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

Comparing Coro/Coro.pm (file contents):
Revision 1.229 by root, Thu Nov 20 06:32:55 2008 UTC vs.
Revision 1.294 by root, Fri May 6 21:15:17 2011 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
11	print "2\n";	11	print "2\n";
12	cede; # yield back to main	12	cede; # yield back to main
13	print "4\n";	13	print "4\n";
14	};	14	};
15	print "1\n";	15	print "1\n";
16	cede; # yield to coroutine	16	cede; # yield to coro
17	print "3\n";	17	print "3\n";
18	cede; # and again	18	cede; # and again
19		19
20	# use locking	20	# use locking
21	use Coro::Semaphore;	21	use Coro::Semaphore;
…		…
26	$locked = 1;	26	$locked = 1;
27	$lock->up;	27	$lock->up;
28		28
29	=head1 DESCRIPTION	29	=head1 DESCRIPTION
30		30
31	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
32	threads but don't (in general) run in parallel at the same time even	32	manpage. This manpage mainly contains reference information.
33	on SMP machines. The specific flavor of coroutine used in this module
34	also guarantees you that it will not switch between coroutines unless
35	necessary, at easily-identified points in your program, so locking and
36	parallel access are rarely an issue, making coroutine programming much
37	safer and easier than threads programming.
38		33
39	Unlike a normal perl program, however, coroutines allow you to have	34	This module collection manages continuations in general, most often in
40	multiple running interpreters that share data, which is especially useful	35	the form of cooperative threads (also called coros, or simply "coro"
41	to code pseudo-parallel processes and for event-based programming, such as	36	in the documentation). They are similar to kernel threads but don't (in
42	multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to	37	general) run in parallel at the same time even on SMP machines. The
43	learn more.	38	specific flavor of thread offered by this module also guarantees you that
		39	it will not switch between threads unless necessary, at easily-identified
		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
		42	thread models.
44		43
45	Coroutines are also useful because Perl has no support for threads (the so	44	Unlike the so-called "Perl threads" (which are not actually real threads
46	called "threads" that perl offers are nothing more than the (bad) process	45	but only the windows process emulation (see section of same name for
47	emulation coming from the Windows platform: On standard operating systems	46	more details) ported to UNIX, and as such act as processes), Coro
48	they serve no purpose whatsoever, except by making your programs slow and	47	provides a full shared address space, which makes communication between
49	making them use a lot of memory. Best disable them when building perl, or	48	threads very easy. And coro threads are fast, too: disabling the Windows
50	aks your software vendor/distributor to do it for you).	49	process emulation code in your perl and using Coro can easily result in
		50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark (very communication-intensive) runs over 300
		52	times faster on a single core than perls pseudo-threads on a quad core
		53	using all four cores.
51		54
		55	Coro achieves that by supporting multiple running interpreters that share
		56	data, which is especially useful to code pseudo-parallel processes and
		57	for event-based programming, such as multiple HTTP-GET requests running
		58	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		59	into an event-based environment.
		60
52	In this module, coroutines are defined as "callchain + lexical variables +	61	In this module, a thread is defined as "callchain + lexical variables +
53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	62	some package variables + C stack), that is, a thread has its own callchain,
54	its own set of lexicals and its own set of perls most important global	63	its own set of lexicals and its own set of perls most important global
55	variables (see L<Coro::State> for more configuration).	64	variables (see L<Coro::State> for more configuration and background info).
		65
		66	See also the C<SEE ALSO> section at the end of this document - the Coro
		67	module family is quite large.
		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
56		316
57	=cut	317	=cut
58		318
59	package Coro;	319	package Coro;
60		320
61	use strict qw(vars subs);	321	use common::sense;
62	no warnings "uninitialized";	322
		323	use Carp ();
		324
		325	use Guard ();
63		326
64	use Coro::State;	327	use Coro::State;
65		328
66	use base qw(Coro::State Exporter);	329	use base qw(Coro::State Exporter);
67		330
68	our $idle; # idle handler	331	our $idle; # idle handler
69	our $main; # main coroutine	332	our $main; # main coro
70	our $current; # current coroutine	333	our $current; # current coro
71		334
72	our $VERSION = 5.0;	335	our $VERSION = 5.372;
73		336
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	337	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	338	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	339	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	340	);
78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	341	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
79		342
		343	=head1 GLOBAL VARIABLES
		344
80	=over 4	345	=over 4
81		346
82	=item $Coro::main	347	=item $Coro::main
83		348
84	This variable stores the coroutine object that represents the main	349	This variable stores the Coro object that represents the main
85	program. While you cna C<ready> it and do most other things you can do to	350	program. While you cna C<ready> it and do most other things you can do to
86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	351	coro, it is mainly useful to compare again C<$Coro::current>, to see
87	whether you are running in the main program or not.	352	whether you are running in the main program or not.
88		353
89	=cut	354	=cut
90		355
91	# $main is now being initialised by Coro::State	356	# $main is now being initialised by Coro::State
92		357
93	=item $Coro::current	358	=item $Coro::current
94		359
95	The coroutine object representing the current coroutine (the last	360	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	361	coro that the Coro scheduler switched to). The initial value is
97	C<$Coro::main> (of course).	362	C<$Coro::main> (of course).
98		363
99	This variable is B<strictly> I<read-only>. You can take copies of the	364	This variable is B<strictly> I<read-only>. You can take copies of the
100	value stored in it and use it as any other coroutine object, but you must	365	value stored in it and use it as any other Coro object, but you must
101	not otherwise modify the variable itself.	366	not otherwise modify the variable itself.
102		367
103	=cut	368	=cut
104		369
105	sub current() { $current } # [DEPRECATED]	370	sub current() { $current } # [DEPRECATED]
106		371
107	=item $Coro::idle	372	=item $Coro::idle
108		373
109	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
110	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is	375	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
111	pretty low-level functionality.	376	pretty low-level functionality.
112		377
113	This variable stores a callback that is called whenever the scheduler	378	This variable stores a Coro object that is put into the ready queue when
114	finds no ready coroutines to run. The default implementation prints	379	there are no other ready threads (without invoking any ready hooks).
115	"FATAL: deadlock detected" and exits, because the program has no other way
116	to continue.
117		380
		381	The default implementation dies with "FATAL: deadlock detected.", followed
		382	by a thread listing, because the program has no other way to continue.
		383
118	This hook is overwritten by modules such as C<Coro::Timer> and	384	This hook is overwritten by modules such as C<Coro::EV> and
119	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
120	coroutine so the scheduler can run it.	386	coro so the scheduler can run it.
121		387
122	Note that the callback I<must not>, under any circumstances, block
123	the current coroutine. Normally, this is achieved by having an "idle
124	coroutine" that calls the event loop and then blocks again, and then
125	readying that coroutine in the idle handler.
126
127	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.
128	technique.
129		389
130	Please note that if your callback recursively invokes perl (e.g. for event
131	handlers), then it must be prepared to be called recursively itself.
132
133	=cut	390	=cut
134		391
135	$idle = sub {	392	# \|\|= because other modules could have provided their own by now
136	require Carp;	393	$idle \|\|= new Coro sub {
137	Carp::croak ("FATAL: deadlock detected");	394	require Coro::Debug;
		395	die "FATAL: deadlock detected.\n"
		396	. Coro::Debug::ps_listing ();
138	};	397	};
139		398
140	sub _cancel {
141	my ($self) = @_;
142
143	# free coroutine data and mark as destructed
144	$self->_destroy
145	or return;
146
147	# call all destruction callbacks
148	$_->(@{$self->{_status}})
149	for @{ delete $self->{_on_destroy} \|\| [] };
150	}
151
152	# this coroutine is necessary because a coroutine	399	# this coro is necessary because a coro
153	# cannot destroy itself.	400	# cannot destroy itself.
154	our @destroy;	401	our @destroy;
155	our $manager;	402	our $manager;
156		403
157	$manager = new Coro sub {	404	$manager = new Coro sub {
158	while () {	405	while () {
159	(shift @destroy)->_cancel	406	_destroy shift @destroy
160	while @destroy;	407	while @destroy;
161		408
162	&schedule;	409	&schedule;
163	}	410	}
164	};	411	};
165	$manager->{desc} = "[coro manager]";	412	$manager->{desc} = "[coro manager]";
166	$manager->prio (PRIO_MAX);	413	$manager->prio (PRIO_MAX);
167		414
168	=back	415	=back
169		416
170	=head2 SIMPLE COROUTINE CREATION	417	=head1 SIMPLE CORO CREATION
171		418
172	=over 4	419	=over 4
173		420
174	=item async { ... } [@args...]	421	=item async { ... } [@args...]
175		422
176	Create a new coroutine and return it's coroutine object (usually	423	Create a new coro and return its Coro object (usually
177	unused). The coroutine will be put into the ready queue, so	424	unused). The coro will be put into the ready queue, so
178	it will start running automatically on the next scheduler run.	425	it will start running automatically on the next scheduler run.
179		426
180	The first argument is a codeblock/closure that should be executed in the	427	The first argument is a codeblock/closure that should be executed in the
181	coroutine. When it returns argument returns the coroutine is automatically	428	coro. When it returns argument returns the coro is automatically
182	terminated.	429	terminated.
183		430
184	The remaining arguments are passed as arguments to the closure.	431	The remaining arguments are passed as arguments to the closure.
185		432
186	See the C<Coro::State::new> constructor for info about the coroutine	433	See the C<Coro::State::new> constructor for info about the coro
187	environment in which coroutines are executed.	434	environment in which coro are executed.
188		435
189	Calling C<exit> in a coroutine will do the same as calling exit outside	436	Calling C<exit> in a coro will do the same as calling exit outside
190	the coroutine. Likewise, when the coroutine dies, the program will exit,	437	the coro. Likewise, when the coro dies, the program will exit,
191	just as it would in the main program.	438	just as it would in the main program.
192		439
193	If you do not want that, you can provide a default C<die> handler, or	440	If you do not want that, you can provide a default C<die> handler, or
194	simply avoid dieing (by use of C<eval>).	441	simply avoid dieing (by use of C<eval>).
195		442
196	Example: Create a new coroutine that just prints its arguments.	443	Example: Create a new coro that just prints its arguments.
197		444
198	async {	445	async {
199	print "@_\n";	446	print "@_\n";
200	} 1,2,3,4;	447	} 1,2,3,4;
201		448
202	=cut
203
204	sub async(&@) {
205	my $coro = new Coro @_;
206	$coro->ready;
207	$coro
208	}
209
210	=item async_pool { ... } [@args...]	449	=item async_pool { ... } [@args...]
211		450
212	Similar to C<async>, but uses a coroutine pool, so you should not call	451	Similar to C<async>, but uses a coro pool, so you should not call
213	terminate or join on it (although you are allowed to), and you get a	452	terminate or join on it (although you are allowed to), and you get a
214	coroutine that might have executed other code already (which can be good	453	coro that might have executed other code already (which can be good
215	or bad :).	454	or bad :).
216		455
217	On the plus side, this function is about twice as fast as creating (and	456	On the plus side, this function is about twice as fast as creating (and
218	destroying) a completely new coroutine, so if you need a lot of generic	457	destroying) a completely new coro, so if you need a lot of generic
219	coroutines in quick successsion, use C<async_pool>, not C<async>.	458	coros in quick successsion, use C<async_pool>, not C<async>.
220		459
221	The code block is executed in an C<eval> context and a warning will be	460	The code block is executed in an C<eval> context and a warning will be
222	issued in case of an exception instead of terminating the program, as	461	issued in case of an exception instead of terminating the program, as
223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	462	C<async> does. As the coro is being reused, stuff like C<on_destroy>
224	will not work in the expected way, unless you call terminate or cancel,	463	will not work in the expected way, unless you call terminate or cancel,
225	which somehow defeats the purpose of pooling (but is fine in the	464	which somehow defeats the purpose of pooling (but is fine in the
226	exceptional case).	465	exceptional case).
227		466
228	The priority will be reset to C<0> after each run, tracing will be	467	The priority will be reset to C<0> after each run, tracing will be
229	disabled, the description will be reset and the default output filehandle	468	disabled, the description will be reset and the default output filehandle
230	gets restored, so you can change all these. Otherwise the coroutine will	469	gets restored, so you can change all these. Otherwise the coro will
231	be re-used "as-is": most notably if you change other per-coroutine global	470	be re-used "as-is": most notably if you change other per-coro global
232	stuff such as C<$/> you I<must needs> revert that change, which is most	471	stuff such as C<$/> you I<must needs> revert that change, which is most
233	simply done by using local as in: C<< local $/ >>.	472	simply done by using local as in: C<< local $/ >>.
234		473
235	The idle pool size is limited to C<8> idle coroutines (this can be	474	The idle pool size is limited to C<8> idle coros (this can be
236	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle	475	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
237	coros as required.	476	coros as required.
238		477
239	If you are concerned about pooled coroutines growing a lot because a	478	If you are concerned about pooled coros growing a lot because a
240	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	479	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
241	{ terminate }> once per second or so to slowly replenish the pool. In	480	{ terminate }> once per second or so to slowly replenish the pool. In
242	addition to that, when the stacks used by a handler grows larger than 16kb	481	addition to that, when the stacks used by a handler grows larger than 32kb
243	(adjustable via $Coro::POOL_RSS) it will also be destroyed.	482	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
244		483
245	=cut	484	=cut
246		485
247	our $POOL_SIZE = 8;	486	our $POOL_SIZE = 8;
248	our $POOL_RSS = 16 * 1024;	487	our $POOL_RSS = 32 * 1024;
249	our @async_pool;	488	our @async_pool;
250		489
251	sub pool_handler {	490	sub pool_handler {
252	while () {	491	while () {
253	eval {	492	eval {
…		…
258	}	497	}
259	}	498	}
260		499
261	=back	500	=back
262		501
263	=head2 STATIC METHODS	502	=head1 STATIC METHODS
264		503
265	Static methods are actually functions that operate on the current coroutine.	504	Static methods are actually functions that implicitly operate on the
		505	current coro.
266		506
267	=over 4	507	=over 4
268		508
269	=item schedule	509	=item schedule
270		510
271	Calls the scheduler. The scheduler will find the next coroutine that is	511	Calls the scheduler. The scheduler will find the next coro that is
272	to be run from the ready queue and switches to it. The next coroutine	512	to be run from the ready queue and switches to it. The next coro
273	to be run is simply the one with the highest priority that is longest	513	to be run is simply the one with the highest priority that is longest
274	in its ready queue. If there is no coroutine ready, it will clal the	514	in its ready queue. If there is no coro ready, it will call the
275	C<$Coro::idle> hook.	515	C<$Coro::idle> hook.
276		516
277	Please note that the current coroutine will I<not> be put into the ready	517	Please note that the current coro will I<not> be put into the ready
278	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
279	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 >>,
280	thus waking you up.	520	thus waking you up.
281		521
282	This makes C<schedule> I<the> generic method to use to block the current	522	This makes C<schedule> I<the> generic method to use to block the current
283	coroutine and wait for events: first you remember the current coroutine in	523	coro and wait for events: first you remember the current coro in
284	a variable, then arrange for some callback of yours to call C<< ->ready	524	a variable, then arrange for some callback of yours to call C<< ->ready
285	>> on that once some event happens, and last you call C<schedule> to put	525	>> on that once some event happens, and last you call C<schedule> to put
286	yourself to sleep. Note that a lot of things can wake your coroutine up,	526	yourself to sleep. Note that a lot of things can wake your coro up,
287	so you need to check whether the event indeed happened, e.g. by storing the	527	so you need to check whether the event indeed happened, e.g. by storing the
288	status in a variable.	528	status in a variable.
289		529
290	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	530	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
291		531
292	=item cede	532	=item cede
293		533
294	"Cede" to other coroutines. This function puts the current coroutine into	534	"Cede" to other coros. This function puts the current coro into
295	the ready queue and calls C<schedule>, which has the effect of giving	535	the ready queue and calls C<schedule>, which has the effect of giving
296	up the current "timeslice" to other coroutines of the same or higher	536	up the current "timeslice" to other coros of the same or higher
297	priority. Once your coroutine gets its turn again it will automatically be	537	priority. Once your coro gets its turn again it will automatically be
298	resumed.	538	resumed.
299		539
300	This function is often called C<yield> in other languages.	540	This function is often called C<yield> in other languages.
301		541
302	=item Coro::cede_notself	542	=item Coro::cede_notself
303		543
304	Works like cede, but is not exported by default and will cede to I<any>	544	Works like cede, but is not exported by default and will cede to I<any>
305	coroutine, regardless of priority. This is useful sometimes to ensure	545	coro, regardless of priority. This is useful sometimes to ensure
306	progress is made.	546	progress is made.
307		547
308	=item terminate [arg...]	548	=item terminate [arg...]
309		549
310	Terminates the current coroutine 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.
		552
		553	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		554
		555	These function install enter and leave winders in the current scope. The
		556	enter block will be executed when on_enter is called and whenever the
		557	current coro is re-entered by the scheduler, while the leave block is
		558	executed whenever the current coro is blocked by the scheduler, and
		559	also when the containing scope is exited (by whatever means, be it exit,
		560	die, last etc.).
		561
		562	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		563	BLOCKs>. That means: do not even think about calling C<die> without an
		564	eval, and do not even think of entering the scheduler in any way.
		565
		566	Since both BLOCKs are tied to the current scope, they will automatically
		567	be removed when the current scope exits.
		568
		569	These functions implement the same concept as C<dynamic-wind> in scheme
		570	does, and are useful when you want to localise some resource to a specific
		571	coro.
		572
		573	They slow down thread switching considerably for coros that use them
		574	(about 40% for a BLOCK with a single assignment, so thread switching is
		575	still reasonably fast if the handlers are fast).
		576
		577	These functions are best understood by an example: The following function
		578	will change the current timezone to "Antarctica/South_Pole", which
		579	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		580	which remember/change the current timezone and restore the previous
		581	value, respectively, the timezone is only changed for the coro that
		582	installed those handlers.
		583
		584	use POSIX qw(tzset);
		585
		586	async {
		587	my $old_tz; # store outside TZ value here
		588
		589	Coro::on_enter {
		590	$old_tz = $ENV{TZ}; # remember the old value
		591
		592	$ENV{TZ} = "Antarctica/South_Pole";
		593	tzset; # enable new value
		594	};
		595
		596	Coro::on_leave {
		597	$ENV{TZ} = $old_tz;
		598	tzset; # restore old value
		599	};
		600
		601	# at this place, the timezone is Antarctica/South_Pole,
		602	# without disturbing the TZ of any other coro.
		603	};
		604
		605	This can be used to localise about any resource (locale, uid, current
		606	working directory etc.) to a block, despite the existance of other
		607	coros.
		608
		609	Another interesting example implements time-sliced multitasking using
		610	interval timers (this could obviously be optimised, but does the job):
		611
		612	# "timeslice" the given block
		613	sub timeslice(&) {
		614	use Time::HiRes ();
		615
		616	Coro::on_enter {
		617	# on entering the thread, we set an VTALRM handler to cede
		618	$SIG{VTALRM} = sub { cede };
		619	# and then start the interval timer
		620	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		621	};
		622	Coro::on_leave {
		623	# on leaving the thread, we stop the interval timer again
		624	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		625	};
		626
		627	&{+shift};
		628	}
		629
		630	# use like this:
		631	timeslice {
		632	# The following is an endless loop that would normally
		633	# monopolise the process. Since it runs in a timesliced
		634	# environment, it will regularly cede to other threads.
		635	while () { }
		636	};
		637
311		638
312	=item killall	639	=item killall
313		640
314	Kills/terminates/cancels all coroutines except the currently running	641	Kills/terminates/cancels all coros except the currently running one.
315	one. This is useful after a fork, either in the child or the parent, as
316	usually only one of them should inherit the running coroutines.
317		642
318	Note that while this will try to free some of the main programs resources,	643	Note that while this will try to free some of the main interpreter
		644	resources if the calling coro isn't the main coro, but one
319	you cannot free all of them, so if a coroutine that is not the main	645	cannot free all of them, so if a coro that is not the main coro
320	program calls this function, there will be some one-time resource leak.	646	calls this function, there will be some one-time resource leak.
321		647
322	=cut	648	=cut
323
324	sub terminate {
325	$current->{_status} = [@_];
326	push @destroy, $current;
327	$manager->ready;
328	do { &schedule } while 1;
329	}
330		649
331	sub killall {	650	sub killall {
332	for (Coro::State::list) {	651	for (Coro::State::list) {
333	$_->cancel	652	$_->cancel
334	if $_ != $current && UNIVERSAL::isa $_, "Coro";	653	if $_ != $current && UNIVERSAL::isa $_, "Coro";
335	}	654	}
336	}	655	}
337		656
338	=back	657	=back
339		658
340	=head2 COROUTINE METHODS	659	=head1 CORO OBJECT METHODS
341		660
342	These are the methods you can call on coroutine objects (or to create	661	These are the methods you can call on coro objects (or to create
343	them).	662	them).
344		663
345	=over 4	664	=over 4
346		665
347	=item new Coro \&sub [, @args...]	666	=item new Coro \&sub [, @args...]
348		667
349	Create a new coroutine and return it. When the sub returns, the coroutine	668	Create a new coro and return it. When the sub returns, the coro
350	automatically terminates as if C<terminate> with the returned values were	669	automatically terminates as if C<terminate> with the returned values were
351	called. To make the coroutine run you must first put it into the ready	670	called. To make the coro run you must first put it into the ready
352	queue by calling the ready method.	671	queue by calling the ready method.
353		672
354	See C<async> and C<Coro::State::new> for additional info about the	673	See C<async> and C<Coro::State::new> for additional info about the
355	coroutine environment.	674	coro environment.
356		675
357	=cut	676	=cut
358		677
359	sub _terminate {	678	sub _coro_run {
360	terminate &{+shift};	679	terminate &{+shift};
361	}	680	}
362		681
363	=item $success = $coroutine->ready	682	=item $success = $coro->ready
364		683
365	Put the given coroutine into the end of its ready queue (there is one	684	Put the given coro into the end of its ready queue (there is one
366	queue for each priority) and return true. If the coroutine is already in	685	queue for each priority) and return true. If the coro is already in
367	the ready queue, do nothing and return false.	686	the ready queue, do nothing and return false.
368		687
369	This ensures that the scheduler will resume this coroutine automatically	688	This ensures that the scheduler will resume this coro automatically
370	once all the coroutines of higher priority and all coroutines of the same	689	once all the coro of higher priority and all coro of the same
371	priority that were put into the ready queue earlier have been resumed.	690	priority that were put into the ready queue earlier have been resumed.
372		691
		692	=item $coro->suspend
		693
		694	Suspends the specified coro. A suspended coro works just like any other
		695	coro, except that the scheduler will not select a suspended coro for
		696	execution.
		697
		698	Suspending a coro can be useful when you want to keep the coro from
		699	running, but you don't want to destroy it, or when you want to temporarily
		700	freeze a coro (e.g. for debugging) to resume it later.
		701
		702	A scenario for the former would be to suspend all (other) coros after a
		703	fork and keep them alive, so their destructors aren't called, but new
		704	coros can be created.
		705
		706	=item $coro->resume
		707
		708	If the specified coro was suspended, it will be resumed. Note that when
		709	the coro was in the ready queue when it was suspended, it might have been
		710	unreadied by the scheduler, so an activation might have been lost.
		711
		712	To avoid this, it is best to put a suspended coro into the ready queue
		713	unconditionally, as every synchronisation mechanism must protect itself
		714	against spurious wakeups, and the one in the Coro family certainly do
		715	that.
		716
373	=item $is_ready = $coroutine->is_ready	717	=item $is_ready = $coro->is_ready
374		718
375	Return whether the coroutine is currently the ready queue or not,	719	Returns true iff the Coro object is in the ready queue. Unless the Coro
		720	object gets destroyed, it will eventually be scheduled by the scheduler.
376		721
		722	=item $is_running = $coro->is_running
		723
		724	Returns true iff the Coro object is currently running. Only one Coro object
		725	can ever be in the running state (but it currently is possible to have
		726	multiple running Coro::States).
		727
		728	=item $is_suspended = $coro->is_suspended
		729
		730	Returns true iff this Coro object has been suspended. Suspended Coros will
		731	not ever be scheduled.
		732
377	=item $coroutine->cancel (arg...)	733	=item $coro->cancel (arg...)
378		734
379	Terminates the given coroutine and makes it return the given arguments as	735	Terminates the given Coro thread and makes it return the given arguments as
380	status (default: the empty list). Never returns if the coroutine is the	736	status (default: an empty list). Never returns if the Coro is the
381	current coroutine.	737	current Coro.
382		738
383	=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.
384		744
385	sub cancel {	745	Sometimes it is safer to C<< ->throw >> an exception, or use C<<
386	my $self = shift;	746	->safe_cancel >>.
387		747
388	if ($current == $self) {	748	The arguments are not copied, but instead will be referenced directly
389	terminate @_;	749	(e.g. if you pass C<$var> and after the call change that variable, then
390	} else {	750	you might change the return values passed to e.g. C<join>, so don't do
391	$self->{_status} = [@_];	751	that).
392	$self->_cancel;	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: $@";
393	}	781	}
394	}
395		782
396	=item $coroutine->schedule_to	783	=item $coro->schedule_to
397		784
398	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead	785	Puts the current coro to sleep (like C<Coro::schedule>), but instead
399	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
400	the given coroutine object (regardless of priority etc.). The readyness	787	the given coro object (regardless of priority etc.). The readyness
401	state of that coroutine isn't changed.	788	state of that coro isn't changed.
402		789
403	This is an advanced method for special cases - I'd love to hear about any	790	This is an advanced method for special cases - I'd love to hear about any
404	uses for this one.	791	uses for this one.
405		792
406	=item $coroutine->cede_to	793	=item $coro->cede_to
407		794
408	Like C<schedule_to>, but puts the current coroutine into the ready	795	Like C<schedule_to>, but puts the current coro into the ready
409	queue. This has the effect of temporarily switching to the given	796	queue. This has the effect of temporarily switching to the given
410	coroutine, and continuing some time later.	797	coro, and continuing some time later.
411		798
412	This is an advanced method for special cases - I'd love to hear about any	799	This is an advanced method for special cases - I'd love to hear about any
413	uses for this one.	800	uses for this one.
414		801
415	=item $coroutine->throw ([$scalar])	802	=item $coro->throw ([$scalar])
416		803
417	If C<$throw> is specified and defined, it will be thrown as an exception	804	If C<$throw> is specified and defined, it will be thrown as an exception
418	inside the coroutine at the next convenient point in time. Otherwise	805	inside the coro at the next convenient point in time. Otherwise
419	clears the exception object.	806	clears the exception object.
420		807
421	Coro will check for the exception each time a schedule-like-function	808	Coro will check for the exception each time a schedule-like-function
422	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down	809	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
423	>>, C<< Coro::Handle->readable >> and so on. Most of these functions	810	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
…		…
425		812
426	The exception object will be thrown "as is" with the specified scalar in	813	The exception object will be thrown "as is" with the specified scalar in
427	C<$@>, i.e. if it is a string, no line number or newline will be appended	814	C<$@>, i.e. if it is a string, no line number or newline will be appended
428	(unlike with C<die>).	815	(unlike with C<die>).
429		816
430	This can be used as a softer means than C<cancel> to ask a coroutine to	817	This can be used as a softer means than C<cancel> to ask a coro to
431	end itself, although there is no guarantee that the exception will lead to	818	end itself, although there is no guarantee that the exception will lead to
432	termination, and if the exception isn't caught it might well end the whole	819	termination, and if the exception isn't caught it might well end the whole
433	program.	820	program.
434		821
435	You might also think of C<throw> as being the moral equivalent of	822	You might also think of C<throw> as being the moral equivalent of
436	C<kill>ing a coroutine with a signal (in this case, a scalar).	823	C<kill>ing a coro with a signal (in this case, a scalar).
437		824
438	=item $coroutine->join	825	=item $coro->join
439		826
440	Wait until the coroutine terminates and return any values given to the	827	Wait until the coro terminates and return any values given to the
441	C<terminate> or C<cancel> functions. C<join> can be called concurrently	828	C<terminate> or C<cancel> functions. C<join> can be called concurrently
442	from multiple coroutines, and all will be resumed and given the status	829	from multiple threads, and all will be resumed and given the status
443	return once the C<$coroutine> terminates.	830	return once the C<$coro> terminates.
444		831
445	=cut	832	=cut
446		833
447	sub join {	834	sub join {
448	my $self = shift;	835	my $self = shift;
…		…
459	}	846	}
460		847
461	wantarray ? @{$self->{_status}} : $self->{_status}[0];	848	wantarray ? @{$self->{_status}} : $self->{_status}[0];
462	}	849	}
463		850
464	=item $coroutine->on_destroy (\&cb)	851	=item $coro->on_destroy (\&cb)
465		852
466	Registers a callback that is called when this coroutine gets destroyed,	853	Registers a callback that is called when this coro thread gets destroyed,
467	but before it is joined. The callback gets passed the terminate arguments,	854	that is, after it's resources have been freed but before it is joined. The
		855	callback gets passed the terminate/cancel arguments, if any, and I<must
468	if any, and I<must not> die, under any circumstances.	856	not> die, under any circumstances.
		857
		858	There can be any number of C<on_destroy> callbacks per coro, and there is
		859	no way currently to remove a callback once added.
469		860
470	=cut	861	=cut
471		862
472	sub on_destroy {	863	sub on_destroy {
473	my ($self, $cb) = @_;	864	my ($self, $cb) = @_;
474		865
475	push @{ $self->{_on_destroy} }, $cb;	866	push @{ $self->{_on_destroy} }, $cb;
476	}	867	}
477		868
478	=item $oldprio = $coroutine->prio ($newprio)	869	=item $oldprio = $coro->prio ($newprio)
479		870
480	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
481	coroutine. Higher priority coroutines get run before lower priority	872	coro thread. Higher priority coro get run before lower priority
482	coroutines. Priorities are small signed integers (currently -4 .. +3),	873	coros. Priorities are small signed integers (currently -4 .. +3),
483	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
484	to get then):	875	to get then):
485		876
486	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
487	3 > 1 > 0 > -1 > -3 > -4	878	3 > 1 > 0 > -1 > -3 > -4
488		879
489	# set priority to HIGH	880	# set priority to HIGH
490	current->prio(PRIO_HIGH);	881	current->prio (PRIO_HIGH);
491		882
492	The idle coroutine ($Coro::idle) always has a lower priority than any	883	The idle coro thread ($Coro::idle) always has a lower priority than any
493	existing coroutine.	884	existing coro.
494		885
495	Changing the priority of the current coroutine will take effect immediately,	886	Changing the priority of the current coro will take effect immediately,
496	but changing the priority of coroutines in the ready queue (but not	887	but changing the priority of a coro in the ready queue (but not running)
497	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
498	coroutine). This is a bug that will be fixed in some future version.	889	bug that will be fixed in some future version.
499		890
500	=item $newprio = $coroutine->nice ($change)	891	=item $newprio = $coro->nice ($change)
501		892
502	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.
503	higher values mean lower priority, just as in unix).	894	higher values mean lower priority, just as in UNIX's nice command).
504		895
505	=item $olddesc = $coroutine->desc ($newdesc)	896	=item $olddesc = $coro->desc ($newdesc)
506		897
507	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
508	coroutine. 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
509	coroutine.	900	coro.
510		901
511	This method simply sets the C<< $coroutine->{desc} >> member to the given	902	This method simply sets the C<< $coro->{desc} >> member to the given
512	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	}
513		915
514	=cut	916	=cut
515		917
516	sub desc {	918	sub desc {
517	my $old = $_[0]{desc};	919	my $old = $_[0]{desc};
518	$_[0]{desc} = $_[1] if @_ > 1;	920	$_[0]{desc} = $_[1] if @_ > 1;
519	$old;	921	$old;
520	}	922	}
521		923
		924	sub transfer {
		925	require Carp;
		926	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		927	}
		928
522	=back	929	=back
523		930
524	=head2 GLOBAL FUNCTIONS	931	=head1 GLOBAL FUNCTIONS
525		932
526	=over 4	933	=over 4
527		934
528	=item Coro::nready	935	=item Coro::nready
529		936
530	Returns the number of coroutines that are currently in the ready state,	937	Returns the number of coro that are currently in the ready state,
531	i.e. that can be switched to by calling C<schedule> directory or	938	i.e. that can be switched to by calling C<schedule> directory or
532	indirectly. The value C<0> means that the only runnable coroutine is the	939	indirectly. The value C<0> means that the only runnable coro is the
533	currently running one, so C<cede> would have no effect, and C<schedule>	940	currently running one, so C<cede> would have no effect, and C<schedule>
534	would cause a deadlock unless there is an idle handler that wakes up some	941	would cause a deadlock unless there is an idle handler that wakes up some
535	coroutines.	942	coro.
536		943
537	=item my $guard = Coro::guard { ... }	944	=item my $guard = Coro::guard { ... }
538		945
539	This creates and returns a guard object. Nothing happens until the object	946	This function still exists, but is deprecated. Please use the
540	gets destroyed, in which case the codeblock given as argument will be	947	C<Guard::guard> function instead.
541	executed. This is useful to free locks or other resources in case of a
542	runtime error or when the coroutine gets canceled, as in both cases the
543	guard block will be executed. The guard object supports only one method,
544	C<< ->cancel >>, which will keep the codeblock from being executed.
545		948
546	Example: set some flag and clear it again when the coroutine gets canceled
547	or the function returns:
548
549	sub do_something {
550	my $guard = Coro::guard { $busy = 0 };
551	$busy = 1;
552
553	# do something that requires $busy to be true
554	}
555
556	=cut	949	=cut
557		950
558	sub guard(&) {	951	BEGIN { *guard = \&Guard::guard }
559	bless \(my $cb = $_[0]), "Coro::guard"
560	}
561
562	sub Coro::guard::cancel {
563	${$_[0]} = sub { };
564	}
565
566	sub Coro::guard::DESTROY {
567	${$_[0]}->();
568	}
569
570		952
571	=item unblock_sub { ... }	953	=item unblock_sub { ... }
572		954
573	This utility function takes a BLOCK or code reference and "unblocks" it,	955	This utility function takes a BLOCK or code reference and "unblocks" it,
574	returning a new coderef. Unblocking means that calling the new coderef	956	returning a new coderef. Unblocking means that calling the new coderef
575	will return immediately without blocking, returning nothing, while the	957	will return immediately without blocking, returning nothing, while the
576	original code ref will be called (with parameters) from within another	958	original code ref will be called (with parameters) from within another
577	coroutine.	959	coro.
578		960
579	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
580	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	962	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
581	of thread-safety). This means you must not block within event callbacks,	963	of reentrancy). This means you must not block within event callbacks,
582	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
583	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:$Coro::IDLE blocked itself"), but this is just best effort and
		970	only works when you do not run your own event loop.
584		971
585	This function allows your callbacks to block by executing them in another	972	This function allows your callbacks to block by executing them in another
586	coroutine where it is safe to block. One example where blocking is handy	973	coro where it is safe to block. One example where blocking is handy
587	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	974	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
588	disk, for example.	975	disk, for example.
589		976
590	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	977	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
591	creating event callbacks that want to block.	978	creating event callbacks that want to block.
592		979
593	If your handler does not plan to block (e.g. simply sends a message to	980	If your handler does not plan to block (e.g. simply sends a message to
594	another coroutine, or puts some other coroutine into the ready queue),	981	another coro, or puts some other coro into the ready queue), there is
595	there is no reason to use C<unblock_sub>.	982	no reason to use C<unblock_sub>.
596		983
597	Note that you also need to use C<unblock_sub> for any other callbacks that	984	Note that you also need to use C<unblock_sub> for any other callbacks that
598	are indirectly executed by any C-based event loop. For example, when you	985	are indirectly executed by any C-based event loop. For example, when you
599	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	986	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
600	provides callbacks that are the result of some event callback, then you	987	provides callbacks that are the result of some event callback, then you
…		…
630	unshift @unblock_queue, [$cb, @_];	1017	unshift @unblock_queue, [$cb, @_];
631	$unblock_scheduler->ready;	1018	$unblock_scheduler->ready;
632	}	1019	}
633	}	1020	}
634		1021
635	=item $cb = Coro::rouse_cb	1022	=item $cb = rouse_cb
636		1023
637	Create and return a "rouse callback". That's a code reference that, when	1024	Create and return a "rouse callback". That's a code reference that,
638	called, will save its arguments and notify the owner coroutine of the	1025	when called, will remember a copy of its arguments and notify the owner
639	callback.	1026	coro of the callback.
640		1027
641	See the next function.	1028	See the next function.
642		1029
643	=item @args = Coro::rouse_wait [$cb]	1030	=item @args = rouse_wait [$cb]
644		1031
645	Wait for the specified rouse callback (or the last one tht was created in	1032	Wait for the specified rouse callback (or the last one that was created in
646	this coroutine).	1033	this coro).
647		1034
648	As soon as the callback is invoked (or when the calback was invoked before	1035	As soon as the callback is invoked (or when the callback was invoked
649	C<rouse_wait>), it will return a copy of the arguments originally passed	1036	before C<rouse_wait>), it will return the arguments originally passed to
650	to the rouse callback.	1037	the rouse callback. In scalar context, that means you get the I<last>
		1038	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1039	statement at the end.
651		1040
652	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.
653		1042
654	=back	1043	=back
655		1044
656	=cut	1045	=cut
657		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	}
		1060
658	1;	1061	1;
659		1062
660	=head1 HOW TO WAIT FOR A CALLBACK	1063	=head1 HOW TO WAIT FOR A CALLBACK
661		1064
662	It is very common for a coroutine to wait for some callback to be	1065	It is very common for a coro to wait for some callback to be
663	called. This occurs naturally when you use coroutines in an otherwise	1066	called. This occurs naturally when you use coro in an otherwise
664	event-based program, or when you use event-based libraries.	1067	event-based program, or when you use event-based libraries.
665		1068
666	These typically register a callback for some event, and call that callback	1069	These typically register a callback for some event, and call that callback
667	when the event occured. In a coroutine, however, you typically want to	1070	when the event occured. In a coro, however, you typically want to
668	just wait for the event, simplyifying things.	1071	just wait for the event, simplyifying things.
669		1072
670	For example C<< AnyEvent->child >> registers a callback to be called when	1073	For example C<< AnyEvent->child >> registers a callback to be called when
671	a specific child has exited:	1074	a specific child has exited:
672		1075
673	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	1076	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
674		1077
675	But from withina coroutine, you often just want to write this:	1078	But from within a coro, you often just want to write this:
676		1079
677	my $status = wait_for_child $pid;	1080	my $status = wait_for_child $pid;
678		1081
679	Coro offers two functions specifically designed to make this easy,	1082	Coro offers two functions specifically designed to make this easy,
680	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	1083	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
681		1084
682	The first function, C<rouse_cb>, generates and returns a callback that,	1085	The first function, C<rouse_cb>, generates and returns a callback that,
683	when invoked, will save it's arguments and notify the coroutine that	1086	when invoked, will save its arguments and notify the coro that
684	created the callback.	1087	created the callback.
685		1088
686	The second function, C<rouse_wait>, waits for the callback to be called	1089	The second function, C<rouse_wait>, waits for the callback to be called
687	(by calling C<schedule> to go to sleep) and returns the arguments	1090	(by calling C<schedule> to go to sleep) and returns the arguments
688	originally passed to the callback.	1091	originally passed to the callback.
…		…
703	you can roll your own, using C<schedule>:	1106	you can roll your own, using C<schedule>:
704		1107
705	sub wait_for_child($) {	1108	sub wait_for_child($) {
706	my ($pid) = @_;	1109	my ($pid) = @_;
707		1110
708	# store the current coroutine in $current,	1111	# store the current coro in $current,
709	# and provide result variables for the closure passed to ->child	1112	# and provide result variables for the closure passed to ->child
710	my $current = $Coro::current;	1113	my $current = $Coro::current;
711	my ($done, $rstatus);	1114	my ($done, $rstatus);
712		1115
713	# pass a closure to ->child	1116	# pass a closure to ->child
…		…
729		1132
730	=item fork with pthread backend	1133	=item fork with pthread backend
731		1134
732	When Coro is compiled using the pthread backend (which isn't recommended	1135	When Coro is compiled using the pthread backend (which isn't recommended
733	but required on many BSDs as their libcs are completely broken), then	1136	but required on many BSDs as their libcs are completely broken), then
734	coroutines will not survive a fork. There is no known workaround except to	1137	coro will not survive a fork. There is no known workaround except to
735	fix your libc and use a saner backend.	1138	fix your libc and use a saner backend.
736		1139
737	=item perl process emulation ("threads")	1140	=item perl process emulation ("threads")
738		1141
739	This module is not perl-pseudo-thread-safe. You should only ever use this	1142	This module is not perl-pseudo-thread-safe. You should only ever use this
740	module from the same thread (this requirement might be removed in the	1143	module from the first thread (this requirement might be removed in the
741	future to allow per-thread schedulers, but Coro::State does not yet allow	1144	future to allow per-thread schedulers, but Coro::State does not yet allow
742	this). I recommend disabling thread support and using processes, as having	1145	this). I recommend disabling thread support and using processes, as having
743	the windows process emulation enabled under unix roughly halves perl	1146	the windows process emulation enabled under unix roughly halves perl
744	performance, even when not used.	1147	performance, even when not used.
745		1148
746	=item coroutine switching not signal safe	1149	=item coro switching is not signal safe
747		1150
748	You must not switch to another coroutine from within a signal handler	1151	You must not switch to another coro from within a signal handler (only
749	(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.
750		1154
751	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
752	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1156	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
753	anything that calls those. Everything else, including calling C<ready>,	1157	anything that calls those. Everything else, including calling C<ready>,
754	works.	1158	works.
755		1159
756	=back	1160	=back
757		1161
758		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
759	=head1 SEE ALSO	1224	=head1 SEE ALSO
760		1225
761	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>.
762		1227
763	Debugging: L<Coro::Debug>.	1228	Debugging: L<Coro::Debug>.
764		1229
765	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1230	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
766		1231
767	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1232	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1233	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
768		1234
769	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1235	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
770		1236
771	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1237	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1238	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1239	L<Coro::Select>.
772		1240
773	XS API: L<Coro::MakeMaker>.	1241	XS API: L<Coro::MakeMaker>.
774		1242
775	Low level Configuration, Coroutine Environment: L<Coro::State>.	1243	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
776		1244
777	=head1 AUTHOR	1245	=head1 AUTHOR
778		1246
779	Marc Lehmann <schmorp@schmorp.de>	1247	Marc Lehmann <schmorp@schmorp.de>
780	http://home.schmorp.de/	1248	http://home.schmorp.de/

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Revision 1.229 by root, Thu Nov 20 06:32:55 2008 UTC vs.
Revision 1.294 by root, Fri May 6 21:15:17 2011 UTC