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Revision 1.28 by root, Sun Feb 13 04:39:15 2011 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";	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	use Coro::Semaphore;
19	my $lock = new Coro::Semaphore;	20	my $lock = new Coro::Semaphore;
20	my $locked;	21	my $locked;
21		22
22	$lock->down;	23	$lock->down;
23	$locked = 1;	24	$locked = 1;
24	$lock->up;	25	$lock->up;
25		26
26	DESCRIPTION	27	DESCRIPTION
27	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
28	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
29	The specific flavor of coroutine used in this module also guarantees you	35	specific flavor of thread offered by this module also guarantees you
30	that it will not switch between coroutines unless necessary, at	36	that it will not switch between threads unless necessary, at
31	easily-identified points in your program, so locking and parallel access	37	easily-identified points in your program, so locking and parallel access
32	are rarely an issue, making coroutine programming much safer than	38	are rarely an issue, making thread programming much safer and easier
33	threads programming.	39	than using other thread models.
34		40
35	(Perl, however, does not natively support real threads but instead does	41	Unlike the so-called "Perl threads" (which are not actually real threads
36	a very slow and memory-intensive emulation of processes using threads.	42	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	43	more details) ported to unix, and as such act as processes), Coro
38	else).	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.
39		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
40	In this module, coroutines are defined as "callchain + lexical variables	58	In this module, a thread is defined as "callchain + lexical variables +
41	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	59	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	60	callchain, its own set of lexicals and its own set of perls most
43	important global variables (see Coro::State for more configuration).	61	important global variables (see Coro::State for more configuration and
		62	background info).
44		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
45	$main	68	$Coro::main
46	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.
47		73
48	$current (or as function: current)	74	$Coro::current
49	The current coroutine (the last coroutine switched to). The initial	75	The Coro object representing the current coro (the last coro that
50	value is $main (of course).	76	the Coro scheduler switched to). The initial value is $Coro::main
		77	(of course).
51		78
52	This variable is strictly read-only. It is provided for	79	This variable is strictly read-only. You can take copies of the
53	performance reasons. If performance is not essential you are	80	value stored in it and use it as any other Coro object, but you must
54	encouraged to use the "Coro::current" function instead.	81	not otherwise modify the variable itself.
55		82
56	$idle	83	$Coro::idle
57	A callback that is called whenever the scheduler finds no ready	84	This variable is mainly useful to integrate Coro into event loops.
58	coroutines to run. The default implementation prints "FATAL:	85	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	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
		92	The default implementation dies with "FATAL: deadlock detected.",
		93	followed by a thread listing, because the program has no other way
60	to continue.	94	to continue.
61		95
62	This hook is overwritten by modules such as "Coro::Timer" and	96	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	97	"Coro::AnyEvent" to wait on an external event that hopefully wake up
64	coroutine so the scheduler can run it.	98	a coro so the scheduler can run it.
65		99
66	Please note that if your callback recursively invokes perl (e.g. for	100	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		101
70	STATIC METHODS	102	SIMPLE CORO CREATION
71	Static methods are actually functions that operate on the current
72	coroutine only.
73
74	async { ... } [@args...]	103	async { ... } [@args...]
75	Create a new asynchronous coroutine and return it's coroutine object	104	Create a new coro and return its Coro object (usually unused). The
76	(usually unused). When the sub returns the new coroutine is	105	coro will be put into the ready queue, so it will start running
77	automatically terminated.	106	automatically on the next scheduler run.
78		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
79	See the "Coro::State::new" constructor for info about the coroutine	114	See the "Coro::State::new" constructor for info about the coro
80	environment in which coroutines run.	115	environment in which coro are executed.
81		116
82	Calling "exit" in a coroutine will do the same as calling exit	117	Calling "exit" in a coro will do the same as calling exit outside
83	outside the coroutine. Likewise, when the coroutine dies, the	118	the coro. Likewise, when the coro dies, the program will exit, just
84	program will exit, just as it would in the main program.	119	as it would in the main program.
85		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
86	# create a new coroutine that just prints its arguments	124	Example: Create a new coro that just prints its arguments.
		125
87	async {	126	async {
88	print "@_\n";	127	print "@_\n";
89	} 1,2,3,4;	128	} 1,2,3,4;
90		129
91	async_pool { ... } [@args...]	130	async_pool { ... } [@args...]
92	Similar to "async", but uses a coroutine pool, so you should not	131	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	132	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	133	coro that might have executed other code already (which can be good
95	good or bad :).	134	or bad :).
96		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
97	Also, the block is executed in an "eval" context and a warning will	140	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	141	be issued in case of an exception instead of terminating the
99	program, as "async" does. As the coroutine is being reused, stuff	142	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	143	"on_destroy" will not work in the expected way, unless you call
101	terminate or cancel, which somehow defeats the purpose of pooling.	144	terminate or cancel, which somehow defeats the purpose of pooling
		145	(but is fine in the exceptional case).
102		146
103	The priority will be reset to 0 after each job, tracing will be	147	The priority will be reset to 0 after each run, tracing will be
104	disabled, the description will be reset and the default output	148	disabled, the description will be reset and the default output
105	filehandle gets restored, so you can change alkl these. Otherwise	149	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	150	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	151	per-coro global stuff such as $/ you must needs revert that
108	change, which is most simply done by using local as in " local $/ ".	152	change, which is most simply done by using local as in: "local $/".
109		153
110	The pool size is limited to 8 idle coroutines (this can be adjusted	154	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	155	by changing $Coro::POOL_SIZE), but there can be as many non-idle
112	coros as required.	156	coros as required.
113		157
114	If you are concerned about pooled coroutines growing a lot because a	158	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.	159	single "async_pool" used a lot of stackspace you can e.g.
116	"async_pool { terminate }" once per second or so to slowly replenish	160	"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	161	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	162	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
119	also exit.	163	be destroyed.
		164
		165	STATIC METHODS
		166	Static methods are actually functions that implicitly operate on the
		167	current coro.
120		168
121	schedule	169	schedule
122	Calls the scheduler. Please note that the current coroutine will not	170	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	171	to be run from the ready queue and switches to it. The next coro to
		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
124	you will never be called again unless something else (e.g. an event	178	called again unless something else (e.g. an event handler) calls
125	handler) calls ready.	179	"->ready", thus waking you up.
126		180
127	The canonical way to wait on external events is this:	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.
128		188
		189	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
		190	callbacks.
		191
		192	cede
		193	"Cede" to other coros. This function puts the current coro into the
		194	ready queue and calls "schedule", which has the effect of giving up
		195	the current "timeslice" to other coros of the same or higher
		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.
		205
		206	terminate [arg...]
		207	Terminates the current coro with the given status values (see
		208	cancel).
		209
		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.).
		217
		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
129	{	243	async {
130	# remember current coroutine	244	my $old_tz; # store outside TZ value here
131	my $current = $Coro::current;
132		245
133	# register a hypothetical event handler	246	Coro::on_enter {
134	on_event_invoke sub {	247	$old_tz = $ENV{TZ}; # remember the old value
135	# wake up sleeping coroutine	248
136	$current->ready;	249	$ENV{TZ} = "Antarctica/South_Pole";
137	undef $current;	250	tzset; # enable new value
138	};	251	};
139		252
140	# call schedule until event occurred.	253	Coro::on_leave {
141	# in case we are woken up for other reasons	254	$ENV{TZ} = $old_tz;
142	# (current still defined), loop.	255	tzset; # restore old value
143	Coro::schedule while $current;	256	};
		257
		258	# at this place, the timezone is Antarctica/South_Pole,
		259	# without disturbing the TZ of any other coro.
144	}	260	};
145		261
146	cede	262	This can be used to localise about any resource (locale, uid,
147	"Cede" to other coroutines. This function puts the current coroutine	263	current working directory etc.) to a block, despite the existance of
148	into the ready queue and calls "schedule", which has the effect of	264	other coros.
149	giving up the current "timeslice" to other coroutines of the same or
150	higher priority.
151		265
152	Coro::cede_notself	266	Another interesting example implements time-sliced multitasking
153	Works like cede, but is not exported by default and will cede to any	267	using interval timers (this could obviously be optimised, but does
154	coroutine, regardless of priority, once.	268	the job):
155		269
156	terminate [arg...]	270	# "timeslice" the given block
157	Terminates the current coroutine with the given status values (see	271	sub timeslice(&) {
158	cancel).	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	};
159		295
160	killall	296	killall
161	Kills/terminates/cancels all coroutines except the currently running	297	Kills/terminates/cancels all coros except the currently running one.
162	one. This is useful after a fork, either in the child or the parent,
163	as usually only one of them should inherit the running coroutines.
164		298
165	# dynamic methods	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.
166		303
167	COROUTINE METHODS	304	CORO OBJECT METHODS
168	These are the methods you can call on coroutine objects.	305	These are the methods you can call on coro objects (or to create them).
169		306
170	new Coro \&sub [, @args...]	307	new Coro \&sub [, @args...]
171	Create a new coroutine and return it. When the sub returns the	308	Create a new coro and return it. When the sub returns, the coro
172	coroutine automatically terminates as if "terminate" with the	309	automatically terminates as if "terminate" with the returned values
173	returned values were called. To make the coroutine run you must	310	were called. To make the coro run you must first put it into the
174	first put it into the ready queue by calling the ready method.	311	ready queue by calling the ready method.
175		312
176	See "async" and "Coro::State::new" for additional info about the	313	See "async" and "Coro::State::new" for additional info about the
177	coroutine environment.	314	coro environment.
178		315
179	$success = $coroutine->ready	316	$success = $coro->ready
180	Put the given coroutine into the ready queue (according to it's	317	Put the given coro into the end of its ready queue (there is one
181	priority) and return true. If the coroutine is already in the ready	318	queue for each priority) and return true. If the coro is already in
182	queue, do nothing and return false.	319	the ready queue, do nothing and return false.
183		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
184	$is_ready = $coroutine->is_ready	350	$is_ready = $coro->is_ready
185	Return wether the coroutine is currently the ready queue or not,	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.
186		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
187	$coroutine->cancel (arg...)	364	$coro->cancel (arg...)
188	Terminates the given coroutine and makes it return the given	365	Terminates the given Coro and makes it return the given arguments as
189	arguments as status (default: the empty list). Never returns if the	366	status (default: the empty list). Never returns if the Coro is the
190	coroutine is the current coroutine.	367	current Coro.
191		368
192	$coroutine->join	369	$coro->schedule_to
193	Wait until the coroutine terminates and return any values given to	370	Puts the current coro to sleep (like "Coro::schedule"), but instead
194	the "terminate" or "cancel" functions. "join" can be called	371	of continuing with the next coro from the ready queue, always switch
195	concurrently from multiple coroutines.	372	to the given coro object (regardless of priority etc.). The
		373	readyness state of that coro isn't changed.
196		374
197	$coroutine->on_destroy (\&cb)	375	This is an advanced method for special cases - I'd love to hear
198	Registers a callback that is called when this coroutine gets	376	about any uses for this one.
199	destroyed, but before it is joined. The callback gets passed the
200	terminate arguments, if any.
201		377
202	$oldprio = $coroutine->prio ($newprio)	378	$coro->cede_to
203	Sets (or gets, if the argument is missing) the priority of the	379	Like "schedule_to", but puts the current coro into the ready queue.
204	coroutine. Higher priority coroutines get run before lower priority	380	This has the effect of temporarily switching to the given coro, and
205	coroutines. Priorities are small signed integers (currently -4 ..	381	continuing some time later.
206	+3), that you can refer to using PRIO_xxx constants (use the import
207	tag :prio to get then):
208		382
209	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	383	This is an advanced method for special cases - I'd love to hear
210	3 > 1 > 0 > -1 > -3 > -4	384	about any uses for this one.
211		385
212	# set priority to HIGH
213	current->prio(PRIO_HIGH);
214
215	The idle coroutine ($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])	386	$coro->throw ([$scalar])
237	If $throw is specified and defined, it will be thrown as an	387	If $throw is specified and defined, it will be thrown as an
238	exception inside the coroutine at the next convinient point in time	388	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.	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.
241		396
242	The exception object will be thrown "as is" with the specified	397	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	398	scalar in $@, i.e. if it is a string, no line number or newline will
244	be appended (unlike with "die").	399	be appended (unlike with "die").
245		400
246	This can be used as a softer means than "cancel" to ask a coroutine	401	This can be used as a softer means than "cancel" to ask a coro to
247	to end itself, although there is no guarentee that the exception	402	end itself, although there is no guarantee that the exception will
248	will lead to termination, and if the exception isn't caught it might	403	lead to termination, and if the exception isn't caught it might well
249	well end the whole program.	404	end the whole program.
250		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
		409	$coro->join
		410	Wait until the coro terminates and return any values given to the
		411	"terminate" or "cancel" functions. "join" can be called concurrently
		412	from multiple coro, and all will be resumed and given the status
		413	return once the $coro terminates.
		414
		415	$coro->on_destroy (\&cb)
		416	Registers a callback that is called when this coro thread gets
		417	destroyed, but before it is joined. The callback gets passed the
		418	terminate arguments, if any, and must not die, under any
		419	circumstances.
		420
		421	There can be any number of "on_destroy" callbacks per coro.
		422
		423	$oldprio = $coro->prio ($newprio)
		424	Sets (or gets, if the argument is missing) the priority of the coro
		425	thread. Higher priority coro get run before lower priority coros.
		426	Priorities are small signed integers (currently -4 .. +3), that you
		427	can refer to using PRIO_xxx constants (use the import tag :prio to
		428	get then):
		429
		430	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		431	3 > 1 > 0 > -1 > -3 > -4
		432
		433	# set priority to HIGH
		434	current->prio (PRIO_HIGH);
		435
		436	The idle coro thread ($Coro::idle) always has a lower priority than
		437	any existing coro.
		438
		439	Changing the priority of the current coro will take effect
		440	immediately, but changing the priority of a coro in the ready queue
		441	(but not running) will only take effect after the next schedule (of
		442	that coro). This is a bug that will be fixed in some future version.
		443
		444	$newprio = $coro->nice ($change)
		445	Similar to "prio", but subtract the given value from the priority
		446	(i.e. higher values mean lower priority, just as in UNIX's nice
		447	command).
		448
		449	$olddesc = $coro->desc ($newdesc)
		450	Sets (or gets in case the argument is missing) the description for
		451	this coro thread. This is just a free-form string you can associate
		452	with a coro.
		453
		454	This method simply sets the "$coro->{desc}" member to the given
		455	string. You can modify this member directly if you wish, and in
		456	fact, this is often preferred to indicate major processing states
		457	that cna then be seen for example in a Coro::Debug session:
		458
		459	sub my_long_function {
		460	local $Coro::current->{desc} = "now in my_long_function";
		461	...
		462	$Coro::current->{desc} = "my_long_function: phase 1";
		463	...
		464	$Coro::current->{desc} = "my_long_function: phase 2";
		465	...
		466	}
		467
251	GLOBAL FUNCTIONS	468	GLOBAL FUNCTIONS
252	Coro::nready	469	Coro::nready
253	Returns the number of coroutines that are currently in the ready	470	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	471	i.e. that can be switched to by calling "schedule" directory or
255	runnable coroutine is the currently running one, so "cede" would	472	indirectly. The value 0 means that the only runnable coro is the
256	have no effect, and "schedule" would cause a deadlock unless there	473	currently running one, so "cede" would have no effect, and
257	is an idle handler that wakes up some coroutines.	474	"schedule" would cause a deadlock unless there is an idle handler
		475	that wakes up some coro.
258		476
259	my $guard = Coro::guard { ... }	477	my $guard = Coro::guard { ... }
260	This creates and returns a guard object. Nothing happens until the	478	This function still exists, but is deprecated. Please use the
261	object gets destroyed, in which case the codeblock given as argument	479	"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 $busy to be true
276	}
277		480
278	unblock_sub { ... }	481	unblock_sub { ... }
279	This utility function takes a BLOCK or code reference and "unblocks"	482	This utility function takes a BLOCK or code reference and "unblocks"
280	it, returning the new coderef. This means that the new coderef will	483	it, returning a new coderef. Unblocking means that calling the new
281	return immediately without blocking, returning nothing, while the	484	coderef will return immediately without blocking, returning nothing,
282	original code ref will be called (with parameters) from within its	485	while the original code ref will be called (with parameters) from
283	own coroutine.	486	within another coro.
284		487
285	The reason this function exists is that many event libraries (such	488	The reason this function exists is that many event libraries (such
286	as the venerable Event module) are not coroutine-safe (a weaker form	489	as the venerable Event module) are not thread-safe (a weaker form of
287	of thread-safety). This means you must not block within event	490	reentrancy). This means you must not block within event callbacks,
288	callbacks, otherwise you might suffer from crashes or worse.	491	otherwise you might suffer from crashes or worse. The only event
		492	library currently known that is safe to use without "unblock_sub" is
		493	EV (but you might still run into deadlocks if all event loops are
		494	blocked).
		495
		496	Coro will try to catch you when you block in the event loop
		497	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		498	and only works when you do not run your own event loop.
289		499
290	This function allows your callbacks to block by executing them in	500	This function allows your callbacks to block by executing them in
291	another coroutine where it is safe to block. One example where	501	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	502	is handy is when you use the Coro::AIO functions to save results to
293	results to disk.	503	disk, for example.
294		504
295	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	505	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
296	when creating event callbacks that want to block.	506	when creating event callbacks that want to block.
297		507
		508	If your handler does not plan to block (e.g. simply sends a message
		509	to another coro, or puts some other coro into the ready queue),
		510	there is no reason to use "unblock_sub".
		511
		512	Note that you also need to use "unblock_sub" for any other callbacks
		513	that are indirectly executed by any C-based event loop. For example,
		514	when you use a module that uses AnyEvent (and you use
		515	Coro::AnyEvent) and it provides callbacks that are the result of
		516	some event callback, then you must not block either, or use
		517	"unblock_sub".
		518
		519	$cb = rouse_cb
		520	Create and return a "rouse callback". That's a code reference that,
		521	when called, will remember a copy of its arguments and notify the
		522	owner coro of the callback.
		523
		524	See the next function.
		525
		526	@args = rouse_wait [$cb]
		527	Wait for the specified rouse callback (or the last one that was
		528	created in this coro).
		529
		530	As soon as the callback is invoked (or when the callback was invoked
		531	before "rouse_wait"), it will return the arguments originally passed
		532	to the rouse callback. In scalar context, that means you get the
		533	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		534	$a3...)" statement at the end.
		535
		536	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
		537	example.
		538
		539	HOW TO WAIT FOR A CALLBACK
		540	It is very common for a coro to wait for some callback to be called.
		541	This occurs naturally when you use coro in an otherwise event-based
		542	program, or when you use event-based libraries.
		543
		544	These typically register a callback for some event, and call that
		545	callback when the event occured. In a coro, however, you typically want
		546	to just wait for the event, simplyifying things.
		547
		548	For example "AnyEvent->child" registers a callback to be called when a
		549	specific child has exited:
		550
		551	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		552
		553	But from within a coro, you often just want to write this:
		554
		555	my $status = wait_for_child $pid;
		556
		557	Coro offers two functions specifically designed to make this easy,
		558	"Coro::rouse_cb" and "Coro::rouse_wait".
		559
		560	The first function, "rouse_cb", generates and returns a callback that,
		561	when invoked, will save its arguments and notify the coro that created
		562	the callback.
		563
		564	The second function, "rouse_wait", waits for the callback to be called
		565	(by calling "schedule" to go to sleep) and returns the arguments
		566	originally passed to the callback.
		567
		568	Using these functions, it becomes easy to write the "wait_for_child"
		569	function mentioned above:
		570
		571	sub wait_for_child($) {
		572	my ($pid) = @_;
		573
		574	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		575
		576	my ($rpid, $rstatus) = Coro::rouse_wait;
		577	$rstatus
		578	}
		579
		580	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
		581	you can roll your own, using "schedule":
		582
		583	sub wait_for_child($) {
		584	my ($pid) = @_;
		585
		586	# store the current coro in $current,
		587	# and provide result variables for the closure passed to ->child
		588	my $current = $Coro::current;
		589	my ($done, $rstatus);
		590
		591	# pass a closure to ->child
		592	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		593	$rstatus = $_[1]; # remember rstatus
		594	$done = 1; # mark $rstatus as valud
		595	});
		596
		597	# wait until the closure has been called
		598	schedule while !$done;
		599
		600	$rstatus
		601	}
		602
298	BUGS/LIMITATIONS	603	BUGS/LIMITATIONS
299	- you must make very sure that no coro is still active on global	604	fork with pthread backend
300	destruction. very bad things might happen otherwise (usually segfaults).	605	When Coro is compiled using the pthread backend (which isn't
		606	recommended but required on many BSDs as their libcs are completely
		607	broken), then coro will not survive a fork. There is no known
		608	workaround except to fix your libc and use a saner backend.
301		609
		610	perl process emulation ("threads")
302	- this module is not thread-safe. You should only ever use this module	611	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	612	this module from the first thread (this requirement might be removed
304	to allow per-thread schedulers, but Coro::State does not yet allow	613	in the future to allow per-thread schedulers, but Coro::State does
305	this).	614	not yet allow this). I recommend disabling thread support and using
		615	processes, as having the windows process emulation enabled under
		616	unix roughly halves perl performance, even when not used.
		617
		618	coro switching is not signal safe
		619	You must not switch to another coro from within a signal handler
		620	(only relevant with %SIG - most event libraries provide safe
		621	signals), unless you are sure you are not interrupting a Coro
		622	function.
		623
		624	That means you MUST NOT call any function that might "block" the
		625	current coro - "cede", "schedule" "Coro::Semaphore->down" or
		626	anything that calls those. Everything else, including calling
		627	"ready", works.
		628
		629	WINDOWS PROCESS EMULATION
		630	A great many people seem to be confused about ithreads (for example,
		631	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		632	while in the same mail making rather confused statements about perl
		633	ithreads (for example, that memory or files would be shared), showing
		634	his lack of understanding of this area - if it is hard to understand for
		635	Chip, it is probably not obvious to everybody).
		636
		637	What follows is an ultra-condensed version of my talk about threads in
		638	scripting languages given on the perl workshop 2009:
		639
		640	The so-called "ithreads" were originally implemented for two reasons:
		641	first, to (badly) emulate unix processes on native win32 perls, and
		642	secondly, to replace the older, real thread model ("5.005-threads").
		643
		644	It does that by using threads instead of OS processes. The difference
		645	between processes and threads is that threads share memory (and other
		646	state, such as files) between threads within a single process, while
		647	processes do not share anything (at least not semantically). That means
		648	that modifications done by one thread are seen by others, while
		649	modifications by one process are not seen by other processes.
		650
		651	The "ithreads" work exactly like that: when creating a new ithreads
		652	process, all state is copied (memory is copied physically, files and
		653	code is copied logically). Afterwards, it isolates all modifications. On
		654	UNIX, the same behaviour can be achieved by using operating system
		655	processes, except that UNIX typically uses hardware built into the
		656	system to do this efficiently, while the windows process emulation
		657	emulates this hardware in software (rather efficiently, but of course it
		658	is still much slower than dedicated hardware).
		659
		660	As mentioned before, loading code, modifying code, modifying data
		661	structures and so on is only visible in the ithreads process doing the
		662	modification, not in other ithread processes within the same OS process.
		663
		664	This is why "ithreads" do not implement threads for perl at all, only
		665	processes. What makes it so bad is that on non-windows platforms, you
		666	can actually take advantage of custom hardware for this purpose (as
		667	evidenced by the forks module, which gives you the (i-) threads API,
		668	just much faster).
		669
		670	Sharing data is in the i-threads model is done by transfering data
		671	structures between threads using copying semantics, which is very slow -
		672	shared data simply does not exist. Benchmarks using i-threads which are
		673	communication-intensive show extremely bad behaviour with i-threads (in
		674	fact, so bad that Coro, which cannot take direct advantage of multiple
		675	CPUs, is often orders of magnitude faster because it shares data using
		676	real threads, refer to my talk for details).
		677
		678	As summary, i-threads use threads to implement processes, while the
		679	compatible forks module uses processes to emulate, uhm, processes.
		680	I-threads slow down every perl program when enabled, and outside of
		681	windows, serve no (or little) practical purpose, but disadvantages every
		682	single-threaded Perl program.
		683
		684	This is the reason that I try to avoid the name "ithreads", as it is
		685	misleading as it implies that it implements some kind of thread model
		686	for perl, and prefer the name "windows process emulation", which
		687	describes the actual use and behaviour of it much better.
306		688
307	SEE ALSO	689	SEE ALSO
308	Lower level Configuration, Coroutine Environment: Coro::State.	690	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
309		691
310	Debugging: Coro::Debug.	692	Debugging: Coro::Debug.
311		693
312	Support/Utility: Coro::Specific, Coro::Util.	694	Support/Utility: Coro::Specific, Coro::Util.
313		695
314	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	696	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
315	Coro::SemaphoreSet, Coro::RWLock.	697	Coro::SemaphoreSet, Coro::RWLock.
316		698
317	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket.	699	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
318		700
319	Compatibility: Coro::LWP, Coro::Storable, Coro::Select.	701	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		702	for a better-working alternative), Coro::BDB, Coro::Storable,
		703	Coro::Select.
320		704
321	Embedding: Coro::MakeMaker.	705	XS API: Coro::MakeMaker.
		706
		707	Low level Configuration, Thread Environment, Continuations: Coro::State.
322		708
323	AUTHOR	709	AUTHOR
324	Marc Lehmann <schmorp@schmorp.de>	710	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	711	http://home.schmorp.de/
326		712

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