ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/EV/README
(Generate patch)

Comparing EV/README (file contents):
Revision 1.2 by root, Sat Oct 27 19:11:27 2007 UTC vs.
Revision 1.18 by root, Tue Dec 11 21:18:25 2007 UTC

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

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines