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

Comparing Coro/Coro.pm (file contents):
Revision 1.20 by root, Sat Jul 21 18:21:45 2001 UTC vs.
Revision 1.246 by root, Mon Dec 15 00:30:40 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
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
23	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
24	Threads but don't run in parallel.	32	manpage. This manpage mainly contains reference information.
25		33
26	This module is still experimental, see the BUGS section below.	34	This module collection manages continuations in general, most often
		35	in the form of cooperative threads (also called coroutines in the
		36	documentation). They are similar to kernel threads but don't (in general)
		37	run in parallel at the same time even on SMP machines. The specific flavor
		38	of thread offered by this module also guarantees you that it will not
		39	switch between threads unless necessary, at easily-identified points in
		40	your program, so locking and parallel access are rarely an issue, making
		41	thread programming much safer and easier than using other thread models.
27		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 threads
		46	very easy. And threads 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
28	In this module, coroutines are defined as "callchain + lexical variables	56	In this module, a thread is defined as "callchain + lexical variables +
29	+ @_ + $_ + $@ + $^W), that is, a coroutine has it's own callchain, it's	57	@_ + $_ + $@ + $/ + C stack), that is, a thread has its own callchain,
30	own set of lexicals and it's own set of perl's most important global	58	its own set of lexicals and its own set of perls most important global
31	variables.	59	variables (see L<Coro::State> for more configuration and background info).
		60
		61	See also the C<SEE ALSO> section at the end of this document - the Coro
		62	module family is quite large.
32		63
33	=cut	64	=cut
34		65
35	package Coro;	66	package Coro;
36		67
		68	use strict qw(vars subs);
		69	no warnings "uninitialized";
		70
		71	use Guard ();
		72
37	use Coro::State;	73	use Coro::State;
38		74
39	use base Exporter;	75	use base qw(Coro::State Exporter);
40		76
		77	our $idle; # idle handler
		78	our $main; # main coroutine
		79	our $current; # current coroutine
		80
41	$VERSION = 0.10;	81	our $VERSION = 5.13;
42		82
43	@EXPORT = qw(async yield schedule terminate current);	83	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
44	@EXPORT_OK = qw($current);	84	our %EXPORT_TAGS = (
		85	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		86	);
		87	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
45		88
46	{	89	=head1 GLOBAL VARIABLES
47	my @async;
48		90
49	# this way of handling attributes simply is NOT scalable ;()	91	=over 4
50	sub import {
51	Coro->export_to_level(1, @_);
52	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
53	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
54	my ($package, $ref) = (shift, shift);
55	my @attrs;
56	for (@_) {
57	if ($_ eq "Coro") {
58	push @async, $ref;
59	} else {
60	push @attrs, $_;
61	}
62	}
63	return $old ? $old->($package, $ref, @attrs) : @attrs;
64	};
65	}
66		92
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	}
71
72	=item $main	93	=item $Coro::main
73		94
74	This coroutine represents the main program.	95	This variable stores the coroutine object that represents the main
		96	program. While you cna C<ready> it and do most other things you can do to
		97	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		98	whether you are running in the main program or not.
75		99
76	=cut	100	=cut
77		101
78	our $main = new Coro;	102	# $main is now being initialised by Coro::State
79		103
80	=item $current (or as function: current)	104	=item $Coro::current
81		105
82	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	106	The coroutine object representing the current coroutine (the last
		107	coroutine that the Coro scheduler switched to). The initial value is
		108	C<$Coro::main> (of course).
83		109
84	=cut	110	This variable is B<strictly> I<read-only>. You can take copies of the
		111	value stored in it and use it as any other coroutine object, but you must
		112	not otherwise modify the variable itself.
85		113
86	# maybe some other module used Coro::Specific before...	114	=cut
87	if ($current) {
88	$main->{specific} = $current->{specific};
89	}
90		115
91	our $current = $main;
92
93	sub current() { $current }	116	sub current() { $current } # [DEPRECATED]
94		117
95	=item $idle	118	=item $Coro::idle
96		119
97	The coroutine to switch to when no other coroutine is running. The default	120	This variable is mainly useful to integrate Coro into event loops. It is
98	implementation prints "FATAL: deadlock detected" and exits.	121	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		122	pretty low-level functionality.
99		123
100	=cut	124	This variable stores either a coroutine or a callback.
101		125
102	# should be done using priorities :(	126	If it is a callback, the it is called whenever the scheduler finds no
103	our $idle = new Coro sub {	127	ready coroutines to run. The default implementation prints "FATAL:
104	print STDERR "FATAL: deadlock detected\n";	128	deadlock detected" and exits, because the program has no other way to
105	exit(51);	129	continue.
		130
		131	If it is a coroutine object, then this object will be readied (without
		132	invoking any ready hooks, however) when the scheduler finds no other ready
		133	coroutines to run.
		134
		135	This hook is overwritten by modules such as C<Coro::EV> and
		136	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
		137	coroutine so the scheduler can run it.
		138
		139	Note that the callback I<must not>, under any circumstances, block
		140	the current coroutine. Normally, this is achieved by having an "idle
		141	coroutine" that calls the event loop and then blocks again, and then
		142	readying that coroutine in the idle handler, or by simply placing the idle
		143	coroutine in this variable.
		144
		145	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
		146	technique.
		147
		148	Please note that if your callback recursively invokes perl (e.g. for event
		149	handlers), then it must be prepared to be called recursively itself.
		150
		151	=cut
		152
		153	$idle = sub {
		154	require Carp;
		155	Carp::croak ("FATAL: deadlock detected");
106	};	156	};
107		157
108	# we really need priorities...	158	# this coroutine is necessary because a coroutine
109	my @ready; # the ready queue. hehe, rather broken ;)	159	# cannot destroy itself.
		160	our @destroy;
		161	our $manager;
110		162
111	# static methods. not really.	163	$manager = new Coro sub {
		164	while () {
		165	Coro::_cancel shift @destroy
		166	while @destroy;
112		167
113	=head2 STATIC METHODS	168	&schedule;
		169	}
		170	};
		171	$manager->{desc} = "[coro manager]";
		172	$manager->prio (PRIO_MAX);
114		173
115	Static methods are actually functions that operate on the current process only.	174	=back
		175
		176	=head1 SIMPLE COROUTINE CREATION
116		177
117	=over 4	178	=over 4
118		179
119	=item async { ... } [@args...]	180	=item async { ... } [@args...]
120		181
121	Create a new asynchronous process and return it's process object	182	Create a new coroutine and return its coroutine object (usually
122	(usually unused). When the sub returns the new process is automatically	183	unused). The coroutine will be put into the ready queue, so
		184	it will start running automatically on the next scheduler run.
		185
		186	The first argument is a codeblock/closure that should be executed in the
		187	coroutine. When it returns argument returns the coroutine is automatically
123	terminated.	188	terminated.
124		189
		190	The remaining arguments are passed as arguments to the closure.
		191
		192	See the C<Coro::State::new> constructor for info about the coroutine
		193	environment in which coroutines are executed.
		194
		195	Calling C<exit> in a coroutine will do the same as calling exit outside
		196	the coroutine. Likewise, when the coroutine dies, the program will exit,
		197	just as it would in the main program.
		198
		199	If you do not want that, you can provide a default C<die> handler, or
		200	simply avoid dieing (by use of C<eval>).
		201
125	# create a new coroutine that just prints its arguments	202	Example: Create a new coroutine that just prints its arguments.
		203
126	async {	204	async {
127	print "@_\n";	205	print "@_\n";
128	} 1,2,3,4;	206	} 1,2,3,4;
129		207
130	The coderef you submit MUST NOT be a closure that refers to variables
131	in an outer scope. This does NOT work. Pass arguments into it instead.
132
133	=cut	208	=cut
134		209
135	sub async(&@) {	210	sub async(&@) {
136	my $pid = new Coro @_;	211	my $coro = new Coro @_;
137	$pid->ready;	212	$coro->ready;
138	$pid;	213	$coro
139	}	214	}
		215
		216	=item async_pool { ... } [@args...]
		217
		218	Similar to C<async>, but uses a coroutine pool, so you should not call
		219	terminate or join on it (although you are allowed to), and you get a
		220	coroutine that might have executed other code already (which can be good
		221	or bad :).
		222
		223	On the plus side, this function is about twice as fast as creating (and
		224	destroying) a completely new coroutine, so if you need a lot of generic
		225	coroutines in quick successsion, use C<async_pool>, not C<async>.
		226
		227	The code block is executed in an C<eval> context and a warning will be
		228	issued in case of an exception instead of terminating the program, as
		229	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		230	will not work in the expected way, unless you call terminate or cancel,
		231	which somehow defeats the purpose of pooling (but is fine in the
		232	exceptional case).
		233
		234	The priority will be reset to C<0> after each run, tracing will be
		235	disabled, the description will be reset and the default output filehandle
		236	gets restored, so you can change all these. Otherwise the coroutine will
		237	be re-used "as-is": most notably if you change other per-coroutine global
		238	stuff such as C<$/> you I<must needs> revert that change, which is most
		239	simply done by using local as in: C<< local $/ >>.
		240
		241	The idle pool size is limited to C<8> idle coroutines (this can be
		242	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		243	coros as required.
		244
		245	If you are concerned about pooled coroutines growing a lot because a
		246	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		247	{ terminate }> once per second or so to slowly replenish the pool. In
		248	addition to that, when the stacks used by a handler grows larger than 32kb
		249	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		250
		251	=cut
		252
		253	our $POOL_SIZE = 8;
		254	our $POOL_RSS = 32 * 1024;
		255	our @async_pool;
		256
		257	sub pool_handler {
		258	while () {
		259	eval {
		260	&{&_pool_handler} while 1;
		261	};
		262
		263	warn $@ if $@;
		264	}
		265	}
		266
		267	=back
		268
		269	=head1 STATIC METHODS
		270
		271	Static methods are actually functions that implicitly operate on the
		272	current coroutine.
		273
		274	=over 4
140		275
141	=item schedule	276	=item schedule
142		277
143	Calls the scheduler. Please note that the current process will not be put	278	Calls the scheduler. The scheduler will find the next coroutine that is
		279	to be run from the ready queue and switches to it. The next coroutine
		280	to be run is simply the one with the highest priority that is longest
		281	in its ready queue. If there is no coroutine ready, it will clal the
		282	C<$Coro::idle> hook.
		283
		284	Please note that the current coroutine will I<not> be put into the ready
144	into the ready queue, so calling this function usually means you will	285	queue, so calling this function usually means you will never be called
145	never be called again.	286	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		287	thus waking you up.
146		288
147	=cut	289	This makes C<schedule> I<the> generic method to use to block the current
		290	coroutine and wait for events: first you remember the current coroutine in
		291	a variable, then arrange for some callback of yours to call C<< ->ready
		292	>> on that once some event happens, and last you call C<schedule> to put
		293	yourself to sleep. Note that a lot of things can wake your coroutine up,
		294	so you need to check whether the event indeed happened, e.g. by storing the
		295	status in a variable.
148		296
149	my $prev;	297	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
150		298
151	sub schedule {
152	# should be done using priorities :(
153	($prev, $current) = ($current, shift @ready \|\| $idle);
154	Coro::State::transfer($prev, $current);
155	}
156
157	=item yield	299	=item cede
158		300
159	Yield to other processes. This function puts the current process into the	301	"Cede" to other coroutines. This function puts the current coroutine into
160	ready queue and calls C<schedule>.	302	the ready queue and calls C<schedule>, which has the effect of giving
		303	up the current "timeslice" to other coroutines of the same or higher
		304	priority. Once your coroutine gets its turn again it will automatically be
		305	resumed.
161		306
162	=cut	307	This function is often called C<yield> in other languages.
163		308
164	sub yield {	309	=item Coro::cede_notself
165	$current->ready;
166	&schedule;
167	}
168		310
		311	Works like cede, but is not exported by default and will cede to I<any>
		312	coroutine, regardless of priority. This is useful sometimes to ensure
		313	progress is made.
		314
169	=item terminate	315	=item terminate [arg...]
170		316
171	Terminates the current process.	317	Terminates the current coroutine with the given status values (see L<cancel>).
172		318
173	Future versions of this function will allow result arguments.	319	=item killall
174		320
175	=cut	321	Kills/terminates/cancels all coroutines except the currently running
		322	one. This can be useful after a fork, either in the child or the parent,
		323	as usually only one of them should inherit the running coroutines.
176		324
177	sub terminate {	325	Note that in the implementation, destructors run as normal, making this
178	$current->{_results} = [@_];	326	function not so useful after a fork. Future versions of this function
179	&schedule;	327	might try to free resources without running any code.
		328
		329	Note that while this will try to free some of the main programs resources,
		330	you cannot free all of them, so if a coroutine that is not the main
		331	program calls this function, there will be some one-time resource leak.
		332
		333	=cut
		334
		335	sub killall {
		336	for (Coro::State::list) {
		337	$_->cancel
		338	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		339	}
180	}	340	}
181		341
182	=back	342	=back
183		343
184	# dynamic methods	344	=head1 COROUTINE OBJECT METHODS
185		345
186	=head2 PROCESS METHODS
187
188	These are the methods you can call on process objects.	346	These are the methods you can call on coroutine objects (or to create
		347	them).
189		348
190	=over 4	349	=over 4
191		350
192	=item new Coro \&sub [, @args...]	351	=item new Coro \&sub [, @args...]
193		352
194	Create a new process and return it. When the sub returns the process	353	Create a new coroutine and return it. When the sub returns, the coroutine
195	automatically terminates. To start the process you must first put it into	354	automatically terminates as if C<terminate> with the returned values were
		355	called. To make the coroutine run you must first put it into the ready
196	the ready queue by calling the ready method.	356	queue by calling the ready method.
197		357
198	The coderef you submit MUST NOT be a closure that refers to variables	358	See C<async> and C<Coro::State::new> for additional info about the
199	in an outer scope. This does NOT work. Pass arguments into it instead.	359	coroutine environment.
200		360
201	=cut	361	=cut
202		362
203	sub _newcoro {	363	sub _coro_run {
204	terminate &{+shift};	364	terminate &{+shift};
205	}	365	}
206		366
		367	=item $success = $coroutine->ready
		368
		369	Put the given coroutine into the end of its ready queue (there is one
		370	queue for each priority) and return true. If the coroutine is already in
		371	the ready queue, do nothing and return false.
		372
		373	This ensures that the scheduler will resume this coroutine automatically
		374	once all the coroutines of higher priority and all coroutines of the same
		375	priority that were put into the ready queue earlier have been resumed.
		376
		377	=item $is_ready = $coroutine->is_ready
		378
		379	Return whether the coroutine is currently the ready queue or not,
		380
		381	=item $coroutine->cancel (arg...)
		382
		383	Terminates the given coroutine and makes it return the given arguments as
		384	status (default: the empty list). Never returns if the coroutine is the
		385	current coroutine.
		386
		387	=cut
		388
207	sub new {	389	sub cancel {
208	my $class = shift;	390	my $self = shift;
209	bless {
210	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
211	}, $class;
212	}
213		391
214	=item $process->ready	392	if ($current == $self) {
		393	terminate @_;
		394	} else {
		395	$self->{_status} = [@_];
		396	$self->_cancel;
		397	}
		398	}
215		399
216	Put the current process into the ready queue.	400	=item $coroutine->schedule_to
217		401
218	=cut	402	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead
		403	of continuing with the next coro from the ready queue, always switch to
		404	the given coroutine object (regardless of priority etc.). The readyness
		405	state of that coroutine isn't changed.
219		406
220	sub ready {	407	This is an advanced method for special cases - I'd love to hear about any
221	push @ready, $_[0];	408	uses for this one.
		409
		410	=item $coroutine->cede_to
		411
		412	Like C<schedule_to>, but puts the current coroutine into the ready
		413	queue. This has the effect of temporarily switching to the given
		414	coroutine, and continuing some time later.
		415
		416	This is an advanced method for special cases - I'd love to hear about any
		417	uses for this one.
		418
		419	=item $coroutine->throw ([$scalar])
		420
		421	If C<$throw> is specified and defined, it will be thrown as an exception
		422	inside the coroutine at the next convenient point in time. Otherwise
		423	clears the exception object.
		424
		425	Coro will check for the exception each time a schedule-like-function
		426	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		427	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		428	detect this case and return early in case an exception is pending.
		429
		430	The exception object will be thrown "as is" with the specified scalar in
		431	C<$@>, i.e. if it is a string, no line number or newline will be appended
		432	(unlike with C<die>).
		433
		434	This can be used as a softer means than C<cancel> to ask a coroutine to
		435	end itself, although there is no guarantee that the exception will lead to
		436	termination, and if the exception isn't caught it might well end the whole
		437	program.
		438
		439	You might also think of C<throw> as being the moral equivalent of
		440	C<kill>ing a coroutine with a signal (in this case, a scalar).
		441
		442	=item $coroutine->join
		443
		444	Wait until the coroutine terminates and return any values given to the
		445	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		446	from multiple coroutines, and all will be resumed and given the status
		447	return once the C<$coroutine> terminates.
		448
		449	=cut
		450
		451	sub join {
		452	my $self = shift;
		453
		454	unless ($self->{_status}) {
		455	my $current = $current;
		456
		457	push @{$self->{_on_destroy}}, sub {
		458	$current->ready;
		459	undef $current;
		460	};
		461
		462	&schedule while $current;
		463	}
		464
		465	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		466	}
		467
		468	=item $coroutine->on_destroy (\&cb)
		469
		470	Registers a callback that is called when this coroutine gets destroyed,
		471	but before it is joined. The callback gets passed the terminate arguments,
		472	if any, and I<must not> die, under any circumstances.
		473
		474	=cut
		475
		476	sub on_destroy {
		477	my ($self, $cb) = @_;
		478
		479	push @{ $self->{_on_destroy} }, $cb;
		480	}
		481
		482	=item $oldprio = $coroutine->prio ($newprio)
		483
		484	Sets (or gets, if the argument is missing) the priority of the
		485	coroutine. Higher priority coroutines get run before lower priority
		486	coroutines. Priorities are small signed integers (currently -4 .. +3),
		487	that you can refer to using PRIO_xxx constants (use the import tag :prio
		488	to get then):
		489
		490	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		491	3 > 1 > 0 > -1 > -3 > -4
		492
		493	# set priority to HIGH
		494	current->prio(PRIO_HIGH);
		495
		496	The idle coroutine ($Coro::idle) always has a lower priority than any
		497	existing coroutine.
		498
		499	Changing the priority of the current coroutine will take effect immediately,
		500	but changing the priority of coroutines in the ready queue (but not
		501	running) will only take effect after the next schedule (of that
		502	coroutine). This is a bug that will be fixed in some future version.
		503
		504	=item $newprio = $coroutine->nice ($change)
		505
		506	Similar to C<prio>, but subtract the given value from the priority (i.e.
		507	higher values mean lower priority, just as in unix).
		508
		509	=item $olddesc = $coroutine->desc ($newdesc)
		510
		511	Sets (or gets in case the argument is missing) the description for this
		512	coroutine. This is just a free-form string you can associate with a
		513	coroutine.
		514
		515	This method simply sets the C<< $coroutine->{desc} >> member to the given
		516	string. You can modify this member directly if you wish.
		517
		518	=cut
		519
		520	sub desc {
		521	my $old = $_[0]{desc};
		522	$_[0]{desc} = $_[1] if @_ > 1;
		523	$old;
		524	}
		525
		526	sub transfer {
		527	require Carp;
		528	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
222	}	529	}
223		530
224	=back	531	=back
225		532
		533	=head1 GLOBAL FUNCTIONS
		534
		535	=over 4
		536
		537	=item Coro::nready
		538
		539	Returns the number of coroutines that are currently in the ready state,
		540	i.e. that can be switched to by calling C<schedule> directory or
		541	indirectly. The value C<0> means that the only runnable coroutine is the
		542	currently running one, so C<cede> would have no effect, and C<schedule>
		543	would cause a deadlock unless there is an idle handler that wakes up some
		544	coroutines.
		545
		546	=item my $guard = Coro::guard { ... }
		547
		548	This function still exists, but is deprecated. Please use the
		549	C<Guard::guard> function instead.
		550
		551	=cut
		552
		553	BEGIN { *guard = \&Guard::guard }
		554
		555	=item unblock_sub { ... }
		556
		557	This utility function takes a BLOCK or code reference and "unblocks" it,
		558	returning a new coderef. Unblocking means that calling the new coderef
		559	will return immediately without blocking, returning nothing, while the
		560	original code ref will be called (with parameters) from within another
		561	coroutine.
		562
		563	The reason this function exists is that many event libraries (such as the
		564	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		565	of reentrancy). This means you must not block within event callbacks,
		566	otherwise you might suffer from crashes or worse. The only event library
		567	currently known that is safe to use without C<unblock_sub> is L<EV>.
		568
		569	This function allows your callbacks to block by executing them in another
		570	coroutine where it is safe to block. One example where blocking is handy
		571	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		572	disk, for example.
		573
		574	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		575	creating event callbacks that want to block.
		576
		577	If your handler does not plan to block (e.g. simply sends a message to
		578	another coroutine, or puts some other coroutine into the ready queue),
		579	there is no reason to use C<unblock_sub>.
		580
		581	Note that you also need to use C<unblock_sub> for any other callbacks that
		582	are indirectly executed by any C-based event loop. For example, when you
		583	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		584	provides callbacks that are the result of some event callback, then you
		585	must not block either, or use C<unblock_sub>.
		586
		587	=cut
		588
		589	our @unblock_queue;
		590
		591	# we create a special coro because we want to cede,
		592	# to reduce pressure on the coro pool (because most callbacks
		593	# return immediately and can be reused) and because we cannot cede
		594	# inside an event callback.
		595	our $unblock_scheduler = new Coro sub {
		596	while () {
		597	while (my $cb = pop @unblock_queue) {
		598	&async_pool (@$cb);
		599
		600	# for short-lived callbacks, this reduces pressure on the coro pool
		601	# as the chance is very high that the async_poll coro will be back
		602	# in the idle state when cede returns
		603	cede;
		604	}
		605	schedule; # sleep well
		606	}
		607	};
		608	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		609
		610	sub unblock_sub(&) {
		611	my $cb = shift;
		612
		613	sub {
		614	unshift @unblock_queue, [$cb, @_];
		615	$unblock_scheduler->ready;
		616	}
		617	}
		618
		619	=item $cb = Coro::rouse_cb
		620
		621	Create and return a "rouse callback". That's a code reference that,
		622	when called, will remember a copy of its arguments and notify the owner
		623	coroutine of the callback.
		624
		625	See the next function.
		626
		627	=item @args = Coro::rouse_wait [$cb]
		628
		629	Wait for the specified rouse callback (or the last one that was created in
		630	this coroutine).
		631
		632	As soon as the callback is invoked (or when the callback was invoked
		633	before C<rouse_wait>), it will return the arguments originally passed to
		634	the rouse callback.
		635
		636	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		637
		638	=back
		639
226	=cut	640	=cut
227		641
228	1;	642	1;
229		643
		644	=head1 HOW TO WAIT FOR A CALLBACK
		645
		646	It is very common for a coroutine to wait for some callback to be
		647	called. This occurs naturally when you use coroutines in an otherwise
		648	event-based program, or when you use event-based libraries.
		649
		650	These typically register a callback for some event, and call that callback
		651	when the event occured. In a coroutine, however, you typically want to
		652	just wait for the event, simplyifying things.
		653
		654	For example C<< AnyEvent->child >> registers a callback to be called when
		655	a specific child has exited:
		656
		657	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		658
		659	But from withina coroutine, you often just want to write this:
		660
		661	my $status = wait_for_child $pid;
		662
		663	Coro offers two functions specifically designed to make this easy,
		664	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		665
		666	The first function, C<rouse_cb>, generates and returns a callback that,
		667	when invoked, will save its arguments and notify the coroutine that
		668	created the callback.
		669
		670	The second function, C<rouse_wait>, waits for the callback to be called
		671	(by calling C<schedule> to go to sleep) and returns the arguments
		672	originally passed to the callback.
		673
		674	Using these functions, it becomes easy to write the C<wait_for_child>
		675	function mentioned above:
		676
		677	sub wait_for_child($) {
		678	my ($pid) = @_;
		679
		680	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		681
		682	my ($rpid, $rstatus) = Coro::rouse_wait;
		683	$rstatus
		684	}
		685
		686	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		687	you can roll your own, using C<schedule>:
		688
		689	sub wait_for_child($) {
		690	my ($pid) = @_;
		691
		692	# store the current coroutine in $current,
		693	# and provide result variables for the closure passed to ->child
		694	my $current = $Coro::current;
		695	my ($done, $rstatus);
		696
		697	# pass a closure to ->child
		698	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		699	$rstatus = $_[1]; # remember rstatus
		700	$done = 1; # mark $rstatus as valud
		701	});
		702
		703	# wait until the closure has been called
		704	schedule while !$done;
		705
		706	$rstatus
		707	}
		708
		709
230	=head1 BUGS/LIMITATIONS	710	=head1 BUGS/LIMITATIONS
231		711
232	- could be faster, especially when the core would introduce special	712	=over 4
233	support for coroutines (like it does for threads).	713
234	- there is still a memleak on coroutine termination that I could not	714	=item fork with pthread backend
235	identify. Could be as small as a single SV.	715
236	- this module is not well-tested.	716	When Coro is compiled using the pthread backend (which isn't recommended
237	- if variables or arguments "disappear" (become undef) or become	717	but required on many BSDs as their libcs are completely broken), then
238	corrupted please contact the author so he cen iron out the	718	coroutines will not survive a fork. There is no known workaround except to
239	remaining bugs.	719	fix your libc and use a saner backend.
240	- this module is not thread-safe. You must only ever use this module from	720
241	the same thread (this requirement might be loosened in the future to	721	=item perl process emulation ("threads")
		722
		723	This module is not perl-pseudo-thread-safe. You should only ever use this
		724	module from the first thread (this requirement might be removed in the
242	allow per-thread schedulers, but Coro::State does not yet allow this).	725	future to allow per-thread schedulers, but Coro::State does not yet allow
		726	this). I recommend disabling thread support and using processes, as having
		727	the windows process emulation enabled under unix roughly halves perl
		728	performance, even when not used.
		729
		730	=item coroutine switching not signal safe
		731
		732	You must not switch to another coroutine from within a signal handler
		733	(only relevant with %SIG - most event libraries provide safe signals).
		734
		735	That means you I<MUST NOT> call any function that might "block" the
		736	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		737	anything that calls those. Everything else, including calling C<ready>,
		738	works.
		739
		740	=back
		741
243		742
244	=head1 SEE ALSO	743	=head1 SEE ALSO
245		744
246	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	745	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
247	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	746
		747	Debugging: L<Coro::Debug>.
		748
		749	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		750
		751	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		752	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		753
		754	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		755
		756	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		757	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		758	L<Coro::Select>.
		759
		760	XS API: L<Coro::MakeMaker>.
		761
		762	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
248		763
249	=head1 AUTHOR	764	=head1 AUTHOR
250		765
251	Marc Lehmann <pcg@goof.com>	766	Marc Lehmann <schmorp@schmorp.de>
252	http://www.goof.com/pcg/marc/	767	http://home.schmorp.de/
253		768
254	=cut	769	=cut
255		770

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Revision 1.246 by root, Mon Dec 15 00:30:40 2008 UTC