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Revision: 1.13
Committed: Mon Nov 12 08:35:36 2007 UTC (16 years, 6 months ago) by root
Branch: MAIN
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# User Rev Content
1 root 1.1 =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 root 1.4 these event sources and provide your program with events.
14 root 1.1
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 root 1.5 loop mechanism itself (idle, prepare and check watchers). It also is quite
31 root 1.7 fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
32     it to libevent for example).
33 root 1.1
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 root 1.7 about various configuration options please have a look at the file
39 root 1.1 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 root 1.2 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 root 1.1 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 root 1.9 Usually, it's a good idea to terminate if the major versions mismatch,
69 root 1.1 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 root 1.7 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 root 1.1
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 root 1.7 matter what, when it returns. That is, libev will generally retry the
92 root 1.1 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 root 1.7 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 root 1.9 done correctly, because it's hideous and inefficient).
109 root 1.1
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 root 1.8 backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
124 root 1.1
125     It supports the following flags:
126    
127     =over 4
128    
129 root 1.10 =item C<EVFLAG_AUTO>
130 root 1.1
131 root 1.9 The default flags value. Use this if you have no clue (it's the right
132 root 1.1 thing, believe me).
133    
134 root 1.10 =item C<EVFLAG_NOENV>
135 root 1.1
136 root 1.8 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 root 1.1
143 root 1.10 =item C<EVMETHOD_SELECT> (portable select backend)
144 root 1.1
145 root 1.10 =item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
146 root 1.1
147 root 1.10 =item C<EVMETHOD_EPOLL> (linux only)
148 root 1.1
149 root 1.10 =item C<EVMETHOD_KQUEUE> (some bsds only)
150 root 1.1
151 root 1.10 =item C<EVMETHOD_DEVPOLL> (solaris 8 only)
152 root 1.1
153 root 1.10 =item C<EVMETHOD_PORT> (solaris 10 only)
154 root 1.1
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 root 1.9 any way whatsoever, although you cannot rely on this :).
173 root 1.1
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 root 1.9 The function itself is quite fast and it's usually not a problem to call
191 root 1.1 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 root 1.9 =item ev_tstamp ev_now (loop)
208 root 1.1
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 root 1.9 case there are no events and will return after one iteration of the loop.
227 root 1.1
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 root 1.9 your process until at least one new event arrives, and will return after
231     one iteration of the loop.
232 root 1.1
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 root 1.9 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 root 1.1
244     =item ev_ref (loop)
245    
246     =item ev_unref (loop)
247    
248 root 1.9 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 root 1.1
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 root 1.10 become readable, you would create an C<ev_io> watcher for that:
266 root 1.1
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 root 1.4 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 root 1.1 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 root 1.10 =item C<EV_READ>
320 root 1.1
321 root 1.10 =item C<EV_WRITE>
322 root 1.1
323 root 1.10 The file descriptor in the C<ev_io> watcher has become readable and/or
324 root 1.1 writable.
325    
326 root 1.10 =item C<EV_TIMEOUT>
327 root 1.1
328 root 1.10 The C<ev_timer> watcher has timed out.
329 root 1.1
330 root 1.10 =item C<EV_PERIODIC>
331 root 1.1
332 root 1.10 The C<ev_periodic> watcher has timed out.
333 root 1.1
334 root 1.10 =item C<EV_SIGNAL>
335 root 1.1
336 root 1.10 The signal specified in the C<ev_signal> watcher has been received by a thread.
337 root 1.1
338 root 1.10 =item C<EV_CHILD>
339 root 1.1
340 root 1.10 The pid specified in the C<ev_child> watcher has received a status change.
341 root 1.1
342 root 1.10 =item C<EV_IDLE>
343 root 1.1
344 root 1.10 The C<ev_idle> watcher has determined that you have nothing better to do.
345 root 1.1
346 root 1.10 =item C<EV_PREPARE>
347 root 1.1
348 root 1.10 =item C<EV_CHECK>
349 root 1.1
350 root 1.10 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 root 1.1 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 root 1.10 (for example, a C<ev_prepare> watcher might start an idle watcher to keep
356 root 1.1 C<ev_loop> from blocking).
357    
358 root 1.10 =item C<EV_ERROR>
359 root 1.1
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 root 1.11 =head2 C<ev_io> - is this file descriptor readable or writable
410 root 1.1
411 root 1.4 I/O watchers check whether a file descriptor is readable or writable
412 root 1.1 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 root 1.8 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 root 1.1 =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 root 1.10 Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
438 root 1.1 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 root 1.10 =head2 C<ev_timer> - relative and optionally recurring timeouts
444 root 1.1
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 root 1.9 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 root 1.1 =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 root 1.10 configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
494 root 1.1 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 root 1.10 =head2 C<ev_periodic> - to cron or not to cron it
501 root 1.1
502     Periodic watchers are also timers of a kind, but they are very versatile
503     (and unfortunately a bit complex).
504    
505 root 1.10 Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506 root 1.1 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 root 1.10 take a year to trigger the event (unlike an C<ev_timer>, which would trigger
511 root 1.1 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 root 1.12 full hour (UTC), or more correctly, when the system time is evenly divisible
550 root 1.1 by 3600.
551    
552     Another way to think about it (for the mathematically inclined) is that
553 root 1.10 C<ev_periodic> will try to run the callback in this mode at the next possible
554 root 1.1 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 root 1.12 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 root 1.13 Also, I<< this callback must always return a time that is later than the
568 root 1.12 passed C<now> value >>. Not even C<now> itself will be ok.
569 root 1.1
570 root 1.13 Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571 root 1.1 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 root 1.10 =head2 C<ev_signal> - signal me when a signal gets signalled
600 root 1.1
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 root 1.9 will try it's best to deliver signals synchronously, i.e. as part of the
604 root 1.1 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 root 1.10 =head2 C<ev_child> - wait for pid status changes
625 root 1.1
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 root 1.10 =head2 C<ev_idle> - when you've got nothing better to do
644 root 1.1
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 root 1.10 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 root 1.1 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 root 1.10 ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set
719 root 1.1 will be craeted and started.
720    
721     If C<timeout> is less than 0, then no timeout watcher will be
722 root 1.10 started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat
723 root 1.1 = 0) will be started.
724    
725     The callback has the type C<void (*cb)(int revents, void *arg)> and
726 root 1.10 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 root 1.1
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