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129 .\" ========================================================================
131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation"
134 libev \- a high performance full\-featured event loop written in C
136 .IX Header "SYNOPSIS"
141 .IX Header "DESCRIPTION"
142 Libev is an event loop: you register interest in certain events (such as a
143 file descriptor being readable or a timeout occuring), and it will manage
144 these event sources and provide your program with events.
146 To do this, it must take more or less complete control over your process
147 (or thread) by executing the \fIevent loop\fR handler, and will then
148 communicate events via a callback mechanism.
150 You register interest in certain events by registering so-called \fIevent
151 watchers\fR, which are relatively small C structures you initialise with the
152 details of the event, and then hand it over to libev by \fIstarting\fR the
155 .IX Header "FEATURES"
156 Libev supports select, poll, the linux-specific epoll and the bsd-specific
157 kqueue mechanisms for file descriptor events, relative timers, absolute
158 timers with customised rescheduling, signal events, process status change
159 events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event
160 loop mechanism itself (idle, prepare and check watchers). It also is quite
161 fast (see this benchmark comparing
162 it to libevent for example).
164 .IX Header "CONVENTIONS"
165 Libev is very configurable. In this manual the default configuration
166 will be described, which supports multiple event loops. For more info
167 about various configuration options please have a look at the file
168 \&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without
169 support for multiple event loops, then all functions taking an initial
170 argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR)
171 will not have this argument.
172 .SH "TIME REPRESENTATION"
173 .IX Header "TIME REPRESENTATION"
174 Libev represents time as a single floating point number, representing the
175 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176 the beginning of 1970, details are complicated, don't ask). This type is
177 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
178 to the double type in C.
179 .SH "GLOBAL FUNCTIONS"
180 .IX Header "GLOBAL FUNCTIONS"
181 These functions can be called anytime, even before initialising the
183 .IP "ev_tstamp ev_time ()" 4
184 .IX Item "ev_tstamp ev_time ()"
185 Returns the current time as libev would use it. Please note that the
186 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187 you actually want to know.
188 .IP "int ev_version_major ()" 4
189 .IX Item "int ev_version_major ()"
191 .IP "int ev_version_minor ()" 4
192 .IX Item "int ev_version_minor ()"
194 You can find out the major and minor version numbers of the library
195 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
196 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
197 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
198 version of the library your program was compiled against.
200 Usually, it's a good idea to terminate if the major versions mismatch,
201 as this indicates an incompatible change. Minor versions are usually
202 compatible to older versions, so a larger minor version alone is usually
204 .IP "unsigned int ev_supported_backends ()" 4
205 .IX Item "unsigned int ev_supported_backends ()"
206 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
207 value) compiled into this binary of libev (independent of their
208 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
209 a description of the set values.
210 .IP "unsigned int ev_recommended_backends ()" 4
211 .IX Item "unsigned int ev_recommended_backends ()"
212 Return the set of all backends compiled into this binary of libev and also
213 recommended for this platform. This set is often smaller than the one
214 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
215 most BSDs and will not be autodetected unless you explicitly request it
216 (assuming you know what you are doing). This is the set of backends that
217 \&\f(CW\*(C`EVFLAG_AUTO\*(C'\fR will probe for.
218 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
219 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
220 Sets the allocation function to use (the prototype is similar to the
221 realloc C function, the semantics are identical). It is used to allocate
222 and free memory (no surprises here). If it returns zero when memory
223 needs to be allocated, the library might abort or take some potentially
224 destructive action. The default is your system realloc function.
226 You could override this function in high-availability programs to, say,
227 free some memory if it cannot allocate memory, to use a special allocator,
228 or even to sleep a while and retry until some memory is available.
229 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
230 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
231 Set the callback function to call on a retryable syscall error (such
232 as failed select, poll, epoll_wait). The message is a printable string
233 indicating the system call or subsystem causing the problem. If this
234 callback is set, then libev will expect it to remedy the sitution, no
235 matter what, when it returns. That is, libev will generally retry the
236 requested operation, or, if the condition doesn't go away, do bad stuff
238 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
239 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
240 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
241 types of such loops, the \fIdefault\fR loop, which supports signals and child
242 events, and dynamically created loops which do not.
244 If you use threads, a common model is to run the default event loop
245 in your main thread (or in a separate thread) and for each thread you
246 create, you also create another event loop. Libev itself does no locking
247 whatsoever, so if you mix calls to the same event loop in different
248 threads, make sure you lock (this is usually a bad idea, though, even if
249 done correctly, because it's hideous and inefficient).
250 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
251 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
252 This will initialise the default event loop if it hasn't been initialised
253 yet and return it. If the default loop could not be initialised, returns
254 false. If it already was initialised it simply returns it (and ignores the
255 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
257 If you don't know what event loop to use, use the one returned from this
260 The flags argument can be used to specify special behaviour or specific
261 backends to use, and is usually specified as \f(CW0\fR (or \s-1EVFLAG_AUTO\s0).
263 It supports the following flags:
265 .ie n .IP """EVFLAG_AUTO""" 4
266 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
267 .IX Item "EVFLAG_AUTO"
268 The default flags value. Use this if you have no clue (it's the right
270 .ie n .IP """EVFLAG_NOENV""" 4
271 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
272 .IX Item "EVFLAG_NOENV"
273 If this flag bit is ored into the flag value (or the program runs setuid
274 or setgid) then libev will \fInot\fR look at the environment variable
275 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
276 override the flags completely if it is found in the environment. This is
277 useful to try out specific backends to test their performance, or to work
279 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
280 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
281 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
282 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
283 libev tries to roll its own fd_set with no limits on the number of fds,
284 but if that fails, expect a fairly low limit on the number of fds when
285 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
286 the fastest backend for a low number of fds.
287 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
288 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
289 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
290 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
291 select, but handles sparse fds better and has no artificial limit on the
292 number of fds you can use (except it will slow down considerably with a
293 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
294 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
295 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
296 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
297 For few fds, this backend is a bit little slower than poll and select,
298 but it scales phenomenally better. While poll and select usually scale like
299 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
300 either O(1) or O(active_fds).
302 While stopping and starting an I/O watcher in the same iteration will
303 result in some caching, there is still a syscall per such incident
304 (because the fd could point to a different file description now), so its
305 best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
306 well if you register events for both fds.
308 Please note that epoll sometimes generates spurious notifications, so you
309 need to use non-blocking I/O or other means to avoid blocking when no data
310 (or space) is available.
311 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
312 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
313 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
314 Kqueue deserves special mention, as at the time of this writing, it
315 was broken on all BSDs except NetBSD (usually it doesn't work with
316 anything but sockets and pipes, except on Darwin, where of course its
317 completely useless). For this reason its not being \*(L"autodetected\*(R" unless
318 you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0).
320 It scales in the same way as the epoll backend, but the interface to the
321 kernel is more efficient (which says nothing about its actual speed, of
322 course). While starting and stopping an I/O watcher does not cause an
323 extra syscall as with epoll, it still adds up to four event changes per
324 incident, so its best to avoid that.
325 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
326 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
327 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
328 This is not implemented yet (and might never be).
329 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
330 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
331 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
332 This uses the Solaris 10 port mechanism. As with everything on Solaris,
333 it's really slow, but it still scales very well (O(active_fds)).
335 Please note that solaris ports can result in a lot of spurious
336 notifications, so you need to use non-blocking I/O or other means to avoid
337 blocking when no data (or space) is available.
338 .ie n .IP """EVBACKEND_ALL""" 4
339 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
340 .IX Item "EVBACKEND_ALL"
341 Try all backends (even potentially broken ones that wouldn't be tried
342 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
343 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
347 If one or more of these are ored into the flags value, then only these
348 backends will be tried (in the reverse order as given here). If none are
349 specified, most compiled-in backend will be tried, usually in reverse
350 order of their flag values :)
352 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
353 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
354 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
355 always distinct from the default loop. Unlike the default loop, it cannot
356 handle signal and child watchers, and attempts to do so will be greeted by
357 undefined behaviour (or a failed assertion if assertions are enabled).
358 .IP "ev_default_destroy ()" 4
359 .IX Item "ev_default_destroy ()"
360 Destroys the default loop again (frees all memory and kernel state
361 etc.). This stops all registered event watchers (by not touching them in
362 any way whatsoever, although you cannot rely on this :).
363 .IP "ev_loop_destroy (loop)" 4
364 .IX Item "ev_loop_destroy (loop)"
365 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
366 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
367 .IP "ev_default_fork ()" 4
368 .IX Item "ev_default_fork ()"
369 This function reinitialises the kernel state for backends that have
370 one. Despite the name, you can call it anytime, but it makes most sense
371 after forking, in either the parent or child process (or both, but that
372 again makes little sense).
374 You \fImust\fR call this function in the child process after forking if and
375 only if you want to use the event library in both processes. If you just
376 fork+exec, you don't have to call it.
378 The function itself is quite fast and it's usually not a problem to call
379 it just in case after a fork. To make this easy, the function will fit in
380 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
383 \& pthread_atfork (0, 0, ev_default_fork);
386 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
387 without calling this function, so if you force one of those backends you
389 .IP "ev_loop_fork (loop)" 4
390 .IX Item "ev_loop_fork (loop)"
391 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
392 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
393 after fork, and how you do this is entirely your own problem.
394 .IP "unsigned int ev_backend (loop)" 4
395 .IX Item "unsigned int ev_backend (loop)"
396 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
398 .IP "ev_tstamp ev_now (loop)" 4
399 .IX Item "ev_tstamp ev_now (loop)"
400 Returns the current \*(L"event loop time\*(R", which is the time the event loop
401 got events and started processing them. This timestamp does not change
402 as long as callbacks are being processed, and this is also the base time
403 used for relative timers. You can treat it as the timestamp of the event
404 occuring (or more correctly, the mainloop finding out about it).
405 .IP "ev_loop (loop, int flags)" 4
406 .IX Item "ev_loop (loop, int flags)"
407 Finally, this is it, the event handler. This function usually is called
408 after you initialised all your watchers and you want to start handling
411 If the flags argument is specified as 0, it will not return until either
412 no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
414 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
415 those events and any outstanding ones, but will not block your process in
416 case there are no events and will return after one iteration of the loop.
418 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
419 neccessary) and will handle those and any outstanding ones. It will block
420 your process until at least one new event arrives, and will return after
421 one iteration of the loop.
423 This flags value could be used to implement alternative looping
424 constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
425 more generic mechanism.
427 Here are the gory details of what ev_loop does:
430 \& 1. If there are no active watchers (reference count is zero), return.
431 \& 2. Queue and immediately call all prepare watchers.
432 \& 3. If we have been forked, recreate the kernel state.
433 \& 4. Update the kernel state with all outstanding changes.
434 \& 5. Update the "event loop time".
435 \& 6. Calculate for how long to block.
436 \& 7. Block the process, waiting for events.
437 \& 8. Update the "event loop time" and do time jump handling.
438 \& 9. Queue all outstanding timers.
439 \& 10. Queue all outstanding periodics.
440 \& 11. If no events are pending now, queue all idle watchers.
441 \& 12. Queue all check watchers.
442 \& 13. Call all queued watchers in reverse order (i.e. check watchers first).
443 \& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
444 \& was used, return, otherwise continue with step #1.
446 .IP "ev_unloop (loop, how)" 4
447 .IX Item "ev_unloop (loop, how)"
448 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
449 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
450 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
451 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
452 .IP "ev_ref (loop)" 4
453 .IX Item "ev_ref (loop)"
455 .IP "ev_unref (loop)" 4
456 .IX Item "ev_unref (loop)"
458 Ref/unref can be used to add or remove a reference count on the event
459 loop: Every watcher keeps one reference, and as long as the reference
460 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
461 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
462 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
463 example, libev itself uses this for its internal signal pipe: It is not
464 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
465 no event watchers registered by it are active. It is also an excellent
466 way to do this for generic recurring timers or from within third-party
467 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
468 .SH "ANATOMY OF A WATCHER"
469 .IX Header "ANATOMY OF A WATCHER"
470 A watcher is a structure that you create and register to record your
471 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
472 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
475 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
478 \& ev_unloop (loop, EVUNLOOP_ALL);
483 \& struct ev_loop *loop = ev_default_loop (0);
484 \& struct ev_io stdin_watcher;
485 \& ev_init (&stdin_watcher, my_cb);
486 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
487 \& ev_io_start (loop, &stdin_watcher);
488 \& ev_loop (loop, 0);
491 As you can see, you are responsible for allocating the memory for your
492 watcher structures (and it is usually a bad idea to do this on the stack,
493 although this can sometimes be quite valid).
495 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
496 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
497 callback gets invoked each time the event occurs (or, in the case of io
498 watchers, each time the event loop detects that the file descriptor given
499 is readable and/or writable).
501 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
502 with arguments specific to this watcher type. There is also a macro
503 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
504 (watcher *, callback, ...)\*(C'\fR.
506 To make the watcher actually watch out for events, you have to start it
507 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
508 *)\*(C'\fR), and you can stop watching for events at any time by calling the
509 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
511 As long as your watcher is active (has been started but not stopped) you
512 must not touch the values stored in it. Most specifically you must never
513 reinitialise it or call its set macro.
515 You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
516 (watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
517 callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
518 (watcher *)\*(C'\fR macro.
520 Each and every callback receives the event loop pointer as first, the
521 registered watcher structure as second, and a bitset of received events as
524 The received events usually include a single bit per event type received
525 (you can receive multiple events at the same time). The possible bit masks
527 .ie n .IP """EV_READ""" 4
528 .el .IP "\f(CWEV_READ\fR" 4
531 .ie n .IP """EV_WRITE""" 4
532 .el .IP "\f(CWEV_WRITE\fR" 4
535 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
537 .ie n .IP """EV_TIMEOUT""" 4
538 .el .IP "\f(CWEV_TIMEOUT\fR" 4
539 .IX Item "EV_TIMEOUT"
540 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
541 .ie n .IP """EV_PERIODIC""" 4
542 .el .IP "\f(CWEV_PERIODIC\fR" 4
543 .IX Item "EV_PERIODIC"
544 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
545 .ie n .IP """EV_SIGNAL""" 4
546 .el .IP "\f(CWEV_SIGNAL\fR" 4
548 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
549 .ie n .IP """EV_CHILD""" 4
550 .el .IP "\f(CWEV_CHILD\fR" 4
552 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
553 .ie n .IP """EV_IDLE""" 4
554 .el .IP "\f(CWEV_IDLE\fR" 4
556 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
557 .ie n .IP """EV_PREPARE""" 4
558 .el .IP "\f(CWEV_PREPARE\fR" 4
559 .IX Item "EV_PREPARE"
561 .ie n .IP """EV_CHECK""" 4
562 .el .IP "\f(CWEV_CHECK\fR" 4
565 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
566 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
567 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
568 received events. Callbacks of both watcher types can start and stop as
569 many watchers as they want, and all of them will be taken into account
570 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
571 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
572 .ie n .IP """EV_ERROR""" 4
573 .el .IP "\f(CWEV_ERROR\fR" 4
575 An unspecified error has occured, the watcher has been stopped. This might
576 happen because the watcher could not be properly started because libev
577 ran out of memory, a file descriptor was found to be closed or any other
578 problem. You best act on it by reporting the problem and somehow coping
579 with the watcher being stopped.
581 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
582 for example it might indicate that a fd is readable or writable, and if
583 your callbacks is well-written it can just attempt the operation and cope
584 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
585 programs, though, so beware.
586 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
587 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
588 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
589 and read at any time, libev will completely ignore it. This can be used
590 to associate arbitrary data with your watcher. If you need more data and
591 don't want to allocate memory and store a pointer to it in that data
592 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
601 \& struct whatever *mostinteresting;
605 And since your callback will be called with a pointer to the watcher, you
606 can cast it back to your own type:
609 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
611 \& struct my_io *w = (struct my_io *)w_;
616 More interesting and less C\-conformant ways of catsing your callback type
617 have been omitted....
619 .IX Header "WATCHER TYPES"
620 This section describes each watcher in detail, but will not repeat
621 information given in the last section.
622 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
623 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
624 .IX Subsection "ev_io - is this file descriptor readable or writable"
625 I/O watchers check whether a file descriptor is readable or writable
626 in each iteration of the event loop (This behaviour is called
627 level-triggering because you keep receiving events as long as the
628 condition persists. Remember you can stop the watcher if you don't want to
629 act on the event and neither want to receive future events).
631 In general you can register as many read and/or write event watchers per
632 fd as you want (as long as you don't confuse yourself). Setting all file
633 descriptors to non-blocking mode is also usually a good idea (but not
634 required if you know what you are doing).
636 You have to be careful with dup'ed file descriptors, though. Some backends
637 (the linux epoll backend is a notable example) cannot handle dup'ed file
638 descriptors correctly if you register interest in two or more fds pointing
639 to the same underlying file/socket etc. description (that is, they share
640 the same underlying \*(L"file open\*(R").
642 If you must do this, then force the use of a known-to-be-good backend
643 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
644 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
645 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
646 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
648 .IP "ev_io_set (ev_io *, int fd, int events)" 4
649 .IX Item "ev_io_set (ev_io *, int fd, int events)"
651 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
652 events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ |
653 EV_WRITE\*(C'\fR to receive the given events.
655 Please note that most of the more scalable backend mechanisms (for example
656 epoll and solaris ports) can result in spurious readyness notifications
657 for file descriptors, so you practically need to use non-blocking I/O (and
658 treat callback invocation as hint only), or retest separately with a safe
659 interface before doing I/O (XLib can do this), or force the use of either
660 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
661 problem. Also note that it is quite easy to have your callback invoked
662 when the readyness condition is no longer valid even when employing
663 typical ways of handling events, so its a good idea to use non-blocking
665 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
666 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
667 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
668 Timer watchers are simple relative timers that generate an event after a
669 given time, and optionally repeating in regular intervals after that.
671 The timers are based on real time, that is, if you register an event that
672 times out after an hour and you reset your system clock to last years
673 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
674 detecting time jumps is hard, and some inaccuracies are unavoidable (the
675 monotonic clock option helps a lot here).
677 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
678 time. This is usually the right thing as this timestamp refers to the time
679 of the event triggering whatever timeout you are modifying/starting. If
680 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
681 on the current time, use something like this to adjust for this:
684 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
687 The callback is guarenteed to be invoked only when its timeout has passed,
688 but if multiple timers become ready during the same loop iteration then
689 order of execution is undefined.
690 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
691 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
693 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
694 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
696 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
697 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
698 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
699 later, again, and again, until stopped manually.
701 The timer itself will do a best-effort at avoiding drift, that is, if you
702 configure a timer to trigger every 10 seconds, then it will trigger at
703 exactly 10 second intervals. If, however, your program cannot keep up with
704 the timer (because it takes longer than those 10 seconds to do stuff) the
705 timer will not fire more than once per event loop iteration.
706 .IP "ev_timer_again (loop)" 4
707 .IX Item "ev_timer_again (loop)"
708 This will act as if the timer timed out and restart it again if it is
709 repeating. The exact semantics are:
711 If the timer is started but nonrepeating, stop it.
713 If the timer is repeating, either start it if necessary (with the repeat
714 value), or reset the running timer to the repeat value.
716 This sounds a bit complicated, but here is a useful and typical
717 example: Imagine you have a tcp connection and you want a so-called idle
718 timeout, that is, you want to be called when there have been, say, 60
719 seconds of inactivity on the socket. The easiest way to do this is to
720 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
721 time you successfully read or write some data. If you go into an idle
722 state where you do not expect data to travel on the socket, you can stop
723 the timer, and again will automatically restart it if need be.
724 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
725 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
726 .IX Subsection "ev_periodic - to cron or not to cron"
727 Periodic watchers are also timers of a kind, but they are very versatile
728 (and unfortunately a bit complex).
730 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
731 but on wallclock time (absolute time). You can tell a periodic watcher
732 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
733 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
734 + 10.>) and then reset your system clock to the last year, then it will
735 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
736 roughly 10 seconds later and of course not if you reset your system time
739 They can also be used to implement vastly more complex timers, such as
740 triggering an event on eahc midnight, local time.
742 As with timers, the callback is guarenteed to be invoked only when the
743 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
744 during the same loop iteration then order of execution is undefined.
745 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
746 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
748 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
749 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
751 Lots of arguments, lets sort it out... There are basically three modes of
752 operation, and we will explain them from simplest to complex:
754 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
755 .IX Item "absolute timer (interval = reschedule_cb = 0)"
756 In this configuration the watcher triggers an event at the wallclock time
757 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
758 that is, if it is to be run at January 1st 2011 then it will run when the
759 system time reaches or surpasses this time.
760 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
761 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
762 In this mode the watcher will always be scheduled to time out at the next
763 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
766 This can be used to create timers that do not drift with respect to system
770 \& ev_periodic_set (&periodic, 0., 3600., 0);
773 This doesn't mean there will always be 3600 seconds in between triggers,
774 but only that the the callback will be called when the system time shows a
775 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
778 Another way to think about it (for the mathematically inclined) is that
779 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
780 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
781 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
782 .IX Item "manual reschedule mode (reschedule_cb = callback)"
783 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
784 ignored. Instead, each time the periodic watcher gets scheduled, the
785 reschedule callback will be called with the watcher as first, and the
786 current time as second argument.
788 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
789 ever, or make any event loop modifications\fR. If you need to stop it,
790 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
791 starting a prepare watcher).
793 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
794 ev_tstamp now)\*(C'\fR, e.g.:
797 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
803 It must return the next time to trigger, based on the passed time value
804 (that is, the lowest time value larger than to the second argument). It
805 will usually be called just before the callback will be triggered, but
806 might be called at other times, too.
808 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
809 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.
811 This can be used to create very complex timers, such as a timer that
812 triggers on each midnight, local time. To do this, you would calculate the
813 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
814 you do this is, again, up to you (but it is not trivial, which is the main
815 reason I omitted it as an example).
819 .IP "ev_periodic_again (loop, ev_periodic *)" 4
820 .IX Item "ev_periodic_again (loop, ev_periodic *)"
821 Simply stops and restarts the periodic watcher again. This is only useful
822 when you changed some parameters or the reschedule callback would return
823 a different time than the last time it was called (e.g. in a crond like
824 program when the crontabs have changed).
825 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
826 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
827 .IX Subsection "ev_signal - signal me when a signal gets signalled"
828 Signal watchers will trigger an event when the process receives a specific
829 signal one or more times. Even though signals are very asynchronous, libev
830 will try it's best to deliver signals synchronously, i.e. as part of the
831 normal event processing, like any other event.
833 You can configure as many watchers as you like per signal. Only when the
834 first watcher gets started will libev actually register a signal watcher
835 with the kernel (thus it coexists with your own signal handlers as long
836 as you don't register any with libev). Similarly, when the last signal
837 watcher for a signal is stopped libev will reset the signal handler to
838 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
839 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
840 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
842 .IP "ev_signal_set (ev_signal *, int signum)" 4
843 .IX Item "ev_signal_set (ev_signal *, int signum)"
845 Configures the watcher to trigger on the given signal number (usually one
846 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
847 .ie n .Sh """ev_child"" \- wait for pid status changes"
848 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
849 .IX Subsection "ev_child - wait for pid status changes"
850 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
851 some child status changes (most typically when a child of yours dies).
852 .IP "ev_child_init (ev_child *, callback, int pid)" 4
853 .IX Item "ev_child_init (ev_child *, callback, int pid)"
855 .IP "ev_child_set (ev_child *, int pid)" 4
856 .IX Item "ev_child_set (ev_child *, int pid)"
858 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
859 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
860 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
861 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
862 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
863 process causing the status change.
864 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
865 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
866 .IX Subsection "ev_idle - when you've got nothing better to do"
867 Idle watchers trigger events when there are no other events are pending
868 (prepare, check and other idle watchers do not count). That is, as long
869 as your process is busy handling sockets or timeouts (or even signals,
870 imagine) it will not be triggered. But when your process is idle all idle
871 watchers are being called again and again, once per event loop iteration \-
872 until stopped, that is, or your process receives more events and becomes
875 The most noteworthy effect is that as long as any idle watchers are
876 active, the process will not block when waiting for new events.
878 Apart from keeping your process non-blocking (which is a useful
879 effect on its own sometimes), idle watchers are a good place to do
880 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
881 event loop has handled all outstanding events.
882 .IP "ev_idle_init (ev_signal *, callback)" 4
883 .IX Item "ev_idle_init (ev_signal *, callback)"
884 Initialises and configures the idle watcher \- it has no parameters of any
885 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
887 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
888 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
889 .IX Subsection "ev_prepare and ev_check - customise your event loop"
890 Prepare and check watchers are usually (but not always) used in tandem:
891 prepare watchers get invoked before the process blocks and check watchers
894 Their main purpose is to integrate other event mechanisms into libev. This
895 could be used, for example, to track variable changes, implement your own
896 watchers, integrate net-snmp or a coroutine library and lots more.
898 This is done by examining in each prepare call which file descriptors need
899 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
900 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
901 provide just this functionality). Then, in the check watcher you check for
902 any events that occured (by checking the pending status of all watchers
903 and stopping them) and call back into the library. The I/O and timer
904 callbacks will never actually be called (but must be valid nevertheless,
905 because you never know, you know?).
907 As another example, the Perl Coro module uses these hooks to integrate
908 coroutines into libev programs, by yielding to other active coroutines
909 during each prepare and only letting the process block if no coroutines
910 are ready to run (it's actually more complicated: it only runs coroutines
911 with priority higher than or equal to the event loop and one coroutine
912 of lower priority, but only once, using idle watchers to keep the event
913 loop from blocking if lower-priority coroutines are active, thus mapping
914 low-priority coroutines to idle/background tasks).
915 .IP "ev_prepare_init (ev_prepare *, callback)" 4
916 .IX Item "ev_prepare_init (ev_prepare *, callback)"
918 .IP "ev_check_init (ev_check *, callback)" 4
919 .IX Item "ev_check_init (ev_check *, callback)"
921 Initialises and configures the prepare or check watcher \- they have no
922 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
923 macros, but using them is utterly, utterly and completely pointless.
924 .SH "OTHER FUNCTIONS"
925 .IX Header "OTHER FUNCTIONS"
926 There are some other functions of possible interest. Described. Here. Now.
927 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
928 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
929 This function combines a simple timer and an I/O watcher, calls your
930 callback on whichever event happens first and automatically stop both
931 watchers. This is useful if you want to wait for a single event on an fd
932 or timeout without having to allocate/configure/start/stop/free one or
933 more watchers yourself.
935 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
936 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
937 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
939 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
940 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
941 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
944 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
945 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
946 \&\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
947 value passed to \f(CW\*(C`ev_once\*(C'\fR:
950 \& static void stdin_ready (int revents, void *arg)
952 \& if (revents & EV_TIMEOUT)
953 \& /* doh, nothing entered */;
954 \& else if (revents & EV_READ)
955 \& /* stdin might have data for us, joy! */;
960 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
962 .IP "ev_feed_event (loop, watcher, int events)" 4
963 .IX Item "ev_feed_event (loop, watcher, int events)"
964 Feeds the given event set into the event loop, as if the specified event
965 had happened for the specified watcher (which must be a pointer to an
966 initialised but not necessarily started event watcher).
967 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
968 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
969 Feed an event on the given fd, as if a file descriptor backend detected
971 .IP "ev_feed_signal_event (loop, int signum)" 4
972 .IX Item "ev_feed_signal_event (loop, int signum)"
973 Feed an event as if the given signal occured (loop must be the default loop!).
974 .SH "LIBEVENT EMULATION"
975 .IX Header "LIBEVENT EMULATION"
976 Libev offers a compatibility emulation layer for libevent. It cannot
977 emulate the internals of libevent, so here are some usage hints:
978 .IP "* Use it by including <event.h>, as usual." 4
979 .IX Item "Use it by including <event.h>, as usual."
981 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
982 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
983 .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
984 .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)."
985 .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
986 .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."
987 .IP "* Other members are not supported." 4
988 .IX Item "Other members are not supported."
989 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
990 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
993 .IX Header " SUPPORT"
997 Marc Lehmann <libev@schmorp.de>.
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