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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.
… …
123 These watchers are normal Perl objects with normal Perl lifetime. After 139 These watchers are normal Perl objects with normal Perl lifetime. After
124 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
125 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
126 in control). 142 in control).
127 143
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
128 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
129 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
130 to it). 152 to it).
131 153
132 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.
… …
147 169
148 I/O WATCHERS 170 I/O WATCHERS
149 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
150 the following mandatory key-value pairs as arguments: 172 the following mandatory key-value pairs as arguments:
151 173
152 "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
153 (AnyEvent might or might not keep a reference to this file handle). 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
154 "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
155 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 182 watcher waiting for "r"eadable or "w"ritable events, respectively.
183
156 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.
157 185
158 Although the callback might get passed parameters, their value and 186 Although the callback might get passed parameters, their value and
159 presence is undefined and you cannot rely on them. Portable AnyEvent 187 presence is undefined and you cannot rely on them. Portable AnyEvent
160 callbacks cannot use arguments passed to I/O watcher callbacks. 188 callbacks cannot use arguments passed to I/O watcher callbacks.
161 189
… …
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* in uppercase and without any "SIG" prefix, "cb" is the Perl 342 *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301 callback to be invoked whenever a signal occurs. 343 callback to be invoked whenever a signal occurs.
302 344
… …
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
… …
742 844
743 AnyEvent::IGS 845 AnyEvent::IGS
744 A non-blocking interface to the Internet Go Server protocol (used by 846 A non-blocking interface to the Internet Go Server protocol (used by
745 App::IGS). 847 App::IGS).
746 848
849 AnyEvent::IRC
850 AnyEvent based IRC client module family (replacing the older
747 Net::IRC3 851 Net::IRC3).
748 AnyEvent based IRC client module family.
749 852
750 Net::XMPP2 853 Net::XMPP2
751 AnyEvent based XMPP (Jabber protocol) module family. 854 AnyEvent based XMPP (Jabber protocol) module family.
752 855
753 Net::FCP 856 Net::FCP
… …
762 865
763 IO::Lambda 866 IO::Lambda
764 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
765 AnyEvent. 868 AnyEvent.
766 869
767SUPPLYING YOUR OWN EVENT MODEL INTERFACE 870ERROR AND EXCEPTION HANDLING
768 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
769 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
770 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.
771 876
772 If you need to support another event library which isn't directly 877 As for exception handling (i.e. runtime errors and exceptions thrown
773 supported by AnyEvent, you can supply your own interface to it by 878 while executing a callback), this is not only highly event-loop
774 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
775 event module and the package name of the interface to use onto 880 job of the main program.
776 @AnyEvent::REGISTRY. You can do that before and even without loading
777 AnyEvent, so it is reasonably cheap.
778 881
779 Example: 882 The pure perl event loop simply re-throws the exception (usually within
780 883 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
781 push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; 884 Glib uses "install_exception_handler" and so on.
782
783 This tells AnyEvent to (literally) use the "urxvt::anyevent::"
784 package/class when it finds the "urxvt" package/module is already
785 loaded.
786
787 When AnyEvent is loaded and asked to find a suitable event model, it
788 will first check for the presence of urxvt by trying to "use" the
789 "urxvt::anyevent" module.
790
791 The class should provide implementations for all watcher types. See
792 AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
793 so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
794 the sources.
795
796 If you don't provide "signal" and "child" watchers than AnyEvent will
797 provide suitable (hopefully) replacements.
798
799 The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
800 terminal emulator uses the above line as-is. An interface isn't included
801 in AnyEvent because it doesn't make sense outside the embedded
802 interpreter inside *rxvt-unicode*, and it is updated and maintained as
803 part of the *rxvt-unicode* distribution.
804
805 *rxvt-unicode* also cheats a bit by not providing blocking access to
806 condition variables: code blocking while waiting for a condition will
807 "die". This still works with most modules/usages, and blocking calls
808 must not be done in an interactive application, so it makes sense.
809 885
810ENVIRONMENT VARIABLES 886ENVIRONMENT VARIABLES
811 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.
812 893
813 "PERL_ANYEVENT_VERBOSE" 894 "PERL_ANYEVENT_VERBOSE"
814 By default, AnyEvent will be completely silent except in fatal 895 By default, AnyEvent will be completely silent except in fatal
815 conditions. You can set this environment variable to make AnyEvent 896 conditions. You can set this environment variable to make AnyEvent
816 more talkative. 897 more talkative.
… …
829 thoroughly check the arguments passed to most method calls. If it 910 thoroughly check the arguments passed to most method calls. If it
830 finds any problems it will croak. 911 finds any problems it will croak.
831 912
832 In other words, enables "strict" mode. 913 In other words, enables "strict" mode.
833 914
834 Unlike "use strict" it is definitely recommended ot keep it off in 915 Unlike "use strict", it is definitely recommended ot keep it off in
835 production. 916 production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
917 while developing programs can be very useful, however.
836 918
837 "PERL_ANYEVENT_MODEL" 919 "PERL_ANYEVENT_MODEL"
838 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,
839 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
840 consisting entirely of ASCII letters. The string "AnyEvent::Impl::" 922 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
… …
859 mentioned will be used, and preference will be given to protocols 941 mentioned will be used, and preference will be given to protocols
860 mentioned earlier in the list. 942 mentioned earlier in the list.
861 943
862 This variable can effectively be used for denial-of-service attacks 944 This variable can effectively be used for denial-of-service attacks
863 against local programs (e.g. when setuid), although the impact is 945 against local programs (e.g. when setuid), although the impact is
864 likely small, as the program has to handle connection errors 946 likely small, as the program has to handle conenction and other
865 already- 947 failures anyways.
866 948
867 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over 949 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
868 IPv6, but support both and try to use both. 950 IPv6, but support both and try to use both.
869 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to 951 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
870 resolve or contact IPv6 addresses. 952 resolve or contact IPv6 addresses.
… …
881 EDNS0 in its DNS requests. 963 EDNS0 in its DNS requests.
882 964
883 "PERL_ANYEVENT_MAX_FORKS" 965 "PERL_ANYEVENT_MAX_FORKS"
884 The maximum number of child processes that 966 The maximum number of child processes that
885 "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.
886 1011
887EXAMPLE PROGRAM 1012EXAMPLE PROGRAM
888 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
889 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
890 quit the program when the user enters quit: 1015 quit the program when the user enters quit:
… …
1077 *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
1078 single watcher. 1203 single watcher.
1079 1204
1080 Results 1205 Results
1081 name watchers bytes create invoke destroy comment 1206 name watchers bytes create invoke destroy comment
1082 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
1083 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
1084 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
1085 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
1086 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
1087 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
1088 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
1089 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
1090 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
1091 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
1092 1217
1093 Discussion 1218 Discussion
1094 The benchmark does *not* measure scalability of the event loop very 1219 The benchmark does *not* measure scalability of the event loop very
1095 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)
1096 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
… …
1277 1402
1278 Summary 1403 Summary
1279 * 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,
1280 as the management overhead dominates. 1405 as the management overhead dominates.
1281 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
1282FORK 1489FORK
1283 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
1284 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.
1285 Only EV is fully fork-aware. 1492 Only EV is fully fork-aware.
1286 1493
… …
1297 1504
1298 You can make AnyEvent completely ignore this variable by deleting it 1505 You can make AnyEvent completely ignore this variable by deleting it
1299 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:
1300 1507
1301 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 1508 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1302 1509
1303 use AnyEvent; 1510 use AnyEvent;
1304 1511
1305 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can 1512 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1306 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
1307 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),
1308 and $ENV{PERL_ANYEGENT_STRICT}. 1515 and $ENV{PERL_ANYEVENT_STRICT}.
1309 1516
1310BUGS 1517BUGS
1311 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
1312 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
1313 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
1314 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
1315 not as pronounced). 1522 not as pronounced).
1316 1523
1317SEE ALSO 1524SEE ALSO
1318 Utility functions: AnyEvent::Util. 1525 Utility functions: AnyEvent::Util.
1319 1526

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