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Revision 1.7 by root, Fri Jul 13 13:05:38 2001 UTC vs.
Revision 1.237 by root, Sat Nov 22 16:37:11 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - create and manage simple coroutines	3	Coro - real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
9	$new = new Coro sub {	9	async {
10	print "in coroutine, switching back\n";	10	# some asynchronous thread of execution
11	$new->transfer($main);	11	print "2\n";
12	print "in coroutine again, switching back\n";	12	cede; # yield back to main
13	$new->transfer($main);	13	print "4\n";
14	};	14	};
15		15	print "1\n";
16	$main = new Coro;	16	cede; # yield to coroutine
17		17	print "3\n";
18	print "in main, switching to coroutine\n";	18	cede; # and again
19	$main->transfer($new);	19
20	print "back in main, switch to coroutine again\n";	20	# use locking
21	$main->transfer($new);	21	use Coro::Semaphore;
22	print "back in main\n";	22	my $lock = new Coro::Semaphore;
		23	my $locked;
		24
		25	$lock->down;
		26	$locked = 1;
		27	$lock->up;
23		28
24	=head1 DESCRIPTION	29	=head1 DESCRIPTION
25		30
26	This module implements coroutines. Coroutines, similar to continuations,	31	For a tutorial-style introduction, please read the L<Coro::Intro>
27	allow you to run more than one "thread of execution" in parallel. Unlike	32	manpage. This manpage mainly contains reference information.
28	threads this, only voluntary switching is used so locking problems are
29	greatly reduced.
30		33
31	Although this is the "main" module of the Coro family it provides only	34	This module collection manages coroutines, that is, cooperative
32	low-level functionality. See L<Coro::Process> and related modules for a	35	threads. Coroutines are similar to kernel threads but don't (in general)
33	more useful process abstraction including scheduling.	36	run in parallel at the same time even on SMP machines. The specific flavor
		37	of coroutine used in this module also guarantees you that it will not
		38	switch between coroutines unless necessary, at easily-identified points
		39	in your program, so locking and parallel access are rarely an issue,
		40	making coroutine programming much safer and easier than using other thread
		41	models.
		42
		43	Unlike the so-called "Perl threads" (which are not actually real threads
		44	but only the windows process emulation ported to unix), Coro provides a
		45	full shared address space, which makes communication between coroutines
		46	very easy. And coroutines are fast, too: disabling the Windows process
		47	emulation code in your perl and using Coro can easily result in a two to
		48	four times speed increase for your programs.
		49
		50	Coro achieves that by supporting multiple running interpreters that share
		51	data, which is especially useful to code pseudo-parallel processes and
		52	for event-based programming, such as multiple HTTP-GET requests running
		53	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		54	into an event-based environment.
		55
		56	In this module, a coroutines is defined as "callchain + lexical variables
		57	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
		58	callchain, its own set of lexicals and its own set of perls most important
		59	global variables (see L<Coro::State> for more configuration and background
		60	info).
		61
		62	See also the C<SEE ALSO> section at the end of this document - the Coro
		63	module family is quite large.
		64
		65	=cut
		66
		67	package Coro;
		68
		69	use strict qw(vars subs);
		70	no warnings "uninitialized";
		71
		72	use Coro::State;
		73
		74	use base qw(Coro::State Exporter);
		75
		76	our $idle; # idle handler
		77	our $main; # main coroutine
		78	our $current; # current coroutine
		79
		80	our $VERSION = "5.0";
		81
		82	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
		83	our %EXPORT_TAGS = (
		84	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		85	);
		86	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
		87
		88	=head1 GLOBAL VARIABLES
34		89
35	=over 4	90	=over 4
36		91
37	=cut	92	=item $Coro::main
38		93
39	package Coro;	94	This variable stores the coroutine object that represents the main
		95	program. While you cna C<ready> it and do most other things you can do to
		96	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		97	whether you are running in the main program or not.
40		98
41	BEGIN {	99	=cut
42	$VERSION = 0.03;
43		100
		101	# $main is now being initialised by Coro::State
		102
		103	=item $Coro::current
		104
		105	The coroutine object representing the current coroutine (the last
		106	coroutine that the Coro scheduler switched to). The initial value is
		107	C<$Coro::main> (of course).
		108
		109	This variable is B<strictly> I<read-only>. You can take copies of the
		110	value stored in it and use it as any other coroutine object, but you must
		111	not otherwise modify the variable itself.
		112
		113	=cut
		114
		115	sub current() { $current } # [DEPRECATED]
		116
		117	=item $Coro::idle
		118
		119	This variable is mainly useful to integrate Coro into event loops. It is
		120	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is
		121	pretty low-level functionality.
		122
		123	This variable stores a callback that is called whenever the scheduler
		124	finds no ready coroutines to run. The default implementation prints
		125	"FATAL: deadlock detected" and exits, because the program has no other way
		126	to continue.
		127
		128	This hook is overwritten by modules such as C<Coro::Timer> and
		129	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
		130	coroutine so the scheduler can run it.
		131
		132	Note that the callback I<must not>, under any circumstances, block
		133	the current coroutine. Normally, this is achieved by having an "idle
		134	coroutine" that calls the event loop and then blocks again, and then
		135	readying that coroutine in the idle handler.
		136
		137	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
		138	technique.
		139
		140	Please note that if your callback recursively invokes perl (e.g. for event
		141	handlers), then it must be prepared to be called recursively itself.
		142
		143	=cut
		144
		145	$idle = sub {
44	require XSLoader;	146	require Carp;
45	XSLoader::load Coro, $VERSION;	147	Carp::croak ("FATAL: deadlock detected");
46	}	148	};
47		149
48	=item $coro = new [$coderef [, @args]]	150	# this coroutine is necessary because a coroutine
		151	# cannot destroy itself.
		152	our @destroy;
		153	our $manager;
49		154
50	Create a new coroutine and return it. The first C<transfer> call to this	155	$manager = new Coro sub {
51	coroutine will start execution at the given coderef. If, the subroutine	156	while () {
52	returns it will be executed again.	157	Coro::_cancel shift @destroy
		158	while @destroy;
53		159
54	If the coderef is omitted this function will create a new "empty"	160	&schedule;
55	coroutine, i.e. a coroutine that cannot be transfered to but can be used
56	to save the current coroutine in.
57
58	=cut
59
60	sub new {
61	my $class = $_[0];
62	my $proc = $_[1] \|\| sub { die "tried to transfer to an empty coroutine" };
63	bless _newprocess {
64	do {
65	eval { &$proc };
66	if ($@) {
67	$error_msg = $@;
68	$error_coro = _newprocess { };
69	&transfer($error_coro, $error);
70	}
71	} while (1);
72	}, $class;
73	}
74
75	=item $prev->transfer($next)
76
77	Save the state of the current subroutine in C<$prev> and switch to the
78	coroutine saved in C<$next>.
79
80	The "state" of a subroutine only ever includes scope, i.e. lexical
81	variables and the current execution state. It does not save/restore any
82	global variables such as C<$_> or C<$@> or any other special or non
83	special variables. So remember that every function call that might call
84	C<transfer> (such as C<Coro::Channel::put>) might clobber any global
85	and/or special variables. Yes, this is by design ;) You cna always create
86	your own process abstraction model that saves these variables.
87
88	The easiest way to do this is to create your own scheduling primitive like this:
89
90	sub schedule {
91	local ($_, $@, ...);
92	$old->transfer($new);
93	}	161	}
		162	};
		163	$manager->{desc} = "[coro manager]";
		164	$manager->prio (PRIO_MAX);
94		165
95	=cut	166	=back
96		167
97	# I call the _transfer function from a perl function	168	=head1 SIMPLE COROUTINE CREATION
98	# because that way perl saves all important things on	169
99	# the stack. Actually, I'd do it from within XS, but	170	=over 4
100	# I couldn't get it to work.	171
		172	=item async { ... } [@args...]
		173
		174	Create a new coroutine and return it's coroutine object (usually
		175	unused). The coroutine will be put into the ready queue, so
		176	it will start running automatically on the next scheduler run.
		177
		178	The first argument is a codeblock/closure that should be executed in the
		179	coroutine. When it returns argument returns the coroutine is automatically
		180	terminated.
		181
		182	The remaining arguments are passed as arguments to the closure.
		183
		184	See the C<Coro::State::new> constructor for info about the coroutine
		185	environment in which coroutines are executed.
		186
		187	Calling C<exit> in a coroutine will do the same as calling exit outside
		188	the coroutine. Likewise, when the coroutine dies, the program will exit,
		189	just as it would in the main program.
		190
		191	If you do not want that, you can provide a default C<die> handler, or
		192	simply avoid dieing (by use of C<eval>).
		193
		194	Example: Create a new coroutine that just prints its arguments.
		195
		196	async {
		197	print "@_\n";
		198	} 1,2,3,4;
		199
		200	=cut
		201
		202	sub async(&@) {
		203	my $coro = new Coro @_;
		204	$coro->ready;
		205	$coro
		206	}
		207
		208	=item async_pool { ... } [@args...]
		209
		210	Similar to C<async>, but uses a coroutine pool, so you should not call
		211	terminate or join on it (although you are allowed to), and you get a
		212	coroutine that might have executed other code already (which can be good
		213	or bad :).
		214
		215	On the plus side, this function is about twice as fast as creating (and
		216	destroying) a completely new coroutine, so if you need a lot of generic
		217	coroutines in quick successsion, use C<async_pool>, not C<async>.
		218
		219	The code block is executed in an C<eval> context and a warning will be
		220	issued in case of an exception instead of terminating the program, as
		221	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		222	will not work in the expected way, unless you call terminate or cancel,
		223	which somehow defeats the purpose of pooling (but is fine in the
		224	exceptional case).
		225
		226	The priority will be reset to C<0> after each run, tracing will be
		227	disabled, the description will be reset and the default output filehandle
		228	gets restored, so you can change all these. Otherwise the coroutine will
		229	be re-used "as-is": most notably if you change other per-coroutine global
		230	stuff such as C<$/> you I<must needs> revert that change, which is most
		231	simply done by using local as in: C<< local $/ >>.
		232
		233	The idle pool size is limited to C<8> idle coroutines (this can be
		234	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		235	coros as required.
		236
		237	If you are concerned about pooled coroutines growing a lot because a
		238	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		239	{ terminate }> once per second or so to slowly replenish the pool. In
		240	addition to that, when the stacks used by a handler grows larger than 32kb
		241	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		242
		243	=cut
		244
		245	our $POOL_SIZE = 8;
		246	our $POOL_RSS = 32 * 1024;
		247	our @async_pool;
		248
		249	sub pool_handler {
		250	while () {
		251	eval {
		252	&{&_pool_handler} while 1;
		253	};
		254
		255	warn $@ if $@;
		256	}
		257	}
		258
		259	=back
		260
		261	=head1 STATIC METHODS
		262
		263	Static methods are actually functions that implicitly operate on the
		264	current coroutine.
		265
		266	=over 4
		267
		268	=item schedule
		269
		270	Calls the scheduler. The scheduler will find the next coroutine that is
		271	to be run from the ready queue and switches to it. The next coroutine
		272	to be run is simply the one with the highest priority that is longest
		273	in its ready queue. If there is no coroutine ready, it will clal the
		274	C<$Coro::idle> hook.
		275
		276	Please note that the current coroutine will I<not> be put into the ready
		277	queue, so calling this function usually means you will never be called
		278	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		279	thus waking you up.
		280
		281	This makes C<schedule> I<the> generic method to use to block the current
		282	coroutine and wait for events: first you remember the current coroutine in
		283	a variable, then arrange for some callback of yours to call C<< ->ready
		284	>> on that once some event happens, and last you call C<schedule> to put
		285	yourself to sleep. Note that a lot of things can wake your coroutine up,
		286	so you need to check whether the event indeed happened, e.g. by storing the
		287	status in a variable.
		288
		289	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
		290
		291	=item cede
		292
		293	"Cede" to other coroutines. This function puts the current coroutine into
		294	the ready queue and calls C<schedule>, which has the effect of giving
		295	up the current "timeslice" to other coroutines of the same or higher
		296	priority. Once your coroutine gets its turn again it will automatically be
		297	resumed.
		298
		299	This function is often called C<yield> in other languages.
		300
		301	=item Coro::cede_notself
		302
		303	Works like cede, but is not exported by default and will cede to I<any>
		304	coroutine, regardless of priority. This is useful sometimes to ensure
		305	progress is made.
		306
		307	=item terminate [arg...]
		308
		309	Terminates the current coroutine with the given status values (see L<cancel>).
		310
		311	=item killall
		312
		313	Kills/terminates/cancels all coroutines except the currently running
		314	one. This is useful after a fork, either in the child or the parent, as
		315	usually only one of them should inherit the running coroutines.
		316
		317	Note that while this will try to free some of the main programs resources,
		318	you cannot free all of them, so if a coroutine that is not the main
		319	program calls this function, there will be some one-time resource leak.
		320
		321	=cut
		322
		323	sub killall {
		324	for (Coro::State::list) {
		325	$_->cancel
		326	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		327	}
		328	}
		329
		330	=back
		331
		332	=head1 COROUTINE OBJECT METHODS
		333
		334	These are the methods you can call on coroutine objects (or to create
		335	them).
		336
		337	=over 4
		338
		339	=item new Coro \&sub [, @args...]
		340
		341	Create a new coroutine and return it. When the sub returns, the coroutine
		342	automatically terminates as if C<terminate> with the returned values were
		343	called. To make the coroutine run you must first put it into the ready
		344	queue by calling the ready method.
		345
		346	See C<async> and C<Coro::State::new> for additional info about the
		347	coroutine environment.
		348
		349	=cut
		350
		351	sub _terminate {
		352	terminate &{+shift};
		353	}
		354
		355	=item $success = $coroutine->ready
		356
		357	Put the given coroutine into the end of its ready queue (there is one
		358	queue for each priority) and return true. If the coroutine is already in
		359	the ready queue, do nothing and return false.
		360
		361	This ensures that the scheduler will resume this coroutine automatically
		362	once all the coroutines of higher priority and all coroutines of the same
		363	priority that were put into the ready queue earlier have been resumed.
		364
		365	=item $is_ready = $coroutine->is_ready
		366
		367	Return whether the coroutine is currently the ready queue or not,
		368
		369	=item $coroutine->cancel (arg...)
		370
		371	Terminates the given coroutine and makes it return the given arguments as
		372	status (default: the empty list). Never returns if the coroutine is the
		373	current coroutine.
		374
		375	=cut
		376
		377	sub cancel {
		378	my $self = shift;
		379
		380	if ($current == $self) {
		381	terminate @_;
		382	} else {
		383	$self->{_status} = [@_];
		384	$self->_cancel;
		385	}
		386	}
		387
		388	=item $coroutine->schedule_to
		389
		390	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead
		391	of continuing with the next coro from the ready queue, always switch to
		392	the given coroutine object (regardless of priority etc.). The readyness
		393	state of that coroutine isn't changed.
		394
		395	This is an advanced method for special cases - I'd love to hear about any
		396	uses for this one.
		397
		398	=item $coroutine->cede_to
		399
		400	Like C<schedule_to>, but puts the current coroutine into the ready
		401	queue. This has the effect of temporarily switching to the given
		402	coroutine, and continuing some time later.
		403
		404	This is an advanced method for special cases - I'd love to hear about any
		405	uses for this one.
		406
		407	=item $coroutine->throw ([$scalar])
		408
		409	If C<$throw> is specified and defined, it will be thrown as an exception
		410	inside the coroutine at the next convenient point in time. Otherwise
		411	clears the exception object.
		412
		413	Coro will check for the exception each time a schedule-like-function
		414	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		415	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		416	detect this case and return early in case an exception is pending.
		417
		418	The exception object will be thrown "as is" with the specified scalar in
		419	C<$@>, i.e. if it is a string, no line number or newline will be appended
		420	(unlike with C<die>).
		421
		422	This can be used as a softer means than C<cancel> to ask a coroutine to
		423	end itself, although there is no guarantee that the exception will lead to
		424	termination, and if the exception isn't caught it might well end the whole
		425	program.
		426
		427	You might also think of C<throw> as being the moral equivalent of
		428	C<kill>ing a coroutine with a signal (in this case, a scalar).
		429
		430	=item $coroutine->join
		431
		432	Wait until the coroutine terminates and return any values given to the
		433	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		434	from multiple coroutines, and all will be resumed and given the status
		435	return once the C<$coroutine> terminates.
		436
		437	=cut
		438
		439	sub join {
		440	my $self = shift;
		441
		442	unless ($self->{_status}) {
		443	my $current = $current;
		444
		445	push @{$self->{_on_destroy}}, sub {
		446	$current->ready;
		447	undef $current;
		448	};
		449
		450	&schedule while $current;
		451	}
		452
		453	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		454	}
		455
		456	=item $coroutine->on_destroy (\&cb)
		457
		458	Registers a callback that is called when this coroutine gets destroyed,
		459	but before it is joined. The callback gets passed the terminate arguments,
		460	if any, and I<must not> die, under any circumstances.
		461
		462	=cut
		463
		464	sub on_destroy {
		465	my ($self, $cb) = @_;
		466
		467	push @{ $self->{_on_destroy} }, $cb;
		468	}
		469
		470	=item $oldprio = $coroutine->prio ($newprio)
		471
		472	Sets (or gets, if the argument is missing) the priority of the
		473	coroutine. Higher priority coroutines get run before lower priority
		474	coroutines. Priorities are small signed integers (currently -4 .. +3),
		475	that you can refer to using PRIO_xxx constants (use the import tag :prio
		476	to get then):
		477
		478	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		479	3 > 1 > 0 > -1 > -3 > -4
		480
		481	# set priority to HIGH
		482	current->prio(PRIO_HIGH);
		483
		484	The idle coroutine ($Coro::idle) always has a lower priority than any
		485	existing coroutine.
		486
		487	Changing the priority of the current coroutine will take effect immediately,
		488	but changing the priority of coroutines in the ready queue (but not
		489	running) will only take effect after the next schedule (of that
		490	coroutine). This is a bug that will be fixed in some future version.
		491
		492	=item $newprio = $coroutine->nice ($change)
		493
		494	Similar to C<prio>, but subtract the given value from the priority (i.e.
		495	higher values mean lower priority, just as in unix).
		496
		497	=item $olddesc = $coroutine->desc ($newdesc)
		498
		499	Sets (or gets in case the argument is missing) the description for this
		500	coroutine. This is just a free-form string you can associate with a
		501	coroutine.
		502
		503	This method simply sets the C<< $coroutine->{desc} >> member to the given
		504	string. You can modify this member directly if you wish.
		505
		506	=cut
		507
		508	sub desc {
		509	my $old = $_[0]{desc};
		510	$_[0]{desc} = $_[1] if @_ > 1;
		511	$old;
		512	}
		513
101	sub transfer {	514	sub transfer {
102	_transfer($_[0], $_[1]);	515	require Carp;
		516	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
103	}	517	}
104		518
105	=item $error, $error_msg, $error_coro	519	=back
106		520
107	This coroutine will be called on fatal errors. C<$error_msg> and	521	=head1 GLOBAL FUNCTIONS
108	C<$error_coro> return the error message and the error-causing coroutine
109	(NOT an object) respectively. This API might change.
110		522
111	=cut	523	=over 4
112		524
113	$error_msg =	525	=item Coro::nready
114	$error_coro = undef;
115		526
116	$error = _newprocess {	527	Returns the number of coroutines that are currently in the ready state,
117	print STDERR "FATAL: $error_msg\nprogram aborted\n";	528	i.e. that can be switched to by calling C<schedule> directory or
118	exit 50;	529	indirectly. The value C<0> means that the only runnable coroutine is the
		530	currently running one, so C<cede> would have no effect, and C<schedule>
		531	would cause a deadlock unless there is an idle handler that wakes up some
		532	coroutines.
		533
		534	=item my $guard = Coro::guard { ... }
		535
		536	This creates and returns a guard object. Nothing happens until the object
		537	gets destroyed, in which case the codeblock given as argument will be
		538	executed. This is useful to free locks or other resources in case of a
		539	runtime error or when the coroutine gets canceled, as in both cases the
		540	guard block will be executed. The guard object supports only one method,
		541	C<< ->cancel >>, which will keep the codeblock from being executed.
		542
		543	Example: set some flag and clear it again when the coroutine gets canceled
		544	or the function returns:
		545
		546	sub do_something {
		547	my $guard = Coro::guard { $busy = 0 };
		548	$busy = 1;
		549
		550	# do something that requires $busy to be true
		551	}
		552
		553	=cut
		554
		555	sub guard(&) {
		556	bless \(my $cb = $_[0]), "Coro::guard"
		557	}
		558
		559	sub Coro::guard::cancel {
		560	${$_[0]} = sub { };
		561	}
		562
		563	sub Coro::guard::DESTROY {
		564	${$_[0]}->();
		565	}
		566
		567
		568	=item unblock_sub { ... }
		569
		570	This utility function takes a BLOCK or code reference and "unblocks" it,
		571	returning a new coderef. Unblocking means that calling the new coderef
		572	will return immediately without blocking, returning nothing, while the
		573	original code ref will be called (with parameters) from within another
		574	coroutine.
		575
		576	The reason this function exists is that many event libraries (such as the
		577	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		578	of thread-safety). This means you must not block within event callbacks,
		579	otherwise you might suffer from crashes or worse. The only event library
		580	currently known that is safe to use without C<unblock_sub> is L<EV>.
		581
		582	This function allows your callbacks to block by executing them in another
		583	coroutine where it is safe to block. One example where blocking is handy
		584	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		585	disk, for example.
		586
		587	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		588	creating event callbacks that want to block.
		589
		590	If your handler does not plan to block (e.g. simply sends a message to
		591	another coroutine, or puts some other coroutine into the ready queue),
		592	there is no reason to use C<unblock_sub>.
		593
		594	Note that you also need to use C<unblock_sub> for any other callbacks that
		595	are indirectly executed by any C-based event loop. For example, when you
		596	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		597	provides callbacks that are the result of some event callback, then you
		598	must not block either, or use C<unblock_sub>.
		599
		600	=cut
		601
		602	our @unblock_queue;
		603
		604	# we create a special coro because we want to cede,
		605	# to reduce pressure on the coro pool (because most callbacks
		606	# return immediately and can be reused) and because we cannot cede
		607	# inside an event callback.
		608	our $unblock_scheduler = new Coro sub {
		609	while () {
		610	while (my $cb = pop @unblock_queue) {
		611	&async_pool (@$cb);
		612
		613	# for short-lived callbacks, this reduces pressure on the coro pool
		614	# as the chance is very high that the async_poll coro will be back
		615	# in the idle state when cede returns
		616	cede;
		617	}
		618	schedule; # sleep well
		619	}
119	};	620	};
		621	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		622
		623	sub unblock_sub(&) {
		624	my $cb = shift;
		625
		626	sub {
		627	unshift @unblock_queue, [$cb, @_];
		628	$unblock_scheduler->ready;
		629	}
		630	}
		631
		632	=item $cb = Coro::rouse_cb
		633
		634	Create and return a "rouse callback". That's a code reference that, when
		635	called, will save its arguments and notify the owner coroutine of the
		636	callback.
		637
		638	See the next function.
		639
		640	=item @args = Coro::rouse_wait [$cb]
		641
		642	Wait for the specified rouse callback (or the last one tht was created in
		643	this coroutine).
		644
		645	As soon as the callback is invoked (or when the calback was invoked before
		646	C<rouse_wait>), it will return a copy of the arguments originally passed
		647	to the rouse callback.
		648
		649	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		650
		651	=back
		652
		653	=cut
120		654
121	1;	655	1;
122		656
		657	=head1 HOW TO WAIT FOR A CALLBACK
		658
		659	It is very common for a coroutine to wait for some callback to be
		660	called. This occurs naturally when you use coroutines in an otherwise
		661	event-based program, or when you use event-based libraries.
		662
		663	These typically register a callback for some event, and call that callback
		664	when the event occured. In a coroutine, however, you typically want to
		665	just wait for the event, simplyifying things.
		666
		667	For example C<< AnyEvent->child >> registers a callback to be called when
		668	a specific child has exited:
		669
		670	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		671
		672	But from withina coroutine, you often just want to write this:
		673
		674	my $status = wait_for_child $pid;
		675
		676	Coro offers two functions specifically designed to make this easy,
		677	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		678
		679	The first function, C<rouse_cb>, generates and returns a callback that,
		680	when invoked, will save it's arguments and notify the coroutine that
		681	created the callback.
		682
		683	The second function, C<rouse_wait>, waits for the callback to be called
		684	(by calling C<schedule> to go to sleep) and returns the arguments
		685	originally passed to the callback.
		686
		687	Using these functions, it becomes easy to write the C<wait_for_child>
		688	function mentioned above:
		689
		690	sub wait_for_child($) {
		691	my ($pid) = @_;
		692
		693	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		694
		695	my ($rpid, $rstatus) = Coro::rouse_wait;
		696	$rstatus
		697	}
		698
		699	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		700	you can roll your own, using C<schedule>:
		701
		702	sub wait_for_child($) {
		703	my ($pid) = @_;
		704
		705	# store the current coroutine in $current,
		706	# and provide result variables for the closure passed to ->child
		707	my $current = $Coro::current;
		708	my ($done, $rstatus);
		709
		710	# pass a closure to ->child
		711	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		712	$rstatus = $_[1]; # remember rstatus
		713	$done = 1; # mark $rstatus as valud
		714	});
		715
		716	# wait until the closure has been called
		717	schedule while !$done;
		718
		719	$rstatus
		720	}
		721
		722
		723	=head1 BUGS/LIMITATIONS
		724
		725	=over 4
		726
		727	=item fork with pthread backend
		728
		729	When Coro is compiled using the pthread backend (which isn't recommended
		730	but required on many BSDs as their libcs are completely broken), then
		731	coroutines will not survive a fork. There is no known workaround except to
		732	fix your libc and use a saner backend.
		733
		734	=item perl process emulation ("threads")
		735
		736	This module is not perl-pseudo-thread-safe. You should only ever use this
		737	module from the same thread (this requirement might be removed in the
		738	future to allow per-thread schedulers, but Coro::State does not yet allow
		739	this). I recommend disabling thread support and using processes, as having
		740	the windows process emulation enabled under unix roughly halves perl
		741	performance, even when not used.
		742
		743	=item coroutine switching not signal safe
		744
		745	You must not switch to another coroutine from within a signal handler
		746	(only relevant with %SIG - most event libraries provide safe signals).
		747
		748	That means you I<MUST NOT> call any function that might "block" the
		749	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		750	anything that calls those. Everything else, including calling C<ready>,
		751	works.
		752
123	=back	753	=back
124		754
125	=head1 BUGS
126
127	This module has not yet been extensively tested.
128		755
129	=head1 SEE ALSO	756	=head1 SEE ALSO
130		757
131	L<Coro::Process>, L<Coro::Signal>.	758	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		759
		760	Debugging: L<Coro::Debug>.
		761
		762	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		763
		764	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		765	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		766
		767	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		768
		769	Compatibility: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		770	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		771	L<Coro::Select>.
		772
		773	XS API: L<Coro::MakeMaker>.
		774
		775	Low level Configuration, Coroutine Environment: L<Coro::State>.
132		776
133	=head1 AUTHOR	777	=head1 AUTHOR
134		778
135	Marc Lehmann <pcg@goof.com>	779	Marc Lehmann <schmorp@schmorp.de>
136	http://www.goof.com/pcg/marc/	780	http://home.schmorp.de/
137		781
138	=cut	782	=cut
139		783

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Revision 1.237 by root, Sat Nov 22 16:37:11 2008 UTC