[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 1.238 by root, Mon Nov 24 04:56:38 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
37	use Coro::State;	71	use Coro::State;
38		72
39	use base Exporter;	73	use base qw(Coro::State Exporter);
40		74
41	$VERSION = 0.10;	75	our $idle; # idle handler
		76	our $main; # main coroutine
		77	our $current; # current coroutine
42		78
		79	our $VERSION = "5.0";
		80
43	@EXPORT = qw(async yield schedule terminate current);	81	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
44	@EXPORT_OK = qw($current);	82	our %EXPORT_TAGS = (
		83	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		84	);
		85	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
45		86
46	{	87	=head1 GLOBAL VARIABLES
47	my @async;
48		88
49	# this way of handling attributes simply is NOT scalable ;()	89	=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		90
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	}
71
72	=item $main	91	=item $Coro::main
73		92
74	This coroutine represents the main program.	93	This variable stores the coroutine object that represents the main
		94	program. While you cna C<ready> it and do most other things you can do to
		95	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		96	whether you are running in the main program or not.
75		97
76	=cut	98	=cut
77		99
78	our $main = new Coro;	100	# $main is now being initialised by Coro::State
79		101
80	=item $current (or as function: current)	102	=item $Coro::current
81		103
82	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	104	The coroutine object representing the current coroutine (the last
		105	coroutine that the Coro scheduler switched to). The initial value is
		106	C<$Coro::main> (of course).
83		107
84	=cut	108	This variable is B<strictly> I<read-only>. You can take copies of the
		109	value stored in it and use it as any other coroutine object, but you must
		110	not otherwise modify the variable itself.
85		111
86	# maybe some other module used Coro::Specific before...	112	=cut
87	if ($current) {
88	$main->{specific} = $current->{specific};
89	}
90		113
91	our $current = $main;
92
93	sub current() { $current }	114	sub current() { $current } # [DEPRECATED]
94		115
95	=item $idle	116	=item $Coro::idle
96		117
97	The coroutine to switch to when no other coroutine is running. The default	118	This variable is mainly useful to integrate Coro into event loops. It is
98	implementation prints "FATAL: deadlock detected" and exits.	119	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		120	pretty low-level functionality.
99		121
100	=cut	122	This variable stores either a coroutine or a callback.
101		123
102	# should be done using priorities :(	124	If it is a callback, the it is called whenever the scheduler finds no
103	our $idle = new Coro sub {	125	ready coroutines to run. The default implementation prints "FATAL:
104	print STDERR "FATAL: deadlock detected\n";	126	deadlock detected" and exits, because the program has no other way to
105	exit(51);	127	continue.
		128
		129	If it is a coroutine object, then this object will be readied (without
		130	invoking any ready hooks, however) when the scheduler finds no other ready
		131	coroutines to run.
		132
		133	This hook is overwritten by modules such as C<Coro::EV> and
		134	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
		135	coroutine so the scheduler can run it.
		136
		137	Note that the callback I<must not>, under any circumstances, block
		138	the current coroutine. Normally, this is achieved by having an "idle
		139	coroutine" that calls the event loop and then blocks again, and then
		140	readying that coroutine in the idle handler, or by simply placing the idle
		141	coroutine in this variable.
		142
		143	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
		144	technique.
		145
		146	Please note that if your callback recursively invokes perl (e.g. for event
		147	handlers), then it must be prepared to be called recursively itself.
		148
		149	=cut
		150
		151	$idle = sub {
		152	require Carp;
		153	Carp::croak ("FATAL: deadlock detected");
106	};	154	};
107		155
108	# we really need priorities...	156	# this coroutine is necessary because a coroutine
109	my @ready; # the ready queue. hehe, rather broken ;)	157	# cannot destroy itself.
		158	our @destroy;
		159	our $manager;
110		160
111	# static methods. not really.	161	$manager = new Coro sub {
		162	while () {
		163	Coro::_cancel shift @destroy
		164	while @destroy;
112		165
113	=head2 STATIC METHODS	166	&schedule;
		167	}
		168	};
		169	$manager->{desc} = "[coro manager]";
		170	$manager->prio (PRIO_MAX);
114		171
115	Static methods are actually functions that operate on the current process only.	172	=back
		173
		174	=head1 SIMPLE COROUTINE CREATION
116		175
117	=over 4	176	=over 4
118		177
119	=item async { ... } [@args...]	178	=item async { ... } [@args...]
120		179
121	Create a new asynchronous process and return it's process object	180	Create a new coroutine and return it's coroutine object (usually
122	(usually unused). When the sub returns the new process is automatically	181	unused). The coroutine will be put into the ready queue, so
		182	it will start running automatically on the next scheduler run.
		183
		184	The first argument is a codeblock/closure that should be executed in the
		185	coroutine. When it returns argument returns the coroutine is automatically
123	terminated.	186	terminated.
124		187
		188	The remaining arguments are passed as arguments to the closure.
		189
		190	See the C<Coro::State::new> constructor for info about the coroutine
		191	environment in which coroutines are executed.
		192
		193	Calling C<exit> in a coroutine will do the same as calling exit outside
		194	the coroutine. Likewise, when the coroutine dies, the program will exit,
		195	just as it would in the main program.
		196
		197	If you do not want that, you can provide a default C<die> handler, or
		198	simply avoid dieing (by use of C<eval>).
		199
125	# create a new coroutine that just prints its arguments	200	Example: Create a new coroutine that just prints its arguments.
		201
126	async {	202	async {
127	print "@_\n";	203	print "@_\n";
128	} 1,2,3,4;	204	} 1,2,3,4;
129		205
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	206	=cut
134		207
135	sub async(&@) {	208	sub async(&@) {
136	my $pid = new Coro @_;	209	my $coro = new Coro @_;
137	$pid->ready;	210	$coro->ready;
138	$pid;	211	$coro
139	}	212	}
		213
		214	=item async_pool { ... } [@args...]
		215
		216	Similar to C<async>, but uses a coroutine pool, so you should not call
		217	terminate or join on it (although you are allowed to), and you get a
		218	coroutine that might have executed other code already (which can be good
		219	or bad :).
		220
		221	On the plus side, this function is about twice as fast as creating (and
		222	destroying) a completely new coroutine, so if you need a lot of generic
		223	coroutines in quick successsion, use C<async_pool>, not C<async>.
		224
		225	The code block is executed in an C<eval> context and a warning will be
		226	issued in case of an exception instead of terminating the program, as
		227	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		228	will not work in the expected way, unless you call terminate or cancel,
		229	which somehow defeats the purpose of pooling (but is fine in the
		230	exceptional case).
		231
		232	The priority will be reset to C<0> after each run, tracing will be
		233	disabled, the description will be reset and the default output filehandle
		234	gets restored, so you can change all these. Otherwise the coroutine will
		235	be re-used "as-is": most notably if you change other per-coroutine global
		236	stuff such as C<$/> you I<must needs> revert that change, which is most
		237	simply done by using local as in: C<< local $/ >>.
		238
		239	The idle pool size is limited to C<8> idle coroutines (this can be
		240	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		241	coros as required.
		242
		243	If you are concerned about pooled coroutines growing a lot because a
		244	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		245	{ terminate }> once per second or so to slowly replenish the pool. In
		246	addition to that, when the stacks used by a handler grows larger than 32kb
		247	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		248
		249	=cut
		250
		251	our $POOL_SIZE = 8;
		252	our $POOL_RSS = 32 * 1024;
		253	our @async_pool;
		254
		255	sub pool_handler {
		256	while () {
		257	eval {
		258	&{&_pool_handler} while 1;
		259	};
		260
		261	warn $@ if $@;
		262	}
		263	}
		264
		265	=back
		266
		267	=head1 STATIC METHODS
		268
		269	Static methods are actually functions that implicitly operate on the
		270	current coroutine.
		271
		272	=over 4
140		273
141	=item schedule	274	=item schedule
142		275
143	Calls the scheduler. Please note that the current process will not be put	276	Calls the scheduler. The scheduler will find the next coroutine that is
		277	to be run from the ready queue and switches to it. The next coroutine
		278	to be run is simply the one with the highest priority that is longest
		279	in its ready queue. If there is no coroutine ready, it will clal the
		280	C<$Coro::idle> hook.
		281
		282	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	283	queue, so calling this function usually means you will never be called
145	never be called again.	284	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		285	thus waking you up.
146		286
147	=cut	287	This makes C<schedule> I<the> generic method to use to block the current
		288	coroutine and wait for events: first you remember the current coroutine in
		289	a variable, then arrange for some callback of yours to call C<< ->ready
		290	>> on that once some event happens, and last you call C<schedule> to put
		291	yourself to sleep. Note that a lot of things can wake your coroutine up,
		292	so you need to check whether the event indeed happened, e.g. by storing the
		293	status in a variable.
148		294
149	my $prev;	295	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
150		296
151	sub schedule {
152	# should be done using priorities :(
153	($prev, $current) = ($current, shift @ready \|\| $idle);
154	Coro::State::transfer($prev, $current);
155	}
156
157	=item yield	297	=item cede
158		298
159	Yield to other processes. This function puts the current process into the	299	"Cede" to other coroutines. This function puts the current coroutine into
160	ready queue and calls C<schedule>.	300	the ready queue and calls C<schedule>, which has the effect of giving
		301	up the current "timeslice" to other coroutines of the same or higher
		302	priority. Once your coroutine gets its turn again it will automatically be
		303	resumed.
161		304
162	=cut	305	This function is often called C<yield> in other languages.
163		306
164	sub yield {	307	=item Coro::cede_notself
165	$current->ready;
166	&schedule;
167	}
168		308
		309	Works like cede, but is not exported by default and will cede to I<any>
		310	coroutine, regardless of priority. This is useful sometimes to ensure
		311	progress is made.
		312
169	=item terminate	313	=item terminate [arg...]
170		314
171	Terminates the current process.	315	Terminates the current coroutine with the given status values (see L<cancel>).
172		316
173	Future versions of this function will allow result arguments.	317	=item killall
174		318
175	=cut	319	Kills/terminates/cancels all coroutines except the currently running
		320	one. This is useful after a fork, either in the child or the parent, as
		321	usually only one of them should inherit the running coroutines.
176		322
177	sub terminate {	323	Note that while this will try to free some of the main programs resources,
178	$current->{_results} = [@_];	324	you cannot free all of them, so if a coroutine that is not the main
179	&schedule;	325	program calls this function, there will be some one-time resource leak.
		326
		327	=cut
		328
		329	sub killall {
		330	for (Coro::State::list) {
		331	$_->cancel
		332	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		333	}
180	}	334	}
181		335
182	=back	336	=back
183		337
184	# dynamic methods	338	=head1 COROUTINE OBJECT METHODS
185		339
186	=head2 PROCESS METHODS
187
188	These are the methods you can call on process objects.	340	These are the methods you can call on coroutine objects (or to create
		341	them).
189		342
190	=over 4	343	=over 4
191		344
192	=item new Coro \&sub [, @args...]	345	=item new Coro \&sub [, @args...]
193		346
194	Create a new process and return it. When the sub returns the process	347	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	348	automatically terminates as if C<terminate> with the returned values were
		349	called. To make the coroutine run you must first put it into the ready
196	the ready queue by calling the ready method.	350	queue by calling the ready method.
197		351
198	The coderef you submit MUST NOT be a closure that refers to variables	352	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.	353	coroutine environment.
200		354
201	=cut	355	=cut
202		356
203	sub _newcoro {	357	sub _terminate {
204	terminate &{+shift};	358	terminate &{+shift};
205	}	359	}
206		360
		361	=item $success = $coroutine->ready
		362
		363	Put the given coroutine into the end of its ready queue (there is one
		364	queue for each priority) and return true. If the coroutine is already in
		365	the ready queue, do nothing and return false.
		366
		367	This ensures that the scheduler will resume this coroutine automatically
		368	once all the coroutines of higher priority and all coroutines of the same
		369	priority that were put into the ready queue earlier have been resumed.
		370
		371	=item $is_ready = $coroutine->is_ready
		372
		373	Return whether the coroutine is currently the ready queue or not,
		374
		375	=item $coroutine->cancel (arg...)
		376
		377	Terminates the given coroutine and makes it return the given arguments as
		378	status (default: the empty list). Never returns if the coroutine is the
		379	current coroutine.
		380
		381	=cut
		382
207	sub new {	383	sub cancel {
208	my $class = shift;	384	my $self = shift;
209	bless {
210	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
211	}, $class;
212	}
213		385
214	=item $process->ready	386	if ($current == $self) {
		387	terminate @_;
		388	} else {
		389	$self->{_status} = [@_];
		390	$self->_cancel;
		391	}
		392	}
215		393
216	Put the current process into the ready queue.	394	=item $coroutine->schedule_to
217		395
218	=cut	396	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead
		397	of continuing with the next coro from the ready queue, always switch to
		398	the given coroutine object (regardless of priority etc.). The readyness
		399	state of that coroutine isn't changed.
219		400
220	sub ready {	401	This is an advanced method for special cases - I'd love to hear about any
221	push @ready, $_[0];	402	uses for this one.
		403
		404	=item $coroutine->cede_to
		405
		406	Like C<schedule_to>, but puts the current coroutine into the ready
		407	queue. This has the effect of temporarily switching to the given
		408	coroutine, and continuing some time later.
		409
		410	This is an advanced method for special cases - I'd love to hear about any
		411	uses for this one.
		412
		413	=item $coroutine->throw ([$scalar])
		414
		415	If C<$throw> is specified and defined, it will be thrown as an exception
		416	inside the coroutine at the next convenient point in time. Otherwise
		417	clears the exception object.
		418
		419	Coro will check for the exception each time a schedule-like-function
		420	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		421	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		422	detect this case and return early in case an exception is pending.
		423
		424	The exception object will be thrown "as is" with the specified scalar in
		425	C<$@>, i.e. if it is a string, no line number or newline will be appended
		426	(unlike with C<die>).
		427
		428	This can be used as a softer means than C<cancel> to ask a coroutine to
		429	end itself, although there is no guarantee that the exception will lead to
		430	termination, and if the exception isn't caught it might well end the whole
		431	program.
		432
		433	You might also think of C<throw> as being the moral equivalent of
		434	C<kill>ing a coroutine with a signal (in this case, a scalar).
		435
		436	=item $coroutine->join
		437
		438	Wait until the coroutine terminates and return any values given to the
		439	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		440	from multiple coroutines, and all will be resumed and given the status
		441	return once the C<$coroutine> terminates.
		442
		443	=cut
		444
		445	sub join {
		446	my $self = shift;
		447
		448	unless ($self->{_status}) {
		449	my $current = $current;
		450
		451	push @{$self->{_on_destroy}}, sub {
		452	$current->ready;
		453	undef $current;
		454	};
		455
		456	&schedule while $current;
		457	}
		458
		459	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		460	}
		461
		462	=item $coroutine->on_destroy (\&cb)
		463
		464	Registers a callback that is called when this coroutine gets destroyed,
		465	but before it is joined. The callback gets passed the terminate arguments,
		466	if any, and I<must not> die, under any circumstances.
		467
		468	=cut
		469
		470	sub on_destroy {
		471	my ($self, $cb) = @_;
		472
		473	push @{ $self->{_on_destroy} }, $cb;
		474	}
		475
		476	=item $oldprio = $coroutine->prio ($newprio)
		477
		478	Sets (or gets, if the argument is missing) the priority of the
		479	coroutine. Higher priority coroutines get run before lower priority
		480	coroutines. Priorities are small signed integers (currently -4 .. +3),
		481	that you can refer to using PRIO_xxx constants (use the import tag :prio
		482	to get then):
		483
		484	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		485	3 > 1 > 0 > -1 > -3 > -4
		486
		487	# set priority to HIGH
		488	current->prio(PRIO_HIGH);
		489
		490	The idle coroutine ($Coro::idle) always has a lower priority than any
		491	existing coroutine.
		492
		493	Changing the priority of the current coroutine will take effect immediately,
		494	but changing the priority of coroutines in the ready queue (but not
		495	running) will only take effect after the next schedule (of that
		496	coroutine). This is a bug that will be fixed in some future version.
		497
		498	=item $newprio = $coroutine->nice ($change)
		499
		500	Similar to C<prio>, but subtract the given value from the priority (i.e.
		501	higher values mean lower priority, just as in unix).
		502
		503	=item $olddesc = $coroutine->desc ($newdesc)
		504
		505	Sets (or gets in case the argument is missing) the description for this
		506	coroutine. This is just a free-form string you can associate with a
		507	coroutine.
		508
		509	This method simply sets the C<< $coroutine->{desc} >> member to the given
		510	string. You can modify this member directly if you wish.
		511
		512	=cut
		513
		514	sub desc {
		515	my $old = $_[0]{desc};
		516	$_[0]{desc} = $_[1] if @_ > 1;
		517	$old;
		518	}
		519
		520	sub transfer {
		521	require Carp;
		522	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
222	}	523	}
223		524
224	=back	525	=back
225		526
		527	=head1 GLOBAL FUNCTIONS
		528
		529	=over 4
		530
		531	=item Coro::nready
		532
		533	Returns the number of coroutines that are currently in the ready state,
		534	i.e. that can be switched to by calling C<schedule> directory or
		535	indirectly. The value C<0> means that the only runnable coroutine is the
		536	currently running one, so C<cede> would have no effect, and C<schedule>
		537	would cause a deadlock unless there is an idle handler that wakes up some
		538	coroutines.
		539
		540	=item my $guard = Coro::guard { ... }
		541
		542	This creates and returns a guard object. Nothing happens until the object
		543	gets destroyed, in which case the codeblock given as argument will be
		544	executed. This is useful to free locks or other resources in case of a
		545	runtime error or when the coroutine gets canceled, as in both cases the
		546	guard block will be executed. The guard object supports only one method,
		547	C<< ->cancel >>, which will keep the codeblock from being executed.
		548
		549	Example: set some flag and clear it again when the coroutine gets canceled
		550	or the function returns:
		551
		552	sub do_something {
		553	my $guard = Coro::guard { $busy = 0 };
		554	$busy = 1;
		555
		556	# do something that requires $busy to be true
		557	}
		558
		559	=cut
		560
		561	sub guard(&) {
		562	bless \(my $cb = $_[0]), "Coro::guard"
		563	}
		564
		565	sub Coro::guard::cancel {
		566	${$_[0]} = sub { };
		567	}
		568
		569	sub Coro::guard::DESTROY {
		570	${$_[0]}->();
		571	}
		572
		573
		574	=item unblock_sub { ... }
		575
		576	This utility function takes a BLOCK or code reference and "unblocks" it,
		577	returning a new coderef. Unblocking means that calling the new coderef
		578	will return immediately without blocking, returning nothing, while the
		579	original code ref will be called (with parameters) from within another
		580	coroutine.
		581
		582	The reason this function exists is that many event libraries (such as the
		583	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		584	of reentrancy). This means you must not block within event callbacks,
		585	otherwise you might suffer from crashes or worse. The only event library
		586	currently known that is safe to use without C<unblock_sub> is L<EV>.
		587
		588	This function allows your callbacks to block by executing them in another
		589	coroutine where it is safe to block. One example where blocking is handy
		590	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		591	disk, for example.
		592
		593	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		594	creating event callbacks that want to block.
		595
		596	If your handler does not plan to block (e.g. simply sends a message to
		597	another coroutine, or puts some other coroutine into the ready queue),
		598	there is no reason to use C<unblock_sub>.
		599
		600	Note that you also need to use C<unblock_sub> for any other callbacks that
		601	are indirectly executed by any C-based event loop. For example, when you
		602	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		603	provides callbacks that are the result of some event callback, then you
		604	must not block either, or use C<unblock_sub>.
		605
		606	=cut
		607
		608	our @unblock_queue;
		609
		610	# we create a special coro because we want to cede,
		611	# to reduce pressure on the coro pool (because most callbacks
		612	# return immediately and can be reused) and because we cannot cede
		613	# inside an event callback.
		614	our $unblock_scheduler = new Coro sub {
		615	while () {
		616	while (my $cb = pop @unblock_queue) {
		617	&async_pool (@$cb);
		618
		619	# for short-lived callbacks, this reduces pressure on the coro pool
		620	# as the chance is very high that the async_poll coro will be back
		621	# in the idle state when cede returns
		622	cede;
		623	}
		624	schedule; # sleep well
		625	}
		626	};
		627	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		628
		629	sub unblock_sub(&) {
		630	my $cb = shift;
		631
		632	sub {
		633	unshift @unblock_queue, [$cb, @_];
		634	$unblock_scheduler->ready;
		635	}
		636	}
		637
		638	=item $cb = Coro::rouse_cb
		639
		640	Create and return a "rouse callback". That's a code reference that,
		641	when called, will remember a copy of its arguments and notify the owner
		642	coroutine of the callback.
		643
		644	See the next function.
		645
		646	=item @args = Coro::rouse_wait [$cb]
		647
		648	Wait for the specified rouse callback (or the last one that was created in
		649	this coroutine).
		650
		651	As soon as the callback is invoked (or when the callback was invoked
		652	before C<rouse_wait>), it will return the arguments originally passed to
		653	the rouse callback.
		654
		655	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		656
		657	=back
		658
226	=cut	659	=cut
227		660
228	1;	661	1;
229		662
		663	=head1 HOW TO WAIT FOR A CALLBACK
		664
		665	It is very common for a coroutine to wait for some callback to be
		666	called. This occurs naturally when you use coroutines in an otherwise
		667	event-based program, or when you use event-based libraries.
		668
		669	These typically register a callback for some event, and call that callback
		670	when the event occured. In a coroutine, however, you typically want to
		671	just wait for the event, simplyifying things.
		672
		673	For example C<< AnyEvent->child >> registers a callback to be called when
		674	a specific child has exited:
		675
		676	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		677
		678	But from withina coroutine, you often just want to write this:
		679
		680	my $status = wait_for_child $pid;
		681
		682	Coro offers two functions specifically designed to make this easy,
		683	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		684
		685	The first function, C<rouse_cb>, generates and returns a callback that,
		686	when invoked, will save it's arguments and notify the coroutine that
		687	created the callback.
		688
		689	The second function, C<rouse_wait>, waits for the callback to be called
		690	(by calling C<schedule> to go to sleep) and returns the arguments
		691	originally passed to the callback.
		692
		693	Using these functions, it becomes easy to write the C<wait_for_child>
		694	function mentioned above:
		695
		696	sub wait_for_child($) {
		697	my ($pid) = @_;
		698
		699	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		700
		701	my ($rpid, $rstatus) = Coro::rouse_wait;
		702	$rstatus
		703	}
		704
		705	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		706	you can roll your own, using C<schedule>:
		707
		708	sub wait_for_child($) {
		709	my ($pid) = @_;
		710
		711	# store the current coroutine in $current,
		712	# and provide result variables for the closure passed to ->child
		713	my $current = $Coro::current;
		714	my ($done, $rstatus);
		715
		716	# pass a closure to ->child
		717	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		718	$rstatus = $_[1]; # remember rstatus
		719	$done = 1; # mark $rstatus as valud
		720	});
		721
		722	# wait until the closure has been called
		723	schedule while !$done;
		724
		725	$rstatus
		726	}
		727
		728
230	=head1 BUGS/LIMITATIONS	729	=head1 BUGS/LIMITATIONS
231		730
232	- could be faster, especially when the core would introduce special	731	=over 4
233	support for coroutines (like it does for threads).	732
234	- there is still a memleak on coroutine termination that I could not	733	=item fork with pthread backend
235	identify. Could be as small as a single SV.	734
236	- this module is not well-tested.	735	When Coro is compiled using the pthread backend (which isn't recommended
237	- if variables or arguments "disappear" (become undef) or become	736	but required on many BSDs as their libcs are completely broken), then
238	corrupted please contact the author so he cen iron out the	737	coroutines will not survive a fork. There is no known workaround except to
239	remaining bugs.	738	fix your libc and use a saner backend.
240	- this module is not thread-safe. You must only ever use this module from	739
241	the same thread (this requirement might be loosened in the future to	740	=item perl process emulation ("threads")
		741
		742	This module is not perl-pseudo-thread-safe. You should only ever use this
		743	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).	744	future to allow per-thread schedulers, but Coro::State does not yet allow
		745	this). I recommend disabling thread support and using processes, as having
		746	the windows process emulation enabled under unix roughly halves perl
		747	performance, even when not used.
		748
		749	=item coroutine switching not signal safe
		750
		751	You must not switch to another coroutine from within a signal handler
		752	(only relevant with %SIG - most event libraries provide safe signals).
		753
		754	That means you I<MUST NOT> call any function that might "block" the
		755	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		756	anything that calls those. Everything else, including calling C<ready>,
		757	works.
		758
		759	=back
		760
243		761
244	=head1 SEE ALSO	762	=head1 SEE ALSO
245		763
246	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	764	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
247	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	765
		766	Debugging: L<Coro::Debug>.
		767
		768	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		769
		770	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		771	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		772
		773	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		774
		775	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		776	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		777	L<Coro::Select>.
		778
		779	XS API: L<Coro::MakeMaker>.
		780
		781	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
248		782
249	=head1 AUTHOR	783	=head1 AUTHOR
250		784
251	Marc Lehmann <pcg@goof.com>	785	Marc Lehmann <schmorp@schmorp.de>
252	http://www.goof.com/pcg/marc/	786	http://home.schmorp.de/
253		787
254	=cut	788	=cut
255		789

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Revision 1.238 by root, Mon Nov 24 04:56:38 2008 UTC