… | |
… | |
80 | module. |
80 | module. |
81 | |
81 | |
82 | During the first call of any watcher-creation method, the module tries |
82 | During the first call of any watcher-creation method, the module tries |
83 | to detect the currently loaded event loop by probing whether one of the |
83 | to detect the currently loaded event loop by probing whether one of the |
84 | following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, |
84 | following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, |
85 | L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>, |
85 | L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>, |
86 | L<POE>. The first one found is used. If none are found, the module tries |
86 | L<POE>. The first one found is used. If none are found, the module tries |
87 | to load these modules (excluding Event::Lib, Qt and POE as the pure perl |
87 | to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl |
88 | adaptor should always succeed) in the order given. The first one that can |
88 | adaptor should always succeed) in the order given. The first one that can |
89 | be successfully loaded will be used. If, after this, still none could be |
89 | be successfully loaded will be used. If, after this, still none could be |
90 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
90 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
91 | very efficient, but should work everywhere. |
91 | very efficient, but should work everywhere. |
92 | |
92 | |
… | |
… | |
136 | |
136 | |
137 | Note that C<my $w; $w => combination. This is necessary because in Perl, |
137 | Note that C<my $w; $w => combination. This is necessary because in Perl, |
138 | my variables are only visible after the statement in which they are |
138 | my variables are only visible after the statement in which they are |
139 | declared. |
139 | declared. |
140 | |
140 | |
141 | =head2 IO WATCHERS |
141 | =head2 I/O WATCHERS |
142 | |
142 | |
143 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
143 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
144 | with the following mandatory key-value pairs as arguments: |
144 | with the following mandatory key-value pairs as arguments: |
145 | |
145 | |
146 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for |
146 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for |
147 | events. C<poll> must be a string that is either C<r> or C<w>, which |
147 | events. C<poll> must be a string that is either C<r> or C<w>, which |
148 | creates a watcher waiting for "r"eadable or "w"ritable events, |
148 | creates a watcher waiting for "r"eadable or "w"ritable events, |
149 | respectively. C<cb> is the callback to invoke each time the file handle |
149 | respectively. C<cb> is the callback to invoke each time the file handle |
150 | becomes ready. |
150 | becomes ready. |
151 | |
151 | |
152 | As long as the I/O watcher exists it will keep the file descriptor or a |
152 | The I/O watcher might use the underlying file descriptor or a copy of it. |
153 | copy of it alive/open. |
|
|
154 | |
|
|
155 | It is not allowed to close a file handle as long as any watcher is active |
153 | It is not allowed to close a file handle as long as any watcher is active |
156 | on the underlying file descriptor. |
154 | on the underlying file descriptor. |
157 | |
155 | |
158 | Some event loops issue spurious readyness notifications, so you should |
156 | Some event loops issue spurious readyness notifications, so you should |
159 | always use non-blocking calls when reading/writing from/to your file |
157 | always use non-blocking calls when reading/writing from/to your file |
… | |
… | |
253 | watches for any child process exit). The watcher will trigger as often |
251 | watches for any child process exit). The watcher will trigger as often |
254 | as status change for the child are received. This works by installing a |
252 | as status change for the child are received. This works by installing a |
255 | signal handler for C<SIGCHLD>. The callback will be called with the pid |
253 | signal handler for C<SIGCHLD>. The callback will be called with the pid |
256 | and exit status (as returned by waitpid). |
254 | and exit status (as returned by waitpid). |
257 | |
255 | |
258 | Example: wait for pid 1333 |
256 | There is a slight catch to child watchers, however: you usually start them |
|
|
257 | I<after> the child process was created, and this means the process could |
|
|
258 | have exited already (and no SIGCHLD will be sent anymore). |
|
|
259 | |
|
|
260 | Not all event models handle this correctly (POE doesn't), but even for |
|
|
261 | event models that I<do> handle this correctly, they usually need to be |
|
|
262 | loaded before the process exits (i.e. before you fork in the first place). |
|
|
263 | |
|
|
264 | This means you cannot create a child watcher as the very first thing in an |
|
|
265 | AnyEvent program, you I<have> to create at least one watcher before you |
|
|
266 | C<fork> the child (alternatively, you can call C<AnyEvent::detect>). |
|
|
267 | |
|
|
268 | Example: fork a process and wait for it |
|
|
269 | |
|
|
270 | my $done = AnyEvent->condvar; |
|
|
271 | |
|
|
272 | AnyEvent::detect; # force event module to be initialised |
|
|
273 | |
|
|
274 | my $pid = fork or exit 5; |
259 | |
275 | |
260 | my $w = AnyEvent->child ( |
276 | my $w = AnyEvent->child ( |
261 | pid => 1333, |
277 | pid => $pid, |
262 | cb => sub { |
278 | cb => sub { |
263 | my ($pid, $status) = @_; |
279 | my ($pid, $status) = @_; |
264 | warn "pid $pid exited with status $status"; |
280 | warn "pid $pid exited with status $status"; |
|
|
281 | $done->broadcast; |
265 | }, |
282 | }, |
266 | ); |
283 | ); |
|
|
284 | |
|
|
285 | # do something else, then wait for process exit |
|
|
286 | $done->wait; |
267 | |
287 | |
268 | =head2 CONDITION VARIABLES |
288 | =head2 CONDITION VARIABLES |
269 | |
289 | |
270 | Condition variables can be created by calling the C<< AnyEvent->condvar >> |
290 | Condition variables can be created by calling the C<< AnyEvent->condvar >> |
271 | method without any arguments. |
291 | method without any arguments. |
… | |
… | |
359 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
379 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
360 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
380 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
361 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
381 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
362 | AnyEvent::Impl::Event based on Event, second best choice. |
382 | AnyEvent::Impl::Event based on Event, second best choice. |
363 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
383 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
|
|
384 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
364 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
385 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
365 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
|
|
366 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
386 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
367 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
387 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
368 | AnyEvent::Impl::POE based on POE, not generic enough for full support. |
388 | AnyEvent::Impl::POE based on POE, not generic enough for full support. |
369 | |
389 | |
370 | There is no support for WxWidgets, as WxWidgets has no support for |
390 | There is no support for WxWidgets, as WxWidgets has no support for |
… | |
… | |
706 | |
726 | |
707 | =back |
727 | =back |
708 | |
728 | |
709 | =head1 EXAMPLE PROGRAM |
729 | =head1 EXAMPLE PROGRAM |
710 | |
730 | |
711 | The following program uses an IO watcher to read data from STDIN, a timer |
731 | The following program uses an I/O watcher to read data from STDIN, a timer |
712 | to display a message once per second, and a condition variable to quit the |
732 | to display a message once per second, and a condition variable to quit the |
713 | program when the user enters quit: |
733 | program when the user enters quit: |
714 | |
734 | |
715 | use AnyEvent; |
735 | use AnyEvent; |
716 | |
736 | |
… | |
… | |
860 | $quit->broadcast; |
880 | $quit->broadcast; |
861 | }); |
881 | }); |
862 | |
882 | |
863 | $quit->wait; |
883 | $quit->wait; |
864 | |
884 | |
|
|
885 | |
|
|
886 | =head1 BENCHMARK |
|
|
887 | |
|
|
888 | To give you an idea of the performance and overheads that AnyEvent adds |
|
|
889 | over the event loops themselves (and to give you an impression of the |
|
|
890 | speed of various event loops), here is a benchmark of various supported |
|
|
891 | event models natively and with anyevent. The benchmark creates a lot of |
|
|
892 | timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to |
|
|
893 | become writable, which it is), lets them fire exactly once and destroys |
|
|
894 | them again. |
|
|
895 | |
|
|
896 | Rewriting the benchmark to use many different sockets instead of using |
|
|
897 | the same filehandle for all I/O watchers results in a much longer runtime |
|
|
898 | (socket creation is expensive), but qualitatively the same figures, so it |
|
|
899 | was not used. |
|
|
900 | |
|
|
901 | =head2 Explanation of the columns |
|
|
902 | |
|
|
903 | I<watcher> is the number of event watchers created/destroyed. Since |
|
|
904 | different event models feature vastly different performances, each event |
|
|
905 | loop was given a number of watchers so that overall runtime is acceptable |
|
|
906 | and similar between tested event loop (and keep them from crashing): Glib |
|
|
907 | would probably take thousands of years if asked to process the same number |
|
|
908 | of watchers as EV in this benchmark. |
|
|
909 | |
|
|
910 | I<bytes> is the number of bytes (as measured by the resident set size, |
|
|
911 | RSS) consumed by each watcher. This method of measuring captures both C |
|
|
912 | and Perl-based overheads. |
|
|
913 | |
|
|
914 | I<create> is the time, in microseconds (millionths of seconds), that it |
|
|
915 | takes to create a single watcher. The callback is a closure shared between |
|
|
916 | all watchers, to avoid adding memory overhead. That means closure creation |
|
|
917 | and memory usage is not included in the figures. |
|
|
918 | |
|
|
919 | I<invoke> is the time, in microseconds, used to invoke a simple |
|
|
920 | callback. The callback simply counts down a Perl variable and after it was |
|
|
921 | invoked "watcher" times, it would C<< ->broadcast >> a condvar once to |
|
|
922 | signal the end of this phase. |
|
|
923 | |
|
|
924 | I<destroy> is the time, in microseconds, that it takes to destroy a single |
|
|
925 | watcher. |
|
|
926 | |
|
|
927 | =head2 Results |
|
|
928 | |
|
|
929 | name watchers bytes create invoke destroy comment |
|
|
930 | EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
|
|
931 | EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers |
|
|
932 | CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal |
|
|
933 | Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation |
|
|
934 | Event/Event 16000 523 28.05 21.38 0.86 Event native interface |
|
|
935 | Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers |
|
|
936 | Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour |
|
|
937 | Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers |
|
|
938 | POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event |
|
|
939 | POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select |
|
|
940 | |
|
|
941 | =head2 Discussion |
|
|
942 | |
|
|
943 | The benchmark does I<not> measure scalability of the event loop very |
|
|
944 | well. For example, a select-based event loop (such as the pure perl one) |
|
|
945 | can never compete with an event loop that uses epoll when the number of |
|
|
946 | file descriptors grows high. In this benchmark, all events become ready at |
|
|
947 | the same time, so select/poll-based implementations get an unnatural speed |
|
|
948 | boost. |
|
|
949 | |
|
|
950 | C<EV> is the sole leader regarding speed and memory use, which are both |
|
|
951 | maximal/minimal, respectively. Even when going through AnyEvent, there are |
|
|
952 | only two event loops that use slightly less memory (the C<Event> module |
|
|
953 | natively and the pure perl backend), and no faster event models, not even |
|
|
954 | C<Event> natively. |
|
|
955 | |
|
|
956 | The pure perl implementation is hit in a few sweet spots (both the |
|
|
957 | zero timeout and the use of a single fd hit optimisations in the perl |
|
|
958 | interpreter and the backend itself, and all watchers become ready at the |
|
|
959 | same time). Nevertheless this shows that it adds very little overhead in |
|
|
960 | itself. Like any select-based backend its performance becomes really bad |
|
|
961 | with lots of file descriptors (and few of them active), of course, but |
|
|
962 | this was not subject of this benchmark. |
|
|
963 | |
|
|
964 | The C<Event> module has a relatively high setup and callback invocation cost, |
|
|
965 | but overall scores on the third place. |
|
|
966 | |
|
|
967 | C<Glib>'s memory usage is quite a bit bit higher, but it features a |
|
|
968 | faster callback invocation and overall ends up in the same class as |
|
|
969 | C<Event>. However, Glib scales extremely badly, doubling the number of |
|
|
970 | watchers increases the processing time by more than a factor of four, |
|
|
971 | making it completely unusable when using larger numbers of watchers |
|
|
972 | (note that only a single file descriptor was used in the benchmark, so |
|
|
973 | inefficiencies of C<poll> do not account for this). |
|
|
974 | |
|
|
975 | The C<Tk> adaptor works relatively well. The fact that it crashes with |
|
|
976 | more than 2000 watchers is a big setback, however, as correctness takes |
|
|
977 | precedence over speed. Nevertheless, its performance is surprising, as the |
|
|
978 | file descriptor is dup()ed for each watcher. This shows that the dup() |
|
|
979 | employed by some adaptors is not a big performance issue (it does incur a |
|
|
980 | hidden memory cost inside the kernel, though, that is not reflected in the |
|
|
981 | figures above). |
|
|
982 | |
|
|
983 | C<POE>, regardless of underlying event loop (wether using its pure perl |
|
|
984 | select-based backend or the Event module) shows abysmal performance and |
|
|
985 | memory usage: Watchers use almost 30 times as much memory as EV watchers, |
|
|
986 | and 10 times as much memory as both Event or EV via AnyEvent. Watcher |
|
|
987 | invocation is almost 900 times slower than with AnyEvent's pure perl |
|
|
988 | implementation. The design of the POE adaptor class in AnyEvent can not |
|
|
989 | really account for this, as session creation overhead is small compared |
|
|
990 | to execution of the state machine, which is coded pretty optimally within |
|
|
991 | L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow. |
|
|
992 | |
|
|
993 | =head2 Summary |
|
|
994 | |
|
|
995 | Using EV through AnyEvent is faster than any other event loop, but most |
|
|
996 | event loops have acceptable performance with or without AnyEvent. |
|
|
997 | |
|
|
998 | The overhead AnyEvent adds is usually much smaller than the overhead of |
|
|
999 | the actual event loop, only with extremely fast event loops such as the EV |
|
|
1000 | adds AnyEvent significant overhead. |
|
|
1001 | |
|
|
1002 | And you should simply avoid POE like the plague if you want performance or |
|
|
1003 | reasonable memory usage. |
|
|
1004 | |
|
|
1005 | |
865 | =head1 FORK |
1006 | =head1 FORK |
866 | |
1007 | |
867 | Most event libraries are not fork-safe. The ones who are usually are |
1008 | Most event libraries are not fork-safe. The ones who are usually are |
868 | because they are so inefficient. Only L<EV> is fully fork-aware. |
1009 | because they are so inefficient. Only L<EV> is fully fork-aware. |
869 | |
1010 | |
870 | If you have to fork, you must either do so I<before> creating your first |
1011 | If you have to fork, you must either do so I<before> creating your first |
871 | watcher OR you must not use AnyEvent at all in the child. |
1012 | watcher OR you must not use AnyEvent at all in the child. |
|
|
1013 | |
872 | |
1014 | |
873 | =head1 SECURITY CONSIDERATIONS |
1015 | =head1 SECURITY CONSIDERATIONS |
874 | |
1016 | |
875 | AnyEvent can be forced to load any event model via |
1017 | AnyEvent can be forced to load any event model via |
876 | $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to |
1018 | $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to |
… | |
… | |
884 | |
1026 | |
885 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
1027 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
886 | |
1028 | |
887 | use AnyEvent; |
1029 | use AnyEvent; |
888 | |
1030 | |
|
|
1031 | |
889 | =head1 SEE ALSO |
1032 | =head1 SEE ALSO |
890 | |
1033 | |
891 | Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, |
1034 | Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, |
892 | L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>, |
1035 | L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>, |
893 | L<Event::Lib>, L<Qt>, L<POE>. |
1036 | L<Event::Lib>, L<Qt>, L<POE>. |
… | |
… | |
897 | L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>, |
1040 | L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>, |
898 | L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>. |
1041 | L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>. |
899 | |
1042 | |
900 | Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. |
1043 | Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. |
901 | |
1044 | |
|
|
1045 | |
902 | =head1 AUTHOR |
1046 | =head1 AUTHOR |
903 | |
1047 | |
904 | Marc Lehmann <schmorp@schmorp.de> |
1048 | Marc Lehmann <schmorp@schmorp.de> |
905 | http://home.schmorp.de/ |
1049 | http://home.schmorp.de/ |
906 | |
1050 | |