 In addition to a working ISO-C implementation and of course the
3865 backend-specific APIs, libev relies on a few additional extensions:
3866 .ie n .IP """void (*)(ev_watcher_type *, int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
3867 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
3868 .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
3869 Libev assumes not only that all watcher pointers have the same internal
3870 structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
3871 assumes that the same (machine) code can be used to call any watcher
3872 callback: The watcher callbacks have different type signatures, but libev
3873 calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
3874 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
3875 .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
3876 .IX Item "sig_atomic_t volatile must be thread-atomic as well"
3877 The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
3878 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
3879 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
3880 believed to be sufficiently portable.
3881 .ie n .IP """sigprocmask"" must work in a threaded environment" 4
3882 .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
3883 .IX Item "sigprocmask must work in a threaded environment"
3884 Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
3885 allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
3886 pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
3887 thread\*(R" or will block signals process-wide, both behaviours would
3888 be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
3889 \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
3890 .Sp
3891 The most portable way to handle signals is to block signals in all threads
3892 except the initial one, and run the default loop in the initial thread as
3893 well.
3894 .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
3895 .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
3896 .IX Item "long must be large enough for common memory allocation sizes"
3897 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
3898 instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
3899 systems (Microsoft...) this might be unexpectedly low, but is still at
3900 least 31 bits everywhere, which is enough for hundreds of millions of
3901 watchers.
3902 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
3903 .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
3904 .IX Item "double must hold a time value in seconds with enough accuracy"
3905 The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
3906 have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3907 enough for at least into the year 4000. This requirement is fulfilled by
3908 implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
3909 .PP
3910 If you know of other additional requirements drop me a note.
3911 .SH "ALGORITHMIC COMPLEXITIES"
3912 .IX Header "ALGORITHMIC COMPLEXITIES"
3913 In this section the complexities of (many of) the algorithms used inside
3914 libev will be documented. For complexity discussions about backends see
3915 the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
3916 .PP
3917 All of the following are about amortised time: If an array needs to be
3918 extended, libev needs to realloc and move the whole array, but this
3919 happens asymptotically rarer with higher number of elements, so O(1) might
3920 mean that libev does a lengthy realloc operation in rare cases, but on
3921 average it is much faster and asymptotically approaches constant time.
3922 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
3923 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
3924 This means that, when you have a watcher that triggers in one hour and
3925 there are 100 watchers that would trigger before that, then inserting will
3926 have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
3927 .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
3928 .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
3929 That means that changing a timer costs less than removing/adding them,
3930 as only the relative motion in the event queue has to be paid for.
3931 .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
3932 .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
3933 These just add the watcher into an array or at the head of a list.
3934 .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
3935 .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
3936 .PD 0
3937 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
3938 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
3939 .PD
3940 These watchers are stored in lists, so they need to be walked to find the
3941 correct watcher to remove. The lists are usually short (you don't usually
3942 have many watchers waiting for the same fd or signal: one is typical, two
3943 is rare).
3944 .IP "Finding the next timer in each loop iteration: O(1)" 4
3945 .IX Item "Finding the next timer in each loop iteration: O(1)"
3946 By virtue of using a binary or 4\-heap, the next timer is always found at a
3947 fixed position in the storage array.
3948 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
3949 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
3950 A change means an I/O watcher gets started or stopped, which requires
3951 libev to recalculate its status (and possibly tell the kernel, depending
3952 on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
3953 .IP "Activating one watcher (putting it into the pending state): O(1)" 4
3954 .IX Item "Activating one watcher (putting it into the pending state): O(1)"
3955 .PD 0
3956 .IP "Priority handling: O(number_of_priorities)" 4
3957 .IX Item "Priority handling: O(number_of_priorities)"
3958 .PD
3959 Priorities are implemented by allocating some space for each
3960 priority. When doing priority-based operations, libev usually has to
3961 linearly search all the priorities, but starting/stopping and activating
3962 watchers becomes O(1) with respect to priority handling.
3963 .IP "Sending an ev_async: O(1)" 4
3964 .IX Item "Sending an ev_async: O(1)"
3965 .PD 0
3966 .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
3967 .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
3968 .IP "Processing signals: O(max_signal_number)" 4
3969 .IX Item "Processing signals: O(max_signal_number)"
3970 .PD
3971 Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
3972 calls in the current loop iteration. Checking for async and signal events
3973 involves iterating over all running async watchers or all signal numbers.
3974 .SH "AUTHOR"
3975 .IX Header "AUTHOR"
3976 Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.