ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/EV/EV.pm
Revision: 1.71
Committed: Mon Dec 17 07:24:12 2007 UTC (16 years, 5 months ago) by root
Branch: MAIN
CVS Tags: rel-1_86
Changes since 1.70: +5 -1 lines
Log Message:
*** empty log message ***

File Contents

# Content
1 =head1 NAME
2
3 EV - perl interface to libev, a high performance full-featured event loop
4
5 =head1 SYNOPSIS
6
7 use EV;
8
9 # TIMERS
10
11 my $w = EV::timer 2, 0, sub {
12 warn "is called after 2s";
13 };
14
15 my $w = EV::timer 2, 2, sub {
16 warn "is called roughly every 2s (repeat = 2)";
17 };
18
19 undef $w; # destroy event watcher again
20
21 my $w = EV::periodic 0, 60, 0, sub {
22 warn "is called every minute, on the minute, exactly";
23 };
24
25 # IO
26
27 my $w = EV::io *STDIN, EV::READ, sub {
28 my ($w, $revents) = @_; # all callbacks receive the watcher and event mask
29 warn "stdin is readable, you entered: ", <STDIN>;
30 };
31
32 # SIGNALS
33
34 my $w = EV::signal 'QUIT', sub {
35 warn "sigquit received\n";
36 };
37
38 # CHILD/PID STATUS CHANGES
39
40 my $w = EV::child 666, sub {
41 my ($w, $revents) = @_;
42 my $status = $w->rstatus;
43 };
44
45 # STAT CHANGES
46 my $w = EV::stat "/etc/passwd", 10, sub {
47 my ($w, $revents) = @_;
48 warn $w->path, " has changed somehow.\n";
49 };
50
51 # MAINLOOP
52 EV::loop; # loop until EV::unloop is called or all watchers stop
53 EV::loop EV::LOOP_ONESHOT; # block until at least one event could be handled
54 EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block
55
56 =head1 DESCRIPTION
57
58 This module provides an interface to libev
59 (L<http://software.schmorp.de/pkg/libev.html>). While the documentation
60 below is comprehensive, one might also consult the documentation of libev
61 itself (L<http://cvs.schmorp.de/libev/ev.html>) for more subtle details on
62 watcher semantics or some discussion on the available backends, or how to
63 force a specific backend with C<LIBEV_FLAGS>, or just about in any case
64 because it has much more detailed information.
65
66 =cut
67
68 package EV;
69
70 use strict;
71
72 BEGIN {
73 our $VERSION = '1.86';
74 use XSLoader;
75 XSLoader::load "EV", $VERSION;
76 }
77
78 @EV::IO::ISA =
79 @EV::Timer::ISA =
80 @EV::Periodic::ISA =
81 @EV::Signal::ISA =
82 @EV::Child::ISA =
83 @EV::Stat::ISA =
84 @EV::Idle::ISA =
85 @EV::Prepare::ISA =
86 @EV::Check::ISA =
87 @EV::Embed::ISA =
88 @EV::Fork::ISA =
89 "EV::Watcher";
90
91 =head1 BASIC INTERFACE
92
93 =over 4
94
95 =item $EV::DIED
96
97 Must contain a reference to a function that is called when a callback
98 throws an exception (with $@ containing the error). The default prints an
99 informative message and continues.
100
101 If this callback throws an exception it will be silently ignored.
102
103 =item $time = EV::time
104
105 Returns the current time in (fractional) seconds since the epoch.
106
107 =item $time = EV::now
108
109 Returns the time the last event loop iteration has been started. This
110 is the time that (relative) timers are based on, and refering to it is
111 usually faster then calling EV::time.
112
113 =item $method = EV::method
114
115 Returns an integer describing the backend used by libev (EV::METHOD_SELECT
116 or EV::METHOD_EPOLL).
117
118 =item EV::loop [$flags]
119
120 Begin checking for events and calling callbacks. It returns when a
121 callback calls EV::unloop.
122
123 The $flags argument can be one of the following:
124
125 0 as above
126 EV::LOOP_ONESHOT block at most once (wait, but do not loop)
127 EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
128
129 =item EV::unloop [$how]
130
131 When called with no arguments or an argument of EV::UNLOOP_ONE, makes the
132 innermost call to EV::loop return.
133
134 When called with an argument of EV::UNLOOP_ALL, all calls to EV::loop will return as
135 fast as possible.
136
137 =item $count = EV::loop_count
138
139 Return the number of times the event loop has polled for new
140 events. Sometiems useful as a generation counter.
141
142 =item EV::once $fh_or_undef, $events, $timeout, $cb->($revents)
143
144 This function rolls together an I/O and a timer watcher for a single
145 one-shot event without the need for managing a watcher object.
146
147 If C<$fh_or_undef> is a filehandle or file descriptor, then C<$events>
148 must be a bitset containing either C<EV::READ>, C<EV::WRITE> or C<EV::READ
149 | EV::WRITE>, indicating the type of I/O event you want to wait for. If
150 you do not want to wait for some I/O event, specify C<undef> for
151 C<$fh_or_undef> and C<0> for C<$events>).
152
153 If timeout is C<undef> or negative, then there will be no
154 timeout. Otherwise a EV::timer with this value will be started.
155
156 When an error occurs or either the timeout or I/O watcher triggers, then
157 the callback will be called with the received event set (in general
158 you can expect it to be a combination of C<EV:ERROR>, C<EV::READ>,
159 C<EV::WRITE> and C<EV::TIMEOUT>).
160
161 EV::once doesn't return anything: the watchers stay active till either
162 of them triggers, then they will be stopped and freed, and the callback
163 invoked.
164
165 =item EV::feed_fd_event ($fd, $revents)
166
167 Feed an event on a file descriptor into EV. EV will react to this call as
168 if the readyness notifications specified by C<$revents> (a combination of
169 C<EV::READ> and C<EV::WRITE>) happened on the file descriptor C<$fd>.
170
171 =item EV::feed_signal_event ($signal)
172
173 Feed a signal event into EV. EV will react to this call as if the signal
174 specified by C<$signal> had occured.
175
176 =back
177
178
179 =head2 WATCHER OBJECTS
180
181 A watcher is an object that gets created to record your interest in some
182 event. For instance, if you want to wait for STDIN to become readable, you
183 would create an EV::io watcher for that:
184
185 my $watcher = EV::io *STDIN, EV::READ, sub {
186 my ($watcher, $revents) = @_;
187 warn "yeah, STDIN should not be readable without blocking!\n"
188 };
189
190 All watchers can be active (waiting for events) or inactive (paused). Only
191 active watchers will have their callbacks invoked. All callbacks will be
192 called with at least two arguments: the watcher and a bitmask of received
193 events.
194
195 Each watcher type has its associated bit in revents, so you can use the
196 same callback for multiple watchers. The event mask is named after the
197 type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE,
198 EV::periodic sets EV::PERIODIC and so on, with the exception of I/O events
199 (which can set both EV::READ and EV::WRITE bits), and EV::timer (which
200 uses EV::TIMEOUT).
201
202 In the rare case where one wants to create a watcher but not start it at
203 the same time, each constructor has a variant with a trailing C<_ns> in
204 its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.
205
206 Please note that a watcher will automatically be stopped when the watcher
207 object is destroyed, so you I<need> to keep the watcher objects returned by
208 the constructors.
209
210 Also, all methods changing some aspect of a watcher (->set, ->priority,
211 ->fh and so on) automatically stop and start it again if it is active,
212 which means pending events get lost.
213
214 =head2 COMMON WATCHER METHODS
215
216 This section lists methods common to all watchers.
217
218 =over 4
219
220 =item $w->start
221
222 Starts a watcher if it isn't active already. Does nothing to an already
223 active watcher. By default, all watchers start out in the active state
224 (see the description of the C<_ns> variants if you need stopped watchers).
225
226 =item $w->stop
227
228 Stop a watcher if it is active. Also clear any pending events (events that
229 have been received but that didn't yet result in a callback invocation),
230 regardless of whether the watcher was active or not.
231
232 =item $bool = $w->is_active
233
234 Returns true if the watcher is active, false otherwise.
235
236 =item $current_data = $w->data
237
238 =item $old_data = $w->data ($new_data)
239
240 Queries a freely usable data scalar on the watcher and optionally changes
241 it. This is a way to associate custom data with a watcher:
242
243 my $w = EV::timer 60, 0, sub {
244 warn $_[0]->data;
245 };
246 $w->data ("print me!");
247
248 =item $current_cb = $w->cb
249
250 =item $old_cb = $w->cb ($new_cb)
251
252 Queries the callback on the watcher and optionally changes it. You can do
253 this at any time without the watcher restarting.
254
255 =item $current_priority = $w->priority
256
257 =item $old_priority = $w->priority ($new_priority)
258
259 Queries the priority on the watcher and optionally changes it. Pending
260 watchers with higher priority will be invoked first. The valid range of
261 priorities lies between EV::MAXPRI (default 2) and EV::MINPRI (default
262 -2). If the priority is outside this range it will automatically be
263 normalised to the nearest valid priority.
264
265 The default priority of any newly-created watcher is 0.
266
267 Note that the priority semantics have not yet been fleshed out and are
268 subject to almost certain change.
269
270 =item $w->invoke ($revents)
271
272 Call the callback *now* with the given event mask.
273
274 =item $w->feed_event ($revents)
275
276 Feed some events on this watcher into EV. EV will react to this call as if
277 the watcher had received the given C<$revents> mask.
278
279 =item $revents = $w->clear_pending
280
281 If the watcher is pending, this function returns clears its pending status
282 and returns its C<$revents> bitset (as if its callback was invoked). If the
283 watcher isn't pending it does nothing and returns C<0>.
284
285 =item $previous_state = $w->keepalive ($bool)
286
287 Normally, C<EV::loop> will return when there are no active watchers
288 (which is a "deadlock" because no progress can be made anymore). This is
289 convinient because it allows you to start your watchers (and your jobs),
290 call C<EV::loop> once and when it returns you know that all your jobs are
291 finished (or they forgot to register some watchers for their task :).
292
293 Sometimes, however, this gets in your way, for example when you the module
294 that calls C<EV::loop> (usually the main program) is not the same module
295 as a long-living watcher (for example a DNS client module written by
296 somebody else even). Then you might want any outstanding requests to be
297 handled, but you would not want to keep C<EV::loop> from returning just
298 because you happen to have this long-running UDP port watcher.
299
300 In this case you can clear the keepalive status, which means that even
301 though your watcher is active, it won't keep C<EV::loop> from returning.
302
303 The initial value for keepalive is true (enabled), and you cna change it
304 any time.
305
306 Example: Register an I/O watcher for some UDP socket but do not keep the
307 event loop from running just because of that watcher.
308
309 my $udp_socket = ...
310 my $udp_watcher = EV::io $udp_socket, EV::READ, sub { ... };
311 $udp_watcher->keepalive (0);
312
313 =back
314
315
316 =head2 WATCHER TYPES
317
318 Each of the following subsections describes a single watcher type.
319
320 =head3 I/O WATCHERS - is this file descriptor readable or writable?
321
322 =over 4
323
324 =item $w = EV::io $fileno_or_fh, $eventmask, $callback
325
326 =item $w = EV::io_ns $fileno_or_fh, $eventmask, $callback
327
328 As long as the returned watcher object is alive, call the C<$callback>
329 when at least one of events specified in C<$eventmask> occurs.
330
331 The $eventmask can be one or more of these constants ORed together:
332
333 EV::READ wait until read() wouldn't block anymore
334 EV::WRITE wait until write() wouldn't block anymore
335
336 The C<io_ns> variant doesn't start (activate) the newly created watcher.
337
338 =item $w->set ($fileno_or_fh, $eventmask)
339
340 Reconfigures the watcher, see the constructor above for details. Can be
341 called at any time.
342
343 =item $current_fh = $w->fh
344
345 =item $old_fh = $w->fh ($new_fh)
346
347 Returns the previously set filehandle and optionally set a new one.
348
349 =item $current_eventmask = $w->events
350
351 =item $old_eventmask = $w->events ($new_eventmask)
352
353 Returns the previously set event mask and optionally set a new one.
354
355 =back
356
357
358 =head3 TIMER WATCHERS - relative and optionally repeating timeouts
359
360 =over 4
361
362 =item $w = EV::timer $after, $repeat, $callback
363
364 =item $w = EV::timer_ns $after, $repeat, $callback
365
366 Calls the callback after C<$after> seconds (which may be fractional). If
367 C<$repeat> is non-zero, the timer will be restarted (with the $repeat
368 value as $after) after the callback returns.
369
370 This means that the callback would be called roughly after C<$after>
371 seconds, and then every C<$repeat> seconds. The timer does his best not
372 to drift, but it will not invoke the timer more often then once per event
373 loop iteration, and might drift in other cases. If that isn't acceptable,
374 look at EV::periodic, which can provide long-term stable timers.
375
376 The timer is based on a monotonic clock, that is, if somebody is sitting
377 in front of the machine while the timer is running and changes the system
378 clock, the timer will nevertheless run (roughly) the same time.
379
380 The C<timer_ns> variant doesn't start (activate) the newly created watcher.
381
382 =item $w->set ($after, $repeat)
383
384 Reconfigures the watcher, see the constructor above for details. Can be called at
385 any time.
386
387 =item $w->again
388
389 Similar to the C<start> method, but has special semantics for repeating timers:
390
391 If the timer is active and non-repeating, it will be stopped.
392
393 If the timer is active and repeating, reset the timeout to occur
394 C<$repeat> seconds after now.
395
396 If the timer is inactive and repeating, start it using the repeat value.
397
398 Otherwise do nothing.
399
400 This behaviour is useful when you have a timeout for some IO
401 operation. You create a timer object with the same value for C<$after> and
402 C<$repeat>, and then, in the read/write watcher, run the C<again> method
403 on the timeout.
404
405 =back
406
407
408 =head3 PERIODIC WATCHERS - to cron or not to cron?
409
410 =over 4
411
412 =item $w = EV::periodic $at, $interval, $reschedule_cb, $callback
413
414 =item $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
415
416 Similar to EV::timer, but is not based on relative timeouts but on
417 absolute times. Apart from creating "simple" timers that trigger "at" the
418 specified time, it can also be used for non-drifting absolute timers and
419 more complex, cron-like, setups that are not adversely affected by time
420 jumps (i.e. when the system clock is changed by explicit date -s or other
421 means such as ntpd). It is also the most complex watcher type in EV.
422
423 It has three distinct "modes":
424
425 =over 4
426
427 =item * absolute timer ($interval = $reschedule_cb = 0)
428
429 This time simply fires at the wallclock time C<$at> and doesn't repeat. It
430 will not adjust when a time jump occurs, that is, if it is to be run
431 at January 1st 2011 then it will run when the system time reaches or
432 surpasses this time.
433
434 =item * non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
435
436 In this mode the watcher will always be scheduled to time out at the
437 next C<$at + N * $interval> time (for some integer N) and then repeat,
438 regardless of any time jumps.
439
440 This can be used to create timers that do not drift with respect to system
441 time:
442
443 my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
444
445 That doesn't mean there will always be 3600 seconds in between triggers,
446 but only that the the clalback will be called when the system time shows a
447 full hour (UTC).
448
449 Another way to think about it (for the mathematically inclined) is that
450 EV::periodic will try to run the callback in this mode at the next
451 possible time where C<$time = $at (mod $interval)>, regardless of any time
452 jumps.
453
454 =item * manual reschedule mode ($reschedule_cb = coderef)
455
456 In this mode $interval and $at are both being ignored. Instead, each
457 time the periodic watcher gets scheduled, the reschedule callback
458 ($reschedule_cb) will be called with the watcher as first, and the current
459 time as second argument.
460
461 I<This callback MUST NOT stop or destroy this or any other periodic
462 watcher, ever>. If you need to stop it, return 1e30 and stop it
463 afterwards.
464
465 It must return the next time to trigger, based on the passed time value
466 (that is, the lowest time value larger than to the second argument). It
467 will usually be called just before the callback will be triggered, but
468 might be called at other times, too.
469
470 This can be used to create very complex timers, such as a timer that
471 triggers on each midnight, local time (actually 24 hours after the last
472 midnight, to keep the example simple. If you know a way to do it correctly
473 in about the same space (without requiring elaborate modules), drop me a
474 note :):
475
476 my $daily = EV::periodic 0, 0, sub {
477 my ($w, $now) = @_;
478
479 use Time::Local ();
480 my (undef, undef, undef, $d, $m, $y) = localtime $now;
481 86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
482 }, sub {
483 print "it's midnight or likely shortly after, now\n";
484 };
485
486 =back
487
488 The C<periodic_ns> variant doesn't start (activate) the newly created watcher.
489
490 =item $w->set ($at, $interval, $reschedule_cb)
491
492 Reconfigures the watcher, see the constructor above for details. Can be called at
493 any time.
494
495 =item $w->again
496
497 Simply stops and starts the watcher again.
498
499 =item $time = $w->at
500
501 Return the time that the watcher is expected to trigger next.
502
503 =back
504
505
506 =head3 SIGNAL WATCHERS - signal me when a signal gets signalled!
507
508 =over 4
509
510 =item $w = EV::signal $signal, $callback
511
512 =item $w = EV::signal_ns $signal, $callback
513
514 Call the callback when $signal is received (the signal can be specified by
515 number or by name, just as with C<kill> or C<%SIG>).
516
517 EV will grab the signal for the process (the kernel only allows one
518 component to receive a signal at a time) when you start a signal watcher,
519 and removes it again when you stop it. Perl does the same when you
520 add/remove callbacks to C<%SIG>, so watch out.
521
522 You can have as many signal watchers per signal as you want.
523
524 The C<signal_ns> variant doesn't start (activate) the newly created watcher.
525
526 =item $w->set ($signal)
527
528 Reconfigures the watcher, see the constructor above for details. Can be
529 called at any time.
530
531 =item $current_signum = $w->signal
532
533 =item $old_signum = $w->signal ($new_signal)
534
535 Returns the previously set signal (always as a number not name) and
536 optionally set a new one.
537
538 =back
539
540
541 =head3 CHILD WATCHERS - watch out for process status changes
542
543 =over 4
544
545 =item $w = EV::child $pid, $callback
546
547 =item $w = EV::child_ns $pid, $callback
548
549 Call the callback when a status change for pid C<$pid> (or any pid if
550 C<$pid> is 0) has been received. More precisely: when the process receives
551 a C<SIGCHLD>, EV will fetch the outstanding exit/wait status for all
552 changed/zombie children and call the callback.
553
554 It is valid (and fully supported) to install a child watcher after a child
555 has exited but before the event loop has started its next iteration (for
556 example, first you C<fork>, then the new child process might exit, and
557 only then do you install a child watcher in the parent for the new pid).
558
559 You can access both exit (or tracing) status and pid by using the
560 C<rstatus> and C<rpid> methods on the watcher object.
561
562 You can have as many pid watchers per pid as you want, they will all be
563 called.
564
565 The C<child_ns> variant doesn't start (activate) the newly created watcher.
566
567 =item $w->set ($pid)
568
569 Reconfigures the watcher, see the constructor above for details. Can be called at
570 any time.
571
572 =item $current_pid = $w->pid
573
574 =item $old_pid = $w->pid ($new_pid)
575
576 Returns the previously set process id and optionally set a new one.
577
578 =item $exit_status = $w->rstatus
579
580 Return the exit/wait status (as returned by waitpid, see the waitpid entry
581 in perlfunc).
582
583 =item $pid = $w->rpid
584
585 Return the pid of the awaited child (useful when you have installed a
586 watcher for all pids).
587
588 =back
589
590
591 =head3 STAT WATCHERS - did the file attributes just change?
592
593 =over 4
594
595 =item $w = EV::stat $path, $interval, $callback
596
597 =item $w = EV::stat_ns $path, $interval, $callback
598
599 Call the callback when a file status change has been detected on
600 C<$path>. The C<$path> does not need to exist, changing from "path exists"
601 to "path does not exist" is a status change like any other.
602
603 The C<$interval> is a recommended polling interval for systems where
604 OS-supported change notifications don't exist or are not supported. If
605 you use C<0> then an unspecified default is used (which is highly
606 recommended!), which is to be expected to be around five seconds usually.
607
608 This watcher type is not meant for massive numbers of stat watchers,
609 as even with OS-supported change notifications, this can be
610 resource-intensive.
611
612 The C<stat_ns> variant doesn't start (activate) the newly created watcher.
613
614 =item ... = $w->stat
615
616 This call is very similar to the perl C<stat> built-in: It stats (using
617 C<lstat>) the path specified in the watcher and sets perls stat cache (as
618 well as EV's idea of the current stat values) to the values found.
619
620 In scalar context, a boolean is return indicating success or failure of
621 the stat. In list context, the same 13-value list as with stat is returned
622 (except that the blksize and blocks fields are not reliable).
623
624 In the case of an error, errno is set to C<ENOENT> (regardless of the
625 actual error value) and the C<nlink> value is forced to zero (if the stat
626 was successful then nlink is guaranteed to be non-zero).
627
628 See also the next two entries for more info.
629
630 =item ... = $w->attr
631
632 Just like C<< $w->stat >>, but without the initial stat'ing: this returns
633 the values most recently detected by EV. See the next entry for more info.
634
635 =item ... = $w->prev
636
637 Just like C<< $w->stat >>, but without the initial stat'ing: this returns
638 the previous set of values, before the change.
639
640 That is, when the watcher callback is invoked, C<< $w->prev >> will be set
641 to the values found I<before> a change was detected, while C<< $w->attr >>
642 returns the values found leading to the change detection. The difference (if any)
643 between C<prev> and C<attr> is what triggered the callback.
644
645 If you did something to the filesystem object and do not want to trigger
646 yet another change, you can call C<stat> to update EV's idea of what the
647 current attributes are.
648
649 =item $w->set ($path, $interval)
650
651 Reconfigures the watcher, see the constructor above for details. Can be
652 called at any time.
653
654 =item $current_path = $w->path
655
656 =item $old_path = $w->path ($new_path)
657
658 Returns the previously set path and optionally set a new one.
659
660 =item $current_interval = $w->interval
661
662 =item $old_interval = $w->interval ($new_interval)
663
664 Returns the previously set interval and optionally set a new one. Can be
665 used to query the actual interval used.
666
667 =back
668
669
670 =head3 IDLE WATCHERS - when you've got nothing better to do...
671
672 =over 4
673
674 =item $w = EV::idle $callback
675
676 =item $w = EV::idle_ns $callback
677
678 Call the callback when there are no other pending watchers of the same or
679 higher priority (excluding check, prepare and other idle watchers of the
680 same or lower priority, of course). They are called idle watchers because
681 when the watcher is the highest priority pending event in the process, the
682 process is considered to be idle at that priority.
683
684 If you want a watcher that is only ever called when I<no> other events are
685 outstanding you have to set the priority to C<EV::MINPRI>.
686
687 The process will not block as long as any idle watchers are active, and
688 they will be called repeatedly until stopped.
689
690 For example, if you have idle watchers at priority C<0> and C<1>, and
691 an I/O watcher at priority C<0>, then the idle watcher at priority C<1>
692 and the I/O watcher will always run when ready. Only when the idle watcher
693 at priority C<1> is stopped and the I/O watcher at priority C<0> is not
694 pending with the C<0>-priority idle watcher be invoked.
695
696 The C<idle_ns> variant doesn't start (activate) the newly created watcher.
697
698 =back
699
700
701 =head3 PREPARE WATCHERS - customise your event loop!
702
703 =over 4
704
705 =item $w = EV::prepare $callback
706
707 =item $w = EV::prepare_ns $callback
708
709 Call the callback just before the process would block. You can still
710 create/modify any watchers at this point.
711
712 See the EV::check watcher, below, for explanations and an example.
713
714 The C<prepare_ns> variant doesn't start (activate) the newly created watcher.
715
716 =back
717
718
719 =head3 CHECK WATCHERS - customise your event loop even more!
720
721 =over 4
722
723 =item $w = EV::check $callback
724
725 =item $w = EV::check_ns $callback
726
727 Call the callback just after the process wakes up again (after it has
728 gathered events), but before any other callbacks have been invoked.
729
730 This is used to integrate other event-based software into the EV
731 mainloop: You register a prepare callback and in there, you create io and
732 timer watchers as required by the other software. Here is a real-world
733 example of integrating Net::SNMP (with some details left out):
734
735 our @snmp_watcher;
736
737 our $snmp_prepare = EV::prepare sub {
738 # do nothing unless active
739 $dispatcher->{_event_queue_h}
740 or return;
741
742 # make the dispatcher handle any outstanding stuff
743 ... not shown
744
745 # create an I/O watcher for each and every socket
746 @snmp_watcher = (
747 (map { EV::io $_, EV::READ, sub { } }
748 keys %{ $dispatcher->{_descriptors} }),
749
750 EV::timer +($event->[Net::SNMP::Dispatcher::_ACTIVE]
751 ? $event->[Net::SNMP::Dispatcher::_TIME] - EV::now : 0),
752 0, sub { },
753 );
754 };
755
756 The callbacks are irrelevant (and are not even being called), the
757 only purpose of those watchers is to wake up the process as soon as
758 one of those events occurs (socket readable, or timer timed out). The
759 corresponding EV::check watcher will then clean up:
760
761 our $snmp_check = EV::check sub {
762 # destroy all watchers
763 @snmp_watcher = ();
764
765 # make the dispatcher handle any new stuff
766 ... not shown
767 };
768
769 The callbacks of the created watchers will not be called as the watchers
770 are destroyed before this cna happen (remember EV::check gets called
771 first).
772
773 The C<check_ns> variant doesn't start (activate) the newly created watcher.
774
775 =back
776
777
778 =head3 FORK WATCHERS - the audacity to resume the event loop after a fork
779
780 Fork watchers are called when a C<fork ()> was detected. The invocation
781 is done before the event loop blocks next and before C<check> watchers
782 are being called, and only in the child after the fork.
783
784 =over 4
785
786 =item $w = EV::fork $callback
787
788 =item $w = EV::fork_ns $callback
789
790 Call the callback before the event loop is resumed in the child process
791 after a fork.
792
793 The C<fork_ns> variant doesn't start (activate) the newly created watcher.
794
795 =back
796
797
798 =head1 PERL SIGNALS
799
800 While Perl signal handling (C<%SIG>) is not affected by EV, the behaviour
801 with EV is as the same as any other C library: Perl-signals will only be
802 handled when Perl runs, which means your signal handler might be invoked
803 only the next time an event callback is invoked.
804
805 The solution is to use EV signal watchers (see C<EV::signal>), which will
806 ensure proper operations with regards to other event watchers.
807
808 If you cannot do this for whatever reason, you can also force a watcher
809 to be called on every event loop iteration by installing a C<EV::check>
810 watcher:
811
812 my $async_check = EV::check sub { };
813
814 This ensures that perl shortly gets into control for a short time, and
815 also ensures slower overall operation.
816
817 =head1 THREADS
818
819 Threads are not supported by this module in any way. Perl pseudo-threads
820 is evil stuff and must die. As soon as Perl gains real threads I will work
821 on thread support for it.
822
823 =head1 FORK
824
825 Most of the "improved" event delivering mechanisms of modern operating
826 systems have quite a few problems with fork(2) (to put it bluntly: it is
827 not supported and usually destructive). Libev makes it possible to work
828 around this by having a function that recreates the kernel state after
829 fork in the child.
830
831 On non-win32 platforms, this module requires the pthread_atfork
832 functionality to do this automatically for you. This function is quite
833 buggy on most BSDs, though, so YMMV. The overhead for this is quite
834 negligible, because everything the function currently does is set a flag
835 that is checked only when the event loop gets used the next time, so when
836 you do fork but not use EV, the overhead is minimal.
837
838 On win32, there is no notion of fork so all this doesn't apply, of course.
839
840 =cut
841
842 our $DIED = sub {
843 warn "EV: error in callback (ignoring): $@";
844 };
845
846 default_loop
847 or die 'EV: cannot initialise libev backend. bad $ENV{LIBEV_FLAGS}?';
848
849 1;
850
851 =head1 SEE ALSO
852
853 L<EV::ADNS> (asynchronous dns), L<Glib::EV> (makes Glib/Gtk2 use EV as
854 event loop), L<Coro::EV> (efficient coroutines with EV).
855
856 =head1 AUTHOR
857
858 Marc Lehmann <schmorp@schmorp.de>
859 http://home.schmorp.de/
860
861 =cut
862