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Revision 1.26 by root, Sun Oct 4 12:55:21 2009 UTC

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";
		10	cede; # yield back to main
		11	print "4\n";
9	};	12	};
10		13	print "1\n";
11	# alternatively create an async process like this:	14	cede; # yield to coro
12		15	print "3\n";
13	sub some_func : Coro {	16	cede; # and again
14	# some more async code	17
15	}	18	# use locking
16		19	use Coro::Semaphore;
17	cede;	20	my $lock = new Coro::Semaphore;
		21	my $locked;
		22
		23	$lock->down;
		24	$locked = 1;
		25	$lock->up;
18		26
19	DESCRIPTION	27	DESCRIPTION
20	This module collection manages coroutines. Coroutines are similar to	28	For a tutorial-style introduction, please read the Coro::Intro manpage.
21	threads but don't run in parallel.	29	This manpage mainly contains reference information.
22		30
		31	This module collection manages continuations in general, most often in
		32	the form of cooperative threads (also called coros, or simply "coro" in
		33	the documentation). They are similar to kernel threads but don't (in
		34	general) run in parallel at the same time even on SMP machines. The
		35	specific flavor of thread offered by this module also guarantees you
		36	that it will not switch between threads unless necessary, at
		37	easily-identified points in your program, so locking and parallel access
		38	are rarely an issue, making thread programming much safer and easier
		39	than using other thread models.
		40
		41	Unlike the so-called "Perl threads" (which are not actually real threads
		42	but only the windows process emulation (see section of same name for
		43	more details) ported to unix, and as such act as processes), Coro
		44	provides a full shared address space, which makes communication between
		45	threads very easy. And Coro's threads are fast, too: disabling the
		46	Windows process emulation code in your perl and using Coro can easily
		47	result in a two to four times speed increase for your programs. A
		48	parallel matrix multiplication benchmark runs over 300 times faster on a
		49	single core than perl's pseudo-threads on a quad core using all four
		50	cores.
		51
		52	Coro achieves that by supporting multiple running interpreters that
		53	share data, which is especially useful to code pseudo-parallel processes
		54	and for event-based programming, such as multiple HTTP-GET requests
		55	running concurrently. See Coro::AnyEvent to learn more on how to
		56	integrate Coro into an event-based environment.
		57
23	In this module, coroutines are defined as "callchain + lexical variables	58	In this module, a thread is defined as "callchain + lexical variables +
24	+ @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own	59	some package variables + C stack), that is, a thread has its own
25	callchain, it's own set of lexicals and it's own set of perl's most	60	callchain, its own set of lexicals and its own set of perls most
26	important global variables.	61	important global variables (see Coro::State for more configuration and
		62	background info).
27		63
		64	See also the "SEE ALSO" section at the end of this document - the Coro
		65	module family is quite large.
		66
		67	GLOBAL VARIABLES
28	$main	68	$Coro::main
29	This coroutine represents the main program.	69	This variable stores the Coro object that represents the main
		70	program. While you cna "ready" it and do most other things you can
		71	do to coro, it is mainly useful to compare again $Coro::current, to
		72	see whether you are running in the main program or not.
30		73
31	$current (or as function: current)	74	$Coro::current
32	The current coroutine (the last coroutine switched to). The initial	75	The Coro object representing the current coro (the last coro that
33	value is $main (of course).	76	the Coro scheduler switched to). The initial value is $Coro::main
		77	(of course).
34		78
		79	This variable is strictly read-only. You can take copies of the
		80	value stored in it and use it as any other Coro object, but you must
		81	not otherwise modify the variable itself.
		82
35	$idle	83	$Coro::idle
36	The coroutine to switch to when no other coroutine is running. The	84	This variable is mainly useful to integrate Coro into event loops.
		85	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
		86	is pretty low-level functionality.
		87
		88	This variable stores a Coro object that is put into the ready queue
		89	when there are no other ready threads (without invoking any ready
		90	hooks).
		91
37	default implementation prints "FATAL: deadlock detected" and exits.	92	The default implementation dies with "FATAL: deadlock detected.",
		93	followed by a thread listing, because the program has no other way
		94	to continue.
38		95
39	STATIC METHODS	96	This hook is overwritten by modules such as "Coro::EV" and
40	Static methods are actually functions that operate on the current	97	"Coro::AnyEvent" to wait on an external event that hopefully wake up
41	process only.	98	a coro so the scheduler can run it.
42		99
		100	See Coro::EV or Coro::AnyEvent for examples of using this technique.
		101
		102	SIMPLE CORO CREATION
43	async { ... } [@args...]	103	async { ... } [@args...]
44	Create a new asynchronous process and return it's process object	104	Create a new coro and return its Coro object (usually unused). The
45	(usually unused). When the sub returns the new process is	105	coro will be put into the ready queue, so it will start running
46	automatically terminated.	106	automatically on the next scheduler run.
47		107
		108	The first argument is a codeblock/closure that should be executed in
		109	the coro. When it returns argument returns the coro is automatically
		110	terminated.
		111
		112	The remaining arguments are passed as arguments to the closure.
		113
		114	See the "Coro::State::new" constructor for info about the coro
		115	environment in which coro are executed.
		116
		117	Calling "exit" in a coro will do the same as calling exit outside
		118	the coro. Likewise, when the coro dies, the program will exit, just
		119	as it would in the main program.
		120
		121	If you do not want that, you can provide a default "die" handler, or
		122	simply avoid dieing (by use of "eval").
		123
48	# create a new coroutine that just prints its arguments	124	Example: Create a new coro that just prints its arguments.
		125
49	async {	126	async {
50	print "@_\n";	127	print "@_\n";
51	} 1,2,3,4;	128	} 1,2,3,4;
52		129
		130	async_pool { ... } [@args...]
		131	Similar to "async", but uses a coro pool, so you should not call
		132	terminate or join on it (although you are allowed to), and you get a
		133	coro that might have executed other code already (which can be good
		134	or bad :).
		135
		136	On the plus side, this function is about twice as fast as creating
		137	(and destroying) a completely new coro, so if you need a lot of
		138	generic coros in quick successsion, use "async_pool", not "async".
		139
		140	The code block is executed in an "eval" context and a warning will
		141	be issued in case of an exception instead of terminating the
		142	program, as "async" does. As the coro is being reused, stuff like
		143	"on_destroy" will not work in the expected way, unless you call
		144	terminate or cancel, which somehow defeats the purpose of pooling
		145	(but is fine in the exceptional case).
		146
		147	The priority will be reset to 0 after each run, tracing will be
		148	disabled, the description will be reset and the default output
		149	filehandle gets restored, so you can change all these. Otherwise the
		150	coro will be re-used "as-is": most notably if you change other
		151	per-coro global stuff such as $/ you must needs revert that
		152	change, which is most simply done by using local as in: "local $/".
		153
		154	The idle pool size is limited to 8 idle coros (this can be adjusted
		155	by changing $Coro::POOL_SIZE), but there can be as many non-idle
		156	coros as required.
		157
		158	If you are concerned about pooled coros growing a lot because a
		159	single "async_pool" used a lot of stackspace you can e.g.
		160	"async_pool { terminate }" once per second or so to slowly replenish
		161	the pool. In addition to that, when the stacks used by a handler
		162	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
		163	be destroyed.
		164
		165	STATIC METHODS
		166	Static methods are actually functions that implicitly operate on the
		167	current coro.
		168
53	schedule	169	schedule
54	Calls the scheduler. Please note that the current process will not	170	Calls the scheduler. The scheduler will find the next coro that is
55	be put into the ready queue, so calling this function usually means	171	to be run from the ready queue and switches to it. The next coro to
56	you will never be called again.	172	be run is simply the one with the highest priority that is longest
		173	in its ready queue. If there is no coro ready, it will call the
		174	$Coro::idle hook.
		175
		176	Please note that the current coro will not be put into the ready
		177	queue, so calling this function usually means you will never be
		178	called again unless something else (e.g. an event handler) calls
		179	"->ready", thus waking you up.
		180
		181	This makes "schedule" the generic method to use to block the
		182	current coro and wait for events: first you remember the current
		183	coro in a variable, then arrange for some callback of yours to call
		184	"->ready" on that once some event happens, and last you call
		185	"schedule" to put yourself to sleep. Note that a lot of things can
		186	wake your coro up, so you need to check whether the event indeed
		187	happened, e.g. by storing the status in a variable.
		188
		189	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
		190	callbacks.
57		191
58	cede	192	cede
59	"Cede" to other processes. This function puts the current process	193	"Cede" to other coros. This function puts the current coro into the
60	into the ready queue and calls "schedule", which has the effect of	194	ready queue and calls "schedule", which has the effect of giving up
61	giving up the current "timeslice" to other coroutines of the same or	195	the current "timeslice" to other coros of the same or higher
62	higher priority.	196	priority. Once your coro gets its turn again it will automatically
		197	be resumed.
		198
		199	This function is often called "yield" in other languages.
		200
		201	Coro::cede_notself
		202	Works like cede, but is not exported by default and will cede to
		203	any coro, regardless of priority. This is useful sometimes to
		204	ensure progress is made.
63		205
64	terminate [arg...]	206	terminate [arg...]
65	Terminates the current process with the given status values (see	207	Terminates the current coro with the given status values (see
66	cancel).	208	cancel).
67		209
68	# dynamic methods	210	Coro::on_enter BLOCK, Coro::on_leave BLOCK
		211	These function install enter and leave winders in the current scope.
		212	The enter block will be executed when on_enter is called and
		213	whenever the current coro is re-entered by the scheduler, while the
		214	leave block is executed whenever the current coro is blocked by the
		215	scheduler, and also when the containing scope is exited (by whatever
		216	means, be it exit, die, last etc.).
69		217
70	PROCESS METHODS	218	*Neither invoking the scheduler, nor exceptions, are allowed within
		219	those BLOCKs*. That means: do not even think about calling "die"
		220	without an eval, and do not even think of entering the scheduler in
		221	any way.
		222
		223	Since both BLOCKs are tied to the current scope, they will
		224	automatically be removed when the current scope exits.
		225
		226	These functions implement the same concept as "dynamic-wind" in
		227	scheme does, and are useful when you want to localise some resource
		228	to a specific coro.
		229
		230	They slow down thread switching considerably for coros that use them
		231	(about 40% for a BLOCK with a single assignment, so thread switching
		232	is still reasonably fast if the handlers are fast).
		233
		234	These functions are best understood by an example: The following
		235	function will change the current timezone to
		236	"Antarctica/South_Pole", which requires a call to "tzset", but by
		237	using "on_enter" and "on_leave", which remember/change the current
		238	timezone and restore the previous value, respectively, the timezone
		239	is only changed for the coro that installed those handlers.
		240
		241	use POSIX qw(tzset);
		242
		243	async {
		244	my $old_tz; # store outside TZ value here
		245
		246	Coro::on_enter {
		247	$old_tz = $ENV{TZ}; # remember the old value
		248
		249	$ENV{TZ} = "Antarctica/South_Pole";
		250	tzset; # enable new value
		251	};
		252
		253	Coro::on_leave {
		254	$ENV{TZ} = $old_tz;
		255	tzset; # restore old value
		256	};
		257
		258	# at this place, the timezone is Antarctica/South_Pole,
		259	# without disturbing the TZ of any other coro.
		260	};
		261
		262	This can be used to localise about any resource (locale, uid,
		263	current working directory etc.) to a block, despite the existance of
		264	other coros.
		265
		266	Another interesting example implements time-sliced multitasking
		267	using interval timers (this could obviously be optimised, but does
		268	the job):
		269
		270	# "timeslice" the given block
		271	sub timeslice(&) {
		272	use Time::HiRes ();
		273
		274	Coro::on_enter {
		275	# on entering the thread, we set an VTALRM handler to cede
		276	$SIG{VTALRM} = sub { cede };
		277	# and then start the interval timer
		278	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		279	};
		280	Coro::on_leave {
		281	# on leaving the thread, we stop the interval timer again
		282	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		283	};
		284
		285	&{+shift};
		286	}
		287
		288	# use like this:
		289	timeslice {
		290	# The following is an endless loop that would normally
		291	# monopolise the process. Since it runs in a timesliced
		292	# environment, it will regularly cede to other threads.
		293	while () { }
		294	};
		295
		296	killall
		297	Kills/terminates/cancels all coros except the currently running one.
		298
		299	Note that while this will try to free some of the main interpreter
		300	resources if the calling coro isn't the main coro, but one cannot
		301	free all of them, so if a coro that is not the main coro calls this
		302	function, there will be some one-time resource leak.
		303
		304	CORO OBJECT METHODS
71	These are the methods you can call on process objects.	305	These are the methods you can call on coro objects (or to create them).
72		306
73	new Coro \&sub [, @args...]	307	new Coro \&sub [, @args...]
74	Create a new process and return it. When the sub returns the process	308	Create a new coro and return it. When the sub returns, the coro
75	automatically terminates as if "terminate" with the returned values	309	automatically terminates as if "terminate" with the returned values
76	were called. To make the process run you must first put it into the	310	were called. To make the coro run you must first put it into the
77	ready queue by calling the ready method.	311	ready queue by calling the ready method.
78		312
79	$process->ready	313	See "async" and "Coro::State::new" for additional info about the
80	Put the given process into the ready queue.	314	coro environment.
81		315
		316	$success = $coro->ready
		317	Put the given coro into the end of its ready queue (there is one
		318	queue for each priority) and return true. If the coro is already in
		319	the ready queue, do nothing and return false.
		320
		321	This ensures that the scheduler will resume this coro automatically
		322	once all the coro of higher priority and all coro of the same
		323	priority that were put into the ready queue earlier have been
		324	resumed.
		325
		326	$coro->suspend
		327	Suspends the specified coro. A suspended coro works just like any
		328	other coro, except that the scheduler will not select a suspended
		329	coro for execution.
		330
		331	Suspending a coro can be useful when you want to keep the coro from
		332	running, but you don't want to destroy it, or when you want to
		333	temporarily freeze a coro (e.g. for debugging) to resume it later.
		334
		335	A scenario for the former would be to suspend all (other) coros
		336	after a fork and keep them alive, so their destructors aren't
		337	called, but new coros can be created.
		338
		339	$coro->resume
		340	If the specified coro was suspended, it will be resumed. Note that
		341	when the coro was in the ready queue when it was suspended, it might
		342	have been unreadied by the scheduler, so an activation might have
		343	been lost.
		344
		345	To avoid this, it is best to put a suspended coro into the ready
		346	queue unconditionally, as every synchronisation mechanism must
		347	protect itself against spurious wakeups, and the one in the Coro
		348	family certainly do that.
		349
		350	$is_ready = $coro->is_ready
		351	Returns true iff the Coro object is in the ready queue. Unless the
		352	Coro object gets destroyed, it will eventually be scheduled by the
		353	scheduler.
		354
		355	$is_running = $coro->is_running
		356	Returns true iff the Coro object is currently running. Only one Coro
		357	object can ever be in the running state (but it currently is
		358	possible to have multiple running Coro::States).
		359
		360	$is_suspended = $coro->is_suspended
		361	Returns true iff this Coro object has been suspended. Suspended
		362	Coros will not ever be scheduled.
		363
82	$process->cancel (arg...)	364	$coro->cancel (arg...)
83	Temrinates the given process and makes it return the given arguments	365	Terminates the given Coro and makes it return the given arguments as
84	as status (default: the empty list).	366	status (default: the empty list). Never returns if the Coro is the
		367	current Coro.
85		368
		369	$coro->schedule_to
		370	Puts the current coro to sleep (like "Coro::schedule"), but instead
		371	of continuing with the next coro from the ready queue, always switch
		372	to the given coro object (regardless of priority etc.). The
		373	readyness state of that coro isn't changed.
		374
		375	This is an advanced method for special cases - I'd love to hear
		376	about any uses for this one.
		377
		378	$coro->cede_to
		379	Like "schedule_to", but puts the current coro into the ready queue.
		380	This has the effect of temporarily switching to the given coro, and
		381	continuing some time later.
		382
		383	This is an advanced method for special cases - I'd love to hear
		384	about any uses for this one.
		385
		386	$coro->throw ([$scalar])
		387	If $throw is specified and defined, it will be thrown as an
		388	exception inside the coro at the next convenient point in time.
		389	Otherwise clears the exception object.
		390
		391	Coro will check for the exception each time a schedule-like-function
		392	returns, i.e. after each "schedule", "cede",
		393	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
		394	these functions detect this case and return early in case an
		395	exception is pending.
		396
		397	The exception object will be thrown "as is" with the specified
		398	scalar in $@, i.e. if it is a string, no line number or newline will
		399	be appended (unlike with "die").
		400
		401	This can be used as a softer means than "cancel" to ask a coro to
		402	end itself, although there is no guarantee that the exception will
		403	lead to termination, and if the exception isn't caught it might well
		404	end the whole program.
		405
		406	You might also think of "throw" as being the moral equivalent of
		407	"kill"ing a coro with a signal (in this case, a scalar).
		408
86	$process->join	409	$coro->join
87	Wait until the coroutine terminates and return any values given to	410	Wait until the coro terminates and return any values given to the
88	the "terminate" or "cancel" functions. "join" can be called multiple	411	"terminate" or "cancel" functions. "join" can be called concurrently
89	times from multiple processes.	412	from multiple coro, and all will be resumed and given the status
		413	return once the $coro terminates.
90		414
		415	$coro->on_destroy (\&cb)
		416	Registers a callback that is called when this coro gets destroyed,
		417	but before it is joined. The callback gets passed the terminate
		418	arguments, if any, and must not die, under any circumstances.
		419
91	$oldprio = $process->prio($newprio)	420	$oldprio = $coro->prio ($newprio)
92	Sets (or gets, if the argument is missing) the priority of the	421	Sets (or gets, if the argument is missing) the priority of the coro.
93	process. Higher priority processes get run before lower priority	422	Higher priority coro get run before lower priority coro. Priorities
94	processes. Priorities are small signed integers (currently -4 ..	423	are small signed integers (currently -4 .. +3), that you can refer
95	+3), that you can refer to using PRIO_xxx constants (use the import	424	to using PRIO_xxx constants (use the import tag :prio to get then):
96	tag :prio to get then):
97		425
98	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	426	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
99	3 > 1 > 0 > -1 > -3 > -4	427	3 > 1 > 0 > -1 > -3 > -4
100		428
101	# set priority to HIGH	429	# set priority to HIGH
102	current->prio(PRIO_HIGH);	430	current->prio (PRIO_HIGH);
103		431
104	The idle coroutine ($Coro::idle) always has a lower priority than	432	The idle coro ($Coro::idle) always has a lower priority than any
105	any existing coroutine.	433	existing coro.
106		434
107	Changing the priority of the current process will take effect	435	Changing the priority of the current coro will take effect
108	immediately, but changing the priority of processes in the ready	436	immediately, but changing the priority of coro in the ready queue
109	queue (but not running) will only take effect after the next	437	(but not running) will only take effect after the next schedule (of
110	schedule (of that process). This is a bug that will be fixed in some	438	that coro). This is a bug that will be fixed in some future version.
111	future version.
112		439
113	$newprio = $process->nice($change)	440	$newprio = $coro->nice ($change)
114	Similar to "prio", but subtract the given value from the priority	441	Similar to "prio", but subtract the given value from the priority
115	(i.e. higher values mean lower priority, just as in unix).	442	(i.e. higher values mean lower priority, just as in unix).
116		443
117	$olddesc = $process->desc($newdesc)	444	$olddesc = $coro->desc ($newdesc)
118	Sets (or gets in case the argument is missing) the description for	445	Sets (or gets in case the argument is missing) the description for
119	this process. This is just a free-form string you can associate with	446	this coro. This is just a free-form string you can associate with a
120	a process.	447	coro.
		448
		449	This method simply sets the "$coro->{desc}" member to the given
		450	string. You can modify this member directly if you wish.
		451
		452	GLOBAL FUNCTIONS
		453	Coro::nready
		454	Returns the number of coro that are currently in the ready state,
		455	i.e. that can be switched to by calling "schedule" directory or
		456	indirectly. The value 0 means that the only runnable coro is the
		457	currently running one, so "cede" would have no effect, and
		458	"schedule" would cause a deadlock unless there is an idle handler
		459	that wakes up some coro.
		460
		461	my $guard = Coro::guard { ... }
		462	This function still exists, but is deprecated. Please use the
		463	"Guard::guard" function instead.
		464
		465	unblock_sub { ... }
		466	This utility function takes a BLOCK or code reference and "unblocks"
		467	it, returning a new coderef. Unblocking means that calling the new
		468	coderef will return immediately without blocking, returning nothing,
		469	while the original code ref will be called (with parameters) from
		470	within another coro.
		471
		472	The reason this function exists is that many event libraries (such
		473	as the venerable Event module) are not thread-safe (a weaker form of
		474	reentrancy). This means you must not block within event callbacks,
		475	otherwise you might suffer from crashes or worse. The only event
		476	library currently known that is safe to use without "unblock_sub" is
		477	EV.
		478
		479	This function allows your callbacks to block by executing them in
		480	another coro where it is safe to block. One example where blocking
		481	is handy is when you use the Coro::AIO functions to save results to
		482	disk, for example.
		483
		484	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
		485	when creating event callbacks that want to block.
		486
		487	If your handler does not plan to block (e.g. simply sends a message
		488	to another coro, or puts some other coro into the ready queue),
		489	there is no reason to use "unblock_sub".
		490
		491	Note that you also need to use "unblock_sub" for any other callbacks
		492	that are indirectly executed by any C-based event loop. For example,
		493	when you use a module that uses AnyEvent (and you use
		494	Coro::AnyEvent) and it provides callbacks that are the result of
		495	some event callback, then you must not block either, or use
		496	"unblock_sub".
		497
		498	$cb = rouse_cb
		499	Create and return a "rouse callback". That's a code reference that,
		500	when called, will remember a copy of its arguments and notify the
		501	owner coro of the callback.
		502
		503	See the next function.
		504
		505	@args = rouse_wait [$cb]
		506	Wait for the specified rouse callback (or the last one that was
		507	created in this coro).
		508
		509	As soon as the callback is invoked (or when the callback was invoked
		510	before "rouse_wait"), it will return the arguments originally passed
		511	to the rouse callback. In scalar context, that means you get the
		512	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		513	$a3...)" statement at the end.
		514
		515	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
		516	example.
		517
		518	HOW TO WAIT FOR A CALLBACK
		519	It is very common for a coro to wait for some callback to be called.
		520	This occurs naturally when you use coro in an otherwise event-based
		521	program, or when you use event-based libraries.
		522
		523	These typically register a callback for some event, and call that
		524	callback when the event occured. In a coro, however, you typically want
		525	to just wait for the event, simplyifying things.
		526
		527	For example "AnyEvent->child" registers a callback to be called when a
		528	specific child has exited:
		529
		530	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		531
		532	But from within a coro, you often just want to write this:
		533
		534	my $status = wait_for_child $pid;
		535
		536	Coro offers two functions specifically designed to make this easy,
		537	"Coro::rouse_cb" and "Coro::rouse_wait".
		538
		539	The first function, "rouse_cb", generates and returns a callback that,
		540	when invoked, will save its arguments and notify the coro that created
		541	the callback.
		542
		543	The second function, "rouse_wait", waits for the callback to be called
		544	(by calling "schedule" to go to sleep) and returns the arguments
		545	originally passed to the callback.
		546
		547	Using these functions, it becomes easy to write the "wait_for_child"
		548	function mentioned above:
		549
		550	sub wait_for_child($) {
		551	my ($pid) = @_;
		552
		553	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		554
		555	my ($rpid, $rstatus) = Coro::rouse_wait;
		556	$rstatus
		557	}
		558
		559	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
		560	you can roll your own, using "schedule":
		561
		562	sub wait_for_child($) {
		563	my ($pid) = @_;
		564
		565	# store the current coro in $current,
		566	# and provide result variables for the closure passed to ->child
		567	my $current = $Coro::current;
		568	my ($done, $rstatus);
		569
		570	# pass a closure to ->child
		571	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		572	$rstatus = $_[1]; # remember rstatus
		573	$done = 1; # mark $rstatus as valud
		574	});
		575
		576	# wait until the closure has been called
		577	schedule while !$done;
		578
		579	$rstatus
		580	}
121		581
122	BUGS/LIMITATIONS	582	BUGS/LIMITATIONS
123	- you must make very sure that no coro is still active on global	583	fork with pthread backend
124	destruction. very bad things might happen otherwise (usually segfaults).	584	When Coro is compiled using the pthread backend (which isn't
		585	recommended but required on many BSDs as their libcs are completely
		586	broken), then coro will not survive a fork. There is no known
		587	workaround except to fix your libc and use a saner backend.
125		588
		589	perl process emulation ("threads")
126	- this module is not thread-safe. You should only ever use this module	590	This module is not perl-pseudo-thread-safe. You should only ever use
127	from the same thread (this requirement might be losened in the future	591	this module from the first thread (this requirement might be removed
128	to allow per-thread schedulers, but Coro::State does not yet allow	592	in the future to allow per-thread schedulers, but Coro::State does
129	this).	593	not yet allow this). I recommend disabling thread support and using
		594	processes, as having the windows process emulation enabled under
		595	unix roughly halves perl performance, even when not used.
		596
		597	coro switching is not signal safe
		598	You must not switch to another coro from within a signal handler
		599	(only relevant with %SIG - most event libraries provide safe
		600	signals).
		601
		602	That means you MUST NOT call any function that might "block" the
		603	current coro - "cede", "schedule" "Coro::Semaphore->down" or
		604	anything that calls those. Everything else, including calling
		605	"ready", works.
		606
		607	WINDOWS PROCESS EMULATION
		608	A great many people seem to be confused about ithreads (for example,
		609	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		610	while in the same mail making rather confused statements about perl
		611	ithreads (for example, that memory or files would be shared), showing
		612	his lack of understanding of this area - if it is hard to understand for
		613	Chip, it is probably not obvious to everybody).
		614
		615	What follows is an ultra-condensed version of my talk about threads in
		616	scripting languages given onthe perl workshop 2009:
		617
		618	The so-called "ithreads" were originally implemented for two reasons:
		619	first, to (badly) emulate unix processes on native win32 perls, and
		620	secondly, to replace the older, real thread model ("5.005-threads").
		621
		622	It does that by using threads instead of OS processes. The difference
		623	between processes and threads is that threads share memory (and other
		624	state, such as files) between threads within a single process, while
		625	processes do not share anything (at least not semantically). That means
		626	that modifications done by one thread are seen by others, while
		627	modifications by one process are not seen by other processes.
		628
		629	The "ithreads" work exactly like that: when creating a new ithreads
		630	process, all state is copied (memory is copied physically, files and
		631	code is copied logically). Afterwards, it isolates all modifications. On
		632	UNIX, the same behaviour can be achieved by using operating system
		633	processes, except that UNIX typically uses hardware built into the
		634	system to do this efficiently, while the windows process emulation
		635	emulates this hardware in software (rather efficiently, but of course it
		636	is still much slower than dedicated hardware).
		637
		638	As mentioned before, loading code, modifying code, modifying data
		639	structures and so on is only visible in the ithreads process doing the
		640	modification, not in other ithread processes within the same OS process.
		641
		642	This is why "ithreads" do not implement threads for perl at all, only
		643	processes. What makes it so bad is that on non-windows platforms, you
		644	can actually take advantage of custom hardware for this purpose (as
		645	evidenced by the forks module, which gives you the (i-) threads API,
		646	just much faster).
		647
		648	Sharing data is in the i-threads model is done by transfering data
		649	structures between threads using copying semantics, which is very slow -
		650	shared data simply does not exist. Benchmarks using i-threads which are
		651	communication-intensive show extremely bad behaviour with i-threads (in
		652	fact, so bad that Coro, which cannot take direct advantage of multiple
		653	CPUs, is often orders of magnitude faster because it shares data using
		654	real threads, refer to my talk for details).
		655
		656	As summary, i-threads use threads to implement processes, while the
		657	compatible forks module uses processes to emulate, uhm, processes.
		658	I-threads slow down every perl program when enabled, and outside of
		659	windows, serve no (or little) practical purpose, but disadvantages every
		660	single-threaded Perl program.
		661
		662	This is the reason that I try to avoid the name "ithreads", as it is
		663	misleading as it implies that it implements some kind of thread model
		664	for perl, and prefer the name "windows process emulation", which
		665	describes the actual use and behaviour of it much better.
130		666
131	SEE ALSO	667	SEE ALSO
		668	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
		669
		670	Debugging: Coro::Debug.
		671
132	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.	672	Support/Utility: Coro::Specific, Coro::Util.
133		673
134	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	674	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
135	Coro::SemaphoreSet, Coro::RWLock.	675	Coro::SemaphoreSet, Coro::RWLock.
136		676
137	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,	677	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
		678
		679	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		680	for a better-working alternative), Coro::BDB, Coro::Storable,
138	Coro::Select.	681	Coro::Select.
139		682
140	Embedding: <Coro:MakeMaker>	683	XS API: Coro::MakeMaker.
		684
		685	Low level Configuration, Thread Environment, Continuations: Coro::State.
141		686
142	AUTHOR	687	AUTHOR
143	Marc Lehmann <schmorp@schmorp.de>	688	Marc Lehmann <schmorp@schmorp.de>
144	http://home.schmorp.de/	689	http://home.schmorp.de/
145		690

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