… | |
… | |
66 | |
66 | |
67 | Of course, if you want lots of policy (this can arguably be somewhat |
67 | Of course, if you want lots of policy (this can arguably be somewhat |
68 | useful) and you want to force your users to use the one and only event |
68 | useful) and you want to force your users to use the one and only event |
69 | model, you should I<not> use this module. |
69 | model, you should I<not> use this module. |
70 | |
70 | |
71 | |
|
|
72 | =head1 DESCRIPTION |
71 | =head1 DESCRIPTION |
73 | |
72 | |
74 | L<AnyEvent> provides an identical interface to multiple event loops. This |
73 | L<AnyEvent> provides an identical interface to multiple event loops. This |
75 | allows module authors to utilise an event loop without forcing module |
74 | allows module authors to utilise an event loop without forcing module |
76 | users to use the same event loop (as only a single event loop can coexist |
75 | users to use the same event loop (as only a single event loop can coexist |
… | |
… | |
80 | module. |
79 | module. |
81 | |
80 | |
82 | During the first call of any watcher-creation method, the module tries |
81 | 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 |
82 | 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>, |
83 | 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>, |
84 | 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 |
85 | 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 |
86 | 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 |
87 | 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 |
88 | 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 |
89 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
91 | very efficient, but should work everywhere. |
90 | very efficient, but should work everywhere. |
92 | |
91 | |
… | |
… | |
136 | |
135 | |
137 | Note that C<my $w; $w => combination. This is necessary because in Perl, |
136 | 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 |
137 | my variables are only visible after the statement in which they are |
139 | declared. |
138 | declared. |
140 | |
139 | |
141 | =head2 IO WATCHERS |
140 | =head2 I/O WATCHERS |
142 | |
141 | |
143 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
142 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
144 | with the following mandatory key-value pairs as arguments: |
143 | with the following mandatory key-value pairs as arguments: |
145 | |
144 | |
146 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for |
145 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch |
147 | events. C<poll> must be a string that is either C<r> or C<w>, which |
146 | for events. C<poll> must be a string that is either C<r> or C<w>, |
148 | creates a watcher waiting for "r"eadable or "w"ritable events, |
147 | which 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 |
148 | respectively. C<cb> is the callback to invoke each time the file handle |
150 | becomes ready. |
149 | becomes ready. |
151 | |
150 | |
152 | As long as the I/O watcher exists it will keep the file descriptor or a |
151 | Although the callback might get passed parameters, their value and |
153 | copy of it alive/open. |
152 | presence is undefined and you cannot rely on them. Portable AnyEvent |
|
|
153 | callbacks cannot use arguments passed to I/O watcher callbacks. |
154 | |
154 | |
|
|
155 | The I/O watcher might use the underlying file descriptor or a copy of it. |
155 | It is not allowed to close a file handle as long as any watcher is active |
156 | You must not close a file handle as long as any watcher is active on the |
156 | on the underlying file descriptor. |
157 | underlying file descriptor. |
157 | |
158 | |
158 | Some event loops issue spurious readyness notifications, so you should |
159 | Some event loops issue spurious readyness notifications, so you should |
159 | always use non-blocking calls when reading/writing from/to your file |
160 | always use non-blocking calls when reading/writing from/to your file |
160 | handles. |
161 | handles. |
161 | |
162 | |
… | |
… | |
172 | |
173 | |
173 | You can create a time watcher by calling the C<< AnyEvent->timer >> |
174 | You can create a time watcher by calling the C<< AnyEvent->timer >> |
174 | method with the following mandatory arguments: |
175 | method with the following mandatory arguments: |
175 | |
176 | |
176 | C<after> specifies after how many seconds (fractional values are |
177 | C<after> specifies after how many seconds (fractional values are |
177 | supported) should the timer activate. C<cb> the callback to invoke in that |
178 | supported) the callback should be invoked. C<cb> is the callback to invoke |
178 | case. |
179 | in that case. |
|
|
180 | |
|
|
181 | Although the callback might get passed parameters, their value and |
|
|
182 | presence is undefined and you cannot rely on them. Portable AnyEvent |
|
|
183 | callbacks cannot use arguments passed to time watcher callbacks. |
179 | |
184 | |
180 | The timer callback will be invoked at most once: if you want a repeating |
185 | The timer callback will be invoked at most once: if you want a repeating |
181 | timer you have to create a new watcher (this is a limitation by both Tk |
186 | timer you have to create a new watcher (this is a limitation by both Tk |
182 | and Glib). |
187 | and Glib). |
183 | |
188 | |
… | |
… | |
228 | |
233 | |
229 | You can watch for signals using a signal watcher, C<signal> is the signal |
234 | You can watch for signals using a signal watcher, C<signal> is the signal |
230 | I<name> without any C<SIG> prefix, C<cb> is the Perl callback to |
235 | I<name> without any C<SIG> prefix, C<cb> is the Perl callback to |
231 | be invoked whenever a signal occurs. |
236 | be invoked whenever a signal occurs. |
232 | |
237 | |
|
|
238 | Although the callback might get passed parameters, their value and |
|
|
239 | presence is undefined and you cannot rely on them. Portable AnyEvent |
|
|
240 | callbacks cannot use arguments passed to signal watcher callbacks. |
|
|
241 | |
233 | Multiple signal occurances can be clumped together into one callback |
242 | Multiple signal occurances can be clumped together into one callback |
234 | invocation, and callback invocation will be synchronous. synchronous means |
243 | invocation, and callback invocation will be synchronous. synchronous means |
235 | that it might take a while until the signal gets handled by the process, |
244 | that it might take a while until the signal gets handled by the process, |
236 | but it is guarenteed not to interrupt any other callbacks. |
245 | but it is guarenteed not to interrupt any other callbacks. |
237 | |
246 | |
… | |
… | |
251 | |
260 | |
252 | The child process is specified by the C<pid> argument (if set to C<0>, it |
261 | The child process is specified by the C<pid> argument (if set to C<0>, it |
253 | watches for any child process exit). The watcher will trigger as often |
262 | 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 |
263 | 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 |
264 | signal handler for C<SIGCHLD>. The callback will be called with the pid |
256 | and exit status (as returned by waitpid). |
265 | and exit status (as returned by waitpid), so unlike other watcher types, |
|
|
266 | you I<can> rely on child watcher callback arguments. |
257 | |
267 | |
258 | Example: wait for pid 1333 |
268 | There is a slight catch to child watchers, however: you usually start them |
|
|
269 | I<after> the child process was created, and this means the process could |
|
|
270 | have exited already (and no SIGCHLD will be sent anymore). |
|
|
271 | |
|
|
272 | Not all event models handle this correctly (POE doesn't), but even for |
|
|
273 | event models that I<do> handle this correctly, they usually need to be |
|
|
274 | loaded before the process exits (i.e. before you fork in the first place). |
|
|
275 | |
|
|
276 | This means you cannot create a child watcher as the very first thing in an |
|
|
277 | AnyEvent program, you I<have> to create at least one watcher before you |
|
|
278 | C<fork> the child (alternatively, you can call C<AnyEvent::detect>). |
|
|
279 | |
|
|
280 | Example: fork a process and wait for it |
|
|
281 | |
|
|
282 | my $done = AnyEvent->condvar; |
|
|
283 | |
|
|
284 | AnyEvent::detect; # force event module to be initialised |
|
|
285 | |
|
|
286 | my $pid = fork or exit 5; |
259 | |
287 | |
260 | my $w = AnyEvent->child ( |
288 | my $w = AnyEvent->child ( |
261 | pid => 1333, |
289 | pid => $pid, |
262 | cb => sub { |
290 | cb => sub { |
263 | my ($pid, $status) = @_; |
291 | my ($pid, $status) = @_; |
264 | warn "pid $pid exited with status $status"; |
292 | warn "pid $pid exited with status $status"; |
|
|
293 | $done->broadcast; |
265 | }, |
294 | }, |
266 | ); |
295 | ); |
|
|
296 | |
|
|
297 | # do something else, then wait for process exit |
|
|
298 | $done->wait; |
267 | |
299 | |
268 | =head2 CONDITION VARIABLES |
300 | =head2 CONDITION VARIABLES |
269 | |
301 | |
270 | Condition variables can be created by calling the C<< AnyEvent->condvar >> |
302 | Condition variables can be created by calling the C<< AnyEvent->condvar >> |
271 | method without any arguments. |
303 | method without any arguments. |
… | |
… | |
359 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
391 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
360 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
392 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
361 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
393 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
362 | AnyEvent::Impl::Event based on Event, second best choice. |
394 | AnyEvent::Impl::Event based on Event, second best choice. |
363 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
395 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
|
|
396 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
364 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
397 | 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). |
398 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
367 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
399 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
368 | AnyEvent::Impl::POE based on POE, not generic enough for full support. |
400 | AnyEvent::Impl::POE based on POE, not generic enough for full support. |
369 | |
401 | |
370 | There is no support for WxWidgets, as WxWidgets has no support for |
402 | There is no support for WxWidgets, as WxWidgets has no support for |
… | |
… | |
424 | might chose the wrong one unless you load the correct one yourself. |
456 | might chose the wrong one unless you load the correct one yourself. |
425 | |
457 | |
426 | You can chose to use a rather inefficient pure-perl implementation by |
458 | You can chose to use a rather inefficient pure-perl implementation by |
427 | loading the C<AnyEvent::Impl::Perl> module, which gives you similar |
459 | loading the C<AnyEvent::Impl::Perl> module, which gives you similar |
428 | behaviour everywhere, but letting AnyEvent chose is generally better. |
460 | behaviour everywhere, but letting AnyEvent chose is generally better. |
|
|
461 | |
|
|
462 | =head1 OTHER MODULES |
|
|
463 | |
|
|
464 | The following is a non-exhaustive list of additional modules that use |
|
|
465 | AnyEvent and can therefore be mixed easily with other AnyEvent modules |
|
|
466 | in the same program. Some of the modules come with AnyEvent, some are |
|
|
467 | available via CPAN. |
|
|
468 | |
|
|
469 | =over 4 |
|
|
470 | |
|
|
471 | =item L<AnyEvent::Util> |
|
|
472 | |
|
|
473 | Contains various utility functions that replace often-used but blocking |
|
|
474 | functions such as C<inet_aton> by event-/callback-based versions. |
|
|
475 | |
|
|
476 | =item L<AnyEvent::Handle> |
|
|
477 | |
|
|
478 | Provide read and write buffers and manages watchers for reads and writes. |
|
|
479 | |
|
|
480 | =item L<AnyEvent::Socket> |
|
|
481 | |
|
|
482 | Provides a means to do non-blocking connects, accepts etc. |
|
|
483 | |
|
|
484 | =item L<AnyEvent::HTTPD> |
|
|
485 | |
|
|
486 | Provides a simple web application server framework. |
|
|
487 | |
|
|
488 | =item L<AnyEvent::DNS> |
|
|
489 | |
|
|
490 | Provides asynchronous DNS resolver capabilities, beyond what |
|
|
491 | L<AnyEvent::Util> offers. |
|
|
492 | |
|
|
493 | =item L<AnyEvent::FastPing> |
|
|
494 | |
|
|
495 | The fastest ping in the west. |
|
|
496 | |
|
|
497 | =item L<Net::IRC3> |
|
|
498 | |
|
|
499 | AnyEvent based IRC client module family. |
|
|
500 | |
|
|
501 | =item L<Net::XMPP2> |
|
|
502 | |
|
|
503 | AnyEvent based XMPP (Jabber protocol) module family. |
|
|
504 | |
|
|
505 | =item L<Net::FCP> |
|
|
506 | |
|
|
507 | AnyEvent-based implementation of the Freenet Client Protocol, birthplace |
|
|
508 | of AnyEvent. |
|
|
509 | |
|
|
510 | =item L<Event::ExecFlow> |
|
|
511 | |
|
|
512 | High level API for event-based execution flow control. |
|
|
513 | |
|
|
514 | =item L<Coro> |
|
|
515 | |
|
|
516 | Has special support for AnyEvent. |
|
|
517 | |
|
|
518 | =item L<IO::Lambda> |
|
|
519 | |
|
|
520 | The lambda approach to I/O - don't ask, look there. Can use AnyEvent. |
|
|
521 | |
|
|
522 | =item L<IO::AIO> |
|
|
523 | |
|
|
524 | Truly asynchronous I/O, should be in the toolbox of every event |
|
|
525 | programmer. Can be trivially made to use AnyEvent. |
|
|
526 | |
|
|
527 | =item L<BDB> |
|
|
528 | |
|
|
529 | Truly asynchronous Berkeley DB access. Can be trivially made to use |
|
|
530 | AnyEvent. |
|
|
531 | |
|
|
532 | =back |
429 | |
533 | |
430 | =cut |
534 | =cut |
431 | |
535 | |
432 | package AnyEvent; |
536 | package AnyEvent; |
433 | |
537 | |
… | |
… | |
706 | |
810 | |
707 | =back |
811 | =back |
708 | |
812 | |
709 | =head1 EXAMPLE PROGRAM |
813 | =head1 EXAMPLE PROGRAM |
710 | |
814 | |
711 | The following program uses an IO watcher to read data from STDIN, a timer |
815 | 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 |
816 | to display a message once per second, and a condition variable to quit the |
713 | program when the user enters quit: |
817 | program when the user enters quit: |
714 | |
818 | |
715 | use AnyEvent; |
819 | use AnyEvent; |
716 | |
820 | |
… | |
… | |
861 | }); |
965 | }); |
862 | |
966 | |
863 | $quit->wait; |
967 | $quit->wait; |
864 | |
968 | |
865 | |
969 | |
866 | =head1 BENCHMARK |
970 | =head1 BENCHMARKS |
867 | |
971 | |
868 | To give you an idea of the performance and overheads that AnyEvent adds |
972 | To give you an idea of the performance and overheads that AnyEvent adds |
869 | over the event loops themselves (and to give you an impression of the |
973 | over the event loops themselves and to give you an impression of the speed |
870 | speed of various event loops), here is a benchmark of various supported |
974 | of various event loops I prepared some benchmarks. |
871 | event models natively and with anyevent. The benchmark creates a lot of |
975 | |
872 | timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to |
976 | =head2 BENCHMARKING ANYEVENT OVERHEAD |
|
|
977 | |
|
|
978 | Here is a benchmark of various supported event models used natively and |
|
|
979 | through anyevent. The benchmark creates a lot of timers (with a zero |
|
|
980 | timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
873 | become writable, which it is), lets them fire exactly once and destroys |
981 | which it is), lets them fire exactly once and destroys them again. |
874 | them again. |
|
|
875 | |
982 | |
|
|
983 | Source code for this benchmark is found as F<eg/bench> in the AnyEvent |
|
|
984 | distribution. |
|
|
985 | |
876 | =head2 Explanation of the columns |
986 | =head3 Explanation of the columns |
877 | |
987 | |
878 | I<watcher> is the number of event watchers created/destroyed. Since |
988 | I<watcher> is the number of event watchers created/destroyed. Since |
879 | different event models feature vastly different performances, each event |
989 | different event models feature vastly different performances, each event |
880 | loop was given a number of watchers so that overall runtime is acceptable |
990 | loop was given a number of watchers so that overall runtime is acceptable |
881 | and similar between tested event loop (and keep them from crashing): Glib |
991 | and similar between tested event loop (and keep them from crashing): Glib |
… | |
… | |
897 | signal the end of this phase. |
1007 | signal the end of this phase. |
898 | |
1008 | |
899 | I<destroy> is the time, in microseconds, that it takes to destroy a single |
1009 | I<destroy> is the time, in microseconds, that it takes to destroy a single |
900 | watcher. |
1010 | watcher. |
901 | |
1011 | |
902 | =head2 Results |
1012 | =head3 Results |
903 | |
1013 | |
904 | name watcher bytes create invoke destroy comment |
1014 | name watchers bytes create invoke destroy comment |
905 | EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
1015 | EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
906 | EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers |
1016 | EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers |
907 | CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal |
1017 | CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal |
908 | Perl/Any 16000 654 4.64 1.22 0.77 pure perl implementation |
1018 | Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation |
909 | Event/Event 16000 523 28.05 21.38 0.86 Event native interface |
1019 | Event/Event 16000 516 31.88 31.30 0.85 Event native interface |
910 | Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers |
1020 | Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers |
911 | Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour |
1021 | Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour |
912 | Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers |
1022 | Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers |
913 | POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event |
1023 | POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event |
914 | POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select |
1024 | POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select |
915 | |
1025 | |
916 | =head2 Discussion |
1026 | =head3 Discussion |
917 | |
1027 | |
918 | The benchmark does I<not> measure scalability of the event loop very |
1028 | The benchmark does I<not> measure scalability of the event loop very |
919 | well. For example, a select-based event loop (such as the pure perl one) |
1029 | well. For example, a select-based event loop (such as the pure perl one) |
920 | can never compete with an event loop that uses epoll when the number of |
1030 | can never compete with an event loop that uses epoll when the number of |
921 | file descriptors grows high. In this benchmark, only a single filehandle |
1031 | file descriptors grows high. In this benchmark, all events become ready at |
922 | is used (although some of the AnyEvent adaptors dup() its file descriptor |
1032 | the same time, so select/poll-based implementations get an unnatural speed |
923 | to worka round bugs). |
1033 | boost. |
|
|
1034 | |
|
|
1035 | Also, note that the number of watchers usually has a nonlinear effect on |
|
|
1036 | overall speed, that is, creating twice as many watchers doesn't take twice |
|
|
1037 | the time - usually it takes longer. This puts event loops tested with a |
|
|
1038 | higher number of watchers at a disadvantage. |
|
|
1039 | |
|
|
1040 | To put the range of results into perspective, consider that on the |
|
|
1041 | benchmark machine, handling an event takes roughly 1600 CPU cycles with |
|
|
1042 | EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU |
|
|
1043 | cycles with POE. |
924 | |
1044 | |
925 | C<EV> is the sole leader regarding speed and memory use, which are both |
1045 | C<EV> is the sole leader regarding speed and memory use, which are both |
926 | maximal/minimal, respectively. Even when going through AnyEvent, there is |
1046 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
927 | only one event loop that uses less memory (the C<Event> module natively), and |
1047 | far less memory than any other event loop and is still faster than Event |
928 | no faster event model, not event C<Event> natively. |
1048 | natively. |
929 | |
1049 | |
930 | The pure perl implementation is hit in a few sweet spots (both the |
1050 | The pure perl implementation is hit in a few sweet spots (both the |
931 | zero timeout and the use of a single fd hit optimisations in the perl |
1051 | constant timeout and the use of a single fd hit optimisations in the perl |
932 | interpreter and the backend itself). Nevertheless tis shows that it |
1052 | interpreter and the backend itself). Nevertheless this shows that it |
933 | adds very little overhead in itself. Like any select-based backend its |
1053 | adds very little overhead in itself. Like any select-based backend its |
934 | performance becomes really bad with lots of file descriptors, of course, |
1054 | performance becomes really bad with lots of file descriptors (and few of |
935 | but this was not subjetc of this benchmark. |
1055 | them active), of course, but this was not subject of this benchmark. |
936 | |
1056 | |
937 | The C<Event> module has a relatively high setup and callback invocation cost, |
1057 | The C<Event> module has a relatively high setup and callback invocation |
938 | but overall scores on the third place. |
1058 | cost, but overall scores in on the third place. |
939 | |
1059 | |
940 | C<Glib>'s memory usage is quite a bit bit higher, features a faster |
1060 | C<Glib>'s memory usage is quite a bit higher, but it features a |
941 | callback invocation and overall lands in the same class as C<Event>. |
1061 | faster callback invocation and overall ends up in the same class as |
|
|
1062 | C<Event>. However, Glib scales extremely badly, doubling the number of |
|
|
1063 | watchers increases the processing time by more than a factor of four, |
|
|
1064 | making it completely unusable when using larger numbers of watchers |
|
|
1065 | (note that only a single file descriptor was used in the benchmark, so |
|
|
1066 | inefficiencies of C<poll> do not account for this). |
942 | |
1067 | |
943 | The C<Tk> adaptor works relatively well, the fact that it crashes with |
1068 | The C<Tk> adaptor works relatively well. The fact that it crashes with |
944 | more than 2000 watchers is a big setback, however, as correctness takes |
1069 | more than 2000 watchers is a big setback, however, as correctness takes |
945 | precedence over speed. Nevertheless, its performance is surprising, as the |
1070 | precedence over speed. Nevertheless, its performance is surprising, as the |
946 | file descriptor is dup()ed for each watcher. This shows that the dup() |
1071 | file descriptor is dup()ed for each watcher. This shows that the dup() |
947 | employed by some adaptors is not a big performance issue (it does incur a |
1072 | employed by some adaptors is not a big performance issue (it does incur a |
948 | hidden memory cost inside the kernel, though). |
1073 | hidden memory cost inside the kernel which is not reflected in the figures |
|
|
1074 | above). |
949 | |
1075 | |
950 | C<POE>, regardless of backend (wether using its pure perl select-based |
1076 | C<POE>, regardless of underlying event loop (whether using its pure perl |
951 | backend or the Event backend) shows abysmal performance and memory |
1077 | select-based backend or the Event module, the POE-EV backend couldn't |
952 | usage: Watchers use almost 30 times as much memory as EV watchers, and 10 |
1078 | be tested because it wasn't working) shows abysmal performance and |
953 | times as much memory as both Event or EV via AnyEvent. Watcher invocation |
1079 | memory usage with AnyEvent: Watchers use almost 30 times as much memory |
954 | is almost 700 times slower as with AnyEvent's pure perl implementation. |
1080 | as EV watchers, and 10 times as much memory as Event (the high memory |
|
|
1081 | requirements are caused by requiring a session for each watcher). Watcher |
|
|
1082 | invocation speed is almost 900 times slower than with AnyEvent's pure perl |
|
|
1083 | implementation. |
955 | |
1084 | |
|
|
1085 | The design of the POE adaptor class in AnyEvent can not really account |
|
|
1086 | for the performance issues, though, as session creation overhead is |
|
|
1087 | small compared to execution of the state machine, which is coded pretty |
|
|
1088 | optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that |
|
|
1089 | using multiple sessions is not a good approach, especially regarding |
|
|
1090 | memory usage, even the author of POE could not come up with a faster |
|
|
1091 | design). |
|
|
1092 | |
|
|
1093 | =head3 Summary |
|
|
1094 | |
|
|
1095 | =over 4 |
|
|
1096 | |
956 | Summary: using EV through AnyEvent is faster than any other event |
1097 | =item * Using EV through AnyEvent is faster than any other event loop |
957 | loop. The overhead AnyEvent adds can be very small, and you should avoid |
1098 | (even when used without AnyEvent), but most event loops have acceptable |
958 | POE like the plague if you want performance or reasonable memory usage. |
1099 | performance with or without AnyEvent. |
|
|
1100 | |
|
|
1101 | =item * The overhead AnyEvent adds is usually much smaller than the overhead of |
|
|
1102 | the actual event loop, only with extremely fast event loops such as EV |
|
|
1103 | adds AnyEvent significant overhead. |
|
|
1104 | |
|
|
1105 | =item * You should avoid POE like the plague if you want performance or |
|
|
1106 | reasonable memory usage. |
|
|
1107 | |
|
|
1108 | =back |
|
|
1109 | |
|
|
1110 | =head2 BENCHMARKING THE LARGE SERVER CASE |
|
|
1111 | |
|
|
1112 | This benchmark atcually benchmarks the event loop itself. It works by |
|
|
1113 | creating a number of "servers": each server consists of a socketpair, a |
|
|
1114 | timeout watcher that gets reset on activity (but never fires), and an I/O |
|
|
1115 | watcher waiting for input on one side of the socket. Each time the socket |
|
|
1116 | watcher reads a byte it will write that byte to a random other "server". |
|
|
1117 | |
|
|
1118 | The effect is that there will be a lot of I/O watchers, only part of which |
|
|
1119 | are active at any one point (so there is a constant number of active |
|
|
1120 | fds for each loop iterstaion, but which fds these are is random). The |
|
|
1121 | timeout is reset each time something is read because that reflects how |
|
|
1122 | most timeouts work (and puts extra pressure on the event loops). |
|
|
1123 | |
|
|
1124 | In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100 |
|
|
1125 | (1%) are active. This mirrors the activity of large servers with many |
|
|
1126 | connections, most of which are idle at any one point in time. |
|
|
1127 | |
|
|
1128 | Source code for this benchmark is found as F<eg/bench2> in the AnyEvent |
|
|
1129 | distribution. |
|
|
1130 | |
|
|
1131 | =head3 Explanation of the columns |
|
|
1132 | |
|
|
1133 | I<sockets> is the number of sockets, and twice the number of "servers" (as |
|
|
1134 | each server has a read and write socket end). |
|
|
1135 | |
|
|
1136 | I<create> is the time it takes to create a socketpair (which is |
|
|
1137 | nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
|
|
1138 | |
|
|
1139 | I<request>, the most important value, is the time it takes to handle a |
|
|
1140 | single "request", that is, reading the token from the pipe and forwarding |
|
|
1141 | it to another server. This includes deleting the old timeout and creating |
|
|
1142 | a new one that moves the timeout into the future. |
|
|
1143 | |
|
|
1144 | =head3 Results |
|
|
1145 | |
|
|
1146 | name sockets create request |
|
|
1147 | EV 20000 69.01 11.16 |
|
|
1148 | Perl 20000 73.32 35.87 |
|
|
1149 | Event 20000 212.62 257.32 |
|
|
1150 | Glib 20000 651.16 1896.30 |
|
|
1151 | POE 20000 349.67 12317.24 uses POE::Loop::Event |
|
|
1152 | |
|
|
1153 | =head3 Discussion |
|
|
1154 | |
|
|
1155 | This benchmark I<does> measure scalability and overall performance of the |
|
|
1156 | particular event loop. |
|
|
1157 | |
|
|
1158 | EV is again fastest. Since it is using epoll on my system, the setup time |
|
|
1159 | is relatively high, though. |
|
|
1160 | |
|
|
1161 | Perl surprisingly comes second. It is much faster than the C-based event |
|
|
1162 | loops Event and Glib. |
|
|
1163 | |
|
|
1164 | Event suffers from high setup time as well (look at its code and you will |
|
|
1165 | understand why). Callback invocation also has a high overhead compared to |
|
|
1166 | the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event |
|
|
1167 | uses select or poll in basically all documented configurations. |
|
|
1168 | |
|
|
1169 | Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
|
|
1170 | clearly fails to perform with many filehandles or in busy servers. |
|
|
1171 | |
|
|
1172 | POE is still completely out of the picture, taking over 1000 times as long |
|
|
1173 | as EV, and over 100 times as long as the Perl implementation, even though |
|
|
1174 | it uses a C-based event loop in this case. |
|
|
1175 | |
|
|
1176 | =head3 Summary |
|
|
1177 | |
|
|
1178 | =over 4 |
|
|
1179 | |
|
|
1180 | =item * The pure perl implementation performs extremely well. |
|
|
1181 | |
|
|
1182 | =item * Avoid Glib or POE in large projects where performance matters. |
|
|
1183 | |
|
|
1184 | =back |
|
|
1185 | |
|
|
1186 | =head2 BENCHMARKING SMALL SERVERS |
|
|
1187 | |
|
|
1188 | While event loops should scale (and select-based ones do not...) even to |
|
|
1189 | large servers, most programs we (or I :) actually write have only a few |
|
|
1190 | I/O watchers. |
|
|
1191 | |
|
|
1192 | In this benchmark, I use the same benchmark program as in the large server |
|
|
1193 | case, but it uses only eight "servers", of which three are active at any |
|
|
1194 | one time. This should reflect performance for a small server relatively |
|
|
1195 | well. |
|
|
1196 | |
|
|
1197 | The columns are identical to the previous table. |
|
|
1198 | |
|
|
1199 | =head3 Results |
|
|
1200 | |
|
|
1201 | name sockets create request |
|
|
1202 | EV 16 20.00 6.54 |
|
|
1203 | Perl 16 25.75 12.62 |
|
|
1204 | Event 16 81.27 35.86 |
|
|
1205 | Glib 16 32.63 15.48 |
|
|
1206 | POE 16 261.87 276.28 uses POE::Loop::Event |
|
|
1207 | |
|
|
1208 | =head3 Discussion |
|
|
1209 | |
|
|
1210 | The benchmark tries to test the performance of a typical small |
|
|
1211 | server. While knowing how various event loops perform is interesting, keep |
|
|
1212 | in mind that their overhead in this case is usually not as important, due |
|
|
1213 | to the small absolute number of watchers (that is, you need efficiency and |
|
|
1214 | speed most when you have lots of watchers, not when you only have a few of |
|
|
1215 | them). |
|
|
1216 | |
|
|
1217 | EV is again fastest. |
|
|
1218 | |
|
|
1219 | Perl again comes second. It is noticably faster than the C-based event |
|
|
1220 | loops Event and Glib, although the difference is too small to really |
|
|
1221 | matter. |
|
|
1222 | |
|
|
1223 | POE also performs much better in this case, but is is still far behind the |
|
|
1224 | others. |
|
|
1225 | |
|
|
1226 | =head3 Summary |
|
|
1227 | |
|
|
1228 | =over 4 |
|
|
1229 | |
|
|
1230 | =item * C-based event loops perform very well with small number of |
|
|
1231 | watchers, as the management overhead dominates. |
|
|
1232 | |
|
|
1233 | =back |
959 | |
1234 | |
960 | |
1235 | |
961 | =head1 FORK |
1236 | =head1 FORK |
962 | |
1237 | |
963 | Most event libraries are not fork-safe. The ones who are usually are |
1238 | Most event libraries are not fork-safe. The ones who are usually are |