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Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC

1NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - provide framework for multiple event loops
3 3
4 Event, Coro, Glib, Tk, Perl - various supported event loops 4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5 loops
5 6
6SYNOPSIS 7SYNOPSIS
7 use AnyEvent; 8 use AnyEvent;
8 9
9 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
… …
12 13
13 my $w = AnyEvent->timer (after => $seconds, cb => sub { 14 my $w = AnyEvent->timer (after => $seconds, cb => sub {
14 ... 15 ...
15 }); 16 });
16 17
17 my $w = AnyEvent->condvar; # stores wether 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
18 $w->wait; # enters "main loop" till $condvar gets ->broadcast 20 $w->recv; # enters "main loop" till $condvar gets ->send
19 $w->broadcast; # wake up current and all future wait's 21
22WHY YOU SHOULD USE THIS MODULE (OR NOT)
23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24 nowadays. So what is different about AnyEvent?
25
26 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
27 policy* and AnyEvent is *small and efficient*.
28
29 First and foremost, *AnyEvent is not an event model* itself, it only
30 interfaces to whatever event model the main program happens to use in a
31 pragmatic way. For event models and certain classes of immortals alike,
32 the statement "there can only be one" is a bitter reality: In general,
33 only one event loop can be active at the same time in a process.
34 AnyEvent helps hiding the differences between those event loops.
35
36 The goal of AnyEvent is to offer module authors the ability to do event
37 programming (waiting for I/O or timer events) without subscribing to a
38 religion, a way of living, and most importantly: without forcing your
39 module users into the same thing by forcing them to use the same event
40 model you use.
41
42 For modules like POE or IO::Async (which is a total misnomer as it is
43 actually doing all I/O *synchronously*...), using them in your module is
44 like joining a cult: After you joined, you are dependent on them and you
45 cannot use anything else, as it is simply incompatible to everything
46 that isn't itself. What's worse, all the potential users of your module
47 are *also* forced to use the same event loop you use.
48
49 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50 fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51 with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your
52 module uses one of those, every user of your module has to use it, too.
53 But if your module uses AnyEvent, it works transparently with all event
54 models it supports (including stuff like POE and IO::Async, as long as
55 those use one of the supported event loops. It is trivial to add new
56 event loops to AnyEvent, too, so it is future-proof).
57
58 In addition to being free of having to use *the one and only true event
59 model*, AnyEvent also is free of bloat and policy: with POE or similar
60 modules, you get an enourmous amount of code and strict rules you have
61 to follow. AnyEvent, on the other hand, is lean and up to the point, by
62 only offering the functionality that is necessary, in as thin as a
63 wrapper as technically possible.
64
65 Of course, if you want lots of policy (this can arguably be somewhat
66 useful) and you want to force your users to use the one and only event
67 model, you should *not* use this module.
20 68
21DESCRIPTION 69DESCRIPTION
22 AnyEvent provides an identical interface to multiple event loops. This 70 AnyEvent provides an identical interface to multiple event loops. This
23 allows module authors to utilise an event loop without forcing module 71 allows module authors to utilise an event loop without forcing module
24 users to use the same event loop (as only a single event loop can 72 users to use the same event loop (as only a single event loop can
25 coexist peacefully at any one time). 73 coexist peacefully at any one time).
26 74
27 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
28 module. 76 module.
29 77
30 On the first call of any method, the module tries to detect the 78 During the first call of any watcher-creation method, the module tries
31 currently loaded event loop by probing wether any of the following 79 to detect the currently loaded event loop by probing whether one of the
32 modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is 80 following modules is already loaded: EV, Event, Glib,
81 AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
33 used. If none is found, the module tries to load these modules in the 82 used. If none are found, the module tries to load these modules
34 order given. The first one that could be successfully loaded will be 83 (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
35 used. If still none could be found, AnyEvent will fall back to a 84 always succeed) in the order given. The first one that can be
36 pure-perl event loop, which is also not very efficient. 85 successfully loaded will be used. If, after this, still none could be
86 found, AnyEvent will fall back to a pure-perl event loop, which is not
87 very efficient, but should work everywhere.
37 88
38 Because AnyEvent first checks for modules that are already loaded, 89 Because AnyEvent first checks for modules that are already loaded,
39 loading an Event model explicitly before first using AnyEvent will 90 loading an event model explicitly before first using AnyEvent will
40 likely make that model the default. For example: 91 likely make that model the default. For example:
41 92
42 use Tk; 93 use Tk;
43 use AnyEvent; 94 use AnyEvent;
44 95
45 # .. AnyEvent will likely default to Tk 96 # .. AnyEvent will likely default to Tk
97
98 The *likely* means that, if any module loads another event model and
99 starts using it, all bets are off. Maybe you should tell their authors
100 to use AnyEvent so their modules work together with others seamlessly...
46 101
47 The pure-perl implementation of AnyEvent is called 102 The pure-perl implementation of AnyEvent is called
48 "AnyEvent::Impl::Perl". Like other event modules you can load it 103 "AnyEvent::Impl::Perl". Like other event modules you can load it
49 explicitly. 104 explicitly.
50 105
… …
53 stores relevant data for each kind of event you are waiting for, such as 108 stores relevant data for each kind of event you are waiting for, such as
54 the callback to call, the filehandle to watch, etc. 109 the callback to call, the filehandle to watch, etc.
55 110
56 These watchers are normal Perl objects with normal Perl lifetime. After 111 These watchers are normal Perl objects with normal Perl lifetime. After
57 creating a watcher it will immediately "watch" for events and invoke the 112 creating a watcher it will immediately "watch" for events and invoke the
113 callback when the event occurs (of course, only when the event model is
114 in control).
115
58 callback. To disable the watcher you have to destroy it (e.g. by setting 116 To disable the watcher you have to destroy it (e.g. by setting the
59 the variable that stores it to "undef" or otherwise deleting all 117 variable you store it in to "undef" or otherwise deleting all references
60 references to it). 118 to it).
61 119
62 All watchers are created by calling a method on the "AnyEvent" class. 120 All watchers are created by calling a method on the "AnyEvent" class.
63 121
122 Many watchers either are used with "recursion" (repeating timers for
123 example), or need to refer to their watcher object in other ways.
124
125 An any way to achieve that is this pattern:
126
127 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128 # you can use $w here, for example to undef it
129 undef $w;
130 });
131
132 Note that "my $w; $w =" combination. This is necessary because in Perl,
133 my variables are only visible after the statement in which they are
134 declared.
135
64 IO WATCHERS 136 I/O WATCHERS
65 You can create I/O watcher by calling the "AnyEvent->io" method with the 137 You can create an I/O watcher by calling the "AnyEvent->io" method with
66 following mandatory arguments: 138 the following mandatory key-value pairs as arguments:
67 139
68 "fh" the Perl *filehandle* (not filedescriptor) to watch for events. 140 "fh" the Perl *file handle* (*not* file descriptor) to watch for events.
69 "poll" must be a string that is either "r" or "w", that creates a 141 "poll" must be a string that is either "r" or "w", which creates a
70 watcher waiting for "r"eadable or "w"ritable events. "cb" teh callback 142 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
71 to invoke everytime the filehandle becomes ready. 143 is the callback to invoke each time the file handle becomes ready.
72 144
73 Only one io watcher per "fh" and "poll" combination is allowed (i.e. on 145 Although the callback might get passed parameters, their value and
74 a socket you can have one r + one w, not any more (limitation comes from 146 presence is undefined and you cannot rely on them. Portable AnyEvent
75 Tk - if you are sure you are not using Tk this limitation is gone). 147 callbacks cannot use arguments passed to I/O watcher callbacks.
76 148
77 Filehandles will be kept alive, so as long as the watcher exists, the 149 The I/O watcher might use the underlying file descriptor or a copy of
78 filehandle exists, too. 150 it. You must not close a file handle as long as any watcher is active on
151 the underlying file descriptor.
152
153 Some event loops issue spurious readyness notifications, so you should
154 always use non-blocking calls when reading/writing from/to your file
155 handles.
79 156
80 Example: 157 Example:
81 158
82 # wait for readability of STDIN, then read a line and disable the watcher 159 # wait for readability of STDIN, then read a line and disable the watcher
83 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 160 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
… …
88 165
89 TIME WATCHERS 166 TIME WATCHERS
90 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
91 with the following mandatory arguments: 168 with the following mandatory arguments:
92 169
93 "after" after how many seconds (fractions are supported) should the 170 "after" specifies after how many seconds (fractional values are
94 timer activate. "cb" the callback to invoke. 171 supported) the callback should be invoked. "cb" is the callback to
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.
95 177
96 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
97 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
98 and Glib). 180 and Glib).
99 181
… …
103 my $w = AnyEvent->timer (after => 7.7, cb => sub { 185 my $w = AnyEvent->timer (after => 7.7, cb => sub {
104 warn "timeout\n"; 186 warn "timeout\n";
105 }); 187 });
106 188
107 # to cancel the timer: 189 # to cancel the timer:
108 undef $w 190 undef $w;
109 191
110 CONDITION WATCHERS
111 Condition watchers can be created by calling the "AnyEvent->condvar"
112 method without any arguments.
113
114 A condition watcher watches for a condition - precisely that the
115 "->broadcast" method has been called.
116
117 The watcher has only two methods:
118
119 $cv->wait
120 Wait (blocking if necessary) until the "->broadcast" method has been
121 called on c<$cv>, while servicing other watchers normally.
122
123 Not all event models support a blocking wait - some die in that
124 case, so if you are using this from a module, never require a
125 blocking wait, but let the caller decide wether the call will block
126 or not (for example, by coupling condition variables with some kind
127 of request results and supporting callbacks so the caller knows that
128 getting the result will not block, while still suppporting blockign
129 waits if the caller so desires).
130
131 You can only wait once on a condition - additional calls will return
132 immediately.
133
134 $cv->broadcast
135 Flag the condition as ready - a running "->wait" and all further
136 calls to "wait" will return after this method has been called. If
137 nobody is waiting the broadcast will be remembered..
138
139 Example: 192 Example 2:
140 193
141 # wait till the result is ready 194 # fire an event after 0.5 seconds, then roughly every second
142 my $result_ready = AnyEvent->condvar; 195 my $w;
143 196
144 # do something such as adding a timer 197 my $cb = sub {
145 # or socket watcher the calls $result_ready->broadcast 198 # cancel the old timer while creating a new one
146 # when the "result" is ready. 199 $w = AnyEvent->timer (after => 1, cb => $cb);
200 };
147 201
148 $result_ready->wait; 202 # start the "loop" by creating the first watcher
203 $w = AnyEvent->timer (after => 0.5, cb => $cb);
204
205 TIMING ISSUES
206 There are two ways to handle timers: based on real time (relative, "fire
207 in 10 seconds") and based on wallclock time (absolute, "fire at 12
208 o'clock").
209
210 While most event loops expect timers to specified in a relative way,
211 they use absolute time internally. This makes a difference when your
212 clock "jumps", for example, when ntp decides to set your clock backwards
213 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
214 supposed to fire "after" a second might actually take six years to
215 finally fire.
216
217 AnyEvent cannot compensate for this. The only event loop that is
218 conscious about these issues is EV, which offers both relative
219 (ev_timer, based on true relative time) and absolute (ev_periodic, based
220 on wallclock time) timers.
221
222 AnyEvent always prefers relative timers, if available, matching the
223 AnyEvent API.
149 224
150 SIGNAL WATCHERS 225 SIGNAL WATCHERS
151 You can listen for signals using a signal watcher, "signal" is the 226 You can watch for signals using a signal watcher, "signal" is the signal
152 signal *name* without any "SIG" prefix. Multiple signals events can be 227 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked
153 clumped together into one callback invocation, and callback invocation 228 whenever a signal occurs.
154 might or might not be asynchronous.
155 229
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
234 Multiple signal occurances can be clumped together into one callback
235 invocation, and callback invocation will be synchronous. synchronous
236 means that it might take a while until the signal gets handled by the
237 process, but it is guarenteed not to interrupt any other callbacks.
238
239 The main advantage of using these watchers is that you can share a
240 signal between multiple watchers.
241
156 These watchers might use %SIG, so programs overwriting those signals 242 This watcher might use %SIG, so programs overwriting those signals
157 directly will likely not work correctly. 243 directly will likely not work correctly.
158 244
159 Example: exit on SIGINT 245 Example: exit on SIGINT
160 246
161 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); 247 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
162 248
163 CHILD PROCESS WATCHERS 249 CHILD PROCESS WATCHERS
164 You can also listen for the status of a child process specified by the 250 You can also watch on a child process exit and catch its exit status.
165 "pid" argument (or any child if the pid argument is 0). The watcher will 251
252 The child process is specified by the "pid" argument (if set to 0, it
253 watches for any child process exit). The watcher will trigger as often
166 trigger as often as status change for the child are received. This works 254 as status change for the child are received. This works by installing a
167 by installing a signal handler for "SIGCHLD". The callback will be 255 signal handler for "SIGCHLD". The callback will be called with the pid
168 called with the pid 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.
169 258
170 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).
171 262
172 my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); 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).
173 267
174GLOBALS 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;
277
278 my $w = AnyEvent->child (
279 pid => $pid,
280 cb => sub {
281 my ($pid, $status) = @_;
282 warn "pid $pid exited with status $status";
283 $done->send;
284 },
285 );
286
287 # do something else, then wait for process exit
288 $done->recv;
289
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
301 Condition variables can be created by calling the "AnyEvent->condvar"
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.
305
306 After creation, the conditon variable is "false" until it becomes "true"
307 by calling the "send" method.
308
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
317 finished, for example, if you write a module that does asynchronous http
318 requests, then a condition variable would be the ideal candidate to
319 signal the availability of results. The user can either act when the
320 callback is called or can synchronously "->recv" for the results.
321
322 You can also use them to simulate traditional event loops - for example,
323 you can block your main program until an event occurs - for example, you
324 could "->recv" in your main program until the user clicks the Quit
325 button of your app, which would "->send" the "quit" event.
326
327 Note that condition variables recurse into the event loop - if you have
328 two pieces of code that call "->recv" in a round-robbin fashion, you
329 lose. Therefore, condition variables are good to export to your caller,
330 but you should avoid making a blocking wait yourself, at least in
331 callbacks, as this asks for trouble.
332
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.
338
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 $cv->recv
440 Wait (blocking if necessary) until the "->send" or "->croak" methods
441 have been called on c<$cv>, while servicing other watchers normally.
442
443 You can only wait once on a condition - additional calls are valid
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.
451
452 Not all event models support a blocking wait - some die in that case
453 (programs might want to do that to stay interactive), so *if you are
454 using this from a module, never require a blocking wait*, but let
455 the caller decide whether the call will block or not (for example,
456 by coupling condition variables with some kind of request results
457 and supporting callbacks so the caller knows that getting the result
458 will not block, while still suppporting blocking waits if the caller
459 so desires).
460
461 Another reason *never* to "->recv" in a module is that you cannot
462 sensibly have two "->recv"'s in parallel, as that would require
463 multiple interpreters or coroutines/threads, none of which
464 "AnyEvent" can supply.
465
466 The Coro module, however, *can* and *does* supply coroutines and, in
467 fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
468 versions and also integrates coroutines into AnyEvent, making
469 blocking "->recv" calls perfectly safe as long as they are done from
470 another coroutine (one that doesn't run the event loop).
471
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.
476
477 $bool = $cv->ready
478 Returns true when the condition is "true", i.e. whether "send" or
479 "croak" have been called.
480
481 $cb = $cv->cb ([new callback])
482 This is a mutator function that returns the callback set and
483 optionally replaces it before doing so.
484
485 The callback will be called when the condition becomes "true", i.e.
486 when "send" or "croak" are called. Calling "recv" inside the
487 callback or at any later time is guaranteed not to block.
488
489GLOBAL VARIABLES AND FUNCTIONS
175 $AnyEvent::MODEL 490 $AnyEvent::MODEL
176 Contains "undef" until the first watcher is being created. Then it 491 Contains "undef" until the first watcher is being created. Then it
177 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
178 the Perl class implementing the model. This class is usually one of 493 the Perl class implementing the model. This class is usually one of
179 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
180 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*).
181 496
182 The known classes so far are: 497 The known classes so far are:
183 498
184 EV::AnyEvent based on EV (an interface to libev, best choice) 499 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
185 AnyEvent::Impl::Coro based on Coro::Event, second best choice.
186 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.
187 AnyEvent::Impl::Glib based on Glib, second-best choice. 502 AnyEvent::Impl::Glib based on Glib, third-best choice.
188 AnyEvent::Impl::Tk based on Tk, very bad choice. 503 AnyEvent::Impl::Tk based on Tk, very bad choice.
189 AnyEvent::Impl::Perl pure-perl implementation, inefficient. 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.
190 517
191 AnyEvent::detect 518 AnyEvent::detect
192 Returns $AnyEvent::MODEL, forcing autodetection of the event model 519 Returns $AnyEvent::MODEL, forcing autodetection of the event model
193 if necessary. You should only call this function right before you 520 if necessary. You should only call this function right before you
194 would have created an AnyEvent watcher anyway, that is, very late at 521 would have created an AnyEvent watcher anyway, that is, as late as
195 runtime. 522 possible at runtime.
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.
196 542
197WHAT TO DO IN A MODULE 543WHAT TO DO IN A MODULE
198 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
199 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.
200 546
201 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
202 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,
203 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
204 module to load the event module first. 550 module to load the event module first.
205 551
552 Never call "->recv" on a condition variable unless you *know* that the
553 "->send" method has been called on it already. This is because it will
554 stall the whole program, and the whole point of using events is to stay
555 interactive.
556
557 It is fine, however, to call "->recv" when the user of your module
558 requests it (i.e. if you create a http request object ad have a method
559 called "results" that returns the results, it should call "->recv"
560 freely, as the user of your module knows what she is doing. always).
561
206WHAT TO DO IN THE MAIN PROGRAM 562WHAT TO DO IN THE MAIN PROGRAM
207 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
208 dictate which event model to use. 564 dictate which event model to use.
209 565
210 If it doesn't care, it can just "use AnyEvent" and use it itself, or not 566 If it doesn't care, it can just "use AnyEvent" and use it itself, or not
211 do anything special and let AnyEvent decide which implementation to 567 do anything special (it does not need to be event-based) and let
212 chose. 568 AnyEvent decide which implementation to chose if some module relies on
569 it.
213 570
214 If the main program relies on a specific event model (for example, in 571 If the main program relies on a specific event model. For example, in
215 Gtk2 programs you have to rely on either Glib or Glib::Event), you 572 Gtk2 programs you have to rely on the Glib module. You should load the
216 should load it before loading AnyEvent or any module that uses it, 573 event module before loading AnyEvent or any module that uses it:
217 generally, as early as possible. The reason is that modules might create 574 generally speaking, you should load it as early as possible. The reason
218 watchers when they are loaded, and AnyEvent will decide on the event 575 is that modules might create watchers when they are loaded, and AnyEvent
219 model to use as soon as it creates watchers, and it might chose the 576 will decide on the event model to use as soon as it creates watchers,
220 wrong one unless you load the correct one yourself. 577 and it might chose the wrong one unless you load the correct one
578 yourself.
221 579
222 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
223 loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is 581 loading the "AnyEvent::Impl::Perl" module, which gives you similar
224 generally better. 582 behaviour everywhere, but letting AnyEvent chose is generally better.
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.
225 637
226SUPPLYING YOUR OWN EVENT MODEL INTERFACE 638SUPPLYING YOUR OWN EVENT MODEL INTERFACE
639 This is an advanced topic that you do not normally need to use AnyEvent
640 in a module. This section is only of use to event loop authors who want
641 to provide AnyEvent compatibility.
642
227 If you need to support another event library which isn't directly 643 If you need to support another event library which isn't directly
228 supported by AnyEvent, you can supply your own interface to it by 644 supported by AnyEvent, you can supply your own interface to it by
229 pushing, before the first watcher gets created, the package name of the 645 pushing, before the first watcher gets created, the package name of the
230 event module and the package name of the interface to use onto 646 event module and the package name of the interface to use onto
231 @AnyEvent::REGISTRY. You can do that before and even without loading 647 @AnyEvent::REGISTRY. You can do that before and even without loading
232 AnyEvent. 648 AnyEvent, so it is reasonably cheap.
233 649
234 Example: 650 Example:
235 651
236 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; 652 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
237 653
238 This tells AnyEvent to (literally) use the "urxvt::anyevent::" 654 This tells AnyEvent to (literally) use the "urxvt::anyevent::"
239 package/class when it finds the "urxvt" package/module is loaded. When 655 package/class when it finds the "urxvt" package/module is already
656 loaded.
657
240 AnyEvent is loaded and asked to find a suitable event model, it will 658 When AnyEvent is loaded and asked to find a suitable event model, it
241 first check for the presence of urxvt. 659 will first check for the presence of urxvt by trying to "use" the
660 "urxvt::anyevent" module.
242 661
243 The class should provide implementations for all watcher types (see 662 The class should provide implementations for all watcher types. See
244 AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) 663 AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
245 and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to 664 so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
246 see the sources). 665 the sources.
247 666
667 If you don't provide "signal" and "child" watchers than AnyEvent will
668 provide suitable (hopefully) replacements.
669
248 The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the 670 The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
249 above line as-is. An interface isn't included in AnyEvent because it 671 terminal emulator uses the above line as-is. An interface isn't included
250 doesn't make sense outside the embedded interpreter inside 672 in AnyEvent because it doesn't make sense outside the embedded
251 *rxvt-unicode*, and it is updated and maintained as part of the 673 interpreter inside *rxvt-unicode*, and it is updated and maintained as
252 *rxvt-unicode* distribution. 674 part of the *rxvt-unicode* distribution.
253 675
254 *rxvt-unicode* also cheats a bit by not providing blocking access to 676 *rxvt-unicode* also cheats a bit by not providing blocking access to
255 condition variables: code blocking while waiting for a condition will 677 condition variables: code blocking while waiting for a condition will
256 "die". This still works with most modules/usages, and blocking calls 678 "die". This still works with most modules/usages, and blocking calls
257 must not be in an interactive application, so it makes sense. 679 must not be done in an interactive application, so it makes sense.
258 680
259ENVIRONMENT VARIABLES 681ENVIRONMENT VARIABLES
260 The following environment variables are used by this module: 682 The following environment variables are used by this module:
261 683
262 "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event 684 "PERL_ANYEVENT_VERBOSE"
263 model gets used. 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.
264 688
265EXAMPLE 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 ...
710
711EXAMPLE PROGRAM
266 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
267 timer to display a message once per second, and a condvar to exit the 713 timer to display a message once per second, and a condition variable to
268 program when the user enters quit: 714 quit the program when the user enters quit:
269 715
270 use AnyEvent; 716 use AnyEvent;
271 717
272 my $cv = AnyEvent->condvar; 718 my $cv = AnyEvent->condvar;
273 719
274 my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 720 my $io_watcher = AnyEvent->io (
721 fh => \*STDIN,
722 poll => 'r',
723 cb => sub {
275 warn "io event <$_[0]>\n"; # will always output <r> 724 warn "io event <$_[0]>\n"; # will always output <r>
276 chomp (my $input = <STDIN>); # read a line 725 chomp (my $input = <STDIN>); # read a line
277 warn "read: $input\n"; # output what has been read 726 warn "read: $input\n"; # output what has been read
278 $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i 727 $cv->send if $input =~ /^q/i; # quit program if /^q/i
728 },
279 }); 729 );
280 730
281 my $time_watcher; # can only be used once 731 my $time_watcher; # can only be used once
282 732
283 sub new_timer { 733 sub new_timer {
284 $timer = AnyEvent->timer (after => 1, cb => sub { 734 $timer = AnyEvent->timer (after => 1, cb => sub {
… …
287 }); 737 });
288 } 738 }
289 739
290 new_timer; # create first timer 740 new_timer; # create first timer
291 741
292 $cv->wait; # wait until user enters /^q/i 742 $cv->recv; # wait until user enters /^q/i
293 743
294REAL-WORLD EXAMPLE 744REAL-WORLD EXAMPLE
295 Consider the Net::FCP module. It features (among others) the following 745 Consider the Net::FCP module. It features (among others) the following
296 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:
297 747
… …
352 802
353 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; 803 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
354 804
355 if (end-of-file or data complete) { 805 if (end-of-file or data complete) {
356 $txn->{result} = $txn->{buf}; 806 $txn->{result} = $txn->{buf};
357 $txn->{finished}->broadcast; 807 $txn->{finished}->send;
358 $txb->{cb}->($txn) of $txn->{cb}; # also call callback 808 $txb->{cb}->($txn) of $txn->{cb}; # also call callback
359 } 809 }
360 810
361 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
362 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
363 the data: 813 the data:
364 814
365 $txn->{finished}->wait; 815 $txn->{finished}->recv;
366 return $txn->{result}; 816 return $txn->{result};
367 817
368 The actual code goes further and collects all errors ("die"s, 818 The actual code goes further and collects all errors ("die"s,
369 exceptions) that occured during request processing. The "result" method 819 exceptions) that occured during request processing. The "result" method
370 detects wether an exception as thrown (it is stored inside the $txn 820 detects whether an exception as thrown (it is stored inside the $txn
371 object) and just throws the exception, which means connection errors and 821 object) and just throws the exception, which means connection errors and
372 other problems get reported tot he code that tries to use the result, 822 other problems get reported tot he code that tries to use the result,
373 not in a random callback. 823 not in a random callback.
374 824
375 All of this enables the following usage styles: 825 All of this enables the following usage styles:
376 826
377 1. Blocking: 827 1. Blocking:
378 828
379 my $data = $fcp->client_get ($url); 829 my $data = $fcp->client_get ($url);
380 830
381 2. Blocking, but parallelizing: 831 2. Blocking, but running in parallel:
382 832
383 my @datas = map $_->result, 833 my @datas = map $_->result,
384 map $fcp->txn_client_get ($_), 834 map $fcp->txn_client_get ($_),
385 @urls; 835 @urls;
386 836
387 Both blocking examples work without the module user having to know 837 Both blocking examples work without the module user having to know
388 anything about events. 838 anything about events.
389 839
390 3a. Event-based in a main program, using any support Event module: 840 3a. Event-based in a main program, using any supported event module:
391 841
392 use Event; 842 use EV;
393 843
394 $fcp->txn_client_get ($url)->cb (sub { 844 $fcp->txn_client_get ($url)->cb (sub {
395 my $txn = shift; 845 my $txn = shift;
396 my $data = $txn->result; 846 my $data = $txn->result;
397 ... 847 ...
398 }); 848 });
399 849
400 Event::loop; 850 EV::loop;
401 851
402 3b. The module user could use AnyEvent, too: 852 3b. The module user could use AnyEvent, too:
403 853
404 use AnyEvent; 854 use AnyEvent;
405 855
406 my $quit = AnyEvent->condvar; 856 my $quit = AnyEvent->condvar;
407 857
408 $fcp->txn_client_get ($url)->cb (sub { 858 $fcp->txn_client_get ($url)->cb (sub {
409 ... 859 ...
410 $quit->broadcast; 860 $quit->send;
411 }); 861 });
412 862
413 $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).
414 1132
415SEE ALSO 1133SEE ALSO
416 Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. 1134 Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1135 Event::Lib, Qt, POE.
417 1136
418 Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, 1137 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
419 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. 1138 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1139 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
420 1140
1141 Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1142
421 Nontrivial usage example: Net::FCP. 1143 Nontrivial usage examples: Net::FCP, Net::XMPP2.
422 1144
1145AUTHOR
1146 Marc Lehmann <schmorp@schmorp.de>
1147 http://home.schmorp.de/
423 1148

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