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129 .\" ========================================================================
131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-11-18" "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 "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
205 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
206 Sets the allocation function to use (the prototype is similar to the
207 realloc C function, the semantics are identical). It is used to allocate
208 and free memory (no surprises here). If it returns zero when memory
209 needs to be allocated, the library might abort or take some potentially
210 destructive action. The default is your system realloc function.
212 You could override this function in high-availability programs to, say,
213 free some memory if it cannot allocate memory, to use a special allocator,
214 or even to sleep a while and retry until some memory is available.
215 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
216 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
217 Set the callback function to call on a retryable syscall error (such
218 as failed select, poll, epoll_wait). The message is a printable string
219 indicating the system call or subsystem causing the problem. If this
220 callback is set, then libev will expect it to remedy the sitution, no
221 matter what, when it returns. That is, libev will generally retry the
222 requested operation, or, if the condition doesn't go away, do bad stuff
224 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
225 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
226 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
227 types of such loops, the \fIdefault\fR loop, which supports signals and child
228 events, and dynamically created loops which do not.
230 If you use threads, a common model is to run the default event loop
231 in your main thread (or in a separate thread) and for each thread you
232 create, you also create another event loop. Libev itself does no locking
233 whatsoever, so if you mix calls to the same event loop in different
234 threads, make sure you lock (this is usually a bad idea, though, even if
235 done correctly, because it's hideous and inefficient).
236 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238 This will initialise the default event loop if it hasn't been initialised
239 yet and return it. If the default loop could not be initialised, returns
240 false. If it already was initialised it simply returns it (and ignores the
243 If you don't know what event loop to use, use the one returned from this
246 The flags argument can be used to specify special behaviour or specific
247 backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0).
249 It supports the following flags:
251 .ie n .IP """EVFLAG_AUTO""" 4
252 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
253 .IX Item "EVFLAG_AUTO"
254 The default flags value. Use this if you have no clue (it's the right
256 .ie n .IP """EVFLAG_NOENV""" 4
257 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
258 .IX Item "EVFLAG_NOENV"
259 If this flag bit is ored into the flag value (or the program runs setuid
260 or setgid) then libev will \fInot\fR look at the environment variable
261 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
262 override the flags completely if it is found in the environment. This is
263 useful to try out specific backends to test their performance, or to work
265 .ie n .IP """EVMETHOD_SELECT"" (portable select backend)" 4
266 .el .IP "\f(CWEVMETHOD_SELECT\fR (portable select backend)" 4
267 .IX Item "EVMETHOD_SELECT (portable select backend)"
269 .ie n .IP """EVMETHOD_POLL"" (poll backend, available everywhere except on windows)" 4
270 .el .IP "\f(CWEVMETHOD_POLL\fR (poll backend, available everywhere except on windows)" 4
271 .IX Item "EVMETHOD_POLL (poll backend, available everywhere except on windows)"
272 .ie n .IP """EVMETHOD_EPOLL"" (linux only)" 4
273 .el .IP "\f(CWEVMETHOD_EPOLL\fR (linux only)" 4
274 .IX Item "EVMETHOD_EPOLL (linux only)"
275 .ie n .IP """EVMETHOD_KQUEUE"" (some bsds only)" 4
276 .el .IP "\f(CWEVMETHOD_KQUEUE\fR (some bsds only)" 4
277 .IX Item "EVMETHOD_KQUEUE (some bsds only)"
278 .ie n .IP """EVMETHOD_DEVPOLL"" (solaris 8 only)" 4
279 .el .IP "\f(CWEVMETHOD_DEVPOLL\fR (solaris 8 only)" 4
280 .IX Item "EVMETHOD_DEVPOLL (solaris 8 only)"
281 .ie n .IP """EVMETHOD_PORT"" (solaris 10 only)" 4
282 .el .IP "\f(CWEVMETHOD_PORT\fR (solaris 10 only)" 4
283 .IX Item "EVMETHOD_PORT (solaris 10 only)"
285 If one or more of these are ored into the flags value, then only these
286 backends will be tried (in the reverse order as given here). If one are
287 specified, any backend will do.
291 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
292 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
293 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
294 always distinct from the default loop. Unlike the default loop, it cannot
295 handle signal and child watchers, and attempts to do so will be greeted by
296 undefined behaviour (or a failed assertion if assertions are enabled).
297 .IP "ev_default_destroy ()" 4
298 .IX Item "ev_default_destroy ()"
299 Destroys the default loop again (frees all memory and kernel state
300 etc.). This stops all registered event watchers (by not touching them in
301 any way whatsoever, although you cannot rely on this :).
302 .IP "ev_loop_destroy (loop)" 4
303 .IX Item "ev_loop_destroy (loop)"
304 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
305 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
306 .IP "ev_default_fork ()" 4
307 .IX Item "ev_default_fork ()"
308 This function reinitialises the kernel state for backends that have
309 one. Despite the name, you can call it anytime, but it makes most sense
310 after forking, in either the parent or child process (or both, but that
311 again makes little sense).
313 You \fImust\fR call this function after forking if and only if you want to
314 use the event library in both processes. If you just fork+exec, you don't
317 The function itself is quite fast and it's usually not a problem to call
318 it just in case after a fork. To make this easy, the function will fit in
319 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
322 \& pthread_atfork (0, 0, ev_default_fork);
324 .IP "ev_loop_fork (loop)" 4
325 .IX Item "ev_loop_fork (loop)"
326 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
327 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
328 after fork, and how you do this is entirely your own problem.
329 .IP "unsigned int ev_method (loop)" 4
330 .IX Item "unsigned int ev_method (loop)"
331 Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in
333 .IP "ev_tstamp ev_now (loop)" 4
334 .IX Item "ev_tstamp ev_now (loop)"
335 Returns the current \*(L"event loop time\*(R", which is the time the event loop
336 got events and started processing them. This timestamp does not change
337 as long as callbacks are being processed, and this is also the base time
338 used for relative timers. You can treat it as the timestamp of the event
339 occuring (or more correctly, the mainloop finding out about it).
340 .IP "ev_loop (loop, int flags)" 4
341 .IX Item "ev_loop (loop, int flags)"
342 Finally, this is it, the event handler. This function usually is called
343 after you initialised all your watchers and you want to start handling
346 If the flags argument is specified as 0, it will not return until either
347 no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
349 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
350 those events and any outstanding ones, but will not block your process in
351 case there are no events and will return after one iteration of the loop.
353 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
354 neccessary) and will handle those and any outstanding ones. It will block
355 your process until at least one new event arrives, and will return after
356 one iteration of the loop.
358 This flags value could be used to implement alternative looping
359 constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
360 more generic mechanism.
362 Here are the gory details of what ev_loop does:
365 \& 1. If there are no active watchers (reference count is zero), return.
366 \& 2. Queue and immediately call all prepare watchers.
367 \& 3. If we have been forked, recreate the kernel state.
368 \& 4. Update the kernel state with all outstanding changes.
369 \& 5. Update the "event loop time".
370 \& 6. Calculate for how long to block.
371 \& 7. Block the process, waiting for events.
372 \& 8. Update the "event loop time" and do time jump handling.
373 \& 9. Queue all outstanding timers.
374 \& 10. Queue all outstanding periodics.
375 \& 11. If no events are pending now, queue all idle watchers.
376 \& 12. Queue all check watchers.
377 \& 13. Call all queued watchers in reverse order (i.e. check watchers first).
378 \& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
379 \& was used, return, otherwise continue with step #1.
381 .IP "ev_unloop (loop, how)" 4
382 .IX Item "ev_unloop (loop, how)"
383 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
384 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
385 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
386 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
387 .IP "ev_ref (loop)" 4
388 .IX Item "ev_ref (loop)"
390 .IP "ev_unref (loop)" 4
391 .IX Item "ev_unref (loop)"
393 Ref/unref can be used to add or remove a reference count on the event
394 loop: Every watcher keeps one reference, and as long as the reference
395 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
396 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
397 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
398 example, libev itself uses this for its internal signal pipe: It is not
399 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
400 no event watchers registered by it are active. It is also an excellent
401 way to do this for generic recurring timers or from within third-party
402 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
403 .SH "ANATOMY OF A WATCHER"
404 .IX Header "ANATOMY OF A WATCHER"
405 A watcher is a structure that you create and register to record your
406 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
407 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
410 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
413 \& ev_unloop (loop, EVUNLOOP_ALL);
418 \& struct ev_loop *loop = ev_default_loop (0);
419 \& struct ev_io stdin_watcher;
420 \& ev_init (&stdin_watcher, my_cb);
421 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
422 \& ev_io_start (loop, &stdin_watcher);
423 \& ev_loop (loop, 0);
426 As you can see, you are responsible for allocating the memory for your
427 watcher structures (and it is usually a bad idea to do this on the stack,
428 although this can sometimes be quite valid).
430 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
431 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
432 callback gets invoked each time the event occurs (or, in the case of io
433 watchers, each time the event loop detects that the file descriptor given
434 is readable and/or writable).
436 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
437 with arguments specific to this watcher type. There is also a macro
438 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
439 (watcher *, callback, ...)\*(C'\fR.
441 To make the watcher actually watch out for events, you have to start it
442 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
443 *)\*(C'\fR), and you can stop watching for events at any time by calling the
444 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
446 As long as your watcher is active (has been started but not stopped) you
447 must not touch the values stored in it. Most specifically you must never
448 reinitialise it or call its set method.
450 You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
451 (watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
452 callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
453 (watcher *)\*(C'\fR macro.
455 Each and every callback receives the event loop pointer as first, the
456 registered watcher structure as second, and a bitset of received events as
459 The received events usually include a single bit per event type received
460 (you can receive multiple events at the same time). The possible bit masks
462 .ie n .IP """EV_READ""" 4
463 .el .IP "\f(CWEV_READ\fR" 4
466 .ie n .IP """EV_WRITE""" 4
467 .el .IP "\f(CWEV_WRITE\fR" 4
470 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
472 .ie n .IP """EV_TIMEOUT""" 4
473 .el .IP "\f(CWEV_TIMEOUT\fR" 4
474 .IX Item "EV_TIMEOUT"
475 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
476 .ie n .IP """EV_PERIODIC""" 4
477 .el .IP "\f(CWEV_PERIODIC\fR" 4
478 .IX Item "EV_PERIODIC"
479 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
480 .ie n .IP """EV_SIGNAL""" 4
481 .el .IP "\f(CWEV_SIGNAL\fR" 4
483 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
484 .ie n .IP """EV_CHILD""" 4
485 .el .IP "\f(CWEV_CHILD\fR" 4
487 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
488 .ie n .IP """EV_IDLE""" 4
489 .el .IP "\f(CWEV_IDLE\fR" 4
491 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
492 .ie n .IP """EV_PREPARE""" 4
493 .el .IP "\f(CWEV_PREPARE\fR" 4
494 .IX Item "EV_PREPARE"
496 .ie n .IP """EV_CHECK""" 4
497 .el .IP "\f(CWEV_CHECK\fR" 4
500 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
501 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
502 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
503 received events. Callbacks of both watcher types can start and stop as
504 many watchers as they want, and all of them will be taken into account
505 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
506 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
507 .ie n .IP """EV_ERROR""" 4
508 .el .IP "\f(CWEV_ERROR\fR" 4
510 An unspecified error has occured, the watcher has been stopped. This might
511 happen because the watcher could not be properly started because libev
512 ran out of memory, a file descriptor was found to be closed or any other
513 problem. You best act on it by reporting the problem and somehow coping
514 with the watcher being stopped.
516 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
517 for example it might indicate that a fd is readable or writable, and if
518 your callbacks is well-written it can just attempt the operation and cope
519 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
520 programs, though, so beware.
521 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
522 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
523 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
524 and read at any time, libev will completely ignore it. This can be used
525 to associate arbitrary data with your watcher. If you need more data and
526 don't want to allocate memory and store a pointer to it in that data
527 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
536 \& struct whatever *mostinteresting;
540 And since your callback will be called with a pointer to the watcher, you
541 can cast it back to your own type:
544 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
546 \& struct my_io *w = (struct my_io *)w_;
551 More interesting and less C\-conformant ways of catsing your callback type
552 have been omitted....
554 .IX Header "WATCHER TYPES"
555 This section describes each watcher in detail, but will not repeat
556 information given in the last section.
557 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
558 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
559 .IX Subsection "ev_io - is this file descriptor readable or writable"
560 I/O watchers check whether a file descriptor is readable or writable
561 in each iteration of the event loop (This behaviour is called
562 level-triggering because you keep receiving events as long as the
563 condition persists. Remember you can stop the watcher if you don't want to
564 act on the event and neither want to receive future events).
566 In general you can register as many read and/or write event watchers per
567 fd as you want (as long as you don't confuse yourself). Setting all file
568 descriptors to non-blocking mode is also usually a good idea (but not
569 required if you know what you are doing).
571 You have to be careful with dup'ed file descriptors, though. Some backends
572 (the linux epoll backend is a notable example) cannot handle dup'ed file
573 descriptors correctly if you register interest in two or more fds pointing
574 to the same underlying file/socket etc. description (that is, they share
575 the same underlying \*(L"file open\*(R").
577 If you must do this, then force the use of a known-to-be-good backend
578 (at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and
579 \&\s-1EVMETHOD_POLL\s0).
580 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
581 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
583 .IP "ev_io_set (ev_io *, int fd, int events)" 4
584 .IX Item "ev_io_set (ev_io *, int fd, int events)"
586 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
587 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 |
588 EV_WRITE\*(C'\fR to receive the given events.
589 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
590 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
591 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
592 Timer watchers are simple relative timers that generate an event after a
593 given time, and optionally repeating in regular intervals after that.
595 The timers are based on real time, that is, if you register an event that
596 times out after an hour and you reset your system clock to last years
597 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
598 detecting time jumps is hard, and some inaccuracies are unavoidable (the
599 monotonic clock option helps a lot here).
601 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
602 time. This is usually the right thing as this timestamp refers to the time
603 of the event triggering whatever timeout you are modifying/starting. If
604 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
605 on the current time, use something like this to adjust for this:
608 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
611 The callback is guarenteed to be invoked only when its timeout has passed,
612 but if multiple timers become ready during the same loop iteration then
613 order of execution is undefined.
614 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
615 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
617 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
618 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
620 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
621 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
622 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
623 later, again, and again, until stopped manually.
625 The timer itself will do a best-effort at avoiding drift, that is, if you
626 configure a timer to trigger every 10 seconds, then it will trigger at
627 exactly 10 second intervals. If, however, your program cannot keep up with
628 the timer (because it takes longer than those 10 seconds to do stuff) the
629 timer will not fire more than once per event loop iteration.
630 .IP "ev_timer_again (loop)" 4
631 .IX Item "ev_timer_again (loop)"
632 This will act as if the timer timed out and restart it again if it is
633 repeating. The exact semantics are:
635 If the timer is started but nonrepeating, stop it.
637 If the timer is repeating, either start it if necessary (with the repeat
638 value), or reset the running timer to the repeat value.
640 This sounds a bit complicated, but here is a useful and typical
641 example: Imagine you have a tcp connection and you want a so-called idle
642 timeout, that is, you want to be called when there have been, say, 60
643 seconds of inactivity on the socket. The easiest way to do this is to
644 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
645 time you successfully read or write some data. If you go into an idle
646 state where you do not expect data to travel on the socket, you can stop
647 the timer, and again will automatically restart it if need be.
648 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
649 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
650 .IX Subsection "ev_periodic - to cron or not to cron"
651 Periodic watchers are also timers of a kind, but they are very versatile
652 (and unfortunately a bit complex).
654 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
655 but on wallclock time (absolute time). You can tell a periodic watcher
656 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
657 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
658 + 10.>) and then reset your system clock to the last year, then it will
659 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
660 roughly 10 seconds later and of course not if you reset your system time
663 They can also be used to implement vastly more complex timers, such as
664 triggering an event on eahc midnight, local time.
666 As with timers, the callback is guarenteed to be invoked only when the
667 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
668 during the same loop iteration then order of execution is undefined.
669 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
670 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
672 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
673 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
675 Lots of arguments, lets sort it out... There are basically three modes of
676 operation, and we will explain them from simplest to complex:
678 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
679 .IX Item "absolute timer (interval = reschedule_cb = 0)"
680 In this configuration the watcher triggers an event at the wallclock time
681 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
682 that is, if it is to be run at January 1st 2011 then it will run when the
683 system time reaches or surpasses this time.
684 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
685 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
686 In this mode the watcher will always be scheduled to time out at the next
687 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
690 This can be used to create timers that do not drift with respect to system
694 \& ev_periodic_set (&periodic, 0., 3600., 0);
697 This doesn't mean there will always be 3600 seconds in between triggers,
698 but only that the the callback will be called when the system time shows a
699 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
702 Another way to think about it (for the mathematically inclined) is that
703 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
704 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
705 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
706 .IX Item "manual reschedule mode (reschedule_cb = callback)"
707 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
708 ignored. Instead, each time the periodic watcher gets scheduled, the
709 reschedule callback will be called with the watcher as first, and the
710 current time as second argument.
712 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
713 ever, or make any event loop modifications\fR. If you need to stop it,
714 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
715 starting a prepare watcher).
717 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
718 ev_tstamp now)\*(C'\fR, e.g.:
721 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
727 It must return the next time to trigger, based on the passed time value
728 (that is, the lowest time value larger than to the second argument). It
729 will usually be called just before the callback will be triggered, but
730 might be called at other times, too.
732 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
733 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.
735 This can be used to create very complex timers, such as a timer that
736 triggers on each midnight, local time. To do this, you would calculate the
737 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
738 you do this is, again, up to you (but it is not trivial, which is the main
739 reason I omitted it as an example).
743 .IP "ev_periodic_again (loop, ev_periodic *)" 4
744 .IX Item "ev_periodic_again (loop, ev_periodic *)"
745 Simply stops and restarts the periodic watcher again. This is only useful
746 when you changed some parameters or the reschedule callback would return
747 a different time than the last time it was called (e.g. in a crond like
748 program when the crontabs have changed).
749 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
750 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
751 .IX Subsection "ev_signal - signal me when a signal gets signalled"
752 Signal watchers will trigger an event when the process receives a specific
753 signal one or more times. Even though signals are very asynchronous, libev
754 will try it's best to deliver signals synchronously, i.e. as part of the
755 normal event processing, like any other event.
757 You can configure as many watchers as you like per signal. Only when the
758 first watcher gets started will libev actually register a signal watcher
759 with the kernel (thus it coexists with your own signal handlers as long
760 as you don't register any with libev). Similarly, when the last signal
761 watcher for a signal is stopped libev will reset the signal handler to
762 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
763 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
764 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
766 .IP "ev_signal_set (ev_signal *, int signum)" 4
767 .IX Item "ev_signal_set (ev_signal *, int signum)"
769 Configures the watcher to trigger on the given signal number (usually one
770 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
771 .ie n .Sh """ev_child"" \- wait for pid status changes"
772 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
773 .IX Subsection "ev_child - wait for pid status changes"
774 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
775 some child status changes (most typically when a child of yours dies).
776 .IP "ev_child_init (ev_child *, callback, int pid)" 4
777 .IX Item "ev_child_init (ev_child *, callback, int pid)"
779 .IP "ev_child_set (ev_child *, int pid)" 4
780 .IX Item "ev_child_set (ev_child *, int pid)"
782 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
783 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
784 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
785 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
786 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
787 process causing the status change.
788 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
789 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
790 .IX Subsection "ev_idle - when you've got nothing better to do"
791 Idle watchers trigger events when there are no other events are pending
792 (prepare, check and other idle watchers do not count). That is, as long
793 as your process is busy handling sockets or timeouts (or even signals,
794 imagine) it will not be triggered. But when your process is idle all idle
795 watchers are being called again and again, once per event loop iteration \-
796 until stopped, that is, or your process receives more events and becomes
799 The most noteworthy effect is that as long as any idle watchers are
800 active, the process will not block when waiting for new events.
802 Apart from keeping your process non-blocking (which is a useful
803 effect on its own sometimes), idle watchers are a good place to do
804 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
805 event loop has handled all outstanding events.
806 .IP "ev_idle_init (ev_signal *, callback)" 4
807 .IX Item "ev_idle_init (ev_signal *, callback)"
808 Initialises and configures the idle watcher \- it has no parameters of any
809 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
811 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
812 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
813 .IX Subsection "ev_prepare and ev_check - customise your event loop"
814 Prepare and check watchers are usually (but not always) used in tandem:
815 prepare watchers get invoked before the process blocks and check watchers
818 Their main purpose is to integrate other event mechanisms into libev. This
819 could be used, for example, to track variable changes, implement your own
820 watchers, integrate net-snmp or a coroutine library and lots more.
822 This is done by examining in each prepare call which file descriptors need
823 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
824 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
825 provide just this functionality). Then, in the check watcher you check for
826 any events that occured (by checking the pending status of all watchers
827 and stopping them) and call back into the library. The I/O and timer
828 callbacks will never actually be called (but must be valid nevertheless,
829 because you never know, you know?).
831 As another example, the Perl Coro module uses these hooks to integrate
832 coroutines into libev programs, by yielding to other active coroutines
833 during each prepare and only letting the process block if no coroutines
834 are ready to run (it's actually more complicated: it only runs coroutines
835 with priority higher than or equal to the event loop and one coroutine
836 of lower priority, but only once, using idle watchers to keep the event
837 loop from blocking if lower-priority coroutines are active, thus mapping
838 low-priority coroutines to idle/background tasks).
839 .IP "ev_prepare_init (ev_prepare *, callback)" 4
840 .IX Item "ev_prepare_init (ev_prepare *, callback)"
842 .IP "ev_check_init (ev_check *, callback)" 4
843 .IX Item "ev_check_init (ev_check *, callback)"
845 Initialises and configures the prepare or check watcher \- they have no
846 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
847 macros, but using them is utterly, utterly and completely pointless.
848 .SH "OTHER FUNCTIONS"
849 .IX Header "OTHER FUNCTIONS"
850 There are some other functions of possible interest. Described. Here. Now.
851 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
852 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
853 This function combines a simple timer and an I/O watcher, calls your
854 callback on whichever event happens first and automatically stop both
855 watchers. This is useful if you want to wait for a single event on an fd
856 or timeout without having to allocate/configure/start/stop/free one or
857 more watchers yourself.
859 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
860 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
861 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
863 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
864 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
865 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
868 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
869 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
870 \&\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
871 value passed to \f(CW\*(C`ev_once\*(C'\fR:
874 \& static void stdin_ready (int revents, void *arg)
876 \& if (revents & EV_TIMEOUT)
877 \& /* doh, nothing entered */;
878 \& else if (revents & EV_READ)
879 \& /* stdin might have data for us, joy! */;
884 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
886 .IP "ev_feed_event (loop, watcher, int events)" 4
887 .IX Item "ev_feed_event (loop, watcher, int events)"
888 Feeds the given event set into the event loop, as if the specified event
889 had happened for the specified watcher (which must be a pointer to an
890 initialised but not necessarily started event watcher).
891 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
892 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
893 Feed an event on the given fd, as if a file descriptor backend detected
895 .IP "ev_feed_signal_event (loop, int signum)" 4
896 .IX Item "ev_feed_signal_event (loop, int signum)"
897 Feed an event as if the given signal occured (loop must be the default loop!).
898 .SH "LIBEVENT EMULATION"
899 .IX Header "LIBEVENT EMULATION"
900 Libev offers a compatibility emulation layer for libevent. It cannot
901 emulate the internals of libevent, so here are some usage hints:
902 .IP "* Use it by including <event.h>, as usual." 4
903 .IX Item "Use it by including <event.h>, as usual."
905 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
906 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
907 .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
908 .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)."
909 .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
910 .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."
911 .IP "* Other members are not supported." 4
912 .IX Item "Other members are not supported."
913 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
914 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
917 .IX Header " SUPPORT"
921 Marc Lehmann <libev@schmorp.de>.
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