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1NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - provide framework for multiple event loops
3 3
4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event 4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5 loops 5 event loops.
6 6
7SYNOPSIS 7SYNOPSIS
8 use AnyEvent; 8 use AnyEvent;
9 9
10 # file descriptor readable
10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 11 my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12
13 # one-shot or repeating timers
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15 my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
16
17 print AnyEvent->now; # prints current event loop time
18 print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19
20 # POSIX signal
21 my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
22
23 # child process exit
24 my $w = AnyEvent->child (pid => $pid, cb => sub {
25 my ($pid, $status) = @_;
11 ... 26 ...
12 }); 27 });
13 28
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { 29 # called when event loop idle (if applicable)
15 ... 30 my $w = AnyEvent->idle (cb => sub { ... });
16 });
17 31
18 my $w = AnyEvent->condvar; # stores whether a condition was flagged 32 my $w = AnyEvent->condvar; # stores whether a condition was flagged
19 $w->send; # wake up current and all future recv's 33 $w->send; # wake up current and all future recv's
20 $w->recv; # enters "main loop" till $condvar gets ->send 34 $w->recv; # enters "main loop" till $condvar gets ->send
35 # use a condvar in callback mode:
36 $w->cb (sub { $_[0]->recv });
21 37
22INTRODUCTION/TUTORIAL 38INTRODUCTION/TUTORIAL
23 This manpage is mainly a reference manual. If you are interested in a 39 This manpage is mainly a reference manual. If you are interested in a
24 tutorial or some gentle introduction, have a look at the AnyEvent::Intro 40 tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25 manpage. 41 manpage.
… …
30 46
31 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of 47 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
32 policy* and AnyEvent is *small and efficient*. 48 policy* and AnyEvent is *small and efficient*.
33 49
34 First and foremost, *AnyEvent is not an event model* itself, it only 50 First and foremost, *AnyEvent is not an event model* itself, it only
35 interfaces to whatever event model the main program happens to use in a 51 interfaces to whatever event model the main program happens to use, in a
36 pragmatic way. For event models and certain classes of immortals alike, 52 pragmatic way. For event models and certain classes of immortals alike,
37 the statement "there can only be one" is a bitter reality: In general, 53 the statement "there can only be one" is a bitter reality: In general,
38 only one event loop can be active at the same time in a process. 54 only one event loop can be active at the same time in a process.
39 AnyEvent helps hiding the differences between those event loops. 55 AnyEvent cannot change this, but it can hide the differences between
56 those event loops.
40 57
41 The goal of AnyEvent is to offer module authors the ability to do event 58 The goal of AnyEvent is to offer module authors the ability to do event
42 programming (waiting for I/O or timer events) without subscribing to a 59 programming (waiting for I/O or timer events) without subscribing to a
43 religion, a way of living, and most importantly: without forcing your 60 religion, a way of living, and most importantly: without forcing your
44 module users into the same thing by forcing them to use the same event 61 module users into the same thing by forcing them to use the same event
45 model you use. 62 model you use.
46 63
47 For modules like POE or IO::Async (which is a total misnomer as it is 64 For modules like POE or IO::Async (which is a total misnomer as it is
48 actually doing all I/O *synchronously*...), using them in your module is 65 actually doing all I/O *synchronously*...), using them in your module is
49 like joining a cult: After you joined, you are dependent on them and you 66 like joining a cult: After you joined, you are dependent on them and you
50 cannot use anything else, as it is simply incompatible to everything 67 cannot use anything else, as they are simply incompatible to everything
51 that isn't itself. What's worse, all the potential users of your module 68 that isn't them. What's worse, all the potential users of your module
52 are *also* forced to use the same event loop you use. 69 are *also* forced to use the same event loop you use.
53 70
54 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works 71 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
55 fine. AnyEvent + Tk works fine etc. etc. but none of these work together 72 fine. AnyEvent + Tk works fine etc. etc. but none of these work together
56 with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your 73 with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
57 module uses one of those, every user of your module has to use it, too. 74 module uses one of those, every user of your module has to use it, too.
58 But if your module uses AnyEvent, it works transparently with all event 75 But if your module uses AnyEvent, it works transparently with all event
59 models it supports (including stuff like POE and IO::Async, as long as 76 models it supports (including stuff like IO::Async, as long as those use
60 those use one of the supported event loops. It is trivial to add new 77 one of the supported event loops. It is trivial to add new event loops
61 event loops to AnyEvent, too, so it is future-proof). 78 to AnyEvent, too, so it is future-proof).
62 79
63 In addition to being free of having to use *the one and only true event 80 In addition to being free of having to use *the one and only true event
64 model*, AnyEvent also is free of bloat and policy: with POE or similar 81 model*, AnyEvent also is free of bloat and policy: with POE or similar
65 modules, you get an enormous amount of code and strict rules you have to 82 modules, you get an enormous amount of code and strict rules you have to
66 follow. AnyEvent, on the other hand, is lean and up to the point, by 83 follow. AnyEvent, on the other hand, is lean and up to the point, by
… …
122 These watchers are normal Perl objects with normal Perl lifetime. After 139 These watchers are normal Perl objects with normal Perl lifetime. After
123 creating a watcher it will immediately "watch" for events and invoke the 140 creating a watcher it will immediately "watch" for events and invoke the
124 callback when the event occurs (of course, only when the event model is 141 callback when the event occurs (of course, only when the event model is
125 in control). 142 in control).
126 143
144 Note that callbacks must not permanently change global variables
145 potentially in use by the event loop (such as $_ or $[) and that
146 callbacks must not "die". The former is good programming practise in
147 Perl and the latter stems from the fact that exception handling differs
148 widely between event loops.
149
127 To disable the watcher you have to destroy it (e.g. by setting the 150 To disable the watcher you have to destroy it (e.g. by setting the
128 variable you store it in to "undef" or otherwise deleting all references 151 variable you store it in to "undef" or otherwise deleting all references
129 to it). 152 to it).
130 153
131 All watchers are created by calling a method on the "AnyEvent" class. 154 All watchers are created by calling a method on the "AnyEvent" class.
… …
146 169
147 I/O WATCHERS 170 I/O WATCHERS
148 You can create an I/O watcher by calling the "AnyEvent->io" method with 171 You can create an I/O watcher by calling the "AnyEvent->io" method with
149 the following mandatory key-value pairs as arguments: 172 the following mandatory key-value pairs as arguments:
150 173
151 "fh" the Perl *file handle* (*not* file descriptor) to watch for events. 174 "fh" is the Perl *file handle* (*not* file descriptor) to watch for
175 events (AnyEvent might or might not keep a reference to this file
176 handle). Note that only file handles pointing to things for which
177 non-blocking operation makes sense are allowed. This includes sockets,
178 most character devices, pipes, fifos and so on, but not for example
179 files or block devices.
180
152 "poll" must be a string that is either "r" or "w", which creates a 181 "poll" must be a string that is either "r" or "w", which creates a
153 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 182 watcher waiting for "r"eadable or "w"ritable events, respectively.
183
154 is the callback to invoke each time the file handle becomes ready. 184 "cb" is the callback to invoke each time the file handle becomes ready.
155 185
156 Although the callback might get passed parameters, their value and 186 Although the callback might get passed parameters, their value and
157 presence is undefined and you cannot rely on them. Portable AnyEvent 187 presence is undefined and you cannot rely on them. Portable AnyEvent
158 callbacks cannot use arguments passed to I/O watcher callbacks. 188 callbacks cannot use arguments passed to I/O watcher callbacks.
159 189
… …
163 193
164 Some event loops issue spurious readyness notifications, so you should 194 Some event loops issue spurious readyness notifications, so you should
165 always use non-blocking calls when reading/writing from/to your file 195 always use non-blocking calls when reading/writing from/to your file
166 handles. 196 handles.
167 197
168 Example:
169
170 # wait for readability of STDIN, then read a line and disable the watcher 198 Example: wait for readability of STDIN, then read a line and disable the
199 watcher.
200
171 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 201 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
172 chomp (my $input = <STDIN>); 202 chomp (my $input = <STDIN>);
173 warn "read: $input\n"; 203 warn "read: $input\n";
174 undef $w; 204 undef $w;
175 }); 205 });
… …
184 214
185 Although the callback might get passed parameters, their value and 215 Although the callback might get passed parameters, their value and
186 presence is undefined and you cannot rely on them. Portable AnyEvent 216 presence is undefined and you cannot rely on them. Portable AnyEvent
187 callbacks cannot use arguments passed to time watcher callbacks. 217 callbacks cannot use arguments passed to time watcher callbacks.
188 218
189 The timer callback will be invoked at most once: if you want a repeating 219 The callback will normally be invoked once only. If you specify another
190 timer you have to create a new watcher (this is a limitation by both Tk 220 parameter, "interval", as a strictly positive number (> 0), then the
191 and Glib). 221 callback will be invoked regularly at that interval (in fractional
222 seconds) after the first invocation. If "interval" is specified with a
223 false value, then it is treated as if it were missing.
192 224
193 Example: 225 The callback will be rescheduled before invoking the callback, but no
226 attempt is done to avoid timer drift in most backends, so the interval
227 is only approximate.
194 228
195 # fire an event after 7.7 seconds 229 Example: fire an event after 7.7 seconds.
230
196 my $w = AnyEvent->timer (after => 7.7, cb => sub { 231 my $w = AnyEvent->timer (after => 7.7, cb => sub {
197 warn "timeout\n"; 232 warn "timeout\n";
198 }); 233 });
199 234
200 # to cancel the timer: 235 # to cancel the timer:
201 undef $w; 236 undef $w;
202 237
203 Example 2:
204
205 # fire an event after 0.5 seconds, then roughly every second 238 Example 2: fire an event after 0.5 seconds, then roughly every second.
206 my $w;
207 239
208 my $cb = sub {
209 # cancel the old timer while creating a new one
210 $w = AnyEvent->timer (after => 1, cb => $cb); 240 my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
241 warn "timeout\n";
211 }; 242 };
212
213 # start the "loop" by creating the first watcher
214 $w = AnyEvent->timer (after => 0.5, cb => $cb);
215 243
216 TIMING ISSUES 244 TIMING ISSUES
217 There are two ways to handle timers: based on real time (relative, "fire 245 There are two ways to handle timers: based on real time (relative, "fire
218 in 10 seconds") and based on wallclock time (absolute, "fire at 12 246 in 10 seconds") and based on wallclock time (absolute, "fire at 12
219 o'clock"). 247 o'clock").
… …
293 In either case, if you care (and in most cases, you don't), then you 321 In either case, if you care (and in most cases, you don't), then you
294 can get whatever behaviour you want with any event loop, by taking 322 can get whatever behaviour you want with any event loop, by taking
295 the difference between "AnyEvent->time" and "AnyEvent->now" into 323 the difference between "AnyEvent->time" and "AnyEvent->now" into
296 account. 324 account.
297 325
326 AnyEvent->now_update
327 Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
328 current time for each loop iteration (see the discussion of
329 AnyEvent->now, above).
330
331 When a callback runs for a long time (or when the process sleeps),
332 then this "current" time will differ substantially from the real
333 time, which might affect timers and time-outs.
334
335 When this is the case, you can call this method, which will update
336 the event loop's idea of "current time".
337
338 Note that updating the time *might* cause some events to be handled.
339
298 SIGNAL WATCHERS 340 SIGNAL WATCHERS
299 You can watch for signals using a signal watcher, "signal" is the signal 341 You can watch for signals using a signal watcher, "signal" is the signal
300 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked 342 *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301 whenever a signal occurs. 343 callback to be invoked whenever a signal occurs.
302 344
303 Although the callback might get passed parameters, their value and 345 Although the callback might get passed parameters, their value and
304 presence is undefined and you cannot rely on them. Portable AnyEvent 346 presence is undefined and you cannot rely on them. Portable AnyEvent
305 callbacks cannot use arguments passed to signal watcher callbacks. 347 callbacks cannot use arguments passed to signal watcher callbacks.
306 348
… …
321 363
322 CHILD PROCESS WATCHERS 364 CHILD PROCESS WATCHERS
323 You can also watch on a child process exit and catch its exit status. 365 You can also watch on a child process exit and catch its exit status.
324 366
325 The child process is specified by the "pid" argument (if set to 0, it 367 The child process is specified by the "pid" argument (if set to 0, it
326 watches for any child process exit). The watcher will trigger as often 368 watches for any child process exit). The watcher will triggered only
327 as status change for the child are received. This works by installing a 369 when the child process has finished and an exit status is available, not
328 signal handler for "SIGCHLD". The callback will be called with the pid 370 on any trace events (stopped/continued).
329 and exit status (as returned by waitpid), so unlike other watcher types, 371
330 you *can* rely on child watcher callback arguments. 372 The callback will be called with the pid and exit status (as returned by
373 waitpid), so unlike other watcher types, you *can* rely on child watcher
374 callback arguments.
375
376 This watcher type works by installing a signal handler for "SIGCHLD",
377 and since it cannot be shared, nothing else should use SIGCHLD or reap
378 random child processes (waiting for specific child processes, e.g.
379 inside "system", is just fine).
331 380
332 There is a slight catch to child watchers, however: you usually start 381 There is a slight catch to child watchers, however: you usually start
333 them *after* the child process was created, and this means the process 382 them *after* the child process was created, and this means the process
334 could have exited already (and no SIGCHLD will be sent anymore). 383 could have exited already (and no SIGCHLD will be sent anymore).
335 384
… …
343 you "fork" the child (alternatively, you can call "AnyEvent::detect"). 392 you "fork" the child (alternatively, you can call "AnyEvent::detect").
344 393
345 Example: fork a process and wait for it 394 Example: fork a process and wait for it
346 395
347 my $done = AnyEvent->condvar; 396 my $done = AnyEvent->condvar;
348 397
349 my $pid = fork or exit 5; 398 my $pid = fork or exit 5;
350 399
351 my $w = AnyEvent->child ( 400 my $w = AnyEvent->child (
352 pid => $pid, 401 pid => $pid,
353 cb => sub { 402 cb => sub {
354 my ($pid, $status) = @_; 403 my ($pid, $status) = @_;
355 warn "pid $pid exited with status $status"; 404 warn "pid $pid exited with status $status";
356 $done->send; 405 $done->send;
357 }, 406 },
358 ); 407 );
359 408
360 # do something else, then wait for process exit 409 # do something else, then wait for process exit
361 $done->recv; 410 $done->recv;
411
412 IDLE WATCHERS
413 Sometimes there is a need to do something, but it is not so important to
414 do it instantly, but only when there is nothing better to do. This
415 "nothing better to do" is usually defined to be "no other events need
416 attention by the event loop".
417
418 Idle watchers ideally get invoked when the event loop has nothing better
419 to do, just before it would block the process to wait for new events.
420 Instead of blocking, the idle watcher is invoked.
421
422 Most event loops unfortunately do not really support idle watchers (only
423 EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
424 will simply call the callback "from time to time".
425
426 Example: read lines from STDIN, but only process them when the program
427 is otherwise idle:
428
429 my @lines; # read data
430 my $idle_w;
431 my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
432 push @lines, scalar <STDIN>;
433
434 # start an idle watcher, if not already done
435 $idle_w ||= AnyEvent->idle (cb => sub {
436 # handle only one line, when there are lines left
437 if (my $line = shift @lines) {
438 print "handled when idle: $line";
439 } else {
440 # otherwise disable the idle watcher again
441 undef $idle_w;
442 }
443 });
444 });
362 445
363 CONDITION VARIABLES 446 CONDITION VARIABLES
364 If you are familiar with some event loops you will know that all of them 447 If you are familiar with some event loops you will know that all of them
365 require you to run some blocking "loop", "run" or similar function that 448 require you to run some blocking "loop", "run" or similar function that
366 will actively watch for new events and call your callbacks. 449 will actively watch for new events and call your callbacks.
… …
371 The instrument to do that is called a "condition variable", so called 454 The instrument to do that is called a "condition variable", so called
372 because they represent a condition that must become true. 455 because they represent a condition that must become true.
373 456
374 Condition variables can be created by calling the "AnyEvent->condvar" 457 Condition variables can be created by calling the "AnyEvent->condvar"
375 method, usually without arguments. The only argument pair allowed is 458 method, usually without arguments. The only argument pair allowed is
459
376 "cb", which specifies a callback to be called when the condition 460 "cb", which specifies a callback to be called when the condition
377 variable becomes true. 461 variable becomes true, with the condition variable as the first argument
462 (but not the results).
378 463
379 After creation, the condition variable is "false" until it becomes 464 After creation, the condition variable is "false" until it becomes
380 "true" by calling the "send" method (or calling the condition variable 465 "true" by calling the "send" method (or calling the condition variable
381 as if it were a callback, read about the caveats in the description for 466 as if it were a callback, read about the caveats in the description for
382 the "->send" method). 467 the "->send" method).
… …
438 523
439 my $done = AnyEvent->condvar; 524 my $done = AnyEvent->condvar;
440 my $delay = AnyEvent->timer (after => 5, cb => $done); 525 my $delay = AnyEvent->timer (after => 5, cb => $done);
441 $done->recv; 526 $done->recv;
442 527
528 Example: Imagine an API that returns a condvar and doesn't support
529 callbacks. This is how you make a synchronous call, for example from the
530 main program:
531
532 use AnyEvent::CouchDB;
533
534 ...
535
536 my @info = $couchdb->info->recv;
537
538 And this is how you would just ste a callback to be called whenever the
539 results are available:
540
541 $couchdb->info->cb (sub {
542 my @info = $_[0]->recv;
543 });
544
443 METHODS FOR PRODUCERS 545 METHODS FOR PRODUCERS
444 These methods should only be used by the producing side, i.e. the 546 These methods should only be used by the producing side, i.e. the
445 code/module that eventually sends the signal. Note that it is also the 547 code/module that eventually sends the signal. Note that it is also the
446 producer side which creates the condvar in most cases, but it isn't 548 producer side which creates the condvar in most cases, but it isn't
447 uncommon for the consumer to create it as well. 549 uncommon for the consumer to create it as well.
… …
567 669
568 $bool = $cv->ready 670 $bool = $cv->ready
569 Returns true when the condition is "true", i.e. whether "send" or 671 Returns true when the condition is "true", i.e. whether "send" or
570 "croak" have been called. 672 "croak" have been called.
571 673
572 $cb = $cv->cb ([new callback]) 674 $cb = $cv->cb ($cb->($cv))
573 This is a mutator function that returns the callback set and 675 This is a mutator function that returns the callback set and
574 optionally replaces it before doing so. 676 optionally replaces it before doing so.
575 677
576 The callback will be called when the condition becomes "true", i.e. 678 The callback will be called when the condition becomes "true", i.e.
577 when "send" or "croak" are called, with the only argument being the 679 when "send" or "croak" are called, with the only argument being the
… …
698 AnyEvent::Util 800 AnyEvent::Util
699 Contains various utility functions that replace often-used but 801 Contains various utility functions that replace often-used but
700 blocking functions such as "inet_aton" by event-/callback-based 802 blocking functions such as "inet_aton" by event-/callback-based
701 versions. 803 versions.
702 804
703 AnyEvent::Handle
704 Provide read and write buffers and manages watchers for reads and
705 writes.
706
707 AnyEvent::Socket 805 AnyEvent::Socket
708 Provides various utility functions for (internet protocol) sockets, 806 Provides various utility functions for (internet protocol) sockets,
709 addresses and name resolution. Also functions to create non-blocking 807 addresses and name resolution. Also functions to create non-blocking
710 tcp connections or tcp servers, with IPv6 and SRV record support and 808 tcp connections or tcp servers, with IPv6 and SRV record support and
711 more. 809 more.
712 810
811 AnyEvent::Handle
812 Provide read and write buffers, manages watchers for reads and
813 writes, supports raw and formatted I/O, I/O queued and fully
814 transparent and non-blocking SSL/TLS.
815
713 AnyEvent::DNS 816 AnyEvent::DNS
714 Provides rich asynchronous DNS resolver capabilities. 817 Provides rich asynchronous DNS resolver capabilities.
715 818
716 AnyEvent::HTTP 819 AnyEvent::HTTP
717 A simple-to-use HTTP library that is capable of making a lot of 820 A simple-to-use HTTP library that is capable of making a lot of
… …
721 Provides a simple web application server framework. 824 Provides a simple web application server framework.
722 825
723 AnyEvent::FastPing 826 AnyEvent::FastPing
724 The fastest ping in the west. 827 The fastest ping in the west.
725 828
829 AnyEvent::DBI
830 Executes DBI requests asynchronously in a proxy process.
831
832 AnyEvent::AIO
833 Truly asynchronous I/O, should be in the toolbox of every event
834 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
835 together.
836
837 AnyEvent::BDB
838 Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
839 fuses BDB and AnyEvent together.
840
841 AnyEvent::GPSD
842 A non-blocking interface to gpsd, a daemon delivering GPS
843 information.
844
845 AnyEvent::IGS
846 A non-blocking interface to the Internet Go Server protocol (used by
847 App::IGS).
848
849 AnyEvent::IRC
850 AnyEvent based IRC client module family (replacing the older
726 Net::IRC3 851 Net::IRC3).
727 AnyEvent based IRC client module family.
728 852
729 Net::XMPP2 853 Net::XMPP2
730 AnyEvent based XMPP (Jabber protocol) module family. 854 AnyEvent based XMPP (Jabber protocol) module family.
731 855
732 Net::FCP 856 Net::FCP
… …
737 High level API for event-based execution flow control. 861 High level API for event-based execution flow control.
738 862
739 Coro 863 Coro
740 Has special support for AnyEvent via Coro::AnyEvent. 864 Has special support for AnyEvent via Coro::AnyEvent.
741 865
742 AnyEvent::AIO, IO::AIO
743 Truly asynchronous I/O, should be in the toolbox of every event
744 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
745 together.
746
747 AnyEvent::BDB, BDB
748 Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
749 fuses IO::AIO and AnyEvent together.
750
751 IO::Lambda 866 IO::Lambda
752 The lambda approach to I/O - don't ask, look there. Can use 867 The lambda approach to I/O - don't ask, look there. Can use
753 AnyEvent. 868 AnyEvent.
754 869
755SUPPLYING YOUR OWN EVENT MODEL INTERFACE 870ERROR AND EXCEPTION HANDLING
756 This is an advanced topic that you do not normally need to use AnyEvent 871 In general, AnyEvent does not do any error handling - it relies on the
757 in a module. This section is only of use to event loop authors who want 872 caller to do that if required. The AnyEvent::Strict module (see also the
758 to provide AnyEvent compatibility. 873 "PERL_ANYEVENT_STRICT" environment variable, below) provides strict
874 checking of all AnyEvent methods, however, which is highly useful during
875 development.
759 876
760 If you need to support another event library which isn't directly 877 As for exception handling (i.e. runtime errors and exceptions thrown
761 supported by AnyEvent, you can supply your own interface to it by 878 while executing a callback), this is not only highly event-loop
762 pushing, before the first watcher gets created, the package name of the 879 specific, but also not in any way wrapped by this module, as this is the
763 event module and the package name of the interface to use onto 880 job of the main program.
764 @AnyEvent::REGISTRY. You can do that before and even without loading
765 AnyEvent, so it is reasonably cheap.
766 881
767 Example: 882 The pure perl event loop simply re-throws the exception (usually within
768 883 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
769 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; 884 Glib uses "install_exception_handler" and so on.
770
771 This tells AnyEvent to (literally) use the "urxvt::anyevent::"
772 package/class when it finds the "urxvt" package/module is already
773 loaded.
774
775 When AnyEvent is loaded and asked to find a suitable event model, it
776 will first check for the presence of urxvt by trying to "use" the
777 "urxvt::anyevent" module.
778
779 The class should provide implementations for all watcher types. See
780 AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
781 so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
782 the sources.
783
784 If you don't provide "signal" and "child" watchers than AnyEvent will
785 provide suitable (hopefully) replacements.
786
787 The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
788 terminal emulator uses the above line as-is. An interface isn't included
789 in AnyEvent because it doesn't make sense outside the embedded
790 interpreter inside *rxvt-unicode*, and it is updated and maintained as
791 part of the *rxvt-unicode* distribution.
792
793 *rxvt-unicode* also cheats a bit by not providing blocking access to
794 condition variables: code blocking while waiting for a condition will
795 "die". This still works with most modules/usages, and blocking calls
796 must not be done in an interactive application, so it makes sense.
797 885
798ENVIRONMENT VARIABLES 886ENVIRONMENT VARIABLES
799 The following environment variables are used by this module: 887 The following environment variables are used by this module or its
888 submodules.
889
890 Note that AnyEvent will remove *all* environment variables starting with
891 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
892 enabled.
800 893
801 "PERL_ANYEVENT_VERBOSE" 894 "PERL_ANYEVENT_VERBOSE"
802 By default, AnyEvent will be completely silent except in fatal 895 By default, AnyEvent will be completely silent except in fatal
803 conditions. You can set this environment variable to make AnyEvent 896 conditions. You can set this environment variable to make AnyEvent
804 more talkative. 897 more talkative.
… …
807 conditions, such as not being able to load the event model specified 900 conditions, such as not being able to load the event model specified
808 by "PERL_ANYEVENT_MODEL". 901 by "PERL_ANYEVENT_MODEL".
809 902
810 When set to 2 or higher, cause AnyEvent to report to STDERR which 903 When set to 2 or higher, cause AnyEvent to report to STDERR which
811 event model it chooses. 904 event model it chooses.
905
906 "PERL_ANYEVENT_STRICT"
907 AnyEvent does not do much argument checking by default, as thorough
908 argument checking is very costly. Setting this variable to a true
909 value will cause AnyEvent to load "AnyEvent::Strict" and then to
910 thoroughly check the arguments passed to most method calls. If it
911 finds any problems it will croak.
912
913 In other words, enables "strict" mode.
914
915 Unlike "use strict", it is definitely recommended ot keep it off in
916 production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
917 while developing programs can be very useful, however.
812 918
813 "PERL_ANYEVENT_MODEL" 919 "PERL_ANYEVENT_MODEL"
814 This can be used to specify the event model to be used by AnyEvent, 920 This can be used to specify the event model to be used by AnyEvent,
815 before auto detection and -probing kicks in. It must be a string 921 before auto detection and -probing kicks in. It must be a string
816 consisting entirely of ASCII letters. The string "AnyEvent::Impl::" 922 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
… …
835 mentioned will be used, and preference will be given to protocols 941 mentioned will be used, and preference will be given to protocols
836 mentioned earlier in the list. 942 mentioned earlier in the list.
837 943
838 This variable can effectively be used for denial-of-service attacks 944 This variable can effectively be used for denial-of-service attacks
839 against local programs (e.g. when setuid), although the impact is 945 against local programs (e.g. when setuid), although the impact is
840 likely small, as the program has to handle connection errors 946 likely small, as the program has to handle conenction and other
841 already- 947 failures anyways.
842 948
843 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over 949 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
844 IPv6, but support both and try to use both. 950 IPv6, but support both and try to use both.
845 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to 951 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
846 resolve or contact IPv6 addresses. 952 resolve or contact IPv6 addresses.
… …
857 EDNS0 in its DNS requests. 963 EDNS0 in its DNS requests.
858 964
859 "PERL_ANYEVENT_MAX_FORKS" 965 "PERL_ANYEVENT_MAX_FORKS"
860 The maximum number of child processes that 966 The maximum number of child processes that
861 "AnyEvent::Util::fork_call" will create in parallel. 967 "AnyEvent::Util::fork_call" will create in parallel.
968
969SUPPLYING YOUR OWN EVENT MODEL INTERFACE
970 This is an advanced topic that you do not normally need to use AnyEvent
971 in a module. This section is only of use to event loop authors who want
972 to provide AnyEvent compatibility.
973
974 If you need to support another event library which isn't directly
975 supported by AnyEvent, you can supply your own interface to it by
976 pushing, before the first watcher gets created, the package name of the
977 event module and the package name of the interface to use onto
978 @AnyEvent::REGISTRY. You can do that before and even without loading
979 AnyEvent, so it is reasonably cheap.
980
981 Example:
982
983 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
984
985 This tells AnyEvent to (literally) use the "urxvt::anyevent::"
986 package/class when it finds the "urxvt" package/module is already
987 loaded.
988
989 When AnyEvent is loaded and asked to find a suitable event model, it
990 will first check for the presence of urxvt by trying to "use" the
991 "urxvt::anyevent" module.
992
993 The class should provide implementations for all watcher types. See
994 AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
995 so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
996 the sources.
997
998 If you don't provide "signal" and "child" watchers than AnyEvent will
999 provide suitable (hopefully) replacements.
1000
1001 The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
1002 terminal emulator uses the above line as-is. An interface isn't included
1003 in AnyEvent because it doesn't make sense outside the embedded
1004 interpreter inside *rxvt-unicode*, and it is updated and maintained as
1005 part of the *rxvt-unicode* distribution.
1006
1007 *rxvt-unicode* also cheats a bit by not providing blocking access to
1008 condition variables: code blocking while waiting for a condition will
1009 "die". This still works with most modules/usages, and blocking calls
1010 must not be done in an interactive application, so it makes sense.
862 1011
863EXAMPLE PROGRAM 1012EXAMPLE PROGRAM
864 The following program uses an I/O watcher to read data from STDIN, a 1013 The following program uses an I/O watcher to read data from STDIN, a
865 timer to display a message once per second, and a condition variable to 1014 timer to display a message once per second, and a condition variable to
866 quit the program when the user enters quit: 1015 quit the program when the user enters quit:
… …
1053 *destroy* is the time, in microseconds, that it takes to destroy a 1202 *destroy* is the time, in microseconds, that it takes to destroy a
1054 single watcher. 1203 single watcher.
1055 1204
1056 Results 1205 Results
1057 name watchers bytes create invoke destroy comment 1206 name watchers bytes create invoke destroy comment
1058 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 1207 EV/EV 400000 224 0.47 0.35 0.27 EV native interface
1059 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers 1208 EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
1060 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal 1209 CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
1061 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation 1210 Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
1062 Event/Event 16000 516 31.88 31.30 0.85 Event native interface 1211 Event/Event 16000 517 32.20 31.80 0.81 Event native interface
1063 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers 1212 Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
1064 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour 1213 Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
1065 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers 1214 Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
1066 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event 1215 POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
1067 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select 1216 POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
1068 1217
1069 Discussion 1218 Discussion
1070 The benchmark does *not* measure scalability of the event loop very 1219 The benchmark does *not* measure scalability of the event loop very
1071 well. For example, a select-based event loop (such as the pure perl one) 1220 well. For example, a select-based event loop (such as the pure perl one)
1072 can never compete with an event loop that uses epoll when the number of 1221 can never compete with an event loop that uses epoll when the number of
… …
1253 1402
1254 Summary 1403 Summary
1255 * C-based event loops perform very well with small number of watchers, 1404 * C-based event loops perform very well with small number of watchers,
1256 as the management overhead dominates. 1405 as the management overhead dominates.
1257 1406
1407 THE IO::Lambda BENCHMARK
1408 Recently I was told about the benchmark in the IO::Lambda manpage, which
1409 could be misinterpreted to make AnyEvent look bad. In fact, the
1410 benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
1411 better (which shouldn't come as a surprise to anybody). As such, the
1412 benchmark is fine, and shows that the AnyEvent backend from IO::Lambda
1413 isn't very optimal. But how would AnyEvent compare when used without the
1414 extra baggage? To explore this, I wrote the equivalent benchmark for
1415 AnyEvent.
1416
1417 The benchmark itself creates an echo-server, and then, for 500 times,
1418 connects to the echo server, sends a line, waits for the reply, and then
1419 creates the next connection. This is a rather bad benchmark, as it
1420 doesn't test the efficiency of the framework, but it is a benchmark
1421 nevertheless.
1422
1423 name runtime
1424 Lambda/select 0.330 sec
1425 + optimized 0.122 sec
1426 Lambda/AnyEvent 0.327 sec
1427 + optimized 0.138 sec
1428 Raw sockets/select 0.077 sec
1429 POE/select, components 0.662 sec
1430 POE/select, raw sockets 0.226 sec
1431 POE/select, optimized 0.404 sec
1432
1433 AnyEvent/select/nb 0.085 sec
1434 AnyEvent/EV/nb 0.068 sec
1435 +state machine 0.134 sec
1436
1437 The benchmark is also a bit unfair (my fault) - the IO::Lambda
1438 benchmarks actually make blocking connects and use 100% blocking I/O,
1439 defeating the purpose of an event-based solution. All of the newly
1440 written AnyEvent benchmarks use 100% non-blocking connects (using
1441 AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
1442 resolver), so AnyEvent is at a disadvantage here as non-blocking
1443 connects generally require a lot more bookkeeping and event handling
1444 than blocking connects (which involve a single syscall only).
1445
1446 The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
1447 offers similar expressive power as POE and IO::Lambda (using
1448 conventional Perl syntax), which means both the echo server and the
1449 client are 100% non-blocking w.r.t. I/O, further placing it at a
1450 disadvantage.
1451
1452 As you can see, AnyEvent + EV even beats the hand-optimised "raw sockets
1453 benchmark", while AnyEvent + its pure perl backend easily beats
1454 IO::Lambda and POE.
1455
1456 And even the 100% non-blocking version written using the high-level (and
1457 slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda, even
1458 thought it does all of DNS, tcp-connect and socket I/O in a non-blocking
1459 way.
1460
1461 The two AnyEvent benchmarks can be found as eg/ae0.pl and eg/ae2.pl in
1462 the AnyEvent distribution, the remaining benchmarks are part of the
1463 IO::lambda distribution and were used without any changes.
1464
1465SIGNALS
1466 AnyEvent currently installs handlers for these signals:
1467
1468 SIGCHLD
1469 A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1470 emulation for event loops that do not support them natively. Also,
1471 some event loops install a similar handler.
1472
1473 SIGPIPE
1474 A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1475 "undef" when AnyEvent gets loaded.
1476
1477 The rationale for this is that AnyEvent users usually do not really
1478 depend on SIGPIPE delivery (which is purely an optimisation for
1479 shell use, or badly-written programs), but "SIGPIPE" can cause
1480 spurious and rare program exits as a lot of people do not expect
1481 "SIGPIPE" when writing to some random socket.
1482
1483 The rationale for installing a no-op handler as opposed to ignoring
1484 it is that this way, the handler will be restored to defaults on
1485 exec.
1486
1487 Feel free to install your own handler, or reset it to defaults.
1488
1258FORK 1489FORK
1259 Most event libraries are not fork-safe. The ones who are usually are 1490 Most event libraries are not fork-safe. The ones who are usually are
1260 because they rely on inefficient but fork-safe "select" or "poll" calls. 1491 because they rely on inefficient but fork-safe "select" or "poll" calls.
1261 Only EV is fully fork-aware. 1492 Only EV is fully fork-aware.
1262 1493
… …
1273 1504
1274 You can make AnyEvent completely ignore this variable by deleting it 1505 You can make AnyEvent completely ignore this variable by deleting it
1275 before the first watcher gets created, e.g. with a "BEGIN" block: 1506 before the first watcher gets created, e.g. with a "BEGIN" block:
1276 1507
1277 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 1508 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1278 1509
1279 use AnyEvent; 1510 use AnyEvent;
1280 1511
1281 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can 1512 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1282 be used to probe what backend is used and gain other information (which 1513 be used to probe what backend is used and gain other information (which
1283 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). 1514 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1515 and $ENV{PERL_ANYEVENT_STRICT}.
1284 1516
1285BUGS 1517BUGS
1286 Perl 5.8 has numerous memleaks that sometimes hit this module and are 1518 Perl 5.8 has numerous memleaks that sometimes hit this module and are
1287 hard to work around. If you suffer from memleaks, first upgrade to Perl 1519 hard to work around. If you suffer from memleaks, first upgrade to Perl
1288 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other 1520 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1289 annoying mamleaks, such as leaking on "map" and "grep" but it is usually 1521 annoying memleaks, such as leaking on "map" and "grep" but it is usually
1290 not as pronounced). 1522 not as pronounced).
1291 1523
1292SEE ALSO 1524SEE ALSO
1293 Utility functions: AnyEvent::Util. 1525 Utility functions: AnyEvent::Util.
1294 1526

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