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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<Tk>, L<AnyEvent::Impl::Perl>, 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 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
90found, AnyEvent will fall back to a pure-perl event loop, which is not 89found, AnyEvent will fall back to a pure-perl event loop, which is not
91very efficient, but should work everywhere. 90very efficient, but should work everywhere.
92 91
136 135
137Note that C<my $w; $w => combination. This is necessary because in Perl, 136Note that C<my $w; $w => combination. This is necessary because in Perl,
138my variables are only visible after the statement in which they are 137my variables are only visible after the statement in which they are
139declared. 138declared.
140 139
141=head2 IO 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 $result_ready->wait;
344 513
345=head1 GLOBAL VARIABLES AND FUNCTIONS 514=head1 GLOBAL VARIABLES AND FUNCTIONS
346 515
347=over 4 516=over 4
348 517
354C<AnyEvent::Impl:xxx> modules, but can be any other class in the case 523C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
355AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>). 524AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
356 525
357The known classes so far are: 526The known classes so far are:
358 527
359 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361 AnyEvent::Impl::EV based on EV (an interface to libev, best choice). 528 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362 AnyEvent::Impl::Event based on Event, second best choice. 529 AnyEvent::Impl::Event based on Event, second best choice.
530 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
363 AnyEvent::Impl::Glib based on Glib, third-best choice. 531 AnyEvent::Impl::Glib based on Glib, third-best choice.
364 AnyEvent::Impl::Tk based on Tk, very bad choice. 532 AnyEvent::Impl::Tk based on Tk, very bad choice.
365 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
366 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). 533 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. 534 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368 AnyEvent::Impl::POE based on POE, not generic enough for full support. 535 AnyEvent::Impl::POE based on POE, not generic enough for full support.
369 536
370There is no support for WxWidgets, as WxWidgets has no support for 537There is no support for WxWidgets, as WxWidgets has no support for
382Returns C<$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 $guard = AnyEvent::post_detect { BLOCK }
555
556Arranges for the code block to be executed as soon as the event model is
557autodetected (or immediately if this has already happened).
558
559If called in scalar or list context, then it creates and returns an object
560that automatically removes the callback again when it is destroyed. See
561L<Coro::BDB> for a case where this is useful.
562
563=item @AnyEvent::post_detect
564
565If there are any code references in this array (you can C<push> to it
566before or after loading AnyEvent), then they will called directly after
567the event loop has been chosen.
568
569You should check C<$AnyEvent::MODEL> before adding to this array, though:
570if it contains a true value then the event loop has already been detected,
571and the array will be ignored.
572
573Best use C<AnyEvent::post_detect { BLOCK }> instead.
574
387=back 575=back
388 576
389=head1 WHAT TO DO IN A MODULE 577=head1 WHAT TO DO IN A MODULE
390 578
391As a module author, you should C<use AnyEvent> and call AnyEvent methods 579As 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 583decide 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 584by calling AnyEvent in your module body you force the user of your module
397to load the event module first. 585to load the event module first.
398 586
399Never call C<< ->wait >> on a condition variable unless you I<know> that 587Never call C<< ->wait >> on a condition variable unless you I<know> that
400the C<< ->broadcast >> method has been called on it already. This is 588the C<< ->send >> method has been called on it already. This is
401because it will stall the whole program, and the whole point of using 589because it will stall the whole program, and the whole point of using
402events is to stay interactive. 590events is to stay interactive.
403 591
404It is fine, however, to call C<< ->wait >> when the user of your module 592It 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 593requests it (i.e. if you create a http request object ad have a method
425 613
426You can chose to use a rather inefficient pure-perl implementation by 614You can chose to use a rather inefficient pure-perl implementation by
427loading the C<AnyEvent::Impl::Perl> module, which gives you similar 615loading the C<AnyEvent::Impl::Perl> module, which gives you similar
428behaviour everywhere, but letting AnyEvent chose is generally better. 616behaviour everywhere, but letting AnyEvent chose is generally better.
429 617
618=head1 OTHER MODULES
619
620The following is a non-exhaustive list of additional modules that use
621AnyEvent and can therefore be mixed easily with other AnyEvent modules
622in the same program. Some of the modules come with AnyEvent, some are
623available via CPAN.
624
625=over 4
626
627=item L<AnyEvent::Util>
628
629Contains various utility functions that replace often-used but blocking
630functions such as C<inet_aton> by event-/callback-based versions.
631
632=item L<AnyEvent::Handle>
633
634Provide read and write buffers and manages watchers for reads and writes.
635
636=item L<AnyEvent::HTTPD>
637
638Provides a simple web application server framework.
639
640=item L<AnyEvent::DNS>
641
642Provides asynchronous DNS resolver capabilities, beyond what
643L<AnyEvent::Util> offers.
644
645=item L<AnyEvent::FastPing>
646
647The fastest ping in the west.
648
649=item L<Net::IRC3>
650
651AnyEvent based IRC client module family.
652
653=item L<Net::XMPP2>
654
655AnyEvent based XMPP (Jabber protocol) module family.
656
657=item L<Net::FCP>
658
659AnyEvent-based implementation of the Freenet Client Protocol, birthplace
660of AnyEvent.
661
662=item L<Event::ExecFlow>
663
664High level API for event-based execution flow control.
665
666=item L<Coro>
667
668Has special support for AnyEvent via L<Coro::AnyEvent>.
669
670=item L<AnyEvent::AIO>, L<IO::AIO>
671
672Truly asynchronous I/O, should be in the toolbox of every event
673programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
674together.
675
676=item L<AnyEvent::BDB>, L<BDB>
677
678Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
679IO::AIO and AnyEvent together.
680
681=item L<IO::Lambda>
682
683The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
684
685=back
686
430=cut 687=cut
431 688
432package AnyEvent; 689package AnyEvent;
433 690
434no warnings; 691no warnings;
435use strict; 692use strict;
436 693
437use Carp; 694use Carp;
438 695
439our $VERSION = '3.3'; 696our $VERSION = '3.4';
440our $MODEL; 697our $MODEL;
441 698
442our $AUTOLOAD; 699our $AUTOLOAD;
443our @ISA; 700our @ISA;
444 701
445our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1; 702our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
446 703
447our @REGISTRY; 704our @REGISTRY;
448 705
449my @models = ( 706my @models = (
450 [Coro::EV:: => AnyEvent::Impl::CoroEV::],
451 [Coro::Event:: => AnyEvent::Impl::CoroEvent::],
452 [EV:: => AnyEvent::Impl::EV::], 707 [EV:: => AnyEvent::Impl::EV::],
453 [Event:: => AnyEvent::Impl::Event::], 708 [Event:: => AnyEvent::Impl::Event::],
454 [Glib:: => AnyEvent::Impl::Glib::],
455 [Tk:: => AnyEvent::Impl::Tk::], 709 [Tk:: => AnyEvent::Impl::Tk::],
456 [Wx:: => AnyEvent::Impl::POE::], 710 [Wx:: => AnyEvent::Impl::POE::],
457 [Prima:: => AnyEvent::Impl::POE::], 711 [Prima:: => AnyEvent::Impl::POE::],
458 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], 712 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
459 # everything below here will not be autoprobed as the pureperl backend should work everywhere 713 # everything below here will not be autoprobed as the pureperl backend should work everywhere
714 [Glib:: => AnyEvent::Impl::Glib::],
460 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy 715 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
461 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program 716 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program
462 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza 717 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
463); 718);
464 719
465our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY); 720our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
721
722our @post_detect;
723
724sub post_detect(&) {
725 my ($cb) = @_;
726
727 if ($MODEL) {
728 $cb->();
729
730 1
731 } else {
732 push @post_detect, $cb;
733
734 defined wantarray
735 ? bless \$cb, "AnyEvent::Util::Guard"
736 : ()
737 }
738}
739
740sub AnyEvent::Util::Guard::DESTROY {
741 @post_detect = grep $_ != ${$_[0]}, @post_detect;
742}
466 743
467sub detect() { 744sub detect() {
468 unless ($MODEL) { 745 unless ($MODEL) {
469 no strict 'refs'; 746 no strict 'refs';
470 747
504 last; 781 last;
505 } 782 }
506 } 783 }
507 784
508 $MODEL 785 $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."; 786 or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
510 } 787 }
511 } 788 }
512 789
513 unshift @ISA, $MODEL; 790 unshift @ISA, $MODEL;
514 push @{"$MODEL\::ISA"}, "AnyEvent::Base"; 791 push @{"$MODEL\::ISA"}, "AnyEvent::Base";
792
793 (shift @post_detect)->() while @post_detect;
515 } 794 }
516 795
517 $MODEL 796 $MODEL
518} 797}
519 798
706 985
707=back 986=back
708 987
709=head1 EXAMPLE PROGRAM 988=head1 EXAMPLE PROGRAM
710 989
711The following program uses an IO watcher to read data from STDIN, a timer 990The following program uses an I/O watcher to read data from STDIN, a timer
712to display a message once per second, and a condition variable to quit the 991to display a message once per second, and a condition variable to quit the
713program when the user enters quit: 992program when the user enters quit:
714 993
715 use AnyEvent; 994 use AnyEvent;
716 995
861 }); 1140 });
862 1141
863 $quit->wait; 1142 $quit->wait;
864 1143
865 1144
866=head1 BENCHMARK 1145=head1 BENCHMARKS
867 1146
868To give you an idea of the performance an doverheads that AnyEvent adds 1147To give you an idea of the performance and overheads that AnyEvent adds
869over the backends, here is a benchmark of various supported backends. The 1148over the event loops themselves and to give you an impression of the speed
870benchmark creates a lot of timers (with zero timeout) and io events 1149of various event loops I prepared some benchmarks.
871(watching STDOUT, a pty, to become writable).
872 1150
873Explanation of the fields: 1151=head2 BENCHMARKING ANYEVENT OVERHEAD
874 1152
1153Here is a benchmark of various supported event models used natively and
1154through anyevent. The benchmark creates a lot of timers (with a zero
1155timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1156which it is), lets them fire exactly once and destroys them again.
1157
1158Source code for this benchmark is found as F<eg/bench> in the AnyEvent
1159distribution.
1160
1161=head3 Explanation of the columns
1162
875I<watcher> is the number of event watchers created/destroyed. Sicne 1163I<watcher> is the number of event watchers created/destroyed. Since
876different event models have vastly different performance each backend was 1164different event models feature vastly different performances, each event
877handed a number of watchers so that overall runtime is acceptable and 1165loop was given a number of watchers so that overall runtime is acceptable
878similar to all backends (and keep them from crashing). 1166and similar between tested event loop (and keep them from crashing): Glib
1167would probably take thousands of years if asked to process the same number
1168of watchers as EV in this benchmark.
879 1169
880I<bytes> is the number of bytes (as measured by resident set size) used by 1170I<bytes> is the number of bytes (as measured by the resident set size,
881each watcher. 1171RSS) consumed by each watcher. This method of measuring captures both C
1172and Perl-based overheads.
882 1173
883I<create> is the time, in microseconds, to create a single watcher. 1174I<create> is the time, in microseconds (millionths of seconds), that it
1175takes to create a single watcher. The callback is a closure shared between
1176all watchers, to avoid adding memory overhead. That means closure creation
1177and memory usage is not included in the figures.
884 1178
885I<invoke> is the time, in microseconds, used to invoke a simple callback 1179I<invoke> is the time, in microseconds, used to invoke a simple
886that simply counts down. 1180callback. The callback simply counts down a Perl variable and after it was
1181invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
1182signal the end of this phase.
887 1183
888I<destroy> is the time, in microseconds, to destroy a single watcher. 1184I<destroy> is the time, in microseconds, that it takes to destroy a single
1185watcher.
889 1186
1187=head3 Results
1188
890 name watcher bytes create invoke destroy comment 1189 name watchers bytes create invoke destroy comment
891 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 1190 EV/EV 400000 244 0.56 0.46 0.31 EV native interface
892 EV/Any 100000 610 3.52 0.91 0.75 1191 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
893 CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal 1192 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
894 Perl/Any 10000 654 4.64 1.22 0.77 pure perl implementation 1193 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
895 Event/Event 10000 523 28.05 21.38 5.22 Event native interface 1194 Event/Event 16000 516 31.88 31.30 0.85 Event native interface
896 Event/Any 10000 943 34.43 20.48 1.39 1195 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
897 Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour 1196 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
898 Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers 1197 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
899 POE/Select 2000 6343 94.69 807.65 562.69 POE::Loop::Select
900 POE/Event 2000 6644 108.15 768.19 14.33 POE::Loop::Event 1198 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
1199 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
901 1200
902Discussion: The benchmark does I<not> bench scalability of the 1201=head3 Discussion
1202
1203The benchmark does I<not> measure scalability of the event loop very
903backend. For example a select-based backend (such as the pureperl one) can 1204well. For example, a select-based event loop (such as the pure perl one)
904never compete with a backend using epoll. In this benchmark, only a single 1205can never compete with an event loop that uses epoll when the number of
905filehandle is used. 1206file descriptors grows high. In this benchmark, all events become ready at
1207the same time, so select/poll-based implementations get an unnatural speed
1208boost.
906 1209
1210Also, note that the number of watchers usually has a nonlinear effect on
1211overall speed, that is, creating twice as many watchers doesn't take twice
1212the time - usually it takes longer. This puts event loops tested with a
1213higher number of watchers at a disadvantage.
1214
1215To put the range of results into perspective, consider that on the
1216benchmark machine, handling an event takes roughly 1600 CPU cycles with
1217EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
1218cycles with POE.
1219
907EV is the sole leader regarding speed and memory use, which are both 1220C<EV> is the sole leader regarding speed and memory use, which are both
908maximal/minimal. Even when going through AnyEvent, there is only one event 1221maximal/minimal, respectively. Even when going through AnyEvent, it uses
909loop that uses less memory (the Event module natively), and no faster 1222far less memory than any other event loop and is still faster than Event
910event model. 1223natively.
911 1224
912The pure perl implementation is hit in a few sweet spots (both the 1225The pure perl implementation is hit in a few sweet spots (both the
913zero timeout and the use of a single fd hit optimisations in the perl 1226constant timeout and the use of a single fd hit optimisations in the perl
914interpreter and the backend itself), but it shows that it adds very little 1227interpreter and the backend itself). Nevertheless this shows that it
915overhead in itself. Like any select-based backend it's performance becomes 1228adds very little overhead in itself. Like any select-based backend its
916really bad with lots of file descriptors. 1229performance becomes really bad with lots of file descriptors (and few of
1230them active), of course, but this was not subject of this benchmark.
917 1231
918The Event module has a relatively high setup and callback invocation cost, 1232The C<Event> module has a relatively high setup and callback invocation
919but overall scores on the third place. 1233cost, but overall scores in on the third place.
920 1234
921Glib has a little higher memory cost, a bit fster callback invocation and 1235C<Glib>'s memory usage is quite a bit higher, but it features a
922has a similar speed as Event. 1236faster callback invocation and overall ends up in the same class as
1237C<Event>. However, Glib scales extremely badly, doubling the number of
1238watchers increases the processing time by more than a factor of four,
1239making it completely unusable when using larger numbers of watchers
1240(note that only a single file descriptor was used in the benchmark, so
1241inefficiencies of C<poll> do not account for this).
923 1242
924The Tk backend works relatively well, the fact that it crashes with 1243The C<Tk> adaptor works relatively well. The fact that it crashes with
925more than 2000 watchers is a big setback, however, as correctness takes 1244more than 2000 watchers is a big setback, however, as correctness takes
926precedence over speed. 1245precedence over speed. Nevertheless, its performance is surprising, as the
1246file descriptor is dup()ed for each watcher. This shows that the dup()
1247employed by some adaptors is not a big performance issue (it does incur a
1248hidden memory cost inside the kernel which is not reflected in the figures
1249above).
927 1250
928POE, regardless of backend (wether it's pure perl select backend or the 1251C<POE>, regardless of underlying event loop (whether using its pure perl
929Event backend) shows abysmal performance and memory usage: Watchers use 1252select-based backend or the Event module, the POE-EV backend couldn't
930almost 30 times as much memory as EV watchers, and 10 times as much memory 1253be tested because it wasn't working) shows abysmal performance and
931as both Event or EV via AnyEvent. 1254memory usage with AnyEvent: Watchers use almost 30 times as much memory
1255as EV watchers, and 10 times as much memory as Event (the high memory
1256requirements are caused by requiring a session for each watcher). Watcher
1257invocation speed is almost 900 times slower than with AnyEvent's pure perl
1258implementation.
932 1259
1260The design of the POE adaptor class in AnyEvent can not really account
1261for the performance issues, though, as session creation overhead is
1262small compared to execution of the state machine, which is coded pretty
1263optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
1264using multiple sessions is not a good approach, especially regarding
1265memory usage, even the author of POE could not come up with a faster
1266design).
1267
1268=head3 Summary
1269
1270=over 4
1271
933Summary: using EV through AnyEvent is faster than any other event 1272=item * Using EV through AnyEvent is faster than any other event loop
934loop. The overhead AnyEvent adds can be very small, and you should avoid 1273(even when used without AnyEvent), but most event loops have acceptable
935POE like the plague if you want performance or reasonable memory usage. 1274performance with or without AnyEvent.
1275
1276=item * The overhead AnyEvent adds is usually much smaller than the overhead of
1277the actual event loop, only with extremely fast event loops such as EV
1278adds AnyEvent significant overhead.
1279
1280=item * You should avoid POE like the plague if you want performance or
1281reasonable memory usage.
1282
1283=back
1284
1285=head2 BENCHMARKING THE LARGE SERVER CASE
1286
1287This benchmark atcually benchmarks the event loop itself. It works by
1288creating a number of "servers": each server consists of a socketpair, a
1289timeout watcher that gets reset on activity (but never fires), and an I/O
1290watcher waiting for input on one side of the socket. Each time the socket
1291watcher reads a byte it will write that byte to a random other "server".
1292
1293The effect is that there will be a lot of I/O watchers, only part of which
1294are active at any one point (so there is a constant number of active
1295fds for each loop iterstaion, but which fds these are is random). The
1296timeout is reset each time something is read because that reflects how
1297most timeouts work (and puts extra pressure on the event loops).
1298
1299In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
1300(1%) are active. This mirrors the activity of large servers with many
1301connections, most of which are idle at any one point in time.
1302
1303Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
1304distribution.
1305
1306=head3 Explanation of the columns
1307
1308I<sockets> is the number of sockets, and twice the number of "servers" (as
1309each server has a read and write socket end).
1310
1311I<create> is the time it takes to create a socketpair (which is
1312nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1313
1314I<request>, the most important value, is the time it takes to handle a
1315single "request", that is, reading the token from the pipe and forwarding
1316it to another server. This includes deleting the old timeout and creating
1317a new one that moves the timeout into the future.
1318
1319=head3 Results
1320
1321 name sockets create request
1322 EV 20000 69.01 11.16
1323 Perl 20000 73.32 35.87
1324 Event 20000 212.62 257.32
1325 Glib 20000 651.16 1896.30
1326 POE 20000 349.67 12317.24 uses POE::Loop::Event
1327
1328=head3 Discussion
1329
1330This benchmark I<does> measure scalability and overall performance of the
1331particular event loop.
1332
1333EV is again fastest. Since it is using epoll on my system, the setup time
1334is relatively high, though.
1335
1336Perl surprisingly comes second. It is much faster than the C-based event
1337loops Event and Glib.
1338
1339Event suffers from high setup time as well (look at its code and you will
1340understand why). Callback invocation also has a high overhead compared to
1341the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
1342uses select or poll in basically all documented configurations.
1343
1344Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
1345clearly fails to perform with many filehandles or in busy servers.
1346
1347POE is still completely out of the picture, taking over 1000 times as long
1348as EV, and over 100 times as long as the Perl implementation, even though
1349it uses a C-based event loop in this case.
1350
1351=head3 Summary
1352
1353=over 4
1354
1355=item * The pure perl implementation performs extremely well.
1356
1357=item * Avoid Glib or POE in large projects where performance matters.
1358
1359=back
1360
1361=head2 BENCHMARKING SMALL SERVERS
1362
1363While event loops should scale (and select-based ones do not...) even to
1364large servers, most programs we (or I :) actually write have only a few
1365I/O watchers.
1366
1367In this benchmark, I use the same benchmark program as in the large server
1368case, but it uses only eight "servers", of which three are active at any
1369one time. This should reflect performance for a small server relatively
1370well.
1371
1372The columns are identical to the previous table.
1373
1374=head3 Results
1375
1376 name sockets create request
1377 EV 16 20.00 6.54
1378 Perl 16 25.75 12.62
1379 Event 16 81.27 35.86
1380 Glib 16 32.63 15.48
1381 POE 16 261.87 276.28 uses POE::Loop::Event
1382
1383=head3 Discussion
1384
1385The benchmark tries to test the performance of a typical small
1386server. While knowing how various event loops perform is interesting, keep
1387in mind that their overhead in this case is usually not as important, due
1388to the small absolute number of watchers (that is, you need efficiency and
1389speed most when you have lots of watchers, not when you only have a few of
1390them).
1391
1392EV is again fastest.
1393
1394Perl again comes second. It is noticably faster than the C-based event
1395loops Event and Glib, although the difference is too small to really
1396matter.
1397
1398POE also performs much better in this case, but is is still far behind the
1399others.
1400
1401=head3 Summary
1402
1403=over 4
1404
1405=item * C-based event loops perform very well with small number of
1406watchers, as the management overhead dominates.
1407
1408=back
936 1409
937 1410
938=head1 FORK 1411=head1 FORK
939 1412
940Most event libraries are not fork-safe. The ones who are usually are 1413Most event libraries are not fork-safe. The ones who are usually are
941because they are so inefficient. Only L<EV> is fully fork-aware. 1414because they rely on inefficient but fork-safe C<select> or C<poll>
1415calls. Only L<EV> is fully fork-aware.
942 1416
943If you have to fork, you must either do so I<before> creating your first 1417If you have to fork, you must either do so I<before> creating your first
944watcher OR you must not use AnyEvent at all in the child. 1418watcher OR you must not use AnyEvent at all in the child.
945 1419
946 1420
958 1432
959 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 1433 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
960 1434
961 use AnyEvent; 1435 use AnyEvent;
962 1436
1437Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1438be used to probe what backend is used and gain other information (which is
1439probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
1440
963 1441
964=head1 SEE ALSO 1442=head1 SEE ALSO
965 1443
966Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, 1444Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
967L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
968L<Event::Lib>, L<Qt>, L<POE>. 1445L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
969 1446
970Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>, 1447Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
971L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, 1448L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
972L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>, 1449L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
973L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>. 1450L<AnyEvent::Impl::POE>.
1451
1452Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
974 1453
975Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. 1454Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
976 1455
977 1456
978=head1 AUTHOR 1457=head1 AUTHOR

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