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Revision 1.22 by root, Mon Mar 16 22:22:12 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 coroutine 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
15	}	17
16		18	# use locking
17	cede;	19	use Coro::Semaphore;
		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.
		29	This manpage mainly contains reference information.
		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
21	threads but don't run in parallel at the same time even on SMP machines.	34	general) run in parallel at the same time even on SMP machines. The
22	The specific flavor of coroutine used in this module also guarantees you	35	specific flavor of thread offered by this module also guarantees you
23	that it will not switch between coroutines unless necessary, at	36	that it will not switch between threads unless necessary, at
24	easily-identified points in your program, so locking and parallel access	37	easily-identified points in your program, so locking and parallel access
25	are rarely an issue, making coroutine programming much safer than	38	are rarely an issue, making thread programming much safer and easier
26	threads programming.	39	than using other thread models.
27		40
28	(Perl, however, does not natively support real threads but instead does	41	Unlike the so-called "Perl threads" (which are not actually real threads
29	a very slow and memory-intensive emulation of processes using threads.	42	but only the windows process emulation ported to unix, and as such act
30	This is a performance win on Windows machines, and a loss everywhere	43	as processes), Coro provides a full shared address space, which makes
31	else).	44	communication between threads very easy. And Coro's threads are fast,
		45	too: disabling the Windows process emulation code in your perl and using
		46	Coro can easily result in a two to four times speed increase for your
		47	programs. A parallel matrix multiplication benchmark runs over 300 times
		48	faster on a single core than perl's pseudo-threads on a quad core using
		49	all four cores.
32		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
33	In this module, coroutines are defined as "callchain + lexical variables	57	In this module, a thread is defined as "callchain + lexical variables +
34	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	58	some package variables + C stack), that is, a thread has its own
35	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
36	important global variables.	60	important global variables (see Coro::State for more configuration and
		61	background info).
37		62
		63	See also the "SEE ALSO" section at the end of this document - the Coro
		64	module family is quite large.
		65
		66	GLOBAL VARIABLES
38	$main	67	$Coro::main
39	This coroutine represents the main program.	68	This variable stores the Coro object that represents the main
		69	program. While you cna "ready" it and do most other things you can
		70	do to coro, it is mainly useful to compare again $Coro::current, to
		71	see whether you are running in the main program or not.
40		72
41	$current (or as function: current)	73	$Coro::current
42	The current coroutine (the last coroutine switched to). The initial	74	The Coro object representing the current coro (the last coro that
43	value is $main (of course).	75	the Coro scheduler switched to). The initial value is $Coro::main
		76	(of course).
44		77
45	This variable is strictly read-only. It is provided for	78	This variable is strictly read-only. You can take copies of the
46	performance reasons. If performance is not essential you are	79	value stored in it and use it as any other Coro object, but you must
47	encouraged to use the "Coro::current" function instead.	80	not otherwise modify the variable itself.
48		81
49	$idle	82	$Coro::idle
		83	This variable is mainly useful to integrate Coro into event loops.
		84	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
		85	is pretty low-level functionality.
		86
		87	This variable stores either a Coro object or a callback.
		88
50	A callback that is called whenever the scheduler finds no ready	89	If it is a callback, the it is called whenever the scheduler finds
51	coroutines to run. The default implementation prints "FATAL:	90	no ready coros to run. The default implementation prints "FATAL:
52	deadlock detected" and exits, because the program has no other way	91	deadlock detected" and exits, because the program has no other way
53	to continue.	92	to continue.
54		93
		94	If it is a coro object, then this object will be readied (without
		95	invoking any ready hooks, however) when the scheduler finds no other
		96	ready coros to run.
		97
55	This hook is overwritten by modules such as "Coro::Timer" and	98	This hook is overwritten by modules such as "Coro::EV" and
56	"Coro::Event" to wait on an external event that hopefully wake up a	99	"Coro::AnyEvent" to wait on an external event that hopefully wake up
57	coroutine so the scheduler can run it.	100	a coro so the scheduler can run it.
		101
		102	Note that the callback must not, under any circumstances, block
		103	the current coro. Normally, this is achieved by having an "idle
		104	coro" that calls the event loop and then blocks again, and then
		105	readying that coro in the idle handler, or by simply placing the
		106	idle coro in this variable.
		107
		108	See Coro::Event or Coro::AnyEvent for examples of using this
		109	technique.
58		110
59	Please note that if your callback recursively invokes perl (e.g. for	111	Please note that if your callback recursively invokes perl (e.g. for
60	event handlers), then it must be prepared to be called recursively.	112	event handlers), then it must be prepared to be called recursively
		113	itself.
61		114
62	STATIC METHODS	115	SIMPLE CORO CREATION
63	Static methods are actually functions that operate on the current
64	coroutine only.
65
66	async { ... } [@args...]	116	async { ... } [@args...]
67	Create a new asynchronous coroutine and return it's coroutine object	117	Create a new coro and return its Coro object (usually unused). The
68	(usually unused). When the sub returns the new coroutine is	118	coro will be put into the ready queue, so it will start running
69	automatically terminated.	119	automatically on the next scheduler run.
70		120
		121	The first argument is a codeblock/closure that should be executed in
		122	the coro. When it returns argument returns the coro is automatically
		123	terminated.
		124
		125	The remaining arguments are passed as arguments to the closure.
		126
		127	See the "Coro::State::new" constructor for info about the coro
		128	environment in which coro are executed.
		129
71	Calling "exit" in a coroutine will do the same as calling exit	130	Calling "exit" in a coro will do the same as calling exit outside
72	outside the coroutine. Likewise, when the coroutine dies, the	131	the coro. Likewise, when the coro dies, the program will exit, just
73	program will exit, just as it would in the main program.	132	as it would in the main program.
74		133
		134	If you do not want that, you can provide a default "die" handler, or
		135	simply avoid dieing (by use of "eval").
		136
75	# create a new coroutine that just prints its arguments	137	Example: Create a new coro that just prints its arguments.
		138
76	async {	139	async {
77	print "@_\n";	140	print "@_\n";
78	} 1,2,3,4;	141	} 1,2,3,4;
79		142
80	async_pool { ... } [@args...]	143	async_pool { ... } [@args...]
81	Similar to "async", but uses a coroutine pool, so you should not	144	Similar to "async", but uses a coro pool, so you should not call
82	call terminate or join (although you are allowed to), and you get a	145	terminate or join on it (although you are allowed to), and you get a
83	coroutine that might have executed other code already (which can be	146	coro that might have executed other code already (which can be good
84	good or bad :).	147	or bad :).
85		148
		149	On the plus side, this function is about twice as fast as creating
		150	(and destroying) a completely new coro, so if you need a lot of
		151	generic coros in quick successsion, use "async_pool", not "async".
		152
86	Also, the block is executed in an "eval" context and a warning will	153	The code block is executed in an "eval" context and a warning will
87	be issued in case of an exception instead of terminating the	154	be issued in case of an exception instead of terminating the
88	program, as "async" does. As the coroutine is being reused, stuff	155	program, as "async" does. As the coro is being reused, stuff like
89	like "on_destroy" will not work in the expected way, unless you call	156	"on_destroy" will not work in the expected way, unless you call
90	terminate or cancel, which somehow defeats the purpose of pooling.	157	terminate or cancel, which somehow defeats the purpose of pooling
		158	(but is fine in the exceptional case).
91		159
92	The priority will be reset to 0 after each job, otherwise the	160	The priority will be reset to 0 after each run, tracing will be
93	coroutine will be re-used "as-is".	161	disabled, the description will be reset and the default output
		162	filehandle gets restored, so you can change all these. Otherwise the
		163	coro will be re-used "as-is": most notably if you change other
		164	per-coro global stuff such as $/ you must needs revert that
		165	change, which is most simply done by using local as in: "local $/".
94		166
95	The pool size is limited to 8 idle coroutines (this can be adjusted	167	The idle pool size is limited to 8 idle coros (this can be adjusted
96	by changing $Coro::POOL_SIZE), and there can be as many non-idle	168	by changing $Coro::POOL_SIZE), but there can be as many non-idle
97	coros as required.	169	coros as required.
98		170
99	If you are concerned about pooled coroutines growing a lot because a	171	If you are concerned about pooled coros growing a lot because a
100	single "async_pool" used a lot of stackspace you can e.g.	172	single "async_pool" used a lot of stackspace you can e.g.
101	"async_pool { terminate }" once per second or so to slowly replenish	173	"async_pool { terminate }" once per second or so to slowly replenish
102	the pool. In addition to that, when the stacks used by a handler	174	the pool. In addition to that, when the stacks used by a handler
103	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will	175	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
104	also exit.	176	be destroyed.
		177
		178	STATIC METHODS
		179	Static methods are actually functions that implicitly operate on the
		180	current coro.
105		181
106	schedule	182	schedule
107	Calls the scheduler. Please note that the current coroutine will not	183	Calls the scheduler. The scheduler will find the next coro that is
108	be put into the ready queue, so calling this function usually means	184	to be run from the ready queue and switches to it. The next coro to
		185	be run is simply the one with the highest priority that is longest
		186	in its ready queue. If there is no coro ready, it will clal the
		187	$Coro::idle hook.
		188
		189	Please note that the current coro will not be put into the ready
		190	queue, so calling this function usually means you will never be
109	you will never be called again unless something else (e.g. an event	191	called again unless something else (e.g. an event handler) calls
110	handler) calls ready.	192	"->ready", thus waking you up.
111		193
112	The canonical way to wait on external events is this:	194	This makes "schedule" the generic method to use to block the
		195	current coro and wait for events: first you remember the current
		196	coro in a variable, then arrange for some callback of yours to call
		197	"->ready" on that once some event happens, and last you call
		198	"schedule" to put yourself to sleep. Note that a lot of things can
		199	wake your coro up, so you need to check whether the event indeed
		200	happened, e.g. by storing the status in a variable.
113		201
		202	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
		203	callbacks.
		204
		205	cede
		206	"Cede" to other coros. This function puts the current coro into the
		207	ready queue and calls "schedule", which has the effect of giving up
		208	the current "timeslice" to other coros of the same or higher
		209	priority. Once your coro gets its turn again it will automatically
		210	be resumed.
		211
		212	This function is often called "yield" in other languages.
		213
		214	Coro::cede_notself
		215	Works like cede, but is not exported by default and will cede to
		216	any coro, regardless of priority. This is useful sometimes to
		217	ensure progress is made.
		218
		219	terminate [arg...]
		220	Terminates the current coro with the given status values (see
		221	cancel).
		222
		223	Coro::on_enter BLOCK, Coro::on_leave BLOCK
		224	These function install enter and leave winders in the current scope.
		225	The enter block will be executed when on_enter is called and
		226	whenever the current coro is re-entered by the scheduler, while the
		227	leave block is executed whenever the current coro is blocked by the
		228	scheduler, and also when the containing scope is exited (by whatever
		229	means, be it exit, die, last etc.).
		230
		231	*Neither invoking the scheduler, nor exceptions, are allowed within
		232	those BLOCKs*. That means: do not even think about calling "die"
		233	without an eval, and do not even think of entering the scheduler in
		234	any way.
		235
		236	Since both BLOCKs are tied to the current scope, they will
		237	automatically be removed when the current scope exits.
		238
		239	These functions implement the same concept as "dynamic-wind" in
		240	scheme does, and are useful when you want to localise some resource
		241	to a specific coro.
		242
		243	They slow down coro switching considerably for coros that use them
		244	(But coro switching is still reasonably fast if the handlers are
		245	fast).
		246
		247	These functions are best understood by an example: The following
		248	function will change the current timezone to
		249	"Antarctica/South_Pole", which requires a call to "tzset", but by
		250	using "on_enter" and "on_leave", which remember/change the current
		251	timezone and restore the previous value, respectively, the timezone
		252	is only changes for the coro that installed those handlers.
		253
		254	use POSIX qw(tzset);
		255
114	{	256	async {
115	# remember current coroutine	257	my $old_tz; # store outside TZ value here
116	my $current = $Coro::current;
117		258
118	# register a hypothetical event handler	259	Coro::on_enter {
119	on_event_invoke sub {	260	$old_tz = $ENV{TZ}; # remember the old value
120	# wake up sleeping coroutine	261
121	$current->ready;	262	$ENV{TZ} = "Antarctica/South_Pole";
122	undef $current;	263	tzset; # enable new value
123	};	264	};
124		265
125	# call schedule until event occurred.	266	Coro::on_leave {
126	# in case we are woken up for other reasons	267	$ENV{TZ} = $old_tz;
127	# (current still defined), loop.	268	tzset; # restore old value
128	Coro::schedule while $current;	269	};
		270
		271	# at this place, the timezone is Antarctica/South_Pole,
		272	# without disturbing the TZ of any other coro.
129	}	273	};
130		274
131	cede	275	This can be used to localise about any resource (locale, uid,
132	"Cede" to other coroutines. This function puts the current coroutine	276	current working directory etc.) to a block, despite the existance of
133	into the ready queue and calls "schedule", which has the effect of	277	other coros.
134	giving up the current "timeslice" to other coroutines of the same or
135	higher priority.
136		278
137	Returns true if at least one coroutine switch has happened.	279	killall
		280	Kills/terminates/cancels all coros except the currently running one.
138		281
139	Coro::cede_notself	282	Note that while this will try to free some of the main interpreter
140	Works like cede, but is not exported by default and will cede to any	283	resources if the calling coro isn't the main coro, but one cannot
141	coroutine, regardless of priority, once.	284	free all of them, so if a coro that is not the main coro calls this
		285	function, there will be some one-time resource leak.
142		286
143	Returns true if at least one coroutine switch has happened.	287	CORO OBJECT METHODS
144
145	terminate [arg...]
146	Terminates the current coroutine with the given status values (see
147	cancel).
148
149	# dynamic methods
150
151	COROUTINE METHODS
152	These are the methods you can call on coroutine objects.	288	These are the methods you can call on coro objects (or to create them).
153		289
154	new Coro \&sub [, @args...]	290	new Coro \&sub [, @args...]
155	Create a new coroutine and return it. When the sub returns the	291	Create a new coro and return it. When the sub returns, the coro
156	coroutine automatically terminates as if "terminate" with the	292	automatically terminates as if "terminate" with the returned values
157	returned values were called. To make the coroutine run you must	293	were called. To make the coro run you must first put it into the
158	first put it into the ready queue by calling the ready method.	294	ready queue by calling the ready method.
159		295
160	See "async" for additional discussion.	296	See "async" and "Coro::State::new" for additional info about the
		297	coro environment.
161		298
162	$success = $coroutine->ready	299	$success = $coro->ready
163	Put the given coroutine into the ready queue (according to it's	300	Put the given coro into the end of its ready queue (there is one
164	priority) and return true. If the coroutine is already in the ready	301	queue for each priority) and return true. If the coro is already in
165	queue, do nothing and return false.	302	the ready queue, do nothing and return false.
166		303
		304	This ensures that the scheduler will resume this coro automatically
		305	once all the coro of higher priority and all coro of the same
		306	priority that were put into the ready queue earlier have been
		307	resumed.
		308
		309	$coro->suspend
		310	Suspends the specified coro. A suspended coro works just like any
		311	other coro, except that the scheduler will not select a suspended
		312	coro for execution.
		313
		314	Suspending a coro can be useful when you want to keep the coro from
		315	running, but you don't want to destroy it, or when you want to
		316	temporarily freeze a coro (e.g. for debugging) to resume it later.
		317
		318	A scenario for the former would be to suspend all (other) coros
		319	after a fork and keep them alive, so their destructors aren't
		320	called, but new coros can be created.
		321
		322	$coro->resume
		323	If the specified coro was suspended, it will be resumed. Note that
		324	when the coro was in the ready queue when it was suspended, it might
		325	have been unreadied by the scheduler, so an activation might have
		326	been lost.
		327
		328	To avoid this, it is best to put a suspended coro into the ready
		329	queue unconditionally, as every synchronisation mechanism must
		330	protect itself against spurious wakeups, and the one in the Coro
		331	family certainly do that.
		332
167	$is_ready = $coroutine->is_ready	333	$is_ready = $coro->is_ready
168	Return wether the coroutine is currently the ready queue or not,	334	Returns true iff the Coro object is in the ready queue. Unless the
		335	Coro object gets destroyed, it will eventually be scheduled by the
		336	scheduler.
169		337
		338	$is_running = $coro->is_running
		339	Returns true iff the Coro object is currently running. Only one Coro
		340	object can ever be in the running state (but it currently is
		341	possible to have multiple running Coro::States).
		342
		343	$is_suspended = $coro->is_suspended
		344	Returns true iff this Coro object has been suspended. Suspended
		345	Coros will not ever be scheduled.
		346
170	$coroutine->cancel (arg...)	347	$coro->cancel (arg...)
171	Terminates the given coroutine and makes it return the given	348	Terminates the given Coro and makes it return the given arguments as
172	arguments as status (default: the empty list). Never returns if the	349	status (default: the empty list). Never returns if the Coro is the
173	coroutine is the current coroutine.	350	current Coro.
174		351
		352	$coro->schedule_to
		353	Puts the current coro to sleep (like "Coro::schedule"), but instead
		354	of continuing with the next coro from the ready queue, always switch
		355	to the given coro object (regardless of priority etc.). The
		356	readyness state of that coro isn't changed.
		357
		358	This is an advanced method for special cases - I'd love to hear
		359	about any uses for this one.
		360
		361	$coro->cede_to
		362	Like "schedule_to", but puts the current coro into the ready queue.
		363	This has the effect of temporarily switching to the given coro, and
		364	continuing some time later.
		365
		366	This is an advanced method for special cases - I'd love to hear
		367	about any uses for this one.
		368
		369	$coro->throw ([$scalar])
		370	If $throw is specified and defined, it will be thrown as an
		371	exception inside the coro at the next convenient point in time.
		372	Otherwise clears the exception object.
		373
		374	Coro will check for the exception each time a schedule-like-function
		375	returns, i.e. after each "schedule", "cede",
		376	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
		377	these functions detect this case and return early in case an
		378	exception is pending.
		379
		380	The exception object will be thrown "as is" with the specified
		381	scalar in $@, i.e. if it is a string, no line number or newline will
		382	be appended (unlike with "die").
		383
		384	This can be used as a softer means than "cancel" to ask a coro to
		385	end itself, although there is no guarantee that the exception will
		386	lead to termination, and if the exception isn't caught it might well
		387	end the whole program.
		388
		389	You might also think of "throw" as being the moral equivalent of
		390	"kill"ing a coro with a signal (in this case, a scalar).
		391
175	$coroutine->join	392	$coro->join
176	Wait until the coroutine terminates and return any values given to	393	Wait until the coro terminates and return any values given to the
177	the "terminate" or "cancel" functions. "join" can be called multiple	394	"terminate" or "cancel" functions. "join" can be called concurrently
178	times from multiple coroutine.	395	from multiple coro, and all will be resumed and given the status
		396	return once the $coro terminates.
179		397
180	$coroutine->on_destroy (\&cb)	398	$coro->on_destroy (\&cb)
181	Registers a callback that is called when this coroutine gets	399	Registers a callback that is called when this coro gets destroyed,
182	destroyed, but before it is joined. The callback gets passed the	400	but before it is joined. The callback gets passed the terminate
183	terminate arguments, if any.	401	arguments, if any, and must not die, under any circumstances.
184		402
185	$oldprio = $coroutine->prio ($newprio)	403	$oldprio = $coro->prio ($newprio)
186	Sets (or gets, if the argument is missing) the priority of the	404	Sets (or gets, if the argument is missing) the priority of the coro.
187	coroutine. Higher priority coroutines get run before lower priority	405	Higher priority coro get run before lower priority coro. Priorities
188	coroutines. Priorities are small signed integers (currently -4 ..	406	are small signed integers (currently -4 .. +3), that you can refer
189	+3), that you can refer to using PRIO_xxx constants (use the import	407	to using PRIO_xxx constants (use the import tag :prio to get then):
190	tag :prio to get then):
191		408
192	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	409	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
193	3 > 1 > 0 > -1 > -3 > -4	410	3 > 1 > 0 > -1 > -3 > -4
194		411
195	# set priority to HIGH	412	# set priority to HIGH
196	current->prio(PRIO_HIGH);	413	current->prio (PRIO_HIGH);
197		414
198	The idle coroutine ($Coro::idle) always has a lower priority than	415	The idle coro ($Coro::idle) always has a lower priority than any
199	any existing coroutine.	416	existing coro.
200		417
201	Changing the priority of the current coroutine will take effect	418	Changing the priority of the current coro will take effect
202	immediately, but changing the priority of coroutines in the ready	419	immediately, but changing the priority of coro in the ready queue
203	queue (but not running) will only take effect after the next	420	(but not running) will only take effect after the next schedule (of
204	schedule (of that coroutine). This is a bug that will be fixed in	421	that coro). This is a bug that will be fixed in some future version.
205	some future version.
206		422
207	$newprio = $coroutine->nice ($change)	423	$newprio = $coro->nice ($change)
208	Similar to "prio", but subtract the given value from the priority	424	Similar to "prio", but subtract the given value from the priority
209	(i.e. higher values mean lower priority, just as in unix).	425	(i.e. higher values mean lower priority, just as in unix).
210		426
211	$olddesc = $coroutine->desc ($newdesc)	427	$olddesc = $coro->desc ($newdesc)
212	Sets (or gets in case the argument is missing) the description for	428	Sets (or gets in case the argument is missing) the description for
213	this coroutine. This is just a free-form string you can associate	429	this coro. This is just a free-form string you can associate with a
214	with a coroutine.	430	coro.
215		431
		432	This method simply sets the "$coro->{desc}" member to the given
		433	string. You can modify this member directly if you wish.
		434
216	GLOBAL FUNCTIONS	435	GLOBAL FUNCTIONS
217	Coro::nready	436	Coro::nready
218	Returns the number of coroutines that are currently in the ready	437	Returns the number of coro that are currently in the ready state,
219	state, i.e. that can be switched to. The value 0 means that the only	438	i.e. that can be switched to by calling "schedule" directory or
220	runnable coroutine is the currently running one, so "cede" would	439	indirectly. The value 0 means that the only runnable coro is the
221	have no effect, and "schedule" would cause a deadlock unless there	440	currently running one, so "cede" would have no effect, and
222	is an idle handler that wakes up some coroutines.	441	"schedule" would cause a deadlock unless there is an idle handler
		442	that wakes up some coro.
223		443
224	my $guard = Coro::guard { ... }	444	my $guard = Coro::guard { ... }
225	This creates and returns a guard object. Nothing happens until the	445	This function still exists, but is deprecated. Please use the
226	object gets destroyed, in which case the codeblock given as argument	446	"Guard::guard" function instead.
227	will be executed. This is useful to free locks or other resources in
228	case of a runtime error or when the coroutine gets canceled, as in
229	both cases the guard block will be executed. The guard object
230	supports only one method, "->cancel", which will keep the codeblock
231	from being executed.
232
233	Example: set some flag and clear it again when the coroutine gets
234	canceled or the function returns:
235
236	sub do_something {
237	my $guard = Coro::guard { $busy = 0 };
238	$busy = 1;
239
240	# do something that requires $busy to be true
241	}
242		447
243	unblock_sub { ... }	448	unblock_sub { ... }
244	This utility function takes a BLOCK or code reference and "unblocks"	449	This utility function takes a BLOCK or code reference and "unblocks"
245	it, returning the new coderef. This means that the new coderef will	450	it, returning a new coderef. Unblocking means that calling the new
246	return immediately without blocking, returning nothing, while the	451	coderef will return immediately without blocking, returning nothing,
247	original code ref will be called (with parameters) from within its	452	while the original code ref will be called (with parameters) from
248	own coroutine.	453	within another coro.
249		454
250	The reason this function exists is that many event libraries (such	455	The reason this function exists is that many event libraries (such
251	as the venerable Event module) are not coroutine-safe (a weaker form	456	as the venerable Event module) are not thread-safe (a weaker form of
252	of thread-safety). This means you must not block within event	457	reentrancy). This means you must not block within event callbacks,
253	callbacks, otherwise you might suffer from crashes or worse.	458	otherwise you might suffer from crashes or worse. The only event
		459	library currently known that is safe to use without "unblock_sub" is
		460	EV.
254		461
255	This function allows your callbacks to block by executing them in	462	This function allows your callbacks to block by executing them in
256	another coroutine where it is safe to block. One example where	463	another coro where it is safe to block. One example where blocking
257	blocking is handy is when you use the Coro::AIO functions to save	464	is handy is when you use the Coro::AIO functions to save results to
258	results to disk.	465	disk, for example.
259		466
260	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	467	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
261	when creating event callbacks that want to block.	468	when creating event callbacks that want to block.
262		469
		470	If your handler does not plan to block (e.g. simply sends a message
		471	to another coro, or puts some other coro into the ready queue),
		472	there is no reason to use "unblock_sub".
		473
		474	Note that you also need to use "unblock_sub" for any other callbacks
		475	that are indirectly executed by any C-based event loop. For example,
		476	when you use a module that uses AnyEvent (and you use
		477	Coro::AnyEvent) and it provides callbacks that are the result of
		478	some event callback, then you must not block either, or use
		479	"unblock_sub".
		480
		481	$cb = Coro::rouse_cb
		482	Create and return a "rouse callback". That's a code reference that,
		483	when called, will remember a copy of its arguments and notify the
		484	owner coro of the callback.
		485
		486	See the next function.
		487
		488	@args = Coro::rouse_wait [$cb]
		489	Wait for the specified rouse callback (or the last one that was
		490	created in this coro).
		491
		492	As soon as the callback is invoked (or when the callback was invoked
		493	before "rouse_wait"), it will return the arguments originally passed
		494	to the rouse callback.
		495
		496	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
		497	example.
		498
		499	HOW TO WAIT FOR A CALLBACK
		500	It is very common for a coro to wait for some callback to be called.
		501	This occurs naturally when you use coro in an otherwise event-based
		502	program, or when you use event-based libraries.
		503
		504	These typically register a callback for some event, and call that
		505	callback when the event occured. In a coro, however, you typically want
		506	to just wait for the event, simplyifying things.
		507
		508	For example "AnyEvent->child" registers a callback to be called when a
		509	specific child has exited:
		510
		511	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		512
		513	But from within a coro, you often just want to write this:
		514
		515	my $status = wait_for_child $pid;
		516
		517	Coro offers two functions specifically designed to make this easy,
		518	"Coro::rouse_cb" and "Coro::rouse_wait".
		519
		520	The first function, "rouse_cb", generates and returns a callback that,
		521	when invoked, will save its arguments and notify the coro that created
		522	the callback.
		523
		524	The second function, "rouse_wait", waits for the callback to be called
		525	(by calling "schedule" to go to sleep) and returns the arguments
		526	originally passed to the callback.
		527
		528	Using these functions, it becomes easy to write the "wait_for_child"
		529	function mentioned above:
		530
		531	sub wait_for_child($) {
		532	my ($pid) = @_;
		533
		534	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		535
		536	my ($rpid, $rstatus) = Coro::rouse_wait;
		537	$rstatus
		538	}
		539
		540	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
		541	you can roll your own, using "schedule":
		542
		543	sub wait_for_child($) {
		544	my ($pid) = @_;
		545
		546	# store the current coro in $current,
		547	# and provide result variables for the closure passed to ->child
		548	my $current = $Coro::current;
		549	my ($done, $rstatus);
		550
		551	# pass a closure to ->child
		552	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		553	$rstatus = $_[1]; # remember rstatus
		554	$done = 1; # mark $rstatus as valud
		555	});
		556
		557	# wait until the closure has been called
		558	schedule while !$done;
		559
		560	$rstatus
		561	}
		562
263	BUGS/LIMITATIONS	563	BUGS/LIMITATIONS
264	- you must make very sure that no coro is still active on global	564	fork with pthread backend
265	destruction. very bad things might happen otherwise (usually segfaults).	565	When Coro is compiled using the pthread backend (which isn't
		566	recommended but required on many BSDs as their libcs are completely
		567	broken), then coro will not survive a fork. There is no known
		568	workaround except to fix your libc and use a saner backend.
266		569
		570	perl process emulation ("threads")
267	- this module is not thread-safe. You should only ever use this module	571	This module is not perl-pseudo-thread-safe. You should only ever use
268	from the same thread (this requirement might be loosened in the future	572	this module from the first thread (this requirement might be removed
269	to allow per-thread schedulers, but Coro::State does not yet allow	573	in the future to allow per-thread schedulers, but Coro::State does
270	this).	574	not yet allow this). I recommend disabling thread support and using
		575	processes, as having the windows process emulation enabled under
		576	unix roughly halves perl performance, even when not used.
		577
		578	coro switching is not signal safe
		579	You must not switch to another coro from within a signal handler
		580	(only relevant with %SIG - most event libraries provide safe
		581	signals).
		582
		583	That means you MUST NOT call any function that might "block" the
		584	current coro - "cede", "schedule" "Coro::Semaphore->down" or
		585	anything that calls those. Everything else, including calling
		586	"ready", works.
271		587
272	SEE ALSO	588	SEE ALSO
		589	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
		590
		591	Debugging: Coro::Debug.
		592
273	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.	593	Support/Utility: Coro::Specific, Coro::Util.
274		594
275	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	595	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
276	Coro::SemaphoreSet, Coro::RWLock.	596	Coro::SemaphoreSet, Coro::RWLock.
277		597
278	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,	598	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
		599
		600	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		601	for a better-working alternative), Coro::BDB, Coro::Storable,
279	Coro::Select.	602	Coro::Select.
280		603
281	Embedding: <Coro:MakeMaker>	604	XS API: Coro::MakeMaker.
		605
		606	Low level Configuration, Thread Environment, Continuations: Coro::State.
282		607
283	AUTHOR	608	AUTHOR
284	Marc Lehmann <schmorp@schmorp.de>	609	Marc Lehmann <schmorp@schmorp.de>
285	http://home.schmorp.de/	610	http://home.schmorp.de/
286		611

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Revision 1.22 by root, Mon Mar 16 22:22:12 2009 UTC