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

Comparing Coro/Coro.pm (file contents):
Revision 1.233 by root, Fri Nov 21 06:02:07 2008 UTC vs.
Revision 1.297 by root, Thu May 12 23:55:39 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 - a thread that is running, ready to run or waiting
		97	for some event is alive on it's 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 $coro;
		116
		117	=item 2. Startup
		118
		119	When a new coro thread is created, only a copy of the code reference
		120	and the arguments are stored, no extra memory for stacks and so on is
		121	allocated, keeping the coro thread in a low-memory state.
		122
		123	Only when it actually starts executing will all the resources be finally
		124	allocated.
		125
		126	The optional arguments specified at coro creation are available in C<@_>,
		127	similar to function calls.
		128
		129	=item 3. Running / Blocking
		130
		131	A lot can happen after the coro thread has started running. Quite usually,
		132	it will not run to the end in one go (because you could use a function
		133	instead), but it will give up the CPU regularly because it waits for
		134	external events.
		135
		136	As long as a coro thread runs, its Coro object is available in the global
		137	variable C<$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	$coro->cancel; # also accepts values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state, and for those cases where you want to do truly marvellous things
		215	with your coro while it is being cancelled - that is, make sure all
		216	cleanup code is executed from the thread being cancelled - there is even a
		217	C<< ->safe_cancel >> method.
		218
		219	So, cancelling a thread that runs in an XS event loop might not be the
		220	best idea, but any other combination that deals with perl only (cancelling
		221	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		222	safe.
		223
		224	Lastly, a coro thread object that isn't referenced is C<< ->cancel >>'ed
		225	automatically - just like other objects in Perl. This is not such a common
		226	case, however - a running thread is referencedy b C<$Coro::current>, a
		227	thread ready to run is referenced by the ready queue, a thread waiting
		228	on a lock or semaphore is referenced by being in some wait list and so
		229	on. But a thread that isn't in any of those queues gets cancelled:
		230
		231	async {
		232	schedule; # cede to other coros, don't go into the ready queue
		233	};
		234
		235	cede;
		236	# now the async above is destroyed, as it is not referenced by anything.
		237
		238	=item 5. Cleanup
		239
		240	Threads will allocate various resources. Most but not all will be returned
		241	when a thread terminates, during clean-up.
		242
		243	Cleanup is quite similar to throwing an uncaught exception: perl will
		244	work it's way up through all subroutine calls and blocks. On it's way, it
		245	will release all C<my> variables, undo all C<local>'s and free any other
		246	resources truly local to the thread.
		247
		248	So, a common way to free resources is to keep them referenced only by my
		249	variables:
		250
		251	async {
		252	my $big_cache = new Cache ...;
		253	};
		254
		255	If there are no other references, then the C<$big_cache> object will be
		256	freed when the thread terminates, regardless of how it does so.
		257
		258	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		259	resources, but that's where the C<guard> methods come in handy:
		260
		261	my $sem = new Coro::Semaphore;
		262
		263	async {
		264	my $lock_guard = $sem->guard;
		265	# if we reutrn, or die or get cancelled, here,
		266	# then the semaphore will be "up"ed.
		267	};
		268
		269	The C<Guard::guard> function comes in handy for any custom cleanup you
		270	might want to do (but you cannot switch to other coroutines form those
		271	code blocks):
		272
		273	async {
		274	my $window = new Gtk2::Window "toplevel";
		275	# The window will not be cleaned up automatically, even when $window
		276	# gets freed, so use a guard to ensure it's destruction
		277	# in case of an error:
		278	my $window_guard = Guard::guard { $window->destroy };
		279
		280	# we are safe here
		281	};
		282
		283	Last not least, C<local> can often be handy, too, e.g. when temporarily
		284	replacing the coro thread description:
		285
		286	sub myfunction {
		287	local $Coro::current->{desc} = "inside myfunction(@_)";
		288
		289	# if we return or die here, the description will be restored
		290	}
		291
		292	=item 6. Viva La Zombie Muerte
		293
		294	Even after a thread has terminated and cleaned up its resources, the Coro
		295	object still is there and stores the return values of the thread.
		296
		297	The means the Coro object gets freed automatically when the thread has
		298	terminated and cleaned up and there arenot other references.
		299
		300	If there are, the Coro object will stay around, and you can call C<<
		301	->join >> as many times as you wish to retrieve the result values:
		302
		303	async {
		304	print "hi\n";
		305	1
		306	};
		307
		308	# run the async above, and free everything before returning
		309	# from Coro::cede:
		310	Coro::cede;
		311
		312	{
		313	my $coro = async {
		314	print "hi\n";
		315	1
		316	};
		317
		318	# run the async above, and clean up, but do not free the coro
		319	# object:
		320	Coro::cede;
		321
		322	# optionally retrieve the result values
		323	my @results = $coro->join;
		324
		325	# now $coro goes out of scope, and presumably gets freed
		326	};
		327
		328	=back
56		329
57	=cut	330	=cut
58		331
59	package Coro;	332	package Coro;
60		333
61	use strict qw(vars subs);	334	use common::sense;
62	no warnings "uninitialized";	335
		336	use Carp ();
		337
		338	use Guard ();
63		339
64	use Coro::State;	340	use Coro::State;
65		341
66	use base qw(Coro::State Exporter);	342	use base qw(Coro::State Exporter);
67		343
68	our $idle; # idle handler	344	our $idle; # idle handler
69	our $main; # main coroutine	345	our $main; # main coro
70	our $current; # current coroutine	346	our $current; # current coro
71		347
72	our $VERSION = "5.0";	348	our $VERSION = 5.372;
73		349
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	350	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	351	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	352	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	353	);
78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	354	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
79		355
		356	=head1 GLOBAL VARIABLES
		357
80	=over 4	358	=over 4
81		359
82	=item $Coro::main	360	=item $Coro::main
83		361
84	This variable stores the coroutine object that represents the main	362	This variable stores the Coro object that represents the main
85	program. While you cna C<ready> it and do most other things you can do to	363	program. While you cna C<ready> it and do most other things you can do to
86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	364	coro, it is mainly useful to compare again C<$Coro::current>, to see
87	whether you are running in the main program or not.	365	whether you are running in the main program or not.
88		366
89	=cut	367	=cut
90		368
91	# $main is now being initialised by Coro::State	369	# $main is now being initialised by Coro::State
92		370
93	=item $Coro::current	371	=item $Coro::current
94		372
95	The coroutine object representing the current coroutine (the last	373	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	374	coro that the Coro scheduler switched to). The initial value is
97	C<$Coro::main> (of course).	375	C<$Coro::main> (of course).
98		376
99	This variable is B<strictly> I<read-only>. You can take copies of the	377	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	378	value stored in it and use it as any other Coro object, but you must
101	not otherwise modify the variable itself.	379	not otherwise modify the variable itself.
102		380
103	=cut	381	=cut
104		382
105	sub current() { $current } # [DEPRECATED]	383	sub current() { $current } # [DEPRECATED]
106		384
107	=item $Coro::idle	385	=item $Coro::idle
108		386
109	This variable is mainly useful to integrate Coro into event loops. It is	387	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	388	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
111	pretty low-level functionality.	389	pretty low-level functionality.
112		390
113	This variable stores a callback that is called whenever the scheduler	391	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	392	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		393
		394	The default implementation dies with "FATAL: deadlock detected.", followed
		395	by a thread listing, because the program has no other way to continue.
		396
118	This hook is overwritten by modules such as C<Coro::Timer> and	397	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	398	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
120	coroutine so the scheduler can run it.	399	coro so the scheduler can run it.
121		400
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	401	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
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		402
133	=cut	403	=cut
134		404
135	$idle = sub {	405	# \|\|= because other modules could have provided their own by now
136	require Carp;	406	$idle \|\|= new Coro sub {
137	Carp::croak ("FATAL: deadlock detected");	407	require Coro::Debug;
		408	die "FATAL: deadlock detected.\n"
		409	. Coro::Debug::ps_listing ();
138	};	410	};
139		411
140	# this coroutine is necessary because a coroutine	412	# this coro is necessary because a coro
141	# cannot destroy itself.	413	# cannot destroy itself.
142	our @destroy;	414	our @destroy;
143	our $manager;	415	our $manager;
144		416
145	$manager = new Coro sub {	417	$manager = new Coro sub {
146	while () {	418	while () {
147	Coro::_cancel shift @destroy	419	_destroy shift @destroy
148	while @destroy;	420	while @destroy;
149		421
150	&schedule;	422	&schedule;
151	}	423	}
152	};	424	};
153	$manager->{desc} = "[coro manager]";	425	$manager->{desc} = "[coro manager]";
154	$manager->prio (PRIO_MAX);	426	$manager->prio (PRIO_MAX);
155		427
156	=back	428	=back
157		429
158	=head2 SIMPLE COROUTINE CREATION	430	=head1 SIMPLE CORO CREATION
159		431
160	=over 4	432	=over 4
161		433
162	=item async { ... } [@args...]	434	=item async { ... } [@args...]
163		435
164	Create a new coroutine and return it's coroutine object (usually	436	Create a new coro and return its Coro object (usually
165	unused). The coroutine will be put into the ready queue, so	437	unused). The coro will be put into the ready queue, so
166	it will start running automatically on the next scheduler run.	438	it will start running automatically on the next scheduler run.
167		439
168	The first argument is a codeblock/closure that should be executed in the	440	The first argument is a codeblock/closure that should be executed in the
169	coroutine. When it returns argument returns the coroutine is automatically	441	coro. When it returns argument returns the coro is automatically
170	terminated.	442	terminated.
171		443
172	The remaining arguments are passed as arguments to the closure.	444	The remaining arguments are passed as arguments to the closure.
173		445
174	See the C<Coro::State::new> constructor for info about the coroutine	446	See the C<Coro::State::new> constructor for info about the coro
175	environment in which coroutines are executed.	447	environment in which coro are executed.
176		448
177	Calling C<exit> in a coroutine will do the same as calling exit outside	449	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,	450	the coro. Likewise, when the coro dies, the program will exit,
179	just as it would in the main program.	451	just as it would in the main program.
180		452
181	If you do not want that, you can provide a default C<die> handler, or	453	If you do not want that, you can provide a default C<die> handler, or
182	simply avoid dieing (by use of C<eval>).	454	simply avoid dieing (by use of C<eval>).
183		455
184	Example: Create a new coroutine that just prints its arguments.	456	Example: Create a new coro that just prints its arguments.
185		457
186	async {	458	async {
187	print "@_\n";	459	print "@_\n";
188	} 1,2,3,4;	460	} 1,2,3,4;
189		461
190	=cut
191
192	sub async(&@) {
193	my $coro = new Coro @_;
194	$coro->ready;
195	$coro
196	}
197
198	=item async_pool { ... } [@args...]	462	=item async_pool { ... } [@args...]
199		463
200	Similar to C<async>, but uses a coroutine pool, so you should not call	464	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	465	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	466	coro that might have executed other code already (which can be good
203	or bad :).	467	or bad :).
204		468
205	On the plus side, this function is about twice as fast as creating (and	469	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	470	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>.	471	coros in quick successsion, use C<async_pool>, not C<async>.
208		472
209	The code block is executed in an C<eval> context and a warning will be	473	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	474	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>	475	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,	476	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	477	which somehow defeats the purpose of pooling (but is fine in the
214	exceptional case).	478	exceptional case).
215		479
216	The priority will be reset to C<0> after each run, tracing will be	480	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	481	disabled, the description will be reset and the default output filehandle
218	gets restored, so you can change all these. Otherwise the coroutine will	482	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	483	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	484	stuff such as C<$/> you I<must needs> revert that change, which is most
221	simply done by using local as in: C<< local $/ >>.	485	simply done by using local as in: C<< local $/ >>.
222		486
223	The idle pool size is limited to C<8> idle coroutines (this can be	487	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	488	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
225	coros as required.	489	coros as required.
226		490
227	If you are concerned about pooled coroutines growing a lot because a	491	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	492	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	493	{ terminate }> once per second or so to slowly replenish the pool. In
230	addition to that, when the stacks used by a handler grows larger than 32kb	494	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.	495	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
232		496
…		…
246	}	510	}
247	}	511	}
248		512
249	=back	513	=back
250		514
251	=head2 STATIC METHODS	515	=head1 STATIC METHODS
252		516
253	Static methods are actually functions that operate on the current coroutine.	517	Static methods are actually functions that implicitly operate on the
		518	current coro.
254		519
255	=over 4	520	=over 4
256		521
257	=item schedule	522	=item schedule
258		523
259	Calls the scheduler. The scheduler will find the next coroutine that is	524	Calls the scheduler. The scheduler will find the next coro that is
260	to be run from the ready queue and switches to it. The next coroutine	525	to be run from the ready queue and switches to it. The next coro
261	to be run is simply the one with the highest priority that is longest	526	to be run is simply the one with the highest priority that is longest
262	in its ready queue. If there is no coroutine ready, it will clal the	527	in its ready queue. If there is no coro ready, it will call the
263	C<$Coro::idle> hook.	528	C<$Coro::idle> hook.
264		529
265	Please note that the current coroutine will I<not> be put into the ready	530	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	531	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 >>,	532	again unless something else (e.g. an event handler) calls C<< ->ready >>,
268	thus waking you up.	533	thus waking you up.
269		534
270	This makes C<schedule> I<the> generic method to use to block the current	535	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	536	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	537	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	538	>> 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,	539	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	540	so you need to check whether the event indeed happened, e.g. by storing the
276	status in a variable.	541	status in a variable.
277		542
278	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	543	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
279		544
280	=item cede	545	=item cede
281		546
282	"Cede" to other coroutines. This function puts the current coroutine into	547	"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	548	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	549	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	550	priority. Once your coro gets its turn again it will automatically be
286	resumed.	551	resumed.
287		552
288	This function is often called C<yield> in other languages.	553	This function is often called C<yield> in other languages.
289		554
290	=item Coro::cede_notself	555	=item Coro::cede_notself
291		556
292	Works like cede, but is not exported by default and will cede to I<any>	557	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	558	coro, regardless of priority. This is useful sometimes to ensure
294	progress is made.	559	progress is made.
295		560
296	=item terminate [arg...]	561	=item terminate [arg...]
297		562
298	Terminates the current coroutine with the given status values (see L<cancel>).	563	Terminates the current coro with the given status values (see
		564	L<cancel>). The values will not be copied, but referenced directly.
		565
		566	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		567
		568	These function install enter and leave winders in the current scope. The
		569	enter block will be executed when on_enter is called and whenever the
		570	current coro is re-entered by the scheduler, while the leave block is
		571	executed whenever the current coro is blocked by the scheduler, and
		572	also when the containing scope is exited (by whatever means, be it exit,
		573	die, last etc.).
		574
		575	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		576	BLOCKs>. That means: do not even think about calling C<die> without an
		577	eval, and do not even think of entering the scheduler in any way.
		578
		579	Since both BLOCKs are tied to the current scope, they will automatically
		580	be removed when the current scope exits.
		581
		582	These functions implement the same concept as C<dynamic-wind> in scheme
		583	does, and are useful when you want to localise some resource to a specific
		584	coro.
		585
		586	They slow down thread switching considerably for coros that use them
		587	(about 40% for a BLOCK with a single assignment, so thread switching is
		588	still reasonably fast if the handlers are fast).
		589
		590	These functions are best understood by an example: The following function
		591	will change the current timezone to "Antarctica/South_Pole", which
		592	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		593	which remember/change the current timezone and restore the previous
		594	value, respectively, the timezone is only changed for the coro that
		595	installed those handlers.
		596
		597	use POSIX qw(tzset);
		598
		599	async {
		600	my $old_tz; # store outside TZ value here
		601
		602	Coro::on_enter {
		603	$old_tz = $ENV{TZ}; # remember the old value
		604
		605	$ENV{TZ} = "Antarctica/South_Pole";
		606	tzset; # enable new value
		607	};
		608
		609	Coro::on_leave {
		610	$ENV{TZ} = $old_tz;
		611	tzset; # restore old value
		612	};
		613
		614	# at this place, the timezone is Antarctica/South_Pole,
		615	# without disturbing the TZ of any other coro.
		616	};
		617
		618	This can be used to localise about any resource (locale, uid, current
		619	working directory etc.) to a block, despite the existance of other
		620	coros.
		621
		622	Another interesting example implements time-sliced multitasking using
		623	interval timers (this could obviously be optimised, but does the job):
		624
		625	# "timeslice" the given block
		626	sub timeslice(&) {
		627	use Time::HiRes ();
		628
		629	Coro::on_enter {
		630	# on entering the thread, we set an VTALRM handler to cede
		631	$SIG{VTALRM} = sub { cede };
		632	# and then start the interval timer
		633	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		634	};
		635	Coro::on_leave {
		636	# on leaving the thread, we stop the interval timer again
		637	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		638	};
		639
		640	&{+shift};
		641	}
		642
		643	# use like this:
		644	timeslice {
		645	# The following is an endless loop that would normally
		646	# monopolise the process. Since it runs in a timesliced
		647	# environment, it will regularly cede to other threads.
		648	while () { }
		649	};
		650
299		651
300	=item killall	652	=item killall
301		653
302	Kills/terminates/cancels all coroutines except the currently running	654	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		655
306	Note that while this will try to free some of the main programs resources,	656	Note that while this will try to free some of the main interpreter
		657	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	658	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.	659	calls this function, there will be some one-time resource leak.
309		660
310	=cut	661	=cut
311		662
312	sub killall {	663	sub killall {
313	for (Coro::State::list) {	664	for (Coro::State::list) {
…		…
316	}	667	}
317	}	668	}
318		669
319	=back	670	=back
320		671
321	=head2 COROUTINE METHODS	672	=head1 CORO OBJECT METHODS
322		673
323	These are the methods you can call on coroutine objects (or to create	674	These are the methods you can call on coro objects (or to create
324	them).	675	them).
325		676
326	=over 4	677	=over 4
327		678
328	=item new Coro \&sub [, @args...]	679	=item new Coro \&sub [, @args...]
329		680
330	Create a new coroutine and return it. When the sub returns, the coroutine	681	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	682	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	683	called. To make the coro run you must first put it into the ready
333	queue by calling the ready method.	684	queue by calling the ready method.
334		685
335	See C<async> and C<Coro::State::new> for additional info about the	686	See C<async> and C<Coro::State::new> for additional info about the
336	coroutine environment.	687	coro environment.
337		688
338	=cut	689	=cut
339		690
340	sub _terminate {	691	sub _coro_run {
341	terminate &{+shift};	692	terminate &{+shift};
342	}	693	}
343		694
344	=item $success = $coroutine->ready	695	=item $success = $coro->ready
345		696
346	Put the given coroutine into the end of its ready queue (there is one	697	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	698	queue for each priority) and return true. If the coro is already in
348	the ready queue, do nothing and return false.	699	the ready queue, do nothing and return false.
349		700
350	This ensures that the scheduler will resume this coroutine automatically	701	This ensures that the scheduler will resume this coro automatically
351	once all the coroutines of higher priority and all coroutines of the same	702	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.	703	priority that were put into the ready queue earlier have been resumed.
353		704
		705	=item $coro->suspend
		706
		707	Suspends the specified coro. A suspended coro works just like any other
		708	coro, except that the scheduler will not select a suspended coro for
		709	execution.
		710
		711	Suspending a coro can be useful when you want to keep the coro from
		712	running, but you don't want to destroy it, or when you want to temporarily
		713	freeze a coro (e.g. for debugging) to resume it later.
		714
		715	A scenario for the former would be to suspend all (other) coros after a
		716	fork and keep them alive, so their destructors aren't called, but new
		717	coros can be created.
		718
		719	=item $coro->resume
		720
		721	If the specified coro was suspended, it will be resumed. Note that when
		722	the coro was in the ready queue when it was suspended, it might have been
		723	unreadied by the scheduler, so an activation might have been lost.
		724
		725	To avoid this, it is best to put a suspended coro into the ready queue
		726	unconditionally, as every synchronisation mechanism must protect itself
		727	against spurious wakeups, and the one in the Coro family certainly do
		728	that.
		729
		730	=item $state->is_new
		731
		732	Returns true iff this Coro object is "new", i.e. has never been run
		733	yet. Those states basically consist of only the code reference to call and
		734	the arguments, but consumes very little other resources. New states will
		735	automatically get assigned a perl interpreter when they are transfered to.
		736
		737	=item $state->is_zombie
		738
		739	Returns true iff the Coro object has been cancelled, i.e.
		740	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		741	C<safe_cancel>'ed or simply went out of scope.
		742
		743	The name "zombie" stems from UNIX culture, where a process that has
		744	exited and only stores and exit status and no other resources is called a
		745	"zombie".
		746
354	=item $is_ready = $coroutine->is_ready	747	=item $is_ready = $coro->is_ready
355		748
356	Return whether the coroutine is currently the ready queue or not,	749	Returns true iff the Coro object is in the ready queue. Unless the Coro
		750	object gets destroyed, it will eventually be scheduled by the scheduler.
357		751
		752	=item $is_running = $coro->is_running
		753
		754	Returns true iff the Coro object is currently running. Only one Coro object
		755	can ever be in the running state (but it currently is possible to have
		756	multiple running Coro::States).
		757
		758	=item $is_suspended = $coro->is_suspended
		759
		760	Returns true iff this Coro object has been suspended. Suspended Coros will
		761	not ever be scheduled.
		762
358	=item $coroutine->cancel (arg...)	763	=item $coro->cancel (arg...)
359		764
360	Terminates the given coroutine and makes it return the given arguments as	765	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	766	status (default: an empty list). Never returns if the Coro is the
362	current coroutine.	767	current Coro.
363		768
364	=cut	769	This is a rather brutal way to free a coro, with some limitations - if
		770	the thread is inside a C callback that doesn't expect to be canceled,
		771	bad things can happen, or if the cancelled thread insists on running
		772	complicated cleanup handlers that rely on it'S thread context, things will
		773	not work.
365		774
366	sub cancel {	775	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
367	my $self = shift;	776	a thread context, and is not allowed to switch to other threads. On the
		777	plus side, C<< ->cancel >> will always clean up the thread, no matter
		778	what. If your cleanup code is complex or you want to avoid cancelling a
		779	C-thread that doesn't know how to clean up itself, it can be better to C<<
		780	->throw >> an exception, or use C<< ->safe_cancel >>.
368		781
369	if ($current == $self) {	782	The arguments to C<< ->cancel >> are not copied, but instead will
370	terminate @_;	783	be referenced directly (e.g. if you pass C<$var> and after the call
371	} else {	784	change that variable, then you might change the return values passed to
372	$self->{_status} = [@_];	785	e.g. C<join>, so don't do that).
373	$self->_cancel;	786
		787	The resources of the Coro are usually freed (or destructed) before this
		788	call returns, but this can be delayed for an indefinite amount of time, as
		789	in some cases the manager thread has to run first to actually destruct the
		790	Coro object.
		791
		792	=item $coro->safe_cancel ($arg...)
		793
		794	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		795	consequently, can fail with an exception in cases the thread is not in a
		796	cancellable state.
		797
		798	This method works a bit like throwing an exception that cannot be caught
		799	- specifically, it will clean up the thread from within itself, so
		800	all cleanup handlers (e.g. C<guard> blocks) are run with full thread
		801	context and can block if they wish. The downside is that there is no
		802	guarantee that the thread can be cancelled when you call this method, and
		803	therefore, it might fail. It is also considerably slower than C<cancel> or
		804	C<terminate>.
		805
		806	A thread is in a safe-cancellable state if it either hasn't been run yet,
		807	or it has no C context attached and is inside an SLF function.
		808
		809	The latter two basically mean that the thread isn't currently inside a
		810	perl callback called from some C function (usually via some XS modules)
		811	and isn't currently executing inside some C function itself (via Coro's XS
		812	API).
		813
		814	This call returns true when it could cancel the thread, or croaks with an
		815	error otherwise (i.e. it either returns true or doesn't return at all).
		816
		817	Why the weird interface? Well, there are two common models on how and
		818	when to cancel things. In the first, you have the expectation that your
		819	coro thread can be cancelled when you want to cancel it - if the thread
		820	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		821	croaks to notify of the bug.
		822
		823	In the second model you sometimes want to ask nicely to cancel a thread,
		824	but if it's not a good time, well, then don't cancel. This can be done
		825	relatively easy like this:
		826
		827	if (! eval { $coro->safe_cancel }) {
		828	warn "unable to cancel thread: $@";
374	}	829	}
375	}
376		830
		831	However, what you never should do is first try to cancel "safely" and
		832	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		833	no sense: either you rely on being able to execute cleanup code in your
		834	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		835	only way, and if you don't, then C<< ->cancel >> is always faster and more
		836	direct.
		837
377	=item $coroutine->schedule_to	838	=item $coro->schedule_to
378		839
379	Puts the current coroutine to sleep (like C<Coro::schedule>), but instead	840	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	841	of continuing with the next coro from the ready queue, always switch to
381	the given coroutine object (regardless of priority etc.). The readyness	842	the given coro object (regardless of priority etc.). The readyness
382	state of that coroutine isn't changed.	843	state of that coro isn't changed.
383		844
384	This is an advanced method for special cases - I'd love to hear about any	845	This is an advanced method for special cases - I'd love to hear about any
385	uses for this one.	846	uses for this one.
386		847
387	=item $coroutine->cede_to	848	=item $coro->cede_to
388		849
389	Like C<schedule_to>, but puts the current coroutine into the ready	850	Like C<schedule_to>, but puts the current coro into the ready
390	queue. This has the effect of temporarily switching to the given	851	queue. This has the effect of temporarily switching to the given
391	coroutine, and continuing some time later.	852	coro, and continuing some time later.
392		853
393	This is an advanced method for special cases - I'd love to hear about any	854	This is an advanced method for special cases - I'd love to hear about any
394	uses for this one.	855	uses for this one.
395		856
396	=item $coroutine->throw ([$scalar])	857	=item $coro->throw ([$scalar])
397		858
398	If C<$throw> is specified and defined, it will be thrown as an exception	859	If C<$throw> is specified and defined, it will be thrown as an exception
399	inside the coroutine at the next convenient point in time. Otherwise	860	inside the coro at the next convenient point in time. Otherwise
400	clears the exception object.	861	clears the exception object.
401		862
402	Coro will check for the exception each time a schedule-like-function	863	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	864	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	865	>>, 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.	866	that are part of Coro itself) detect this case and return early in case an
		867	exception is pending.
406		868
407	The exception object will be thrown "as is" with the specified scalar in	869	The exception object will be thrown "as is" with the specified scalar in
408	C<$@>, i.e. if it is a string, no line number or newline will be appended	870	C<$@>, i.e. if it is a string, no line number or newline will be appended
409	(unlike with C<die>).	871	(unlike with C<die>).
410		872
411	This can be used as a softer means than C<cancel> to ask a coroutine to	873	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	874	>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	875	exception will lead to termination, and if the exception isn't caught it
414	program.	876	might well end the whole program.
415		877
416	You might also think of C<throw> as being the moral equivalent of	878	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).	879	C<kill>ing a coro with a signal (in this case, a scalar).
418		880
419	=item $coroutine->join	881	=item $coro->join
420		882
421	Wait until the coroutine terminates and return any values given to the	883	Wait until the coro terminates and return any values given to the
422	C<terminate> or C<cancel> functions. C<join> can be called concurrently	884	C<terminate> or C<cancel> functions. C<join> can be called concurrently
423	from multiple coroutines, and all will be resumed and given the status	885	from multiple threads, and all will be resumed and given the status
424	return once the C<$coroutine> terminates.	886	return once the C<$coro> terminates.
425		887
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)	888	=item $coro->on_destroy (\&cb)
446		889
447	Registers a callback that is called when this coroutine gets destroyed,	890	Registers a callback that is called when this coro thread gets destroyed,
448	but before it is joined. The callback gets passed the terminate arguments,	891	that is, after it's resources have been freed but before it is joined. The
		892	callback gets passed the terminate/cancel arguments, if any, and I<must
449	if any, and I<must not> die, under any circumstances.	893	not> die, under any circumstances.
450		894
451	=cut	895	There can be any number of C<on_destroy> callbacks per coro, and there is
		896	no way currently to remove a callback once added.
452		897
453	sub on_destroy {
454	my ($self, $cb) = @_;
455
456	push @{ $self->{_on_destroy} }, $cb;
457	}
458
459	=item $oldprio = $coroutine->prio ($newprio)	898	=item $oldprio = $coro->prio ($newprio)
460		899
461	Sets (or gets, if the argument is missing) the priority of the	900	Sets (or gets, if the argument is missing) the priority of the
462	coroutine. Higher priority coroutines get run before lower priority	901	coro thread. Higher priority coro get run before lower priority
463	coroutines. Priorities are small signed integers (currently -4 .. +3),	902	coros. Priorities are small signed integers (currently -4 .. +3),
464	that you can refer to using PRIO_xxx constants (use the import tag :prio	903	that you can refer to using PRIO_xxx constants (use the import tag :prio
465	to get then):	904	to get then):
466		905
467	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	906	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
468	3 > 1 > 0 > -1 > -3 > -4	907	3 > 1 > 0 > -1 > -3 > -4
469		908
470	# set priority to HIGH	909	# set priority to HIGH
471	current->prio(PRIO_HIGH);	910	current->prio (PRIO_HIGH);
472		911
473	The idle coroutine ($Coro::idle) always has a lower priority than any	912	The idle coro thread ($Coro::idle) always has a lower priority than any
474	existing coroutine.	913	existing coro.
475		914
476	Changing the priority of the current coroutine will take effect immediately,	915	Changing the priority of the current coro will take effect immediately,
477	but changing the priority of coroutines in the ready queue (but not	916	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	917	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.	918	bug that will be fixed in some future version.
480		919
481	=item $newprio = $coroutine->nice ($change)	920	=item $newprio = $coro->nice ($change)
482		921
483	Similar to C<prio>, but subtract the given value from the priority (i.e.	922	Similar to C<prio>, but subtract the given value from the priority (i.e.
484	higher values mean lower priority, just as in unix).	923	higher values mean lower priority, just as in UNIX's nice command).
485		924
486	=item $olddesc = $coroutine->desc ($newdesc)	925	=item $olddesc = $coro->desc ($newdesc)
487		926
488	Sets (or gets in case the argument is missing) the description for this	927	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	928	coro thread. This is just a free-form string you can associate with a
490	coroutine.	929	coro.
491		930
492	This method simply sets the C<< $coroutine->{desc} >> member to the given	931	This method simply sets the C<< $coro->{desc} >> member to the given
493	string. You can modify this member directly if you wish.	932	string. You can modify this member directly if you wish, and in fact, this
		933	is often preferred to indicate major processing states that cna then be
		934	seen for example in a L<Coro::Debug> session:
		935
		936	sub my_long_function {
		937	local $Coro::current->{desc} = "now in my_long_function";
		938	...
		939	$Coro::current->{desc} = "my_long_function: phase 1";
		940	...
		941	$Coro::current->{desc} = "my_long_function: phase 2";
		942	...
		943	}
494		944
495	=cut	945	=cut
496		946
497	sub desc {	947	sub desc {
498	my $old = $_[0]{desc};	948	my $old = $_[0]{desc};
…		…
505	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");	955	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
506	}	956	}
507		957
508	=back	958	=back
509		959
510	=head2 GLOBAL FUNCTIONS	960	=head1 GLOBAL FUNCTIONS
511		961
512	=over 4	962	=over 4
513		963
514	=item Coro::nready	964	=item Coro::nready
515		965
516	Returns the number of coroutines that are currently in the ready state,	966	Returns the number of coro that are currently in the ready state,
517	i.e. that can be switched to by calling C<schedule> directory or	967	i.e. that can be switched to by calling C<schedule> directory or
518	indirectly. The value C<0> means that the only runnable coroutine is the	968	indirectly. The value C<0> means that the only runnable coro is the
519	currently running one, so C<cede> would have no effect, and C<schedule>	969	currently running one, so C<cede> would have no effect, and C<schedule>
520	would cause a deadlock unless there is an idle handler that wakes up some	970	would cause a deadlock unless there is an idle handler that wakes up some
521	coroutines.	971	coro.
522		972
523	=item my $guard = Coro::guard { ... }	973	=item my $guard = Coro::guard { ... }
524		974
525	This creates and returns a guard object. Nothing happens until the object	975	This function still exists, but is deprecated. Please use the
526	gets destroyed, in which case the codeblock given as argument will be	976	C<Guard::guard> function instead.
527	executed. This is useful to free locks or other resources in case of a
528	runtime error or when the coroutine gets canceled, as in both cases the
529	guard block will be executed. The guard object supports only one method,
530	C<< ->cancel >>, which will keep the codeblock from being executed.
531
532	Example: set some flag and clear it again when the coroutine gets canceled
533	or the function returns:
534
535	sub do_something {
536	my $guard = Coro::guard { $busy = 0 };
537	$busy = 1;
538
539	# do something that requires $busy to be true
540	}
541		977
542	=cut	978	=cut
543		979
544	sub guard(&) {	980	BEGIN { *guard = \&Guard::guard }
545	bless \(my $cb = $_[0]), "Coro::guard"
546	}
547
548	sub Coro::guard::cancel {
549	${$_[0]} = sub { };
550	}
551
552	sub Coro::guard::DESTROY {
553	${$_[0]}->();
554	}
555
556		981
557	=item unblock_sub { ... }	982	=item unblock_sub { ... }
558		983
559	This utility function takes a BLOCK or code reference and "unblocks" it,	984	This utility function takes a BLOCK or code reference and "unblocks" it,
560	returning a new coderef. Unblocking means that calling the new coderef	985	returning a new coderef. Unblocking means that calling the new coderef
561	will return immediately without blocking, returning nothing, while the	986	will return immediately without blocking, returning nothing, while the
562	original code ref will be called (with parameters) from within another	987	original code ref will be called (with parameters) from within another
563	coroutine.	988	coro.
564		989
565	The reason this function exists is that many event libraries (such as the	990	The reason this function exists is that many event libraries (such as
566	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	991	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
567	of thread-safety). This means you must not block within event callbacks,	992	of reentrancy). This means you must not block within event callbacks,
568	otherwise you might suffer from crashes or worse. The only event library	993	otherwise you might suffer from crashes or worse. The only event library
569	currently known that is safe to use without C<unblock_sub> is L<EV>.	994	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		995	you might still run into deadlocks if all event loops are blocked).
		996
		997	Coro will try to catch you when you block in the event loop
		998	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		999	only works when you do not run your own event loop.
570		1000
571	This function allows your callbacks to block by executing them in another	1001	This function allows your callbacks to block by executing them in another
572	coroutine where it is safe to block. One example where blocking is handy	1002	coro where it is safe to block. One example where blocking is handy
573	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	1003	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
574	disk, for example.	1004	disk, for example.
575		1005
576	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	1006	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
577	creating event callbacks that want to block.	1007	creating event callbacks that want to block.
578		1008
579	If your handler does not plan to block (e.g. simply sends a message to	1009	If your handler does not plan to block (e.g. simply sends a message to
580	another coroutine, or puts some other coroutine into the ready queue),	1010	another coro, or puts some other coro into the ready queue), there is
581	there is no reason to use C<unblock_sub>.	1011	no reason to use C<unblock_sub>.
582		1012
583	Note that you also need to use C<unblock_sub> for any other callbacks that	1013	Note that you also need to use C<unblock_sub> for any other callbacks that
584	are indirectly executed by any C-based event loop. For example, when you	1014	are indirectly executed by any C-based event loop. For example, when you
585	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	1015	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
586	provides callbacks that are the result of some event callback, then you	1016	provides callbacks that are the result of some event callback, then you
…		…
616	unshift @unblock_queue, [$cb, @_];	1046	unshift @unblock_queue, [$cb, @_];
617	$unblock_scheduler->ready;	1047	$unblock_scheduler->ready;
618	}	1048	}
619	}	1049	}
620		1050
621	=item $cb = Coro::rouse_cb	1051	=item $cb = rouse_cb
622		1052
623	Create and return a "rouse callback". That's a code reference that, when	1053	Create and return a "rouse callback". That's a code reference that,
624	called, will save its arguments and notify the owner coroutine of the	1054	when called, will remember a copy of its arguments and notify the owner
625	callback.	1055	coro of the callback.
626		1056
627	See the next function.	1057	See the next function.
628		1058
629	=item @args = Coro::rouse_wait [$cb]	1059	=item @args = rouse_wait [$cb]
630		1060
631	Wait for the specified rouse callback (or the last one tht was created in	1061	Wait for the specified rouse callback (or the last one that was created in
632	this coroutine).	1062	this coro).
633		1063
634	As soon as the callback is invoked (or when the calback was invoked before	1064	As soon as the callback is invoked (or when the callback was invoked
635	C<rouse_wait>), it will return a copy of the arguments originally passed	1065	before C<rouse_wait>), it will return the arguments originally passed to
636	to the rouse callback.	1066	the rouse callback. In scalar context, that means you get the I<last>
		1067	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1068	statement at the end.
637		1069
638	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1070	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
639		1071
640	=back	1072	=back
641		1073
642	=cut	1074	=cut
643		1075
		1076	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1077	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1078
		1079	*{"Coro::$module\::new"} = sub {
		1080	require "Coro/$module.pm";
		1081
		1082	# some modules have their new predefined in State.xs, some don't
		1083	*{"Coro::$module\::new"} = $old
		1084	if $old;
		1085
		1086	goto &{"Coro::$module\::new"};
		1087	};
		1088	}
		1089
644	1;	1090	1;
645		1091
646	=head1 HOW TO WAIT FOR A CALLBACK	1092	=head1 HOW TO WAIT FOR A CALLBACK
647		1093
648	It is very common for a coroutine to wait for some callback to be	1094	It is very common for a coro to wait for some callback to be
649	called. This occurs naturally when you use coroutines in an otherwise	1095	called. This occurs naturally when you use coro in an otherwise
650	event-based program, or when you use event-based libraries.	1096	event-based program, or when you use event-based libraries.
651		1097
652	These typically register a callback for some event, and call that callback	1098	These typically register a callback for some event, and call that callback
653	when the event occured. In a coroutine, however, you typically want to	1099	when the event occured. In a coro, however, you typically want to
654	just wait for the event, simplyifying things.	1100	just wait for the event, simplyifying things.
655		1101
656	For example C<< AnyEvent->child >> registers a callback to be called when	1102	For example C<< AnyEvent->child >> registers a callback to be called when
657	a specific child has exited:	1103	a specific child has exited:
658		1104
659	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	1105	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
660		1106
661	But from withina coroutine, you often just want to write this:	1107	But from within a coro, you often just want to write this:
662		1108
663	my $status = wait_for_child $pid;	1109	my $status = wait_for_child $pid;
664		1110
665	Coro offers two functions specifically designed to make this easy,	1111	Coro offers two functions specifically designed to make this easy,
666	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	1112	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
667		1113
668	The first function, C<rouse_cb>, generates and returns a callback that,	1114	The first function, C<rouse_cb>, generates and returns a callback that,
669	when invoked, will save it's arguments and notify the coroutine that	1115	when invoked, will save its arguments and notify the coro that
670	created the callback.	1116	created the callback.
671		1117
672	The second function, C<rouse_wait>, waits for the callback to be called	1118	The second function, C<rouse_wait>, waits for the callback to be called
673	(by calling C<schedule> to go to sleep) and returns the arguments	1119	(by calling C<schedule> to go to sleep) and returns the arguments
674	originally passed to the callback.	1120	originally passed to the callback.
…		…
689	you can roll your own, using C<schedule>:	1135	you can roll your own, using C<schedule>:
690		1136
691	sub wait_for_child($) {	1137	sub wait_for_child($) {
692	my ($pid) = @_;	1138	my ($pid) = @_;
693		1139
694	# store the current coroutine in $current,	1140	# store the current coro in $current,
695	# and provide result variables for the closure passed to ->child	1141	# and provide result variables for the closure passed to ->child
696	my $current = $Coro::current;	1142	my $current = $Coro::current;
697	my ($done, $rstatus);	1143	my ($done, $rstatus);
698		1144
699	# pass a closure to ->child	1145	# pass a closure to ->child
…		…
715		1161
716	=item fork with pthread backend	1162	=item fork with pthread backend
717		1163
718	When Coro is compiled using the pthread backend (which isn't recommended	1164	When Coro is compiled using the pthread backend (which isn't recommended
719	but required on many BSDs as their libcs are completely broken), then	1165	but required on many BSDs as their libcs are completely broken), then
720	coroutines will not survive a fork. There is no known workaround except to	1166	coro will not survive a fork. There is no known workaround except to
721	fix your libc and use a saner backend.	1167	fix your libc and use a saner backend.
722		1168
723	=item perl process emulation ("threads")	1169	=item perl process emulation ("threads")
724		1170
725	This module is not perl-pseudo-thread-safe. You should only ever use this	1171	This module is not perl-pseudo-thread-safe. You should only ever use this
726	module from the same thread (this requirement might be removed in the	1172	module from the first thread (this requirement might be removed in the
727	future to allow per-thread schedulers, but Coro::State does not yet allow	1173	future to allow per-thread schedulers, but Coro::State does not yet allow
728	this). I recommend disabling thread support and using processes, as having	1174	this). I recommend disabling thread support and using processes, as having
729	the windows process emulation enabled under unix roughly halves perl	1175	the windows process emulation enabled under unix roughly halves perl
730	performance, even when not used.	1176	performance, even when not used.
731		1177
		1178	Attempts to use threads created in another emulated process will crash
		1179	("cleanly", with a null pointer exception).
		1180
732	=item coroutine switching not signal safe	1181	=item coro switching is not signal safe
733		1182
734	You must not switch to another coroutine from within a signal handler	1183	You must not switch to another coro from within a signal handler (only
735	(only relevant with %SIG - most event libraries provide safe signals).	1184	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1185	you are sure you are not interrupting a Coro function.
736		1186
737	That means you I<MUST NOT> call any function that might "block" the	1187	That means you I<MUST NOT> call any function that might "block" the
738	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1188	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
739	anything that calls those. Everything else, including calling C<ready>,	1189	anything that calls those. Everything else, including calling C<ready>,
740	works.	1190	works.
741		1191
742	=back	1192	=back
743		1193
744		1194
		1195	=head1 WINDOWS PROCESS EMULATION
		1196
		1197	A great many people seem to be confused about ithreads (for example, Chip
		1198	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1199	while in the same mail making rather confused statements about perl
		1200	ithreads (for example, that memory or files would be shared), showing his
		1201	lack of understanding of this area - if it is hard to understand for Chip,
		1202	it is probably not obvious to everybody).
		1203
		1204	What follows is an ultra-condensed version of my talk about threads in
		1205	scripting languages given on the perl workshop 2009:
		1206
		1207	The so-called "ithreads" were originally implemented for two reasons:
		1208	first, to (badly) emulate unix processes on native win32 perls, and
		1209	secondly, to replace the older, real thread model ("5.005-threads").
		1210
		1211	It does that by using threads instead of OS processes. The difference
		1212	between processes and threads is that threads share memory (and other
		1213	state, such as files) between threads within a single process, while
		1214	processes do not share anything (at least not semantically). That
		1215	means that modifications done by one thread are seen by others, while
		1216	modifications by one process are not seen by other processes.
		1217
		1218	The "ithreads" work exactly like that: when creating a new ithreads
		1219	process, all state is copied (memory is copied physically, files and code
		1220	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1221	the same behaviour can be achieved by using operating system processes,
		1222	except that UNIX typically uses hardware built into the system to do this
		1223	efficiently, while the windows process emulation emulates this hardware in
		1224	software (rather efficiently, but of course it is still much slower than
		1225	dedicated hardware).
		1226
		1227	As mentioned before, loading code, modifying code, modifying data
		1228	structures and so on is only visible in the ithreads process doing the
		1229	modification, not in other ithread processes within the same OS process.
		1230
		1231	This is why "ithreads" do not implement threads for perl at all, only
		1232	processes. What makes it so bad is that on non-windows platforms, you can
		1233	actually take advantage of custom hardware for this purpose (as evidenced
		1234	by the forks module, which gives you the (i-) threads API, just much
		1235	faster).
		1236
		1237	Sharing data is in the i-threads model is done by transfering data
		1238	structures between threads using copying semantics, which is very slow -
		1239	shared data simply does not exist. Benchmarks using i-threads which are
		1240	communication-intensive show extremely bad behaviour with i-threads (in
		1241	fact, so bad that Coro, which cannot take direct advantage of multiple
		1242	CPUs, is often orders of magnitude faster because it shares data using
		1243	real threads, refer to my talk for details).
		1244
		1245	As summary, i-threads use threads to implement processes, while
		1246	the compatible forks module uses processes to emulate, uhm,
		1247	processes. I-threads slow down every perl program when enabled, and
		1248	outside of windows, serve no (or little) practical purpose, but
		1249	disadvantages every single-threaded Perl program.
		1250
		1251	This is the reason that I try to avoid the name "ithreads", as it is
		1252	misleading as it implies that it implements some kind of thread model for
		1253	perl, and prefer the name "windows process emulation", which describes the
		1254	actual use and behaviour of it much better.
		1255
745	=head1 SEE ALSO	1256	=head1 SEE ALSO
746		1257
747	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1258	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
748		1259
749	Debugging: L<Coro::Debug>.	1260	Debugging: L<Coro::Debug>.
750		1261
751	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1262	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
752		1263
753	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1264	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1265	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
754		1266
755	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1267	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
756		1268
757	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1269	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1270	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1271	L<Coro::Select>.
758		1272
759	XS API: L<Coro::MakeMaker>.	1273	XS API: L<Coro::MakeMaker>.
760		1274
761	Low level Configuration, Coroutine Environment: L<Coro::State>.	1275	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
762		1276
763	=head1 AUTHOR	1277	=head1 AUTHOR
764		1278
765	Marc Lehmann <schmorp@schmorp.de>	1279	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	1280	http://home.schmorp.de/

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Revision 1.233 by root, Fri Nov 21 06:02:07 2008 UTC vs.
Revision 1.297 by root, Thu May 12 23:55:39 2011 UTC