1AnyEvent(3) User Contributed Perl Documentation AnyEvent(3)
2
6 AnyEvent - the DBI of event loop programming
7 EV, Event, Glib, Tk, UV, Perl, Event::Lib, Irssi, rxvt-unicode,
9 IO::Async, Qt, FLTK and POE are various supported event
10 loops/environments.
11
13 use AnyEvent;
14 # if you prefer function calls, look at the AE manpage for
16 # an alternative API.
17 # file handle or descriptor readable
19 my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
20 # one-shot or repeating timers
22 my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
23 my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
24 print AnyEvent->now; # prints current event loop time
26 print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
27 # POSIX signal
29 my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
30 # child process exit
32 my $w = AnyEvent->child (pid => $pid, cb => sub {
33 my ($pid, $status) = @_;
34 ...
35 });
36 # called when event loop idle (if applicable)
38 my $w = AnyEvent->idle (cb => sub { ... });
39 my $w = AnyEvent->condvar; # stores whether a condition was flagged
41 $w->send; # wake up current and all future recv's
42 $w->recv; # enters "main loop" till $condvar gets ->send
43 # use a condvar in callback mode:
44 $w->cb (sub { $_[0]->recv });
45
47 This manpage is mainly a reference manual. If you are interested in a
48 tutorial or some gentle introduction, have a look at the
49 AnyEvent::Intro manpage.
50
52 An FAQ document is available as AnyEvent::FAQ.
53 There also is a mailinglist for discussing all things AnyEvent, and an
55 IRC channel, too.
56 See the AnyEvent project page at the Schmorpforge Ta-Sa Software
58 Repository, at <http://anyevent.schmorp.de>, for more info.
59
61 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
62 nowadays. So what is different about AnyEvent?
63 Executive Summary: AnyEvent is compatible, AnyEvent is free of policy
65 and AnyEvent is small and efficient.
66 First and foremost, AnyEvent is not an event model itself, it only
68 interfaces to whatever event model the main program happens to use, in
69 a pragmatic way. For event models and certain classes of immortals
70 alike, the statement "there can only be one" is a bitter reality: In
71 general, only one event loop can be active at the same time in a
72 process. AnyEvent cannot change this, but it can hide the differences
73 between those event loops.
74 The goal of AnyEvent is to offer module authors the ability to do event
76 programming (waiting for I/O or timer events) without subscribing to a
77 religion, a way of living, and most importantly: without forcing your
78 module users into the same thing by forcing them to use the same event
79 model you use.
80 For modules like POE or IO::Async (which is a total misnomer as it is
82 actually doing all I/O synchronously...), using them in your module is
83 like joining a cult: After you join, you are dependent on them and you
84 cannot use anything else, as they are simply incompatible to everything
85 that isn't them. What's worse, all the potential users of your module
86 are also forced to use the same event loop you use.
87 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
89 fine. AnyEvent + Tk works fine etc. etc. but none of these work
90 together with the rest: POE + EV? No go. Tk + Event? No go. Again: if
91 your module uses one of those, every user of your module has to use it,
92 too. But if your module uses AnyEvent, it works transparently with all
93 event models it supports (including stuff like IO::Async, as long as
94 those use one of the supported event loops. It is easy to add new event
95 loops to AnyEvent, too, so it is future-proof).
96 In addition to being free of having to use the one and only true event
98 model, AnyEvent also is free of bloat and policy: with POE or similar
99 modules, you get an enormous amount of code and strict rules you have
100 to follow. AnyEvent, on the other hand, is lean and to the point, by
101 only offering the functionality that is necessary, in as thin as a
102 wrapper as technically possible.
103 Of course, AnyEvent comes with a big (and fully optional!) toolbox of
105 useful functionality, such as an asynchronous DNS resolver, 100% non-
106 blocking connects (even with TLS/SSL, IPv6 and on broken platforms such
107 as Windows) and lots of real-world knowledge and workarounds for
108 platform bugs and differences.
109 Now, if you do want lots of policy (this can arguably be somewhat
111 useful) and you want to force your users to use the one and only event
112 model, you should not use this module.
113
115 AnyEvent provides a uniform interface to various event loops. This
116 allows module authors to use event loop functionality without forcing
117 module users to use a specific event loop implementation (since more
118 than one event loop cannot coexist peacefully).
119 The interface itself is vaguely similar, but not identical to the Event
121 module.
122 During the first call of any watcher-creation method, the module tries
124 to detect the currently loaded event loop by probing whether one of the
125 following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
126 Tk, Event::Lib, Qt, POE. The first one found is used. If none are
127 detected, the module tries to load the first four modules in the order
128 given; but note that if EV is not available, the pure-perl
129 AnyEvent::Loop should always work, so the other two are not normally
130 tried.
131 Because AnyEvent first checks for modules that are already loaded,
133 loading an event model explicitly before first using AnyEvent will
134 likely make that model the default. For example:
135 use Tk;
137 use AnyEvent;
138 # .. AnyEvent will likely default to Tk
140 The likely means that, if any module loads another event model and
142 starts using it, all bets are off - this case should be very rare
143 though, as very few modules hardcode event loops without announcing
144 this very loudly.
145 The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
147 Like other event modules you can load it explicitly and enjoy the high
148 availability of that event loop :)
149
151 AnyEvent has the central concept of a watcher, which is an object that
152 stores relevant data for each kind of event you are waiting for, such
153 as the callback to call, the file handle to watch, etc.
154 These watchers are normal Perl objects with normal Perl lifetime. After
156 creating a watcher it will immediately "watch" for events and invoke
157 the callback when the event occurs (of course, only when the event
158 model is in control).
159 Note that callbacks must not permanently change global variables
161 potentially in use by the event loop (such as $_ or $[) and that
162 callbacks must not "die". The former is good programming practice in
163 Perl and the latter stems from the fact that exception handling differs
164 widely between event loops.
165 To disable a watcher you have to destroy it (e.g. by setting the
167 variable you store it in to "undef" or otherwise deleting all
168 references to it).
169 All watchers are created by calling a method on the "AnyEvent" class.
171 Many watchers either are used with "recursion" (repeating timers for
173 example), or need to refer to their watcher object in other ways.
174 One way to achieve that is this pattern:
176 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
178 # you can use $w here, for example to undef it
179 undef $w;
180 });
181 Note that "my $w; $w =" combination. This is necessary because in Perl,
183 my variables are only visible after the statement in which they are
184 declared.
185 I/O WATCHERS
187 $w = AnyEvent->io (
188 fh => <filehandle_or_fileno>,
189 poll => <"r" or "w">,
190 cb => <callback>,
191 );
192 You can create an I/O watcher by calling the "AnyEvent->io" method with
194 the following mandatory key-value pairs as arguments:
195 "fh" is the Perl file handle (or a naked file descriptor) to watch for
197 events (AnyEvent might or might not keep a reference to this file
198 handle). Note that only file handles pointing to things for which non-
199 blocking operation makes sense are allowed. This includes sockets, most
200 character devices, pipes, fifos and so on, but not for example files or
201 block devices.
202 "poll" must be a string that is either "r" or "w", which creates a
204 watcher waiting for "r"eadable or "w"ritable events, respectively.
205 "cb" is the callback to invoke each time the file handle becomes ready.
207 Although the callback might get passed parameters, their value and
209 presence is undefined and you cannot rely on them. Portable AnyEvent
210 callbacks cannot use arguments passed to I/O watcher callbacks.
211 The I/O watcher might use the underlying file descriptor or a copy of
213 it. You must not close a file handle as long as any watcher is active
214 on the underlying file descriptor.
215 Some event loops issue spurious readiness notifications, so you should
217 always use non-blocking calls when reading/writing from/to your file
218 handles.
219 Example: wait for readability of STDIN, then read a line and disable
221 the watcher.
222 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
224 chomp (my $input = <STDIN>);
225 warn "read: $input\n";
226 undef $w;
227 });
228 TIME WATCHERS
230 $w = AnyEvent->timer (after => <seconds>, cb => <callback>);
231 $w = AnyEvent->timer (
233 after => <fractional_seconds>,
234 interval => <fractional_seconds>,
235 cb => <callback>,
236 );
237 You can create a time watcher by calling the "AnyEvent->timer" method
239 with the following mandatory arguments:
240 "after" specifies after how many seconds (fractional values are
242 supported) the callback should be invoked. "cb" is the callback to
243 invoke in that case.
244 Although the callback might get passed parameters, their value and
246 presence is undefined and you cannot rely on them. Portable AnyEvent
247 callbacks cannot use arguments passed to time watcher callbacks.
248 The callback will normally be invoked only once. If you specify another
250 parameter, "interval", as a strictly positive number (> 0), then the
251 callback will be invoked regularly at that interval (in fractional
252 seconds) after the first invocation. If "interval" is specified with a
253 false value, then it is treated as if it were not specified at all.
254 The callback will be rescheduled before invoking the callback, but no
256 attempt is made to avoid timer drift in most backends, so the interval
257 is only approximate.
258 Example: fire an event after 7.7 seconds.
260 my $w = AnyEvent->timer (after => 7.7, cb => sub {
262 warn "timeout\n";
263 });
264 # to cancel the timer:
266 undef $w;
267 Example 2: fire an event after 0.5 seconds, then roughly every second.
269 my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
271 warn "timeout\n";
272 });
273 TIMING ISSUES
275 There are two ways to handle timers: based on real time (relative,
277 "fire in 10 seconds") and based on wallclock time (absolute, "fire at
278 12 o'clock").
279 While most event loops expect timers to specified in a relative way,
281 they use absolute time internally. This makes a difference when your
282 clock "jumps", for example, when ntp decides to set your clock
283 backwards from the wrong date of 2014-01-01 to 2008-01-01, a watcher
284 that is supposed to fire "after a second" might actually take six years
285 to finally fire.
286 AnyEvent cannot compensate for this. The only event loop that is
288 conscious of these issues is EV, which offers both relative (ev_timer,
289 based on true relative time) and absolute (ev_periodic, based on
290 wallclock time) timers.
291 AnyEvent always prefers relative timers, if available, matching the
293 AnyEvent API.
294 AnyEvent has two additional methods that return the "current time":
296 AnyEvent->time
298 This returns the "current wallclock time" as a fractional number of
299 seconds since the Epoch (the same thing as "time" or
300 "Time::HiRes::time" return, and the result is guaranteed to be
301 compatible with those).
302 It progresses independently of any event loop processing, i.e. each
304 call will check the system clock, which usually gets updated
305 frequently.
306 AnyEvent->now
308 This also returns the "current wallclock time", but unlike "time",
309 above, this value might change only once per event loop iteration,
310 depending on the event loop (most return the same time as "time",
311 above). This is the time that AnyEvent's timers get scheduled
312 against.
313 In almost all cases (in all cases if you don't care), this is the
315 function to call when you want to know the current time.
316 This function is also often faster then "AnyEvent->time", and thus
318 the preferred method if you want some timestamp (for example,
319 AnyEvent::Handle uses this to update its activity timeouts).
320 The rest of this section is only of relevance if you try to be very
322 exact with your timing; you can skip it without a bad conscience.
323 For a practical example of when these times differ, consider
325 Event::Lib and EV and the following set-up:
326 The event loop is running and has just invoked one of your
328 callbacks at time=500 (assume no other callbacks delay processing).
329 In your callback, you wait a second by executing "sleep 1"
330 (blocking the process for a second) and then (at time=501) you
331 create a relative timer that fires after three seconds.
332 With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
334 return 501, because that is the current time, and the timer will be
335 scheduled to fire at time=504 (501 + 3).
336 With EV, "AnyEvent->time" returns 501 (as that is the current
338 time), but "AnyEvent->now" returns 500, as that is the time the
339 last event processing phase started. With EV, your timer gets
340 scheduled to run at time=503 (500 + 3).
341 In one sense, Event::Lib is more exact, as it uses the current time
343 regardless of any delays introduced by event processing. However,
344 most callbacks do not expect large delays in processing, so this
345 causes a higher drift (and a lot more system calls to get the
346 current time).
347 In another sense, EV is more exact, as your timer will be scheduled
349 at the same time, regardless of how long event processing actually
350 took.
351 In either case, if you care (and in most cases, you don't), then
353 you can get whatever behaviour you want with any event loop, by
354 taking the difference between "AnyEvent->time" and "AnyEvent->now"
355 into account.
356 AnyEvent->now_update
358 Some event loops (such as EV or AnyEvent::Loop) cache the current
359 time for each loop iteration (see the discussion of AnyEvent->now,
360 above).
361 When a callback runs for a long time (or when the process sleeps),
363 then this "current" time will differ substantially from the real
364 time, which might affect timers and time-outs.
365 When this is the case, you can call this method, which will update
367 the event loop's idea of "current time".
368 A typical example would be a script in a web server (e.g.
370 "mod_perl") - when mod_perl executes the script, then the event
371 loop will have the wrong idea about the "current time" (being
372 potentially far in the past, when the script ran the last time). In
373 that case you should arrange a call to "AnyEvent->now_update" each
374 time the web server process wakes up again (e.g. at the start of
375 your script, or in a handler).
376 Note that updating the time might cause some events to be handled.
378 SIGNAL WATCHERS
380 $w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
381 You can watch for signals using a signal watcher, "signal" is the
383 signal name in uppercase and without any "SIG" prefix, "cb" is the Perl
384 callback to be invoked whenever a signal occurs.
385 Although the callback might get passed parameters, their value and
387 presence is undefined and you cannot rely on them. Portable AnyEvent
388 callbacks cannot use arguments passed to signal watcher callbacks.
389 Multiple signal occurrences can be clumped together into one callback
391 invocation, and callback invocation will be synchronous. Synchronous
392 means that it might take a while until the signal gets handled by the
393 process, but it is guaranteed not to interrupt any other callbacks.
394 The main advantage of using these watchers is that you can share a
396 signal between multiple watchers, and AnyEvent will ensure that signals
397 will not interrupt your program at bad times.
398 This watcher might use %SIG (depending on the event loop used), so
400 programs overwriting those signals directly will likely not work
401 correctly.
402 Example: exit on SIGINT
404 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
406 Restart Behaviour
408 While restart behaviour is up to the event loop implementation, most
410 will not restart syscalls (that includes Async::Interrupt and
411 AnyEvent's pure perl implementation).
412 Safe/Unsafe Signals
414 Perl signals can be either "safe" (synchronous to opcode handling) or
416 "unsafe" (asynchronous) - the former might delay signal delivery
417 indefinitely, the latter might corrupt your memory.
418 AnyEvent signal handlers are, in addition, synchronous to the event
420 loop, i.e. they will not interrupt your running perl program but will
421 only be called as part of the normal event handling (just like timer,
422 I/O etc. callbacks, too).
423 Signal Races, Delays and Workarounds
425 Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support
427 attaching callbacks to signals in a generic way, which is a pity, as
428 you cannot do race-free signal handling in perl, requiring C libraries
429 for this. AnyEvent will try to do its best, which means in some cases,
430 signals will be delayed. The maximum time a signal might be delayed is
431 10 seconds by default, but can be overriden via
432 $ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
433 - see the "ENVIRONMENT VARIABLES" section for details.
434 All these problems can be avoided by installing the optional
436 Async::Interrupt module, which works with most event loops. It will not
437 work with inherently broken event loops such as Event or Event::Lib
438 (and not with POE currently). For those, you just have to suffer the
439 delays.
440 CHILD PROCESS WATCHERS
442 $w = AnyEvent->child (pid => <process id>, cb => <callback>);
443 You can also watch for a child process exit and catch its exit status.
445 The child process is specified by the "pid" argument (on some backends,
447 using 0 watches for any child process exit, on others this will croak).
448 The watcher will be triggered only when the child process has finished
449 and an exit status is available, not on any trace events
450 (stopped/continued).
451 The callback will be called with the pid and exit status (as returned
453 by waitpid), so unlike other watcher types, you can rely on child
454 watcher callback arguments.
455 This watcher type works by installing a signal handler for "SIGCHLD",
457 and since it cannot be shared, nothing else should use SIGCHLD or reap
458 random child processes (waiting for specific child processes, e.g.
459 inside "system", is just fine).
460 There is a slight catch to child watchers, however: you usually start
462 them after the child process was created, and this means the process
463 could have exited already (and no SIGCHLD will be sent anymore).
464 Not all event models handle this correctly (neither POE nor IO::Async
466 do, see their AnyEvent::Impl manpages for details), but even for event
467 models that do handle this correctly, they usually need to be loaded
468 before the process exits (i.e. before you fork in the first place).
469 AnyEvent's pure perl event loop handles all cases correctly regardless
470 of when you start the watcher.
471 This means you cannot create a child watcher as the very first thing in
473 an AnyEvent program, you have to create at least one watcher before you
474 "fork" the child (alternatively, you can call "AnyEvent::detect").
475 As most event loops do not support waiting for child events, they will
477 be emulated by AnyEvent in most cases, in which case the latency and
478 race problems mentioned in the description of signal watchers apply.
479 Example: fork a process and wait for it
481 my $done = AnyEvent->condvar;
483 # this forks and immediately calls exit in the child. this
485 # normally has all sorts of bad consequences for your parent,
486 # so take this as an example only. always fork and exec,
487 # or call POSIX::_exit, in real code.
488 my $pid = fork or exit 5;
489 my $w = AnyEvent->child (
491 pid => $pid,
492 cb => sub {
493 my ($pid, $status) = @_;
494 warn "pid $pid exited with status $status";
495 $done->send;
496 },
497 );
498 # do something else, then wait for process exit
500 $done->recv;
501 IDLE WATCHERS
503 $w = AnyEvent->idle (cb => <callback>);
504 This will repeatedly invoke the callback after the process becomes
506 idle, until either the watcher is destroyed or new events have been
507 detected.
508 Idle watchers are useful when there is a need to do something, but it
510 is not so important (or wise) to do it instantly. The callback will be
511 invoked only when there is "nothing better to do", which is usually
512 defined as "all outstanding events have been handled and no new events
513 have been detected". That means that idle watchers ideally get invoked
514 when the event loop has just polled for new events but none have been
515 detected. Instead of blocking to wait for more events, the idle
516 watchers will be invoked.
517 Unfortunately, most event loops do not really support idle watchers
519 (only EV, Event and Glib do it in a usable fashion) - for the rest,
520 AnyEvent will simply call the callback "from time to time".
521 Example: read lines from STDIN, but only process them when the program
523 is otherwise idle:
524 my @lines; # read data
526 my $idle_w;
527 my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
528 push @lines, scalar <STDIN>;
529 # start an idle watcher, if not already done
531 $idle_w ||= AnyEvent->idle (cb => sub {
532 # handle only one line, when there are lines left
533 if (my $line = shift @lines) {
534 print "handled when idle: $line";
535 } else {
536 # otherwise disable the idle watcher again
537 undef $idle_w;
538 }
539 });
540 });
541 CONDITION VARIABLES
543 $cv = AnyEvent->condvar;
544 $cv->send (<list>);
546 my @res = $cv->recv;
547 If you are familiar with some event loops you will know that all of
549 them require you to run some blocking "loop", "run" or similar function
550 that will actively watch for new events and call your callbacks.
551 AnyEvent is slightly different: it expects somebody else to run the
553 event loop and will only block when necessary (usually when told by the
554 user).
555 The tool to do that is called a "condition variable", so called because
557 they represent a condition that must become true.
558 Now is probably a good time to look at the examples further below.
560 Condition variables can be created by calling the "AnyEvent->condvar"
562 method, usually without arguments. The only argument pair allowed is
563 "cb", which specifies a callback to be called when the condition
564 variable becomes true, with the condition variable as the first
565 argument (but not the results).
566 After creation, the condition variable is "false" until it becomes
568 "true" by calling the "send" method (or calling the condition variable
569 as if it were a callback, read about the caveats in the description for
570 the "->send" method).
571 Since condition variables are the most complex part of the AnyEvent
573 API, here are some different mental models of what they are - pick the
574 ones you can connect to:
575 • Condition variables are like callbacks - you can call them (and
577 pass them instead of callbacks). Unlike callbacks however, you can
578 also wait for them to be called.
579 • Condition variables are signals - one side can emit or send them,
581 the other side can wait for them, or install a handler that is
582 called when the signal fires.
583 • Condition variables are like "Merge Points" - points in your
585 program where you merge multiple independent results/control flows
586 into one.
587 • Condition variables represent a transaction - functions that start
589 some kind of transaction can return them, leaving the caller the
590 choice between waiting in a blocking fashion, or setting a
591 callback.
592 • Condition variables represent future values, or promises to deliver
594 some result, long before the result is available.
595 Condition variables are very useful to signal that something has
597 finished, for example, if you write a module that does asynchronous
598 http requests, then a condition variable would be the ideal candidate
599 to signal the availability of results. The user can either act when the
600 callback is called or can synchronously "->recv" for the results.
601 You can also use them to simulate traditional event loops - for
603 example, you can block your main program until an event occurs - for
604 example, you could "->recv" in your main program until the user clicks
605 the Quit button of your app, which would "->send" the "quit" event.
606 Note that condition variables recurse into the event loop - if you have
608 two pieces of code that call "->recv" in a round-robin fashion, you
609 lose. Therefore, condition variables are good to export to your caller,
610 but you should avoid making a blocking wait yourself, at least in
611 callbacks, as this asks for trouble.
612 Condition variables are represented by hash refs in perl, and the keys
614 used by AnyEvent itself are all named "_ae_XXX" to make subclassing
615 easy (it is often useful to build your own transaction class on top of
616 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
617 its "new" method in your own "new" method.
618 There are two "sides" to a condition variable - the "producer side"
620 which eventually calls "-> send", and the "consumer side", which waits
621 for the send to occur.
622 Example: wait for a timer.
624 # condition: "wait till the timer is fired"
626 my $timer_fired = AnyEvent->condvar;
627 # create the timer - we could wait for, say
629 # a handle becomign ready, or even an
630 # AnyEvent::HTTP request to finish, but
631 # in this case, we simply use a timer:
632 my $w = AnyEvent->timer (
633 after => 1,
634 cb => sub { $timer_fired->send },
635 );
636 # this "blocks" (while handling events) till the callback
638 # calls ->send
639 $timer_fired->recv;
640 Example: wait for a timer, but take advantage of the fact that
642 condition variables are also callable directly.
643 my $done = AnyEvent->condvar;
645 my $delay = AnyEvent->timer (after => 5, cb => $done);
646 $done->recv;
647 Example: Imagine an API that returns a condvar and doesn't support
649 callbacks. This is how you make a synchronous call, for example from
650 the main program:
651 use AnyEvent::CouchDB;
653 ...
655 my @info = $couchdb->info->recv;
657 And this is how you would just set a callback to be called whenever the
659 results are available:
660 $couchdb->info->cb (sub {
662 my @info = $_[0]->recv;
663 });
664 METHODS FOR PRODUCERS
666 These methods should only be used by the producing side, i.e. the
668 code/module that eventually sends the signal. Note that it is also the
669 producer side which creates the condvar in most cases, but it isn't
670 uncommon for the consumer to create it as well.
671 $cv->send (...)
673 Flag the condition as ready - a running "->recv" and all further
674 calls to "recv" will (eventually) return after this method has been
675 called. If nobody is waiting the send will be remembered.
676 If a callback has been set on the condition variable, it is called
678 immediately from within send.
679 Any arguments passed to the "send" call will be returned by all
681 future "->recv" calls.
682 Condition variables are overloaded so one can call them directly
684 (as if they were a code reference). Calling them directly is the
685 same as calling "send".
686 $cv->croak ($error)
688 Similar to send, but causes all calls to "->recv" to invoke
689 "Carp::croak" with the given error message/object/scalar.
690 This can be used to signal any errors to the condition variable
692 user/consumer. Doing it this way instead of calling "croak"
693 directly delays the error detection, but has the overwhelming
694 advantage that it diagnoses the error at the place where the result
695 is expected, and not deep in some event callback with no connection
696 to the actual code causing the problem.
697 $cv->begin ([group callback])
699 $cv->end
700 These two methods can be used to combine many transactions/events
701 into one. For example, a function that pings many hosts in parallel
702 might want to use a condition variable for the whole process.
703 Every call to "->begin" will increment a counter, and every call to
705 "->end" will decrement it. If the counter reaches 0 in "->end",
706 the (last) callback passed to "begin" will be executed, passing the
707 condvar as first argument. That callback is supposed to call
708 "->send", but that is not required. If no group callback was set,
709 "send" will be called without any arguments.
710 You can think of "$cv->send" giving you an OR condition (one call
712 sends), while "$cv->begin" and "$cv->end" giving you an AND
713 condition (all "begin" calls must be "end"'ed before the condvar
714 sends).
715 Let's start with a simple example: you have two I/O watchers (for
717 example, STDOUT and STDERR for a program), and you want to wait for
718 both streams to close before activating a condvar:
719 my $cv = AnyEvent->condvar;
721 $cv->begin; # first watcher
723 my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
724 defined sysread $fh1, my $buf, 4096
725 or $cv->end;
726 });
727 $cv->begin; # second watcher
729 my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
730 defined sysread $fh2, my $buf, 4096
731 or $cv->end;
732 });
733 $cv->recv;
735 This works because for every event source (EOF on file handle),
737 there is one call to "begin", so the condvar waits for all calls to
738 "end" before sending.
739 The ping example mentioned above is slightly more complicated, as
741 the there are results to be passed back, and the number of tasks
742 that are begun can potentially be zero:
743 my $cv = AnyEvent->condvar;
745 my %result;
747 $cv->begin (sub { shift->send (\%result) });
748 for my $host (@list_of_hosts) {
750 $cv->begin;
751 ping_host_then_call_callback $host, sub {
752 $result{$host} = ...;
753 $cv->end;
754 };
755 }
756 $cv->end;
758 ...
760 my $results = $cv->recv;
762 This code fragment supposedly pings a number of hosts and calls
764 "send" after results for all then have have been gathered - in any
765 order. To achieve this, the code issues a call to "begin" when it
766 starts each ping request and calls "end" when it has received some
767 result for it. Since "begin" and "end" only maintain a counter, the
768 order in which results arrive is not relevant.
769 There is an additional bracketing call to "begin" and "end" outside
771 the loop, which serves two important purposes: first, it sets the
772 callback to be called once the counter reaches 0, and second, it
773 ensures that "send" is called even when "no" hosts are being pinged
774 (the loop doesn't execute once).
775 This is the general pattern when you "fan out" into multiple (but
777 potentially zero) subrequests: use an outer "begin"/"end" pair to
778 set the callback and ensure "end" is called at least once, and
779 then, for each subrequest you start, call "begin" and for each
780 subrequest you finish, call "end".
781 METHODS FOR CONSUMERS
783 These methods should only be used by the consuming side, i.e. the code
785 awaits the condition.
786 $cv->recv
788 Wait (blocking if necessary) until the "->send" or "->croak"
789 methods have been called on $cv, while servicing other watchers
790 normally.
791 You can only wait once on a condition - additional calls are valid
793 but will return immediately.
794 If an error condition has been set by calling "->croak", then this
796 function will call "croak".
797 In list context, all parameters passed to "send" will be returned,
799 in scalar context only the first one will be returned.
800 Note that doing a blocking wait in a callback is not supported by
802 any event loop, that is, recursive invocation of a blocking
803 "->recv" is not allowed and the "recv" call will "croak" if such a
804 condition is detected. This requirement can be dropped by relying
805 on Coro::AnyEvent , which allows you to do a blocking "->recv" from
806 any thread that doesn't run the event loop itself. Coro::AnyEvent
807 is loaded automatically when Coro is used with AnyEvent, so code
808 does not need to do anything special to take advantage of that: any
809 code that would normally block your program because it calls
810 "recv", be executed in an "async" thread instead without blocking
811 other threads.
812 Not all event models support a blocking wait - some die in that
814 case (programs might want to do that to stay interactive), so if
815 you are using this from a module, never require a blocking wait.
816 Instead, let the caller decide whether the call will block or not
817 (for example, by coupling condition variables with some kind of
818 request results and supporting callbacks so the caller knows that
819 getting the result will not block, while still supporting blocking
820 waits if the caller so desires).
821 You can ensure that "->recv" never blocks by setting a callback and
823 only calling "->recv" from within that callback (or at a later
824 time). This will work even when the event loop does not support
825 blocking waits otherwise.
826 $bool = $cv->ready
828 Returns true when the condition is "true", i.e. whether "send" or
829 "croak" have been called.
830 $cb = $cv->cb ($cb->($cv))
832 This is a mutator function that returns the callback set (or
833 "undef" if not) and optionally replaces it before doing so.
834 The callback will be called when the condition becomes "true", i.e.
836 when "send" or "croak" are called, with the only argument being the
837 condition variable itself. If the condition is already true, the
838 callback is called immediately when it is set. Calling "recv"
839 inside the callback or at any later time is guaranteed not to
840 block.
841 Additionally, when the callback is invoked, it is also removed from
843 the condvar (reset to "undef"), so the condvar does not keep a
844 reference to the callback after invocation.
845
847 The following backend classes are part of the AnyEvent distribution
848 (every class has its own manpage):
849 Backends that are autoprobed when no other event loop can be found.
851 EV is the preferred backend when no other event loop seems to be in
852 use. If EV is not installed, then AnyEvent will fall back to its
853 own pure-perl implementation, which is available everywhere as it
854 comes with AnyEvent itself.
855 AnyEvent::Impl::EV based on EV (interface to libev, best choice).
857 AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
858 Backends that are transparently being picked up when they are used.
860 These will be used if they are already loaded when the first
861 watcher is created, in which case it is assumed that the
862 application is using them. This means that AnyEvent will
863 automatically pick the right backend when the main program loads an
864 event module before anything starts to create watchers. Nothing
865 special needs to be done by the main program.
866 AnyEvent::Impl::Event based on Event, very stable, few glitches.
868 AnyEvent::Impl::Glib based on Glib, slow but very stable.
869 AnyEvent::Impl::Tk based on Tk, very broken.
870 AnyEvent::Impl::UV based on UV, innovated square wheels.
871 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
872 AnyEvent::Impl::POE based on POE, very slow, some limitations.
873 AnyEvent::Impl::Irssi used when running within irssi.
874 AnyEvent::Impl::IOAsync based on IO::Async.
875 AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
876 AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
877 Backends with special needs.
879 Qt requires the Qt::Application to be instantiated first, but will
880 otherwise be picked up automatically. As long as the main program
881 instantiates the application before any AnyEvent watchers are
882 created, everything should just work.
883 AnyEvent::Impl::Qt based on Qt.
885 Event loops that are indirectly supported via other backends.
887 Some event loops can be supported via other modules:
888 There is no direct support for WxWidgets (Wx) or Prima.
890 WxWidgets has no support for watching file handles. However, you
892 can use WxWidgets through the POE adaptor, as POE has a Wx backend
893 that simply polls 20 times per second, which was considered to be
894 too horrible to even consider for AnyEvent.
895 Prima is not supported as nobody seems to be using it, but it has a
897 POE backend, so it can be supported through POE.
898 AnyEvent knows about both Prima and Wx, however, and will try to
900 load POE when detecting them, in the hope that POE will pick them
901 up, in which case everything will be automatic.
902 Known event loops outside the AnyEvent distribution
904 The following event loops or programs support AnyEvent by providing
905 their own AnyEvent backend. They will be picked up automatically.
906 urxvt::anyevent available to rxvt-unicode extensions
908
910 These are not normally required to use AnyEvent, but can be useful to
911 write AnyEvent extension modules.
912 $AnyEvent::MODEL
914 Contains "undef" until the first watcher is being created, before
915 the backend has been autodetected.
916 Afterwards it contains the event model that is being used, which is
918 the name of the Perl class implementing the model. This class is
919 usually one of the "AnyEvent::Impl::xxx" modules, but can be any
920 other class in the case AnyEvent has been extended at runtime (e.g.
921 in rxvt-unicode it will be "urxvt::anyevent").
922 AnyEvent::detect
924 Returns $AnyEvent::MODEL, forcing autodetection of the event model
925 if necessary. You should only call this function right before you
926 would have created an AnyEvent watcher anyway, that is, as late as
927 possible at runtime, and not e.g. during initialisation of your
928 module.
929 The effect of calling this function is as if a watcher had been
931 created (specifically, actions that happen "when the first watcher
932 is created" happen when calling detetc as well).
933 If you need to do some initialisation before AnyEvent watchers are
935 created, use "post_detect".
936 $guard = AnyEvent::post_detect { BLOCK }
938 Arranges for the code block to be executed as soon as the event
939 model is autodetected (or immediately if that has already
940 happened).
941 The block will be executed after the actual backend has been
943 detected ($AnyEvent::MODEL is set), so it is possible to do some
944 initialisation only when AnyEvent is actually initialised - see the
945 sources of AnyEvent::AIO to see how this is used.
946 The most common usage is to create some global watchers, without
948 forcing event module detection too early. For example,
949 AnyEvent::AIO creates and installs the global IO::AIO watcher in a
950 "post_detect" block to avoid autodetecting the event module at load
951 time.
952 If called in scalar or list context, then it creates and returns an
954 object that automatically removes the callback again when it is
955 destroyed (or "undef" when the hook was immediately executed). See
956 AnyEvent::AIO for a case where this is useful.
957 Example: Create a watcher for the IO::AIO module and store it in
959 $WATCHER, but do so only do so after the event loop is initialised.
960 our WATCHER;
962 my $guard = AnyEvent::post_detect {
964 $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
965 };
966 # the ||= is important in case post_detect immediately runs the block,
968 # as to not clobber the newly-created watcher. assigning both watcher and
969 # post_detect guard to the same variable has the advantage of users being
970 # able to just C<undef $WATCHER> if the watcher causes them grief.
971 $WATCHER ||= $guard;
973 @AnyEvent::post_detect
975 This is a lower level interface then "AnyEvent::post_detect" (the
976 function). This variable is mainly useful for modules that can do
977 something useful when AnyEvent is used and thus want to know when
978 it is initialised, but do not need to even load it by default. This
979 array provides the means to hook into AnyEvent passively, without
980 loading it.
981 Here is how it works: If there are any code references in this
983 array (you can "push" to it before or after loading AnyEvent), then
984 they will be called directly after the event loop has been chosen.
985 You should check $AnyEvent::MODEL before adding to this array,
987 though: if it is defined then the event loop has already been
988 detected, and the array will be ignored.
989 Best use "AnyEvent::post_detect { BLOCK }" when your application
991 allows it, as it takes care of these details.
992 Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
994 together, you could put this into Coro (this is the actual code
995 used by Coro to accomplish this):
996 if (defined $AnyEvent::MODEL) {
998 # AnyEvent already initialised, so load Coro::AnyEvent
999 require Coro::AnyEvent;
1000 } else {
1001 # AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
1002 # as soon as it is
1003 push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
1004 }
1005 AnyEvent::postpone { BLOCK }
1007 Arranges for the block to be executed as soon as possible, but not
1008 before the call itself returns. In practise, the block will be
1009 executed just before the event loop polls for new events, or
1010 shortly afterwards.
1011 This function never returns anything (to make the "return postpone
1013 { ... }" idiom more useful.
1014 To understand the usefulness of this function, consider a function
1016 that asynchronously does something for you and returns some
1017 transaction object or guard to let you cancel the operation. For
1018 example, "AnyEvent::Socket::tcp_connect":
1019 # start a connection attempt unless one is active
1021 $self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
1022 delete $self->{connect_guard};
1023 ...
1024 };
1025 Imagine that this function could instantly call the callback, for
1027 example, because it detects an obvious error such as a negative
1028 port number. Invoking the callback before the function returns
1029 causes problems however: the callback will be called and will try
1030 to delete the guard object. But since the function hasn't returned
1031 yet, there is nothing to delete. When the function eventually
1032 returns it will assign the guard object to
1033 "$self->{connect_guard}", where it will likely never be deleted, so
1034 the program thinks it is still trying to connect.
1035 This is where "AnyEvent::postpone" should be used. Instead of
1037 calling the callback directly on error:
1038 $cb->(undef), return # signal error to callback, BAD!
1040 if $some_error_condition;
1041 It should use "postpone":
1043 AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
1045 if $some_error_condition;
1046 AnyEvent::log $level, $msg[, @args]
1048 Log the given $msg at the given $level.
1049 If AnyEvent::Log is not loaded then this function makes a simple
1051 test to see whether the message will be logged. If the test
1052 succeeds it will load AnyEvent::Log and call "AnyEvent::Log::log" -
1053 consequently, look at the AnyEvent::Log documentation for details.
1054 If the test fails it will simply return. Right now this happens
1056 when a numerical loglevel is used and it is larger than the level
1057 specified via $ENV{PERL_ANYEVENT_VERBOSE}.
1058 If you want to sprinkle loads of logging calls around your code,
1060 consider creating a logger callback with the
1061 "AnyEvent::Log::logger" function, which can reduce typing, codesize
1062 and can reduce the logging overhead enourmously.
1063 AnyEvent::fh_block $filehandle
1065 AnyEvent::fh_unblock $filehandle
1066 Sets blocking or non-blocking behaviour for the given filehandle.
1067
1069 As a module author, you should "use AnyEvent" and call AnyEvent methods
1070 freely, but you should not load a specific event module or rely on it.
1071 Be careful when you create watchers in the module body - AnyEvent will
1073 decide which event module to use as soon as the first method is called,
1074 so by calling AnyEvent in your module body you force the user of your
1075 module to load the event module first.
1076 Never call "->recv" on a condition variable unless you know that the
1078 "->send" method has been called on it already. This is because it will
1079 stall the whole program, and the whole point of using events is to stay
1080 interactive.
1081 It is fine, however, to call "->recv" when the user of your module
1083 requests it (i.e. if you create a http request object ad have a method
1084 called "results" that returns the results, it may call "->recv" freely,
1085 as the user of your module knows what she is doing. Always).
1086
1088 There will always be a single main program - the only place that should
1089 dictate which event model to use.
1090 If the program is not event-based, it need not do anything special,
1092 even when it depends on a module that uses an AnyEvent. If the program
1093 itself uses AnyEvent, but does not care which event loop is used, all
1094 it needs to do is "use AnyEvent". In either case, AnyEvent will choose
1095 the best available loop implementation.
1096 If the main program relies on a specific event model - for example, in
1098 Gtk2 programs you have to rely on the Glib module - you should load the
1099 event module before loading AnyEvent or any module that uses it:
1100 generally speaking, you should load it as early as possible. The reason
1101 is that modules might create watchers when they are loaded, and
1102 AnyEvent will decide on the event model to use as soon as it creates
1103 watchers, and it might choose the wrong one unless you load the correct
1104 one yourself.
1105 You can chose to use a pure-perl implementation by loading the
1107 "AnyEvent::Loop" module, which gives you similar behaviour everywhere,
1108 but letting AnyEvent chose the model is generally better.
1109 MAINLOOP EMULATION
1111 Sometimes (often for short test scripts, or even standalone programs
1112 who only want to use AnyEvent), you do not want to run a specific event
1113 loop.
1114 In that case, you can use a condition variable like this:
1116 AnyEvent->condvar->recv;
1118 This has the effect of entering the event loop and looping forever.
1120 Note that usually your program has some exit condition, in which case
1122 it is better to use the "traditional" approach of storing a condition
1123 variable somewhere, waiting for it, and sending it when the program
1124 should exit cleanly.
1125
1127 The following is a non-exhaustive list of additional modules that use
1128 AnyEvent as a client and can therefore be mixed easily with other
1129 AnyEvent modules and other event loops in the same program. Some of the
1130 modules come as part of AnyEvent, the others are available via CPAN
1131 (see <http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a
1132 longer non-exhaustive list), and the list is heavily biased towards
1133 modules of the AnyEvent author himself :)
1134 AnyEvent::Util (part of the AnyEvent distribution)
1136 Contains various utility functions that replace often-used blocking
1137 functions such as "inet_aton" with event/callback-based versions.
1138 AnyEvent::Socket (part of the AnyEvent distribution)
1140 Provides various utility functions for (internet protocol) sockets,
1141 addresses and name resolution. Also functions to create non-
1142 blocking tcp connections or tcp servers, with IPv6 and SRV record
1143 support and more.
1144 AnyEvent::Handle (part of the AnyEvent distribution)
1146 Provide read and write buffers, manages watchers for reads and
1147 writes, supports raw and formatted I/O, I/O queued and fully
1148 transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
1149 AnyEvent::DNS (part of the AnyEvent distribution)
1151 Provides rich asynchronous DNS resolver capabilities.
1152 AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
1154 AnyEvent::IGS, AnyEvent::FCP
1155 Implement event-based interfaces to the protocols of the same name
1156 (for the curious, IGS is the International Go Server and FCP is the
1157 Freenet Client Protocol).
1158 AnyEvent::AIO (part of the AnyEvent distribution)
1160 Truly asynchronous (as opposed to non-blocking) I/O, should be in
1161 the toolbox of every event programmer. AnyEvent::AIO transparently
1162 fuses IO::AIO and AnyEvent together, giving AnyEvent access to
1163 event-based file I/O, and much more.
1164 AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
1166 AnyEvent::Fork::Remote
1167 These let you safely fork new subprocesses, either locally or
1168 remotely (e.g.v ia ssh), using some RPC protocol or not, without
1169 the limitations normally imposed by fork (AnyEvent works fine for
1170 example). Dynamically-resized worker pools are obviously included
1171 as well.
1172 And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
1174 just to exec external programs can easily beat using "fork" and
1175 "exec" (or even "system") in most programs.
1176 AnyEvent::Filesys::Notify
1178 AnyEvent is good for non-blocking stuff, but it can't detect file
1179 or path changes (e.g. "watch this directory for new files", "watch
1180 this file for changes"). The AnyEvent::Filesys::Notify module
1181 promises to do just that in a portbale fashion, supporting inotify
1182 on GNU/Linux and some weird, without doubt broken, stuff on OS X to
1183 monitor files. It can fall back to blocking scans at regular
1184 intervals transparently on other platforms, so it's about as
1185 portable as it gets.
1186 (I haven't used it myself, but it seems the biggest problem with it
1188 is it quite bad performance).
1189 AnyEvent::DBI
1191 Executes DBI requests asynchronously in a proxy process for you,
1192 notifying you in an event-based way when the operation is finished.
1193 AnyEvent::FastPing
1195 The fastest ping in the west.
1196 Coro
1198 Has special support for AnyEvent via Coro::AnyEvent, which allows
1199 you to simply invert the flow control - don't call us, we will call
1200 you:
1201 async {
1203 Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
1204 print "5 seconds later!\n";
1205 Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
1207 my $line = <STDIN>; # works for ttys
1208 AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
1210 my ($body, $hdr) = Coro::rouse_wait;
1211 };
1212
1214 Starting with version 5.0, AnyEvent officially supports a second, much
1215 simpler, API that is designed to reduce the calling, typing and memory
1216 overhead by using function call syntax and a fixed number of
1217 parameters.
1218 See the AE manpage for details.
1220
1222 In general, AnyEvent does not do any error handling - it relies on the
1223 caller to do that if required. The AnyEvent::Strict module (see also
1224 the "PERL_ANYEVENT_STRICT" environment variable, below) provides strict
1225 checking of all AnyEvent methods, however, which is highly useful
1226 during development.
1227 As for exception handling (i.e. runtime errors and exceptions thrown
1229 while executing a callback), this is not only highly event-loop
1230 specific, but also not in any way wrapped by this module, as this is
1231 the job of the main program.
1232 The pure perl event loop simply re-throws the exception (usually within
1234 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
1235 Glib uses "install_exception_handler" and so on.
1236
1238 AnyEvent supports a number of environment variables that tune the
1239 runtime behaviour. They are usually evaluated when AnyEvent is loaded,
1240 initialised, or a submodule that uses them is loaded. Many of them also
1241 cause AnyEvent to load additional modules - for example,
1242 "PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
1243 loaded.
1244 All the environment variables documented here start with
1246 "PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
1247 Other modules are encouraged (but by no means required) to use
1248 "PERL_ANYEVENT_SUBMODULE" if they have registered the
1249 AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
1250 AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
1251 should not access env variables starting with "AE_", see below).
1252 All variables can also be set via the "AE_" prefix, that is, instead of
1254 setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
1255 there is a clash btween anyevent and another program that uses
1256 "AE_something" you can set the corresponding "PERL_ANYEVENT_something"
1257 variable to the empty string, as those variables take precedence.
1258 When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
1260 their "PERL_ANYEVENT_xxx" counterpart unless that variable already
1261 exists. If taint mode is on, then AnyEvent will remove all environment
1262 variables starting with "PERL_ANYEVENT_" from %ENV (or replace them
1263 with "undef" or the empty string, if the corresaponding "AE_" variable
1264 is set).
1265 The exact algorithm is currently:
1267 1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
1269 2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
1270 3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
1271 This ensures that child processes will not see the "AE_" variables.
1273 The following environment variables are currently known to AnyEvent:
1275 "PERL_ANYEVENT_VERBOSE"
1277 By default, AnyEvent will log messages with loglevel 4 ("error") or
1278 higher (see AnyEvent::Log). You can set this environment variable
1279 to a numerical loglevel to make AnyEvent more (or less) talkative.
1280 If you want to do more than just set the global logging level you
1282 should have a look at "PERL_ANYEVENT_LOG", which allows much more
1283 complex specifications.
1284 When set to 0 ("off"), then no messages whatsoever will be logged
1286 with everything else at defaults.
1287 When set to 5 or higher ("warn"), AnyEvent warns about unexpected
1289 conditions, such as not being able to load the event model
1290 specified by "PERL_ANYEVENT_MODEL", or a guard callback throwing an
1291 exception - this is the minimum recommended level for use during
1292 development.
1293 When set to 7 or higher (info), AnyEvent reports which event model
1295 it chooses.
1296 When set to 8 or higher (debug), then AnyEvent will report extra
1298 information on which optional modules it loads and how it
1299 implements certain features.
1300 "PERL_ANYEVENT_LOG"
1302 Accepts rather complex logging specifications. For example, you
1303 could log all "debug" messages of some module to stderr, warnings
1304 and above to stderr, and errors and above to syslog, with:
1305 PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
1307 For the rather extensive details, see AnyEvent::Log.
1309 This variable is evaluated when AnyEvent (or AnyEvent::Log) is
1311 loaded, so will take effect even before AnyEvent has initialised
1312 itself.
1313 Note that specifying this environment variable causes the
1315 AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
1316 does not, so only using the latter saves a few hundred kB of memory
1317 unless a module explicitly needs the extra features of
1318 AnyEvent::Log.
1319 "PERL_ANYEVENT_STRICT"
1321 AnyEvent does not do much argument checking by default, as thorough
1322 argument checking is very costly. Setting this variable to a true
1323 value will cause AnyEvent to load "AnyEvent::Strict" and then to
1324 thoroughly check the arguments passed to most method calls. If it
1325 finds any problems, it will croak.
1326 In other words, enables "strict" mode.
1328 Unlike "use strict" (or its modern cousin, "use common::sense", it
1330 is definitely recommended to keep it off in production. Keeping
1331 "PERL_ANYEVENT_STRICT=1" in your environment while developing
1332 programs can be very useful, however.
1333 "PERL_ANYEVENT_DEBUG_SHELL"
1335 If this env variable is nonempty, then its contents will be
1336 interpreted by "AnyEvent::Socket::parse_hostport" and
1337 "AnyEvent::Debug::shell" (after replacing every occurance of $$ by
1338 the process pid). The shell object is saved in
1339 $AnyEvent::Debug::SHELL.
1340 This happens when the first watcher is created.
1342 For example, to bind a debug shell on a unix domain socket in
1344 /tmp/debug<pid>.sock, you could use this:
1345 PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
1347 # connect with e.g.: socat readline /tmp/debug123.sock
1348 Or to bind to tcp port 4545 on localhost:
1350 PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
1352 # connect with e.g.: telnet localhost 4545
1353 Note that creating sockets in /tmp or on localhost is very unsafe
1355 on multiuser systems.
1356 "PERL_ANYEVENT_DEBUG_WRAP"
1358 Can be set to 0, 1 or 2 and enables wrapping of all watchers for
1359 debugging purposes. See "AnyEvent::Debug::wrap" for details.
1360 "PERL_ANYEVENT_MODEL"
1362 This can be used to specify the event model to be used by AnyEvent,
1363 before auto detection and -probing kicks in.
1364 It normally is a string consisting entirely of ASCII letters (e.g.
1366 "EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended
1367 and the resulting module name is loaded and - if the load was
1368 successful - used as event model backend. If it fails to load then
1369 AnyEvent will proceed with auto detection and -probing.
1370 If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
1372 then nothing gets prepended and the module name is used as-is
1373 (hint: "::" at the end of a string designates a module name and
1374 quotes it appropriately).
1375 For example, to force the pure perl model (AnyEvent::Loop::Perl)
1377 you could start your program like this:
1378 PERL_ANYEVENT_MODEL=Perl perl ...
1380 "PERL_ANYEVENT_IO_MODEL"
1382 The current file I/O model - see AnyEvent::IO for more info.
1383 At the moment, only "Perl" (small, pure-perl, synchronous) and
1385 "IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
1386 if AnyEvent::AIO can be loaded, otherwise it is "Perl".
1387 "PERL_ANYEVENT_PROTOCOLS"
1389 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1390 preferences for IPv4 or IPv6. The default is unspecified (and might
1391 change, or be the result of auto probing).
1392 Must be set to a comma-separated list of protocols or address
1394 families, current supported: "ipv4" and "ipv6". Only protocols
1395 mentioned will be used, and preference will be given to protocols
1396 mentioned earlier in the list.
1397 This variable can effectively be used for denial-of-service attacks
1399 against local programs (e.g. when setuid), although the impact is
1400 likely small, as the program has to handle connection and other
1401 failures anyways.
1402 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1404 IPv6, but support both and try to use both.
1405 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1406 resolve or contact IPv6 addresses.
1407 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6,
1408 but prefer IPv6 over IPv4.
1409 "PERL_ANYEVENT_HOSTS"
1411 This variable, if specified, overrides the /etc/hosts file used by
1412 AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
1413 read from that file instead.
1414 "PERL_ANYEVENT_EDNS0"
1416 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1417 for DNS. This extension is generally useful to reduce DNS traffic,
1418 especially when DNSSEC is involved, but some (broken) firewalls
1419 drop such DNS packets, which is why it is off by default.
1420 Setting this variable to 1 will cause AnyEvent::DNS to announce
1422 EDNS0 in its DNS requests.
1423 "PERL_ANYEVENT_MAX_FORKS"
1425 The maximum number of child processes that
1426 "AnyEvent::Util::fork_call" will create in parallel.
1427 "PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1429 The default value for the "max_outstanding" parameter for the
1430 default DNS resolver - this is the maximum number of parallel DNS
1431 requests that are sent to the DNS server.
1432 "PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
1434 Perl has inherently racy signal handling (you can basically choose
1435 between losing signals and memory corruption) - pure perl event
1436 loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
1437 available) therefore have to poll regularly to avoid losing
1438 signals.
1439 Some event loops are racy, but don't poll regularly, and some event
1441 loops are written in C but are still racy. For those event loops,
1442 AnyEvent installs a timer that regularly wakes up the event loop.
1443 By default, the interval for this timer is 10 seconds, but you can
1445 override this delay with this environment variable (or by setting
1446 the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
1447 watchers).
1448 Lower values increase CPU (and energy) usage, higher values can
1450 introduce long delays when reaping children or waiting for signals.
1451 The AnyEvent::Async module, if available, will be used to avoid
1453 this polling (with most event loops).
1454 "PERL_ANYEVENT_RESOLV_CONF"
1456 The absolute path to a resolv.conf-style file to use instead of
1457 /etc/resolv.conf (or the OS-specific configuration) in the default
1458 resolver, or the empty string to select the default configuration.
1459 "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1461 When neither "ca_file" nor "ca_path" was specified during
1462 AnyEvent::TLS context creation, and either of these environment
1463 variables are nonempty, they will be used to specify CA certificate
1464 locations instead of a system-dependent default.
1465 "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
1467 When these are set to 1, then the respective modules are not
1468 loaded. Mostly good for testing AnyEvent itself.
1469
1471 This is an advanced topic that you do not normally need to use AnyEvent
1472 in a module. This section is only of use to event loop authors who want
1473 to provide AnyEvent compatibility.
1474 If you need to support another event library which isn't directly
1476 supported by AnyEvent, you can supply your own interface to it by
1477 pushing, before the first watcher gets created, the package name of the
1478 event module and the package name of the interface to use onto
1479 @AnyEvent::REGISTRY. You can do that before and even without loading
1480 AnyEvent, so it is reasonably cheap.
1481 Example:
1483 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
1485 This tells AnyEvent to (literally) use the "urxvt::anyevent::"
1487 package/class when it finds the "urxvt" package/module is already
1488 loaded.
1489 When AnyEvent is loaded and asked to find a suitable event model, it
1491 will first check for the presence of urxvt by trying to "use" the
1492 "urxvt::anyevent" module.
1493 The class should provide implementations for all watcher types. See
1495 AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code)
1496 and so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to
1497 see the sources.
1498 If you don't provide "signal" and "child" watchers than AnyEvent will
1500 provide suitable (hopefully) replacements.
1501 The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
1503 terminal emulator uses the above line as-is. An interface isn't
1504 included in AnyEvent because it doesn't make sense outside the embedded
1505 interpreter inside rxvt-unicode, and it is updated and maintained as
1506 part of the rxvt-unicode distribution.
1507 rxvt-unicode also cheats a bit by not providing blocking access to
1509 condition variables: code blocking while waiting for a condition will
1510 "die". This still works with most modules/usages, and blocking calls
1511 must not be done in an interactive application, so it makes sense.
1512
1514 The following program uses an I/O watcher to read data from STDIN, a
1515 timer to display a message once per second, and a condition variable to
1516 quit the program when the user enters quit:
1517 use AnyEvent;
1519 my $cv = AnyEvent->condvar;
1521 my $io_watcher = AnyEvent->io (
1523 fh => \*STDIN,
1524 poll => 'r',
1525 cb => sub {
1526 warn "io event <$_[0]>\n"; # will always output <r>
1527 chomp (my $input = <STDIN>); # read a line
1528 warn "read: $input\n"; # output what has been read
1529 $cv->send if $input =~ /^q/i; # quit program if /^q/i
1530 },
1531 );
1532 my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1534 warn "timeout\n"; # print 'timeout' at most every second
1535 });
1536 $cv->recv; # wait until user enters /^q/i
1538
1540 Consider the Net::FCP module. It features (among others) the following
1541 API calls, which are to freenet what HTTP GET requests are to http:
1542 my $data = $fcp->client_get ($url); # blocks
1544 my $transaction = $fcp->txn_client_get ($url); # does not block
1546 $transaction->cb ( sub { ... } ); # set optional result callback
1547 my $data = $transaction->result; # possibly blocks
1548 The "client_get" method works like "LWP::Simple::get": it requests the
1550 given URL and waits till the data has arrived. It is defined to be:
1551 sub client_get { $_[0]->txn_client_get ($_[1])->result }
1553 And in fact is automatically generated. This is the blocking API of
1555 Net::FCP, and it works as simple as in any other, similar, module.
1556 More complicated is "txn_client_get": It only creates a transaction
1558 (completion, result, ...) object and initiates the transaction.
1559 my $txn = bless { }, Net::FCP::Txn::;
1561 It also creates a condition variable that is used to signal the
1563 completion of the request:
1564 $txn->{finished} = AnyAvent->condvar;
1566 It then creates a socket in non-blocking mode.
1568 socket $txn->{fh}, ...;
1570 fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
1571 connect $txn->{fh}, ...
1572 and !$!{EWOULDBLOCK}
1573 and !$!{EINPROGRESS}
1574 and Carp::croak "unable to connect: $!\n";
1575 Then it creates a write-watcher which gets called whenever an error
1577 occurs or the connection succeeds:
1578 $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
1580 And returns this transaction object. The "fh_ready_w" callback gets
1582 called as soon as the event loop detects that the socket is ready for
1583 writing.
1584 The "fh_ready_w" method makes the socket blocking again, writes the
1586 request data and replaces the watcher by a read watcher (waiting for
1587 reply data). The actual code is more complicated, but that doesn't
1588 matter for this example:
1589 fcntl $txn->{fh}, F_SETFL, 0;
1591 syswrite $txn->{fh}, $txn->{request}
1592 or die "connection or write error";
1593 $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
1594 Again, "fh_ready_r" waits till all data has arrived, and then stores
1596 the result and signals any possible waiters that the request has
1597 finished:
1598 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
1600 if (end-of-file or data complete) {
1602 $txn->{result} = $txn->{buf};
1603 $txn->{finished}->send;
1604 $txb->{cb}->($txn) of $txn->{cb}; # also call callback
1605 }
1606 The "result" method, finally, just waits for the finished signal (if
1608 the request was already finished, it doesn't wait, of course, and
1609 returns the data:
1610 $txn->{finished}->recv;
1612 return $txn->{result};
1613 The actual code goes further and collects all errors ("die"s,
1615 exceptions) that occurred during request processing. The "result"
1616 method detects whether an exception as thrown (it is stored inside the
1617 $txn object) and just throws the exception, which means connection
1618 errors and other problems get reported to the code that tries to use
1619 the result, not in a random callback.
1620 All of this enables the following usage styles:
1622 1. Blocking:
1624 my $data = $fcp->client_get ($url);
1626 2. Blocking, but running in parallel:
1628 my @datas = map $_->result,
1630 map $fcp->txn_client_get ($_),
1631 @urls;
1632 Both blocking examples work without the module user having to know
1634 anything about events.
1635 3a. Event-based in a main program, using any supported event module:
1637 use EV;
1639 $fcp->txn_client_get ($url)->cb (sub {
1641 my $txn = shift;
1642 my $data = $txn->result;
1643 ...
1644 });
1645 EV::run;
1647 3b. The module user could use AnyEvent, too:
1649 use AnyEvent;
1651 my $quit = AnyEvent->condvar;
1653 $fcp->txn_client_get ($url)->cb (sub {
1655 ...
1656 $quit->send;
1657 });
1658 $quit->recv;
1660
1662 To give you an idea of the performance and overheads that AnyEvent adds
1663 over the event loops themselves and to give you an impression of the
1664 speed of various event loops I prepared some benchmarks.
1665 BENCHMARKING ANYEVENT OVERHEAD
1667 Here is a benchmark of various supported event models used natively and
1668 through AnyEvent. The benchmark creates a lot of timers (with a zero
1669 timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1670 which it is), lets them fire exactly once and destroys them again.
1671 Source code for this benchmark is found as eg/bench in the AnyEvent
1673 distribution. It uses the AE interface, which makes a real difference
1674 for the EV and Perl backends only.
1675 Explanation of the columns
1677 watcher is the number of event watchers created/destroyed. Since
1679 different event models feature vastly different performances, each
1680 event loop was given a number of watchers so that overall runtime is
1681 acceptable and similar between tested event loop (and keep them from
1682 crashing): Glib would probably take thousands of years if asked to
1683 process the same number of watchers as EV in this benchmark.
1684 bytes is the number of bytes (as measured by the resident set size,
1686 RSS) consumed by each watcher. This method of measuring captures both C
1687 and Perl-based overheads.
1688 create is the time, in microseconds (millionths of seconds), that it
1690 takes to create a single watcher. The callback is a closure shared
1691 between all watchers, to avoid adding memory overhead. That means
1692 closure creation and memory usage is not included in the figures.
1693 invoke is the time, in microseconds, used to invoke a simple callback.
1695 The callback simply counts down a Perl variable and after it was
1696 invoked "watcher" times, it would "->send" a condvar once to signal the
1697 end of this phase.
1698 destroy is the time, in microseconds, that it takes to destroy a single
1700 watcher.
1701 Results
1703 name watchers bytes create invoke destroy comment
1705 EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1706 EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1707 Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1708 Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1709 Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1710 Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1711 IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1712 IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1713 Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1714 Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1715 POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1716 POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1717 Discussion
1719 The benchmark does not measure scalability of the event loop very well.
1721 For example, a select-based event loop (such as the pure perl one) can
1722 never compete with an event loop that uses epoll when the number of
1723 file descriptors grows high. In this benchmark, all events become ready
1724 at the same time, so select/poll-based implementations get an unnatural
1725 speed boost.
1726 Also, note that the number of watchers usually has a nonlinear effect
1728 on overall speed, that is, creating twice as many watchers doesn't take
1729 twice the time - usually it takes longer. This puts event loops tested
1730 with a higher number of watchers at a disadvantage.
1731 To put the range of results into perspective, consider that on the
1733 benchmark machine, handling an event takes roughly 1600 CPU cycles with
1734 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1735 CPU cycles with POE.
1736 "EV" is the sole leader regarding speed and memory use, which are both
1738 maximal/minimal, respectively. When using the AE API there is zero
1739 overhead (when going through the AnyEvent API create is about 5-6 times
1740 slower, with other times being equal, so still uses far less memory
1741 than any other event loop and is still faster than Event natively).
1742 The pure perl implementation is hit in a few sweet spots (both the
1744 constant timeout and the use of a single fd hit optimisations in the
1745 perl interpreter and the backend itself). Nevertheless this shows that
1746 it adds very little overhead in itself. Like any select-based backend
1747 its performance becomes really bad with lots of file descriptors (and
1748 few of them active), of course, but this was not subject of this
1749 benchmark.
1750 The "Event" module has a relatively high setup and callback invocation
1752 cost, but overall scores in on the third place.
1753 "IO::Async" performs admirably well, about on par with "Event", even
1755 when using its pure perl backend.
1756 "Glib"'s memory usage is quite a bit higher, but it features a faster
1758 callback invocation and overall ends up in the same class as "Event".
1759 However, Glib scales extremely badly, doubling the number of watchers
1760 increases the processing time by more than a factor of four, making it
1761 completely unusable when using larger numbers of watchers (note that
1762 only a single file descriptor was used in the benchmark, so
1763 inefficiencies of "poll" do not account for this).
1764 The "Tk" adaptor works relatively well. The fact that it crashes with
1766 more than 2000 watchers is a big setback, however, as correctness takes
1767 precedence over speed. Nevertheless, its performance is surprising, as
1768 the file descriptor is dup()ed for each watcher. This shows that the
1769 dup() employed by some adaptors is not a big performance issue (it does
1770 incur a hidden memory cost inside the kernel which is not reflected in
1771 the figures above).
1772 "POE", regardless of underlying event loop (whether using its pure perl
1774 select-based backend or the Event module, the POE-EV backend couldn't
1775 be tested because it wasn't working) shows abysmal performance and
1776 memory usage with AnyEvent: Watchers use almost 30 times as much memory
1777 as EV watchers, and 10 times as much memory as Event (the high memory
1778 requirements are caused by requiring a session for each watcher).
1779 Watcher invocation speed is almost 900 times slower than with
1780 AnyEvent's pure perl implementation.
1781 The design of the POE adaptor class in AnyEvent can not really account
1783 for the performance issues, though, as session creation overhead is
1784 small compared to execution of the state machine, which is coded pretty
1785 optimally within AnyEvent::Impl::POE (and while everybody agrees that
1786 using multiple sessions is not a good approach, especially regarding
1787 memory usage, even the author of POE could not come up with a faster
1788 design).
1789 Summary
1791 • Using EV through AnyEvent is faster than any other event loop (even
1793 when used without AnyEvent), but most event loops have acceptable
1794 performance with or without AnyEvent.
1795 • The overhead AnyEvent adds is usually much smaller than the
1797 overhead of the actual event loop, only with extremely fast event
1798 loops such as EV does AnyEvent add significant overhead.
1799 • You should avoid POE like the plague if you want performance or
1801 reasonable memory usage.
1802 BENCHMARKING THE LARGE SERVER CASE
1804 This benchmark actually benchmarks the event loop itself. It works by
1805 creating a number of "servers": each server consists of a socket pair,
1806 a timeout watcher that gets reset on activity (but never fires), and an
1807 I/O watcher waiting for input on one side of the socket. Each time the
1808 socket watcher reads a byte it will write that byte to a random other
1809 "server".
1810 The effect is that there will be a lot of I/O watchers, only part of
1812 which are active at any one point (so there is a constant number of
1813 active fds for each loop iteration, but which fds these are is random).
1814 The timeout is reset each time something is read because that reflects
1815 how most timeouts work (and puts extra pressure on the event loops).
1816 In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1818 100 (1%) are active. This mirrors the activity of large servers with
1819 many connections, most of which are idle at any one point in time.
1820 Source code for this benchmark is found as eg/bench2 in the AnyEvent
1822 distribution. It uses the AE interface, which makes a real difference
1823 for the EV and Perl backends only.
1824 Explanation of the columns
1826 sockets is the number of sockets, and twice the number of "servers" (as
1828 each server has a read and write socket end).
1829 create is the time it takes to create a socket pair (which is
1831 nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1832 request, the most important value, is the time it takes to handle a
1834 single "request", that is, reading the token from the pipe and
1835 forwarding it to another server. This includes deleting the old timeout
1836 and creating a new one that moves the timeout into the future.
1837 Results
1839 name sockets create request
1841 EV 20000 62.66 7.99
1842 Perl 20000 68.32 32.64
1843 IOAsync 20000 174.06 101.15 epoll
1844 IOAsync 20000 174.67 610.84 poll
1845 Event 20000 202.69 242.91
1846 Glib 20000 557.01 1689.52
1847 POE 20000 341.54 12086.32 uses POE::Loop::Event
1848 Discussion
1850 This benchmark does measure scalability and overall performance of the
1852 particular event loop.
1853 EV is again fastest. Since it is using epoll on my system, the setup
1855 time is relatively high, though.
1856 Perl surprisingly comes second. It is much faster than the C-based
1858 event loops Event and Glib.
1859 IO::Async performs very well when using its epoll backend, and still
1861 quite good compared to Glib when using its pure perl backend.
1862 Event suffers from high setup time as well (look at its code and you
1864 will understand why). Callback invocation also has a high overhead
1865 compared to the "$_->() for .."-style loop that the Perl event loop
1866 uses. Event uses select or poll in basically all documented
1867 configurations.
1868 Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
1870 clearly fails to perform with many filehandles or in busy servers.
1871 POE is still completely out of the picture, taking over 1000 times as
1873 long as EV, and over 100 times as long as the Perl implementation, even
1874 though it uses a C-based event loop in this case.
1875 Summary
1877 • The pure perl implementation performs extremely well.
1879 • Avoid Glib or POE in large projects where performance matters.
1881 BENCHMARKING SMALL SERVERS
1883 While event loops should scale (and select-based ones do not...) even
1884 to large servers, most programs we (or I :) actually write have only a
1885 few I/O watchers.
1886 In this benchmark, I use the same benchmark program as in the large
1888 server case, but it uses only eight "servers", of which three are
1889 active at any one time. This should reflect performance for a small
1890 server relatively well.
1891 The columns are identical to the previous table.
1893 Results
1895 name sockets create request
1897 EV 16 20.00 6.54
1898 Perl 16 25.75 12.62
1899 Event 16 81.27 35.86
1900 Glib 16 32.63 15.48
1901 POE 16 261.87 276.28 uses POE::Loop::Event
1902 Discussion
1904 The benchmark tries to test the performance of a typical small server.
1906 While knowing how various event loops perform is interesting, keep in
1907 mind that their overhead in this case is usually not as important, due
1908 to the small absolute number of watchers (that is, you need efficiency
1909 and speed most when you have lots of watchers, not when you only have a
1910 few of them).
1911 EV is again fastest.
1913 Perl again comes second. It is noticeably faster than the C-based event
1915 loops Event and Glib, although the difference is too small to really
1916 matter.
1917 POE also performs much better in this case, but is is still far behind
1919 the others.
1920 Summary
1922 • C-based event loops perform very well with small number of
1924 watchers, as the management overhead dominates.
1925 THE IO::Lambda BENCHMARK
1927 Recently I was told about the benchmark in the IO::Lambda manpage,
1928 which could be misinterpreted to make AnyEvent look bad. In fact, the
1929 benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
1930 better (which shouldn't come as a surprise to anybody). As such, the
1931 benchmark is fine, and mostly shows that the AnyEvent backend from
1932 IO::Lambda isn't very optimal. But how would AnyEvent compare when used
1933 without the extra baggage? To explore this, I wrote the equivalent
1934 benchmark for AnyEvent.
1935 The benchmark itself creates an echo-server, and then, for 500 times,
1937 connects to the echo server, sends a line, waits for the reply, and
1938 then creates the next connection. This is a rather bad benchmark, as it
1939 doesn't test the efficiency of the framework or much non-blocking I/O,
1940 but it is a benchmark nevertheless.
1941 name runtime
1943 Lambda/select 0.330 sec
1944 + optimized 0.122 sec
1945 Lambda/AnyEvent 0.327 sec
1946 + optimized 0.138 sec
1947 Raw sockets/select 0.077 sec
1948 POE/select, components 0.662 sec
1949 POE/select, raw sockets 0.226 sec
1950 POE/select, optimized 0.404 sec
1951 AnyEvent/select/nb 0.085 sec
1953 AnyEvent/EV/nb 0.068 sec
1954 +state machine 0.134 sec
1955 The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
1957 benchmarks actually make blocking connects and use 100% blocking I/O,
1958 defeating the purpose of an event-based solution. All of the newly
1959 written AnyEvent benchmarks use 100% non-blocking connects (using
1960 AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
1961 resolver), so AnyEvent is at a disadvantage here, as non-blocking
1962 connects generally require a lot more bookkeeping and event handling
1963 than blocking connects (which involve a single syscall only).
1964 The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
1966 offers similar expressive power as POE and IO::Lambda, using
1967 conventional Perl syntax. This means that both the echo server and the
1968 client are 100% non-blocking, further placing it at a disadvantage.
1969 As you can see, the AnyEvent + EV combination even beats the hand-
1971 optimised "raw sockets benchmark", while AnyEvent + its pure perl
1972 backend easily beats IO::Lambda and POE.
1973 And even the 100% non-blocking version written using the high-level
1975 (and slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1976 higher level ("unoptimised") abstractions by a large margin, even
1977 though it does all of DNS, tcp-connect and socket I/O in a non-blocking
1978 way.
1979 The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1981 eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1982 part of the IO::Lambda distribution and were used without any changes.
1983
1985 AnyEvent currently installs handlers for these signals:
1986 SIGCHLD
1988 A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1989 emulation for event loops that do not support them natively. Also,
1990 some event loops install a similar handler.
1991 Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1993 then AnyEvent will reset it to default, to avoid losing child exit
1994 statuses.
1995 SIGPIPE
1997 A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1998 "undef" when AnyEvent gets loaded.
1999 The rationale for this is that AnyEvent users usually do not really
2001 depend on SIGPIPE delivery (which is purely an optimisation for
2002 shell use, or badly-written programs), but "SIGPIPE" can cause
2003 spurious and rare program exits as a lot of people do not expect
2004 "SIGPIPE" when writing to some random socket.
2005 The rationale for installing a no-op handler as opposed to ignoring
2007 it is that this way, the handler will be restored to defaults on
2008 exec.
2009 Feel free to install your own handler, or reset it to defaults.
2011
2013 One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl
2014 (and its built-in modules) are required to use it.
2015 That does not mean that AnyEvent won't take advantage of some
2017 additional modules if they are installed.
2018 This section explains which additional modules will be used, and how
2020 they affect AnyEvent's operation.
2021 Async::Interrupt
2023 This slightly arcane module is used to implement fast signal
2024 handling: To my knowledge, there is no way to do completely race-
2025 free and quick signal handling in pure perl. To ensure that signals
2026 still get delivered, AnyEvent will start an interval timer to wake
2027 up perl (and catch the signals) with some delay (default is 10
2028 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
2029 If this module is available, then it will be used to implement
2031 signal catching, which means that signals will not be delayed, and
2032 the event loop will not be interrupted regularly, which is more
2033 efficient (and good for battery life on laptops).
2034 This affects not just the pure-perl event loop, but also other
2036 event loops that have no signal handling on their own (e.g. Glib,
2037 Tk, Qt).
2038 Some event loops (POE, Event, Event::Lib) offer signal watchers
2040 natively, and either employ their own workarounds (POE) or use
2041 AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
2042 Installing Async::Interrupt does nothing for those backends.
2043 EV This module isn't really "optional", as it is simply one of the
2045 backend event loops that AnyEvent can use. However, it is simply
2046 the best event loop available in terms of features, speed and
2047 stability: It supports the AnyEvent API optimally, implements all
2048 the watcher types in XS, does automatic timer adjustments even when
2049 no monotonic clock is available, can take avdantage of advanced
2050 kernel interfaces such as "epoll" and "kqueue", and is the fastest
2051 backend by far. You can even embed Glib/Gtk2 in it (or vice versa,
2052 see EV::Glib and Glib::EV).
2053 If you only use backends that rely on another event loop (e.g.
2055 "Tk"), then this module will do nothing for you.
2056 Guard
2058 The guard module, when used, will be used to implement
2059 "AnyEvent::Util::guard". This speeds up guards considerably (and
2060 uses a lot less memory), but otherwise doesn't affect guard
2061 operation much. It is purely used for performance.
2062 JSON and JSON::XS
2064 One of these modules is required when you want to read or write
2065 JSON data via AnyEvent::Handle. JSON is also written in pure-perl,
2066 but can take advantage of the ultra-high-speed JSON::XS module when
2067 it is installed.
2068 Net::SSLeay
2070 Implementing TLS/SSL in Perl is certainly interesting, but not very
2071 worthwhile: If this module is installed, then AnyEvent::Handle
2072 (with the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
2073 Time::HiRes
2075 This module is part of perl since release 5.008. It will be used
2076 when the chosen event library does not come with a timing source of
2077 its own. The pure-perl event loop (AnyEvent::Loop) will
2078 additionally load it to try to use a monotonic clock for timing
2079 stability.
2080 AnyEvent::AIO (and IO::AIO)
2082 The default implementation of AnyEvent::IO is to do I/O
2083 synchronously, stopping programs while they access the disk, which
2084 is fine for a lot of programs.
2085 Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
2087 switch to a true asynchronous implementation, so event processing
2088 can continue even while waiting for disk I/O.
2089
2091 Most event libraries are not fork-safe. The ones who are usually are
2092 because they rely on inefficient but fork-safe "select" or "poll" calls
2093 - higher performance APIs such as BSD's kqueue or the dreaded Linux
2094 epoll are usually badly thought-out hacks that are incompatible with
2095 fork in one way or another. Only EV is fully fork-aware and ensures
2096 that you continue event-processing in both parent and child (or both,
2097 if you know what you are doing).
2098 This means that, in general, you cannot fork and do event processing in
2100 the child if the event library was initialised before the fork (which
2101 usually happens when the first AnyEvent watcher is created, or the
2102 library is loaded).
2103 If you have to fork, you must either do so before creating your first
2105 watcher OR you must not use AnyEvent at all in the child OR you must do
2106 something completely out of the scope of AnyEvent (see below).
2107 The problem of doing event processing in the parent and the child is
2109 much more complicated: even for backends that are fork-aware or fork-
2110 safe, their behaviour is not usually what you want: fork clones all
2111 watchers, that means all timers, I/O watchers etc. are active in both
2112 parent and child, which is almost never what you want. Using "exec" to
2113 start worker children from some kind of manage prrocess is usually
2114 preferred, because it is much easier and cleaner, at the expense of
2115 having to have another binary.
2116 In addition to logical problems with fork, there are also
2118 implementation problems. For example, on POSIX systems, you cannot fork
2119 at all in Perl code if a thread (I am talking of pthreads here) was
2120 ever created in the process, and this is just the tip of the iceberg.
2121 In general, using fork from Perl is difficult, and attempting to use
2122 fork without an exec to implement some kind of parallel processing is
2123 almost certainly doomed.
2124 To safely fork and exec, you should use a module such as
2126 Proc::FastSpawn that let's you safely fork and exec new processes.
2127 If you want to do multiprocessing using processes, you can look at the
2129 AnyEvent::Fork module (and some related modules such as
2130 AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
2131 This module allows you to safely create subprocesses without any
2132 limitations - you can use X11 toolkits or AnyEvent in the children
2133 created by AnyEvent::Fork safely and without any special precautions.
2134
2136 AnyEvent can be forced to load any event model via
2137 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
2138 to execute arbitrary code or directly gain access, it can easily be
2139 used to make the program hang or malfunction in subtle ways, as
2140 AnyEvent watchers will not be active when the program uses a different
2141 event model than specified in the variable.
2142 You can make AnyEvent completely ignore this variable by deleting it
2144 before the first watcher gets created, e.g. with a "BEGIN" block:
2145 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
2147 use AnyEvent;
2149 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that
2151 can be used to probe what backend is used and gain other information
2152 (which is probably even less useful to an attacker than
2153 PERL_ANYEVENT_MODEL), and $ENV{PERL_ANYEVENT_STRICT}.
2154 Note that AnyEvent will remove all environment variables starting with
2156 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
2157 enabled.
2158
2160 Perl 5.8 has numerous memleaks that sometimes hit this module and are
2161 hard to work around. If you suffer from memleaks, first upgrade to Perl
2162 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
2163 annoying memleaks, such as leaking on "map" and "grep" but it is
2164 usually not as pronounced).
2165
2167 Tutorial/Introduction: AnyEvent::Intro.
2168 FAQ: AnyEvent::FAQ.
2170 Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
2172 (simply logging).
2173 Development/Debugging: AnyEvent::Strict (stricter checking),
2175 AnyEvent::Debug (interactive shell, watcher tracing).
2176 Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
2178 Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK, Cocoa::EventLoop, UV.
2179 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
2181 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
2182 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
2183 AnyEvent::Impl::IOAsync, AnyEvent::Impl::Irssi, AnyEvent::Impl::FLTK,
2184 AnyEvent::Impl::Cocoa, AnyEvent::Impl::UV.
2185 Non-blocking handles, pipes, stream sockets, TCP clients and servers:
2187 AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
2188 Asynchronous File I/O: AnyEvent::IO.
2190 Asynchronous DNS: AnyEvent::DNS.
2192 Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
2194 Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
2196 AnyEvent::HTTP.
2197
2199 Marc Lehmann <schmorp@schmorp.de>
2200 http://anyevent.schmorp.de
2201perl v5.34.0 2021-07-22 AnyEvent(3)