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

Comparing Coro/Coro.pm (file contents):
Revision 1.37 by root, Mon Sep 24 02:25:44 2001 UTC vs.
Revision 1.227 by root, Thu Nov 20 03:10:30 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);
37	no warnings qw(uninitialized);	62	no warnings "uninitialized";
38		63
39	use Coro::State;	64	use Coro::State;
40		65
41	use base Exporter;	66	use base qw(Coro::State Exporter);
42		67
		68	our $idle; # idle handler
		69	our $main; # main coroutine
		70	our $current; # current coroutine
		71
43	$VERSION = 0.5;	72	our $VERSION = 5.0;
44		73
45	@EXPORT = qw(async cede schedule terminate current);	74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
46	%EXPORT_TAGS = (	75	our %EXPORT_TAGS = (
47	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
48	);	77	);
49	@EXPORT_OK = @{$EXPORT_TAGS{prio}};	78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
50		79
51	{	80	=over 4
52	my @async;
53	my $init;
54		81
55	# this way of handling attributes simply is NOT scalable ;()
56	sub import {
57	Coro->export_to_level(1, @_);
58	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
59	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
60	my ($package, $ref) = (shift, shift);
61	my @attrs;
62	for (@_) {
63	if ($_ eq "Coro") {
64	push @async, $ref;
65	unless ($init++) {
66	eval q{
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	};
71	}
72	} else {
73	push @attrs, $_;
74	}
75	}
76	return $old ? $old->($package, $ref, @attrs) : @attrs;
77	};
78	}
79
80	}
81
82	=item $main	82	=item $Coro::main
83		83
84	This coroutine represents the main program.	84	This variable stores the coroutine object that represents the main
		85	program. While you cna C<ready> it and do most other things you can do to
		86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see
		87	whether you are running in the main program or not.
85		88
86	=cut	89	=cut
87		90
88	our $main = new Coro;	91	# $main is now being initialised by Coro::State
89		92
90	=item $current (or as function: current)	93	=item $Coro::current
91		94
92	The current coroutine (the last coroutine switched to). The initial value is C<$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<$Coro::main> (of course).
93		98
94	=cut	99	This variable is B<strictly> I<read-only>. You can take copies of the
		100	value stored in it and use it as any other coroutine object, but you must
		101	not otherwise modify the variable itself.
95		102
96	# maybe some other module used Coro::Specific before...	103	=cut
97	if ($current) {
98	$main->{specific} = $current->{specific};
99	}
100		104
101	our $current = $main;
102
103	sub current() { $current }	105	sub current() { $current } # [DEPRECATED]
104		106
105	=item $idle	107	=item $Coro::idle
106		108
107	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
108	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.
109		112
110	=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.
111		117
112	# should be done using priorities :(	118	This hook is overwritten by modules such as C<Coro::Timer> and
113	our $idle = new Coro sub {	119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
114	print STDERR "FATAL: deadlock detected\n";	120	coroutine so the scheduler can run it.
115	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	$idle = sub {
		136	require Carp;
		137	Carp::croak ("FATAL: deadlock detected");
116	};	138	};
		139
		140	sub _cancel {
		141	my ($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	}
117		151
118	# this coroutine is necessary because a coroutine	152	# this coroutine is necessary because a coroutine
119	# cannot destroy itself.	153	# cannot destroy itself.
120	my @destroy;	154	our @destroy;
		155	our $manager;
		156
121	my $manager = new Coro sub {	157	$manager = new Coro sub {
122	while() {	158	while () {
123	# by overwriting the state object with the manager we destroy it	159	(shift @destroy)->_cancel
124	# while still being able to schedule this coroutine (in case it has	160	while @destroy;
125	# been readied multiple times. this is harmless since the manager	161
126	# can be called as many times as neccessary and will always
127	# remove itself from the runqueue
128	(pop @destroy)->{_coro_state} = $manager->{_coro_state} while @destroy;
129	&schedule;	162	&schedule;
130	}	163	}
131	};	164	};
		165	$manager->{desc} = "[coro manager]";
		166	$manager->prio (PRIO_MAX);
132		167
133	# static methods. not really.	168	=back
134		169
135	=head2 STATIC METHODS	170	=head2 SIMPLE COROUTINE CREATION
136
137	Static methods are actually functions that operate on the current process only.
138		171
139	=over 4	172	=over 4
140		173
141	=item async { ... } [@args...]	174	=item async { ... } [@args...]
142		175
143	Create a new asynchronous process and return it's process object	176	Create a new coroutine and return it's coroutine object (usually
144	(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
145	terminated.	182	terminated.
146		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
147	# create a new coroutine that just prints its arguments	196	Example: Create a new coroutine that just prints its arguments.
		197
148	async {	198	async {
149	print "@_\n";	199	print "@_\n";
150	} 1,2,3,4;	200	} 1,2,3,4;
151		201
152	The coderef you submit MUST NOT be a closure that refers to variables
153	in an outer scope. This does NOT work. Pass arguments into it instead.
154
155	=cut	202	=cut
156		203
157	sub async(&@) {	204	sub async(&@) {
158	my $pid = new Coro @_;	205	my $coro = new Coro @_;
159	$manager->ready; # this ensures that the stack is cloned from the manager
160	$pid->ready;	206	$coro->ready;
161	$pid;	207	$coro
162	}	208	}
		209
		210	=item async_pool { ... } [@args...]
		211
		212	Similar to C<async>, but uses a coroutine pool, so you should not call
		213	terminate or join on it (although you are allowed to), and you get a
		214	coroutine that might have executed other code already (which can be good
		215	or bad :).
		216
		217	On the plus side, this function is faster than creating (and destroying)
		218	a completly new coroutine, so if you need a lot of generic coroutines in
		219	quick successsion, use C<async_pool>, not C<async>.
		220
		221	The code block is executed in an C<eval> context and a warning will be
		222	issued in case of an exception instead of terminating the program, as
		223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		224	will not work in the expected way, unless you call terminate or cancel,
		225	which somehow defeats the purpose of pooling (but is fine in the
		226	exceptional case).
		227
		228	The priority will be reset to C<0> after each run, tracing will be
		229	disabled, the description will be reset and the default output filehandle
		230	gets restored, so you can change all these. Otherwise the coroutine will
		231	be re-used "as-is": most notably if you change other per-coroutine global
		232	stuff such as C<$/> 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	while () {
		253	eval {
		254	&{&_pool_handler} while 1;
		255	};
		256
		257	warn $@ if $@;
		258	}
		259	}
		260
		261	=back
		262
		263	=head2 STATIC METHODS
		264
		265	Static methods are actually functions that operate on the current coroutine.
		266
		267	=over 4
163		268
164	=item schedule	269	=item schedule
165		270
166	Calls the scheduler. Please note that the current process will not be put	271	Calls the scheduler. The scheduler will find the next coroutine that is
		272	to be run from the ready queue and switches to it. The next coroutine
		273	to be run is simply the one with the highest priority that is longest
		274	in its ready queue. If there is no coroutine ready, it will clal the
		275	C<$Coro::idle> hook.
		276
		277	Please note that the current coroutine will I<not> be put into the ready
167	into the ready queue, so calling this function usually means you will	278	queue, so calling this function usually means you will never be called
168	never be called again.	279	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		280	thus waking you up.
169		281
170	=cut	282	This makes C<schedule> I<the> generic method to use to block the current
		283	coroutine and wait for events: first you remember the current coroutine in
		284	a variable, then arrange for some callback of yours to call C<< ->ready
		285	>> on that once some event happens, and last you call C<schedule> to put
		286	yourself to sleep. Note that a lot of things can wake your coroutine up,
		287	so you need to check whether the event indeed happened, e.g. by storing the
		288	status in a variable.
		289
		290	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
171		291
172	=item cede	292	=item cede
173		293
174	"Cede" to other processes. This function puts the current process into the	294	"Cede" to other coroutines. This function puts the current coroutine into
175	ready queue and calls C<schedule>, which has the effect of giving up the	295	the ready queue and calls C<schedule>, which has the effect of giving
176	current "timeslice" to other coroutines of the same or higher priority.	296	up the current "timeslice" to other coroutines of the same or higher
		297	priority. Once your coroutine gets its turn again it will automatically be
		298	resumed.
177		299
178	=cut	300	This function is often called C<yield> in other languages.
179		301
		302	=item Coro::cede_notself
		303
		304	Works like cede, but is not exported by default and will cede to I<any>
		305	coroutine, regardless of priority. This is useful sometimes to ensure
		306	progress is made.
		307
180	=item terminate	308	=item terminate [arg...]
181		309
182	Terminates the current process.	310	Terminates the current coroutine with the given status values (see L<cancel>).
183		311
184	Future versions of this function will allow result arguments.	312	=item killall
		313
		314	Kills/terminates/cancels all coroutines except the currently running
		315	one. This is useful after a fork, either in the child or the parent, as
		316	usually only one of them should inherit the running coroutines.
		317
		318	Note that while this will try to free some of the main programs resources,
		319	you cannot free all of them, so if a coroutine that is not the main
		320	program calls this function, there will be some one-time resource leak.
185		321
186	=cut	322	=cut
187		323
188	sub terminate {	324	sub terminate {
189	$current->cancel;	325	$current->{_status} = [@_];
190	&schedule;	326	push @destroy, $current;
191	die; # NORETURN	327	$manager->ready;
		328	do { &schedule } while 1;
		329	}
		330
		331	sub killall {
		332	for (Coro::State::list) {
		333	$_->cancel
		334	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		335	}
192	}	336	}
193		337
194	=back	338	=back
195		339
196	# dynamic methods
197
198	=head2 PROCESS METHODS	340	=head2 COROUTINE METHODS
199		341
200	These are the methods you can call on process objects.	342	These are the methods you can call on coroutine objects (or to create
		343	them).
201		344
202	=over 4	345	=over 4
203		346
204	=item new Coro \&sub [, @args...]	347	=item new Coro \&sub [, @args...]
205		348
206	Create a new process and return it. When the sub returns the process	349	Create a new coroutine and return it. When the sub returns, the coroutine
207	automatically terminates. To start the process you must first put it into	350	automatically terminates as if C<terminate> with the returned values were
		351	called. To make the coroutine run you must first put it into the ready
208	the ready queue by calling the ready method.	352	queue by calling the ready method.
209		353
210	The coderef you submit MUST NOT be a closure that refers to variables	354	See C<async> and C<Coro::State::new> for additional info about the
211	in an outer scope. This does NOT work. Pass arguments into it instead.	355	coroutine environment.
212		356
213	=cut	357	=cut
214		358
215	sub _newcoro {	359	sub _terminate {
216	terminate &{+shift};	360	terminate &{+shift};
217	}	361	}
218		362
219	sub new {	363	=item $success = $coroutine->ready
220	my $class = shift;
221	bless {
222	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
223	}, $class;
224	}
225		364
226	=item $process->ready	365	Put the given coroutine into the end of its ready queue (there is one
		366	queue for each priority) and return true. If the coroutine is already in
		367	the ready queue, do nothing and return false.
227		368
228	Put the current process into the ready queue.	369	This ensures that the scheduler will resume this coroutine automatically
		370	once all the coroutines of higher priority and all coroutines of the same
		371	priority that were put into the ready queue earlier have been resumed.
229		372
230	=cut	373	=item $is_ready = $coroutine->is_ready
231		374
232	=item $process->cancel	375	Return whether the coroutine is currently the ready queue or not,
233		376
234	Like C<terminate>, but terminates the specified process instead.	377	=item $coroutine->cancel (arg...)
		378
		379	Terminates the given coroutine and makes it return the given arguments as
		380	status (default: the empty list). Never returns if the coroutine is the
		381	current coroutine.
235		382
236	=cut	383	=cut
237		384
238	sub cancel {	385	sub cancel {
239	push @destroy, $_[0];	386	my $self = shift;
240	$manager->ready;
241	&schedule if $current == $_[0];
242	}
243		387
		388	if ($current == $self) {
		389	terminate @_;
		390	} else {
		391	$self->{_status} = [@_];
		392	$self->_cancel;
		393	}
		394	}
		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
244	=item $oldprio = $process->prio($newprio)	459	=item $oldprio = $coroutine->prio ($newprio)
245		460
246	Sets the priority of the process. Higher priority processes get run before	461	Sets (or gets, if the argument is missing) the priority of the
247	lower priority processes. Priorities are smalled signed integer (currently	462	coroutine. Higher priority coroutines get run before lower priority
		463	coroutines. Priorities are small signed integers (currently -4 .. +3),
248	-4 .. +3), that you can refer to using PRIO_xxx constants (use the import	464	that you can refer to using PRIO_xxx constants (use the import tag :prio
249	tag :prio to get then):	465	to get then):
250		466
251	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	467	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
252	3 > 1 > 0 > -1 > -3 > -4	468	3 > 1 > 0 > -1 > -3 > -4
253		469
254	# set priority to HIGH	470	# set priority to HIGH
255	current->prio(PRIO_HIGH);	471	current->prio(PRIO_HIGH);
256		472
257	The idle coroutine ($Coro::idle) always has a lower priority than any	473	The idle coroutine ($Coro::idle) always has a lower priority than any
258	existing coroutine.	474	existing coroutine.
259		475
260	Changing the priority of the current process will take effect immediately,	476	Changing the priority of the current coroutine will take effect immediately,
261	but changing the priority of processes in the ready queue (but not	477	but changing the priority of coroutines in the ready queue (but not
262	running) will only take effect after the next schedule (of that	478	running) will only take effect after the next schedule (of that
263	process). This is a bug that will be fixed in some future version.	479	coroutine). This is a bug that will be fixed in some future version.
264		480
265	=cut
266
267	sub prio {
268	my $old = $_[0]{prio};
269	$_[0]{prio} = $_[1] if @_ > 1;
270	$old;
271	}
272
273	=item $newprio = $process->nice($change)	481	=item $newprio = $coroutine->nice ($change)
274		482
275	Similar to C<prio>, but subtract the given value from the priority (i.e.	483	Similar to C<prio>, but subtract the given value from the priority (i.e.
276	higher values mean lower priority, just as in unix).	484	higher values mean lower priority, just as in unix).
277		485
278	=cut	486	=item $olddesc = $coroutine->desc ($newdesc)
279		487
280	sub nice {	488	Sets (or gets in case the argument is missing) the description for this
281	$_[0]{prio} -= $_[1];	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;
282	}	501	}
283		502
284	=back	503	=back
285		504
		505	=head2 GLOBAL FUNCTIONS
		506
		507	=over 4
		508
		509	=item Coro::nready
		510
		511	Returns the number of coroutines that are currently in the ready state,
		512	i.e. that can be switched to by calling C<schedule> directory or
		513	indirectly. The value C<0> means that the only runnable coroutine is the
		514	currently running one, so C<cede> would have no effect, and C<schedule>
		515	would cause a deadlock unless there is an idle handler that wakes up some
		516	coroutines.
		517
		518	=item my $guard = Coro::guard { ... }
		519
		520	This creates and returns a guard object. Nothing happens until the object
		521	gets destroyed, in which case the codeblock given as argument will be
		522	executed. This is useful to free locks or other resources in case of a
		523	runtime error or when the coroutine gets canceled, as in both cases the
		524	guard block will be executed. The guard object supports only one method,
		525	C<< ->cancel >>, which will keep the codeblock from being executed.
		526
		527	Example: set some flag and clear it again when the coroutine gets canceled
		528	or the function returns:
		529
		530	sub do_something {
		531	my $guard = Coro::guard { $busy = 0 };
		532	$busy = 1;
		533
		534	# do something that requires $busy to be true
		535	}
		536
		537	=cut
		538
		539	sub guard(&) {
		540	bless \(my $cb = $_[0]), "Coro::guard"
		541	}
		542
		543	sub Coro::guard::cancel {
		544	${$_[0]} = sub { };
		545	}
		546
		547	sub Coro::guard::DESTROY {
		548	${$_[0]}->();
		549	}
		550
		551
		552	=item unblock_sub { ... }
		553
		554	This utility function takes a BLOCK or code reference and "unblocks" it,
		555	returning a new coderef. Unblocking means that calling the new coderef
		556	will return immediately without blocking, returning nothing, while the
		557	original code ref will be called (with parameters) from within another
		558	coroutine.
		559
		560	The reason this function exists is that many event libraries (such as the
		561	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		562	of thread-safety). This means you must not block within event callbacks,
		563	otherwise you might suffer from crashes or worse. The only event library
		564	currently known that is safe to use without C<unblock_sub> is L<EV>.
		565
		566	This function allows your callbacks to block by executing them in another
		567	coroutine where it is safe to block. One example where blocking is handy
		568	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		569	disk, for example.
		570
		571	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		572	creating event callbacks that want to block.
		573
		574	If your handler does not plan to block (e.g. simply sends a message to
		575	another coroutine, or puts some other coroutine into the ready queue),
		576	there is no reason to use C<unblock_sub>.
		577
		578	Note that you also need to use C<unblock_sub> for any other callbacks that
		579	are indirectly executed by any C-based event loop. For example, when you
		580	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		581	provides callbacks that are the result of some event callback, then you
		582	must not block either, or use C<unblock_sub>.
		583
		584	=cut
		585
		586	our @unblock_queue;
		587
		588	# we create a special coro because we want to cede,
		589	# to reduce pressure on the coro pool (because most callbacks
		590	# return immediately and can be reused) and because we cannot cede
		591	# inside an event callback.
		592	our $unblock_scheduler = new Coro sub {
		593	while () {
		594	while (my $cb = pop @unblock_queue) {
		595	&async_pool (@$cb);
		596
		597	# for short-lived callbacks, this reduces pressure on the coro pool
		598	# as the chance is very high that the async_poll coro will be back
		599	# in the idle state when cede returns
		600	cede;
		601	}
		602	schedule; # sleep well
		603	}
		604	};
		605	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		606
		607	sub unblock_sub(&) {
		608	my $cb = shift;
		609
		610	sub {
		611	unshift @unblock_queue, [$cb, @_];
		612	$unblock_scheduler->ready;
		613	}
		614	}
		615
		616	=item $cb = Coro::rouse_cb
		617
		618	Create and return a "rouse callback". That's a code reference that, when
		619	called, will save its arguments and notify the owner coroutine of the
		620	callback.
		621
		622	See the next function.
		623
		624	=item @args = Coro::rouse_wait [$cb]
		625
		626	Wait for the specified rouse callback (or the last one tht was created in
		627	this coroutine).
		628
		629	As soon as the callback is invoked (or when the calback was invoked before
		630	C<rouse_wait>), it will return a copy of the arguments originally passed
		631	to the rouse callback.
		632
		633	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		634
		635	=back
		636
286	=cut	637	=cut
287		638
288	1;	639	1;
289		640
		641	=head1 HOW TO WAIT FOR A CALLBACK
		642
		643	It is very common for a coroutine to wait for some callback to be
		644	called. This occurs naturally when you use coroutines in an otherwise
		645	event-based program, or when you use event-based libraries.
		646
		647	These typically register a callback for some event, and call that callback
		648	when the event occured. In a coroutine, however, you typically want to
		649	just wait for the event, simplyifying things.
		650
		651	For example C<< AnyEvent->child >> registers a callback to be called when
		652	a specific child has exited:
		653
		654	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		655
		656	But from withina coroutine, you often just want to write this:
		657
		658	my $status = wait_for_child $pid;
		659
		660	Coro offers two functions specifically designed to make this easy,
		661	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		662
		663	The first function, C<rouse_cb>, generates and returns a callback that,
		664	when invoked, will save it's arguments and notify the coroutine that
		665	created the callback.
		666
		667	The second function, C<rouse_wait>, waits for the callback to be called
		668	(by calling C<schedule> to go to sleep) and returns the arguments
		669	originally passed to the callback.
		670
		671	Using these functions, it becomes easy to write the C<wait_for_child>
		672	function mentioned above:
		673
		674	sub wait_for_child($) {
		675	my ($pid) = @_;
		676
		677	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		678
		679	my ($rpid, $rstatus) = Coro::rouse_wait;
		680	$rstatus
		681	}
		682
		683	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		684	you can roll your own, using C<schedule>:
		685
		686	sub wait_for_child($) {
		687	my ($pid) = @_;
		688
		689	# store the current coroutine in $current,
		690	# and provide result variables for the closure passed to ->child
		691	my $current = $Coro::current;
		692	my ($done, $rstatus);
		693
		694	# pass a closure to ->child
		695	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		696	$rstatus = $_[1]; # remember rstatus
		697	$done = 1; # mark $rstatus as valud
		698	});
		699
		700	# wait until the closure has been called
		701	schedule while !$done;
		702
		703	$rstatus
		704	}
		705
		706
290	=head1 BUGS/LIMITATIONS	707	=head1 BUGS/LIMITATIONS
291		708
292	- you must make very sure that no coro is still active on global destruction.	709	=over 4
293	very bad things might happen otherwise (usually segfaults).	710
294	- this module is not thread-safe. You must only ever use this module from	711	=item fork with pthread backend
		712
		713	When Coro is compiled using the pthread backend (which isn't recommended
		714	but required on many BSDs as their libcs are completely broken), then
		715	coroutines will not survive a fork. There is no known workaround except to
		716	fix your libc and use a saner backend.
		717
		718	=item perl process emulation ("threads")
		719
		720	This module is not perl-pseudo-thread-safe. You should only ever use this
295	the same thread (this requirement might be loosened in the future to	721	module from the same thread (this requirement might be removed in the
296	allow per-thread schedulers, but Coro::State does not yet allow this).	722	future to allow per-thread schedulers, but Coro::State does not yet allow
		723	this). I recommend disabling thread support and using processes, as having
		724	the windows process emulation enabled under unix roughly halves perl
		725	performance, even when not used.
		726
		727	=item coroutine switching not signal safe
		728
		729	You must not switch to another coroutine from within a signal handler
		730	(only relevant with %SIG - most event libraries provide safe signals).
		731
		732	That means you I<MUST NOT> call any function that might "block" the
		733	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		734	anything that calls those. Everything else, including calling C<ready>,
		735	works.
		736
		737	=back
		738
297		739
298	=head1 SEE ALSO	740	=head1 SEE ALSO
299		741
300	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	742	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
301	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>, L<Coro::RWLock>,	743
302	L<Coro::Handle>, L<Coro::Socket>.	744	Debugging: L<Coro::Debug>.
		745
		746	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		747
		748	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		749
		750	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		751
		752	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
		753
		754	XS API: L<Coro::MakeMaker>.
		755
		756	Low level Configuration, Coroutine Environment: L<Coro::State>.
303		757
304	=head1 AUTHOR	758	=head1 AUTHOR
305		759
306	Marc Lehmann <pcg@goof.com>	760	Marc Lehmann <schmorp@schmorp.de>
307	http://www.goof.com/pcg/marc/	761	http://home.schmorp.de/
308		762
309	=cut	763	=cut
310		764

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Revision 1.227 by root, Thu Nov 20 03:10:30 2008 UTC