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1	NAME	1	NAME
2	Coro - coroutine process abstraction	2	Coro - the only real threads in perl
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use Coro;	5	use Coro;
6		6
7	async {	7	async {
8	# some asynchronous thread of execution	8	# some asynchronous thread of execution
9	print "2\n";	9	print "2\n";
10	cede; # yield back to main	10	cede; # yield back to main
11	print "4\n";	11	print "4\n";
12	};	12	};
13	print "1\n";	13	print "1\n";
14	cede; # yield to coroutine	14	cede; # yield to coro
15	print "3\n";	15	print "3\n";
16	cede; # and again	16	cede; # and again
17		17
18	# use locking	18	# use locking
19	use Coro::Semaphore;	19	use Coro::Semaphore;
20	my $lock = new Coro::Semaphore;	20	my $lock = new Coro::Semaphore;
21	my $locked;	21	my $locked;
22		22
23	$lock->down;	23	$lock->down;
24	$locked = 1;	24	$locked = 1;
25	$lock->up;	25	$lock->up;
26		26
27	DESCRIPTION	27	DESCRIPTION
28	This module collection manages coroutines. Coroutines are similar to	28	For a tutorial-style introduction, please read the Coro::Intro manpage.
29	threads but don't (in general) run in parallel at the same time even on	29	This manpage mainly contains reference information.
30	SMP machines. The specific flavor of coroutine used in this module also	30
31	guarantees you that it will not switch between coroutines unless	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
32	necessary, at easily-identified points in your program, so locking and	37	easily-identified points in your program, so locking and parallel access
33	parallel access are rarely an issue, making coroutine programming much	38	are rarely an issue, making thread programming much safer and easier
34	safer and easier than threads programming.	39	than using other thread models.
35		40
36	Unlike a normal perl program, however, coroutines allow you to have	41	Unlike the so-called "Perl threads" (which are not actually real threads
37	multiple running interpreters that share data, which is especially	42	but only the windows process emulation (see section of same name for
38	useful to code pseudo-parallel processes and for event-based	43	more details) ported to unix, and as such act as processes), Coro
39	programming, such as multiple HTTP-GET requests running concurrently.	44	provides a full shared address space, which makes communication between
40	See Coro::AnyEvent to learn more.	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.
41		51
42	Coroutines are also useful because Perl has no support for threads (the	52	Coro achieves that by supporting multiple running interpreters that
43	so called "threads" that perl offers are nothing more than the (bad)	53	share data, which is especially useful to code pseudo-parallel processes
44	process emulation coming from the Windows platform: On standard	54	and for event-based programming, such as multiple HTTP-GET requests
45	operating systems they serve no purpose whatsoever, except by making	55	running concurrently. See Coro::AnyEvent to learn more on how to
46	your programs slow and making them use a lot of memory. Best disable	56	integrate Coro into an event-based environment.
47	them when building perl, or aks your software vendor/distributor to do
48	it for you).
49		57
50	In this module, coroutines are defined as "callchain + lexical variables	58	In this module, a thread is defined as "callchain + lexical variables +
51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	59	some package variables + C stack), that is, a thread has its own
52	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
53	important global variables (see Coro::State for more configuration).	61	important global variables (see Coro::State for more configuration and
		62	background info).
54		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
55	$Coro::main	68	$Coro::main
56	This variable stores the coroutine object that represents the main	69	This variable stores the Coro object that represents the main
57	program. While you cna "ready" it and do most other things you can	70	program. While you cna "ready" it and do most other things you can
58	do to coroutines, it is mainly useful to compare again	71	do to coro, it is mainly useful to compare again $Coro::current, to
59	$Coro::current, to see whether you are running in the main program	72	see whether you are running in the main program or not.
60	or not.
61		73
62	$Coro::current	74	$Coro::current
63	The coroutine object representing the current coroutine (the last	75	The Coro object representing the current coro (the last coro that
64	coroutine that the Coro scheduler switched to). The initial value is	76	the Coro scheduler switched to). The initial value is $Coro::main
65	$main (of course).	77	(of course).
66		78
67	This variable is strictly read-only. You can take copies of the	79	This variable is strictly read-only. You can take copies of the
68	value stored in it and use it as any other coroutine object, but you	80	value stored in it and use it as any other Coro object, but you must
69	must not otherwise modify the variable itself.	81	not otherwise modify the variable itself.
70		82
71	$Coro::idle	83	$Coro::idle
72	This variable is mainly useful to integrate Coro into event loops.	84	This variable is mainly useful to integrate Coro into event loops.
73	It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as	85	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
74	this is pretty low-level functionality.	86	is pretty low-level functionality.
75		87
76	This variable stores a callback that is called whenever the	88	This variable stores a Coro object that is put into the ready queue
77	scheduler finds no ready coroutines to run. The default	89	when there are no other ready threads (without invoking any ready
78	implementation prints "FATAL: deadlock detected" and exits, because	90	hooks).
79	the program has no other way to continue.
80		91
		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.
		95
81	This hook is overwritten by modules such as "Coro::Timer" and	96	This hook is overwritten by modules such as "Coro::EV" and
82	"Coro::AnyEvent" to wait on an external event that hopefully wake up	97	"Coro::AnyEvent" to wait on an external event that hopefully wake up
83	a coroutine so the scheduler can run it.	98	a coro so the scheduler can run it.
84		99
85	Note that the callback must not, under any circumstances, block
86	the current coroutine. Normally, this is achieved by having an "idle
87	coroutine" that calls the event loop and then blocks again, and then
88	readying that coroutine in the idle handler.
89
90	See Coro::Event or Coro::AnyEvent for examples of using this	100	See Coro::EV or Coro::AnyEvent for examples of using this technique.
91	technique.
92		101
93	Please note that if your callback recursively invokes perl (e.g. for
94	event handlers), then it must be prepared to be called recursively
95	itself.
96
97	SIMPLE COROUTINE CREATION	102	SIMPLE CORO CREATION
98	async { ... } [@args...]	103	async { ... } [@args...]
99	Create a new coroutine and return it's coroutine object (usually	104	Create a new coro and return its Coro object (usually unused). The
100	unused). The coroutine will be put into the ready queue, so it will	105	coro will be put into the ready queue, so it will start running
101	start running automatically on the next scheduler run.	106	automatically on the next scheduler run.
102		107
103	The first argument is a codeblock/closure that should be executed in	108	The first argument is a codeblock/closure that should be executed in
104	the coroutine. When it returns argument returns the coroutine is	109	the coro. When it returns argument returns the coro is automatically
105	automatically terminated.	110	terminated.
106		111
107	The remaining arguments are passed as arguments to the closure.	112	The remaining arguments are passed as arguments to the closure.
108		113
109	See the "Coro::State::new" constructor for info about the coroutine	114	See the "Coro::State::new" constructor for info about the coro
110	environment in which coroutines are executed.	115	environment in which coro are executed.
111		116
112	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
113	outside the coroutine. Likewise, when the coroutine dies, the	118	the coro. Likewise, when the coro dies, the program will exit, just
114	program will exit, just as it would in the main program.	119	as it would in the main program.
115		120
116	If you do not want that, you can provide a default "die" handler, or	121	If you do not want that, you can provide a default "die" handler, or
117	simply avoid dieing (by use of "eval").	122	simply avoid dieing (by use of "eval").
118		123
119	Example: Create a new coroutine that just prints its arguments.	124	Example: Create a new coro that just prints its arguments.
120		125
121	async {	126	async {
122	print "@_\n";	127	print "@_\n";
123	} 1,2,3,4;	128	} 1,2,3,4;
124		129
125	async_pool { ... } [@args...]	130	async_pool { ... } [@args...]
126	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
127	call terminate or join on it (although you are allowed to), and you	132	terminate or join on it (although you are allowed to), and you get a
128	get a coroutine that might have executed other code already (which	133	coro that might have executed other code already (which can be good
129	can be good or bad :).	134	or bad :).
130		135
131	On the plus side, this function is faster than creating (and	136	On the plus side, this function is about twice as fast as creating
132	destroying) a completly new coroutine, so if you need a lot of	137	(and destroying) a completely new coro, so if you need a lot of
133	generic coroutines in quick successsion, use "async_pool", not	138	generic coros in quick successsion, use "async_pool", not "async".
134	"async".
135		139
136	The code 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
137	be issued in case of an exception instead of terminating the	141	be issued in case of an exception instead of terminating the
138	program, as "async" does. As the coroutine is being reused, stuff	142	program, as "async" does. As the coro is being reused, stuff like
139	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
140	terminate or cancel, which somehow defeats the purpose of pooling	144	terminate or cancel, which somehow defeats the purpose of pooling
141	(but is fine in the exceptional case).	145	(but is fine in the exceptional case).
142		146
143	The priority will be reset to 0 after each run, tracing will be	147	The priority will be reset to 0 after each run, tracing will be
144	disabled, the description will be reset and the default output	148	disabled, the description will be reset and the default output
145	filehandle gets restored, so you can change all these. Otherwise the	149	filehandle gets restored, so you can change all these. Otherwise the
146	coroutine will be re-used "as-is": most notably if you change other	150	coro will be re-used "as-is": most notably if you change other
147	per-coroutine global stuff such as $/ you must needs revert that	151	per-coro global stuff such as $/ you must needs revert that
148	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 $/".
149		153
150	The idle pool size is limited to 8 idle coroutines (this can be	154	The idle pool size is limited to 8 idle coros (this can be adjusted
151	adjusted by changing $Coro::POOL_SIZE), but there can be as many	155	by changing $Coro::POOL_SIZE), but there can be as many non-idle
152	non-idle coros as required.	156	coros as required.
153		157
154	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
155	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.
156	"async_pool { terminate }" once per second or so to slowly replenish	160	"async_pool { terminate }" once per second or so to slowly replenish
157	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
158	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also	162	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
159	be destroyed.	163	be destroyed.
160		164
161	STATIC METHODS	165	STATIC METHODS
162	Static methods are actually functions that operate on the current	166	Static methods are actually functions that implicitly operate on the
163	coroutine.	167	current coro.
164		168
165	schedule	169	schedule
166	Calls the scheduler. The scheduler will find the next coroutine that	170	Calls the scheduler. The scheduler will find the next coro that is
167	is to be run from the ready queue and switches to it. The next	171	to be run from the ready queue and switches to it. The next coro to
168	coroutine to be run is simply the one with the highest priority that	172	be run is simply the one with the highest priority that is longest
169	is longest in its ready queue. If there is no coroutine ready, it	173	in its ready queue. If there is no coro ready, it will call the
170	will clal the $Coro::idle hook.	174	$Coro::idle hook.
171		175
172	Please note that the current coroutine will not be put into the	176	Please note that the current coro will not be put into the ready
173	ready queue, so calling this function usually means you will never	177	queue, so calling this function usually means you will never be
174	be called again unless something else (e.g. an event handler) calls	178	called again unless something else (e.g. an event handler) calls
175	"->ready", thus waking you up.	179	"->ready", thus waking you up.
176		180
177	This makes "schedule" the generic method to use to block the	181	This makes "schedule" the generic method to use to block the
178	current coroutine and wait for events: first you remember the	182	current coro and wait for events: first you remember the current
179	current coroutine in a variable, then arrange for some callback of	183	coro in a variable, then arrange for some callback of yours to call
180	yours to call "->ready" on that once some event happens, and last	184	"->ready" on that once some event happens, and last you call
181	you call "schedule" to put yourself to sleep. Note that a lot of	185	"schedule" to put yourself to sleep. Note that a lot of things can
182	things can wake your coroutine up, so you need to check whether the	186	wake your coro up, so you need to check whether the event indeed
183	event indeed happened, e.g. by storing the status in a variable.	187	happened, e.g. by storing the status in a variable.
184		188
185	The canonical way to wait on external events is this:	189	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
186		190	callbacks.
187	{
188	# remember current coroutine
189	my $current = $Coro::current;
190
191	# register a hypothetical event handler
192	on_event_invoke sub {
193	# wake up sleeping coroutine
194	$current->ready;
195	undef $current;
196	};
197
198	# call schedule until event occurred.
199	# in case we are woken up for other reasons
200	# (current still defined), loop.
201	Coro::schedule while $current;
202	}
203		191
204	cede	192	cede
205	"Cede" to other coroutines. This function puts the current coroutine	193	"Cede" to other coros. This function puts the current coro into the
206	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
207	giving up the current "timeslice" to other coroutines of the same or	195	the current "timeslice" to other coros of the same or higher
208	higher priority. Once your coroutine gets its turn again it will	196	priority. Once your coro gets its turn again it will automatically
209	automatically be resumed.	197	be resumed.
210		198
211	This function is often called "yield" in other languages.	199	This function is often called "yield" in other languages.
212		200
213	Coro::cede_notself	201	Coro::cede_notself
214	Works like cede, but is not exported by default and will cede to	202	Works like cede, but is not exported by default and will cede to
215	any coroutine, regardless of priority. This is useful sometimes to	203	any coro, regardless of priority. This is useful sometimes to
216	ensure progress is made.	204	ensure progress is made.
217		205
218	terminate [arg...]	206	terminate [arg...]
219	Terminates the current coroutine with the given status values (see	207	Terminates the current coro with the given status values (see
220	cancel).	208	cancel).
221		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
		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
222	killall	296	killall
223	Kills/terminates/cancels all coroutines except the currently running	297	Kills/terminates/cancels all coros except the currently running one.
224	one. This is useful after a fork, either in the child or the parent,
225	as usually only one of them should inherit the running coroutines.
226		298
227	Note that while this will try to free some of the main programs	299	Note that while this will try to free some of the main interpreter
228	resources, you cannot free all of them, so if a coroutine that is	300	resources if the calling coro isn't the main coro, but one cannot
229	not the main program calls this function, there will be some	301	free all of them, so if a coro that is not the main coro calls this
230	one-time resource leak.	302	function, there will be some one-time resource leak.
231		303
232	COROUTINE METHODS	304	CORO OBJECT METHODS
233	These are the methods you can call on coroutine objects (or to create	305	These are the methods you can call on coro objects (or to create them).
234	them).
235		306
236	new Coro \&sub [, @args...]	307	new Coro \&sub [, @args...]
237	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
238	coroutine automatically terminates as if "terminate" with the	309	automatically terminates as if "terminate" with the returned values
239	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
240	first put it into the ready queue by calling the ready method.	311	ready queue by calling the ready method.
241		312
242	See "async" and "Coro::State::new" for additional info about the	313	See "async" and "Coro::State::new" for additional info about the
243	coroutine environment.	314	coro environment.
244		315
245	$success = $coroutine->ready	316	$success = $coro->ready
246	Put the given coroutine into the end of its ready queue (there is	317	Put the given coro into the end of its ready queue (there is one
247	one queue for each priority) and return true. If the coroutine is	318	queue for each priority) and return true. If the coro is already in
248	already in the ready queue, do nothing and return false.	319	the ready queue, do nothing and return false.
249		320
250	This ensures that the scheduler will resume this coroutine	321	This ensures that the scheduler will resume this coro automatically
251	automatically once all the coroutines of higher priority and all	322	once all the coro of higher priority and all coro of the same
252	coroutines of the same priority that were put into the ready queue	323	priority that were put into the ready queue earlier have been
253	earlier have been resumed.	324	resumed.
254		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
255	$is_ready = $coroutine->is_ready	350	$is_ready = $coro->is_ready
256	Return whether 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.
257		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
258	$coroutine->cancel (arg...)	364	$coro->cancel (arg...)
259	Terminates the given coroutine and makes it return the given	365	Terminates the given Coro and makes it return the given arguments as
260	arguments as status (default: the empty list). Never returns if the	366	status (default: the empty list). Never returns if the Coro is the
261	coroutine is the current coroutine.	367	current Coro.
262		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
263	$coroutine->throw ([$scalar])	386	$coro->throw ([$scalar])
264	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
265	exception inside the coroutine at the next convenient point in time	388	exception inside the coro at the next convenient point in time.
266	(usually after it gains control at the next schedule/transfer/cede).
267	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.
268		396
269	The exception object will be thrown "as is" with the specified	397	The exception object will be thrown "as is" with the specified
270	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
271	be appended (unlike with "die").	399	be appended (unlike with "die").
272		400
273	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
274	to end itself, although there is no guarantee that the exception	402	end itself, although there is no guarantee that the exception will
275	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
276	well end the whole program.	404	end the whole program.
277		405
278	You might also think of "throw" as being the moral equivalent of	406	You might also think of "throw" as being the moral equivalent of
279	"kill"ing a coroutine with a signal (in this case, a scalar).	407	"kill"ing a coro with a signal (in this case, a scalar).
280		408
281	$coroutine->join	409	$coro->join
282	Wait until the coroutine terminates and return any values given to	410	Wait until the coro terminates and return any values given to the
283	the "terminate" or "cancel" functions. "join" can be called	411	"terminate" or "cancel" functions. "join" can be called concurrently
284	concurrently from multiple coroutines, and all will be resumed and	412	from multiple coro, and all will be resumed and given the status
285	given the status return once the $coroutine terminates.	413	return once the $coro terminates.
286		414
287	$coroutine->on_destroy (\&cb)	415	$coro->on_destroy (\&cb)
288	Registers a callback that is called when this coroutine gets	416	Registers a callback that is called when this coro gets destroyed,
289	destroyed, but before it is joined. The callback gets passed the	417	but before it is joined. The callback gets passed the terminate
290	terminate arguments, if any, and must not die, under any	418	arguments, if any, and must not die, under any circumstances.
291	circumstances.
292		419
293	$oldprio = $coroutine->prio ($newprio)	420	$oldprio = $coro->prio ($newprio)
294	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.
295	coroutine. Higher priority coroutines get run before lower priority	422	Higher priority coro get run before lower priority coro. Priorities
296	coroutines. Priorities are small signed integers (currently -4 ..	423	are small signed integers (currently -4 .. +3), that you can refer
297	+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):
298	tag :prio to get then):
299		425
300	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
301	3 > 1 > 0 > -1 > -3 > -4	427	3 > 1 > 0 > -1 > -3 > -4
302		428
303	# set priority to HIGH	429	# set priority to HIGH
304	current->prio(PRIO_HIGH);	430	current->prio (PRIO_HIGH);
305		431
306	The idle coroutine ($Coro::idle) always has a lower priority than	432	The idle coro ($Coro::idle) always has a lower priority than any
307	any existing coroutine.	433	existing coro.
308		434
309	Changing the priority of the current coroutine will take effect	435	Changing the priority of the current coro will take effect
310	immediately, but changing the priority of coroutines in the ready	436	immediately, but changing the priority of coro in the ready queue
311	queue (but not running) will only take effect after the next	437	(but not running) will only take effect after the next schedule (of
312	schedule (of that coroutine). This is a bug that will be fixed in	438	that coro). This is a bug that will be fixed in some future version.
313	some future version.
314		439
315	$newprio = $coroutine->nice ($change)	440	$newprio = $coro->nice ($change)
316	Similar to "prio", but subtract the given value from the priority	441	Similar to "prio", but subtract the given value from the priority
317	(i.e. higher values mean lower priority, just as in unix).	442	(i.e. higher values mean lower priority, just as in unix).
318		443
319	$olddesc = $coroutine->desc ($newdesc)	444	$olddesc = $coro->desc ($newdesc)
320	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
321	this coroutine. This is just a free-form string you can associate	446	this coro. This is just a free-form string you can associate with a
322	with a coroutine.	447	coro.
323		448
324	This method simply sets the "$coroutine->{desc}" member to the given	449	This method simply sets the "$coro->{desc}" member to the given
325	string. You can modify this member directly if you wish.	450	string. You can modify this member directly if you wish.
326		451
327	GLOBAL FUNCTIONS	452	GLOBAL FUNCTIONS
328	Coro::nready	453	Coro::nready
329	Returns the number of coroutines that are currently in the ready	454	Returns the number of coro that are currently in the ready state,
330	state, i.e. that can be switched to by calling "schedule" directory	455	i.e. that can be switched to by calling "schedule" directory or
331	or indirectly. The value 0 means that the only runnable coroutine is	456	indirectly. The value 0 means that the only runnable coro is the
332	the currently running one, so "cede" would have no effect, and	457	currently running one, so "cede" would have no effect, and
333	"schedule" would cause a deadlock unless there is an idle handler	458	"schedule" would cause a deadlock unless there is an idle handler
334	that wakes up some coroutines.	459	that wakes up some coro.
335		460
336	my $guard = Coro::guard { ... }	461	my $guard = Coro::guard { ... }
337	This creates and returns a guard object. Nothing happens until the	462	This function still exists, but is deprecated. Please use the
338	object gets destroyed, in which case the codeblock given as argument	463	"Guard::guard" function instead.
339	will be executed. This is useful to free locks or other resources in
340	case of a runtime error or when the coroutine gets canceled, as in
341	both cases the guard block will be executed. The guard object
342	supports only one method, "->cancel", which will keep the codeblock
343	from being executed.
344
345	Example: set some flag and clear it again when the coroutine gets
346	canceled or the function returns:
347
348	sub do_something {
349	my $guard = Coro::guard { $busy = 0 };
350	$busy = 1;
351
352	# do something that requires $busy to be true
353	}
354		464
355	unblock_sub { ... }	465	unblock_sub { ... }
356	This utility function takes a BLOCK or code reference and "unblocks"	466	This utility function takes a BLOCK or code reference and "unblocks"
357	it, returning a new coderef. Unblocking means that calling the new	467	it, returning a new coderef. Unblocking means that calling the new
358	coderef will return immediately without blocking, returning nothing,	468	coderef will return immediately without blocking, returning nothing,
359	while the original code ref will be called (with parameters) from	469	while the original code ref will be called (with parameters) from
360	within another coroutine.	470	within another coro.
361		471
362	The reason this function exists is that many event libraries (such	472	The reason this function exists is that many event libraries (such
363	as the venerable Event module) are not coroutine-safe (a weaker form	473	as the venerable Event module) are not thread-safe (a weaker form of
364	of thread-safety). This means you must not block within event	474	reentrancy). This means you must not block within event callbacks,
365	callbacks, otherwise you might suffer from crashes or worse. The	475	otherwise you might suffer from crashes or worse. The only event
366	only event library currently known that is safe to use without	476	library currently known that is safe to use without "unblock_sub" is
367	"unblock_sub" is EV.	477	EV.
368		478
369	This function allows your callbacks to block by executing them in	479	This function allows your callbacks to block by executing them in
370	another coroutine where it is safe to block. One example where	480	another coro where it is safe to block. One example where blocking
371	blocking is handy is when you use the Coro::AIO functions to save	481	is handy is when you use the Coro::AIO functions to save results to
372	results to disk, for example.	482	disk, for example.
373		483
374	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	484	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
375	when creating event callbacks that want to block.	485	when creating event callbacks that want to block.
376		486
377	If your handler does not plan to block (e.g. simply sends a message	487	If your handler does not plan to block (e.g. simply sends a message
378	to another coroutine, or puts some other coroutine into the ready	488	to another coro, or puts some other coro into the ready queue),
379	queue), there is no reason to use "unblock_sub".	489	there is no reason to use "unblock_sub".
380		490
381	Note that you also need to use "unblock_sub" for any other callbacks	491	Note that you also need to use "unblock_sub" for any other callbacks
382	that are indirectly executed by any C-based event loop. For example,	492	that are indirectly executed by any C-based event loop. For example,
383	when you use a module that uses AnyEvent (and you use	493	when you use a module that uses AnyEvent (and you use
384	Coro::AnyEvent) and it provides callbacks that are the result of	494	Coro::AnyEvent) and it provides callbacks that are the result of
385	some event callback, then you must not block either, or use	495	some event callback, then you must not block either, or use
386	"unblock_sub".	496	"unblock_sub".
387		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	}
		581
388	BUGS/LIMITATIONS	582	BUGS/LIMITATIONS
		583	fork with pthread backend
		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.
		588
		589	perl process emulation ("threads")
389	This module is not perl-pseudo-thread-safe. You should only ever use	590	This module is not perl-pseudo-thread-safe. You should only ever use
390	this module from the same thread (this requirement might be removed in	591	this module from the first thread (this requirement might be removed
391	the future to allow per-thread schedulers, but Coro::State does not yet	592	in the future to allow per-thread schedulers, but Coro::State does
392	allow this). I recommend disabling thread support and using processes,	593	not yet allow this). I recommend disabling thread support and using
393	as this is much faster and uses less memory.	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.
394		666
395	SEE ALSO	667	SEE ALSO
396	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	668	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
397		669
398	Debugging: Coro::Debug.	670	Debugging: Coro::Debug.
399		671
400	Support/Utility: Coro::Specific, Coro::Util.	672	Support/Utility: Coro::Specific, Coro::Util.
401		673
402	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	674	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
403	Coro::SemaphoreSet, Coro::RWLock.	675	Coro::SemaphoreSet, Coro::RWLock.
404		676
405	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.	677	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
406		678
407	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.	679	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		680	for a better-working alternative), Coro::BDB, Coro::Storable,
		681	Coro::Select.
408		682
409	XS API: Coro::MakeMaker.	683	XS API: Coro::MakeMaker.
410		684
411	Low level Configuration, Coroutine Environment: Coro::State.	685	Low level Configuration, Thread Environment, Continuations: Coro::State.
412		686
413	AUTHOR	687	AUTHOR
414	Marc Lehmann <schmorp@schmorp.de>	688	Marc Lehmann <schmorp@schmorp.de>
415	http://home.schmorp.de/	689	http://home.schmorp.de/
416		690

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