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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 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 its 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 its 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 >>, the
		194	thread-equivalent of C<exit>, which works at any subroutine call nesting
		195	level:
		196
		197	async {
		198	Coro::terminate "return value 1", "return value 2";
		199	};
		200
		201	Yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the coro
		202	thread from another thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # also accepts values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state, and for those cases where you want to do truly marvellous things
		215	with your coro while it is being cancelled - that is, make sure all
		216	cleanup code is executed from the thread being cancelled - there is even a
		217	C<< ->safe_cancel >> method.
		218
		219	So, cancelling a thread that runs in an XS event loop might not be the
		220	best idea, but any other combination that deals with perl only (cancelling
		221	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		222	safe.
		223
		224	Last not least, a coro thread object that isn't referenced is C<<
		225	->cancel >>'ed automatically - just like other objects in Perl. This
		226	is not such a common case, however - a running thread is referencedy by
		227	C<$Coro::current>, a thread ready to run is referenced by the ready queue,
		228	a thread waiting on a lock or semaphore is referenced by being in some
		229	wait list and so on. But a thread that isn't in any of those queues gets
		230	cancelled:
		231
		232	async {
		233	schedule; # cede to other coros, don't go into the ready queue
		234	};
		235
		236	cede;
		237	# now the async above is destroyed, as it is not referenced by anything.
		238
		239	A slightly embellished example might make it clearer:
		240
		241	async {
		242	my $guard = Guard::guard { print "destroyed\n" };
		243	schedule while 1;
		244	};
		245
		246	cede;
		247
		248	Superficially one might not expect any output - since the C<async>
		249	implements an endless loop, the C<$guard> will not be cleaned up. However,
		250	since the thread object returned by C<async> is not stored anywhere, the
		251	thread is initially referenced because it is in the ready queue, when it
		252	runs it is referenced by C<$Coro::current>, but when it calls C<schedule>,
		253	it gets C<cancel>ed causing the guard object to be destroyed (see the next
		254	section), and printing its message.
		255
		256	If this seems a bit drastic, remember that this only happens when nothing
		257	references the thread anymore, which means there is no way to further
		258	execute it, ever. The only options at this point are leaking the thread,
		259	or cleaning it up, which brings us to...
		260
		261	=item 5. Cleanup
		262
		263	Threads will allocate various resources. Most but not all will be returned
		264	when a thread terminates, during clean-up.
		265
		266	Cleanup is quite similar to throwing an uncaught exception: perl will
		267	work its way up through all subroutine calls and blocks. On its way, it
		268	will release all C<my> variables, undo all C<local>'s and free any other
		269	resources truly local to the thread.
		270
		271	So, a common way to free resources is to keep them referenced only by my
		272	variables:
		273
		274	async {
		275	my $big_cache = new Cache ...;
		276	};
		277
		278	If there are no other references, then the C<$big_cache> object will be
		279	freed when the thread terminates, regardless of how it does so.
		280
		281	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		282	resources, but that's where the C<guard> methods come in handy:
		283
		284	my $sem = new Coro::Semaphore;
		285
		286	async {
		287	my $lock_guard = $sem->guard;
		288	# if we return, or die or get cancelled, here,
		289	# then the semaphore will be "up"ed.
		290	};
		291
		292	The C<Guard::guard> function comes in handy for any custom cleanup you
		293	might want to do (but you cannot switch to other coroutines from those
		294	code blocks):
		295
		296	async {
		297	my $window = new Gtk2::Window "toplevel";
		298	# The window will not be cleaned up automatically, even when $window
		299	# gets freed, so use a guard to ensure its destruction
		300	# in case of an error:
		301	my $window_guard = Guard::guard { $window->destroy };
		302
		303	# we are safe here
		304	};
		305
		306	Last not least, C<local> can often be handy, too, e.g. when temporarily
		307	replacing the coro thread description:
		308
		309	sub myfunction {
		310	local $Coro::current->{desc} = "inside myfunction(@_)";
		311
		312	# if we return or die here, the description will be restored
		313	}
		314
		315	=item 6. Viva La Zombie Muerte
		316
		317	Even after a thread has terminated and cleaned up its resources, the Coro
		318	object still is there and stores the return values of the thread.
		319
		320	When there are no other references, it will simply be cleaned up and
		321	freed.
		322
		323	If there areany references, the Coro object will stay around, and you
		324	can call C<< ->join >> as many times as you wish to retrieve the result
		325	values:
		326
		327	async {
		328	print "hi\n";
		329	1
		330	};
		331
		332	# run the async above, and free everything before returning
		333	# from Coro::cede:
		334	Coro::cede;
		335
		336	{
		337	my $coro = async {
		338	print "hi\n";
		339	1
		340	};
		341
		342	# run the async above, and clean up, but do not free the coro
		343	# object:
		344	Coro::cede;
		345
		346	# optionally retrieve the result values
		347	my @results = $coro->join;
		348
		349	# now $coro goes out of scope, and presumably gets freed
		350	};
		351
		352	=back
30		353
31	=cut	354	=cut
32		355
33	package Coro;	356	package Coro;
34		357
35	BEGIN { eval { require warnings } && warnings->unimport ("uninitialized") }	358	use common::sense;
		359
		360	use Carp ();
		361
		362	use Guard ();
36		363
37	use Coro::State;	364	use Coro::State;
38		365
39	use vars qw($idle $main $current);	366	use base qw(Coro::State Exporter);
40		367
41	use base Exporter;	368	our $idle; # idle handler
		369	our $main; # main coro
		370	our $current; # current coro
42		371
43	$VERSION = 0.95;	372	our $VERSION = 6.57;
44		373
45	@EXPORT = qw(async cede schedule terminate current);	374	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
46	%EXPORT_TAGS = (	375	our %EXPORT_TAGS = (
47	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	376	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
48	);	377	);
49	@EXPORT_OK = @{$EXPORT_TAGS{prio}};	378	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
50		379
51	{	380	=head1 GLOBAL VARIABLES
52	my @async;
53	my $init;
54
55	# this way of handling attributes simply is NOT scalable ;()
56	sub import {
57	Coro->export_to_level(1, @_);
58	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
59	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
60	my ($package, $ref) = (shift, shift);
61	my @attrs;
62	for (@_) {
63	if ($_ eq "Coro") {
64	push @async, $ref;
65	unless ($init++) {
66	eval q{
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	};
71	}
72	} else {
73	push @attrs, $_;
74	}
75	}
76	return $old ? $old->($package, $ref, @attrs) : @attrs;
77	};
78	}
79
80	}
81		381
82	=over 4	382	=over 4
83		383
84	=item $main	384	=item $Coro::main
85		385
86	This coroutine represents the main program.	386	This variable stores the Coro object that represents the main
		387	program. While you can C<ready> it and do most other things you can do to
		388	coro, it is mainly useful to compare again C<$Coro::current>, to see
		389	whether you are running in the main program or not.
87		390
88	=cut	391	=cut
89		392
90	$main = new Coro;	393	# $main is now being initialised by Coro::State
91		394
92	=item $current (or as function: current)	395	=item $Coro::current
93		396
94	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	397	The Coro object representing the current coro (the last
		398	coro that the Coro scheduler switched to). The initial value is
		399	C<$Coro::main> (of course).
		400
		401	This variable is B<strictly> I<read-only>. You can take copies of the
		402	value stored in it and use it as any other Coro object, but you must
		403	not otherwise modify the variable itself.
95		404
96	=cut	405	=cut
97		406
98	# maybe some other module used Coro::Specific before...
99	if ($current) {
100	$main->{specific} = $current->{specific};
101	}
102
103	$current = $main;
104
105	sub current() { $current }	407	sub current() { $current } # [DEPRECATED]
106		408
107	=item $idle	409	=item $Coro::idle
108		410
109	The coroutine to switch to when no other coroutine is running. The default	411	This variable is mainly useful to integrate Coro into event loops. It is
110	implementation prints "FATAL: deadlock detected" and exits.	412	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		413	pretty low-level functionality.
		414
		415	This variable stores a Coro object that is put into the ready queue when
		416	there are no other ready threads (without invoking any ready hooks).
		417
		418	The default implementation dies with "FATAL: deadlock detected.", followed
		419	by a thread listing, because the program has no other way to continue.
		420
		421	This hook is overwritten by modules such as C<Coro::EV> and
		422	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
		423	coro so the scheduler can run it.
		424
		425	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
111		426
112	=cut	427	=cut
113		428
114	# should be done using priorities :(	429	# ||= because other modules could have provided their own by now
115	$idle = new Coro sub {	430	$idle ||= new Coro sub {
		431	require Coro::Debug;
116	print STDERR "FATAL: deadlock detected\n";	432	die "FATAL: deadlock detected.\n"
117	exit(51);	433	. Coro::Debug::ps_listing ();
118	};	434	};
119		435
120	# this coroutine is necessary because a coroutine	436	# this coro is necessary because a coro
121	# cannot destroy itself.	437	# cannot destroy itself.
122	my @destroy;	438	our @destroy;
123	my $manager;	439	our $manager;
		440
124	$manager = new Coro sub {	441	$manager = new Coro sub {
125	while () {	442	while () {
126	# by overwriting the state object with the manager we destroy it	443	_destroy shift @destroy
127	# while still being able to schedule this coroutine (in case it has
128	# been readied multiple times. this is harmless since the manager
129	# can be called as many times as neccessary and will always
130	# remove itself from the runqueue
131	while (@destroy) {	444	while @destroy;
132	my $coro = pop @destroy;	445
133	$coro->{status} ||= [];
134	$_->ready for @{delete $coro->{join} || []};
135	$coro->{_coro_state} = $manager->{_coro_state};
136	}
137	&schedule;	446	&schedule;
138	}	447	}
139	};	448	};
140		449	$manager->{desc} = "[coro manager]";
141	# static methods. not really.	450	$manager->prio (PRIO_MAX);
142		451
143	=back	452	=back
144		453
145	=head2 STATIC METHODS	454	=head1 SIMPLE CORO CREATION
146
147	Static methods are actually functions that operate on the current process only.
148		455
149	=over 4	456	=over 4
150		457
151	=item async { ... } [@args...]	458	=item async { ... } [@args...]
152		459
153	Create a new asynchronous process and return it's process object	460	Create a new coro and return its Coro object (usually
154	(usually unused). When the sub returns the new process is automatically	461	unused). The coro will be put into the ready queue, so
		462	it will start running automatically on the next scheduler run.
		463
		464	The first argument is a codeblock/closure that should be executed in the
		465	coro. When it returns argument returns the coro is automatically
155	terminated.	466	terminated.
156		467
		468	The remaining arguments are passed as arguments to the closure.
		469
		470	See the C<Coro::State::new> constructor for info about the coro
		471	environment in which coro are executed.
		472
		473	Calling C<exit> in a coro will do the same as calling exit outside
		474	the coro. Likewise, when the coro dies, the program will exit,
		475	just as it would in the main program.
		476
		477	If you do not want that, you can provide a default C<die> handler, or
		478	simply avoid dieing (by use of C<eval>).
		479
157	# create a new coroutine that just prints its arguments	480	Example: Create a new coro that just prints its arguments.
		481
158	async {	482	async {
159	print "@_\n";	483	print "@_\n";
160	} 1,2,3,4;	484	} 1,2,3,4;
161		485
		486	=item async_pool { ... } [@args...]
		487
		488	Similar to C<async>, but uses a coro pool, so you should not call
		489	terminate or join on it (although you are allowed to), and you get a
		490	coro that might have executed other code already (which can be good
		491	or bad :).
		492
		493	On the plus side, this function is about twice as fast as creating (and
		494	destroying) a completely new coro, so if you need a lot of generic
		495	coros in quick successsion, use C<async_pool>, not C<async>.
		496
		497	The code block is executed in an C<eval> context and a warning will be
		498	issued in case of an exception instead of terminating the program, as
		499	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		500	will not work in the expected way, unless you call terminate or cancel,
		501	which somehow defeats the purpose of pooling (but is fine in the
		502	exceptional case).
		503
		504	The priority will be reset to C<0> after each run, all C<swap_sv> calls
		505	will be undone, tracing will be disabled, the description will be reset
		506	and the default output filehandle gets restored, so you can change all
		507	these. Otherwise the coro will be re-used "as-is": most notably if you
		508	change other per-coro global stuff such as C<$/> you I<must needs> revert
		509	that change, which is most simply done by using local as in: C<< local $/
		510	>>.
		511
		512	The idle pool size is limited to C<8> idle coros (this can be
		513	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		514	coros as required.
		515
		516	If you are concerned about pooled coros growing a lot because a
		517	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		518	{ terminate }> once per second or so to slowly replenish the pool. In
		519	addition to that, when the stacks used by a handler grows larger than 32kb
		520	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		521
162	=cut	522	=cut
163		523
164	sub async(&@) {	524	our $POOL_SIZE = 8;
165	my $pid = new Coro @_;	525	our $POOL_RSS = 32 * 1024;
166	$manager->ready; # this ensures that the stack is cloned from the manager	526	our @async_pool;
167	$pid->ready;	527
168	$pid;	528	sub pool_handler {
		529	while () {
		530	eval {
		531	&{&_pool_handler} while 1;
		532	};
		533
		534	warn $@ if $@;
		535	}
169	}	536	}
170		537
		538	=back
		539
		540	=head1 STATIC METHODS
		541
		542	Static methods are actually functions that implicitly operate on the
		543	current coro.
		544
		545	=over 4
		546
171	=item schedule	547	=item schedule
172		548
173	Calls the scheduler. Please note that the current process will not be put	549	Calls the scheduler. The scheduler will find the next coro that is
		550	to be run from the ready queue and switches to it. The next coro
		551	to be run is simply the one with the highest priority that is longest
		552	in its ready queue. If there is no coro ready, it will call the
		553	C<$Coro::idle> hook.
		554
		555	Please note that the current coro will I<not> be put into the ready
174	into the ready queue, so calling this function usually means you will	556	queue, so calling this function usually means you will never be called
175	never be called again.	557	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		558	thus waking you up.
		559
		560	This makes C<schedule> I<the> generic method to use to block the current
		561	coro and wait for events: first you remember the current coro in
		562	a variable, then arrange for some callback of yours to call C<< ->ready
		563	>> on that once some event happens, and last you call C<schedule> to put
		564	yourself to sleep. Note that a lot of things can wake your coro up,
		565	so you need to check whether the event indeed happened, e.g. by storing the
		566	status in a variable.
		567
		568	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
		569
		570	=item cede
		571
		572	"Cede" to other coros. This function puts the current coro into
		573	the ready queue and calls C<schedule>, which has the effect of giving
		574	up the current "timeslice" to other coros of the same or higher
		575	priority. Once your coro gets its turn again it will automatically be
		576	resumed.
		577
		578	This function is often called C<yield> in other languages.
		579
		580	=item Coro::cede_notself
		581
		582	Works like cede, but is not exported by default and will cede to I<any>
		583	coro, regardless of priority. This is useful sometimes to ensure
		584	progress is made.
		585
		586	=item terminate [arg...]
		587
		588	Terminates the current coro with the given status values (see
		589	L<cancel>). The values will not be copied, but referenced directly.
		590
		591	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		592
		593	These function install enter and leave winders in the current scope. The
		594	enter block will be executed when on_enter is called and whenever the
		595	current coro is re-entered by the scheduler, while the leave block is
		596	executed whenever the current coro is blocked by the scheduler, and
		597	also when the containing scope is exited (by whatever means, be it exit,
		598	die, last etc.).
		599
		600	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		601	BLOCKs>. That means: do not even think about calling C<die> without an
		602	eval, and do not even think of entering the scheduler in any way.
		603
		604	Since both BLOCKs are tied to the current scope, they will automatically
		605	be removed when the current scope exits.
		606
		607	These functions implement the same concept as C<dynamic-wind> in scheme
		608	does, and are useful when you want to localise some resource to a specific
		609	coro.
		610
		611	They slow down thread switching considerably for coros that use them
		612	(about 40% for a BLOCK with a single assignment, so thread switching is
		613	still reasonably fast if the handlers are fast).
		614
		615	These functions are best understood by an example: The following function
		616	will change the current timezone to "Antarctica/South_Pole", which
		617	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		618	which remember/change the current timezone and restore the previous
		619	value, respectively, the timezone is only changed for the coro that
		620	installed those handlers.
		621
		622	use POSIX qw(tzset);
		623
		624	async {
		625	my $old_tz; # store outside TZ value here
		626
		627	Coro::on_enter {
		628	$old_tz = $ENV{TZ}; # remember the old value
		629
		630	$ENV{TZ} = "Antarctica/South_Pole";
		631	tzset; # enable new value
		632	};
		633
		634	Coro::on_leave {
		635	$ENV{TZ} = $old_tz;
		636	tzset; # restore old value
		637	};
		638
		639	# at this place, the timezone is Antarctica/South_Pole,
		640	# without disturbing the TZ of any other coro.
		641	};
		642
		643	This can be used to localise about any resource (locale, uid, current
		644	working directory etc.) to a block, despite the existence of other
		645	coros.
		646
		647	Another interesting example implements time-sliced multitasking using
		648	interval timers (this could obviously be optimised, but does the job):
		649
		650	# "timeslice" the given block
		651	sub timeslice(&) {
		652	use Time::HiRes ();
		653
		654	Coro::on_enter {
		655	# on entering the thread, we set an VTALRM handler to cede
		656	$SIG{VTALRM} = sub { cede };
		657	# and then start the interval timer
		658	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		659	};
		660	Coro::on_leave {
		661	# on leaving the thread, we stop the interval timer again
		662	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		663	};
		664
		665	&{+shift};
		666	}
		667
		668	# use like this:
		669	timeslice {
		670	# The following is an endless loop that would normally
		671	# monopolise the process. Since it runs in a timesliced
		672	# environment, it will regularly cede to other threads.
		673	while () { }
		674	};
		675
		676
		677	=item killall
		678
		679	Kills/terminates/cancels all coros except the currently running one.
		680
		681	Note that while this will try to free some of the main interpreter
		682	resources if the calling coro isn't the main coro, but one
		683	cannot free all of them, so if a coro that is not the main coro
		684	calls this function, there will be some one-time resource leak.
176		685
177	=cut	686	=cut
178		687
179	=item cede	688	sub killall {
		689	for (Coro::State::list) {
		690	$_->cancel
		691	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		692	}
		693	}
180		694
181	"Cede" to other processes. This function puts the current process into the	695	=back
182	ready queue and calls C<schedule>, which has the effect of giving up the	696
183	current "timeslice" to other coroutines of the same or higher priority.	697	=head1 CORO OBJECT METHODS
		698
		699	These are the methods you can call on coro objects (or to create
		700	them).
		701
		702	=over 4
		703
		704	=item new Coro \&sub [, @args...]
		705
		706	Create a new coro and return it. When the sub returns, the coro
		707	automatically terminates as if C<terminate> with the returned values were
		708	called. To make the coro run you must first put it into the ready
		709	queue by calling the ready method.
		710
		711	See C<async> and C<Coro::State::new> for additional info about the
		712	coro environment.
184		713
185	=cut	714	=cut
186		715
187	=item terminate [arg...]
188
189	Terminates the current process.
190
191	Future versions of this function will allow result arguments.
192
193	=cut
194
195	sub terminate {
196	$current->{status} = [@_];
197	$current->cancel;
198	&schedule;
199	die; # NORETURN
200	}
201
202	=back
203
204	# dynamic methods
205
206	=head2 PROCESS METHODS
207
208	These are the methods you can call on process objects.
209
210	=over 4
211
212	=item new Coro \&sub [, @args...]
213
214	Create a new process and return it. When the sub returns the process
215	automatically terminates as if C<terminate> with the returned values were
216	called. To make the process run you must first put it into the ready queue
217	by calling the ready method.
218
219	=cut
220
221	sub _newcoro {	716	sub _coro_run {
222	terminate &{+shift};	717	terminate &{+shift};
223	}	718	}
224		719
225	sub new {	720	=item $success = $coro->ready
226	my $class = shift;
227	bless {
228	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
229	}, $class;
230	}
231		721
232	=item $process->ready	722	Put the given coro into the end of its ready queue (there is one
		723	queue for each priority) and return true. If the coro is already in
		724	the ready queue, do nothing and return false.
233		725
234	Put the given process into the ready queue.	726	This ensures that the scheduler will resume this coro automatically
		727	once all the coro of higher priority and all coro of the same
		728	priority that were put into the ready queue earlier have been resumed.
235		729
236	=cut	730	=item $coro->suspend
237		731
238	=item $process->cancel	732	Suspends the specified coro. A suspended coro works just like any other
		733	coro, except that the scheduler will not select a suspended coro for
		734	execution.
239		735
240	Like C<terminate>, but terminates the specified process instead.	736	Suspending a coro can be useful when you want to keep the coro from
		737	running, but you don't want to destroy it, or when you want to temporarily
		738	freeze a coro (e.g. for debugging) to resume it later.
241		739
242	=cut	740	A scenario for the former would be to suspend all (other) coros after a
		741	fork and keep them alive, so their destructors aren't called, but new
		742	coros can be created.
243		743
244	sub cancel {	744	=item $coro->resume
245	push @destroy, $_[0];
246	$manager->ready;
247	&schedule if $current == $_[0];
248	}
249		745
250	=item $process->join	746	If the specified coro was suspended, it will be resumed. Note that when
		747	the coro was in the ready queue when it was suspended, it might have been
		748	unreadied by the scheduler, so an activation might have been lost.
251		749
252	Wait until the coroutine terminates and return any values given to the	750	To avoid this, it is best to put a suspended coro into the ready queue
253	C<terminate> function. C<join> can be called multiple times from multiple	751	unconditionally, as every synchronisation mechanism must protect itself
254	processes.	752	against spurious wakeups, and the one in the Coro family certainly do
		753	that.
255		754
256	=cut	755	=item $state->is_new
257		756
258	sub join {	757	Returns true iff this Coro object is "new", i.e. has never been run
259	my $self = shift;	758	yet. Those states basically consist of only the code reference to call and
260	unless ($self->{status}) {	759	the arguments, but consumes very little other resources. New states will
261	push @{$self->{join}}, $current;	760	automatically get assigned a perl interpreter when they are transferred to.
262	&schedule;	761
		762	=item $state->is_zombie
		763
		764	Returns true iff the Coro object has been cancelled, i.e.
		765	its resources freed because they were C<cancel>'ed, C<terminate>'d,
		766	C<safe_cancel>'ed or simply went out of scope.
		767
		768	The name "zombie" stems from UNIX culture, where a process that has
		769	exited and only stores and exit status and no other resources is called a
		770	"zombie".
		771
		772	=item $is_ready = $coro->is_ready
		773
		774	Returns true iff the Coro object is in the ready queue. Unless the Coro
		775	object gets destroyed, it will eventually be scheduled by the scheduler.
		776
		777	=item $is_running = $coro->is_running
		778
		779	Returns true iff the Coro object is currently running. Only one Coro object
		780	can ever be in the running state (but it currently is possible to have
		781	multiple running Coro::States).
		782
		783	=item $is_suspended = $coro->is_suspended
		784
		785	Returns true iff this Coro object has been suspended. Suspended Coros will
		786	not ever be scheduled.
		787
		788	=item $coro->cancel ($arg...)
		789
		790	Terminate the given Coro thread and make it return the given arguments as
		791	status (default: an empty list). Never returns if the Coro is the
		792	current Coro.
		793
		794	This is a rather brutal way to free a coro, with some limitations - if
		795	the thread is inside a C callback that doesn't expect to be canceled,
		796	bad things can happen, or if the cancelled thread insists on running
		797	complicated cleanup handlers that rely on its thread context, things will
		798	not work.
		799
		800	Any cleanup code being run (e.g. from C<guard> blocks, destructors and so
		801	on) will be run without a thread context, and is not allowed to switch
		802	to other threads. A common mistake is to call C<< ->cancel >> from a
		803	destructor called by die'ing inside the thread to be cancelled for
		804	example.
		805
		806	On the plus side, C<< ->cancel >> will always clean up the thread, no
		807	matter what. If your cleanup code is complex or you want to avoid
		808	cancelling a C-thread that doesn't know how to clean up itself, it can be
		809	better to C<< ->throw >> an exception, or use C<< ->safe_cancel >>.
		810
		811	The arguments to C<< ->cancel >> are not copied, but instead will
		812	be referenced directly (e.g. if you pass C<$var> and after the call
		813	change that variable, then you might change the return values passed to
		814	e.g. C<join>, so don't do that).
		815
		816	The resources of the Coro are usually freed (or destructed) before this
		817	call returns, but this can be delayed for an indefinite amount of time, as
		818	in some cases the manager thread has to run first to actually destruct the
		819	Coro object.
		820
		821	=item $coro->safe_cancel ($arg...)
		822
		823	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		824	consequently, can fail with an exception in cases the thread is not in a
		825	cancellable state. Essentially, C<< ->safe_cancel >> is a C<< ->cancel >>
		826	with extra checks before canceling.
		827
		828	It works a bit like throwing an exception that cannot be caught -
		829	specifically, it will clean up the thread from within itself, so all
		830	cleanup handlers (e.g. C<guard> blocks) are run with full thread
		831	context and can block if they wish. The downside is that there is no
		832	guarantee that the thread can be cancelled when you call this method, and
		833	therefore, it might fail. It is also considerably slower than C<cancel> or
		834	C<terminate>.
		835
		836	A thread is in a safe-cancellable state if it either has never been run
		837	yet, has already been canceled/terminated or otherwise destroyed, or has
		838	no C context attached and is inside an SLF function.
		839
		840	The first two states are trivial - a thread that has not started or has
		841	already finished is safe to cancel.
		842
		843	The last state basically means that the thread isn't currently inside a
		844	perl callback called from some C function (usually via some XS modules)
		845	and isn't currently executing inside some C function itself (via Coro's XS
		846	API).
		847
		848	This call returns true when it could cancel the thread, or croaks with an
		849	error otherwise (i.e. it either returns true or doesn't return at all).
		850
		851	Why the weird interface? Well, there are two common models on how and
		852	when to cancel things. In the first, you have the expectation that your
		853	coro thread can be cancelled when you want to cancel it - if the thread
		854	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		855	croaks to notify of the bug.
		856
		857	In the second model you sometimes want to ask nicely to cancel a thread,
		858	but if it's not a good time, well, then don't cancel. This can be done
		859	relatively easy like this:
		860
		861	if (! eval { $coro->safe_cancel }) {
		862	warn "unable to cancel thread: $@";
263	}	863	}
264	wantarray ? @{$self->{status}} : $self->{status}[0];
265	}
266		864
		865	However, what you never should do is first try to cancel "safely" and
		866	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		867	no sense: either you rely on being able to execute cleanup code in your
		868	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		869	only way, and if you don't, then C<< ->cancel >> is always faster and more
		870	direct.
		871
		872	=item $coro->schedule_to
		873
		874	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		875	of continuing with the next coro from the ready queue, always switch to
		876	the given coro object (regardless of priority etc.). The readyness
		877	state of that coro isn't changed.
		878
		879	This is an advanced method for special cases - I'd love to hear about any
		880	uses for this one.
		881
		882	=item $coro->cede_to
		883
		884	Like C<schedule_to>, but puts the current coro into the ready
		885	queue. This has the effect of temporarily switching to the given
		886	coro, and continuing some time later.
		887
		888	This is an advanced method for special cases - I'd love to hear about any
		889	uses for this one.
		890
		891	=item $coro->throw ([$scalar])
		892
		893	If C<$throw> is specified and defined, it will be thrown as an exception
		894	inside the coro at the next convenient point in time. Otherwise
		895	clears the exception object.
		896
		897	Coro will check for the exception each time a schedule-like-function
		898	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		899	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
		900	that are part of Coro itself) detect this case and return early in case an
		901	exception is pending.
		902
		903	The exception object will be thrown "as is" with the specified scalar in
		904	C<$@>, i.e. if it is a string, no line number or newline will be appended
		905	(unlike with C<die>).
		906
		907	This can be used as a softer means than either C<cancel> or C<safe_cancel
		908	>to ask a coro to end itself, although there is no guarantee that the
		909	exception will lead to termination, and if the exception isn't caught it
		910	might well end the whole program.
		911
		912	You might also think of C<throw> as being the moral equivalent of
		913	C<kill>ing a coro with a signal (in this case, a scalar).
		914
		915	=item $coro->join
		916
		917	Wait until the coro terminates and return any values given to the
		918	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		919	from multiple threads, and all will be resumed and given the status
		920	return once the C<$coro> terminates.
		921
		922	=item $coro->on_destroy (\&cb)
		923
		924	Registers a callback that is called when this coro thread gets destroyed,
		925	that is, after its resources have been freed but before it is joined. The
		926	callback gets passed the terminate/cancel arguments, if any, and I<must
		927	not> die, under any circumstances.
		928
		929	There can be any number of C<on_destroy> callbacks per coro, and there is
		930	currently no way to remove a callback once added.
		931
267	=item $oldprio = $process->prio($newprio)	932	=item $oldprio = $coro->prio ($newprio)
268		933
269	Sets (or gets, if the argument is missing) the priority of the	934	Sets (or gets, if the argument is missing) the priority of the
270	process. Higher priority processes get run before lower priority	935	coro thread. Higher priority coro get run before lower priority
271	processes. Priorities are small signed integers (currently -4 .. +3),	936	coros. Priorities are small signed integers (currently -4 .. +3),
272	that you can refer to using PRIO_xxx constants (use the import tag :prio	937	that you can refer to using PRIO_xxx constants (use the import tag :prio
273	to get then):	938	to get then):
274		939
275	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	940	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
276	3 > 1 > 0 > -1 > -3 > -4	941	3 > 1 > 0 > -1 > -3 > -4
277		942
278	# set priority to HIGH	943	# set priority to HIGH
279	current->prio(PRIO_HIGH);	944	current->prio (PRIO_HIGH);
280		945
281	The idle coroutine ($Coro::idle) always has a lower priority than any	946	The idle coro thread ($Coro::idle) always has a lower priority than any
282	existing coroutine.	947	existing coro.
283		948
284	Changing the priority of the current process will take effect immediately,	949	Changing the priority of the current coro will take effect immediately,
285	but changing the priority of processes in the ready queue (but not	950	but changing the priority of a coro in the ready queue (but not running)
286	running) will only take effect after the next schedule (of that	951	will only take effect after the next schedule (of that coro). This is a
287	process). This is a bug that will be fixed in some future version.	952	bug that will be fixed in some future version.
288		953
289	=cut
290
291	sub prio {
292	my $old = $_[0]{prio};
293	$_[0]{prio} = $_[1] if @_ > 1;
294	$old;
295	}
296
297	=item $newprio = $process->nice($change)	954	=item $newprio = $coro->nice ($change)
298		955
299	Similar to C<prio>, but subtract the given value from the priority (i.e.	956	Similar to C<prio>, but subtract the given value from the priority (i.e.
300	higher values mean lower priority, just as in unix).	957	higher values mean lower priority, just as in UNIX's nice command).
301		958
302	=cut
303
304	sub nice {
305	$_[0]{prio} -= $_[1];
306	}
307
308	=item $olddesc = $process->desc($newdesc)	959	=item $olddesc = $coro->desc ($newdesc)
309		960
310	Sets (or gets in case the argument is missing) the description for this	961	Sets (or gets in case the argument is missing) the description for this
311	process. This is just a free-form string you can associate with a process.	962	coro thread. This is just a free-form string you can associate with a
		963	coro.
		964
		965	This method simply sets the C<< $coro->{desc} >> member to the given
		966	string. You can modify this member directly if you wish, and in fact, this
		967	is often preferred to indicate major processing states that can then be
		968	seen for example in a L<Coro::Debug> session:
		969
		970	sub my_long_function {
		971	local $Coro::current->{desc} = "now in my_long_function";
		972	...
		973	$Coro::current->{desc} = "my_long_function: phase 1";
		974	...
		975	$Coro::current->{desc} = "my_long_function: phase 2";
		976	...
		977	}
312		978
313	=cut	979	=cut
314		980
315	sub desc {	981	sub desc {
316	my $old = $_[0]{desc};	982	my $old = $_[0]{desc};
317	$_[0]{desc} = $_[1] if @_ > 1;	983	$_[0]{desc} = $_[1] if @_ > 1;
318	$old;	984	$old;
319	}	985	}
320		986
		987	sub transfer {
		988	require Carp;
		989	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		990	}
		991
321	=back	992	=back
322		993
		994	=head1 GLOBAL FUNCTIONS
		995
		996	=over 4
		997
		998	=item Coro::nready
		999
		1000	Returns the number of coro that are currently in the ready state,
		1001	i.e. that can be switched to by calling C<schedule> directory or
		1002	indirectly. The value C<0> means that the only runnable coro is the
		1003	currently running one, so C<cede> would have no effect, and C<schedule>
		1004	would cause a deadlock unless there is an idle handler that wakes up some
		1005	coro.
		1006
		1007	=item my $guard = Coro::guard { ... }
		1008
		1009	This function still exists, but is deprecated. Please use the
		1010	C<Guard::guard> function instead.
		1011
323	=cut	1012	=cut
324		1013
		1014	BEGIN { *guard = \&Guard::guard }
		1015
		1016	=item unblock_sub { ... }
		1017
		1018	This utility function takes a BLOCK or code reference and "unblocks" it,
		1019	returning a new coderef. Unblocking means that calling the new coderef
		1020	will return immediately without blocking, returning nothing, while the
		1021	original code ref will be called (with parameters) from within another
		1022	coro.
		1023
		1024	The reason this function exists is that many event libraries (such as
		1025	the venerable L<Event|Event> module) are not thread-safe (a weaker form
		1026	of reentrancy). This means you must not block within event callbacks,
		1027	otherwise you might suffer from crashes or worse. The only event library
		1028	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		1029	you might still run into deadlocks if all event loops are blocked).
		1030
		1031	Coro will try to catch you when you block in the event loop
		1032	("FATAL: $Coro::idle blocked itself"), but this is just best effort and
		1033	only works when you do not run your own event loop.
		1034
		1035	This function allows your callbacks to block by executing them in another
		1036	coro where it is safe to block. One example where blocking is handy
		1037	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
		1038	disk, for example.
		1039
		1040	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		1041	creating event callbacks that want to block.
		1042
		1043	If your handler does not plan to block (e.g. simply sends a message to
		1044	another coro, or puts some other coro into the ready queue), there is
		1045	no reason to use C<unblock_sub>.
		1046
		1047	Note that you also need to use C<unblock_sub> for any other callbacks that
		1048	are indirectly executed by any C-based event loop. For example, when you
		1049	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		1050	provides callbacks that are the result of some event callback, then you
		1051	must not block either, or use C<unblock_sub>.
		1052
		1053	=cut
		1054
		1055	our @unblock_queue;
		1056
		1057	# we create a special coro because we want to cede,
		1058	# to reduce pressure on the coro pool (because most callbacks
		1059	# return immediately and can be reused) and because we cannot cede
		1060	# inside an event callback.
		1061	our $unblock_scheduler = new Coro sub {
		1062	while () {
		1063	while (my $cb = pop @unblock_queue) {
		1064	&async_pool (@$cb);
		1065
		1066	# for short-lived callbacks, this reduces pressure on the coro pool
		1067	# as the chance is very high that the async_poll coro will be back
		1068	# in the idle state when cede returns
		1069	cede;
		1070	}
		1071	schedule; # sleep well
		1072	}
		1073	};
		1074	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		1075
		1076	sub unblock_sub(&) {
		1077	my $cb = shift;
		1078
		1079	sub {
		1080	unshift @unblock_queue, [$cb, @_];
		1081	$unblock_scheduler->ready;
		1082	}
		1083	}
		1084
		1085	=item $cb = rouse_cb
		1086
		1087	Create and return a "rouse callback". That's a code reference that,
		1088	when called, will remember a copy of its arguments and notify the owner
		1089	coro of the callback.
		1090
		1091	Only the first invocation will store agruments and signal any waiter -
		1092	further calls will effectively be ignored, but it is ok to try.
		1093
		1094	Also see the next function.
		1095
		1096	=item @args = rouse_wait [$cb]
		1097
		1098	Wait for the specified rouse callback to be invoked (or if the argument is
		1099	missing, use the most recently created callback in the current coro).
		1100
		1101	As soon as the callback is invoked (or when the callback was invoked
		1102	before C<rouse_wait>), it will return the arguments originally passed to
		1103	the rouse callback. In scalar context, that means you get the I<last>
		1104	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1105	statement at the end.
		1106
		1107	You are only allowed to wait once for a given rouse callback.
		1108
		1109	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1110
		1111	As of Coro 6.57, you can reliably wait for a rouse callback in a different
		1112	thread than from where it was created.
		1113
		1114	=back
		1115
		1116	=cut
		1117
		1118	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1119	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1120
		1121	*{"Coro::$module\::new"} = sub {
		1122	require "Coro/$module.pm";
		1123
		1124	# some modules have their new predefined in State.xs, some don't
		1125	*{"Coro::$module\::new"} = $old
		1126	if $old;
		1127
		1128	goto &{"Coro::$module\::new"}
		1129	};
		1130	}
		1131
325	1;	1132	1;
326		1133
		1134	=head1 HOW TO WAIT FOR A CALLBACK
		1135
		1136	It is very common for a coro to wait for some callback to be
		1137	called. This occurs naturally when you use coro in an otherwise
		1138	event-based program, or when you use event-based libraries.
		1139
		1140	These typically register a callback for some event, and call that callback
		1141	when the event occurred. In a coro, however, you typically want to
		1142	just wait for the event, simplyifying things.
		1143
		1144	For example C<< AnyEvent->child >> registers a callback to be called when
		1145	a specific child has exited:
		1146
		1147	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1148
		1149	But from within a coro, you often just want to write this:
		1150
		1151	my $status = wait_for_child $pid;
		1152
		1153	Coro offers two functions specifically designed to make this easy,
		1154	C<rouse_cb> and C<rouse_wait>.
		1155
		1156	The first function, C<rouse_cb>, generates and returns a callback that,
		1157	when invoked, will save its arguments and notify the coro that
		1158	created the callback.
		1159
		1160	The second function, C<rouse_wait>, waits for the callback to be called
		1161	(by calling C<schedule> to go to sleep) and returns the arguments
		1162	originally passed to the callback.
		1163
		1164	Using these functions, it becomes easy to write the C<wait_for_child>
		1165	function mentioned above:
		1166
		1167	sub wait_for_child($) {
		1168	my ($pid) = @_;
		1169
		1170	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
		1171
		1172	my ($rpid, $rstatus) = rouse_wait;
		1173	$rstatus
		1174	}
		1175
		1176	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1177	you can roll your own, using C<schedule> and C<ready>:
		1178
		1179	sub wait_for_child($) {
		1180	my ($pid) = @_;
		1181
		1182	# store the current coro in $current,
		1183	# and provide result variables for the closure passed to ->child
		1184	my $current = $Coro::current;
		1185	my ($done, $rstatus);
		1186
		1187	# pass a closure to ->child
		1188	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1189	$rstatus = $_[1]; # remember rstatus
		1190	$done = 1; # mark $rstatus as valid
		1191	$current->ready; # wake up the waiting thread
		1192	});
		1193
		1194	# wait until the closure has been called
		1195	schedule while !$done;
		1196
		1197	$rstatus
		1198	}
		1199
		1200
327	=head1 BUGS/LIMITATIONS	1201	=head1 BUGS/LIMITATIONS
328		1202
329	- you must make very sure that no coro is still active on global	1203	=over 4
330	destruction. very bad things might happen otherwise (usually segfaults).
331		1204
		1205	=item fork with pthread backend
		1206
		1207	When Coro is compiled using the pthread backend (which isn't recommended
		1208	but required on many BSDs as their libcs are completely broken), then
		1209	coro will not survive a fork. There is no known workaround except to
		1210	fix your libc and use a saner backend.
		1211
		1212	=item perl process emulation ("threads")
		1213
332	- this module is not thread-safe. You should only ever use this module	1214	This module is not perl-pseudo-thread-safe. You should only ever use this
333	from the same thread (this requirement might be losened in the future	1215	module from the first thread (this requirement might be removed in the
334	to allow per-thread schedulers, but Coro::State does not yet allow	1216	future to allow per-thread schedulers, but Coro::State does not yet allow
335	this).	1217	this). I recommend disabling thread support and using processes, as having
		1218	the windows process emulation enabled under unix roughly halves perl
		1219	performance, even when not used.
		1220
		1221	Attempts to use threads created in another emulated process will crash
		1222	("cleanly", with a null pointer exception).
		1223
		1224	=item coro switching is not signal safe
		1225
		1226	You must not switch to another coro from within a signal handler (only
		1227	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1228	you are sure you are not interrupting a Coro function.
		1229
		1230	That means you I<MUST NOT> call any function that might "block" the
		1231	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		1232	anything that calls those. Everything else, including calling C<ready>,
		1233	works.
		1234
		1235	=back
		1236
		1237
		1238	=head1 WINDOWS PROCESS EMULATION
		1239
		1240	A great many people seem to be confused about ithreads (for example, Chip
		1241	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1242	while in the same mail making rather confused statements about perl
		1243	ithreads (for example, that memory or files would be shared), showing his
		1244	lack of understanding of this area - if it is hard to understand for Chip,
		1245	it is probably not obvious to everybody).
		1246
		1247	What follows is an ultra-condensed version of my talk about threads in
		1248	scripting languages given on the perl workshop 2009:
		1249
		1250	The so-called "ithreads" were originally implemented for two reasons:
		1251	first, to (badly) emulate unix processes on native win32 perls, and
		1252	secondly, to replace the older, real thread model ("5.005-threads").
		1253
		1254	It does that by using threads instead of OS processes. The difference
		1255	between processes and threads is that threads share memory (and other
		1256	state, such as files) between threads within a single process, while
		1257	processes do not share anything (at least not semantically). That
		1258	means that modifications done by one thread are seen by others, while
		1259	modifications by one process are not seen by other processes.
		1260
		1261	The "ithreads" work exactly like that: when creating a new ithreads
		1262	process, all state is copied (memory is copied physically, files and code
		1263	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1264	the same behaviour can be achieved by using operating system processes,
		1265	except that UNIX typically uses hardware built into the system to do this
		1266	efficiently, while the windows process emulation emulates this hardware in
		1267	software (rather efficiently, but of course it is still much slower than
		1268	dedicated hardware).
		1269
		1270	As mentioned before, loading code, modifying code, modifying data
		1271	structures and so on is only visible in the ithreads process doing the
		1272	modification, not in other ithread processes within the same OS process.
		1273
		1274	This is why "ithreads" do not implement threads for perl at all, only
		1275	processes. What makes it so bad is that on non-windows platforms, you can
		1276	actually take advantage of custom hardware for this purpose (as evidenced
		1277	by the forks module, which gives you the (i-) threads API, just much
		1278	faster).
		1279
		1280	Sharing data is in the i-threads model is done by transferring data
		1281	structures between threads using copying semantics, which is very slow -
		1282	shared data simply does not exist. Benchmarks using i-threads which are
		1283	communication-intensive show extremely bad behaviour with i-threads (in
		1284	fact, so bad that Coro, which cannot take direct advantage of multiple
		1285	CPUs, is often orders of magnitude faster because it shares data using
		1286	real threads, refer to my talk for details).
		1287
		1288	As summary, i-threads *use* threads to implement processes, while
		1289	the compatible forks module *uses* processes to emulate, uhm,
		1290	processes. I-threads slow down every perl program when enabled, and
		1291	outside of windows, serve no (or little) practical purpose, but
		1292	disadvantages every single-threaded Perl program.
		1293
		1294	This is the reason that I try to avoid the name "ithreads", as it is
		1295	misleading as it implies that it implements some kind of thread model for
		1296	perl, and prefer the name "windows process emulation", which describes the
		1297	actual use and behaviour of it much better.
336		1298
337	=head1 SEE ALSO	1299	=head1 SEE ALSO
338		1300
339	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	1301	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
340	L<Coro::Signal>, L<Coro::State>, L<Coro::Timer>, L<Coro::Event>,
341	L<Coro::L<Coro::RWLock>, Handle>, L<Coro::Socket>.
342		1302
343	=head1 AUTHOR	1303	Debugging: L<Coro::Debug>.
344		1304
345	Marc Lehmann <pcg@goof.com>	1305	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
346	http://www.goof.com/pcg/marc/	1306
		1307	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1308	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		1309
		1310	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		1311
		1312	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1313	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1314	L<Coro::Select>.
		1315
		1316	XS API: L<Coro::MakeMaker>.
		1317
		1318	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
		1319
		1320	=head1 AUTHOR/SUPPORT/CONTACT
		1321
		1322	Marc A. Lehmann <schmorp@schmorp.de>
		1323	http://software.schmorp.de/pkg/Coro.html
347		1324
348	=cut	1325	=cut
349		1326

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