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# Content
1 =head1 NAME
2
3 libev - a high performance full-featured event loop written in C
4
5 =head1 SYNOPSIS
6
7 #include <ev.h>
8
9 =head1 DESCRIPTION
10
11 Libev is an event loop: you register interest in certain events (such as a
12 file descriptor being readable or a timeout occuring), and it will manage
13 these event sources and provide your program with events.
14
15 To do this, it must take more or less complete control over your process
16 (or thread) by executing the I<event loop> handler, and will then
17 communicate events via a callback mechanism.
18
19 You register interest in certain events by registering so-called I<event
20 watchers>, which are relatively small C structures you initialise with the
21 details of the event, and then hand it over to libev by I<starting> the
22 watcher.
23
24 =head1 FEATURES
25
26 Libev supports select, poll, the linux-specific epoll and the bsd-specific
27 kqueue mechanisms for file descriptor events, relative timers, absolute
28 timers with customised rescheduling, signal events, process status change
29 events (related to SIGCHLD), and event watchers dealing with the event
30 loop mechanism itself (idle, prepare and check watchers). It also is quite
31 fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
32 it to libevent for example).
33
34 =head1 CONVENTIONS
35
36 Libev is very configurable. In this manual the default configuration
37 will be described, which supports multiple event loops. For more info
38 about various configuration options please have a look at the file
39 F<README.embed> in the libev distribution. If libev was configured without
40 support for multiple event loops, then all functions taking an initial
41 argument of name C<loop> (which is always of type C<struct ev_loop *>)
42 will not have this argument.
43
44 =head1 TIME AND OTHER GLOBAL FUNCTIONS
45
46 Libev represents time as a single floating point number, representing the
47 (fractional) number of seconds since the (POSIX) epoch (somewhere near
48 the beginning of 1970, details are complicated, don't ask). This type is
49 called C<ev_tstamp>, which is what you should use too. It usually aliases
50 to the double type in C.
51
52 =over 4
53
54 =item ev_tstamp ev_time ()
55
56 Returns the current time as libev would use it.
57
58 =item int ev_version_major ()
59
60 =item int ev_version_minor ()
61
62 You can find out the major and minor version numbers of the library
63 you linked against by calling the functions C<ev_version_major> and
64 C<ev_version_minor>. If you want, you can compare against the global
65 symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66 version of the library your program was compiled against.
67
68 Usually, it's a good idea to terminate if the major versions mismatch,
69 as this indicates an incompatible change. Minor versions are usually
70 compatible to older versions, so a larger minor version alone is usually
71 not a problem.
72
73 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
74
75 Sets the allocation function to use (the prototype is similar to the
76 realloc C function, the semantics are identical). It is used to allocate
77 and free memory (no surprises here). If it returns zero when memory
78 needs to be allocated, the library might abort or take some potentially
79 destructive action. The default is your system realloc function.
80
81 You could override this function in high-availability programs to, say,
82 free some memory if it cannot allocate memory, to use a special allocator,
83 or even to sleep a while and retry until some memory is available.
84
85 =item ev_set_syserr_cb (void (*cb)(const char *msg));
86
87 Set the callback function to call on a retryable syscall error (such
88 as failed select, poll, epoll_wait). The message is a printable string
89 indicating the system call or subsystem causing the problem. If this
90 callback is set, then libev will expect it to remedy the sitution, no
91 matter what, when it returns. That is, libev will generally retry the
92 requested operation, or, if the condition doesn't go away, do bad stuff
93 (such as abort).
94
95 =back
96
97 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98
99 An event loop is described by a C<struct ev_loop *>. The library knows two
100 types of such loops, the I<default> loop, which supports signals and child
101 events, and dynamically created loops which do not.
102
103 If you use threads, a common model is to run the default event loop
104 in your main thread (or in a separate thrad) and for each thread you
105 create, you also create another event loop. Libev itself does no locking
106 whatsoever, so if you mix calls to the same event loop in different
107 threads, make sure you lock (this is usually a bad idea, though, even if
108 done correctly, because it's hideous and inefficient).
109
110 =over 4
111
112 =item struct ev_loop *ev_default_loop (unsigned int flags)
113
114 This will initialise the default event loop if it hasn't been initialised
115 yet and return it. If the default loop could not be initialised, returns
116 false. If it already was initialised it simply returns it (and ignores the
117 flags).
118
119 If you don't know what event loop to use, use the one returned from this
120 function.
121
122 The flags argument can be used to specify special behaviour or specific
123 backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
124
125 It supports the following flags:
126
127 =over 4
128
129 =item C<EVFLAG_AUTO>
130
131 The default flags value. Use this if you have no clue (it's the right
132 thing, believe me).
133
134 =item C<EVFLAG_NOENV>
135
136 If this flag bit is ored into the flag value (or the program runs setuid
137 or setgid) then libev will I<not> look at the environment variable
138 C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139 override the flags completely if it is found in the environment. This is
140 useful to try out specific backends to test their performance, or to work
141 around bugs.
142
143 =item C<EVMETHOD_SELECT> (portable select backend)
144
145 =item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
146
147 =item C<EVMETHOD_EPOLL> (linux only)
148
149 =item C<EVMETHOD_KQUEUE> (some bsds only)
150
151 =item C<EVMETHOD_DEVPOLL> (solaris 8 only)
152
153 =item C<EVMETHOD_PORT> (solaris 10 only)
154
155 If one or more of these are ored into the flags value, then only these
156 backends will be tried (in the reverse order as given here). If one are
157 specified, any backend will do.
158
159 =back
160
161 =item struct ev_loop *ev_loop_new (unsigned int flags)
162
163 Similar to C<ev_default_loop>, but always creates a new event loop that is
164 always distinct from the default loop. Unlike the default loop, it cannot
165 handle signal and child watchers, and attempts to do so will be greeted by
166 undefined behaviour (or a failed assertion if assertions are enabled).
167
168 =item ev_default_destroy ()
169
170 Destroys the default loop again (frees all memory and kernel state
171 etc.). This stops all registered event watchers (by not touching them in
172 any way whatsoever, although you cannot rely on this :).
173
174 =item ev_loop_destroy (loop)
175
176 Like C<ev_default_destroy>, but destroys an event loop created by an
177 earlier call to C<ev_loop_new>.
178
179 =item ev_default_fork ()
180
181 This function reinitialises the kernel state for backends that have
182 one. Despite the name, you can call it anytime, but it makes most sense
183 after forking, in either the parent or child process (or both, but that
184 again makes little sense).
185
186 You I<must> call this function after forking if and only if you want to
187 use the event library in both processes. If you just fork+exec, you don't
188 have to call it.
189
190 The function itself is quite fast and it's usually not a problem to call
191 it just in case after a fork. To make this easy, the function will fit in
192 quite nicely into a call to C<pthread_atfork>:
193
194 pthread_atfork (0, 0, ev_default_fork);
195
196 =item ev_loop_fork (loop)
197
198 Like C<ev_default_fork>, but acts on an event loop created by
199 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
200 after fork, and how you do this is entirely your own problem.
201
202 =item unsigned int ev_method (loop)
203
204 Returns one of the C<EVMETHOD_*> flags indicating the event backend in
205 use.
206
207 =item ev_tstamp ev_now (loop)
208
209 Returns the current "event loop time", which is the time the event loop
210 got events and started processing them. This timestamp does not change
211 as long as callbacks are being processed, and this is also the base time
212 used for relative timers. You can treat it as the timestamp of the event
213 occuring (or more correctly, the mainloop finding out about it).
214
215 =item ev_loop (loop, int flags)
216
217 Finally, this is it, the event handler. This function usually is called
218 after you initialised all your watchers and you want to start handling
219 events.
220
221 If the flags argument is specified as 0, it will not return until either
222 no event watchers are active anymore or C<ev_unloop> was called.
223
224 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
225 those events and any outstanding ones, but will not block your process in
226 case there are no events and will return after one iteration of the loop.
227
228 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
229 neccessary) and will handle those and any outstanding ones. It will block
230 your process until at least one new event arrives, and will return after
231 one iteration of the loop.
232
233 This flags value could be used to implement alternative looping
234 constructs, but the C<prepare> and C<check> watchers provide a better and
235 more generic mechanism.
236
237 =item ev_unloop (loop, how)
238
239 Can be used to make a call to C<ev_loop> return early (but only after it
240 has processed all outstanding events). The C<how> argument must be either
241 C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
242 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
243
244 =item ev_ref (loop)
245
246 =item ev_unref (loop)
247
248 Ref/unref can be used to add or remove a reference count on the event
249 loop: Every watcher keeps one reference, and as long as the reference
250 count is nonzero, C<ev_loop> will not return on its own. If you have
251 a watcher you never unregister that should not keep C<ev_loop> from
252 returning, ev_unref() after starting, and ev_ref() before stopping it. For
253 example, libev itself uses this for its internal signal pipe: It is not
254 visible to the libev user and should not keep C<ev_loop> from exiting if
255 no event watchers registered by it are active. It is also an excellent
256 way to do this for generic recurring timers or from within third-party
257 libraries. Just remember to I<unref after start> and I<ref before stop>.
258
259 =back
260
261 =head1 ANATOMY OF A WATCHER
262
263 A watcher is a structure that you create and register to record your
264 interest in some event. For instance, if you want to wait for STDIN to
265 become readable, you would create an C<ev_io> watcher for that:
266
267 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
268 {
269 ev_io_stop (w);
270 ev_unloop (loop, EVUNLOOP_ALL);
271 }
272
273 struct ev_loop *loop = ev_default_loop (0);
274 struct ev_io stdin_watcher;
275 ev_init (&stdin_watcher, my_cb);
276 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277 ev_io_start (loop, &stdin_watcher);
278 ev_loop (loop, 0);
279
280 As you can see, you are responsible for allocating the memory for your
281 watcher structures (and it is usually a bad idea to do this on the stack,
282 although this can sometimes be quite valid).
283
284 Each watcher structure must be initialised by a call to C<ev_init
285 (watcher *, callback)>, which expects a callback to be provided. This
286 callback gets invoked each time the event occurs (or, in the case of io
287 watchers, each time the event loop detects that the file descriptor given
288 is readable and/or writable).
289
290 Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
291 with arguments specific to this watcher type. There is also a macro
292 to combine initialisation and setting in one call: C<< ev_<type>_init
293 (watcher *, callback, ...) >>.
294
295 To make the watcher actually watch out for events, you have to start it
296 with a watcher-specific start function (C<< ev_<type>_start (loop, watcher
297 *) >>), and you can stop watching for events at any time by calling the
298 corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
299
300 As long as your watcher is active (has been started but not stopped) you
301 must not touch the values stored in it. Most specifically you must never
302 reinitialise it or call its set method.
303
304 You cna check whether an event is active by calling the C<ev_is_active
305 (watcher *)> macro. To see whether an event is outstanding (but the
306 callback for it has not been called yet) you cna use the C<ev_is_pending
307 (watcher *)> macro.
308
309 Each and every callback receives the event loop pointer as first, the
310 registered watcher structure as second, and a bitset of received events as
311 third argument.
312
313 The rceeived events usually include a single bit per event type received
314 (you can receive multiple events at the same time). The possible bit masks
315 are:
316
317 =over 4
318
319 =item C<EV_READ>
320
321 =item C<EV_WRITE>
322
323 The file descriptor in the C<ev_io> watcher has become readable and/or
324 writable.
325
326 =item C<EV_TIMEOUT>
327
328 The C<ev_timer> watcher has timed out.
329
330 =item C<EV_PERIODIC>
331
332 The C<ev_periodic> watcher has timed out.
333
334 =item C<EV_SIGNAL>
335
336 The signal specified in the C<ev_signal> watcher has been received by a thread.
337
338 =item C<EV_CHILD>
339
340 The pid specified in the C<ev_child> watcher has received a status change.
341
342 =item C<EV_IDLE>
343
344 The C<ev_idle> watcher has determined that you have nothing better to do.
345
346 =item C<EV_PREPARE>
347
348 =item C<EV_CHECK>
349
350 All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
351 to gather new events, and all C<ev_check> watchers are invoked just after
352 C<ev_loop> has gathered them, but before it invokes any callbacks for any
353 received events. Callbacks of both watcher types can start and stop as
354 many watchers as they want, and all of them will be taken into account
355 (for example, a C<ev_prepare> watcher might start an idle watcher to keep
356 C<ev_loop> from blocking).
357
358 =item C<EV_ERROR>
359
360 An unspecified error has occured, the watcher has been stopped. This might
361 happen because the watcher could not be properly started because libev
362 ran out of memory, a file descriptor was found to be closed or any other
363 problem. You best act on it by reporting the problem and somehow coping
364 with the watcher being stopped.
365
366 Libev will usually signal a few "dummy" events together with an error,
367 for example it might indicate that a fd is readable or writable, and if
368 your callbacks is well-written it can just attempt the operation and cope
369 with the error from read() or write(). This will not work in multithreaded
370 programs, though, so beware.
371
372 =back
373
374 =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375
376 Each watcher has, by default, a member C<void *data> that you can change
377 and read at any time, libev will completely ignore it. This cna be used
378 to associate arbitrary data with your watcher. If you need more data and
379 don't want to allocate memory and store a pointer to it in that data
380 member, you can also "subclass" the watcher type and provide your own
381 data:
382
383 struct my_io
384 {
385 struct ev_io io;
386 int otherfd;
387 void *somedata;
388 struct whatever *mostinteresting;
389 }
390
391 And since your callback will be called with a pointer to the watcher, you
392 can cast it back to your own type:
393
394 static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
395 {
396 struct my_io *w = (struct my_io *)w_;
397 ...
398 }
399
400 More interesting and less C-conformant ways of catsing your callback type
401 have been omitted....
402
403
404 =head1 WATCHER TYPES
405
406 This section describes each watcher in detail, but will not repeat
407 information given in the last section.
408
409 =head2 C<ev_io> - is this file descriptor readable or writable
410
411 I/O watchers check whether a file descriptor is readable or writable
412 in each iteration of the event loop (This behaviour is called
413 level-triggering because you keep receiving events as long as the
414 condition persists. Remember you cna stop the watcher if you don't want to
415 act on the event and neither want to receive future events).
416
417 In general you can register as many read and/or write event watchers oer
418 fd as you want (as long as you don't confuse yourself). Setting all file
419 descriptors to non-blocking mode is also usually a good idea (but not
420 required if you know what you are doing).
421
422 You have to be careful with dup'ed file descriptors, though. Some backends
423 (the linux epoll backend is a notable example) cannot handle dup'ed file
424 descriptors correctly if you register interest in two or more fds pointing
425 to the same file/socket etc. description.
426
427 If you must do this, then force the use of a known-to-be-good backend
428 (at the time of this writing, this includes only EVMETHOD_SELECT and
429 EVMETHOD_POLL).
430
431 =over 4
432
433 =item ev_io_init (ev_io *, callback, int fd, int events)
434
435 =item ev_io_set (ev_io *, int fd, int events)
436
437 Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
438 events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
439 EV_WRITE> to receive the given events.
440
441 =back
442
443 =head2 C<ev_timer> - relative and optionally recurring timeouts
444
445 Timer watchers are simple relative timers that generate an event after a
446 given time, and optionally repeating in regular intervals after that.
447
448 The timers are based on real time, that is, if you register an event that
449 times out after an hour and youreset your system clock to last years
450 time, it will still time out after (roughly) and hour. "Roughly" because
451 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
452 monotonic clock option helps a lot here).
453
454 The relative timeouts are calculated relative to the C<ev_now ()>
455 time. This is usually the right thing as this timestamp refers to the time
456 of the event triggering whatever timeout you are modifying/starting. If
457 you suspect event processing to be delayed and you *need* to base the timeout
458 ion the current time, use something like this to adjust for this:
459
460 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461
462 =over 4
463
464 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465
466 =item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467
468 Configure the timer to trigger after C<after> seconds. If C<repeat> is
469 C<0.>, then it will automatically be stopped. If it is positive, then the
470 timer will automatically be configured to trigger again C<repeat> seconds
471 later, again, and again, until stopped manually.
472
473 The timer itself will do a best-effort at avoiding drift, that is, if you
474 configure a timer to trigger every 10 seconds, then it will trigger at
475 exactly 10 second intervals. If, however, your program cannot keep up with
476 the timer (ecause it takes longer than those 10 seconds to do stuff) the
477 timer will not fire more than once per event loop iteration.
478
479 =item ev_timer_again (loop)
480
481 This will act as if the timer timed out and restart it again if it is
482 repeating. The exact semantics are:
483
484 If the timer is started but nonrepeating, stop it.
485
486 If the timer is repeating, either start it if necessary (with the repeat
487 value), or reset the running timer to the repeat value.
488
489 This sounds a bit complicated, but here is a useful and typical
490 example: Imagine you have a tcp connection and you want a so-called idle
491 timeout, that is, you want to be called when there have been, say, 60
492 seconds of inactivity on the socket. The easiest way to do this is to
493 configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
494 time you successfully read or write some data. If you go into an idle
495 state where you do not expect data to travel on the socket, you can stop
496 the timer, and again will automatically restart it if need be.
497
498 =back
499
500 =head2 C<ev_periodic> - to cron or not to cron it
501
502 Periodic watchers are also timers of a kind, but they are very versatile
503 (and unfortunately a bit complex).
504
505 Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506 but on wallclock time (absolute time). You can tell a periodic watcher
507 to trigger "at" some specific point in time. For example, if you tell a
508 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
509 + 10.>) and then reset your system clock to the last year, then it will
510 take a year to trigger the event (unlike an C<ev_timer>, which would trigger
511 roughly 10 seconds later and of course not if you reset your system time
512 again).
513
514 They can also be used to implement vastly more complex timers, such as
515 triggering an event on eahc midnight, local time.
516
517 =over 4
518
519 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520
521 =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522
523 Lots of arguments, lets sort it out... There are basically three modes of
524 operation, and we will explain them from simplest to complex:
525
526
527 =over 4
528
529 =item * absolute timer (interval = reschedule_cb = 0)
530
531 In this configuration the watcher triggers an event at the wallclock time
532 C<at> and doesn't repeat. It will not adjust when a time jump occurs,
533 that is, if it is to be run at January 1st 2011 then it will run when the
534 system time reaches or surpasses this time.
535
536 =item * non-repeating interval timer (interval > 0, reschedule_cb = 0)
537
538 In this mode the watcher will always be scheduled to time out at the next
539 C<at + N * interval> time (for some integer N) and then repeat, regardless
540 of any time jumps.
541
542 This can be used to create timers that do not drift with respect to system
543 time:
544
545 ev_periodic_set (&periodic, 0., 3600., 0);
546
547 This doesn't mean there will always be 3600 seconds in between triggers,
548 but only that the the callback will be called when the system time shows a
549 full hour (UTC), or more correctly, when the system time is evenly divisible
550 by 3600.
551
552 Another way to think about it (for the mathematically inclined) is that
553 C<ev_periodic> will try to run the callback in this mode at the next possible
554 time where C<time = at (mod interval)>, regardless of any time jumps.
555
556 =item * manual reschedule mode (reschedule_cb = callback)
557
558 In this mode the values for C<interval> and C<at> are both being
559 ignored. Instead, each time the periodic watcher gets scheduled, the
560 reschedule callback will be called with the watcher as first, and the
561 current time as second argument.
562
563 NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
564 periodic watcher, ever, or make any event loop modifications>. If you need
565 to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
566
567 Also, I<<this callback must always return a time that is later than the
568 passed C<now> value >>. Not even C<now> itself will be ok.
569
570 Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571 ev_tstamp now)>, e.g.:
572
573 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
574 {
575 return now + 60.;
576 }
577
578 It must return the next time to trigger, based on the passed time value
579 (that is, the lowest time value larger than to the second argument). It
580 will usually be called just before the callback will be triggered, but
581 might be called at other times, too.
582
583 This can be used to create very complex timers, such as a timer that
584 triggers on each midnight, local time. To do this, you would calculate the
585 next midnight after C<now> and return the timestamp value for this. How you do this
586 is, again, up to you (but it is not trivial).
587
588 =back
589
590 =item ev_periodic_again (loop, ev_periodic *)
591
592 Simply stops and restarts the periodic watcher again. This is only useful
593 when you changed some parameters or the reschedule callback would return
594 a different time than the last time it was called (e.g. in a crond like
595 program when the crontabs have changed).
596
597 =back
598
599 =head2 C<ev_signal> - signal me when a signal gets signalled
600
601 Signal watchers will trigger an event when the process receives a specific
602 signal one or more times. Even though signals are very asynchronous, libev
603 will try it's best to deliver signals synchronously, i.e. as part of the
604 normal event processing, like any other event.
605
606 You cna configure as many watchers as you like per signal. Only when the
607 first watcher gets started will libev actually register a signal watcher
608 with the kernel (thus it coexists with your own signal handlers as long
609 as you don't register any with libev). Similarly, when the last signal
610 watcher for a signal is stopped libev will reset the signal handler to
611 SIG_DFL (regardless of what it was set to before).
612
613 =over 4
614
615 =item ev_signal_init (ev_signal *, callback, int signum)
616
617 =item ev_signal_set (ev_signal *, int signum)
618
619 Configures the watcher to trigger on the given signal number (usually one
620 of the C<SIGxxx> constants).
621
622 =back
623
624 =head2 C<ev_child> - wait for pid status changes
625
626 Child watchers trigger when your process receives a SIGCHLD in response to
627 some child status changes (most typically when a child of yours dies).
628
629 =over 4
630
631 =item ev_child_init (ev_child *, callback, int pid)
632
633 =item ev_child_set (ev_child *, int pid)
634
635 Configures the watcher to wait for status changes of process C<pid> (or
636 I<any> process if C<pid> is specified as C<0>). The callback can look
637 at the C<rstatus> member of the C<ev_child> watcher structure to see
638 the status word (use the macros from C<sys/wait.h>). The C<rpid> member
639 contains the pid of the process causing the status change.
640
641 =back
642
643 =head2 C<ev_idle> - when you've got nothing better to do
644
645 Idle watchers trigger events when there are no other I/O or timer (or
646 periodic) events pending. That is, as long as your process is busy
647 handling sockets or timeouts it will not be called. But when your process
648 is idle all idle watchers are being called again and again - until
649 stopped, that is, or your process receives more events.
650
651 The most noteworthy effect is that as long as any idle watchers are
652 active, the process will not block when waiting for new events.
653
654 Apart from keeping your process non-blocking (which is a useful
655 effect on its own sometimes), idle watchers are a good place to do
656 "pseudo-background processing", or delay processing stuff to after the
657 event loop has handled all outstanding events.
658
659 =over 4
660
661 =item ev_idle_init (ev_signal *, callback)
662
663 Initialises and configures the idle watcher - it has no parameters of any
664 kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
665 believe me.
666
667 =back
668
669 =head2 prepare and check - your hooks into the event loop
670
671 Prepare and check watchers usually (but not always) are used in
672 tandom. Prepare watchers get invoked before the process blocks and check
673 watchers afterwards.
674
675 Their main purpose is to integrate other event mechanisms into libev. This
676 could be used, for example, to track variable changes, implement your own
677 watchers, integrate net-snmp or a coroutine library and lots more.
678
679 This is done by examining in each prepare call which file descriptors need
680 to be watched by the other library, registering C<ev_io> watchers for them
681 and starting an C<ev_timer> watcher for any timeouts (many libraries provide
682 just this functionality). Then, in the check watcher you check for any
683 events that occured (by making your callbacks set soem flags for example)
684 and call back into the library.
685
686 As another example, the perl Coro module uses these hooks to integrate
687 coroutines into libev programs, by yielding to other active coroutines
688 during each prepare and only letting the process block if no coroutines
689 are ready to run.
690
691 =over 4
692
693 =item ev_prepare_init (ev_prepare *, callback)
694
695 =item ev_check_init (ev_check *, callback)
696
697 Initialises and configures the prepare or check watcher - they have no
698 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
699 macros, but using them is utterly, utterly pointless.
700
701 =back
702
703 =head1 OTHER FUNCTIONS
704
705 There are some other fucntions of possible interest. Described. Here. Now.
706
707 =over 4
708
709 =item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
710
711 This function combines a simple timer and an I/O watcher, calls your
712 callback on whichever event happens first and automatically stop both
713 watchers. This is useful if you want to wait for a single event on an fd
714 or timeout without havign to allocate/configure/start/stop/free one or
715 more watchers yourself.
716
717 If C<fd> is less than 0, then no I/O watcher will be started and events is
718 ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set
719 will be craeted and started.
720
721 If C<timeout> is less than 0, then no timeout watcher will be
722 started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat
723 = 0) will be started.
724
725 The callback has the type C<void (*cb)(int revents, void *arg)> and
726 gets passed an events set (normally a combination of C<EV_ERROR>, C<EV_READ>,
727 C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> value passed to C<ev_once>:
728
729 static void stdin_ready (int revents, void *arg)
730 {
731 if (revents & EV_TIMEOUT)
732 /* doh, nothing entered */
733 else if (revents & EV_READ)
734 /* stdin might have data for us, joy! */
735 }
736
737 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
738
739 =item ev_feed_event (loop, watcher, int events)
740
741 Feeds the given event set into the event loop, as if the specified event
742 has happened for the specified watcher (which must be a pointer to an
743 initialised but not necessarily active event watcher).
744
745 =item ev_feed_fd_event (loop, int fd, int revents)
746
747 Feed an event on the given fd, as if a file descriptor backend detected it.
748
749 =item ev_feed_signal_event (loop, int signum)
750
751 Feed an event as if the given signal occured (loop must be the default loop!).
752
753 =back
754
755 =head1 AUTHOR
756
757 Marc Lehmann <libev@schmorp.de>.
758