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1	NAME	1	NAME
2	Coro - coroutine process abstraction	2	Coro - the only real threads in perl
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use Coro;	5	use Coro;
6		6
7	async {	7	async {
8	# some asynchronous thread of execution	8	# some asynchronous thread of execution
9	print "2\n";	9	print "2\n";
10	cede; # yield back to main	10	cede; # yield back to main
11	print "4\n";	11	print "4\n";
12	};	12	};
13	print "1\n";	13	print "1\n";
14	cede; # yield to coroutine	14	cede; # yield to coro
15	print "3\n";	15	print "3\n";
16	cede; # and again	16	cede; # and again
17		17
18	# use locking	18	# use locking
19	my $lock = new Coro::Semaphore;	19	my $lock = new Coro::Semaphore;
20	my $locked;	20	my $locked;
21		21
22	$lock->down;	22	$lock->down;
23	$locked = 1;	23	$locked = 1;
24	$lock->up;	24	$lock->up;
25		25
26	DESCRIPTION	26	DESCRIPTION
27	This module collection manages coroutines. Coroutines are similar to	27	For a tutorial-style introduction, please read the Coro::Intro manpage.
		28	This manpage mainly contains reference information.
		29
		30	This module collection manages continuations in general, most often in
		31	the form of cooperative threads (also called coros, or simply "coro" in
		32	the documentation). They are similar to kernel threads but don't (in
28	threads but don't run in parallel at the same time even on SMP machines.	33	general) run in parallel at the same time even on SMP machines. The
29	The specific flavor of coroutine used in this module also guarantees you	34	specific flavor of thread offered by this module also guarantees you
30	that it will not switch between coroutines unless necessary, at	35	that it will not switch between threads unless necessary, at
31	easily-identified points in your program, so locking and parallel access	36	easily-identified points in your program, so locking and parallel access
32	are rarely an issue, making coroutine programming much safer than	37	are rarely an issue, making thread programming much safer and easier
33	threads programming.	38	than using other thread models.
34		39
35	(Perl, however, does not natively support real threads but instead does	40	Unlike the so-called "Perl threads" (which are not actually real threads
36	a very slow and memory-intensive emulation of processes using threads.	41	but only the windows process emulation (see section of same name for
37	This is a performance win on Windows machines, and a loss everywhere	42	more details) ported to UNIX, and as such act as processes), Coro
38	else).	43	provides a full shared address space, which makes communication between
		44	threads very easy. And coro threads are fast, too: disabling the Windows
		45	process emulation code in your perl and using Coro can easily result in
		46	a two to four times speed increase for your programs. A parallel matrix
		47	multiplication benchmark (very communication-intensive) runs over 300
		48	times faster on a single core than perls pseudo-threads on a quad core
		49	using all four cores.
39		50
		51	Coro achieves that by supporting multiple running interpreters that
		52	share data, which is especially useful to code pseudo-parallel processes
		53	and for event-based programming, such as multiple HTTP-GET requests
		54	running concurrently. See Coro::AnyEvent to learn more on how to
		55	integrate Coro into an event-based environment.
		56
40	In this module, coroutines are defined as "callchain + lexical variables	57	In this module, a thread is defined as "callchain + lexical variables +
41	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	58	some package variables + C stack), that is, a thread has its own
42	callchain, its own set of lexicals and its own set of perls most	59	callchain, its own set of lexicals and its own set of perls most
43	important global variables (see Coro::State for more configuration).	60	important global variables (see Coro::State for more configuration and
		61	background info).
44		62
		63	See also the "SEE ALSO" section at the end of this document - the Coro
		64	module family is quite large.
		65
		66	CORO THREAD LIFE CYCLE
		67	During the long and exciting (or not) life of a coro thread, it goes
		68	through a number of states:
		69
		70	1. Creation
		71	The first thing in the life of a coro thread is it's creation -
		72	obviously. The typical way to create a thread is to call the "async
		73	BLOCK" function:
		74
		75	async {
		76	# thread code goes here
		77	};
		78
		79	You can also pass arguments, which are put in @_:
		80
		81	async {
		82	print $_[1]; # prints 2
		83	} 1, 2, 3;
		84
		85	This creates a new coro thread and puts it into the ready queue,
		86	meaning it will run as soon as the CPU is free for it.
		87
		88	"async" will return a Coro object - you can store this for future
		89	reference or ignore it - a thread that is running, ready to run or
		90	waiting for some event is alive on it's own.
		91
		92	Another way to create a thread is to call the "new" constructor with
		93	a code-reference:
		94
		95	new Coro sub {
		96	# thread code goes here
		97	}, @optional_arguments;
		98
		99	This is quite similar to calling "async", but the important
		100	difference is that the new thread is not put into the ready queue,
		101	so the thread will not run until somebody puts it there. "async" is,
		102	therefore, identical to this sequence:
		103
		104	my $coro = new Coro sub {
		105	# thread code goes here
		106	};
		107	$coro->ready;
		108	return $coro;
		109
		110	2. Startup
		111	When a new coro thread is created, only a copy of the code reference
		112	and the arguments are stored, no extra memory for stacks and so on
		113	is allocated, keeping the coro thread in a low-memory state.
		114
		115	Only when it actually starts executing will all the resources be
		116	finally allocated.
		117
		118	The optional arguments specified at coro creation are available in
		119	@_, similar to function calls.
		120
		121	3. Running / Blocking
		122	A lot can happen after the coro thread has started running. Quite
		123	usually, it will not run to the end in one go (because you could use
		124	a function instead), but it will give up the CPU regularly because
		125	it waits for external events.
		126
		127	As long as a coro thread runs, its Coro object is available in the
		128	global variable $Coro::current.
		129
		130	The low-level way to give up the CPU is to call the scheduler, which
		131	selects a new coro thread to run:
		132
		133	Coro::schedule;
		134
		135	Since running threads are not in the ready queue, calling the
		136	scheduler without doing anything else will block the coro thread
		137	forever - you need to arrange either for the coro to put woken up
		138	(readied) by some other event or some other thread, or you can put
		139	it into the ready queue before scheduling:
		140
		141	# this is exactly what Coro::cede does
		142	$Coro::current->ready;
		143	Coro::schedule;
		144
		145	All the higher-level synchronisation methods (Coro::Semaphore,
		146	Coro::rouse_*...) are actually implemented via "->ready" and
		147	"Coro::schedule".
		148
		149	While the coro thread is running it also might get assigned a
		150	C-level thread, or the C-level thread might be unassigned from it,
		151	as the Coro runtime wishes. A C-level thread needs to be assigned
		152	when your perl thread calls into some C-level function and that
		153	function in turn calls perl and perl then wants to switch
		154	coroutines. This happens most often when you run an event loop and
		155	block in the callback, or when perl itself calls some function such
		156	as "AUTOLOAD" or methods via the "tie" mechanism.
		157
		158	4. Termination
		159	Many threads actually terminate after some time. There are a number
		160	of ways to terminate a coro thread, the simplest is returning from
		161	the top-level code reference:
		162
		163	async {
		164	# after returning from here, the coro thread is terminated
		165	};
		166
		167	async {
		168	return if 0.5 < rand; # terminate a little earlier, maybe
		169	print "got a chance to print this\n";
		170	# or here
		171	};
		172
		173	Any values returned from the coroutine can be recovered using
		174	"->join":
		175
		176	my $coro = async {
		177	"hello, world\n" # return a string
		178	};
		179
		180	my $hello_world = $coro->join;
		181
		182	print $hello_world;
		183
		184	Another way to terminate is to call "Coro::terminate", which at any
		185	subroutine call nesting level:
		186
		187	async {
		188	Coro::terminate "return value 1", "return value 2";
		189	};
		190
		191	Yet another way is to "->cancel" (or "->safe_cancel") the coro
		192	thread from another thread:
		193
		194	my $coro = async {
		195	exit 1;
		196	};
		197
		198	$coro->cancel; # also accepts values for ->join to retrieve
		199
		200	Cancellation can be dangerous - it's a bit like calling "exit"
		201	without actually exiting, and might leave C libraries and XS modules
		202	in a weird state. Unlike other thread implementations, however, Coro
		203	is exceptionally safe with regards to cancellation, as perl will
		204	always be in a consistent state, and for those cases where you want
		205	to do truly marvellous things with your coro while it is being
		206	cancelled - that is, make sure all cleanup code is executed from the
		207	thread being cancelled - there is even a "->safe_cancel" method.
		208
		209	So, cancelling a thread that runs in an XS event loop might not be
		210	the best idea, but any other combination that deals with perl only
		211	(cancelling when a thread is in a "tie" method or an "AUTOLOAD" for
		212	example) is safe.
		213
		214	Last not least, a coro thread object that isn't referenced is
		215	"->cancel"'ed automatically - just like other objects in Perl. This
		216	is not such a common case, however - a running thread is referencedy
		217	by $Coro::current, a thread ready to run is referenced by the ready
		218	queue, a thread waiting on a lock or semaphore is referenced by
		219	being in some wait list and so on. But a thread that isn't in any of
		220	those queues gets cancelled:
		221
		222	async {
		223	schedule; # cede to other coros, don't go into the ready queue
		224	};
		225
		226	cede;
		227	# now the async above is destroyed, as it is not referenced by anything.
		228
		229	A slightly embellished example might make it clearer:
		230
		231	async {
		232	my $guard = Guard::guard { print "destroyed\n" };
		233	schedule while 1;
		234	};
		235
		236	cede;
		237
		238	Superficially one might not expect any output - since the "async"
		239	implements an endless loop, the $guard will not be cleaned up.
		240	However, since the thread object returned by "async" is not stored
		241	anywhere, the thread is initially referenced because it is in the
		242	ready queue, when it runs it is referenced by $Coro::current, but
		243	when it calls "schedule", it gets "cancel"ed causing the guard
		244	object to be destroyed (see the next section), and printing it's
		245	message.
		246
		247	If this seems a bit drastic, remember that this only happens when
		248	nothing references the thread anymore, which means there is no way
		249	to further execute it, ever. The only options at this point are
		250	leaking the thread, or cleaning it up, which brings us to...
		251
		252	5. Cleanup
		253	Threads will allocate various resources. Most but not all will be
		254	returned when a thread terminates, during clean-up.
		255
		256	Cleanup is quite similar to throwing an uncaught exception: perl
		257	will work it's way up through all subroutine calls and blocks. On
		258	it's way, it will release all "my" variables, undo all "local"'s and
		259	free any other resources truly local to the thread.
		260
		261	So, a common way to free resources is to keep them referenced only
		262	by my variables:
		263
		264	async {
		265	my $big_cache = new Cache ...;
		266	};
		267
		268	If there are no other references, then the $big_cache object will be
		269	freed when the thread terminates, regardless of how it does so.
		270
		271	What it does "NOT" do is unlock any Coro::Semaphores or similar
		272	resources, but that's where the "guard" methods come in handy:
		273
		274	my $sem = new Coro::Semaphore;
		275
		276	async {
		277	my $lock_guard = $sem->guard;
		278	# if we return, or die or get cancelled, here,
		279	# then the semaphore will be "up"ed.
		280	};
		281
		282	The "Guard::guard" function comes in handy for any custom cleanup
		283	you might want to do (but you cannot switch to other coroutines from
		284	those code blocks):
		285
		286	async {
		287	my $window = new Gtk2::Window "toplevel";
		288	# The window will not be cleaned up automatically, even when $window
		289	# gets freed, so use a guard to ensure it's destruction
		290	# in case of an error:
		291	my $window_guard = Guard::guard { $window->destroy };
		292
		293	# we are safe here
		294	};
		295
		296	Last not least, "local" can often be handy, too, e.g. when
		297	temporarily replacing the coro thread description:
		298
		299	sub myfunction {
		300	local $Coro::current->{desc} = "inside myfunction(@_)";
		301
		302	# if we return or die here, the description will be restored
		303	}
		304
		305	6. Viva La Zombie Muerte
		306	Even after a thread has terminated and cleaned up its resources, the
		307	Coro object still is there and stores the return values of the
		308	thread.
		309
		310	When there are no other references, it will simply be cleaned up and
		311	freed.
		312
		313	If there areany references, the Coro object will stay around, and
		314	you can call "->join" as many times as you wish to retrieve the
		315	result values:
		316
		317	async {
		318	print "hi\n";
		319	1
		320	};
		321
		322	# run the async above, and free everything before returning
		323	# from Coro::cede:
		324	Coro::cede;
		325
		326	{
		327	my $coro = async {
		328	print "hi\n";
		329	1
		330	};
		331
		332	# run the async above, and clean up, but do not free the coro
		333	# object:
		334	Coro::cede;
		335
		336	# optionally retrieve the result values
		337	my @results = $coro->join;
		338
		339	# now $coro goes out of scope, and presumably gets freed
		340	};
		341
		342	GLOBAL VARIABLES
45	$main	343	$Coro::main
46	This coroutine represents the main program.	344	This variable stores the Coro object that represents the main
		345	program. While you can "ready" it and do most other things you can
		346	do to coro, it is mainly useful to compare again $Coro::current, to
		347	see whether you are running in the main program or not.
47		348
48	$current (or as function: current)	349	$Coro::current
49	The current coroutine (the last coroutine switched to). The initial	350	The Coro object representing the current coro (the last coro that
50	value is $main (of course).	351	the Coro scheduler switched to). The initial value is $Coro::main
		352	(of course).
51		353
52	This variable is strictly read-only. It is provided for	354	This variable is strictly read-only. You can take copies of the
53	performance reasons. If performance is not essential you are	355	value stored in it and use it as any other Coro object, but you must
54	encouraged to use the "Coro::current" function instead.	356	not otherwise modify the variable itself.
55		357
56	$idle	358	$Coro::idle
57	A callback that is called whenever the scheduler finds no ready	359	This variable is mainly useful to integrate Coro into event loops.
58	coroutines to run. The default implementation prints "FATAL:	360	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
59	deadlock detected" and exits, because the program has no other way	361	is pretty low-level functionality.
		362
		363	This variable stores a Coro object that is put into the ready queue
		364	when there are no other ready threads (without invoking any ready
		365	hooks).
		366
		367	The default implementation dies with "FATAL: deadlock detected.",
		368	followed by a thread listing, because the program has no other way
60	to continue.	369	to continue.
61		370
62	This hook is overwritten by modules such as "Coro::Timer" and	371	This hook is overwritten by modules such as "Coro::EV" and
63	"Coro::Event" to wait on an external event that hopefully wake up a	372	"Coro::AnyEvent" to wait on an external event that hopefully wakes
64	coroutine so the scheduler can run it.	373	up a coro so the scheduler can run it.
65		374
66	Please note that if your callback recursively invokes perl (e.g. for	375	See Coro::EV or Coro::AnyEvent for examples of using this technique.
67	event handlers), then it must be prepared to be called recursively
68	itself.
69		376
70	STATIC METHODS	377	SIMPLE CORO CREATION
71	Static methods are actually functions that operate on the current
72	coroutine only.
73
74	async { ... } [@args...]	378	async { ... } [@args...]
75	Create a new asynchronous coroutine and return it's coroutine object	379	Create a new coro and return its Coro object (usually unused). The
76	(usually unused). When the sub returns the new coroutine is	380	coro will be put into the ready queue, so it will start running
77	automatically terminated.	381	automatically on the next scheduler run.
78		382
		383	The first argument is a codeblock/closure that should be executed in
		384	the coro. When it returns argument returns the coro is automatically
		385	terminated.
		386
		387	The remaining arguments are passed as arguments to the closure.
		388
79	See the "Coro::State::new" constructor for info about the coroutine	389	See the "Coro::State::new" constructor for info about the coro
80	environment in which coroutines run.	390	environment in which coro are executed.
81		391
82	Calling "exit" in a coroutine will do the same as calling exit	392	Calling "exit" in a coro will do the same as calling exit outside
83	outside the coroutine. Likewise, when the coroutine dies, the	393	the coro. Likewise, when the coro dies, the program will exit, just
84	program will exit, just as it would in the main program.	394	as it would in the main program.
85		395
		396	If you do not want that, you can provide a default "die" handler, or
		397	simply avoid dieing (by use of "eval").
		398
86	# create a new coroutine that just prints its arguments	399	Example: Create a new coro that just prints its arguments.
		400
87	async {	401	async {
88	print "@_\n";	402	print "@_\n";
89	} 1,2,3,4;	403	} 1,2,3,4;
90		404
91	async_pool { ... } [@args...]	405	async_pool { ... } [@args...]
92	Similar to "async", but uses a coroutine pool, so you should not	406	Similar to "async", but uses a coro pool, so you should not call
93	call terminate or join (although you are allowed to), and you get a	407	terminate or join on it (although you are allowed to), and you get a
94	coroutine that might have executed other code already (which can be	408	coro that might have executed other code already (which can be good
95	good or bad :).	409	or bad :).
96		410
		411	On the plus side, this function is about twice as fast as creating
		412	(and destroying) a completely new coro, so if you need a lot of
		413	generic coros in quick successsion, use "async_pool", not "async".
		414
97	Also, the block is executed in an "eval" context and a warning will	415	The code block is executed in an "eval" context and a warning will
98	be issued in case of an exception instead of terminating the	416	be issued in case of an exception instead of terminating the
99	program, as "async" does. As the coroutine is being reused, stuff	417	program, as "async" does. As the coro is being reused, stuff like
100	like "on_destroy" will not work in the expected way, unless you call	418	"on_destroy" will not work in the expected way, unless you call
101	terminate or cancel, which somehow defeats the purpose of pooling.	419	terminate or cancel, which somehow defeats the purpose of pooling
		420	(but is fine in the exceptional case).
102		421
103	The priority will be reset to 0 after each job, tracing will be	422	The priority will be reset to 0 after each run, tracing will be
104	disabled, the description will be reset and the default output	423	disabled, the description will be reset and the default output
105	filehandle gets restored, so you can change alkl these. Otherwise	424	filehandle gets restored, so you can change all these. Otherwise the
106	the coroutine will be re-used "as-is": most notably if you change	425	coro will be re-used "as-is": most notably if you change other
107	other per-coroutine global stuff such as $/ you need to revert that	426	per-coro global stuff such as $/ you must needs revert that
108	change, which is most simply done by using local as in " local $/ ".	427	change, which is most simply done by using local as in: "local $/".
109		428
110	The pool size is limited to 8 idle coroutines (this can be adjusted	429	The idle pool size is limited to 8 idle coros (this can be adjusted
111	by changing $Coro::POOL_SIZE), and there can be as many non-idle	430	by changing $Coro::POOL_SIZE), but there can be as many non-idle
112	coros as required.	431	coros as required.
113		432
114	If you are concerned about pooled coroutines growing a lot because a	433	If you are concerned about pooled coros growing a lot because a
115	single "async_pool" used a lot of stackspace you can e.g.	434	single "async_pool" used a lot of stackspace you can e.g.
116	"async_pool { terminate }" once per second or so to slowly replenish	435	"async_pool { terminate }" once per second or so to slowly replenish
117	the pool. In addition to that, when the stacks used by a handler	436	the pool. In addition to that, when the stacks used by a handler
118	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will	437	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
119	also exit.	438	be destroyed.
		439
		440	STATIC METHODS
		441	Static methods are actually functions that implicitly operate on the
		442	current coro.
120		443
121	schedule	444	schedule
122	Calls the scheduler. Please note that the current coroutine will not	445	Calls the scheduler. The scheduler will find the next coro that is
123	be put into the ready queue, so calling this function usually means	446	to be run from the ready queue and switches to it. The next coro to
		447	be run is simply the one with the highest priority that is longest
		448	in its ready queue. If there is no coro ready, it will call the
		449	$Coro::idle hook.
		450
		451	Please note that the current coro will not be put into the ready
		452	queue, so calling this function usually means you will never be
124	you will never be called again unless something else (e.g. an event	453	called again unless something else (e.g. an event handler) calls
125	handler) calls ready.	454	"->ready", thus waking you up.
126		455
127	The canonical way to wait on external events is this:	456	This makes "schedule" the generic method to use to block the
		457	current coro and wait for events: first you remember the current
		458	coro in a variable, then arrange for some callback of yours to call
		459	"->ready" on that once some event happens, and last you call
		460	"schedule" to put yourself to sleep. Note that a lot of things can
		461	wake your coro up, so you need to check whether the event indeed
		462	happened, e.g. by storing the status in a variable.
128		463
		464	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
		465	callbacks.
		466
		467	cede
		468	"Cede" to other coros. This function puts the current coro into the
		469	ready queue and calls "schedule", which has the effect of giving up
		470	the current "timeslice" to other coros of the same or higher
		471	priority. Once your coro gets its turn again it will automatically
		472	be resumed.
		473
		474	This function is often called "yield" in other languages.
		475
		476	Coro::cede_notself
		477	Works like cede, but is not exported by default and will cede to
		478	any coro, regardless of priority. This is useful sometimes to
		479	ensure progress is made.
		480
		481	terminate [arg...]
		482	Terminates the current coro with the given status values (see
		483	cancel). The values will not be copied, but referenced directly.
		484
		485	Coro::on_enter BLOCK, Coro::on_leave BLOCK
		486	These function install enter and leave winders in the current scope.
		487	The enter block will be executed when on_enter is called and
		488	whenever the current coro is re-entered by the scheduler, while the
		489	leave block is executed whenever the current coro is blocked by the
		490	scheduler, and also when the containing scope is exited (by whatever
		491	means, be it exit, die, last etc.).
		492
		493	*Neither invoking the scheduler, nor exceptions, are allowed within
		494	those BLOCKs*. That means: do not even think about calling "die"
		495	without an eval, and do not even think of entering the scheduler in
		496	any way.
		497
		498	Since both BLOCKs are tied to the current scope, they will
		499	automatically be removed when the current scope exits.
		500
		501	These functions implement the same concept as "dynamic-wind" in
		502	scheme does, and are useful when you want to localise some resource
		503	to a specific coro.
		504
		505	They slow down thread switching considerably for coros that use them
		506	(about 40% for a BLOCK with a single assignment, so thread switching
		507	is still reasonably fast if the handlers are fast).
		508
		509	These functions are best understood by an example: The following
		510	function will change the current timezone to
		511	"Antarctica/South_Pole", which requires a call to "tzset", but by
		512	using "on_enter" and "on_leave", which remember/change the current
		513	timezone and restore the previous value, respectively, the timezone
		514	is only changed for the coro that installed those handlers.
		515
		516	use POSIX qw(tzset);
		517
129	{	518	async {
130	# remember current coroutine	519	my $old_tz; # store outside TZ value here
131	my $current = $Coro::current;
132		520
133	# register a hypothetical event handler	521	Coro::on_enter {
134	on_event_invoke sub {	522	$old_tz = $ENV{TZ}; # remember the old value
135	# wake up sleeping coroutine	523
136	$current->ready;	524	$ENV{TZ} = "Antarctica/South_Pole";
137	undef $current;	525	tzset; # enable new value
138	};	526	};
139		527
140	# call schedule until event occurred.	528	Coro::on_leave {
141	# in case we are woken up for other reasons	529	$ENV{TZ} = $old_tz;
142	# (current still defined), loop.	530	tzset; # restore old value
143	Coro::schedule while $current;	531	};
		532
		533	# at this place, the timezone is Antarctica/South_Pole,
		534	# without disturbing the TZ of any other coro.
		535	};
		536
		537	This can be used to localise about any resource (locale, uid,
		538	current working directory etc.) to a block, despite the existance of
		539	other coros.
		540
		541	Another interesting example implements time-sliced multitasking
		542	using interval timers (this could obviously be optimised, but does
		543	the job):
		544
		545	# "timeslice" the given block
		546	sub timeslice(&) {
		547	use Time::HiRes ();
		548
		549	Coro::on_enter {
		550	# on entering the thread, we set an VTALRM handler to cede
		551	$SIG{VTALRM} = sub { cede };
		552	# and then start the interval timer
		553	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		554	};
		555	Coro::on_leave {
		556	# on leaving the thread, we stop the interval timer again
		557	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		558	};
		559
		560	&{+shift};
		561	}
		562
		563	# use like this:
		564	timeslice {
		565	# The following is an endless loop that would normally
		566	# monopolise the process. Since it runs in a timesliced
		567	# environment, it will regularly cede to other threads.
		568	while () { }
		569	};
		570
		571	killall
		572	Kills/terminates/cancels all coros except the currently running one.
		573
		574	Note that while this will try to free some of the main interpreter
		575	resources if the calling coro isn't the main coro, but one cannot
		576	free all of them, so if a coro that is not the main coro calls this
		577	function, there will be some one-time resource leak.
		578
		579	CORO OBJECT METHODS
		580	These are the methods you can call on coro objects (or to create them).
		581
		582	new Coro \&sub [, @args...]
		583	Create a new coro and return it. When the sub returns, the coro
		584	automatically terminates as if "terminate" with the returned values
		585	were called. To make the coro run you must first put it into the
		586	ready queue by calling the ready method.
		587
		588	See "async" and "Coro::State::new" for additional info about the
		589	coro environment.
		590
		591	$success = $coro->ready
		592	Put the given coro into the end of its ready queue (there is one
		593	queue for each priority) and return true. If the coro is already in
		594	the ready queue, do nothing and return false.
		595
		596	This ensures that the scheduler will resume this coro automatically
		597	once all the coro of higher priority and all coro of the same
		598	priority that were put into the ready queue earlier have been
		599	resumed.
		600
		601	$coro->suspend
		602	Suspends the specified coro. A suspended coro works just like any
		603	other coro, except that the scheduler will not select a suspended
		604	coro for execution.
		605
		606	Suspending a coro can be useful when you want to keep the coro from
		607	running, but you don't want to destroy it, or when you want to
		608	temporarily freeze a coro (e.g. for debugging) to resume it later.
		609
		610	A scenario for the former would be to suspend all (other) coros
		611	after a fork and keep them alive, so their destructors aren't
		612	called, but new coros can be created.
		613
		614	$coro->resume
		615	If the specified coro was suspended, it will be resumed. Note that
		616	when the coro was in the ready queue when it was suspended, it might
		617	have been unreadied by the scheduler, so an activation might have
		618	been lost.
		619
		620	To avoid this, it is best to put a suspended coro into the ready
		621	queue unconditionally, as every synchronisation mechanism must
		622	protect itself against spurious wakeups, and the one in the Coro
		623	family certainly do that.
		624
		625	$state->is_new
		626	Returns true iff this Coro object is "new", i.e. has never been run
		627	yet. Those states basically consist of only the code reference to
		628	call and the arguments, but consumes very little other resources.
		629	New states will automatically get assigned a perl interpreter when
		630	they are transfered to.
		631
		632	$state->is_zombie
		633	Returns true iff the Coro object has been cancelled, i.e. it's
		634	resources freed because they were "cancel"'ed, "terminate"'d,
		635	"safe_cancel"'ed or simply went out of scope.
		636
		637	The name "zombie" stems from UNIX culture, where a process that has
		638	exited and only stores and exit status and no other resources is
		639	called a "zombie".
		640
		641	$is_ready = $coro->is_ready
		642	Returns true iff the Coro object is in the ready queue. Unless the
		643	Coro object gets destroyed, it will eventually be scheduled by the
		644	scheduler.
		645
		646	$is_running = $coro->is_running
		647	Returns true iff the Coro object is currently running. Only one Coro
		648	object can ever be in the running state (but it currently is
		649	possible to have multiple running Coro::States).
		650
		651	$is_suspended = $coro->is_suspended
		652	Returns true iff this Coro object has been suspended. Suspended
		653	Coros will not ever be scheduled.
		654
		655	$coro->cancel (arg...)
		656	Terminates the given Coro thread and makes it return the given
		657	arguments as status (default: an empty list). Never returns if the
		658	Coro is the current Coro.
		659
		660	This is a rather brutal way to free a coro, with some limitations -
		661	if the thread is inside a C callback that doesn't expect to be
		662	canceled, bad things can happen, or if the cancelled thread insists
		663	on running complicated cleanup handlers that rely on its thread
		664	context, things will not work.
		665
		666	Any cleanup code being run (e.g. from "guard" blocks) will be run
		667	without a thread context, and is not allowed to switch to other
		668	threads. On the plus side, "->cancel" will always clean up the
		669	thread, no matter what. If your cleanup code is complex or you want
		670	to avoid cancelling a C-thread that doesn't know how to clean up
		671	itself, it can be better to "->throw" an exception, or use
		672	"->safe_cancel".
		673
		674	The arguments to "->cancel" are not copied, but instead will be
		675	referenced directly (e.g. if you pass $var and after the call change
		676	that variable, then you might change the return values passed to
		677	e.g. "join", so don't do that).
		678
		679	The resources of the Coro are usually freed (or destructed) before
		680	this call returns, but this can be delayed for an indefinite amount
		681	of time, as in some cases the manager thread has to run first to
		682	actually destruct the Coro object.
		683
		684	$coro->safe_cancel ($arg...)
		685	Works mostly like "->cancel", but is inherently "safer", and
		686	consequently, can fail with an exception in cases the thread is not
		687	in a cancellable state.
		688
		689	This method works a bit like throwing an exception that cannot be
		690	caught - specifically, it will clean up the thread from within
		691	itself, so all cleanup handlers (e.g. "guard" blocks) are run with
		692	full thread context and can block if they wish. The downside is that
		693	there is no guarantee that the thread can be cancelled when you call
		694	this method, and therefore, it might fail. It is also considerably
		695	slower than "cancel" or "terminate".
		696
		697	A thread is in a safe-cancellable state if it either hasn't been run
		698	yet, or it has no C context attached and is inside an SLF function.
		699
		700	The latter two basically mean that the thread isn't currently inside
		701	a perl callback called from some C function (usually via some XS
		702	modules) and isn't currently executing inside some C function itself
		703	(via Coro's XS API).
		704
		705	This call returns true when it could cancel the thread, or croaks
		706	with an error otherwise (i.e. it either returns true or doesn't
		707	return at all).
		708
		709	Why the weird interface? Well, there are two common models on how
		710	and when to cancel things. In the first, you have the expectation
		711	that your coro thread can be cancelled when you want to cancel it -
		712	if the thread isn't cancellable, this would be a bug somewhere, so
		713	"->safe_cancel" croaks to notify of the bug.
		714
		715	In the second model you sometimes want to ask nicely to cancel a
		716	thread, but if it's not a good time, well, then don't cancel. This
		717	can be done relatively easy like this:
		718
		719	if (! eval { $coro->safe_cancel }) {
		720	warn "unable to cancel thread: $@";
144	}	721	}
145		722
146	cede	723	However, what you never should do is first try to cancel "safely"
147	"Cede" to other coroutines. This function puts the current coroutine	724	and if that fails, cancel the "hard" way with "->cancel". That makes
148	into the ready queue and calls "schedule", which has the effect of	725	no sense: either you rely on being able to execute cleanup code in
149	giving up the current "timeslice" to other coroutines of the same or	726	your thread context, or you don't. If you do, then "->safe_cancel"
150	higher priority.	727	is the only way, and if you don't, then "->cancel" is always faster
		728	and more direct.
151		729
152	Coro::cede_notself	730	$coro->schedule_to
153	Works like cede, but is not exported by default and will cede to any	731	Puts the current coro to sleep (like "Coro::schedule"), but instead
154	coroutine, regardless of priority, once.	732	of continuing with the next coro from the ready queue, always switch
		733	to the given coro object (regardless of priority etc.). The
		734	readyness state of that coro isn't changed.
155		735
156	terminate [arg...]	736	This is an advanced method for special cases - I'd love to hear
157	Terminates the current coroutine with the given status values (see	737	about any uses for this one.
158	cancel).
159		738
160	killall	739	$coro->cede_to
161	Kills/terminates/cancels all coroutines except the currently running	740	Like "schedule_to", but puts the current coro into the ready queue.
162	one. This is useful after a fork, either in the child or the parent,	741	This has the effect of temporarily switching to the given coro, and
163	as usually only one of them should inherit the running coroutines.	742	continuing some time later.
164		743
165	# dynamic methods	744	This is an advanced method for special cases - I'd love to hear
		745	about any uses for this one.
166		746
167	COROUTINE METHODS
168	These are the methods you can call on coroutine objects.
169
170	new Coro \&sub [, @args...]
171	Create a new coroutine and return it. When the sub returns the
172	coroutine automatically terminates as if "terminate" with the
173	returned values were called. To make the coroutine run you must
174	first put it into the ready queue by calling the ready method.
175
176	See "async" and "Coro::State::new" for additional info about the
177	coroutine environment.
178
179	$success = $coroutine->ready
180	Put the given coroutine into the ready queue (according to it's
181	priority) and return true. If the coroutine is already in the ready
182	queue, do nothing and return false.
183
184	$is_ready = $coroutine->is_ready
185	Return wether the coroutine is currently the ready queue or not,
186
187	$coroutine->cancel (arg...)
188	Terminates the given coroutine and makes it return the given
189	arguments as status (default: the empty list). Never returns if the
190	coroutine is the current coroutine.
191
192	$coroutine->join
193	Wait until the coroutine terminates and return any values given to
194	the "terminate" or "cancel" functions. "join" can be called
195	concurrently from multiple coroutines.
196
197	$coroutine->on_destroy (\&cb)
198	Registers a callback that is called when this coroutine gets
199	destroyed, but before it is joined. The callback gets passed the
200	terminate arguments, if any.
201
202	$oldprio = $coroutine->prio ($newprio)
203	Sets (or gets, if the argument is missing) the priority of the
204	coroutine. Higher priority coroutines get run before lower priority
205	coroutines. Priorities are small signed integers (currently -4 ..
206	+3), that you can refer to using PRIO_xxx constants (use the import
207	tag :prio to get then):
208
209	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
210	3 > 1 > 0 > -1 > -3 > -4
211
212	# set priority to HIGH
213	current->prio(PRIO_HIGH);
214
215	The idle coroutine ($Coro::idle) always has a lower priority than
216	any existing coroutine.
217
218	Changing the priority of the current coroutine will take effect
219	immediately, but changing the priority of coroutines in the ready
220	queue (but not running) will only take effect after the next
221	schedule (of that coroutine). This is a bug that will be fixed in
222	some future version.
223
224	$newprio = $coroutine->nice ($change)
225	Similar to "prio", but subtract the given value from the priority
226	(i.e. higher values mean lower priority, just as in unix).
227
228	$olddesc = $coroutine->desc ($newdesc)
229	Sets (or gets in case the argument is missing) the description for
230	this coroutine. This is just a free-form string you can associate
231	with a coroutine.
232
233	This method simply sets the "$coroutine->{desc}" member to the given
234	string. You can modify this member directly if you wish.
235
236	$coroutine->throw ([$scalar])	747	$coro->throw ([$scalar])
237	If $throw is specified and defined, it will be thrown as an	748	If $throw is specified and defined, it will be thrown as an
238	exception inside the coroutine at the next convinient point in time	749	exception inside the coro at the next convenient point in time.
239	(usually after it gains control at the next schedule/transfer/cede).
240	Otherwise clears the exception object.	750	Otherwise clears the exception object.
		751
		752	Coro will check for the exception each time a schedule-like-function
		753	returns, i.e. after each "schedule", "cede",
		754	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
		755	those functions (all that are part of Coro itself) detect this case
		756	and return early in case an exception is pending.
241		757
242	The exception object will be thrown "as is" with the specified	758	The exception object will be thrown "as is" with the specified
243	scalar in $@, i.e. if it is a string, no line number or newline will	759	scalar in $@, i.e. if it is a string, no line number or newline will
244	be appended (unlike with "die").	760	be appended (unlike with "die").
245		761
246	This can be used as a softer means than "cancel" to ask a coroutine	762	This can be used as a softer means than either "cancel" or
247	to end itself, although there is no guarentee that the exception	763	"safe_cancel "to ask a coro to end itself, although there is no
248	will lead to termination, and if the exception isn't caught it might	764	guarantee that the exception will lead to termination, and if the
249	well end the whole program.	765	exception isn't caught it might well end the whole program.
250		766
		767	You might also think of "throw" as being the moral equivalent of
		768	"kill"ing a coro with a signal (in this case, a scalar).
		769
		770	$coro->join
		771	Wait until the coro terminates and return any values given to the
		772	"terminate" or "cancel" functions. "join" can be called concurrently
		773	from multiple threads, and all will be resumed and given the status
		774	return once the $coro terminates.
		775
		776	$coro->on_destroy (\&cb)
		777	Registers a callback that is called when this coro thread gets
		778	destroyed, that is, after it's resources have been freed but before
		779	it is joined. The callback gets passed the terminate/cancel
		780	arguments, if any, and must not die, under any circumstances.
		781
		782	There can be any number of "on_destroy" callbacks per coro, and
		783	there is no way currently to remove a callback once added.
		784
		785	$oldprio = $coro->prio ($newprio)
		786	Sets (or gets, if the argument is missing) the priority of the coro
		787	thread. Higher priority coro get run before lower priority coros.
		788	Priorities are small signed integers (currently -4 .. +3), that you
		789	can refer to using PRIO_xxx constants (use the import tag :prio to
		790	get then):
		791
		792	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		793	3 > 1 > 0 > -1 > -3 > -4
		794
		795	# set priority to HIGH
		796	current->prio (PRIO_HIGH);
		797
		798	The idle coro thread ($Coro::idle) always has a lower priority than
		799	any existing coro.
		800
		801	Changing the priority of the current coro will take effect
		802	immediately, but changing the priority of a coro in the ready queue
		803	(but not running) will only take effect after the next schedule (of
		804	that coro). This is a bug that will be fixed in some future version.
		805
		806	$newprio = $coro->nice ($change)
		807	Similar to "prio", but subtract the given value from the priority
		808	(i.e. higher values mean lower priority, just as in UNIX's nice
		809	command).
		810
		811	$olddesc = $coro->desc ($newdesc)
		812	Sets (or gets in case the argument is missing) the description for
		813	this coro thread. This is just a free-form string you can associate
		814	with a coro.
		815
		816	This method simply sets the "$coro->{desc}" member to the given
		817	string. You can modify this member directly if you wish, and in
		818	fact, this is often preferred to indicate major processing states
		819	that can then be seen for example in a Coro::Debug session:
		820
		821	sub my_long_function {
		822	local $Coro::current->{desc} = "now in my_long_function";
		823	...
		824	$Coro::current->{desc} = "my_long_function: phase 1";
		825	...
		826	$Coro::current->{desc} = "my_long_function: phase 2";
		827	...
		828	}
		829
251	GLOBAL FUNCTIONS	830	GLOBAL FUNCTIONS
252	Coro::nready	831	Coro::nready
253	Returns the number of coroutines that are currently in the ready	832	Returns the number of coro that are currently in the ready state,
254	state, i.e. that can be switched to. The value 0 means that the only	833	i.e. that can be switched to by calling "schedule" directory or
255	runnable coroutine is the currently running one, so "cede" would	834	indirectly. The value 0 means that the only runnable coro is the
256	have no effect, and "schedule" would cause a deadlock unless there	835	currently running one, so "cede" would have no effect, and
257	is an idle handler that wakes up some coroutines.	836	"schedule" would cause a deadlock unless there is an idle handler
		837	that wakes up some coro.
258		838
259	my $guard = Coro::guard { ... }	839	my $guard = Coro::guard { ... }
260	This creates and returns a guard object. Nothing happens until the	840	This function still exists, but is deprecated. Please use the
261	object gets destroyed, in which case the codeblock given as argument	841	"Guard::guard" function instead.
262	will be executed. This is useful to free locks or other resources in
263	case of a runtime error or when the coroutine gets canceled, as in
264	both cases the guard block will be executed. The guard object
265	supports only one method, "->cancel", which will keep the codeblock
266	from being executed.
267
268	Example: set some flag and clear it again when the coroutine gets
269	canceled or the function returns:
270
271	sub do_something {
272	my $guard = Coro::guard { $busy = 0 };
273	$busy = 1;
274
275	# do something that requires $busy to be true
276	}
277		842
278	unblock_sub { ... }	843	unblock_sub { ... }
279	This utility function takes a BLOCK or code reference and "unblocks"	844	This utility function takes a BLOCK or code reference and "unblocks"
280	it, returning the new coderef. This means that the new coderef will	845	it, returning a new coderef. Unblocking means that calling the new
281	return immediately without blocking, returning nothing, while the	846	coderef will return immediately without blocking, returning nothing,
282	original code ref will be called (with parameters) from within its	847	while the original code ref will be called (with parameters) from
283	own coroutine.	848	within another coro.
284		849
285	The reason this function exists is that many event libraries (such	850	The reason this function exists is that many event libraries (such
286	as the venerable Event module) are not coroutine-safe (a weaker form	851	as the venerable Event module) are not thread-safe (a weaker form of
287	of thread-safety). This means you must not block within event	852	reentrancy). This means you must not block within event callbacks,
288	callbacks, otherwise you might suffer from crashes or worse.	853	otherwise you might suffer from crashes or worse. The only event
		854	library currently known that is safe to use without "unblock_sub" is
		855	EV (but you might still run into deadlocks if all event loops are
		856	blocked).
		857
		858	Coro will try to catch you when you block in the event loop
		859	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		860	and only works when you do not run your own event loop.
289		861
290	This function allows your callbacks to block by executing them in	862	This function allows your callbacks to block by executing them in
291	another coroutine where it is safe to block. One example where	863	another coro where it is safe to block. One example where blocking
292	blocking is handy is when you use the Coro::AIO functions to save	864	is handy is when you use the Coro::AIO functions to save results to
293	results to disk.	865	disk, for example.
294		866
295	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	867	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
296	when creating event callbacks that want to block.	868	when creating event callbacks that want to block.
297		869
		870	If your handler does not plan to block (e.g. simply sends a message
		871	to another coro, or puts some other coro into the ready queue),
		872	there is no reason to use "unblock_sub".
		873
		874	Note that you also need to use "unblock_sub" for any other callbacks
		875	that are indirectly executed by any C-based event loop. For example,
		876	when you use a module that uses AnyEvent (and you use
		877	Coro::AnyEvent) and it provides callbacks that are the result of
		878	some event callback, then you must not block either, or use
		879	"unblock_sub".
		880
		881	$cb = rouse_cb
		882	Create and return a "rouse callback". That's a code reference that,
		883	when called, will remember a copy of its arguments and notify the
		884	owner coro of the callback.
		885
		886	See the next function.
		887
		888	@args = rouse_wait [$cb]
		889	Wait for the specified rouse callback (or the last one that was
		890	created in this coro).
		891
		892	As soon as the callback is invoked (or when the callback was invoked
		893	before "rouse_wait"), it will return the arguments originally passed
		894	to the rouse callback. In scalar context, that means you get the
		895	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		896	$a3...)" statement at the end.
		897
		898	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
		899	example.
		900
		901	HOW TO WAIT FOR A CALLBACK
		902	It is very common for a coro to wait for some callback to be called.
		903	This occurs naturally when you use coro in an otherwise event-based
		904	program, or when you use event-based libraries.
		905
		906	These typically register a callback for some event, and call that
		907	callback when the event occured. In a coro, however, you typically want
		908	to just wait for the event, simplyifying things.
		909
		910	For example "AnyEvent->child" registers a callback to be called when a
		911	specific child has exited:
		912
		913	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		914
		915	But from within a coro, you often just want to write this:
		916
		917	my $status = wait_for_child $pid;
		918
		919	Coro offers two functions specifically designed to make this easy,
		920	"rouse_cb" and "rouse_wait".
		921
		922	The first function, "rouse_cb", generates and returns a callback that,
		923	when invoked, will save its arguments and notify the coro that created
		924	the callback.
		925
		926	The second function, "rouse_wait", waits for the callback to be called
		927	(by calling "schedule" to go to sleep) and returns the arguments
		928	originally passed to the callback.
		929
		930	Using these functions, it becomes easy to write the "wait_for_child"
		931	function mentioned above:
		932
		933	sub wait_for_child($) {
		934	my ($pid) = @_;
		935
		936	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
		937
		938	my ($rpid, $rstatus) = rouse_wait;
		939	$rstatus
		940	}
		941
		942	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
		943	you can roll your own, using "schedule" and "ready":
		944
		945	sub wait_for_child($) {
		946	my ($pid) = @_;
		947
		948	# store the current coro in $current,
		949	# and provide result variables for the closure passed to ->child
		950	my $current = $Coro::current;
		951	my ($done, $rstatus);
		952
		953	# pass a closure to ->child
		954	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		955	$rstatus = $_[1]; # remember rstatus
		956	$done = 1; # mark $rstatus as valid
		957	$current->ready; # wake up the waiting thread
		958	});
		959
		960	# wait until the closure has been called
		961	schedule while !$done;
		962
		963	$rstatus
		964	}
		965
298	BUGS/LIMITATIONS	966	BUGS/LIMITATIONS
299	- you must make very sure that no coro is still active on global	967	fork with pthread backend
300	destruction. very bad things might happen otherwise (usually segfaults).	968	When Coro is compiled using the pthread backend (which isn't
		969	recommended but required on many BSDs as their libcs are completely
		970	broken), then coro will not survive a fork. There is no known
		971	workaround except to fix your libc and use a saner backend.
301		972
		973	perl process emulation ("threads")
302	- this module is not thread-safe. You should only ever use this module	974	This module is not perl-pseudo-thread-safe. You should only ever use
303	from the same thread (this requirement might be loosened in the future	975	this module from the first thread (this requirement might be removed
304	to allow per-thread schedulers, but Coro::State does not yet allow	976	in the future to allow per-thread schedulers, but Coro::State does
305	this).	977	not yet allow this). I recommend disabling thread support and using
		978	processes, as having the windows process emulation enabled under
		979	unix roughly halves perl performance, even when not used.
		980
		981	Attempts to use threads created in another emulated process will
		982	crash ("cleanly", with a null pointer exception).
		983
		984	coro switching is not signal safe
		985	You must not switch to another coro from within a signal handler
		986	(only relevant with %SIG - most event libraries provide safe
		987	signals), unless you are sure you are not interrupting a Coro
		988	function.
		989
		990	That means you MUST NOT call any function that might "block" the
		991	current coro - "cede", "schedule" "Coro::Semaphore->down" or
		992	anything that calls those. Everything else, including calling
		993	"ready", works.
		994
		995	WINDOWS PROCESS EMULATION
		996	A great many people seem to be confused about ithreads (for example,
		997	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		998	while in the same mail making rather confused statements about perl
		999	ithreads (for example, that memory or files would be shared), showing
		1000	his lack of understanding of this area - if it is hard to understand for
		1001	Chip, it is probably not obvious to everybody).
		1002
		1003	What follows is an ultra-condensed version of my talk about threads in
		1004	scripting languages given on the perl workshop 2009:
		1005
		1006	The so-called "ithreads" were originally implemented for two reasons:
		1007	first, to (badly) emulate unix processes on native win32 perls, and
		1008	secondly, to replace the older, real thread model ("5.005-threads").
		1009
		1010	It does that by using threads instead of OS processes. The difference
		1011	between processes and threads is that threads share memory (and other
		1012	state, such as files) between threads within a single process, while
		1013	processes do not share anything (at least not semantically). That means
		1014	that modifications done by one thread are seen by others, while
		1015	modifications by one process are not seen by other processes.
		1016
		1017	The "ithreads" work exactly like that: when creating a new ithreads
		1018	process, all state is copied (memory is copied physically, files and
		1019	code is copied logically). Afterwards, it isolates all modifications. On
		1020	UNIX, the same behaviour can be achieved by using operating system
		1021	processes, except that UNIX typically uses hardware built into the
		1022	system to do this efficiently, while the windows process emulation
		1023	emulates this hardware in software (rather efficiently, but of course it
		1024	is still much slower than dedicated hardware).
		1025
		1026	As mentioned before, loading code, modifying code, modifying data
		1027	structures and so on is only visible in the ithreads process doing the
		1028	modification, not in other ithread processes within the same OS process.
		1029
		1030	This is why "ithreads" do not implement threads for perl at all, only
		1031	processes. What makes it so bad is that on non-windows platforms, you
		1032	can actually take advantage of custom hardware for this purpose (as
		1033	evidenced by the forks module, which gives you the (i-) threads API,
		1034	just much faster).
		1035
		1036	Sharing data is in the i-threads model is done by transfering data
		1037	structures between threads using copying semantics, which is very slow -
		1038	shared data simply does not exist. Benchmarks using i-threads which are
		1039	communication-intensive show extremely bad behaviour with i-threads (in
		1040	fact, so bad that Coro, which cannot take direct advantage of multiple
		1041	CPUs, is often orders of magnitude faster because it shares data using
		1042	real threads, refer to my talk for details).
		1043
		1044	As summary, i-threads use threads to implement processes, while the
		1045	compatible forks module uses processes to emulate, uhm, processes.
		1046	I-threads slow down every perl program when enabled, and outside of
		1047	windows, serve no (or little) practical purpose, but disadvantages every
		1048	single-threaded Perl program.
		1049
		1050	This is the reason that I try to avoid the name "ithreads", as it is
		1051	misleading as it implies that it implements some kind of thread model
		1052	for perl, and prefer the name "windows process emulation", which
		1053	describes the actual use and behaviour of it much better.
306		1054
307	SEE ALSO	1055	SEE ALSO
308	Lower level Configuration, Coroutine Environment: Coro::State.	1056	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
309		1057
310	Debugging: Coro::Debug.	1058	Debugging: Coro::Debug.
311		1059
312	Support/Utility: Coro::Specific, Coro::Util.	1060	Support/Utility: Coro::Specific, Coro::Util.
313		1061
314	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	1062	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
315	Coro::SemaphoreSet, Coro::RWLock.	1063	Coro::SemaphoreSet, Coro::RWLock.
316		1064
317	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket.	1065	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
318		1066
319	Compatibility: Coro::LWP, Coro::Storable, Coro::Select.	1067	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		1068	for a better-working alternative), Coro::BDB, Coro::Storable,
		1069	Coro::Select.
320		1070
321	Embedding: Coro::MakeMaker.	1071	XS API: Coro::MakeMaker.
		1072
		1073	Low level Configuration, Thread Environment, Continuations: Coro::State.
322		1074
323	AUTHOR	1075	AUTHOR
324	Marc Lehmann <schmorp@schmorp.de>	1076	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	1077	http://home.schmorp.de/
326		1078

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