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

Comparing Coro/Coro.pm (file contents):
Revision 1.29 by root, Sat Aug 11 00:37:31 2001 UTC vs.
Revision 1.226 by root, Wed Nov 19 16:01:32 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	cede;	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 + C stack), that is, a coroutine has it's own	53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
30	callchain, it's own set of lexicals and it's own set of perl's most	54	its own set of lexicals and its own set of perls most important global
31	important global 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
41	$VERSION = 0.45;	68	our $idle; # idle handler
		69	our $main; # main coroutine
		70	our $current; # current coroutine
42		71
		72	our $VERSION = 5.0;
		73
43	@EXPORT = qw(async cede schedule terminate current);	74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
44	@EXPORT_OK = qw($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	my $init;
49		81
50	# this way of handling attributes simply is NOT scalable ;()
51	sub import {
52	Coro->export_to_level(1, @_);
53	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
54	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
55	my ($package, $ref) = (shift, shift);
56	my @attrs;
57	for (@_) {
58	if ($_ eq "Coro") {
59	push @async, $ref;
60	unless ($init++) {
61	eval q{
62	sub INIT {
63	&async(pop @async) while @async;
64	}
65	};
66	}
67	} else {
68	push @attrs, $_;
69	}
70	}
71	return $old ? $old->($package, $ref, @attrs) : @attrs;
72	};
73	}
74
75	}
76
77	=item $main	82	=item $Coro::main
78		83
79	This coroutine represents the main program.	84	This variable stores the coroutine object that represents the main
		85	program. While you cna C<ready> it and do most other things you can do to
		86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		87	whether you are running in the main program or not.
80		88
81	=cut	89	=cut
82		90
83	our $main = new Coro;	91	# $main is now being initialised by Coro::State
84		92
85	=item $current (or as function: current)	93	=item $Coro::current
86		94
87	The current coroutine (the last coroutine switched to). The initial value is C<$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<$Coro::main> (of course).
88		98
89	=cut	99	This variable is B<strictly> I<read-only>. You can take copies of the
		100	value stored in it and use it as any other coroutine object, but you must
		101	not otherwise modify the variable itself.
90		102
91	# maybe some other module used Coro::Specific before...	103	=cut
92	if ($current) {
93	$main->{specific} = $current->{specific};
94	}
95		104
96	our $current = $main;
97
98	sub current() { $current }	105	sub current() { $current } # [DEPRECATED]
99		106
100	=item $idle	107	=item $Coro::idle
101		108
102	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
103	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.
104		112
105	=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.
106		117
107	# should be done using priorities :(	118	This hook is overwritten by modules such as C<Coro::Timer> and
108	our $idle = new Coro sub {	119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
109	print STDERR "FATAL: deadlock detected\n";	120	coroutine so the scheduler can run it.
110	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	$idle = sub {
		136	require Carp;
		137	Carp::croak ("FATAL: deadlock detected");
111	};	138	};
		139
		140	sub _cancel {
		141	my ($self) = @_;
		142
		143	# free coroutine data and mark as destructed
		144	$self->_destroy
		145	or return;
		146
		147	# call all destruction callbacks
		148	$_->(@{$self->{_status}})
		149	for @{ delete $self->{_on_destroy} \|\| [] };
		150	}
112		151
113	# this coroutine is necessary because a coroutine	152	# this coroutine is necessary because a coroutine
114	# cannot destroy itself.	153	# cannot destroy itself.
115	my @destroy;	154	our @destroy;
		155	our $manager;
		156
116	my $manager = new Coro sub {	157	$manager = new Coro sub {
117	while() {	158	while () {
118	delete ((pop @destroy)->{_coro_state}) while @destroy;	159	(shift @destroy)->_cancel
		160	while @destroy;
		161
119	&schedule;	162	&schedule;
120	}	163	}
121	};	164	};
		165	$manager->{desc} = "[coro manager]";
		166	$manager->prio (PRIO_MAX);
122		167
123	# we really need priorities...	168	=back
124	my @ready; # the ready queue. hehe, rather broken ;)
125		169
126	# static methods. not really.	170	=head2 SIMPLE COROUTINE CREATION
127
128	=head2 STATIC METHODS
129
130	Static methods are actually functions that operate on the current process only.
131		171
132	=over 4	172	=over 4
133		173
134	=item async { ... } [@args...]	174	=item async { ... } [@args...]
135		175
136	Create a new asynchronous process and return it's process object	176	Create a new coroutine and return it's coroutine object (usually
137	(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
138	terminated.	182	terminated.
139		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
140	# create a new coroutine that just prints its arguments	196	Example: Create a new coroutine that just prints its arguments.
		197
141	async {	198	async {
142	print "@_\n";	199	print "@_\n";
143	} 1,2,3,4;	200	} 1,2,3,4;
144		201
145	The coderef you submit MUST NOT be a closure that refers to variables
146	in an outer scope. This does NOT work. Pass arguments into it instead.
147
148	=cut	202	=cut
149		203
150	sub async(&@) {	204	sub async(&@) {
151	my $pid = new Coro @_;	205	my $coro = new Coro @_;
152	$manager->ready; # this ensures that the stack is cloned from the manager
153	$pid->ready;	206	$coro->ready;
154	$pid;	207	$coro
155	}	208	}
		209
		210	=item async_pool { ... } [@args...]
		211
		212	Similar to C<async>, but uses a coroutine pool, so you should not call
		213	terminate or join on it (although you are allowed to), and you get a
		214	coroutine that might have executed other code already (which can be good
		215	or bad :).
		216
		217	On the plus side, this function is faster than creating (and destroying)
		218	a completly new coroutine, so if you need a lot of generic coroutines in
		219	quick successsion, use C<async_pool>, not C<async>.
		220
		221	The code block is executed in an C<eval> context and a warning will be
		222	issued in case of an exception instead of terminating the program, as
		223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		224	will not work in the expected way, unless you call terminate or cancel,
		225	which somehow defeats the purpose of pooling (but is fine in the
		226	exceptional case).
		227
		228	The priority will be reset to C<0> after each run, tracing will be
		229	disabled, the description will be reset and the default output filehandle
		230	gets restored, so you can change all these. Otherwise the coroutine will
		231	be re-used "as-is": most notably if you change other per-coroutine global
		232	stuff such as C<$/> 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	$coro
		279	}
		280
		281	=back
		282
		283	=head2 STATIC METHODS
		284
		285	Static methods are actually functions that operate on the current coroutine.
		286
		287	=over 4
156		288
157	=item schedule	289	=item schedule
158		290
159	Calls the scheduler. Please note that the current process will not be put	291	Calls the scheduler. The scheduler will find the next coroutine that is
		292	to be run from the ready queue and switches to it. The next coroutine
		293	to be run is simply the one with the highest priority that is longest
		294	in its ready queue. If there is no coroutine ready, it will clal the
		295	C<$Coro::idle> hook.
		296
		297	Please note that the current coroutine will I<not> be put into the ready
160	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
161	never be called again.	299	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		300	thus waking you up.
162		301
163	=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.
164		309
165	my $prev;	310	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
166
167	sub schedule {
168	# should be done using priorities :(
169	($prev, $current) = ($current, shift @ready \|\| $idle);
170	Coro::State::transfer($prev, $current);
171	}
172		311
173	=item cede	312	=item cede
174		313
175	"Cede" to other processes. This function puts the current process into the	314	"Cede" to other coroutines. This function puts the current coroutine into
176	ready queue and calls C<schedule>, which has the effect of giving up the	315	the ready queue and calls C<schedule>, which has the effect of giving
177	current "timeslice" to other coroutines of the same or higher priority.	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.
178		319
179	=cut	320	This function is often called C<yield> in other languages.
180		321
181	sub cede {	322	=item Coro::cede_notself
182	$current->ready;
183	&schedule;
184	}
185		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
186	=item terminate	328	=item terminate [arg...]
187		329
188	Terminates the current process.	330	Terminates the current coroutine with the given status values (see L<cancel>).
189		331
190	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.
191		341
192	=cut	342	=cut
193		343
194	sub terminate {	344	sub terminate {
195	$current->cancel;	345	$current->{_status} = [@_];
196	&schedule;	346	push @destroy, $current;
197	die; # NORETURN	347	$manager->ready;
		348	do { &schedule } while 1;
		349	}
		350
		351	sub killall {
		352	for (Coro::State::list) {
		353	$_->cancel
		354	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		355	}
198	}	356	}
199		357
200	=back	358	=back
201		359
202	# dynamic methods
203
204	=head2 PROCESS METHODS	360	=head2 COROUTINE METHODS
205		361
206	These are the methods you can call on process objects.	362	These are the methods you can call on coroutine objects (or to create
		363	them).
207		364
208	=over 4	365	=over 4
209		366
210	=item new Coro \&sub [, @args...]	367	=item new Coro \&sub [, @args...]
211		368
212	Create a new process and return it. When the sub returns the process	369	Create a new coroutine and return it. When the sub returns, the coroutine
213	automatically terminates. To start the process you must first put it into	370	automatically terminates as if C<terminate> with the returned values were
		371	called. To make the coroutine run you must first put it into the ready
214	the ready queue by calling the ready method.	372	queue by calling the ready method.
215		373
216	The coderef you submit MUST NOT be a closure that refers to variables	374	See C<async> and C<Coro::State::new> for additional info about the
217	in an outer scope. This does NOT work. Pass arguments into it instead.	375	coroutine environment.
218		376
219	=cut	377	=cut
220		378
221	sub _newcoro {	379	sub _terminate {
222	terminate &{+shift};	380	terminate &{+shift};
223	}	381	}
224		382
225	sub new {	383	=item $success = $coroutine->ready
226	my $class = shift;
227	bless {
228	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
229	}, $class;
230	}
231		384
232	=item $process->ready	385	Put the given coroutine into the end of its ready queue (there is one
		386	queue for each priority) and return true. If the coroutine is already in
		387	the ready queue, do nothing and return false.
233		388
234	Put the current process into the ready queue.	389	This ensures that the scheduler will resume this coroutine automatically
		390	once all the coroutines of higher priority and all coroutines of the same
		391	priority that were put into the ready queue earlier have been resumed.
235		392
236	=cut	393	=item $is_ready = $coroutine->is_ready
237		394
238	sub ready {	395	Return whether the coroutine is currently the ready queue or not,
239	push @ready, $_[0];
240	}
241		396
242	=item $process->cancel	397	=item $coroutine->cancel (arg...)
243		398
244	Like C<terminate>, but terminates the specified process instead.	399	Terminates the given coroutine and makes it return the given arguments as
		400	status (default: the empty list). Never returns if the coroutine is the
		401	current coroutine.
245		402
246	=cut	403	=cut
247		404
248	sub cancel {	405	sub cancel {
249	push @destroy, $_[0];	406	my $self = shift;
250	$manager->ready;	407
		408	if ($current == $self) {
		409	terminate @_;
		410	} else {
		411	$self->{_status} = [@_];
		412	$self->_cancel;
		413	}
		414	}
		415
		416	=item $coroutine->throw ([$scalar])
		417
		418	If C<$throw> is specified and defined, it will be thrown as an exception
		419	inside the coroutine at the next convenient point in time. Otherwise
		420	clears the exception object.
		421
		422	Coro will check for the exception each time a schedule-like-function
		423	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		424	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		425	detect this case and return early in case an exception is pending.
		426
		427	The exception object will be thrown "as is" with the specified scalar in
		428	C<$@>, i.e. if it is a string, no line number or newline will be appended
		429	(unlike with C<die>).
		430
		431	This can be used as a softer means than C<cancel> to ask a coroutine to
		432	end itself, although there is no guarantee that the exception will lead to
		433	termination, and if the exception isn't caught it might well end the whole
		434	program.
		435
		436	You might also think of C<throw> as being the moral equivalent of
		437	C<kill>ing a coroutine with a signal (in this case, a scalar).
		438
		439	=item $coroutine->join
		440
		441	Wait until the coroutine terminates and return any values given to the
		442	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		443	from multiple coroutines, and all will be resumed and given the status
		444	return once the C<$coroutine> terminates.
		445
		446	=cut
		447
		448	sub join {
		449	my $self = shift;
		450
		451	unless ($self->{_status}) {
		452	my $current = $current;
		453
		454	push @{$self->{_on_destroy}}, sub {
		455	$current->ready;
		456	undef $current;
		457	};
		458
		459	&schedule while $current;
		460	}
		461
		462	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		463	}
		464
		465	=item $coroutine->on_destroy (\&cb)
		466
		467	Registers a callback that is called when this coroutine gets destroyed,
		468	but before it is joined. The callback gets passed the terminate arguments,
		469	if any, and I<must not> die, under any circumstances.
		470
		471	=cut
		472
		473	sub on_destroy {
		474	my ($self, $cb) = @_;
		475
		476	push @{ $self->{_on_destroy} }, $cb;
		477	}
		478
		479	=item $oldprio = $coroutine->prio ($newprio)
		480
		481	Sets (or gets, if the argument is missing) the priority of the
		482	coroutine. Higher priority coroutines get run before lower priority
		483	coroutines. Priorities are small signed integers (currently -4 .. +3),
		484	that you can refer to using PRIO_xxx constants (use the import tag :prio
		485	to get then):
		486
		487	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		488	3 > 1 > 0 > -1 > -3 > -4
		489
		490	# set priority to HIGH
		491	current->prio(PRIO_HIGH);
		492
		493	The idle coroutine ($Coro::idle) always has a lower priority than any
		494	existing coroutine.
		495
		496	Changing the priority of the current coroutine will take effect immediately,
		497	but changing the priority of coroutines in the ready queue (but not
		498	running) will only take effect after the next schedule (of that
		499	coroutine). This is a bug that will be fixed in some future version.
		500
		501	=item $newprio = $coroutine->nice ($change)
		502
		503	Similar to C<prio>, but subtract the given value from the priority (i.e.
		504	higher values mean lower priority, just as in unix).
		505
		506	=item $olddesc = $coroutine->desc ($newdesc)
		507
		508	Sets (or gets in case the argument is missing) the description for this
		509	coroutine. This is just a free-form string you can associate with a
		510	coroutine.
		511
		512	This method simply sets the C<< $coroutine->{desc} >> member to the given
		513	string. You can modify this member directly if you wish.
		514
		515	=cut
		516
		517	sub desc {
		518	my $old = $_[0]{desc};
		519	$_[0]{desc} = $_[1] if @_ > 1;
		520	$old;
251	}	521	}
252		522
253	=back	523	=back
254		524
		525	=head2 GLOBAL FUNCTIONS
		526
		527	=over 4
		528
		529	=item Coro::nready
		530
		531	Returns the number of coroutines that are currently in the ready state,
		532	i.e. that can be switched to by calling C<schedule> directory or
		533	indirectly. The value C<0> means that the only runnable coroutine is the
		534	currently running one, so C<cede> would have no effect, and C<schedule>
		535	would cause a deadlock unless there is an idle handler that wakes up some
		536	coroutines.
		537
		538	=item my $guard = Coro::guard { ... }
		539
		540	This creates and returns a guard object. Nothing happens until the object
		541	gets destroyed, in which case the codeblock given as argument will be
		542	executed. This is useful to free locks or other resources in case of a
		543	runtime error or when the coroutine gets canceled, as in both cases the
		544	guard block will be executed. The guard object supports only one method,
		545	C<< ->cancel >>, which will keep the codeblock from being executed.
		546
		547	Example: set some flag and clear it again when the coroutine gets canceled
		548	or the function returns:
		549
		550	sub do_something {
		551	my $guard = Coro::guard { $busy = 0 };
		552	$busy = 1;
		553
		554	# do something that requires $busy to be true
		555	}
		556
		557	=cut
		558
		559	sub guard(&) {
		560	bless \(my $cb = $_[0]), "Coro::guard"
		561	}
		562
		563	sub Coro::guard::cancel {
		564	${$_[0]} = sub { };
		565	}
		566
		567	sub Coro::guard::DESTROY {
		568	${$_[0]}->();
		569	}
		570
		571
		572	=item unblock_sub { ... }
		573
		574	This utility function takes a BLOCK or code reference and "unblocks" it,
		575	returning a new coderef. Unblocking means that calling the new coderef
		576	will return immediately without blocking, returning nothing, while the
		577	original code ref will be called (with parameters) from within another
		578	coroutine.
		579
		580	The reason this function exists is that many event libraries (such as the
		581	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		582	of thread-safety). This means you must not block within event callbacks,
		583	otherwise you might suffer from crashes or worse. The only event library
		584	currently known that is safe to use without C<unblock_sub> is L<EV>.
		585
		586	This function allows your callbacks to block by executing them in another
		587	coroutine where it is safe to block. One example where blocking is handy
		588	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		589	disk, for example.
		590
		591	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		592	creating event callbacks that want to block.
		593
		594	If your handler does not plan to block (e.g. simply sends a message to
		595	another coroutine, or puts some other coroutine into the ready queue),
		596	there is no reason to use C<unblock_sub>.
		597
		598	Note that you also need to use C<unblock_sub> for any other callbacks that
		599	are indirectly executed by any C-based event loop. For example, when you
		600	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		601	provides callbacks that are the result of some event callback, then you
		602	must not block either, or use C<unblock_sub>.
		603
		604	=cut
		605
		606	our @unblock_queue;
		607
		608	# we create a special coro because we want to cede,
		609	# to reduce pressure on the coro pool (because most callbacks
		610	# return immediately and can be reused) and because we cannot cede
		611	# inside an event callback.
		612	our $unblock_scheduler = new Coro sub {
		613	while () {
		614	while (my $cb = pop @unblock_queue) {
		615	# this is an inlined copy of async_pool
		616	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
		617
		618	$coro->{_invoke} = $cb;
		619	$coro->ready;
		620	cede; # for short-lived callbacks, this reduces pressure on the coro pool
		621	}
		622	schedule; # sleep well
		623	}
		624	};
		625	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		626
		627	sub unblock_sub(&) {
		628	my $cb = shift;
		629
		630	sub {
		631	unshift @unblock_queue, [$cb, @_];
		632	$unblock_scheduler->ready;
		633	}
		634	}
		635
		636	=item $cb = Coro::rouse_cb
		637
		638	Create and return a "rouse callback". That's a code reference that, when
		639	called, will save its arguments and notify the owner coroutine of the
		640	callback.
		641
		642	See the next function.
		643
		644	=item @args = Coro::rouse_wait [$cb]
		645
		646	Wait for the specified rouse callback (or the last one tht was created in
		647	this coroutine).
		648
		649	As soon as the callback is invoked (or when the calback was invoked before
		650	C<rouse_wait>), it will return a copy of the arguments originally passed
		651	to the rouse callback.
		652
		653	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		654
		655	=back
		656
255	=cut	657	=cut
256		658
257	1;	659	1;
258		660
		661	=head1 HOW TO WAIT FOR A CALLBACK
		662
		663	It is very common for a coroutine to wait for some callback to be
		664	called. This occurs naturally when you use coroutines in an otherwise
		665	event-based program, or when you use event-based libraries.
		666
		667	These typically register a callback for some event, and call that callback
		668	when the event occured. In a coroutine, however, you typically want to
		669	just wait for the event, simplyifying things.
		670
		671	For example C<< AnyEvent->child >> registers a callback to be called when
		672	a specific child has exited:
		673
		674	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		675
		676	But from withina coroutine, you often just want to write this:
		677
		678	my $status = wait_for_child $pid;
		679
		680	Coro offers two functions specifically designed to make this easy,
		681	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		682
		683	The first function, C<rouse_cb>, generates and returns a callback that,
		684	when invoked, will save it's arguments and notify the coroutine that
		685	created the callback.
		686
		687	The second function, C<rouse_wait>, waits for the callback to be called
		688	(by calling C<schedule> to go to sleep) and returns the arguments
		689	originally passed to the callback.
		690
		691	Using these functions, it becomes easy to write the C<wait_for_child>
		692	function mentioned above:
		693
		694	sub wait_for_child($) {
		695	my ($pid) = @_;
		696
		697	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		698
		699	my ($rpid, $rstatus) = Coro::rouse_wait;
		700	$rstatus
		701	}
		702
		703	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		704	you can roll your own, using C<schedule>:
		705
		706	sub wait_for_child($) {
		707	my ($pid) = @_;
		708
		709	# store the current coroutine in $current,
		710	# and provide result variables for the closure passed to ->child
		711	my $current = $Coro::current;
		712	my ($done, $rstatus);
		713
		714	# pass a closure to ->child
		715	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		716	$rstatus = $_[1]; # remember rstatus
		717	$done = 1; # mark $rstatus as valud
		718	});
		719
		720	# wait until the closure has been called
		721	schedule while !$done;
		722
		723	$rstatus
		724	}
		725
		726
259	=head1 BUGS/LIMITATIONS	727	=head1 BUGS/LIMITATIONS
260		728
261	- could be faster, especially when the core would introduce special	729	=over 4
262	support for coroutines (like it does for threads).	730
263	- there is still a memleak on coroutine termination that I could not	731	=item fork with pthread backend
264	identify. Could be as small as a single SV.	732
265	- this module is not well-tested.	733	When Coro is compiled using the pthread backend (which isn't recommended
266	- if variables or arguments "disappear" (become undef) or become	734	but required on many BSDs as their libcs are completely broken), then
267	corrupted please contact the author so he cen iron out the	735	coroutines will not survive a fork. There is no known workaround except to
268	remaining bugs.	736	fix your libc and use a saner backend.
269	- this module is not thread-safe. You must only ever use this module from	737
		738	=item perl process emulation ("threads")
		739
		740	This module is not perl-pseudo-thread-safe. You should only ever use this
270	the same thread (this requirement might be loosened in the future to	741	module from the same thread (this requirement might be removed in the
271	allow per-thread schedulers, but Coro::State does not yet allow this).	742	future to allow per-thread schedulers, but Coro::State does not yet allow
		743	this). I recommend disabling thread support and using processes, as having
		744	the windows process emulation enabled under unix roughly halves perl
		745	performance, even when not used.
		746
		747	=item coroutine switching not signal safe
		748
		749	You must not switch to another coroutine from within a signal handler
		750	(only relevant with %SIG - most event libraries provide safe signals).
		751
		752	That means you I<MUST NOT> call any function that might "block" the
		753	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		754	anything that calls those. Everything else, including calling C<ready>,
		755	works.
		756
		757	=back
		758
272		759
273	=head1 SEE ALSO	760	=head1 SEE ALSO
274		761
275	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	762	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
276	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>, L<Coro::RWLock>,	763
277	L<Coro::Handle>, L<Coro::Socket>.	764	Debugging: L<Coro::Debug>.
		765
		766	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		767
		768	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		769
		770	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		771
		772	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
		773
		774	XS API: L<Coro::MakeMaker>.
		775
		776	Low level Configuration, Coroutine Environment: L<Coro::State>.
278		777
279	=head1 AUTHOR	778	=head1 AUTHOR
280		779
281	Marc Lehmann <pcg@goof.com>	780	Marc Lehmann <schmorp@schmorp.de>
282	http://www.goof.com/pcg/marc/	781	http://home.schmorp.de/
283		782
284	=cut	783	=cut
285		784

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Revision 1.226 by root, Wed Nov 19 16:01:32 2008 UTC