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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
9	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
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	my $lock = new Coro::Semaphore;	22	my $lock = new Coro::Semaphore;
22	my $locked;	23	my $locked;
23		24
24	$lock->down;	25	$lock->down;
25	$locked = 1;	26	$locked = 1;
26	$lock->up;	27	$lock->up;
27		28
28	=head1 DESCRIPTION	29	=head1 DESCRIPTION
29		30
30	This module collection manages coroutines. Coroutines are similar	31	For a tutorial-style introduction, please read the L<Coro::Intro>
31	to threads but don't run in parallel at the same time even on SMP	32	manpage. This manpage mainly contains reference information.
32	machines. The specific flavor of coroutine used in this module also
33	guarantees you that it will not switch between coroutines unless
34	necessary, at easily-identified points in your program, so locking and
35	parallel access are rarely an issue, making coroutine programming much
36	safer than threads programming.
37		33
38	(Perl, however, does not natively support real threads but instead does a	34	This module collection manages continuations in general, most often in
39	very slow and memory-intensive emulation of processes using threads. This	35	the form of cooperative threads (also called coros, or simply "coro"
40	is a performance win on Windows machines, and a loss everywhere else).	36	in the documentation). They are similar to kernel threads but don't (in
		37	general) run in parallel at the same time even on SMP machines. The
		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.
41		43
		44	Unlike the so-called "Perl threads" (which are not actually real threads
		45	but only the windows process emulation (see section of same name for
		46	more details) ported to UNIX, and as such act as processes), Coro
		47	provides a full shared address space, which makes communication between
		48	threads very easy. And coro threads are fast, too: disabling the Windows
		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.
		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
42	In this module, coroutines are defined as "callchain + lexical variables +	61	In this module, a thread is defined as "callchain + lexical variables +
43	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	62	some package variables + C stack), that is, a thread has its own callchain,
44	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
45	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 >> the coro thread from another
		202	thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # an also accept values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state.
		215
		216	So, cancelling a thread that runs in an XS event loop might not be the
		217	best idea, but any other combination that deals with perl only (cancelling
		218	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		219	safe.
		220
		221	=item 5. Cleanup
		222
		223	Threads will allocate various resources. Most but not all will be returned
		224	when a thread terminates, during clean-up.
		225
		226	Cleanup is quite similar to throwing an uncaught exception: perl will
		227	work it's way up through all subroutine calls and blocks. On it's way, it
		228	will release all C<my> variables, undo all C<local>'s and free any other
		229	resources truly local to the thread.
		230
		231	So, a common way to free resources is to keep them referenced only by my
		232	variables:
		233
		234	async {
		235	my $big_cache = new Cache ...;
		236	};
		237
		238	If there are no other references, then the C<$big_cache> object will be
		239	freed when the thread terminates, regardless of how it does so.
		240
		241	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		242	resources, but that's where the C<guard> methods come in handy:
		243
		244	my $sem = new Coro::Semaphore;
		245
		246	async {
		247	my $lock_guard = $sem->guard;
		248	# if we reutrn, or die or get cancelled, here,
		249	# then the semaphore will be "up"ed.
		250	};
		251
		252	The C<Guard::guard> function comes in handy for any custom cleanup you
		253	might want to do:
		254
		255	async {
		256	my $window = new Gtk2::Window "toplevel";
		257	# The window will not be cleaned up automatically, even when $window
		258	# gets freed, so use a guard to ensure it's destruction
		259	# in case of an error:
		260	my $window_guard = Guard::guard { $window->destroy };
		261
		262	# we are safe here
		263	};
		264
		265	Last not least, C<local> can often be handy, too, e.g. when temporarily
		266	replacing the coro thread description:
		267
		268	sub myfunction {
		269	local $Coro::current->{desc} = "inside myfunction(@_)";
		270
		271	# if we return or die here, the description will be restored
		272	}
		273
		274	=item 6. Viva La Zombie Muerte
		275
		276	Even after a thread has terminated and cleaned up it's resources, the coro
		277	object still is there and stores the return values of the thread. Only in
		278	this state will the coro object be "reference counted" in the normal perl
		279	sense: the thread code keeps a reference to it when it is active, but not
		280	after it has terminated.
		281
		282	The means the coro object gets freed automatically when the thread has
		283	terminated and cleaned up and there arenot other references.
		284
		285	If there are, the coro object will stay around, and you can call C<<
		286	->join >> as many times as you wish to retrieve the result values:
		287
		288	async {
		289	print "hi\n";
		290	1
		291	};
		292
		293	# run the async above, and free everything before returning
		294	# from Coro::cede:
		295	Coro::cede;
		296
		297	{
		298	my $coro = async {
		299	print "hi\n";
		300	1
		301	};
		302
		303	# run the async above, and clean up, but do not free the coro
		304	# object:
		305	Coro::cede;
		306
		307	# optionally retrieve the result values
		308	my @results = $coro->join;
		309
		310	# now $coro goes out of scope, and presumably gets freed
		311	};
		312
		313	=back
46		314
47	=cut	315	=cut
48		316
49	package Coro;	317	package Coro;
50		318
51	use strict;	319	use common::sense;
52	no warnings "uninitialized";	320
		321	use Carp ();
		322
		323	use Guard ();
53		324
54	use Coro::State;	325	use Coro::State;
55		326
56	use base qw(Coro::State Exporter);	327	use base qw(Coro::State Exporter);
57		328
58	our $idle; # idle handler	329	our $idle; # idle handler
59	our $main; # main coroutine	330	our $main; # main coro
60	our $current; # current coroutine	331	our $current; # current coro
61		332
62	our $VERSION = '4.51';	333	our $VERSION = 5.372;
63		334
64	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	335	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
65	our %EXPORT_TAGS = (	336	our %EXPORT_TAGS = (
66	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	337	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
67	);	338	);
68	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	339	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
69		340
70	{	341	=head1 GLOBAL VARIABLES
71	my @async;
72	my $init;
73
74	# this way of handling attributes simply is NOT scalable ;()
75	sub import {
76	no strict 'refs';
77
78	Coro->export_to_level (1, @_);
79
80	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
81	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
82	my ($package, $ref) = (shift, shift);
83	my @attrs;
84	for (@_) {
85	if ($_ eq "Coro") {
86	push @async, $ref;
87	unless ($init++) {
88	eval q{
89	sub INIT {
90	&async(pop @async) while @async;
91	}
92	};
93	}
94	} else {
95	push @attrs, $_;
96	}
97	}
98	return $old ? $old->($package, $ref, @attrs) : @attrs;
99	};
100	}
101
102	}
103		342
104	=over 4	343	=over 4
105		344
106	=item $main	345	=item $Coro::main
107		346
108	This coroutine represents the main program.	347	This variable stores the Coro object that represents the main
		348	program. While you cna C<ready> it and do most other things you can do to
		349	coro, it is mainly useful to compare again C<$Coro::current>, to see
		350	whether you are running in the main program or not.
109		351
110	=cut	352	=cut
111		353
112	$main = new Coro;	354	# $main is now being initialised by Coro::State
113		355
114	=item $current (or as function: current)	356	=item $Coro::current
115		357
116	The current coroutine (the last coroutine switched to). The initial value	358	The Coro object representing the current coro (the last
		359	coro that the Coro scheduler switched to). The initial value is
117	is C<$main> (of course).	360	C<$Coro::main> (of course).
118		361
119	This variable is B<strictly> I<read-only>. It is provided for performance	362	This variable is B<strictly> I<read-only>. You can take copies of the
120	reasons. If performance is not essential you are encouraged to use the	363	value stored in it and use it as any other Coro object, but you must
121	C<Coro::current> function instead.	364	not otherwise modify the variable itself.
122		365
123	=cut	366	=cut
124		367
125	$main->{desc} = "[main::]";
126
127	# maybe some other module used Coro::Specific before...
128	$main->{_specific} = $current->{_specific}
129	if $current;
130
131	_set_current $main;
132
133	sub current() { $current }	368	sub current() { $current } # [DEPRECATED]
134		369
135	=item $idle	370	=item $Coro::idle
136		371
137	A callback that is called whenever the scheduler finds no ready coroutines	372	This variable is mainly useful to integrate Coro into event loops. It is
		373	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		374	pretty low-level functionality.
		375
		376	This variable stores a Coro object that is put into the ready queue when
		377	there are no other ready threads (without invoking any ready hooks).
		378
138	to run. The default implementation prints "FATAL: deadlock detected" and	379	The default implementation dies with "FATAL: deadlock detected.", followed
139	exits, because the program has no other way to continue.	380	by a thread listing, because the program has no other way to continue.
140		381
141	This hook is overwritten by modules such as C<Coro::Timer> and	382	This hook is overwritten by modules such as C<Coro::EV> and
142	C<Coro::Event> to wait on an external event that hopefully wake up a	383	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
143	coroutine so the scheduler can run it.	384	coro so the scheduler can run it.
144		385
145	Please note that if your callback recursively invokes perl (e.g. for event	386	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
146	handlers), then it must be prepared to be called recursively itself.
147		387
148	=cut	388	=cut
149		389
150	$idle = sub {	390	# ||= because other modules could have provided their own by now
151	require Carp;	391	$idle ||= new Coro sub {
152	Carp::croak ("FATAL: deadlock detected");	392	require Coro::Debug;
		393	die "FATAL: deadlock detected.\n"
		394	. Coro::Debug::ps_listing ();
153	};	395	};
154		396
155	sub _cancel {
156	my ($self) = @_;
157
158	# free coroutine data and mark as destructed
159	$self->_destroy
160	or return;
161
162	# call all destruction callbacks
163	$_->(@{$self->{_status}})
164	for @{(delete $self->{_on_destroy}) || []};
165	}
166
167	# this coroutine is necessary because a coroutine	397	# this coro is necessary because a coro
168	# cannot destroy itself.	398	# cannot destroy itself.
169	my @destroy;	399	our @destroy;
170	my $manager;	400	our $manager;
171		401
172	$manager = new Coro sub {	402	$manager = new Coro sub {
173	while () {	403	while () {
174	(shift @destroy)->_cancel	404	_destroy shift @destroy
175	while @destroy;	405	while @destroy;
176		406
177	&schedule;	407	&schedule;
178	}	408	}
179	};	409	};
180	$manager->desc ("[coro manager]");	410	$manager->{desc} = "[coro manager]";
181	$manager->prio (PRIO_MAX);	411	$manager->prio (PRIO_MAX);
182		412
183	=back	413	=back
184		414
185	=head2 STATIC METHODS	415	=head1 SIMPLE CORO CREATION
186
187	Static methods are actually functions that operate on the current coroutine only.
188		416
189	=over 4	417	=over 4
190		418
191	=item async { ... } [@args...]	419	=item async { ... } [@args...]
192		420
193	Create a new asynchronous coroutine and return it's coroutine object	421	Create a new coro and return its Coro object (usually
194	(usually unused). When the sub returns the new coroutine is automatically	422	unused). The coro will be put into the ready queue, so
		423	it will start running automatically on the next scheduler run.
		424
		425	The first argument is a codeblock/closure that should be executed in the
		426	coro. When it returns argument returns the coro is automatically
195	terminated.	427	terminated.
196		428
		429	The remaining arguments are passed as arguments to the closure.
		430
197	See the C<Coro::State::new> constructor for info about the coroutine	431	See the C<Coro::State::new> constructor for info about the coro
198	environment in which coroutines run.	432	environment in which coro are executed.
199		433
200	Calling C<exit> in a coroutine will do the same as calling exit outside	434	Calling C<exit> in a coro will do the same as calling exit outside
201	the coroutine. Likewise, when the coroutine dies, the program will exit,	435	the coro. Likewise, when the coro dies, the program will exit,
202	just as it would in the main program.	436	just as it would in the main program.
203		437
		438	If you do not want that, you can provide a default C<die> handler, or
		439	simply avoid dieing (by use of C<eval>).
		440
204	# create a new coroutine that just prints its arguments	441	Example: Create a new coro that just prints its arguments.
		442
205	async {	443	async {
206	print "@_\n";	444	print "@_\n";
207	} 1,2,3,4;	445	} 1,2,3,4;
208		446
209	=cut
210
211	sub async(&@) {
212	my $coro = new Coro @_;
213	$coro->ready;
214	$coro
215	}
216
217	=item async_pool { ... } [@args...]	447	=item async_pool { ... } [@args...]
218		448
219	Similar to C<async>, but uses a coroutine pool, so you should not call	449	Similar to C<async>, but uses a coro pool, so you should not call
220	terminate or join (although you are allowed to), and you get a coroutine	450	terminate or join on it (although you are allowed to), and you get a
221	that might have executed other code already (which can be good or bad :).	451	coro that might have executed other code already (which can be good
		452	or bad :).
222		453
		454	On the plus side, this function is about twice as fast as creating (and
		455	destroying) a completely new coro, so if you need a lot of generic
		456	coros in quick successsion, use C<async_pool>, not C<async>.
		457
223	Also, the block is executed in an C<eval> context and a warning will be	458	The code block is executed in an C<eval> context and a warning will be
224	issued in case of an exception instead of terminating the program, as	459	issued in case of an exception instead of terminating the program, as
225	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	460	C<async> does. As the coro is being reused, stuff like C<on_destroy>
226	will not work in the expected way, unless you call terminate or cancel,	461	will not work in the expected way, unless you call terminate or cancel,
227	which somehow defeats the purpose of pooling.	462	which somehow defeats the purpose of pooling (but is fine in the
		463	exceptional case).
228		464
229	The priority will be reset to C<0> after each job, tracing will be	465	The priority will be reset to C<0> after each run, tracing will be
230	disabled, the description will be reset and the default output filehandle	466	disabled, the description will be reset and the default output filehandle
231	gets restored, so you can change alkl these. Otherwise the coroutine will	467	gets restored, so you can change all these. Otherwise the coro will
232	be re-used "as-is": most notably if you change other per-coroutine global	468	be re-used "as-is": most notably if you change other per-coro global
233	stuff such as C<$/> you need to revert that change, which is most simply	469	stuff such as C<$/> you I<must needs> revert that change, which is most
234	done by using local as in C< local $/ >.	470	simply done by using local as in: C<< local $/ >>.
235		471
236	The pool size is limited to 8 idle coroutines (this can be adjusted by	472	The idle pool size is limited to C<8> idle coros (this can be
237	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as	473	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
238	required.	474	coros as required.
239		475
240	If you are concerned about pooled coroutines growing a lot because a	476	If you are concerned about pooled coros growing a lot because a
241	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	477	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
242	{ terminate }> once per second or so to slowly replenish the pool. In	478	{ terminate }> once per second or so to slowly replenish the pool. In
243	addition to that, when the stacks used by a handler grows larger than 16kb	479	addition to that, when the stacks used by a handler grows larger than 32kb
244	(adjustable with $Coro::POOL_RSS) it will also exit.	480	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
245		481
246	=cut	482	=cut
247		483
248	our $POOL_SIZE = 8;	484	our $POOL_SIZE = 8;
249	our $POOL_RSS = 16 * 1024;	485	our $POOL_RSS = 32 * 1024;
250	our @async_pool;	486	our @async_pool;
251		487
252	sub pool_handler {	488	sub pool_handler {
253	my $cb;
254
255	while () {	489	while () {
256	eval {	490	eval {
257	while () {	491	&{&_pool_handler} while 1;
258	_pool_1 $cb;
259	&$cb;
260	_pool_2 $cb;
261	&schedule;
262	}
263	};	492	};
264		493
265	last if $@ eq "\3async_pool terminate\2\n";
266	warn $@ if $@;	494	warn $@ if $@;
267	}	495	}
268	}	496	}
269		497
270	sub async_pool(&@) {	498	=back
271	# this is also inlined into the unlock_scheduler
272	my $coro = (pop @async_pool) || new Coro \&pool_handler;
273		499
274	$coro->{_invoke} = [@_];	500	=head1 STATIC METHODS
275	$coro->ready;
276		501
277	$coro	502	Static methods are actually functions that implicitly operate on the
278	}	503	current coro.
		504
		505	=over 4
279		506
280	=item schedule	507	=item schedule
281		508
282	Calls the scheduler. Please note that the current coroutine will not be put	509	Calls the scheduler. The scheduler will find the next coro that is
		510	to be run from the ready queue and switches to it. The next coro
		511	to be run is simply the one with the highest priority that is longest
		512	in its ready queue. If there is no coro ready, it will call the
		513	C<$Coro::idle> hook.
		514
		515	Please note that the current coro will I<not> be put into the ready
283	into the ready queue, so calling this function usually means you will	516	queue, so calling this function usually means you will never be called
284	never be called again unless something else (e.g. an event handler) calls	517	again unless something else (e.g. an event handler) calls C<< ->ready >>,
285	ready.	518	thus waking you up.
286		519
287	The canonical way to wait on external events is this:	520	This makes C<schedule> I<the> generic method to use to block the current
		521	coro and wait for events: first you remember the current coro in
		522	a variable, then arrange for some callback of yours to call C<< ->ready
		523	>> on that once some event happens, and last you call C<schedule> to put
		524	yourself to sleep. Note that a lot of things can wake your coro up,
		525	so you need to check whether the event indeed happened, e.g. by storing the
		526	status in a variable.
288		527
289	{	528	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
290	# remember current coroutine
291	my $current = $Coro::current;
292		529
293	# register a hypothetical event handler	530	=item cede
294	on_event_invoke sub {	531
295	# wake up sleeping coroutine	532	"Cede" to other coros. This function puts the current coro into
296	$current->ready;	533	the ready queue and calls C<schedule>, which has the effect of giving
297	undef $current;	534	up the current "timeslice" to other coros of the same or higher
		535	priority. Once your coro gets its turn again it will automatically be
		536	resumed.
		537
		538	This function is often called C<yield> in other languages.
		539
		540	=item Coro::cede_notself
		541
		542	Works like cede, but is not exported by default and will cede to I<any>
		543	coro, regardless of priority. This is useful sometimes to ensure
		544	progress is made.
		545
		546	=item terminate [arg...]
		547
		548	Terminates the current coro with the given status values (see
		549	L<cancel>). The values will not be copied, but referenced directly.
		550
		551	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		552
		553	These function install enter and leave winders in the current scope. The
		554	enter block will be executed when on_enter is called and whenever the
		555	current coro is re-entered by the scheduler, while the leave block is
		556	executed whenever the current coro is blocked by the scheduler, and
		557	also when the containing scope is exited (by whatever means, be it exit,
		558	die, last etc.).
		559
		560	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		561	BLOCKs>. That means: do not even think about calling C<die> without an
		562	eval, and do not even think of entering the scheduler in any way.
		563
		564	Since both BLOCKs are tied to the current scope, they will automatically
		565	be removed when the current scope exits.
		566
		567	These functions implement the same concept as C<dynamic-wind> in scheme
		568	does, and are useful when you want to localise some resource to a specific
		569	coro.
		570
		571	They slow down thread switching considerably for coros that use them
		572	(about 40% for a BLOCK with a single assignment, so thread switching is
		573	still reasonably fast if the handlers are fast).
		574
		575	These functions are best understood by an example: The following function
		576	will change the current timezone to "Antarctica/South_Pole", which
		577	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		578	which remember/change the current timezone and restore the previous
		579	value, respectively, the timezone is only changed for the coro that
		580	installed those handlers.
		581
		582	use POSIX qw(tzset);
		583
		584	async {
		585	my $old_tz; # store outside TZ value here
		586
		587	Coro::on_enter {
		588	$old_tz = $ENV{TZ}; # remember the old value
		589
		590	$ENV{TZ} = "Antarctica/South_Pole";
		591	tzset; # enable new value
298	};	592	};
299		593
300	# call schedule until event occurred.	594	Coro::on_leave {
301	# in case we are woken up for other reasons	595	$ENV{TZ} = $old_tz;
302	# (current still defined), loop.	596	tzset; # restore old value
303	Coro::schedule while $current;	597	};
		598
		599	# at this place, the timezone is Antarctica/South_Pole,
		600	# without disturbing the TZ of any other coro.
304	}	601	};
305		602
306	=item cede	603	This can be used to localise about any resource (locale, uid, current
		604	working directory etc.) to a block, despite the existance of other
		605	coros.
307		606
308	"Cede" to other coroutines. This function puts the current coroutine into the	607	Another interesting example implements time-sliced multitasking using
309	ready queue and calls C<schedule>, which has the effect of giving up the	608	interval timers (this could obviously be optimised, but does the job):
310	current "timeslice" to other coroutines of the same or higher priority.
311		609
312	=item Coro::cede_notself	610	# "timeslice" the given block
		611	sub timeslice(&) {
		612	use Time::HiRes ();
313		613
314	Works like cede, but is not exported by default and will cede to any	614	Coro::on_enter {
315	coroutine, regardless of priority, once.	615	# on entering the thread, we set an VTALRM handler to cede
		616	$SIG{VTALRM} = sub { cede };
		617	# and then start the interval timer
		618	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		619	};
		620	Coro::on_leave {
		621	# on leaving the thread, we stop the interval timer again
		622	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		623	};
316		624
317	=item terminate [arg...]	625	&{+shift};
		626	}
318		627
319	Terminates the current coroutine with the given status values (see L<cancel>).	628	# use like this:
		629	timeslice {
		630	# The following is an endless loop that would normally
		631	# monopolise the process. Since it runs in a timesliced
		632	# environment, it will regularly cede to other threads.
		633	while () { }
		634	};
		635
320		636
321	=item killall	637	=item killall
322		638
323	Kills/terminates/cancels all coroutines except the currently running	639	Kills/terminates/cancels all coros except the currently running one.
324	one. This is useful after a fork, either in the child or the parent, as
325	usually only one of them should inherit the running coroutines.
326		640
327	=cut	641	Note that while this will try to free some of the main interpreter
		642	resources if the calling coro isn't the main coro, but one
		643	cannot free all of them, so if a coro that is not the main coro
		644	calls this function, there will be some one-time resource leak.
328		645
329	sub terminate {	646	=cut
330	$current->cancel (@_);
331	}
332		647
333	sub killall {	648	sub killall {
334	for (Coro::State::list) {	649	for (Coro::State::list) {
335	$_->cancel	650	$_->cancel
336	if $_ != $current && UNIVERSAL::isa $_, "Coro";	651	if $_ != $current && UNIVERSAL::isa $_, "Coro";
337	}	652	}
338	}	653	}
339		654
340	=back	655	=back
341		656
342	=head2 COROUTINE METHODS	657	=head1 CORO OBJECT METHODS
343		658
344	These are the methods you can call on coroutine objects.	659	These are the methods you can call on coro objects (or to create
		660	them).
345		661
346	=over 4	662	=over 4
347		663
348	=item new Coro \&sub [, @args...]	664	=item new Coro \&sub [, @args...]
349		665
350	Create a new coroutine and return it. When the sub returns the coroutine	666	Create a new coro and return it. When the sub returns, the coro
351	automatically terminates as if C<terminate> with the returned values were	667	automatically terminates as if C<terminate> with the returned values were
352	called. To make the coroutine run you must first put it into the ready queue	668	called. To make the coro run you must first put it into the ready
353	by calling the ready method.	669	queue by calling the ready method.
354		670
355	See C<async> and C<Coro::State::new> for additional info about the	671	See C<async> and C<Coro::State::new> for additional info about the
356	coroutine environment.	672	coro environment.
357		673
358	=cut	674	=cut
359		675
360	sub _run_coro {	676	sub _coro_run {
361	terminate &{+shift};	677	terminate &{+shift};
362	}	678	}
363		679
364	sub new {
365	my $class = shift;
366
367	$class->SUPER::new (\&_run_coro, @_)
368	}
369
370	=item $success = $coroutine->ready	680	=item $success = $coro->ready
371		681
372	Put the given coroutine into the ready queue (according to it's priority)	682	Put the given coro into the end of its ready queue (there is one
373	and return true. If the coroutine is already in the ready queue, do nothing	683	queue for each priority) and return true. If the coro is already in
374	and return false.	684	the ready queue, do nothing and return false.
375		685
		686	This ensures that the scheduler will resume this coro automatically
		687	once all the coro of higher priority and all coro of the same
		688	priority that were put into the ready queue earlier have been resumed.
		689
		690	=item $coro->suspend
		691
		692	Suspends the specified coro. A suspended coro works just like any other
		693	coro, except that the scheduler will not select a suspended coro for
		694	execution.
		695
		696	Suspending a coro can be useful when you want to keep the coro from
		697	running, but you don't want to destroy it, or when you want to temporarily
		698	freeze a coro (e.g. for debugging) to resume it later.
		699
		700	A scenario for the former would be to suspend all (other) coros after a
		701	fork and keep them alive, so their destructors aren't called, but new
		702	coros can be created.
		703
		704	=item $coro->resume
		705
		706	If the specified coro was suspended, it will be resumed. Note that when
		707	the coro was in the ready queue when it was suspended, it might have been
		708	unreadied by the scheduler, so an activation might have been lost.
		709
		710	To avoid this, it is best to put a suspended coro into the ready queue
		711	unconditionally, as every synchronisation mechanism must protect itself
		712	against spurious wakeups, and the one in the Coro family certainly do
		713	that.
		714
376	=item $is_ready = $coroutine->is_ready	715	=item $is_ready = $coro->is_ready
377		716
378	Return wether the coroutine is currently the ready queue or not,	717	Returns true iff the Coro object is in the ready queue. Unless the Coro
		718	object gets destroyed, it will eventually be scheduled by the scheduler.
379		719
		720	=item $is_running = $coro->is_running
		721
		722	Returns true iff the Coro object is currently running. Only one Coro object
		723	can ever be in the running state (but it currently is possible to have
		724	multiple running Coro::States).
		725
		726	=item $is_suspended = $coro->is_suspended
		727
		728	Returns true iff this Coro object has been suspended. Suspended Coros will
		729	not ever be scheduled.
		730
380	=item $coroutine->cancel (arg...)	731	=item $coro->cancel (arg...)
381		732
382	Terminates the given coroutine and makes it return the given arguments as	733	Terminates the given Coro object and makes it return the given arguments as
383	status (default: the empty list). Never returns if the coroutine is the	734	status (default: an empty list). Never returns if the Coro is the
384	current coroutine.	735	current Coro.
385		736
386	=cut	737	The arguments are not copied, but instead will be referenced directly
		738	(e.g. if you pass C<$var> and after the call change that variable, then
		739	you might change the return values passed to e.g. C<join>, so don't do
		740	that).
387		741
388	sub cancel {	742	The resources of the Coro are usually freed (or destructed) before this
389	my $self = shift;	743	call returns, but this can be delayed for an indefinite amount of time, as
390	$self->{_status} = [@_];	744	in some cases the manager thread has to run first to actually destruct the
		745	Coro object.
391		746
392	if ($current == $self) {	747	=item $coro->schedule_to
393	push @destroy, $self;
394	$manager->ready;
395	&schedule while 1;
396	} else {
397	$self->_cancel;
398	}
399	}
400		748
		749	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		750	of continuing with the next coro from the ready queue, always switch to
		751	the given coro object (regardless of priority etc.). The readyness
		752	state of that coro isn't changed.
		753
		754	This is an advanced method for special cases - I'd love to hear about any
		755	uses for this one.
		756
		757	=item $coro->cede_to
		758
		759	Like C<schedule_to>, but puts the current coro into the ready
		760	queue. This has the effect of temporarily switching to the given
		761	coro, and continuing some time later.
		762
		763	This is an advanced method for special cases - I'd love to hear about any
		764	uses for this one.
		765
		766	=item $coro->throw ([$scalar])
		767
		768	If C<$throw> is specified and defined, it will be thrown as an exception
		769	inside the coro at the next convenient point in time. Otherwise
		770	clears the exception object.
		771
		772	Coro will check for the exception each time a schedule-like-function
		773	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		774	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		775	detect this case and return early in case an exception is pending.
		776
		777	The exception object will be thrown "as is" with the specified scalar in
		778	C<$@>, i.e. if it is a string, no line number or newline will be appended
		779	(unlike with C<die>).
		780
		781	This can be used as a softer means than C<cancel> to ask a coro to
		782	end itself, although there is no guarantee that the exception will lead to
		783	termination, and if the exception isn't caught it might well end the whole
		784	program.
		785
		786	You might also think of C<throw> as being the moral equivalent of
		787	C<kill>ing a coro with a signal (in this case, a scalar).
		788
401	=item $coroutine->join	789	=item $coro->join
402		790
403	Wait until the coroutine terminates and return any values given to the	791	Wait until the coro terminates and return any values given to the
404	C<terminate> or C<cancel> functions. C<join> can be called concurrently	792	C<terminate> or C<cancel> functions. C<join> can be called concurrently
405	from multiple coroutines.	793	from multiple threads, and all will be resumed and given the status
		794	return once the C<$coro> terminates.
406		795
407	=cut	796	=cut
408		797
409	sub join {	798	sub join {
410	my $self = shift;	799	my $self = shift;
…		…
421	}	810	}
422		811
423	wantarray ? @{$self->{_status}} : $self->{_status}[0];	812	wantarray ? @{$self->{_status}} : $self->{_status}[0];
424	}	813	}
425		814
426	=item $coroutine->on_destroy (\&cb)	815	=item $coro->on_destroy (\&cb)
427		816
428	Registers a callback that is called when this coroutine gets destroyed,	817	Registers a callback that is called when this coro thread gets destroyed,
429	but before it is joined. The callback gets passed the terminate arguments,	818	but before it is joined. The callback gets passed the terminate arguments,
430	if any.	819	if any, and I<must not> die, under any circumstances.
		820
		821	There can be any number of C<on_destroy> callbacks per coro.
431		822
432	=cut	823	=cut
433		824
434	sub on_destroy {	825	sub on_destroy {
435	my ($self, $cb) = @_;	826	my ($self, $cb) = @_;
436		827
437	push @{ $self->{_on_destroy} }, $cb;	828	push @{ $self->{_on_destroy} }, $cb;
438	}	829	}
439		830
440	=item $oldprio = $coroutine->prio ($newprio)	831	=item $oldprio = $coro->prio ($newprio)
441		832
442	Sets (or gets, if the argument is missing) the priority of the	833	Sets (or gets, if the argument is missing) the priority of the
443	coroutine. Higher priority coroutines get run before lower priority	834	coro thread. Higher priority coro get run before lower priority
444	coroutines. Priorities are small signed integers (currently -4 .. +3),	835	coros. Priorities are small signed integers (currently -4 .. +3),
445	that you can refer to using PRIO_xxx constants (use the import tag :prio	836	that you can refer to using PRIO_xxx constants (use the import tag :prio
446	to get then):	837	to get then):
447		838
448	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	839	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
449	3 > 1 > 0 > -1 > -3 > -4	840	3 > 1 > 0 > -1 > -3 > -4
450		841
451	# set priority to HIGH	842	# set priority to HIGH
452	current->prio(PRIO_HIGH);	843	current->prio (PRIO_HIGH);
453		844
454	The idle coroutine ($Coro::idle) always has a lower priority than any	845	The idle coro thread ($Coro::idle) always has a lower priority than any
455	existing coroutine.	846	existing coro.
456		847
457	Changing the priority of the current coroutine will take effect immediately,	848	Changing the priority of the current coro will take effect immediately,
458	but changing the priority of coroutines in the ready queue (but not	849	but changing the priority of a coro in the ready queue (but not running)
459	running) will only take effect after the next schedule (of that	850	will only take effect after the next schedule (of that coro). This is a
460	coroutine). This is a bug that will be fixed in some future version.	851	bug that will be fixed in some future version.
461		852
462	=item $newprio = $coroutine->nice ($change)	853	=item $newprio = $coro->nice ($change)
463		854
464	Similar to C<prio>, but subtract the given value from the priority (i.e.	855	Similar to C<prio>, but subtract the given value from the priority (i.e.
465	higher values mean lower priority, just as in unix).	856	higher values mean lower priority, just as in UNIX's nice command).
466		857
467	=item $olddesc = $coroutine->desc ($newdesc)	858	=item $olddesc = $coro->desc ($newdesc)
468		859
469	Sets (or gets in case the argument is missing) the description for this	860	Sets (or gets in case the argument is missing) the description for this
470	coroutine. This is just a free-form string you can associate with a coroutine.	861	coro thread. This is just a free-form string you can associate with a
		862	coro.
471		863
472	This method simply sets the C<< $coroutine->{desc} >> member to the given string. You	864	This method simply sets the C<< $coro->{desc} >> member to the given
473	can modify this member directly if you wish.	865	string. You can modify this member directly if you wish, and in fact, this
		866	is often preferred to indicate major processing states that cna then be
		867	seen for example in a L<Coro::Debug> session:
474		868
475	=item $coroutine->throw ([$scalar])	869	sub my_long_function {
476		870	local $Coro::current->{desc} = "now in my_long_function";
477	If C<$throw> is specified and defined, it will be thrown as an exception	871	...
478	inside the coroutine at the next convinient point in time (usually after	872	$Coro::current->{desc} = "my_long_function: phase 1";
479	it gains control at the next schedule/transfer/cede). Otherwise clears the	873	...
480	exception object.	874	$Coro::current->{desc} = "my_long_function: phase 2";
481		875	...
482	The exception object will be thrown "as is" with the specified scalar in	876	}
483	C<$@>, i.e. if it is a string, no line number or newline will be appended
484	(unlike with C<die>).
485
486	This can be used as a softer means than C<cancel> to ask a coroutine to
487	end itself, although there is no guarentee that the exception will lead to
488	termination, and if the exception isn't caught it might well end the whole
489	program.
490		877
491	=cut	878	=cut
492		879
493	sub desc {	880	sub desc {
494	my $old = $_[0]{desc};	881	my $old = $_[0]{desc};
495	$_[0]{desc} = $_[1] if @_ > 1;	882	$_[0]{desc} = $_[1] if @_ > 1;
496	$old;	883	$old;
497	}	884	}
498		885
		886	sub transfer {
		887	require Carp;
		888	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		889	}
		890
499	=back	891	=back
500		892
501	=head2 GLOBAL FUNCTIONS	893	=head1 GLOBAL FUNCTIONS
502		894
503	=over 4	895	=over 4
504		896
505	=item Coro::nready	897	=item Coro::nready
506		898
507	Returns the number of coroutines that are currently in the ready state,	899	Returns the number of coro that are currently in the ready state,
508	i.e. that can be switched to. The value C<0> means that the only runnable	900	i.e. that can be switched to by calling C<schedule> directory or
		901	indirectly. The value C<0> means that the only runnable coro is the
509	coroutine is the currently running one, so C<cede> would have no effect,	902	currently running one, so C<cede> would have no effect, and C<schedule>
510	and C<schedule> would cause a deadlock unless there is an idle handler	903	would cause a deadlock unless there is an idle handler that wakes up some
511	that wakes up some coroutines.	904	coro.
512		905
513	=item my $guard = Coro::guard { ... }	906	=item my $guard = Coro::guard { ... }
514		907
515	This creates and returns a guard object. Nothing happens until the object	908	This function still exists, but is deprecated. Please use the
516	gets destroyed, in which case the codeblock given as argument will be	909	C<Guard::guard> function instead.
517	executed. This is useful to free locks or other resources in case of a
518	runtime error or when the coroutine gets canceled, as in both cases the
519	guard block will be executed. The guard object supports only one method,
520	C<< ->cancel >>, which will keep the codeblock from being executed.
521		910
522	Example: set some flag and clear it again when the coroutine gets canceled
523	or the function returns:
524
525	sub do_something {
526	my $guard = Coro::guard { $busy = 0 };
527	$busy = 1;
528
529	# do something that requires $busy to be true
530	}
531
532	=cut	911	=cut
533		912
534	sub guard(&) {	913	BEGIN { *guard = \&Guard::guard }
535	bless \(my $cb = $_[0]), "Coro::guard"
536	}
537
538	sub Coro::guard::cancel {
539	${$_[0]} = sub { };
540	}
541
542	sub Coro::guard::DESTROY {
543	${$_[0]}->();
544	}
545
546		914
547	=item unblock_sub { ... }	915	=item unblock_sub { ... }
548		916
549	This utility function takes a BLOCK or code reference and "unblocks" it,	917	This utility function takes a BLOCK or code reference and "unblocks" it,
550	returning the new coderef. This means that the new coderef will return	918	returning a new coderef. Unblocking means that calling the new coderef
551	immediately without blocking, returning nothing, while the original code	919	will return immediately without blocking, returning nothing, while the
552	ref will be called (with parameters) from within its own coroutine.	920	original code ref will be called (with parameters) from within another
		921	coro.
553		922
554	The reason this function exists is that many event libraries (such as the	923	The reason this function exists is that many event libraries (such as
555	venerable L<Event|Event> module) are not coroutine-safe (a weaker form	924	the venerable L<Event|Event> module) are not thread-safe (a weaker form
556	of thread-safety). This means you must not block within event callbacks,	925	of reentrancy). This means you must not block within event callbacks,
557	otherwise you might suffer from crashes or worse.	926	otherwise you might suffer from crashes or worse. The only event library
		927	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		928	you might still run into deadlocks if all event loops are blocked).
		929
		930	Coro will try to catch you when you block in the event loop
		931	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		932	only works when you do not run your own event loop.
558		933
559	This function allows your callbacks to block by executing them in another	934	This function allows your callbacks to block by executing them in another
560	coroutine where it is safe to block. One example where blocking is handy	935	coro where it is safe to block. One example where blocking is handy
561	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to	936	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
562	disk.	937	disk, for example.
563		938
564	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	939	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
565	creating event callbacks that want to block.	940	creating event callbacks that want to block.
		941
		942	If your handler does not plan to block (e.g. simply sends a message to
		943	another coro, or puts some other coro into the ready queue), there is
		944	no reason to use C<unblock_sub>.
		945
		946	Note that you also need to use C<unblock_sub> for any other callbacks that
		947	are indirectly executed by any C-based event loop. For example, when you
		948	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		949	provides callbacks that are the result of some event callback, then you
		950	must not block either, or use C<unblock_sub>.
566		951
567	=cut	952	=cut
568		953
569	our @unblock_queue;	954	our @unblock_queue;
570		955
…		…
573	# return immediately and can be reused) and because we cannot cede	958	# return immediately and can be reused) and because we cannot cede
574	# inside an event callback.	959	# inside an event callback.
575	our $unblock_scheduler = new Coro sub {	960	our $unblock_scheduler = new Coro sub {
576	while () {	961	while () {
577	while (my $cb = pop @unblock_queue) {	962	while (my $cb = pop @unblock_queue) {
578	# this is an inlined copy of async_pool	963	&async_pool (@$cb);
579	my $coro = (pop @async_pool) || new Coro \&pool_handler;
580		964
581	$coro->{_invoke} = $cb;
582	$coro->ready;
583	cede; # for short-lived callbacks, this reduces pressure on the coro pool	965	# for short-lived callbacks, this reduces pressure on the coro pool
		966	# as the chance is very high that the async_poll coro will be back
		967	# in the idle state when cede returns
		968	cede;
584	}	969	}
585	schedule; # sleep well	970	schedule; # sleep well
586	}	971	}
587	};	972	};
588	$unblock_scheduler->desc ("[unblock_sub scheduler]");	973	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
589		974
590	sub unblock_sub(&) {	975	sub unblock_sub(&) {
591	my $cb = shift;	976	my $cb = shift;
592		977
593	sub {	978	sub {
594	unshift @unblock_queue, [$cb, @_];	979	unshift @unblock_queue, [$cb, @_];
595	$unblock_scheduler->ready;	980	$unblock_scheduler->ready;
596	}	981	}
597	}	982	}
598		983
		984	=item $cb = rouse_cb
		985
		986	Create and return a "rouse callback". That's a code reference that,
		987	when called, will remember a copy of its arguments and notify the owner
		988	coro of the callback.
		989
		990	See the next function.
		991
		992	=item @args = rouse_wait [$cb]
		993
		994	Wait for the specified rouse callback (or the last one that was created in
		995	this coro).
		996
		997	As soon as the callback is invoked (or when the callback was invoked
		998	before C<rouse_wait>), it will return the arguments originally passed to
		999	the rouse callback. In scalar context, that means you get the I<last>
		1000	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1001	statement at the end.
		1002
		1003	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1004
599	=back	1005	=back
600		1006
601	=cut	1007	=cut
602		1008
		1009	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1010	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1011
		1012	*{"Coro::$module\::new"} = sub {
		1013	require "Coro/$module.pm";
		1014
		1015	# some modules have their new predefined in State.xs, some don't
		1016	*{"Coro::$module\::new"} = $old
		1017	if $old;
		1018
		1019	goto &{"Coro::$module\::new"};
		1020	};
		1021	}
		1022
603	1;	1023	1;
604		1024
		1025	=head1 HOW TO WAIT FOR A CALLBACK
		1026
		1027	It is very common for a coro to wait for some callback to be
		1028	called. This occurs naturally when you use coro in an otherwise
		1029	event-based program, or when you use event-based libraries.
		1030
		1031	These typically register a callback for some event, and call that callback
		1032	when the event occured. In a coro, however, you typically want to
		1033	just wait for the event, simplyifying things.
		1034
		1035	For example C<< AnyEvent->child >> registers a callback to be called when
		1036	a specific child has exited:
		1037
		1038	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1039
		1040	But from within a coro, you often just want to write this:
		1041
		1042	my $status = wait_for_child $pid;
		1043
		1044	Coro offers two functions specifically designed to make this easy,
		1045	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		1046
		1047	The first function, C<rouse_cb>, generates and returns a callback that,
		1048	when invoked, will save its arguments and notify the coro that
		1049	created the callback.
		1050
		1051	The second function, C<rouse_wait>, waits for the callback to be called
		1052	(by calling C<schedule> to go to sleep) and returns the arguments
		1053	originally passed to the callback.
		1054
		1055	Using these functions, it becomes easy to write the C<wait_for_child>
		1056	function mentioned above:
		1057
		1058	sub wait_for_child($) {
		1059	my ($pid) = @_;
		1060
		1061	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		1062
		1063	my ($rpid, $rstatus) = Coro::rouse_wait;
		1064	$rstatus
		1065	}
		1066
		1067	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1068	you can roll your own, using C<schedule>:
		1069
		1070	sub wait_for_child($) {
		1071	my ($pid) = @_;
		1072
		1073	# store the current coro in $current,
		1074	# and provide result variables for the closure passed to ->child
		1075	my $current = $Coro::current;
		1076	my ($done, $rstatus);
		1077
		1078	# pass a closure to ->child
		1079	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1080	$rstatus = $_[1]; # remember rstatus
		1081	$done = 1; # mark $rstatus as valud
		1082	});
		1083
		1084	# wait until the closure has been called
		1085	schedule while !$done;
		1086
		1087	$rstatus
		1088	}
		1089
		1090
605	=head1 BUGS/LIMITATIONS	1091	=head1 BUGS/LIMITATIONS
606		1092
607	- you must make very sure that no coro is still active on global	1093	=over 4
608	destruction. very bad things might happen otherwise (usually segfaults).
609		1094
		1095	=item fork with pthread backend
		1096
		1097	When Coro is compiled using the pthread backend (which isn't recommended
		1098	but required on many BSDs as their libcs are completely broken), then
		1099	coro will not survive a fork. There is no known workaround except to
		1100	fix your libc and use a saner backend.
		1101
		1102	=item perl process emulation ("threads")
		1103
610	- this module is not thread-safe. You should only ever use this module	1104	This module is not perl-pseudo-thread-safe. You should only ever use this
611	from the same thread (this requirement might be loosened in the future	1105	module from the first thread (this requirement might be removed in the
612	to allow per-thread schedulers, but Coro::State does not yet allow	1106	future to allow per-thread schedulers, but Coro::State does not yet allow
613	this).	1107	this). I recommend disabling thread support and using processes, as having
		1108	the windows process emulation enabled under unix roughly halves perl
		1109	performance, even when not used.
		1110
		1111	=item coro switching is not signal safe
		1112
		1113	You must not switch to another coro from within a signal handler (only
		1114	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1115	you are sure you are not interrupting a Coro function.
		1116
		1117	That means you I<MUST NOT> call any function that might "block" the
		1118	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		1119	anything that calls those. Everything else, including calling C<ready>,
		1120	works.
		1121
		1122	=back
		1123
		1124
		1125	=head1 WINDOWS PROCESS EMULATION
		1126
		1127	A great many people seem to be confused about ithreads (for example, Chip
		1128	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1129	while in the same mail making rather confused statements about perl
		1130	ithreads (for example, that memory or files would be shared), showing his
		1131	lack of understanding of this area - if it is hard to understand for Chip,
		1132	it is probably not obvious to everybody).
		1133
		1134	What follows is an ultra-condensed version of my talk about threads in
		1135	scripting languages given on the perl workshop 2009:
		1136
		1137	The so-called "ithreads" were originally implemented for two reasons:
		1138	first, to (badly) emulate unix processes on native win32 perls, and
		1139	secondly, to replace the older, real thread model ("5.005-threads").
		1140
		1141	It does that by using threads instead of OS processes. The difference
		1142	between processes and threads is that threads share memory (and other
		1143	state, such as files) between threads within a single process, while
		1144	processes do not share anything (at least not semantically). That
		1145	means that modifications done by one thread are seen by others, while
		1146	modifications by one process are not seen by other processes.
		1147
		1148	The "ithreads" work exactly like that: when creating a new ithreads
		1149	process, all state is copied (memory is copied physically, files and code
		1150	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1151	the same behaviour can be achieved by using operating system processes,
		1152	except that UNIX typically uses hardware built into the system to do this
		1153	efficiently, while the windows process emulation emulates this hardware in
		1154	software (rather efficiently, but of course it is still much slower than
		1155	dedicated hardware).
		1156
		1157	As mentioned before, loading code, modifying code, modifying data
		1158	structures and so on is only visible in the ithreads process doing the
		1159	modification, not in other ithread processes within the same OS process.
		1160
		1161	This is why "ithreads" do not implement threads for perl at all, only
		1162	processes. What makes it so bad is that on non-windows platforms, you can
		1163	actually take advantage of custom hardware for this purpose (as evidenced
		1164	by the forks module, which gives you the (i-) threads API, just much
		1165	faster).
		1166
		1167	Sharing data is in the i-threads model is done by transfering data
		1168	structures between threads using copying semantics, which is very slow -
		1169	shared data simply does not exist. Benchmarks using i-threads which are
		1170	communication-intensive show extremely bad behaviour with i-threads (in
		1171	fact, so bad that Coro, which cannot take direct advantage of multiple
		1172	CPUs, is often orders of magnitude faster because it shares data using
		1173	real threads, refer to my talk for details).
		1174
		1175	As summary, i-threads *use* threads to implement processes, while
		1176	the compatible forks module *uses* processes to emulate, uhm,
		1177	processes. I-threads slow down every perl program when enabled, and
		1178	outside of windows, serve no (or little) practical purpose, but
		1179	disadvantages every single-threaded Perl program.
		1180
		1181	This is the reason that I try to avoid the name "ithreads", as it is
		1182	misleading as it implies that it implements some kind of thread model for
		1183	perl, and prefer the name "windows process emulation", which describes the
		1184	actual use and behaviour of it much better.
614		1185
615	=head1 SEE ALSO	1186	=head1 SEE ALSO
616		1187
617	Lower level Configuration, Coroutine Environment: L<Coro::State>.	1188	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
618		1189
619	Debugging: L<Coro::Debug>.	1190	Debugging: L<Coro::Debug>.
620		1191
621	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1192	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
622		1193
623	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1194	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1195	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
624		1196
625	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>.	1197	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
626		1198
627	Compatibility: L<Coro::LWP>, L<Coro::Storable>, L<Coro::Select>.	1199	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1200	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1201	L<Coro::Select>.
628		1202
629	Embedding: L<Coro::MakeMaker>.	1203	XS API: L<Coro::MakeMaker>.
		1204
		1205	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
630		1206
631	=head1 AUTHOR	1207	=head1 AUTHOR
632		1208
633	Marc Lehmann <schmorp@schmorp.de>	1209	Marc Lehmann <schmorp@schmorp.de>
634	http://home.schmorp.de/	1210	http://home.schmorp.de/

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