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Revision 1.8 by root, Sat Jul 14 22:14:21 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 - coroutine process abstraction	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	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
		11	print "2\n";
		12	cede; # yield back to main
		13	print "4\n";
11	};	14	};
12		15	print "1\n";
13	# alternatively create an async process like this:	16	cede; # yield to coroutine
14		17	print "3\n";
15	sub some_func : Coro {	18	cede; # and again
16	# some more async code	19
17	}	20	# use locking
18		21	use Coro::Semaphore;
19	yield;	22	my $lock = new Coro::Semaphore;
		23	my $locked;
		24
		25	$lock->down;
		26	$locked = 1;
		27	$lock->up;
20		28
21	=head1 DESCRIPTION	29	=head1 DESCRIPTION
22		30
		31	For a tutorial-style introduction, please read the L<Coro::Intro>
		32	manpage. This manpage mainly contains reference information.
		33
		34	This module collection manages coroutines, that is, cooperative
		35	threads. Coroutines are similar to kernel threads but don't (in general)
		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
23	=cut	65	=cut
24		66
25	package Coro;	67	package Coro;
26		68
		69	use strict qw(vars subs);
		70	no warnings "uninitialized";
		71
27	use Coro::State;	72	use Coro::State;
28		73
29	use base Exporter;	74	use base qw(Coro::State Exporter);
30		75
		76	our $idle; # idle handler
		77	our $main; # main coroutine
		78	our $current; # current coroutine
		79
31	$VERSION = 0.03;	80	our $VERSION = "5.0";
32		81
33	@EXPORT = qw(async yield schedule);	82	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
34	@EXPORT_OK = qw($current);	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));
35		87
36	{	88	=head1 GLOBAL VARIABLES
37	use subs 'async';
38		89
39	my @async;	90	=over 4
40		91
41	# this way of handling attributes simply is NOT scalable ;()	92	=item $Coro::main
42	sub import {	93
43	Coro->export_to_level(1, @_);	94	This variable stores the coroutine object that represents the main
44	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};	95	program. While you cna C<ready> it and do most other things you can do to
45	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {	96	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
46	my ($package, $ref) = (shift, shift);	97	whether you are running in the main program or not.
47	my @attrs;	98
48	for (@_) {	99	=cut
49	if ($_ eq "Coro") {	100
50	push @async, $ref;	101	# $main is now being initialised by Coro::State
51	} else {	102
52	push @attrs, @_;	103	=item $Coro::current
53	}	104
54	}	105	The coroutine object representing the current coroutine (the last
55	return $old ? $old->($package, $name, @attrs) : @attrs;	106	coroutine that the Coro scheduler switched to). The initial value is
		107	C<$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 {
		146	require Carp;
		147	Carp::croak ("FATAL: deadlock detected");
		148	};
		149
		150	# this coroutine is necessary because a coroutine
		151	# cannot destroy itself.
		152	our @destroy;
		153	our $manager;
		154
		155	$manager = new Coro sub {
		156	while () {
		157	Coro::_cancel shift @destroy
		158	while @destroy;
		159
		160	&schedule;
		161	}
		162	};
		163	$manager->{desc} = "[coro manager]";
		164	$manager->prio (PRIO_MAX);
		165
		166	=back
		167
		168	=head1 SIMPLE COROUTINE CREATION
		169
		170	=over 4
		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;
56	};	253	};
57	}
58		254
59	sub INIT {	255	warn $@ if $@;
60	async pop @async while @async;
61	}	256	}
62	}	257	}
63		258
64	my $idle = new Coro sub {	259	=back
65	&yield while 1;	260
		261	=head1 STATIC METHODS
		262
		263	Static methods are actually functions that implicitly operate on the
		264	current coroutine.
		265
		266	=over 4
		267
		268	=item schedule
		269
		270	Calls the scheduler. The scheduler will find the next coroutine that is
		271	to be run from the ready queue and switches to it. The next coroutine
		272	to be run is simply the one with the highest priority that is longest
		273	in its ready queue. If there is no coroutine ready, it will clal the
		274	C<$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
		514	sub transfer {
		515	require Carp;
		516	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		517	}
		518
		519	=back
		520
		521	=head1 GLOBAL FUNCTIONS
		522
		523	=over 4
		524
		525	=item Coro::nready
		526
		527	Returns the number of coroutines that are currently in the ready state,
		528	i.e. that can be switched to by calling C<schedule> directory or
		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	}
66	};	620	};
		621	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
67		622
68	=item $main	623	sub unblock_sub(&) {
		624	my $cb = shift;
69		625
70	This coroutine represents the main program.	626	sub {
71		627	unshift @unblock_queue, [$cb, @_];
72	=cut	628	$unblock_scheduler->ready;
73		629	}
74	$main = new Coro;
75
76	=item $current
77
78	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).
79
80	=cut
81
82	# maybe some other module used Coro::Specific before...
83	if ($current) {
84	$main->{specific} = $current->{specific};
85	}	630	}
86		631
87	$current = $main;	632	=item $cb = Coro::rouse_cb
88		633
89	# we really need priorities...	634	Create and return a "rouse callback". That's a code reference that, when
90	my @ready = (); # the ready queue. hehe, rather broken ;)	635	called, will save its arguments and notify the owner coroutine of the
		636	callback.
91		637
92	# static methods. not really.	638	See the next function.
93		639
94	=head2 STATIC METHODS	640	=item @args = Coro::rouse_wait [$cb]
95		641
96	Static methods are actually functions that operate on the current process only.	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
		654
		655	1;
		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
97		724
98	=over 4	725	=over 4
99		726
100	=item async { ... };	727	=item fork with pthread backend
101		728
102	Create a new asynchronous process and return it's process object	729	When Coro is compiled using the pthread backend (which isn't recommended
103	(usually unused). When the sub returns the new process is automatically	730	but required on many BSDs as their libcs are completely broken), then
104	terminated.	731	coroutines will not survive a fork. There is no known workaround except to
		732	fix your libc and use a saner backend.
105		733
106	=cut	734	=item perl process emulation ("threads")
107		735
108	sub async(&) {	736	This module is not perl-pseudo-thread-safe. You should only ever use this
109	(new Coro $_[0])->ready;	737	module from the same thread (this requirement might be removed in the
110	}	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.
111		742
112	=item schedule	743	=item coroutine switching not signal safe
113		744
114	Calls the scheduler. Please note that the current process will not be put	745	You must not switch to another coroutine from within a signal handler
115	into the ready queue, so calling this function usually means you will	746	(only relevant with %SIG - most event libraries provide safe signals).
116	never be called again.
117		747
118	=cut	748	That means you I<MUST NOT> call any function that might "block" the
119		749	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
120	my $prev;	750	anything that calls those. Everything else, including calling C<ready>,
121		751	works.
122	sub schedule {
123	($prev, $current) = ($current, shift @ready);
124	Coro::State::transfer($prev, $current);
125	}
126
127	=item yield
128
129	Yield to other processes. This function puts the current process into the
130	ready queue and calls C<schedule>.
131
132	=cut
133
134	sub yield {
135	$current->ready;
136	&schedule;
137	}
138
139	=item terminate
140
141	Terminates the current process.
142
143	=cut
144
145	sub terminate {
146	&schedule;
147	}
148		752
149	=back	753	=back
150		754
151	# dynamic methods
152		755
153	=head2 PROCESS METHODS	756	=head1 SEE ALSO
154		757
155	These are the methods you can call on process objects.	758	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
156		759
157	=over 4	760	Debugging: L<Coro::Debug>.
158		761
159	=item new Coro \⊂	762	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
160		763
161	Create a new process and return it. When the sub returns the process	764	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
162	automatically terminates. To start the process you must first put it into	765	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
163	the ready queue by calling the ready method.
164		766
165	=cut	767	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
166		768
167	sub new {	769	Compatibility: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
168	my $class = shift;	770	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
169	my $proc = $_[0];	771	L<Coro::Select>.
170	bless {
171	_coro_state => new Coro::State ($proc ? sub { &$proc; &terminate } : $proc),
172	}, $class;
173	}
174		772
175	=item $process->ready	773	XS API: L<Coro::MakeMaker>.
176		774
177	Put the current process into the ready queue.	775	Low level Configuration, Coroutine Environment: L<Coro::State>.
178
179	=cut
180
181	sub ready {
182	push @ready, $_[0];
183	}
184
185	=back
186
187	=cut
188
189	1;
190		776
191	=head1 AUTHOR	777	=head1 AUTHOR
192		778
193	Marc Lehmann <pcg@goof.com>	779	Marc Lehmann <schmorp@schmorp.de>
194	http://www.goof.com/pcg/marc/	780	http://home.schmorp.de/
195		781
196	=cut	782	=cut
197		783

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