[ViewVC] Diff of: cvs/Coro/Coro.pm

Comparing Coro/Coro.pm (file contents):
Revision 1.251 by root, Mon Mar 16 22:22:12 2009 UTC vs.
Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC

…		…
40	points in your program, so locking and parallel access are rarely an	40	points in your program, so locking and parallel access are rarely an
41	issue, making thread programming much safer and easier than using other	41	issue, making thread programming much safer and easier than using other
42	thread models.	42	thread models.
43		43
44	Unlike the so-called "Perl threads" (which are not actually real threads	44	Unlike the so-called "Perl threads" (which are not actually real threads
45	but only the windows process emulation ported to unix, and as such act	45	but only the windows process emulation (see section of same name for more
46	as processes), Coro provides a full shared address space, which makes	46	details) ported to unix, and as such act as processes), Coro provides
47	communication between threads very easy. And Coro's threads are fast,	47	a full shared address space, which makes communication between threads
48	too: disabling the Windows process emulation code in your perl and using	48	very easy. And Coro's threads are fast, too: disabling the Windows
49	Coro can easily result in a two to four times speed increase for your	49	process emulation code in your perl and using Coro can easily result in
50	programs. A parallel matrix multiplication benchmark runs over 300 times	50	a two to four times speed increase for your programs. A parallel matrix
51	faster on a single core than perl's pseudo-threads on a quad core using	51	multiplication benchmark runs over 300 times faster on a single core than
52	all four cores.	52	perl's pseudo-threads on a quad core using all four cores.
53		53
54	Coro achieves that by supporting multiple running interpreters that share	54	Coro achieves that by supporting multiple running interpreters that share
55	data, which is especially useful to code pseudo-parallel processes and	55	data, which is especially useful to code pseudo-parallel processes and
56	for event-based programming, such as multiple HTTP-GET requests running	56	for event-based programming, such as multiple HTTP-GET requests running
57	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro	57	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
…		…
67		67
68	=cut	68	=cut
69		69
70	package Coro;	70	package Coro;
71		71
72	use strict qw(vars subs);	72	use common::sense;
73	no warnings "uninitialized";	73
		74	use Carp ();
74		75
75	use Guard ();	76	use Guard ();
76		77
77	use Coro::State;	78	use Coro::State;
78		79
…		…
80		81
81	our $idle; # idle handler	82	our $idle; # idle handler
82	our $main; # main coro	83	our $main; # main coro
83	our $current; # current coro	84	our $current; # current coro
84		85
85	our $VERSION = 5.131;	86	our $VERSION = 5.21;
86		87
87	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
88	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
89	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
90	);	91	);
91	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	92	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
92		93
…		…
123		124
124	This variable is mainly useful to integrate Coro into event loops. It is	125	This variable is mainly useful to integrate Coro into event loops. It is
125	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is	126	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
126	pretty low-level functionality.	127	pretty low-level functionality.
127		128
128	This variable stores either a Coro object or a callback.	129	This variable stores a Coro object that is put into the ready queue when
		130	there are no other ready threads (without invoking any ready hooks).
129		131
130	If it is a callback, the it is called whenever the scheduler finds no	132	The default implementation dies with "FATAL: deadlock detected.", followed
131	ready coros to run. The default implementation prints "FATAL:	133	by a thread listing, because the program has no other way to continue.
132	deadlock detected" and exits, because the program has no other way to
133	continue.
134
135	If it is a coro object, then this object will be readied (without
136	invoking any ready hooks, however) when the scheduler finds no other ready
137	coros to run.
138		134
139	This hook is overwritten by modules such as C<Coro::EV> and	135	This hook is overwritten by modules such as C<Coro::EV> and
140	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	136	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
141	coro so the scheduler can run it.	137	coro so the scheduler can run it.
142		138
143	Note that the callback I<must not>, under any circumstances, block
144	the current coro. Normally, this is achieved by having an "idle
145	coro" that calls the event loop and then blocks again, and then
146	readying that coro in the idle handler, or by simply placing the idle
147	coro in this variable.
148
149	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this	139	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
150	technique.
151		140
152	Please note that if your callback recursively invokes perl (e.g. for event
153	handlers), then it must be prepared to be called recursively itself.
154
155	=cut	141	=cut
156		142
157	$idle = sub {	143	# \|\|= because other modules could have provided their own by now
158	require Carp;	144	$idle \|\|= new Coro sub {
159	Carp::croak ("FATAL: deadlock detected");	145	require Coro::Debug;
		146	die "FATAL: deadlock detected.\n"
		147	. Coro::Debug::ps_listing ();
160	};	148	};
161		149
162	# this coro is necessary because a coro	150	# this coro is necessary because a coro
163	# cannot destroy itself.	151	# cannot destroy itself.
164	our @destroy;	152	our @destroy;
…		…
206	Example: Create a new coro that just prints its arguments.	194	Example: Create a new coro that just prints its arguments.
207		195
208	async {	196	async {
209	print "@_\n";	197	print "@_\n";
210	} 1,2,3,4;	198	} 1,2,3,4;
211
212	=cut
213
214	sub async(&@) {
215	my $coro = new Coro @_;
216	$coro->ready;
217	$coro
218	}
219		199
220	=item async_pool { ... } [@args...]	200	=item async_pool { ... } [@args...]
221		201
222	Similar to C<async>, but uses a coro pool, so you should not call	202	Similar to C<async>, but uses a coro pool, so you should not call
223	terminate or join on it (although you are allowed to), and you get a	203	terminate or join on it (although you are allowed to), and you get a
…		…
280	=item schedule	260	=item schedule
281		261
282	Calls the scheduler. The scheduler will find the next coro that is	262	Calls the scheduler. The scheduler will find the next coro that is
283	to be run from the ready queue and switches to it. The next coro	263	to be run from the ready queue and switches to it. The next coro
284	to be run is simply the one with the highest priority that is longest	264	to be run is simply the one with the highest priority that is longest
285	in its ready queue. If there is no coro ready, it will clal the	265	in its ready queue. If there is no coro ready, it will call the
286	C<$Coro::idle> hook.	266	C<$Coro::idle> hook.
287		267
288	Please note that the current coro will I<not> be put into the ready	268	Please note that the current coro will I<not> be put into the ready
289	queue, so calling this function usually means you will never be called	269	queue, so calling this function usually means you will never be called
290	again unless something else (e.g. an event handler) calls C<< ->ready >>,	270	again unless something else (e.g. an event handler) calls C<< ->ready >>,
…		…
338		318
339	These functions implement the same concept as C<dynamic-wind> in scheme	319	These functions implement the same concept as C<dynamic-wind> in scheme
340	does, and are useful when you want to localise some resource to a specific	320	does, and are useful when you want to localise some resource to a specific
341	coro.	321	coro.
342		322
343	They slow down coro switching considerably for coros that use	323	They slow down thread switching considerably for coros that use them
344	them (But coro switching is still reasonably fast if the handlers are	324	(about 40% for a BLOCK with a single assignment, so thread switching is
345	fast).	325	still reasonably fast if the handlers are fast).
346		326
347	These functions are best understood by an example: The following function	327	These functions are best understood by an example: The following function
348	will change the current timezone to "Antarctica/South_Pole", which	328	will change the current timezone to "Antarctica/South_Pole", which
349	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,	329	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
350	which remember/change the current timezone and restore the previous	330	which remember/change the current timezone and restore the previous
351	value, respectively, the timezone is only changes for the coro that	331	value, respectively, the timezone is only changed for the coro that
352	installed those handlers.	332	installed those handlers.
353		333
354	use POSIX qw(tzset);	334	use POSIX qw(tzset);
355		335
356	async {	336	async {
…		…
373	};	353	};
374		354
375	This can be used to localise about any resource (locale, uid, current	355	This can be used to localise about any resource (locale, uid, current
376	working directory etc.) to a block, despite the existance of other	356	working directory etc.) to a block, despite the existance of other
377	coros.	357	coros.
		358
		359	Another interesting example implements time-sliced multitasking using
		360	interval timers (this could obviously be optimised, but does the job):
		361
		362	# "timeslice" the given block
		363	sub timeslice(&) {
		364	use Time::HiRes ();
		365
		366	Coro::on_enter {
		367	# on entering the thread, we set an VTALRM handler to cede
		368	$SIG{VTALRM} = sub { cede };
		369	# and then start the interval timer
		370	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		371	};
		372	Coro::on_leave {
		373	# on leaving the thread, we stop the interval timer again
		374	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		375	};
		376
		377	&{+shift};
		378	}
		379
		380	# use like this:
		381	timeslice {
		382	# The following is an endless loop that would normally
		383	# monopolise the process. Since it runs in a timesliced
		384	# environment, it will regularly cede to other threads.
		385	while () { }
		386	};
		387
378		388
379	=item killall	389	=item killall
380		390
381	Kills/terminates/cancels all coros except the currently running one.	391	Kills/terminates/cancels all coros except the currently running one.
382		392
…		…
655	The reason this function exists is that many event libraries (such as the	665	The reason this function exists is that many event libraries (such as the
656	venerable L<Event\|Event> module) are not thread-safe (a weaker form	666	venerable L<Event\|Event> module) are not thread-safe (a weaker form
657	of reentrancy). This means you must not block within event callbacks,	667	of reentrancy). This means you must not block within event callbacks,
658	otherwise you might suffer from crashes or worse. The only event library	668	otherwise you might suffer from crashes or worse. The only event library
659	currently known that is safe to use without C<unblock_sub> is L<EV>.	669	currently known that is safe to use without C<unblock_sub> is L<EV>.
		670
		671	Coro will try to catch you when you block in the event loop
		672	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		673	only works when you do not run your own event loop.
660		674
661	This function allows your callbacks to block by executing them in another	675	This function allows your callbacks to block by executing them in another
662	coro where it is safe to block. One example where blocking is handy	676	coro where it is safe to block. One example where blocking is handy
663	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	677	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
664	disk, for example.	678	disk, for example.
…		…
706	unshift @unblock_queue, [$cb, @_];	720	unshift @unblock_queue, [$cb, @_];
707	$unblock_scheduler->ready;	721	$unblock_scheduler->ready;
708	}	722	}
709	}	723	}
710		724
711	=item $cb = Coro::rouse_cb	725	=item $cb = rouse_cb
712		726
713	Create and return a "rouse callback". That's a code reference that,	727	Create and return a "rouse callback". That's a code reference that,
714	when called, will remember a copy of its arguments and notify the owner	728	when called, will remember a copy of its arguments and notify the owner
715	coro of the callback.	729	coro of the callback.
716		730
717	See the next function.	731	See the next function.
718		732
719	=item @args = Coro::rouse_wait [$cb]	733	=item @args = rouse_wait [$cb]
720		734
721	Wait for the specified rouse callback (or the last one that was created in	735	Wait for the specified rouse callback (or the last one that was created in
722	this coro).	736	this coro).
723		737
724	As soon as the callback is invoked (or when the callback was invoked	738	As soon as the callback is invoked (or when the callback was invoked
725	before C<rouse_wait>), it will return the arguments originally passed to	739	before C<rouse_wait>), it will return the arguments originally passed to
726	the rouse callback.	740	the rouse callback. In scalar context, that means you get the I<last>
		741	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		742	statement at the end.
727		743
728	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	744	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
729		745
730	=back	746	=back
731		747
…		…
819	the windows process emulation enabled under unix roughly halves perl	835	the windows process emulation enabled under unix roughly halves perl
820	performance, even when not used.	836	performance, even when not used.
821		837
822	=item coro switching is not signal safe	838	=item coro switching is not signal safe
823		839
824	You must not switch to another coro from within a signal handler	840	You must not switch to another coro from within a signal handler (only
825	(only relevant with %SIG - most event libraries provide safe signals).	841	relevant with %SIG - most event libraries provide safe signals), I<unless>
		842	you are sure you are not interrupting a Coro function.
826		843
827	That means you I<MUST NOT> call any function that might "block" the	844	That means you I<MUST NOT> call any function that might "block" the
828	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	845	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
829	anything that calls those. Everything else, including calling C<ready>,	846	anything that calls those. Everything else, including calling C<ready>,
830	works.	847	works.
831		848
832	=back	849	=back
833		850
834		851
		852	=head1 WINDOWS PROCESS EMULATION
		853
		854	A great many people seem to be confused about ithreads (for example, Chip
		855	Salzenberg called me unintelligent, incapable, stupid and gullible,
		856	while in the same mail making rather confused statements about perl
		857	ithreads (for example, that memory or files would be shared), showing his
		858	lack of understanding of this area - if it is hard to understand for Chip,
		859	it is probably not obvious to everybody).
		860
		861	What follows is an ultra-condensed version of my talk about threads in
		862	scripting languages given onthe perl workshop 2009:
		863
		864	The so-called "ithreads" were originally implemented for two reasons:
		865	first, to (badly) emulate unix processes on native win32 perls, and
		866	secondly, to replace the older, real thread model ("5.005-threads").
		867
		868	It does that by using threads instead of OS processes. The difference
		869	between processes and threads is that threads share memory (and other
		870	state, such as files) between threads within a single process, while
		871	processes do not share anything (at least not semantically). That
		872	means that modifications done by one thread are seen by others, while
		873	modifications by one process are not seen by other processes.
		874
		875	The "ithreads" work exactly like that: when creating a new ithreads
		876	process, all state is copied (memory is copied physically, files and code
		877	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		878	the same behaviour can be achieved by using operating system processes,
		879	except that UNIX typically uses hardware built into the system to do this
		880	efficiently, while the windows process emulation emulates this hardware in
		881	software (rather efficiently, but of course it is still much slower than
		882	dedicated hardware).
		883
		884	As mentioned before, loading code, modifying code, modifying data
		885	structures and so on is only visible in the ithreads process doing the
		886	modification, not in other ithread processes within the same OS process.
		887
		888	This is why "ithreads" do not implement threads for perl at all, only
		889	processes. What makes it so bad is that on non-windows platforms, you can
		890	actually take advantage of custom hardware for this purpose (as evidenced
		891	by the forks module, which gives you the (i-) threads API, just much
		892	faster).
		893
		894	Sharing data is in the i-threads model is done by transfering data
		895	structures between threads using copying semantics, which is very slow -
		896	shared data simply does not exist. Benchmarks using i-threads which are
		897	communication-intensive show extremely bad behaviour with i-threads (in
		898	fact, so bad that Coro, which cannot take direct advantage of multiple
		899	CPUs, is often orders of magnitude faster because it shares data using
		900	real threads, refer to my talk for details).
		901
		902	As summary, i-threads use threads to implement processes, while
		903	the compatible forks module uses processes to emulate, uhm,
		904	processes. I-threads slow down every perl program when enabled, and
		905	outside of windows, serve no (or little) practical purpose, but
		906	disadvantages every single-threaded Perl program.
		907
		908	This is the reason that I try to avoid the name "ithreads", as it is
		909	misleading as it implies that it implements some kind of thread model for
		910	perl, and prefer the name "windows process emulation", which describes the
		911	actual use and behaviour of it much better.
		912
835	=head1 SEE ALSO	913	=head1 SEE ALSO
836		914
837	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	915	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
838		916
839	Debugging: L<Coro::Debug>.	917	Debugging: L<Coro::Debug>.

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Comparing Coro/Coro.pm (file contents): Revision 1.251 by root, Mon Mar 16 22:22:12 2009 UTC vs. Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC

Diff Legend

Comparing Coro/Coro.pm (file contents):
Revision 1.251 by root, Mon Mar 16 22:22:12 2009 UTC vs.
Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC