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Revision 1.55 by root, Wed Apr 23 11:25:42 2008 UTC vs.
Revision 1.70 by root, Fri Apr 25 07:25:44 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, Event::Lib - 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
… …
80module. 80module.
81 81
82During the first call of any watcher-creation method, the module tries 82During the first call of any watcher-creation method, the module tries
83to detect the currently loaded event loop by probing whether one of the 83to detect the currently loaded event loop by probing whether one of the
84following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, 84following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
85L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found, 85L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>,
86the module tries to load these modules in the stated order. The first one 86L<POE>. The first one found is used. If none are found, the module tries
87to load these modules (excluding Event::Lib, Qt and POE as the pure perl
88adaptor should always succeed) in the order given. The first one that can
87that can be successfully loaded will be used. If, after this, still none 89be successfully loaded will be used. If, after this, still none could be
88could be found, AnyEvent will fall back to a pure-perl event loop, which 90found, AnyEvent will fall back to a pure-perl event loop, which is not
89is not very efficient, but should work everywhere. 91very efficient, but should work everywhere.
90 92
91Because AnyEvent first checks for modules that are already loaded, loading 93Because AnyEvent first checks for modules that are already loaded, loading
92an event model explicitly before first using AnyEvent will likely make 94an event model explicitly before first using AnyEvent will likely make
93that model the default. For example: 95that model the default. For example:
94 96
… …
145events. C<poll> must be a string that is either C<r> or C<w>, which 147events. C<poll> must be a string that is either C<r> or C<w>, which
146creates a watcher waiting for "r"eadable or "w"ritable events, 148creates a watcher waiting for "r"eadable or "w"ritable events,
147respectively. C<cb> is the callback to invoke each time the file handle 149respectively. C<cb> is the callback to invoke each time the file handle
148becomes ready. 150becomes ready.
149 151
150File handles will be kept alive, so as long as the watcher exists, the 152As long as the I/O watcher exists it will keep the file descriptor or a
151file handle exists, too. 153copy of it alive/open.
152 154
153It is not allowed to close a file handle as long as any watcher is active 155It is not allowed to close a file handle as long as any watcher is active
154on the underlying file descriptor. 156on the underlying file descriptor.
155 157
156Some event loops issue spurious readyness notifications, so you should 158Some event loops issue spurious readyness notifications, so you should
… …
206 208
207There are two ways to handle timers: based on real time (relative, "fire 209There are two ways to handle timers: based on real time (relative, "fire
208in 10 seconds") and based on wallclock time (absolute, "fire at 12 210in 10 seconds") and based on wallclock time (absolute, "fire at 12
209o'clock"). 211o'clock").
210 212
211While most event loops expect timers to specified in a relative way, they use 213While most event loops expect timers to specified in a relative way, they
212absolute time internally. This makes a difference when your clock "jumps", 214use absolute time internally. This makes a difference when your clock
213for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to 215"jumps", for example, when ntp decides to set your clock backwards from
2142008-01-01, a watcher that you created to fire "after" a second might actually take 216the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215six years to finally fire. 217fire "after" a second might actually take six years to finally fire.
216 218
217AnyEvent cannot compensate for this. The only event loop that is conscious 219AnyEvent cannot compensate for this. The only event loop that is conscious
218about these issues is L<EV>, which offers both relative (ev_timer) and 220about these issues is L<EV>, which offers both relative (ev_timer, based
219absolute (ev_periodic) timers. 221on true relative time) and absolute (ev_periodic, based on wallclock time)
222timers.
220 223
221AnyEvent always prefers relative timers, if available, matching the 224AnyEvent always prefers relative timers, if available, matching the
222AnyEvent API. 225AnyEvent API.
223 226
224=head2 SIGNAL WATCHERS 227=head2 SIGNAL WATCHERS
225 228
226You can watch for signals using a signal watcher, C<signal> is the signal 229You can watch for signals using a signal watcher, C<signal> is the signal
227I<name> without any C<SIG> prefix, C<cb> is the Perl callback to 230I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
228be invoked whenever a signal occurs. 231be invoked whenever a signal occurs.
229 232
230Multiple signals occurances can be clumped together into one callback 233Multiple signal occurances can be clumped together into one callback
231invocation, and callback invocation will be synchronous. synchronous means 234invocation, and callback invocation will be synchronous. synchronous means
232that it might take a while until the signal gets handled by the process, 235that it might take a while until the signal gets handled by the process,
233but it is guarenteed not to interrupt any other callbacks. 236but it is guarenteed not to interrupt any other callbacks.
234 237
235The main advantage of using these watchers is that you can share a signal 238The main advantage of using these watchers is that you can share a signal
… …
353 356
354The known classes so far are: 357The known classes so far are:
355 358
356 AnyEvent::Impl::CoroEV based on Coro::EV, best choice. 359 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. 360 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358 AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). 361 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359 AnyEvent::Impl::Event based on Event, also second best choice :) 362 AnyEvent::Impl::Event based on Event, second best choice.
360 AnyEvent::Impl::Glib based on Glib, third-best choice. 363 AnyEvent::Impl::Glib based on Glib, third-best choice.
361 AnyEvent::Impl::Tk based on Tk, very bad choice. 364 AnyEvent::Impl::Tk based on Tk, very bad choice.
362 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. 365 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
366 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
363 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. 367 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368 AnyEvent::Impl::POE based on POE, not generic enough for full support.
369
370There is no support for WxWidgets, as WxWidgets has no support for
371watching file handles. However, you can use WxWidgets through the
372POE Adaptor, as POE has a Wx backend that simply polls 20 times per
373second, which was considered to be too horrible to even consider for
374AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
375it's adaptor.
376
377AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
378autodetecting them.
364 379
365=item AnyEvent::detect 380=item AnyEvent::detect
366 381
367Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model 382Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
368if necessary. You should only call this function right before you would 383if necessary. You should only call this function right before you would
… …
419no warnings; 434no warnings;
420use strict; 435use strict;
421 436
422use Carp; 437use Carp;
423 438
424our $VERSION = '3.12'; 439our $VERSION = '3.3';
425our $MODEL; 440our $MODEL;
426 441
427our $AUTOLOAD; 442our $AUTOLOAD;
428our @ISA; 443our @ISA;
429 444
… …
436 [Coro::Event:: => AnyEvent::Impl::CoroEvent::], 451 [Coro::Event:: => AnyEvent::Impl::CoroEvent::],
437 [EV:: => AnyEvent::Impl::EV::], 452 [EV:: => AnyEvent::Impl::EV::],
438 [Event:: => AnyEvent::Impl::Event::], 453 [Event:: => AnyEvent::Impl::Event::],
439 [Glib:: => AnyEvent::Impl::Glib::], 454 [Glib:: => AnyEvent::Impl::Glib::],
440 [Tk:: => AnyEvent::Impl::Tk::], 455 [Tk:: => AnyEvent::Impl::Tk::],
456 [Wx:: => AnyEvent::Impl::POE::],
457 [Prima:: => AnyEvent::Impl::POE::],
441 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], 458 [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
459 # everything below here will not be autoprobed as the pureperl backend should work everywhere
442 [Event::Lib:: => AnyEvent::Impl::EventLib::], 460 [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
461 [Qt:: => AnyEvent::Impl::Qt::], # requires special main program
462 [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
443); 463);
444 464
445our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); 465our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
446 466
447sub detect() { 467sub detect() {
448 unless ($MODEL) { 468 unless ($MODEL) {
449 no strict 'refs'; 469 no strict 'refs';
450 470
451 if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) { 471 if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
452 my $model = "AnyEvent::Impl::$1"; 472 my $model = "AnyEvent::Impl::$1";
453 if (eval "require $model") { 473 if (eval "require $model") {
454 $MODEL = $model; 474 $MODEL = $model;
455 warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1; 475 warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
476 } else {
477 warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
456 } 478 }
457 } 479 }
458 480
459 # check for already loaded models 481 # check for already loaded models
460 unless ($MODEL) { 482 unless ($MODEL) {
… …
653 675
654=over 4 676=over 4
655 677
656=item C<PERL_ANYEVENT_VERBOSE> 678=item C<PERL_ANYEVENT_VERBOSE>
657 679
680By default, AnyEvent will be completely silent except in fatal
681conditions. You can set this environment variable to make AnyEvent more
682talkative.
683
684When set to C<1> or higher, causes AnyEvent to warn about unexpected
685conditions, such as not being able to load the event model specified by
686C<PERL_ANYEVENT_MODEL>.
687
658When set to C<2> or higher, cause AnyEvent to report to STDERR which event 688When set to C<2> or higher, cause AnyEvent to report to STDERR which event
659model it chooses. 689model it chooses.
660 690
661=item C<PERL_ANYEVENT_MODEL> 691=item C<PERL_ANYEVENT_MODEL>
662 692
… …
830 $quit->broadcast; 860 $quit->broadcast;
831 }); 861 });
832 862
833 $quit->wait; 863 $quit->wait;
834 864
865
866=head1 BENCHMARK
867
868To give you an idea of the performance and overheads that AnyEvent adds
869over the event loops directly, here is a benchmark of various supported
870event models natively and with anyevent. The benchmark creates a lot of
871timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to
872become writable, which it is), lets them fire exactly once and destroys
873them again.
874
875=head2 Explanation of the columns
876
877I<watcher> is the number of event watchers created/destroyed. Since
878different event models feature vastly different performances, each event
879loop was given a number of watchers so that overall runtime is acceptable
880and similar between tested event loop (and keep them from crashing): Glib
881would probably take thousands of years if asked to process the same number
882of watchers as EV in this benchmark.
883
884I<bytes> is the number of bytes (as measured by the resident set size,
885RSS) consumed by each watcher. This method of measuring captures both C
886and Perl-based overheads.
887
888I<create> is the time, in microseconds (millionths of seconds), that it
889takes to create a single watcher. The callback is a closure shared between
890all watchers, to avoid adding memory overhead. That means closure creation
891and memory usage is not included in the figures.
892
893I<invoke> is the time, in microseconds, used to invoke a simple
894callback. The callback simply counts down a Perl variable and after it was
895invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
896signal the end of this phase.
897
898I<destroy> is the time, in microseconds, that it takes destroy a single
899watcher.
900
901=head2 Results
902
903 name watcher bytes create invoke destroy comment
904 EV/EV 400000 244 0.56 0.46 0.31 EV native interface
905 EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers
906 CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal
907 Perl/Any 16000 654 4.64 1.22 0.77 pure perl implementation
908 Event/Event 16000 523 28.05 21.38 0.86 Event native interface
909 Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers
910 Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour
911 Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers
912 POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event
913 POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select
914
915=head2 Discussion
916
917The benchmark does I<not> measure scalability of the event loop very
918well. For example, a select-based event loop (such as the pure perl one)
919can never compete with an event loop that uses epoll when the number of
920file descriptors grows high. In this benchmark, only a single filehandle
921is used (although some of the AnyEvent adaptors dup() its file descriptor
922to worka round bugs).
923
924C<EV> is the sole leader regarding speed and memory use, which are both
925maximal/minimal, respectively. Even when going through AnyEvent, there is
926only one event loop that uses less memory (the C<Event> module natively), and
927no faster event model, not event C<Event> natively.
928
929The pure perl implementation is hit in a few sweet spots (both the
930zero timeout and the use of a single fd hit optimisations in the perl
931interpreter and the backend itself). Nevertheless tis shows that it
932adds very little overhead in itself. Like any select-based backend its
933performance becomes really bad with lots of file descriptors, of course,
934but this was not subjetc of this benchmark.
935
936The C<Event> module has a relatively high setup and callback invocation cost,
937but overall scores on the third place.
938
939C<Glib>'s memory usage is quite a bit bit higher, features a faster
940callback invocation and overall lands in the same class as C<Event>.
941
942The C<Tk> adaptor works relatively well, the fact that it crashes with
943more than 2000 watchers is a big setback, however, as correctness takes
944precedence over speed. Nevertheless, its performance is surprising, as the
945file descriptor is dup()ed for each watcher. This shows that the dup()
946employed by some adaptors is not a big performance issue (it does incur a
947hidden memory cost inside the kernel, though).
948
949C<POE>, regardless of backend (wether using its pure perl select-based
950backend or the Event backend) shows abysmal performance and memory
951usage: Watchers use almost 30 times as much memory as EV watchers, and 10
952times as much memory as both Event or EV via AnyEvent. Watcher invocation
953is almost 700 times slower as with AnyEvent's pure perl implementation.
954
955Summary: using EV through AnyEvent is faster than any other event
956loop. The overhead AnyEvent adds can be very small, and you should avoid
957POE like the plague if you want performance or reasonable memory usage.
958
959
835=head1 FORK 960=head1 FORK
836 961
837Most event libraries are not fork-safe. The ones who are usually are 962Most event libraries are not fork-safe. The ones who are usually are
838because they are so inefficient. Only L<EV> is fully fork-aware. 963because they are so inefficient. Only L<EV> is fully fork-aware.
839 964
840If you have to fork, you must either do so I<before> creating your first 965If you have to fork, you must either do so I<before> creating your first
841watcher OR you must not use AnyEvent at all in the child. 966watcher OR you must not use AnyEvent at all in the child.
967
842 968
843=head1 SECURITY CONSIDERATIONS 969=head1 SECURITY CONSIDERATIONS
844 970
845AnyEvent can be forced to load any event model via 971AnyEvent can be forced to load any event model via
846$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to 972$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
… …
854 980
855 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 981 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
856 982
857 use AnyEvent; 983 use AnyEvent;
858 984
985
859=head1 SEE ALSO 986=head1 SEE ALSO
860 987
861Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, 988Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
862L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>, 989L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
863L<Event::Lib>. 990L<Event::Lib>, L<Qt>, L<POE>.
864 991
865Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>, 992Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
866L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, 993L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
867L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>. 994L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
995L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
868 996
869Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. 997Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
998
870 999
871=head1 AUTHOR 1000=head1 AUTHOR
872 1001
873 Marc Lehmann <schmorp@schmorp.de> 1002 Marc Lehmann <schmorp@schmorp.de>
874 http://home.schmorp.de/ 1003 http://home.schmorp.de/

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