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

Comparing Coro/Coro.pm (file contents):
Revision 1.13 by root, Tue Jul 17 00:24:14 2001 UTC vs.
Revision 1.233 by root, Fri Nov 21 06:02:07 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
		31	This module collection manages coroutines. Coroutines are similar to
		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.
		38
		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.
		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
		52	In this module, coroutines are defined as "callchain + lexical variables +
		53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
		54	its own set of lexicals and its own set of perls most important global
		55	variables (see L<Coro::State> for more configuration).
		56
23	=cut	57	=cut
24		58
25	package Coro;	59	package Coro;
26		60
		61	use strict qw(vars subs);
		62	no warnings "uninitialized";
		63
27	use Coro::State;	64	use Coro::State;
28		65
29	use base Exporter;	66	use base qw(Coro::State Exporter);
30		67
		68	our $idle; # idle handler
		69	our $main; # main coroutine
		70	our $current; # current coroutine
		71
31	$VERSION = 0.05;	72	our $VERSION = "5.0";
32		73
33	@EXPORT = qw(async yield schedule terminate);	74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
34	@EXPORT_OK = qw($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));
35		79
36	{	80	=over 4
37	use subs 'async';
38		81
39	my @async;
40
41	# this way of handling attributes simply is NOT scalable ;()
42	sub import {
43	Coro->export_to_level(1, @_);
44	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
45	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
46	my ($package, $ref) = (shift, shift);
47	my @attrs;
48	for (@_) {
49	if ($_ eq "Coro") {
50	push @async, $ref;
51	} else {
52	push @attrs, @_;
53	}
54	}
55	return $old ? $old->($package, $name, @attrs) : @attrs;
56	};
57	}
58
59	sub INIT {
60	async pop @async while @async;
61	}
62	}
63
64	=item $main	82	=item $Coro::main
65		83
66	This coroutine represents the main program.	84	This variable stores the coroutine object that represents the main
		85	program. While you cna C<ready> it and do most other things you can do to
		86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		87	whether you are running in the main program or not.
67		88
68	=cut	89	=cut
69		90
70	our $main = new Coro;	91	# $main is now being initialised by Coro::State
71		92
72	=item $current	93	=item $Coro::current
73		94
74	The current coroutine (the last coroutine switched to). The initial value is C<$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<$Coro::main> (of course).
75		98
76	=cut	99	This variable is B<strictly> I<read-only>. You can take copies of the
		100	value stored in it and use it as any other coroutine object, but you must
		101	not otherwise modify the variable itself.
77		102
78	# maybe some other module used Coro::Specific before...	103	=cut
79	if ($current) {
80	$main->{specific} = $current->{specific};
81	}
82		104
83	our $current = $main;	105	sub current() { $current } # [DEPRECATED]
84		106
85	=item $idle	107	=item $Coro::idle
86		108
87	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
88	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.
89		112
90	=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.
91		117
92	# should be done using priorities :(	118	This hook is overwritten by modules such as C<Coro::Timer> and
93	our $idle = new Coro sub {	119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
94	print STDERR "FATAL: deadlock detected\n";	120	coroutine so the scheduler can run it.
95	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");
96	};	138	};
97		139
98	# we really need priorities...	140	# this coroutine is necessary because a coroutine
99	## my @ready; #d#	141	# cannot destroy itself.
100	our @ready = (); # the ready queue. hehe, rather broken ;)	142	our @destroy;
		143	our $manager;
101		144
102	# static methods. not really.	145	$manager = new Coro sub {
		146	while () {
		147	Coro::_cancel shift @destroy
		148	while @destroy;
103		149
104	=head2 STATIC METHODS	150	&schedule;
		151	}
		152	};
		153	$manager->{desc} = "[coro manager]";
		154	$manager->prio (PRIO_MAX);
105		155
106	Static methods are actually functions that operate on the current process only.	156	=back
		157
		158	=head2 SIMPLE COROUTINE CREATION
107		159
108	=over 4	160	=over 4
109		161
110	=item async { ... } [@args...]	162	=item async { ... } [@args...]
111		163
112	Create a new asynchronous process and return it's process object	164	Create a new coroutine and return it's coroutine object (usually
113	(usually unused). When the sub returns the new process is automatically	165	unused). The coroutine will be put into the ready queue, so
		166	it will start running automatically on the next scheduler run.
		167
		168	The first argument is a codeblock/closure that should be executed in the
		169	coroutine. When it returns argument returns the coroutine is automatically
114	terminated.	170	terminated.
115		171
		172	The remaining arguments are passed as arguments to the closure.
		173
		174	See the C<Coro::State::new> constructor for info about the coroutine
		175	environment in which coroutines are executed.
		176
		177	Calling C<exit> in a coroutine will do the same as calling exit outside
		178	the coroutine. Likewise, when the coroutine dies, the program will exit,
		179	just as it would in the main program.
		180
		181	If you do not want that, you can provide a default C<die> handler, or
		182	simply avoid dieing (by use of C<eval>).
		183
116	# create a new coroutine that just prints its arguments	184	Example: Create a new coroutine that just prints its arguments.
		185
117	async {	186	async {
118	print "@_\n";	187	print "@_\n";
119	} 1,2,3,4;	188	} 1,2,3,4;
120		189
121	The coderef you submit MUST NOT be a closure that refers to variables
122	in an outer scope. This does NOT work. Pass arguments into it instead.
123
124	=cut	190	=cut
125		191
126	sub async(&@) {	192	sub async(&@) {
127	my $pid = new Coro @_;	193	my $coro = new Coro @_;
128	$pid->ready;	194	$coro->ready;
129	$pid;	195	$coro
130	}	196	}
		197
		198	=item async_pool { ... } [@args...]
		199
		200	Similar to C<async>, but uses a coroutine pool, so you should not call
		201	terminate or join on it (although you are allowed to), and you get a
		202	coroutine that might have executed other code already (which can be good
		203	or bad :).
		204
		205	On the plus side, this function is about twice as fast as creating (and
		206	destroying) a completely new coroutine, so if you need a lot of generic
		207	coroutines in quick successsion, use C<async_pool>, not C<async>.
		208
		209	The code block is executed in an C<eval> context and a warning will be
		210	issued in case of an exception instead of terminating the program, as
		211	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		212	will not work in the expected way, unless you call terminate or cancel,
		213	which somehow defeats the purpose of pooling (but is fine in the
		214	exceptional case).
		215
		216	The priority will be reset to C<0> after each run, tracing will be
		217	disabled, the description will be reset and the default output filehandle
		218	gets restored, so you can change all these. Otherwise the coroutine will
		219	be re-used "as-is": most notably if you change other per-coroutine global
		220	stuff such as C<$/> you I<must needs> revert that change, which is most
		221	simply done by using local as in: C<< local $/ >>.
		222
		223	The idle pool size is limited to C<8> idle coroutines (this can be
		224	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		225	coros as required.
		226
		227	If you are concerned about pooled coroutines growing a lot because a
		228	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		229	{ terminate }> once per second or so to slowly replenish the pool. In
		230	addition to that, when the stacks used by a handler grows larger than 32kb
		231	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		232
		233	=cut
		234
		235	our $POOL_SIZE = 8;
		236	our $POOL_RSS = 32 * 1024;
		237	our @async_pool;
		238
		239	sub pool_handler {
		240	while () {
		241	eval {
		242	&{&_pool_handler} while 1;
		243	};
		244
		245	warn $@ if $@;
		246	}
		247	}
		248
		249	=back
		250
		251	=head2 STATIC METHODS
		252
		253	Static methods are actually functions that operate on the current coroutine.
		254
		255	=over 4
131		256
132	=item schedule	257	=item schedule
133		258
134	Calls the scheduler. Please note that the current process will not be put	259	Calls the scheduler. The scheduler will find the next coroutine that is
		260	to be run from the ready queue and switches to it. The next coroutine
		261	to be run is simply the one with the highest priority that is longest
		262	in its ready queue. If there is no coroutine ready, it will clal the
		263	C<$Coro::idle> hook.
		264
		265	Please note that the current coroutine will I<not> be put into the ready
135	into the ready queue, so calling this function usually means you will	266	queue, so calling this function usually means you will never be called
136	never be called again.	267	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		268	thus waking you up.
137		269
138	=cut	270	This makes C<schedule> I<the> generic method to use to block the current
		271	coroutine and wait for events: first you remember the current coroutine in
		272	a variable, then arrange for some callback of yours to call C<< ->ready
		273	>> on that once some event happens, and last you call C<schedule> to put
		274	yourself to sleep. Note that a lot of things can wake your coroutine up,
		275	so you need to check whether the event indeed happened, e.g. by storing the
		276	status in a variable.
139		277
140	my $prev;	278	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
141		279
142	sub schedule {
143	# should be done using priorities :(
144	($prev, $current) = ($current, shift @ready \|\| $idle);
145	Coro::State::transfer($prev, $current);
146	}
147
148	=item yield	280	=item cede
149		281
150	Yield to other processes. This function puts the current process into the	282	"Cede" to other coroutines. This function puts the current coroutine into
151	ready queue and calls C<schedule>.	283	the ready queue and calls C<schedule>, which has the effect of giving
		284	up the current "timeslice" to other coroutines of the same or higher
		285	priority. Once your coroutine gets its turn again it will automatically be
		286	resumed.
152		287
153	=cut	288	This function is often called C<yield> in other languages.
154		289
155	sub yield {	290	=item Coro::cede_notself
156	$current->ready;
157	&schedule;
158	}
159		291
		292	Works like cede, but is not exported by default and will cede to I<any>
		293	coroutine, regardless of priority. This is useful sometimes to ensure
		294	progress is made.
		295
160	=item terminate	296	=item terminate [arg...]
161		297
162	Terminates the current process.	298	Terminates the current coroutine with the given status values (see L<cancel>).
163		299
164	Future versions of this function will allow result arguments.	300	=item killall
165		301
166	=cut	302	Kills/terminates/cancels all coroutines except the currently running
		303	one. This is useful after a fork, either in the child or the parent, as
		304	usually only one of them should inherit the running coroutines.
167		305
168	sub terminate {	306	Note that while this will try to free some of the main programs resources,
169	$current->{_results} = [@_];	307	you cannot free all of them, so if a coroutine that is not the main
170	&schedule;	308	program calls this function, there will be some one-time resource leak.
		309
		310	=cut
		311
		312	sub killall {
		313	for (Coro::State::list) {
		314	$_->cancel
		315	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		316	}
171	}	317	}
172		318
173	=back	319	=back
174		320
175	# dynamic methods
176
177	=head2 PROCESS METHODS	321	=head2 COROUTINE METHODS
178		322
179	These are the methods you can call on process objects.	323	These are the methods you can call on coroutine objects (or to create
		324	them).
180		325
181	=over 4	326	=over 4
182		327
183	=item new Coro \&sub [, @args...]	328	=item new Coro \&sub [, @args...]
184		329
185	Create a new process and return it. When the sub returns the process	330	Create a new coroutine and return it. When the sub returns, the coroutine
186	automatically terminates. To start the process you must first put it into	331	automatically terminates as if C<terminate> with the returned values were
		332	called. To make the coroutine run you must first put it into the ready
187	the ready queue by calling the ready method.	333	queue by calling the ready method.
188		334
189	The coderef you submit MUST NOT be a closure that refers to variables	335	See C<async> and C<Coro::State::new> for additional info about the
190	in an outer scope. This does NOT work. Pass arguments into it instead.	336	coroutine environment.
191		337
192	=cut	338	=cut
193		339
194	sub _newcoro {	340	sub _terminate {
195	terminate &{+shift};	341	terminate &{+shift};
196	}	342	}
197		343
		344	=item $success = $coroutine->ready
		345
		346	Put the given coroutine into the end of its ready queue (there is one
		347	queue for each priority) and return true. If the coroutine is already in
		348	the ready queue, do nothing and return false.
		349
		350	This ensures that the scheduler will resume this coroutine automatically
		351	once all the coroutines of higher priority and all coroutines of the same
		352	priority that were put into the ready queue earlier have been resumed.
		353
		354	=item $is_ready = $coroutine->is_ready
		355
		356	Return whether the coroutine is currently the ready queue or not,
		357
		358	=item $coroutine->cancel (arg...)
		359
		360	Terminates the given coroutine and makes it return the given arguments as
		361	status (default: the empty list). Never returns if the coroutine is the
		362	current coroutine.
		363
		364	=cut
		365
198	sub new {	366	sub cancel {
199	my $class = shift;	367	my $self = shift;
200	bless {
201	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
202	}, $class;
203	}
204		368
205	=item $process->ready	369	if ($current == $self) {
		370	terminate @_;
		371	} else {
		372	$self->{_status} = [@_];
		373	$self->_cancel;
		374	}
		375	}
206		376
207	Put the current process into the ready queue.	377	=item $coroutine->schedule_to
208		378
209	=cut	379	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead
		380	of continuing with the next coro from the ready queue, always switch to
		381	the given coroutine object (regardless of priority etc.). The readyness
		382	state of that coroutine isn't changed.
210		383
211	sub ready {	384	This is an advanced method for special cases - I'd love to hear about any
212	push @ready, $_[0];	385	uses for this one.
		386
		387	=item $coroutine->cede_to
		388
		389	Like C<schedule_to>, but puts the current coroutine into the ready
		390	queue. This has the effect of temporarily switching to the given
		391	coroutine, and continuing some time later.
		392
		393	This is an advanced method for special cases - I'd love to hear about any
		394	uses for this one.
		395
		396	=item $coroutine->throw ([$scalar])
		397
		398	If C<$throw> is specified and defined, it will be thrown as an exception
		399	inside the coroutine at the next convenient point in time. Otherwise
		400	clears the exception object.
		401
		402	Coro will check for the exception each time a schedule-like-function
		403	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		404	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		405	detect this case and return early in case an exception is pending.
		406
		407	The exception object will be thrown "as is" with the specified scalar in
		408	C<$@>, i.e. if it is a string, no line number or newline will be appended
		409	(unlike with C<die>).
		410
		411	This can be used as a softer means than C<cancel> to ask a coroutine to
		412	end itself, although there is no guarantee that the exception will lead to
		413	termination, and if the exception isn't caught it might well end the whole
		414	program.
		415
		416	You might also think of C<throw> as being the moral equivalent of
		417	C<kill>ing a coroutine with a signal (in this case, a scalar).
		418
		419	=item $coroutine->join
		420
		421	Wait until the coroutine terminates and return any values given to the
		422	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		423	from multiple coroutines, and all will be resumed and given the status
		424	return once the C<$coroutine> terminates.
		425
		426	=cut
		427
		428	sub join {
		429	my $self = shift;
		430
		431	unless ($self->{_status}) {
		432	my $current = $current;
		433
		434	push @{$self->{_on_destroy}}, sub {
		435	$current->ready;
		436	undef $current;
		437	};
		438
		439	&schedule while $current;
		440	}
		441
		442	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		443	}
		444
		445	=item $coroutine->on_destroy (\&cb)
		446
		447	Registers a callback that is called when this coroutine gets destroyed,
		448	but before it is joined. The callback gets passed the terminate arguments,
		449	if any, and I<must not> die, under any circumstances.
		450
		451	=cut
		452
		453	sub on_destroy {
		454	my ($self, $cb) = @_;
		455
		456	push @{ $self->{_on_destroy} }, $cb;
		457	}
		458
		459	=item $oldprio = $coroutine->prio ($newprio)
		460
		461	Sets (or gets, if the argument is missing) the priority of the
		462	coroutine. Higher priority coroutines get run before lower priority
		463	coroutines. Priorities are small signed integers (currently -4 .. +3),
		464	that you can refer to using PRIO_xxx constants (use the import tag :prio
		465	to get then):
		466
		467	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		468	3 > 1 > 0 > -1 > -3 > -4
		469
		470	# set priority to HIGH
		471	current->prio(PRIO_HIGH);
		472
		473	The idle coroutine ($Coro::idle) always has a lower priority than any
		474	existing coroutine.
		475
		476	Changing the priority of the current coroutine will take effect immediately,
		477	but changing the priority of coroutines in the ready queue (but not
		478	running) will only take effect after the next schedule (of that
		479	coroutine). This is a bug that will be fixed in some future version.
		480
		481	=item $newprio = $coroutine->nice ($change)
		482
		483	Similar to C<prio>, but subtract the given value from the priority (i.e.
		484	higher values mean lower priority, just as in unix).
		485
		486	=item $olddesc = $coroutine->desc ($newdesc)
		487
		488	Sets (or gets in case the argument is missing) the description for this
		489	coroutine. This is just a free-form string you can associate with a
		490	coroutine.
		491
		492	This method simply sets the C<< $coroutine->{desc} >> member to the given
		493	string. You can modify this member directly if you wish.
		494
		495	=cut
		496
		497	sub desc {
		498	my $old = $_[0]{desc};
		499	$_[0]{desc} = $_[1] if @_ > 1;
		500	$old;
		501	}
		502
		503	sub transfer {
		504	require Carp;
		505	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
213	}	506	}
214		507
215	=back	508	=back
216		509
		510	=head2 GLOBAL FUNCTIONS
		511
		512	=over 4
		513
		514	=item Coro::nready
		515
		516	Returns the number of coroutines that are currently in the ready state,
		517	i.e. that can be switched to by calling C<schedule> directory or
		518	indirectly. The value C<0> means that the only runnable coroutine is the
		519	currently running one, so C<cede> would have no effect, and C<schedule>
		520	would cause a deadlock unless there is an idle handler that wakes up some
		521	coroutines.
		522
		523	=item my $guard = Coro::guard { ... }
		524
		525	This creates and returns a guard object. Nothing happens until the object
		526	gets destroyed, in which case the codeblock given as argument will be
		527	executed. This is useful to free locks or other resources in case of a
		528	runtime error or when the coroutine gets canceled, as in both cases the
		529	guard block will be executed. The guard object supports only one method,
		530	C<< ->cancel >>, which will keep the codeblock from being executed.
		531
		532	Example: set some flag and clear it again when the coroutine gets canceled
		533	or the function returns:
		534
		535	sub do_something {
		536	my $guard = Coro::guard { $busy = 0 };
		537	$busy = 1;
		538
		539	# do something that requires $busy to be true
		540	}
		541
		542	=cut
		543
		544	sub guard(&) {
		545	bless \(my $cb = $_[0]), "Coro::guard"
		546	}
		547
		548	sub Coro::guard::cancel {
		549	${$_[0]} = sub { };
		550	}
		551
		552	sub Coro::guard::DESTROY {
		553	${$_[0]}->();
		554	}
		555
		556
		557	=item unblock_sub { ... }
		558
		559	This utility function takes a BLOCK or code reference and "unblocks" it,
		560	returning a new coderef. Unblocking means that calling the new coderef
		561	will return immediately without blocking, returning nothing, while the
		562	original code ref will be called (with parameters) from within another
		563	coroutine.
		564
		565	The reason this function exists is that many event libraries (such as the
		566	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		567	of thread-safety). This means you must not block within event callbacks,
		568	otherwise you might suffer from crashes or worse. The only event library
		569	currently known that is safe to use without C<unblock_sub> is L<EV>.
		570
		571	This function allows your callbacks to block by executing them in another
		572	coroutine where it is safe to block. One example where blocking is handy
		573	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		574	disk, for example.
		575
		576	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		577	creating event callbacks that want to block.
		578
		579	If your handler does not plan to block (e.g. simply sends a message to
		580	another coroutine, or puts some other coroutine into the ready queue),
		581	there is no reason to use C<unblock_sub>.
		582
		583	Note that you also need to use C<unblock_sub> for any other callbacks that
		584	are indirectly executed by any C-based event loop. For example, when you
		585	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		586	provides callbacks that are the result of some event callback, then you
		587	must not block either, or use C<unblock_sub>.
		588
		589	=cut
		590
		591	our @unblock_queue;
		592
		593	# we create a special coro because we want to cede,
		594	# to reduce pressure on the coro pool (because most callbacks
		595	# return immediately and can be reused) and because we cannot cede
		596	# inside an event callback.
		597	our $unblock_scheduler = new Coro sub {
		598	while () {
		599	while (my $cb = pop @unblock_queue) {
		600	&async_pool (@$cb);
		601
		602	# for short-lived callbacks, this reduces pressure on the coro pool
		603	# as the chance is very high that the async_poll coro will be back
		604	# in the idle state when cede returns
		605	cede;
		606	}
		607	schedule; # sleep well
		608	}
		609	};
		610	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		611
		612	sub unblock_sub(&) {
		613	my $cb = shift;
		614
		615	sub {
		616	unshift @unblock_queue, [$cb, @_];
		617	$unblock_scheduler->ready;
		618	}
		619	}
		620
		621	=item $cb = Coro::rouse_cb
		622
		623	Create and return a "rouse callback". That's a code reference that, when
		624	called, will save its arguments and notify the owner coroutine of the
		625	callback.
		626
		627	See the next function.
		628
		629	=item @args = Coro::rouse_wait [$cb]
		630
		631	Wait for the specified rouse callback (or the last one tht was created in
		632	this coroutine).
		633
		634	As soon as the callback is invoked (or when the calback was invoked before
		635	C<rouse_wait>), it will return a copy of the arguments originally passed
		636	to the rouse callback.
		637
		638	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		639
		640	=back
		641
217	=cut	642	=cut
218		643
219	1;	644	1;
220		645
		646	=head1 HOW TO WAIT FOR A CALLBACK
		647
		648	It is very common for a coroutine to wait for some callback to be
		649	called. This occurs naturally when you use coroutines in an otherwise
		650	event-based program, or when you use event-based libraries.
		651
		652	These typically register a callback for some event, and call that callback
		653	when the event occured. In a coroutine, however, you typically want to
		654	just wait for the event, simplyifying things.
		655
		656	For example C<< AnyEvent->child >> registers a callback to be called when
		657	a specific child has exited:
		658
		659	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		660
		661	But from withina coroutine, you often just want to write this:
		662
		663	my $status = wait_for_child $pid;
		664
		665	Coro offers two functions specifically designed to make this easy,
		666	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		667
		668	The first function, C<rouse_cb>, generates and returns a callback that,
		669	when invoked, will save it's arguments and notify the coroutine that
		670	created the callback.
		671
		672	The second function, C<rouse_wait>, waits for the callback to be called
		673	(by calling C<schedule> to go to sleep) and returns the arguments
		674	originally passed to the callback.
		675
		676	Using these functions, it becomes easy to write the C<wait_for_child>
		677	function mentioned above:
		678
		679	sub wait_for_child($) {
		680	my ($pid) = @_;
		681
		682	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		683
		684	my ($rpid, $rstatus) = Coro::rouse_wait;
		685	$rstatus
		686	}
		687
		688	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		689	you can roll your own, using C<schedule>:
		690
		691	sub wait_for_child($) {
		692	my ($pid) = @_;
		693
		694	# store the current coroutine in $current,
		695	# and provide result variables for the closure passed to ->child
		696	my $current = $Coro::current;
		697	my ($done, $rstatus);
		698
		699	# pass a closure to ->child
		700	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		701	$rstatus = $_[1]; # remember rstatus
		702	$done = 1; # mark $rstatus as valud
		703	});
		704
		705	# wait until the closure has been called
		706	schedule while !$done;
		707
		708	$rstatus
		709	}
		710
		711
		712	=head1 BUGS/LIMITATIONS
		713
		714	=over 4
		715
		716	=item fork with pthread backend
		717
		718	When Coro is compiled using the pthread backend (which isn't recommended
		719	but required on many BSDs as their libcs are completely broken), then
		720	coroutines will not survive a fork. There is no known workaround except to
		721	fix your libc and use a saner backend.
		722
		723	=item perl process emulation ("threads")
		724
		725	This module is not perl-pseudo-thread-safe. You should only ever use this
		726	module from the same thread (this requirement might be removed in the
		727	future to allow per-thread schedulers, but Coro::State does not yet allow
		728	this). I recommend disabling thread support and using processes, as having
		729	the windows process emulation enabled under unix roughly halves perl
		730	performance, even when not used.
		731
		732	=item coroutine switching not signal safe
		733
		734	You must not switch to another coroutine from within a signal handler
		735	(only relevant with %SIG - most event libraries provide safe signals).
		736
		737	That means you I<MUST NOT> call any function that might "block" the
		738	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		739	anything that calls those. Everything else, including calling C<ready>,
		740	works.
		741
		742	=back
		743
		744
221	=head1 SEE ALSO	745	=head1 SEE ALSO
222		746
223	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	747	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
224	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	748
		749	Debugging: L<Coro::Debug>.
		750
		751	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		752
		753	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		754
		755	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		756
		757	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
		758
		759	XS API: L<Coro::MakeMaker>.
		760
		761	Low level Configuration, Coroutine Environment: L<Coro::State>.
225		762
226	=head1 AUTHOR	763	=head1 AUTHOR
227		764
228	Marc Lehmann <pcg@goof.com>	765	Marc Lehmann <schmorp@schmorp.de>
229	http://www.goof.com/pcg/marc/	766	http://home.schmorp.de/
230		767
231	=cut	768	=cut
232		769

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Revision 1.233 by root, Fri Nov 21 06:02:07 2008 UTC