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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	use Coro::Semaphore;
19	cede;	22	my $lock = new Coro::Semaphore;
		23	my $locked;
		24
		25	$lock->down;
		26	$locked = 1;
		27	$lock->up;
20		28
21	=head1 DESCRIPTION	29	=head1 DESCRIPTION
22		30
23	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
24	threads but don't run in parallel.	32	manpage. This manpage mainly contains reference information.
25		33
		34	This module collection manages continuations in general, most often in
		35	the form of cooperative threads (also called coros, or simply "coro"
		36	in the documentation). They are similar to kernel threads but don't (in
		37	general) run in parallel at the same time even on SMP machines. The
		38	specific flavor of thread offered by this module also guarantees you that
		39	it will not switch between threads unless necessary, at easily-identified
		40	points in your program, so locking and parallel access are rarely an
		41	issue, making thread programming much safer and easier than using other
		42	thread models.
		43
		44	Unlike the so-called "Perl threads" (which are not actually real threads
		45	but only the windows process emulation (see section of same name for
		46	more details) ported to UNIX, and as such act as processes), Coro
		47	provides a full shared address space, which makes communication between
		48	threads very easy. And coro threads are fast, too: disabling the Windows
		49	process emulation code in your perl and using Coro can easily result in
		50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark (very communication-intensive) runs over 300
		52	times faster on a single core than perls pseudo-threads on a quad core
		53	using all four cores.
		54
		55	Coro achieves that by supporting multiple running interpreters that share
		56	data, which is especially useful to code pseudo-parallel processes and
		57	for event-based programming, such as multiple HTTP-GET requests running
		58	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		59	into an event-based environment.
		60
26	In this module, coroutines are defined as "callchain + lexical variables	61	In this module, a thread is defined as "callchain + lexical variables +
27	+ @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own	62	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	63	its own set of lexicals and its own set of perls most important global
29	important global variables.	64	variables (see L<Coro::State> for more configuration and background info).
		65
		66	See also the C<SEE ALSO> section at the end of this document - the Coro
		67	module family is quite large.
		68
		69	=head1 CORO THREAD LIFE CYCLE
		70
		71	During the long and exciting (or not) life of a coro thread, it goes
		72	through a number of states:
		73
		74	=over 4
		75
		76	=item 1. Creation
		77
		78	The first thing in the life of a coro thread is it's creation -
		79	obviously. The typical way to create a thread is to call the C<async
		80	BLOCK> function:
		81
		82	async {
		83	# thread code goes here
		84	};
		85
		86	You can also pass arguments, which are put in C<@_>:
		87
		88	async {
		89	print $_[1]; # prints 2
		90	} 1, 2, 3;
		91
		92	This creates a new coro thread and puts it into the ready queue, meaning
		93	it will run as soon as the CPU is free for it.
		94
		95	C<async> will return a coro object - you can store this for future
		96	reference or ignore it, the thread itself will keep a reference to it's
		97	thread object - threads are alive on their own.
		98
		99	Another way to create a thread is to call the C<new> constructor with a
		100	code-reference:
		101
		102	new Coro sub {
		103	# thread code goes here
		104	}, @optional_arguments;
		105
		106	This is quite similar to calling C<async>, but the important difference is
		107	that the new thread is not put into the ready queue, so the thread will
		108	not run until somebody puts it there. C<async> is, therefore, identical to
		109	this sequence:
		110
		111	my $coro = new Coro sub {
		112	# thread code goes here
		113	};
		114	$coro->ready;
		115	return $coro;
		116
		117	=item 2. Startup
		118
		119	When a new coro thread is created, only a copy of the code reference
		120	and the arguments are stored, no extra memory for stacks and so on is
		121	allocated, keeping the coro thread in a low-memory state.
		122
		123	Only when it actually starts executing will all the resources be finally
		124	allocated.
		125
		126	The optional arguments specified at coro creation are available in C<@_>,
		127	similar to function calls.
		128
		129	=item 3. Running / Blocking
		130
		131	A lot can happen after the coro thread has started running. Quite usually,
		132	it will not run to the end in one go (because you could use a function
		133	instead), but it will give up the CPU regularly because it waits for
		134	external events.
		135
		136	As long as a coro thread runs, it's coro object is available in the global
		137	variable C<$Coro::current>.
		138
		139	The low-level way to give up the CPU is to call the scheduler, which
		140	selects a new coro thread to run:
		141
		142	Coro::schedule;
		143
		144	Since running threads are not in the ready queue, calling the scheduler
		145	without doing anything else will block the coro thread forever - you need
		146	to arrange either for the coro to put woken up (readied) by some other
		147	event or some other thread, or you can put it into the ready queue before
		148	scheduling:
		149
		150	# this is exactly what Coro::cede does
		151	$Coro::current->ready;
		152	Coro::schedule;
		153
		154	All the higher-level synchronisation methods (Coro::Semaphore,
		155	Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
		156	Coro::schedule >>.
		157
		158	While the coro thread is running it also might get assigned a C-level
		159	thread, or the C-level thread might be unassigned from it, as the Coro
		160	runtime wishes. A C-level thread needs to be assigned when your perl
		161	thread calls into some C-level function and that function in turn calls
		162	perl and perl then wants to switch coroutines. This happens most often
		163	when you run an event loop and block in the callback, or when perl
		164	itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
		165	mechanism.
		166
		167	=item 4. Termination
		168
		169	Many threads actually terminate after some time. There are a number of
		170	ways to terminate a coro thread, the simplest is returning from the
		171	top-level code reference:
		172
		173	async {
		174	# after returning from here, the coro thread is terminated
		175	};
		176
		177	async {
		178	return if 0.5 < rand; # terminate a little earlier, maybe
		179	print "got a chance to print this\n";
		180	# or here
		181	};
		182
		183	Any values returned from the coroutine can be recovered using C<< ->join
		184	>>:
		185
		186	my $coro = async {
		187	"hello, world\n" # return a string
		188	};
		189
		190	my $hello_world = $coro->join;
		191
		192	print $hello_world;
		193
		194	Another way to terminate is to call C<< Coro::terminate >>, which at any
		195	subroutine call nesting level:
		196
		197	async {
		198	Coro::terminate "return value 1", "return value 2";
		199	};
		200
		201	And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
		202	coro thread from another thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # an also accept values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit>
		211	without actually exiting, and might leave C libraries and XS modules in
		212	a weird state. Unlike other thread implementations, however, Coro is
		213	exceptionally safe with regards to cancellation, as perl will always be
		214	in a consistent state, and for those cases where you want to do truly
		215	marvellous things with your coro while it is being cancelled, there is
		216	even a 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	=item 5. Cleanup
		224
		225	Threads will allocate various resources. Most but not all will be returned
		226	when a thread terminates, during clean-up.
		227
		228	Cleanup is quite similar to throwing an uncaught exception: perl will
		229	work it's way up through all subroutine calls and blocks. On it's way, it
		230	will release all C<my> variables, undo all C<local>'s and free any other
		231	resources truly local to the thread.
		232
		233	So, a common way to free resources is to keep them referenced only by my
		234	variables:
		235
		236	async {
		237	my $big_cache = new Cache ...;
		238	};
		239
		240	If there are no other references, then the C<$big_cache> object will be
		241	freed when the thread terminates, regardless of how it does so.
		242
		243	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		244	resources, but that's where the C<guard> methods come in handy:
		245
		246	my $sem = new Coro::Semaphore;
		247
		248	async {
		249	my $lock_guard = $sem->guard;
		250	# if we reutrn, or die or get cancelled, here,
		251	# then the semaphore will be "up"ed.
		252	};
		253
		254	The C<Guard::guard> function comes in handy for any custom cleanup you
		255	might want to do:
		256
		257	async {
		258	my $window = new Gtk2::Window "toplevel";
		259	# The window will not be cleaned up automatically, even when $window
		260	# gets freed, so use a guard to ensure it's destruction
		261	# in case of an error:
		262	my $window_guard = Guard::guard { $window->destroy };
		263
		264	# we are safe here
		265	};
		266
		267	Last not least, C<local> can often be handy, too, e.g. when temporarily
		268	replacing the coro thread description:
		269
		270	sub myfunction {
		271	local $Coro::current->{desc} = "inside myfunction(@_)";
		272
		273	# if we return or die here, the description will be restored
		274	}
		275
		276	=item 6. Viva La Zombie Muerte
		277
		278	Even after a thread has terminated and cleaned up it's resources, the coro
		279	object still is there and stores the return values of the thread. Only in
		280	this state will the coro object be "reference counted" in the normal perl
		281	sense: the thread code keeps a reference to it when it is active, but not
		282	after it has terminated.
		283
		284	The means the coro object gets freed automatically when the thread has
		285	terminated and cleaned up and there arenot other references.
		286
		287	If there are, the coro object will stay around, and you can call C<<
		288	->join >> as many times as you wish to retrieve the result values:
		289
		290	async {
		291	print "hi\n";
		292	1
		293	};
		294
		295	# run the async above, and free everything before returning
		296	# from Coro::cede:
		297	Coro::cede;
		298
		299	{
		300	my $coro = async {
		301	print "hi\n";
		302	1
		303	};
		304
		305	# run the async above, and clean up, but do not free the coro
		306	# object:
		307	Coro::cede;
		308
		309	# optionally retrieve the result values
		310	my @results = $coro->join;
		311
		312	# now $coro goes out of scope, and presumably gets freed
		313	};
		314
		315	=back
30		316
31	=cut	317	=cut
32		318
33	package Coro;	319	package Coro;
34		320
35	use strict;	321	use common::sense;
36	no warnings "uninitialized";	322
		323	use Carp ();
		324
		325	use Guard ();
37		326
38	use Coro::State;	327	use Coro::State;
39		328
40	use base Exporter::;	329	use base qw(Coro::State Exporter);
41		330
42	our $idle; # idle coroutine	331	our $idle; # idle handler
43	our $main; # main coroutine	332	our $main; # main coro
44	our $current; # current coroutine	333	our $current; # current coro
45		334
46	our $VERSION = '2.1';	335	our $VERSION = 5.372;
47		336
48	our @EXPORT = qw(async cede schedule terminate current);	337	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
49	our %EXPORT_TAGS = (	338	our %EXPORT_TAGS = (
50	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	339	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
51	);	340	);
52	our @EXPORT_OK = @{$EXPORT_TAGS{prio}};	341	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
53		342
54	{	343	=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		344
88	=over 4	345	=over 4
89		346
90	=item $main	347	=item $Coro::main
91		348
92	This coroutine represents the main program.	349	This variable stores the Coro object that represents the main
		350	program. While you cna C<ready> it and do most other things you can do to
		351	coro, it is mainly useful to compare again C<$Coro::current>, to see
		352	whether you are running in the main program or not.
93		353
94	=cut	354	=cut
95		355
96	$main = new Coro;	356	# $main is now being initialised by Coro::State
97		357
98	=item $current (or as function: current)	358	=item $Coro::current
99		359
100	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	360	The Coro object representing the current coro (the last
		361	coro that the Coro scheduler switched to). The initial value is
		362	C<$Coro::main> (of course).
101		363
102	=cut	364	This variable is B<strictly> I<read-only>. You can take copies of the
		365	value stored in it and use it as any other Coro object, but you must
		366	not otherwise modify the variable itself.
103		367
104	# maybe some other module used Coro::Specific before...	368	=cut
105	if ($current) {
106	$main->{specific} = $current->{specific};
107	}
108		369
109	$current = $main;
110
111	sub current() { $current }	370	sub current() { $current } # [DEPRECATED]
112		371
113	=item $idle	372	=item $Coro::idle
114		373
115	The coroutine to switch to when no other coroutine is running. The default	374	This variable is mainly useful to integrate Coro into event loops. It is
116	implementation prints "FATAL: deadlock detected" and exits.	375	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		376	pretty low-level functionality.
117		377
118	=cut	378	This variable stores a Coro object that is put into the ready queue when
		379	there are no other ready threads (without invoking any ready hooks).
119		380
120	# should be done using priorities :(	381	The default implementation dies with "FATAL: deadlock detected.", followed
		382	by a thread listing, because the program has no other way to continue.
		383
		384	This hook is overwritten by modules such as C<Coro::EV> and
		385	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
		386	coro so the scheduler can run it.
		387
		388	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
		389
		390	=cut
		391
		392	# ||= because other modules could have provided their own by now
121	$idle = new Coro sub {	393	$idle ||= new Coro sub {
		394	require Coro::Debug;
122	print STDERR "FATAL: deadlock detected\n";	395	die "FATAL: deadlock detected.\n"
123	exit(51);	396	. Coro::Debug::ps_listing ();
124	};	397	};
125		398
126	# this coroutine is necessary because a coroutine	399	# this coro is necessary because a coro
127	# cannot destroy itself.	400	# cannot destroy itself.
128	my @destroy;	401	our @destroy;
129	my $manager;	402	our $manager;
		403
130	$manager = new Coro sub {	404	$manager = new Coro sub {
131	while () {	405	while () {
132	# by overwriting the state object with the manager we destroy it	406	_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) {	407	while @destroy;
138	my $coro = pop @destroy;
139	$coro->{status} ||= [];
140	$_->ready for @{delete $coro->{join} || []};
141		408
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;	409	&schedule;
149	}	410	}
150	};	411	};
151		412	$manager->{desc} = "[coro manager]";
152	# static methods. not really.	413	$manager->prio (PRIO_MAX);
153		414
154	=back	415	=back
155		416
156	=head2 STATIC METHODS	417	=head1 SIMPLE CORO CREATION
157
158	Static methods are actually functions that operate on the current process only.
159		418
160	=over 4	419	=over 4
161		420
162	=item async { ... } [@args...]	421	=item async { ... } [@args...]
163		422
164	Create a new asynchronous process and return it's process object	423	Create a new coro and return its Coro object (usually
165	(usually unused). When the sub returns the new process is automatically	424	unused). The coro will be put into the ready queue, so
		425	it will start running automatically on the next scheduler run.
		426
		427	The first argument is a codeblock/closure that should be executed in the
		428	coro. When it returns argument returns the coro is automatically
166	terminated.	429	terminated.
167		430
		431	The remaining arguments are passed as arguments to the closure.
		432
		433	See the C<Coro::State::new> constructor for info about the coro
		434	environment in which coro are executed.
		435
		436	Calling C<exit> in a coro will do the same as calling exit outside
		437	the coro. Likewise, when the coro dies, the program will exit,
		438	just as it would in the main program.
		439
		440	If you do not want that, you can provide a default C<die> handler, or
		441	simply avoid dieing (by use of C<eval>).
		442
168	# create a new coroutine that just prints its arguments	443	Example: Create a new coro that just prints its arguments.
		444
169	async {	445	async {
170	print "@_\n";	446	print "@_\n";
171	} 1,2,3,4;	447	} 1,2,3,4;
172		448
173	=cut	449	=item async_pool { ... } [@args...]
174		450
175	sub async(&@) {	451	Similar to C<async>, but uses a coro pool, so you should not call
176	my $pid = new Coro @_;	452	terminate or join on it (although you are allowed to), and you get a
177	$manager->ready; # this ensures that the stack is cloned from the manager	453	coro that might have executed other code already (which can be good
178	$pid->ready;	454	or bad :).
179	$pid;	455
		456	On the plus side, this function is about twice as fast as creating (and
		457	destroying) a completely new coro, so if you need a lot of generic
		458	coros in quick successsion, use C<async_pool>, not C<async>.
		459
		460	The code block is executed in an C<eval> context and a warning will be
		461	issued in case of an exception instead of terminating the program, as
		462	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		463	will not work in the expected way, unless you call terminate or cancel,
		464	which somehow defeats the purpose of pooling (but is fine in the
		465	exceptional case).
		466
		467	The priority will be reset to C<0> after each run, tracing will be
		468	disabled, the description will be reset and the default output filehandle
		469	gets restored, so you can change all these. Otherwise the coro will
		470	be re-used "as-is": most notably if you change other per-coro global
		471	stuff such as C<$/> you I<must needs> revert that change, which is most
		472	simply done by using local as in: C<< local $/ >>.
		473
		474	The idle pool size is limited to C<8> idle coros (this can be
		475	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		476	coros as required.
		477
		478	If you are concerned about pooled coros growing a lot because a
		479	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		480	{ terminate }> once per second or so to slowly replenish the pool. In
		481	addition to that, when the stacks used by a handler grows larger than 32kb
		482	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		483
		484	=cut
		485
		486	our $POOL_SIZE = 8;
		487	our $POOL_RSS = 32 * 1024;
		488	our @async_pool;
		489
		490	sub pool_handler {
		491	while () {
		492	eval {
		493	&{&_pool_handler} while 1;
		494	};
		495
		496	warn $@ if $@;
		497	}
180	}	498	}
181		499
		500	=back
		501
		502	=head1 STATIC METHODS
		503
		504	Static methods are actually functions that implicitly operate on the
		505	current coro.
		506
		507	=over 4
		508
182	=item schedule	509	=item schedule
183		510
184	Calls the scheduler. Please note that the current process will not be put	511	Calls the scheduler. The scheduler will find the next coro that is
		512	to be run from the ready queue and switches to it. The next coro
		513	to be run is simply the one with the highest priority that is longest
		514	in its ready queue. If there is no coro ready, it will call the
		515	C<$Coro::idle> hook.
		516
		517	Please note that the current coro will I<not> be put into the ready
185	into the ready queue, so calling this function usually means you will	518	queue, so calling this function usually means you will never be called
186	never be called again.	519	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		520	thus waking you up.
187		521
188	=cut	522	This makes C<schedule> I<the> generic method to use to block the current
		523	coro and wait for events: first you remember the current coro in
		524	a variable, then arrange for some callback of yours to call C<< ->ready
		525	>> on that once some event happens, and last you call C<schedule> to put
		526	yourself to sleep. Note that a lot of things can wake your coro up,
		527	so you need to check whether the event indeed happened, e.g. by storing the
		528	status in a variable.
		529
		530	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
189		531
190	=item cede	532	=item cede
191		533
192	"Cede" to other processes. This function puts the current process into the	534	"Cede" to other coros. This function puts the current coro into
193	ready queue and calls C<schedule>, which has the effect of giving up the	535	the ready queue and calls C<schedule>, which has the effect of giving
194	current "timeslice" to other coroutines of the same or higher priority.	536	up the current "timeslice" to other coros of the same or higher
		537	priority. Once your coro gets its turn again it will automatically be
		538	resumed.
195		539
196	=cut	540	This function is often called C<yield> in other languages.
		541
		542	=item Coro::cede_notself
		543
		544	Works like cede, but is not exported by default and will cede to I<any>
		545	coro, regardless of priority. This is useful sometimes to ensure
		546	progress is made.
197		547
198	=item terminate [arg...]	548	=item terminate [arg...]
199		549
200	Terminates the current process with the given status values (see L<cancel>).	550	Terminates the current coro with the given status values (see
		551	L<cancel>). The values will not be copied, but referenced directly.
201		552
202	=cut	553	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
203		554
204	sub terminate {	555	These function install enter and leave winders in the current scope. The
205	$current->cancel (@_);	556	enter block will be executed when on_enter is called and whenever the
		557	current coro is re-entered by the scheduler, while the leave block is
		558	executed whenever the current coro is blocked by the scheduler, and
		559	also when the containing scope is exited (by whatever means, be it exit,
		560	die, last etc.).
		561
		562	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		563	BLOCKs>. That means: do not even think about calling C<die> without an
		564	eval, and do not even think of entering the scheduler in any way.
		565
		566	Since both BLOCKs are tied to the current scope, they will automatically
		567	be removed when the current scope exits.
		568
		569	These functions implement the same concept as C<dynamic-wind> in scheme
		570	does, and are useful when you want to localise some resource to a specific
		571	coro.
		572
		573	They slow down thread switching considerably for coros that use them
		574	(about 40% for a BLOCK with a single assignment, so thread switching is
		575	still reasonably fast if the handlers are fast).
		576
		577	These functions are best understood by an example: The following function
		578	will change the current timezone to "Antarctica/South_Pole", which
		579	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		580	which remember/change the current timezone and restore the previous
		581	value, respectively, the timezone is only changed for the coro that
		582	installed those handlers.
		583
		584	use POSIX qw(tzset);
		585
		586	async {
		587	my $old_tz; # store outside TZ value here
		588
		589	Coro::on_enter {
		590	$old_tz = $ENV{TZ}; # remember the old value
		591
		592	$ENV{TZ} = "Antarctica/South_Pole";
		593	tzset; # enable new value
		594	};
		595
		596	Coro::on_leave {
		597	$ENV{TZ} = $old_tz;
		598	tzset; # restore old value
		599	};
		600
		601	# at this place, the timezone is Antarctica/South_Pole,
		602	# without disturbing the TZ of any other coro.
		603	};
		604
		605	This can be used to localise about any resource (locale, uid, current
		606	working directory etc.) to a block, despite the existance of other
		607	coros.
		608
		609	Another interesting example implements time-sliced multitasking using
		610	interval timers (this could obviously be optimised, but does the job):
		611
		612	# "timeslice" the given block
		613	sub timeslice(&) {
		614	use Time::HiRes ();
		615
		616	Coro::on_enter {
		617	# on entering the thread, we set an VTALRM handler to cede
		618	$SIG{VTALRM} = sub { cede };
		619	# and then start the interval timer
		620	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		621	};
		622	Coro::on_leave {
		623	# on leaving the thread, we stop the interval timer again
		624	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		625	};
		626
		627	&{+shift};
		628	}
		629
		630	# use like this:
		631	timeslice {
		632	# The following is an endless loop that would normally
		633	# monopolise the process. Since it runs in a timesliced
		634	# environment, it will regularly cede to other threads.
		635	while () { }
		636	};
		637
		638
		639	=item killall
		640
		641	Kills/terminates/cancels all coros except the currently running one.
		642
		643	Note that while this will try to free some of the main interpreter
		644	resources if the calling coro isn't the main coro, but one
		645	cannot free all of them, so if a coro that is not the main coro
		646	calls this function, there will be some one-time resource leak.
		647
		648	=cut
		649
		650	sub killall {
		651	for (Coro::State::list) {
		652	$_->cancel
		653	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		654	}
206	}	655	}
207		656
208	=back	657	=back
209		658
210	# dynamic methods	659	=head1 CORO OBJECT METHODS
211		660
212	=head2 PROCESS METHODS
213
214	These are the methods you can call on process objects.	661	These are the methods you can call on coro objects (or to create
		662	them).
215		663
216	=over 4	664	=over 4
217		665
218	=item new Coro \&sub [, @args...]	666	=item new Coro \&sub [, @args...]
219		667
220	Create a new process and return it. When the sub returns the process	668	Create a new coro and return it. When the sub returns, the coro
221	automatically terminates as if C<terminate> with the returned values were	669	automatically terminates as if C<terminate> with the returned values were
222	called. To make the process run you must first put it into the ready queue	670	called. To make the coro run you must first put it into the ready
223	by calling the ready method.	671	queue by calling the ready method.
224		672
225	=cut	673	See C<async> and C<Coro::State::new> for additional info about the
		674	coro environment.
226		675
		676	=cut
		677
227	sub _newcoro {	678	sub _coro_run {
228	terminate &{+shift};	679	terminate &{+shift};
229	}	680	}
230		681
231	sub new {	682	=item $success = $coro->ready
232	my $class = shift;
233	bless {
234	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
235	}, $class;
236	}
237		683
238	=item $process->ready	684	Put the given coro into the end of its ready queue (there is one
		685	queue for each priority) and return true. If the coro is already in
		686	the ready queue, do nothing and return false.
239		687
240	Put the given process into the ready queue.	688	This ensures that the scheduler will resume this coro automatically
		689	once all the coro of higher priority and all coro of the same
		690	priority that were put into the ready queue earlier have been resumed.
241		691
242	=cut	692	=item $coro->suspend
243		693
		694	Suspends the specified coro. A suspended coro works just like any other
		695	coro, except that the scheduler will not select a suspended coro for
		696	execution.
		697
		698	Suspending a coro can be useful when you want to keep the coro from
		699	running, but you don't want to destroy it, or when you want to temporarily
		700	freeze a coro (e.g. for debugging) to resume it later.
		701
		702	A scenario for the former would be to suspend all (other) coros after a
		703	fork and keep them alive, so their destructors aren't called, but new
		704	coros can be created.
		705
		706	=item $coro->resume
		707
		708	If the specified coro was suspended, it will be resumed. Note that when
		709	the coro was in the ready queue when it was suspended, it might have been
		710	unreadied by the scheduler, so an activation might have been lost.
		711
		712	To avoid this, it is best to put a suspended coro into the ready queue
		713	unconditionally, as every synchronisation mechanism must protect itself
		714	against spurious wakeups, and the one in the Coro family certainly do
		715	that.
		716
		717	=item $is_ready = $coro->is_ready
		718
		719	Returns true iff the Coro object is in the ready queue. Unless the Coro
		720	object gets destroyed, it will eventually be scheduled by the scheduler.
		721
		722	=item $is_running = $coro->is_running
		723
		724	Returns true iff the Coro object is currently running. Only one Coro object
		725	can ever be in the running state (but it currently is possible to have
		726	multiple running Coro::States).
		727
		728	=item $is_suspended = $coro->is_suspended
		729
		730	Returns true iff this Coro object has been suspended. Suspended Coros will
		731	not ever be scheduled.
		732
244	=item $process->cancel (arg...)	733	=item $coro->cancel (arg...)
245		734
246	Temrinates the given process and makes it return the given arguments as	735	Terminates the given Coro thread and makes it return the given arguments as
247	status (default: the empty list).	736	status (default: an empty list). Never returns if the Coro is the
		737	current Coro.
248		738
249	=cut	739	This is a rather brutal way to free a coro, with some limitations - if
		740	the thread is inside a C callback that doesn't expect to be canceled,
		741	bad things can happen, or if the cancelled thread insists on running
		742	complicated cleanup handlers that rely on it'S thread context, things will
		743	not work.
250		744
251	sub cancel {	745	Sometimes it is safer to C<< ->throw >> an exception, or use C<<
252	my $self = shift;	746	->safe_cancel >>.
253	$self->{status} = [@_];
254	push @destroy, $self;
255	$manager->ready;
256	&schedule if $current == $self;
257	}
258		747
		748	The arguments are not copied, but instead will be referenced directly
		749	(e.g. if you pass C<$var> and after the call change that variable, then
		750	you might change the return values passed to e.g. C<join>, so don't do
		751	that).
		752
		753	The resources of the Coro are usually freed (or destructed) before this
		754	call returns, but this can be delayed for an indefinite amount of time, as
		755	in some cases the manager thread has to run first to actually destruct the
		756	Coro object.
		757
		758	=item $coro->safe_cancel ($arg...)
		759
		760	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		761	consequently, can fail with an exception in cases the thread is not in a
		762	cancellable state.
		763
		764	This method works a bit like throwing an exception that cannot be caught
		765	- specifically, it will clean up the thread from within itself, so all
		766	cleanup handlers (e.g. C<guard> blocks) are run with full thread context
		767	and can block if they wish.
		768
		769	A thread is safe-cancellable if it either hasn't been run yet, or
		770	it has no C context attached and is inside an SLF function.
		771
		772	The latter two basically mean that the thread isn't currently inside a
		773	perl callback called from some C function (usually XS modules) and isn't
		774	currently inside some C function itself.
		775
		776	This call always returns true when it could cancel the thread, or croaks
		777	with an error otherwise, so you can write things like this:
		778
		779	if (! eval { $coro->safe_cancel }) {
		780	warn "unable to cancel thread: $@";
		781	}
		782
		783	=item $coro->schedule_to
		784
		785	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		786	of continuing with the next coro from the ready queue, always switch to
		787	the given coro object (regardless of priority etc.). The readyness
		788	state of that coro isn't changed.
		789
		790	This is an advanced method for special cases - I'd love to hear about any
		791	uses for this one.
		792
		793	=item $coro->cede_to
		794
		795	Like C<schedule_to>, but puts the current coro into the ready
		796	queue. This has the effect of temporarily switching to the given
		797	coro, and continuing some time later.
		798
		799	This is an advanced method for special cases - I'd love to hear about any
		800	uses for this one.
		801
		802	=item $coro->throw ([$scalar])
		803
		804	If C<$throw> is specified and defined, it will be thrown as an exception
		805	inside the coro at the next convenient point in time. Otherwise
		806	clears the exception object.
		807
		808	Coro will check for the exception each time a schedule-like-function
		809	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		810	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		811	detect this case and return early in case an exception is pending.
		812
		813	The exception object will be thrown "as is" with the specified scalar in
		814	C<$@>, i.e. if it is a string, no line number or newline will be appended
		815	(unlike with C<die>).
		816
		817	This can be used as a softer means than C<cancel> to ask a coro to
		818	end itself, although there is no guarantee that the exception will lead to
		819	termination, and if the exception isn't caught it might well end the whole
		820	program.
		821
		822	You might also think of C<throw> as being the moral equivalent of
		823	C<kill>ing a coro with a signal (in this case, a scalar).
		824
259	=item $process->join	825	=item $coro->join
260		826
261	Wait until the coroutine terminates and return any values given to the	827	Wait until the coro terminates and return any values given to the
262	C<terminate> or C<cancel> functions. C<join> can be called multiple times	828	C<terminate> or C<cancel> functions. C<join> can be called concurrently
263	from multiple processes.	829	from multiple threads, and all will be resumed and given the status
		830	return once the C<$coro> terminates.
264		831
265	=cut	832	=cut
266		833
267	sub join {	834	sub join {
268	my $self = shift;	835	my $self = shift;
		836
269	unless ($self->{status}) {	837	unless ($self->{_status}) {
270	push @{$self->{join}}, $current;	838	my $current = $current;
271	&schedule;	839
		840	push @{$self->{_on_destroy}}, sub {
		841	$current->ready;
		842	undef $current;
		843	};
		844
		845	&schedule while $current;
272	}	846	}
		847
273	wantarray ? @{$self->{status}} : $self->{status}[0];	848	wantarray ? @{$self->{_status}} : $self->{_status}[0];
274	}	849	}
275		850
		851	=item $coro->on_destroy (\&cb)
		852
		853	Registers a callback that is called when this coro thread gets destroyed,
		854	that is, after it's resources have been freed but before it is joined. The
		855	callback gets passed the terminate/cancel arguments, if any, and I<must
		856	not> die, under any circumstances.
		857
		858	There can be any number of C<on_destroy> callbacks per coro, and there is
		859	no way currently to remove a callback once added.
		860
		861	=cut
		862
		863	sub on_destroy {
		864	my ($self, $cb) = @_;
		865
		866	push @{ $self->{_on_destroy} }, $cb;
		867	}
		868
276	=item $oldprio = $process->prio($newprio)	869	=item $oldprio = $coro->prio ($newprio)
277		870
278	Sets (or gets, if the argument is missing) the priority of the	871	Sets (or gets, if the argument is missing) the priority of the
279	process. Higher priority processes get run before lower priority	872	coro thread. Higher priority coro get run before lower priority
280	processes. Priorities are small signed integers (currently -4 .. +3),	873	coros. Priorities are small signed integers (currently -4 .. +3),
281	that you can refer to using PRIO_xxx constants (use the import tag :prio	874	that you can refer to using PRIO_xxx constants (use the import tag :prio
282	to get then):	875	to get then):
283		876
284	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	877	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
285	3 > 1 > 0 > -1 > -3 > -4	878	3 > 1 > 0 > -1 > -3 > -4
286		879
287	# set priority to HIGH	880	# set priority to HIGH
288	current->prio(PRIO_HIGH);	881	current->prio (PRIO_HIGH);
289		882
290	The idle coroutine ($Coro::idle) always has a lower priority than any	883	The idle coro thread ($Coro::idle) always has a lower priority than any
291	existing coroutine.	884	existing coro.
292		885
293	Changing the priority of the current process will take effect immediately,	886	Changing the priority of the current coro will take effect immediately,
294	but changing the priority of processes in the ready queue (but not	887	but changing the priority of a coro in the ready queue (but not running)
295	running) will only take effect after the next schedule (of that	888	will only take effect after the next schedule (of that coro). This is a
296	process). This is a bug that will be fixed in some future version.	889	bug that will be fixed in some future version.
297		890
298	=cut
299
300	sub prio {
301	my $old = $_[0]{prio};
302	$_[0]{prio} = $_[1] if @_ > 1;
303	$old;
304	}
305
306	=item $newprio = $process->nice($change)	891	=item $newprio = $coro->nice ($change)
307		892
308	Similar to C<prio>, but subtract the given value from the priority (i.e.	893	Similar to C<prio>, but subtract the given value from the priority (i.e.
309	higher values mean lower priority, just as in unix).	894	higher values mean lower priority, just as in UNIX's nice command).
310		895
311	=cut
312
313	sub nice {
314	$_[0]{prio} -= $_[1];
315	}
316
317	=item $olddesc = $process->desc($newdesc)	896	=item $olddesc = $coro->desc ($newdesc)
318		897
319	Sets (or gets in case the argument is missing) the description for this	898	Sets (or gets in case the argument is missing) the description for this
320	process. This is just a free-form string you can associate with a process.	899	coro thread. This is just a free-form string you can associate with a
		900	coro.
		901
		902	This method simply sets the C<< $coro->{desc} >> member to the given
		903	string. You can modify this member directly if you wish, and in fact, this
		904	is often preferred to indicate major processing states that cna then be
		905	seen for example in a L<Coro::Debug> session:
		906
		907	sub my_long_function {
		908	local $Coro::current->{desc} = "now in my_long_function";
		909	...
		910	$Coro::current->{desc} = "my_long_function: phase 1";
		911	...
		912	$Coro::current->{desc} = "my_long_function: phase 2";
		913	...
		914	}
321		915
322	=cut	916	=cut
323		917
324	sub desc {	918	sub desc {
325	my $old = $_[0]{desc};	919	my $old = $_[0]{desc};
326	$_[0]{desc} = $_[1] if @_ > 1;	920	$_[0]{desc} = $_[1] if @_ > 1;
327	$old;	921	$old;
328	}	922	}
329		923
		924	sub transfer {
		925	require Carp;
		926	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		927	}
		928
330	=back	929	=back
331		930
		931	=head1 GLOBAL FUNCTIONS
		932
		933	=over 4
		934
		935	=item Coro::nready
		936
		937	Returns the number of coro that are currently in the ready state,
		938	i.e. that can be switched to by calling C<schedule> directory or
		939	indirectly. The value C<0> means that the only runnable coro is the
		940	currently running one, so C<cede> would have no effect, and C<schedule>
		941	would cause a deadlock unless there is an idle handler that wakes up some
		942	coro.
		943
		944	=item my $guard = Coro::guard { ... }
		945
		946	This function still exists, but is deprecated. Please use the
		947	C<Guard::guard> function instead.
		948
332	=cut	949	=cut
		950
		951	BEGIN { *guard = \&Guard::guard }
		952
		953	=item unblock_sub { ... }
		954
		955	This utility function takes a BLOCK or code reference and "unblocks" it,
		956	returning a new coderef. Unblocking means that calling the new coderef
		957	will return immediately without blocking, returning nothing, while the
		958	original code ref will be called (with parameters) from within another
		959	coro.
		960
		961	The reason this function exists is that many event libraries (such as
		962	the venerable L<Event|Event> module) are not thread-safe (a weaker form
		963	of reentrancy). This means you must not block within event callbacks,
		964	otherwise you might suffer from crashes or worse. The only event library
		965	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		966	you might still run into deadlocks if all event loops are blocked).
		967
		968	Coro will try to catch you when you block in the event loop
		969	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		970	only works when you do not run your own event loop.
		971
		972	This function allows your callbacks to block by executing them in another
		973	coro where it is safe to block. One example where blocking is handy
		974	is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
		975	disk, for example.
		976
		977	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		978	creating event callbacks that want to block.
		979
		980	If your handler does not plan to block (e.g. simply sends a message to
		981	another coro, or puts some other coro into the ready queue), there is
		982	no reason to use C<unblock_sub>.
		983
		984	Note that you also need to use C<unblock_sub> for any other callbacks that
		985	are indirectly executed by any C-based event loop. For example, when you
		986	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		987	provides callbacks that are the result of some event callback, then you
		988	must not block either, or use C<unblock_sub>.
		989
		990	=cut
		991
		992	our @unblock_queue;
		993
		994	# we create a special coro because we want to cede,
		995	# to reduce pressure on the coro pool (because most callbacks
		996	# return immediately and can be reused) and because we cannot cede
		997	# inside an event callback.
		998	our $unblock_scheduler = new Coro sub {
		999	while () {
		1000	while (my $cb = pop @unblock_queue) {
		1001	&async_pool (@$cb);
		1002
		1003	# for short-lived callbacks, this reduces pressure on the coro pool
		1004	# as the chance is very high that the async_poll coro will be back
		1005	# in the idle state when cede returns
		1006	cede;
		1007	}
		1008	schedule; # sleep well
		1009	}
		1010	};
		1011	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		1012
		1013	sub unblock_sub(&) {
		1014	my $cb = shift;
		1015
		1016	sub {
		1017	unshift @unblock_queue, [$cb, @_];
		1018	$unblock_scheduler->ready;
		1019	}
		1020	}
		1021
		1022	=item $cb = rouse_cb
		1023
		1024	Create and return a "rouse callback". That's a code reference that,
		1025	when called, will remember a copy of its arguments and notify the owner
		1026	coro of the callback.
		1027
		1028	See the next function.
		1029
		1030	=item @args = rouse_wait [$cb]
		1031
		1032	Wait for the specified rouse callback (or the last one that was created in
		1033	this coro).
		1034
		1035	As soon as the callback is invoked (or when the callback was invoked
		1036	before C<rouse_wait>), it will return the arguments originally passed to
		1037	the rouse callback. In scalar context, that means you get the I<last>
		1038	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1039	statement at the end.
		1040
		1041	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		1042
		1043	=back
		1044
		1045	=cut
		1046
		1047	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1048	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1049
		1050	*{"Coro::$module\::new"} = sub {
		1051	require "Coro/$module.pm";
		1052
		1053	# some modules have their new predefined in State.xs, some don't
		1054	*{"Coro::$module\::new"} = $old
		1055	if $old;
		1056
		1057	goto &{"Coro::$module\::new"};
		1058	};
		1059	}
333		1060
334	1;	1061	1;
335		1062
		1063	=head1 HOW TO WAIT FOR A CALLBACK
		1064
		1065	It is very common for a coro to wait for some callback to be
		1066	called. This occurs naturally when you use coro in an otherwise
		1067	event-based program, or when you use event-based libraries.
		1068
		1069	These typically register a callback for some event, and call that callback
		1070	when the event occured. In a coro, however, you typically want to
		1071	just wait for the event, simplyifying things.
		1072
		1073	For example C<< AnyEvent->child >> registers a callback to be called when
		1074	a specific child has exited:
		1075
		1076	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		1077
		1078	But from within a coro, you often just want to write this:
		1079
		1080	my $status = wait_for_child $pid;
		1081
		1082	Coro offers two functions specifically designed to make this easy,
		1083	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		1084
		1085	The first function, C<rouse_cb>, generates and returns a callback that,
		1086	when invoked, will save its arguments and notify the coro that
		1087	created the callback.
		1088
		1089	The second function, C<rouse_wait>, waits for the callback to be called
		1090	(by calling C<schedule> to go to sleep) and returns the arguments
		1091	originally passed to the callback.
		1092
		1093	Using these functions, it becomes easy to write the C<wait_for_child>
		1094	function mentioned above:
		1095
		1096	sub wait_for_child($) {
		1097	my ($pid) = @_;
		1098
		1099	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		1100
		1101	my ($rpid, $rstatus) = Coro::rouse_wait;
		1102	$rstatus
		1103	}
		1104
		1105	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		1106	you can roll your own, using C<schedule>:
		1107
		1108	sub wait_for_child($) {
		1109	my ($pid) = @_;
		1110
		1111	# store the current coro in $current,
		1112	# and provide result variables for the closure passed to ->child
		1113	my $current = $Coro::current;
		1114	my ($done, $rstatus);
		1115
		1116	# pass a closure to ->child
		1117	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		1118	$rstatus = $_[1]; # remember rstatus
		1119	$done = 1; # mark $rstatus as valud
		1120	});
		1121
		1122	# wait until the closure has been called
		1123	schedule while !$done;
		1124
		1125	$rstatus
		1126	}
		1127
		1128
336	=head1 BUGS/LIMITATIONS	1129	=head1 BUGS/LIMITATIONS
337		1130
338	- you must make very sure that no coro is still active on global	1131	=over 4
339	destruction. very bad things might happen otherwise (usually segfaults).
340		1132
		1133	=item fork with pthread backend
		1134
		1135	When Coro is compiled using the pthread backend (which isn't recommended
		1136	but required on many BSDs as their libcs are completely broken), then
		1137	coro will not survive a fork. There is no known workaround except to
		1138	fix your libc and use a saner backend.
		1139
		1140	=item perl process emulation ("threads")
		1141
341	- this module is not thread-safe. You should only ever use this module	1142	This module is not perl-pseudo-thread-safe. You should only ever use this
342	from the same thread (this requirement might be losened in the future	1143	module from the first thread (this requirement might be removed in the
343	to allow per-thread schedulers, but Coro::State does not yet allow	1144	future to allow per-thread schedulers, but Coro::State does not yet allow
344	this).	1145	this). I recommend disabling thread support and using processes, as having
		1146	the windows process emulation enabled under unix roughly halves perl
		1147	performance, even when not used.
		1148
		1149	=item coro switching is not signal safe
		1150
		1151	You must not switch to another coro from within a signal handler (only
		1152	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1153	you are sure you are not interrupting a Coro function.
		1154
		1155	That means you I<MUST NOT> call any function that might "block" the
		1156	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		1157	anything that calls those. Everything else, including calling C<ready>,
		1158	works.
		1159
		1160	=back
		1161
		1162
		1163	=head1 WINDOWS PROCESS EMULATION
		1164
		1165	A great many people seem to be confused about ithreads (for example, Chip
		1166	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1167	while in the same mail making rather confused statements about perl
		1168	ithreads (for example, that memory or files would be shared), showing his
		1169	lack of understanding of this area - if it is hard to understand for Chip,
		1170	it is probably not obvious to everybody).
		1171
		1172	What follows is an ultra-condensed version of my talk about threads in
		1173	scripting languages given on the perl workshop 2009:
		1174
		1175	The so-called "ithreads" were originally implemented for two reasons:
		1176	first, to (badly) emulate unix processes on native win32 perls, and
		1177	secondly, to replace the older, real thread model ("5.005-threads").
		1178
		1179	It does that by using threads instead of OS processes. The difference
		1180	between processes and threads is that threads share memory (and other
		1181	state, such as files) between threads within a single process, while
		1182	processes do not share anything (at least not semantically). That
		1183	means that modifications done by one thread are seen by others, while
		1184	modifications by one process are not seen by other processes.
		1185
		1186	The "ithreads" work exactly like that: when creating a new ithreads
		1187	process, all state is copied (memory is copied physically, files and code
		1188	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1189	the same behaviour can be achieved by using operating system processes,
		1190	except that UNIX typically uses hardware built into the system to do this
		1191	efficiently, while the windows process emulation emulates this hardware in
		1192	software (rather efficiently, but of course it is still much slower than
		1193	dedicated hardware).
		1194
		1195	As mentioned before, loading code, modifying code, modifying data
		1196	structures and so on is only visible in the ithreads process doing the
		1197	modification, not in other ithread processes within the same OS process.
		1198
		1199	This is why "ithreads" do not implement threads for perl at all, only
		1200	processes. What makes it so bad is that on non-windows platforms, you can
		1201	actually take advantage of custom hardware for this purpose (as evidenced
		1202	by the forks module, which gives you the (i-) threads API, just much
		1203	faster).
		1204
		1205	Sharing data is in the i-threads model is done by transfering data
		1206	structures between threads using copying semantics, which is very slow -
		1207	shared data simply does not exist. Benchmarks using i-threads which are
		1208	communication-intensive show extremely bad behaviour with i-threads (in
		1209	fact, so bad that Coro, which cannot take direct advantage of multiple
		1210	CPUs, is often orders of magnitude faster because it shares data using
		1211	real threads, refer to my talk for details).
		1212
		1213	As summary, i-threads *use* threads to implement processes, while
		1214	the compatible forks module *uses* processes to emulate, uhm,
		1215	processes. I-threads slow down every perl program when enabled, and
		1216	outside of windows, serve no (or little) practical purpose, but
		1217	disadvantages every single-threaded Perl program.
		1218
		1219	This is the reason that I try to avoid the name "ithreads", as it is
		1220	misleading as it implies that it implements some kind of thread model for
		1221	perl, and prefer the name "windows process emulation", which describes the
		1222	actual use and behaviour of it much better.
345		1223
346	=head1 SEE ALSO	1224	=head1 SEE ALSO
347		1225
		1226	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		1227
		1228	Debugging: L<Coro::Debug>.
		1229
348	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.	1230	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
349		1231
350	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	1232	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		1233	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
351		1234
352	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.	1235	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
353		1236
354	Embedding: L<Coro:MakeMaker>	1237	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		1238	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		1239	L<Coro::Select>.
		1240
		1241	XS API: L<Coro::MakeMaker>.
		1242
		1243	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
355		1244
356	=head1 AUTHOR	1245	=head1 AUTHOR
357		1246
358	Marc Lehmann <schmorp@schmorp.de>	1247	Marc Lehmann <schmorp@schmorp.de>
359	http://home.schmorp.de/	1248	http://home.schmorp.de/

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