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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
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File Contents

# User Rev Content
1 root 1.1 =head1 NAME
2    
3 root 1.20 EV - perl interface to libev, a high performance full-featured event loop
4 root 1.1
5     =head1 SYNOPSIS
6    
7 root 1.11 use EV;
8    
9 root 1.20 # TIMERS
10 root 1.11
11     my $w = EV::timer 2, 0, sub {
12     warn "is called after 2s";
13     };
14    
15 root 1.35 my $w = EV::timer 2, 2, sub {
16     warn "is called roughly every 2s (repeat = 2)";
17 root 1.11 };
18    
19     undef $w; # destroy event watcher again
20    
21 root 1.30 my $w = EV::periodic 0, 60, 0, sub {
22 root 1.11 warn "is called every minute, on the minute, exactly";
23     };
24    
25     # IO
26    
27 root 1.20 my $w = EV::io *STDIN, EV::READ, sub {
28 root 1.35 my ($w, $revents) = @_; # all callbacks receive the watcher and event mask
29 root 1.20 warn "stdin is readable, you entered: ", <STDIN>;
30 root 1.11 };
31    
32     # SIGNALS
33    
34     my $w = EV::signal 'QUIT', sub {
35     warn "sigquit received\n";
36     };
37    
38 root 1.16 # CHILD/PID STATUS CHANGES
39    
40     my $w = EV::child 666, sub {
41 root 1.27 my ($w, $revents) = @_;
42     my $status = $w->rstatus;
43 root 1.16 };
44 root 1.54
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 root 1.11
51     # MAINLOOP
52 root 1.39 EV::loop; # loop until EV::unloop is called or all watchers stop
53 root 1.20 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 root 1.2
56 root 1.1 =head1 DESCRIPTION
57    
58 root 1.16 This module provides an interface to libev
59 root 1.52 (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 root 1.62 force a specific backend with C<LIBEV_FLAGS>, or just about in any case
64     because it has much more detailed information.
65 root 1.1
66     =cut
67    
68     package EV;
69    
70     use strict;
71    
72     BEGIN {
73 root 1.71 our $VERSION = '1.86';
74 root 1.1 use XSLoader;
75     XSLoader::load "EV", $VERSION;
76     }
77    
78 root 1.49 @EV::IO::ISA =
79 root 1.18 @EV::Timer::ISA =
80     @EV::Periodic::ISA =
81     @EV::Signal::ISA =
82 root 1.56 @EV::Child::ISA =
83     @EV::Stat::ISA =
84 root 1.18 @EV::Idle::ISA =
85     @EV::Prepare::ISA =
86     @EV::Check::ISA =
87 root 1.54 @EV::Embed::ISA =
88 root 1.56 @EV::Fork::ISA =
89     "EV::Watcher";
90 root 1.15
91 root 1.8 =head1 BASIC INTERFACE
92 root 1.1
93     =over 4
94    
95 root 1.8 =item $EV::DIED
96    
97     Must contain a reference to a function that is called when a callback
98 root 1.67 throws an exception (with $@ containing the error). The default prints an
99 root 1.8 informative message and continues.
100    
101     If this callback throws an exception it will be silently ignored.
102    
103 root 1.20 =item $time = EV::time
104    
105     Returns the current time in (fractional) seconds since the epoch.
106    
107 root 1.2 =item $time = EV::now
108    
109 root 1.20 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 root 1.41 =item $method = EV::method
114 root 1.20
115     Returns an integer describing the backend used by libev (EV::METHOD_SELECT
116     or EV::METHOD_EPOLL).
117    
118     =item EV::loop [$flags]
119 root 1.2
120 root 1.20 Begin checking for events and calling callbacks. It returns when a
121 root 1.39 callback calls EV::unloop.
122 root 1.2
123 root 1.20 The $flags argument can be one of the following:
124 root 1.2
125 root 1.20 0 as above
126     EV::LOOP_ONESHOT block at most once (wait, but do not loop)
127     EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
128 root 1.2
129 root 1.39 =item EV::unloop [$how]
130 root 1.2
131 root 1.39 When called with no arguments or an argument of EV::UNLOOP_ONE, makes the
132     innermost call to EV::loop return.
133 root 1.2
134 root 1.39 When called with an argument of EV::UNLOOP_ALL, all calls to EV::loop will return as
135 root 1.20 fast as possible.
136 root 1.2
137 root 1.60 =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 root 1.48 =item EV::once $fh_or_undef, $events, $timeout, $cb->($revents)
143 root 1.47
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 root 1.65 =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 root 1.20 =back
177    
178 root 1.65
179 root 1.54 =head2 WATCHER OBJECTS
180 root 1.2
181 root 1.20 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 root 1.2
190 root 1.20 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 root 1.62 EV::periodic sets EV::PERIODIC and so on, with the exception of I/O events
199 root 1.20 (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 root 1.23 object is destroyed, so you I<need> to keep the watcher objects returned by
208 root 1.20 the constructors.
209    
210 root 1.23 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 root 1.54 =head2 COMMON WATCHER METHODS
215 root 1.20
216 root 1.54 This section lists methods common to all watchers.
217 root 1.20
218     =over 4
219 root 1.2
220 root 1.20 =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 root 1.2
228 root 1.20 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 root 1.62 regardless of whether the watcher was active or not.
231 root 1.2
232 root 1.20 =item $bool = $w->is_active
233 root 1.2
234 root 1.20 Returns true if the watcher is active, false otherwise.
235    
236 root 1.30 =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 root 1.20 =item $current_cb = $w->cb
249    
250     =item $old_cb = $w->cb ($new_cb)
251    
252 root 1.23 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 root 1.24 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 root 1.23 normalised to the nearest valid priority.
264    
265 root 1.50 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 root 1.20
270 root 1.65 =item $w->invoke ($revents)
271 root 1.20
272     Call the callback *now* with the given event mask.
273    
274 root 1.65 =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 root 1.50 =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 root 1.62 Example: Register an I/O watcher for some UDP socket but do not keep the
307 root 1.50 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 root 1.20
313 root 1.54 =back
314    
315    
316     =head2 WATCHER TYPES
317    
318     Each of the following subsections describes a single watcher type.
319    
320 root 1.62 =head3 I/O WATCHERS - is this file descriptor readable or writable?
321 root 1.54
322     =over 4
323    
324 root 1.20 =item $w = EV::io $fileno_or_fh, $eventmask, $callback
325 root 1.2
326 root 1.20 =item $w = EV::io_ns $fileno_or_fh, $eventmask, $callback
327 root 1.7
328 root 1.20 As long as the returned watcher object is alive, call the C<$callback>
329 root 1.54 when at least one of events specified in C<$eventmask> occurs.
330 root 1.2
331 root 1.20 The $eventmask can be one or more of these constants ORed together:
332 root 1.2
333     EV::READ wait until read() wouldn't block anymore
334     EV::WRITE wait until write() wouldn't block anymore
335 root 1.7
336 root 1.20 The C<io_ns> variant doesn't start (activate) the newly created watcher.
337 root 1.2
338 root 1.20 =item $w->set ($fileno_or_fh, $eventmask)
339 root 1.10
340 root 1.20 Reconfigures the watcher, see the constructor above for details. Can be
341     called at any time.
342 root 1.10
343 root 1.20 =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 root 1.10
349 root 1.20 =item $current_eventmask = $w->events
350    
351     =item $old_eventmask = $w->events ($new_eventmask)
352 root 1.10
353 root 1.20 Returns the previously set event mask and optionally set a new one.
354 root 1.10
355 root 1.54 =back
356    
357    
358     =head3 TIMER WATCHERS - relative and optionally repeating timeouts
359    
360     =over 4
361 root 1.10
362 root 1.20 =item $w = EV::timer $after, $repeat, $callback
363 root 1.2
364 root 1.20 =item $w = EV::timer_ns $after, $repeat, $callback
365 root 1.2
366 root 1.53 Calls the callback after C<$after> seconds (which may be fractional). If
367     C<$repeat> is non-zero, the timer will be restarted (with the $repeat
368     value as $after) after the callback returns.
369 root 1.2
370 root 1.20 This means that the callback would be called roughly after C<$after>
371 root 1.39 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 root 1.2
376 root 1.39 The timer is based on a monotonic clock, that is, if somebody is sitting
377 root 1.20 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 root 1.2
380 root 1.20 The C<timer_ns> variant doesn't start (activate) the newly created watcher.
381    
382     =item $w->set ($after, $repeat)
383    
384 root 1.54 Reconfigures the watcher, see the constructor above for details. Can be called at
385 root 1.20 any time.
386    
387     =item $w->again
388    
389     Similar to the C<start> method, but has special semantics for repeating timers:
390    
391 root 1.39 If the timer is active and non-repeating, it will be stopped.
392    
393 root 1.20 If the timer is active and repeating, reset the timeout to occur
394     C<$repeat> seconds after now.
395    
396 root 1.39 If the timer is inactive and repeating, start it using the repeat value.
397 root 1.20
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 root 1.54 =back
406    
407    
408     =head3 PERIODIC WATCHERS - to cron or not to cron?
409    
410     =over 4
411 root 1.20
412 root 1.30 =item $w = EV::periodic $at, $interval, $reschedule_cb, $callback
413 root 1.20
414 root 1.30 =item $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
415    
416     Similar to EV::timer, but is not based on relative timeouts but on
417     absolute times. Apart from creating "simple" timers that trigger "at" the
418     specified time, it can also be used for non-drifting absolute timers and
419     more complex, cron-like, setups that are not adversely affected by time
420     jumps (i.e. when the system clock is changed by explicit date -s or other
421     means such as ntpd). It is also the most complex watcher type in EV.
422    
423     It has three distinct "modes":
424    
425     =over 4
426 root 1.2
427 root 1.30 =item * absolute timer ($interval = $reschedule_cb = 0)
428 root 1.2
429 root 1.30 This time simply fires at the wallclock time C<$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 root 1.2
434 root 1.30 =item * non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
435 root 1.2
436 root 1.30 In this mode the watcher will always be scheduled to time out at the
437     next C<$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 $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
444    
445     That doesn't mean there will always be 3600 seconds in between triggers,
446     but only that the the clalback will be called when the system time shows a
447     full hour (UTC).
448 root 1.2
449 root 1.7 Another way to think about it (for the mathematically inclined) is that
450 root 1.30 EV::periodic will try to run the callback in this mode at the next
451     possible time where C<$time = $at (mod $interval)>, regardless of any time
452     jumps.
453    
454     =item * manual reschedule mode ($reschedule_cb = coderef)
455    
456 root 1.37 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 root 1.30
461 root 1.31 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 root 1.30
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 root 1.7
486 root 1.30 =back
487 root 1.20
488     The C<periodic_ns> variant doesn't start (activate) the newly created watcher.
489 root 1.2
490 root 1.30 =item $w->set ($at, $interval, $reschedule_cb)
491 root 1.11
492 root 1.54 Reconfigures the watcher, see the constructor above for details. Can be called at
493 root 1.20 any time.
494    
495 root 1.30 =item $w->again
496    
497     Simply stops and starts the watcher again.
498    
499 root 1.71 =item $time = $w->at
500    
501     Return the time that the watcher is expected to trigger next.
502    
503 root 1.54 =back
504    
505    
506     =head3 SIGNAL WATCHERS - signal me when a signal gets signalled!
507    
508     =over 4
509 root 1.20
510     =item $w = EV::signal $signal, $callback
511    
512     =item $w = EV::signal_ns $signal, $callback
513 root 1.11
514 root 1.54 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 root 1.2
517 root 1.11 EV will grab the signal for the process (the kernel only allows one
518 root 1.20 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 root 1.54 add/remove callbacks to C<%SIG>, so watch out.
521 root 1.20
522     You can have as many signal watchers per signal as you want.
523 root 1.2
524 root 1.20 The C<signal_ns> variant doesn't start (activate) the newly created watcher.
525 root 1.2
526 root 1.20 =item $w->set ($signal)
527 root 1.2
528 root 1.54 Reconfigures the watcher, see the constructor above for details. Can be
529     called at any time.
530 root 1.20
531 root 1.22 =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 root 1.54 =back
539    
540    
541     =head3 CHILD WATCHERS - watch out for process status changes
542    
543     =over 4
544 root 1.20
545     =item $w = EV::child $pid, $callback
546    
547     =item $w = EV::child_ns $pid, $callback
548    
549 root 1.54 Call the callback when a status change for pid C<$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 root 1.20 changed/zombie children and call the callback.
553    
554 root 1.54 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 root 1.20
562 root 1.54 You can have as many pid watchers per pid as you want, they will all be
563     called.
564 root 1.20
565     The C<child_ns> variant doesn't start (activate) the newly created watcher.
566    
567     =item $w->set ($pid)
568 root 1.1
569 root 1.54 Reconfigures the watcher, see the constructor above for details. Can be called at
570 root 1.20 any time.
571 root 1.2
572 root 1.22 =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 root 1.27 =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 root 1.54 =back
589    
590    
591 root 1.56 =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 root 1.57 =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 root 1.56 =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 root 1.54 =head3 IDLE WATCHERS - when you've got nothing better to do...
671    
672     =over 4
673 root 1.2
674 root 1.20 =item $w = EV::idle $callback
675 root 1.2
676 root 1.20 =item $w = EV::idle_ns $callback
677 root 1.2
678 root 1.62 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 root 1.2
687 root 1.20 The process will not block as long as any idle watchers are active, and
688     they will be called repeatedly until stopped.
689 root 1.2
690 root 1.62 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 root 1.20 The C<idle_ns> variant doesn't start (activate) the newly created watcher.
697 root 1.2
698 root 1.54 =back
699    
700    
701     =head3 PREPARE WATCHERS - customise your event loop!
702    
703     =over 4
704 root 1.2
705 root 1.20 =item $w = EV::prepare $callback
706 root 1.1
707 root 1.20 =item $w = EV::prepare_ns $callback
708 root 1.1
709 root 1.20 Call the callback just before the process would block. You can still
710     create/modify any watchers at this point.
711 root 1.1
712 root 1.20 See the EV::check watcher, below, for explanations and an example.
713 root 1.2
714 root 1.20 The C<prepare_ns> variant doesn't start (activate) the newly created watcher.
715 root 1.2
716 root 1.54 =back
717    
718    
719     =head3 CHECK WATCHERS - customise your event loop even more!
720    
721     =over 4
722 root 1.2
723 root 1.20 =item $w = EV::check $callback
724 root 1.2
725 root 1.20 =item $w = EV::check_ns $callback
726 root 1.10
727 root 1.20 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 root 1.10
730 root 1.20 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 root 1.10
735 root 1.20 our @snmp_watcher;
736 root 1.2
737 root 1.20 our $snmp_prepare = EV::prepare sub {
738     # do nothing unless active
739     $dispatcher->{_event_queue_h}
740     or return;
741 root 1.2
742 root 1.20 # make the dispatcher handle any outstanding stuff
743 root 1.45 ... not shown
744 root 1.2
745 root 1.62 # create an I/O watcher for each and every socket
746 root 1.20 @snmp_watcher = (
747     (map { EV::io $_, EV::READ, sub { } }
748     keys %{ $dispatcher->{_descriptors} }),
749 root 1.45
750     EV::timer +($event->[Net::SNMP::Dispatcher::_ACTIVE]
751     ? $event->[Net::SNMP::Dispatcher::_TIME] - EV::now : 0),
752     0, sub { },
753 root 1.20 );
754     };
755 root 1.2
756 root 1.45 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 root 1.2
761 root 1.20 our $snmp_check = EV::check sub {
762     # destroy all watchers
763     @snmp_watcher = ();
764 root 1.2
765 root 1.20 # make the dispatcher handle any new stuff
766 root 1.45 ... not shown
767 root 1.20 };
768 root 1.2
769 root 1.20 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 root 1.2
773 root 1.20 The C<check_ns> variant doesn't start (activate) the newly created watcher.
774 root 1.1
775     =back
776    
777 root 1.54
778 root 1.56 =head3 FORK WATCHERS - the audacity to resume the event loop after a fork
779 root 1.54
780 root 1.56 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 root 1.54
784 root 1.56 =over 4
785 root 1.54
786 root 1.56 =item $w = EV::fork $callback
787 root 1.54
788 root 1.56 =item $w = EV::fork_ns $callback
789 root 1.54
790 root 1.56 Call the callback before the event loop is resumed in the child process
791     after a fork.
792 root 1.54
793 root 1.56 The C<fork_ns> variant doesn't start (activate) the newly created watcher.
794 root 1.54
795     =back
796    
797    
798 root 1.61 =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 root 1.13 =head1 THREADS
818    
819 root 1.45 Threads are not supported by this module in any way. Perl pseudo-threads
820 root 1.46 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 root 1.13
840 root 1.1 =cut
841    
842 root 1.8 our $DIED = sub {
843     warn "EV: error in callback (ignoring): $@";
844     };
845    
846 root 1.28 default_loop
847 root 1.68 or die 'EV: cannot initialise libev backend. bad $ENV{LIBEV_FLAGS}?';
848 root 1.1
849     1;
850    
851 root 1.3 =head1 SEE ALSO
852    
853 root 1.59 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 root 1.3
856 root 1.1 =head1 AUTHOR
857    
858     Marc Lehmann <schmorp@schmorp.de>
859     http://home.schmorp.de/
860    
861     =cut
862