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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;
22	my $lock = new Coro::Semaphore;	21	my $lock = new Coro::Semaphore;
23	my $locked;	22	my $locked;
24		23
25	$lock->down;	24	$lock->down;
26	$locked = 1;	25	$locked = 1;
27	$lock->up;	26	$lock->up;
28		27
29	=head1 DESCRIPTION	28	=head1 DESCRIPTION
30		29
31	This module collection manages coroutines. Coroutines are similar to	30	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	31	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		32
39	Unlike a normal perl program, however, coroutines allow you to have	33	This module collection manages continuations in general, most often in
40	multiple running interpreters that share data, which is especially useful	34	the form of cooperative threads (also called coros, or simply "coro"
41	to code pseudo-parallel processes and for event-based programming, such as	35	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	36	general) run in parallel at the same time even on SMP machines. The
43	learn more.	37	specific flavor of thread offered by this module also guarantees you that
		38	it will not switch between threads unless necessary, at easily-identified
		39	points in your program, so locking and parallel access are rarely an
		40	issue, making thread programming much safer and easier than using other
		41	thread models.
44		42
45	Coroutines are also useful because Perl has no support for threads (the so	43	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	44	but only the windows process emulation (see section of same name for
47	emulation coming from the Windows platform: On standard operating systems	45	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	46	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	47	threads very easy. And coro threads are fast, too: disabling the Windows
50	aks your software vendor/distributor to do it for you).	48	process emulation code in your perl and using Coro can easily result in
		49	a two to four times speed increase for your programs. A parallel matrix
		50	multiplication benchmark (very communication-intensive) runs over 300
		51	times faster on a single core than perls pseudo-threads on a quad core
		52	using all four cores.
51		53
		54	Coro achieves that by supporting multiple running interpreters that share
		55	data, which is especially useful to code pseudo-parallel processes and
		56	for event-based programming, such as multiple HTTP-GET requests running
		57	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		58	into an event-based environment.
		59
52	In this module, coroutines are defined as "callchain + lexical variables +	60	In this module, a thread is defined as "callchain + lexical variables +
53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	61	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	62	its own set of lexicals and its own set of perls most important global
55	variables (see L<Coro::State> for more configuration).	63	variables (see L<Coro::State> for more configuration and background info).
		64
		65	See also the C<SEE ALSO> section at the end of this document - the Coro
		66	module family is quite large.
		67
		68	=head1 CORO THREAD LIFE CYCLE
		69
		70	During the long and exciting (or not) life of a coro thread, it goes
		71	through a number of states:
		72
		73	=over 4
		74
		75	=item 1. Creation
		76
		77	The first thing in the life of a coro thread is it's creation -
		78	obviously. The typical way to create a thread is to call the C<async
		79	BLOCK> function:
		80
		81	async {
		82	# thread code goes here
		83	};
		84
		85	You can also pass arguments, which are put in C<@_>:
		86
		87	async {
		88	print $_[1]; # prints 2
		89	} 1, 2, 3;
		90
		91	This creates a new coro thread and puts it into the ready queue, meaning
		92	it will run as soon as the CPU is free for it.
		93
		94	C<async> will return a Coro object - you can store this for future
		95	reference or ignore it - a thread that is running, ready to run or waiting
		96	for some event is alive on it's own.
		97
		98	Another way to create a thread is to call the C<new> constructor with a
		99	code-reference:
		100
		101	new Coro sub {
		102	# thread code goes here
		103	}, @optional_arguments;
		104
		105	This is quite similar to calling C<async>, but the important difference is
		106	that the new thread is not put into the ready queue, so the thread will
		107	not run until somebody puts it there. C<async> is, therefore, identical to
		108	this sequence:
		109
		110	my $coro = new Coro sub {
		111	# thread code goes here
		112	};
		113	$coro->ready;
		114	return $coro;
		115
		116	=item 2. Startup
		117
		118	When a new coro thread is created, only a copy of the code reference
		119	and the arguments are stored, no extra memory for stacks and so on is
		120	allocated, keeping the coro thread in a low-memory state.
		121
		122	Only when it actually starts executing will all the resources be finally
		123	allocated.
		124
		125	The optional arguments specified at coro creation are available in C<@_>,
		126	similar to function calls.
		127
		128	=item 3. Running / Blocking
		129
		130	A lot can happen after the coro thread has started running. Quite usually,
		131	it will not run to the end in one go (because you could use a function
		132	instead), but it will give up the CPU regularly because it waits for
		133	external events.
		134
		135	As long as a coro thread runs, its Coro object is available in the global
		136	variable C<$Coro::current>.
		137
		138	The low-level way to give up the CPU is to call the scheduler, which
		139	selects a new coro thread to run:
		140
		141	Coro::schedule;
		142
		143	Since running threads are not in the ready queue, calling the scheduler
		144	without doing anything else will block the coro thread forever - you need
		145	to arrange either for the coro to put woken up (readied) by some other
		146	event or some other thread, or you can put it into the ready queue before
		147	scheduling:
		148
		149	# this is exactly what Coro::cede does
		150	$Coro::current->ready;
		151	Coro::schedule;
		152
		153	All the higher-level synchronisation methods (Coro::Semaphore,
		154	Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
		155	Coro::schedule >>.
		156
		157	While the coro thread is running it also might get assigned a C-level
		158	thread, or the C-level thread might be unassigned from it, as the Coro
		159	runtime wishes. A C-level thread needs to be assigned when your perl
		160	thread calls into some C-level function and that function in turn calls
		161	perl and perl then wants to switch coroutines. This happens most often
		162	when you run an event loop and block in the callback, or when perl
		163	itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
		164	mechanism.
		165
		166	=item 4. Termination
		167
		168	Many threads actually terminate after some time. There are a number of
		169	ways to terminate a coro thread, the simplest is returning from the
		170	top-level code reference:
		171
		172	async {
		173	# after returning from here, the coro thread is terminated
		174	};
		175
		176	async {
		177	return if 0.5 < rand; # terminate a little earlier, maybe
		178	print "got a chance to print this\n";
		179	# or here
		180	};
		181
		182	Any values returned from the coroutine can be recovered using C<< ->join
		183	>>:
		184
		185	my $coro = async {
		186	"hello, world\n" # return a string
		187	};
		188
		189	my $hello_world = $coro->join;
		190
		191	print $hello_world;
		192
		193	Another way to terminate is to call C<< Coro::terminate >>, which at any
		194	subroutine call nesting level:
		195
		196	async {
		197	Coro::terminate "return value 1", "return value 2";
		198	};
		199
		200	Yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the coro
		201	thread from another thread:
		202
		203	my $coro = async {
		204	exit 1;
		205	};
		206
		207	$coro->cancel; # also accepts values for ->join to retrieve
		208
		209	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		210	actually exiting, and might leave C libraries and XS modules in a weird
		211	state. Unlike other thread implementations, however, Coro is exceptionally
		212	safe with regards to cancellation, as perl will always be in a consistent
		213	state, and for those cases where you want to do truly marvellous things
		214	with your coro while it is being cancelled - that is, make sure all
		215	cleanup code is executed from the thread being cancelled - there is even a
		216	C<< ->safe_cancel >> method.
		217
		218	So, cancelling a thread that runs in an XS event loop might not be the
		219	best idea, but any other combination that deals with perl only (cancelling
		220	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		221	safe.
		222
		223	Last not least, a coro thread object that isn't referenced is C<<
		224	->cancel >>'ed automatically - just like other objects in Perl. This
		225	is not such a common case, however - a running thread is referencedy by
		226	C<$Coro::current>, a thread ready to run is referenced by the ready queue,
		227	a thread waiting on a lock or semaphore is referenced by being in some
		228	wait list and so on. But a thread that isn't in any of those queues gets
		229	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	A slightly embellished example might make it clearer:
		239
		240	async {
		241	my $guard = Guard::guard { print "destroyed\n" };
		242	schedule while 1;
		243	};
		244
		245	cede;
		246
		247	Superficially one might not expect any output - since the C<async>
		248	implements an endless loop, the C<$guard> will not be cleaned up. However,
		249	since the thread object returned by C<async> is not stored anywhere, the
		250	thread is initially referenced because it is in the ready queue, when it
		251	runs it is referenced by C<$Coro::current>, but when it calls C<schedule>,
		252	it gets C<cancel>ed causing the guard object to be destroyed (see the next
		253	section), and printing it's message.
		254
		255	If this seems a bit drastic, remember that this only happens when nothing
		256	references the thread anymore, which means there is no way to further
		257	execute it, ever. The only options at this point are leaking the thread,
		258	or cleaning it up, which brings us to...
		259
		260	=item 5. Cleanup
		261
		262	Threads will allocate various resources. Most but not all will be returned
		263	when a thread terminates, during clean-up.
		264
		265	Cleanup is quite similar to throwing an uncaught exception: perl will
		266	work it's way up through all subroutine calls and blocks. On it's way, it
		267	will release all C<my> variables, undo all C<local>'s and free any other
		268	resources truly local to the thread.
		269
		270	So, a common way to free resources is to keep them referenced only by my
		271	variables:
		272
		273	async {
		274	my $big_cache = new Cache ...;
		275	};
		276
		277	If there are no other references, then the C<$big_cache> object will be
		278	freed when the thread terminates, regardless of how it does so.
		279
		280	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		281	resources, but that's where the C<guard> methods come in handy:
		282
		283	my $sem = new Coro::Semaphore;
		284
		285	async {
		286	my $lock_guard = $sem->guard;
		287	# if we return, or die or get cancelled, here,
		288	# then the semaphore will be "up"ed.
		289	};
		290
		291	The C<Guard::guard> function comes in handy for any custom cleanup you
		292	might want to do (but you cannot switch to other coroutines from those
		293	code blocks):
		294
		295	async {
		296	my $window = new Gtk2::Window "toplevel";
		297	# The window will not be cleaned up automatically, even when $window
		298	# gets freed, so use a guard to ensure it's destruction
		299	# in case of an error:
		300	my $window_guard = Guard::guard { $window->destroy };
		301
		302	# we are safe here
		303	};
		304
		305	Last not least, C<local> can often be handy, too, e.g. when temporarily
		306	replacing the coro thread description:
		307
		308	sub myfunction {
		309	local $Coro::current->{desc} = "inside myfunction(@_)";
		310
		311	# if we return or die here, the description will be restored
		312	}
		313
		314	=item 6. Viva La Zombie Muerte
		315
		316	Even after a thread has terminated and cleaned up its resources, the Coro
		317	object still is there and stores the return values of the thread.
		318
		319	When there are no other references, it will simply be cleaned up and
		320	freed.
		321
		322	If there areany references, the Coro object will stay around, and you
		323	can call C<< ->join >> as many times as you wish to retrieve the result
		324	values:
		325
		326	async {
		327	print "hi\n";
		328	1
		329	};
		330
		331	# run the async above, and free everything before returning
		332	# from Coro::cede:
		333	Coro::cede;
		334
		335	{
		336	my $coro = async {
		337	print "hi\n";
		338	1
		339	};
		340
		341	# run the async above, and clean up, but do not free the coro
		342	# object:
		343	Coro::cede;
		344
		345	# optionally retrieve the result values
		346	my @results = $coro->join;
		347
		348	# now $coro goes out of scope, and presumably gets freed
		349	};
		350
		351	=back
56		352
57	=cut	353	=cut
58		354
59	package Coro;	355	package Coro;
60		356
61	use strict qw(vars subs);	357	use common::sense;
62	no warnings "uninitialized";	358
		359	use Carp ();
		360
		361	use Guard ();
63		362
64	use Coro::State;	363	use Coro::State;
65		364
66	use base qw(Coro::State Exporter);	365	use base qw(Coro::State Exporter);
67		366
68	our $idle; # idle handler	367	our $idle; # idle handler
69	our $main; # main coroutine	368	our $main; # main coro
70	our $current; # current coroutine	369	our $current; # current coro
71		370
72	our $VERSION = 5.0;	371	our $VERSION = 6.513;
73		372
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	373	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	374	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	375	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	376	);
78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	377	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
79		378
		379	=head1 GLOBAL VARIABLES
		380
80	=over 4	381	=over 4
81		382
82	=item $Coro::main	383	=item $Coro::main
83		384
84	This variable stores the coroutine object that represents the main	385	This variable stores the Coro object that represents the main
85	program. While you cna C<ready> it and do most other things you can do to	386	program. While you can C<ready> it and do most other things you can do to
86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	387	coro, it is mainly useful to compare again C<$Coro::current>, to see
87	whether you are running in the main program or not.	388	whether you are running in the main program or not.
88		389
89	=cut	390	=cut
90		391
91	# $main is now being initialised by Coro::State	392	# $main is now being initialised by Coro::State
92		393
93	=item $Coro::current	394	=item $Coro::current
94		395
95	The coroutine object representing the current coroutine (the last	396	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	397	coro that the Coro scheduler switched to). The initial value is
97	C<$Coro::main> (of course).	398	C<$Coro::main> (of course).
98		399
99	This variable is B<strictly> I<read-only>. You can take copies of the	400	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	401	value stored in it and use it as any other Coro object, but you must
101	not otherwise modify the variable itself.	402	not otherwise modify the variable itself.
102		403
103	=cut	404	=cut
104		405
105	sub current() { $current } # [DEPRECATED]	406	sub current() { $current } # [DEPRECATED]
106		407
107	=item $Coro::idle	408	=item $Coro::idle
108		409
109	This variable is mainly useful to integrate Coro into event loops. It is	410	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	411	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
111	pretty low-level functionality.	412	pretty low-level functionality.
112		413
113	This variable stores a callback that is called whenever the scheduler	414	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	415	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		416
		417	The default implementation dies with "FATAL: deadlock detected.", followed
		418	by a thread listing, because the program has no other way to continue.
		419
118	This hook is overwritten by modules such as C<Coro::Timer> and	420	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	421	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
120	coroutine so the scheduler can run it.	422	coro so the scheduler can run it.
121		423
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	424	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		425
133	=cut	426	=cut
134		427
135	$idle = sub {	428	# ||= because other modules could have provided their own by now
136	require Carp;	429	$idle ||= new Coro sub {
137	Carp::croak ("FATAL: deadlock detected");	430	require Coro::Debug;
		431	die "FATAL: deadlock detected.\n"
		432	. Coro::Debug::ps_listing ();
138	};	433	};
139		434
140	sub _cancel {
141	my ($self) = @_;
142
143	# free coroutine data and mark as destructed
144	$self->_destroy
145	or return;
146
147	# call all destruction callbacks
148	$_->(@{$self->{_status}})
149	for @{ delete $self->{_on_destroy} || [] };
150	}
151
152	# this coroutine is necessary because a coroutine	435	# this coro is necessary because a coro
153	# cannot destroy itself.	436	# cannot destroy itself.
154	my @destroy;	437	our @destroy;
155	my $manager;	438	our $manager;
156		439
157	$manager = new Coro sub {	440	$manager = new Coro sub {
158	while () {	441	while () {
159	(shift @destroy)->_cancel	442	_destroy shift @destroy
160	while @destroy;	443	while @destroy;
161		444
162	&schedule;	445	&schedule;
163	}	446	}
164	};	447	};
165	$manager->{desc} = "[coro manager]";	448	$manager->{desc} = "[coro manager]";
166	$manager->prio (PRIO_MAX);	449	$manager->prio (PRIO_MAX);
167		450
168	=back	451	=back
169		452
170	=head2 SIMPLE COROUTINE CREATION	453	=head1 SIMPLE CORO CREATION
171		454
172	=over 4	455	=over 4
173		456
174	=item async { ... } [@args...]	457	=item async { ... } [@args...]
175		458
176	Create a new coroutine and return it's coroutine object (usually	459	Create a new coro and return its Coro object (usually
177	unused). The coroutine will be put into the ready queue, so	460	unused). The coro will be put into the ready queue, so
178	it will start running automatically on the next scheduler run.	461	it will start running automatically on the next scheduler run.
179		462
180	The first argument is a codeblock/closure that should be executed in the	463	The first argument is a codeblock/closure that should be executed in the
181	coroutine. When it returns argument returns the coroutine is automatically	464	coro. When it returns argument returns the coro is automatically
182	terminated.	465	terminated.
183		466
184	The remaining arguments are passed as arguments to the closure.	467	The remaining arguments are passed as arguments to the closure.
185		468
186	See the C<Coro::State::new> constructor for info about the coroutine	469	See the C<Coro::State::new> constructor for info about the coro
187	environment in which coroutines are executed.	470	environment in which coro are executed.
188		471
189	Calling C<exit> in a coroutine will do the same as calling exit outside	472	Calling C<exit> in a coro will do the same as calling exit outside
190	the coroutine. Likewise, when the coroutine dies, the program will exit,	473	the coro. Likewise, when the coro dies, the program will exit,
191	just as it would in the main program.	474	just as it would in the main program.
192		475
193	If you do not want that, you can provide a default C<die> handler, or	476	If you do not want that, you can provide a default C<die> handler, or
194	simply avoid dieing (by use of C<eval>).	477	simply avoid dieing (by use of C<eval>).
195		478
196	Example: Create a new coroutine that just prints its arguments.	479	Example: Create a new coro that just prints its arguments.
197		480
198	async {	481	async {
199	print "@_\n";	482	print "@_\n";
200	} 1,2,3,4;	483	} 1,2,3,4;
201		484
202	=cut
203
204	sub async(&@) {
205	my $coro = new Coro @_;
206	$coro->ready;
207	$coro
208	}
209
210	=item async_pool { ... } [@args...]	485	=item async_pool { ... } [@args...]
211		486
212	Similar to C<async>, but uses a coroutine pool, so you should not call	487	Similar to C<async>, but uses a coro pool, so you should not call
213	terminate or join on it (although you are allowed to), and you get a	488	terminate or join on it (although you are allowed to), and you get a
214	coroutine that might have executed other code already (which can be good	489	coro that might have executed other code already (which can be good
215	or bad :).	490	or bad :).
216		491
217	On the plus side, this function is faster than creating (and destroying)	492	On the plus side, this function is about twice as fast as creating (and
218	a completly new coroutine, so if you need a lot of generic coroutines in	493	destroying) a completely new coro, so if you need a lot of generic
219	quick successsion, use C<async_pool>, not C<async>.	494	coros in quick successsion, use C<async_pool>, not C<async>.
220		495
221	The code block is executed in an C<eval> context and a warning will be	496	The code block is executed in an C<eval> context and a warning will be
222	issued in case of an exception instead of terminating the program, as	497	issued in case of an exception instead of terminating the program, as
223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	498	C<async> does. As the coro is being reused, stuff like C<on_destroy>
224	will not work in the expected way, unless you call terminate or cancel,	499	will not work in the expected way, unless you call terminate or cancel,
225	which somehow defeats the purpose of pooling (but is fine in the	500	which somehow defeats the purpose of pooling (but is fine in the
226	exceptional case).	501	exceptional case).
227		502
228	The priority will be reset to C<0> after each run, tracing will be	503	The priority will be reset to C<0> after each run, all C<swap_sv> calls
229	disabled, the description will be reset and the default output filehandle	504	will be undone, tracing will be disabled, the description will be reset
230	gets restored, so you can change all these. Otherwise the coroutine will	505	and the default output filehandle gets restored, so you can change all
231	be re-used "as-is": most notably if you change other per-coroutine global	506	these. Otherwise the coro will be re-used "as-is": most notably if you
232	stuff such as C<$/> you I<must needs> revert that change, which is most	507	change other per-coro global stuff such as C<$/> you I<must needs> revert
233	simply done by using local as in: C<< local $/ >>.	508	that change, which is most simply done by using local as in: C<< local $/
		509	>>.
234		510
235	The idle pool size is limited to C<8> idle coroutines (this can be	511	The idle pool size is limited to C<8> idle coros (this can be
236	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle	512	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
237	coros as required.	513	coros as required.
238		514
239	If you are concerned about pooled coroutines growing a lot because a	515	If you are concerned about pooled coros growing a lot because a
240	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	516	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
241	{ terminate }> once per second or so to slowly replenish the pool. In	517	{ terminate }> once per second or so to slowly replenish the pool. In
242	addition to that, when the stacks used by a handler grows larger than 16kb	518	addition to that, when the stacks used by a handler grows larger than 32kb
243	(adjustable via $Coro::POOL_RSS) it will also be destroyed.	519	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
244		520
245	=cut	521	=cut
246		522
247	our $POOL_SIZE = 8;	523	our $POOL_SIZE = 8;
248	our $POOL_RSS = 16 * 1024;	524	our $POOL_RSS = 32 * 1024;
249	our @async_pool;	525	our @async_pool;
250		526
251	sub pool_handler {	527	sub pool_handler {
252	my $cb;
253
254	while () {	528	while () {
255	eval {	529	eval {
256	while () {	530	&{&_pool_handler} while 1;
257	_pool_1 $cb;
258	&$cb;
259	_pool_2 $cb;
260	&schedule;
261	}
262	};	531	};
263		532
264	if ($@) {
265	last if $@ eq "\3async_pool terminate\2\n";
266	warn $@;	533	warn $@ if $@;
267	}
268	}	534	}
269	}	535	}
270		536
271	sub async_pool(&@) {
272	# this is also inlined into the unblock_scheduler
273	my $coro = (pop @async_pool) || new Coro \&pool_handler;
274
275	$coro->{_invoke} = [@_];
276	$coro->ready;
277
278	$coro
279	}
280
281	=back	537	=back
282		538
283	=head2 STATIC METHODS	539	=head1 STATIC METHODS
284		540
285	Static methods are actually functions that operate on the current coroutine.	541	Static methods are actually functions that implicitly operate on the
		542	current coro.
286		543
287	=over 4	544	=over 4
288		545
289	=item schedule	546	=item schedule
290		547
291	Calls the scheduler. The scheduler will find the next coroutine that is	548	Calls the scheduler. The scheduler will find the next coro that is
292	to be run from the ready queue and switches to it. The next coroutine	549	to be run from the ready queue and switches to it. The next coro
293	to be run is simply the one with the highest priority that is longest	550	to be run is simply the one with the highest priority that is longest
294	in its ready queue. If there is no coroutine ready, it will clal the	551	in its ready queue. If there is no coro ready, it will call the
295	C<$Coro::idle> hook.	552	C<$Coro::idle> hook.
296		553
297	Please note that the current coroutine will I<not> be put into the ready	554	Please note that the current coro will I<not> be put into the ready
298	queue, so calling this function usually means you will never be called	555	queue, so calling this function usually means you will never be called
299	again unless something else (e.g. an event handler) calls C<< ->ready >>,	556	again unless something else (e.g. an event handler) calls C<< ->ready >>,
300	thus waking you up.	557	thus waking you up.
301		558
302	This makes C<schedule> I<the> generic method to use to block the current	559	This makes C<schedule> I<the> generic method to use to block the current
303	coroutine and wait for events: first you remember the current coroutine in	560	coro and wait for events: first you remember the current coro in
304	a variable, then arrange for some callback of yours to call C<< ->ready	561	a variable, then arrange for some callback of yours to call C<< ->ready
305	>> on that once some event happens, and last you call C<schedule> to put	562	>> on that once some event happens, and last you call C<schedule> to put
306	yourself to sleep. Note that a lot of things can wake your coroutine up,	563	yourself to sleep. Note that a lot of things can wake your coro up,
307	so you need to check whether the event indeed happened, e.g. by storing the	564	so you need to check whether the event indeed happened, e.g. by storing the
308	status in a variable.	565	status in a variable.
309		566
310	The canonical way to wait on external events is this:	567	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
311		568
312	{	569	=item cede
313	# remember current coroutine
314	my $current = $Coro::current;
315		570
316	# register a hypothetical event handler	571	"Cede" to other coros. This function puts the current coro into
317	on_event_invoke sub {	572	the ready queue and calls C<schedule>, which has the effect of giving
318	# wake up sleeping coroutine	573	up the current "timeslice" to other coros of the same or higher
319	$current->ready;	574	priority. Once your coro gets its turn again it will automatically be
320	undef $current;	575	resumed.
		576
		577	This function is often called C<yield> in other languages.
		578
		579	=item Coro::cede_notself
		580
		581	Works like cede, but is not exported by default and will cede to I<any>
		582	coro, regardless of priority. This is useful sometimes to ensure
		583	progress is made.
		584
		585	=item terminate [arg...]
		586
		587	Terminates the current coro with the given status values (see
		588	L<cancel>). The values will not be copied, but referenced directly.
		589
		590	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		591
		592	These function install enter and leave winders in the current scope. The
		593	enter block will be executed when on_enter is called and whenever the
		594	current coro is re-entered by the scheduler, while the leave block is
		595	executed whenever the current coro is blocked by the scheduler, and
		596	also when the containing scope is exited (by whatever means, be it exit,
		597	die, last etc.).
		598
		599	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		600	BLOCKs>. That means: do not even think about calling C<die> without an
		601	eval, and do not even think of entering the scheduler in any way.
		602
		603	Since both BLOCKs are tied to the current scope, they will automatically
		604	be removed when the current scope exits.
		605
		606	These functions implement the same concept as C<dynamic-wind> in scheme
		607	does, and are useful when you want to localise some resource to a specific
		608	coro.
		609
		610	They slow down thread switching considerably for coros that use them
		611	(about 40% for a BLOCK with a single assignment, so thread switching is
		612	still reasonably fast if the handlers are fast).
		613
		614	These functions are best understood by an example: The following function
		615	will change the current timezone to "Antarctica/South_Pole", which
		616	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		617	which remember/change the current timezone and restore the previous
		618	value, respectively, the timezone is only changed for the coro that
		619	installed those handlers.
		620
		621	use POSIX qw(tzset);
		622
		623	async {
		624	my $old_tz; # store outside TZ value here
		625
		626	Coro::on_enter {
		627	$old_tz = $ENV{TZ}; # remember the old value
		628
		629	$ENV{TZ} = "Antarctica/South_Pole";
		630	tzset; # enable new value
321	};	631	};
322		632
323	# call schedule until event occurred.	633	Coro::on_leave {
324	# in case we are woken up for other reasons	634	$ENV{TZ} = $old_tz;
325	# (current still defined), loop.	635	tzset; # restore old value
326	Coro::schedule while $current;	636	};
		637
		638	# at this place, the timezone is Antarctica/South_Pole,
		639	# without disturbing the TZ of any other coro.
		640	};
		641
		642	This can be used to localise about any resource (locale, uid, current
		643	working directory etc.) to a block, despite the existence of other
		644	coros.
		645
		646	Another interesting example implements time-sliced multitasking using
		647	interval timers (this could obviously be optimised, but does the job):
		648
		649	# "timeslice" the given block
		650	sub timeslice(&) {
		651	use Time::HiRes ();
		652
		653	Coro::on_enter {
		654	# on entering the thread, we set an VTALRM handler to cede
		655	$SIG{VTALRM} = sub { cede };
		656	# and then start the interval timer
		657	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		658	};
		659	Coro::on_leave {
		660	# on leaving the thread, we stop the interval timer again
		661	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		662	};
		663
		664	&{+shift};
327	}	665	}
328		666
329	=item cede	667	# use like this:
		668	timeslice {
		669	# The following is an endless loop that would normally
		670	# monopolise the process. Since it runs in a timesliced
		671	# environment, it will regularly cede to other threads.
		672	while () { }
		673	};
330		674
331	"Cede" to other coroutines. This function puts the current coroutine into
332	the ready queue and calls C<schedule>, which has the effect of giving
333	up the current "timeslice" to other coroutines of the same or higher
334	priority. Once your coroutine gets its turn again it will automatically be
335	resumed.
336
337	This function is often called C<yield> in other languages.
338
339	=item Coro::cede_notself
340
341	Works like cede, but is not exported by default and will cede to I<any>
342	coroutine, regardless of priority. This is useful sometimes to ensure
343	progress is made.
344
345	=item terminate [arg...]
346
347	Terminates the current coroutine with the given status values (see L<cancel>).
348		675
349	=item killall	676	=item killall
350		677
351	Kills/terminates/cancels all coroutines except the currently running	678	Kills/terminates/cancels all coros except the currently running one.
352	one. This is useful after a fork, either in the child or the parent, as
353	usually only one of them should inherit the running coroutines.
354		679
355	Note that while this will try to free some of the main programs resources,	680	Note that while this will try to free some of the main interpreter
		681	resources if the calling coro isn't the main coro, but one
356	you cannot free all of them, so if a coroutine that is not the main	682	cannot free all of them, so if a coro that is not the main coro
357	program calls this function, there will be some one-time resource leak.	683	calls this function, there will be some one-time resource leak.
358		684
359	=cut	685	=cut
360
361	sub terminate {
362	$current->cancel (@_);
363	}
364		686
365	sub killall {	687	sub killall {
366	for (Coro::State::list) {	688	for (Coro::State::list) {
367	$_->cancel	689	$_->cancel
368	if $_ != $current && UNIVERSAL::isa $_, "Coro";	690	if $_ != $current && UNIVERSAL::isa $_, "Coro";
369	}	691	}
370	}	692	}
371		693
372	=back	694	=back
373		695
374	=head2 COROUTINE METHODS	696	=head1 CORO OBJECT METHODS
375		697
376	These are the methods you can call on coroutine objects (or to create	698	These are the methods you can call on coro objects (or to create
377	them).	699	them).
378		700
379	=over 4	701	=over 4
380		702
381	=item new Coro \&sub [, @args...]	703	=item new Coro \&sub [, @args...]
382		704
383	Create a new coroutine and return it. When the sub returns, the coroutine	705	Create a new coro and return it. When the sub returns, the coro
384	automatically terminates as if C<terminate> with the returned values were	706	automatically terminates as if C<terminate> with the returned values were
385	called. To make the coroutine run you must first put it into the ready	707	called. To make the coro run you must first put it into the ready
386	queue by calling the ready method.	708	queue by calling the ready method.
387		709
388	See C<async> and C<Coro::State::new> for additional info about the	710	See C<async> and C<Coro::State::new> for additional info about the
389	coroutine environment.	711	coro environment.
390		712
391	=cut	713	=cut
392		714
393	sub _run_coro {	715	sub _coro_run {
394	terminate &{+shift};	716	terminate &{+shift};
395	}	717	}
396		718
397	sub new {
398	my $class = shift;
399
400	$class->SUPER::new (\&_run_coro, @_)
401	}
402
403	=item $success = $coroutine->ready	719	=item $success = $coro->ready
404		720
405	Put the given coroutine into the end of its ready queue (there is one	721	Put the given coro into the end of its ready queue (there is one
406	queue for each priority) and return true. If the coroutine is already in	722	queue for each priority) and return true. If the coro is already in
407	the ready queue, do nothing and return false.	723	the ready queue, do nothing and return false.
408		724
409	This ensures that the scheduler will resume this coroutine automatically	725	This ensures that the scheduler will resume this coro automatically
410	once all the coroutines of higher priority and all coroutines of the same	726	once all the coro of higher priority and all coro of the same
411	priority that were put into the ready queue earlier have been resumed.	727	priority that were put into the ready queue earlier have been resumed.
412		728
		729	=item $coro->suspend
		730
		731	Suspends the specified coro. A suspended coro works just like any other
		732	coro, except that the scheduler will not select a suspended coro for
		733	execution.
		734
		735	Suspending a coro can be useful when you want to keep the coro from
		736	running, but you don't want to destroy it, or when you want to temporarily
		737	freeze a coro (e.g. for debugging) to resume it later.
		738
		739	A scenario for the former would be to suspend all (other) coros after a
		740	fork and keep them alive, so their destructors aren't called, but new
		741	coros can be created.
		742
		743	=item $coro->resume
		744
		745	If the specified coro was suspended, it will be resumed. Note that when
		746	the coro was in the ready queue when it was suspended, it might have been
		747	unreadied by the scheduler, so an activation might have been lost.
		748
		749	To avoid this, it is best to put a suspended coro into the ready queue
		750	unconditionally, as every synchronisation mechanism must protect itself
		751	against spurious wakeups, and the one in the Coro family certainly do
		752	that.
		753
		754	=item $state->is_new
		755
		756	Returns true iff this Coro object is "new", i.e. has never been run
		757	yet. Those states basically consist of only the code reference to call and
		758	the arguments, but consumes very little other resources. New states will
		759	automatically get assigned a perl interpreter when they are transferred to.
		760
		761	=item $state->is_zombie
		762
		763	Returns true iff the Coro object has been cancelled, i.e.
		764	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		765	C<safe_cancel>'ed or simply went out of scope.
		766
		767	The name "zombie" stems from UNIX culture, where a process that has
		768	exited and only stores and exit status and no other resources is called a
		769	"zombie".
		770
413	=item $is_ready = $coroutine->is_ready	771	=item $is_ready = $coro->is_ready
414		772
415	Return whether the coroutine is currently the ready queue or not,	773	Returns true iff the Coro object is in the ready queue. Unless the Coro
		774	object gets destroyed, it will eventually be scheduled by the scheduler.
416		775
		776	=item $is_running = $coro->is_running
		777
		778	Returns true iff the Coro object is currently running. Only one Coro object
		779	can ever be in the running state (but it currently is possible to have
		780	multiple running Coro::States).
		781
		782	=item $is_suspended = $coro->is_suspended
		783
		784	Returns true iff this Coro object has been suspended. Suspended Coros will
		785	not ever be scheduled.
		786
417	=item $coroutine->cancel (arg...)	787	=item $coro->cancel (arg...)
418		788
419	Terminates the given coroutine and makes it return the given arguments as	789	Terminates the given Coro thread and makes it return the given arguments as
420	status (default: the empty list). Never returns if the coroutine is the	790	status (default: an empty list). Never returns if the Coro is the
421	current coroutine.	791	current Coro.
422		792
423	=cut	793	This is a rather brutal way to free a coro, with some limitations - if
		794	the thread is inside a C callback that doesn't expect to be canceled,
		795	bad things can happen, or if the cancelled thread insists on running
		796	complicated cleanup handlers that rely on its thread context, things will
		797	not work.
424		798
425	sub cancel {	799	Any cleanup code being run (e.g. from C<guard> blocks, destructors and so
426	my $self = shift;	800	on) will be run without a thread context, and is not allowed to switch
427	$self->{_status} = [@_];	801	to other threads. A common mistake is to call C<< ->cancel >> from a
		802	destructor called by die'ing inside the thread to be cancelled for
		803	example.
428		804
429	if ($current == $self) {	805	On the plus side, C<< ->cancel >> will always clean up the thread, no
430	push @destroy, $self;	806	matter what. If your cleanup code is complex or you want to avoid
431	$manager->ready;	807	cancelling a C-thread that doesn't know how to clean up itself, it can be
432	&schedule while 1;	808	better to C<< ->throw >> an exception, or use C<< ->safe_cancel >>.
433	} else {	809
434	$self->_cancel;	810	The arguments to C<< ->cancel >> are not copied, but instead will
		811	be referenced directly (e.g. if you pass C<$var> and after the call
		812	change that variable, then you might change the return values passed to
		813	e.g. C<join>, so don't do that).
		814
		815	The resources of the Coro are usually freed (or destructed) before this
		816	call returns, but this can be delayed for an indefinite amount of time, as
		817	in some cases the manager thread has to run first to actually destruct the
		818	Coro object.
		819
		820	=item $coro->safe_cancel ($arg...)
		821
		822	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		823	consequently, can fail with an exception in cases the thread is not in a
		824	cancellable state. Essentially, C<< ->safe_cancel >> is a C<< ->cancel >>
		825	with extra checks before canceling.
		826
		827	It works a bit like throwing an exception that cannot be caught -
		828	specifically, it will clean up the thread from within itself, so all
		829	cleanup handlers (e.g. C<guard> blocks) are run with full thread
		830	context and can block if they wish. The downside is that there is no
		831	guarantee that the thread can be cancelled when you call this method, and
		832	therefore, it might fail. It is also considerably slower than C<cancel> or
		833	C<terminate>.
		834
		835	A thread is in a safe-cancellable state if it either hasn't been run yet,
		836	or it has no C context attached and is inside an SLF function.
		837
		838	The latter two basically mean that the thread isn't currently inside a
		839	perl callback called from some C function (usually via some XS modules)
		840	and isn't currently executing inside some C function itself (via Coro's XS
		841	API).
		842
		843	This call returns true when it could cancel the thread, or croaks with an
		844	error otherwise (i.e. it either returns true or doesn't return at all).
		845
		846	Why the weird interface? Well, there are two common models on how and
		847	when to cancel things. In the first, you have the expectation that your
		848	coro thread can be cancelled when you want to cancel it - if the thread
		849	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		850	croaks to notify of the bug.
		851
		852	In the second model you sometimes want to ask nicely to cancel a thread,
		853	but if it's not a good time, well, then don't cancel. This can be done
		854	relatively easy like this:
		855
		856	if (! eval { $coro->safe_cancel }) {
		857	warn "unable to cancel thread: $@";
435	}	858	}
436	}
437		859
		860	However, what you never should do is first try to cancel "safely" and
		861	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		862	no sense: either you rely on being able to execute cleanup code in your
		863	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		864	only way, and if you don't, then C<< ->cancel >> is always faster and more
		865	direct.
		866
		867	=item $coro->schedule_to
		868
		869	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		870	of continuing with the next coro from the ready queue, always switch to
		871	the given coro object (regardless of priority etc.). The readyness
		872	state of that coro isn't changed.
		873
		874	This is an advanced method for special cases - I'd love to hear about any
		875	uses for this one.
		876
		877	=item $coro->cede_to
		878
		879	Like C<schedule_to>, but puts the current coro into the ready
		880	queue. This has the effect of temporarily switching to the given
		881	coro, and continuing some time later.
		882
		883	This is an advanced method for special cases - I'd love to hear about any
		884	uses for this one.
		885
438	=item $coroutine->throw ([$scalar])	886	=item $coro->throw ([$scalar])
439		887
440	If C<$throw> is specified and defined, it will be thrown as an exception	888	If C<$throw> is specified and defined, it will be thrown as an exception
441	inside the coroutine at the next convenient point in time (usually after	889	inside the coro at the next convenient point in time. Otherwise
442	it gains control at the next schedule/transfer/cede). Otherwise clears the
443	exception object.	890	clears the exception object.
		891
		892	Coro will check for the exception each time a schedule-like-function
		893	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		894	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
		895	that are part of Coro itself) detect this case and return early in case an
		896	exception is pending.
444		897
445	The exception object will be thrown "as is" with the specified scalar in	898	The exception object will be thrown "as is" with the specified scalar in
446	C<$@>, i.e. if it is a string, no line number or newline will be appended	899	C<$@>, i.e. if it is a string, no line number or newline will be appended
447	(unlike with C<die>).	900	(unlike with C<die>).
448		901
449	This can be used as a softer means than C<cancel> to ask a coroutine to	902	This can be used as a softer means than either C<cancel> or C<safe_cancel
450	end itself, although there is no guarantee that the exception will lead to	903	>to ask a coro to end itself, although there is no guarantee that the
451	termination, and if the exception isn't caught it might well end the whole	904	exception will lead to termination, and if the exception isn't caught it
452	program.	905	might well end the whole program.
453		906
454	You might also think of C<throw> as being the moral equivalent of	907	You might also think of C<throw> as being the moral equivalent of
455	C<kill>ing a coroutine with a signal (in this case, a scalar).	908	C<kill>ing a coro with a signal (in this case, a scalar).
456		909
457	=item $coroutine->join	910	=item $coro->join
458		911
459	Wait until the coroutine terminates and return any values given to the	912	Wait until the coro terminates and return any values given to the
460	C<terminate> or C<cancel> functions. C<join> can be called concurrently	913	C<terminate> or C<cancel> functions. C<join> can be called concurrently
461	from multiple coroutines, and all will be resumed and given the status	914	from multiple threads, and all will be resumed and given the status
462	return once the C<$coroutine> terminates.	915	return once the C<$coro> terminates.
463		916
464	=cut
465
466	sub join {
467	my $self = shift;
468
469	unless ($self->{_status}) {
470	my $current = $current;
471
472	push @{$self->{_on_destroy}}, sub {
473	$current->ready;
474	undef $current;
475	};
476
477	&schedule while $current;
478	}
479
480	wantarray ? @{$self->{_status}} : $self->{_status}[0];
481	}
482
483	=item $coroutine->on_destroy (\&cb)	917	=item $coro->on_destroy (\&cb)
484		918
485	Registers a callback that is called when this coroutine gets destroyed,	919	Registers a callback that is called when this coro thread gets destroyed,
486	but before it is joined. The callback gets passed the terminate arguments,	920	that is, after it's resources have been freed but before it is joined. The
		921	callback gets passed the terminate/cancel arguments, if any, and I<must
487	if any, and I<must not> die, under any circumstances.	922	not> die, under any circumstances.
488		923
489	=cut	924	There can be any number of C<on_destroy> callbacks per coro, and there is
		925	currently no way to remove a callback once added.
490		926
491	sub on_destroy {
492	my ($self, $cb) = @_;
493
494	push @{ $self->{_on_destroy} }, $cb;
495	}
496
497	=item $oldprio = $coroutine->prio ($newprio)	927	=item $oldprio = $coro->prio ($newprio)
498		928
499	Sets (or gets, if the argument is missing) the priority of the	929	Sets (or gets, if the argument is missing) the priority of the
500	coroutine. Higher priority coroutines get run before lower priority	930	coro thread. Higher priority coro get run before lower priority
501	coroutines. Priorities are small signed integers (currently -4 .. +3),	931	coros. Priorities are small signed integers (currently -4 .. +3),
502	that you can refer to using PRIO_xxx constants (use the import tag :prio	932	that you can refer to using PRIO_xxx constants (use the import tag :prio
503	to get then):	933	to get then):
504		934
505	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	935	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
506	3 > 1 > 0 > -1 > -3 > -4	936	3 > 1 > 0 > -1 > -3 > -4
507		937
508	# set priority to HIGH	938	# set priority to HIGH
509	current->prio(PRIO_HIGH);	939	current->prio (PRIO_HIGH);
510		940
511	The idle coroutine ($Coro::idle) always has a lower priority than any	941	The idle coro thread ($Coro::idle) always has a lower priority than any
512	existing coroutine.	942	existing coro.
513		943
514	Changing the priority of the current coroutine will take effect immediately,	944	Changing the priority of the current coro will take effect immediately,
515	but changing the priority of coroutines in the ready queue (but not	945	but changing the priority of a coro in the ready queue (but not running)
516	running) will only take effect after the next schedule (of that	946	will only take effect after the next schedule (of that coro). This is a
517	coroutine). This is a bug that will be fixed in some future version.	947	bug that will be fixed in some future version.
518		948
519	=item $newprio = $coroutine->nice ($change)	949	=item $newprio = $coro->nice ($change)
520		950
521	Similar to C<prio>, but subtract the given value from the priority (i.e.	951	Similar to C<prio>, but subtract the given value from the priority (i.e.
522	higher values mean lower priority, just as in unix).	952	higher values mean lower priority, just as in UNIX's nice command).
523		953
524	=item $olddesc = $coroutine->desc ($newdesc)	954	=item $olddesc = $coro->desc ($newdesc)
525		955
526	Sets (or gets in case the argument is missing) the description for this	956	Sets (or gets in case the argument is missing) the description for this
527	coroutine. This is just a free-form string you can associate with a	957	coro thread. This is just a free-form string you can associate with a
528	coroutine.	958	coro.
529		959
530	This method simply sets the C<< $coroutine->{desc} >> member to the given	960	This method simply sets the C<< $coro->{desc} >> member to the given
531	string. You can modify this member directly if you wish.	961	string. You can modify this member directly if you wish, and in fact, this
		962	is often preferred to indicate major processing states that can then be
		963	seen for example in a L<Coro::Debug> session:
		964
		965	sub my_long_function {
		966	local $Coro::current->{desc} = "now in my_long_function";
		967	...
		968	$Coro::current->{desc} = "my_long_function: phase 1";
		969	...
		970	$Coro::current->{desc} = "my_long_function: phase 2";
		971	...
		972	}
532		973
533	=cut	974	=cut
534		975
535	sub desc {	976	sub desc {
536	my $old = $_[0]{desc};	977	my $old = $_[0]{desc};
537	$_[0]{desc} = $_[1] if @_ > 1;	978	$_[0]{desc} = $_[1] if @_ > 1;
538	$old;	979	$old;
539	}	980	}
540		981
		982	sub transfer {
		983	require Carp;
		984	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		985	}
		986
541	=back	987	=back
542		988
543	=head2 GLOBAL FUNCTIONS	989	=head1 GLOBAL FUNCTIONS
544		990
545	=over 4	991	=over 4
546		992
547	=item Coro::nready	993	=item Coro::nready
548		994
549	Returns the number of coroutines that are currently in the ready state,	995	Returns the number of coro that are currently in the ready state,
550	i.e. that can be switched to by calling C<schedule> directory or	996	i.e. that can be switched to by calling C<schedule> directory or
551	indirectly. The value C<0> means that the only runnable coroutine is the	997	indirectly. The value C<0> means that the only runnable coro is the
552	currently running one, so C<cede> would have no effect, and C<schedule>	998	currently running one, so C<cede> would have no effect, and C<schedule>
553	would cause a deadlock unless there is an idle handler that wakes up some	999	would cause a deadlock unless there is an idle handler that wakes up some
554	coroutines.	1000	coro.
555		1001
556	=item my $guard = Coro::guard { ... }	1002	=item my $guard = Coro::guard { ... }
557		1003
558	This creates and returns a guard object. Nothing happens until the object	1004	This function still exists, but is deprecated. Please use the
559	gets destroyed, in which case the codeblock given as argument will be	1005	C<Guard::guard> function instead.
560	executed. This is useful to free locks or other resources in case of a
561	runtime error or when the coroutine gets canceled, as in both cases the
562	guard block will be executed. The guard object supports only one method,
563	C<< ->cancel >>, which will keep the codeblock from being executed.
564
565	Example: set some flag and clear it again when the coroutine gets canceled
566	or the function returns:
567
568	sub do_something {
569	my $guard = Coro::guard { $busy = 0 };
570	$busy = 1;
571
572	# do something that requires $busy to be true
573	}
574		1006
575	=cut	1007	=cut
576		1008
577	sub guard(&) {	1009	BEGIN { *guard = \&Guard::guard }
578	bless \(my $cb = $_[0]), "Coro::guard"
579	}
580
581	sub Coro::guard::cancel {
582	${$_[0]} = sub { };
583	}
584
585	sub Coro::guard::DESTROY {
586	${$_[0]}->();
587	}
588
589		1010
590	=item unblock_sub { ... }	1011	=item unblock_sub { ... }
591		1012
592	This utility function takes a BLOCK or code reference and "unblocks" it,	1013	This utility function takes a BLOCK or code reference and "unblocks" it,
593	returning a new coderef. Unblocking means that calling the new coderef	1014	returning a new coderef. Unblocking means that calling the new coderef
594	will return immediately without blocking, returning nothing, while the	1015	will return immediately without blocking, returning nothing, while the
595	original code ref will be called (with parameters) from within another	1016	original code ref will be called (with parameters) from within another
596	coroutine.	1017	coro.
597		1018
598	The reason this function exists is that many event libraries (such as the	1019	The reason this function exists is that many event libraries (such as
599	venerable L<Event|Event> module) are not coroutine-safe (a weaker form	1020	the venerable L<Event|Event> module) are not thread-safe (a weaker form
600	of thread-safety). This means you must not block within event callbacks,	1021	of reentrancy). This means you must not block within event callbacks,
601	otherwise you might suffer from crashes or worse. The only event library	1022	otherwise you might suffer from crashes or worse. The only event library
602	currently known that is safe to use without C<unblock_sub> is L<EV>.	1023	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		1024	you might still run into deadlocks if all event loops are blocked).
		1025
		1026	Coro will try to catch you when you block in the event loop
		1027	("FATAL: $Coro::idle blocked itself"), but this is just best effort and
		1028	only works when you do not run your own event loop.
603		1029
604	This function allows your callbacks to block by executing them in another	1030	This function allows your callbacks to block by executing them in another
605	coroutine where it is safe to block. One example where blocking is handy	1031	coro where it is safe to block. One example where blocking is handy
606	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to	1032	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
607	disk, for example.	1033	disk, for example.
608		1034
609	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	1035	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
610	creating event callbacks that want to block.	1036	creating event callbacks that want to block.
611		1037
612	If your handler does not plan to block (e.g. simply sends a message to	1038	If your handler does not plan to block (e.g. simply sends a message to
613	another coroutine, or puts some other coroutine into the ready queue),	1039	another coro, or puts some other coro into the ready queue), there is
614	there is no reason to use C<unblock_sub>.	1040	no reason to use C<unblock_sub>.
615		1041
616	Note that you also need to use C<unblock_sub> for any other callbacks that	1042	Note that you also need to use C<unblock_sub> for any other callbacks that
617	are indirectly executed by any C-based event loop. For example, when you	1043	are indirectly executed by any C-based event loop. For example, when you
618	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	1044	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
619	provides callbacks that are the result of some event callback, then you	1045	provides callbacks that are the result of some event callback, then you
…		…
628	# return immediately and can be reused) and because we cannot cede	1054	# return immediately and can be reused) and because we cannot cede
629	# inside an event callback.	1055	# inside an event callback.
630	our $unblock_scheduler = new Coro sub {	1056	our $unblock_scheduler = new Coro sub {
631	while () {	1057	while () {
632	while (my $cb = pop @unblock_queue) {	1058	while (my $cb = pop @unblock_queue) {
633	# this is an inlined copy of async_pool	1059	&async_pool (@$cb);
634	my $coro = (pop @async_pool) || new Coro \&pool_handler;
635		1060
636	$coro->{_invoke} = $cb;
637	$coro->ready;
638	cede; # for short-lived callbacks, this reduces pressure on the coro pool	1061	# for short-lived callbacks, this reduces pressure on the coro pool
		1062	# as the chance is very high that the async_poll coro will be back
		1063	# in the idle state when cede returns
		1064	cede;
639	}	1065	}
640	schedule; # sleep well	1066	schedule; # sleep well
641	}	1067	}
642	};	1068	};
643	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	1069	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
649	unshift @unblock_queue, [$cb, @_];	1075	unshift @unblock_queue, [$cb, @_];
650	$unblock_scheduler->ready;	1076	$unblock_scheduler->ready;
651	}	1077	}
652	}	1078	}
653		1079
		1080	=item $cb = rouse_cb
		1081
		1082	Create and return a "rouse callback". That's a code reference that,
		1083	when called, will remember a copy of its arguments and notify the owner
		1084	coro of the callback.
		1085
		1086	See the next function.
		1087
		1088	=item @args = rouse_wait [$cb]
		1089
		1090	Wait for the specified rouse callback (or the last one that was created in
		1091	this coro).
		1092
		1093	As soon as the callback is invoked (or when the callback was invoked
		1094	before C<rouse_wait>), it will return the arguments originally passed to
		1095	the rouse callback. In scalar context, that means you get the I<last>
		1096	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1097	statement at the end.
		1098
		1099	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1100
654	=back	1101	=back
655		1102
656	=cut	1103	=cut
657		1104
		1105	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1106	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1107
		1108	*{"Coro::$module\::new"} = sub {
		1109	require "Coro/$module.pm";
		1110
		1111	# some modules have their new predefined in State.xs, some don't
		1112	*{"Coro::$module\::new"} = $old
		1113	if $old;
		1114
		1115	goto &{"Coro::$module\::new"};
		1116	};
		1117	}
		1118
658	1;	1119	1;
		1120
		1121	=head1 HOW TO WAIT FOR A CALLBACK
		1122
		1123	It is very common for a coro to wait for some callback to be
		1124	called. This occurs naturally when you use coro in an otherwise
		1125	event-based program, or when you use event-based libraries.
		1126
		1127	These typically register a callback for some event, and call that callback
		1128	when the event occurred. In a coro, however, you typically want to
		1129	just wait for the event, simplyifying things.
		1130
		1131	For example C<< AnyEvent->child >> registers a callback to be called when
		1132	a specific child has exited:
		1133
		1134	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1135
		1136	But from within a coro, you often just want to write this:
		1137
		1138	my $status = wait_for_child $pid;
		1139
		1140	Coro offers two functions specifically designed to make this easy,
		1141	C<rouse_cb> and C<rouse_wait>.
		1142
		1143	The first function, C<rouse_cb>, generates and returns a callback that,
		1144	when invoked, will save its arguments and notify the coro that
		1145	created the callback.
		1146
		1147	The second function, C<rouse_wait>, waits for the callback to be called
		1148	(by calling C<schedule> to go to sleep) and returns the arguments
		1149	originally passed to the callback.
		1150
		1151	Using these functions, it becomes easy to write the C<wait_for_child>
		1152	function mentioned above:
		1153
		1154	sub wait_for_child($) {
		1155	my ($pid) = @_;
		1156
		1157	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
		1158
		1159	my ($rpid, $rstatus) = rouse_wait;
		1160	$rstatus
		1161	}
		1162
		1163	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1164	you can roll your own, using C<schedule> and C<ready>:
		1165
		1166	sub wait_for_child($) {
		1167	my ($pid) = @_;
		1168
		1169	# store the current coro in $current,
		1170	# and provide result variables for the closure passed to ->child
		1171	my $current = $Coro::current;
		1172	my ($done, $rstatus);
		1173
		1174	# pass a closure to ->child
		1175	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1176	$rstatus = $_[1]; # remember rstatus
		1177	$done = 1; # mark $rstatus as valid
		1178	$current->ready; # wake up the waiting thread
		1179	});
		1180
		1181	# wait until the closure has been called
		1182	schedule while !$done;
		1183
		1184	$rstatus
		1185	}
		1186
659		1187
660	=head1 BUGS/LIMITATIONS	1188	=head1 BUGS/LIMITATIONS
661		1189
662	=over 4	1190	=over 4
663		1191
664	=item fork with pthread backend	1192	=item fork with pthread backend
665		1193
666	When Coro is compiled using the pthread backend (which isn't recommended	1194	When Coro is compiled using the pthread backend (which isn't recommended
667	but required on many BSDs as their libcs are completely broken), then	1195	but required on many BSDs as their libcs are completely broken), then
668	coroutines will not survive a fork. There is no known workaround except to	1196	coro will not survive a fork. There is no known workaround except to
669	fix your libc and use a saner backend.	1197	fix your libc and use a saner backend.
670		1198
671	=item perl process emulation ("threads")	1199	=item perl process emulation ("threads")
672		1200
673	This module is not perl-pseudo-thread-safe. You should only ever use this	1201	This module is not perl-pseudo-thread-safe. You should only ever use this
674	module from the same thread (this requirement might be removed in the	1202	module from the first thread (this requirement might be removed in the
675	future to allow per-thread schedulers, but Coro::State does not yet allow	1203	future to allow per-thread schedulers, but Coro::State does not yet allow
676	this). I recommend disabling thread support and using processes, as having	1204	this). I recommend disabling thread support and using processes, as having
677	the windows process emulation enabled under unix roughly halves perl	1205	the windows process emulation enabled under unix roughly halves perl
678	performance, even when not used.	1206	performance, even when not used.
679		1207
		1208	Attempts to use threads created in another emulated process will crash
		1209	("cleanly", with a null pointer exception).
		1210
680	=item coroutine switching not signal safe	1211	=item coro switching is not signal safe
681		1212
682	You must not switch to another coroutine from within a signal handler	1213	You must not switch to another coro from within a signal handler (only
683	(only relevant with %SIG - most event libraries provide safe signals).	1214	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1215	you are sure you are not interrupting a Coro function.
684		1216
685	That means you I<MUST NOT> call any function that might "block" the	1217	That means you I<MUST NOT> call any function that might "block" the
686	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1218	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
687	anything that calls those. Everything else, including calling C<ready>,	1219	anything that calls those. Everything else, including calling C<ready>,
688	works.	1220	works.
689		1221
690	=back	1222	=back
691		1223
692		1224
		1225	=head1 WINDOWS PROCESS EMULATION
		1226
		1227	A great many people seem to be confused about ithreads (for example, Chip
		1228	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1229	while in the same mail making rather confused statements about perl
		1230	ithreads (for example, that memory or files would be shared), showing his
		1231	lack of understanding of this area - if it is hard to understand for Chip,
		1232	it is probably not obvious to everybody).
		1233
		1234	What follows is an ultra-condensed version of my talk about threads in
		1235	scripting languages given on the perl workshop 2009:
		1236
		1237	The so-called "ithreads" were originally implemented for two reasons:
		1238	first, to (badly) emulate unix processes on native win32 perls, and
		1239	secondly, to replace the older, real thread model ("5.005-threads").
		1240
		1241	It does that by using threads instead of OS processes. The difference
		1242	between processes and threads is that threads share memory (and other
		1243	state, such as files) between threads within a single process, while
		1244	processes do not share anything (at least not semantically). That
		1245	means that modifications done by one thread are seen by others, while
		1246	modifications by one process are not seen by other processes.
		1247
		1248	The "ithreads" work exactly like that: when creating a new ithreads
		1249	process, all state is copied (memory is copied physically, files and code
		1250	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1251	the same behaviour can be achieved by using operating system processes,
		1252	except that UNIX typically uses hardware built into the system to do this
		1253	efficiently, while the windows process emulation emulates this hardware in
		1254	software (rather efficiently, but of course it is still much slower than
		1255	dedicated hardware).
		1256
		1257	As mentioned before, loading code, modifying code, modifying data
		1258	structures and so on is only visible in the ithreads process doing the
		1259	modification, not in other ithread processes within the same OS process.
		1260
		1261	This is why "ithreads" do not implement threads for perl at all, only
		1262	processes. What makes it so bad is that on non-windows platforms, you can
		1263	actually take advantage of custom hardware for this purpose (as evidenced
		1264	by the forks module, which gives you the (i-) threads API, just much
		1265	faster).
		1266
		1267	Sharing data is in the i-threads model is done by transferring data
		1268	structures between threads using copying semantics, which is very slow -
		1269	shared data simply does not exist. Benchmarks using i-threads which are
		1270	communication-intensive show extremely bad behaviour with i-threads (in
		1271	fact, so bad that Coro, which cannot take direct advantage of multiple
		1272	CPUs, is often orders of magnitude faster because it shares data using
		1273	real threads, refer to my talk for details).
		1274
		1275	As summary, i-threads *use* threads to implement processes, while
		1276	the compatible forks module *uses* processes to emulate, uhm,
		1277	processes. I-threads slow down every perl program when enabled, and
		1278	outside of windows, serve no (or little) practical purpose, but
		1279	disadvantages every single-threaded Perl program.
		1280
		1281	This is the reason that I try to avoid the name "ithreads", as it is
		1282	misleading as it implies that it implements some kind of thread model for
		1283	perl, and prefer the name "windows process emulation", which describes the
		1284	actual use and behaviour of it much better.
		1285
693	=head1 SEE ALSO	1286	=head1 SEE ALSO
694		1287
695	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1288	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
696		1289
697	Debugging: L<Coro::Debug>.	1290	Debugging: L<Coro::Debug>.
698		1291
699	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1292	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
700		1293
701	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1294	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1295	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
702		1296
703	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1297	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
704		1298
705	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1299	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1300	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1301	L<Coro::Select>.
706		1302
707	XS API: L<Coro::MakeMaker>.	1303	XS API: L<Coro::MakeMaker>.
708		1304
709	Low level Configuration, Coroutine Environment: L<Coro::State>.	1305	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
710		1306
711	=head1 AUTHOR	1307	=head1 AUTHOR/SUPPORT/CONTACT
712		1308
713	Marc Lehmann <schmorp@schmorp.de>	1309	Marc A. Lehmann <schmorp@schmorp.de>
714	http://home.schmorp.de/	1310	http://software.schmorp.de/pkg/Coro.html
715		1311
716	=cut	1312	=cut
717		1313

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