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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.82 by root, Fri Apr 25 13:32:39 2008 UTC vs.
Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC

…		…
65	technically possible.	65	technically possible.
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
71		70
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
…		…
141	=head2 I/O 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
		151	Although the callback might get passed parameters, their value and
		152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
		154
152	The I/O watcher might use the underlying file descriptor or a copy of it.	155	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	156	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	157	underlying file descriptor.
155		158
156	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
157	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
158	handles.	161	handles.
159		162
…		…
170		173
171	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 >>
172	method with the following mandatory arguments:	175	method with the following mandatory arguments:
173		176
174	C<after> specifies after how many seconds (fractional values are	177	C<after> specifies after how many seconds (fractional values are
175	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
176	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.
177		184
178	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
179	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
180	and Glib).	187	and Glib).
181		188
…		…
226		233
227	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
228	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
229	be invoked whenever a signal occurs.	236	be invoked whenever a signal occurs.
230		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
231	Multiple signal occurances can be clumped together into one callback	242	Multiple signal occurances can be clumped together into one callback
232	invocation, and callback invocation will be synchronous. synchronous means	243	invocation, and callback invocation will be synchronous. synchronous means
233	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,
234	but it is guarenteed not to interrupt any other callbacks.	245	but it is guarenteed not to interrupt any other callbacks.
235		246
…		…
249		260
250	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
251	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
252	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
253	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
254	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.
255		267
256	There is a slight catch to child watchers, however: you usually start them	268	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	269	I<after> the child process was created, and this means the process could
258	have exited already (and no SIGCHLD will be sent anymore).	270	have exited already (and no SIGCHLD will be sent anymore).
259		271
…		…
444	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.
445		457
446	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
447	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	459	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
448	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
449		533
450	=cut	534	=cut
451		535
452	package AnyEvent;	536	package AnyEvent;
453		537
…		…
881	});	965	});
882		966
883	$quit->wait;	967	$quit->wait;
884		968
885		969
886	=head1 BENCHMARK	970	=head1 BENCHMARKS
887		971
888	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
889	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
890	speed of various event loops), here is a benchmark of various supported	974	of various event loops I prepared some benchmarks.
891	event models natively and with anyevent. The benchmark creates a lot of	975
892	timers (with a zero timeout) and I/O 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,
893	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.
894	them again.
895		982
896	Rewriting the benchmark to use many different sockets instead of using	983	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	984	distribution.
898	(socket creation is expensive), but qualitatively the same figures, so it
899	was not used.
900		985
901	=head2 Explanation of the columns	986	=head3 Explanation of the columns
902		987
903	I<watcher> is the number of event watchers created/destroyed. Since	988	I<watcher> is the number of event watchers created/destroyed. Since
904	different event models feature vastly different performances, each event	989	different event models feature vastly different performances, each event
905	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
906	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
…		…
922	signal the end of this phase.	1007	signal the end of this phase.
923		1008
924	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
925	watcher.	1010	watcher.
926		1011
927	=head2 Results	1012	=head3 Results
928		1013
929	name watchers bytes create invoke destroy comment	1014	name watchers bytes create invoke destroy comment
930	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
931	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
932	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
933	Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation	1018	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
934	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
935	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
936	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
937	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
938	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
939	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
940		1025
941	=head2 Discussion	1026	=head3 Discussion
942		1027
943	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
944	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)
945	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
946	file descriptors grows high. In this benchmark, all events become ready at	1031	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	1032	the same time, so select/poll-based implementations get an unnatural speed
948	boost.	1033	boost.
949		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.
		1044
950	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
951	maximal/minimal, respectively. Even when going through AnyEvent, there are	1046	maximal/minimal, respectively. Even when going through AnyEvent, it uses
952	only two event loops that use slightly less memory (the C<Event> module	1047	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	1048	natively.
954	C<Event> natively.
955		1049
956	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
957	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
958	interpreter and the backend itself, and all watchers become ready at the	1052	interpreter and the backend itself). Nevertheless this shows that it
959	same time). Nevertheless this shows that it adds very little overhead in	1053	adds very little overhead in itself. Like any select-based backend its
960	itself. Like any select-based backend its performance becomes really bad	1054	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	1055	them active), of course, but this was not subject of this benchmark.
962	this was not subject of this benchmark.
963		1056
964	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
965	but overall scores on the third place.	1058	cost, but overall scores in on the third place.
966		1059
967	C<Glib>'s memory usage is quite a bit bit higher, but it features a	1060	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	1061	faster callback invocation and overall ends up in the same class as
969	C<Event>. However, Glib scales extremely badly, doubling the number of	1062	C<Event>. However, Glib scales extremely badly, doubling the number of
970	watchers increases the processing time by more than a factor of four,	1063	watchers increases the processing time by more than a factor of four,
971	making it completely unusable when using larger numbers of watchers	1064	making it completely unusable when using larger numbers of watchers
972	(note that only a single file descriptor was used in the benchmark, so	1065	(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	1068	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	1069	more than 2000 watchers is a big setback, however, as correctness takes
977	precedence over speed. Nevertheless, its performance is surprising, as the	1070	precedence over speed. Nevertheless, its performance is surprising, as the
978	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()
979	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
980	hidden memory cost inside the kernel, though, that is not reflected in the	1073	hidden memory cost inside the kernel which is not reflected in the figures
981	figures above).	1074	above).
982		1075
983	C<POE>, regardless of underlying event loop (wether using its pure perl	1076	C<POE>, regardless of underlying event loop (whether using its pure
984	select-based backend or the Event module) shows abysmal performance and	1077	perl select-based backend or the Event module, the POE-EV backend
		1078	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,	1079	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	1080	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
987	invocation is almost 900 times slower than with AnyEvent's pure perl	1082	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	1083	implementation. The design of the POE adaptor class in AnyEvent can not
989	really account for this, as session creation overhead is small compared	1084	really account for this, as session creation overhead is small compared
990	to execution of the state machine, which is coded pretty optimally within	1085	to execution of the state machine, which is coded pretty optimally within
991	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.	1086	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
992		1087
993	=head2 Summary	1088	=head3 Summary
994		1089
		1090	=over 4
		1091
995	Using EV through AnyEvent is faster than any other event loop, but most	1092	=item * Using EV through AnyEvent is faster than any other event loop
996	event loops have acceptable performance with or without AnyEvent.	1093	(even when used without AnyEvent), but most event loops have acceptable
		1094	performance with or without AnyEvent.
997		1095
998	The overhead AnyEvent adds is usually much smaller than the overhead of	1096	=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	1097	the actual event loop, only with extremely fast event loops such as EV
1000	adds AnyEvent significant overhead.	1098	adds AnyEvent significant overhead.
1001		1099
1002	And you should simply avoid POE like the plague if you want performance or	1100	=item * You should avoid POE like the plague if you want performance or
1003	reasonable memory usage.	1101	reasonable memory usage.
		1102
		1103	=back
		1104
		1105	=head2 BENCHMARKING THE LARGE SERVER CASE
		1106
		1107	This benchmark atcually benchmarks the event loop itself. It works by
		1108	creating a number of "servers": each server consists of a socketpair, a
		1109	timeout watcher that gets reset on activity (but never fires), and an I/O
		1110	watcher waiting for input on one side of the socket. Each time the socket
		1111	watcher reads a byte it will write that byte to a random other "server".
		1112
		1113	The effect is that there will be a lot of I/O watchers, only part of which
		1114	are active at any one point (so there is a constant number of active
		1115	fds for each loop iterstaion, but which fds these are is random). The
		1116	timeout is reset each time something is read because that reflects how
		1117	most timeouts work (and puts extra pressure on the event loops).
		1118
		1119	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1120	(1%) are active. This mirrors the activity of large servers with many
		1121	connections, most of which are idle at any one point in time.
		1122
		1123	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1124	distribution.
		1125
		1126	=head3 Explanation of the columns
		1127
		1128	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1129	each server has a read and write socket end).
		1130
		1131	I<create> is the time it takes to create a socketpair (which is
		1132	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1133
		1134	I<request>, the most important value, is the time it takes to handle a
		1135	single "request", that is, reading the token from the pipe and forwarding
		1136	it to another server. This includes deleting the old timeout and creating
		1137	a new one that moves the timeout into the future.
		1138
		1139	=head3 Results
		1140
		1141	name sockets create request
		1142	EV 20000 69.01 11.16
		1143	Perl 20000 73.32 35.87
		1144	Event 20000 212.62 257.32
		1145	Glib 20000 651.16 1896.30
		1146	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1147
		1148	=head3 Discussion
		1149
		1150	This benchmark I<does> measure scalability and overall performance of the
		1151	particular event loop.
		1152
		1153	EV is again fastest. Since it is using epoll on my system, the setup time
		1154	is relatively high, though.
		1155
		1156	Perl surprisingly comes second. It is much faster than the C-based event
		1157	loops Event and Glib.
		1158
		1159	Event suffers from high setup time as well (look at its code and you will
		1160	understand why). Callback invocation also has a high overhead compared to
		1161	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1162	uses select or poll in basically all documented configurations.
		1163
		1164	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1165	clearly fails to perform with many filehandles or in busy servers.
		1166
		1167	POE is still completely out of the picture, taking over 1000 times as long
		1168	as EV, and over 100 times as long as the Perl implementation, even though
		1169	it uses a C-based event loop in this case.
		1170
		1171	=head3 Summary
		1172
		1173	=over 4
		1174
		1175	=item * The pure perl implementation performs extremely well, considering
		1176	that it uses select.
		1177
		1178	=item * Avoid Glib or POE in large projects where performance matters.
		1179
		1180	=back
		1181
		1182	=head2 BENCHMARKING SMALL SERVERS
		1183
		1184	While event loops should scale (and select-based ones do not...) even to
		1185	large servers, most programs we (or I :) actually write have only a few
		1186	I/O watchers.
		1187
		1188	In this benchmark, I use the same benchmark program as in the large server
		1189	case, but it uses only eight "servers", of which three are active at any
		1190	one time. This should reflect performance for a small server relatively
		1191	well.
		1192
		1193	The columns are identical to the previous table.
		1194
		1195	=head3 Results
		1196
		1197	name sockets create request
		1198	EV 16 20.00 6.54
		1199	Perl 16 25.75 12.62
		1200	Event 16 81.27 35.86
		1201	Glib 16 32.63 15.48
		1202	POE 16 261.87 276.28 uses POE::Loop::Event
		1203
		1204	=head3 Discussion
		1205
		1206	The benchmark tries to test the performance of a typical small
		1207	server. While knowing how various event loops perform is interesting, keep
		1208	in mind that their overhead in this case is usually not as important, due
		1209	to the small absolute number of watchers (that is, you need efficiency and
		1210	speed most when you have lots of watchers, not when you only have a few of
		1211	them).
		1212
		1213	EV is again fastest.
		1214
		1215	Perl again comes second. It is noticably faster than the C-based event
		1216	loops Event and Glib, although the difference is too small to really
		1217	matter.
		1218
		1219	POE also performs much better in this case, but is is still far behind the
		1220	others.
		1221
		1222	=head3 Summary
		1223
		1224	=over 4
		1225
		1226	=item * C-based event loops perform very well with small number of
		1227	watchers, as the management overhead dominates.
		1228
		1229	=back
1004		1230
1005		1231
1006	=head1 FORK	1232	=head1 FORK
1007		1233
1008	Most event libraries are not fork-safe. The ones who are usually are	1234	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 1.82 by root, Fri Apr 25 13:32:39 2008 UTC vs. Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.82 by root, Fri Apr 25 13:32:39 2008 UTC vs.
Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC