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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 completely 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 to revert	151	per-coro global stuff such as $/ you must needs revert that
148	that 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	$/ ".
150		153
151	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
152	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
153	coros as required.	156	coros as required.
154		157
155	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
156	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.
157	"async_pool { terminate }" once per second or so to slowly replenish	160	"async_pool { terminate }" once per second or so to slowly replenish
158	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
159	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
160	be destroyed.	163	be destroyed.
161		164
162	STATIC METHODS	165	STATIC METHODS
163	Static methods are actually functions that operate on the current	166	Static methods are actually functions that implicitly operate on the
164	coroutine.	167	current coro.
165		168
166	schedule	169	schedule
167	Calls the scheduler. The scheduler will find the next coroutine that	170	Calls the scheduler. The scheduler will find the next coro that is
168	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
169	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
170	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
171	will clal the $Coro::idle hook.	174	$Coro::idle hook.
172		175
173	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
174	ready queue, so calling this function usually means you will never	177	queue, so calling this function usually means you will never be
175	be called again unless something else (e.g. an event handler) calls	178	called again unless something else (e.g. an event handler) calls
176	"->ready", thus waking you up.	179	"->ready", thus waking you up.
177		180
178	This makes "schedule" the generic method to use to block the	181	This makes "schedule" the generic method to use to block the
179	current coroutine and wait for events: first you remember the	182	current coro and wait for events: first you remember the current
180	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
181	yours to call "->ready" on that once some event happens, and last	184	"->ready" on that once some event happens, and last you call
182	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
183	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
184	event indeed happened, e.g. by storing the status in a variable.	187	happened, e.g. by storing the status in a variable.
185		188
186	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
187		190	callbacks.
188	{
189	# remember current coroutine
190	my $current = $Coro::current;
191
192	# register a hypothetical event handler
193	on_event_invoke sub {
194	# wake up sleeping coroutine
195	$current->ready;
196	undef $current;
197	};
198
199	# call schedule until event occurred.
200	# in case we are woken up for other reasons
201	# (current still defined), loop.
202	Coro::schedule while $current;
203	}
204		191
205	cede	192	cede
206	"Cede" to other coroutines. This function puts the current coroutine	193	"Cede" to other coros. This function puts the current coro into the
207	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
208	giving up the current "timeslice" to other coroutines of the same or	195	the current "timeslice" to other coros of the same or higher
209	higher priority. Once your coroutine gets its turn again it will	196	priority. Once your coro gets its turn again it will automatically
210	automatically be resumed.	197	be resumed.
211		198
212	This function is often called "yield" in other languages.	199	This function is often called "yield" in other languages.
213		200
214	Coro::cede_notself	201	Coro::cede_notself
215	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
216	any coroutine, regardless of priority. This is useful sometimes to	203	any coro, regardless of priority. This is useful sometimes to
217	ensure progress is made.	204	ensure progress is made.
218		205
219	terminate [arg...]	206	terminate [arg...]
220	Terminates the current coroutine with the given status values (see	207	Terminates the current coro with the given status values (see
221	cancel).	208	cancel).
222		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
223	killall	296	killall
224	Kills/terminates/cancels all coroutines except the currently running	297	Kills/terminates/cancels all coros except the currently running one.
225	one. This is useful after a fork, either in the child or the parent,
226	as usually only one of them should inherit the running coroutines.
227		298
228	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
229	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
230	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
231	one-time resource leak.	302	function, there will be some one-time resource leak.
232		303
233	COROUTINE METHODS	304	CORO OBJECT METHODS
234	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).
235	them).
236		306
237	new Coro \&sub [, @args...]	307	new Coro \&sub [, @args...]
238	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
239	coroutine automatically terminates as if "terminate" with the	309	automatically terminates as if "terminate" with the returned values
240	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
241	first put it into the ready queue by calling the ready method.	311	ready queue by calling the ready method.
242		312
243	See "async" and "Coro::State::new" for additional info about the	313	See "async" and "Coro::State::new" for additional info about the
244	coroutine environment.	314	coro environment.
245		315
246	$success = $coroutine->ready	316	$success = $coro->ready
247	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
248	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
249	already in the ready queue, do nothing and return false.	319	the ready queue, do nothing and return false.
250		320
251	This ensures that the scheduler will resume this coroutine	321	This ensures that the scheduler will resume this coro automatically
252	automatically once all the coroutines of higher priority and all	322	once all the coro of higher priority and all coro of the same
253	coroutines of the same priority that were put into the ready queue	323	priority that were put into the ready queue earlier have been
254	earlier have been resumed.	324	resumed.
255		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
256	$is_ready = $coroutine->is_ready	350	$is_ready = $coro->is_ready
257	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.
258		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
259	$coroutine->cancel (arg...)	364	$coro->cancel (arg...)
260	Terminates the given coroutine and makes it return the given	365	Terminates the given Coro and makes it return the given arguments as
261	arguments as status (default: the empty list). Never returns if the	366	status (default: the empty list). Never returns if the Coro is the
262	coroutine is the current coroutine.	367	current Coro.
263		368
		369	$coro->schedule_to
		370	Puts the current coro to sleep (like "Coro::schedule"), but instead
		371	of continuing with the next coro from the ready queue, always switch
		372	to the given coro object (regardless of priority etc.). The
		373	readyness state of that coro isn't changed.
		374
		375	This is an advanced method for special cases - I'd love to hear
		376	about any uses for this one.
		377
		378	$coro->cede_to
		379	Like "schedule_to", but puts the current coro into the ready queue.
		380	This has the effect of temporarily switching to the given coro, and
		381	continuing some time later.
		382
		383	This is an advanced method for special cases - I'd love to hear
		384	about any uses for this one.
		385
		386	$coro->throw ([$scalar])
		387	If $throw is specified and defined, it will be thrown as an
		388	exception inside the coro at the next convenient point in time.
		389	Otherwise clears the exception object.
		390
		391	Coro will check for the exception each time a schedule-like-function
		392	returns, i.e. after each "schedule", "cede",
		393	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
		394	these functions detect this case and return early in case an
		395	exception is pending.
		396
		397	The exception object will be thrown "as is" with the specified
		398	scalar in $@, i.e. if it is a string, no line number or newline will
		399	be appended (unlike with "die").
		400
		401	This can be used as a softer means than "cancel" to ask a coro to
		402	end itself, although there is no guarantee that the exception will
		403	lead to termination, and if the exception isn't caught it might well
		404	end the whole program.
		405
		406	You might also think of "throw" as being the moral equivalent of
		407	"kill"ing a coro with a signal (in this case, a scalar).
		408
264	$coroutine->join	409	$coro->join
265	Wait until the coroutine terminates and return any values given to	410	Wait until the coro terminates and return any values given to the
266	the "terminate" or "cancel" functions. "join" can be called	411	"terminate" or "cancel" functions. "join" can be called concurrently
267	concurrently from multiple coroutines, and all will be resumed and	412	from multiple coro, and all will be resumed and given the status
268	given the status return once the $coroutine terminates.	413	return once the $coro terminates.
269		414
270	$coroutine->on_destroy (\&cb)	415	$coro->on_destroy (\&cb)
271	Registers a callback that is called when this coroutine gets	416	Registers a callback that is called when this coro thread gets
272	destroyed, but before it is joined. The callback gets passed the	417	destroyed, but before it is joined. The callback gets passed the
273	terminate arguments, if any, and must not die, under any	418	terminate arguments, if any, and must not die, under any
274	circumstances.	419	circumstances.
275		420
		421	There can be any number of "on_destroy" callbacks per coro.
		422
276	$oldprio = $coroutine->prio ($newprio)	423	$oldprio = $coro->prio ($newprio)
277	Sets (or gets, if the argument is missing) the priority of the	424	Sets (or gets, if the argument is missing) the priority of the coro
278	coroutine. Higher priority coroutines get run before lower priority	425	thread. Higher priority coro get run before lower priority coros.
279	coroutines. Priorities are small signed integers (currently -4 ..	426	Priorities are small signed integers (currently -4 .. +3), that you
280	+3), that you can refer to using PRIO_xxx constants (use the import	427	can refer to using PRIO_xxx constants (use the import tag :prio to
281	tag :prio to get then):	428	get then):
282		429
283	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	430	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
284	3 > 1 > 0 > -1 > -3 > -4	431	3 > 1 > 0 > -1 > -3 > -4
285		432
286	# set priority to HIGH	433	# set priority to HIGH
287	current->prio(PRIO_HIGH);	434	current->prio (PRIO_HIGH);
288		435
289	The idle coroutine ($Coro::idle) always has a lower priority than	436	The idle coro thread ($Coro::idle) always has a lower priority than
290	any existing coroutine.	437	any existing coro.
291		438
292	Changing the priority of the current coroutine will take effect	439	Changing the priority of the current coro will take effect
293	immediately, but changing the priority of coroutines in the ready	440	immediately, but changing the priority of a coro in the ready queue
294	queue (but not running) will only take effect after the next	441	(but not running) will only take effect after the next schedule (of
295	schedule (of that coroutine). This is a bug that will be fixed in	442	that coro). This is a bug that will be fixed in some future version.
296	some future version.
297		443
298	$newprio = $coroutine->nice ($change)	444	$newprio = $coro->nice ($change)
299	Similar to "prio", but subtract the given value from the priority	445	Similar to "prio", but subtract the given value from the priority
300	(i.e. higher values mean lower priority, just as in unix).	446	(i.e. higher values mean lower priority, just as in UNIX's nice
		447	command).
301		448
302	$olddesc = $coroutine->desc ($newdesc)	449	$olddesc = $coro->desc ($newdesc)
303	Sets (or gets in case the argument is missing) the description for	450	Sets (or gets in case the argument is missing) the description for
304	this coroutine. This is just a free-form string you can associate	451	this coro thread. This is just a free-form string you can associate
305	with a coroutine.	452	with a coro.
306		453
307	This method simply sets the "$coroutine->{desc}" member to the given	454	This method simply sets the "$coro->{desc}" member to the given
308	string. You can modify this member directly if you wish.	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:
309		458
310	$coroutine->throw ([$scalar])	459	sub my_long_function {
311	If $throw is specified and defined, it will be thrown as an	460	local $Coro::current->{desc} = "now in my_long_function";
312	exception inside the coroutine at the next convinient point in time	461	...
313	(usually after it gains control at the next schedule/transfer/cede).	462	$Coro::current->{desc} = "my_long_function: phase 1";
314	Otherwise clears the exception object.	463	...
		464	$Coro::current->{desc} = "my_long_function: phase 2";
		465	...
		466	}
315		467
316	The exception object will be thrown "as is" with the specified
317	scalar in $@, i.e. if it is a string, no line number or newline will
318	be appended (unlike with "die").
319
320	This can be used as a softer means than "cancel" to ask a coroutine
321	to end itself, although there is no guarentee that the exception
322	will lead to termination, and if the exception isn't caught it might
323	well end the whole program.
324
325	GLOBAL FUNCTIONS	468	GLOBAL FUNCTIONS
326	Coro::nready	469	Coro::nready
327	Returns the number of coroutines that are currently in the ready	470	Returns the number of coro that are currently in the ready state,
328	state, i.e. that can be switched to by calling "schedule" directory	471	i.e. that can be switched to by calling "schedule" directory or
329	or indirectly. The value 0 means that the only runnable coroutine is	472	indirectly. The value 0 means that the only runnable coro is the
330	the currently running one, so "cede" would have no effect, and	473	currently running one, so "cede" would have no effect, and
331	"schedule" would cause a deadlock unless there is an idle handler	474	"schedule" would cause a deadlock unless there is an idle handler
332	that wakes up some coroutines.	475	that wakes up some coro.
333		476
334	my $guard = Coro::guard { ... }	477	my $guard = Coro::guard { ... }
335	This creates and returns a guard object. Nothing happens until the	478	This function still exists, but is deprecated. Please use the
336	object gets destroyed, in which case the codeblock given as argument	479	"Guard::guard" function instead.
337	will be executed. This is useful to free locks or other resources in
338	case of a runtime error or when the coroutine gets canceled, as in
339	both cases the guard block will be executed. The guard object
340	supports only one method, "->cancel", which will keep the codeblock
341	from being executed.
342
343	Example: set some flag and clear it again when the coroutine gets
344	canceled or the function returns:
345
346	sub do_something {
347	my $guard = Coro::guard { $busy = 0 };
348	$busy = 1;
349
350	# do something that requires $busy to be true
351	}
352		480
353	unblock_sub { ... }	481	unblock_sub { ... }
354	This utility function takes a BLOCK or code reference and "unblocks"	482	This utility function takes a BLOCK or code reference and "unblocks"
355	it, returning a new coderef. Unblocking means that calling the new	483	it, returning a new coderef. Unblocking means that calling the new
356	coderef will return immediately without blocking, returning nothing,	484	coderef will return immediately without blocking, returning nothing,
357	while the original code ref will be called (with parameters) from	485	while the original code ref will be called (with parameters) from
358	within another coroutine.	486	within another coro.
359		487
360	The reason this function exists is that many event libraries (such	488	The reason this function exists is that many event libraries (such
361	as the venerable Event module) are not coroutine-safe (a weaker form	489	as the venerable Event module) are not thread-safe (a weaker form of
362	of thread-safety). This means you must not block within event	490	reentrancy). This means you must not block within event callbacks,
363	callbacks, otherwise you might suffer from crashes or worse. The	491	otherwise you might suffer from crashes or worse. The only event
364	only event library currently known that is safe to use without	492	library currently known that is safe to use without "unblock_sub" is
365	"unblock_sub" is EV.	493	EV (but you might still run into deadlocks if all event loops are
		494	blocked).
		495
		496	Coro will try to catch you when you block in the event loop
		497	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		498	and only works when you do not run your own event loop.
366		499
367	This function allows your callbacks to block by executing them in	500	This function allows your callbacks to block by executing them in
368	another coroutine where it is safe to block. One example where	501	another coro where it is safe to block. One example where blocking
369	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
370	results to disk, for example.	503	disk, for example.
371		504
372	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	505	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
373	when creating event callbacks that want to block.	506	when creating event callbacks that want to block.
374		507
375	If your handler does not plan to block (e.g. simply sends a message	508	If your handler does not plan to block (e.g. simply sends a message
376	to another coroutine, or puts some other coroutine into the ready	509	to another coro, or puts some other coro into the ready queue),
377	queue), there is no reason to use "unblock_sub".	510	there is no reason to use "unblock_sub".
378		511
379	Note that you also need to use "unblock_sub" for any other callbacks	512	Note that you also need to use "unblock_sub" for any other callbacks
380	that are indirectly executed by any C-based event loop. For example,	513	that are indirectly executed by any C-based event loop. For example,
381	when you use a module that uses AnyEvent (and you use	514	when you use a module that uses AnyEvent (and you use
382	Coro::AnyEvent) and it provides callbacks that are the result of	515	Coro::AnyEvent) and it provides callbacks that are the result of
383	some event callback, then you must not block either, or use	516	some event callback, then you must not block either, or use
384	"unblock_sub".	517	"unblock_sub".
385		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
386	BUGS/LIMITATIONS	603	BUGS/LIMITATIONS
		604	fork with pthread backend
		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.
		609
		610	perl process emulation ("threads")
387	This module is not perl-pseudo-thread-safe. You should only ever use	611	This module is not perl-pseudo-thread-safe. You should only ever use
388	this module from the same thread (this requirement might be removed in	612	this module from the first thread (this requirement might be removed
389	the future to allow per-thread schedulers, but Coro::State does not yet	613	in the future to allow per-thread schedulers, but Coro::State does
390	allow this). I recommend disabling thread support and using processes,	614	not yet allow this). I recommend disabling thread support and using
391	as this is much faster and uses less memory.	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.
392		688
393	SEE ALSO	689	SEE ALSO
394	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	690	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
395		691
396	Debugging: Coro::Debug.	692	Debugging: Coro::Debug.
397		693
398	Support/Utility: Coro::Specific, Coro::Util.	694	Support/Utility: Coro::Specific, Coro::Util.
399		695
400	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	696	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
401	Coro::SemaphoreSet, Coro::RWLock.	697	Coro::SemaphoreSet, Coro::RWLock.
402		698
403	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.	699	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
404		700
405	Compatibility: Coro::LWP, Coro::BDB, 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.
406		704
407	XS API: Coro::MakeMaker.	705	XS API: Coro::MakeMaker.
408		706
409	Low level Configuration, Coroutine Environment: Coro::State.	707	Low level Configuration, Thread Environment, Continuations: Coro::State.
410		708
411	AUTHOR	709	AUTHOR
412	Marc Lehmann <schmorp@schmorp.de>	710	Marc Lehmann <schmorp@schmorp.de>
413	http://home.schmorp.de/	711	http://home.schmorp.de/
414		712

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Revision 1.28 by root, Sun Feb 13 04:39:15 2011 UTC