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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.
307 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
308 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
309 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
310 Kqueue deserves special mention, as at the time of this writing, it
311 was broken on all BSDs except NetBSD (usually it doesn't work with
312 anything but sockets and pipes, except on Darwin, where of course its
313 completely useless). For this reason its not being \*(L"autodetected\*(R" unless
314 you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0).
316 It scales in the same way as the epoll backend, but the interface to the
317 kernel is more efficient (which says nothing about its actual speed, of
318 course). While starting and stopping an I/O watcher does not cause an
319 extra syscall as with epoll, it still adds up to four event changes per
320 incident, so its best to avoid that.
321 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
322 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
323 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
324 This is not implemented yet (and might never be).
325 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
326 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
327 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
328 This uses the Solaris 10 port mechanism. As with everything on Solaris,
329 it's really slow, but it still scales very well (O(active_fds)).
330 .ie n .IP """EVBACKEND_ALL""" 4
331 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
332 .IX Item "EVBACKEND_ALL"
333 Try all backends (even potentially broken ones that wouldn't be tried
334 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
335 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
339 If one or more of these are ored into the flags value, then only these
340 backends will be tried (in the reverse order as given here). If none are
341 specified, most compiled-in backend will be tried, usually in reverse
342 order of their flag values :)
344 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
345 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
346 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
347 always distinct from the default loop. Unlike the default loop, it cannot
348 handle signal and child watchers, and attempts to do so will be greeted by
349 undefined behaviour (or a failed assertion if assertions are enabled).
350 .IP "ev_default_destroy ()" 4
351 .IX Item "ev_default_destroy ()"
352 Destroys the default loop again (frees all memory and kernel state
353 etc.). This stops all registered event watchers (by not touching them in
354 any way whatsoever, although you cannot rely on this :).
355 .IP "ev_loop_destroy (loop)" 4
356 .IX Item "ev_loop_destroy (loop)"
357 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
358 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
359 .IP "ev_default_fork ()" 4
360 .IX Item "ev_default_fork ()"
361 This function reinitialises the kernel state for backends that have
362 one. Despite the name, you can call it anytime, but it makes most sense
363 after forking, in either the parent or child process (or both, but that
364 again makes little sense).
366 You \fImust\fR call this function in the child process after forking if and
367 only if you want to use the event library in both processes. If you just
368 fork+exec, you don't have to call it.
370 The function itself is quite fast and it's usually not a problem to call
371 it just in case after a fork. To make this easy, the function will fit in
372 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
375 \& pthread_atfork (0, 0, ev_default_fork);
378 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
379 without calling this function, so if you force one of those backends you
381 .IP "ev_loop_fork (loop)" 4
382 .IX Item "ev_loop_fork (loop)"
383 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
384 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
385 after fork, and how you do this is entirely your own problem.
386 .IP "unsigned int ev_backend (loop)" 4
387 .IX Item "unsigned int ev_backend (loop)"
388 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
390 .IP "ev_tstamp ev_now (loop)" 4
391 .IX Item "ev_tstamp ev_now (loop)"
392 Returns the current \*(L"event loop time\*(R", which is the time the event loop
393 got events and started processing them. This timestamp does not change
394 as long as callbacks are being processed, and this is also the base time
395 used for relative timers. You can treat it as the timestamp of the event
396 occuring (or more correctly, the mainloop finding out about it).
397 .IP "ev_loop (loop, int flags)" 4
398 .IX Item "ev_loop (loop, int flags)"
399 Finally, this is it, the event handler. This function usually is called
400 after you initialised all your watchers and you want to start handling
403 If the flags argument is specified as 0, it will not return until either
404 no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
406 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
407 those events and any outstanding ones, but will not block your process in
408 case there are no events and will return after one iteration of the loop.
410 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
411 neccessary) and will handle those and any outstanding ones. It will block
412 your process until at least one new event arrives, and will return after
413 one iteration of the loop.
415 This flags value could be used to implement alternative looping
416 constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
417 more generic mechanism.
419 Here are the gory details of what ev_loop does:
422 \& 1. If there are no active watchers (reference count is zero), return.
423 \& 2. Queue and immediately call all prepare watchers.
424 \& 3. If we have been forked, recreate the kernel state.
425 \& 4. Update the kernel state with all outstanding changes.
426 \& 5. Update the "event loop time".
427 \& 6. Calculate for how long to block.
428 \& 7. Block the process, waiting for events.
429 \& 8. Update the "event loop time" and do time jump handling.
430 \& 9. Queue all outstanding timers.
431 \& 10. Queue all outstanding periodics.
432 \& 11. If no events are pending now, queue all idle watchers.
433 \& 12. Queue all check watchers.
434 \& 13. Call all queued watchers in reverse order (i.e. check watchers first).
435 \& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
436 \& was used, return, otherwise continue with step #1.
438 .IP "ev_unloop (loop, how)" 4
439 .IX Item "ev_unloop (loop, how)"
440 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
441 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
442 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
443 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
444 .IP "ev_ref (loop)" 4
445 .IX Item "ev_ref (loop)"
447 .IP "ev_unref (loop)" 4
448 .IX Item "ev_unref (loop)"
450 Ref/unref can be used to add or remove a reference count on the event
451 loop: Every watcher keeps one reference, and as long as the reference
452 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
453 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
454 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
455 example, libev itself uses this for its internal signal pipe: It is not
456 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
457 no event watchers registered by it are active. It is also an excellent
458 way to do this for generic recurring timers or from within third-party
459 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
460 .SH "ANATOMY OF A WATCHER"
461 .IX Header "ANATOMY OF A WATCHER"
462 A watcher is a structure that you create and register to record your
463 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
464 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
467 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
470 \& ev_unloop (loop, EVUNLOOP_ALL);
475 \& struct ev_loop *loop = ev_default_loop (0);
476 \& struct ev_io stdin_watcher;
477 \& ev_init (&stdin_watcher, my_cb);
478 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
479 \& ev_io_start (loop, &stdin_watcher);
480 \& ev_loop (loop, 0);
483 As you can see, you are responsible for allocating the memory for your
484 watcher structures (and it is usually a bad idea to do this on the stack,
485 although this can sometimes be quite valid).
487 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
488 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
489 callback gets invoked each time the event occurs (or, in the case of io
490 watchers, each time the event loop detects that the file descriptor given
491 is readable and/or writable).
493 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
494 with arguments specific to this watcher type. There is also a macro
495 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
496 (watcher *, callback, ...)\*(C'\fR.
498 To make the watcher actually watch out for events, you have to start it
499 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
500 *)\*(C'\fR), and you can stop watching for events at any time by calling the
501 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
503 As long as your watcher is active (has been started but not stopped) you
504 must not touch the values stored in it. Most specifically you must never
505 reinitialise it or call its set macro.
507 You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
508 (watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
509 callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
510 (watcher *)\*(C'\fR macro.
512 Each and every callback receives the event loop pointer as first, the
513 registered watcher structure as second, and a bitset of received events as
516 The received events usually include a single bit per event type received
517 (you can receive multiple events at the same time). The possible bit masks
519 .ie n .IP """EV_READ""" 4
520 .el .IP "\f(CWEV_READ\fR" 4
523 .ie n .IP """EV_WRITE""" 4
524 .el .IP "\f(CWEV_WRITE\fR" 4
527 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
529 .ie n .IP """EV_TIMEOUT""" 4
530 .el .IP "\f(CWEV_TIMEOUT\fR" 4
531 .IX Item "EV_TIMEOUT"
532 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
533 .ie n .IP """EV_PERIODIC""" 4
534 .el .IP "\f(CWEV_PERIODIC\fR" 4
535 .IX Item "EV_PERIODIC"
536 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
537 .ie n .IP """EV_SIGNAL""" 4
538 .el .IP "\f(CWEV_SIGNAL\fR" 4
540 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
541 .ie n .IP """EV_CHILD""" 4
542 .el .IP "\f(CWEV_CHILD\fR" 4
544 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
545 .ie n .IP """EV_IDLE""" 4
546 .el .IP "\f(CWEV_IDLE\fR" 4
548 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
549 .ie n .IP """EV_PREPARE""" 4
550 .el .IP "\f(CWEV_PREPARE\fR" 4
551 .IX Item "EV_PREPARE"
553 .ie n .IP """EV_CHECK""" 4
554 .el .IP "\f(CWEV_CHECK\fR" 4
557 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
558 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
559 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
560 received events. Callbacks of both watcher types can start and stop as
561 many watchers as they want, and all of them will be taken into account
562 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
563 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
564 .ie n .IP """EV_ERROR""" 4
565 .el .IP "\f(CWEV_ERROR\fR" 4
567 An unspecified error has occured, the watcher has been stopped. This might
568 happen because the watcher could not be properly started because libev
569 ran out of memory, a file descriptor was found to be closed or any other
570 problem. You best act on it by reporting the problem and somehow coping
571 with the watcher being stopped.
573 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
574 for example it might indicate that a fd is readable or writable, and if
575 your callbacks is well-written it can just attempt the operation and cope
576 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
577 programs, though, so beware.
578 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
579 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
580 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
581 and read at any time, libev will completely ignore it. This can be used
582 to associate arbitrary data with your watcher. If you need more data and
583 don't want to allocate memory and store a pointer to it in that data
584 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
593 \& struct whatever *mostinteresting;
597 And since your callback will be called with a pointer to the watcher, you
598 can cast it back to your own type:
601 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
603 \& struct my_io *w = (struct my_io *)w_;
608 More interesting and less C\-conformant ways of catsing your callback type
609 have been omitted....
611 .IX Header "WATCHER TYPES"
612 This section describes each watcher in detail, but will not repeat
613 information given in the last section.
614 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
615 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
616 .IX Subsection "ev_io - is this file descriptor readable or writable"
617 I/O watchers check whether a file descriptor is readable or writable
618 in each iteration of the event loop (This behaviour is called
619 level-triggering because you keep receiving events as long as the
620 condition persists. Remember you can stop the watcher if you don't want to
621 act on the event and neither want to receive future events).
623 In general you can register as many read and/or write event watchers per
624 fd as you want (as long as you don't confuse yourself). Setting all file
625 descriptors to non-blocking mode is also usually a good idea (but not
626 required if you know what you are doing).
628 You have to be careful with dup'ed file descriptors, though. Some backends
629 (the linux epoll backend is a notable example) cannot handle dup'ed file
630 descriptors correctly if you register interest in two or more fds pointing
631 to the same underlying file/socket etc. description (that is, they share
632 the same underlying \*(L"file open\*(R").
634 If you must do this, then force the use of a known-to-be-good backend
635 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
636 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
637 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
638 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
640 .IP "ev_io_set (ev_io *, int fd, int events)" 4
641 .IX Item "ev_io_set (ev_io *, int fd, int events)"
643 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
644 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 |
645 EV_WRITE\*(C'\fR to receive the given events.
646 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
647 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
648 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
649 Timer watchers are simple relative timers that generate an event after a
650 given time, and optionally repeating in regular intervals after that.
652 The timers are based on real time, that is, if you register an event that
653 times out after an hour and you reset your system clock to last years
654 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
655 detecting time jumps is hard, and some inaccuracies are unavoidable (the
656 monotonic clock option helps a lot here).
658 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
659 time. This is usually the right thing as this timestamp refers to the time
660 of the event triggering whatever timeout you are modifying/starting. If
661 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
662 on the current time, use something like this to adjust for this:
665 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
668 The callback is guarenteed to be invoked only when its timeout has passed,
669 but if multiple timers become ready during the same loop iteration then
670 order of execution is undefined.
671 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
672 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
674 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
675 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
677 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
678 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
679 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
680 later, again, and again, until stopped manually.
682 The timer itself will do a best-effort at avoiding drift, that is, if you
683 configure a timer to trigger every 10 seconds, then it will trigger at
684 exactly 10 second intervals. If, however, your program cannot keep up with
685 the timer (because it takes longer than those 10 seconds to do stuff) the
686 timer will not fire more than once per event loop iteration.
687 .IP "ev_timer_again (loop)" 4
688 .IX Item "ev_timer_again (loop)"
689 This will act as if the timer timed out and restart it again if it is
690 repeating. The exact semantics are:
692 If the timer is started but nonrepeating, stop it.
694 If the timer is repeating, either start it if necessary (with the repeat
695 value), or reset the running timer to the repeat value.
697 This sounds a bit complicated, but here is a useful and typical
698 example: Imagine you have a tcp connection and you want a so-called idle
699 timeout, that is, you want to be called when there have been, say, 60
700 seconds of inactivity on the socket. The easiest way to do this is to
701 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
702 time you successfully read or write some data. If you go into an idle
703 state where you do not expect data to travel on the socket, you can stop
704 the timer, and again will automatically restart it if need be.
705 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
706 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
707 .IX Subsection "ev_periodic - to cron or not to cron"
708 Periodic watchers are also timers of a kind, but they are very versatile
709 (and unfortunately a bit complex).
711 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
712 but on wallclock time (absolute time). You can tell a periodic watcher
713 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
714 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
715 + 10.>) and then reset your system clock to the last year, then it will
716 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
717 roughly 10 seconds later and of course not if you reset your system time
720 They can also be used to implement vastly more complex timers, such as
721 triggering an event on eahc midnight, local time.
723 As with timers, the callback is guarenteed to be invoked only when the
724 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
725 during the same loop iteration then order of execution is undefined.
726 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
727 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
729 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
730 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
732 Lots of arguments, lets sort it out... There are basically three modes of
733 operation, and we will explain them from simplest to complex:
735 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
736 .IX Item "absolute timer (interval = reschedule_cb = 0)"
737 In this configuration the watcher triggers an event at the wallclock time
738 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
739 that is, if it is to be run at January 1st 2011 then it will run when the
740 system time reaches or surpasses this time.
741 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
742 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
743 In this mode the watcher will always be scheduled to time out at the next
744 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
747 This can be used to create timers that do not drift with respect to system
751 \& ev_periodic_set (&periodic, 0., 3600., 0);
754 This doesn't mean there will always be 3600 seconds in between triggers,
755 but only that the the callback will be called when the system time shows a
756 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
759 Another way to think about it (for the mathematically inclined) is that
760 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
761 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
762 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
763 .IX Item "manual reschedule mode (reschedule_cb = callback)"
764 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
765 ignored. Instead, each time the periodic watcher gets scheduled, the
766 reschedule callback will be called with the watcher as first, and the
767 current time as second argument.
769 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
770 ever, or make any event loop modifications\fR. If you need to stop it,
771 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
772 starting a prepare watcher).
774 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
775 ev_tstamp now)\*(C'\fR, e.g.:
778 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
784 It must return the next time to trigger, based on the passed time value
785 (that is, the lowest time value larger than to the second argument). It
786 will usually be called just before the callback will be triggered, but
787 might be called at other times, too.
789 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
790 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.
792 This can be used to create very complex timers, such as a timer that
793 triggers on each midnight, local time. To do this, you would calculate the
794 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
795 you do this is, again, up to you (but it is not trivial, which is the main
796 reason I omitted it as an example).
800 .IP "ev_periodic_again (loop, ev_periodic *)" 4
801 .IX Item "ev_periodic_again (loop, ev_periodic *)"
802 Simply stops and restarts the periodic watcher again. This is only useful
803 when you changed some parameters or the reschedule callback would return
804 a different time than the last time it was called (e.g. in a crond like
805 program when the crontabs have changed).
806 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
807 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
808 .IX Subsection "ev_signal - signal me when a signal gets signalled"
809 Signal watchers will trigger an event when the process receives a specific
810 signal one or more times. Even though signals are very asynchronous, libev
811 will try it's best to deliver signals synchronously, i.e. as part of the
812 normal event processing, like any other event.
814 You can configure as many watchers as you like per signal. Only when the
815 first watcher gets started will libev actually register a signal watcher
816 with the kernel (thus it coexists with your own signal handlers as long
817 as you don't register any with libev). Similarly, when the last signal
818 watcher for a signal is stopped libev will reset the signal handler to
819 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
820 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
821 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
823 .IP "ev_signal_set (ev_signal *, int signum)" 4
824 .IX Item "ev_signal_set (ev_signal *, int signum)"
826 Configures the watcher to trigger on the given signal number (usually one
827 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
828 .ie n .Sh """ev_child"" \- wait for pid status changes"
829 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
830 .IX Subsection "ev_child - wait for pid status changes"
831 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
832 some child status changes (most typically when a child of yours dies).
833 .IP "ev_child_init (ev_child *, callback, int pid)" 4
834 .IX Item "ev_child_init (ev_child *, callback, int pid)"
836 .IP "ev_child_set (ev_child *, int pid)" 4
837 .IX Item "ev_child_set (ev_child *, int pid)"
839 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
840 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
841 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
842 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
843 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
844 process causing the status change.
845 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
846 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
847 .IX Subsection "ev_idle - when you've got nothing better to do"
848 Idle watchers trigger events when there are no other events are pending
849 (prepare, check and other idle watchers do not count). That is, as long
850 as your process is busy handling sockets or timeouts (or even signals,
851 imagine) it will not be triggered. But when your process is idle all idle
852 watchers are being called again and again, once per event loop iteration \-
853 until stopped, that is, or your process receives more events and becomes
856 The most noteworthy effect is that as long as any idle watchers are
857 active, the process will not block when waiting for new events.
859 Apart from keeping your process non-blocking (which is a useful
860 effect on its own sometimes), idle watchers are a good place to do
861 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
862 event loop has handled all outstanding events.
863 .IP "ev_idle_init (ev_signal *, callback)" 4
864 .IX Item "ev_idle_init (ev_signal *, callback)"
865 Initialises and configures the idle watcher \- it has no parameters of any
866 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
868 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
869 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
870 .IX Subsection "ev_prepare and ev_check - customise your event loop"
871 Prepare and check watchers are usually (but not always) used in tandem:
872 prepare watchers get invoked before the process blocks and check watchers
875 Their main purpose is to integrate other event mechanisms into libev. This
876 could be used, for example, to track variable changes, implement your own
877 watchers, integrate net-snmp or a coroutine library and lots more.
879 This is done by examining in each prepare call which file descriptors need
880 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
881 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
882 provide just this functionality). Then, in the check watcher you check for
883 any events that occured (by checking the pending status of all watchers
884 and stopping them) and call back into the library. The I/O and timer
885 callbacks will never actually be called (but must be valid nevertheless,
886 because you never know, you know?).
888 As another example, the Perl Coro module uses these hooks to integrate
889 coroutines into libev programs, by yielding to other active coroutines
890 during each prepare and only letting the process block if no coroutines
891 are ready to run (it's actually more complicated: it only runs coroutines
892 with priority higher than or equal to the event loop and one coroutine
893 of lower priority, but only once, using idle watchers to keep the event
894 loop from blocking if lower-priority coroutines are active, thus mapping
895 low-priority coroutines to idle/background tasks).
896 .IP "ev_prepare_init (ev_prepare *, callback)" 4
897 .IX Item "ev_prepare_init (ev_prepare *, callback)"
899 .IP "ev_check_init (ev_check *, callback)" 4
900 .IX Item "ev_check_init (ev_check *, callback)"
902 Initialises and configures the prepare or check watcher \- they have no
903 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
904 macros, but using them is utterly, utterly and completely pointless.
905 .SH "OTHER FUNCTIONS"
906 .IX Header "OTHER FUNCTIONS"
907 There are some other functions of possible interest. Described. Here. Now.
908 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
909 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
910 This function combines a simple timer and an I/O watcher, calls your
911 callback on whichever event happens first and automatically stop both
912 watchers. This is useful if you want to wait for a single event on an fd
913 or timeout without having to allocate/configure/start/stop/free one or
914 more watchers yourself.
916 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
917 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
918 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
920 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
921 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
922 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
925 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
926 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
927 \&\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
928 value passed to \f(CW\*(C`ev_once\*(C'\fR:
931 \& static void stdin_ready (int revents, void *arg)
933 \& if (revents & EV_TIMEOUT)
934 \& /* doh, nothing entered */;
935 \& else if (revents & EV_READ)
936 \& /* stdin might have data for us, joy! */;
941 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
943 .IP "ev_feed_event (loop, watcher, int events)" 4
944 .IX Item "ev_feed_event (loop, watcher, int events)"
945 Feeds the given event set into the event loop, as if the specified event
946 had happened for the specified watcher (which must be a pointer to an
947 initialised but not necessarily started event watcher).
948 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
949 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
950 Feed an event on the given fd, as if a file descriptor backend detected
952 .IP "ev_feed_signal_event (loop, int signum)" 4
953 .IX Item "ev_feed_signal_event (loop, int signum)"
954 Feed an event as if the given signal occured (loop must be the default loop!).
955 .SH "LIBEVENT EMULATION"
956 .IX Header "LIBEVENT EMULATION"
957 Libev offers a compatibility emulation layer for libevent. It cannot
958 emulate the internals of libevent, so here are some usage hints:
959 .IP "* Use it by including <event.h>, as usual." 4
960 .IX Item "Use it by including <event.h>, as usual."
962 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
963 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
964 .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
965 .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)."
966 .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
967 .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."
968 .IP "* Other members are not supported." 4
969 .IX Item "Other members are not supported."
970 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
971 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
974 .IX Header " SUPPORT"
978 Marc Lehmann <libev@schmorp.de>.
projects / software / libev.git / blob