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1NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - provide framework for multiple event loops
3 3
4 EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported 4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5 event loops 5 loops
6 6
7SYNOPSIS 7SYNOPSIS
8 use AnyEvent; 8 use AnyEvent;
9 9
10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
… …
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { 14 my $w = AnyEvent->timer (after => $seconds, cb => sub {
15 ... 15 ...
16 }); 16 });
17 17
18 my $w = AnyEvent->condvar; # stores whether a condition was flagged 18 my $w = AnyEvent->condvar; # stores whether a condition was flagged
19 $w->send; # wake up current and all future recv's
19 $w->wait; # enters "main loop" till $condvar gets ->broadcast 20 $w->recv; # enters "main loop" till $condvar gets ->send
20 $w->broadcast; # wake up current and all future wait's
21 21
22WHY YOU SHOULD USE THIS MODULE (OR NOT) 22WHY YOU SHOULD USE THIS MODULE (OR NOT)
23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen 23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24 nowadays. So what is different about AnyEvent? 24 nowadays. So what is different about AnyEvent?
25 25
… …
75 The interface itself is vaguely similar, but not identical to the Event 75 The interface itself is vaguely similar, but not identical to the Event
76 module. 76 module.
77 77
78 During the first call of any watcher-creation method, the module tries 78 During the first call of any watcher-creation method, the module tries
79 to detect the currently loaded event loop by probing whether one of the 79 to detect the currently loaded event loop by probing whether one of the
80 following modules is already loaded: Coro::EV, Coro::Event, EV, Event, 80 following modules is already loaded: EV, Event, Glib,
81 Glib, Tk. The first one found is used. If none are found, the module 81 AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82 tries to load these modules in the stated order. The first one that can 82 used. If none are found, the module tries to load these modules
83 (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84 always succeed) in the order given. The first one that can be
83 be successfully loaded will be used. If, after this, still none could be 85 successfully loaded will be used. If, after this, still none could be
84 found, AnyEvent will fall back to a pure-perl event loop, which is not 86 found, AnyEvent will fall back to a pure-perl event loop, which is not
85 very efficient, but should work everywhere. 87 very efficient, but should work everywhere.
86 88
87 Because AnyEvent first checks for modules that are already loaded, 89 Because AnyEvent first checks for modules that are already loaded,
88 loading an event model explicitly before first using AnyEvent will 90 loading an event model explicitly before first using AnyEvent will
… …
129 131
130 Note that "my $w; $w =" combination. This is necessary because in Perl, 132 Note that "my $w; $w =" combination. This is necessary because in Perl,
131 my variables are only visible after the statement in which they are 133 my variables are only visible after the statement in which they are
132 declared. 134 declared.
133 135
134 IO WATCHERS 136 I/O WATCHERS
135 You can create an I/O watcher by calling the "AnyEvent->io" method with 137 You can create an I/O watcher by calling the "AnyEvent->io" method with
136 the following mandatory key-value pairs as arguments: 138 the following mandatory key-value pairs as arguments:
137 139
138 "fh" the Perl *file handle* (*not* file descriptor) to watch for events. 140 "fh" the Perl *file handle* (*not* file descriptor) to watch for events.
139 "poll" must be a string that is either "r" or "w", which creates a 141 "poll" must be a string that is either "r" or "w", which creates a
140 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 142 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
141 is the callback to invoke each time the file handle becomes ready. 143 is the callback to invoke each time the file handle becomes ready.
142 144
143 File handles will be kept alive, so as long as the watcher exists, the 145 Although the callback might get passed parameters, their value and
144 file handle exists, too. 146 presence is undefined and you cannot rely on them. Portable AnyEvent
147 callbacks cannot use arguments passed to I/O watcher callbacks.
145 148
149 The I/O watcher might use the underlying file descriptor or a copy of
146 It is not allowed to close a file handle as long as any watcher is 150 it. You must not close a file handle as long as any watcher is active on
147 active on the underlying file descriptor. 151 the underlying file descriptor.
148 152
149 Some event loops issue spurious readyness notifications, so you should 153 Some event loops issue spurious readyness notifications, so you should
150 always use non-blocking calls when reading/writing from/to your file 154 always use non-blocking calls when reading/writing from/to your file
151 handles. 155 handles.
152 156
… …
162 TIME WATCHERS 166 TIME WATCHERS
163 You can create a time watcher by calling the "AnyEvent->timer" method 167 You can create a time watcher by calling the "AnyEvent->timer" method
164 with the following mandatory arguments: 168 with the following mandatory arguments:
165 169
166 "after" specifies after how many seconds (fractional values are 170 "after" specifies after how many seconds (fractional values are
167 supported) should the timer activate. "cb" the callback to invoke in 171 supported) the callback should be invoked. "cb" is the callback to
168 that case. 172 invoke in that case.
173
174 Although the callback might get passed parameters, their value and
175 presence is undefined and you cannot rely on them. Portable AnyEvent
176 callbacks cannot use arguments passed to time watcher callbacks.
169 177
170 The timer callback will be invoked at most once: if you want a repeating 178 The timer callback will be invoked at most once: if you want a repeating
171 timer you have to create a new watcher (this is a limitation by both Tk 179 timer you have to create a new watcher (this is a limitation by both Tk
172 and Glib). 180 and Glib).
173 181
… …
200 o'clock"). 208 o'clock").
201 209
202 While most event loops expect timers to specified in a relative way, 210 While most event loops expect timers to specified in a relative way,
203 they use absolute time internally. This makes a difference when your 211 they use absolute time internally. This makes a difference when your
204 clock "jumps", for example, when ntp decides to set your clock backwards 212 clock "jumps", for example, when ntp decides to set your clock backwards
205 from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to 213 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
206 fire "after" a second might actually take six years to finally fire. 214 supposed to fire "after" a second might actually take six years to
215 finally fire.
207 216
208 AnyEvent cannot compensate for this. The only event loop that is 217 AnyEvent cannot compensate for this. The only event loop that is
209 conscious about these issues is EV, which offers both relative 218 conscious about these issues is EV, which offers both relative
210 (ev_timer) and absolute (ev_periodic) timers. 219 (ev_timer, based on true relative time) and absolute (ev_periodic, based
220 on wallclock time) timers.
211 221
212 AnyEvent always prefers relative timers, if available, matching the 222 AnyEvent always prefers relative timers, if available, matching the
213 AnyEvent API. 223 AnyEvent API.
214 224
215 SIGNAL WATCHERS 225 SIGNAL WATCHERS
216 You can watch for signals using a signal watcher, "signal" is the signal 226 You can watch for signals using a signal watcher, "signal" is the signal
217 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked 227 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked
218 whenever a signal occurs. 228 whenever a signal occurs.
219 229
230 Although the callback might get passed parameters, their value and
231 presence is undefined and you cannot rely on them. Portable AnyEvent
232 callbacks cannot use arguments passed to signal watcher callbacks.
233
220 Multiple signals occurances can be clumped together into one callback 234 Multiple signal occurances can be clumped together into one callback
221 invocation, and callback invocation will be synchronous. synchronous 235 invocation, and callback invocation will be synchronous. synchronous
222 means that it might take a while until the signal gets handled by the 236 means that it might take a while until the signal gets handled by the
223 process, but it is guarenteed not to interrupt any other callbacks. 237 process, but it is guarenteed not to interrupt any other callbacks.
224 238
225 The main advantage of using these watchers is that you can share a 239 The main advantage of using these watchers is that you can share a
… …
237 251
238 The child process is specified by the "pid" argument (if set to 0, it 252 The child process is specified by the "pid" argument (if set to 0, it
239 watches for any child process exit). The watcher will trigger as often 253 watches for any child process exit). The watcher will trigger as often
240 as status change for the child are received. This works by installing a 254 as status change for the child are received. This works by installing a
241 signal handler for "SIGCHLD". The callback will be called with the pid 255 signal handler for "SIGCHLD". The callback will be called with the pid
242 and exit status (as returned by waitpid). 256 and exit status (as returned by waitpid), so unlike other watcher types,
257 you *can* rely on child watcher callback arguments.
243 258
244 Example: wait for pid 1333 259 There is a slight catch to child watchers, however: you usually start
260 them *after* the child process was created, and this means the process
261 could have exited already (and no SIGCHLD will be sent anymore).
262
263 Not all event models handle this correctly (POE doesn't), but even for
264 event models that *do* handle this correctly, they usually need to be
265 loaded before the process exits (i.e. before you fork in the first
266 place).
267
268 This means you cannot create a child watcher as the very first thing in
269 an AnyEvent program, you *have* to create at least one watcher before
270 you "fork" the child (alternatively, you can call "AnyEvent::detect").
271
272 Example: fork a process and wait for it
273
274 my $done = AnyEvent->condvar;
275
276 my $pid = fork or exit 5;
245 277
246 my $w = AnyEvent->child ( 278 my $w = AnyEvent->child (
247 pid => 1333, 279 pid => $pid,
248 cb => sub { 280 cb => sub {
249 my ($pid, $status) = @_; 281 my ($pid, $status) = @_;
250 warn "pid $pid exited with status $status"; 282 warn "pid $pid exited with status $status";
283 $done->send;
251 }, 284 },
252 ); 285 );
253 286
287 # do something else, then wait for process exit
288 $done->recv;
289
254 CONDITION VARIABLES 290 CONDITION VARIABLES
291 If you are familiar with some event loops you will know that all of them
292 require you to run some blocking "loop", "run" or similar function that
293 will actively watch for new events and call your callbacks.
294
295 AnyEvent is different, it expects somebody else to run the event loop
296 and will only block when necessary (usually when told by the user).
297
298 The instrument to do that is called a "condition variable", so called
299 because they represent a condition that must become true.
300
255 Condition variables can be created by calling the "AnyEvent->condvar" 301 Condition variables can be created by calling the "AnyEvent->condvar"
256 method without any arguments. 302 method, usually without arguments. The only argument pair allowed is
303 "cb", which specifies a callback to be called when the condition
304 variable becomes true.
257 305
258 A condition variable waits for a condition - precisely that the 306 After creation, the conditon variable is "false" until it becomes "true"
259 "->broadcast" method has been called. 307 by calling the "send" method.
260 308
261 They are very useful to signal that a condition has been fulfilled, for 309 Condition variables are similar to callbacks, except that you can
310 optionally wait for them. They can also be called merge points - points
311 in time where multiple outstandign events have been processed. And yet
312 another way to call them is transations - each condition variable can be
313 used to represent a transaction, which finishes at some point and
314 delivers a result.
315
316 Condition variables are very useful to signal that something has
262 example, if you write a module that does asynchronous http requests, 317 finished, for example, if you write a module that does asynchronous http
263 then a condition variable would be the ideal candidate to signal the 318 requests, then a condition variable would be the ideal candidate to
264 availability of results. 319 signal the availability of results. The user can either act when the
320 callback is called or can synchronously "->recv" for the results.
265 321
266 You can also use condition variables to block your main program until an 322 You can also use them to simulate traditional event loops - for example,
267 event occurs - for example, you could "->wait" in your main program 323 you can block your main program until an event occurs - for example, you
268 until the user clicks the Quit button in your app, which would 324 could "->recv" in your main program until the user clicks the Quit
269 "->broadcast" the "quit" event. 325 button of your app, which would "->send" the "quit" event.
270 326
271 Note that condition variables recurse into the event loop - if you have 327 Note that condition variables recurse into the event loop - if you have
272 two pirces of code that call "->wait" in a round-robbin fashion, you 328 two pieces of code that call "->recv" in a round-robbin fashion, you
273 lose. Therefore, condition variables are good to export to your caller, 329 lose. Therefore, condition variables are good to export to your caller,
274 but you should avoid making a blocking wait yourself, at least in 330 but you should avoid making a blocking wait yourself, at least in
275 callbacks, as this asks for trouble. 331 callbacks, as this asks for trouble.
276 332
277 This object has two methods: 333 Condition variables are represented by hash refs in perl, and the keys
334 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
335 (it is often useful to build your own transaction class on top of
336 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
337 it's "new" method in your own "new" method.
278 338
279 $cv->wait 339 There are two "sides" to a condition variable - the "producer side"
340 which eventually calls "-> send", and the "consumer side", which waits
341 for the send to occur.
342
343 Example:
344
345 # wait till the result is ready
346 my $result_ready = AnyEvent->condvar;
347
348 # do something such as adding a timer
349 # or socket watcher the calls $result_ready->send
350 # when the "result" is ready.
351 # in this case, we simply use a timer:
352 my $w = AnyEvent->timer (
353 after => 1,
354 cb => sub { $result_ready->send },
355 );
356
357 # this "blocks" (while handling events) till the callback
358 # calls send
359 $result_ready->recv;
360
361 METHODS FOR PRODUCERS
362 These methods should only be used by the producing side, i.e. the
363 code/module that eventually sends the signal. Note that it is also the
364 producer side which creates the condvar in most cases, but it isn't
365 uncommon for the consumer to create it as well.
366
367 $cv->send (...)
368 Flag the condition as ready - a running "->recv" and all further
369 calls to "recv" will (eventually) return after this method has been
370 called. If nobody is waiting the send will be remembered.
371
372 If a callback has been set on the condition variable, it is called
373 immediately from within send.
374
375 Any arguments passed to the "send" call will be returned by all
376 future "->recv" calls.
377
378 $cv->croak ($error)
379 Similar to send, but causes all call's to "->recv" to invoke
380 "Carp::croak" with the given error message/object/scalar.
381
382 This can be used to signal any errors to the condition variable
383 user/consumer.
384
385 $cv->begin ([group callback])
386 $cv->end
387 These two methods are EXPERIMENTAL and MIGHT CHANGE.
388
389 These two methods can be used to combine many transactions/events
390 into one. For example, a function that pings many hosts in parallel
391 might want to use a condition variable for the whole process.
392
393 Every call to "->begin" will increment a counter, and every call to
394 "->end" will decrement it. If the counter reaches 0 in "->end", the
395 (last) callback passed to "begin" will be executed. That callback is
396 *supposed* to call "->send", but that is not required. If no
397 callback was set, "send" will be called without any arguments.
398
399 Let's clarify this with the ping example:
400
401 my $cv = AnyEvent->condvar;
402
403 my %result;
404 $cv->begin (sub { $cv->send (\%result) });
405
406 for my $host (@list_of_hosts) {
407 $cv->begin;
408 ping_host_then_call_callback $host, sub {
409 $result{$host} = ...;
410 $cv->end;
411 };
412 }
413
414 $cv->end;
415
416 This code fragment supposedly pings a number of hosts and calls
417 "send" after results for all then have have been gathered - in any
418 order. To achieve this, the code issues a call to "begin" when it
419 starts each ping request and calls "end" when it has received some
420 result for it. Since "begin" and "end" only maintain a counter, the
421 order in which results arrive is not relevant.
422
423 There is an additional bracketing call to "begin" and "end" outside
424 the loop, which serves two important purposes: first, it sets the
425 callback to be called once the counter reaches 0, and second, it
426 ensures that "send" is called even when "no" hosts are being pinged
427 (the loop doesn't execute once).
428
429 This is the general pattern when you "fan out" into multiple
430 subrequests: use an outer "begin"/"end" pair to set the callback and
431 ensure "end" is called at least once, and then, for each subrequest
432 you start, call "begin" and for eahc subrequest you finish, call
433 "end".
434
435 METHODS FOR CONSUMERS
436 These methods should only be used by the consuming side, i.e. the code
437 awaits the condition.
438
439 $cv->recv
280 Wait (blocking if necessary) until the "->broadcast" method has been 440 Wait (blocking if necessary) until the "->send" or "->croak" methods
281 called on c<$cv>, while servicing other watchers normally. 441 have been called on c<$cv>, while servicing other watchers normally.
282 442
283 You can only wait once on a condition - additional calls will return 443 You can only wait once on a condition - additional calls are valid
284 immediately. 444 but will return immediately.
445
446 If an error condition has been set by calling "->croak", then this
447 function will call "croak".
448
449 In list context, all parameters passed to "send" will be returned,
450 in scalar context only the first one will be returned.
285 451
286 Not all event models support a blocking wait - some die in that case 452 Not all event models support a blocking wait - some die in that case
287 (programs might want to do that to stay interactive), so *if you are 453 (programs might want to do that to stay interactive), so *if you are
288 using this from a module, never require a blocking wait*, but let 454 using this from a module, never require a blocking wait*, but let
289 the caller decide whether the call will block or not (for example, 455 the caller decide whether the call will block or not (for example,
290 by coupling condition variables with some kind of request results 456 by coupling condition variables with some kind of request results
291 and supporting callbacks so the caller knows that getting the result 457 and supporting callbacks so the caller knows that getting the result
292 will not block, while still suppporting blocking waits if the caller 458 will not block, while still suppporting blocking waits if the caller
293 so desires). 459 so desires).
294 460
295 Another reason *never* to "->wait" in a module is that you cannot 461 Another reason *never* to "->recv" in a module is that you cannot
296 sensibly have two "->wait"'s in parallel, as that would require 462 sensibly have two "->recv"'s in parallel, as that would require
297 multiple interpreters or coroutines/threads, none of which 463 multiple interpreters or coroutines/threads, none of which
298 "AnyEvent" can supply (the coroutine-aware backends 464 "AnyEvent" can supply.
299 AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
300 support concurrent "->wait"'s from different coroutines, however).
301 465
302 $cv->broadcast 466 The Coro module, however, *can* and *does* supply coroutines and, in
303 Flag the condition as ready - a running "->wait" and all further 467 fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
304 calls to "wait" will (eventually) return after this method has been 468 versions and also integrates coroutines into AnyEvent, making
305 called. If nobody is waiting the broadcast will be remembered.. 469 blocking "->recv" calls perfectly safe as long as they are done from
470 another coroutine (one that doesn't run the event loop).
306 471
307 Example: 472 You can ensure that "-recv" never blocks by setting a callback and
473 only calling "->recv" from within that callback (or at a later
474 time). This will work even when the event loop does not support
475 blocking waits otherwise.
308 476
309 # wait till the result is ready 477 $bool = $cv->ready
310 my $result_ready = AnyEvent->condvar; 478 Returns true when the condition is "true", i.e. whether "send" or
479 "croak" have been called.
311 480
312 # do something such as adding a timer 481 $cb = $cv->cb ([new callback])
313 # or socket watcher the calls $result_ready->broadcast 482 This is a mutator function that returns the callback set and
314 # when the "result" is ready. 483 optionally replaces it before doing so.
315 # in this case, we simply use a timer:
316 my $w = AnyEvent->timer (
317 after => 1,
318 cb => sub { $result_ready->broadcast },
319 );
320 484
321 # this "blocks" (while handling events) till the watcher 485 The callback will be called when the condition becomes "true", i.e.
322 # calls broadcast 486 when "send" or "croak" are called. Calling "recv" inside the
323 $result_ready->wait; 487 callback or at any later time is guaranteed not to block.
324 488
325GLOBAL VARIABLES AND FUNCTIONS 489GLOBAL VARIABLES AND FUNCTIONS
326 $AnyEvent::MODEL 490 $AnyEvent::MODEL
327 Contains "undef" until the first watcher is being created. Then it 491 Contains "undef" until the first watcher is being created. Then it
328 contains the event model that is being used, which is the name of 492 contains the event model that is being used, which is the name of
… …
330 the "AnyEvent::Impl:xxx" modules, but can be any other class in the 494 the "AnyEvent::Impl:xxx" modules, but can be any other class in the
331 case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). 495 case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).
332 496
333 The known classes so far are: 497 The known classes so far are:
334 498
335 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
336 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
337 AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). 499 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
338 AnyEvent::Impl::Event based on Event, also second best choice :) 500 AnyEvent::Impl::Event based on Event, second best choice.
501 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
339 AnyEvent::Impl::Glib based on Glib, third-best choice. 502 AnyEvent::Impl::Glib based on Glib, third-best choice.
340 AnyEvent::Impl::Tk based on Tk, very bad choice. 503 AnyEvent::Impl::Tk based on Tk, very bad choice.
341 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. 504 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
505 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
506 AnyEvent::Impl::POE based on POE, not generic enough for full support.
507
508 There is no support for WxWidgets, as WxWidgets has no support for
509 watching file handles. However, you can use WxWidgets through the
510 POE Adaptor, as POE has a Wx backend that simply polls 20 times per
511 second, which was considered to be too horrible to even consider for
512 AnyEvent. Likewise, other POE backends can be used by AnyEvent by
513 using it's adaptor.
514
515 AnyEvent knows about Prima and Wx and will try to use POE when
516 autodetecting them.
342 517
343 AnyEvent::detect 518 AnyEvent::detect
344 Returns $AnyEvent::MODEL, forcing autodetection of the event model 519 Returns $AnyEvent::MODEL, forcing autodetection of the event model
345 if necessary. You should only call this function right before you 520 if necessary. You should only call this function right before you
346 would have created an AnyEvent watcher anyway, that is, as late as 521 would have created an AnyEvent watcher anyway, that is, as late as
347 possible at runtime. 522 possible at runtime.
348 523
524 $guard = AnyEvent::post_detect { BLOCK }
525 Arranges for the code block to be executed as soon as the event
526 model is autodetected (or immediately if this has already happened).
527
528 If called in scalar or list context, then it creates and returns an
529 object that automatically removes the callback again when it is
530 destroyed. See Coro::BDB for a case where this is useful.
531
532 @AnyEvent::post_detect
533 If there are any code references in this array (you can "push" to it
534 before or after loading AnyEvent), then they will called directly
535 after the event loop has been chosen.
536
537 You should check $AnyEvent::MODEL before adding to this array,
538 though: if it contains a true value then the event loop has already
539 been detected, and the array will be ignored.
540
541 Best use "AnyEvent::post_detect { BLOCK }" instead.
542
349WHAT TO DO IN A MODULE 543WHAT TO DO IN A MODULE
350 As a module author, you should "use AnyEvent" and call AnyEvent methods 544 As a module author, you should "use AnyEvent" and call AnyEvent methods
351 freely, but you should not load a specific event module or rely on it. 545 freely, but you should not load a specific event module or rely on it.
352 546
353 Be careful when you create watchers in the module body - AnyEvent will 547 Be careful when you create watchers in the module body - AnyEvent will
354 decide which event module to use as soon as the first method is called, 548 decide which event module to use as soon as the first method is called,
355 so by calling AnyEvent in your module body you force the user of your 549 so by calling AnyEvent in your module body you force the user of your
356 module to load the event module first. 550 module to load the event module first.
357 551
358 Never call "->wait" on a condition variable unless you *know* that the 552 Never call "->recv" on a condition variable unless you *know* that the
359 "->broadcast" method has been called on it already. This is because it 553 "->send" method has been called on it already. This is because it will
360 will stall the whole program, and the whole point of using events is to 554 stall the whole program, and the whole point of using events is to stay
361 stay interactive. 555 interactive.
362 556
363 It is fine, however, to call "->wait" when the user of your module 557 It is fine, however, to call "->recv" when the user of your module
364 requests it (i.e. if you create a http request object ad have a method 558 requests it (i.e. if you create a http request object ad have a method
365 called "results" that returns the results, it should call "->wait" 559 called "results" that returns the results, it should call "->recv"
366 freely, as the user of your module knows what she is doing. always). 560 freely, as the user of your module knows what she is doing. always).
367 561
368WHAT TO DO IN THE MAIN PROGRAM 562WHAT TO DO IN THE MAIN PROGRAM
369 There will always be a single main program - the only place that should 563 There will always be a single main program - the only place that should
370 dictate which event model to use. 564 dictate which event model to use.
… …
385 579
386 You can chose to use a rather inefficient pure-perl implementation by 580 You can chose to use a rather inefficient pure-perl implementation by
387 loading the "AnyEvent::Impl::Perl" module, which gives you similar 581 loading the "AnyEvent::Impl::Perl" module, which gives you similar
388 behaviour everywhere, but letting AnyEvent chose is generally better. 582 behaviour everywhere, but letting AnyEvent chose is generally better.
389 583
584OTHER MODULES
585 The following is a non-exhaustive list of additional modules that use
586 AnyEvent and can therefore be mixed easily with other AnyEvent modules
587 in the same program. Some of the modules come with AnyEvent, some are
588 available via CPAN.
589
590 AnyEvent::Util
591 Contains various utility functions that replace often-used but
592 blocking functions such as "inet_aton" by event-/callback-based
593 versions.
594
595 AnyEvent::Handle
596 Provide read and write buffers and manages watchers for reads and
597 writes.
598
599 AnyEvent::HTTPD
600 Provides a simple web application server framework.
601
602 AnyEvent::DNS
603 Provides asynchronous DNS resolver capabilities, beyond what
604 AnyEvent::Util offers.
605
606 AnyEvent::FastPing
607 The fastest ping in the west.
608
609 Net::IRC3
610 AnyEvent based IRC client module family.
611
612 Net::XMPP2
613 AnyEvent based XMPP (Jabber protocol) module family.
614
615 Net::FCP
616 AnyEvent-based implementation of the Freenet Client Protocol,
617 birthplace of AnyEvent.
618
619 Event::ExecFlow
620 High level API for event-based execution flow control.
621
622 Coro
623 Has special support for AnyEvent via Coro::AnyEvent.
624
625 AnyEvent::AIO, IO::AIO
626 Truly asynchronous I/O, should be in the toolbox of every event
627 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
628 together.
629
630 AnyEvent::BDB, BDB
631 Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
632 fuses IO::AIO and AnyEvent together.
633
634 IO::Lambda
635 The lambda approach to I/O - don't ask, look there. Can use
636 AnyEvent.
637
390SUPPLYING YOUR OWN EVENT MODEL INTERFACE 638SUPPLYING YOUR OWN EVENT MODEL INTERFACE
391 This is an advanced topic that you do not normally need to use AnyEvent 639 This is an advanced topic that you do not normally need to use AnyEvent
392 in a module. This section is only of use to event loop authors who want 640 in a module. This section is only of use to event loop authors who want
393 to provide AnyEvent compatibility. 641 to provide AnyEvent compatibility.
394 642
… …
431 must not be done in an interactive application, so it makes sense. 679 must not be done in an interactive application, so it makes sense.
432 680
433ENVIRONMENT VARIABLES 681ENVIRONMENT VARIABLES
434 The following environment variables are used by this module: 682 The following environment variables are used by this module:
435 683
436 "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to 684 "PERL_ANYEVENT_VERBOSE"
437 report to STDERR which event model it chooses. 685 By default, AnyEvent will be completely silent except in fatal
686 conditions. You can set this environment variable to make AnyEvent
687 more talkative.
688
689 When set to 1 or higher, causes AnyEvent to warn about unexpected
690 conditions, such as not being able to load the event model specified
691 by "PERL_ANYEVENT_MODEL".
692
693 When set to 2 or higher, cause AnyEvent to report to STDERR which
694 event model it chooses.
695
696 "PERL_ANYEVENT_MODEL"
697 This can be used to specify the event model to be used by AnyEvent,
698 before autodetection and -probing kicks in. It must be a string
699 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
700 gets prepended and the resulting module name is loaded and if the
701 load was successful, used as event model. If it fails to load
702 AnyEvent will proceed with autodetection and -probing.
703
704 This functionality might change in future versions.
705
706 For example, to force the pure perl model (AnyEvent::Impl::Perl) you
707 could start your program like this:
708
709 PERL_ANYEVENT_MODEL=Perl perl ...
438 710
439EXAMPLE PROGRAM 711EXAMPLE PROGRAM
440 The following program uses an IO watcher to read data from STDIN, a 712 The following program uses an I/O watcher to read data from STDIN, a
441 timer to display a message once per second, and a condition variable to 713 timer to display a message once per second, and a condition variable to
442 quit the program when the user enters quit: 714 quit the program when the user enters quit:
443 715
444 use AnyEvent; 716 use AnyEvent;
445 717
… …
450 poll => 'r', 722 poll => 'r',
451 cb => sub { 723 cb => sub {
452 warn "io event <$_[0]>\n"; # will always output <r> 724 warn "io event <$_[0]>\n"; # will always output <r>
453 chomp (my $input = <STDIN>); # read a line 725 chomp (my $input = <STDIN>); # read a line
454 warn "read: $input\n"; # output what has been read 726 warn "read: $input\n"; # output what has been read
455 $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i 727 $cv->send if $input =~ /^q/i; # quit program if /^q/i
456 }, 728 },
457 ); 729 );
458 730
459 my $time_watcher; # can only be used once 731 my $time_watcher; # can only be used once
460 732
… …
465 }); 737 });
466 } 738 }
467 739
468 new_timer; # create first timer 740 new_timer; # create first timer
469 741
470 $cv->wait; # wait until user enters /^q/i 742 $cv->recv; # wait until user enters /^q/i
471 743
472REAL-WORLD EXAMPLE 744REAL-WORLD EXAMPLE
473 Consider the Net::FCP module. It features (among others) the following 745 Consider the Net::FCP module. It features (among others) the following
474 API calls, which are to freenet what HTTP GET requests are to http: 746 API calls, which are to freenet what HTTP GET requests are to http:
475 747
… …
530 802
531 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; 803 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
532 804
533 if (end-of-file or data complete) { 805 if (end-of-file or data complete) {
534 $txn->{result} = $txn->{buf}; 806 $txn->{result} = $txn->{buf};
535 $txn->{finished}->broadcast; 807 $txn->{finished}->send;
536 $txb->{cb}->($txn) of $txn->{cb}; # also call callback 808 $txb->{cb}->($txn) of $txn->{cb}; # also call callback
537 } 809 }
538 810
539 The "result" method, finally, just waits for the finished signal (if the 811 The "result" method, finally, just waits for the finished signal (if the
540 request was already finished, it doesn't wait, of course, and returns 812 request was already finished, it doesn't wait, of course, and returns
541 the data: 813 the data:
542 814
543 $txn->{finished}->wait; 815 $txn->{finished}->recv;
544 return $txn->{result}; 816 return $txn->{result};
545 817
546 The actual code goes further and collects all errors ("die"s, 818 The actual code goes further and collects all errors ("die"s,
547 exceptions) that occured during request processing. The "result" method 819 exceptions) that occured during request processing. The "result" method
548 detects whether an exception as thrown (it is stored inside the $txn 820 detects whether an exception as thrown (it is stored inside the $txn
… …
583 855
584 my $quit = AnyEvent->condvar; 856 my $quit = AnyEvent->condvar;
585 857
586 $fcp->txn_client_get ($url)->cb (sub { 858 $fcp->txn_client_get ($url)->cb (sub {
587 ... 859 ...
588 $quit->broadcast; 860 $quit->send;
589 }); 861 });
590 862
591 $quit->wait; 863 $quit->recv;
864
865BENCHMARKS
866 To give you an idea of the performance and overheads that AnyEvent adds
867 over the event loops themselves and to give you an impression of the
868 speed of various event loops I prepared some benchmarks.
869
870 BENCHMARKING ANYEVENT OVERHEAD
871 Here is a benchmark of various supported event models used natively and
872 through anyevent. The benchmark creates a lot of timers (with a zero
873 timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
874 which it is), lets them fire exactly once and destroys them again.
875
876 Source code for this benchmark is found as eg/bench in the AnyEvent
877 distribution.
878
879 Explanation of the columns
880 *watcher* is the number of event watchers created/destroyed. Since
881 different event models feature vastly different performances, each event
882 loop was given a number of watchers so that overall runtime is
883 acceptable and similar between tested event loop (and keep them from
884 crashing): Glib would probably take thousands of years if asked to
885 process the same number of watchers as EV in this benchmark.
886
887 *bytes* is the number of bytes (as measured by the resident set size,
888 RSS) consumed by each watcher. This method of measuring captures both C
889 and Perl-based overheads.
890
891 *create* is the time, in microseconds (millionths of seconds), that it
892 takes to create a single watcher. The callback is a closure shared
893 between all watchers, to avoid adding memory overhead. That means
894 closure creation and memory usage is not included in the figures.
895
896 *invoke* is the time, in microseconds, used to invoke a simple callback.
897 The callback simply counts down a Perl variable and after it was invoked
898 "watcher" times, it would "->send" a condvar once to signal the end of
899 this phase.
900
901 *destroy* is the time, in microseconds, that it takes to destroy a
902 single watcher.
903
904 Results
905 name watchers bytes create invoke destroy comment
906 EV/EV 400000 244 0.56 0.46 0.31 EV native interface
907 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
908 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
909 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
910 Event/Event 16000 516 31.88 31.30 0.85 Event native interface
911 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
912 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
913 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
914 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
915 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
916
917 Discussion
918 The benchmark does *not* measure scalability of the event loop very
919 well. For example, a select-based event loop (such as the pure perl one)
920 can never compete with an event loop that uses epoll when the number of
921 file descriptors grows high. In this benchmark, all events become ready
922 at the same time, so select/poll-based implementations get an unnatural
923 speed boost.
924
925 Also, note that the number of watchers usually has a nonlinear effect on
926 overall speed, that is, creating twice as many watchers doesn't take
927 twice the time - usually it takes longer. This puts event loops tested
928 with a higher number of watchers at a disadvantage.
929
930 To put the range of results into perspective, consider that on the
931 benchmark machine, handling an event takes roughly 1600 CPU cycles with
932 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
933 CPU cycles with POE.
934
935 "EV" is the sole leader regarding speed and memory use, which are both
936 maximal/minimal, respectively. Even when going through AnyEvent, it uses
937 far less memory than any other event loop and is still faster than Event
938 natively.
939
940 The pure perl implementation is hit in a few sweet spots (both the
941 constant timeout and the use of a single fd hit optimisations in the
942 perl interpreter and the backend itself). Nevertheless this shows that
943 it adds very little overhead in itself. Like any select-based backend
944 its performance becomes really bad with lots of file descriptors (and
945 few of them active), of course, but this was not subject of this
946 benchmark.
947
948 The "Event" module has a relatively high setup and callback invocation
949 cost, but overall scores in on the third place.
950
951 "Glib"'s memory usage is quite a bit higher, but it features a faster
952 callback invocation and overall ends up in the same class as "Event".
953 However, Glib scales extremely badly, doubling the number of watchers
954 increases the processing time by more than a factor of four, making it
955 completely unusable when using larger numbers of watchers (note that
956 only a single file descriptor was used in the benchmark, so
957 inefficiencies of "poll" do not account for this).
958
959 The "Tk" adaptor works relatively well. The fact that it crashes with
960 more than 2000 watchers is a big setback, however, as correctness takes
961 precedence over speed. Nevertheless, its performance is surprising, as
962 the file descriptor is dup()ed for each watcher. This shows that the
963 dup() employed by some adaptors is not a big performance issue (it does
964 incur a hidden memory cost inside the kernel which is not reflected in
965 the figures above).
966
967 "POE", regardless of underlying event loop (whether using its pure perl
968 select-based backend or the Event module, the POE-EV backend couldn't be
969 tested because it wasn't working) shows abysmal performance and memory
970 usage with AnyEvent: Watchers use almost 30 times as much memory as EV
971 watchers, and 10 times as much memory as Event (the high memory
972 requirements are caused by requiring a session for each watcher).
973 Watcher invocation speed is almost 900 times slower than with AnyEvent's
974 pure perl implementation.
975
976 The design of the POE adaptor class in AnyEvent can not really account
977 for the performance issues, though, as session creation overhead is
978 small compared to execution of the state machine, which is coded pretty
979 optimally within AnyEvent::Impl::POE (and while everybody agrees that
980 using multiple sessions is not a good approach, especially regarding
981 memory usage, even the author of POE could not come up with a faster
982 design).
983
984 Summary
985 * Using EV through AnyEvent is faster than any other event loop (even
986 when used without AnyEvent), but most event loops have acceptable
987 performance with or without AnyEvent.
988
989 * The overhead AnyEvent adds is usually much smaller than the overhead
990 of the actual event loop, only with extremely fast event loops such
991 as EV adds AnyEvent significant overhead.
992
993 * You should avoid POE like the plague if you want performance or
994 reasonable memory usage.
995
996 BENCHMARKING THE LARGE SERVER CASE
997 This benchmark atcually benchmarks the event loop itself. It works by
998 creating a number of "servers": each server consists of a socketpair, a
999 timeout watcher that gets reset on activity (but never fires), and an
1000 I/O watcher waiting for input on one side of the socket. Each time the
1001 socket watcher reads a byte it will write that byte to a random other
1002 "server".
1003
1004 The effect is that there will be a lot of I/O watchers, only part of
1005 which are active at any one point (so there is a constant number of
1006 active fds for each loop iterstaion, but which fds these are is random).
1007 The timeout is reset each time something is read because that reflects
1008 how most timeouts work (and puts extra pressure on the event loops).
1009
1010 In this benchmark, we use 10000 socketpairs (20000 sockets), of which
1011 100 (1%) are active. This mirrors the activity of large servers with
1012 many connections, most of which are idle at any one point in time.
1013
1014 Source code for this benchmark is found as eg/bench2 in the AnyEvent
1015 distribution.
1016
1017 Explanation of the columns
1018 *sockets* is the number of sockets, and twice the number of "servers"
1019 (as each server has a read and write socket end).
1020
1021 *create* is the time it takes to create a socketpair (which is
1022 nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1023
1024 *request*, the most important value, is the time it takes to handle a
1025 single "request", that is, reading the token from the pipe and
1026 forwarding it to another server. This includes deleting the old timeout
1027 and creating a new one that moves the timeout into the future.
1028
1029 Results
1030 name sockets create request
1031 EV 20000 69.01 11.16
1032 Perl 20000 73.32 35.87
1033 Event 20000 212.62 257.32
1034 Glib 20000 651.16 1896.30
1035 POE 20000 349.67 12317.24 uses POE::Loop::Event
1036
1037 Discussion
1038 This benchmark *does* measure scalability and overall performance of the
1039 particular event loop.
1040
1041 EV is again fastest. Since it is using epoll on my system, the setup
1042 time is relatively high, though.
1043
1044 Perl surprisingly comes second. It is much faster than the C-based event
1045 loops Event and Glib.
1046
1047 Event suffers from high setup time as well (look at its code and you
1048 will understand why). Callback invocation also has a high overhead
1049 compared to the "$_->() for .."-style loop that the Perl event loop
1050 uses. Event uses select or poll in basically all documented
1051 configurations.
1052
1053 Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
1054 clearly fails to perform with many filehandles or in busy servers.
1055
1056 POE is still completely out of the picture, taking over 1000 times as
1057 long as EV, and over 100 times as long as the Perl implementation, even
1058 though it uses a C-based event loop in this case.
1059
1060 Summary
1061 * The pure perl implementation performs extremely well.
1062
1063 * Avoid Glib or POE in large projects where performance matters.
1064
1065 BENCHMARKING SMALL SERVERS
1066 While event loops should scale (and select-based ones do not...) even to
1067 large servers, most programs we (or I :) actually write have only a few
1068 I/O watchers.
1069
1070 In this benchmark, I use the same benchmark program as in the large
1071 server case, but it uses only eight "servers", of which three are active
1072 at any one time. This should reflect performance for a small server
1073 relatively well.
1074
1075 The columns are identical to the previous table.
1076
1077 Results
1078 name sockets create request
1079 EV 16 20.00 6.54
1080 Perl 16 25.75 12.62
1081 Event 16 81.27 35.86
1082 Glib 16 32.63 15.48
1083 POE 16 261.87 276.28 uses POE::Loop::Event
1084
1085 Discussion
1086 The benchmark tries to test the performance of a typical small server.
1087 While knowing how various event loops perform is interesting, keep in
1088 mind that their overhead in this case is usually not as important, due
1089 to the small absolute number of watchers (that is, you need efficiency
1090 and speed most when you have lots of watchers, not when you only have a
1091 few of them).
1092
1093 EV is again fastest.
1094
1095 Perl again comes second. It is noticably faster than the C-based event
1096 loops Event and Glib, although the difference is too small to really
1097 matter.
1098
1099 POE also performs much better in this case, but is is still far behind
1100 the others.
1101
1102 Summary
1103 * C-based event loops perform very well with small number of watchers,
1104 as the management overhead dominates.
1105
1106FORK
1107 Most event libraries are not fork-safe. The ones who are usually are
1108 because they rely on inefficient but fork-safe "select" or "poll" calls.
1109 Only EV is fully fork-aware.
1110
1111 If you have to fork, you must either do so *before* creating your first
1112 watcher OR you must not use AnyEvent at all in the child.
1113
1114SECURITY CONSIDERATIONS
1115 AnyEvent can be forced to load any event model via
1116 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1117 to execute arbitrary code or directly gain access, it can easily be used
1118 to make the program hang or malfunction in subtle ways, as AnyEvent
1119 watchers will not be active when the program uses a different event
1120 model than specified in the variable.
1121
1122 You can make AnyEvent completely ignore this variable by deleting it
1123 before the first watcher gets created, e.g. with a "BEGIN" block:
1124
1125 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1126
1127 use AnyEvent;
1128
1129 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1130 be used to probe what backend is used and gain other information (which
1131 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
592 1132
593SEE ALSO 1133SEE ALSO
594 Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, 1134 Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
595 Glib::Event, Glib, Coro, Tk. 1135 Event::Lib, Qt, POE.
596 1136
597 Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, 1137 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
598 AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,
599 AnyEvent::Impl::Tk, AnyEvent::Impl::Perl. 1138 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1139 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
1140
1141 Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
600 1142
601 Nontrivial usage examples: Net::FCP, Net::XMPP2. 1143 Nontrivial usage examples: Net::FCP, Net::XMPP2.
602 1144
603AUTHOR 1145AUTHOR
604 Marc Lehmann <schmorp@schmorp.de> 1146 Marc Lehmann <schmorp@schmorp.de>

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