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Revision 1.70 by root, Fri Apr 25 07:25:44 2008 UTC vs.
Revision 1.78 by root, Fri Apr 25 09:06:27 2008 UTC

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136 136
137Note that C<my $w; $w => combination. This is necessary because in Perl, 137Note that C<my $w; $w => combination. This is necessary because in Perl,
138my variables are only visible after the statement in which they are 138my variables are only visible after the statement in which they are
139declared. 139declared.
140 140
141=head2 IO WATCHERS 141=head2 I/O WATCHERS
142 142
143You can create an I/O watcher by calling the C<< AnyEvent->io >> method 143You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144with the following mandatory key-value pairs as arguments: 144with the following mandatory key-value pairs as arguments:
145 145
146C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for 146C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for
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706 706
707=back 707=back
708 708
709=head1 EXAMPLE PROGRAM 709=head1 EXAMPLE PROGRAM
710 710
711The following program uses an IO watcher to read data from STDIN, a timer 711The following program uses an I/O watcher to read data from STDIN, a timer
712to display a message once per second, and a condition variable to quit the 712to display a message once per second, and a condition variable to quit the
713program when the user enters quit: 713program when the user enters quit:
714 714
715 use AnyEvent; 715 use AnyEvent;
716 716
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864 864
865 865
866=head1 BENCHMARK 866=head1 BENCHMARK
867 867
868To give you an idea of the performance and overheads that AnyEvent adds 868To give you an idea of the performance and overheads that AnyEvent adds
869over the event loops themselves (and to give you an impression of the
869over the event loops directly, here is a benchmark of various supported 870speed of various event loops), here is a benchmark of various supported
870event models natively and with anyevent. The benchmark creates a lot of 871event models natively and with anyevent. The benchmark creates a lot of
871timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to 872timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
872become writable, which it is), lets them fire exactly once and destroys 873become writable, which it is), lets them fire exactly once and destroys
873them again. 874them again.
875
876Rewriting the benchmark to use many different sockets instead of using
877the same filehandle for all I/O watchers results in a much longer runtime
878(socket creation is expensive), but qualitatively the same figures, so it
879was not used.
874 880
875=head2 Explanation of the columns 881=head2 Explanation of the columns
876 882
877I<watcher> is the number of event watchers created/destroyed. Since 883I<watcher> is the number of event watchers created/destroyed. Since
878different event models feature vastly different performances, each event 884different event models feature vastly different performances, each event
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893I<invoke> is the time, in microseconds, used to invoke a simple 899I<invoke> is the time, in microseconds, used to invoke a simple
894callback. The callback simply counts down a Perl variable and after it was 900callback. The callback simply counts down a Perl variable and after it was
895invoked "watcher" times, it would C<< ->broadcast >> a condvar once to 901invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
896signal the end of this phase. 902signal the end of this phase.
897 903
898I<destroy> is the time, in microseconds, that it takes destroy a single 904I<destroy> is the time, in microseconds, that it takes to destroy a single
899watcher. 905watcher.
900 906
901=head2 Results 907=head2 Results
902 908
903 name watcher bytes create invoke destroy comment 909 name watchers bytes create invoke destroy comment
904 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 910 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 911 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 912 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 913 Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation
908 Event/Event 16000 523 28.05 21.38 0.86 Event native interface 914 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 915 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 916 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 917 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 918 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 919 POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select
914 920
915=head2 Discussion 921=head2 Discussion
916 922
917The benchmark does I<not> measure scalability of the event loop very 923The 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) 924well. For example, a select-based event loop (such as the pure perl one)
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920file descriptors grows high. In this benchmark, only a single filehandle 926file descriptors grows high. In this benchmark, only a single filehandle
921is used (although some of the AnyEvent adaptors dup() its file descriptor 927is used (although some of the AnyEvent adaptors dup() its file descriptor
922to worka round bugs). 928to worka round bugs).
923 929
924C<EV> is the sole leader regarding speed and memory use, which are both 930C<EV> is the sole leader regarding speed and memory use, which are both
925maximal/minimal, respectively. Even when going through AnyEvent, there is 931maximal/minimal, respectively. Even when going through AnyEvent, there are
926only one event loop that uses less memory (the C<Event> module natively), and 932only two event loops that use slightly less memory (the C<Event> module
927no faster event model, not event C<Event> natively. 933natively and the pure perl backend), and no faster event models, not even
934C<Event> natively.
928 935
929The pure perl implementation is hit in a few sweet spots (both the 936The 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 937zero timeout and the use of a single fd hit optimisations in the perl
931interpreter and the backend itself). Nevertheless tis shows that it 938interpreter and the backend itself, and all watchers become ready at the
932adds very little overhead in itself. Like any select-based backend its 939same time). Nevertheless this shows that it adds very little overhead in
933performance becomes really bad with lots of file descriptors, of course, 940itself. Like any select-based backend its performance becomes really bad
941with lots of file descriptors (and few of them active), of course, but
934but this was not subjetc of this benchmark. 942this was not subject of this benchmark.
935 943
936The C<Event> module has a relatively high setup and callback invocation cost, 944The C<Event> module has a relatively high setup and callback invocation cost,
937but overall scores on the third place. 945but overall scores on the third place.
938 946
939C<Glib>'s memory usage is quite a bit bit higher, features a faster 947C<Glib>'s memory usage is quite a bit bit higher, but it features a
940callback invocation and overall lands in the same class as C<Event>. 948faster callback invocation and overall ends up in the same class as
949C<Event>. However, Glib scales extremely badly, doubling the number of
950watchers increases the processing time by more than a factor of four,
951making it completely unusable when using larger numbers of watchers
952(note that only a single file descriptor was used in the benchmark, so
953inefficiencies of C<poll> do not account for this).
941 954
942The C<Tk> adaptor works relatively well, the fact that it crashes with 955The C<Tk> adaptor works relatively well. The fact that it crashes with
943more than 2000 watchers is a big setback, however, as correctness takes 956more than 2000 watchers is a big setback, however, as correctness takes
944precedence over speed. Nevertheless, its performance is surprising, as the 957precedence over speed. Nevertheless, its performance is surprising, as the
945file descriptor is dup()ed for each watcher. This shows that the dup() 958file 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 959employed by some adaptors is not a big performance issue (it does incur a
947hidden memory cost inside the kernel, though). 960hidden memory cost inside the kernel, though, that is not reflected in the
961figures above).
948 962
949C<POE>, regardless of backend (wether using its pure perl select-based 963C<POE>, regardless of underlying event loop (wether using its pure perl
950backend or the Event backend) shows abysmal performance and memory 964select-based backend or the Event module) shows abysmal performance and
951usage: Watchers use almost 30 times as much memory as EV watchers, and 10 965memory usage: Watchers use almost 30 times as much memory as EV watchers,
952times as much memory as both Event or EV via AnyEvent. Watcher invocation 966and 10 times as much memory as both Event or EV via AnyEvent. Watcher
953is almost 700 times slower as with AnyEvent's pure perl implementation. 967invocation is almost 700 times slower than with AnyEvent's pure perl
968implementation. The design of the POE adaptor class in AnyEvent can not
969really account for this, as session creation overhead is small compared
970to execution of the state machine, which is coded pretty optimally within
971L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
954 972
973=head2 Summary
974
955Summary: using EV through AnyEvent is faster than any other event 975Using EV through AnyEvent is faster than any other event loop, but most
956loop. The overhead AnyEvent adds can be very small, and you should avoid 976event loops have acceptable performance with or without AnyEvent.
957POE like the plague if you want performance or reasonable memory usage. 977
978The overhead AnyEvent adds is usually much smaller than the overhead of
979the actual event loop, only with extremely fast event loops such as the EV
980adds AnyEvent significant overhead.
981
982And you should simply avoid POE like the plague if you want performance or
983reasonable memory usage.
958 984
959 985
960=head1 FORK 986=head1 FORK
961 987
962Most event libraries are not fork-safe. The ones who are usually are 988Most event libraries are not fork-safe. The ones who are usually are

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