[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.83 by root, Fri Apr 25 13:39:08 2008 UTC vs.
Revision 1.99 by root, Sun Apr 27 17:09:33 2008 UTC

…		…
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	#TODO#
		72
		73	Net::IRC3
		74	AnyEvent::HTTPD
		75	AnyEvent::DNS
		76	IO::AnyEvent
		77	Net::FPing
		78	Net::XMPP2
		79	Coro
		80
		81	AnyEvent::IRC
		82	AnyEvent::HTTPD
		83	AnyEvent::DNS
		84	AnyEvent::Handle
		85	AnyEvent::Socket
		86	AnyEvent::FPing
		87	AnyEvent::XMPP
		88	AnyEvent::SNMP
		89	Coro
71		90
72	=head1 DESCRIPTION	91	=head1 DESCRIPTION
73		92
74	L<AnyEvent> provides an identical interface to multiple event loops. This	93	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	94	allows module authors to utilise an event loop without forcing module
…		…
141	=head2 I/O WATCHERS	160	=head2 I/O WATCHERS
142		161
143	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	162	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144	with the following mandatory key-value pairs as arguments:	163	with the following mandatory key-value pairs as arguments:
145		164
146	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	165	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	166	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,	167	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	168	respectively. C<cb> is the callback to invoke each time the file handle
150	becomes ready.	169	becomes ready.
151		170
		171	Although the callback might get passed parameters, their value and
		172	presence is undefined and you cannot rely on them. Portable AnyEvent
		173	callbacks cannot use arguments passed to I/O watcher callbacks.
		174
152	The I/O watcher might use the underlying file descriptor or a copy of it.	175	The I/O watcher might use the underlying file descriptor or a copy of it.
153	It is not allowed to close a file handle as long as any watcher is active	176	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	177	underlying file descriptor.
155		178
156	Some event loops issue spurious readyness notifications, so you should	179	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	180	always use non-blocking calls when reading/writing from/to your file
158	handles.	181	handles.
159		182
…		…
170		193
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	194	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	195	method with the following mandatory arguments:
173		196
174	C<after> specifies after how many seconds (fractional values are	197	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	198	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	199	in that case.
		200
		201	Although the callback might get passed parameters, their value and
		202	presence is undefined and you cannot rely on them. Portable AnyEvent
		203	callbacks cannot use arguments passed to time watcher callbacks.
177		204
178	The timer callback will be invoked at most once: if you want a repeating	205	The timer callback will be invoked at most once: if you want a repeating
179	timer you have to create a new watcher (this is a limitation by both Tk	206	timer you have to create a new watcher (this is a limitation by both Tk
180	and Glib).	207	and Glib).
181		208
…		…
226		253
227	You can watch for signals using a signal watcher, C<signal> is the signal	254	You can watch for signals using a signal watcher, C<signal> is the signal
228	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	255	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
229	be invoked whenever a signal occurs.	256	be invoked whenever a signal occurs.
230		257
		258	Although the callback might get passed parameters, their value and
		259	presence is undefined and you cannot rely on them. Portable AnyEvent
		260	callbacks cannot use arguments passed to signal watcher callbacks.
		261
231	Multiple signal occurances can be clumped together into one callback	262	Multiple signal occurances can be clumped together into one callback
232	invocation, and callback invocation will be synchronous. synchronous means	263	invocation, and callback invocation will be synchronous. synchronous means
233	that it might take a while until the signal gets handled by the process,	264	that it might take a while until the signal gets handled by the process,
234	but it is guarenteed not to interrupt any other callbacks.	265	but it is guarenteed not to interrupt any other callbacks.
235		266
…		…
249		280
250	The child process is specified by the C<pid> argument (if set to C<0>, it	281	The child process is specified by the C<pid> argument (if set to C<0>, it
251	watches for any child process exit). The watcher will trigger as often	282	watches for any child process exit). The watcher will trigger as often
252	as status change for the child are received. This works by installing a	283	as status change for the child are received. This works by installing a
253	signal handler for C<SIGCHLD>. The callback will be called with the pid	284	signal handler for C<SIGCHLD>. The callback will be called with the pid
254	and exit status (as returned by waitpid).	285	and exit status (as returned by waitpid), so unlike other watcher types,
		286	you I<can> rely on child watcher callback arguments.
255		287
256	There is a slight catch to child watchers, however: you usually start them	288	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	289	I<after> the child process was created, and this means the process could
258	have exited already (and no SIGCHLD will be sent anymore).	290	have exited already (and no SIGCHLD will be sent anymore).
259		291
…		…
881	});	913	});
882		914
883	$quit->wait;	915	$quit->wait;
884		916
885		917
886	=head1 BENCHMARK	918	=head1 BENCHMARKS
887		919
888	To give you an idea of the performance and overheads that AnyEvent adds	920	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	921	over the event loops themselves and to give you an impression of the speed
890	speed of various event loops), here is a benchmark of various supported	922	of various event loops I prepared some benchmarks.
891	event models natively and with anyevent. The benchmark creates a lot of	923
892	timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to	924	=head2 BENCHMARKING ANYEVENT OVERHEAD
		925
		926	Here is a benchmark of various supported event models used natively and
		927	through anyevent. The benchmark creates a lot of timers (with a zero
		928	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
893	become writable, which it is), lets them fire exactly once and destroys	929	which it is), lets them fire exactly once and destroys them again.
894	them again.
895		930
896	Rewriting the benchmark to use many different sockets instead of using	931	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
897	the same filehandle for all I/O watchers results in a much longer runtime	932	distribution.
898	(socket creation is expensive), but qualitatively the same figures, so it
899	was not used.
900		933
901	=head2 Explanation of the columns	934	=head3 Explanation of the columns
902		935
903	I<watcher> is the number of event watchers created/destroyed. Since	936	I<watcher> is the number of event watchers created/destroyed. Since
904	different event models feature vastly different performances, each event	937	different event models feature vastly different performances, each event
905	loop was given a number of watchers so that overall runtime is acceptable	938	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	939	and similar between tested event loop (and keep them from crashing): Glib
…		…
922	signal the end of this phase.	955	signal the end of this phase.
923		956
924	I<destroy> is the time, in microseconds, that it takes to destroy a single	957	I<destroy> is the time, in microseconds, that it takes to destroy a single
925	watcher.	958	watcher.
926		959
927	=head2 Results	960	=head3 Results
928		961
929	name watchers bytes create invoke destroy comment	962	name watchers bytes create invoke destroy comment
930	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	963	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
931	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	964	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
932	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	965	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
933	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	966	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
934	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	967	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
935	Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers	968	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
936	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	969	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
937	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	970	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
938	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	971	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
939	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	972	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
940		973
941	=head2 Discussion	974	=head3 Discussion
942		975
943	The benchmark does I<not> measure scalability of the event loop very	976	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)	977	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	978	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	979	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	980	the same time, so select/poll-based implementations get an unnatural speed
948	boost.	981	boost.
949		982
		983	Also, note that the number of watchers usually has a nonlinear effect on
		984	overall speed, that is, creating twice as many watchers doesn't take twice
		985	the time - usually it takes longer. This puts event loops tested with a
		986	higher number of watchers at a disadvantage.
		987
		988	To put the range of results into perspective, consider that on the
		989	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		990	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		991	cycles with POE.
		992
950	C<EV> is the sole leader regarding speed and memory use, which are both	993	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	994	maximal/minimal, respectively. Even when going through AnyEvent, it uses
952	only two event loops that use slightly less memory (the C<Event> module	995	far less memory than any other event loop and is still faster than Event
953	natively and the pure perl backend), and no faster event models, not even	996	natively.
954	C<Event> natively.
955		997
956	The pure perl implementation is hit in a few sweet spots (both the	998	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	999	constant 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	1000	interpreter and the backend itself). Nevertheless this shows that it
959	same time). Nevertheless this shows that it adds very little overhead in	1001	adds very little overhead in itself. Like any select-based backend its
960	itself. Like any select-based backend its performance becomes really bad	1002	performance becomes really bad with lots of file descriptors (and few of
961	with lots of file descriptors (and few of them active), of course, but	1003	them active), of course, but this was not subject of this benchmark.
962	this was not subject of this benchmark.
963		1004
964	The C<Event> module has a relatively high setup and callback invocation cost,	1005	The C<Event> module has a relatively high setup and callback invocation
965	but overall scores on the third place.	1006	cost, but overall scores in on the third place.
966		1007
967	C<Glib>'s memory usage is quite a bit bit higher, but it features a	1008	C<Glib>'s memory usage is quite a bit higher, but it features a
968	faster callback invocation and overall ends up in the same class as	1009	faster callback invocation and overall ends up in the same class as
969	C<Event>. However, Glib scales extremely badly, doubling the number of	1010	C<Event>. However, Glib scales extremely badly, doubling the number of
970	watchers increases the processing time by more than a factor of four,	1011	watchers increases the processing time by more than a factor of four,
971	making it completely unusable when using larger numbers of watchers	1012	making it completely unusable when using larger numbers of watchers
972	(note that only a single file descriptor was used in the benchmark, so	1013	(note that only a single file descriptor was used in the benchmark, so
…		…
975	The C<Tk> adaptor works relatively well. The fact that it crashes with	1016	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	1017	more than 2000 watchers is a big setback, however, as correctness takes
977	precedence over speed. Nevertheless, its performance is surprising, as the	1018	precedence over speed. Nevertheless, its performance is surprising, as the
978	file descriptor is dup()ed for each watcher. This shows that the dup()	1019	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	1020	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	1021	hidden memory cost inside the kernel which is not reflected in the figures
981	figures above).	1022	above).
982		1023
983	C<POE>, regardless of underlying event loop (wether using its pure perl	1024	C<POE>, regardless of underlying event loop (whether using its pure
984	select-based backend or the Event module) shows abysmal performance and	1025	perl select-based backend or the Event module, the POE-EV backend
		1026	couldn't be tested because it wasn't working) shows abysmal performance
985	memory usage: Watchers use almost 30 times as much memory as EV watchers,	1027	and memory usage: Watchers use almost 30 times as much memory as
986	and 10 times as much memory as both Event or EV via AnyEvent. Watcher	1028	EV watchers, and 10 times as much memory as Event (the high memory
		1029	requirements are caused by requiring a session for each watcher). Watcher
987	invocation is almost 900 times slower than with AnyEvent's pure perl	1030	invocation speed is almost 900 times slower than with AnyEvent's pure perl
988	implementation. The design of the POE adaptor class in AnyEvent can not	1031	implementation. The design of the POE adaptor class in AnyEvent can not
989	really account for this, as session creation overhead is small compared	1032	really account for this, as session creation overhead is small compared
990	to execution of the state machine, which is coded pretty optimally within	1033	to execution of the state machine, which is coded pretty optimally within
991	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.	1034	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
992		1035
993	=head2 Summary	1036	=head3 Summary
994		1037
		1038	=over 4
		1039
995	Using EV through AnyEvent is faster than any other event loop, but most	1040	=item * Using EV through AnyEvent is faster than any other event loop
996	event loops have acceptable performance with or without AnyEvent.	1041	(even when used without AnyEvent), but most event loops have acceptable
		1042	performance with or without AnyEvent.
997		1043
998	The overhead AnyEvent adds is usually much smaller than the overhead of	1044	=item * 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	1045	the actual event loop, only with extremely fast event loops such as EV
1000	adds AnyEvent significant overhead.	1046	adds AnyEvent significant overhead.
1001		1047
1002	And you should simply avoid POE like the plague if you want performance or	1048	=item * You should avoid POE like the plague if you want performance or
1003	reasonable memory usage.	1049	reasonable memory usage.
		1050
		1051	=back
		1052
		1053	=head2 BENCHMARKING THE LARGE SERVER CASE
		1054
		1055	This benchmark atcually benchmarks the event loop itself. It works by
		1056	creating a number of "servers": each server consists of a socketpair, a
		1057	timeout watcher that gets reset on activity (but never fires), and an I/O
		1058	watcher waiting for input on one side of the socket. Each time the socket
		1059	watcher reads a byte it will write that byte to a random other "server".
		1060
		1061	The effect is that there will be a lot of I/O watchers, only part of which
		1062	are active at any one point (so there is a constant number of active
		1063	fds for each loop iterstaion, but which fds these are is random). The
		1064	timeout is reset each time something is read because that reflects how
		1065	most timeouts work (and puts extra pressure on the event loops).
		1066
		1067	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1068	(1%) are active. This mirrors the activity of large servers with many
		1069	connections, most of which are idle at any one point in time.
		1070
		1071	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1072	distribution.
		1073
		1074	=head3 Explanation of the columns
		1075
		1076	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1077	each server has a read and write socket end).
		1078
		1079	I<create> is the time it takes to create a socketpair (which is
		1080	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1081
		1082	I<request>, the most important value, is the time it takes to handle a
		1083	single "request", that is, reading the token from the pipe and forwarding
		1084	it to another server. This includes deleting the old timeout and creating
		1085	a new one that moves the timeout into the future.
		1086
		1087	=head3 Results
		1088
		1089	name sockets create request
		1090	EV 20000 69.01 11.16
		1091	Perl 20000 73.32 35.87
		1092	Event 20000 212.62 257.32
		1093	Glib 20000 651.16 1896.30
		1094	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1095
		1096	=head3 Discussion
		1097
		1098	This benchmark I<does> measure scalability and overall performance of the
		1099	particular event loop.
		1100
		1101	EV is again fastest. Since it is using epoll on my system, the setup time
		1102	is relatively high, though.
		1103
		1104	Perl surprisingly comes second. It is much faster than the C-based event
		1105	loops Event and Glib.
		1106
		1107	Event suffers from high setup time as well (look at its code and you will
		1108	understand why). Callback invocation also has a high overhead compared to
		1109	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1110	uses select or poll in basically all documented configurations.
		1111
		1112	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1113	clearly fails to perform with many filehandles or in busy servers.
		1114
		1115	POE is still completely out of the picture, taking over 1000 times as long
		1116	as EV, and over 100 times as long as the Perl implementation, even though
		1117	it uses a C-based event loop in this case.
		1118
		1119	=head3 Summary
		1120
		1121	=over 4
		1122
		1123	=item * The pure perl implementation performs extremely well, considering
		1124	that it uses select.
		1125
		1126	=item * Avoid Glib or POE in large projects where performance matters.
		1127
		1128	=back
		1129
		1130	=head2 BENCHMARKING SMALL SERVERS
		1131
		1132	While event loops should scale (and select-based ones do not...) even to
		1133	large servers, most programs we (or I :) actually write have only a few
		1134	I/O watchers.
		1135
		1136	In this benchmark, I use the same benchmark program as in the large server
		1137	case, but it uses only eight "servers", of which three are active at any
		1138	one time. This should reflect performance for a small server relatively
		1139	well.
		1140
		1141	The columns are identical to the previous table.
		1142
		1143	=head3 Results
		1144
		1145	name sockets create request
		1146	EV 16 20.00 6.54
		1147	Perl 16 25.75 12.62
		1148	Event 16 81.27 35.86
		1149	Glib 16 32.63 15.48
		1150	POE 16 261.87 276.28 uses POE::Loop::Event
		1151
		1152	=head3 Discussion
		1153
		1154	The benchmark tries to test the performance of a typical small
		1155	server. While knowing how various event loops perform is interesting, keep
		1156	in mind that their overhead in this case is usually not as important, due
		1157	to the small absolute number of watchers (that is, you need efficiency and
		1158	speed most when you have lots of watchers, not when you only have a few of
		1159	them).
		1160
		1161	EV is again fastest.
		1162
		1163	The C-based event loops Event and Glib come in second this time, as the
		1164	overhead of running an iteration is much smaller in C than in Perl (little
		1165	code to execute in the inner loop, and perl's function calling overhead is
		1166	high, and updating all the data structures is costly).
		1167
		1168	The pure perl event loop is much slower, but still competitive.
		1169
		1170	POE also performs much better in this case, but is is still far behind the
		1171	others.
		1172
		1173	=head3 Summary
		1174
		1175	=over 4
		1176
		1177	=item * C-based event loops perform very well with small number of
		1178	watchers, as the management overhead dominates.
		1179
		1180	=back
1004		1181
1005		1182
1006	=head1 FORK	1183	=head1 FORK
1007		1184
1008	Most event libraries are not fork-safe. The ones who are usually are	1185	Most event libraries are not fork-safe. The ones who are usually are

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.83 by root, Fri Apr 25 13:39:08 2008 UTC vs. Revision 1.99 by root, Sun Apr 27 17:09:33 2008 UTC

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.83 by root, Fri Apr 25 13:39:08 2008 UTC vs.
Revision 1.99 by root, Sun Apr 27 17:09:33 2008 UTC