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

Comparing Coro/Coro.pm (file contents):
Revision 1.262 by root, Wed Jul 22 03:02:07 2009 UTC vs.
Revision 1.287 by root, Sat Feb 19 06:51:22 2011 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
46	as processes), Coro provides a full shared address space, which makes	46	more details) ported to UNIX, and as such act as processes), Coro
47	communication between threads very easy. And Coro's threads are fast,	47	provides a full shared address space, which makes communication between
48	too: disabling the Windows process emulation code in your perl and using	48	threads very easy. And coro 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	multiplication benchmark (very communication-intensive) runs over 300
51	faster on a single core than perl's pseudo-threads on a quad core using	52	times faster on a single core than perls pseudo-threads on a quad core
52	all four cores.	53	using all four cores.
53		54
54	Coro achieves that by supporting multiple running interpreters that share	55	Coro achieves that by supporting multiple running interpreters that share
55	data, which is especially useful to code pseudo-parallel processes and	56	data, which is especially useful to code pseudo-parallel processes and
56	for event-based programming, such as multiple HTTP-GET requests running	57	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	58	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
…		…
63	variables (see L<Coro::State> for more configuration and background info).	64	variables (see L<Coro::State> for more configuration and background info).
64		65
65	See also the C<SEE ALSO> section at the end of this document - the Coro	66	See also the C<SEE ALSO> section at the end of this document - the Coro
66	module family is quite large.	67	module family is quite large.
67		68
		69	=head1 CORO THREAD LIFE CYCLE
		70
		71	During the long and exciting (or not) life of a coro thread, it goes
		72	through a number of states:
		73
		74	=over 4
		75
		76	=item 1. Creation
		77
		78	The first thing in the life of a coro thread is it's creation -
		79	obviously. The typical way to create a thread is to call the C<async
		80	BLOCK> function:
		81
		82	async {
		83	# thread code goes here
		84	};
		85
		86	You can also pass arguments, which are put in C<@_>:
		87
		88	async {
		89	print $_[1]; # prints 2
		90	} 1, 2, 3;
		91
		92	This creates a new coro thread and puts it into the ready queue, meaning
		93	it will run as soon as the CPU is free for it.
		94
		95	C<async> will return a coro object - you can store this for future
		96	reference or ignore it, the thread itself will keep a reference to it's
		97	thread object - threads are alive on their own.
		98
		99	Another way to create a thread is to call the C<new> constructor with a
		100	code-reference:
		101
		102	new Coro sub {
		103	# thread code goes here
		104	}, @optional_arguments;
		105
		106	This is quite similar to calling C<async>, but the important difference is
		107	that the new thread is not put into the ready queue, so the thread will
		108	not run until somebody puts it there. C<async> is, therefore, identical to
		109	this sequence:
		110
		111	my $coro = new Coro sub {
		112	# thread code goes here
		113	};
		114	$coro->ready;
		115	return $coro;
		116
		117	=item 2. Startup
		118
		119	When a new coro thread is created, only a copy of the code reference
		120	and the arguments are stored, no extra memory for stacks and so on is
		121	allocated, keeping the coro thread in a low-memory state.
		122
		123	Only when it actually starts executing will all the resources be finally
		124	allocated.
		125
		126	The optional arguments specified at coro creation are available in C<@_>,
		127	similar to function calls.
		128
		129	=item 3. Running / Blocking
		130
		131	A lot can happen after the coro thread has started running. Quite usually,
		132	it will not run to the end in one go (because you could use a function
		133	instead), but it will give up the CPU regularly because it waits for
		134	external events.
		135
		136	As long as a coro thread runs, it's coro object is available in the global
		137	variable C<$Coro::current>.
		138
		139	The low-level way to give up the CPU is to call the scheduler, which
		140	selects a new coro thread to run:
		141
		142	Coro::schedule;
		143
		144	Since running threads are not in the ready queue, calling the scheduler
		145	without doing anything else will block the coro thread forever - you need
		146	to arrange either for the coro to put woken up (readied) by some other
		147	event or some other thread, or you can put it into the ready queue before
		148	scheduling:
		149
		150	# this is exactly what Coro::cede does
		151	$Coro::current->ready;
		152	Coro::schedule;
		153
		154	All the higher-level synchronisation methods (Coro::Semaphore,
		155	Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
		156	Coro::schedule >>.
		157
		158	While the coro thread is running it also might get assigned a C-level
		159	thread, or the C-level thread might be unassigned from it, as the Coro
		160	runtime wishes. A C-level thread needs to be assigned when your perl
		161	thread calls into some C-level function and that function in turn calls
		162	perl and perl then wants to switch coroutines. This happens most often
		163	when you run an event loop and block in the callback, or when perl
		164	itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
		165	mechanism.
		166
		167	=item 4. Termination
		168
		169	Many threads actually terminate after some time. There are a number of
		170	ways to terminate a coro thread, the simplest is returning from the
		171	top-level code reference:
		172
		173	async {
		174	# after returning from here, the coro thread is terminated
		175	};
		176
		177	async {
		178	return if 0.5 < rand; # terminate a little earlier, maybe
		179	print "got a chance to print this\n";
		180	# or here
		181	};
		182
		183	Any values returned from the coroutine can be recovered using C<< ->join
		184	>>:
		185
		186	my $coro = async {
		187	"hello, world\n" # return a string
		188	};
		189
		190	my $hello_world = $coro->join;
		191
		192	print $hello_world;
		193
		194	Another way to terminate is to call C<< Coro::terminate >>, which at any
		195	subroutine call nesting level:
		196
		197	async {
		198	Coro::terminate "return value 1", "return value 2";
		199	};
		200
		201	And yet another way is to C<< ->cancel >> the coro thread from another
		202	thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # an also accept values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state.
		215
		216	So, cancelling a thread that runs in an XS event loop might not be the
		217	best idea, but any other combination that deals with perl only (cancelling
		218	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		219	safe.
		220
		221	=item 5. Cleanup
		222
		223	Threads will allocate various resources. Most but not all will be returned
		224	when a thread terminates, during clean-up.
		225
		226	Cleanup is quite similar to throwing an uncaught exception: perl will
		227	work it's way up through all subroutine calls and blocks. On it's way, it
		228	will release all C<my> variables, undo all C<local>'s and free any other
		229	resources truly local to the thread.
		230
		231	So, a common way to free resources is to keep them referenced only by my
		232	variables:
		233
		234	async {
		235	my $big_cache = new Cache ...;
		236	};
		237
		238	If there are no other references, then the C<$big_cache> object will be
		239	freed when the thread terminates, regardless of how it does so.
		240
		241	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		242	resources, but that's where the C<guard> methods come in handy:
		243
		244	my $sem = new Coro::Semaphore;
		245
		246	async {
		247	my $lock_guard = $sem->guard;
		248	# if we reutrn, or die or get cancelled, here,
		249	# then the semaphore will be "up"ed.
		250	};
		251
		252	The C<Guard::guard> function comes in handy for any custom cleanup you
		253	might want to do:
		254
		255	async {
		256	my $window = new Gtk2::Window "toplevel";
		257	# The window will not be cleaned up automatically, even when $window
		258	# gets freed, so use a guard to ensure it's destruction
		259	# in case of an error:
		260	my $window_guard = Guard::guard { $window->destroy };
		261
		262	# we are safe here
		263	};
		264
		265	Last not least, C<local> can often be handy, too, e.g. when temporarily
		266	replacing the coro thread description:
		267
		268	sub myfunction {
		269	local $Coro::current->{desc} = "inside myfunction(@_)";
		270
		271	# if we return or die here, the description will be restored
		272	}
		273
		274	=item 6. Viva La Zombie Muerte
		275
		276	Even after a thread has terminated and cleaned up it's resources, the coro
		277	object still is there and stores the return values of the thread. Only in
		278	this state will the coro object be "reference counted" in the normal perl
		279	sense: the thread code keeps a reference to it when it is active, but not
		280	after it has terminated.
		281
		282	The means the coro object gets freed automatically when the thread has
		283	terminated and cleaned up and there arenot other references.
		284
		285	If there are, the coro object will stay around, and you can call C<<
		286	->join >> as many times as you wish to retrieve the result values:
		287
		288	async {
		289	print "hi\n";
		290	1
		291	};
		292
		293	# run the async above, and free everything before returning
		294	# from Coro::cede:
		295	Coro::cede;
		296
		297	{
		298	my $coro = async {
		299	print "hi\n";
		300	1
		301	};
		302
		303	# run the async above, and clean up, but do not free the coro
		304	# object:
		305	Coro::cede;
		306
		307	# optionally retrieve the result values
		308	my @results = $coro->join;
		309
		310	# now $coro goes out of scope, and presumably gets freed
		311	};
		312
		313	=back
		314
68	=cut	315	=cut
69		316
70	package Coro;	317	package Coro;
71		318
72	use strict qw(vars subs);	319	use common::sense;
73	no warnings "uninitialized";	320
		321	use Carp ();
74		322
75	use Guard ();	323	use Guard ();
76		324
77	use Coro::State;	325	use Coro::State;
78		326
…		…
80		328
81	our $idle; # idle handler	329	our $idle; # idle handler
82	our $main; # main coro	330	our $main; # main coro
83	our $current; # current coro	331	our $current; # current coro
84		332
85	our $VERSION = 5.161;	333	our $VERSION = 5.37;
86		334
87	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	335	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
88	our %EXPORT_TAGS = (	336	our %EXPORT_TAGS = (
89	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	337	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
90	);	338	);
91	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	339	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
92		340
…		…
123		371
124	This variable is mainly useful to integrate Coro into event loops. It is	372	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	373	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
126	pretty low-level functionality.	374	pretty low-level functionality.
127		375
128	This variable stores either a Coro object or a callback.	376	This variable stores a Coro object that is put into the ready queue when
		377	there are no other ready threads (without invoking any ready hooks).
129		378
130	If it is a callback, the it is called whenever the scheduler finds no	379	The default implementation dies with "FATAL: deadlock detected.", followed
131	ready coros to run. The default implementation prints "FATAL:	380	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		381
139	This hook is overwritten by modules such as C<Coro::EV> and	382	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	383	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
141	coro so the scheduler can run it.	384	coro so the scheduler can run it.
142		385
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	386	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
150	technique.
151		387
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	388	=cut
156		389
157	$idle = sub {	390	# \|\|= because other modules could have provided their own by now
158	require Carp;	391	$idle \|\|= new Coro sub {
159	Carp::croak ("FATAL: deadlock detected");	392	require Coro::Debug;
		393	die "FATAL: deadlock detected.\n"
		394	. Coro::Debug::ps_listing ();
160	};	395	};
161		396
162	# this coro is necessary because a coro	397	# this coro is necessary because a coro
163	# cannot destroy itself.	398	# cannot destroy itself.
164	our @destroy;	399	our @destroy;
…		…
206	Example: Create a new coro that just prints its arguments.	441	Example: Create a new coro that just prints its arguments.
207		442
208	async {	443	async {
209	print "@_\n";	444	print "@_\n";
210	} 1,2,3,4;	445	} 1,2,3,4;
211
212	=cut
213
214	sub async(&@) {
215	my $coro = new Coro @_;
216	$coro->ready;
217	$coro
218	}
219		446
220	=item async_pool { ... } [@args...]	447	=item async_pool { ... } [@args...]
221		448
222	Similar to C<async>, but uses a coro pool, so you should not call	449	Similar to C<async>, but uses a coro pool, so you should not call
223	terminate or join on it (although you are allowed to), and you get a	450	terminate or join on it (although you are allowed to), and you get a
…		…
280	=item schedule	507	=item schedule
281		508
282	Calls the scheduler. The scheduler will find the next coro that is	509	Calls the scheduler. The scheduler will find the next coro that is
283	to be run from the ready queue and switches to it. The next coro	510	to be run from the ready queue and switches to it. The next coro
284	to be run is simply the one with the highest priority that is longest	511	to be run is simply the one with the highest priority that is longest
285	in its ready queue. If there is no coro ready, it will clal the	512	in its ready queue. If there is no coro ready, it will call the
286	C<$Coro::idle> hook.	513	C<$Coro::idle> hook.
287		514
288	Please note that the current coro will I<not> be put into the ready	515	Please note that the current coro will I<not> be put into the ready
289	queue, so calling this function usually means you will never be called	516	queue, so calling this function usually means you will never be called
290	again unless something else (e.g. an event handler) calls C<< ->ready >>,	517	again unless something else (e.g. an event handler) calls C<< ->ready >>,
…		…
587	wantarray ? @{$self->{_status}} : $self->{_status}[0];	814	wantarray ? @{$self->{_status}} : $self->{_status}[0];
588	}	815	}
589		816
590	=item $coro->on_destroy (\&cb)	817	=item $coro->on_destroy (\&cb)
591		818
592	Registers a callback that is called when this coro gets destroyed,	819	Registers a callback that is called when this coro thread gets destroyed,
593	but before it is joined. The callback gets passed the terminate arguments,	820	but before it is joined. The callback gets passed the terminate arguments,
594	if any, and I<must not> die, under any circumstances.	821	if any, and I<must not> die, under any circumstances.
595		822
		823	There can be any number of C<on_destroy> callbacks per coro.
		824
596	=cut	825	=cut
597		826
598	sub on_destroy {	827	sub on_destroy {
599	my ($self, $cb) = @_;	828	my ($self, $cb) = @_;
600		829
…		…
602	}	831	}
603		832
604	=item $oldprio = $coro->prio ($newprio)	833	=item $oldprio = $coro->prio ($newprio)
605		834
606	Sets (or gets, if the argument is missing) the priority of the	835	Sets (or gets, if the argument is missing) the priority of the
607	coro. Higher priority coro get run before lower priority	836	coro thread. Higher priority coro get run before lower priority
608	coro. Priorities are small signed integers (currently -4 .. +3),	837	coros. Priorities are small signed integers (currently -4 .. +3),
609	that you can refer to using PRIO_xxx constants (use the import tag :prio	838	that you can refer to using PRIO_xxx constants (use the import tag :prio
610	to get then):	839	to get then):
611		840
612	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	841	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
613	3 > 1 > 0 > -1 > -3 > -4	842	3 > 1 > 0 > -1 > -3 > -4
614		843
615	# set priority to HIGH	844	# set priority to HIGH
616	current->prio (PRIO_HIGH);	845	current->prio (PRIO_HIGH);
617		846
618	The idle coro ($Coro::idle) always has a lower priority than any	847	The idle coro thread ($Coro::idle) always has a lower priority than any
619	existing coro.	848	existing coro.
620		849
621	Changing the priority of the current coro will take effect immediately,	850	Changing the priority of the current coro will take effect immediately,
622	but changing the priority of coro in the ready queue (but not	851	but changing the priority of a coro in the ready queue (but not running)
623	running) will only take effect after the next schedule (of that	852	will only take effect after the next schedule (of that coro). This is a
624	coro). This is a bug that will be fixed in some future version.	853	bug that will be fixed in some future version.
625		854
626	=item $newprio = $coro->nice ($change)	855	=item $newprio = $coro->nice ($change)
627		856
628	Similar to C<prio>, but subtract the given value from the priority (i.e.	857	Similar to C<prio>, but subtract the given value from the priority (i.e.
629	higher values mean lower priority, just as in unix).	858	higher values mean lower priority, just as in UNIX's nice command).
630		859
631	=item $olddesc = $coro->desc ($newdesc)	860	=item $olddesc = $coro->desc ($newdesc)
632		861
633	Sets (or gets in case the argument is missing) the description for this	862	Sets (or gets in case the argument is missing) the description for this
634	coro. This is just a free-form string you can associate with a	863	coro thread. This is just a free-form string you can associate with a
635	coro.	864	coro.
636		865
637	This method simply sets the C<< $coro->{desc} >> member to the given	866	This method simply sets the C<< $coro->{desc} >> member to the given
638	string. You can modify this member directly if you wish.	867	string. You can modify this member directly if you wish, and in fact, this
		868	is often preferred to indicate major processing states that cna then be
		869	seen for example in a L<Coro::Debug> session:
		870
		871	sub my_long_function {
		872	local $Coro::current->{desc} = "now in my_long_function";
		873	...
		874	$Coro::current->{desc} = "my_long_function: phase 1";
		875	...
		876	$Coro::current->{desc} = "my_long_function: phase 2";
		877	...
		878	}
639		879
640	=cut	880	=cut
641		881
642	sub desc {	882	sub desc {
643	my $old = $_[0]{desc};	883	my $old = $_[0]{desc};
…		…
680	returning a new coderef. Unblocking means that calling the new coderef	920	returning a new coderef. Unblocking means that calling the new coderef
681	will return immediately without blocking, returning nothing, while the	921	will return immediately without blocking, returning nothing, while the
682	original code ref will be called (with parameters) from within another	922	original code ref will be called (with parameters) from within another
683	coro.	923	coro.
684		924
685	The reason this function exists is that many event libraries (such as the	925	The reason this function exists is that many event libraries (such as
686	venerable L<Event\|Event> module) are not thread-safe (a weaker form	926	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
687	of reentrancy). This means you must not block within event callbacks,	927	of reentrancy). This means you must not block within event callbacks,
688	otherwise you might suffer from crashes or worse. The only event library	928	otherwise you might suffer from crashes or worse. The only event library
689	currently known that is safe to use without C<unblock_sub> is L<EV>.	929	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		930	you might still run into deadlocks if all event loops are blocked).
		931
		932	Coro will try to catch you when you block in the event loop
		933	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		934	only works when you do not run your own event loop.
690		935
691	This function allows your callbacks to block by executing them in another	936	This function allows your callbacks to block by executing them in another
692	coro where it is safe to block. One example where blocking is handy	937	coro where it is safe to block. One example where blocking is handy
693	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	938	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
694	disk, for example.	939	disk, for example.
…		…
736	unshift @unblock_queue, [$cb, @_];	981	unshift @unblock_queue, [$cb, @_];
737	$unblock_scheduler->ready;	982	$unblock_scheduler->ready;
738	}	983	}
739	}	984	}
740		985
741	=item $cb = Coro::rouse_cb	986	=item $cb = rouse_cb
742		987
743	Create and return a "rouse callback". That's a code reference that,	988	Create and return a "rouse callback". That's a code reference that,
744	when called, will remember a copy of its arguments and notify the owner	989	when called, will remember a copy of its arguments and notify the owner
745	coro of the callback.	990	coro of the callback.
746		991
747	See the next function.	992	See the next function.
748		993
749	=item @args = Coro::rouse_wait [$cb]	994	=item @args = rouse_wait [$cb]
750		995
751	Wait for the specified rouse callback (or the last one that was created in	996	Wait for the specified rouse callback (or the last one that was created in
752	this coro).	997	this coro).
753		998
754	As soon as the callback is invoked (or when the callback was invoked	999	As soon as the callback is invoked (or when the callback was invoked
…		…
760	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1005	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
761		1006
762	=back	1007	=back
763		1008
764	=cut	1009	=cut
		1010
		1011	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1012	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1013
		1014	*{"Coro::$module\::new"} = sub {
		1015	require "Coro/$module.pm";
		1016
		1017	# some modules have their new predefined in State.xs, some don't
		1018	*{"Coro::$module\::new"} = $old
		1019	if $old;
		1020
		1021	goto &{"Coro::$module\::new"};
		1022	};
		1023	}
765		1024
766	1;	1025	1;
767		1026
768	=head1 HOW TO WAIT FOR A CALLBACK	1027	=head1 HOW TO WAIT FOR A CALLBACK
769		1028
…		…
851	the windows process emulation enabled under unix roughly halves perl	1110	the windows process emulation enabled under unix roughly halves perl
852	performance, even when not used.	1111	performance, even when not used.
853		1112
854	=item coro switching is not signal safe	1113	=item coro switching is not signal safe
855		1114
856	You must not switch to another coro from within a signal handler	1115	You must not switch to another coro from within a signal handler (only
857	(only relevant with %SIG - most event libraries provide safe signals).	1116	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1117	you are sure you are not interrupting a Coro function.
858		1118
859	That means you I<MUST NOT> call any function that might "block" the	1119	That means you I<MUST NOT> call any function that might "block" the
860	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1120	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
861	anything that calls those. Everything else, including calling C<ready>,	1121	anything that calls those. Everything else, including calling C<ready>,
862	works.	1122	works.
863		1123
864	=back	1124	=back
865		1125
866		1126
		1127	=head1 WINDOWS PROCESS EMULATION
		1128
		1129	A great many people seem to be confused about ithreads (for example, Chip
		1130	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1131	while in the same mail making rather confused statements about perl
		1132	ithreads (for example, that memory or files would be shared), showing his
		1133	lack of understanding of this area - if it is hard to understand for Chip,
		1134	it is probably not obvious to everybody).
		1135
		1136	What follows is an ultra-condensed version of my talk about threads in
		1137	scripting languages given on the perl workshop 2009:
		1138
		1139	The so-called "ithreads" were originally implemented for two reasons:
		1140	first, to (badly) emulate unix processes on native win32 perls, and
		1141	secondly, to replace the older, real thread model ("5.005-threads").
		1142
		1143	It does that by using threads instead of OS processes. The difference
		1144	between processes and threads is that threads share memory (and other
		1145	state, such as files) between threads within a single process, while
		1146	processes do not share anything (at least not semantically). That
		1147	means that modifications done by one thread are seen by others, while
		1148	modifications by one process are not seen by other processes.
		1149
		1150	The "ithreads" work exactly like that: when creating a new ithreads
		1151	process, all state is copied (memory is copied physically, files and code
		1152	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1153	the same behaviour can be achieved by using operating system processes,
		1154	except that UNIX typically uses hardware built into the system to do this
		1155	efficiently, while the windows process emulation emulates this hardware in
		1156	software (rather efficiently, but of course it is still much slower than
		1157	dedicated hardware).
		1158
		1159	As mentioned before, loading code, modifying code, modifying data
		1160	structures and so on is only visible in the ithreads process doing the
		1161	modification, not in other ithread processes within the same OS process.
		1162
		1163	This is why "ithreads" do not implement threads for perl at all, only
		1164	processes. What makes it so bad is that on non-windows platforms, you can
		1165	actually take advantage of custom hardware for this purpose (as evidenced
		1166	by the forks module, which gives you the (i-) threads API, just much
		1167	faster).
		1168
		1169	Sharing data is in the i-threads model is done by transfering data
		1170	structures between threads using copying semantics, which is very slow -
		1171	shared data simply does not exist. Benchmarks using i-threads which are
		1172	communication-intensive show extremely bad behaviour with i-threads (in
		1173	fact, so bad that Coro, which cannot take direct advantage of multiple
		1174	CPUs, is often orders of magnitude faster because it shares data using
		1175	real threads, refer to my talk for details).
		1176
		1177	As summary, i-threads use threads to implement processes, while
		1178	the compatible forks module uses processes to emulate, uhm,
		1179	processes. I-threads slow down every perl program when enabled, and
		1180	outside of windows, serve no (or little) practical purpose, but
		1181	disadvantages every single-threaded Perl program.
		1182
		1183	This is the reason that I try to avoid the name "ithreads", as it is
		1184	misleading as it implies that it implements some kind of thread model for
		1185	perl, and prefer the name "windows process emulation", which describes the
		1186	actual use and behaviour of it much better.
		1187
867	=head1 SEE ALSO	1188	=head1 SEE ALSO
868		1189
869	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1190	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
870		1191
871	Debugging: L<Coro::Debug>.	1192	Debugging: L<Coro::Debug>.

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Comparing Coro/Coro.pm (file contents): Revision 1.262 by root, Wed Jul 22 03:02:07 2009 UTC vs. Revision 1.287 by root, Sat Feb 19 06:51:22 2011 UTC

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Comparing Coro/Coro.pm (file contents):
Revision 1.262 by root, Wed Jul 22 03:02:07 2009 UTC vs.
Revision 1.287 by root, Sat Feb 19 06:51:22 2011 UTC