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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	my $lock = new Coro::Semaphore;	21	my $lock = new Coro::Semaphore;
…		…
25	$locked = 1;	25	$locked = 1;
26	$lock->up;	26	$lock->up;
27		27
28	=head1 DESCRIPTION	28	=head1 DESCRIPTION
29		29
30	This module collection manages coroutines. Coroutines are similar to	30	For a tutorial-style introduction, please read the L<Coro::Intro>
31	threads but don't (in general) run in parallel at the same time even	31	manpage. This manpage mainly contains reference information.
32	on SMP machines. The specific flavor of coroutine used in this module
33	also guarantees you that it will not switch between coroutines unless
34	necessary, at easily-identified points in your program, so locking and
35	parallel access are rarely an issue, making coroutine programming much
36	safer and easier than threads programming.
37		32
38	Unlike a normal perl program, however, coroutines allow you to have	33	This module collection manages continuations in general, most often in
39	multiple running interpreters that share data, which is especially useful	34	the form of cooperative threads (also called coros, or simply "coro"
40	to code pseudo-parallel processes, such as multiple HTTP-GET requests	35	in the documentation). They are similar to kernel threads but don't (in
41	running concurrently.	36	general) run in parallel at the same time even on SMP machines. The
		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.
42		42
43	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
44	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
45	emulation coming from the Windows platform: On standard operating systems	45	more details) ported to UNIX, and as such act as processes), Coro
46	they serve no purpose whatsoever, except by making your programs slow and	46	provides a full shared address space, which makes communication between
47	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
48	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.
49		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
50	In this module, coroutines are defined as "callchain + lexical variables +	60	In this module, a thread is defined as "callchain + lexical variables +
51	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	61	some package variables + C stack), that is, a thread has its own callchain,
52	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
53	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	And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
		201	coro thread from another thread:
		202
		203	my $coro = async {
		204	exit 1;
		205	};
		206
		207	$coro->cancel; # also accepts values for ->join to retrieve
		208
		209	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		210	actually exiting, and might leave C libraries and XS modules in a weird
		211	state. Unlike other thread implementations, however, Coro is exceptionally
		212	safe with regards to cancellation, as perl will always be in a consistent
		213	state, and for those cases where you want to do truly marvellous things
		214	with your coro while it is being cancelled - that is, make sure all
		215	cleanup code is executed from the thread being cancelled - there is even a
		216	C<< ->safe_cancel >> method.
		217
		218	So, cancelling a thread that runs in an XS event loop might not be the
		219	best idea, but any other combination that deals with perl only (cancelling
		220	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		221	safe.
		222
		223	Lastly, a coro thread object that isn't referenced is C<< ->cancel >>'ed
		224	automatically - just like other objects in Perl. This is not such a common
		225	case, however - a running thread is referencedy b C<$Coro::current>, a
		226	thread ready to run is referenced by the ready queue, a thread waiting
		227	on a lock or semaphore is referenced by being in some wait list and so
		228	on. But a thread that isn't in any of those queues gets cancelled:
		229
		230	async {
		231	schedule; # cede to other coros, don't go into the ready queue
		232	};
		233
		234	cede;
		235	# now the async above is destroyed, as it is not referenced by anything.
		236
		237	=item 5. Cleanup
		238
		239	Threads will allocate various resources. Most but not all will be returned
		240	when a thread terminates, during clean-up.
		241
		242	Cleanup is quite similar to throwing an uncaught exception: perl will
		243	work it's way up through all subroutine calls and blocks. On it's way, it
		244	will release all C<my> variables, undo all C<local>'s and free any other
		245	resources truly local to the thread.
		246
		247	So, a common way to free resources is to keep them referenced only by my
		248	variables:
		249
		250	async {
		251	my $big_cache = new Cache ...;
		252	};
		253
		254	If there are no other references, then the C<$big_cache> object will be
		255	freed when the thread terminates, regardless of how it does so.
		256
		257	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		258	resources, but that's where the C<guard> methods come in handy:
		259
		260	my $sem = new Coro::Semaphore;
		261
		262	async {
		263	my $lock_guard = $sem->guard;
		264	# if we reutrn, or die or get cancelled, here,
		265	# then the semaphore will be "up"ed.
		266	};
		267
		268	The C<Guard::guard> function comes in handy for any custom cleanup you
		269	might want to do (but you cannot switch to other coroutines form those
		270	code blocks):
		271
		272	async {
		273	my $window = new Gtk2::Window "toplevel";
		274	# The window will not be cleaned up automatically, even when $window
		275	# gets freed, so use a guard to ensure it's destruction
		276	# in case of an error:
		277	my $window_guard = Guard::guard { $window->destroy };
		278
		279	# we are safe here
		280	};
		281
		282	Last not least, C<local> can often be handy, too, e.g. when temporarily
		283	replacing the coro thread description:
		284
		285	sub myfunction {
		286	local $Coro::current->{desc} = "inside myfunction(@_)";
		287
		288	# if we return or die here, the description will be restored
		289	}
		290
		291	=item 6. Viva La Zombie Muerte
		292
		293	Even after a thread has terminated and cleaned up its resources, the Coro
		294	object still is there and stores the return values of the thread.
		295
		296	The means the Coro object gets freed automatically when the thread has
		297	terminated and cleaned up and there arenot other references.
		298
		299	If there are, the Coro object will stay around, and you can call C<<
		300	->join >> as many times as you wish to retrieve the result values:
		301
		302	async {
		303	print "hi\n";
		304	1
		305	};
		306
		307	# run the async above, and free everything before returning
		308	# from Coro::cede:
		309	Coro::cede;
		310
		311	{
		312	my $coro = async {
		313	print "hi\n";
		314	1
		315	};
		316
		317	# run the async above, and clean up, but do not free the coro
		318	# object:
		319	Coro::cede;
		320
		321	# optionally retrieve the result values
		322	my @results = $coro->join;
		323
		324	# now $coro goes out of scope, and presumably gets freed
		325	};
		326
		327	=back
54		328
55	=cut	329	=cut
56		330
57	package Coro;	331	package Coro;
58		332
59	use strict;	333	use common::sense;
60	no warnings "uninitialized";	334
		335	use Carp ();
		336
		337	use Guard ();
61		338
62	use Coro::State;	339	use Coro::State;
63		340
64	use base qw(Coro::State Exporter);	341	use base qw(Coro::State Exporter);
65		342
66	our $idle; # idle handler	343	our $idle; # idle handler
67	our $main; # main coroutine	344	our $main; # main coro
68	our $current; # current coroutine	345	our $current; # current coro
69		346
70	our $VERSION = 4.6;	347	our $VERSION = 5.372;
71		348
72	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	349	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
73	our %EXPORT_TAGS = (	350	our %EXPORT_TAGS = (
74	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	351	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
75	);	352	);
76	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	353	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
77		354
		355	=head1 GLOBAL VARIABLES
		356
78	=over 4	357	=over 4
79		358
80	=item $Coro::main	359	=item $Coro::main
81		360
82	This variable stores the coroutine object that represents the main	361	This variable stores the Coro object that represents the main
83	program. While you cna C<ready> it and do most other things you can do to	362	program. While you cna C<ready> it and do most other things you can do to
84	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	363	coro, it is mainly useful to compare again C<$Coro::current>, to see
85	wether you are running in the main program or not.	364	whether you are running in the main program or not.
86		365
87	=cut	366	=cut
88		367
89	$main = new Coro;	368	# $main is now being initialised by Coro::State
90		369
91	=item $Coro::current	370	=item $Coro::current
92		371
93	The coroutine object representing the current coroutine (the last	372	The Coro object representing the current coro (the last
94	coroutine that the Coro scheduler switched to). The initial value is	373	coro that the Coro scheduler switched to). The initial value is
95	C<$main> (of course).	374	C<$Coro::main> (of course).
96		375
97	This variable is B<strictly> I<read-only>. You can take copies of the	376	This variable is B<strictly> I<read-only>. You can take copies of the
98	value stored in it and use it as any other coroutine object, but you must	377	value stored in it and use it as any other Coro object, but you must
99	not otherwise modify the variable itself.	378	not otherwise modify the variable itself.
100		379
101	=cut	380	=cut
102		381
103	$main->{desc} = "[main::]";
104
105	# maybe some other module used Coro::Specific before...
106	$main->{_specific} = $current->{_specific}
107	if $current;
108
109	_set_current $main;
110
111	sub current() { $current } # [DEPRECATED]	382	sub current() { $current } # [DEPRECATED]
112		383
113	=item $Coro::idle	384	=item $Coro::idle
114		385
115	This variable is mainly useful to integrate Coro into event loops. It is	386	This variable is mainly useful to integrate Coro into event loops. It is
116	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is	387	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
117	pretty low-level functionality.	388	pretty low-level functionality.
118		389
119	This variable stores a callback that is called whenever the scheduler	390	This variable stores a Coro object that is put into the ready queue when
120	finds no ready coroutines to run. The default implementation prints	391	there are no other ready threads (without invoking any ready hooks).
121	"FATAL: deadlock detected" and exits, because the program has no other way
122	to continue.
123		392
		393	The default implementation dies with "FATAL: deadlock detected.", followed
		394	by a thread listing, because the program has no other way to continue.
		395
124	This hook is overwritten by modules such as C<Coro::Timer> and	396	This hook is overwritten by modules such as C<Coro::EV> and
125	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	397	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
126	coroutine so the scheduler can run it.	398	coro so the scheduler can run it.
127		399
128	Note that the callback I<must not>, under any circumstances, block
129	the current coroutine. Normally, this is achieved by having an "idle
130	coroutine" that calls the event loop and then blocks again, and then
131	readying that coroutine in the idle handler.
132
133	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this	400	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
134	technique.
135
136	Please note that if your callback recursively invokes perl (e.g. for event
137	handlers), then it must be prepared to be called recursively itself.
138		401
139	=cut	402	=cut
140		403
141	$idle = sub {	404	# ||= because other modules could have provided their own by now
142	require Carp;	405	$idle ||= new Coro sub {
143	Carp::croak ("FATAL: deadlock detected");	406	require Coro::Debug;
		407	die "FATAL: deadlock detected.\n"
		408	. Coro::Debug::ps_listing ();
144	};	409	};
145		410
146	sub _cancel {
147	my ($self) = @_;
148
149	# free coroutine data and mark as destructed
150	$self->_destroy
151	or return;
152
153	# call all destruction callbacks
154	$_->(@{$self->{_status}})
155	for @{(delete $self->{_on_destroy}) || []};
156	}
157
158	# this coroutine is necessary because a coroutine	411	# this coro is necessary because a coro
159	# cannot destroy itself.	412	# cannot destroy itself.
160	my @destroy;	413	our @destroy;
161	my $manager;	414	our $manager;
162		415
163	$manager = new Coro sub {	416	$manager = new Coro sub {
164	while () {	417	while () {
165	(shift @destroy)->_cancel	418	_destroy shift @destroy
166	while @destroy;	419	while @destroy;
167		420
168	&schedule;	421	&schedule;
169	}	422	}
170	};	423	};
171	$manager->desc ("[coro manager]");	424	$manager->{desc} = "[coro manager]";
172	$manager->prio (PRIO_MAX);	425	$manager->prio (PRIO_MAX);
173		426
174	=back	427	=back
175		428
176	=head2 SIMPLE COROUTINE CREATION	429	=head1 SIMPLE CORO CREATION
177		430
178	=over 4	431	=over 4
179		432
180	=item async { ... } [@args...]	433	=item async { ... } [@args...]
181		434
182	Create a new coroutine and return it's coroutine object (usually	435	Create a new coro and return its Coro object (usually
183	unused). The coroutine will be put into the ready queue, so	436	unused). The coro will be put into the ready queue, so
184	it will start running automatically on the next scheduler run.	437	it will start running automatically on the next scheduler run.
185		438
186	The first argument is a codeblock/closure that should be executed in the	439	The first argument is a codeblock/closure that should be executed in the
187	coroutine. When it returns argument returns the coroutine is automatically	440	coro. When it returns argument returns the coro is automatically
188	terminated.	441	terminated.
189		442
190	The remaining arguments are passed as arguments to the closure.	443	The remaining arguments are passed as arguments to the closure.
191		444
192	See the C<Coro::State::new> constructor for info about the coroutine	445	See the C<Coro::State::new> constructor for info about the coro
193	environment in which coroutines are executed.	446	environment in which coro are executed.
194		447
195	Calling C<exit> in a coroutine will do the same as calling exit outside	448	Calling C<exit> in a coro will do the same as calling exit outside
196	the coroutine. Likewise, when the coroutine dies, the program will exit,	449	the coro. Likewise, when the coro dies, the program will exit,
197	just as it would in the main program.	450	just as it would in the main program.
198		451
199	If you do not want that, you can provide a default C<die> handler, or	452	If you do not want that, you can provide a default C<die> handler, or
200	simply avoid dieing (by use of C<eval>).	453	simply avoid dieing (by use of C<eval>).
201		454
202	Example: Create a new coroutine that just prints its arguments.	455	Example: Create a new coro that just prints its arguments.
203		456
204	async {	457	async {
205	print "@_\n";	458	print "@_\n";
206	} 1,2,3,4;	459	} 1,2,3,4;
207		460
208	=cut
209
210	sub async(&@) {
211	my $coro = new Coro @_;
212	$coro->ready;
213	$coro
214	}
215
216	=item async_pool { ... } [@args...]	461	=item async_pool { ... } [@args...]
217		462
218	Similar to C<async>, but uses a coroutine pool, so you should not call	463	Similar to C<async>, but uses a coro pool, so you should not call
219	terminate or join on it (although you are allowed to), and you get a	464	terminate or join on it (although you are allowed to), and you get a
220	coroutine that might have executed other code already (which can be good	465	coro that might have executed other code already (which can be good
221	or bad :).	466	or bad :).
222		467
223	On the plus side, this function is faster than creating (and destroying)	468	On the plus side, this function is about twice as fast as creating (and
224	a completely new coroutine, so if you need a lot of generic coroutines in	469	destroying) a completely new coro, so if you need a lot of generic
225	quick successsion, use C<async_pool>, not C<async>.	470	coros in quick successsion, use C<async_pool>, not C<async>.
226		471
227	The code block is executed in an C<eval> context and a warning will be	472	The code block is executed in an C<eval> context and a warning will be
228	issued in case of an exception instead of terminating the program, as	473	issued in case of an exception instead of terminating the program, as
229	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	474	C<async> does. As the coro is being reused, stuff like C<on_destroy>
230	will not work in the expected way, unless you call terminate or cancel,	475	will not work in the expected way, unless you call terminate or cancel,
231	which somehow defeats the purpose of pooling (but is fine in the	476	which somehow defeats the purpose of pooling (but is fine in the
232	exceptional case).	477	exceptional case).
233		478
234	The priority will be reset to C<0> after each run, tracing will be	479	The priority will be reset to C<0> after each run, tracing will be
235	disabled, the description will be reset and the default output filehandle	480	disabled, the description will be reset and the default output filehandle
236	gets restored, so you can change all these. Otherwise the coroutine will	481	gets restored, so you can change all these. Otherwise the coro will
237	be re-used "as-is": most notably if you change other per-coroutine global	482	be re-used "as-is": most notably if you change other per-coro global
238	stuff such as C<$/> you I<must needs> to revert that change, which is most	483	stuff such as C<$/> you I<must needs> revert that change, which is most
239	simply done by using local as in: C< local $/ >.	484	simply done by using local as in: C<< local $/ >>.
240		485
241	The pool size is limited to C<8> idle coroutines (this can be adjusted by	486	The idle pool size is limited to C<8> idle coros (this can be
242	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as	487	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
243	required.	488	coros as required.
244		489
245	If you are concerned about pooled coroutines growing a lot because a	490	If you are concerned about pooled coros growing a lot because a
246	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	491	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
247	{ terminate }> once per second or so to slowly replenish the pool. In	492	{ terminate }> once per second or so to slowly replenish the pool. In
248	addition to that, when the stacks used by a handler grows larger than 16kb	493	addition to that, when the stacks used by a handler grows larger than 32kb
249	(adjustable via $Coro::POOL_RSS) it will also be destroyed.	494	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
250		495
251	=cut	496	=cut
252		497
253	our $POOL_SIZE = 8;	498	our $POOL_SIZE = 8;
254	our $POOL_RSS = 16 * 1024;	499	our $POOL_RSS = 32 * 1024;
255	our @async_pool;	500	our @async_pool;
256		501
257	sub pool_handler {	502	sub pool_handler {
258	my $cb;
259
260	while () {	503	while () {
261	eval {	504	eval {
262	while () {	505	&{&_pool_handler} while 1;
263	_pool_1 $cb;
264	&$cb;
265	_pool_2 $cb;
266	&schedule;
267	}
268	};	506	};
269		507
270	last if $@ eq "\3async_pool terminate\2\n";
271	warn $@ if $@;	508	warn $@ if $@;
272	}	509	}
273	}	510	}
274		511
275	sub async_pool(&@) {
276	# this is also inlined into the unlock_scheduler
277	my $coro = (pop @async_pool) || new Coro \&pool_handler;
278
279	$coro->{_invoke} = [@_];
280	$coro->ready;
281
282	$coro
283	}
284
285	=back	512	=back
286		513
287	=head2 STATIC METHODS	514	=head1 STATIC METHODS
288		515
289	Static methods are actually functions that operate on the current coroutine.	516	Static methods are actually functions that implicitly operate on the
		517	current coro.
290		518
291	=over 4	519	=over 4
292		520
293	=item schedule	521	=item schedule
294		522
295	Calls the scheduler. The scheduler will find the next coroutine that is	523	Calls the scheduler. The scheduler will find the next coro that is
296	to be run from the ready queue and switches to it. The next coroutine	524	to be run from the ready queue and switches to it. The next coro
297	to be run is simply the one with the highest priority that is longest	525	to be run is simply the one with the highest priority that is longest
298	in its ready queue. If there is no coroutine ready, it will clal the	526	in its ready queue. If there is no coro ready, it will call the
299	C<$Coro::idle> hook.	527	C<$Coro::idle> hook.
300		528
301	Please note that the current coroutine will I<not> be put into the ready	529	Please note that the current coro will I<not> be put into the ready
302	queue, so calling this function usually means you will never be called	530	queue, so calling this function usually means you will never be called
303	again unless something else (e.g. an event handler) calls C<< ->ready >>,	531	again unless something else (e.g. an event handler) calls C<< ->ready >>,
304	thus waking you up.	532	thus waking you up.
305		533
306	This makes C<schedule> I<the> generic method to use to block the current	534	This makes C<schedule> I<the> generic method to use to block the current
307	coroutine and wait for events: first you remember the current coroutine in	535	coro and wait for events: first you remember the current coro in
308	a variable, then arrange for some callback of yours to call C<< ->ready	536	a variable, then arrange for some callback of yours to call C<< ->ready
309	>> on that once some event happens, and last you call C<schedule> to put	537	>> on that once some event happens, and last you call C<schedule> to put
310	yourself to sleep. Note that a lot of things can wake your coroutine up,	538	yourself to sleep. Note that a lot of things can wake your coro up,
311	so you need to check wether the event indeed happened, e.g. by storing the	539	so you need to check whether the event indeed happened, e.g. by storing the
312	status in a variable.	540	status in a variable.
313		541
314	The canonical way to wait on external events is this:	542	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
315		543
316	{	544	=item cede
317	# remember current coroutine
318	my $current = $Coro::current;
319		545
320	# register a hypothetical event handler	546	"Cede" to other coros. This function puts the current coro into
321	on_event_invoke sub {	547	the ready queue and calls C<schedule>, which has the effect of giving
322	# wake up sleeping coroutine	548	up the current "timeslice" to other coros of the same or higher
323	$current->ready;	549	priority. Once your coro gets its turn again it will automatically be
324	undef $current;	550	resumed.
		551
		552	This function is often called C<yield> in other languages.
		553
		554	=item Coro::cede_notself
		555
		556	Works like cede, but is not exported by default and will cede to I<any>
		557	coro, regardless of priority. This is useful sometimes to ensure
		558	progress is made.
		559
		560	=item terminate [arg...]
		561
		562	Terminates the current coro with the given status values (see
		563	L<cancel>). The values will not be copied, but referenced directly.
		564
		565	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		566
		567	These function install enter and leave winders in the current scope. The
		568	enter block will be executed when on_enter is called and whenever the
		569	current coro is re-entered by the scheduler, while the leave block is
		570	executed whenever the current coro is blocked by the scheduler, and
		571	also when the containing scope is exited (by whatever means, be it exit,
		572	die, last etc.).
		573
		574	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		575	BLOCKs>. That means: do not even think about calling C<die> without an
		576	eval, and do not even think of entering the scheduler in any way.
		577
		578	Since both BLOCKs are tied to the current scope, they will automatically
		579	be removed when the current scope exits.
		580
		581	These functions implement the same concept as C<dynamic-wind> in scheme
		582	does, and are useful when you want to localise some resource to a specific
		583	coro.
		584
		585	They slow down thread switching considerably for coros that use them
		586	(about 40% for a BLOCK with a single assignment, so thread switching is
		587	still reasonably fast if the handlers are fast).
		588
		589	These functions are best understood by an example: The following function
		590	will change the current timezone to "Antarctica/South_Pole", which
		591	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		592	which remember/change the current timezone and restore the previous
		593	value, respectively, the timezone is only changed for the coro that
		594	installed those handlers.
		595
		596	use POSIX qw(tzset);
		597
		598	async {
		599	my $old_tz; # store outside TZ value here
		600
		601	Coro::on_enter {
		602	$old_tz = $ENV{TZ}; # remember the old value
		603
		604	$ENV{TZ} = "Antarctica/South_Pole";
		605	tzset; # enable new value
325	};	606	};
326		607
327	# call schedule until event occurred.	608	Coro::on_leave {
328	# in case we are woken up for other reasons	609	$ENV{TZ} = $old_tz;
329	# (current still defined), loop.	610	tzset; # restore old value
330	Coro::schedule while $current;	611	};
		612
		613	# at this place, the timezone is Antarctica/South_Pole,
		614	# without disturbing the TZ of any other coro.
331	}	615	};
332		616
333	=item cede	617	This can be used to localise about any resource (locale, uid, current
		618	working directory etc.) to a block, despite the existance of other
		619	coros.
334		620
335	"Cede" to other coroutines. This function puts the current coroutine into	621	Another interesting example implements time-sliced multitasking using
336	the ready queue and calls C<schedule>, which has the effect of giving	622	interval timers (this could obviously be optimised, but does the job):
337	up the current "timeslice" to other coroutines of the same or higher
338	priority. Once your coroutine gets its turn again it will automatically be
339	resumed.
340		623
341	This function is often called C<yield> in other languages.	624	# "timeslice" the given block
		625	sub timeslice(&) {
		626	use Time::HiRes ();
342		627
343	=item Coro::cede_notself	628	Coro::on_enter {
		629	# on entering the thread, we set an VTALRM handler to cede
		630	$SIG{VTALRM} = sub { cede };
		631	# and then start the interval timer
		632	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		633	};
		634	Coro::on_leave {
		635	# on leaving the thread, we stop the interval timer again
		636	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		637	};
344		638
345	Works like cede, but is not exported by default and will cede to I<any>	639	&{+shift};
346	coroutine, regardless of priority. This is useful sometimes to ensure	640	}
347	progress is made.
348		641
349	=item terminate [arg...]	642	# use like this:
		643	timeslice {
		644	# The following is an endless loop that would normally
		645	# monopolise the process. Since it runs in a timesliced
		646	# environment, it will regularly cede to other threads.
		647	while () { }
		648	};
350		649
351	Terminates the current coroutine with the given status values (see L<cancel>).
352		650
353	=item killall	651	=item killall
354		652
355	Kills/terminates/cancels all coroutines except the currently running	653	Kills/terminates/cancels all coros except the currently running one.
356	one. This is useful after a fork, either in the child or the parent, as
357	usually only one of them should inherit the running coroutines.
358		654
359	Note that while this will try to free some of the main programs resources,	655	Note that while this will try to free some of the main interpreter
		656	resources if the calling coro isn't the main coro, but one
360	you cnanot free all of them, so if a coroutine that is not the main	657	cannot free all of them, so if a coro that is not the main coro
361	program calls this function, there will be some one-time resource leak.	658	calls this function, there will be some one-time resource leak.
362		659
363	=cut	660	=cut
364
365	sub terminate {
366	$current->cancel (@_);
367	}
368		661
369	sub killall {	662	sub killall {
370	for (Coro::State::list) {	663	for (Coro::State::list) {
371	$_->cancel	664	$_->cancel
372	if $_ != $current && UNIVERSAL::isa $_, "Coro";	665	if $_ != $current && UNIVERSAL::isa $_, "Coro";
373	}	666	}
374	}	667	}
375		668
376	=back	669	=back
377		670
378	=head2 COROUTINE METHODS	671	=head1 CORO OBJECT METHODS
379		672
380	These are the methods you can call on coroutine objects (or to create	673	These are the methods you can call on coro objects (or to create
381	them).	674	them).
382		675
383	=over 4	676	=over 4
384		677
385	=item new Coro \&sub [, @args...]	678	=item new Coro \&sub [, @args...]
386		679
387	Create a new coroutine and return it. When the sub returns, the coroutine	680	Create a new coro and return it. When the sub returns, the coro
388	automatically terminates as if C<terminate> with the returned values were	681	automatically terminates as if C<terminate> with the returned values were
389	called. To make the coroutine run you must first put it into the ready	682	called. To make the coro run you must first put it into the ready
390	queue by calling the ready method.	683	queue by calling the ready method.
391		684
392	See C<async> and C<Coro::State::new> for additional info about the	685	See C<async> and C<Coro::State::new> for additional info about the
393	coroutine environment.	686	coro environment.
394		687
395	=cut	688	=cut
396		689
397	sub _run_coro {	690	sub _coro_run {
398	terminate &{+shift};	691	terminate &{+shift};
399	}	692	}
400		693
401	sub new {
402	my $class = shift;
403
404	$class->SUPER::new (\&_run_coro, @_)
405	}
406
407	=item $success = $coroutine->ready	694	=item $success = $coro->ready
408		695
409	Put the given coroutine into the end of its ready queue (there is one	696	Put the given coro into the end of its ready queue (there is one
410	queue for each priority) and return true. If the coroutine is already in	697	queue for each priority) and return true. If the coro is already in
411	the ready queue, do nothing and return false.	698	the ready queue, do nothing and return false.
412		699
413	This ensures that the scheduler will resume this coroutine automatically	700	This ensures that the scheduler will resume this coro automatically
414	once all the coroutines of higher priority and all coroutines of the same	701	once all the coro of higher priority and all coro of the same
415	priority that were put into the ready queue earlier have been resumed.	702	priority that were put into the ready queue earlier have been resumed.
416		703
		704	=item $coro->suspend
		705
		706	Suspends the specified coro. A suspended coro works just like any other
		707	coro, except that the scheduler will not select a suspended coro for
		708	execution.
		709
		710	Suspending a coro can be useful when you want to keep the coro from
		711	running, but you don't want to destroy it, or when you want to temporarily
		712	freeze a coro (e.g. for debugging) to resume it later.
		713
		714	A scenario for the former would be to suspend all (other) coros after a
		715	fork and keep them alive, so their destructors aren't called, but new
		716	coros can be created.
		717
		718	=item $coro->resume
		719
		720	If the specified coro was suspended, it will be resumed. Note that when
		721	the coro was in the ready queue when it was suspended, it might have been
		722	unreadied by the scheduler, so an activation might have been lost.
		723
		724	To avoid this, it is best to put a suspended coro into the ready queue
		725	unconditionally, as every synchronisation mechanism must protect itself
		726	against spurious wakeups, and the one in the Coro family certainly do
		727	that.
		728
		729	=item $state->is_new
		730
		731	Returns true iff this Coro object is "new", i.e. has never been run
		732	yet. Those states basically consist of only the code reference to call and
		733	the arguments, but consumes very little other resources. New states will
		734	automatically get assigned a perl interpreter when they are transfered to.
		735
		736	=item $state->is_zombie
		737
		738	Returns true iff the Coro object has been cancelled, i.e.
		739	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		740	C<safe_cancel>'ed or simply went out of scope.
		741
		742	The name "zombie" stems from UNIX culture, where a process that has
		743	exited and only stores and exit status and no other resources is called a
		744	"zombie".
		745
417	=item $is_ready = $coroutine->is_ready	746	=item $is_ready = $coro->is_ready
418		747
419	Return wether the coroutine is currently the ready queue or not,	748	Returns true iff the Coro object is in the ready queue. Unless the Coro
		749	object gets destroyed, it will eventually be scheduled by the scheduler.
420		750
		751	=item $is_running = $coro->is_running
		752
		753	Returns true iff the Coro object is currently running. Only one Coro object
		754	can ever be in the running state (but it currently is possible to have
		755	multiple running Coro::States).
		756
		757	=item $is_suspended = $coro->is_suspended
		758
		759	Returns true iff this Coro object has been suspended. Suspended Coros will
		760	not ever be scheduled.
		761
421	=item $coroutine->cancel (arg...)	762	=item $coro->cancel (arg...)
422		763
423	Terminates the given coroutine and makes it return the given arguments as	764	Terminates the given Coro thread and makes it return the given arguments as
424	status (default: the empty list). Never returns if the coroutine is the	765	status (default: an empty list). Never returns if the Coro is the
425	current coroutine.	766	current Coro.
426		767
427	=cut	768	This is a rather brutal way to free a coro, with some limitations - if
		769	the thread is inside a C callback that doesn't expect to be canceled,
		770	bad things can happen, or if the cancelled thread insists on running
		771	complicated cleanup handlers that rely on it'S thread context, things will
		772	not work.
428		773
429	sub cancel {	774	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
430	my $self = shift;	775	a thread context, and is not allowed to switch to other threads. On the
431	$self->{_status} = [@_];	776	plus side, C<< ->cancel >> will always clean up the thread, no matter
		777	what. If your cleanup code is complex or you want to avoid cancelling a
		778	C-thread that doesn't know how to clean up itself, it can be better to C<<
		779	->throw >> an exception, or use C<< ->safe_cancel >>.
432		780
433	if ($current == $self) {	781	The arguments to C<< ->cancel >> are not copied, but instead will
434	push @destroy, $self;	782	be referenced directly (e.g. if you pass C<$var> and after the call
435	$manager->ready;	783	change that variable, then you might change the return values passed to
436	&schedule while 1;	784	e.g. C<join>, so don't do that).
437	} else {	785
438	$self->_cancel;	786	The resources of the Coro are usually freed (or destructed) before this
		787	call returns, but this can be delayed for an indefinite amount of time, as
		788	in some cases the manager thread has to run first to actually destruct the
		789	Coro object.
		790
		791	=item $coro->safe_cancel ($arg...)
		792
		793	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		794	consequently, can fail with an exception in cases the thread is not in a
		795	cancellable state.
		796
		797	This method works a bit like throwing an exception that cannot be caught
		798	- specifically, it will clean up the thread from within itself, so
		799	all cleanup handlers (e.g. C<guard> blocks) are run with full thread
		800	context and can block if they wish. The downside is that there is no
		801	guarantee that the thread can be cancelled when you call this method, and
		802	therefore, it might fail. It is also considerably slower than C<cancel> or
		803	C<terminate>.
		804
		805	A thread is in a safe-cancellable state if it either hasn't been run yet,
		806	or it has no C context attached and is inside an SLF function.
		807
		808	The latter two basically mean that the thread isn't currently inside a
		809	perl callback called from some C function (usually via some XS modules)
		810	and isn't currently executing inside some C function itself (via Coro's XS
		811	API).
		812
		813	This call returns true when it could cancel the thread, or croaks with an
		814	error otherwise (i.e. it either returns true or doesn't return at all).
		815
		816	Why the weird interface? Well, there are two common models on how and
		817	when to cancel things. In the first, you have the expectation that your
		818	coro thread can be cancelled when you want to cancel it - if the thread
		819	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		820	croaks to notify of the bug.
		821
		822	In the second model you sometimes want to ask nicely to cancel a thread,
		823	but if it's not a good time, well, then don't cancel. This can be done
		824	relatively easy like this:
		825
		826	if (! eval { $coro->safe_cancel }) {
		827	warn "unable to cancel thread: $@";
439	}	828	}
440	}
441		829
442	=item $coroutine->join	830	However, what you never should do is first try to cancel "safely" and
		831	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		832	no sense: either you rely on being able to execute cleanup code in your
		833	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		834	only way, and if you don't, then C<< ->cancel >> is always faster and more
		835	direct.
443		836
444	Wait until the coroutine terminates and return any values given to the	837	=item $coro->schedule_to
445	C<terminate> or C<cancel> functions. C<join> can be called concurrently
446	from multiple coroutines, and all will be resumed and given the status
447	return once the C<$coroutine> terminates.
448		838
449	=cut	839	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		840	of continuing with the next coro from the ready queue, always switch to
		841	the given coro object (regardless of priority etc.). The readyness
		842	state of that coro isn't changed.
450		843
451	sub join {	844	This is an advanced method for special cases - I'd love to hear about any
452	my $self = shift;	845	uses for this one.
453		846
454	unless ($self->{_status}) {	847	=item $coro->cede_to
455	my $current = $current;
456		848
457	push @{$self->{_on_destroy}}, sub {	849	Like C<schedule_to>, but puts the current coro into the ready
458	$current->ready;	850	queue. This has the effect of temporarily switching to the given
459	undef $current;	851	coro, and continuing some time later.
460	};
461		852
462	&schedule while $current;	853	This is an advanced method for special cases - I'd love to hear about any
463	}	854	uses for this one.
464		855
465	wantarray ? @{$self->{_status}} : $self->{_status}[0];
466	}
467
468	=item $coroutine->on_destroy (\&cb)
469
470	Registers a callback that is called when this coroutine gets destroyed,
471	but before it is joined. The callback gets passed the terminate arguments,
472	if any, and I<must not> die, under any circumstances.
473
474	=cut
475
476	sub on_destroy {
477	my ($self, $cb) = @_;
478
479	push @{ $self->{_on_destroy} }, $cb;
480	}
481
482	=item $oldprio = $coroutine->prio ($newprio)
483
484	Sets (or gets, if the argument is missing) the priority of the
485	coroutine. Higher priority coroutines get run before lower priority
486	coroutines. Priorities are small signed integers (currently -4 .. +3),
487	that you can refer to using PRIO_xxx constants (use the import tag :prio
488	to get then):
489
490	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
491	3 > 1 > 0 > -1 > -3 > -4
492
493	# set priority to HIGH
494	current->prio(PRIO_HIGH);
495
496	The idle coroutine ($Coro::idle) always has a lower priority than any
497	existing coroutine.
498
499	Changing the priority of the current coroutine will take effect immediately,
500	but changing the priority of coroutines in the ready queue (but not
501	running) will only take effect after the next schedule (of that
502	coroutine). This is a bug that will be fixed in some future version.
503
504	=item $newprio = $coroutine->nice ($change)
505
506	Similar to C<prio>, but subtract the given value from the priority (i.e.
507	higher values mean lower priority, just as in unix).
508
509	=item $olddesc = $coroutine->desc ($newdesc)
510
511	Sets (or gets in case the argument is missing) the description for this
512	coroutine. This is just a free-form string you can associate with a coroutine.
513
514	This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
515	can modify this member directly if you wish.
516
517	=item $coroutine->throw ([$scalar])	856	=item $coro->throw ([$scalar])
518		857
519	If C<$throw> is specified and defined, it will be thrown as an exception	858	If C<$throw> is specified and defined, it will be thrown as an exception
520	inside the coroutine at the next convinient point in time (usually after	859	inside the coro at the next convenient point in time. Otherwise
521	it gains control at the next schedule/transfer/cede). Otherwise clears the
522	exception object.	860	clears the exception object.
		861
		862	Coro will check for the exception each time a schedule-like-function
		863	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		864	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
		865	that are part of Coro itself) detect this case and return early in case an
		866	exception is pending.
523		867
524	The exception object will be thrown "as is" with the specified scalar in	868	The exception object will be thrown "as is" with the specified scalar in
525	C<$@>, i.e. if it is a string, no line number or newline will be appended	869	C<$@>, i.e. if it is a string, no line number or newline will be appended
526	(unlike with C<die>).	870	(unlike with C<die>).
527		871
528	This can be used as a softer means than C<cancel> to ask a coroutine to	872	This can be used as a softer means than either C<cancel> or C<safe_cancel
529	end itself, although there is no guarentee that the exception will lead to	873	>to ask a coro to end itself, although there is no guarantee that the
530	termination, and if the exception isn't caught it might well end the whole	874	exception will lead to termination, and if the exception isn't caught it
531	program.	875	might well end the whole program.
		876
		877	You might also think of C<throw> as being the moral equivalent of
		878	C<kill>ing a coro with a signal (in this case, a scalar).
		879
		880	=item $coro->join
		881
		882	Wait until the coro terminates and return any values given to the
		883	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		884	from multiple threads, and all will be resumed and given the status
		885	return once the C<$coro> terminates.
		886
		887	=item $coro->on_destroy (\&cb)
		888
		889	Registers a callback that is called when this coro thread gets destroyed,
		890	that is, after it's resources have been freed but before it is joined. The
		891	callback gets passed the terminate/cancel arguments, if any, and I<must
		892	not> die, under any circumstances.
		893
		894	There can be any number of C<on_destroy> callbacks per coro, and there is
		895	no way currently to remove a callback once added.
		896
		897	=item $oldprio = $coro->prio ($newprio)
		898
		899	Sets (or gets, if the argument is missing) the priority of the
		900	coro thread. Higher priority coro get run before lower priority
		901	coros. Priorities are small signed integers (currently -4 .. +3),
		902	that you can refer to using PRIO_xxx constants (use the import tag :prio
		903	to get then):
		904
		905	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		906	3 > 1 > 0 > -1 > -3 > -4
		907
		908	# set priority to HIGH
		909	current->prio (PRIO_HIGH);
		910
		911	The idle coro thread ($Coro::idle) always has a lower priority than any
		912	existing coro.
		913
		914	Changing the priority of the current coro will take effect immediately,
		915	but changing the priority of a coro in the ready queue (but not running)
		916	will only take effect after the next schedule (of that coro). This is a
		917	bug that will be fixed in some future version.
		918
		919	=item $newprio = $coro->nice ($change)
		920
		921	Similar to C<prio>, but subtract the given value from the priority (i.e.
		922	higher values mean lower priority, just as in UNIX's nice command).
		923
		924	=item $olddesc = $coro->desc ($newdesc)
		925
		926	Sets (or gets in case the argument is missing) the description for this
		927	coro thread. This is just a free-form string you can associate with a
		928	coro.
		929
		930	This method simply sets the C<< $coro->{desc} >> member to the given
		931	string. You can modify this member directly if you wish, and in fact, this
		932	is often preferred to indicate major processing states that cna then be
		933	seen for example in a L<Coro::Debug> session:
		934
		935	sub my_long_function {
		936	local $Coro::current->{desc} = "now in my_long_function";
		937	...
		938	$Coro::current->{desc} = "my_long_function: phase 1";
		939	...
		940	$Coro::current->{desc} = "my_long_function: phase 2";
		941	...
		942	}
532		943
533	=cut	944	=cut
534		945
535	sub desc {	946	sub desc {
536	my $old = $_[0]{desc};	947	my $old = $_[0]{desc};
537	$_[0]{desc} = $_[1] if @_ > 1;	948	$_[0]{desc} = $_[1] if @_ > 1;
538	$old;	949	$old;
539	}	950	}
540		951
		952	sub transfer {
		953	require Carp;
		954	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		955	}
		956
541	=back	957	=back
542		958
543	=head2 GLOBAL FUNCTIONS	959	=head1 GLOBAL FUNCTIONS
544		960
545	=over 4	961	=over 4
546		962
547	=item Coro::nready	963	=item Coro::nready
548		964
549	Returns the number of coroutines that are currently in the ready state,	965	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	966	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	967	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>	968	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	969	would cause a deadlock unless there is an idle handler that wakes up some
554	coroutines.	970	coro.
555		971
556	=item my $guard = Coro::guard { ... }	972	=item my $guard = Coro::guard { ... }
557		973
558	This creates and returns a guard object. Nothing happens until the object	974	This function still exists, but is deprecated. Please use the
559	gets destroyed, in which case the codeblock given as argument will be	975	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		976
575	=cut	977	=cut
576		978
577	sub guard(&) {	979	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		980
590	=item unblock_sub { ... }	981	=item unblock_sub { ... }
591		982
592	This utility function takes a BLOCK or code reference and "unblocks" it,	983	This utility function takes a BLOCK or code reference and "unblocks" it,
593	returning a new coderef. Unblocking means that calling the new coderef	984	returning a new coderef. Unblocking means that calling the new coderef
594	will return immediately without blocking, returning nothing, while the	985	will return immediately without blocking, returning nothing, while the
595	original code ref will be called (with parameters) from within another	986	original code ref will be called (with parameters) from within another
596	coroutine.	987	coro.
597		988
598	The reason this function exists is that many event libraries (such as the	989	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	990	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,	991	of reentrancy). This means you must not block within event callbacks,
601	otherwise you might suffer from crashes or worse. The only event library	992	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>.	993	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		994	you might still run into deadlocks if all event loops are blocked).
		995
		996	Coro will try to catch you when you block in the event loop
		997	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		998	only works when you do not run your own event loop.
603		999
604	This function allows your callbacks to block by executing them in another	1000	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	1001	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	1002	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
607	disk, for example.	1003	disk, for example.
608		1004
609	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	1005	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
610	creating event callbacks that want to block.	1006	creating event callbacks that want to block.
611		1007
612	If your handler does not plan to block (e.g. simply sends a message to	1008	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),	1009	another coro, or puts some other coro into the ready queue), there is
614	there is no reason to use C<unblock_sub>.	1010	no reason to use C<unblock_sub>.
		1011
		1012	Note that you also need to use C<unblock_sub> for any other callbacks that
		1013	are indirectly executed by any C-based event loop. For example, when you
		1014	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		1015	provides callbacks that are the result of some event callback, then you
		1016	must not block either, or use C<unblock_sub>.
615		1017
616	=cut	1018	=cut
617		1019
618	our @unblock_queue;	1020	our @unblock_queue;
619		1021
…		…
622	# return immediately and can be reused) and because we cannot cede	1024	# return immediately and can be reused) and because we cannot cede
623	# inside an event callback.	1025	# inside an event callback.
624	our $unblock_scheduler = new Coro sub {	1026	our $unblock_scheduler = new Coro sub {
625	while () {	1027	while () {
626	while (my $cb = pop @unblock_queue) {	1028	while (my $cb = pop @unblock_queue) {
627	# this is an inlined copy of async_pool	1029	&async_pool (@$cb);
628	my $coro = (pop @async_pool) || new Coro \&pool_handler;
629		1030
630	$coro->{_invoke} = $cb;
631	$coro->ready;
632	cede; # for short-lived callbacks, this reduces pressure on the coro pool	1031	# for short-lived callbacks, this reduces pressure on the coro pool
		1032	# as the chance is very high that the async_poll coro will be back
		1033	# in the idle state when cede returns
		1034	cede;
633	}	1035	}
634	schedule; # sleep well	1036	schedule; # sleep well
635	}	1037	}
636	};	1038	};
637	$unblock_scheduler->desc ("[unblock_sub scheduler]");	1039	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
638		1040
639	sub unblock_sub(&) {	1041	sub unblock_sub(&) {
640	my $cb = shift;	1042	my $cb = shift;
641		1043
642	sub {	1044	sub {
643	unshift @unblock_queue, [$cb, @_];	1045	unshift @unblock_queue, [$cb, @_];
644	$unblock_scheduler->ready;	1046	$unblock_scheduler->ready;
645	}	1047	}
646	}	1048	}
647		1049
		1050	=item $cb = rouse_cb
		1051
		1052	Create and return a "rouse callback". That's a code reference that,
		1053	when called, will remember a copy of its arguments and notify the owner
		1054	coro of the callback.
		1055
		1056	See the next function.
		1057
		1058	=item @args = rouse_wait [$cb]
		1059
		1060	Wait for the specified rouse callback (or the last one that was created in
		1061	this coro).
		1062
		1063	As soon as the callback is invoked (or when the callback was invoked
		1064	before C<rouse_wait>), it will return the arguments originally passed to
		1065	the rouse callback. In scalar context, that means you get the I<last>
		1066	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1067	statement at the end.
		1068
		1069	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1070
648	=back	1071	=back
649		1072
650	=cut	1073	=cut
651		1074
		1075	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1076	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1077
		1078	*{"Coro::$module\::new"} = sub {
		1079	require "Coro/$module.pm";
		1080
		1081	# some modules have their new predefined in State.xs, some don't
		1082	*{"Coro::$module\::new"} = $old
		1083	if $old;
		1084
		1085	goto &{"Coro::$module\::new"};
		1086	};
		1087	}
		1088
652	1;	1089	1;
653		1090
		1091	=head1 HOW TO WAIT FOR A CALLBACK
		1092
		1093	It is very common for a coro to wait for some callback to be
		1094	called. This occurs naturally when you use coro in an otherwise
		1095	event-based program, or when you use event-based libraries.
		1096
		1097	These typically register a callback for some event, and call that callback
		1098	when the event occured. In a coro, however, you typically want to
		1099	just wait for the event, simplyifying things.
		1100
		1101	For example C<< AnyEvent->child >> registers a callback to be called when
		1102	a specific child has exited:
		1103
		1104	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1105
		1106	But from within a coro, you often just want to write this:
		1107
		1108	my $status = wait_for_child $pid;
		1109
		1110	Coro offers two functions specifically designed to make this easy,
		1111	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		1112
		1113	The first function, C<rouse_cb>, generates and returns a callback that,
		1114	when invoked, will save its arguments and notify the coro that
		1115	created the callback.
		1116
		1117	The second function, C<rouse_wait>, waits for the callback to be called
		1118	(by calling C<schedule> to go to sleep) and returns the arguments
		1119	originally passed to the callback.
		1120
		1121	Using these functions, it becomes easy to write the C<wait_for_child>
		1122	function mentioned above:
		1123
		1124	sub wait_for_child($) {
		1125	my ($pid) = @_;
		1126
		1127	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		1128
		1129	my ($rpid, $rstatus) = Coro::rouse_wait;
		1130	$rstatus
		1131	}
		1132
		1133	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1134	you can roll your own, using C<schedule>:
		1135
		1136	sub wait_for_child($) {
		1137	my ($pid) = @_;
		1138
		1139	# store the current coro in $current,
		1140	# and provide result variables for the closure passed to ->child
		1141	my $current = $Coro::current;
		1142	my ($done, $rstatus);
		1143
		1144	# pass a closure to ->child
		1145	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1146	$rstatus = $_[1]; # remember rstatus
		1147	$done = 1; # mark $rstatus as valud
		1148	});
		1149
		1150	# wait until the closure has been called
		1151	schedule while !$done;
		1152
		1153	$rstatus
		1154	}
		1155
		1156
654	=head1 BUGS/LIMITATIONS	1157	=head1 BUGS/LIMITATIONS
655		1158
		1159	=over 4
		1160
		1161	=item fork with pthread backend
		1162
		1163	When Coro is compiled using the pthread backend (which isn't recommended
		1164	but required on many BSDs as their libcs are completely broken), then
		1165	coro will not survive a fork. There is no known workaround except to
		1166	fix your libc and use a saner backend.
		1167
		1168	=item perl process emulation ("threads")
		1169
656	This module is not perl-pseudo-thread-safe. You should only ever use this	1170	This module is not perl-pseudo-thread-safe. You should only ever use this
657	module from the same thread (this requirement might be removed in the	1171	module from the first thread (this requirement might be removed in the
658	future to allow per-thread schedulers, but Coro::State does not yet allow	1172	future to allow per-thread schedulers, but Coro::State does not yet allow
659	this). I recommend disabling thread support and using processes, as this	1173	this). I recommend disabling thread support and using processes, as having
660	is much faster and uses less memory.	1174	the windows process emulation enabled under unix roughly halves perl
		1175	performance, even when not used.
		1176
		1177	Attempts to use threads created in another emulated process will crash
		1178	("cleanly", with a null pointer exception).
		1179
		1180	=item coro switching is not signal safe
		1181
		1182	You must not switch to another coro from within a signal handler (only
		1183	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1184	you are sure you are not interrupting a Coro function.
		1185
		1186	That means you I<MUST NOT> call any function that might "block" the
		1187	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		1188	anything that calls those. Everything else, including calling C<ready>,
		1189	works.
		1190
		1191	=back
		1192
		1193
		1194	=head1 WINDOWS PROCESS EMULATION
		1195
		1196	A great many people seem to be confused about ithreads (for example, Chip
		1197	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1198	while in the same mail making rather confused statements about perl
		1199	ithreads (for example, that memory or files would be shared), showing his
		1200	lack of understanding of this area - if it is hard to understand for Chip,
		1201	it is probably not obvious to everybody).
		1202
		1203	What follows is an ultra-condensed version of my talk about threads in
		1204	scripting languages given on the perl workshop 2009:
		1205
		1206	The so-called "ithreads" were originally implemented for two reasons:
		1207	first, to (badly) emulate unix processes on native win32 perls, and
		1208	secondly, to replace the older, real thread model ("5.005-threads").
		1209
		1210	It does that by using threads instead of OS processes. The difference
		1211	between processes and threads is that threads share memory (and other
		1212	state, such as files) between threads within a single process, while
		1213	processes do not share anything (at least not semantically). That
		1214	means that modifications done by one thread are seen by others, while
		1215	modifications by one process are not seen by other processes.
		1216
		1217	The "ithreads" work exactly like that: when creating a new ithreads
		1218	process, all state is copied (memory is copied physically, files and code
		1219	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1220	the same behaviour can be achieved by using operating system processes,
		1221	except that UNIX typically uses hardware built into the system to do this
		1222	efficiently, while the windows process emulation emulates this hardware in
		1223	software (rather efficiently, but of course it is still much slower than
		1224	dedicated hardware).
		1225
		1226	As mentioned before, loading code, modifying code, modifying data
		1227	structures and so on is only visible in the ithreads process doing the
		1228	modification, not in other ithread processes within the same OS process.
		1229
		1230	This is why "ithreads" do not implement threads for perl at all, only
		1231	processes. What makes it so bad is that on non-windows platforms, you can
		1232	actually take advantage of custom hardware for this purpose (as evidenced
		1233	by the forks module, which gives you the (i-) threads API, just much
		1234	faster).
		1235
		1236	Sharing data is in the i-threads model is done by transfering data
		1237	structures between threads using copying semantics, which is very slow -
		1238	shared data simply does not exist. Benchmarks using i-threads which are
		1239	communication-intensive show extremely bad behaviour with i-threads (in
		1240	fact, so bad that Coro, which cannot take direct advantage of multiple
		1241	CPUs, is often orders of magnitude faster because it shares data using
		1242	real threads, refer to my talk for details).
		1243
		1244	As summary, i-threads *use* threads to implement processes, while
		1245	the compatible forks module *uses* processes to emulate, uhm,
		1246	processes. I-threads slow down every perl program when enabled, and
		1247	outside of windows, serve no (or little) practical purpose, but
		1248	disadvantages every single-threaded Perl program.
		1249
		1250	This is the reason that I try to avoid the name "ithreads", as it is
		1251	misleading as it implies that it implements some kind of thread model for
		1252	perl, and prefer the name "windows process emulation", which describes the
		1253	actual use and behaviour of it much better.
661		1254
662	=head1 SEE ALSO	1255	=head1 SEE ALSO
663		1256
664	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1257	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
665		1258
666	Debugging: L<Coro::Debug>.	1259	Debugging: L<Coro::Debug>.
667		1260
668	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	1261	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
669		1262
670	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1263	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1264	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
671		1265
672	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	1266	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
673		1267
674	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	1268	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1269	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1270	L<Coro::Select>.
675		1271
676	XS API: L<Coro::MakeMaker>.	1272	XS API: L<Coro::MakeMaker>.
677		1273
678	Low level Configuration, Coroutine Environment: L<Coro::State>.	1274	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
679		1275
680	=head1 AUTHOR	1276	=head1 AUTHOR
681		1277
682	Marc Lehmann <schmorp@schmorp.de>	1278	Marc Lehmann <schmorp@schmorp.de>
683	http://home.schmorp.de/	1279	http://home.schmorp.de/

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