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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 $VERSION = 6.33;
73		372
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	373	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	374	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	375	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	376	);
78	our @EXPORT_OK = (@{$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, tracing will be
229	disabled, the description will be reset and the default output filehandle	504	disabled, the description will be reset and the default output filehandle
230	gets restored, so you can change all these. Otherwise the coroutine will	505	gets restored, so you can change all these. Otherwise the coro will
231	be re-used "as-is": most notably if you change other per-coroutine global	506	be re-used "as-is": most notably if you change other per-coro global
232	stuff such as C<$/> you I<must needs> revert that change, which is most	507	stuff such as C<$/> you I<must needs> revert that change, which is most
233	simply done by using local as in: C<< local $/ >>.	508	simply done by using local as in: C<< local $/ >>.
234		509
235	The idle pool size is limited to C<8> idle coroutines (this can be	510	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	511	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
237	coros as required.	512	coros as required.
238		513
239	If you are concerned about pooled coroutines growing a lot because a	514	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	515	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	516	{ 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	517	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.	518	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
244		519
245	=cut	520	=cut
246		521
247	our $POOL_SIZE = 8;	522	our $POOL_SIZE = 8;
248	our $POOL_RSS = 16 * 1024;	523	our $POOL_RSS = 32 * 1024;
249	our @async_pool;	524	our @async_pool;
250		525
251	sub pool_handler {	526	sub pool_handler {
252	my $cb;
253
254	while () {	527	while () {
255	eval {	528	eval {
256	while () {	529	&{&_pool_handler} while 1;
257	_pool_1 $cb;
258	&$cb;
259	_pool_2 $cb;
260	&schedule;
261	}
262	};	530	};
263		531
264	if ($@) {
265	last if $@ eq "\3async_pool terminate\2\n";
266	warn $@;	532	warn $@ if $@;
267	}
268	}	533	}
269	}	534	}
270		535
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	$coro
279	}
280
281	=back	536	=back
282		537
283	=head2 STATIC METHODS	538	=head1 STATIC METHODS
284		539
285	Static methods are actually functions that operate on the current coroutine.	540	Static methods are actually functions that implicitly operate on the
		541	current coro.
286		542
287	=over 4	543	=over 4
288		544
289	=item schedule	545	=item schedule
290		546
291	Calls the scheduler. The scheduler will find the next coroutine that is	547	Calls the scheduler. The scheduler will find the next coro that is
292	to be run from the ready queue and switches to it. The next coroutine	548	to be run from the ready queue and switches to it. The next coro
293	to be run is simply the one with the highest priority that is longest	549	to be run is simply the one with the highest priority that is longest
294	in its ready queue. If there is no coroutine ready, it will clal the	550	in its ready queue. If there is no coro ready, it will call the
295	C<$Coro::idle> hook.	551	C<$Coro::idle> hook.
296		552
297	Please note that the current coroutine will I<not> be put into the ready	553	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	554	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 >>,	555	again unless something else (e.g. an event handler) calls C<< ->ready >>,
300	thus waking you up.	556	thus waking you up.
301		557
302	This makes C<schedule> I<the> generic method to use to block the current	558	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	559	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	560	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	561	>> 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,	562	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	563	so you need to check whether the event indeed happened, e.g. by storing the
308	status in a variable.	564	status in a variable.
309		565
310	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	566	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
311		567
312	=item cede	568	=item cede
313		569
314	"Cede" to other coroutines. This function puts the current coroutine into	570	"Cede" to other coros. This function puts the current coro into
315	the ready queue and calls C<schedule>, which has the effect of giving	571	the ready queue and calls C<schedule>, which has the effect of giving
316	up the current "timeslice" to other coroutines of the same or higher	572	up the current "timeslice" to other coros of the same or higher
317	priority. Once your coroutine gets its turn again it will automatically be	573	priority. Once your coro gets its turn again it will automatically be
318	resumed.	574	resumed.
319		575
320	This function is often called C<yield> in other languages.	576	This function is often called C<yield> in other languages.
321		577
322	=item Coro::cede_notself	578	=item Coro::cede_notself
323		579
324	Works like cede, but is not exported by default and will cede to I<any>	580	Works like cede, but is not exported by default and will cede to I<any>
325	coroutine, regardless of priority. This is useful sometimes to ensure	581	coro, regardless of priority. This is useful sometimes to ensure
326	progress is made.	582	progress is made.
327		583
328	=item terminate [arg...]	584	=item terminate [arg...]
329		585
330	Terminates the current coroutine with the given status values (see L<cancel>).	586	Terminates the current coro with the given status values (see
		587	L<cancel>). The values will not be copied, but referenced directly.
		588
		589	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		590
		591	These function install enter and leave winders in the current scope. The
		592	enter block will be executed when on_enter is called and whenever the
		593	current coro is re-entered by the scheduler, while the leave block is
		594	executed whenever the current coro is blocked by the scheduler, and
		595	also when the containing scope is exited (by whatever means, be it exit,
		596	die, last etc.).
		597
		598	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		599	BLOCKs>. That means: do not even think about calling C<die> without an
		600	eval, and do not even think of entering the scheduler in any way.
		601
		602	Since both BLOCKs are tied to the current scope, they will automatically
		603	be removed when the current scope exits.
		604
		605	These functions implement the same concept as C<dynamic-wind> in scheme
		606	does, and are useful when you want to localise some resource to a specific
		607	coro.
		608
		609	They slow down thread switching considerably for coros that use them
		610	(about 40% for a BLOCK with a single assignment, so thread switching is
		611	still reasonably fast if the handlers are fast).
		612
		613	These functions are best understood by an example: The following function
		614	will change the current timezone to "Antarctica/South_Pole", which
		615	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		616	which remember/change the current timezone and restore the previous
		617	value, respectively, the timezone is only changed for the coro that
		618	installed those handlers.
		619
		620	use POSIX qw(tzset);
		621
		622	async {
		623	my $old_tz; # store outside TZ value here
		624
		625	Coro::on_enter {
		626	$old_tz = $ENV{TZ}; # remember the old value
		627
		628	$ENV{TZ} = "Antarctica/South_Pole";
		629	tzset; # enable new value
		630	};
		631
		632	Coro::on_leave {
		633	$ENV{TZ} = $old_tz;
		634	tzset; # restore old value
		635	};
		636
		637	# at this place, the timezone is Antarctica/South_Pole,
		638	# without disturbing the TZ of any other coro.
		639	};
		640
		641	This can be used to localise about any resource (locale, uid, current
		642	working directory etc.) to a block, despite the existance of other
		643	coros.
		644
		645	Another interesting example implements time-sliced multitasking using
		646	interval timers (this could obviously be optimised, but does the job):
		647
		648	# "timeslice" the given block
		649	sub timeslice(&) {
		650	use Time::HiRes ();
		651
		652	Coro::on_enter {
		653	# on entering the thread, we set an VTALRM handler to cede
		654	$SIG{VTALRM} = sub { cede };
		655	# and then start the interval timer
		656	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		657	};
		658	Coro::on_leave {
		659	# on leaving the thread, we stop the interval timer again
		660	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		661	};
		662
		663	&{+shift};
		664	}
		665
		666	# use like this:
		667	timeslice {
		668	# The following is an endless loop that would normally
		669	# monopolise the process. Since it runs in a timesliced
		670	# environment, it will regularly cede to other threads.
		671	while () { }
		672	};
		673
331		674
332	=item killall	675	=item killall
333		676
334	Kills/terminates/cancels all coroutines except the currently running	677	Kills/terminates/cancels all coros except the currently running one.
335	one. This is useful after a fork, either in the child or the parent, as
336	usually only one of them should inherit the running coroutines.
337		678
338	Note that while this will try to free some of the main programs resources,	679	Note that while this will try to free some of the main interpreter
		680	resources if the calling coro isn't the main coro, but one
339	you cannot free all of them, so if a coroutine that is not the main	681	cannot free all of them, so if a coro that is not the main coro
340	program calls this function, there will be some one-time resource leak.	682	calls this function, there will be some one-time resource leak.
341		683
342	=cut	684	=cut
343
344	sub terminate {
345	$current->cancel (@_);
346	}
347		685
348	sub killall {	686	sub killall {
349	for (Coro::State::list) {	687	for (Coro::State::list) {
350	$_->cancel	688	$_->cancel
351	if $_ != $current && UNIVERSAL::isa $_, "Coro";	689	if $_ != $current && UNIVERSAL::isa $_, "Coro";
352	}	690	}
353	}	691	}
354		692
355	=back	693	=back
356		694
357	=head2 COROUTINE METHODS	695	=head1 CORO OBJECT METHODS
358		696
359	These are the methods you can call on coroutine objects (or to create	697	These are the methods you can call on coro objects (or to create
360	them).	698	them).
361		699
362	=over 4	700	=over 4
363		701
364	=item new Coro \&sub [, @args...]	702	=item new Coro \&sub [, @args...]
365		703
366	Create a new coroutine and return it. When the sub returns, the coroutine	704	Create a new coro and return it. When the sub returns, the coro
367	automatically terminates as if C<terminate> with the returned values were	705	automatically terminates as if C<terminate> with the returned values were
368	called. To make the coroutine run you must first put it into the ready	706	called. To make the coro run you must first put it into the ready
369	queue by calling the ready method.	707	queue by calling the ready method.
370		708
371	See C<async> and C<Coro::State::new> for additional info about the	709	See C<async> and C<Coro::State::new> for additional info about the
372	coroutine environment.	710	coro environment.
373		711
374	=cut	712	=cut
375		713
376	sub _terminate {	714	sub _coro_run {
377	terminate &{+shift};	715	terminate &{+shift};
378	}	716	}
379		717
380	=item $success = $coroutine->ready	718	=item $success = $coro->ready
381		719
382	Put the given coroutine into the end of its ready queue (there is one	720	Put the given coro into the end of its ready queue (there is one
383	queue for each priority) and return true. If the coroutine is already in	721	queue for each priority) and return true. If the coro is already in
384	the ready queue, do nothing and return false.	722	the ready queue, do nothing and return false.
385		723
386	This ensures that the scheduler will resume this coroutine automatically	724	This ensures that the scheduler will resume this coro automatically
387	once all the coroutines of higher priority and all coroutines of the same	725	once all the coro of higher priority and all coro of the same
388	priority that were put into the ready queue earlier have been resumed.	726	priority that were put into the ready queue earlier have been resumed.
389		727
		728	=item $coro->suspend
		729
		730	Suspends the specified coro. A suspended coro works just like any other
		731	coro, except that the scheduler will not select a suspended coro for
		732	execution.
		733
		734	Suspending a coro can be useful when you want to keep the coro from
		735	running, but you don't want to destroy it, or when you want to temporarily
		736	freeze a coro (e.g. for debugging) to resume it later.
		737
		738	A scenario for the former would be to suspend all (other) coros after a
		739	fork and keep them alive, so their destructors aren't called, but new
		740	coros can be created.
		741
		742	=item $coro->resume
		743
		744	If the specified coro was suspended, it will be resumed. Note that when
		745	the coro was in the ready queue when it was suspended, it might have been
		746	unreadied by the scheduler, so an activation might have been lost.
		747
		748	To avoid this, it is best to put a suspended coro into the ready queue
		749	unconditionally, as every synchronisation mechanism must protect itself
		750	against spurious wakeups, and the one in the Coro family certainly do
		751	that.
		752
		753	=item $state->is_new
		754
		755	Returns true iff this Coro object is "new", i.e. has never been run
		756	yet. Those states basically consist of only the code reference to call and
		757	the arguments, but consumes very little other resources. New states will
		758	automatically get assigned a perl interpreter when they are transfered to.
		759
		760	=item $state->is_zombie
		761
		762	Returns true iff the Coro object has been cancelled, i.e.
		763	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		764	C<safe_cancel>'ed or simply went out of scope.
		765
		766	The name "zombie" stems from UNIX culture, where a process that has
		767	exited and only stores and exit status and no other resources is called a
		768	"zombie".
		769
390	=item $is_ready = $coroutine->is_ready	770	=item $is_ready = $coro->is_ready
391		771
392	Return whether the coroutine is currently the ready queue or not,	772	Returns true iff the Coro object is in the ready queue. Unless the Coro
		773	object gets destroyed, it will eventually be scheduled by the scheduler.
393		774
		775	=item $is_running = $coro->is_running
		776
		777	Returns true iff the Coro object is currently running. Only one Coro object
		778	can ever be in the running state (but it currently is possible to have
		779	multiple running Coro::States).
		780
		781	=item $is_suspended = $coro->is_suspended
		782
		783	Returns true iff this Coro object has been suspended. Suspended Coros will
		784	not ever be scheduled.
		785
394	=item $coroutine->cancel (arg...)	786	=item $coro->cancel (arg...)
395		787
396	Terminates the given coroutine and makes it return the given arguments as	788	Terminates the given Coro thread and makes it return the given arguments as
397	status (default: the empty list). Never returns if the coroutine is the	789	status (default: an empty list). Never returns if the Coro is the
398	current coroutine.	790	current Coro.
399		791
400	=cut	792	This is a rather brutal way to free a coro, with some limitations - if
		793	the thread is inside a C callback that doesn't expect to be canceled,
		794	bad things can happen, or if the cancelled thread insists on running
		795	complicated cleanup handlers that rely on its thread context, things will
		796	not work.
401		797
402	sub cancel {	798	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
403	my $self = shift;	799	a thread context, and is not allowed to switch to other threads. On the
404	$self->{_status} = [@_];	800	plus side, C<< ->cancel >> will always clean up the thread, no matter
		801	what. If your cleanup code is complex or you want to avoid cancelling a
		802	C-thread that doesn't know how to clean up itself, it can be better to C<<
		803	->throw >> an exception, or use C<< ->safe_cancel >>.
405		804
406	if ($current == $self) {	805	The arguments to C<< ->cancel >> are not copied, but instead will
407	push @destroy, $self;	806	be referenced directly (e.g. if you pass C<$var> and after the call
408	$manager->ready;	807	change that variable, then you might change the return values passed to
409	&schedule while 1;	808	e.g. C<join>, so don't do that).
410	} else {	809
411	$self->_cancel;	810	The resources of the Coro are usually freed (or destructed) before this
		811	call returns, but this can be delayed for an indefinite amount of time, as
		812	in some cases the manager thread has to run first to actually destruct the
		813	Coro object.
		814
		815	=item $coro->safe_cancel ($arg...)
		816
		817	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		818	consequently, can fail with an exception in cases the thread is not in a
		819	cancellable state.
		820
		821	This method works a bit like throwing an exception that cannot be caught
		822	- specifically, it will clean up the thread from within itself, so
		823	all cleanup handlers (e.g. C<guard> blocks) are run with full thread
		824	context and can block if they wish. The downside is that there is no
		825	guarantee that the thread can be cancelled when you call this method, and
		826	therefore, it might fail. It is also considerably slower than C<cancel> or
		827	C<terminate>.
		828
		829	A thread is in a safe-cancellable state if it either hasn't been run yet,
		830	or it has no C context attached and is inside an SLF function.
		831
		832	The latter two basically mean that the thread isn't currently inside a
		833	perl callback called from some C function (usually via some XS modules)
		834	and isn't currently executing inside some C function itself (via Coro's XS
		835	API).
		836
		837	This call returns true when it could cancel the thread, or croaks with an
		838	error otherwise (i.e. it either returns true or doesn't return at all).
		839
		840	Why the weird interface? Well, there are two common models on how and
		841	when to cancel things. In the first, you have the expectation that your
		842	coro thread can be cancelled when you want to cancel it - if the thread
		843	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		844	croaks to notify of the bug.
		845
		846	In the second model you sometimes want to ask nicely to cancel a thread,
		847	but if it's not a good time, well, then don't cancel. This can be done
		848	relatively easy like this:
		849
		850	if (! eval { $coro->safe_cancel }) {
		851	warn "unable to cancel thread: $@";
412	}	852	}
413	}
414		853
		854	However, what you never should do is first try to cancel "safely" and
		855	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		856	no sense: either you rely on being able to execute cleanup code in your
		857	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		858	only way, and if you don't, then C<< ->cancel >> is always faster and more
		859	direct.
		860
		861	=item $coro->schedule_to
		862
		863	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		864	of continuing with the next coro from the ready queue, always switch to
		865	the given coro object (regardless of priority etc.). The readyness
		866	state of that coro isn't changed.
		867
		868	This is an advanced method for special cases - I'd love to hear about any
		869	uses for this one.
		870
		871	=item $coro->cede_to
		872
		873	Like C<schedule_to>, but puts the current coro into the ready
		874	queue. This has the effect of temporarily switching to the given
		875	coro, and continuing some time later.
		876
		877	This is an advanced method for special cases - I'd love to hear about any
		878	uses for this one.
		879
415	=item $coroutine->throw ([$scalar])	880	=item $coro->throw ([$scalar])
416		881
417	If C<$throw> is specified and defined, it will be thrown as an exception	882	If C<$throw> is specified and defined, it will be thrown as an exception
418	inside the coroutine at the next convenient point in time. Otherwise	883	inside the coro at the next convenient point in time. Otherwise
419	clears the exception object.	884	clears the exception object.
420		885
421	Coro will check for the exception each time a schedule-like-function	886	Coro will check for the exception each time a schedule-like-function
422	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down	887	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
423	>>, C<< Coro::Handle->readable >> and so on. Most of these functions	888	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
424	detect this case and return early in case an exception is pending.	889	that are part of Coro itself) detect this case and return early in case an
		890	exception is pending.
425		891
426	The exception object will be thrown "as is" with the specified scalar in	892	The exception object will be thrown "as is" with the specified scalar in
427	C<$@>, i.e. if it is a string, no line number or newline will be appended	893	C<$@>, i.e. if it is a string, no line number or newline will be appended
428	(unlike with C<die>).	894	(unlike with C<die>).
429		895
430	This can be used as a softer means than C<cancel> to ask a coroutine to	896	This can be used as a softer means than either C<cancel> or C<safe_cancel
431	end itself, although there is no guarantee that the exception will lead to	897	>to ask a coro to end itself, although there is no guarantee that the
432	termination, and if the exception isn't caught it might well end the whole	898	exception will lead to termination, and if the exception isn't caught it
433	program.	899	might well end the whole program.
434		900
435	You might also think of C<throw> as being the moral equivalent of	901	You might also think of C<throw> as being the moral equivalent of
436	C<kill>ing a coroutine with a signal (in this case, a scalar).	902	C<kill>ing a coro with a signal (in this case, a scalar).
437		903
438	=item $coroutine->join	904	=item $coro->join
439		905
440	Wait until the coroutine terminates and return any values given to the	906	Wait until the coro terminates and return any values given to the
441	C<terminate> or C<cancel> functions. C<join> can be called concurrently	907	C<terminate> or C<cancel> functions. C<join> can be called concurrently
442	from multiple coroutines, and all will be resumed and given the status	908	from multiple threads, and all will be resumed and given the status
443	return once the C<$coroutine> terminates.	909	return once the C<$coro> terminates.
444		910
445	=cut
446
447	sub join {
448	my $self = shift;
449
450	unless ($self->{_status}) {
451	my $current = $current;
452
453	push @{$self->{_on_destroy}}, sub {
454	$current->ready;
455	undef $current;
456	};
457
458	&schedule while $current;
459	}
460
461	wantarray ? @{$self->{_status}} : $self->{_status}[0];
462	}
463
464	=item $coroutine->on_destroy (\&cb)	911	=item $coro->on_destroy (\&cb)
465		912
466	Registers a callback that is called when this coroutine gets destroyed,	913	Registers a callback that is called when this coro thread gets destroyed,
467	but before it is joined. The callback gets passed the terminate arguments,	914	that is, after it's resources have been freed but before it is joined. The
		915	callback gets passed the terminate/cancel arguments, if any, and I<must
468	if any, and I<must not> die, under any circumstances.	916	not> die, under any circumstances.
469		917
470	=cut	918	There can be any number of C<on_destroy> callbacks per coro, and there is
		919	currently no way to remove a callback once added.
471		920
472	sub on_destroy {
473	my ($self, $cb) = @_;
474
475	push @{ $self->{_on_destroy} }, $cb;
476	}
477
478	=item $oldprio = $coroutine->prio ($newprio)	921	=item $oldprio = $coro->prio ($newprio)
479		922
480	Sets (or gets, if the argument is missing) the priority of the	923	Sets (or gets, if the argument is missing) the priority of the
481	coroutine. Higher priority coroutines get run before lower priority	924	coro thread. Higher priority coro get run before lower priority
482	coroutines. Priorities are small signed integers (currently -4 .. +3),	925	coros. Priorities are small signed integers (currently -4 .. +3),
483	that you can refer to using PRIO_xxx constants (use the import tag :prio	926	that you can refer to using PRIO_xxx constants (use the import tag :prio
484	to get then):	927	to get then):
485		928
486	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	929	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
487	3 > 1 > 0 > -1 > -3 > -4	930	3 > 1 > 0 > -1 > -3 > -4
488		931
489	# set priority to HIGH	932	# set priority to HIGH
490	current->prio(PRIO_HIGH);	933	current->prio (PRIO_HIGH);
491		934
492	The idle coroutine ($Coro::idle) always has a lower priority than any	935	The idle coro thread ($Coro::idle) always has a lower priority than any
493	existing coroutine.	936	existing coro.
494		937
495	Changing the priority of the current coroutine will take effect immediately,	938	Changing the priority of the current coro will take effect immediately,
496	but changing the priority of coroutines in the ready queue (but not	939	but changing the priority of a coro in the ready queue (but not running)
497	running) will only take effect after the next schedule (of that	940	will only take effect after the next schedule (of that coro). This is a
498	coroutine). This is a bug that will be fixed in some future version.	941	bug that will be fixed in some future version.
499		942
500	=item $newprio = $coroutine->nice ($change)	943	=item $newprio = $coro->nice ($change)
501		944
502	Similar to C<prio>, but subtract the given value from the priority (i.e.	945	Similar to C<prio>, but subtract the given value from the priority (i.e.
503	higher values mean lower priority, just as in unix).	946	higher values mean lower priority, just as in UNIX's nice command).
504		947
505	=item $olddesc = $coroutine->desc ($newdesc)	948	=item $olddesc = $coro->desc ($newdesc)
506		949
507	Sets (or gets in case the argument is missing) the description for this	950	Sets (or gets in case the argument is missing) the description for this
508	coroutine. This is just a free-form string you can associate with a	951	coro thread. This is just a free-form string you can associate with a
509	coroutine.	952	coro.
510		953
511	This method simply sets the C<< $coroutine->{desc} >> member to the given	954	This method simply sets the C<< $coro->{desc} >> member to the given
512	string. You can modify this member directly if you wish.	955	string. You can modify this member directly if you wish, and in fact, this
		956	is often preferred to indicate major processing states that can then be
		957	seen for example in a L<Coro::Debug> session:
		958
		959	sub my_long_function {
		960	local $Coro::current->{desc} = "now in my_long_function";
		961	...
		962	$Coro::current->{desc} = "my_long_function: phase 1";
		963	...
		964	$Coro::current->{desc} = "my_long_function: phase 2";
		965	...
		966	}
513		967
514	=cut	968	=cut
515		969
516	sub desc {	970	sub desc {
517	my $old = $_[0]{desc};	971	my $old = $_[0]{desc};
518	$_[0]{desc} = $_[1] if @_ > 1;	972	$_[0]{desc} = $_[1] if @_ > 1;
519	$old;	973	$old;
520	}	974	}
521		975
		976	sub transfer {
		977	require Carp;
		978	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		979	}
		980
522	=back	981	=back
523		982
524	=head2 GLOBAL FUNCTIONS	983	=head1 GLOBAL FUNCTIONS
525		984
526	=over 4	985	=over 4
527		986
528	=item Coro::nready	987	=item Coro::nready
529		988
530	Returns the number of coroutines that are currently in the ready state,	989	Returns the number of coro that are currently in the ready state,
531	i.e. that can be switched to by calling C<schedule> directory or	990	i.e. that can be switched to by calling C<schedule> directory or
532	indirectly. The value C<0> means that the only runnable coroutine is the	991	indirectly. The value C<0> means that the only runnable coro is the
533	currently running one, so C<cede> would have no effect, and C<schedule>	992	currently running one, so C<cede> would have no effect, and C<schedule>
534	would cause a deadlock unless there is an idle handler that wakes up some	993	would cause a deadlock unless there is an idle handler that wakes up some
535	coroutines.	994	coro.
536		995
537	=item my $guard = Coro::guard { ... }	996	=item my $guard = Coro::guard { ... }
538		997
539	This creates and returns a guard object. Nothing happens until the object	998	This function still exists, but is deprecated. Please use the
540	gets destroyed, in which case the codeblock given as argument will be	999	C<Guard::guard> function instead.
541	executed. This is useful to free locks or other resources in case of a
542	runtime error or when the coroutine gets canceled, as in both cases the
543	guard block will be executed. The guard object supports only one method,
544	C<< ->cancel >>, which will keep the codeblock from being executed.
545
546	Example: set some flag and clear it again when the coroutine gets canceled
547	or the function returns:
548
549	sub do_something {
550	my $guard = Coro::guard { $busy = 0 };
551	$busy = 1;
552
553	# do something that requires $busy to be true
554	}
555		1000
556	=cut	1001	=cut
557		1002
558	sub guard(&) {	1003	BEGIN { *guard = \&Guard::guard }
559	bless \(my $cb = $_[0]), "Coro::guard"
560	}
561
562	sub Coro::guard::cancel {
563	${$_[0]} = sub { };
564	}
565
566	sub Coro::guard::DESTROY {
567	${$_[0]}->();
568	}
569
570		1004
571	=item unblock_sub { ... }	1005	=item unblock_sub { ... }
572		1006
573	This utility function takes a BLOCK or code reference and "unblocks" it,	1007	This utility function takes a BLOCK or code reference and "unblocks" it,
574	returning a new coderef. Unblocking means that calling the new coderef	1008	returning a new coderef. Unblocking means that calling the new coderef
575	will return immediately without blocking, returning nothing, while the	1009	will return immediately without blocking, returning nothing, while the
576	original code ref will be called (with parameters) from within another	1010	original code ref will be called (with parameters) from within another
577	coroutine.	1011	coro.
578		1012
579	The reason this function exists is that many event libraries (such as the	1013	The reason this function exists is that many event libraries (such as
580	venerable L<Event|Event> module) are not coroutine-safe (a weaker form	1014	the venerable L<Event|Event> module) are not thread-safe (a weaker form
581	of thread-safety). This means you must not block within event callbacks,	1015	of reentrancy). This means you must not block within event callbacks,
582	otherwise you might suffer from crashes or worse. The only event library	1016	otherwise you might suffer from crashes or worse. The only event library
583	currently known that is safe to use without C<unblock_sub> is L<EV>.	1017	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		1018	you might still run into deadlocks if all event loops are blocked).
		1019
		1020	Coro will try to catch you when you block in the event loop
		1021	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		1022	only works when you do not run your own event loop.
584		1023
585	This function allows your callbacks to block by executing them in another	1024	This function allows your callbacks to block by executing them in another
586	coroutine where it is safe to block. One example where blocking is handy	1025	coro where it is safe to block. One example where blocking is handy
587	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to	1026	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
588	disk, for example.	1027	disk, for example.
589		1028
590	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	1029	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
591	creating event callbacks that want to block.	1030	creating event callbacks that want to block.
592		1031
593	If your handler does not plan to block (e.g. simply sends a message to	1032	If your handler does not plan to block (e.g. simply sends a message to
594	another coroutine, or puts some other coroutine into the ready queue),	1033	another coro, or puts some other coro into the ready queue), there is
595	there is no reason to use C<unblock_sub>.	1034	no reason to use C<unblock_sub>.
596		1035
597	Note that you also need to use C<unblock_sub> for any other callbacks that	1036	Note that you also need to use C<unblock_sub> for any other callbacks that
598	are indirectly executed by any C-based event loop. For example, when you	1037	are indirectly executed by any C-based event loop. For example, when you
599	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	1038	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
600	provides callbacks that are the result of some event callback, then you	1039	provides callbacks that are the result of some event callback, then you
…		…
609	# return immediately and can be reused) and because we cannot cede	1048	# return immediately and can be reused) and because we cannot cede
610	# inside an event callback.	1049	# inside an event callback.
611	our $unblock_scheduler = new Coro sub {	1050	our $unblock_scheduler = new Coro sub {
612	while () {	1051	while () {
613	while (my $cb = pop @unblock_queue) {	1052	while (my $cb = pop @unblock_queue) {
614	# this is an inlined copy of async_pool	1053	&async_pool (@$cb);
615	my $coro = (pop @async_pool) || new Coro \&pool_handler;
616		1054
617	$coro->{_invoke} = $cb;
618	$coro->ready;
619	cede; # for short-lived callbacks, this reduces pressure on the coro pool	1055	# for short-lived callbacks, this reduces pressure on the coro pool
		1056	# as the chance is very high that the async_poll coro will be back
		1057	# in the idle state when cede returns
		1058	cede;
620	}	1059	}
621	schedule; # sleep well	1060	schedule; # sleep well
622	}	1061	}
623	};	1062	};
624	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	1063	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
630	unshift @unblock_queue, [$cb, @_];	1069	unshift @unblock_queue, [$cb, @_];
631	$unblock_scheduler->ready;	1070	$unblock_scheduler->ready;
632	}	1071	}
633	}	1072	}
634		1073
635	=item $cb = Coro::rouse_cb	1074	=item $cb = rouse_cb
636		1075
637	Create and return a "rouse callback". That's a code reference that, when	1076	Create and return a "rouse callback". That's a code reference that,
638	called, will save its arguments and notify the owner coroutine of the	1077	when called, will remember a copy of its arguments and notify the owner
639	callback.	1078	coro of the callback.
640		1079
641	See the next function.	1080	See the next function.
642		1081
643	=item @args = Coro::rouse_wait [$cb]	1082	=item @args = rouse_wait [$cb]
644		1083
645	Wait for the specified rouse callback (or the last one tht was created in	1084	Wait for the specified rouse callback (or the last one that was created in
646	this coroutine).	1085	this coro).
647		1086
648	As soon as the callback is invoked (or when the calback was invoked before	1087	As soon as the callback is invoked (or when the callback was invoked
649	C<rouse_wait>), it will return a copy of the arguments originally passed	1088	before C<rouse_wait>), it will return the arguments originally passed to
650	to the rouse callback.	1089	the rouse callback. In scalar context, that means you get the I<last>
		1090	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1091	statement at the end.
651		1092
652	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1093	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
653		1094
654	=back	1095	=back
655		1096
656	=cut	1097	=cut
657		1098
		1099	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1100	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1101
		1102	*{"Coro::$module\::new"} = sub {
		1103	require "Coro/$module.pm";
		1104
		1105	# some modules have their new predefined in State.xs, some don't
		1106	*{"Coro::$module\::new"} = $old
		1107	if $old;
		1108
		1109	goto &{"Coro::$module\::new"};
		1110	};
		1111	}
		1112
658	1;	1113	1;
659		1114
660	=head1 HOW TO WAIT FOR A CALLBACK	1115	=head1 HOW TO WAIT FOR A CALLBACK
661		1116
662	It is very common for a coroutine to wait for some callback to be	1117	It is very common for a coro to wait for some callback to be
663	called. This occurs naturally when you use coroutines in an otherwise	1118	called. This occurs naturally when you use coro in an otherwise
664	event-based program, or when you use event-based libraries.	1119	event-based program, or when you use event-based libraries.
665		1120
666	These typically register a callback for some event, and call that callback	1121	These typically register a callback for some event, and call that callback
667	when the event occured. In a coroutine, however, you typically want to	1122	when the event occured. In a coro, however, you typically want to
668	just wait for the event, simplyifying things.	1123	just wait for the event, simplyifying things.
669		1124
670	For example C<< AnyEvent->child >> registers a callback to be called when	1125	For example C<< AnyEvent->child >> registers a callback to be called when
671	a specific child has exited:	1126	a specific child has exited:
672		1127
673	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	1128	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
674		1129
675	But from withina coroutine, you often just want to write this:	1130	But from within a coro, you often just want to write this:
676		1131
677	my $status = wait_for_child $pid;	1132	my $status = wait_for_child $pid;
678		1133
679	Coro offers two functions specifically designed to make this easy,	1134	Coro offers two functions specifically designed to make this easy,
680	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	1135	C<rouse_cb> and C<rouse_wait>.
681		1136
682	The first function, C<rouse_cb>, generates and returns a callback that,	1137	The first function, C<rouse_cb>, generates and returns a callback that,
683	when invoked, will save it's arguments and notify the coroutine that	1138	when invoked, will save its arguments and notify the coro that
684	created the callback.	1139	created the callback.
685		1140
686	The second function, C<rouse_wait>, waits for the callback to be called	1141	The second function, C<rouse_wait>, waits for the callback to be called
687	(by calling C<schedule> to go to sleep) and returns the arguments	1142	(by calling C<schedule> to go to sleep) and returns the arguments
688	originally passed to the callback.	1143	originally passed to the callback.
…		…
691	function mentioned above:	1146	function mentioned above:
692		1147
693	sub wait_for_child($) {	1148	sub wait_for_child($) {
694	my ($pid) = @_;	1149	my ($pid) = @_;
695		1150
696	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);	1151	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
697		1152
698	my ($rpid, $rstatus) = Coro::rouse_wait;	1153	my ($rpid, $rstatus) = rouse_wait;
699	$rstatus	1154	$rstatus
700	}	1155	}
701		1156
702	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,	1157	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
703	you can roll your own, using C<schedule>:	1158	you can roll your own, using C<schedule> and C<ready>:
704		1159
705	sub wait_for_child($) {	1160	sub wait_for_child($) {
706	my ($pid) = @_;	1161	my ($pid) = @_;
707		1162
708	# store the current coroutine in $current,	1163	# store the current coro in $current,
709	# and provide result variables for the closure passed to ->child	1164	# and provide result variables for the closure passed to ->child
710	my $current = $Coro::current;	1165	my $current = $Coro::current;
711	my ($done, $rstatus);	1166	my ($done, $rstatus);
712		1167
713	# pass a closure to ->child	1168	# pass a closure to ->child
714	my $watcher = AnyEvent->child (pid => $pid, cb => sub {	1169	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
715	$rstatus = $_[1]; # remember rstatus	1170	$rstatus = $_[1]; # remember rstatus
716	$done = 1; # mark $rstatus as valud	1171	$done = 1; # mark $rstatus as valid
		1172	$current->ready; # wake up the waiting thread
717	});	1173	});
718		1174
719	# wait until the closure has been called	1175	# wait until the closure has been called
720	schedule while !$done;	1176	schedule while !$done;
721		1177
…		…
729		1185
730	=item fork with pthread backend	1186	=item fork with pthread backend
731		1187
732	When Coro is compiled using the pthread backend (which isn't recommended	1188	When Coro is compiled using the pthread backend (which isn't recommended
733	but required on many BSDs as their libcs are completely broken), then	1189	but required on many BSDs as their libcs are completely broken), then
734	coroutines will not survive a fork. There is no known workaround except to	1190	coro will not survive a fork. There is no known workaround except to
735	fix your libc and use a saner backend.	1191	fix your libc and use a saner backend.
736		1192
737	=item perl process emulation ("threads")	1193	=item perl process emulation ("threads")
738		1194
739	This module is not perl-pseudo-thread-safe. You should only ever use this	1195	This module is not perl-pseudo-thread-safe. You should only ever use this
740	module from the same thread (this requirement might be removed in the	1196	module from the first thread (this requirement might be removed in the
741	future to allow per-thread schedulers, but Coro::State does not yet allow	1197	future to allow per-thread schedulers, but Coro::State does not yet allow
742	this). I recommend disabling thread support and using processes, as having	1198	this). I recommend disabling thread support and using processes, as having
743	the windows process emulation enabled under unix roughly halves perl	1199	the windows process emulation enabled under unix roughly halves perl
744	performance, even when not used.	1200	performance, even when not used.
745		1201
		1202	Attempts to use threads created in another emulated process will crash
		1203	("cleanly", with a null pointer exception).
		1204
746	=item coroutine switching not signal safe	1205	=item coro switching is not signal safe
747		1206
748	You must not switch to another coroutine from within a signal handler	1207	You must not switch to another coro from within a signal handler (only
749	(only relevant with %SIG - most event libraries provide safe signals).	1208	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1209	you are sure you are not interrupting a Coro function.
750		1210
751	That means you I<MUST NOT> call any function that might "block" the	1211	That means you I<MUST NOT> call any function that might "block" the
752	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1212	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
753	anything that calls those. Everything else, including calling C<ready>,	1213	anything that calls those. Everything else, including calling C<ready>,
754	works.	1214	works.
755		1215
756	=back	1216	=back
757		1217
758		1218
		1219	=head1 WINDOWS PROCESS EMULATION
		1220
		1221	A great many people seem to be confused about ithreads (for example, Chip
		1222	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1223	while in the same mail making rather confused statements about perl
		1224	ithreads (for example, that memory or files would be shared), showing his
		1225	lack of understanding of this area - if it is hard to understand for Chip,
		1226	it is probably not obvious to everybody).
		1227
		1228	What follows is an ultra-condensed version of my talk about threads in
		1229	scripting languages given on the perl workshop 2009:
		1230
		1231	The so-called "ithreads" were originally implemented for two reasons:
		1232	first, to (badly) emulate unix processes on native win32 perls, and
		1233	secondly, to replace the older, real thread model ("5.005-threads").
		1234
		1235	It does that by using threads instead of OS processes. The difference
		1236	between processes and threads is that threads share memory (and other
		1237	state, such as files) between threads within a single process, while
		1238	processes do not share anything (at least not semantically). That
		1239	means that modifications done by one thread are seen by others, while
		1240	modifications by one process are not seen by other processes.
		1241
		1242	The "ithreads" work exactly like that: when creating a new ithreads
		1243	process, all state is copied (memory is copied physically, files and code
		1244	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1245	the same behaviour can be achieved by using operating system processes,
		1246	except that UNIX typically uses hardware built into the system to do this
		1247	efficiently, while the windows process emulation emulates this hardware in
		1248	software (rather efficiently, but of course it is still much slower than
		1249	dedicated hardware).
		1250
		1251	As mentioned before, loading code, modifying code, modifying data
		1252	structures and so on is only visible in the ithreads process doing the
		1253	modification, not in other ithread processes within the same OS process.
		1254
		1255	This is why "ithreads" do not implement threads for perl at all, only
		1256	processes. What makes it so bad is that on non-windows platforms, you can
		1257	actually take advantage of custom hardware for this purpose (as evidenced
		1258	by the forks module, which gives you the (i-) threads API, just much
		1259	faster).
		1260
		1261	Sharing data is in the i-threads model is done by transfering data
		1262	structures between threads using copying semantics, which is very slow -
		1263	shared data simply does not exist. Benchmarks using i-threads which are
		1264	communication-intensive show extremely bad behaviour with i-threads (in
		1265	fact, so bad that Coro, which cannot take direct advantage of multiple
		1266	CPUs, is often orders of magnitude faster because it shares data using
		1267	real threads, refer to my talk for details).
		1268
		1269	As summary, i-threads *use* threads to implement processes, while
		1270	the compatible forks module *uses* processes to emulate, uhm,
		1271	processes. I-threads slow down every perl program when enabled, and
		1272	outside of windows, serve no (or little) practical purpose, but
		1273	disadvantages every single-threaded Perl program.
		1274
		1275	This is the reason that I try to avoid the name "ithreads", as it is
		1276	misleading as it implies that it implements some kind of thread model for
		1277	perl, and prefer the name "windows process emulation", which describes the
		1278	actual use and behaviour of it much better.
		1279
759	=head1 SEE ALSO	1280	=head1 SEE ALSO
760		1281
761	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1282	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
762		1283
763	Debugging: L<Coro::Debug>.	1284	Debugging: L<Coro::Debug>.
764		1285
765	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1286	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
766		1287
767	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1288	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1289	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
768		1290
769	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1291	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
770		1292
771	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1293	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1294	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1295	L<Coro::Select>.
772		1296
773	XS API: L<Coro::MakeMaker>.	1297	XS API: L<Coro::MakeMaker>.
774		1298
775	Low level Configuration, Coroutine Environment: L<Coro::State>.	1299	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
776		1300
777	=head1 AUTHOR	1301	=head1 AUTHOR
778		1302
779	Marc Lehmann <schmorp@schmorp.de>	1303	Marc Lehmann <schmorp@schmorp.de>
780	http://home.schmorp.de/	1304	http://home.schmorp.de/

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