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

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Revision 1.230 by root, Thu Nov 20 07:02:43 2008 UTC vs.
Revision 1.296 by root, Thu May 12 23:24:28 2011 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
11	print "2\n";	11	print "2\n";
12	cede; # yield back to main	12	cede; # yield back to main
13	print "4\n";	13	print "4\n";
14	};	14	};
15	print "1\n";	15	print "1\n";
16	cede; # yield to coroutine	16	cede; # yield to coro
17	print "3\n";	17	print "3\n";
18	cede; # and again	18	cede; # and again
19		19
20	# use locking	20	# use locking
21	use Coro::Semaphore;	21	use Coro::Semaphore;
…		…
26	$locked = 1;	26	$locked = 1;
27	$lock->up;	27	$lock->up;
28		28
29	=head1 DESCRIPTION	29	=head1 DESCRIPTION
30		30
31	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
32	threads but don't (in general) run in parallel at the same time even	32	manpage. This manpage mainly contains reference information.
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		33
39	Unlike a normal perl program, however, coroutines allow you to have	34	This module collection manages continuations in general, most often in
40	multiple running interpreters that share data, which is especially useful	35	the form of cooperative threads (also called coros, or simply "coro"
41	to code pseudo-parallel processes and for event-based programming, such as	36	in the documentation). They are similar to kernel threads but don't (in
42	multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to	37	general) run in parallel at the same time even on SMP machines. The
43	learn more.	38	specific flavor of thread offered by this module also guarantees you that
		39	it will not switch between threads unless necessary, at easily-identified
		40	points in your program, so locking and parallel access are rarely an
		41	issue, making thread programming much safer and easier than using other
		42	thread models.
44		43
45	Coroutines are also useful because Perl has no support for threads (the so	44	Unlike the so-called "Perl threads" (which are not actually real threads
46	called "threads" that perl offers are nothing more than the (bad) process	45	but only the windows process emulation (see section of same name for
47	emulation coming from the Windows platform: On standard operating systems	46	more details) ported to UNIX, and as such act as processes), Coro
48	they serve no purpose whatsoever, except by making your programs slow and	47	provides a full shared address space, which makes communication between
49	making them use a lot of memory. Best disable them when building perl, or	48	threads very easy. And coro threads are fast, too: disabling the Windows
50	aks your software vendor/distributor to do it for you).	49	process emulation code in your perl and using Coro can easily result in
		50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark (very communication-intensive) runs over 300
		52	times faster on a single core than perls pseudo-threads on a quad core
		53	using all four cores.
51		54
		55	Coro achieves that by supporting multiple running interpreters that share
		56	data, which is especially useful to code pseudo-parallel processes and
		57	for event-based programming, such as multiple HTTP-GET requests running
		58	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		59	into an event-based environment.
		60
52	In this module, coroutines are defined as "callchain + lexical variables +	61	In this module, a thread is defined as "callchain + lexical variables +
53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	62	some package variables + C stack), that is, a thread has its own callchain,
54	its own set of lexicals and its own set of perls most important global	63	its own set of lexicals and its own set of perls most important global
55	variables (see L<Coro::State> for more configuration).	64	variables (see L<Coro::State> for more configuration and background info).
		65
		66	See also the C<SEE ALSO> section at the end of this document - the Coro
		67	module family is quite large.
		68
		69	=head1 CORO THREAD LIFE CYCLE
		70
		71	During the long and exciting (or not) life of a coro thread, it goes
		72	through a number of states:
		73
		74	=over 4
		75
		76	=item 1. Creation
		77
		78	The first thing in the life of a coro thread is it's creation -
		79	obviously. The typical way to create a thread is to call the C<async
		80	BLOCK> function:
		81
		82	async {
		83	# thread code goes here
		84	};
		85
		86	You can also pass arguments, which are put in C<@_>:
		87
		88	async {
		89	print $_[1]; # prints 2
		90	} 1, 2, 3;
		91
		92	This creates a new coro thread and puts it into the ready queue, meaning
		93	it will run as soon as the CPU is free for it.
		94
		95	C<async> will return a coro object - you can store this for future
		96	reference or ignore it, the thread itself will keep a reference to it's
		97	thread object - threads are alive on their own.
		98
		99	Another way to create a thread is to call the C<new> constructor with a
		100	code-reference:
		101
		102	new Coro sub {
		103	# thread code goes here
		104	}, @optional_arguments;
		105
		106	This is quite similar to calling C<async>, but the important difference is
		107	that the new thread is not put into the ready queue, so the thread will
		108	not run until somebody puts it there. C<async> is, therefore, identical to
		109	this sequence:
		110
		111	my $coro = new Coro sub {
		112	# thread code goes here
		113	};
		114	$coro->ready;
		115	return $coro;
		116
		117	=item 2. Startup
		118
		119	When a new coro thread is created, only a copy of the code reference
		120	and the arguments are stored, no extra memory for stacks and so on is
		121	allocated, keeping the coro thread in a low-memory state.
		122
		123	Only when it actually starts executing will all the resources be finally
		124	allocated.
		125
		126	The optional arguments specified at coro creation are available in C<@_>,
		127	similar to function calls.
		128
		129	=item 3. Running / Blocking
		130
		131	A lot can happen after the coro thread has started running. Quite usually,
		132	it will not run to the end in one go (because you could use a function
		133	instead), but it will give up the CPU regularly because it waits for
		134	external events.
		135
		136	As long as a coro thread runs, it's coro object is available in the global
		137	variable C<$Coro::current>.
		138
		139	The low-level way to give up the CPU is to call the scheduler, which
		140	selects a new coro thread to run:
		141
		142	Coro::schedule;
		143
		144	Since running threads are not in the ready queue, calling the scheduler
		145	without doing anything else will block the coro thread forever - you need
		146	to arrange either for the coro to put woken up (readied) by some other
		147	event or some other thread, or you can put it into the ready queue before
		148	scheduling:
		149
		150	# this is exactly what Coro::cede does
		151	$Coro::current->ready;
		152	Coro::schedule;
		153
		154	All the higher-level synchronisation methods (Coro::Semaphore,
		155	Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
		156	Coro::schedule >>.
		157
		158	While the coro thread is running it also might get assigned a C-level
		159	thread, or the C-level thread might be unassigned from it, as the Coro
		160	runtime wishes. A C-level thread needs to be assigned when your perl
		161	thread calls into some C-level function and that function in turn calls
		162	perl and perl then wants to switch coroutines. This happens most often
		163	when you run an event loop and block in the callback, or when perl
		164	itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
		165	mechanism.
		166
		167	=item 4. Termination
		168
		169	Many threads actually terminate after some time. There are a number of
		170	ways to terminate a coro thread, the simplest is returning from the
		171	top-level code reference:
		172
		173	async {
		174	# after returning from here, the coro thread is terminated
		175	};
		176
		177	async {
		178	return if 0.5 < rand; # terminate a little earlier, maybe
		179	print "got a chance to print this\n";
		180	# or here
		181	};
		182
		183	Any values returned from the coroutine can be recovered using C<< ->join
		184	>>:
		185
		186	my $coro = async {
		187	"hello, world\n" # return a string
		188	};
		189
		190	my $hello_world = $coro->join;
		191
		192	print $hello_world;
		193
		194	Another way to terminate is to call C<< Coro::terminate >>, which at any
		195	subroutine call nesting level:
		196
		197	async {
		198	Coro::terminate "return value 1", "return value 2";
		199	};
		200
		201	And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
		202	coro thread from another thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # also accepts values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state, and for those cases where you want to do truly marvellous things
		215	with your coro while it is being cancelled - that is, make sure all
		216	cleanup code is executed from the thread being cancelled - there is even a
		217	C<< ->safe_cancel >> method.
		218
		219	So, cancelling a thread that runs in an XS event loop might not be the
		220	best idea, but any other combination that deals with perl only (cancelling
		221	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		222	safe.
		223
		224	=item 5. Cleanup
		225
		226	Threads will allocate various resources. Most but not all will be returned
		227	when a thread terminates, during clean-up.
		228
		229	Cleanup is quite similar to throwing an uncaught exception: perl will
		230	work it's way up through all subroutine calls and blocks. On it's way, it
		231	will release all C<my> variables, undo all C<local>'s and free any other
		232	resources truly local to the thread.
		233
		234	So, a common way to free resources is to keep them referenced only by my
		235	variables:
		236
		237	async {
		238	my $big_cache = new Cache ...;
		239	};
		240
		241	If there are no other references, then the C<$big_cache> object will be
		242	freed when the thread terminates, regardless of how it does so.
		243
		244	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		245	resources, but that's where the C<guard> methods come in handy:
		246
		247	my $sem = new Coro::Semaphore;
		248
		249	async {
		250	my $lock_guard = $sem->guard;
		251	# if we reutrn, or die or get cancelled, here,
		252	# then the semaphore will be "up"ed.
		253	};
		254
		255	The C<Guard::guard> function comes in handy for any custom cleanup you
		256	might want to do:
		257
		258	async {
		259	my $window = new Gtk2::Window "toplevel";
		260	# The window will not be cleaned up automatically, even when $window
		261	# gets freed, so use a guard to ensure it's destruction
		262	# in case of an error:
		263	my $window_guard = Guard::guard { $window->destroy };
		264
		265	# we are safe here
		266	};
		267
		268	Last not least, C<local> can often be handy, too, e.g. when temporarily
		269	replacing the coro thread description:
		270
		271	sub myfunction {
		272	local $Coro::current->{desc} = "inside myfunction(@_)";
		273
		274	# if we return or die here, the description will be restored
		275	}
		276
		277	=item 6. Viva La Zombie Muerte
		278
		279	Even after a thread has terminated and cleaned up it's resources, the coro
		280	object still is there and stores the return values of the thread. Only in
		281	this state will the coro object be "reference counted" in the normal perl
		282	sense: the thread code keeps a reference to it when it is active, but not
		283	after it has terminated.
		284
		285	The means the coro object gets freed automatically when the thread has
		286	terminated and cleaned up and there arenot other references.
		287
		288	If there are, the coro object will stay around, and you can call C<<
		289	->join >> as many times as you wish to retrieve the result values:
		290
		291	async {
		292	print "hi\n";
		293	1
		294	};
		295
		296	# run the async above, and free everything before returning
		297	# from Coro::cede:
		298	Coro::cede;
		299
		300	{
		301	my $coro = async {
		302	print "hi\n";
		303	1
		304	};
		305
		306	# run the async above, and clean up, but do not free the coro
		307	# object:
		308	Coro::cede;
		309
		310	# optionally retrieve the result values
		311	my @results = $coro->join;
		312
		313	# now $coro goes out of scope, and presumably gets freed
		314	};
		315
		316	=back
56		317
57	=cut	318	=cut
58		319
59	package Coro;	320	package Coro;
60		321
61	use strict qw(vars subs);	322	use common::sense;
62	no warnings "uninitialized";	323
		324	use Carp ();
		325
		326	use Guard ();
63		327
64	use Coro::State;	328	use Coro::State;
65		329
66	use base qw(Coro::State Exporter);	330	use base qw(Coro::State Exporter);
67		331
68	our $idle; # idle handler	332	our $idle; # idle handler
69	our $main; # main coroutine	333	our $main; # main coro
70	our $current; # current coroutine	334	our $current; # current coro
71		335
72	our $VERSION = 5.0;	336	our $VERSION = 5.372;
73		337
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	338	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	339	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	340	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	341	);
78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	342	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
79		343
		344	=head1 GLOBAL VARIABLES
		345
80	=over 4	346	=over 4
81		347
82	=item $Coro::main	348	=item $Coro::main
83		349
84	This variable stores the coroutine object that represents the main	350	This variable stores the Coro object that represents the main
85	program. While you cna C<ready> it and do most other things you can do to	351	program. While you cna C<ready> it and do most other things you can do to
86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	352	coro, it is mainly useful to compare again C<$Coro::current>, to see
87	whether you are running in the main program or not.	353	whether you are running in the main program or not.
88		354
89	=cut	355	=cut
90		356
91	# $main is now being initialised by Coro::State	357	# $main is now being initialised by Coro::State
92		358
93	=item $Coro::current	359	=item $Coro::current
94		360
95	The coroutine object representing the current coroutine (the last	361	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	362	coro that the Coro scheduler switched to). The initial value is
97	C<$Coro::main> (of course).	363	C<$Coro::main> (of course).
98		364
99	This variable is B<strictly> I<read-only>. You can take copies of the	365	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	366	value stored in it and use it as any other Coro object, but you must
101	not otherwise modify the variable itself.	367	not otherwise modify the variable itself.
102		368
103	=cut	369	=cut
104		370
105	sub current() { $current } # [DEPRECATED]	371	sub current() { $current } # [DEPRECATED]
106		372
107	=item $Coro::idle	373	=item $Coro::idle
108		374
109	This variable is mainly useful to integrate Coro into event loops. It is	375	This variable is mainly useful to integrate Coro into event loops. It is
110	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is	376	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
111	pretty low-level functionality.	377	pretty low-level functionality.
112		378
113	This variable stores a callback that is called whenever the scheduler	379	This variable stores a Coro object that is put into the ready queue when
114	finds no ready coroutines to run. The default implementation prints	380	there are no other ready threads (without invoking any ready hooks).
115	"FATAL: deadlock detected" and exits, because the program has no other way
116	to continue.
117		381
		382	The default implementation dies with "FATAL: deadlock detected.", followed
		383	by a thread listing, because the program has no other way to continue.
		384
118	This hook is overwritten by modules such as C<Coro::Timer> and	385	This hook is overwritten by modules such as C<Coro::EV> and
119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	386	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
120	coroutine so the scheduler can run it.	387	coro so the scheduler can run it.
121		388
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	389	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
128	technique.
129		390
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	391	=cut
134		392
135	$idle = sub {	393	# \|\|= because other modules could have provided their own by now
136	require Carp;	394	$idle \|\|= new Coro sub {
137	Carp::croak ("FATAL: deadlock detected");	395	require Coro::Debug;
		396	die "FATAL: deadlock detected.\n"
		397	. Coro::Debug::ps_listing ();
138	};	398	};
139		399
140	# this coroutine is necessary because a coroutine	400	# this coro is necessary because a coro
141	# cannot destroy itself.	401	# cannot destroy itself.
142	our @destroy;	402	our @destroy;
143	our $manager;	403	our $manager;
144		404
145	$manager = new Coro sub {	405	$manager = new Coro sub {
146	while () {	406	while () {
147	Coro::_cancel shift @destroy	407	_destroy shift @destroy
148	while @destroy;	408	while @destroy;
149		409
150	&schedule;	410	&schedule;
151	}	411	}
152	};	412	};
153	$manager->{desc} = "[coro manager]";	413	$manager->{desc} = "[coro manager]";
154	$manager->prio (PRIO_MAX);	414	$manager->prio (PRIO_MAX);
155		415
156	=back	416	=back
157		417
158	=head2 SIMPLE COROUTINE CREATION	418	=head1 SIMPLE CORO CREATION
159		419
160	=over 4	420	=over 4
161		421
162	=item async { ... } [@args...]	422	=item async { ... } [@args...]
163		423
164	Create a new coroutine and return it's coroutine object (usually	424	Create a new coro and return its Coro object (usually
165	unused). The coroutine will be put into the ready queue, so	425	unused). The coro will be put into the ready queue, so
166	it will start running automatically on the next scheduler run.	426	it will start running automatically on the next scheduler run.
167		427
168	The first argument is a codeblock/closure that should be executed in the	428	The first argument is a codeblock/closure that should be executed in the
169	coroutine. When it returns argument returns the coroutine is automatically	429	coro. When it returns argument returns the coro is automatically
170	terminated.	430	terminated.
171		431
172	The remaining arguments are passed as arguments to the closure.	432	The remaining arguments are passed as arguments to the closure.
173		433
174	See the C<Coro::State::new> constructor for info about the coroutine	434	See the C<Coro::State::new> constructor for info about the coro
175	environment in which coroutines are executed.	435	environment in which coro are executed.
176		436
177	Calling C<exit> in a coroutine will do the same as calling exit outside	437	Calling C<exit> in a coro will do the same as calling exit outside
178	the coroutine. Likewise, when the coroutine dies, the program will exit,	438	the coro. Likewise, when the coro dies, the program will exit,
179	just as it would in the main program.	439	just as it would in the main program.
180		440
181	If you do not want that, you can provide a default C<die> handler, or	441	If you do not want that, you can provide a default C<die> handler, or
182	simply avoid dieing (by use of C<eval>).	442	simply avoid dieing (by use of C<eval>).
183		443
184	Example: Create a new coroutine that just prints its arguments.	444	Example: Create a new coro that just prints its arguments.
185		445
186	async {	446	async {
187	print "@_\n";	447	print "@_\n";
188	} 1,2,3,4;	448	} 1,2,3,4;
189		449
190	=cut
191
192	sub async(&@) {
193	my $coro = new Coro @_;
194	$coro->ready;
195	$coro
196	}
197
198	=item async_pool { ... } [@args...]	450	=item async_pool { ... } [@args...]
199		451
200	Similar to C<async>, but uses a coroutine pool, so you should not call	452	Similar to C<async>, but uses a coro pool, so you should not call
201	terminate or join on it (although you are allowed to), and you get a	453	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	454	coro that might have executed other code already (which can be good
203	or bad :).	455	or bad :).
204		456
205	On the plus side, this function is about twice as fast as creating (and	457	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	458	destroying) a completely new coro, so if you need a lot of generic
207	coroutines in quick successsion, use C<async_pool>, not C<async>.	459	coros in quick successsion, use C<async_pool>, not C<async>.
208		460
209	The code block is executed in an C<eval> context and a warning will be	461	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	462	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>	463	C<async> does. As the coro is being reused, stuff like C<on_destroy>
212	will not work in the expected way, unless you call terminate or cancel,	464	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	465	which somehow defeats the purpose of pooling (but is fine in the
214	exceptional case).	466	exceptional case).
215		467
216	The priority will be reset to C<0> after each run, tracing will be	468	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	469	disabled, the description will be reset and the default output filehandle
218	gets restored, so you can change all these. Otherwise the coroutine will	470	gets restored, so you can change all these. Otherwise the coro will
219	be re-used "as-is": most notably if you change other per-coroutine global	471	be re-used "as-is": most notably if you change other per-coro global
220	stuff such as C<$/> you I<must needs> revert that change, which is most	472	stuff such as C<$/> you I<must needs> revert that change, which is most
221	simply done by using local as in: C<< local $/ >>.	473	simply done by using local as in: C<< local $/ >>.
222		474
223	The idle pool size is limited to C<8> idle coroutines (this can be	475	The idle pool size is limited to C<8> idle coros (this can be
224	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle	476	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
225	coros as required.	477	coros as required.
226		478
227	If you are concerned about pooled coroutines growing a lot because a	479	If you are concerned about pooled coros growing a lot because a
228	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	480	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	481	{ 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 16kb	482	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.	483	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
232		484
233	=cut	485	=cut
234		486
235	our $POOL_SIZE = 8;	487	our $POOL_SIZE = 8;
236	our $POOL_RSS = 16 * 1024;	488	our $POOL_RSS = 32 * 1024;
237	our @async_pool;	489	our @async_pool;
238		490
239	sub pool_handler {	491	sub pool_handler {
240	while () {	492	while () {
241	eval {	493	eval {
…		…
246	}	498	}
247	}	499	}
248		500
249	=back	501	=back
250		502
251	=head2 STATIC METHODS	503	=head1 STATIC METHODS
252		504
253	Static methods are actually functions that operate on the current coroutine.	505	Static methods are actually functions that implicitly operate on the
		506	current coro.
254		507
255	=over 4	508	=over 4
256		509
257	=item schedule	510	=item schedule
258		511
259	Calls the scheduler. The scheduler will find the next coroutine that is	512	Calls the scheduler. The scheduler will find the next coro that is
260	to be run from the ready queue and switches to it. The next coroutine	513	to be run from the ready queue and switches to it. The next coro
261	to be run is simply the one with the highest priority that is longest	514	to be run is simply the one with the highest priority that is longest
262	in its ready queue. If there is no coroutine ready, it will clal the	515	in its ready queue. If there is no coro ready, it will call the
263	C<$Coro::idle> hook.	516	C<$Coro::idle> hook.
264		517
265	Please note that the current coroutine will I<not> be put into the ready	518	Please note that the current coro will I<not> be put into the ready
266	queue, so calling this function usually means you will never be called	519	queue, so calling this function usually means you will never be called
267	again unless something else (e.g. an event handler) calls C<< ->ready >>,	520	again unless something else (e.g. an event handler) calls C<< ->ready >>,
268	thus waking you up.	521	thus waking you up.
269		522
270	This makes C<schedule> I<the> generic method to use to block the current	523	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	524	coro and wait for events: first you remember the current coro in
272	a variable, then arrange for some callback of yours to call C<< ->ready	525	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	526	>> 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,	527	yourself to sleep. Note that a lot of things can wake your coro up,
275	so you need to check whether the event indeed happened, e.g. by storing the	528	so you need to check whether the event indeed happened, e.g. by storing the
276	status in a variable.	529	status in a variable.
277		530
278	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	531	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
279		532
280	=item cede	533	=item cede
281		534
282	"Cede" to other coroutines. This function puts the current coroutine into	535	"Cede" to other coros. This function puts the current coro into
283	the ready queue and calls C<schedule>, which has the effect of giving	536	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	537	up the current "timeslice" to other coros of the same or higher
285	priority. Once your coroutine gets its turn again it will automatically be	538	priority. Once your coro gets its turn again it will automatically be
286	resumed.	539	resumed.
287		540
288	This function is often called C<yield> in other languages.	541	This function is often called C<yield> in other languages.
289		542
290	=item Coro::cede_notself	543	=item Coro::cede_notself
291		544
292	Works like cede, but is not exported by default and will cede to I<any>	545	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	546	coro, regardless of priority. This is useful sometimes to ensure
294	progress is made.	547	progress is made.
295		548
296	=item terminate [arg...]	549	=item terminate [arg...]
297		550
298	Terminates the current coroutine with the given status values (see L<cancel>).	551	Terminates the current coro with the given status values (see
		552	L<cancel>). The values will not be copied, but referenced directly.
		553
		554	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		555
		556	These function install enter and leave winders in the current scope. The
		557	enter block will be executed when on_enter is called and whenever the
		558	current coro is re-entered by the scheduler, while the leave block is
		559	executed whenever the current coro is blocked by the scheduler, and
		560	also when the containing scope is exited (by whatever means, be it exit,
		561	die, last etc.).
		562
		563	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		564	BLOCKs>. That means: do not even think about calling C<die> without an
		565	eval, and do not even think of entering the scheduler in any way.
		566
		567	Since both BLOCKs are tied to the current scope, they will automatically
		568	be removed when the current scope exits.
		569
		570	These functions implement the same concept as C<dynamic-wind> in scheme
		571	does, and are useful when you want to localise some resource to a specific
		572	coro.
		573
		574	They slow down thread switching considerably for coros that use them
		575	(about 40% for a BLOCK with a single assignment, so thread switching is
		576	still reasonably fast if the handlers are fast).
		577
		578	These functions are best understood by an example: The following function
		579	will change the current timezone to "Antarctica/South_Pole", which
		580	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		581	which remember/change the current timezone and restore the previous
		582	value, respectively, the timezone is only changed for the coro that
		583	installed those handlers.
		584
		585	use POSIX qw(tzset);
		586
		587	async {
		588	my $old_tz; # store outside TZ value here
		589
		590	Coro::on_enter {
		591	$old_tz = $ENV{TZ}; # remember the old value
		592
		593	$ENV{TZ} = "Antarctica/South_Pole";
		594	tzset; # enable new value
		595	};
		596
		597	Coro::on_leave {
		598	$ENV{TZ} = $old_tz;
		599	tzset; # restore old value
		600	};
		601
		602	# at this place, the timezone is Antarctica/South_Pole,
		603	# without disturbing the TZ of any other coro.
		604	};
		605
		606	This can be used to localise about any resource (locale, uid, current
		607	working directory etc.) to a block, despite the existance of other
		608	coros.
		609
		610	Another interesting example implements time-sliced multitasking using
		611	interval timers (this could obviously be optimised, but does the job):
		612
		613	# "timeslice" the given block
		614	sub timeslice(&) {
		615	use Time::HiRes ();
		616
		617	Coro::on_enter {
		618	# on entering the thread, we set an VTALRM handler to cede
		619	$SIG{VTALRM} = sub { cede };
		620	# and then start the interval timer
		621	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		622	};
		623	Coro::on_leave {
		624	# on leaving the thread, we stop the interval timer again
		625	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		626	};
		627
		628	&{+shift};
		629	}
		630
		631	# use like this:
		632	timeslice {
		633	# The following is an endless loop that would normally
		634	# monopolise the process. Since it runs in a timesliced
		635	# environment, it will regularly cede to other threads.
		636	while () { }
		637	};
		638
299		639
300	=item killall	640	=item killall
301		641
302	Kills/terminates/cancels all coroutines except the currently running	642	Kills/terminates/cancels all coros except the currently running one.
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.
305		643
306	Note that while this will try to free some of the main programs resources,	644	Note that while this will try to free some of the main interpreter
		645	resources if the calling coro isn't the main coro, but one
307	you cannot free all of them, so if a coroutine that is not the main	646	cannot free all of them, so if a coro that is not the main coro
308	program calls this function, there will be some one-time resource leak.	647	calls this function, there will be some one-time resource leak.
309		648
310	=cut	649	=cut
311		650
312	sub killall {	651	sub killall {
313	for (Coro::State::list) {	652	for (Coro::State::list) {
…		…
316	}	655	}
317	}	656	}
318		657
319	=back	658	=back
320		659
321	=head2 COROUTINE METHODS	660	=head1 CORO OBJECT METHODS
322		661
323	These are the methods you can call on coroutine objects (or to create	662	These are the methods you can call on coro objects (or to create
324	them).	663	them).
325		664
326	=over 4	665	=over 4
327		666
328	=item new Coro \&sub [, @args...]	667	=item new Coro \&sub [, @args...]
329		668
330	Create a new coroutine and return it. When the sub returns, the coroutine	669	Create a new coro and return it. When the sub returns, the coro
331	automatically terminates as if C<terminate> with the returned values were	670	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	671	called. To make the coro run you must first put it into the ready
333	queue by calling the ready method.	672	queue by calling the ready method.
334		673
335	See C<async> and C<Coro::State::new> for additional info about the	674	See C<async> and C<Coro::State::new> for additional info about the
336	coroutine environment.	675	coro environment.
337		676
338	=cut	677	=cut
339		678
340	sub _terminate {	679	sub _coro_run {
341	terminate &{+shift};	680	terminate &{+shift};
342	}	681	}
343		682
344	=item $success = $coroutine->ready	683	=item $success = $coro->ready
345		684
346	Put the given coroutine into the end of its ready queue (there is one	685	Put the given coro into the end of its ready queue (there is one
347	queue for each priority) and return true. If the coroutine is already in	686	queue for each priority) and return true. If the coro is already in
348	the ready queue, do nothing and return false.	687	the ready queue, do nothing and return false.
349		688
350	This ensures that the scheduler will resume this coroutine automatically	689	This ensures that the scheduler will resume this coro automatically
351	once all the coroutines of higher priority and all coroutines of the same	690	once all the coro of higher priority and all coro of the same
352	priority that were put into the ready queue earlier have been resumed.	691	priority that were put into the ready queue earlier have been resumed.
353		692
		693	=item $coro->suspend
		694
		695	Suspends the specified coro. A suspended coro works just like any other
		696	coro, except that the scheduler will not select a suspended coro for
		697	execution.
		698
		699	Suspending a coro can be useful when you want to keep the coro from
		700	running, but you don't want to destroy it, or when you want to temporarily
		701	freeze a coro (e.g. for debugging) to resume it later.
		702
		703	A scenario for the former would be to suspend all (other) coros after a
		704	fork and keep them alive, so their destructors aren't called, but new
		705	coros can be created.
		706
		707	=item $coro->resume
		708
		709	If the specified coro was suspended, it will be resumed. Note that when
		710	the coro was in the ready queue when it was suspended, it might have been
		711	unreadied by the scheduler, so an activation might have been lost.
		712
		713	To avoid this, it is best to put a suspended coro into the ready queue
		714	unconditionally, as every synchronisation mechanism must protect itself
		715	against spurious wakeups, and the one in the Coro family certainly do
		716	that.
		717
354	=item $is_ready = $coroutine->is_ready	718	=item $is_ready = $coro->is_ready
355		719
356	Return whether the coroutine is currently the ready queue or not,	720	Returns true iff the Coro object is in the ready queue. Unless the Coro
		721	object gets destroyed, it will eventually be scheduled by the scheduler.
357		722
		723	=item $is_running = $coro->is_running
		724
		725	Returns true iff the Coro object is currently running. Only one Coro object
		726	can ever be in the running state (but it currently is possible to have
		727	multiple running Coro::States).
		728
		729	=item $is_suspended = $coro->is_suspended
		730
		731	Returns true iff this Coro object has been suspended. Suspended Coros will
		732	not ever be scheduled.
		733
358	=item $coroutine->cancel (arg...)	734	=item $coro->cancel (arg...)
359		735
360	Terminates the given coroutine and makes it return the given arguments as	736	Terminates the given Coro thread and makes it return the given arguments as
361	status (default: the empty list). Never returns if the coroutine is the	737	status (default: an empty list). Never returns if the Coro is the
362	current coroutine.	738	current Coro.
363		739
364	=cut	740	This is a rather brutal way to free a coro, with some limitations - if
		741	the thread is inside a C callback that doesn't expect to be canceled,
		742	bad things can happen, or if the cancelled thread insists on running
		743	complicated cleanup handlers that rely on it'S thread context, things will
		744	not work.
365		745
366	sub cancel {	746	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
367	my $self = shift;	747	a thread context, and is not allowed to switch to other threads. On the
		748	plus side, C<< ->cancel >> will always clean up the thread, no matter
		749	what. If your cleanup code is complex or you want to avoid cancelling a
		750	C-thread that doesn't know how to clean up itself, it can be better to C<<
		751	->throw >> an exception, or use C<< ->safe_cancel >>.
368		752
369	if ($current == $self) {	753	The arguments to C<< ->cancel >> are not copied, but instead will
370	terminate @_;	754	be referenced directly (e.g. if you pass C<$var> and after the call
371	} else {	755	change that variable, then you might change the return values passed to
372	$self->{_status} = [@_];	756	e.g. C<join>, so don't do that).
373	$self->_cancel;	757
		758	The resources of the Coro are usually freed (or destructed) before this
		759	call returns, but this can be delayed for an indefinite amount of time, as
		760	in some cases the manager thread has to run first to actually destruct the
		761	Coro object.
		762
		763	=item $coro->safe_cancel ($arg...)
		764
		765	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		766	consequently, can fail with an exception in cases the thread is not in a
		767	cancellable state.
		768
		769	This method works a bit like throwing an exception that cannot be caught
		770	- specifically, it will clean up the thread from within itself, so
		771	all cleanup handlers (e.g. C<guard> blocks) are run with full thread
		772	context and can block if they wish. The downside is that there is no
		773	guarantee that the thread can be cancelled when you call this method, and
		774	therefore, it might fail. It is also considerably slower than C<cancel> or
		775	C<terminate>.
		776
		777	A thread is in a safe-cancellable state if it either hasn't been run yet,
		778	or it has no C context attached and is inside an SLF function.
		779
		780	The latter two basically mean that the thread isn't currently inside a
		781	perl callback called from some C function (usually via some XS modules)
		782	and isn't currently executing inside some C function itself (via Coro's XS
		783	API).
		784
		785	This call returns true when it could cancel the thread, or croaks with an
		786	error otherwise (i.e. it either returns true or doesn't return at all).
		787
		788	Why the weird interface? Well, there are two common models on how and
		789	when to cancel things. In the first, you have the expectation that your
		790	coro thread can be cancelled when you want to cancel it - if the thread
		791	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		792	croaks to notify of the bug.
		793
		794	In the second model you sometimes want to ask nicely to cancel a thread,
		795	but if it's not a good time, well, then don't cancel. This can be done
		796	relatively easy like this:
		797
		798	if (! eval { $coro->safe_cancel }) {
		799	warn "unable to cancel thread: $@";
374	}	800	}
375	}
376		801
		802	However, what you never should do is first try to cancel "safely" and
		803	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		804	no sense: either you rely on being able to execute cleanup code in your
		805	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		806	only way, and if you don't, then C<< ->cancel >> is always faster and more
		807	direct.
		808
377	=item $coroutine->schedule_to	809	=item $coro->schedule_to
378		810
379	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead	811	Puts the current coro to sleep (like C<Coro::schedule>), but instead
380	of continuing with the next coro from the ready queue, always switch to	812	of continuing with the next coro from the ready queue, always switch to
381	the given coroutine object (regardless of priority etc.). The readyness	813	the given coro object (regardless of priority etc.). The readyness
382	state of that coroutine isn't changed.	814	state of that coro isn't changed.
383		815
384	This is an advanced method for special cases - I'd love to hear about any	816	This is an advanced method for special cases - I'd love to hear about any
385	uses for this one.	817	uses for this one.
386		818
387	=item $coroutine->cede_to	819	=item $coro->cede_to
388		820
389	Like C<schedule_to>, but puts the current coroutine into the ready	821	Like C<schedule_to>, but puts the current coro into the ready
390	queue. This has the effect of temporarily switching to the given	822	queue. This has the effect of temporarily switching to the given
391	coroutine, and continuing some time later.	823	coro, and continuing some time later.
392		824
393	This is an advanced method for special cases - I'd love to hear about any	825	This is an advanced method for special cases - I'd love to hear about any
394	uses for this one.	826	uses for this one.
395		827
396	=item $coroutine->throw ([$scalar])	828	=item $coro->throw ([$scalar])
397		829
398	If C<$throw> is specified and defined, it will be thrown as an exception	830	If C<$throw> is specified and defined, it will be thrown as an exception
399	inside the coroutine at the next convenient point in time. Otherwise	831	inside the coro at the next convenient point in time. Otherwise
400	clears the exception object.	832	clears the exception object.
401		833
402	Coro will check for the exception each time a schedule-like-function	834	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	835	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	836	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
405	detect this case and return early in case an exception is pending.	837	that are part of Coro itself) detect this case and return early in case an
		838	exception is pending.
406		839
407	The exception object will be thrown "as is" with the specified scalar in	840	The exception object will be thrown "as is" with the specified scalar in
408	C<$@>, i.e. if it is a string, no line number or newline will be appended	841	C<$@>, i.e. if it is a string, no line number or newline will be appended
409	(unlike with C<die>).	842	(unlike with C<die>).
410		843
411	This can be used as a softer means than C<cancel> to ask a coroutine to	844	This can be used as a softer means than either C<cancel> or C<safe_cancel
412	end itself, although there is no guarantee that the exception will lead to	845	>to ask a coro to end itself, although there is no guarantee that the
413	termination, and if the exception isn't caught it might well end the whole	846	exception will lead to termination, and if the exception isn't caught it
414	program.	847	might well end the whole program.
415		848
416	You might also think of C<throw> as being the moral equivalent of	849	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).	850	C<kill>ing a coro with a signal (in this case, a scalar).
418		851
419	=item $coroutine->join	852	=item $coro->join
420		853
421	Wait until the coroutine terminates and return any values given to the	854	Wait until the coro terminates and return any values given to the
422	C<terminate> or C<cancel> functions. C<join> can be called concurrently	855	C<terminate> or C<cancel> functions. C<join> can be called concurrently
423	from multiple coroutines, and all will be resumed and given the status	856	from multiple threads, and all will be resumed and given the status
424	return once the C<$coroutine> terminates.	857	return once the C<$coro> terminates.
425		858
426	=cut	859	=cut
427		860
428	sub join {	861	sub xjoin {
429	my $self = shift;	862	my $self = shift;
430		863
431	unless ($self->{_status}) {	864	unless ($self->{_status}) {
432	my $current = $current;	865	my $current = $current;
433		866
…		…
437	};	870	};
438		871
439	&schedule while $current;	872	&schedule while $current;
440	}	873	}
441		874
442	wantarray ? @{$self->{_status}} : $self->{_status}[0];	875	wantarray ? @{$self->{_status}} : $self->{_status}[0]
443	}	876	}
444		877
445	=item $coroutine->on_destroy (\&cb)	878	=item $coro->on_destroy (\&cb)
446		879
447	Registers a callback that is called when this coroutine gets destroyed,	880	Registers a callback that is called when this coro thread gets destroyed,
448	but before it is joined. The callback gets passed the terminate arguments,	881	that is, after it's resources have been freed but before it is joined. The
		882	callback gets passed the terminate/cancel arguments, if any, and I<must
449	if any, and I<must not> die, under any circumstances.	883	not> die, under any circumstances.
450		884
451	=cut	885	There can be any number of C<on_destroy> callbacks per coro, and there is
		886	no way currently to remove a callback once added.
452		887
		888	=cut
		889
453	sub on_destroy {	890	sub xon_destroy {
454	my ($self, $cb) = @_;	891	my ($self, $cb) = @_;
455		892
456	push @{ $self->{_on_destroy} }, $cb;	893	push @{ $self->{_on_destroy} }, $cb;
457	}	894	}
458		895
459	=item $oldprio = $coroutine->prio ($newprio)	896	=item $oldprio = $coro->prio ($newprio)
460		897
461	Sets (or gets, if the argument is missing) the priority of the	898	Sets (or gets, if the argument is missing) the priority of the
462	coroutine. Higher priority coroutines get run before lower priority	899	coro thread. Higher priority coro get run before lower priority
463	coroutines. Priorities are small signed integers (currently -4 .. +3),	900	coros. Priorities are small signed integers (currently -4 .. +3),
464	that you can refer to using PRIO_xxx constants (use the import tag :prio	901	that you can refer to using PRIO_xxx constants (use the import tag :prio
465	to get then):	902	to get then):
466		903
467	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	904	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
468	3 > 1 > 0 > -1 > -3 > -4	905	3 > 1 > 0 > -1 > -3 > -4
469		906
470	# set priority to HIGH	907	# set priority to HIGH
471	current->prio(PRIO_HIGH);	908	current->prio (PRIO_HIGH);
472		909
473	The idle coroutine ($Coro::idle) always has a lower priority than any	910	The idle coro thread ($Coro::idle) always has a lower priority than any
474	existing coroutine.	911	existing coro.
475		912
476	Changing the priority of the current coroutine will take effect immediately,	913	Changing the priority of the current coro will take effect immediately,
477	but changing the priority of coroutines in the ready queue (but not	914	but changing the priority of a coro in the ready queue (but not running)
478	running) will only take effect after the next schedule (of that	915	will only take effect after the next schedule (of that coro). This is a
479	coroutine). This is a bug that will be fixed in some future version.	916	bug that will be fixed in some future version.
480		917
481	=item $newprio = $coroutine->nice ($change)	918	=item $newprio = $coro->nice ($change)
482		919
483	Similar to C<prio>, but subtract the given value from the priority (i.e.	920	Similar to C<prio>, but subtract the given value from the priority (i.e.
484	higher values mean lower priority, just as in unix).	921	higher values mean lower priority, just as in UNIX's nice command).
485		922
486	=item $olddesc = $coroutine->desc ($newdesc)	923	=item $olddesc = $coro->desc ($newdesc)
487		924
488	Sets (or gets in case the argument is missing) the description for this	925	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	926	coro thread. This is just a free-form string you can associate with a
490	coroutine.	927	coro.
491		928
492	This method simply sets the C<< $coroutine->{desc} >> member to the given	929	This method simply sets the C<< $coro->{desc} >> member to the given
493	string. You can modify this member directly if you wish.	930	string. You can modify this member directly if you wish, and in fact, this
		931	is often preferred to indicate major processing states that cna then be
		932	seen for example in a L<Coro::Debug> session:
		933
		934	sub my_long_function {
		935	local $Coro::current->{desc} = "now in my_long_function";
		936	...
		937	$Coro::current->{desc} = "my_long_function: phase 1";
		938	...
		939	$Coro::current->{desc} = "my_long_function: phase 2";
		940	...
		941	}
494		942
495	=cut	943	=cut
496		944
497	sub desc {	945	sub desc {
498	my $old = $_[0]{desc};	946	my $old = $_[0]{desc};
499	$_[0]{desc} = $_[1] if @_ > 1;	947	$_[0]{desc} = $_[1] if @_ > 1;
500	$old;	948	$old;
501	}	949	}
502		950
		951	sub transfer {
		952	require Carp;
		953	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		954	}
		955
503	=back	956	=back
504		957
505	=head2 GLOBAL FUNCTIONS	958	=head1 GLOBAL FUNCTIONS
506		959
507	=over 4	960	=over 4
508		961
509	=item Coro::nready	962	=item Coro::nready
510		963
511	Returns the number of coroutines that are currently in the ready state,	964	Returns the number of coro that are currently in the ready state,
512	i.e. that can be switched to by calling C<schedule> directory or	965	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	966	indirectly. The value C<0> means that the only runnable coro is the
514	currently running one, so C<cede> would have no effect, and C<schedule>	967	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	968	would cause a deadlock unless there is an idle handler that wakes up some
516	coroutines.	969	coro.
517		970
518	=item my $guard = Coro::guard { ... }	971	=item my $guard = Coro::guard { ... }
519		972
520	This creates and returns a guard object. Nothing happens until the object	973	This function still exists, but is deprecated. Please use the
521	gets destroyed, in which case the codeblock given as argument will be	974	C<Guard::guard> function instead.
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		975
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	976	=cut
538		977
539	sub guard(&) {	978	BEGIN { *guard = \&Guard::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		979
552	=item unblock_sub { ... }	980	=item unblock_sub { ... }
553		981
554	This utility function takes a BLOCK or code reference and "unblocks" it,	982	This utility function takes a BLOCK or code reference and "unblocks" it,
555	returning a new coderef. Unblocking means that calling the new coderef	983	returning a new coderef. Unblocking means that calling the new coderef
556	will return immediately without blocking, returning nothing, while the	984	will return immediately without blocking, returning nothing, while the
557	original code ref will be called (with parameters) from within another	985	original code ref will be called (with parameters) from within another
558	coroutine.	986	coro.
559		987
560	The reason this function exists is that many event libraries (such as the	988	The reason this function exists is that many event libraries (such as
561	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	989	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
562	of thread-safety). This means you must not block within event callbacks,	990	of reentrancy). This means you must not block within event callbacks,
563	otherwise you might suffer from crashes or worse. The only event library	991	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>.	992	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		993	you might still run into deadlocks if all event loops are blocked).
		994
		995	Coro will try to catch you when you block in the event loop
		996	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		997	only works when you do not run your own event loop.
565		998
566	This function allows your callbacks to block by executing them in another	999	This function allows your callbacks to block by executing them in another
567	coroutine where it is safe to block. One example where blocking is handy	1000	coro where it is safe to block. One example where blocking is handy
568	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	1001	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
569	disk, for example.	1002	disk, for example.
570		1003
571	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	1004	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
572	creating event callbacks that want to block.	1005	creating event callbacks that want to block.
573		1006
574	If your handler does not plan to block (e.g. simply sends a message to	1007	If your handler does not plan to block (e.g. simply sends a message to
575	another coroutine, or puts some other coroutine into the ready queue),	1008	another coro, or puts some other coro into the ready queue), there is
576	there is no reason to use C<unblock_sub>.	1009	no reason to use C<unblock_sub>.
577		1010
578	Note that you also need to use C<unblock_sub> for any other callbacks that	1011	Note that you also need to use C<unblock_sub> for any other callbacks that
579	are indirectly executed by any C-based event loop. For example, when you	1012	are indirectly executed by any C-based event loop. For example, when you
580	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	1013	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
581	provides callbacks that are the result of some event callback, then you	1014	provides callbacks that are the result of some event callback, then you
…		…
611	unshift @unblock_queue, [$cb, @_];	1044	unshift @unblock_queue, [$cb, @_];
612	$unblock_scheduler->ready;	1045	$unblock_scheduler->ready;
613	}	1046	}
614	}	1047	}
615		1048
616	=item $cb = Coro::rouse_cb	1049	=item $cb = rouse_cb
617		1050
618	Create and return a "rouse callback". That's a code reference that, when	1051	Create and return a "rouse callback". That's a code reference that,
619	called, will save its arguments and notify the owner coroutine of the	1052	when called, will remember a copy of its arguments and notify the owner
620	callback.	1053	coro of the callback.
621		1054
622	See the next function.	1055	See the next function.
623		1056
624	=item @args = Coro::rouse_wait [$cb]	1057	=item @args = rouse_wait [$cb]
625		1058
626	Wait for the specified rouse callback (or the last one tht was created in	1059	Wait for the specified rouse callback (or the last one that was created in
627	this coroutine).	1060	this coro).
628		1061
629	As soon as the callback is invoked (or when the calback was invoked before	1062	As soon as the callback is invoked (or when the callback was invoked
630	C<rouse_wait>), it will return a copy of the arguments originally passed	1063	before C<rouse_wait>), it will return the arguments originally passed to
631	to the rouse callback.	1064	the rouse callback. In scalar context, that means you get the I<last>
		1065	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1066	statement at the end.
632		1067
633	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1068	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
634		1069
635	=back	1070	=back
636		1071
637	=cut	1072	=cut
638		1073
		1074	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1075	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1076
		1077	*{"Coro::$module\::new"} = sub {
		1078	require "Coro/$module.pm";
		1079
		1080	# some modules have their new predefined in State.xs, some don't
		1081	*{"Coro::$module\::new"} = $old
		1082	if $old;
		1083
		1084	goto &{"Coro::$module\::new"};
		1085	};
		1086	}
		1087
639	1;	1088	1;
640		1089
641	=head1 HOW TO WAIT FOR A CALLBACK	1090	=head1 HOW TO WAIT FOR A CALLBACK
642		1091
643	It is very common for a coroutine to wait for some callback to be	1092	It is very common for a coro to wait for some callback to be
644	called. This occurs naturally when you use coroutines in an otherwise	1093	called. This occurs naturally when you use coro in an otherwise
645	event-based program, or when you use event-based libraries.	1094	event-based program, or when you use event-based libraries.
646		1095
647	These typically register a callback for some event, and call that callback	1096	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	1097	when the event occured. In a coro, however, you typically want to
649	just wait for the event, simplyifying things.	1098	just wait for the event, simplyifying things.
650		1099
651	For example C<< AnyEvent->child >> registers a callback to be called when	1100	For example C<< AnyEvent->child >> registers a callback to be called when
652	a specific child has exited:	1101	a specific child has exited:
653		1102
654	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	1103	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
655		1104
656	But from withina coroutine, you often just want to write this:	1105	But from within a coro, you often just want to write this:
657		1106
658	my $status = wait_for_child $pid;	1107	my $status = wait_for_child $pid;
659		1108
660	Coro offers two functions specifically designed to make this easy,	1109	Coro offers two functions specifically designed to make this easy,
661	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	1110	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
662		1111
663	The first function, C<rouse_cb>, generates and returns a callback that,	1112	The first function, C<rouse_cb>, generates and returns a callback that,
664	when invoked, will save it's arguments and notify the coroutine that	1113	when invoked, will save its arguments and notify the coro that
665	created the callback.	1114	created the callback.
666		1115
667	The second function, C<rouse_wait>, waits for the callback to be called	1116	The second function, C<rouse_wait>, waits for the callback to be called
668	(by calling C<schedule> to go to sleep) and returns the arguments	1117	(by calling C<schedule> to go to sleep) and returns the arguments
669	originally passed to the callback.	1118	originally passed to the callback.
…		…
684	you can roll your own, using C<schedule>:	1133	you can roll your own, using C<schedule>:
685		1134
686	sub wait_for_child($) {	1135	sub wait_for_child($) {
687	my ($pid) = @_;	1136	my ($pid) = @_;
688		1137
689	# store the current coroutine in $current,	1138	# store the current coro in $current,
690	# and provide result variables for the closure passed to ->child	1139	# and provide result variables for the closure passed to ->child
691	my $current = $Coro::current;	1140	my $current = $Coro::current;
692	my ($done, $rstatus);	1141	my ($done, $rstatus);
693		1142
694	# pass a closure to ->child	1143	# pass a closure to ->child
…		…
710		1159
711	=item fork with pthread backend	1160	=item fork with pthread backend
712		1161
713	When Coro is compiled using the pthread backend (which isn't recommended	1162	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	1163	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	1164	coro will not survive a fork. There is no known workaround except to
716	fix your libc and use a saner backend.	1165	fix your libc and use a saner backend.
717		1166
718	=item perl process emulation ("threads")	1167	=item perl process emulation ("threads")
719		1168
720	This module is not perl-pseudo-thread-safe. You should only ever use this	1169	This module is not perl-pseudo-thread-safe. You should only ever use this
721	module from the same thread (this requirement might be removed in the	1170	module from the first thread (this requirement might be removed in the
722	future to allow per-thread schedulers, but Coro::State does not yet allow	1171	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	1172	this). I recommend disabling thread support and using processes, as having
724	the windows process emulation enabled under unix roughly halves perl	1173	the windows process emulation enabled under unix roughly halves perl
725	performance, even when not used.	1174	performance, even when not used.
726		1175
		1176	Attempts to use threads created in another emulated process will crash
		1177	("cleanly", with a null pointer exception).
		1178
727	=item coroutine switching not signal safe	1179	=item coro switching is not signal safe
728		1180
729	You must not switch to another coroutine from within a signal handler	1181	You must not switch to another coro from within a signal handler (only
730	(only relevant with %SIG - most event libraries provide safe signals).	1182	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1183	you are sure you are not interrupting a Coro function.
731		1184
732	That means you I<MUST NOT> call any function that might "block" the	1185	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	1186	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
734	anything that calls those. Everything else, including calling C<ready>,	1187	anything that calls those. Everything else, including calling C<ready>,
735	works.	1188	works.
736		1189
737	=back	1190	=back
738		1191
739		1192
		1193	=head1 WINDOWS PROCESS EMULATION
		1194
		1195	A great many people seem to be confused about ithreads (for example, Chip
		1196	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1197	while in the same mail making rather confused statements about perl
		1198	ithreads (for example, that memory or files would be shared), showing his
		1199	lack of understanding of this area - if it is hard to understand for Chip,
		1200	it is probably not obvious to everybody).
		1201
		1202	What follows is an ultra-condensed version of my talk about threads in
		1203	scripting languages given on the perl workshop 2009:
		1204
		1205	The so-called "ithreads" were originally implemented for two reasons:
		1206	first, to (badly) emulate unix processes on native win32 perls, and
		1207	secondly, to replace the older, real thread model ("5.005-threads").
		1208
		1209	It does that by using threads instead of OS processes. The difference
		1210	between processes and threads is that threads share memory (and other
		1211	state, such as files) between threads within a single process, while
		1212	processes do not share anything (at least not semantically). That
		1213	means that modifications done by one thread are seen by others, while
		1214	modifications by one process are not seen by other processes.
		1215
		1216	The "ithreads" work exactly like that: when creating a new ithreads
		1217	process, all state is copied (memory is copied physically, files and code
		1218	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1219	the same behaviour can be achieved by using operating system processes,
		1220	except that UNIX typically uses hardware built into the system to do this
		1221	efficiently, while the windows process emulation emulates this hardware in
		1222	software (rather efficiently, but of course it is still much slower than
		1223	dedicated hardware).
		1224
		1225	As mentioned before, loading code, modifying code, modifying data
		1226	structures and so on is only visible in the ithreads process doing the
		1227	modification, not in other ithread processes within the same OS process.
		1228
		1229	This is why "ithreads" do not implement threads for perl at all, only
		1230	processes. What makes it so bad is that on non-windows platforms, you can
		1231	actually take advantage of custom hardware for this purpose (as evidenced
		1232	by the forks module, which gives you the (i-) threads API, just much
		1233	faster).
		1234
		1235	Sharing data is in the i-threads model is done by transfering data
		1236	structures between threads using copying semantics, which is very slow -
		1237	shared data simply does not exist. Benchmarks using i-threads which are
		1238	communication-intensive show extremely bad behaviour with i-threads (in
		1239	fact, so bad that Coro, which cannot take direct advantage of multiple
		1240	CPUs, is often orders of magnitude faster because it shares data using
		1241	real threads, refer to my talk for details).
		1242
		1243	As summary, i-threads use threads to implement processes, while
		1244	the compatible forks module uses processes to emulate, uhm,
		1245	processes. I-threads slow down every perl program when enabled, and
		1246	outside of windows, serve no (or little) practical purpose, but
		1247	disadvantages every single-threaded Perl program.
		1248
		1249	This is the reason that I try to avoid the name "ithreads", as it is
		1250	misleading as it implies that it implements some kind of thread model for
		1251	perl, and prefer the name "windows process emulation", which describes the
		1252	actual use and behaviour of it much better.
		1253
740	=head1 SEE ALSO	1254	=head1 SEE ALSO
741		1255
742	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1256	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
743		1257
744	Debugging: L<Coro::Debug>.	1258	Debugging: L<Coro::Debug>.
745		1259
746	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1260	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
747		1261
748	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1262	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1263	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
749		1264
750	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1265	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
751		1266
752	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1267	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1268	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1269	L<Coro::Select>.
753		1270
754	XS API: L<Coro::MakeMaker>.	1271	XS API: L<Coro::MakeMaker>.
755		1272
756	Low level Configuration, Coroutine Environment: L<Coro::State>.	1273	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
757		1274
758	=head1 AUTHOR	1275	=head1 AUTHOR
759		1276
760	Marc Lehmann <schmorp@schmorp.de>	1277	Marc Lehmann <schmorp@schmorp.de>
761	http://home.schmorp.de/	1278	http://home.schmorp.de/

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Revision 1.296 by root, Thu May 12 23:24:28 2011 UTC