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Revision 1.90 by root, Fri Apr 25 14:24:29 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3AnyEvent - provide framework for multiple event loops 3AnyEvent - provide framework for multiple event loops
4 4
5EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported event loops 5EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6 6
7=head1 SYNOPSIS 7=head1 SYNOPSIS
8 8
9 use AnyEvent; 9 use AnyEvent;
10 10
14 14
15 my $w = AnyEvent->timer (after => $seconds, cb => sub { 15 my $w = AnyEvent->timer (after => $seconds, cb => sub {
16 ... 16 ...
17 }); 17 });
18 18
19 my $w = AnyEvent->condvar; # stores wether a condition was flagged 19 my $w = AnyEvent->condvar; # stores whether a condition was flagged
20 $w->wait; # enters "main loop" till $condvar gets ->broadcast 20 $w->wait; # enters "main loop" till $condvar gets ->broadcast
21 $w->broadcast; # wake up current and all future wait's 21 $w->broadcast; # wake up current and all future wait's
22 22
23=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT) 23=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24 24
29policy> and AnyEvent is I<small and efficient>. 29policy> and AnyEvent is I<small and efficient>.
30 30
31First and foremost, I<AnyEvent is not an event model> itself, it only 31First and foremost, I<AnyEvent is not an event model> itself, it only
32interfaces to whatever event model the main program happens to use in a 32interfaces to whatever event model the main program happens to use in a
33pragmatic way. For event models and certain classes of immortals alike, 33pragmatic way. For event models and certain classes of immortals alike,
34the statement "there can only be one" is a bitter reality, and AnyEvent 34the statement "there can only be one" is a bitter reality: In general,
35helps hiding the differences. 35only one event loop can be active at the same time in a process. AnyEvent
36helps hiding the differences between those event loops.
36 37
37The goal of AnyEvent is to offer module authors the ability to do event 38The goal of AnyEvent is to offer module authors the ability to do event
38programming (waiting for I/O or timer events) without subscribing to a 39programming (waiting for I/O or timer events) without subscribing to a
39religion, a way of living, and most importantly: without forcing your 40religion, a way of living, and most importantly: without forcing your
40module users into the same thing by forcing them to use the same event 41module users into the same thing by forcing them to use the same event
41model you use. 42model you use.
42 43
43For modules like POE or IO::Async (which is actually doing all I/O 44For modules like POE or IO::Async (which is a total misnomer as it is
44I<synchronously>...), using them in your module is like joining a 45actually doing all I/O I<synchronously>...), using them in your module is
45cult: After you joined, you are dependent on them and you cannot use 46like joining a cult: After you joined, you are dependent on them and you
46anything else, as it is simply incompatible to everything that isn't 47cannot use anything else, as it is simply incompatible to everything that
47itself. 48isn't itself. What's worse, all the potential users of your module are
49I<also> forced to use the same event loop you use.
48 50
49AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk 51AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50works fine etc. etc. but none of these work together with the rest: POE 52fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51+ IO::Async? no go. Tk + Event? no go. If your module uses one of 53with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
52those, every user of your module has to use it, too. If your module 54your module uses one of those, every user of your module has to use it,
53uses AnyEvent, it works transparently with all event models it supports 55too. But if your module uses AnyEvent, it works transparently with all
54(including stuff like POE and IO::Async). 56event models it supports (including stuff like POE and IO::Async, as long
57as those use one of the supported event loops. It is trivial to add new
58event loops to AnyEvent, too, so it is future-proof).
55 59
56In addition of being free of having to use I<the one and only true event 60In addition to being free of having to use I<the one and only true event
57model>, AnyEvent also is free of bloat and policy: with POE or similar 61model>, AnyEvent also is free of bloat and policy: with POE or similar
58modules, you get an enourmous amount of code and strict rules you have 62modules, you get an enourmous amount of code and strict rules you have to
59to follow. AnyEvent, on the other hand, is lean and to the point by only 63follow. AnyEvent, on the other hand, is lean and up to the point, by only
60offering the functionality that is useful, in as thin as a wrapper as 64offering the functionality that is necessary, in as thin as a wrapper as
61technically possible. 65technically possible.
62 66
63Of course, if you want lots of policy (this can arguably be somewhat 67Of course, if you want lots of policy (this can arguably be somewhat
64useful) and you want to force your users to use the one and only event 68useful) and you want to force your users to use the one and only event
65model, you should I<not> use this module. 69model, you should I<not> use this module.
70L<AnyEvent> provides an identical interface to multiple event loops. This 74L<AnyEvent> provides an identical interface to multiple event loops. This
71allows module authors to utilise an event loop without forcing module 75allows module authors to utilise an event loop without forcing module
72users to use the same event loop (as only a single event loop can coexist 76users to use the same event loop (as only a single event loop can coexist
73peacefully at any one time). 77peacefully at any one time).
74 78
75The interface itself is vaguely similar but not identical to the Event 79The interface itself is vaguely similar, but not identical to the L<Event>
76module. 80module.
77 81
78On the first call of any method, the module tries to detect the currently 82During the first call of any watcher-creation method, the module tries
79loaded event loop by probing wether any of the following modules is 83to detect the currently loaded event loop by probing whether one of the
80loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, L<Event>, L<Glib>, L<Tk>. The 84following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
85L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
81first one found is used. If none are found, the module tries to load these 86L<POE>. The first one found is used. If none are found, the module tries
82modules in the order given. The first one that could be successfully 87to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
83loaded will be used. If still none could be found, AnyEvent will fall back 88adaptor should always succeed) in the order given. The first one that can
84to a pure-perl event loop, which is also not very efficient. 89be successfully loaded will be used. If, after this, still none could be
90found, AnyEvent will fall back to a pure-perl event loop, which is not
91very efficient, but should work everywhere.
85 92
86Because AnyEvent first checks for modules that are already loaded, loading 93Because AnyEvent first checks for modules that are already loaded, loading
87an Event model explicitly before first using AnyEvent will likely make 94an event model explicitly before first using AnyEvent will likely make
88that model the default. For example: 95that model the default. For example:
89 96
90 use Tk; 97 use Tk;
91 use AnyEvent; 98 use AnyEvent;
92 99
93 # .. AnyEvent will likely default to Tk 100 # .. AnyEvent will likely default to Tk
101
102The I<likely> means that, if any module loads another event model and
103starts using it, all bets are off. Maybe you should tell their authors to
104use AnyEvent so their modules work together with others seamlessly...
94 105
95The pure-perl implementation of AnyEvent is called 106The pure-perl implementation of AnyEvent is called
96C<AnyEvent::Impl::Perl>. Like other event modules you can load it 107C<AnyEvent::Impl::Perl>. Like other event modules you can load it
97explicitly. 108explicitly.
98 109
101AnyEvent has the central concept of a I<watcher>, which is an object that 112AnyEvent has the central concept of a I<watcher>, which is an object that
102stores relevant data for each kind of event you are waiting for, such as 113stores relevant data for each kind of event you are waiting for, such as
103the callback to call, the filehandle to watch, etc. 114the callback to call, the filehandle to watch, etc.
104 115
105These watchers are normal Perl objects with normal Perl lifetime. After 116These watchers are normal Perl objects with normal Perl lifetime. After
106creating a watcher it will immediately "watch" for events and invoke 117creating a watcher it will immediately "watch" for events and invoke the
118callback when the event occurs (of course, only when the event model
119is in control).
120
107the callback. To disable the watcher you have to destroy it (e.g. by 121To disable the watcher you have to destroy it (e.g. by setting the
108setting the variable that stores it to C<undef> or otherwise deleting all 122variable you store it in to C<undef> or otherwise deleting all references
109references to it). 123to it).
110 124
111All watchers are created by calling a method on the C<AnyEvent> class. 125All watchers are created by calling a method on the C<AnyEvent> class.
112 126
127Many watchers either are used with "recursion" (repeating timers for
128example), or need to refer to their watcher object in other ways.
129
130An any way to achieve that is this pattern:
131
132 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
133 # you can use $w here, for example to undef it
134 undef $w;
135 });
136
137Note that C<my $w; $w => combination. This is necessary because in Perl,
138my variables are only visible after the statement in which they are
139declared.
140
113=head2 IO WATCHERS 141=head2 I/O WATCHERS
114 142
115You can create I/O watcher by calling the C<< AnyEvent->io >> method with 143You can create an I/O watcher by calling the C<< AnyEvent->io >> method
116the following mandatory arguments: 144with the following mandatory key-value pairs as arguments:
117 145
118C<fh> the Perl I<filehandle> (not filedescriptor) to watch for 146C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
119events. C<poll> must be a string that is either C<r> or C<w>, that creates 147for events. C<poll> must be a string that is either C<r> or C<w>,
120a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback 148which creates a watcher waiting for "r"eadable or "w"ritable events,
121to invoke everytime the filehandle becomes ready. 149respectively. C<cb> is the callback to invoke each time the file handle
150becomes ready.
122 151
123Filehandles will be kept alive, so as long as the watcher exists, the 152Although the callback might get passed parameters, their value and
124filehandle exists, too. 153presence is undefined and you cannot rely on them. Portable AnyEvent
154callbacks cannot use arguments passed to I/O watcher callbacks.
155
156The I/O watcher might use the underlying file descriptor or a copy of it.
157You must not close a file handle as long as any watcher is active on the
158underlying file descriptor.
159
160Some event loops issue spurious readyness notifications, so you should
161always use non-blocking calls when reading/writing from/to your file
162handles.
125 163
126Example: 164Example:
127 165
128 # wait for readability of STDIN, then read a line and disable the watcher 166 # wait for readability of STDIN, then read a line and disable the watcher
129 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 167 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
135=head2 TIME WATCHERS 173=head2 TIME WATCHERS
136 174
137You can create a time watcher by calling the C<< AnyEvent->timer >> 175You can create a time watcher by calling the C<< AnyEvent->timer >>
138method with the following mandatory arguments: 176method with the following mandatory arguments:
139 177
140C<after> after how many seconds (fractions are supported) should the timer 178C<after> specifies after how many seconds (fractional values are
141activate. C<cb> the callback to invoke. 179supported) the callback should be invoked. C<cb> is the callback to invoke
180in that case.
181
182Although the callback might get passed parameters, their value and
183presence is undefined and you cannot rely on them. Portable AnyEvent
184callbacks cannot use arguments passed to time watcher callbacks.
142 185
143The timer callback will be invoked at most once: if you want a repeating 186The timer callback will be invoked at most once: if you want a repeating
144timer you have to create a new watcher (this is a limitation by both Tk 187timer you have to create a new watcher (this is a limitation by both Tk
145and Glib). 188and Glib).
146 189
152 }); 195 });
153 196
154 # to cancel the timer: 197 # to cancel the timer:
155 undef $w; 198 undef $w;
156 199
200Example 2:
201
202 # fire an event after 0.5 seconds, then roughly every second
203 my $w;
204
205 my $cb = sub {
206 # cancel the old timer while creating a new one
207 $w = AnyEvent->timer (after => 1, cb => $cb);
208 };
209
210 # start the "loop" by creating the first watcher
211 $w = AnyEvent->timer (after => 0.5, cb => $cb);
212
213=head3 TIMING ISSUES
214
215There are two ways to handle timers: based on real time (relative, "fire
216in 10 seconds") and based on wallclock time (absolute, "fire at 12
217o'clock").
218
219While most event loops expect timers to specified in a relative way, they
220use absolute time internally. This makes a difference when your clock
221"jumps", for example, when ntp decides to set your clock backwards from
222the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
223fire "after" a second might actually take six years to finally fire.
224
225AnyEvent cannot compensate for this. The only event loop that is conscious
226about these issues is L<EV>, which offers both relative (ev_timer, based
227on true relative time) and absolute (ev_periodic, based on wallclock time)
228timers.
229
230AnyEvent always prefers relative timers, if available, matching the
231AnyEvent API.
232
233=head2 SIGNAL WATCHERS
234
235You can watch for signals using a signal watcher, C<signal> is the signal
236I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
237be invoked whenever a signal occurs.
238
239Although the callback might get passed parameters, their value and
240presence is undefined and you cannot rely on them. Portable AnyEvent
241callbacks cannot use arguments passed to signal watcher callbacks.
242
243Multiple signal occurances can be clumped together into one callback
244invocation, and callback invocation will be synchronous. synchronous means
245that it might take a while until the signal gets handled by the process,
246but it is guarenteed not to interrupt any other callbacks.
247
248The main advantage of using these watchers is that you can share a signal
249between multiple watchers.
250
251This watcher might use C<%SIG>, so programs overwriting those signals
252directly will likely not work correctly.
253
254Example: exit on SIGINT
255
256 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
257
258=head2 CHILD PROCESS WATCHERS
259
260You can also watch on a child process exit and catch its exit status.
261
262The child process is specified by the C<pid> argument (if set to C<0>, it
263watches for any child process exit). The watcher will trigger as often
264as status change for the child are received. This works by installing a
265signal handler for C<SIGCHLD>. The callback will be called with the pid
266and exit status (as returned by waitpid), so unlike other watcher types,
267you I<can> rely on child watcher callback arguments.
268
269There is a slight catch to child watchers, however: you usually start them
270I<after> the child process was created, and this means the process could
271have exited already (and no SIGCHLD will be sent anymore).
272
273Not all event models handle this correctly (POE doesn't), but even for
274event models that I<do> handle this correctly, they usually need to be
275loaded before the process exits (i.e. before you fork in the first place).
276
277This means you cannot create a child watcher as the very first thing in an
278AnyEvent program, you I<have> to create at least one watcher before you
279C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
280
281Example: fork a process and wait for it
282
283 my $done = AnyEvent->condvar;
284
285 AnyEvent::detect; # force event module to be initialised
286
287 my $pid = fork or exit 5;
288
289 my $w = AnyEvent->child (
290 pid => $pid,
291 cb => sub {
292 my ($pid, $status) = @_;
293 warn "pid $pid exited with status $status";
294 $done->broadcast;
295 },
296 );
297
298 # do something else, then wait for process exit
299 $done->wait;
300
157=head2 CONDITION WATCHERS 301=head2 CONDITION VARIABLES
158 302
159Condition watchers can be created by calling the C<< AnyEvent->condvar >> 303Condition variables can be created by calling the C<< AnyEvent->condvar >>
160method without any arguments. 304method without any arguments.
161 305
162A condition watcher watches for a condition - precisely that the C<< 306A condition variable waits for a condition - precisely that the C<<
163->broadcast >> method has been called. 307->broadcast >> method has been called.
164 308
309They are very useful to signal that a condition has been fulfilled, for
310example, if you write a module that does asynchronous http requests,
311then a condition variable would be the ideal candidate to signal the
312availability of results.
313
314You can also use condition variables to block your main program until
315an event occurs - for example, you could C<< ->wait >> in your main
316program until the user clicks the Quit button in your app, which would C<<
317->broadcast >> the "quit" event.
318
165Note that condition watchers recurse into the event loop - if you have 319Note that condition variables recurse into the event loop - if you have
166two watchers that call C<< ->wait >> in a round-robbin fashion, you 320two pirces of code that call C<< ->wait >> in a round-robbin fashion, you
167lose. Therefore, condition watchers are good to export to your caller, but 321lose. Therefore, condition variables are good to export to your caller, but
168you should avoid making a blocking wait, at least in callbacks, as this 322you should avoid making a blocking wait yourself, at least in callbacks,
169usually asks for trouble. 323as this asks for trouble.
170 324
171The watcher has only two methods: 325This object has two methods:
172 326
173=over 4 327=over 4
174 328
175=item $cv->wait 329=item $cv->wait
176 330
179 333
180You can only wait once on a condition - additional calls will return 334You can only wait once on a condition - additional calls will return
181immediately. 335immediately.
182 336
183Not all event models support a blocking wait - some die in that case 337Not all event models support a blocking wait - some die in that case
184(programs might want to do that so they stay interactive), so I<if you 338(programs might want to do that to stay interactive), so I<if you are
185are using this from a module, never require a blocking wait>, but let the 339using this from a module, never require a blocking wait>, but let the
186caller decide wether the call will block or not (for example, by coupling 340caller decide whether the call will block or not (for example, by coupling
187condition variables with some kind of request results and supporting 341condition variables with some kind of request results and supporting
188callbacks so the caller knows that getting the result will not block, 342callbacks so the caller knows that getting the result will not block,
189while still suppporting blocking waits if the caller so desires). 343while still suppporting blocking waits if the caller so desires).
190 344
191Another reason I<never> to C<< ->wait >> in a module is that you cannot 345Another reason I<never> to C<< ->wait >> in a module is that you cannot
192sensibly have two C<< ->wait >>'s in parallel, as that would require 346sensibly have two C<< ->wait >>'s in parallel, as that would require
193multiple interpreters or coroutines/threads, none of which C<AnyEvent> 347multiple interpreters or coroutines/threads, none of which C<AnyEvent>
194can supply (the coroutine-aware backends C<Coro::EV> and C<Coro::Event> 348can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
195explicitly support concurrent C<< ->wait >>'s from different coroutines, 349L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
196however). 350from different coroutines, however).
197 351
198=item $cv->broadcast 352=item $cv->broadcast
199 353
200Flag the condition as ready - a running C<< ->wait >> and all further 354Flag the condition as ready - a running C<< ->wait >> and all further
201calls to C<wait> will return after this method has been called. If nobody 355calls to C<wait> will (eventually) return after this method has been
202is waiting the broadcast will be remembered.. 356called. If nobody is waiting the broadcast will be remembered..
357
358=back
203 359
204Example: 360Example:
205 361
206 # wait till the result is ready 362 # wait till the result is ready
207 my $result_ready = AnyEvent->condvar; 363 my $result_ready = AnyEvent->condvar;
208 364
209 # do something such as adding a timer 365 # do something such as adding a timer
210 # or socket watcher the calls $result_ready->broadcast 366 # or socket watcher the calls $result_ready->broadcast
211 # when the "result" is ready. 367 # when the "result" is ready.
368 # in this case, we simply use a timer:
369 my $w = AnyEvent->timer (
370 after => 1,
371 cb => sub { $result_ready->broadcast },
372 );
212 373
374 # this "blocks" (while handling events) till the watcher
375 # calls broadcast
213 $result_ready->wait; 376 $result_ready->wait;
214 377
215=back 378=head1 GLOBAL VARIABLES AND FUNCTIONS
216
217=head2 SIGNAL WATCHERS
218
219You can listen for signals using a signal watcher, C<signal> is the signal
220I<name> without any C<SIG> prefix. Multiple signals events can be clumped
221together into one callback invocation, and callback invocation might or
222might not be asynchronous.
223
224These watchers might use C<%SIG>, so programs overwriting those signals
225directly will likely not work correctly.
226
227Example: exit on SIGINT
228
229 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
230
231=head2 CHILD PROCESS WATCHERS
232
233You can also listen for the status of a child process specified by the
234C<pid> argument (or any child if the pid argument is 0). The watcher will
235trigger as often as status change for the child are received. This works
236by installing a signal handler for C<SIGCHLD>. The callback will be called with
237the pid and exit status (as returned by waitpid).
238
239Example: wait for pid 1333
240
241 my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
242
243=head1 GLOBALS
244 379
245=over 4 380=over 4
246 381
247=item $AnyEvent::MODEL 382=item $AnyEvent::MODEL
248 383
254 389
255The known classes so far are: 390The known classes so far are:
256 391
257 AnyEvent::Impl::CoroEV based on Coro::EV, best choice. 392 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
258 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. 393 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
259 AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). 394 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
260 AnyEvent::Impl::Event based on Event, also second best choice :) 395 AnyEvent::Impl::Event based on Event, second best choice.
261 AnyEvent::Impl::Glib based on Glib, third-best choice. 396 AnyEvent::Impl::Glib based on Glib, third-best choice.
397 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
262 AnyEvent::Impl::Tk based on Tk, very bad choice. 398 AnyEvent::Impl::Tk based on Tk, very bad choice.
263 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. 399 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
400 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
401 AnyEvent::Impl::POE based on POE, not generic enough for full support.
402
403There is no support for WxWidgets, as WxWidgets has no support for
404watching file handles. However, you can use WxWidgets through the
405POE Adaptor, as POE has a Wx backend that simply polls 20 times per
406second, which was considered to be too horrible to even consider for
407AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
408it's adaptor.
409
410AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
411autodetecting them.
264 412
265=item AnyEvent::detect 413=item AnyEvent::detect
266 414
267Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if 415Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
268necessary. You should only call this function right before you would have 416if necessary. You should only call this function right before you would
269created an AnyEvent watcher anyway, that is, very late at runtime. 417have created an AnyEvent watcher anyway, that is, as late as possible at
418runtime.
270 419
271=back 420=back
272 421
273=head1 WHAT TO DO IN A MODULE 422=head1 WHAT TO DO IN A MODULE
274 423
275As a module author, you should "use AnyEvent" and call AnyEvent methods 424As a module author, you should C<use AnyEvent> and call AnyEvent methods
276freely, but you should not load a specific event module or rely on it. 425freely, but you should not load a specific event module or rely on it.
277 426
278Be careful when you create watchers in the module body - Anyevent will 427Be careful when you create watchers in the module body - AnyEvent will
279decide which event module to use as soon as the first method is called, so 428decide which event module to use as soon as the first method is called, so
280by calling AnyEvent in your module body you force the user of your module 429by calling AnyEvent in your module body you force the user of your module
281to load the event module first. 430to load the event module first.
282 431
432Never call C<< ->wait >> on a condition variable unless you I<know> that
433the C<< ->broadcast >> method has been called on it already. This is
434because it will stall the whole program, and the whole point of using
435events is to stay interactive.
436
437It is fine, however, to call C<< ->wait >> when the user of your module
438requests it (i.e. if you create a http request object ad have a method
439called C<results> that returns the results, it should call C<< ->wait >>
440freely, as the user of your module knows what she is doing. always).
441
283=head1 WHAT TO DO IN THE MAIN PROGRAM 442=head1 WHAT TO DO IN THE MAIN PROGRAM
284 443
285There will always be a single main program - the only place that should 444There will always be a single main program - the only place that should
286dictate which event model to use. 445dictate which event model to use.
287 446
288If it doesn't care, it can just "use AnyEvent" and use it itself, or not 447If it doesn't care, it can just "use AnyEvent" and use it itself, or not
289do anything special and let AnyEvent decide which implementation to chose. 448do anything special (it does not need to be event-based) and let AnyEvent
449decide which implementation to chose if some module relies on it.
290 450
291If the main program relies on a specific event model (for example, in Gtk2 451If the main program relies on a specific event model. For example, in
292programs you have to rely on either Glib or Glib::Event), you should load 452Gtk2 programs you have to rely on the Glib module. You should load the
293it before loading AnyEvent or any module that uses it, generally, as early 453event module before loading AnyEvent or any module that uses it: generally
294as possible. The reason is that modules might create watchers when they 454speaking, you should load it as early as possible. The reason is that
295are loaded, and AnyEvent will decide on the event model to use as soon as 455modules might create watchers when they are loaded, and AnyEvent will
296it creates watchers, and it might chose the wrong one unless you load the 456decide on the event model to use as soon as it creates watchers, and it
297correct one yourself. 457might chose the wrong one unless you load the correct one yourself.
298 458
299You can chose to use a rather inefficient pure-perl implementation by 459You can chose to use a rather inefficient pure-perl implementation by
300loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is 460loading the C<AnyEvent::Impl::Perl> module, which gives you similar
301generally better. 461behaviour everywhere, but letting AnyEvent chose is generally better.
302 462
303=cut 463=cut
304 464
305package AnyEvent; 465package AnyEvent;
306 466
307no warnings; 467no warnings;
308use strict; 468use strict;
309 469
310use Carp; 470use Carp;
311 471
312our $VERSION = '3.0'; 472our $VERSION = '3.3';
313our $MODEL; 473our $MODEL;
314 474
315our $AUTOLOAD; 475our $AUTOLOAD;
316our @ISA; 476our @ISA;
317 477
324 [Coro::Event:: => AnyEvent::Impl::CoroEvent::], 484 [Coro::Event:: => AnyEvent::Impl::CoroEvent::],
325 [EV:: => AnyEvent::Impl::EV::], 485 [EV:: => AnyEvent::Impl::EV::],
326 [Event:: => AnyEvent::Impl::Event::], 486 [Event:: => AnyEvent::Impl::Event::],
327 [Glib:: => AnyEvent::Impl::Glib::], 487 [Glib:: => AnyEvent::Impl::Glib::],
328 [Tk:: => AnyEvent::Impl::Tk::], 488 [Tk:: => AnyEvent::Impl::Tk::],
489 [Wx:: => AnyEvent::Impl::POE::],
490 [Prima:: => AnyEvent::Impl::POE::],
329 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], 491 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
492 # everything below here will not be autoprobed as the pureperl backend should work everywhere
493 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
494 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program
495 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
330); 496);
331 497
332our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); 498our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
333 499
334sub detect() { 500sub detect() {
335 unless ($MODEL) { 501 unless ($MODEL) {
336 no strict 'refs'; 502 no strict 'refs';
337 503
504 if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
505 my $model = "AnyEvent::Impl::$1";
506 if (eval "require $model") {
507 $MODEL = $model;
508 warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
509 } else {
510 warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
511 }
512 }
513
338 # check for already loaded models 514 # check for already loaded models
515 unless ($MODEL) {
339 for (@REGISTRY, @models) { 516 for (@REGISTRY, @models) {
340 my ($package, $model) = @$_; 517 my ($package, $model) = @$_;
341 if (${"$package\::VERSION"} > 0) { 518 if (${"$package\::VERSION"} > 0) {
342 if (eval "require $model") { 519 if (eval "require $model") {
343 $MODEL = $model; 520 $MODEL = $model;
344 warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1; 521 warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
345 last; 522 last;
523 }
346 } 524 }
347 } 525 }
348 }
349 526
350 unless ($MODEL) { 527 unless ($MODEL) {
351 # try to load a model 528 # try to load a model
352 529
353 for (@REGISTRY, @models) { 530 for (@REGISTRY, @models) {
354 my ($package, $model) = @$_; 531 my ($package, $model) = @$_;
355 if (eval "require $package" 532 if (eval "require $package"
356 and ${"$package\::VERSION"} > 0 533 and ${"$package\::VERSION"} > 0
357 and eval "require $model") { 534 and eval "require $model") {
358 $MODEL = $model; 535 $MODEL = $model;
359 warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1; 536 warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
360 last; 537 last;
538 }
361 } 539 }
540
541 $MODEL
542 or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";
362 } 543 }
363
364 $MODEL
365 or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
366 } 544 }
367 545
368 unshift @ISA, $MODEL; 546 unshift @ISA, $MODEL;
369 push @{"$MODEL\::ISA"}, "AnyEvent::Base"; 547 push @{"$MODEL\::ISA"}, "AnyEvent::Base";
370 } 548 }
481 undef $CHLD_W unless keys %PID_CB; 659 undef $CHLD_W unless keys %PID_CB;
482} 660}
483 661
484=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE 662=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
485 663
664This is an advanced topic that you do not normally need to use AnyEvent in
665a module. This section is only of use to event loop authors who want to
666provide AnyEvent compatibility.
667
486If you need to support another event library which isn't directly 668If you need to support another event library which isn't directly
487supported by AnyEvent, you can supply your own interface to it by 669supported by AnyEvent, you can supply your own interface to it by
488pushing, before the first watcher gets created, the package name of 670pushing, before the first watcher gets created, the package name of
489the event module and the package name of the interface to use onto 671the event module and the package name of the interface to use onto
490C<@AnyEvent::REGISTRY>. You can do that before and even without loading 672C<@AnyEvent::REGISTRY>. You can do that before and even without loading
491AnyEvent. 673AnyEvent, so it is reasonably cheap.
492 674
493Example: 675Example:
494 676
495 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; 677 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
496 678
497This tells AnyEvent to (literally) use the C<urxvt::anyevent::> 679This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
498package/class when it finds the C<urxvt> package/module is loaded. When 680package/class when it finds the C<urxvt> package/module is already loaded.
681
499AnyEvent is loaded and asked to find a suitable event model, it will 682When AnyEvent is loaded and asked to find a suitable event model, it
500first check for the presence of urxvt. 683will first check for the presence of urxvt by trying to C<use> the
684C<urxvt::anyevent> module.
501 685
502The class should provide implementations for all watcher types (see 686The class should provide implementations for all watcher types. See
503L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib> 687L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
504(Source code) and so on for actual examples, use C<perldoc -m 688and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
505AnyEvent::Impl::Glib> to see the sources). 689see the sources.
506 690
691If you don't provide C<signal> and C<child> watchers than AnyEvent will
692provide suitable (hopefully) replacements.
693
507The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt) 694The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
508uses the above line as-is. An interface isn't included in AnyEvent 695terminal emulator uses the above line as-is. An interface isn't included
509because it doesn't make sense outside the embedded interpreter inside 696in AnyEvent because it doesn't make sense outside the embedded interpreter
510I<rxvt-unicode>, and it is updated and maintained as part of the 697inside I<rxvt-unicode>, and it is updated and maintained as part of the
511I<rxvt-unicode> distribution. 698I<rxvt-unicode> distribution.
512 699
513I<rxvt-unicode> also cheats a bit by not providing blocking access to 700I<rxvt-unicode> also cheats a bit by not providing blocking access to
514condition variables: code blocking while waiting for a condition will 701condition variables: code blocking while waiting for a condition will
515C<die>. This still works with most modules/usages, and blocking calls must 702C<die>. This still works with most modules/usages, and blocking calls must
516not be in an interactive application, so it makes sense. 703not be done in an interactive application, so it makes sense.
517 704
518=head1 ENVIRONMENT VARIABLES 705=head1 ENVIRONMENT VARIABLES
519 706
520The following environment variables are used by this module: 707The following environment variables are used by this module:
521 708
522C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event 709=over 4
523model gets used.
524 710
711=item C<PERL_ANYEVENT_VERBOSE>
712
713By default, AnyEvent will be completely silent except in fatal
714conditions. You can set this environment variable to make AnyEvent more
715talkative.
716
717When set to C<1> or higher, causes AnyEvent to warn about unexpected
718conditions, such as not being able to load the event model specified by
719C<PERL_ANYEVENT_MODEL>.
720
721When set to C<2> or higher, cause AnyEvent to report to STDERR which event
722model it chooses.
723
724=item C<PERL_ANYEVENT_MODEL>
725
726This can be used to specify the event model to be used by AnyEvent, before
727autodetection and -probing kicks in. It must be a string consisting
728entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
729and the resulting module name is loaded and if the load was successful,
730used as event model. If it fails to load AnyEvent will proceed with
731autodetection and -probing.
732
733This functionality might change in future versions.
734
735For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
736could start your program like this:
737
738 PERL_ANYEVENT_MODEL=Perl perl ...
739
740=back
741
525=head1 EXAMPLE 742=head1 EXAMPLE PROGRAM
526 743
527The following program uses an io watcher to read data from stdin, a timer 744The following program uses an I/O watcher to read data from STDIN, a timer
528to display a message once per second, and a condvar to exit the program 745to display a message once per second, and a condition variable to quit the
529when the user enters quit: 746program when the user enters quit:
530 747
531 use AnyEvent; 748 use AnyEvent;
532 749
533 my $cv = AnyEvent->condvar; 750 my $cv = AnyEvent->condvar;
534 751
535 my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 752 my $io_watcher = AnyEvent->io (
753 fh => \*STDIN,
754 poll => 'r',
755 cb => sub {
536 warn "io event <$_[0]>\n"; # will always output <r> 756 warn "io event <$_[0]>\n"; # will always output <r>
537 chomp (my $input = <STDIN>); # read a line 757 chomp (my $input = <STDIN>); # read a line
538 warn "read: $input\n"; # output what has been read 758 warn "read: $input\n"; # output what has been read
539 $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i 759 $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
760 },
540 }); 761 );
541 762
542 my $time_watcher; # can only be used once 763 my $time_watcher; # can only be used once
543 764
544 sub new_timer { 765 sub new_timer {
545 $timer = AnyEvent->timer (after => 1, cb => sub { 766 $timer = AnyEvent->timer (after => 1, cb => sub {
627 $txn->{finished}->wait; 848 $txn->{finished}->wait;
628 return $txn->{result}; 849 return $txn->{result};
629 850
630The actual code goes further and collects all errors (C<die>s, exceptions) 851The actual code goes further and collects all errors (C<die>s, exceptions)
631that occured during request processing. The C<result> method detects 852that occured during request processing. The C<result> method detects
632wether an exception as thrown (it is stored inside the $txn object) 853whether an exception as thrown (it is stored inside the $txn object)
633and just throws the exception, which means connection errors and other 854and just throws the exception, which means connection errors and other
634problems get reported tot he code that tries to use the result, not in a 855problems get reported tot he code that tries to use the result, not in a
635random callback. 856random callback.
636 857
637All of this enables the following usage styles: 858All of this enables the following usage styles:
672 $quit->broadcast; 893 $quit->broadcast;
673 }); 894 });
674 895
675 $quit->wait; 896 $quit->wait;
676 897
898
899=head1 BENCHMARK
900
901To give you an idea of the performance and overheads that AnyEvent adds
902over the event loops themselves (and to give you an impression of the
903speed of various event loops), here is a benchmark of various supported
904event models natively and with anyevent. The benchmark creates a lot of
905timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
906become writable, which it is), lets them fire exactly once and destroys
907them again.
908
909Rewriting the benchmark to use many different sockets instead of using
910the same filehandle for all I/O watchers results in a much longer runtime
911(socket creation is expensive), but qualitatively the same figures, so it
912was not used.
913
914=head2 Explanation of the columns
915
916I<watcher> is the number of event watchers created/destroyed. Since
917different event models feature vastly different performances, each event
918loop was given a number of watchers so that overall runtime is acceptable
919and similar between tested event loop (and keep them from crashing): Glib
920would probably take thousands of years if asked to process the same number
921of watchers as EV in this benchmark.
922
923I<bytes> is the number of bytes (as measured by the resident set size,
924RSS) consumed by each watcher. This method of measuring captures both C
925and Perl-based overheads.
926
927I<create> is the time, in microseconds (millionths of seconds), that it
928takes to create a single watcher. The callback is a closure shared between
929all watchers, to avoid adding memory overhead. That means closure creation
930and memory usage is not included in the figures.
931
932I<invoke> is the time, in microseconds, used to invoke a simple
933callback. The callback simply counts down a Perl variable and after it was
934invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
935signal the end of this phase.
936
937I<destroy> is the time, in microseconds, that it takes to destroy a single
938watcher.
939
940=head2 Results
941
942 name watchers bytes create invoke destroy comment
943 EV/EV 400000 244 0.56 0.46 0.31 EV native interface
944 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
945 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
946 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
947 Event/Event 16000 516 31.88 31.30 0.85 Event native interface
948 Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers
949 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
950 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
951 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
952 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
953
954=head2 Discussion
955
956The benchmark does I<not> measure scalability of the event loop very
957well. For example, a select-based event loop (such as the pure perl one)
958can never compete with an event loop that uses epoll when the number of
959file descriptors grows high. In this benchmark, all events become ready at
960the same time, so select/poll-based implementations get an unnatural speed
961boost.
962
963C<EV> is the sole leader regarding speed and memory use, which are both
964maximal/minimal, respectively. Even when going through AnyEvent, it uses
965far less memory than any other event loop and is still faster than Event
966natively.
967
968The pure perl implementation is hit in a few sweet spots (both the
969constant timeout and the use of a single fd hit optimisations in the perl
970interpreter and the backend itself). Nevertheless this shows that it
971adds very little overhead in itself. Like any select-based backend its
972performance becomes really bad with lots of file descriptors (and few of
973them active), of course, but this was not subject of this benchmark.
974
975The C<Event> module has a relatively high setup and callback invocation
976cost, but overall scores in on the third place.
977
978C<Glib>'s memory usage is quite a bit higher, but it features a
979faster callback invocation and overall ends up in the same class as
980C<Event>. However, Glib scales extremely badly, doubling the number of
981watchers increases the processing time by more than a factor of four,
982making it completely unusable when using larger numbers of watchers
983(note that only a single file descriptor was used in the benchmark, so
984inefficiencies of C<poll> do not account for this).
985
986The C<Tk> adaptor works relatively well. The fact that it crashes with
987more than 2000 watchers is a big setback, however, as correctness takes
988precedence over speed. Nevertheless, its performance is surprising, as the
989file descriptor is dup()ed for each watcher. This shows that the dup()
990employed by some adaptors is not a big performance issue (it does incur a
991hidden memory cost inside the kernel which is not reflected in the figures
992above).
993
994C<POE>, regardless of underlying event loop (whether using its pure
995perl select-based backend or the Event module, the POE-EV backend
996couldn't be tested because it wasn't working) shows abysmal performance
997and memory usage: Watchers use almost 30 times as much memory as
998EV watchers, and 10 times as much memory as Event (the high memory
999requirements are caused by requiring a session for each watcher). Watcher
1000invocation speed is almost 900 times slower than with AnyEvent's pure perl
1001implementation. The design of the POE adaptor class in AnyEvent can not
1002really account for this, as session creation overhead is small compared
1003to execution of the state machine, which is coded pretty optimally within
1004L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
1005
1006=head2 Summary
1007
1008=over 4
1009
1010=item * Using EV through AnyEvent is faster than any other event loop
1011(even when used without AnyEvent), but most event loops have acceptable
1012performance with or without AnyEvent.
1013
1014=item * The overhead AnyEvent adds is usually much smaller than the overhead of
1015the actual event loop, only with extremely fast event loops such as EV
1016adds AnyEvent significant overhead.
1017
1018=item * You should avoid POE like the plague if you want performance or
1019reasonable memory usage.
1020
1021=back
1022
1023
1024=head1 FORK
1025
1026Most event libraries are not fork-safe. The ones who are usually are
1027because they are so inefficient. Only L<EV> is fully fork-aware.
1028
1029If you have to fork, you must either do so I<before> creating your first
1030watcher OR you must not use AnyEvent at all in the child.
1031
1032
1033=head1 SECURITY CONSIDERATIONS
1034
1035AnyEvent can be forced to load any event model via
1036$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
1037execute arbitrary code or directly gain access, it can easily be used to
1038make the program hang or malfunction in subtle ways, as AnyEvent watchers
1039will not be active when the program uses a different event model than
1040specified in the variable.
1041
1042You can make AnyEvent completely ignore this variable by deleting it
1043before the first watcher gets created, e.g. with a C<BEGIN> block:
1044
1045 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1046
1047 use AnyEvent;
1048
1049
677=head1 SEE ALSO 1050=head1 SEE ALSO
678 1051
679Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, 1052Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
680L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>. 1053L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
1054L<Event::Lib>, L<Qt>, L<POE>.
681 1055
682Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>, 1056Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
1057L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
1058L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
683L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, 1059L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
684L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.
685 1060
686Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. 1061Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
687 1062
688=head1 1063
1064=head1 AUTHOR
1065
1066 Marc Lehmann <schmorp@schmorp.de>
1067 http://home.schmorp.de/
689 1068
690=cut 1069=cut
691 1070
6921 10711
693 1072

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