[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 1.225 by root, Wed Nov 19 15:29:57 2008 UTC

…		…
2		2
3	Coro - coroutine process abstraction	3	Coro - coroutine process abstraction
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	This module collection manages coroutines. Coroutines are similar to
24	Threads but don't run in parallel.	32	threads but don't (in general) run in parallel at the same time even
		33	on SMP machines. The specific flavor of coroutine used in this module
		34	also guarantees you that it will not switch between coroutines unless
		35	necessary, at easily-identified points in your program, so locking and
		36	parallel access are rarely an issue, making coroutine programming much
		37	safer and easier than threads programming.
25		38
26	This module is still experimental, see the BUGS section below.	39	Unlike a normal perl program, however, coroutines allow you to have
		40	multiple running interpreters that share data, which is especially useful
		41	to code pseudo-parallel processes and for event-based programming, such as
		42	multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to
		43	learn more.
27		44
		45	Coroutines are also useful because Perl has no support for threads (the so
		46	called "threads" that perl offers are nothing more than the (bad) process
		47	emulation coming from the Windows platform: On standard operating systems
		48	they serve no purpose whatsoever, except by making your programs slow and
		49	making them use a lot of memory. Best disable them when building perl, or
		50	aks your software vendor/distributor to do it for you).
		51
28	In this module, coroutines are defined as "callchain + lexical variables	52	In this module, coroutines are defined as "callchain + lexical variables +
29	+ @_ + $_ + $@ + $^W), that is, a coroutine has it's own callchain, it's	53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
30	own set of lexicals and it's own set of perl's most important global	54	its own set of lexicals and its own set of perls most important global
31	variables.	55	variables (see L<Coro::State> for more configuration).
32		56
33	=cut	57	=cut
34		58
35	package Coro;	59	package Coro;
36		60
		61	use strict qw(vars subs);
		62	no warnings "uninitialized";
		63
37	use Coro::State;	64	use Coro::State;
38		65
39	use base Exporter;	66	use base qw(Coro::State Exporter);
40		67
		68	our $idle; # idle handler
		69	our $main; # main coroutine
		70	our $current; # current coroutine
		71
41	$VERSION = 0.10;	72	our $VERSION = 5.0;
42		73
43	@EXPORT = qw(async yield schedule terminate current);	74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
44	@EXPORT_OK = qw($current);	75	our %EXPORT_TAGS = (
		76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		77	);
		78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
45		79
46	{	80	=over 4
47	my @async;
48		81
49	# this way of handling attributes simply is NOT scalable ;()
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
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	}
71
72	=item $main	82	=item $Coro::main
73		83
74	This coroutine represents the main program.	84	This variable stores the coroutine object that represents the main
		85	program. While you cna C<ready> it and do most other things you can do to
		86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		87	whether you are running in the main program or not.
75		88
76	=cut	89	=cut
77		90
78	our $main = new Coro;	91	# $main is now being initialised by Coro::State
79		92
80	=item $current (or as function: current)	93	=item $Coro::current
81		94
82	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	95	The coroutine object representing the current coroutine (the last
		96	coroutine that the Coro scheduler switched to). The initial value is
		97	C<$Coro::main> (of course).
83		98
84	=cut	99	This variable is B<strictly> I<read-only>. You can take copies of the
		100	value stored in it and use it as any other coroutine object, but you must
		101	not otherwise modify the variable itself.
85		102
86	# maybe some other module used Coro::Specific before...	103	=cut
87	if ($current) {
88	$main->{specific} = $current->{specific};
89	}
90		104
91	our $current = $main;
92
93	sub current() { $current }	105	sub current() { $current } # [DEPRECATED]
94		106
95	=item $idle	107	=item $Coro::idle
96		108
97	The coroutine to switch to when no other coroutine is running. The default	109	This variable is mainly useful to integrate Coro into event loops. It is
98	implementation prints "FATAL: deadlock detected" and exits.	110	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is
		111	pretty low-level functionality.
99		112
100	=cut	113	This variable stores a callback that is called whenever the scheduler
		114	finds no ready coroutines to run. The default implementation prints
		115	"FATAL: deadlock detected" and exits, because the program has no other way
		116	to continue.
101		117
102	# should be done using priorities :(	118	This hook is overwritten by modules such as C<Coro::Timer> and
103	our $idle = new Coro sub {	119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
104	print STDERR "FATAL: deadlock detected\n";	120	coroutine so the scheduler can run it.
105	exit(51);	121
		122	Note that the callback I<must not>, under any circumstances, block
		123	the current coroutine. Normally, this is achieved by having an "idle
		124	coroutine" that calls the event loop and then blocks again, and then
		125	readying that coroutine in the idle handler.
		126
		127	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
		128	technique.
		129
		130	Please note that if your callback recursively invokes perl (e.g. for event
		131	handlers), then it must be prepared to be called recursively itself.
		132
		133	=cut
		134
		135	$idle = sub {
		136	require Carp;
		137	Carp::croak ("FATAL: deadlock detected");
106	};	138	};
107		139
108	# we really need priorities...	140	sub _cancel {
109	my @ready; # the ready queue. hehe, rather broken ;)	141	my ($self) = @_;
110		142
111	# static methods. not really.	143	# free coroutine data and mark as destructed
		144	$self->_destroy
		145	or return;
112		146
113	=head2 STATIC METHODS	147	# call all destruction callbacks
		148	$_->(@{$self->{_status}})
		149	for @{ delete $self->{_on_destroy} \|\| [] };
		150	}
114		151
115	Static methods are actually functions that operate on the current process only.	152	# this coroutine is necessary because a coroutine
		153	# cannot destroy itself.
		154	my @destroy;
		155	my $manager;
		156
		157	$manager = new Coro sub {
		158	while () {
		159	(shift @destroy)->_cancel
		160	while @destroy;
		161
		162	&schedule;
		163	}
		164	};
		165	$manager->{desc} = "[coro manager]";
		166	$manager->prio (PRIO_MAX);
		167
		168	=back
		169
		170	=head2 SIMPLE COROUTINE CREATION
116		171
117	=over 4	172	=over 4
118		173
119	=item async { ... } [@args...]	174	=item async { ... } [@args...]
120		175
121	Create a new asynchronous process and return it's process object	176	Create a new coroutine and return it's coroutine object (usually
122	(usually unused). When the sub returns the new process is automatically	177	unused). The coroutine will be put into the ready queue, so
		178	it will start running automatically on the next scheduler run.
		179
		180	The first argument is a codeblock/closure that should be executed in the
		181	coroutine. When it returns argument returns the coroutine is automatically
123	terminated.	182	terminated.
124		183
		184	The remaining arguments are passed as arguments to the closure.
		185
		186	See the C<Coro::State::new> constructor for info about the coroutine
		187	environment in which coroutines are executed.
		188
		189	Calling C<exit> in a coroutine will do the same as calling exit outside
		190	the coroutine. Likewise, when the coroutine dies, the program will exit,
		191	just as it would in the main program.
		192
		193	If you do not want that, you can provide a default C<die> handler, or
		194	simply avoid dieing (by use of C<eval>).
		195
125	# create a new coroutine that just prints its arguments	196	Example: Create a new coroutine that just prints its arguments.
		197
126	async {	198	async {
127	print "@_\n";	199	print "@_\n";
128	} 1,2,3,4;	200	} 1,2,3,4;
129		201
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	202	=cut
134		203
135	sub async(&@) {	204	sub async(&@) {
136	my $pid = new Coro @_;	205	my $coro = new Coro @_;
137	$pid->ready;	206	$coro->ready;
138	$pid;	207	$coro
139	}	208	}
		209
		210	=item async_pool { ... } [@args...]
		211
		212	Similar to C<async>, but uses a coroutine pool, so you should not call
		213	terminate or join on it (although you are allowed to), and you get a
		214	coroutine that might have executed other code already (which can be good
		215	or bad :).
		216
		217	On the plus side, this function is faster than creating (and destroying)
		218	a completly new coroutine, so if you need a lot of generic coroutines in
		219	quick successsion, use C<async_pool>, not C<async>.
		220
		221	The code block is executed in an C<eval> context and a warning will be
		222	issued in case of an exception instead of terminating the program, as
		223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		224	will not work in the expected way, unless you call terminate or cancel,
		225	which somehow defeats the purpose of pooling (but is fine in the
		226	exceptional case).
		227
		228	The priority will be reset to C<0> after each run, tracing will be
		229	disabled, the description will be reset and the default output filehandle
		230	gets restored, so you can change all these. Otherwise the coroutine will
		231	be re-used "as-is": most notably if you change other per-coroutine global
		232	stuff such as C<$/> you I<must needs> revert that change, which is most
		233	simply done by using local as in: C<< local $/ >>.
		234
		235	The idle pool size is limited to C<8> idle coroutines (this can be
		236	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		237	coros as required.
		238
		239	If you are concerned about pooled coroutines growing a lot because a
		240	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		241	{ terminate }> once per second or so to slowly replenish the pool. In
		242	addition to that, when the stacks used by a handler grows larger than 16kb
		243	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		244
		245	=cut
		246
		247	our $POOL_SIZE = 8;
		248	our $POOL_RSS = 16 * 1024;
		249	our @async_pool;
		250
		251	sub pool_handler {
		252	my $cb;
		253
		254	while () {
		255	eval {
		256	while () {
		257	_pool_1 $cb;
		258	&$cb;
		259	_pool_2 $cb;
		260	&schedule;
		261	}
		262	};
		263
		264	if ($@) {
		265	last if $@ eq "\3async_pool terminate\2\n";
		266	warn $@;
		267	}
		268	}
		269	}
		270
		271	sub async_pool(&@) {
		272	# this is also inlined into the unblock_scheduler
		273	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
		274
		275	$coro->{_invoke} = [@_];
		276	$coro->ready;
		277
		278	$coro
		279	}
		280
		281	=back
		282
		283	=head2 STATIC METHODS
		284
		285	Static methods are actually functions that operate on the current coroutine.
		286
		287	=over 4
140		288
141	=item schedule	289	=item schedule
142		290
143	Calls the scheduler. Please note that the current process will not be put	291	Calls the scheduler. The scheduler will find the next coroutine that is
		292	to be run from the ready queue and switches to it. The next coroutine
		293	to be run is simply the one with the highest priority that is longest
		294	in its ready queue. If there is no coroutine ready, it will clal the
		295	C<$Coro::idle> hook.
		296
		297	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	298	queue, so calling this function usually means you will never be called
145	never be called again.	299	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		300	thus waking you up.
146		301
147	=cut	302	This makes C<schedule> I<the> generic method to use to block the current
		303	coroutine and wait for events: first you remember the current coroutine in
		304	a variable, then arrange for some callback of yours to call C<< ->ready
		305	>> on that once some event happens, and last you call C<schedule> to put
		306	yourself to sleep. Note that a lot of things can wake your coroutine up,
		307	so you need to check whether the event indeed happened, e.g. by storing the
		308	status in a variable.
148		309
149	my $prev;	310	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
150		311
151	sub schedule {
152	# should be done using priorities :(
153	($prev, $current) = ($current, shift @ready \|\| $idle);
154	Coro::State::transfer($prev, $current);
155	}
156
157	=item yield	312	=item cede
158		313
159	Yield to other processes. This function puts the current process into the	314	"Cede" to other coroutines. This function puts the current coroutine into
160	ready queue and calls C<schedule>.	315	the ready queue and calls C<schedule>, which has the effect of giving
		316	up the current "timeslice" to other coroutines of the same or higher
		317	priority. Once your coroutine gets its turn again it will automatically be
		318	resumed.
161		319
162	=cut	320	This function is often called C<yield> in other languages.
163		321
164	sub yield {	322	=item Coro::cede_notself
165	$current->ready;
166	&schedule;
167	}
168		323
		324	Works like cede, but is not exported by default and will cede to I<any>
		325	coroutine, regardless of priority. This is useful sometimes to ensure
		326	progress is made.
		327
169	=item terminate	328	=item terminate [arg...]
170		329
171	Terminates the current process.	330	Terminates the current coroutine with the given status values (see L<cancel>).
172		331
173	Future versions of this function will allow result arguments.	332	=item killall
		333
		334	Kills/terminates/cancels all coroutines except the currently running
		335	one. This is useful after a fork, either in the child or the parent, as
		336	usually only one of them should inherit the running coroutines.
		337
		338	Note that while this will try to free some of the main programs resources,
		339	you cannot free all of them, so if a coroutine that is not the main
		340	program calls this function, there will be some one-time resource leak.
174		341
175	=cut	342	=cut
176		343
177	sub terminate {	344	sub terminate {
178	$current->{_results} = [@_];	345	$current->cancel (@_);
179	&schedule;	346	}
		347
		348	sub killall {
		349	for (Coro::State::list) {
		350	$_->cancel
		351	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		352	}
180	}	353	}
181		354
182	=back	355	=back
183		356
184	# dynamic methods
185
186	=head2 PROCESS METHODS	357	=head2 COROUTINE METHODS
187		358
188	These are the methods you can call on process objects.	359	These are the methods you can call on coroutine objects (or to create
		360	them).
189		361
190	=over 4	362	=over 4
191		363
192	=item new Coro \&sub [, @args...]	364	=item new Coro \&sub [, @args...]
193		365
194	Create a new process and return it. When the sub returns the process	366	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	367	automatically terminates as if C<terminate> with the returned values were
		368	called. To make the coroutine run you must first put it into the ready
196	the ready queue by calling the ready method.	369	queue by calling the ready method.
197		370
198	The coderef you submit MUST NOT be a closure that refers to variables	371	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.	372	coroutine environment.
200		373
201	=cut	374	=cut
202		375
203	sub _newcoro {	376	sub _terminate {
204	terminate &{+shift};	377	terminate &{+shift};
205	}	378	}
206		379
		380	=item $success = $coroutine->ready
		381
		382	Put the given coroutine into the end of its ready queue (there is one
		383	queue for each priority) and return true. If the coroutine is already in
		384	the ready queue, do nothing and return false.
		385
		386	This ensures that the scheduler will resume this coroutine automatically
		387	once all the coroutines of higher priority and all coroutines of the same
		388	priority that were put into the ready queue earlier have been resumed.
		389
		390	=item $is_ready = $coroutine->is_ready
		391
		392	Return whether the coroutine is currently the ready queue or not,
		393
		394	=item $coroutine->cancel (arg...)
		395
		396	Terminates the given coroutine and makes it return the given arguments as
		397	status (default: the empty list). Never returns if the coroutine is the
		398	current coroutine.
		399
		400	=cut
		401
207	sub new {	402	sub cancel {
208	my $class = shift;	403	my $self = shift;
209	bless {	404	$self->{_status} = [@_];
210	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
211	}, $class;
212	}
213		405
214	=item $process->ready	406	if ($current == $self) {
		407	push @destroy, $self;
		408	$manager->ready;
		409	&schedule while 1;
		410	} else {
		411	$self->_cancel;
		412	}
		413	}
215		414
216	Put the current process into the ready queue.	415	=item $coroutine->throw ([$scalar])
217		416
218	=cut	417	If C<$throw> is specified and defined, it will be thrown as an exception
		418	inside the coroutine at the next convenient point in time. Otherwise
		419	clears the exception object.
219		420
220	sub ready {	421	Coro will check for the exception each time a schedule-like-function
221	push @ready, $_[0];	422	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		423	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		424	detect this case and return early in case an exception is pending.
		425
		426	The exception object will be thrown "as is" with the specified scalar in
		427	C<$@>, i.e. if it is a string, no line number or newline will be appended
		428	(unlike with C<die>).
		429
		430	This can be used as a softer means than C<cancel> to ask a coroutine to
		431	end itself, although there is no guarantee that the exception will lead to
		432	termination, and if the exception isn't caught it might well end the whole
		433	program.
		434
		435	You might also think of C<throw> as being the moral equivalent of
		436	C<kill>ing a coroutine with a signal (in this case, a scalar).
		437
		438	=item $coroutine->join
		439
		440	Wait until the coroutine terminates and return any values given to the
		441	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		442	from multiple coroutines, and all will be resumed and given the status
		443	return once the C<$coroutine> terminates.
		444
		445	=cut
		446
		447	sub join {
		448	my $self = shift;
		449
		450	unless ($self->{_status}) {
		451	my $current = $current;
		452
		453	push @{$self->{_on_destroy}}, sub {
		454	$current->ready;
		455	undef $current;
		456	};
		457
		458	&schedule while $current;
		459	}
		460
		461	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		462	}
		463
		464	=item $coroutine->on_destroy (\&cb)
		465
		466	Registers a callback that is called when this coroutine gets destroyed,
		467	but before it is joined. The callback gets passed the terminate arguments,
		468	if any, and I<must not> die, under any circumstances.
		469
		470	=cut
		471
		472	sub on_destroy {
		473	my ($self, $cb) = @_;
		474
		475	push @{ $self->{_on_destroy} }, $cb;
		476	}
		477
		478	=item $oldprio = $coroutine->prio ($newprio)
		479
		480	Sets (or gets, if the argument is missing) the priority of the
		481	coroutine. Higher priority coroutines get run before lower priority
		482	coroutines. Priorities are small signed integers (currently -4 .. +3),
		483	that you can refer to using PRIO_xxx constants (use the import tag :prio
		484	to get then):
		485
		486	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		487	3 > 1 > 0 > -1 > -3 > -4
		488
		489	# set priority to HIGH
		490	current->prio(PRIO_HIGH);
		491
		492	The idle coroutine ($Coro::idle) always has a lower priority than any
		493	existing coroutine.
		494
		495	Changing the priority of the current coroutine will take effect immediately,
		496	but changing the priority of coroutines in the ready queue (but not
		497	running) will only take effect after the next schedule (of that
		498	coroutine). This is a bug that will be fixed in some future version.
		499
		500	=item $newprio = $coroutine->nice ($change)
		501
		502	Similar to C<prio>, but subtract the given value from the priority (i.e.
		503	higher values mean lower priority, just as in unix).
		504
		505	=item $olddesc = $coroutine->desc ($newdesc)
		506
		507	Sets (or gets in case the argument is missing) the description for this
		508	coroutine. This is just a free-form string you can associate with a
		509	coroutine.
		510
		511	This method simply sets the C<< $coroutine->{desc} >> member to the given
		512	string. You can modify this member directly if you wish.
		513
		514	=cut
		515
		516	sub desc {
		517	my $old = $_[0]{desc};
		518	$_[0]{desc} = $_[1] if @_ > 1;
		519	$old;
222	}	520	}
223		521
224	=back	522	=back
225		523
		524	=head2 GLOBAL FUNCTIONS
		525
		526	=over 4
		527
		528	=item Coro::nready
		529
		530	Returns the number of coroutines that are currently in the ready state,
		531	i.e. that can be switched to by calling C<schedule> directory or
		532	indirectly. The value C<0> means that the only runnable coroutine is the
		533	currently running one, so C<cede> would have no effect, and C<schedule>
		534	would cause a deadlock unless there is an idle handler that wakes up some
		535	coroutines.
		536
		537	=item my $guard = Coro::guard { ... }
		538
		539	This creates and returns a guard object. Nothing happens until the object
		540	gets destroyed, in which case the codeblock given as argument will be
		541	executed. This is useful to free locks or other resources in case of a
		542	runtime error or when the coroutine gets canceled, as in both cases the
		543	guard block will be executed. The guard object supports only one method,
		544	C<< ->cancel >>, which will keep the codeblock from being executed.
		545
		546	Example: set some flag and clear it again when the coroutine gets canceled
		547	or the function returns:
		548
		549	sub do_something {
		550	my $guard = Coro::guard { $busy = 0 };
		551	$busy = 1;
		552
		553	# do something that requires $busy to be true
		554	}
		555
		556	=cut
		557
		558	sub guard(&) {
		559	bless \(my $cb = $_[0]), "Coro::guard"
		560	}
		561
		562	sub Coro::guard::cancel {
		563	${$_[0]} = sub { };
		564	}
		565
		566	sub Coro::guard::DESTROY {
		567	${$_[0]}->();
		568	}
		569
		570
		571	=item unblock_sub { ... }
		572
		573	This utility function takes a BLOCK or code reference and "unblocks" it,
		574	returning a new coderef. Unblocking means that calling the new coderef
		575	will return immediately without blocking, returning nothing, while the
		576	original code ref will be called (with parameters) from within another
		577	coroutine.
		578
		579	The reason this function exists is that many event libraries (such as the
		580	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		581	of thread-safety). This means you must not block within event callbacks,
		582	otherwise you might suffer from crashes or worse. The only event library
		583	currently known that is safe to use without C<unblock_sub> is L<EV>.
		584
		585	This function allows your callbacks to block by executing them in another
		586	coroutine where it is safe to block. One example where blocking is handy
		587	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		588	disk, for example.
		589
		590	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		591	creating event callbacks that want to block.
		592
		593	If your handler does not plan to block (e.g. simply sends a message to
		594	another coroutine, or puts some other coroutine into the ready queue),
		595	there is no reason to use C<unblock_sub>.
		596
		597	Note that you also need to use C<unblock_sub> for any other callbacks that
		598	are indirectly executed by any C-based event loop. For example, when you
		599	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		600	provides callbacks that are the result of some event callback, then you
		601	must not block either, or use C<unblock_sub>.
		602
		603	=cut
		604
		605	our @unblock_queue;
		606
		607	# we create a special coro because we want to cede,
		608	# to reduce pressure on the coro pool (because most callbacks
		609	# return immediately and can be reused) and because we cannot cede
		610	# inside an event callback.
		611	our $unblock_scheduler = new Coro sub {
		612	while () {
		613	while (my $cb = pop @unblock_queue) {
		614	# this is an inlined copy of async_pool
		615	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
		616
		617	$coro->{_invoke} = $cb;
		618	$coro->ready;
		619	cede; # for short-lived callbacks, this reduces pressure on the coro pool
		620	}
		621	schedule; # sleep well
		622	}
		623	};
		624	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		625
		626	sub unblock_sub(&) {
		627	my $cb = shift;
		628
		629	sub {
		630	unshift @unblock_queue, [$cb, @_];
		631	$unblock_scheduler->ready;
		632	}
		633	}
		634
		635	=item $cb = Coro::rouse_cb
		636
		637	Create and return a "rouse callback". That's a code reference that, when
		638	called, will save its arguments and notify the owner coroutine of the
		639	callback.
		640
		641	See the next function.
		642
		643	=item @args = Coro::rouse_wait [$cb]
		644
		645	Wait for the specified rouse callback (or the last one tht was created in
		646	this coroutine).
		647
		648	As soon as the callback is invoked (or when the calback was invoked before
		649	C<rouse_wait>), it will return a copy of the arguments originally passed
		650	to the rouse callback.
		651
		652	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		653
		654	=back
		655
226	=cut	656	=cut
227		657
228	1;	658	1;
229		659
		660	=head1 HOW TO WAIT FOR A CALLBACK
		661
		662	It is very common for a coroutine to wait for some callback to be
		663	called. This occurs naturally when you use coroutines in an otherwise
		664	event-based program, or when you use event-based libraries.
		665
		666	These typically register a callback for some event, and call that callback
		667	when the event occured. In a coroutine, however, you typically want to
		668	just wait for the event, simplyifying things.
		669
		670	For example C<< AnyEvent->child >> registers a callback to be called when
		671	a specific child has exited:
		672
		673	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		674
		675	But from withina coroutine, you often just want to write this:
		676
		677	my $status = wait_for_child $pid;
		678
		679	Coro offers two functions specifically designed to make this easy,
		680	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		681
		682	The first function, C<rouse_cb>, generates and returns a callback that,
		683	when invoked, will save it's arguments and notify the coroutine that
		684	created the callback.
		685
		686	The second function, C<rouse_wait>, waits for the callback to be called
		687	(by calling C<schedule> to go to sleep) and returns the arguments
		688	originally passed to the callback.
		689
		690	Using these functions, it becomes easy to write the C<wait_for_child>
		691	function mentioned above:
		692
		693	sub wait_for_child($) {
		694	my ($pid) = @_;
		695
		696	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		697
		698	my ($rpid, $rstatus) = Coro::rouse_wait;
		699	$rstatus
		700	}
		701
		702	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		703	you can roll your own, using C<schedule>:
		704
		705	sub wait_for_child($) {
		706	my ($pid) = @_;
		707
		708	# store the current coroutine in $current,
		709	# and provide result variables for the closure passed to ->child
		710	my $current = $Coro::current;
		711	my ($done, $rstatus);
		712
		713	# pass a closure to ->child
		714	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		715	$rstatus = $_[1]; # remember rstatus
		716	$done = 1; # mark $rstatus as valud
		717	});
		718
		719	# wait until the closure has been called
		720	schedule while !$done;
		721
		722	$rstatus
		723	}
		724
		725
230	=head1 BUGS/LIMITATIONS	726	=head1 BUGS/LIMITATIONS
231		727
232	- could be faster, especially when the core would introduce special	728	=over 4
233	support for coroutines (like it does for threads).	729
234	- there is still a memleak on coroutine termination that I could not	730	=item fork with pthread backend
235	identify. Could be as small as a single SV.	731
236	- this module is not well-tested.	732	When Coro is compiled using the pthread backend (which isn't recommended
237	- if variables or arguments "disappear" (become undef) or become	733	but required on many BSDs as their libcs are completely broken), then
238	corrupted please contact the author so he cen iron out the	734	coroutines will not survive a fork. There is no known workaround except to
239	remaining bugs.	735	fix your libc and use a saner backend.
240	- this module is not thread-safe. You must only ever use this module from	736
		737	=item perl process emulation ("threads")
		738
		739	This module is not perl-pseudo-thread-safe. You should only ever use this
241	the same thread (this requirement might be loosened in the future to	740	module from the same thread (this requirement might be removed in the
242	allow per-thread schedulers, but Coro::State does not yet allow this).	741	future to allow per-thread schedulers, but Coro::State does not yet allow
		742	this). I recommend disabling thread support and using processes, as having
		743	the windows process emulation enabled under unix roughly halves perl
		744	performance, even when not used.
		745
		746	=item coroutine switching not signal safe
		747
		748	You must not switch to another coroutine from within a signal handler
		749	(only relevant with %SIG - most event libraries provide safe signals).
		750
		751	That means you I<MUST NOT> call any function that might "block" the
		752	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		753	anything that calls those. Everything else, including calling C<ready>,
		754	works.
		755
		756	=back
		757
243		758
244	=head1 SEE ALSO	759	=head1 SEE ALSO
245		760
246	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	761	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
247	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	762
		763	Debugging: L<Coro::Debug>.
		764
		765	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		766
		767	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		768
		769	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		770
		771	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
		772
		773	XS API: L<Coro::MakeMaker>.
		774
		775	Low level Configuration, Coroutine Environment: L<Coro::State>.
248		776
249	=head1 AUTHOR	777	=head1 AUTHOR
250		778
251	Marc Lehmann <pcg@goof.com>	779	Marc Lehmann <schmorp@schmorp.de>
252	http://www.goof.com/pcg/marc/	780	http://home.schmorp.de/
253		781
254	=cut	782	=cut
255		783

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Revision 1.225 by root, Wed Nov 19 15:29:57 2008 UTC