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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
9	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
		11	print "2\n";
		12	cede; # yield back to main
		13	print "4\n";
11	};	14	};
12		15	print "1\n";
13	# alternatively create an async coroutine like this:	16	cede; # yield to coro
14		17	print "3\n";
15	sub some_func : Coro {	18	cede; # and again
16	# some more async code	19
17	}	20	# use locking
18		21	my $lock = new Coro::Semaphore;
19	cede;	22	my $locked;
		23
		24	$lock->down;
		25	$locked = 1;
		26	$lock->up;
20		27
21	=head1 DESCRIPTION	28	=head1 DESCRIPTION
22		29
23	This module collection manages coroutines. Coroutines are similar to	30	For a tutorial-style introduction, please read the L<Coro::Intro>
24	threads but don't run in parallel.	31	manpage. This manpage mainly contains reference information.
25		32
		33	This module collection manages continuations in general, most often in
		34	the form of cooperative threads (also called coros, or simply "coro"
		35	in the documentation). They are similar to kernel threads but don't (in
		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
		43	Unlike the so-called "Perl threads" (which are not actually real threads
		44	but only the windows process emulation (see section of same name for
		45	more details) ported to UNIX, and as such act as processes), Coro
		46	provides a full shared address space, which makes communication between
		47	threads very easy. And coro threads are fast, too: disabling the Windows
		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.
		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
26	In this module, coroutines are defined as "callchain + lexical variables	60	In this module, a thread is defined as "callchain + lexical variables +
27	+ @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own	61	some package variables + C stack), that is, a thread has its own callchain,
28	callchain, it's own set of lexicals and it's own set of perl's most	62	its own set of lexicals and its own set of perls most important global
29	important global variables.	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
30		328
31	=cut	329	=cut
32		330
33	package Coro;	331	package Coro;
34		332
35	use strict;	333	use common::sense;
36	no warnings "uninitialized";	334
		335	use Carp ();
		336
		337	use Guard ();
37		338
38	use Coro::State;	339	use Coro::State;
39		340
40	use base qw(Coro::State Exporter);	341	use base qw(Coro::State Exporter);
41		342
42	our $idle; # idle handler	343	our $idle; # idle handler
43	our $main; # main coroutine	344	our $main; # main coro
44	our $current; # current coroutine	345	our $current; # current coro
45		346
46	our $VERSION = '3.01';	347	our $VERSION = 6.09;
47		348
48	our @EXPORT = qw(async cede schedule terminate current unblock_sub);	349	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
49	our %EXPORT_TAGS = (	350	our %EXPORT_TAGS = (
50	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	351	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
51	);	352	);
52	our @EXPORT_OK = @{$EXPORT_TAGS{prio}};	353	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
53		354
54	{	355	=head1 GLOBAL VARIABLES
55	my @async;
56	my $init;
57
58	# this way of handling attributes simply is NOT scalable ;()
59	sub import {
60	no strict 'refs';
61
62	Coro->export_to_level (1, @_);
63
64	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
65	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
66	my ($package, $ref) = (shift, shift);
67	my @attrs;
68	for (@_) {
69	if ($_ eq "Coro") {
70	push @async, $ref;
71	unless ($init++) {
72	eval q{
73	sub INIT {
74	&async(pop @async) while @async;
75	}
76	};
77	}
78	} else {
79	push @attrs, $_;
80	}
81	}
82	return $old ? $old->($package, $ref, @attrs) : @attrs;
83	};
84	}
85
86	}
87		356
88	=over 4	357	=over 4
89		358
90	=item $main	359	=item $Coro::main
91		360
92	This coroutine represents the main program.	361	This variable stores the Coro object that represents the main
		362	program. While you cna C<ready> it and do most other things you can do to
		363	coro, it is mainly useful to compare again C<$Coro::current>, to see
		364	whether you are running in the main program or not.
93		365
94	=cut	366	=cut
95		367
96	$main = new Coro;	368	# $main is now being initialised by Coro::State
97		369
98	=item $current (or as function: current)	370	=item $Coro::current
99		371
100	The current coroutine (the last coroutine switched to). The initial value	372	The Coro object representing the current coro (the last
		373	coro that the Coro scheduler switched to). The initial value is
101	is C<$main> (of course).	374	C<$Coro::main> (of course).
102		375
103	This variable is B<strictly> I<read-only>. It is provided for performance	376	This variable is B<strictly> I<read-only>. You can take copies of the
104	reasons. If performance is not essentiel you are encouraged to use the	377	value stored in it and use it as any other Coro object, but you must
105	C<Coro::current> function instead.	378	not otherwise modify the variable itself.
106		379
107	=cut	380	=cut
108		381
109	# maybe some other module used Coro::Specific before...
110	$main->{specific} = $current->{specific}
111	if $current;
112
113	_set_current $main;
114
115	sub current() { $current }	382	sub current() { $current } # [DEPRECATED]
116		383
117	=item $idle	384	=item $Coro::idle
118		385
119	A callback that is called whenever the scheduler finds no ready coroutines	386	This variable is mainly useful to integrate Coro into event loops. It is
		387	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		388	pretty low-level functionality.
		389
		390	This variable stores a Coro object that is put into the ready queue when
		391	there are no other ready threads (without invoking any ready hooks).
		392
120	to run. The default implementation prints "FATAL: deadlock detected" and	393	The default implementation dies with "FATAL: deadlock detected.", followed
121	exits, because the program has no other way to continue.	394	by a thread listing, because the program has no other way to continue.
122		395
123	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
124	C<Coro::Event> 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
125	coroutine so the scheduler can run it.	398	coro so the scheduler can run it.
126		399
127	Please note that if your callback recursively invokes perl (e.g. for event	400	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
128	handlers), then it must be prepared to be called recursively.
129		401
130	=cut	402	=cut
131		403
132	$idle = sub {	404	# ||= because other modules could have provided their own by now
		405	$idle ||= new Coro sub {
		406	require Coro::Debug;
133	print STDERR "FATAL: deadlock detected\n";	407	die "FATAL: deadlock detected.\n"
134	exit (51);	408	. Coro::Debug::ps_listing ();
135	};	409	};
136		410
137	# this coroutine is necessary because a coroutine	411	# this coro is necessary because a coro
138	# cannot destroy itself.	412	# cannot destroy itself.
139	my @destroy;	413	our @destroy;
		414	our $manager;
		415
140	my $manager; $manager = new Coro sub {	416	$manager = new Coro sub {
141	while () {	417	while () {
142	# by overwriting the state object with the manager we destroy it	418	_destroy shift @destroy
143	# while still being able to schedule this coroutine (in case it has
144	# been readied multiple times. this is harmless since the manager
145	# can be called as many times as neccessary and will always
146	# remove itself from the runqueue
147	while (@destroy) {	419	while @destroy;
148	my $coro = pop @destroy;
149	$coro->{status} ||= [];
150	$_->ready for @{delete $coro->{join} || []};
151		420
152	# the next line destroys the coro state, but keeps the
153	# coroutine itself intact (we basically make it a zombie
154	# coroutine that always runs the manager thread, so it's possible
155	# to transfer() to this coroutine).
156	$coro->_clone_state_from ($manager);
157	}
158	&schedule;	421	&schedule;
159	}	422	}
160	};	423	};
161		424	$manager->{desc} = "[coro manager]";
162	# static methods. not really.	425	$manager->prio (PRIO_MAX);
163		426
164	=back	427	=back
165		428
166	=head2 STATIC METHODS	429	=head1 SIMPLE CORO CREATION
167
168	Static methods are actually functions that operate on the current coroutine only.
169		430
170	=over 4	431	=over 4
171		432
172	=item async { ... } [@args...]	433	=item async { ... } [@args...]
173		434
174	Create a new asynchronous coroutine and return it's coroutine object	435	Create a new coro and return its Coro object (usually
175	(usually unused). When the sub returns the new coroutine is automatically	436	unused). The coro will be put into the ready queue, so
		437	it will start running automatically on the next scheduler run.
		438
		439	The first argument is a codeblock/closure that should be executed in the
		440	coro. When it returns argument returns the coro is automatically
176	terminated.	441	terminated.
177		442
178	Calling C<exit> in a coroutine will not work correctly, so do not do that.	443	The remaining arguments are passed as arguments to the closure.
179		444
180	When the coroutine dies, the program will exit, just as in the main	445	See the C<Coro::State::new> constructor for info about the coro
181	program.	446	environment in which coro are executed.
182		447
		448	Calling C<exit> in a coro will do the same as calling exit outside
		449	the coro. Likewise, when the coro dies, the program will exit,
		450	just as it would in the main program.
		451
		452	If you do not want that, you can provide a default C<die> handler, or
		453	simply avoid dieing (by use of C<eval>).
		454
183	# create a new coroutine that just prints its arguments	455	Example: Create a new coro that just prints its arguments.
		456
184	async {	457	async {
185	print "@_\n";	458	print "@_\n";
186	} 1,2,3,4;	459	} 1,2,3,4;
187		460
		461	=item async_pool { ... } [@args...]
		462
		463	Similar to C<async>, but uses a coro pool, so you should not call
		464	terminate or join on it (although you are allowed to), and you get a
		465	coro that might have executed other code already (which can be good
		466	or bad :).
		467
		468	On the plus side, this function is about twice as fast as creating (and
		469	destroying) a completely new coro, so if you need a lot of generic
		470	coros in quick successsion, use C<async_pool>, not C<async>.
		471
		472	The code block is executed in an C<eval> context and a warning will be
		473	issued in case of an exception instead of terminating the program, as
		474	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		475	will not work in the expected way, unless you call terminate or cancel,
		476	which somehow defeats the purpose of pooling (but is fine in the
		477	exceptional case).
		478
		479	The priority will be reset to C<0> after each run, tracing will be
		480	disabled, the description will be reset and the default output filehandle
		481	gets restored, so you can change all these. Otherwise the coro will
		482	be re-used "as-is": most notably if you change other per-coro global
		483	stuff such as C<$/> you I<must needs> revert that change, which is most
		484	simply done by using local as in: C<< local $/ >>.
		485
		486	The idle pool size is limited to C<8> idle coros (this can be
		487	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		488	coros as required.
		489
		490	If you are concerned about pooled coros growing a lot because a
		491	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		492	{ terminate }> once per second or so to slowly replenish the pool. In
		493	addition to that, when the stacks used by a handler grows larger than 32kb
		494	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		495
188	=cut	496	=cut
189		497
190	sub async(&@) {	498	our $POOL_SIZE = 8;
191	my $pid = new Coro @_;	499	our $POOL_RSS = 32 * 1024;
192	$pid->ready;	500	our @async_pool;
193	$pid	501
		502	sub pool_handler {
		503	while () {
		504	eval {
		505	&{&_pool_handler} while 1;
		506	};
		507
		508	warn $@ if $@;
		509	}
194	}	510	}
195		511
		512	=back
		513
		514	=head1 STATIC METHODS
		515
		516	Static methods are actually functions that implicitly operate on the
		517	current coro.
		518
		519	=over 4
		520
196	=item schedule	521	=item schedule
197		522
198	Calls the scheduler. Please note that the current coroutine will not be put	523	Calls the scheduler. The scheduler will find the next coro that is
		524	to be run from the ready queue and switches to it. The next coro
		525	to be run is simply the one with the highest priority that is longest
		526	in its ready queue. If there is no coro ready, it will call the
		527	C<$Coro::idle> hook.
		528
		529	Please note that the current coro will I<not> be put into the ready
199	into the ready queue, so calling this function usually means you will	530	queue, so calling this function usually means you will never be called
200	never be called again unless something else (e.g. an event handler) calls	531	again unless something else (e.g. an event handler) calls C<< ->ready >>,
201	ready.	532	thus waking you up.
202		533
203	The canonical way to wait on external events is this:	534	This makes C<schedule> I<the> generic method to use to block the current
		535	coro and wait for events: first you remember the current coro in
		536	a variable, then arrange for some callback of yours to call C<< ->ready
		537	>> on that once some event happens, and last you call C<schedule> to put
		538	yourself to sleep. Note that a lot of things can wake your coro up,
		539	so you need to check whether the event indeed happened, e.g. by storing the
		540	status in a variable.
204		541
205	{	542	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
206	# remember current coroutine
207	my $current = $Coro::current;
208		543
209	# register a hypothetical event handler	544	=item cede
210	on_event_invoke sub {	545
211	# wake up sleeping coroutine	546	"Cede" to other coros. This function puts the current coro into
212	$current->ready;	547	the ready queue and calls C<schedule>, which has the effect of giving
213	undef $current;	548	up the current "timeslice" to other coros of the same or higher
		549	priority. Once your coro gets its turn again it will automatically be
		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
214	};	606	};
215		607
216	# call schedule until event occured.	608	Coro::on_leave {
217	# in case we are woken up for other reasons	609	$ENV{TZ} = $old_tz;
218	# (current still defined), loop.	610	tzset; # restore old value
219	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.
		615	};
		616
		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.
		620
		621	Another interesting example implements time-sliced multitasking using
		622	interval timers (this could obviously be optimised, but does the job):
		623
		624	# "timeslice" the given block
		625	sub timeslice(&) {
		626	use Time::HiRes ();
		627
		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	};
		638
		639	&{+shift};
		640	}
		641
		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	};
		649
		650
		651	=item killall
		652
		653	Kills/terminates/cancels all coros except the currently running one.
		654
		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
		657	cannot free all of them, so if a coro that is not the main coro
		658	calls this function, there will be some one-time resource leak.
		659
		660	=cut
		661
		662	sub killall {
		663	for (Coro::State::list) {
		664	$_->cancel
		665	if $_ != $current && UNIVERSAL::isa $_, "Coro";
220	}	666	}
		667	}
221		668
222	=item cede	669	=back
223		670
224	"Cede" to other coroutines. This function puts the current coroutine into the	671	=head1 CORO OBJECT METHODS
225	ready queue and calls C<schedule>, which has the effect of giving up the
226	current "timeslice" to other coroutines of the same or higher priority.
227		672
228	=item terminate [arg...]	673	These are the methods you can call on coro objects (or to create
		674	them).
229		675
230	Terminates the current coroutine with the given status values (see L<cancel>).	676	=over 4
		677
		678	=item new Coro \&sub [, @args...]
		679
		680	Create a new coro and return it. When the sub returns, the coro
		681	automatically terminates as if C<terminate> with the returned values were
		682	called. To make the coro run you must first put it into the ready
		683	queue by calling the ready method.
		684
		685	See C<async> and C<Coro::State::new> for additional info about the
		686	coro environment.
231		687
232	=cut	688	=cut
233		689
234	sub terminate {	690	sub _coro_run {
235	$current->cancel (@_);
236	}
237
238	=back
239
240	# dynamic methods
241
242	=head2 COROUTINE METHODS
243
244	These are the methods you can call on coroutine objects.
245
246	=over 4
247
248	=item new Coro \&sub [, @args...]
249
250	Create a new coroutine and return it. When the sub returns the coroutine
251	automatically terminates as if C<terminate> with the returned values were
252	called. To make the coroutine run you must first put it into the ready queue
253	by calling the ready method.
254
255	Calling C<exit> in a coroutine will not work correctly, so do not do that.
256
257	=cut
258
259	sub _run_coro {
260	terminate &{+shift};	691	terminate &{+shift};
261	}	692	}
262		693
263	sub new {
264	my $class = shift;
265
266	$class->SUPER::new (\&_run_coro, @_)
267	}
268
269	=item $success = $coroutine->ready	694	=item $success = $coro->ready
270		695
271	Put the given coroutine into the ready queue (according to it's priority)	696	Put the given coro into the end of its ready queue (there is one
272	and return true. If the coroutine is already in the ready queue, do nothing	697	queue for each priority) and return true. If the coro is already in
273	and return false.	698	the ready queue, do nothing and return false.
274		699
		700	This ensures that the scheduler will resume this coro automatically
		701	once all the coro of higher priority and all coro of the same
		702	priority that were put into the ready queue earlier have been resumed.
		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
275	=item $is_ready = $coroutine->is_ready	746	=item $is_ready = $coro->is_ready
276		747
277	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.
278		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
279	=item $coroutine->cancel (arg...)	762	=item $coro->cancel (arg...)
280		763
281	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
282	status (default: the empty list).	765	status (default: an empty list). Never returns if the Coro is the
		766	current Coro.
283		767
284	=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 its thread context, things will
		772	not work.
285		773
286	sub cancel {	774	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
287	my $self = shift;	775	a thread context, and is not allowed to switch to other threads. On the
288	$self->{status} = [@_];	776	plus side, C<< ->cancel >> will always clean up the thread, no matter
289	push @destroy, $self;	777	what. If your cleanup code is complex or you want to avoid cancelling a
290	$manager->ready;	778	C-thread that doesn't know how to clean up itself, it can be better to C<<
291	&schedule if $current == $self;	779	->throw >> an exception, or use C<< ->safe_cancel >>.
292	}
293		780
294	=item $coroutine->join	781	The arguments to C<< ->cancel >> are not copied, but instead will
		782	be referenced directly (e.g. if you pass C<$var> and after the call
		783	change that variable, then you might change the return values passed to
		784	e.g. C<join>, so don't do that).
295		785
296	Wait until the coroutine terminates and return any values given to the	786	The resources of the Coro are usually freed (or destructed) before this
297	C<terminate> or C<cancel> functions. C<join> can be called multiple times	787	call returns, but this can be delayed for an indefinite amount of time, as
298	from multiple coroutine.	788	in some cases the manager thread has to run first to actually destruct the
		789	Coro object.
299		790
300	=cut	791	=item $coro->safe_cancel ($arg...)
301		792
302	sub join {	793	Works mostly like C<< ->cancel >>, but is inherently "safer", and
303	my $self = shift;	794	consequently, can fail with an exception in cases the thread is not in a
304	unless ($self->{status}) {	795	cancellable state.
305	push @{$self->{join}}, $current;	796
306	&schedule;	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: $@";
307	}	828	}
308	wantarray ? @{$self->{status}} : $self->{status}[0];
309	}
310		829
		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.
		836
		837	=item $coro->schedule_to
		838
		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.
		843
		844	This is an advanced method for special cases - I'd love to hear about any
		845	uses for this one.
		846
		847	=item $coro->cede_to
		848
		849	Like C<schedule_to>, but puts the current coro into the ready
		850	queue. This has the effect of temporarily switching to the given
		851	coro, and continuing some time later.
		852
		853	This is an advanced method for special cases - I'd love to hear about any
		854	uses for this one.
		855
		856	=item $coro->throw ([$scalar])
		857
		858	If C<$throw> is specified and defined, it will be thrown as an exception
		859	inside the coro at the next convenient point in time. Otherwise
		860	clears the exception object.
		861
		862	Coro will check for the exception each time a schedule-like-function
		863	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		864	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
		865	that are part of Coro itself) detect this case and return early in case an
		866	exception is pending.
		867
		868	The exception object will be thrown "as is" with the specified scalar in
		869	C<$@>, i.e. if it is a string, no line number or newline will be appended
		870	(unlike with C<die>).
		871
		872	This can be used as a softer means than either C<cancel> or C<safe_cancel
		873	>to ask a coro to end itself, although there is no guarantee that the
		874	exception will lead to termination, and if the exception isn't caught it
		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
311	=item $oldprio = $coroutine->prio ($newprio)	897	=item $oldprio = $coro->prio ($newprio)
312		898
313	Sets (or gets, if the argument is missing) the priority of the	899	Sets (or gets, if the argument is missing) the priority of the
314	coroutine. Higher priority coroutines get run before lower priority	900	coro thread. Higher priority coro get run before lower priority
315	coroutines. Priorities are small signed integers (currently -4 .. +3),	901	coros. Priorities are small signed integers (currently -4 .. +3),
316	that you can refer to using PRIO_xxx constants (use the import tag :prio	902	that you can refer to using PRIO_xxx constants (use the import tag :prio
317	to get then):	903	to get then):
318		904
319	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	905	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
320	3 > 1 > 0 > -1 > -3 > -4	906	3 > 1 > 0 > -1 > -3 > -4
321		907
322	# set priority to HIGH	908	# set priority to HIGH
323	current->prio(PRIO_HIGH);	909	current->prio (PRIO_HIGH);
324		910
325	The idle coroutine ($Coro::idle) always has a lower priority than any	911	The idle coro thread ($Coro::idle) always has a lower priority than any
326	existing coroutine.	912	existing coro.
327		913
328	Changing the priority of the current coroutine will take effect immediately,	914	Changing the priority of the current coro will take effect immediately,
329	but changing the priority of coroutines in the ready queue (but not	915	but changing the priority of a coro in the ready queue (but not running)
330	running) will only take effect after the next schedule (of that	916	will only take effect after the next schedule (of that coro). This is a
331	coroutine). This is a bug that will be fixed in some future version.	917	bug that will be fixed in some future version.
332		918
333	=item $newprio = $coroutine->nice ($change)	919	=item $newprio = $coro->nice ($change)
334		920
335	Similar to C<prio>, but subtract the given value from the priority (i.e.	921	Similar to C<prio>, but subtract the given value from the priority (i.e.
336	higher values mean lower priority, just as in unix).	922	higher values mean lower priority, just as in UNIX's nice command).
337		923
338	=item $olddesc = $coroutine->desc ($newdesc)	924	=item $olddesc = $coro->desc ($newdesc)
339		925
340	Sets (or gets in case the argument is missing) the description for this	926	Sets (or gets in case the argument is missing) the description for this
341	coroutine. This is just a free-form string you can associate with a coroutine.	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	}
342		943
343	=cut	944	=cut
344		945
345	sub desc {	946	sub desc {
346	my $old = $_[0]{desc};	947	my $old = $_[0]{desc};
347	$_[0]{desc} = $_[1] if @_ > 1;	948	$_[0]{desc} = $_[1] if @_ > 1;
348	$old;	949	$old;
349	}	950	}
350		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
351	=back	957	=back
352		958
353	=head2 UTILITY FUNCTIONS	959	=head1 GLOBAL FUNCTIONS
354		960
355	=over 4	961	=over 4
356		962
		963	=item Coro::nready
		964
		965	Returns the number of coro that are currently in the ready state,
		966	i.e. that can be switched to by calling C<schedule> directory or
		967	indirectly. The value C<0> means that the only runnable coro is the
		968	currently running one, so C<cede> would have no effect, and C<schedule>
		969	would cause a deadlock unless there is an idle handler that wakes up some
		970	coro.
		971
		972	=item my $guard = Coro::guard { ... }
		973
		974	This function still exists, but is deprecated. Please use the
		975	C<Guard::guard> function instead.
		976
		977	=cut
		978
		979	BEGIN { *guard = \&Guard::guard }
		980
357	=item unblock_sub { ... }	981	=item unblock_sub { ... }
358		982
359	This utility function takes a BLOCK or code reference and "unblocks" it,	983	This utility function takes a BLOCK or code reference and "unblocks" it,
360	returning the new coderef. This means that the new coderef will return	984	returning a new coderef. Unblocking means that calling the new coderef
361	immediately without blocking, returning nothing, while the original code	985	will return immediately without blocking, returning nothing, while the
362	ref will be called (with parameters) from within its own coroutine.	986	original code ref will be called (with parameters) from within another
		987	coro.
363		988
364	The reason this fucntion exists is that many event libraries (such as the	989	The reason this function exists is that many event libraries (such as
365	venerable L<Event|Event> module) are not coroutine-safe (a weaker form	990	the venerable L<Event|Event> module) are not thread-safe (a weaker form
366	of thread-safety). This means you must not block within event callbacks,	991	of reentrancy). This means you must not block within event callbacks,
367	otherwise you might suffer from crashes or worse.	992	otherwise you might suffer from crashes or worse. The only event library
		993	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		994	you might still run into deadlocks if all event loops are blocked).
		995
		996	Coro will try to catch you when you block in the event loop
		997	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		998	only works when you do not run your own event loop.
368		999
369	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
370	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
371	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
372	disk.	1003	disk, for example.
373		1004
374	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
375	creating event callbacks that want to block.	1006	creating event callbacks that want to block.
376		1007
		1008	If your handler does not plan to block (e.g. simply sends a message to
		1009	another coro, or puts some other coro into the ready queue), there is
		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>.
		1017
377	=cut	1018	=cut
378		1019
379	our @unblock_pool;
380	our @unblock_queue;	1020	our @unblock_queue;
381	our $UNBLOCK_POOL_SIZE = 2;
382		1021
383	sub unblock_handler_ {	1022	# we create a special coro because we want to cede,
384	while () {	1023	# to reduce pressure on the coro pool (because most callbacks
385	my ($cb, @arg) = @{ delete $Coro::current->{arg} };	1024	# return immediately and can be reused) and because we cannot cede
386	$cb->(@arg);	1025	# inside an event callback.
387
388	last if @unblock_pool >= $UNBLOCK_POOL_SIZE;
389	push @unblock_pool, $Coro::current;
390	schedule;
391	}
392	}
393
394	our $unblock_scheduler = async {	1026	our $unblock_scheduler = new Coro sub {
395	while () {	1027	while () {
396	while (my $cb = pop @unblock_queue) {	1028	while (my $cb = pop @unblock_queue) {
397	my $handler = (pop @unblock_pool or new Coro \&unblock_handler_);	1029	&async_pool (@$cb);
398	$handler->{arg} = $cb;	1030
399	$handler->ready;	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
400	cede;	1034	cede;
401	}	1035	}
402		1036	schedule; # sleep well
403	schedule;
404	}	1037	}
405	};	1038	};
		1039	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
406		1040
407	sub unblock_sub(&) {	1041	sub unblock_sub(&) {
408	my $cb = shift;	1042	my $cb = shift;
409		1043
410	sub {	1044	sub {
411	push @unblock_queue, [$cb, @_];	1045	unshift @unblock_queue, [$cb, @_];
412	$unblock_scheduler->ready;	1046	$unblock_scheduler->ready;
413	}	1047	}
414	}	1048	}
415		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
416	=back	1071	=back
417		1072
418	=cut	1073	=cut
419		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
420	1;	1089	1;
421		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
422	=head1 BUGS/LIMITATIONS	1157	=head1 BUGS/LIMITATIONS
423		1158
424	- you must make very sure that no coro is still active on global	1159	=over 4
425	destruction. very bad things might happen otherwise (usually segfaults).
426		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
427	- this module is not thread-safe. You should only ever use this module	1170	This module is not perl-pseudo-thread-safe. You should only ever use this
428	from the same thread (this requirement might be losened in the future	1171	module from the first thread (this requirement might be removed in the
429	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
430	this).	1173	this). I recommend disabling thread support and using processes, as having
		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.
431		1254
432	=head1 SEE ALSO	1255	=head1 SEE ALSO
433		1256
		1257	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		1258
		1259	Debugging: L<Coro::Debug>.
		1260
434	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.	1261	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
435		1262
436	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>.
437		1265
438	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.	1266	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
439		1267
440	Embedding: L<Coro:MakeMaker>	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>.
		1271
		1272	XS API: L<Coro::MakeMaker>.
		1273
		1274	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
441		1275
442	=head1 AUTHOR	1276	=head1 AUTHOR
443		1277
444	Marc Lehmann <schmorp@schmorp.de>	1278	Marc Lehmann <schmorp@schmorp.de>
445	http://home.schmorp.de/	1279	http://home.schmorp.de/

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