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

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.264 by root, Thu Aug 13 02:35:41 2009 UTC vs.
Revision 1.294 by root, Fri May 6 21:15:17 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 >> (or C<< ->safe_cancel >>) the
		202	coro thread from another 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>
		211	without actually exiting, and might leave C libraries and XS modules in
		212	a weird state. Unlike other thread implementations, however, Coro is
		213	exceptionally safe with regards to cancellation, as perl will always be
		214	in a consistent state, and for those cases where you want to do truly
		215	marvellous things with your coro while it is being cancelled, there is
		216	even a C<< ->safe_cancel >> method.
		217
		218	So, cancelling a thread that runs in an XS event loop might not be the
		219	best idea, but any other combination that deals with perl only (cancelling
		220	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		221	safe.
		222
		223	=item 5. Cleanup
		224
		225	Threads will allocate various resources. Most but not all will be returned
		226	when a thread terminates, during clean-up.
		227
		228	Cleanup is quite similar to throwing an uncaught exception: perl will
		229	work it's way up through all subroutine calls and blocks. On it's way, it
		230	will release all C<my> variables, undo all C<local>'s and free any other
		231	resources truly local to the thread.
		232
		233	So, a common way to free resources is to keep them referenced only by my
		234	variables:
		235
		236	async {
		237	my $big_cache = new Cache ...;
		238	};
		239
		240	If there are no other references, then the C<$big_cache> object will be
		241	freed when the thread terminates, regardless of how it does so.
		242
		243	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		244	resources, but that's where the C<guard> methods come in handy:
		245
		246	my $sem = new Coro::Semaphore;
		247
		248	async {
		249	my $lock_guard = $sem->guard;
		250	# if we reutrn, or die or get cancelled, here,
		251	# then the semaphore will be "up"ed.
		252	};
		253
		254	The C<Guard::guard> function comes in handy for any custom cleanup you
		255	might want to do:
		256
		257	async {
		258	my $window = new Gtk2::Window "toplevel";
		259	# The window will not be cleaned up automatically, even when $window
		260	# gets freed, so use a guard to ensure it's destruction
		261	# in case of an error:
		262	my $window_guard = Guard::guard { $window->destroy };
		263
		264	# we are safe here
		265	};
		266
		267	Last not least, C<local> can often be handy, too, e.g. when temporarily
		268	replacing the coro thread description:
		269
		270	sub myfunction {
		271	local $Coro::current->{desc} = "inside myfunction(@_)";
		272
		273	# if we return or die here, the description will be restored
		274	}
		275
		276	=item 6. Viva La Zombie Muerte
		277
		278	Even after a thread has terminated and cleaned up it's resources, the coro
		279	object still is there and stores the return values of the thread. Only in
		280	this state will the coro object be "reference counted" in the normal perl
		281	sense: the thread code keeps a reference to it when it is active, but not
		282	after it has terminated.
		283
		284	The means the coro object gets freed automatically when the thread has
		285	terminated and cleaned up and there arenot other references.
		286
		287	If there are, the coro object will stay around, and you can call C<<
		288	->join >> as many times as you wish to retrieve the result values:
		289
		290	async {
		291	print "hi\n";
		292	1
		293	};
		294
		295	# run the async above, and free everything before returning
		296	# from Coro::cede:
		297	Coro::cede;
		298
		299	{
		300	my $coro = async {
		301	print "hi\n";
		302	1
		303	};
		304
		305	# run the async above, and clean up, but do not free the coro
		306	# object:
		307	Coro::cede;
		308
		309	# optionally retrieve the result values
		310	my @results = $coro->join;
		311
		312	# now $coro goes out of scope, and presumably gets freed
		313	};
		314
		315	=back
		316
68	=cut	317	=cut
69		318
70	package Coro;	319	package Coro;
71		320
72	use strict qw(vars subs);	321	use common::sense;
73	no warnings "uninitialized";	322
		323	use Carp ();
74		324
75	use Guard ();	325	use Guard ();
76		326
77	use Coro::State;	327	use Coro::State;
78		328
…		…
80		330
81	our $idle; # idle handler	331	our $idle; # idle handler
82	our $main; # main coro	332	our $main; # main coro
83	our $current; # current coro	333	our $current; # current coro
84		334
85	our $VERSION = 5.162;	335	our $VERSION = 5.372;
86		336
87	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	337	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
88	our %EXPORT_TAGS = (	338	our %EXPORT_TAGS = (
89	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	339	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
90	);	340	);
91	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	341	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
92		342
…		…
123		373
124	This variable is mainly useful to integrate Coro into event loops. It is	374	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	375	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
126	pretty low-level functionality.	376	pretty low-level functionality.
127		377
128	This variable stores either a Coro object or a callback.	378	This variable stores a Coro object that is put into the ready queue when
		379	there are no other ready threads (without invoking any ready hooks).
129		380
130	If it is a callback, the it is called whenever the scheduler finds no	381	The default implementation dies with "FATAL: deadlock detected.", followed
131	ready coros to run. The default implementation prints "FATAL:	382	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		383
139	This hook is overwritten by modules such as C<Coro::EV> and	384	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	385	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
141	coro so the scheduler can run it.	386	coro so the scheduler can run it.
142		387
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	388	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
150	technique.
151		389
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	390	=cut
156		391
157	$idle = sub {	392	# \|\|= because other modules could have provided their own by now
158	require Carp;	393	$idle \|\|= new Coro sub {
159	Carp::croak ("FATAL: deadlock detected");	394	require Coro::Debug;
		395	die "FATAL: deadlock detected.\n"
		396	. Coro::Debug::ps_listing ();
160	};	397	};
161		398
162	# this coro is necessary because a coro	399	# this coro is necessary because a coro
163	# cannot destroy itself.	400	# cannot destroy itself.
164	our @destroy;	401	our @destroy;
165	our $manager;	402	our $manager;
166		403
167	$manager = new Coro sub {	404	$manager = new Coro sub {
168	while () {	405	while () {
169	Coro::State::cancel shift @destroy	406	_destroy shift @destroy
170	while @destroy;	407	while @destroy;
171		408
172	&schedule;	409	&schedule;
173	}	410	}
174	};	411	};
…		…
272	=item schedule	509	=item schedule
273		510
274	Calls the scheduler. The scheduler will find the next coro that is	511	Calls the scheduler. The scheduler will find the next coro that is
275	to be run from the ready queue and switches to it. The next coro	512	to be run from the ready queue and switches to it. The next coro
276	to be run is simply the one with the highest priority that is longest	513	to be run is simply the one with the highest priority that is longest
277	in its ready queue. If there is no coro ready, it will clal the	514	in its ready queue. If there is no coro ready, it will call the
278	C<$Coro::idle> hook.	515	C<$Coro::idle> hook.
279		516
280	Please note that the current coro will I<not> be put into the ready	517	Please note that the current coro will I<not> be put into the ready
281	queue, so calling this function usually means you will never be called	518	queue, so calling this function usually means you will never be called
282	again unless something else (e.g. an event handler) calls C<< ->ready >>,	519	again unless something else (e.g. an event handler) calls C<< ->ready >>,
…		…
308	coro, regardless of priority. This is useful sometimes to ensure	545	coro, regardless of priority. This is useful sometimes to ensure
309	progress is made.	546	progress is made.
310		547
311	=item terminate [arg...]	548	=item terminate [arg...]
312		549
313	Terminates the current coro with the given status values (see L<cancel>).	550	Terminates the current coro with the given status values (see
		551	L<cancel>). The values will not be copied, but referenced directly.
314		552
315	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK	553	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
316		554
317	These function install enter and leave winders in the current scope. The	555	These function install enter and leave winders in the current scope. The
318	enter block will be executed when on_enter is called and whenever the	556	enter block will be executed when on_enter is called and whenever the
…		…
492	Returns true iff this Coro object has been suspended. Suspended Coros will	730	Returns true iff this Coro object has been suspended. Suspended Coros will
493	not ever be scheduled.	731	not ever be scheduled.
494		732
495	=item $coro->cancel (arg...)	733	=item $coro->cancel (arg...)
496		734
497	Terminates the given Coro and makes it return the given arguments as	735	Terminates the given Coro thread and makes it return the given arguments as
498	status (default: the empty list). Never returns if the Coro is the	736	status (default: an empty list). Never returns if the Coro is the
499	current Coro.	737	current Coro.
500		738
501	=cut	739	This is a rather brutal way to free a coro, with some limitations - if
		740	the thread is inside a C callback that doesn't expect to be canceled,
		741	bad things can happen, or if the cancelled thread insists on running
		742	complicated cleanup handlers that rely on it'S thread context, things will
		743	not work.
502		744
503	sub cancel {	745	Sometimes it is safer to C<< ->throw >> an exception, or use C<<
504	my $self = shift;	746	->safe_cancel >>.
505		747
506	if ($current == $self) {	748	The arguments are not copied, but instead will be referenced directly
507	terminate @_;	749	(e.g. if you pass C<$var> and after the call change that variable, then
508	} else {	750	you might change the return values passed to e.g. C<join>, so don't do
509	$self->{_status} = [@_];	751	that).
510	Coro::State::cancel $self;	752
		753	The resources of the Coro are usually freed (or destructed) before this
		754	call returns, but this can be delayed for an indefinite amount of time, as
		755	in some cases the manager thread has to run first to actually destruct the
		756	Coro object.
		757
		758	=item $coro->safe_cancel ($arg...)
		759
		760	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		761	consequently, can fail with an exception in cases the thread is not in a
		762	cancellable state.
		763
		764	This method works a bit like throwing an exception that cannot be caught
		765	- specifically, it will clean up the thread from within itself, so all
		766	cleanup handlers (e.g. C<guard> blocks) are run with full thread context
		767	and can block if they wish.
		768
		769	A thread is safe-cancellable if it either hasn't been run yet, or
		770	it has no C context attached and is inside an SLF function.
		771
		772	The latter two basically mean that the thread isn't currently inside a
		773	perl callback called from some C function (usually XS modules) and isn't
		774	currently inside some C function itself.
		775
		776	This call always returns true when it could cancel the thread, or croaks
		777	with an error otherwise, so you can write things like this:
		778
		779	if (! eval { $coro->safe_cancel }) {
		780	warn "unable to cancel thread: $@";
511	}	781	}
512	}
513		782
514	=item $coro->schedule_to	783	=item $coro->schedule_to
515		784
516	Puts the current coro to sleep (like C<Coro::schedule>), but instead	785	Puts the current coro to sleep (like C<Coro::schedule>), but instead
517	of continuing with the next coro from the ready queue, always switch to	786	of continuing with the next coro from the ready queue, always switch to
…		…
555		824
556	=item $coro->join	825	=item $coro->join
557		826
558	Wait until the coro terminates and return any values given to the	827	Wait until the coro terminates and return any values given to the
559	C<terminate> or C<cancel> functions. C<join> can be called concurrently	828	C<terminate> or C<cancel> functions. C<join> can be called concurrently
560	from multiple coro, and all will be resumed and given the status	829	from multiple threads, and all will be resumed and given the status
561	return once the C<$coro> terminates.	830	return once the C<$coro> terminates.
562		831
563	=cut	832	=cut
564		833
565	sub join {	834	sub join {
…		…
579	wantarray ? @{$self->{_status}} : $self->{_status}[0];	848	wantarray ? @{$self->{_status}} : $self->{_status}[0];
580	}	849	}
581		850
582	=item $coro->on_destroy (\&cb)	851	=item $coro->on_destroy (\&cb)
583		852
584	Registers a callback that is called when this coro gets destroyed,	853	Registers a callback that is called when this coro thread gets destroyed,
585	but before it is joined. The callback gets passed the terminate arguments,	854	that is, after it's resources have been freed but before it is joined. The
		855	callback gets passed the terminate/cancel arguments, if any, and I<must
586	if any, and I<must not> die, under any circumstances.	856	not> die, under any circumstances.
		857
		858	There can be any number of C<on_destroy> callbacks per coro, and there is
		859	no way currently to remove a callback once added.
587		860
588	=cut	861	=cut
589		862
590	sub on_destroy {	863	sub on_destroy {
591	my ($self, $cb) = @_;	864	my ($self, $cb) = @_;
…		…
594	}	867	}
595		868
596	=item $oldprio = $coro->prio ($newprio)	869	=item $oldprio = $coro->prio ($newprio)
597		870
598	Sets (or gets, if the argument is missing) the priority of the	871	Sets (or gets, if the argument is missing) the priority of the
599	coro. Higher priority coro get run before lower priority	872	coro thread. Higher priority coro get run before lower priority
600	coro. Priorities are small signed integers (currently -4 .. +3),	873	coros. Priorities are small signed integers (currently -4 .. +3),
601	that you can refer to using PRIO_xxx constants (use the import tag :prio	874	that you can refer to using PRIO_xxx constants (use the import tag :prio
602	to get then):	875	to get then):
603		876
604	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	877	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
605	3 > 1 > 0 > -1 > -3 > -4	878	3 > 1 > 0 > -1 > -3 > -4
606		879
607	# set priority to HIGH	880	# set priority to HIGH
608	current->prio (PRIO_HIGH);	881	current->prio (PRIO_HIGH);
609		882
610	The idle coro ($Coro::idle) always has a lower priority than any	883	The idle coro thread ($Coro::idle) always has a lower priority than any
611	existing coro.	884	existing coro.
612		885
613	Changing the priority of the current coro will take effect immediately,	886	Changing the priority of the current coro will take effect immediately,
614	but changing the priority of coro in the ready queue (but not	887	but changing the priority of a coro in the ready queue (but not running)
615	running) will only take effect after the next schedule (of that	888	will only take effect after the next schedule (of that coro). This is a
616	coro). This is a bug that will be fixed in some future version.	889	bug that will be fixed in some future version.
617		890
618	=item $newprio = $coro->nice ($change)	891	=item $newprio = $coro->nice ($change)
619		892
620	Similar to C<prio>, but subtract the given value from the priority (i.e.	893	Similar to C<prio>, but subtract the given value from the priority (i.e.
621	higher values mean lower priority, just as in unix).	894	higher values mean lower priority, just as in UNIX's nice command).
622		895
623	=item $olddesc = $coro->desc ($newdesc)	896	=item $olddesc = $coro->desc ($newdesc)
624		897
625	Sets (or gets in case the argument is missing) the description for this	898	Sets (or gets in case the argument is missing) the description for this
626	coro. This is just a free-form string you can associate with a	899	coro thread. This is just a free-form string you can associate with a
627	coro.	900	coro.
628		901
629	This method simply sets the C<< $coro->{desc} >> member to the given	902	This method simply sets the C<< $coro->{desc} >> member to the given
630	string. You can modify this member directly if you wish.	903	string. You can modify this member directly if you wish, and in fact, this
		904	is often preferred to indicate major processing states that cna then be
		905	seen for example in a L<Coro::Debug> session:
		906
		907	sub my_long_function {
		908	local $Coro::current->{desc} = "now in my_long_function";
		909	...
		910	$Coro::current->{desc} = "my_long_function: phase 1";
		911	...
		912	$Coro::current->{desc} = "my_long_function: phase 2";
		913	...
		914	}
631		915
632	=cut	916	=cut
633		917
634	sub desc {	918	sub desc {
635	my $old = $_[0]{desc};	919	my $old = $_[0]{desc};
…		…
672	returning a new coderef. Unblocking means that calling the new coderef	956	returning a new coderef. Unblocking means that calling the new coderef
673	will return immediately without blocking, returning nothing, while the	957	will return immediately without blocking, returning nothing, while the
674	original code ref will be called (with parameters) from within another	958	original code ref will be called (with parameters) from within another
675	coro.	959	coro.
676		960
677	The reason this function exists is that many event libraries (such as the	961	The reason this function exists is that many event libraries (such as
678	venerable L<Event\|Event> module) are not thread-safe (a weaker form	962	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
679	of reentrancy). This means you must not block within event callbacks,	963	of reentrancy). This means you must not block within event callbacks,
680	otherwise you might suffer from crashes or worse. The only event library	964	otherwise you might suffer from crashes or worse. The only event library
681	currently known that is safe to use without C<unblock_sub> is L<EV>.	965	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		966	you might still run into deadlocks if all event loops are blocked).
		967
		968	Coro will try to catch you when you block in the event loop
		969	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		970	only works when you do not run your own event loop.
682		971
683	This function allows your callbacks to block by executing them in another	972	This function allows your callbacks to block by executing them in another
684	coro where it is safe to block. One example where blocking is handy	973	coro where it is safe to block. One example where blocking is handy
685	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	974	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
686	disk, for example.	975	disk, for example.
…		…
728	unshift @unblock_queue, [$cb, @_];	1017	unshift @unblock_queue, [$cb, @_];
729	$unblock_scheduler->ready;	1018	$unblock_scheduler->ready;
730	}	1019	}
731	}	1020	}
732		1021
733	=item $cb = Coro::rouse_cb	1022	=item $cb = rouse_cb
734		1023
735	Create and return a "rouse callback". That's a code reference that,	1024	Create and return a "rouse callback". That's a code reference that,
736	when called, will remember a copy of its arguments and notify the owner	1025	when called, will remember a copy of its arguments and notify the owner
737	coro of the callback.	1026	coro of the callback.
738		1027
739	See the next function.	1028	See the next function.
740		1029
741	=item @args = Coro::rouse_wait [$cb]	1030	=item @args = rouse_wait [$cb]
742		1031
743	Wait for the specified rouse callback (or the last one that was created in	1032	Wait for the specified rouse callback (or the last one that was created in
744	this coro).	1033	this coro).
745		1034
746	As soon as the callback is invoked (or when the callback was invoked	1035	As soon as the callback is invoked (or when the callback was invoked
…		…
752	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1041	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
753		1042
754	=back	1043	=back
755		1044
756	=cut	1045	=cut
		1046
		1047	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1048	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1049
		1050	*{"Coro::$module\::new"} = sub {
		1051	require "Coro/$module.pm";
		1052
		1053	# some modules have their new predefined in State.xs, some don't
		1054	*{"Coro::$module\::new"} = $old
		1055	if $old;
		1056
		1057	goto &{"Coro::$module\::new"};
		1058	};
		1059	}
757		1060
758	1;	1061	1;
759		1062
760	=head1 HOW TO WAIT FOR A CALLBACK	1063	=head1 HOW TO WAIT FOR A CALLBACK
761		1064
…		…
843	the windows process emulation enabled under unix roughly halves perl	1146	the windows process emulation enabled under unix roughly halves perl
844	performance, even when not used.	1147	performance, even when not used.
845		1148
846	=item coro switching is not signal safe	1149	=item coro switching is not signal safe
847		1150
848	You must not switch to another coro from within a signal handler	1151	You must not switch to another coro from within a signal handler (only
849	(only relevant with %SIG - most event libraries provide safe signals).	1152	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1153	you are sure you are not interrupting a Coro function.
850		1154
851	That means you I<MUST NOT> call any function that might "block" the	1155	That means you I<MUST NOT> call any function that might "block" the
852	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1156	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
853	anything that calls those. Everything else, including calling C<ready>,	1157	anything that calls those. Everything else, including calling C<ready>,
854	works.	1158	works.
855		1159
856	=back	1160	=back
857		1161
858		1162
		1163	=head1 WINDOWS PROCESS EMULATION
		1164
		1165	A great many people seem to be confused about ithreads (for example, Chip
		1166	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1167	while in the same mail making rather confused statements about perl
		1168	ithreads (for example, that memory or files would be shared), showing his
		1169	lack of understanding of this area - if it is hard to understand for Chip,
		1170	it is probably not obvious to everybody).
		1171
		1172	What follows is an ultra-condensed version of my talk about threads in
		1173	scripting languages given on the perl workshop 2009:
		1174
		1175	The so-called "ithreads" were originally implemented for two reasons:
		1176	first, to (badly) emulate unix processes on native win32 perls, and
		1177	secondly, to replace the older, real thread model ("5.005-threads").
		1178
		1179	It does that by using threads instead of OS processes. The difference
		1180	between processes and threads is that threads share memory (and other
		1181	state, such as files) between threads within a single process, while
		1182	processes do not share anything (at least not semantically). That
		1183	means that modifications done by one thread are seen by others, while
		1184	modifications by one process are not seen by other processes.
		1185
		1186	The "ithreads" work exactly like that: when creating a new ithreads
		1187	process, all state is copied (memory is copied physically, files and code
		1188	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1189	the same behaviour can be achieved by using operating system processes,
		1190	except that UNIX typically uses hardware built into the system to do this
		1191	efficiently, while the windows process emulation emulates this hardware in
		1192	software (rather efficiently, but of course it is still much slower than
		1193	dedicated hardware).
		1194
		1195	As mentioned before, loading code, modifying code, modifying data
		1196	structures and so on is only visible in the ithreads process doing the
		1197	modification, not in other ithread processes within the same OS process.
		1198
		1199	This is why "ithreads" do not implement threads for perl at all, only
		1200	processes. What makes it so bad is that on non-windows platforms, you can
		1201	actually take advantage of custom hardware for this purpose (as evidenced
		1202	by the forks module, which gives you the (i-) threads API, just much
		1203	faster).
		1204
		1205	Sharing data is in the i-threads model is done by transfering data
		1206	structures between threads using copying semantics, which is very slow -
		1207	shared data simply does not exist. Benchmarks using i-threads which are
		1208	communication-intensive show extremely bad behaviour with i-threads (in
		1209	fact, so bad that Coro, which cannot take direct advantage of multiple
		1210	CPUs, is often orders of magnitude faster because it shares data using
		1211	real threads, refer to my talk for details).
		1212
		1213	As summary, i-threads use threads to implement processes, while
		1214	the compatible forks module uses processes to emulate, uhm,
		1215	processes. I-threads slow down every perl program when enabled, and
		1216	outside of windows, serve no (or little) practical purpose, but
		1217	disadvantages every single-threaded Perl program.
		1218
		1219	This is the reason that I try to avoid the name "ithreads", as it is
		1220	misleading as it implies that it implements some kind of thread model for
		1221	perl, and prefer the name "windows process emulation", which describes the
		1222	actual use and behaviour of it much better.
		1223
859	=head1 SEE ALSO	1224	=head1 SEE ALSO
860		1225
861	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1226	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
862		1227
863	Debugging: L<Coro::Debug>.	1228	Debugging: L<Coro::Debug>.

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Revision 1.294 by root, Fri May 6 21:15:17 2011 UTC