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1=head1 NAME 1=head1 NAME
2 2
3AnyEvent - provide framework for multiple event loops 3AnyEvent - provide framework for multiple event loops
4 4
5EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops 5EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6 6
7=head1 SYNOPSIS 7=head1 SYNOPSIS
8 8
9 use AnyEvent; 9 use AnyEvent;
10 10
15 my $w = AnyEvent->timer (after => $seconds, cb => sub { 15 my $w = AnyEvent->timer (after => $seconds, cb => sub {
16 ... 16 ...
17 }); 17 });
18 18
19 my $w = AnyEvent->condvar; # stores whether a condition was flagged 19 my $w = AnyEvent->condvar; # stores whether a condition was flagged
20 $w->wait; # enters "main loop" till $condvar gets ->broadcast 20 $w->wait; # enters "main loop" till $condvar gets ->send
21 $w->broadcast; # wake up current and all future wait's 21 $w->send; # wake up current and all future wait's
22 22
23=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT) 23=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24 24
25Glib, POE, IO::Async, Event... CPAN offers event models by the dozen 25Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26nowadays. So what is different about AnyEvent? 26nowadays. So what is different about AnyEvent?
66 66
67Of course, if you want lots of policy (this can arguably be somewhat 67Of course, if you want lots of policy (this can arguably be somewhat
68useful) and you want to force your users to use the one and only event 68useful) and you want to force your users to use the one and only event
69model, you should I<not> use this module. 69model, you should I<not> use this module.
70 70
71
72=head1 DESCRIPTION 71=head1 DESCRIPTION
73 72
74L<AnyEvent> provides an identical interface to multiple event loops. This 73L<AnyEvent> provides an identical interface to multiple event loops. This
75allows module authors to utilise an event loop without forcing module 74allows module authors to utilise an event loop without forcing module
76users to use the same event loop (as only a single event loop can coexist 75users to use the same event loop (as only a single event loop can coexist
79The interface itself is vaguely similar, but not identical to the L<Event> 78The interface itself is vaguely similar, but not identical to the L<Event>
80module. 79module.
81 80
82During the first call of any watcher-creation method, the module tries 81During the first call of any watcher-creation method, the module tries
83to detect the currently loaded event loop by probing whether one of the 82to detect the currently loaded event loop by probing whether one of the
84following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, 83following modules is already loaded: L<EV>,
85L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>, 84L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86L<POE>. The first one found is used. If none are found, the module tries 85L<POE>. The first one found is used. If none are found, the module tries
87to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl 86to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
88adaptor should always succeed) in the order given. The first one that can 87adaptor should always succeed) in the order given. The first one that can
89be successfully loaded will be used. If, after this, still none could be 88be successfully loaded will be used. If, after this, still none could be
141=head2 I/O WATCHERS 140=head2 I/O WATCHERS
142 141
143You can create an I/O watcher by calling the C<< AnyEvent->io >> method 142You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144with the following mandatory key-value pairs as arguments: 143with the following mandatory key-value pairs as arguments:
145 144
146C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for 145C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
147events. C<poll> must be a string that is either C<r> or C<w>, which 146for events. C<poll> must be a string that is either C<r> or C<w>,
148creates a watcher waiting for "r"eadable or "w"ritable events, 147which creates a watcher waiting for "r"eadable or "w"ritable events,
149respectively. C<cb> is the callback to invoke each time the file handle 148respectively. C<cb> is the callback to invoke each time the file handle
150becomes ready. 149becomes ready.
151 150
152As long as the I/O watcher exists it will keep the file descriptor or a 151Although the callback might get passed parameters, their value and
153copy of it alive/open. 152presence is undefined and you cannot rely on them. Portable AnyEvent
153callbacks cannot use arguments passed to I/O watcher callbacks.
154 154
155The I/O watcher might use the underlying file descriptor or a copy of it.
155It is not allowed to close a file handle as long as any watcher is active 156You must not close a file handle as long as any watcher is active on the
156on the underlying file descriptor. 157underlying file descriptor.
157 158
158Some event loops issue spurious readyness notifications, so you should 159Some event loops issue spurious readyness notifications, so you should
159always use non-blocking calls when reading/writing from/to your file 160always use non-blocking calls when reading/writing from/to your file
160handles. 161handles.
161 162
172 173
173You can create a time watcher by calling the C<< AnyEvent->timer >> 174You can create a time watcher by calling the C<< AnyEvent->timer >>
174method with the following mandatory arguments: 175method with the following mandatory arguments:
175 176
176C<after> specifies after how many seconds (fractional values are 177C<after> specifies after how many seconds (fractional values are
177supported) should the timer activate. C<cb> the callback to invoke in that 178supported) the callback should be invoked. C<cb> is the callback to invoke
178case. 179in that case.
180
181Although the callback might get passed parameters, their value and
182presence is undefined and you cannot rely on them. Portable AnyEvent
183callbacks cannot use arguments passed to time watcher callbacks.
179 184
180The timer callback will be invoked at most once: if you want a repeating 185The timer callback will be invoked at most once: if you want a repeating
181timer you have to create a new watcher (this is a limitation by both Tk 186timer you have to create a new watcher (this is a limitation by both Tk
182and Glib). 187and Glib).
183 188
228 233
229You can watch for signals using a signal watcher, C<signal> is the signal 234You can watch for signals using a signal watcher, C<signal> is the signal
230I<name> without any C<SIG> prefix, C<cb> is the Perl callback to 235I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
231be invoked whenever a signal occurs. 236be invoked whenever a signal occurs.
232 237
238Although the callback might get passed parameters, their value and
239presence is undefined and you cannot rely on them. Portable AnyEvent
240callbacks cannot use arguments passed to signal watcher callbacks.
241
233Multiple signal occurances can be clumped together into one callback 242Multiple signal occurances can be clumped together into one callback
234invocation, and callback invocation will be synchronous. synchronous means 243invocation, and callback invocation will be synchronous. synchronous means
235that it might take a while until the signal gets handled by the process, 244that it might take a while until the signal gets handled by the process,
236but it is guarenteed not to interrupt any other callbacks. 245but it is guarenteed not to interrupt any other callbacks.
237 246
251 260
252The child process is specified by the C<pid> argument (if set to C<0>, it 261The child process is specified by the C<pid> argument (if set to C<0>, it
253watches for any child process exit). The watcher will trigger as often 262watches for any child process exit). The watcher will trigger as often
254as status change for the child are received. This works by installing a 263as status change for the child are received. This works by installing a
255signal handler for C<SIGCHLD>. The callback will be called with the pid 264signal handler for C<SIGCHLD>. The callback will be called with the pid
256and exit status (as returned by waitpid). 265and exit status (as returned by waitpid), so unlike other watcher types,
266you I<can> rely on child watcher callback arguments.
257 267
258Example: wait for pid 1333 268There is a slight catch to child watchers, however: you usually start them
269I<after> the child process was created, and this means the process could
270have exited already (and no SIGCHLD will be sent anymore).
271
272Not all event models handle this correctly (POE doesn't), but even for
273event models that I<do> handle this correctly, they usually need to be
274loaded before the process exits (i.e. before you fork in the first place).
275
276This means you cannot create a child watcher as the very first thing in an
277AnyEvent program, you I<have> to create at least one watcher before you
278C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
279
280Example: fork a process and wait for it
281
282 my $done = AnyEvent->condvar;
283
284 AnyEvent::detect; # force event module to be initialised
285
286 my $pid = fork or exit 5;
259 287
260 my $w = AnyEvent->child ( 288 my $w = AnyEvent->child (
261 pid => 1333, 289 pid => $pid,
262 cb => sub { 290 cb => sub {
263 my ($pid, $status) = @_; 291 my ($pid, $status) = @_;
264 warn "pid $pid exited with status $status"; 292 warn "pid $pid exited with status $status";
293 $done->send;
265 }, 294 },
266 ); 295 );
267 296
297 # do something else, then wait for process exit
298 $done->wait;
299
268=head2 CONDITION VARIABLES 300=head2 CONDITION VARIABLES
269 301
302If you are familiar with some event loops you will know that all of them
303require you to run some blocking "loop", "run" or similar function that
304will actively watch for new events and call your callbacks.
305
306AnyEvent is different, it expects somebody else to run the event loop and
307will only block when necessary (usually when told by the user).
308
309The instrument to do that is called a "condition variable", so called
310because they represent a condition that must become true.
311
270Condition variables can be created by calling the C<< AnyEvent->condvar >> 312Condition variables can be created by calling the C<< AnyEvent->condvar
271method without any arguments. 313>> method, usually without arguments. The only argument pair allowed is
314C<cb>, which specifies a callback to be called when the condition variable
315becomes true.
272 316
273A condition variable waits for a condition - precisely that the C<< 317After creation, the conditon variable is "false" until it becomes "true"
274->broadcast >> method has been called. 318by calling the C<send> method.
275 319
276They are very useful to signal that a condition has been fulfilled, for 320Condition variables are similar to callbacks, except that you can
321optionally wait for them. They can also be called merge points - points
322in time where multiple outstandign events have been processed. And yet
323another way to call them is transations - each condition variable can be
324used to represent a transaction, which finishes at some point and delivers
325a result.
326
327Condition variables are very useful to signal that something has finished,
277example, if you write a module that does asynchronous http requests, 328for example, if you write a module that does asynchronous http requests,
278then a condition variable would be the ideal candidate to signal the 329then a condition variable would be the ideal candidate to signal the
279availability of results. 330availability of results. The user can either act when the callback is
331called or can synchronously C<< ->wait >> for the results.
280 332
281You can also use condition variables to block your main program until 333You can also use them to simulate traditional event loops - for example,
282an event occurs - for example, you could C<< ->wait >> in your main 334you can block your main program until an event occurs - for example, you
283program until the user clicks the Quit button in your app, which would C<< 335could C<< ->wait >> in your main program until the user clicks the Quit
284->broadcast >> the "quit" event. 336button of your app, which would C<< ->send >> the "quit" event.
285 337
286Note that condition variables recurse into the event loop - if you have 338Note that condition variables recurse into the event loop - if you have
287two pirces of code that call C<< ->wait >> in a round-robbin fashion, you 339two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
288lose. Therefore, condition variables are good to export to your caller, but 340lose. Therefore, condition variables are good to export to your caller, but
289you should avoid making a blocking wait yourself, at least in callbacks, 341you should avoid making a blocking wait yourself, at least in callbacks,
290as this asks for trouble. 342as this asks for trouble.
291 343
292This object has two methods: 344Condition variables are represented by hash refs in perl, and the keys
345used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
346easy (it is often useful to build your own transaction class on top of
347AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
348it's C<new> method in your own C<new> method.
349
350There are two "sides" to a condition variable - the "producer side" which
351eventually calls C<< -> send >>, and the "consumer side", which waits
352for the send to occur.
353
354Example:
355
356 # wait till the result is ready
357 my $result_ready = AnyEvent->condvar;
358
359 # do something such as adding a timer
360 # or socket watcher the calls $result_ready->send
361 # when the "result" is ready.
362 # in this case, we simply use a timer:
363 my $w = AnyEvent->timer (
364 after => 1,
365 cb => sub { $result_ready->send },
366 );
367
368 # this "blocks" (while handling events) till the callback
369 # calls send
370 $result_ready->wait;
371
372=head3 METHODS FOR PRODUCERS
373
374These methods should only be used by the producing side, i.e. the
375code/module that eventually sends the signal. Note that it is also
376the producer side which creates the condvar in most cases, but it isn't
377uncommon for the consumer to create it as well.
293 378
294=over 4 379=over 4
295 380
381=item $cv->send (...)
382
383Flag the condition as ready - a running C<< ->wait >> and all further
384calls to C<wait> will (eventually) return after this method has been
385called. If nobody is waiting the send will be remembered.
386
387If a callback has been set on the condition variable, it is called
388immediately from within send.
389
390Any arguments passed to the C<send> call will be returned by all
391future C<< ->wait >> calls.
392
393=item $cv->croak ($error)
394
395Similar to send, but causes all call's wait C<< ->wait >> to invoke
396C<Carp::croak> with the given error message/object/scalar.
397
398This can be used to signal any errors to the condition variable
399user/consumer.
400
401=item $cv->begin ([group callback])
402
403=item $cv->end
404
405These two methods can be used to combine many transactions/events into
406one. For example, a function that pings many hosts in parallel might want
407to use a condition variable for the whole process.
408
409Every call to C<< ->begin >> will increment a counter, and every call to
410C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
411>>, the (last) callback passed to C<begin> will be executed. That callback
412is I<supposed> to call C<< ->send >>, but that is not required. If no
413callback was set, C<send> will be called without any arguments.
414
415Let's clarify this with the ping example:
416
417 my $cv = AnyEvent->condvar;
418
419 my %result;
420 $cv->begin (sub { $cv->send (\%result) });
421
422 for my $host (@list_of_hosts) {
423 $cv->begin;
424 ping_host_then_call_callback $host, sub {
425 $result{$host} = ...;
426 $cv->end;
427 };
428 }
429
430 $cv->end;
431
432This code fragment supposedly pings a number of hosts and calls
433C<send> after results for all then have have been gathered - in any
434order. To achieve this, the code issues a call to C<begin> when it starts
435each ping request and calls C<end> when it has received some result for
436it. Since C<begin> and C<end> only maintain a counter, the order in which
437results arrive is not relevant.
438
439There is an additional bracketing call to C<begin> and C<end> outside the
440loop, which serves two important purposes: first, it sets the callback
441to be called once the counter reaches C<0>, and second, it ensures that
442C<send> is called even when C<no> hosts are being pinged (the loop
443doesn't execute once).
444
445This is the general pattern when you "fan out" into multiple subrequests:
446use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
447is called at least once, and then, for each subrequest you start, call
448C<begin> and for eahc subrequest you finish, call C<end>.
449
450=back
451
452=head3 METHODS FOR CONSUMERS
453
454These methods should only be used by the consuming side, i.e. the
455code awaits the condition.
456
457=over 4
458
296=item $cv->wait 459=item $cv->wait
297 460
298Wait (blocking if necessary) until the C<< ->broadcast >> method has been 461Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
299called on c<$cv>, while servicing other watchers normally. 462>> methods have been called on c<$cv>, while servicing other watchers
463normally.
300 464
301You can only wait once on a condition - additional calls will return 465You can only wait once on a condition - additional calls are valid but
302immediately. 466will return immediately.
467
468If an error condition has been set by calling C<< ->croak >>, then this
469function will call C<croak>.
470
471In list context, all parameters passed to C<send> will be returned,
472in scalar context only the first one will be returned.
303 473
304Not all event models support a blocking wait - some die in that case 474Not all event models support a blocking wait - some die in that case
305(programs might want to do that to stay interactive), so I<if you are 475(programs might want to do that to stay interactive), so I<if you are
306using this from a module, never require a blocking wait>, but let the 476using this from a module, never require a blocking wait>, but let the
307caller decide whether the call will block or not (for example, by coupling 477caller decide whether the call will block or not (for example, by coupling
310while still suppporting blocking waits if the caller so desires). 480while still suppporting blocking waits if the caller so desires).
311 481
312Another reason I<never> to C<< ->wait >> in a module is that you cannot 482Another reason I<never> to C<< ->wait >> in a module is that you cannot
313sensibly have two C<< ->wait >>'s in parallel, as that would require 483sensibly have two C<< ->wait >>'s in parallel, as that would require
314multiple interpreters or coroutines/threads, none of which C<AnyEvent> 484multiple interpreters or coroutines/threads, none of which C<AnyEvent>
315can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and 485can supply.
316L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
317from different coroutines, however).
318 486
319=item $cv->broadcast 487The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
488fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
489versions and also integrates coroutines into AnyEvent, making blocking
490C<< ->wait >> calls perfectly safe as long as they are done from another
491coroutine (one that doesn't run the event loop).
320 492
321Flag the condition as ready - a running C<< ->wait >> and all further 493You can ensure that C<< -wait >> never blocks by setting a callback and
322calls to C<wait> will (eventually) return after this method has been 494only calling C<< ->wait >> from within that callback (or at a later
323called. If nobody is waiting the broadcast will be remembered.. 495time). This will work even when the event loop does not support blocking
496waits otherwise.
497
498=item $bool = $cv->ready
499
500Returns true when the condition is "true", i.e. whether C<send> or
501C<croak> have been called.
502
503=item $cb = $cv->cb ([new callback])
504
505This is a mutator function that returns the callback set and optionally
506replaces it before doing so.
507
508The callback will be called when the condition becomes "true", i.e. when
509C<send> or C<croak> are called. Calling C<wait> inside the callback
510or at any later time is guaranteed not to block.
324 511
325=back 512=back
326
327Example:
328
329 # wait till the result is ready
330 my $result_ready = AnyEvent->condvar;
331
332 # do something such as adding a timer
333 # or socket watcher the calls $result_ready->broadcast
334 # when the "result" is ready.
335 # in this case, we simply use a timer:
336 my $w = AnyEvent->timer (
337 after => 1,
338 cb => sub { $result_ready->broadcast },
339 );
340
341 # this "blocks" (while handling events) till the watcher
342 # calls broadcast
343 $result_ready->wait;
344 513
345=head1 GLOBAL VARIABLES AND FUNCTIONS 514=head1 GLOBAL VARIABLES AND FUNCTIONS
346 515
347=over 4 516=over 4
348 517
354C<AnyEvent::Impl:xxx> modules, but can be any other class in the case 523C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
355AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>). 524AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
356 525
357The known classes so far are: 526The known classes so far are:
358 527
359 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361 AnyEvent::Impl::EV based on EV (an interface to libev, best choice). 528 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362 AnyEvent::Impl::Event based on Event, second best choice. 529 AnyEvent::Impl::Event based on Event, second best choice.
530 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
363 AnyEvent::Impl::Glib based on Glib, third-best choice. 531 AnyEvent::Impl::Glib based on Glib, third-best choice.
364 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
365 AnyEvent::Impl::Tk based on Tk, very bad choice. 532 AnyEvent::Impl::Tk based on Tk, very bad choice.
366 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). 533 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. 534 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368 AnyEvent::Impl::POE based on POE, not generic enough for full support. 535 AnyEvent::Impl::POE based on POE, not generic enough for full support.
369 536
382Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model 549Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
383if necessary. You should only call this function right before you would 550if necessary. You should only call this function right before you would
384have created an AnyEvent watcher anyway, that is, as late as possible at 551have created an AnyEvent watcher anyway, that is, as late as possible at
385runtime. 552runtime.
386 553
554=item $guard = AnyEvent::on_detect { BLOCK }
555
556Arranges for the code block to be executed as soon as the event model is
557autodetected (or immediately if this has already happened).
558
559If called in scalar or list context, then it creates and returns an object
560that automatically removes the callback again when it is destroyed.
561
562=item @AnyEvent::on_detect
563
564If there are any code references in this array (you can C<push> to it
565before or after loading AnyEvent), then they will called directly after
566the event loop has been chosen.
567
568You should check C<$AnyEvent::MODEL> before adding to this array, though:
569if it contains a true value then the event loop has already been detected,
570and the array will be ignored.
571
572Best use C<AnyEvent::on_detect { BLOCK }> instead.
573
387=back 574=back
388 575
389=head1 WHAT TO DO IN A MODULE 576=head1 WHAT TO DO IN A MODULE
390 577
391As a module author, you should C<use AnyEvent> and call AnyEvent methods 578As a module author, you should C<use AnyEvent> and call AnyEvent methods
395decide which event module to use as soon as the first method is called, so 582decide which event module to use as soon as the first method is called, so
396by calling AnyEvent in your module body you force the user of your module 583by calling AnyEvent in your module body you force the user of your module
397to load the event module first. 584to load the event module first.
398 585
399Never call C<< ->wait >> on a condition variable unless you I<know> that 586Never call C<< ->wait >> on a condition variable unless you I<know> that
400the C<< ->broadcast >> method has been called on it already. This is 587the C<< ->send >> method has been called on it already. This is
401because it will stall the whole program, and the whole point of using 588because it will stall the whole program, and the whole point of using
402events is to stay interactive. 589events is to stay interactive.
403 590
404It is fine, however, to call C<< ->wait >> when the user of your module 591It is fine, however, to call C<< ->wait >> when the user of your module
405requests it (i.e. if you create a http request object ad have a method 592requests it (i.e. if you create a http request object ad have a method
425 612
426You can chose to use a rather inefficient pure-perl implementation by 613You can chose to use a rather inefficient pure-perl implementation by
427loading the C<AnyEvent::Impl::Perl> module, which gives you similar 614loading the C<AnyEvent::Impl::Perl> module, which gives you similar
428behaviour everywhere, but letting AnyEvent chose is generally better. 615behaviour everywhere, but letting AnyEvent chose is generally better.
429 616
617=head1 OTHER MODULES
618
619The following is a non-exhaustive list of additional modules that use
620AnyEvent and can therefore be mixed easily with other AnyEvent modules
621in the same program. Some of the modules come with AnyEvent, some are
622available via CPAN.
623
624=over 4
625
626=item L<AnyEvent::Util>
627
628Contains various utility functions that replace often-used but blocking
629functions such as C<inet_aton> by event-/callback-based versions.
630
631=item L<AnyEvent::Handle>
632
633Provide read and write buffers and manages watchers for reads and writes.
634
635=item L<AnyEvent::Socket>
636
637Provides a means to do non-blocking connects, accepts etc.
638
639=item L<AnyEvent::HTTPD>
640
641Provides a simple web application server framework.
642
643=item L<AnyEvent::DNS>
644
645Provides asynchronous DNS resolver capabilities, beyond what
646L<AnyEvent::Util> offers.
647
648=item L<AnyEvent::FastPing>
649
650The fastest ping in the west.
651
652=item L<Net::IRC3>
653
654AnyEvent based IRC client module family.
655
656=item L<Net::XMPP2>
657
658AnyEvent based XMPP (Jabber protocol) module family.
659
660=item L<Net::FCP>
661
662AnyEvent-based implementation of the Freenet Client Protocol, birthplace
663of AnyEvent.
664
665=item L<Event::ExecFlow>
666
667High level API for event-based execution flow control.
668
669=item L<Coro>
670
671Has special support for AnyEvent via L<Coro::AnyEvent>.
672
673=item L<IO::Lambda>
674
675The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
676
677=item L<IO::AIO>
678
679Truly asynchronous I/O, should be in the toolbox of every event
680programmer. Can be trivially made to use AnyEvent.
681
682=item L<BDB>
683
684Truly asynchronous Berkeley DB access. Can be trivially made to use
685AnyEvent.
686
687=back
688
430=cut 689=cut
431 690
432package AnyEvent; 691package AnyEvent;
433 692
434no warnings; 693no warnings;
435use strict; 694use strict;
436 695
437use Carp; 696use Carp;
438 697
439our $VERSION = '3.3'; 698our $VERSION = '3.4';
440our $MODEL; 699our $MODEL;
441 700
442our $AUTOLOAD; 701our $AUTOLOAD;
443our @ISA; 702our @ISA;
444 703
445our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1; 704our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
446 705
447our @REGISTRY; 706our @REGISTRY;
448 707
449my @models = ( 708my @models = (
450 [Coro::EV:: => AnyEvent::Impl::CoroEV::],
451 [Coro::Event:: => AnyEvent::Impl::CoroEvent::],
452 [EV:: => AnyEvent::Impl::EV::], 709 [EV:: => AnyEvent::Impl::EV::],
453 [Event:: => AnyEvent::Impl::Event::], 710 [Event:: => AnyEvent::Impl::Event::],
454 [Glib:: => AnyEvent::Impl::Glib::],
455 [Tk:: => AnyEvent::Impl::Tk::], 711 [Tk:: => AnyEvent::Impl::Tk::],
456 [Wx:: => AnyEvent::Impl::POE::], 712 [Wx:: => AnyEvent::Impl::POE::],
457 [Prima:: => AnyEvent::Impl::POE::], 713 [Prima:: => AnyEvent::Impl::POE::],
458 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], 714 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
459 # everything below here will not be autoprobed as the pureperl backend should work everywhere 715 # everything below here will not be autoprobed as the pureperl backend should work everywhere
716 [Glib:: => AnyEvent::Impl::Glib::],
460 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy 717 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
461 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program 718 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program
462 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza 719 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
463); 720);
464 721
465our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY); 722our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
723
724our @on_detect;
725
726sub on_detect(&) {
727 my ($cb) = @_;
728
729 if ($MODEL) {
730 $cb->();
731
732 1
733 } else {
734 push @on_detect, $cb;
735
736 defined wantarray
737 ? bless \$cb, "AnyEvent::Util::Guard"
738 : ()
739 }
740}
741
742sub AnyEvent::Util::Guard::DESTROY {
743 @on_detect = grep $_ != ${$_[0]}, @on_detect;
744}
466 745
467sub detect() { 746sub detect() {
468 unless ($MODEL) { 747 unless ($MODEL) {
469 no strict 'refs'; 748 no strict 'refs';
470 749
504 last; 783 last;
505 } 784 }
506 } 785 }
507 786
508 $MODEL 787 $MODEL
509 or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib."; 788 or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
510 } 789 }
511 } 790 }
512 791
513 unshift @ISA, $MODEL; 792 unshift @ISA, $MODEL;
514 push @{"$MODEL\::ISA"}, "AnyEvent::Base"; 793 push @{"$MODEL\::ISA"}, "AnyEvent::Base";
794
795 (shift @on_detect)->() while @on_detect;
515 } 796 }
516 797
517 $MODEL 798 $MODEL
518} 799}
519 800
861 }); 1142 });
862 1143
863 $quit->wait; 1144 $quit->wait;
864 1145
865 1146
866=head1 BENCHMARK 1147=head1 BENCHMARKS
867 1148
868To give you an idea of the performance and overheads that AnyEvent adds 1149To give you an idea of the performance and overheads that AnyEvent adds
869over the event loops themselves (and to give you an impression of the 1150over the event loops themselves and to give you an impression of the speed
870speed of various event loops), here is a benchmark of various supported 1151of various event loops I prepared some benchmarks.
871event models natively and with anyevent. The benchmark creates a lot of 1152
872timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to 1153=head2 BENCHMARKING ANYEVENT OVERHEAD
1154
1155Here is a benchmark of various supported event models used natively and
1156through anyevent. The benchmark creates a lot of timers (with a zero
1157timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
873become writable, which it is), lets them fire exactly once and destroys 1158which it is), lets them fire exactly once and destroys them again.
874them again.
875 1159
876Rewriting the benchmark to use many different sockets instead of using 1160Source code for this benchmark is found as F<eg/bench> in the AnyEvent
877the same filehandle for all I/O watchers results in a much longer runtime 1161distribution.
878(socket creation is expensive), but qualitatively the same figures, so it
879was not used.
880 1162
881=head2 Explanation of the columns 1163=head3 Explanation of the columns
882 1164
883I<watcher> is the number of event watchers created/destroyed. Since 1165I<watcher> is the number of event watchers created/destroyed. Since
884different event models feature vastly different performances, each event 1166different event models feature vastly different performances, each event
885loop was given a number of watchers so that overall runtime is acceptable 1167loop was given a number of watchers so that overall runtime is acceptable
886and similar between tested event loop (and keep them from crashing): Glib 1168and similar between tested event loop (and keep them from crashing): Glib
902signal the end of this phase. 1184signal the end of this phase.
903 1185
904I<destroy> is the time, in microseconds, that it takes to destroy a single 1186I<destroy> is the time, in microseconds, that it takes to destroy a single
905watcher. 1187watcher.
906 1188
907=head2 Results 1189=head3 Results
908 1190
909 name watchers bytes create invoke destroy comment 1191 name watchers bytes create invoke destroy comment
910 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 1192 EV/EV 400000 244 0.56 0.46 0.31 EV native interface
911 EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers 1193 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
912 CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal 1194 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
913 Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation 1195 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
914 Event/Event 16000 523 28.05 21.38 0.86 Event native interface 1196 Event/Event 16000 516 31.88 31.30 0.85 Event native interface
915 Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers 1197 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
916 Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour 1198 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
917 Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers 1199 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
918 POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event 1200 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
919 POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select 1201 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
920 1202
921=head2 Discussion 1203=head3 Discussion
922 1204
923The benchmark does I<not> measure scalability of the event loop very 1205The benchmark does I<not> measure scalability of the event loop very
924well. For example, a select-based event loop (such as the pure perl one) 1206well. For example, a select-based event loop (such as the pure perl one)
925can never compete with an event loop that uses epoll when the number of 1207can never compete with an event loop that uses epoll when the number of
926file descriptors grows high. In this benchmark, all events become ready at 1208file descriptors grows high. In this benchmark, all events become ready at
927the same time, so select/poll-based implementations get an unnatural speed 1209the same time, so select/poll-based implementations get an unnatural speed
928boost. 1210boost.
929 1211
1212Also, note that the number of watchers usually has a nonlinear effect on
1213overall speed, that is, creating twice as many watchers doesn't take twice
1214the time - usually it takes longer. This puts event loops tested with a
1215higher number of watchers at a disadvantage.
1216
1217To put the range of results into perspective, consider that on the
1218benchmark machine, handling an event takes roughly 1600 CPU cycles with
1219EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
1220cycles with POE.
1221
930C<EV> is the sole leader regarding speed and memory use, which are both 1222C<EV> is the sole leader regarding speed and memory use, which are both
931maximal/minimal, respectively. Even when going through AnyEvent, there are 1223maximal/minimal, respectively. Even when going through AnyEvent, it uses
932only two event loops that use slightly less memory (the C<Event> module 1224far less memory than any other event loop and is still faster than Event
933natively and the pure perl backend), and no faster event models, not even 1225natively.
934C<Event> natively.
935 1226
936The pure perl implementation is hit in a few sweet spots (both the 1227The pure perl implementation is hit in a few sweet spots (both the
937zero timeout and the use of a single fd hit optimisations in the perl 1228constant timeout and the use of a single fd hit optimisations in the perl
938interpreter and the backend itself, and all watchers become ready at the 1229interpreter and the backend itself). Nevertheless this shows that it
939same time). Nevertheless this shows that it adds very little overhead in 1230adds very little overhead in itself. Like any select-based backend its
940itself. Like any select-based backend its performance becomes really bad 1231performance becomes really bad with lots of file descriptors (and few of
941with lots of file descriptors (and few of them active), of course, but 1232them active), of course, but this was not subject of this benchmark.
942this was not subject of this benchmark.
943 1233
944The C<Event> module has a relatively high setup and callback invocation cost, 1234The C<Event> module has a relatively high setup and callback invocation
945but overall scores on the third place. 1235cost, but overall scores in on the third place.
946 1236
947C<Glib>'s memory usage is quite a bit bit higher, but it features a 1237C<Glib>'s memory usage is quite a bit higher, but it features a
948faster callback invocation and overall ends up in the same class as 1238faster callback invocation and overall ends up in the same class as
949C<Event>. However, Glib scales extremely badly, doubling the number of 1239C<Event>. However, Glib scales extremely badly, doubling the number of
950watchers increases the processing time by more than a factor of four, 1240watchers increases the processing time by more than a factor of four,
951making it completely unusable when using larger numbers of watchers 1241making it completely unusable when using larger numbers of watchers
952(note that only a single file descriptor was used in the benchmark, so 1242(note that only a single file descriptor was used in the benchmark, so
955The C<Tk> adaptor works relatively well. The fact that it crashes with 1245The C<Tk> adaptor works relatively well. The fact that it crashes with
956more than 2000 watchers is a big setback, however, as correctness takes 1246more than 2000 watchers is a big setback, however, as correctness takes
957precedence over speed. Nevertheless, its performance is surprising, as the 1247precedence over speed. Nevertheless, its performance is surprising, as the
958file descriptor is dup()ed for each watcher. This shows that the dup() 1248file descriptor is dup()ed for each watcher. This shows that the dup()
959employed by some adaptors is not a big performance issue (it does incur a 1249employed by some adaptors is not a big performance issue (it does incur a
960hidden memory cost inside the kernel, though, that is not reflected in the 1250hidden memory cost inside the kernel which is not reflected in the figures
961figures above). 1251above).
962 1252
963C<POE>, regardless of underlying event loop (wether using its pure perl 1253C<POE>, regardless of underlying event loop (whether using its pure perl
964select-based backend or the Event module) shows abysmal performance and 1254select-based backend or the Event module, the POE-EV backend couldn't
1255be tested because it wasn't working) shows abysmal performance and
965memory usage: Watchers use almost 30 times as much memory as EV watchers, 1256memory usage with AnyEvent: Watchers use almost 30 times as much memory
966and 10 times as much memory as both Event or EV via AnyEvent. Watcher 1257as EV watchers, and 10 times as much memory as Event (the high memory
1258requirements are caused by requiring a session for each watcher). Watcher
967invocation is almost 900 times slower than with AnyEvent's pure perl 1259invocation speed is almost 900 times slower than with AnyEvent's pure perl
1260implementation.
1261
968implementation. The design of the POE adaptor class in AnyEvent can not 1262The design of the POE adaptor class in AnyEvent can not really account
969really account for this, as session creation overhead is small compared 1263for the performance issues, though, as session creation overhead is
970to execution of the state machine, which is coded pretty optimally within 1264small compared to execution of the state machine, which is coded pretty
971L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow. 1265optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
1266using multiple sessions is not a good approach, especially regarding
1267memory usage, even the author of POE could not come up with a faster
1268design).
972 1269
973=head2 Summary 1270=head3 Summary
974 1271
1272=over 4
1273
975Using EV through AnyEvent is faster than any other event loop, but most 1274=item * Using EV through AnyEvent is faster than any other event loop
976event loops have acceptable performance with or without AnyEvent. 1275(even when used without AnyEvent), but most event loops have acceptable
1276performance with or without AnyEvent.
977 1277
978The overhead AnyEvent adds is usually much smaller than the overhead of 1278=item * The overhead AnyEvent adds is usually much smaller than the overhead of
979the actual event loop, only with extremely fast event loops such as the EV 1279the actual event loop, only with extremely fast event loops such as EV
980adds AnyEvent significant overhead. 1280adds AnyEvent significant overhead.
981 1281
982And you should simply avoid POE like the plague if you want performance or 1282=item * You should avoid POE like the plague if you want performance or
983reasonable memory usage. 1283reasonable memory usage.
984 1284
1285=back
1286
1287=head2 BENCHMARKING THE LARGE SERVER CASE
1288
1289This benchmark atcually benchmarks the event loop itself. It works by
1290creating a number of "servers": each server consists of a socketpair, a
1291timeout watcher that gets reset on activity (but never fires), and an I/O
1292watcher waiting for input on one side of the socket. Each time the socket
1293watcher reads a byte it will write that byte to a random other "server".
1294
1295The effect is that there will be a lot of I/O watchers, only part of which
1296are active at any one point (so there is a constant number of active
1297fds for each loop iterstaion, but which fds these are is random). The
1298timeout is reset each time something is read because that reflects how
1299most timeouts work (and puts extra pressure on the event loops).
1300
1301In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
1302(1%) are active. This mirrors the activity of large servers with many
1303connections, most of which are idle at any one point in time.
1304
1305Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
1306distribution.
1307
1308=head3 Explanation of the columns
1309
1310I<sockets> is the number of sockets, and twice the number of "servers" (as
1311each server has a read and write socket end).
1312
1313I<create> is the time it takes to create a socketpair (which is
1314nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1315
1316I<request>, the most important value, is the time it takes to handle a
1317single "request", that is, reading the token from the pipe and forwarding
1318it to another server. This includes deleting the old timeout and creating
1319a new one that moves the timeout into the future.
1320
1321=head3 Results
1322
1323 name sockets create request
1324 EV 20000 69.01 11.16
1325 Perl 20000 73.32 35.87
1326 Event 20000 212.62 257.32
1327 Glib 20000 651.16 1896.30
1328 POE 20000 349.67 12317.24 uses POE::Loop::Event
1329
1330=head3 Discussion
1331
1332This benchmark I<does> measure scalability and overall performance of the
1333particular event loop.
1334
1335EV is again fastest. Since it is using epoll on my system, the setup time
1336is relatively high, though.
1337
1338Perl surprisingly comes second. It is much faster than the C-based event
1339loops Event and Glib.
1340
1341Event suffers from high setup time as well (look at its code and you will
1342understand why). Callback invocation also has a high overhead compared to
1343the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
1344uses select or poll in basically all documented configurations.
1345
1346Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
1347clearly fails to perform with many filehandles or in busy servers.
1348
1349POE is still completely out of the picture, taking over 1000 times as long
1350as EV, and over 100 times as long as the Perl implementation, even though
1351it uses a C-based event loop in this case.
1352
1353=head3 Summary
1354
1355=over 4
1356
1357=item * The pure perl implementation performs extremely well.
1358
1359=item * Avoid Glib or POE in large projects where performance matters.
1360
1361=back
1362
1363=head2 BENCHMARKING SMALL SERVERS
1364
1365While event loops should scale (and select-based ones do not...) even to
1366large servers, most programs we (or I :) actually write have only a few
1367I/O watchers.
1368
1369In this benchmark, I use the same benchmark program as in the large server
1370case, but it uses only eight "servers", of which three are active at any
1371one time. This should reflect performance for a small server relatively
1372well.
1373
1374The columns are identical to the previous table.
1375
1376=head3 Results
1377
1378 name sockets create request
1379 EV 16 20.00 6.54
1380 Perl 16 25.75 12.62
1381 Event 16 81.27 35.86
1382 Glib 16 32.63 15.48
1383 POE 16 261.87 276.28 uses POE::Loop::Event
1384
1385=head3 Discussion
1386
1387The benchmark tries to test the performance of a typical small
1388server. While knowing how various event loops perform is interesting, keep
1389in mind that their overhead in this case is usually not as important, due
1390to the small absolute number of watchers (that is, you need efficiency and
1391speed most when you have lots of watchers, not when you only have a few of
1392them).
1393
1394EV is again fastest.
1395
1396Perl again comes second. It is noticably faster than the C-based event
1397loops Event and Glib, although the difference is too small to really
1398matter.
1399
1400POE also performs much better in this case, but is is still far behind the
1401others.
1402
1403=head3 Summary
1404
1405=over 4
1406
1407=item * C-based event loops perform very well with small number of
1408watchers, as the management overhead dominates.
1409
1410=back
1411
985 1412
986=head1 FORK 1413=head1 FORK
987 1414
988Most event libraries are not fork-safe. The ones who are usually are 1415Most event libraries are not fork-safe. The ones who are usually are
989because they are so inefficient. Only L<EV> is fully fork-aware. 1416because they rely on inefficient but fork-safe C<select> or C<poll>
1417calls. Only L<EV> is fully fork-aware.
990 1418
991If you have to fork, you must either do so I<before> creating your first 1419If you have to fork, you must either do so I<before> creating your first
992watcher OR you must not use AnyEvent at all in the child. 1420watcher OR you must not use AnyEvent at all in the child.
993 1421
994 1422
1006 1434
1007 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 1435 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1008 1436
1009 use AnyEvent; 1437 use AnyEvent;
1010 1438
1439Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1440be used to probe what backend is used and gain other information (which is
1441probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
1442
1011 1443
1012=head1 SEE ALSO 1444=head1 SEE ALSO
1013 1445
1014Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, 1446Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
1015L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
1016L<Event::Lib>, L<Qt>, L<POE>. 1447L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
1017 1448
1018Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>, 1449Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
1019L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, 1450L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
1020L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>, 1451L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
1021L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>. 1452L<AnyEvent::Impl::POE>.
1453
1454Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
1022 1455
1023Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. 1456Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
1024 1457
1025 1458
1026=head1 AUTHOR 1459=head1 AUTHOR

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