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Revision 1.350 by root, Sun Dec 16 09:33:44 2018 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
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 process 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	Yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the coro
		201	thread from another thread:
		202
		203	my $coro = async {
		204	exit 1;
		205	};
		206
		207	$coro->cancel; # also accepts values for ->join to retrieve
		208
		209	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		210	actually exiting, and might leave C libraries and XS modules in a weird
		211	state. Unlike other thread implementations, however, Coro is exceptionally
		212	safe with regards to cancellation, as perl will always be in a consistent
		213	state, and for those cases where you want to do truly marvellous things
		214	with your coro while it is being cancelled - that is, make sure all
		215	cleanup code is executed from the thread being cancelled - there is even a
		216	C<< ->safe_cancel >> method.
		217
		218	So, cancelling a thread that runs in an XS event loop might not be the
		219	best idea, but any other combination that deals with perl only (cancelling
		220	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		221	safe.
		222
		223	Last not least, a coro thread object that isn't referenced is C<<
		224	->cancel >>'ed automatically - just like other objects in Perl. This
		225	is not such a common case, however - a running thread is referencedy by
		226	C<$Coro::current>, a thread ready to run is referenced by the ready queue,
		227	a thread waiting on a lock or semaphore is referenced by being in some
		228	wait list and so on. But a thread that isn't in any of those queues gets
		229	cancelled:
		230
		231	async {
		232	schedule; # cede to other coros, don't go into the ready queue
		233	};
		234
		235	cede;
		236	# now the async above is destroyed, as it is not referenced by anything.
		237
		238	A slightly embellished example might make it clearer:
		239
		240	async {
		241	my $guard = Guard::guard { print "destroyed\n" };
		242	schedule while 1;
		243	};
		244
		245	cede;
		246
		247	Superficially one might not expect any output - since the C<async>
		248	implements an endless loop, the C<$guard> will not be cleaned up. However,
		249	since the thread object returned by C<async> is not stored anywhere, the
		250	thread is initially referenced because it is in the ready queue, when it
		251	runs it is referenced by C<$Coro::current>, but when it calls C<schedule>,
		252	it gets C<cancel>ed causing the guard object to be destroyed (see the next
		253	section), and printing it's message.
		254
		255	If this seems a bit drastic, remember that this only happens when nothing
		256	references the thread anymore, which means there is no way to further
		257	execute it, ever. The only options at this point are leaking the thread,
		258	or cleaning it up, which brings us to...
		259
		260	=item 5. Cleanup
		261
		262	Threads will allocate various resources. Most but not all will be returned
		263	when a thread terminates, during clean-up.
		264
		265	Cleanup is quite similar to throwing an uncaught exception: perl will
		266	work it's way up through all subroutine calls and blocks. On it's way, it
		267	will release all C<my> variables, undo all C<local>'s and free any other
		268	resources truly local to the thread.
		269
		270	So, a common way to free resources is to keep them referenced only by my
		271	variables:
		272
		273	async {
		274	my $big_cache = new Cache ...;
		275	};
		276
		277	If there are no other references, then the C<$big_cache> object will be
		278	freed when the thread terminates, regardless of how it does so.
		279
		280	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		281	resources, but that's where the C<guard> methods come in handy:
		282
		283	my $sem = new Coro::Semaphore;
		284
		285	async {
		286	my $lock_guard = $sem->guard;
		287	# if we return, or die or get cancelled, here,
		288	# then the semaphore will be "up"ed.
		289	};
		290
		291	The C<Guard::guard> function comes in handy for any custom cleanup you
		292	might want to do (but you cannot switch to other coroutines from those
		293	code blocks):
		294
		295	async {
		296	my $window = new Gtk2::Window "toplevel";
		297	# The window will not be cleaned up automatically, even when $window
		298	# gets freed, so use a guard to ensure it's destruction
		299	# in case of an error:
		300	my $window_guard = Guard::guard { $window->destroy };
		301
		302	# we are safe here
		303	};
		304
		305	Last not least, C<local> can often be handy, too, e.g. when temporarily
		306	replacing the coro thread description:
		307
		308	sub myfunction {
		309	local $Coro::current->{desc} = "inside myfunction(@_)";
		310
		311	# if we return or die here, the description will be restored
		312	}
		313
		314	=item 6. Viva La Zombie Muerte
		315
		316	Even after a thread has terminated and cleaned up its resources, the Coro
		317	object still is there and stores the return values of the thread.
		318
		319	When there are no other references, it will simply be cleaned up and
		320	freed.
		321
		322	If there areany references, the Coro object will stay around, and you
		323	can call C<< ->join >> as many times as you wish to retrieve the result
		324	values:
		325
		326	async {
		327	print "hi\n";
		328	1
		329	};
		330
		331	# run the async above, and free everything before returning
		332	# from Coro::cede:
		333	Coro::cede;
		334
		335	{
		336	my $coro = async {
		337	print "hi\n";
		338	1
		339	};
		340
		341	# run the async above, and clean up, but do not free the coro
		342	# object:
		343	Coro::cede;
		344
		345	# optionally retrieve the result values
		346	my @results = $coro->join;
		347
		348	# now $coro goes out of scope, and presumably gets freed
		349	};
		350
		351	=back
30		352
31	=cut	353	=cut
32		354
33	package Coro;	355	package Coro;
34		356
35	use strict;	357	use common::sense;
36	no warnings "uninitialized";	358
		359	use Carp ();
		360
		361	use Guard ();
37		362
38	use Coro::State;	363	use Coro::State;
39		364
40	use base Exporter::;	365	use base qw(Coro::State Exporter);
41		366
42	our $idle; # idle coroutine	367	our $idle; # idle handler
43	our $main; # main coroutine	368	our $main; # main coro
44	our $current; # current coroutine	369	our $current; # current coro
45		370
46	our $VERSION = '2.5';	371	our $VERSION = 6.53;
47		372
48	our @EXPORT = qw(async cede schedule terminate current);	373	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
49	our %EXPORT_TAGS = (	374	our %EXPORT_TAGS = (
50	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	375	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
51	);	376	);
52	our @EXPORT_OK = @{$EXPORT_TAGS{prio}};	377	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
53		378
54	{	379	=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		380
88	=over 4	381	=over 4
89		382
90	=item $main	383	=item $Coro::main
91		384
92	This coroutine represents the main program.	385	This variable stores the Coro object that represents the main
		386	program. While you can C<ready> it and do most other things you can do to
		387	coro, it is mainly useful to compare again C<$Coro::current>, to see
		388	whether you are running in the main program or not.
93		389
94	=cut	390	=cut
95		391
96	$main = new Coro;	392	# $main is now being initialised by Coro::State
97		393
98	=item $current (or as function: current)	394	=item $Coro::current
99		395
100	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	396	The Coro object representing the current coro (the last
		397	coro that the Coro scheduler switched to). The initial value is
		398	C<$Coro::main> (of course).
		399
		400	This variable is B<strictly> I<read-only>. You can take copies of the
		401	value stored in it and use it as any other Coro object, but you must
		402	not otherwise modify the variable itself.
101		403
102	=cut	404	=cut
103		405
104	# maybe some other module used Coro::Specific before...
105	if ($current) {
106	$main->{specific} = $current->{specific};
107	}
108
109	$current = $main;
110
111	sub current() { $current }	406	sub current() { $current } # [DEPRECATED]
112		407
113	=item $idle	408	=item $Coro::idle
114		409
115	The coroutine to switch to when no other coroutine is running. The default	410	This variable is mainly useful to integrate Coro into event loops. It is
116	implementation prints "FATAL: deadlock detected" and exits.	411	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		412	pretty low-level functionality.
		413
		414	This variable stores a Coro object that is put into the ready queue when
		415	there are no other ready threads (without invoking any ready hooks).
		416
		417	The default implementation dies with "FATAL: deadlock detected.", followed
		418	by a thread listing, because the program has no other way to continue.
		419
		420	This hook is overwritten by modules such as C<Coro::EV> and
		421	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
		422	coro so the scheduler can run it.
		423
		424	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
117		425
118	=cut	426	=cut
119		427
120	# should be done using priorities :(	428	# ||= because other modules could have provided their own by now
121	$idle = new Coro sub {	429	$idle ||= new Coro sub {
		430	require Coro::Debug;
122	print STDERR "FATAL: deadlock detected\n";	431	die "FATAL: deadlock detected.\n"
123	exit(51);	432	. Coro::Debug::ps_listing ();
124	};	433	};
125		434
126	# this coroutine is necessary because a coroutine	435	# this coro is necessary because a coro
127	# cannot destroy itself.	436	# cannot destroy itself.
128	my @destroy;	437	our @destroy;
129	my $manager;	438	our $manager;
		439
130	$manager = new Coro sub {	440	$manager = new Coro sub {
131	while () {	441	while () {
132	# by overwriting the state object with the manager we destroy it	442	_destroy shift @destroy
133	# while still being able to schedule this coroutine (in case it has
134	# been readied multiple times. this is harmless since the manager
135	# can be called as many times as neccessary and will always
136	# remove itself from the runqueue
137	while (@destroy) {	443	while @destroy;
138	my $coro = pop @destroy;
139	$coro->{status} ||= [];
140	$_->ready for @{delete $coro->{join} || []};
141		444
142	# the next line destroys the _coro_state, but keeps the
143	# process itself intact (we basically make it a zombie
144	# process that always runs the manager thread, so it's possible
145	# to transfer() to this process).
146	$coro->{_coro_state} = $manager->{_coro_state};
147	}
148	&schedule;	445	&schedule;
149	}	446	}
150	};	447	};
151		448	$manager->{desc} = "[coro manager]";
152	# static methods. not really.	449	$manager->prio (PRIO_MAX);
153		450
154	=back	451	=back
155		452
156	=head2 STATIC METHODS	453	=head1 SIMPLE CORO CREATION
157
158	Static methods are actually functions that operate on the current process only.
159		454
160	=over 4	455	=over 4
161		456
162	=item async { ... } [@args...]	457	=item async { ... } [@args...]
163		458
164	Create a new asynchronous process and return it's process object	459	Create a new coro and return its Coro object (usually
165	(usually unused). When the sub returns the new process is automatically	460	unused). The coro will be put into the ready queue, so
		461	it will start running automatically on the next scheduler run.
		462
		463	The first argument is a codeblock/closure that should be executed in the
		464	coro. When it returns argument returns the coro is automatically
166	terminated.	465	terminated.
167		466
168	When the coroutine dies, the program will exit, just as in the main	467	The remaining arguments are passed as arguments to the closure.
169	program.
170		468
		469	See the C<Coro::State::new> constructor for info about the coro
		470	environment in which coro are executed.
		471
		472	Calling C<exit> in a coro will do the same as calling exit outside
		473	the coro. Likewise, when the coro dies, the program will exit,
		474	just as it would in the main program.
		475
		476	If you do not want that, you can provide a default C<die> handler, or
		477	simply avoid dieing (by use of C<eval>).
		478
171	# create a new coroutine that just prints its arguments	479	Example: Create a new coro that just prints its arguments.
		480
172	async {	481	async {
173	print "@_\n";	482	print "@_\n";
174	} 1,2,3,4;	483	} 1,2,3,4;
175		484
		485	=item async_pool { ... } [@args...]
		486
		487	Similar to C<async>, but uses a coro pool, so you should not call
		488	terminate or join on it (although you are allowed to), and you get a
		489	coro that might have executed other code already (which can be good
		490	or bad :).
		491
		492	On the plus side, this function is about twice as fast as creating (and
		493	destroying) a completely new coro, so if you need a lot of generic
		494	coros in quick successsion, use C<async_pool>, not C<async>.
		495
		496	The code block is executed in an C<eval> context and a warning will be
		497	issued in case of an exception instead of terminating the program, as
		498	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		499	will not work in the expected way, unless you call terminate or cancel,
		500	which somehow defeats the purpose of pooling (but is fine in the
		501	exceptional case).
		502
		503	The priority will be reset to C<0> after each run, all C<swap_sv> calls
		504	will be undone, tracing will be disabled, the description will be reset
		505	and the default output filehandle gets restored, so you can change all
		506	these. Otherwise the coro will be re-used "as-is": most notably if you
		507	change other per-coro global stuff such as C<$/> you I<must needs> revert
		508	that change, which is most simply done by using local as in: C<< local $/
		509	>>.
		510
		511	The idle pool size is limited to C<8> idle coros (this can be
		512	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		513	coros as required.
		514
		515	If you are concerned about pooled coros growing a lot because a
		516	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		517	{ terminate }> once per second or so to slowly replenish the pool. In
		518	addition to that, when the stacks used by a handler grows larger than 32kb
		519	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		520
176	=cut	521	=cut
177		522
178	sub async(&@) {	523	our $POOL_SIZE = 8;
179	my $pid = new Coro @_;	524	our $POOL_RSS = 32 * 1024;
180	$manager->ready; # this ensures that the stack is cloned from the manager	525	our @async_pool;
181	$pid->ready;	526
182	$pid;	527	sub pool_handler {
		528	while () {
		529	eval {
		530	&{&_pool_handler} while 1;
		531	};
		532
		533	warn $@ if $@;
		534	}
183	}	535	}
184		536
		537	=back
		538
		539	=head1 STATIC METHODS
		540
		541	Static methods are actually functions that implicitly operate on the
		542	current coro.
		543
		544	=over 4
		545
185	=item schedule	546	=item schedule
186		547
187	Calls the scheduler. Please note that the current process will not be put	548	Calls the scheduler. The scheduler will find the next coro that is
		549	to be run from the ready queue and switches to it. The next coro
		550	to be run is simply the one with the highest priority that is longest
		551	in its ready queue. If there is no coro ready, it will call the
		552	C<$Coro::idle> hook.
		553
		554	Please note that the current coro will I<not> be put into the ready
188	into the ready queue, so calling this function usually means you will	555	queue, so calling this function usually means you will never be called
189	never be called again.	556	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		557	thus waking you up.
		558
		559	This makes C<schedule> I<the> generic method to use to block the current
		560	coro and wait for events: first you remember the current coro in
		561	a variable, then arrange for some callback of yours to call C<< ->ready
		562	>> on that once some event happens, and last you call C<schedule> to put
		563	yourself to sleep. Note that a lot of things can wake your coro up,
		564	so you need to check whether the event indeed happened, e.g. by storing the
		565	status in a variable.
		566
		567	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
		568
		569	=item cede
		570
		571	"Cede" to other coros. This function puts the current coro into
		572	the ready queue and calls C<schedule>, which has the effect of giving
		573	up the current "timeslice" to other coros of the same or higher
		574	priority. Once your coro gets its turn again it will automatically be
		575	resumed.
		576
		577	This function is often called C<yield> in other languages.
		578
		579	=item Coro::cede_notself
		580
		581	Works like cede, but is not exported by default and will cede to I<any>
		582	coro, regardless of priority. This is useful sometimes to ensure
		583	progress is made.
		584
		585	=item terminate [arg...]
		586
		587	Terminates the current coro with the given status values (see
		588	L<cancel>). The values will not be copied, but referenced directly.
		589
		590	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		591
		592	These function install enter and leave winders in the current scope. The
		593	enter block will be executed when on_enter is called and whenever the
		594	current coro is re-entered by the scheduler, while the leave block is
		595	executed whenever the current coro is blocked by the scheduler, and
		596	also when the containing scope is exited (by whatever means, be it exit,
		597	die, last etc.).
		598
		599	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		600	BLOCKs>. That means: do not even think about calling C<die> without an
		601	eval, and do not even think of entering the scheduler in any way.
		602
		603	Since both BLOCKs are tied to the current scope, they will automatically
		604	be removed when the current scope exits.
		605
		606	These functions implement the same concept as C<dynamic-wind> in scheme
		607	does, and are useful when you want to localise some resource to a specific
		608	coro.
		609
		610	They slow down thread switching considerably for coros that use them
		611	(about 40% for a BLOCK with a single assignment, so thread switching is
		612	still reasonably fast if the handlers are fast).
		613
		614	These functions are best understood by an example: The following function
		615	will change the current timezone to "Antarctica/South_Pole", which
		616	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		617	which remember/change the current timezone and restore the previous
		618	value, respectively, the timezone is only changed for the coro that
		619	installed those handlers.
		620
		621	use POSIX qw(tzset);
		622
		623	async {
		624	my $old_tz; # store outside TZ value here
		625
		626	Coro::on_enter {
		627	$old_tz = $ENV{TZ}; # remember the old value
		628
		629	$ENV{TZ} = "Antarctica/South_Pole";
		630	tzset; # enable new value
		631	};
		632
		633	Coro::on_leave {
		634	$ENV{TZ} = $old_tz;
		635	tzset; # restore old value
		636	};
		637
		638	# at this place, the timezone is Antarctica/South_Pole,
		639	# without disturbing the TZ of any other coro.
		640	};
		641
		642	This can be used to localise about any resource (locale, uid, current
		643	working directory etc.) to a block, despite the existence of other
		644	coros.
		645
		646	Another interesting example implements time-sliced multitasking using
		647	interval timers (this could obviously be optimised, but does the job):
		648
		649	# "timeslice" the given block
		650	sub timeslice(&) {
		651	use Time::HiRes ();
		652
		653	Coro::on_enter {
		654	# on entering the thread, we set an VTALRM handler to cede
		655	$SIG{VTALRM} = sub { cede };
		656	# and then start the interval timer
		657	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		658	};
		659	Coro::on_leave {
		660	# on leaving the thread, we stop the interval timer again
		661	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		662	};
		663
		664	&{+shift};
		665	}
		666
		667	# use like this:
		668	timeslice {
		669	# The following is an endless loop that would normally
		670	# monopolise the process. Since it runs in a timesliced
		671	# environment, it will regularly cede to other threads.
		672	while () { }
		673	};
		674
		675
		676	=item killall
		677
		678	Kills/terminates/cancels all coros except the currently running one.
		679
		680	Note that while this will try to free some of the main interpreter
		681	resources if the calling coro isn't the main coro, but one
		682	cannot free all of them, so if a coro that is not the main coro
		683	calls this function, there will be some one-time resource leak.
190		684
191	=cut	685	=cut
192		686
193	=item cede	687	sub killall {
		688	for (Coro::State::list) {
		689	$_->cancel
		690	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		691	}
		692	}
194		693
195	"Cede" to other processes. This function puts the current process into the	694	=back
196	ready queue and calls C<schedule>, which has the effect of giving up the	695
197	current "timeslice" to other coroutines of the same or higher priority.	696	=head1 CORO OBJECT METHODS
		697
		698	These are the methods you can call on coro objects (or to create
		699	them).
		700
		701	=over 4
		702
		703	=item new Coro \&sub [, @args...]
		704
		705	Create a new coro and return it. When the sub returns, the coro
		706	automatically terminates as if C<terminate> with the returned values were
		707	called. To make the coro run you must first put it into the ready
		708	queue by calling the ready method.
		709
		710	See C<async> and C<Coro::State::new> for additional info about the
		711	coro environment.
198		712
199	=cut	713	=cut
200		714
201	=item terminate [arg...]
202
203	Terminates the current process with the given status values (see L<cancel>).
204
205	=cut
206
207	sub terminate {
208	$current->cancel (@_);
209	}
210
211	=back
212
213	# dynamic methods
214
215	=head2 PROCESS METHODS
216
217	These are the methods you can call on process objects.
218
219	=over 4
220
221	=item new Coro \&sub [, @args...]
222
223	Create a new process and return it. When the sub returns the process
224	automatically terminates as if C<terminate> with the returned values were
225	called. To make the process run you must first put it into the ready queue
226	by calling the ready method.
227
228	=cut
229
230	sub _newcoro {	715	sub _coro_run {
231	terminate &{+shift};	716	terminate &{+shift};
232	}	717	}
233		718
234	sub new {	719	=item $success = $coro->ready
235	my $class = shift;
236	bless {
237	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
238	}, $class;
239	}
240		720
241	=item $process->ready	721	Put the given coro into the end of its ready queue (there is one
		722	queue for each priority) and return true. If the coro is already in
		723	the ready queue, do nothing and return false.
242		724
243	Put the given process into the ready queue.	725	This ensures that the scheduler will resume this coro automatically
		726	once all the coro of higher priority and all coro of the same
		727	priority that were put into the ready queue earlier have been resumed.
244		728
245	=cut	729	=item $coro->suspend
246		730
		731	Suspends the specified coro. A suspended coro works just like any other
		732	coro, except that the scheduler will not select a suspended coro for
		733	execution.
		734
		735	Suspending a coro can be useful when you want to keep the coro from
		736	running, but you don't want to destroy it, or when you want to temporarily
		737	freeze a coro (e.g. for debugging) to resume it later.
		738
		739	A scenario for the former would be to suspend all (other) coros after a
		740	fork and keep them alive, so their destructors aren't called, but new
		741	coros can be created.
		742
		743	=item $coro->resume
		744
		745	If the specified coro was suspended, it will be resumed. Note that when
		746	the coro was in the ready queue when it was suspended, it might have been
		747	unreadied by the scheduler, so an activation might have been lost.
		748
		749	To avoid this, it is best to put a suspended coro into the ready queue
		750	unconditionally, as every synchronisation mechanism must protect itself
		751	against spurious wakeups, and the one in the Coro family certainly do
		752	that.
		753
		754	=item $state->is_new
		755
		756	Returns true iff this Coro object is "new", i.e. has never been run
		757	yet. Those states basically consist of only the code reference to call and
		758	the arguments, but consumes very little other resources. New states will
		759	automatically get assigned a perl interpreter when they are transferred to.
		760
		761	=item $state->is_zombie
		762
		763	Returns true iff the Coro object has been cancelled, i.e.
		764	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		765	C<safe_cancel>'ed or simply went out of scope.
		766
		767	The name "zombie" stems from UNIX culture, where a process that has
		768	exited and only stores and exit status and no other resources is called a
		769	"zombie".
		770
		771	=item $is_ready = $coro->is_ready
		772
		773	Returns true iff the Coro object is in the ready queue. Unless the Coro
		774	object gets destroyed, it will eventually be scheduled by the scheduler.
		775
		776	=item $is_running = $coro->is_running
		777
		778	Returns true iff the Coro object is currently running. Only one Coro object
		779	can ever be in the running state (but it currently is possible to have
		780	multiple running Coro::States).
		781
		782	=item $is_suspended = $coro->is_suspended
		783
		784	Returns true iff this Coro object has been suspended. Suspended Coros will
		785	not ever be scheduled.
		786
247	=item $process->cancel (arg...)	787	=item $coro->cancel ($arg...)
248		788
249	Terminates the given process and makes it return the given arguments as	789	Terminate the given Coro thread and make it return the given arguments as
250	status (default: the empty list).	790	status (default: an empty list). Never returns if the Coro is the
		791	current Coro.
251		792
252	=cut	793	This is a rather brutal way to free a coro, with some limitations - if
		794	the thread is inside a C callback that doesn't expect to be canceled,
		795	bad things can happen, or if the cancelled thread insists on running
		796	complicated cleanup handlers that rely on its thread context, things will
		797	not work.
253		798
254	sub cancel {	799	Any cleanup code being run (e.g. from C<guard> blocks, destructors and so
255	my $self = shift;	800	on) will be run without a thread context, and is not allowed to switch
256	$self->{status} = [@_];	801	to other threads. A common mistake is to call C<< ->cancel >> from a
257	push @destroy, $self;	802	destructor called by die'ing inside the thread to be cancelled for
258	$manager->ready;	803	example.
259	&schedule if $current == $self;
260	}
261		804
262	=item $process->join	805	On the plus side, C<< ->cancel >> will always clean up the thread, no
		806	matter what. If your cleanup code is complex or you want to avoid
		807	cancelling a C-thread that doesn't know how to clean up itself, it can be
		808	better to C<< ->throw >> an exception, or use C<< ->safe_cancel >>.
263		809
264	Wait until the coroutine terminates and return any values given to the	810	The arguments to C<< ->cancel >> are not copied, but instead will
265	C<terminate> or C<cancel> functions. C<join> can be called multiple times	811	be referenced directly (e.g. if you pass C<$var> and after the call
266	from multiple processes.	812	change that variable, then you might change the return values passed to
		813	e.g. C<join>, so don't do that).
267		814
268	=cut	815	The resources of the Coro are usually freed (or destructed) before this
		816	call returns, but this can be delayed for an indefinite amount of time, as
		817	in some cases the manager thread has to run first to actually destruct the
		818	Coro object.
269		819
270	sub join {	820	=item $coro->safe_cancel ($arg...)
271	my $self = shift;	821
272	unless ($self->{status}) {	822	Works mostly like C<< ->cancel >>, but is inherently "safer", and
273	push @{$self->{join}}, $current;	823	consequently, can fail with an exception in cases the thread is not in a
274	&schedule;	824	cancellable state. Essentially, C<< ->safe_cancel >> is a C<< ->cancel >>
		825	with extra checks before canceling.
		826
		827	It works a bit like throwing an exception that cannot be caught -
		828	specifically, it will clean up the thread from within itself, so all
		829	cleanup handlers (e.g. C<guard> blocks) are run with full thread
		830	context and can block if they wish. The downside is that there is no
		831	guarantee that the thread can be cancelled when you call this method, and
		832	therefore, it might fail. It is also considerably slower than C<cancel> or
		833	C<terminate>.
		834
		835	A thread is in a safe-cancellable state if it either has never been run
		836	yet, has already been canceled/terminated or otherwise destroyed, or has
		837	no C context attached and is inside an SLF function.
		838
		839	The first two states are trivial - a thread that hasnot started or has
		840	already finished is safe to cancel.
		841
		842	The last state basically means that the thread isn't currently inside a
		843	perl callback called from some C function (usually via some XS modules)
		844	and isn't currently executing inside some C function itself (via Coro's XS
		845	API).
		846
		847	This call returns true when it could cancel the thread, or croaks with an
		848	error otherwise (i.e. it either returns true or doesn't return at all).
		849
		850	Why the weird interface? Well, there are two common models on how and
		851	when to cancel things. In the first, you have the expectation that your
		852	coro thread can be cancelled when you want to cancel it - if the thread
		853	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		854	croaks to notify of the bug.
		855
		856	In the second model you sometimes want to ask nicely to cancel a thread,
		857	but if it's not a good time, well, then don't cancel. This can be done
		858	relatively easy like this:
		859
		860	if (! eval { $coro->safe_cancel }) {
		861	warn "unable to cancel thread: $@";
275	}	862	}
276	wantarray ? @{$self->{status}} : $self->{status}[0];
277	}
278		863
		864	However, what you never should do is first try to cancel "safely" and
		865	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		866	no sense: either you rely on being able to execute cleanup code in your
		867	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		868	only way, and if you don't, then C<< ->cancel >> is always faster and more
		869	direct.
		870
		871	=item $coro->schedule_to
		872
		873	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		874	of continuing with the next coro from the ready queue, always switch to
		875	the given coro object (regardless of priority etc.). The readyness
		876	state of that coro isn't changed.
		877
		878	This is an advanced method for special cases - I'd love to hear about any
		879	uses for this one.
		880
		881	=item $coro->cede_to
		882
		883	Like C<schedule_to>, but puts the current coro into the ready
		884	queue. This has the effect of temporarily switching to the given
		885	coro, and continuing some time later.
		886
		887	This is an advanced method for special cases - I'd love to hear about any
		888	uses for this one.
		889
		890	=item $coro->throw ([$scalar])
		891
		892	If C<$throw> is specified and defined, it will be thrown as an exception
		893	inside the coro at the next convenient point in time. Otherwise
		894	clears the exception object.
		895
		896	Coro will check for the exception each time a schedule-like-function
		897	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		898	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
		899	that are part of Coro itself) detect this case and return early in case an
		900	exception is pending.
		901
		902	The exception object will be thrown "as is" with the specified scalar in
		903	C<$@>, i.e. if it is a string, no line number or newline will be appended
		904	(unlike with C<die>).
		905
		906	This can be used as a softer means than either C<cancel> or C<safe_cancel
		907	>to ask a coro to end itself, although there is no guarantee that the
		908	exception will lead to termination, and if the exception isn't caught it
		909	might well end the whole program.
		910
		911	You might also think of C<throw> as being the moral equivalent of
		912	C<kill>ing a coro with a signal (in this case, a scalar).
		913
		914	=item $coro->join
		915
		916	Wait until the coro terminates and return any values given to the
		917	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		918	from multiple threads, and all will be resumed and given the status
		919	return once the C<$coro> terminates.
		920
		921	=item $coro->on_destroy (\&cb)
		922
		923	Registers a callback that is called when this coro thread gets destroyed,
		924	that is, after it's resources have been freed but before it is joined. The
		925	callback gets passed the terminate/cancel arguments, if any, and I<must
		926	not> die, under any circumstances.
		927
		928	There can be any number of C<on_destroy> callbacks per coro, and there is
		929	currently no way to remove a callback once added.
		930
279	=item $oldprio = $process->prio($newprio)	931	=item $oldprio = $coro->prio ($newprio)
280		932
281	Sets (or gets, if the argument is missing) the priority of the	933	Sets (or gets, if the argument is missing) the priority of the
282	process. Higher priority processes get run before lower priority	934	coro thread. Higher priority coro get run before lower priority
283	processes. Priorities are small signed integers (currently -4 .. +3),	935	coros. Priorities are small signed integers (currently -4 .. +3),
284	that you can refer to using PRIO_xxx constants (use the import tag :prio	936	that you can refer to using PRIO_xxx constants (use the import tag :prio
285	to get then):	937	to get then):
286		938
287	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	939	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
288	3 > 1 > 0 > -1 > -3 > -4	940	3 > 1 > 0 > -1 > -3 > -4
289		941
290	# set priority to HIGH	942	# set priority to HIGH
291	current->prio(PRIO_HIGH);	943	current->prio (PRIO_HIGH);
292		944
293	The idle coroutine ($Coro::idle) always has a lower priority than any	945	The idle coro thread ($Coro::idle) always has a lower priority than any
294	existing coroutine.	946	existing coro.
295		947
296	Changing the priority of the current process will take effect immediately,	948	Changing the priority of the current coro will take effect immediately,
297	but changing the priority of processes in the ready queue (but not	949	but changing the priority of a coro in the ready queue (but not running)
298	running) will only take effect after the next schedule (of that	950	will only take effect after the next schedule (of that coro). This is a
299	process). This is a bug that will be fixed in some future version.	951	bug that will be fixed in some future version.
300		952
301	=cut
302
303	sub prio {
304	my $old = $_[0]{prio};
305	$_[0]{prio} = $_[1] if @_ > 1;
306	$old;
307	}
308
309	=item $newprio = $process->nice($change)	953	=item $newprio = $coro->nice ($change)
310		954
311	Similar to C<prio>, but subtract the given value from the priority (i.e.	955	Similar to C<prio>, but subtract the given value from the priority (i.e.
312	higher values mean lower priority, just as in unix).	956	higher values mean lower priority, just as in UNIX's nice command).
313		957
314	=cut
315
316	sub nice {
317	$_[0]{prio} -= $_[1];
318	}
319
320	=item $olddesc = $process->desc($newdesc)	958	=item $olddesc = $coro->desc ($newdesc)
321		959
322	Sets (or gets in case the argument is missing) the description for this	960	Sets (or gets in case the argument is missing) the description for this
323	process. This is just a free-form string you can associate with a process.	961	coro thread. This is just a free-form string you can associate with a
		962	coro.
		963
		964	This method simply sets the C<< $coro->{desc} >> member to the given
		965	string. You can modify this member directly if you wish, and in fact, this
		966	is often preferred to indicate major processing states that can then be
		967	seen for example in a L<Coro::Debug> session:
		968
		969	sub my_long_function {
		970	local $Coro::current->{desc} = "now in my_long_function";
		971	...
		972	$Coro::current->{desc} = "my_long_function: phase 1";
		973	...
		974	$Coro::current->{desc} = "my_long_function: phase 2";
		975	...
		976	}
324		977
325	=cut	978	=cut
326		979
327	sub desc {	980	sub desc {
328	my $old = $_[0]{desc};	981	my $old = $_[0]{desc};
329	$_[0]{desc} = $_[1] if @_ > 1;	982	$_[0]{desc} = $_[1] if @_ > 1;
330	$old;	983	$old;
331	}	984	}
332		985
		986	sub transfer {
		987	require Carp;
		988	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		989	}
		990
333	=back	991	=back
334		992
		993	=head1 GLOBAL FUNCTIONS
		994
		995	=over 4
		996
		997	=item Coro::nready
		998
		999	Returns the number of coro that are currently in the ready state,
		1000	i.e. that can be switched to by calling C<schedule> directory or
		1001	indirectly. The value C<0> means that the only runnable coro is the
		1002	currently running one, so C<cede> would have no effect, and C<schedule>
		1003	would cause a deadlock unless there is an idle handler that wakes up some
		1004	coro.
		1005
		1006	=item my $guard = Coro::guard { ... }
		1007
		1008	This function still exists, but is deprecated. Please use the
		1009	C<Guard::guard> function instead.
		1010
335	=cut	1011	=cut
336		1012
		1013	BEGIN { *guard = \&Guard::guard }
		1014
		1015	=item unblock_sub { ... }
		1016
		1017	This utility function takes a BLOCK or code reference and "unblocks" it,
		1018	returning a new coderef. Unblocking means that calling the new coderef
		1019	will return immediately without blocking, returning nothing, while the
		1020	original code ref will be called (with parameters) from within another
		1021	coro.
		1022
		1023	The reason this function exists is that many event libraries (such as
		1024	the venerable L<Event|Event> module) are not thread-safe (a weaker form
		1025	of reentrancy). This means you must not block within event callbacks,
		1026	otherwise you might suffer from crashes or worse. The only event library
		1027	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		1028	you might still run into deadlocks if all event loops are blocked).
		1029
		1030	Coro will try to catch you when you block in the event loop
		1031	("FATAL: $Coro::idle blocked itself"), but this is just best effort and
		1032	only works when you do not run your own event loop.
		1033
		1034	This function allows your callbacks to block by executing them in another
		1035	coro where it is safe to block. One example where blocking is handy
		1036	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
		1037	disk, for example.
		1038
		1039	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		1040	creating event callbacks that want to block.
		1041
		1042	If your handler does not plan to block (e.g. simply sends a message to
		1043	another coro, or puts some other coro into the ready queue), there is
		1044	no reason to use C<unblock_sub>.
		1045
		1046	Note that you also need to use C<unblock_sub> for any other callbacks that
		1047	are indirectly executed by any C-based event loop. For example, when you
		1048	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		1049	provides callbacks that are the result of some event callback, then you
		1050	must not block either, or use C<unblock_sub>.
		1051
		1052	=cut
		1053
		1054	our @unblock_queue;
		1055
		1056	# we create a special coro because we want to cede,
		1057	# to reduce pressure on the coro pool (because most callbacks
		1058	# return immediately and can be reused) and because we cannot cede
		1059	# inside an event callback.
		1060	our $unblock_scheduler = new Coro sub {
		1061	while () {
		1062	while (my $cb = pop @unblock_queue) {
		1063	&async_pool (@$cb);
		1064
		1065	# for short-lived callbacks, this reduces pressure on the coro pool
		1066	# as the chance is very high that the async_poll coro will be back
		1067	# in the idle state when cede returns
		1068	cede;
		1069	}
		1070	schedule; # sleep well
		1071	}
		1072	};
		1073	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		1074
		1075	sub unblock_sub(&) {
		1076	my $cb = shift;
		1077
		1078	sub {
		1079	unshift @unblock_queue, [$cb, @_];
		1080	$unblock_scheduler->ready;
		1081	}
		1082	}
		1083
		1084	=item $cb = rouse_cb
		1085
		1086	Create and return a "rouse callback". That's a code reference that,
		1087	when called, will remember a copy of its arguments and notify the owner
		1088	coro of the callback.
		1089
		1090	See the next function.
		1091
		1092	=item @args = rouse_wait [$cb]
		1093
		1094	Wait for the specified rouse callback (or the last one that was created in
		1095	this coro).
		1096
		1097	As soon as the callback is invoked (or when the callback was invoked
		1098	before C<rouse_wait>), it will return the arguments originally passed to
		1099	the rouse callback. In scalar context, that means you get the I<last>
		1100	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1101	statement at the end.
		1102
		1103	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1104
		1105	=back
		1106
		1107	=cut
		1108
		1109	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1110	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1111
		1112	*{"Coro::$module\::new"} = sub {
		1113	require "Coro/$module.pm";
		1114
		1115	# some modules have their new predefined in State.xs, some don't
		1116	*{"Coro::$module\::new"} = $old
		1117	if $old;
		1118
		1119	goto &{"Coro::$module\::new"};
		1120	};
		1121	}
		1122
337	1;	1123	1;
338		1124
		1125	=head1 HOW TO WAIT FOR A CALLBACK
		1126
		1127	It is very common for a coro to wait for some callback to be
		1128	called. This occurs naturally when you use coro in an otherwise
		1129	event-based program, or when you use event-based libraries.
		1130
		1131	These typically register a callback for some event, and call that callback
		1132	when the event occurred. In a coro, however, you typically want to
		1133	just wait for the event, simplyifying things.
		1134
		1135	For example C<< AnyEvent->child >> registers a callback to be called when
		1136	a specific child has exited:
		1137
		1138	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1139
		1140	But from within a coro, you often just want to write this:
		1141
		1142	my $status = wait_for_child $pid;
		1143
		1144	Coro offers two functions specifically designed to make this easy,
		1145	C<rouse_cb> and C<rouse_wait>.
		1146
		1147	The first function, C<rouse_cb>, generates and returns a callback that,
		1148	when invoked, will save its arguments and notify the coro that
		1149	created the callback.
		1150
		1151	The second function, C<rouse_wait>, waits for the callback to be called
		1152	(by calling C<schedule> to go to sleep) and returns the arguments
		1153	originally passed to the callback.
		1154
		1155	Using these functions, it becomes easy to write the C<wait_for_child>
		1156	function mentioned above:
		1157
		1158	sub wait_for_child($) {
		1159	my ($pid) = @_;
		1160
		1161	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
		1162
		1163	my ($rpid, $rstatus) = rouse_wait;
		1164	$rstatus
		1165	}
		1166
		1167	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1168	you can roll your own, using C<schedule> and C<ready>:
		1169
		1170	sub wait_for_child($) {
		1171	my ($pid) = @_;
		1172
		1173	# store the current coro in $current,
		1174	# and provide result variables for the closure passed to ->child
		1175	my $current = $Coro::current;
		1176	my ($done, $rstatus);
		1177
		1178	# pass a closure to ->child
		1179	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1180	$rstatus = $_[1]; # remember rstatus
		1181	$done = 1; # mark $rstatus as valid
		1182	$current->ready; # wake up the waiting thread
		1183	});
		1184
		1185	# wait until the closure has been called
		1186	schedule while !$done;
		1187
		1188	$rstatus
		1189	}
		1190
		1191
339	=head1 BUGS/LIMITATIONS	1192	=head1 BUGS/LIMITATIONS
340		1193
341	- you must make very sure that no coro is still active on global	1194	=over 4
342	destruction. very bad things might happen otherwise (usually segfaults).
343		1195
		1196	=item fork with pthread backend
		1197
		1198	When Coro is compiled using the pthread backend (which isn't recommended
		1199	but required on many BSDs as their libcs are completely broken), then
		1200	coro will not survive a fork. There is no known workaround except to
		1201	fix your libc and use a saner backend.
		1202
		1203	=item perl process emulation ("threads")
		1204
344	- this module is not thread-safe. You should only ever use this module	1205	This module is not perl-pseudo-thread-safe. You should only ever use this
345	from the same thread (this requirement might be losened in the future	1206	module from the first thread (this requirement might be removed in the
346	to allow per-thread schedulers, but Coro::State does not yet allow	1207	future to allow per-thread schedulers, but Coro::State does not yet allow
347	this).	1208	this). I recommend disabling thread support and using processes, as having
		1209	the windows process emulation enabled under unix roughly halves perl
		1210	performance, even when not used.
		1211
		1212	Attempts to use threads created in another emulated process will crash
		1213	("cleanly", with a null pointer exception).
		1214
		1215	=item coro switching is not signal safe
		1216
		1217	You must not switch to another coro from within a signal handler (only
		1218	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1219	you are sure you are not interrupting a Coro function.
		1220
		1221	That means you I<MUST NOT> call any function that might "block" the
		1222	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		1223	anything that calls those. Everything else, including calling C<ready>,
		1224	works.
		1225
		1226	=back
		1227
		1228
		1229	=head1 WINDOWS PROCESS EMULATION
		1230
		1231	A great many people seem to be confused about ithreads (for example, Chip
		1232	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1233	while in the same mail making rather confused statements about perl
		1234	ithreads (for example, that memory or files would be shared), showing his
		1235	lack of understanding of this area - if it is hard to understand for Chip,
		1236	it is probably not obvious to everybody).
		1237
		1238	What follows is an ultra-condensed version of my talk about threads in
		1239	scripting languages given on the perl workshop 2009:
		1240
		1241	The so-called "ithreads" were originally implemented for two reasons:
		1242	first, to (badly) emulate unix processes on native win32 perls, and
		1243	secondly, to replace the older, real thread model ("5.005-threads").
		1244
		1245	It does that by using threads instead of OS processes. The difference
		1246	between processes and threads is that threads share memory (and other
		1247	state, such as files) between threads within a single process, while
		1248	processes do not share anything (at least not semantically). That
		1249	means that modifications done by one thread are seen by others, while
		1250	modifications by one process are not seen by other processes.
		1251
		1252	The "ithreads" work exactly like that: when creating a new ithreads
		1253	process, all state is copied (memory is copied physically, files and code
		1254	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1255	the same behaviour can be achieved by using operating system processes,
		1256	except that UNIX typically uses hardware built into the system to do this
		1257	efficiently, while the windows process emulation emulates this hardware in
		1258	software (rather efficiently, but of course it is still much slower than
		1259	dedicated hardware).
		1260
		1261	As mentioned before, loading code, modifying code, modifying data
		1262	structures and so on is only visible in the ithreads process doing the
		1263	modification, not in other ithread processes within the same OS process.
		1264
		1265	This is why "ithreads" do not implement threads for perl at all, only
		1266	processes. What makes it so bad is that on non-windows platforms, you can
		1267	actually take advantage of custom hardware for this purpose (as evidenced
		1268	by the forks module, which gives you the (i-) threads API, just much
		1269	faster).
		1270
		1271	Sharing data is in the i-threads model is done by transferring data
		1272	structures between threads using copying semantics, which is very slow -
		1273	shared data simply does not exist. Benchmarks using i-threads which are
		1274	communication-intensive show extremely bad behaviour with i-threads (in
		1275	fact, so bad that Coro, which cannot take direct advantage of multiple
		1276	CPUs, is often orders of magnitude faster because it shares data using
		1277	real threads, refer to my talk for details).
		1278
		1279	As summary, i-threads *use* threads to implement processes, while
		1280	the compatible forks module *uses* processes to emulate, uhm,
		1281	processes. I-threads slow down every perl program when enabled, and
		1282	outside of windows, serve no (or little) practical purpose, but
		1283	disadvantages every single-threaded Perl program.
		1284
		1285	This is the reason that I try to avoid the name "ithreads", as it is
		1286	misleading as it implies that it implements some kind of thread model for
		1287	perl, and prefer the name "windows process emulation", which describes the
		1288	actual use and behaviour of it much better.
348		1289
349	=head1 SEE ALSO	1290	=head1 SEE ALSO
350		1291
		1292	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		1293
		1294	Debugging: L<Coro::Debug>.
		1295
351	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.	1296	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
352		1297
353	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1298	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1299	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
354		1300
355	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.	1301	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
356		1302
357	Embedding: L<Coro:MakeMaker>	1303	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1304	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1305	L<Coro::Select>.
358		1306
359	=head1 AUTHOR	1307	XS API: L<Coro::MakeMaker>.
360		1308
		1309	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
		1310
		1311	=head1 AUTHOR/SUPPORT/CONTACT
		1312
361	Marc Lehmann <schmorp@schmorp.de>	1313	Marc A. Lehmann <schmorp@schmorp.de>
362	http://home.schmorp.de/	1314	http://software.schmorp.de/pkg/Coro.html
363		1315
364	=cut	1316	=cut
365		1317

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