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Revision: 1.45
Committed: Sat Dec 8 22:11:14 2007 UTC (16 years, 5 months ago) by root
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# Content
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131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-12-08" "perl v5.8.8" "User Contributed Perl Documentation"
133 .SH "NAME"
134 libev \- a high performance full\-featured event loop written in C
135 .SH "SYNOPSIS"
136 .IX Header "SYNOPSIS"
137 .Vb 1
138 \& #include <ev.h>
139 .Ve
140 .SH "EXAMPLE PROGRAM"
141 .IX Header "EXAMPLE PROGRAM"
142 .Vb 1
143 \& #include <ev.h>
144 .Ve
145 .PP
146 .Vb 2
147 \& ev_io stdin_watcher;
148 \& ev_timer timeout_watcher;
149 .Ve
150 .PP
151 .Vb 8
152 \& /* called when data readable on stdin */
153 \& static void
154 \& stdin_cb (EV_P_ struct ev_io *w, int revents)
155 \& {
156 \& /* puts ("stdin ready"); */
157 \& ev_io_stop (EV_A_ w); /* just a syntax example */
158 \& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
159 \& }
160 .Ve
161 .PP
162 .Vb 6
163 \& static void
164 \& timeout_cb (EV_P_ struct ev_timer *w, int revents)
165 \& {
166 \& /* puts ("timeout"); */
167 \& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
168 \& }
169 .Ve
170 .PP
171 .Vb 4
172 \& int
173 \& main (void)
174 \& {
175 \& struct ev_loop *loop = ev_default_loop (0);
176 .Ve
177 .PP
178 .Vb 3
179 \& /* initialise an io watcher, then start it */
180 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181 \& ev_io_start (loop, &stdin_watcher);
182 .Ve
183 .PP
184 .Vb 3
185 \& /* simple non-repeating 5.5 second timeout */
186 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187 \& ev_timer_start (loop, &timeout_watcher);
188 .Ve
189 .PP
190 .Vb 2
191 \& /* loop till timeout or data ready */
192 \& ev_loop (loop, 0);
193 .Ve
194 .PP
195 .Vb 2
196 \& return 0;
197 \& }
198 .Ve
199 .SH "DESCRIPTION"
200 .IX Header "DESCRIPTION"
201 The newest version of this document is also available as a html-formatted
202 web page you might find easier to navigate when reading it for the first
203 time: <http://cvs.schmorp.de/libev/ev.html>.
204 .PP
205 Libev is an event loop: you register interest in certain events (such as a
206 file descriptor being readable or a timeout occuring), and it will manage
207 these event sources and provide your program with events.
208 .PP
209 To do this, it must take more or less complete control over your process
210 (or thread) by executing the \fIevent loop\fR handler, and will then
211 communicate events via a callback mechanism.
212 .PP
213 You register interest in certain events by registering so-called \fIevent
214 watchers\fR, which are relatively small C structures you initialise with the
215 details of the event, and then hand it over to libev by \fIstarting\fR the
216 watcher.
217 .SH "FEATURES"
218 .IX Header "FEATURES"
219 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
220 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
221 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
222 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
223 with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
224 (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
225 watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
226 \&\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
227 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
228 (\f(CW\*(C`ev_fork\*(C'\fR).
229 .PP
230 It also is quite fast (see this
231 benchmark comparing it to libevent
232 for example).
233 .SH "CONVENTIONS"
234 .IX Header "CONVENTIONS"
235 Libev is very configurable. In this manual the default configuration will
236 be described, which supports multiple event loops. For more info about
237 various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
238 this manual. If libev was configured without support for multiple event
239 loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
240 (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
241 .SH "TIME REPRESENTATION"
242 .IX Header "TIME REPRESENTATION"
243 Libev represents time as a single floating point number, representing the
244 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
245 the beginning of 1970, details are complicated, don't ask). This type is
246 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
247 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
248 it, you should treat it as such.
249 .SH "GLOBAL FUNCTIONS"
250 .IX Header "GLOBAL FUNCTIONS"
251 These functions can be called anytime, even before initialising the
252 library in any way.
253 .IP "ev_tstamp ev_time ()" 4
254 .IX Item "ev_tstamp ev_time ()"
255 Returns the current time as libev would use it. Please note that the
256 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
257 you actually want to know.
258 .IP "int ev_version_major ()" 4
259 .IX Item "int ev_version_major ()"
260 .PD 0
261 .IP "int ev_version_minor ()" 4
262 .IX Item "int ev_version_minor ()"
263 .PD
264 You can find out the major and minor version numbers of the library
265 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
266 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
267 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
268 version of the library your program was compiled against.
269 .Sp
270 Usually, it's a good idea to terminate if the major versions mismatch,
271 as this indicates an incompatible change. Minor versions are usually
272 compatible to older versions, so a larger minor version alone is usually
273 not a problem.
274 .Sp
275 Example: Make sure we haven't accidentally been linked against the wrong
276 version.
277 .Sp
278 .Vb 3
279 \& assert (("libev version mismatch",
280 \& ev_version_major () == EV_VERSION_MAJOR
281 \& && ev_version_minor () >= EV_VERSION_MINOR));
282 .Ve
283 .IP "unsigned int ev_supported_backends ()" 4
284 .IX Item "unsigned int ev_supported_backends ()"
285 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
286 value) compiled into this binary of libev (independent of their
287 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
288 a description of the set values.
289 .Sp
290 Example: make sure we have the epoll method, because yeah this is cool and
291 a must have and can we have a torrent of it please!!!11
292 .Sp
293 .Vb 2
294 \& assert (("sorry, no epoll, no sex",
295 \& ev_supported_backends () & EVBACKEND_EPOLL));
296 .Ve
297 .IP "unsigned int ev_recommended_backends ()" 4
298 .IX Item "unsigned int ev_recommended_backends ()"
299 Return the set of all backends compiled into this binary of libev and also
300 recommended for this platform. This set is often smaller than the one
301 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
302 most BSDs and will not be autodetected unless you explicitly request it
303 (assuming you know what you are doing). This is the set of backends that
304 libev will probe for if you specify no backends explicitly.
305 .IP "unsigned int ev_embeddable_backends ()" 4
306 .IX Item "unsigned int ev_embeddable_backends ()"
307 Returns the set of backends that are embeddable in other event loops. This
308 is the theoretical, all\-platform, value. To find which backends
309 might be supported on the current system, you would need to look at
310 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
311 recommended ones.
312 .Sp
313 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
314 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
315 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
316 Sets the allocation function to use (the prototype is similar \- the
317 semantics is identical \- to the realloc C function). It is used to
318 allocate and free memory (no surprises here). If it returns zero when
319 memory needs to be allocated, the library might abort or take some
320 potentially destructive action. The default is your system realloc
321 function.
322 .Sp
323 You could override this function in high-availability programs to, say,
324 free some memory if it cannot allocate memory, to use a special allocator,
325 or even to sleep a while and retry until some memory is available.
326 .Sp
327 Example: Replace the libev allocator with one that waits a bit and then
328 retries).
329 .Sp
330 .Vb 6
331 \& static void *
332 \& persistent_realloc (void *ptr, size_t size)
333 \& {
334 \& for (;;)
335 \& {
336 \& void *newptr = realloc (ptr, size);
337 .Ve
338 .Sp
339 .Vb 2
340 \& if (newptr)
341 \& return newptr;
342 .Ve
343 .Sp
344 .Vb 3
345 \& sleep (60);
346 \& }
347 \& }
348 .Ve
349 .Sp
350 .Vb 2
351 \& ...
352 \& ev_set_allocator (persistent_realloc);
353 .Ve
354 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
355 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
356 Set the callback function to call on a retryable syscall error (such
357 as failed select, poll, epoll_wait). The message is a printable string
358 indicating the system call or subsystem causing the problem. If this
359 callback is set, then libev will expect it to remedy the sitution, no
360 matter what, when it returns. That is, libev will generally retry the
361 requested operation, or, if the condition doesn't go away, do bad stuff
362 (such as abort).
363 .Sp
364 Example: This is basically the same thing that libev does internally, too.
365 .Sp
366 .Vb 6
367 \& static void
368 \& fatal_error (const char *msg)
369 \& {
370 \& perror (msg);
371 \& abort ();
372 \& }
373 .Ve
374 .Sp
375 .Vb 2
376 \& ...
377 \& ev_set_syserr_cb (fatal_error);
378 .Ve
379 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
380 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
381 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
382 types of such loops, the \fIdefault\fR loop, which supports signals and child
383 events, and dynamically created loops which do not.
384 .PP
385 If you use threads, a common model is to run the default event loop
386 in your main thread (or in a separate thread) and for each thread you
387 create, you also create another event loop. Libev itself does no locking
388 whatsoever, so if you mix calls to the same event loop in different
389 threads, make sure you lock (this is usually a bad idea, though, even if
390 done correctly, because it's hideous and inefficient).
391 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
392 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
393 This will initialise the default event loop if it hasn't been initialised
394 yet and return it. If the default loop could not be initialised, returns
395 false. If it already was initialised it simply returns it (and ignores the
396 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
397 .Sp
398 If you don't know what event loop to use, use the one returned from this
399 function.
400 .Sp
401 The flags argument can be used to specify special behaviour or specific
402 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
403 .Sp
404 The following flags are supported:
405 .RS 4
406 .ie n .IP """EVFLAG_AUTO""" 4
407 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
408 .IX Item "EVFLAG_AUTO"
409 The default flags value. Use this if you have no clue (it's the right
410 thing, believe me).
411 .ie n .IP """EVFLAG_NOENV""" 4
412 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
413 .IX Item "EVFLAG_NOENV"
414 If this flag bit is ored into the flag value (or the program runs setuid
415 or setgid) then libev will \fInot\fR look at the environment variable
416 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
417 override the flags completely if it is found in the environment. This is
418 useful to try out specific backends to test their performance, or to work
419 around bugs.
420 .ie n .IP """EVFLAG_FORKCHECK""" 4
421 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
422 .IX Item "EVFLAG_FORKCHECK"
423 Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
424 a fork, you can also make libev check for a fork in each iteration by
425 enabling this flag.
426 .Sp
427 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
428 and thus this might slow down your event loop if you do a lot of loop
429 iterations and little real work, but is usually not noticeable (on my
430 Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
431 without a syscall and thus \fIvery\fR fast, but my Linux system also has
432 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
433 .Sp
434 The big advantage of this flag is that you can forget about fork (and
435 forget about forgetting to tell libev about forking) when you use this
436 flag.
437 .Sp
438 This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
439 environment variable.
440 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
441 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
442 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
443 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
444 libev tries to roll its own fd_set with no limits on the number of fds,
445 but if that fails, expect a fairly low limit on the number of fds when
446 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
447 the fastest backend for a low number of fds.
448 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
449 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
450 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
451 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
452 select, but handles sparse fds better and has no artificial limit on the
453 number of fds you can use (except it will slow down considerably with a
454 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
455 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
456 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
457 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
458 For few fds, this backend is a bit little slower than poll and select,
459 but it scales phenomenally better. While poll and select usually scale like
460 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
461 either O(1) or O(active_fds).
462 .Sp
463 While stopping and starting an I/O watcher in the same iteration will
464 result in some caching, there is still a syscall per such incident
465 (because the fd could point to a different file description now), so its
466 best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
467 well if you register events for both fds.
468 .Sp
469 Please note that epoll sometimes generates spurious notifications, so you
470 need to use non-blocking I/O or other means to avoid blocking when no data
471 (or space) is available.
472 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
473 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
474 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
475 Kqueue deserves special mention, as at the time of this writing, it
476 was broken on all BSDs except NetBSD (usually it doesn't work with
477 anything but sockets and pipes, except on Darwin, where of course its
478 completely useless). For this reason its not being \*(L"autodetected\*(R"
479 unless you explicitly specify it explicitly in the flags (i.e. using
480 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
481 .Sp
482 It scales in the same way as the epoll backend, but the interface to the
483 kernel is more efficient (which says nothing about its actual speed, of
484 course). While starting and stopping an I/O watcher does not cause an
485 extra syscall as with epoll, it still adds up to four event changes per
486 incident, so its best to avoid that.
487 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
488 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
489 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
490 This is not implemented yet (and might never be).
491 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
492 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
493 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
494 This uses the Solaris 10 port mechanism. As with everything on Solaris,
495 it's really slow, but it still scales very well (O(active_fds)).
496 .Sp
497 Please note that solaris ports can result in a lot of spurious
498 notifications, so you need to use non-blocking I/O or other means to avoid
499 blocking when no data (or space) is available.
500 .ie n .IP """EVBACKEND_ALL""" 4
501 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
502 .IX Item "EVBACKEND_ALL"
503 Try all backends (even potentially broken ones that wouldn't be tried
504 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
505 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
506 .RE
507 .RS 4
508 .Sp
509 If one or more of these are ored into the flags value, then only these
510 backends will be tried (in the reverse order as given here). If none are
511 specified, most compiled-in backend will be tried, usually in reverse
512 order of their flag values :)
513 .Sp
514 The most typical usage is like this:
515 .Sp
516 .Vb 2
517 \& if (!ev_default_loop (0))
518 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
519 .Ve
520 .Sp
521 Restrict libev to the select and poll backends, and do not allow
522 environment settings to be taken into account:
523 .Sp
524 .Vb 1
525 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
526 .Ve
527 .Sp
528 Use whatever libev has to offer, but make sure that kqueue is used if
529 available (warning, breaks stuff, best use only with your own private
530 event loop and only if you know the \s-1OS\s0 supports your types of fds):
531 .Sp
532 .Vb 1
533 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
534 .Ve
535 .RE
536 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
537 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
538 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
539 always distinct from the default loop. Unlike the default loop, it cannot
540 handle signal and child watchers, and attempts to do so will be greeted by
541 undefined behaviour (or a failed assertion if assertions are enabled).
542 .Sp
543 Example: Try to create a event loop that uses epoll and nothing else.
544 .Sp
545 .Vb 3
546 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
547 \& if (!epoller)
548 \& fatal ("no epoll found here, maybe it hides under your chair");
549 .Ve
550 .IP "ev_default_destroy ()" 4
551 .IX Item "ev_default_destroy ()"
552 Destroys the default loop again (frees all memory and kernel state
553 etc.). None of the active event watchers will be stopped in the normal
554 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
555 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
556 calling this function, or cope with the fact afterwards (which is usually
557 the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
558 for example).
559 .IP "ev_loop_destroy (loop)" 4
560 .IX Item "ev_loop_destroy (loop)"
561 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
562 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
563 .IP "ev_default_fork ()" 4
564 .IX Item "ev_default_fork ()"
565 This function reinitialises the kernel state for backends that have
566 one. Despite the name, you can call it anytime, but it makes most sense
567 after forking, in either the parent or child process (or both, but that
568 again makes little sense).
569 .Sp
570 You \fImust\fR call this function in the child process after forking if and
571 only if you want to use the event library in both processes. If you just
572 fork+exec, you don't have to call it.
573 .Sp
574 The function itself is quite fast and it's usually not a problem to call
575 it just in case after a fork. To make this easy, the function will fit in
576 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
577 .Sp
578 .Vb 1
579 \& pthread_atfork (0, 0, ev_default_fork);
580 .Ve
581 .Sp
582 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
583 without calling this function, so if you force one of those backends you
584 do not need to care.
585 .IP "ev_loop_fork (loop)" 4
586 .IX Item "ev_loop_fork (loop)"
587 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
588 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
589 after fork, and how you do this is entirely your own problem.
590 .IP "unsigned int ev_loop_count (loop)" 4
591 .IX Item "unsigned int ev_loop_count (loop)"
592 Returns the count of loop iterations for the loop, which is identical to
593 the number of times libev did poll for new events. It starts at \f(CW0\fR and
594 happily wraps around with enough iterations.
595 .Sp
596 This value can sometimes be useful as a generation counter of sorts (it
597 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
598 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
599 .IP "unsigned int ev_backend (loop)" 4
600 .IX Item "unsigned int ev_backend (loop)"
601 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
602 use.
603 .IP "ev_tstamp ev_now (loop)" 4
604 .IX Item "ev_tstamp ev_now (loop)"
605 Returns the current \*(L"event loop time\*(R", which is the time the event loop
606 received events and started processing them. This timestamp does not
607 change as long as callbacks are being processed, and this is also the base
608 time used for relative timers. You can treat it as the timestamp of the
609 event occuring (or more correctly, libev finding out about it).
610 .IP "ev_loop (loop, int flags)" 4
611 .IX Item "ev_loop (loop, int flags)"
612 Finally, this is it, the event handler. This function usually is called
613 after you initialised all your watchers and you want to start handling
614 events.
615 .Sp
616 If the flags argument is specified as \f(CW0\fR, it will not return until
617 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
618 .Sp
619 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
620 relying on all watchers to be stopped when deciding when a program has
621 finished (especially in interactive programs), but having a program that
622 automatically loops as long as it has to and no longer by virtue of
623 relying on its watchers stopping correctly is a thing of beauty.
624 .Sp
625 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
626 those events and any outstanding ones, but will not block your process in
627 case there are no events and will return after one iteration of the loop.
628 .Sp
629 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
630 neccessary) and will handle those and any outstanding ones. It will block
631 your process until at least one new event arrives, and will return after
632 one iteration of the loop. This is useful if you are waiting for some
633 external event in conjunction with something not expressible using other
634 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
635 usually a better approach for this kind of thing.
636 .Sp
637 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
638 .Sp
639 .Vb 19
640 \& - Before the first iteration, call any pending watchers.
641 \& * If there are no active watchers (reference count is zero), return.
642 \& - Queue all prepare watchers and then call all outstanding watchers.
643 \& - If we have been forked, recreate the kernel state.
644 \& - Update the kernel state with all outstanding changes.
645 \& - Update the "event loop time".
646 \& - Calculate for how long to block.
647 \& - Block the process, waiting for any events.
648 \& - Queue all outstanding I/O (fd) events.
649 \& - Update the "event loop time" and do time jump handling.
650 \& - Queue all outstanding timers.
651 \& - Queue all outstanding periodics.
652 \& - If no events are pending now, queue all idle watchers.
653 \& - Queue all check watchers.
654 \& - Call all queued watchers in reverse order (i.e. check watchers first).
655 \& Signals and child watchers are implemented as I/O watchers, and will
656 \& be handled here by queueing them when their watcher gets executed.
657 \& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
658 \& were used, return, otherwise continue with step *.
659 .Ve
660 .Sp
661 Example: Queue some jobs and then loop until no events are outsanding
662 anymore.
663 .Sp
664 .Vb 4
665 \& ... queue jobs here, make sure they register event watchers as long
666 \& ... as they still have work to do (even an idle watcher will do..)
667 \& ev_loop (my_loop, 0);
668 \& ... jobs done. yeah!
669 .Ve
670 .IP "ev_unloop (loop, how)" 4
671 .IX Item "ev_unloop (loop, how)"
672 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
673 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
674 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
675 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
676 .IP "ev_ref (loop)" 4
677 .IX Item "ev_ref (loop)"
678 .PD 0
679 .IP "ev_unref (loop)" 4
680 .IX Item "ev_unref (loop)"
681 .PD
682 Ref/unref can be used to add or remove a reference count on the event
683 loop: Every watcher keeps one reference, and as long as the reference
684 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
685 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
686 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
687 example, libev itself uses this for its internal signal pipe: It is not
688 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
689 no event watchers registered by it are active. It is also an excellent
690 way to do this for generic recurring timers or from within third-party
691 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
692 .Sp
693 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
694 running when nothing else is active.
695 .Sp
696 .Vb 4
697 \& struct ev_signal exitsig;
698 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
699 \& ev_signal_start (loop, &exitsig);
700 \& evf_unref (loop);
701 .Ve
702 .Sp
703 Example: For some weird reason, unregister the above signal handler again.
704 .Sp
705 .Vb 2
706 \& ev_ref (loop);
707 \& ev_signal_stop (loop, &exitsig);
708 .Ve
709 .SH "ANATOMY OF A WATCHER"
710 .IX Header "ANATOMY OF A WATCHER"
711 A watcher is a structure that you create and register to record your
712 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
713 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
714 .PP
715 .Vb 5
716 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
717 \& {
718 \& ev_io_stop (w);
719 \& ev_unloop (loop, EVUNLOOP_ALL);
720 \& }
721 .Ve
722 .PP
723 .Vb 6
724 \& struct ev_loop *loop = ev_default_loop (0);
725 \& struct ev_io stdin_watcher;
726 \& ev_init (&stdin_watcher, my_cb);
727 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
728 \& ev_io_start (loop, &stdin_watcher);
729 \& ev_loop (loop, 0);
730 .Ve
731 .PP
732 As you can see, you are responsible for allocating the memory for your
733 watcher structures (and it is usually a bad idea to do this on the stack,
734 although this can sometimes be quite valid).
735 .PP
736 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
737 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
738 callback gets invoked each time the event occurs (or, in the case of io
739 watchers, each time the event loop detects that the file descriptor given
740 is readable and/or writable).
741 .PP
742 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
743 with arguments specific to this watcher type. There is also a macro
744 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
745 (watcher *, callback, ...)\*(C'\fR.
746 .PP
747 To make the watcher actually watch out for events, you have to start it
748 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
749 *)\*(C'\fR), and you can stop watching for events at any time by calling the
750 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
751 .PP
752 As long as your watcher is active (has been started but not stopped) you
753 must not touch the values stored in it. Most specifically you must never
754 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
755 .PP
756 Each and every callback receives the event loop pointer as first, the
757 registered watcher structure as second, and a bitset of received events as
758 third argument.
759 .PP
760 The received events usually include a single bit per event type received
761 (you can receive multiple events at the same time). The possible bit masks
762 are:
763 .ie n .IP """EV_READ""" 4
764 .el .IP "\f(CWEV_READ\fR" 4
765 .IX Item "EV_READ"
766 .PD 0
767 .ie n .IP """EV_WRITE""" 4
768 .el .IP "\f(CWEV_WRITE\fR" 4
769 .IX Item "EV_WRITE"
770 .PD
771 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
772 writable.
773 .ie n .IP """EV_TIMEOUT""" 4
774 .el .IP "\f(CWEV_TIMEOUT\fR" 4
775 .IX Item "EV_TIMEOUT"
776 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
777 .ie n .IP """EV_PERIODIC""" 4
778 .el .IP "\f(CWEV_PERIODIC\fR" 4
779 .IX Item "EV_PERIODIC"
780 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
781 .ie n .IP """EV_SIGNAL""" 4
782 .el .IP "\f(CWEV_SIGNAL\fR" 4
783 .IX Item "EV_SIGNAL"
784 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
785 .ie n .IP """EV_CHILD""" 4
786 .el .IP "\f(CWEV_CHILD\fR" 4
787 .IX Item "EV_CHILD"
788 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
789 .ie n .IP """EV_STAT""" 4
790 .el .IP "\f(CWEV_STAT\fR" 4
791 .IX Item "EV_STAT"
792 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
793 .ie n .IP """EV_IDLE""" 4
794 .el .IP "\f(CWEV_IDLE\fR" 4
795 .IX Item "EV_IDLE"
796 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
797 .ie n .IP """EV_PREPARE""" 4
798 .el .IP "\f(CWEV_PREPARE\fR" 4
799 .IX Item "EV_PREPARE"
800 .PD 0
801 .ie n .IP """EV_CHECK""" 4
802 .el .IP "\f(CWEV_CHECK\fR" 4
803 .IX Item "EV_CHECK"
804 .PD
805 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
806 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
807 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
808 received events. Callbacks of both watcher types can start and stop as
809 many watchers as they want, and all of them will be taken into account
810 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
811 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
812 .ie n .IP """EV_EMBED""" 4
813 .el .IP "\f(CWEV_EMBED\fR" 4
814 .IX Item "EV_EMBED"
815 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
816 .ie n .IP """EV_FORK""" 4
817 .el .IP "\f(CWEV_FORK\fR" 4
818 .IX Item "EV_FORK"
819 The event loop has been resumed in the child process after fork (see
820 \&\f(CW\*(C`ev_fork\*(C'\fR).
821 .ie n .IP """EV_ERROR""" 4
822 .el .IP "\f(CWEV_ERROR\fR" 4
823 .IX Item "EV_ERROR"
824 An unspecified error has occured, the watcher has been stopped. This might
825 happen because the watcher could not be properly started because libev
826 ran out of memory, a file descriptor was found to be closed or any other
827 problem. You best act on it by reporting the problem and somehow coping
828 with the watcher being stopped.
829 .Sp
830 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
831 for example it might indicate that a fd is readable or writable, and if
832 your callbacks is well-written it can just attempt the operation and cope
833 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
834 programs, though, so beware.
835 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
836 .IX Subsection "GENERIC WATCHER FUNCTIONS"
837 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
838 e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
839 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
840 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
841 .IX Item "ev_init (ev_TYPE *watcher, callback)"
842 This macro initialises the generic portion of a watcher. The contents
843 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
844 the generic parts of the watcher are initialised, you \fIneed\fR to call
845 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
846 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
847 which rolls both calls into one.
848 .Sp
849 You can reinitialise a watcher at any time as long as it has been stopped
850 (or never started) and there are no pending events outstanding.
851 .Sp
852 The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
853 int revents)\*(C'\fR.
854 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
855 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
856 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
857 This macro initialises the type-specific parts of a watcher. You need to
858 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
859 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
860 macro on a watcher that is active (it can be pending, however, which is a
861 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
862 .Sp
863 Although some watcher types do not have type-specific arguments
864 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
865 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
866 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
867 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
868 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
869 calls into a single call. This is the most convinient method to initialise
870 a watcher. The same limitations apply, of course.
871 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
872 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
873 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
874 Starts (activates) the given watcher. Only active watchers will receive
875 events. If the watcher is already active nothing will happen.
876 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
877 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
878 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
879 Stops the given watcher again (if active) and clears the pending
880 status. It is possible that stopped watchers are pending (for example,
881 non-repeating timers are being stopped when they become pending), but
882 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
883 you want to free or reuse the memory used by the watcher it is therefore a
884 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
885 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
886 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
887 Returns a true value iff the watcher is active (i.e. it has been started
888 and not yet been stopped). As long as a watcher is active you must not modify
889 it.
890 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
891 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
892 Returns a true value iff the watcher is pending, (i.e. it has outstanding
893 events but its callback has not yet been invoked). As long as a watcher
894 is pending (but not active) you must not call an init function on it (but
895 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
896 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
897 it).
898 .IP "callback ev_cb (ev_TYPE *watcher)" 4
899 .IX Item "callback ev_cb (ev_TYPE *watcher)"
900 Returns the callback currently set on the watcher.
901 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
902 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
903 Change the callback. You can change the callback at virtually any time
904 (modulo threads).
905 .IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
906 .IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
907 .PD 0
908 .IP "int ev_priority (ev_TYPE *watcher)" 4
909 .IX Item "int ev_priority (ev_TYPE *watcher)"
910 .PD
911 Set and query the priority of the watcher. The priority is a small
912 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
913 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
914 before watchers with lower priority, but priority will not keep watchers
915 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
916 .Sp
917 This means that priorities are \fIonly\fR used for ordering callback
918 invocation after new events have been received. This is useful, for
919 example, to reduce latency after idling, or more often, to bind two
920 watchers on the same event and make sure one is called first.
921 .Sp
922 If you need to suppress invocation when higher priority events are pending
923 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
924 .Sp
925 You \fImust not\fR change the priority of a watcher as long as it is active or
926 pending.
927 .Sp
928 The default priority used by watchers when no priority has been set is
929 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
930 .Sp
931 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
932 fine, as long as you do not mind that the priority value you query might
933 or might not have been adjusted to be within valid range.
934 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
935 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
936 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
937 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
938 can deal with that fact.
939 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
940 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
941 If the watcher is pending, this function returns clears its pending status
942 and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
943 watcher isn't pending it does nothing and returns \f(CW0\fR.
944 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
945 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
946 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
947 and read at any time, libev will completely ignore it. This can be used
948 to associate arbitrary data with your watcher. If you need more data and
949 don't want to allocate memory and store a pointer to it in that data
950 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
951 data:
952 .PP
953 .Vb 7
954 \& struct my_io
955 \& {
956 \& struct ev_io io;
957 \& int otherfd;
958 \& void *somedata;
959 \& struct whatever *mostinteresting;
960 \& }
961 .Ve
962 .PP
963 And since your callback will be called with a pointer to the watcher, you
964 can cast it back to your own type:
965 .PP
966 .Vb 5
967 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
968 \& {
969 \& struct my_io *w = (struct my_io *)w_;
970 \& ...
971 \& }
972 .Ve
973 .PP
974 More interesting and less C\-conformant ways of casting your callback type
975 instead have been omitted.
976 .PP
977 Another common scenario is having some data structure with multiple
978 watchers:
979 .PP
980 .Vb 6
981 \& struct my_biggy
982 \& {
983 \& int some_data;
984 \& ev_timer t1;
985 \& ev_timer t2;
986 \& }
987 .Ve
988 .PP
989 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
990 you need to use \f(CW\*(C`offsetof\*(C'\fR:
991 .PP
992 .Vb 1
993 \& #include <stddef.h>
994 .Ve
995 .PP
996 .Vb 6
997 \& static void
998 \& t1_cb (EV_P_ struct ev_timer *w, int revents)
999 \& {
1000 \& struct my_biggy big = (struct my_biggy *
1001 \& (((char *)w) - offsetof (struct my_biggy, t1));
1002 \& }
1003 .Ve
1004 .PP
1005 .Vb 6
1006 \& static void
1007 \& t2_cb (EV_P_ struct ev_timer *w, int revents)
1008 \& {
1009 \& struct my_biggy big = (struct my_biggy *
1010 \& (((char *)w) - offsetof (struct my_biggy, t2));
1011 \& }
1012 .Ve
1013 .SH "WATCHER TYPES"
1014 .IX Header "WATCHER TYPES"
1015 This section describes each watcher in detail, but will not repeat
1016 information given in the last section. Any initialisation/set macros,
1017 functions and members specific to the watcher type are explained.
1018 .PP
1019 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1020 while the watcher is active, you can look at the member and expect some
1021 sensible content, but you must not modify it (you can modify it while the
1022 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1023 means you can expect it to have some sensible content while the watcher
1024 is active, but you can also modify it. Modifying it may not do something
1025 sensible or take immediate effect (or do anything at all), but libev will
1026 not crash or malfunction in any way.
1027 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
1028 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1029 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1030 I/O watchers check whether a file descriptor is readable or writable
1031 in each iteration of the event loop, or, more precisely, when reading
1032 would not block the process and writing would at least be able to write
1033 some data. This behaviour is called level-triggering because you keep
1034 receiving events as long as the condition persists. Remember you can stop
1035 the watcher if you don't want to act on the event and neither want to
1036 receive future events.
1037 .PP
1038 In general you can register as many read and/or write event watchers per
1039 fd as you want (as long as you don't confuse yourself). Setting all file
1040 descriptors to non-blocking mode is also usually a good idea (but not
1041 required if you know what you are doing).
1042 .PP
1043 You have to be careful with dup'ed file descriptors, though. Some backends
1044 (the linux epoll backend is a notable example) cannot handle dup'ed file
1045 descriptors correctly if you register interest in two or more fds pointing
1046 to the same underlying file/socket/etc. description (that is, they share
1047 the same underlying \*(L"file open\*(R").
1048 .PP
1049 If you must do this, then force the use of a known-to-be-good backend
1050 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1051 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1052 .PP
1053 Another thing you have to watch out for is that it is quite easy to
1054 receive \*(L"spurious\*(R" readyness notifications, that is your callback might
1055 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1056 because there is no data. Not only are some backends known to create a
1057 lot of those (for example solaris ports), it is very easy to get into
1058 this situation even with a relatively standard program structure. Thus
1059 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1060 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1061 .PP
1062 If you cannot run the fd in non-blocking mode (for example you should not
1063 play around with an Xlib connection), then you have to seperately re-test
1064 whether a file descriptor is really ready with a known-to-be good interface
1065 such as poll (fortunately in our Xlib example, Xlib already does this on
1066 its own, so its quite safe to use).
1067 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1068 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1069 .PD 0
1070 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1071 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1072 .PD
1073 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1074 rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1075 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1076 .IP "int fd [read\-only]" 4
1077 .IX Item "int fd [read-only]"
1078 The file descriptor being watched.
1079 .IP "int events [read\-only]" 4
1080 .IX Item "int events [read-only]"
1081 The events being watched.
1082 .PP
1083 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1084 readable, but only once. Since it is likely line\-buffered, you could
1085 attempt to read a whole line in the callback.
1086 .PP
1087 .Vb 6
1088 \& static void
1089 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1090 \& {
1091 \& ev_io_stop (loop, w);
1092 \& .. read from stdin here (or from w->fd) and haqndle any I/O errors
1093 \& }
1094 .Ve
1095 .PP
1096 .Vb 6
1097 \& ...
1098 \& struct ev_loop *loop = ev_default_init (0);
1099 \& struct ev_io stdin_readable;
1100 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1101 \& ev_io_start (loop, &stdin_readable);
1102 \& ev_loop (loop, 0);
1103 .Ve
1104 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1105 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1106 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1107 Timer watchers are simple relative timers that generate an event after a
1108 given time, and optionally repeating in regular intervals after that.
1109 .PP
1110 The timers are based on real time, that is, if you register an event that
1111 times out after an hour and you reset your system clock to last years
1112 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
1113 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1114 monotonic clock option helps a lot here).
1115 .PP
1116 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1117 time. This is usually the right thing as this timestamp refers to the time
1118 of the event triggering whatever timeout you are modifying/starting. If
1119 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
1120 on the current time, use something like this to adjust for this:
1121 .PP
1122 .Vb 1
1123 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1124 .Ve
1125 .PP
1126 The callback is guarenteed to be invoked only when its timeout has passed,
1127 but if multiple timers become ready during the same loop iteration then
1128 order of execution is undefined.
1129 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1130 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1131 .PD 0
1132 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1133 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1134 .PD
1135 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
1136 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
1137 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
1138 later, again, and again, until stopped manually.
1139 .Sp
1140 The timer itself will do a best-effort at avoiding drift, that is, if you
1141 configure a timer to trigger every 10 seconds, then it will trigger at
1142 exactly 10 second intervals. If, however, your program cannot keep up with
1143 the timer (because it takes longer than those 10 seconds to do stuff) the
1144 timer will not fire more than once per event loop iteration.
1145 .IP "ev_timer_again (loop)" 4
1146 .IX Item "ev_timer_again (loop)"
1147 This will act as if the timer timed out and restart it again if it is
1148 repeating. The exact semantics are:
1149 .Sp
1150 If the timer is pending, its pending status is cleared.
1151 .Sp
1152 If the timer is started but nonrepeating, stop it (as if it timed out).
1153 .Sp
1154 If the timer is repeating, either start it if necessary (with the
1155 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
1156 .Sp
1157 This sounds a bit complicated, but here is a useful and typical
1158 example: Imagine you have a tcp connection and you want a so-called idle
1159 timeout, that is, you want to be called when there have been, say, 60
1160 seconds of inactivity on the socket. The easiest way to do this is to
1161 configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
1162 \&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1163 you go into an idle state where you do not expect data to travel on the
1164 socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1165 automatically restart it if need be.
1166 .Sp
1167 That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1168 altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1169 .Sp
1170 .Vb 8
1171 \& ev_timer_init (timer, callback, 0., 5.);
1172 \& ev_timer_again (loop, timer);
1173 \& ...
1174 \& timer->again = 17.;
1175 \& ev_timer_again (loop, timer);
1176 \& ...
1177 \& timer->again = 10.;
1178 \& ev_timer_again (loop, timer);
1179 .Ve
1180 .Sp
1181 This is more slightly efficient then stopping/starting the timer each time
1182 you want to modify its timeout value.
1183 .IP "ev_tstamp repeat [read\-write]" 4
1184 .IX Item "ev_tstamp repeat [read-write]"
1185 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1186 or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1187 which is also when any modifications are taken into account.
1188 .PP
1189 Example: Create a timer that fires after 60 seconds.
1190 .PP
1191 .Vb 5
1192 \& static void
1193 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1194 \& {
1195 \& .. one minute over, w is actually stopped right here
1196 \& }
1197 .Ve
1198 .PP
1199 .Vb 3
1200 \& struct ev_timer mytimer;
1201 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1202 \& ev_timer_start (loop, &mytimer);
1203 .Ve
1204 .PP
1205 Example: Create a timeout timer that times out after 10 seconds of
1206 inactivity.
1207 .PP
1208 .Vb 5
1209 \& static void
1210 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1211 \& {
1212 \& .. ten seconds without any activity
1213 \& }
1214 .Ve
1215 .PP
1216 .Vb 4
1217 \& struct ev_timer mytimer;
1218 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1219 \& ev_timer_again (&mytimer); /* start timer */
1220 \& ev_loop (loop, 0);
1221 .Ve
1222 .PP
1223 .Vb 3
1224 \& // and in some piece of code that gets executed on any "activity":
1225 \& // reset the timeout to start ticking again at 10 seconds
1226 \& ev_timer_again (&mytimer);
1227 .Ve
1228 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1229 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1230 .IX Subsection "ev_periodic - to cron or not to cron?"
1231 Periodic watchers are also timers of a kind, but they are very versatile
1232 (and unfortunately a bit complex).
1233 .PP
1234 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1235 but on wallclock time (absolute time). You can tell a periodic watcher
1236 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1237 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1238 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1239 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1240 roughly 10 seconds later and of course not if you reset your system time
1241 again).
1242 .PP
1243 They can also be used to implement vastly more complex timers, such as
1244 triggering an event on eahc midnight, local time.
1245 .PP
1246 As with timers, the callback is guarenteed to be invoked only when the
1247 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1248 during the same loop iteration then order of execution is undefined.
1249 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1250 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1251 .PD 0
1252 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1253 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1254 .PD
1255 Lots of arguments, lets sort it out... There are basically three modes of
1256 operation, and we will explain them from simplest to complex:
1257 .RS 4
1258 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
1259 .IX Item "absolute timer (interval = reschedule_cb = 0)"
1260 In this configuration the watcher triggers an event at the wallclock time
1261 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1262 that is, if it is to be run at January 1st 2011 then it will run when the
1263 system time reaches or surpasses this time.
1264 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
1265 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
1266 In this mode the watcher will always be scheduled to time out at the next
1267 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
1268 of any time jumps.
1269 .Sp
1270 This can be used to create timers that do not drift with respect to system
1271 time:
1272 .Sp
1273 .Vb 1
1274 \& ev_periodic_set (&periodic, 0., 3600., 0);
1275 .Ve
1276 .Sp
1277 This doesn't mean there will always be 3600 seconds in between triggers,
1278 but only that the the callback will be called when the system time shows a
1279 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1280 by 3600.
1281 .Sp
1282 Another way to think about it (for the mathematically inclined) is that
1283 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1284 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1285 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
1286 .IX Item "manual reschedule mode (reschedule_cb = callback)"
1287 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1288 ignored. Instead, each time the periodic watcher gets scheduled, the
1289 reschedule callback will be called with the watcher as first, and the
1290 current time as second argument.
1291 .Sp
1292 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1293 ever, or make any event loop modifications\fR. If you need to stop it,
1294 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1295 starting a prepare watcher).
1296 .Sp
1297 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1298 ev_tstamp now)\*(C'\fR, e.g.:
1299 .Sp
1300 .Vb 4
1301 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1302 \& {
1303 \& return now + 60.;
1304 \& }
1305 .Ve
1306 .Sp
1307 It must return the next time to trigger, based on the passed time value
1308 (that is, the lowest time value larger than to the second argument). It
1309 will usually be called just before the callback will be triggered, but
1310 might be called at other times, too.
1311 .Sp
1312 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1313 passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
1314 .Sp
1315 This can be used to create very complex timers, such as a timer that
1316 triggers on each midnight, local time. To do this, you would calculate the
1317 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1318 you do this is, again, up to you (but it is not trivial, which is the main
1319 reason I omitted it as an example).
1320 .RE
1321 .RS 4
1322 .RE
1323 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1324 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1325 Simply stops and restarts the periodic watcher again. This is only useful
1326 when you changed some parameters or the reschedule callback would return
1327 a different time than the last time it was called (e.g. in a crond like
1328 program when the crontabs have changed).
1329 .IP "ev_tstamp interval [read\-write]" 4
1330 .IX Item "ev_tstamp interval [read-write]"
1331 The current interval value. Can be modified any time, but changes only
1332 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1333 called.
1334 .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1335 .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1336 The current reschedule callback, or \f(CW0\fR, if this functionality is
1337 switched off. Can be changed any time, but changes only take effect when
1338 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1339 .PP
1340 Example: Call a callback every hour, or, more precisely, whenever the
1341 system clock is divisible by 3600. The callback invocation times have
1342 potentially a lot of jittering, but good long-term stability.
1343 .PP
1344 .Vb 5
1345 \& static void
1346 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1347 \& {
1348 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1349 \& }
1350 .Ve
1351 .PP
1352 .Vb 3
1353 \& struct ev_periodic hourly_tick;
1354 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1355 \& ev_periodic_start (loop, &hourly_tick);
1356 .Ve
1357 .PP
1358 Example: The same as above, but use a reschedule callback to do it:
1359 .PP
1360 .Vb 1
1361 \& #include <math.h>
1362 .Ve
1363 .PP
1364 .Vb 5
1365 \& static ev_tstamp
1366 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1367 \& {
1368 \& return fmod (now, 3600.) + 3600.;
1369 \& }
1370 .Ve
1371 .PP
1372 .Vb 1
1373 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1374 .Ve
1375 .PP
1376 Example: Call a callback every hour, starting now:
1377 .PP
1378 .Vb 4
1379 \& struct ev_periodic hourly_tick;
1380 \& ev_periodic_init (&hourly_tick, clock_cb,
1381 \& fmod (ev_now (loop), 3600.), 3600., 0);
1382 \& ev_periodic_start (loop, &hourly_tick);
1383 .Ve
1384 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1385 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1386 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1387 Signal watchers will trigger an event when the process receives a specific
1388 signal one or more times. Even though signals are very asynchronous, libev
1389 will try it's best to deliver signals synchronously, i.e. as part of the
1390 normal event processing, like any other event.
1391 .PP
1392 You can configure as many watchers as you like per signal. Only when the
1393 first watcher gets started will libev actually register a signal watcher
1394 with the kernel (thus it coexists with your own signal handlers as long
1395 as you don't register any with libev). Similarly, when the last signal
1396 watcher for a signal is stopped libev will reset the signal handler to
1397 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1398 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1399 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1400 .PD 0
1401 .IP "ev_signal_set (ev_signal *, int signum)" 4
1402 .IX Item "ev_signal_set (ev_signal *, int signum)"
1403 .PD
1404 Configures the watcher to trigger on the given signal number (usually one
1405 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1406 .IP "int signum [read\-only]" 4
1407 .IX Item "int signum [read-only]"
1408 The signal the watcher watches out for.
1409 .ie n .Sh """ev_child"" \- watch out for process status changes"
1410 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1411 .IX Subsection "ev_child - watch out for process status changes"
1412 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1413 some child status changes (most typically when a child of yours dies).
1414 .IP "ev_child_init (ev_child *, callback, int pid)" 4
1415 .IX Item "ev_child_init (ev_child *, callback, int pid)"
1416 .PD 0
1417 .IP "ev_child_set (ev_child *, int pid)" 4
1418 .IX Item "ev_child_set (ev_child *, int pid)"
1419 .PD
1420 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1421 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1422 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1423 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1424 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1425 process causing the status change.
1426 .IP "int pid [read\-only]" 4
1427 .IX Item "int pid [read-only]"
1428 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1429 .IP "int rpid [read\-write]" 4
1430 .IX Item "int rpid [read-write]"
1431 The process id that detected a status change.
1432 .IP "int rstatus [read\-write]" 4
1433 .IX Item "int rstatus [read-write]"
1434 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1435 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1436 .PP
1437 Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1438 .PP
1439 .Vb 5
1440 \& static void
1441 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1442 \& {
1443 \& ev_unloop (loop, EVUNLOOP_ALL);
1444 \& }
1445 .Ve
1446 .PP
1447 .Vb 3
1448 \& struct ev_signal signal_watcher;
1449 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1450 \& ev_signal_start (loop, &sigint_cb);
1451 .Ve
1452 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
1453 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1454 .IX Subsection "ev_stat - did the file attributes just change?"
1455 This watches a filesystem path for attribute changes. That is, it calls
1456 \&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1457 compared to the last time, invoking the callback if it did.
1458 .PP
1459 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1460 not exist\*(R" is a status change like any other. The condition \*(L"path does
1461 not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1462 otherwise always forced to be at least one) and all the other fields of
1463 the stat buffer having unspecified contents.
1464 .PP
1465 The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1466 relative and your working directory changes, the behaviour is undefined.
1467 .PP
1468 Since there is no standard to do this, the portable implementation simply
1469 calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1470 can specify a recommended polling interval for this case. If you specify
1471 a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1472 unspecified default\fR value will be used (which you can expect to be around
1473 five seconds, although this might change dynamically). Libev will also
1474 impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1475 usually overkill.
1476 .PP
1477 This watcher type is not meant for massive numbers of stat watchers,
1478 as even with OS-supported change notifications, this can be
1479 resource\-intensive.
1480 .PP
1481 At the time of this writing, only the Linux inotify interface is
1482 implemented (implementing kqueue support is left as an exercise for the
1483 reader). Inotify will be used to give hints only and should not change the
1484 semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs
1485 to fall back to regular polling again even with inotify, but changes are
1486 usually detected immediately, and if the file exists there will be no
1487 polling.
1488 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1489 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1490 .PD 0
1491 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1492 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1493 .PD
1494 Configures the watcher to wait for status changes of the given
1495 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1496 be detected and should normally be specified as \f(CW0\fR to let libev choose
1497 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1498 path for as long as the watcher is active.
1499 .Sp
1500 The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected,
1501 relative to the attributes at the time the watcher was started (or the
1502 last change was detected).
1503 .IP "ev_stat_stat (ev_stat *)" 4
1504 .IX Item "ev_stat_stat (ev_stat *)"
1505 Updates the stat buffer immediately with new values. If you change the
1506 watched path in your callback, you could call this fucntion to avoid
1507 detecting this change (while introducing a race condition). Can also be
1508 useful simply to find out the new values.
1509 .IP "ev_statdata attr [read\-only]" 4
1510 .IX Item "ev_statdata attr [read-only]"
1511 The most-recently detected attributes of the file. Although the type is of
1512 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1513 suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there
1514 was some error while \f(CW\*(C`stat\*(C'\fRing the file.
1515 .IP "ev_statdata prev [read\-only]" 4
1516 .IX Item "ev_statdata prev [read-only]"
1517 The previous attributes of the file. The callback gets invoked whenever
1518 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR.
1519 .IP "ev_tstamp interval [read\-only]" 4
1520 .IX Item "ev_tstamp interval [read-only]"
1521 The specified interval.
1522 .IP "const char *path [read\-only]" 4
1523 .IX Item "const char *path [read-only]"
1524 The filesystem path that is being watched.
1525 .PP
1526 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1527 .PP
1528 .Vb 15
1529 \& static void
1530 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1531 \& {
1532 \& /* /etc/passwd changed in some way */
1533 \& if (w->attr.st_nlink)
1534 \& {
1535 \& printf ("passwd current size %ld\en", (long)w->attr.st_size);
1536 \& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime);
1537 \& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime);
1538 \& }
1539 \& else
1540 \& /* you shalt not abuse printf for puts */
1541 \& puts ("wow, /etc/passwd is not there, expect problems. "
1542 \& "if this is windows, they already arrived\en");
1543 \& }
1544 .Ve
1545 .PP
1546 .Vb 2
1547 \& ...
1548 \& ev_stat passwd;
1549 .Ve
1550 .PP
1551 .Vb 2
1552 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1553 \& ev_stat_start (loop, &passwd);
1554 .Ve
1555 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1556 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1557 .IX Subsection "ev_idle - when you've got nothing better to do..."
1558 Idle watchers trigger events when no other events of the same or higher
1559 priority are pending (prepare, check and other idle watchers do not
1560 count).
1561 .PP
1562 That is, as long as your process is busy handling sockets or timeouts
1563 (or even signals, imagine) of the same or higher priority it will not be
1564 triggered. But when your process is idle (or only lower-priority watchers
1565 are pending), the idle watchers are being called once per event loop
1566 iteration \- until stopped, that is, or your process receives more events
1567 and becomes busy again with higher priority stuff.
1568 .PP
1569 The most noteworthy effect is that as long as any idle watchers are
1570 active, the process will not block when waiting for new events.
1571 .PP
1572 Apart from keeping your process non-blocking (which is a useful
1573 effect on its own sometimes), idle watchers are a good place to do
1574 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
1575 event loop has handled all outstanding events.
1576 .IP "ev_idle_init (ev_signal *, callback)" 4
1577 .IX Item "ev_idle_init (ev_signal *, callback)"
1578 Initialises and configures the idle watcher \- it has no parameters of any
1579 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1580 believe me.
1581 .PP
1582 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1583 callback, free it. Also, use no error checking, as usual.
1584 .PP
1585 .Vb 7
1586 \& static void
1587 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1588 \& {
1589 \& free (w);
1590 \& // now do something you wanted to do when the program has
1591 \& // no longer asnything immediate to do.
1592 \& }
1593 .Ve
1594 .PP
1595 .Vb 3
1596 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1597 \& ev_idle_init (idle_watcher, idle_cb);
1598 \& ev_idle_start (loop, idle_cb);
1599 .Ve
1600 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1601 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1602 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
1603 Prepare and check watchers are usually (but not always) used in tandem:
1604 prepare watchers get invoked before the process blocks and check watchers
1605 afterwards.
1606 .PP
1607 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1608 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1609 watchers. Other loops than the current one are fine, however. The
1610 rationale behind this is that you do not need to check for recursion in
1611 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1612 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1613 called in pairs bracketing the blocking call.
1614 .PP
1615 Their main purpose is to integrate other event mechanisms into libev and
1616 their use is somewhat advanced. This could be used, for example, to track
1617 variable changes, implement your own watchers, integrate net-snmp or a
1618 coroutine library and lots more. They are also occasionally useful if
1619 you cache some data and want to flush it before blocking (for example,
1620 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1621 watcher).
1622 .PP
1623 This is done by examining in each prepare call which file descriptors need
1624 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1625 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1626 provide just this functionality). Then, in the check watcher you check for
1627 any events that occured (by checking the pending status of all watchers
1628 and stopping them) and call back into the library. The I/O and timer
1629 callbacks will never actually be called (but must be valid nevertheless,
1630 because you never know, you know?).
1631 .PP
1632 As another example, the Perl Coro module uses these hooks to integrate
1633 coroutines into libev programs, by yielding to other active coroutines
1634 during each prepare and only letting the process block if no coroutines
1635 are ready to run (it's actually more complicated: it only runs coroutines
1636 with priority higher than or equal to the event loop and one coroutine
1637 of lower priority, but only once, using idle watchers to keep the event
1638 loop from blocking if lower-priority coroutines are active, thus mapping
1639 low-priority coroutines to idle/background tasks).
1640 .PP
1641 It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
1642 priority, to ensure that they are being run before any other watchers
1643 after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
1644 too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
1645 supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers did
1646 their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event
1647 loops those other event loops might be in an unusable state until their
1648 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1649 others).
1650 .IP "ev_prepare_init (ev_prepare *, callback)" 4
1651 .IX Item "ev_prepare_init (ev_prepare *, callback)"
1652 .PD 0
1653 .IP "ev_check_init (ev_check *, callback)" 4
1654 .IX Item "ev_check_init (ev_check *, callback)"
1655 .PD
1656 Initialises and configures the prepare or check watcher \- they have no
1657 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1658 macros, but using them is utterly, utterly and completely pointless.
1659 .PP
1660 There are a number of principal ways to embed other event loops or modules
1661 into libev. Here are some ideas on how to include libadns into libev
1662 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1663 use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR
1664 embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0
1665 into the Glib event loop).
1666 .PP
1667 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1668 and in a check watcher, destroy them and call into libadns. What follows
1669 is pseudo-code only of course. This requires you to either use a low
1670 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1671 the callbacks for the IO/timeout watchers might not have been called yet.
1672 .PP
1673 .Vb 2
1674 \& static ev_io iow [nfd];
1675 \& static ev_timer tw;
1676 .Ve
1677 .PP
1678 .Vb 4
1679 \& static void
1680 \& io_cb (ev_loop *loop, ev_io *w, int revents)
1681 \& {
1682 \& }
1683 .Ve
1684 .PP
1685 .Vb 8
1686 \& // create io watchers for each fd and a timer before blocking
1687 \& static void
1688 \& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1689 \& {
1690 \& int timeout = 3600000;
1691 \& struct pollfd fds [nfd];
1692 \& // actual code will need to loop here and realloc etc.
1693 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1694 .Ve
1695 .PP
1696 .Vb 3
1697 \& /* the callback is illegal, but won't be called as we stop during check */
1698 \& ev_timer_init (&tw, 0, timeout * 1e-3);
1699 \& ev_timer_start (loop, &tw);
1700 .Ve
1701 .PP
1702 .Vb 6
1703 \& // create one ev_io per pollfd
1704 \& for (int i = 0; i < nfd; ++i)
1705 \& {
1706 \& ev_io_init (iow + i, io_cb, fds [i].fd,
1707 \& ((fds [i].events & POLLIN ? EV_READ : 0)
1708 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1709 .Ve
1710 .PP
1711 .Vb 4
1712 \& fds [i].revents = 0;
1713 \& ev_io_start (loop, iow + i);
1714 \& }
1715 \& }
1716 .Ve
1717 .PP
1718 .Vb 5
1719 \& // stop all watchers after blocking
1720 \& static void
1721 \& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1722 \& {
1723 \& ev_timer_stop (loop, &tw);
1724 .Ve
1725 .PP
1726 .Vb 8
1727 \& for (int i = 0; i < nfd; ++i)
1728 \& {
1729 \& // set the relevant poll flags
1730 \& // could also call adns_processreadable etc. here
1731 \& struct pollfd *fd = fds + i;
1732 \& int revents = ev_clear_pending (iow + i);
1733 \& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1734 \& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1735 .Ve
1736 .PP
1737 .Vb 3
1738 \& // now stop the watcher
1739 \& ev_io_stop (loop, iow + i);
1740 \& }
1741 .Ve
1742 .PP
1743 .Vb 2
1744 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1745 \& }
1746 .Ve
1747 .PP
1748 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
1749 in the prepare watcher and would dispose of the check watcher.
1750 .PP
1751 Method 3: If the module to be embedded supports explicit event
1752 notification (adns does), you can also make use of the actual watcher
1753 callbacks, and only destroy/create the watchers in the prepare watcher.
1754 .PP
1755 .Vb 5
1756 \& static void
1757 \& timer_cb (EV_P_ ev_timer *w, int revents)
1758 \& {
1759 \& adns_state ads = (adns_state)w->data;
1760 \& update_now (EV_A);
1761 .Ve
1762 .PP
1763 .Vb 2
1764 \& adns_processtimeouts (ads, &tv_now);
1765 \& }
1766 .Ve
1767 .PP
1768 .Vb 5
1769 \& static void
1770 \& io_cb (EV_P_ ev_io *w, int revents)
1771 \& {
1772 \& adns_state ads = (adns_state)w->data;
1773 \& update_now (EV_A);
1774 .Ve
1775 .PP
1776 .Vb 3
1777 \& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1778 \& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1779 \& }
1780 .Ve
1781 .PP
1782 .Vb 1
1783 \& // do not ever call adns_afterpoll
1784 .Ve
1785 .PP
1786 Method 4: Do not use a prepare or check watcher because the module you
1787 want to embed is too inflexible to support it. Instead, youc na override
1788 their poll function. The drawback with this solution is that the main
1789 loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
1790 this.
1791 .PP
1792 .Vb 4
1793 \& static gint
1794 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1795 \& {
1796 \& int got_events = 0;
1797 .Ve
1798 .PP
1799 .Vb 2
1800 \& for (n = 0; n < nfds; ++n)
1801 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1802 .Ve
1803 .PP
1804 .Vb 2
1805 \& if (timeout >= 0)
1806 \& // create/start timer
1807 .Ve
1808 .PP
1809 .Vb 2
1810 \& // poll
1811 \& ev_loop (EV_A_ 0);
1812 .Ve
1813 .PP
1814 .Vb 3
1815 \& // stop timer again
1816 \& if (timeout >= 0)
1817 \& ev_timer_stop (EV_A_ &to);
1818 .Ve
1819 .PP
1820 .Vb 3
1821 \& // stop io watchers again - their callbacks should have set
1822 \& for (n = 0; n < nfds; ++n)
1823 \& ev_io_stop (EV_A_ iow [n]);
1824 .Ve
1825 .PP
1826 .Vb 2
1827 \& return got_events;
1828 \& }
1829 .Ve
1830 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
1831 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
1832 .IX Subsection "ev_embed - when one backend isn't enough..."
1833 This is a rather advanced watcher type that lets you embed one event loop
1834 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1835 loop, other types of watchers might be handled in a delayed or incorrect
1836 fashion and must not be used).
1837 .PP
1838 There are primarily two reasons you would want that: work around bugs and
1839 prioritise I/O.
1840 .PP
1841 As an example for a bug workaround, the kqueue backend might only support
1842 sockets on some platform, so it is unusable as generic backend, but you
1843 still want to make use of it because you have many sockets and it scales
1844 so nicely. In this case, you would create a kqueue-based loop and embed it
1845 into your default loop (which might use e.g. poll). Overall operation will
1846 be a bit slower because first libev has to poll and then call kevent, but
1847 at least you can use both at what they are best.
1848 .PP
1849 As for prioritising I/O: rarely you have the case where some fds have
1850 to be watched and handled very quickly (with low latency), and even
1851 priorities and idle watchers might have too much overhead. In this case
1852 you would put all the high priority stuff in one loop and all the rest in
1853 a second one, and embed the second one in the first.
1854 .PP
1855 As long as the watcher is active, the callback will be invoked every time
1856 there might be events pending in the embedded loop. The callback must then
1857 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
1858 their callbacks (you could also start an idle watcher to give the embedded
1859 loop strictly lower priority for example). You can also set the callback
1860 to \f(CW0\fR, in which case the embed watcher will automatically execute the
1861 embedded loop sweep.
1862 .PP
1863 As long as the watcher is started it will automatically handle events. The
1864 callback will be invoked whenever some events have been handled. You can
1865 set the callback to \f(CW0\fR to avoid having to specify one if you are not
1866 interested in that.
1867 .PP
1868 Also, there have not currently been made special provisions for forking:
1869 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
1870 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1871 yourself.
1872 .PP
1873 Unfortunately, not all backends are embeddable, only the ones returned by
1874 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1875 portable one.
1876 .PP
1877 So when you want to use this feature you will always have to be prepared
1878 that you cannot get an embeddable loop. The recommended way to get around
1879 this is to have a separate variables for your embeddable loop, try to
1880 create it, and if that fails, use the normal loop for everything:
1881 .PP
1882 .Vb 3
1883 \& struct ev_loop *loop_hi = ev_default_init (0);
1884 \& struct ev_loop *loop_lo = 0;
1885 \& struct ev_embed embed;
1886 .Ve
1887 .PP
1888 .Vb 5
1889 \& // see if there is a chance of getting one that works
1890 \& // (remember that a flags value of 0 means autodetection)
1891 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1892 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1893 \& : 0;
1894 .Ve
1895 .PP
1896 .Vb 8
1897 \& // if we got one, then embed it, otherwise default to loop_hi
1898 \& if (loop_lo)
1899 \& {
1900 \& ev_embed_init (&embed, 0, loop_lo);
1901 \& ev_embed_start (loop_hi, &embed);
1902 \& }
1903 \& else
1904 \& loop_lo = loop_hi;
1905 .Ve
1906 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1907 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1908 .PD 0
1909 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1910 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1911 .PD
1912 Configures the watcher to embed the given loop, which must be
1913 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1914 invoked automatically, otherwise it is the responsibility of the callback
1915 to invoke it (it will continue to be called until the sweep has been done,
1916 if you do not want thta, you need to temporarily stop the embed watcher).
1917 .IP "ev_embed_sweep (loop, ev_embed *)" 4
1918 .IX Item "ev_embed_sweep (loop, ev_embed *)"
1919 Make a single, non-blocking sweep over the embedded loop. This works
1920 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
1921 apropriate way for embedded loops.
1922 .IP "struct ev_loop *loop [read\-only]" 4
1923 .IX Item "struct ev_loop *loop [read-only]"
1924 The embedded event loop.
1925 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
1926 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1927 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1928 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1929 whoever is a good citizen cared to tell libev about it by calling
1930 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
1931 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
1932 and only in the child after the fork. If whoever good citizen calling
1933 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
1934 handlers will be invoked, too, of course.
1935 .IP "ev_fork_init (ev_signal *, callback)" 4
1936 .IX Item "ev_fork_init (ev_signal *, callback)"
1937 Initialises and configures the fork watcher \- it has no parameters of any
1938 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1939 believe me.
1940 .SH "OTHER FUNCTIONS"
1941 .IX Header "OTHER FUNCTIONS"
1942 There are some other functions of possible interest. Described. Here. Now.
1943 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1944 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1945 This function combines a simple timer and an I/O watcher, calls your
1946 callback on whichever event happens first and automatically stop both
1947 watchers. This is useful if you want to wait for a single event on an fd
1948 or timeout without having to allocate/configure/start/stop/free one or
1949 more watchers yourself.
1950 .Sp
1951 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
1952 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
1953 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
1954 .Sp
1955 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1956 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1957 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
1958 dubious value.
1959 .Sp
1960 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1961 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1962 \&\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
1963 value passed to \f(CW\*(C`ev_once\*(C'\fR:
1964 .Sp
1965 .Vb 7
1966 \& static void stdin_ready (int revents, void *arg)
1967 \& {
1968 \& if (revents & EV_TIMEOUT)
1969 \& /* doh, nothing entered */;
1970 \& else if (revents & EV_READ)
1971 \& /* stdin might have data for us, joy! */;
1972 \& }
1973 .Ve
1974 .Sp
1975 .Vb 1
1976 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1977 .Ve
1978 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1979 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1980 Feeds the given event set into the event loop, as if the specified event
1981 had happened for the specified watcher (which must be a pointer to an
1982 initialised but not necessarily started event watcher).
1983 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
1984 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
1985 Feed an event on the given fd, as if a file descriptor backend detected
1986 the given events it.
1987 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
1988 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
1989 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
1990 loop!).
1991 .SH "LIBEVENT EMULATION"
1992 .IX Header "LIBEVENT EMULATION"
1993 Libev offers a compatibility emulation layer for libevent. It cannot
1994 emulate the internals of libevent, so here are some usage hints:
1995 .IP "* Use it by including <event.h>, as usual." 4
1996 .IX Item "Use it by including <event.h>, as usual."
1997 .PD 0
1998 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
1999 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
2000 .IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4
2001 .IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)."
2002 .IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4
2003 .IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field."
2004 .IP "* Other members are not supported." 4
2005 .IX Item "Other members are not supported."
2006 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
2007 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
2008 .PD
2009 .SH "\*(C+ SUPPORT"
2010 .IX Header " SUPPORT"
2011 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2012 you to use some convinience methods to start/stop watchers and also change
2013 the callback model to a model using method callbacks on objects.
2014 .PP
2015 To use it,
2016 .PP
2017 .Vb 1
2018 \& #include <ev++.h>
2019 .Ve
2020 .PP
2021 This automatically includes \fIev.h\fR and puts all of its definitions (many
2022 of them macros) into the global namespace. All \*(C+ specific things are
2023 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2024 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2025 .PP
2026 Care has been taken to keep the overhead low. The only data member the \*(C+
2027 classes add (compared to plain C\-style watchers) is the event loop pointer
2028 that the watcher is associated with (or no additional members at all if
2029 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2030 .PP
2031 Currently, functions, and static and non-static member functions can be
2032 used as callbacks. Other types should be easy to add as long as they only
2033 need one additional pointer for context. If you need support for other
2034 types of functors please contact the author (preferably after implementing
2035 it).
2036 .PP
2037 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2038 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2039 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2040 .IX Item "ev::READ, ev::WRITE etc."
2041 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2042 macros from \fIev.h\fR.
2043 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2044 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2045 .IX Item "ev::tstamp, ev::now"
2046 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2047 .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
2048 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2049 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2050 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2051 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2052 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2053 defines by many implementations.
2054 .Sp
2055 All of those classes have these methods:
2056 .RS 4
2057 .IP "ev::TYPE::TYPE ()" 4
2058 .IX Item "ev::TYPE::TYPE ()"
2059 .PD 0
2060 .IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2061 .IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2062 .IP "ev::TYPE::~TYPE" 4
2063 .IX Item "ev::TYPE::~TYPE"
2064 .PD
2065 The constructor (optionally) takes an event loop to associate the watcher
2066 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2067 .Sp
2068 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2069 \&\f(CW\*(C`set\*(C'\fR method before starting it.
2070 .Sp
2071 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2072 method to set a callback before you can start the watcher.
2073 .Sp
2074 (The reason why you have to use a method is a limitation in \*(C+ which does
2075 not allow explicit template arguments for constructors).
2076 .Sp
2077 The destructor automatically stops the watcher if it is active.
2078 .IP "w\->set<class, &class::method> (object *)" 4
2079 .IX Item "w->set<class, &class::method> (object *)"
2080 This method sets the callback method to call. The method has to have a
2081 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2082 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2083 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2084 .Sp
2085 This method synthesizes efficient thunking code to call your method from
2086 the C callback that libev requires. If your compiler can inline your
2087 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2088 your compiler is good :), then the method will be fully inlined into the
2089 thunking function, making it as fast as a direct C callback.
2090 .Sp
2091 Example: simple class declaration and watcher initialisation
2092 .Sp
2093 .Vb 4
2094 \& struct myclass
2095 \& {
2096 \& void io_cb (ev::io &w, int revents) { }
2097 \& }
2098 .Ve
2099 .Sp
2100 .Vb 3
2101 \& myclass obj;
2102 \& ev::io iow;
2103 \& iow.set <myclass, &myclass::io_cb> (&obj);
2104 .Ve
2105 .IP "w\->set<function> (void *data = 0)" 4
2106 .IX Item "w->set<function> (void *data = 0)"
2107 Also sets a callback, but uses a static method or plain function as
2108 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2109 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2110 .Sp
2111 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2112 .Sp
2113 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2114 .Sp
2115 Example:
2116 .Sp
2117 .Vb 2
2118 \& static void io_cb (ev::io &w, int revents) { }
2119 \& iow.set <io_cb> ();
2120 .Ve
2121 .IP "w\->set (struct ev_loop *)" 4
2122 .IX Item "w->set (struct ev_loop *)"
2123 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2124 do this when the watcher is inactive (and not pending either).
2125 .IP "w\->set ([args])" 4
2126 .IX Item "w->set ([args])"
2127 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2128 called at least once. Unlike the C counterpart, an active watcher gets
2129 automatically stopped and restarted when reconfiguring it with this
2130 method.
2131 .IP "w\->start ()" 4
2132 .IX Item "w->start ()"
2133 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2134 constructor already stores the event loop.
2135 .IP "w\->stop ()" 4
2136 .IX Item "w->stop ()"
2137 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2138 .ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4
2139 .el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4
2140 .IX Item "w->again () ev::timer, ev::periodic only"
2141 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2142 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2143 .ie n .IP "w\->sweep () ""ev::embed"" only" 4
2144 .el .IP "w\->sweep () \f(CWev::embed\fR only" 4
2145 .IX Item "w->sweep () ev::embed only"
2146 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2147 .ie n .IP "w\->update () ""ev::stat"" only" 4
2148 .el .IP "w\->update () \f(CWev::stat\fR only" 4
2149 .IX Item "w->update () ev::stat only"
2150 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2151 .RE
2152 .RS 4
2153 .RE
2154 .PP
2155 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2156 the constructor.
2157 .PP
2158 .Vb 4
2159 \& class myclass
2160 \& {
2161 \& ev_io io; void io_cb (ev::io &w, int revents);
2162 \& ev_idle idle void idle_cb (ev::idle &w, int revents);
2163 .Ve
2164 .PP
2165 .Vb 2
2166 \& myclass ();
2167 \& }
2168 .Ve
2169 .PP
2170 .Vb 4
2171 \& myclass::myclass (int fd)
2172 \& {
2173 \& io .set <myclass, &myclass::io_cb > (this);
2174 \& idle.set <myclass, &myclass::idle_cb> (this);
2175 .Ve
2176 .PP
2177 .Vb 2
2178 \& io.start (fd, ev::READ);
2179 \& }
2180 .Ve
2181 .SH "MACRO MAGIC"
2182 .IX Header "MACRO MAGIC"
2183 Libev can be compiled with a variety of options, the most fundemantal is
2184 \&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) functions and
2185 callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2186 .PP
2187 To make it easier to write programs that cope with either variant, the
2188 following macros are defined:
2189 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2190 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2191 .IX Item "EV_A, EV_A_"
2192 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2193 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2194 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2195 .Sp
2196 .Vb 3
2197 \& ev_unref (EV_A);
2198 \& ev_timer_add (EV_A_ watcher);
2199 \& ev_loop (EV_A_ 0);
2200 .Ve
2201 .Sp
2202 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2203 which is often provided by the following macro.
2204 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2205 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2206 .IX Item "EV_P, EV_P_"
2207 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2208 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2209 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2210 .Sp
2211 .Vb 2
2212 \& // this is how ev_unref is being declared
2213 \& static void ev_unref (EV_P);
2214 .Ve
2215 .Sp
2216 .Vb 2
2217 \& // this is how you can declare your typical callback
2218 \& static void cb (EV_P_ ev_timer *w, int revents)
2219 .Ve
2220 .Sp
2221 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2222 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2223 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2224 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2225 .IX Item "EV_DEFAULT, EV_DEFAULT_"
2226 Similar to the other two macros, this gives you the value of the default
2227 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2228 .PP
2229 Example: Declare and initialise a check watcher, utilising the above
2230 macros so it will work regardless of whether multiple loops are supported
2231 or not.
2232 .PP
2233 .Vb 5
2234 \& static void
2235 \& check_cb (EV_P_ ev_timer *w, int revents)
2236 \& {
2237 \& ev_check_stop (EV_A_ w);
2238 \& }
2239 .Ve
2240 .PP
2241 .Vb 4
2242 \& ev_check check;
2243 \& ev_check_init (&check, check_cb);
2244 \& ev_check_start (EV_DEFAULT_ &check);
2245 \& ev_loop (EV_DEFAULT_ 0);
2246 .Ve
2247 .SH "EMBEDDING"
2248 .IX Header "EMBEDDING"
2249 Libev can (and often is) directly embedded into host
2250 applications. Examples of applications that embed it include the Deliantra
2251 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2252 and rxvt\-unicode.
2253 .PP
2254 The goal is to enable you to just copy the neecssary files into your
2255 source directory without having to change even a single line in them, so
2256 you can easily upgrade by simply copying (or having a checked-out copy of
2257 libev somewhere in your source tree).
2258 .Sh "\s-1FILESETS\s0"
2259 .IX Subsection "FILESETS"
2260 Depending on what features you need you need to include one or more sets of files
2261 in your app.
2262 .PP
2263 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2264 .IX Subsection "CORE EVENT LOOP"
2265 .PP
2266 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2267 configuration (no autoconf):
2268 .PP
2269 .Vb 2
2270 \& #define EV_STANDALONE 1
2271 \& #include "ev.c"
2272 .Ve
2273 .PP
2274 This will automatically include \fIev.h\fR, too, and should be done in a
2275 single C source file only to provide the function implementations. To use
2276 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2277 done by writing a wrapper around \fIev.h\fR that you can include instead and
2278 where you can put other configuration options):
2279 .PP
2280 .Vb 2
2281 \& #define EV_STANDALONE 1
2282 \& #include "ev.h"
2283 .Ve
2284 .PP
2285 Both header files and implementation files can be compiled with a \*(C+
2286 compiler (at least, thats a stated goal, and breakage will be treated
2287 as a bug).
2288 .PP
2289 You need the following files in your source tree, or in a directory
2290 in your include path (e.g. in libev/ when using \-Ilibev):
2291 .PP
2292 .Vb 4
2293 \& ev.h
2294 \& ev.c
2295 \& ev_vars.h
2296 \& ev_wrap.h
2297 .Ve
2298 .PP
2299 .Vb 1
2300 \& ev_win32.c required on win32 platforms only
2301 .Ve
2302 .PP
2303 .Vb 5
2304 \& ev_select.c only when select backend is enabled (which is enabled by default)
2305 \& ev_poll.c only when poll backend is enabled (disabled by default)
2306 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2307 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2308 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
2309 .Ve
2310 .PP
2311 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
2312 to compile this single file.
2313 .PP
2314 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2315 .IX Subsection "LIBEVENT COMPATIBILITY API"
2316 .PP
2317 To include the libevent compatibility \s-1API\s0, also include:
2318 .PP
2319 .Vb 1
2320 \& #include "event.c"
2321 .Ve
2322 .PP
2323 in the file including \fIev.c\fR, and:
2324 .PP
2325 .Vb 1
2326 \& #include "event.h"
2327 .Ve
2328 .PP
2329 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2330 .PP
2331 You need the following additional files for this:
2332 .PP
2333 .Vb 2
2334 \& event.h
2335 \& event.c
2336 .Ve
2337 .PP
2338 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2339 .IX Subsection "AUTOCONF SUPPORT"
2340 .PP
2341 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2342 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2343 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2344 include \fIconfig.h\fR and configure itself accordingly.
2345 .PP
2346 For this of course you need the m4 file:
2347 .PP
2348 .Vb 1
2349 \& libev.m4
2350 .Ve
2351 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2352 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2353 Libev can be configured via a variety of preprocessor symbols you have to define
2354 before including any of its files. The default is not to build for multiplicity
2355 and only include the select backend.
2356 .IP "\s-1EV_STANDALONE\s0" 4
2357 .IX Item "EV_STANDALONE"
2358 Must always be \f(CW1\fR if you do not use autoconf configuration, which
2359 keeps libev from including \fIconfig.h\fR, and it also defines dummy
2360 implementations for some libevent functions (such as logging, which is not
2361 supported). It will also not define any of the structs usually found in
2362 \&\fIevent.h\fR that are not directly supported by the libev core alone.
2363 .IP "\s-1EV_USE_MONOTONIC\s0" 4
2364 .IX Item "EV_USE_MONOTONIC"
2365 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2366 monotonic clock option at both compiletime and runtime. Otherwise no use
2367 of the monotonic clock option will be attempted. If you enable this, you
2368 usually have to link against librt or something similar. Enabling it when
2369 the functionality isn't available is safe, though, althoguh you have
2370 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2371 function is hiding in (often \fI\-lrt\fR).
2372 .IP "\s-1EV_USE_REALTIME\s0" 4
2373 .IX Item "EV_USE_REALTIME"
2374 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2375 realtime clock option at compiletime (and assume its availability at
2376 runtime if successful). Otherwise no use of the realtime clock option will
2377 be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2378 (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries
2379 in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2380 .IP "\s-1EV_USE_SELECT\s0" 4
2381 .IX Item "EV_USE_SELECT"
2382 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2383 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2384 other method takes over, select will be it. Otherwise the select backend
2385 will not be compiled in.
2386 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2387 .IX Item "EV_SELECT_USE_FD_SET"
2388 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2389 structure. This is useful if libev doesn't compile due to a missing
2390 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2391 exotic systems. This usually limits the range of file descriptors to some
2392 low limit such as 1024 or might have other limitations (winsocket only
2393 allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2394 influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2395 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2396 .IX Item "EV_SELECT_IS_WINSOCKET"
2397 When defined to \f(CW1\fR, the select backend will assume that
2398 select/socket/connect etc. don't understand file descriptors but
2399 wants osf handles on win32 (this is the case when the select to
2400 be used is the winsock select). This means that it will call
2401 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2402 it is assumed that all these functions actually work on fds, even
2403 on win32. Should not be defined on non\-win32 platforms.
2404 .IP "\s-1EV_USE_POLL\s0" 4
2405 .IX Item "EV_USE_POLL"
2406 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2407 backend. Otherwise it will be enabled on non\-win32 platforms. It
2408 takes precedence over select.
2409 .IP "\s-1EV_USE_EPOLL\s0" 4
2410 .IX Item "EV_USE_EPOLL"
2411 If defined to be \f(CW1\fR, libev will compile in support for the Linux
2412 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2413 otherwise another method will be used as fallback. This is the
2414 preferred backend for GNU/Linux systems.
2415 .IP "\s-1EV_USE_KQUEUE\s0" 4
2416 .IX Item "EV_USE_KQUEUE"
2417 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2418 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2419 otherwise another method will be used as fallback. This is the preferred
2420 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2421 supports some types of fds correctly (the only platform we found that
2422 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2423 not be used unless explicitly requested. The best way to use it is to find
2424 out whether kqueue supports your type of fd properly and use an embedded
2425 kqueue loop.
2426 .IP "\s-1EV_USE_PORT\s0" 4
2427 .IX Item "EV_USE_PORT"
2428 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
2429 10 port style backend. Its availability will be detected at runtime,
2430 otherwise another method will be used as fallback. This is the preferred
2431 backend for Solaris 10 systems.
2432 .IP "\s-1EV_USE_DEVPOLL\s0" 4
2433 .IX Item "EV_USE_DEVPOLL"
2434 reserved for future expansion, works like the \s-1USE\s0 symbols above.
2435 .IP "\s-1EV_USE_INOTIFY\s0" 4
2436 .IX Item "EV_USE_INOTIFY"
2437 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2438 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2439 be detected at runtime.
2440 .IP "\s-1EV_H\s0" 4
2441 .IX Item "EV_H"
2442 The name of the \fIev.h\fR header file used to include it. The default if
2443 undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This
2444 can be used to virtually rename the \fIev.h\fR header file in case of conflicts.
2445 .IP "\s-1EV_CONFIG_H\s0" 4
2446 .IX Item "EV_CONFIG_H"
2447 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2448 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2449 \&\f(CW\*(C`EV_H\*(C'\fR, above.
2450 .IP "\s-1EV_EVENT_H\s0" 4
2451 .IX Item "EV_EVENT_H"
2452 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2453 of how the \fIevent.h\fR header can be found.
2454 .IP "\s-1EV_PROTOTYPES\s0" 4
2455 .IX Item "EV_PROTOTYPES"
2456 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2457 prototypes, but still define all the structs and other symbols. This is
2458 occasionally useful if you want to provide your own wrapper functions
2459 around libev functions.
2460 .IP "\s-1EV_MULTIPLICITY\s0" 4
2461 .IX Item "EV_MULTIPLICITY"
2462 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2463 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2464 additional independent event loops. Otherwise there will be no support
2465 for multiple event loops and there is no first event loop pointer
2466 argument. Instead, all functions act on the single default loop.
2467 .IP "\s-1EV_MINPRI\s0" 4
2468 .IX Item "EV_MINPRI"
2469 .PD 0
2470 .IP "\s-1EV_MAXPRI\s0" 4
2471 .IX Item "EV_MAXPRI"
2472 .PD
2473 The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
2474 \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
2475 provide for more priorities by overriding those symbols (usually defined
2476 to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
2477 .Sp
2478 When doing priority-based operations, libev usually has to linearly search
2479 all the priorities, so having many of them (hundreds) uses a lot of space
2480 and time, so using the defaults of five priorities (\-2 .. +2) is usually
2481 fine.
2482 .Sp
2483 If your embedding app does not need any priorities, defining these both to
2484 \&\f(CW0\fR will save some memory and cpu.
2485 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
2486 .IX Item "EV_PERIODIC_ENABLE"
2487 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
2488 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2489 code.
2490 .IP "\s-1EV_IDLE_ENABLE\s0" 4
2491 .IX Item "EV_IDLE_ENABLE"
2492 If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2493 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2494 code.
2495 .IP "\s-1EV_EMBED_ENABLE\s0" 4
2496 .IX Item "EV_EMBED_ENABLE"
2497 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2498 defined to be \f(CW0\fR, then they are not.
2499 .IP "\s-1EV_STAT_ENABLE\s0" 4
2500 .IX Item "EV_STAT_ENABLE"
2501 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2502 defined to be \f(CW0\fR, then they are not.
2503 .IP "\s-1EV_FORK_ENABLE\s0" 4
2504 .IX Item "EV_FORK_ENABLE"
2505 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2506 defined to be \f(CW0\fR, then they are not.
2507 .IP "\s-1EV_MINIMAL\s0" 4
2508 .IX Item "EV_MINIMAL"
2509 If you need to shave off some kilobytes of code at the expense of some
2510 speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override
2511 some inlining decisions, saves roughly 30% codesize of amd64.
2512 .IP "\s-1EV_PID_HASHSIZE\s0" 4
2513 .IX Item "EV_PID_HASHSIZE"
2514 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2515 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
2516 than enough. If you need to manage thousands of children you might want to
2517 increase this value (\fImust\fR be a power of two).
2518 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2519 .IX Item "EV_INOTIFY_HASHSIZE"
2520 \&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by
2521 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
2522 usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
2523 watchers you might want to increase this value (\fImust\fR be a power of
2524 two).
2525 .IP "\s-1EV_COMMON\s0" 4
2526 .IX Item "EV_COMMON"
2527 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2528 this macro to a something else you can include more and other types of
2529 members. You have to define it each time you include one of the files,
2530 though, and it must be identical each time.
2531 .Sp
2532 For example, the perl \s-1EV\s0 module uses something like this:
2533 .Sp
2534 .Vb 3
2535 \& #define EV_COMMON \e
2536 \& SV *self; /* contains this struct */ \e
2537 \& SV *cb_sv, *fh /* note no trailing ";" */
2538 .Ve
2539 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2540 .IX Item "EV_CB_DECLARE (type)"
2541 .PD 0
2542 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
2543 .IX Item "EV_CB_INVOKE (watcher, revents)"
2544 .IP "ev_set_cb (ev, cb)" 4
2545 .IX Item "ev_set_cb (ev, cb)"
2546 .PD
2547 Can be used to change the callback member declaration in each watcher,
2548 and the way callbacks are invoked and set. Must expand to a struct member
2549 definition and a statement, respectively. See the \fIev.v\fR header file for
2550 their default definitions. One possible use for overriding these is to
2551 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2552 method calls instead of plain function calls in \*(C+.
2553 .Sh "\s-1EXAMPLES\s0"
2554 .IX Subsection "EXAMPLES"
2555 For a real-world example of a program the includes libev
2556 verbatim, you can have a look at the \s-1EV\s0 perl module
2557 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2558 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2559 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2560 will be compiled. It is pretty complex because it provides its own header
2561 file.
2562 .Sp
2563 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2564 that everybody includes and which overrides some configure choices:
2565 .Sp
2566 .Vb 9
2567 \& #define EV_MINIMAL 1
2568 \& #define EV_USE_POLL 0
2569 \& #define EV_MULTIPLICITY 0
2570 \& #define EV_PERIODIC_ENABLE 0
2571 \& #define EV_STAT_ENABLE 0
2572 \& #define EV_FORK_ENABLE 0
2573 \& #define EV_CONFIG_H <config.h>
2574 \& #define EV_MINPRI 0
2575 \& #define EV_MAXPRI 0
2576 .Ve
2577 .Sp
2578 .Vb 1
2579 \& #include "ev++.h"
2580 .Ve
2581 .Sp
2582 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2583 .Sp
2584 .Vb 2
2585 \& #include "ev_cpp.h"
2586 \& #include "ev.c"
2587 .Ve
2588 .SH "COMPLEXITIES"
2589 .IX Header "COMPLEXITIES"
2590 In this section the complexities of (many of) the algorithms used inside
2591 libev will be explained. For complexity discussions about backends see the
2592 documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2593 .Sp
2594 All of the following are about amortised time: If an array needs to be
2595 extended, libev needs to realloc and move the whole array, but this
2596 happens asymptotically never with higher number of elements, so O(1) might
2597 mean it might do a lengthy realloc operation in rare cases, but on average
2598 it is much faster and asymptotically approaches constant time.
2599 .RS 4
2600 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2601 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2602 This means that, when you have a watcher that triggers in one hour and
2603 there are 100 watchers that would trigger before that then inserting will
2604 have to skip those 100 watchers.
2605 .IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2606 .IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2607 That means that for changing a timer costs less than removing/adding them
2608 as only the relative motion in the event queue has to be paid for.
2609 .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2610 .IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2611 These just add the watcher into an array or at the head of a list.
2612 =item Stopping check/prepare/idle watchers: O(1)
2613 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2614 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
2615 These watchers are stored in lists then need to be walked to find the
2616 correct watcher to remove. The lists are usually short (you don't usually
2617 have many watchers waiting for the same fd or signal).
2618 .IP "Finding the next timer per loop iteration: O(1)" 4
2619 .IX Item "Finding the next timer per loop iteration: O(1)"
2620 .PD 0
2621 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2622 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2623 .PD
2624 A change means an I/O watcher gets started or stopped, which requires
2625 libev to recalculate its status (and possibly tell the kernel).
2626 .IP "Activating one watcher: O(1)" 4
2627 .IX Item "Activating one watcher: O(1)"
2628 .PD 0
2629 .IP "Priority handling: O(number_of_priorities)" 4
2630 .IX Item "Priority handling: O(number_of_priorities)"
2631 .PD
2632 Priorities are implemented by allocating some space for each
2633 priority. When doing priority-based operations, libev usually has to
2634 linearly search all the priorities.
2635 .RE
2636 .RS 4
2637 .SH "AUTHOR"
2638 .IX Header "AUTHOR"
2639 Marc Lehmann <libev@schmorp.de>.