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…		…
1	NAME	1	NAME
2	Coro - the only real threads in perl	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;
20	my $lock = new Coro::Semaphore;	19	my $lock = new Coro::Semaphore;
21	my $locked;	20	my $locked;
22		21
23	$lock->down;	22	$lock->down;
24	$locked = 1;	23	$locked = 1;
25	$lock->up;	24	$lock->up;
26		25
27	DESCRIPTION	26	DESCRIPTION
28	For a tutorial-style introduction, please read the Coro::Intro manpage.	27	For a tutorial-style introduction, please read the Coro::Intro manpage.
29	This manpage mainly contains reference information.	28	This manpage mainly contains reference information.
30		29
31	This module collection manages continuations in general, most often in	30	This module collection manages continuations in general, most often in
32	the form of cooperative threads (also called coroutines in the	31	the form of cooperative threads (also called coros, or simply "coro" in
33	documentation). They are similar to kernel threads but don't (in	32	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	33	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	34	specific flavor of thread offered by this module also guarantees you
36	that it will not switch between threads unless necessary, at	35	that it will not switch between threads unless necessary, at
37	easily-identified points in your program, so locking and parallel access	36	easily-identified points in your program, so locking and parallel access
38	are rarely an issue, making thread programming much safer and easier	37	are rarely an issue, making thread programming much safer and easier
39	than using other thread models.	38	than using other thread models.
40		39
41	Unlike the so-called "Perl threads" (which are not actually real threads	40	Unlike the so-called "Perl threads" (which are not actually real threads
42	but only the windows process emulation ported to unix), Coro provides a	41	but only the windows process emulation (see section of same name for
		42	more details) ported to UNIX, and as such act as processes), Coro
43	full shared address space, which makes communication between threads	43	provides a full shared address space, which makes communication between
44	very easy. And threads are fast, too: disabling the Windows process	44	threads very easy. And coro threads are fast, too: disabling the Windows
45	emulation code in your perl and using Coro can easily result in a two to	45	process emulation code in your perl and using Coro can easily result in
46	four times speed increase for your programs.	46	a two to four times speed increase for your programs. A parallel matrix
		47	multiplication benchmark (very communication-intensive) runs over 300
		48	times faster on a single core than perls pseudo-threads on a quad core
		49	using all four cores.
47		50
48	Coro achieves that by supporting multiple running interpreters that	51	Coro achieves that by supporting multiple running interpreters that
49	share data, which is especially useful to code pseudo-parallel processes	52	share data, which is especially useful to code pseudo-parallel processes
50	and for event-based programming, such as multiple HTTP-GET requests	53	and for event-based programming, such as multiple HTTP-GET requests
51	running concurrently. See Coro::AnyEvent to learn more on how to	54	running concurrently. See Coro::AnyEvent to learn more on how to
52	integrate Coro into an event-based environment.	55	integrate Coro into an event-based environment.
53		56
54	In this module, a thread is defined as "callchain + lexical variables +	57	In this module, a thread is defined as "callchain + lexical variables +
55	@_ + $_ + $@ + $/ + C stack), that is, a thread has its own callchain,	58	some package variables + C stack), that is, a thread has its own
56	its own set of lexicals and its own set of perls most important global	59	callchain, its own set of lexicals and its own set of perls most
57	variables (see Coro::State for more configuration and background info).	60	important global variables (see Coro::State for more configuration and
		61	background info).
58		62
59	See also the "SEE ALSO" section at the end of this document - the Coro	63	See also the "SEE ALSO" section at the end of this document - the Coro
60	module family is quite large.	64	module family is quite large.
61		65
		66	CORO THREAD LIFE CYCLE
		67	During the long and exciting (or not) life of a coro thread, it goes
		68	through a number of states:
		69
		70	1. Creation
		71	The first thing in the life of a coro thread is it's creation -
		72	obviously. The typical way to create a thread is to call the "async
		73	BLOCK" function:
		74
		75	async {
		76	# thread code goes here
		77	};
		78
		79	You can also pass arguments, which are put in @_:
		80
		81	async {
		82	print $_[1]; # prints 2
		83	} 1, 2, 3;
		84
		85	This creates a new coro thread and puts it into the ready queue,
		86	meaning it will run as soon as the CPU is free for it.
		87
		88	"async" will return a Coro object - you can store this for future
		89	reference or ignore it - a thread that is running, ready to run or
		90	waiting for some event is alive on it's own.
		91
		92	Another way to create a thread is to call the "new" constructor with
		93	a code-reference:
		94
		95	new Coro sub {
		96	# thread code goes here
		97	}, @optional_arguments;
		98
		99	This is quite similar to calling "async", but the important
		100	difference is that the new thread is not put into the ready queue,
		101	so the thread will not run until somebody puts it there. "async" is,
		102	therefore, identical to this sequence:
		103
		104	my $coro = new Coro sub {
		105	# thread code goes here
		106	};
		107	$coro->ready;
		108	return $coro;
		109
		110	2. Startup
		111	When a new coro thread is created, only a copy of the code reference
		112	and the arguments are stored, no extra memory for stacks and so on
		113	is allocated, keeping the coro thread in a low-memory state.
		114
		115	Only when it actually starts executing will all the resources be
		116	finally allocated.
		117
		118	The optional arguments specified at coro creation are available in
		119	@_, similar to function calls.
		120
		121	3. Running / Blocking
		122	A lot can happen after the coro thread has started running. Quite
		123	usually, it will not run to the end in one go (because you could use
		124	a function instead), but it will give up the CPU regularly because
		125	it waits for external events.
		126
		127	As long as a coro thread runs, its Coro object is available in the
		128	global variable $Coro::current.
		129
		130	The low-level way to give up the CPU is to call the scheduler, which
		131	selects a new coro thread to run:
		132
		133	Coro::schedule;
		134
		135	Since running threads are not in the ready queue, calling the
		136	scheduler without doing anything else will block the coro thread
		137	forever - you need to arrange either for the coro to put woken up
		138	(readied) by some other event or some other thread, or you can put
		139	it into the ready queue before scheduling:
		140
		141	# this is exactly what Coro::cede does
		142	$Coro::current->ready;
		143	Coro::schedule;
		144
		145	All the higher-level synchronisation methods (Coro::Semaphore,
		146	Coro::rouse_*...) are actually implemented via "->ready" and
		147	"Coro::schedule".
		148
		149	While the coro thread is running it also might get assigned a
		150	C-level thread, or the C-level thread might be unassigned from it,
		151	as the Coro runtime wishes. A C-level thread needs to be assigned
		152	when your perl thread calls into some C-level function and that
		153	function in turn calls perl and perl then wants to switch
		154	coroutines. This happens most often when you run an event loop and
		155	block in the callback, or when perl itself calls some function such
		156	as "AUTOLOAD" or methods via the "tie" mechanism.
		157
		158	4. Termination
		159	Many threads actually terminate after some time. There are a number
		160	of ways to terminate a coro thread, the simplest is returning from
		161	the top-level code reference:
		162
		163	async {
		164	# after returning from here, the coro thread is terminated
		165	};
		166
		167	async {
		168	return if 0.5 < rand; # terminate a little earlier, maybe
		169	print "got a chance to print this\n";
		170	# or here
		171	};
		172
		173	Any values returned from the coroutine can be recovered using
		174	"->join":
		175
		176	my $coro = async {
		177	"hello, world\n" # return a string
		178	};
		179
		180	my $hello_world = $coro->join;
		181
		182	print $hello_world;
		183
		184	Another way to terminate is to call "Coro::terminate", which at any
		185	subroutine call nesting level:
		186
		187	async {
		188	Coro::terminate "return value 1", "return value 2";
		189	};
		190
		191	Yet another way is to "->cancel" (or "->safe_cancel") the coro
		192	thread from another thread:
		193
		194	my $coro = async {
		195	exit 1;
		196	};
		197
		198	$coro->cancel; # also accepts values for ->join to retrieve
		199
		200	Cancellation can be dangerous - it's a bit like calling "exit"
		201	without actually exiting, and might leave C libraries and XS modules
		202	in a weird state. Unlike other thread implementations, however, Coro
		203	is exceptionally safe with regards to cancellation, as perl will
		204	always be in a consistent state, and for those cases where you want
		205	to do truly marvellous things with your coro while it is being
		206	cancelled - that is, make sure all cleanup code is executed from the
		207	thread being cancelled - there is even a "->safe_cancel" method.
		208
		209	So, cancelling a thread that runs in an XS event loop might not be
		210	the best idea, but any other combination that deals with perl only
		211	(cancelling when a thread is in a "tie" method or an "AUTOLOAD" for
		212	example) is safe.
		213
		214	Last not least, a coro thread object that isn't referenced is
		215	"->cancel"'ed automatically - just like other objects in Perl. This
		216	is not such a common case, however - a running thread is referencedy
		217	by $Coro::current, a thread ready to run is referenced by the ready
		218	queue, a thread waiting on a lock or semaphore is referenced by
		219	being in some wait list and so on. But a thread that isn't in any of
		220	those queues gets cancelled:
		221
		222	async {
		223	schedule; # cede to other coros, don't go into the ready queue
		224	};
		225
		226	cede;
		227	# now the async above is destroyed, as it is not referenced by anything.
		228
		229	A slightly embellished example might make it clearer:
		230
		231	async {
		232	my $guard = Guard::guard { print "destroyed\n" };
		233	schedule while 1;
		234	};
		235
		236	cede;
		237
		238	Superficially one might not expect any output - since the "async"
		239	implements an endless loop, the $guard will not be cleaned up.
		240	However, since the thread object returned by "async" is not stored
		241	anywhere, the thread is initially referenced because it is in the
		242	ready queue, when it runs it is referenced by $Coro::current, but
		243	when it calls "schedule", it gets "cancel"ed causing the guard
		244	object to be destroyed (see the next section), and printing it's
		245	message.
		246
		247	If this seems a bit drastic, remember that this only happens when
		248	nothing references the thread anymore, which means there is no way
		249	to further execute it, ever. The only options at this point are
		250	leaking the thread, or cleaning it up, which brings us to...
		251
		252	5. Cleanup
		253	Threads will allocate various resources. Most but not all will be
		254	returned when a thread terminates, during clean-up.
		255
		256	Cleanup is quite similar to throwing an uncaught exception: perl
		257	will work it's way up through all subroutine calls and blocks. On
		258	it's way, it will release all "my" variables, undo all "local"'s and
		259	free any other resources truly local to the thread.
		260
		261	So, a common way to free resources is to keep them referenced only
		262	by my variables:
		263
		264	async {
		265	my $big_cache = new Cache ...;
		266	};
		267
		268	If there are no other references, then the $big_cache object will be
		269	freed when the thread terminates, regardless of how it does so.
		270
		271	What it does "NOT" do is unlock any Coro::Semaphores or similar
		272	resources, but that's where the "guard" methods come in handy:
		273
		274	my $sem = new Coro::Semaphore;
		275
		276	async {
		277	my $lock_guard = $sem->guard;
		278	# if we return, or die or get cancelled, here,
		279	# then the semaphore will be "up"ed.
		280	};
		281
		282	The "Guard::guard" function comes in handy for any custom cleanup
		283	you might want to do (but you cannot switch to other coroutines from
		284	those code blocks):
		285
		286	async {
		287	my $window = new Gtk2::Window "toplevel";
		288	# The window will not be cleaned up automatically, even when $window
		289	# gets freed, so use a guard to ensure it's destruction
		290	# in case of an error:
		291	my $window_guard = Guard::guard { $window->destroy };
		292
		293	# we are safe here
		294	};
		295
		296	Last not least, "local" can often be handy, too, e.g. when
		297	temporarily replacing the coro thread description:
		298
		299	sub myfunction {
		300	local $Coro::current->{desc} = "inside myfunction(@_)";
		301
		302	# if we return or die here, the description will be restored
		303	}
		304
		305	6. Viva La Zombie Muerte
		306	Even after a thread has terminated and cleaned up its resources, the
		307	Coro object still is there and stores the return values of the
		308	thread.
		309
		310	When there are no other references, it will simply be cleaned up and
		311	freed.
		312
		313	If there areany references, the Coro object will stay around, and
		314	you can call "->join" as many times as you wish to retrieve the
		315	result values:
		316
		317	async {
		318	print "hi\n";
		319	1
		320	};
		321
		322	# run the async above, and free everything before returning
		323	# from Coro::cede:
		324	Coro::cede;
		325
		326	{
		327	my $coro = async {
		328	print "hi\n";
		329	1
		330	};
		331
		332	# run the async above, and clean up, but do not free the coro
		333	# object:
		334	Coro::cede;
		335
		336	# optionally retrieve the result values
		337	my @results = $coro->join;
		338
		339	# now $coro goes out of scope, and presumably gets freed
		340	};
		341
62	GLOBAL VARIABLES	342	GLOBAL VARIABLES
63	$Coro::main	343	$Coro::main
64	This variable stores the coroutine object that represents the main	344	This variable stores the Coro object that represents the main
65	program. While you cna "ready" it and do most other things you can	345	program. While you can "ready" it and do most other things you can
66	do to coroutines, it is mainly useful to compare again	346	do to coro, it is mainly useful to compare again $Coro::current, to
67	$Coro::current, to see whether you are running in the main program	347	see whether you are running in the main program or not.
68	or not.
69		348
70	$Coro::current	349	$Coro::current
71	The coroutine object representing the current coroutine (the last	350	The Coro object representing the current coro (the last coro that
72	coroutine that the Coro scheduler switched to). The initial value is	351	the Coro scheduler switched to). The initial value is $Coro::main
73	$Coro::main (of course).	352	(of course).
74		353
75	This variable is strictly read-only. You can take copies of the	354	This variable is strictly read-only. You can take copies of the
76	value stored in it and use it as any other coroutine object, but you	355	value stored in it and use it as any other Coro object, but you must
77	must not otherwise modify the variable itself.	356	not otherwise modify the variable itself.
78		357
79	$Coro::idle	358	$Coro::idle
80	This variable is mainly useful to integrate Coro into event loops.	359	This variable is mainly useful to integrate Coro into event loops.
81	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this	360	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
82	is pretty low-level functionality.	361	is pretty low-level functionality.
83		362
84	This variable stores either a coroutine or a callback.	363	This variable stores a Coro object that is put into the ready queue
		364	when there are no other ready threads (without invoking any ready
		365	hooks).
85		366
86	If it is a callback, the it is called whenever the scheduler finds	367	The default implementation dies with "FATAL: deadlock detected.",
87	no ready coroutines to run. The default implementation prints	368	followed by a thread listing, because the program has no other way
88	"FATAL: deadlock detected" and exits, because the program has no
89	other way to continue.	369	to continue.
90
91	If it is a coroutine object, then this object will be readied
92	(without invoking any ready hooks, however) when the scheduler finds
93	no other ready coroutines to run.
94		370
95	This hook is overwritten by modules such as "Coro::EV" and	371	This hook is overwritten by modules such as "Coro::EV" and
96	"Coro::AnyEvent" to wait on an external event that hopefully wake up	372	"Coro::AnyEvent" to wait on an external event that hopefully wakes
97	a coroutine so the scheduler can run it.	373	up a coro so the scheduler can run it.
98		374
99	Note that the callback must not, under any circumstances, block
100	the current coroutine. Normally, this is achieved by having an "idle
101	coroutine" that calls the event loop and then blocks again, and then
102	readying that coroutine in the idle handler, or by simply placing
103	the idle coroutine in this variable.
104
105	See Coro::Event or Coro::AnyEvent for examples of using this	375	See Coro::EV or Coro::AnyEvent for examples of using this technique.
106	technique.
107		376
108	Please note that if your callback recursively invokes perl (e.g. for
109	event handlers), then it must be prepared to be called recursively
110	itself.
111
112	SIMPLE COROUTINE CREATION	377	SIMPLE CORO CREATION
113	async { ... } [@args...]	378	async { ... } [@args...]
114	Create a new coroutine and return it's coroutine object (usually	379	Create a new coro and return its Coro object (usually unused). The
115	unused). The coroutine will be put into the ready queue, so it will	380	coro will be put into the ready queue, so it will start running
116	start running automatically on the next scheduler run.	381	automatically on the next scheduler run.
117		382
118	The first argument is a codeblock/closure that should be executed in	383	The first argument is a codeblock/closure that should be executed in
119	the coroutine. When it returns argument returns the coroutine is	384	the coro. When it returns argument returns the coro is automatically
120	automatically terminated.	385	terminated.
121		386
122	The remaining arguments are passed as arguments to the closure.	387	The remaining arguments are passed as arguments to the closure.
123		388
124	See the "Coro::State::new" constructor for info about the coroutine	389	See the "Coro::State::new" constructor for info about the coro
125	environment in which coroutines are executed.	390	environment in which coro are executed.
126		391
127	Calling "exit" in a coroutine will do the same as calling exit	392	Calling "exit" in a coro will do the same as calling exit outside
128	outside the coroutine. Likewise, when the coroutine dies, the	393	the coro. Likewise, when the coro dies, the program will exit, just
129	program will exit, just as it would in the main program.	394	as it would in the main program.
130		395
131	If you do not want that, you can provide a default "die" handler, or	396	If you do not want that, you can provide a default "die" handler, or
132	simply avoid dieing (by use of "eval").	397	simply avoid dieing (by use of "eval").
133		398
134	Example: Create a new coroutine that just prints its arguments.	399	Example: Create a new coro that just prints its arguments.
135		400
136	async {	401	async {
137	print "@_\n";	402	print "@_\n";
138	} 1,2,3,4;	403	} 1,2,3,4;
139		404
140	async_pool { ... } [@args...]	405	async_pool { ... } [@args...]
141	Similar to "async", but uses a coroutine pool, so you should not	406	Similar to "async", but uses a coro pool, so you should not call
142	call terminate or join on it (although you are allowed to), and you	407	terminate or join on it (although you are allowed to), and you get a
143	get a coroutine that might have executed other code already (which	408	coro that might have executed other code already (which can be good
144	can be good or bad :).	409	or bad :).
145		410
146	On the plus side, this function is about twice as fast as creating	411	On the plus side, this function is about twice as fast as creating
147	(and destroying) a completely new coroutine, so if you need a lot of	412	(and destroying) a completely new coro, so if you need a lot of
148	generic coroutines in quick successsion, use "async_pool", not	413	generic coros in quick successsion, use "async_pool", not "async".
149	"async".
150		414
151	The code block is executed in an "eval" context and a warning will	415	The code block is executed in an "eval" context and a warning will
152	be issued in case of an exception instead of terminating the	416	be issued in case of an exception instead of terminating the
153	program, as "async" does. As the coroutine is being reused, stuff	417	program, as "async" does. As the coro is being reused, stuff like
154	like "on_destroy" will not work in the expected way, unless you call	418	"on_destroy" will not work in the expected way, unless you call
155	terminate or cancel, which somehow defeats the purpose of pooling	419	terminate or cancel, which somehow defeats the purpose of pooling
156	(but is fine in the exceptional case).	420	(but is fine in the exceptional case).
157		421
158	The priority will be reset to 0 after each run, tracing will be	422	The priority will be reset to 0 after each run, all "swap_sv" calls
159	disabled, the description will be reset and the default output	423	will be undone, tracing will be disabled, the description will be
160	filehandle gets restored, so you can change all these. Otherwise the	424	reset and the default output filehandle gets restored, so you can
161	coroutine will be re-used "as-is": most notably if you change other	425	change all these. Otherwise the coro will be re-used "as-is": most
162	per-coroutine global stuff such as $/ you must needs revert that	426	notably if you change other per-coro global stuff such as $/ you
163	change, which is most simply done by using local as in: "local $/".	427	must needs revert that change, which is most simply done by using
		428	local as in: "local $/".
164		429
165	The idle pool size is limited to 8 idle coroutines (this can be	430	The idle pool size is limited to 8 idle coros (this can be adjusted
166	adjusted by changing $Coro::POOL_SIZE), but there can be as many	431	by changing $Coro::POOL_SIZE), but there can be as many non-idle
167	non-idle coros as required.	432	coros as required.
168		433
169	If you are concerned about pooled coroutines growing a lot because a	434	If you are concerned about pooled coros growing a lot because a
170	single "async_pool" used a lot of stackspace you can e.g.	435	single "async_pool" used a lot of stackspace you can e.g.
171	"async_pool { terminate }" once per second or so to slowly replenish	436	"async_pool { terminate }" once per second or so to slowly replenish
172	the pool. In addition to that, when the stacks used by a handler	437	the pool. In addition to that, when the stacks used by a handler
173	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also	438	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
174	be destroyed.	439	be destroyed.
175		440
176	STATIC METHODS	441	STATIC METHODS
177	Static methods are actually functions that implicitly operate on the	442	Static methods are actually functions that implicitly operate on the
178	current coroutine.	443	current coro.
179		444
180	schedule	445	schedule
181	Calls the scheduler. The scheduler will find the next coroutine that	446	Calls the scheduler. The scheduler will find the next coro that is
182	is to be run from the ready queue and switches to it. The next	447	to be run from the ready queue and switches to it. The next coro to
183	coroutine to be run is simply the one with the highest priority that	448	be run is simply the one with the highest priority that is longest
184	is longest in its ready queue. If there is no coroutine ready, it	449	in its ready queue. If there is no coro ready, it will call the
185	will clal the $Coro::idle hook.	450	$Coro::idle hook.
186		451
187	Please note that the current coroutine will not be put into the	452	Please note that the current coro will not be put into the ready
188	ready queue, so calling this function usually means you will never	453	queue, so calling this function usually means you will never be
189	be called again unless something else (e.g. an event handler) calls	454	called again unless something else (e.g. an event handler) calls
190	"->ready", thus waking you up.	455	"->ready", thus waking you up.
191		456
192	This makes "schedule" the generic method to use to block the	457	This makes "schedule" the generic method to use to block the
193	current coroutine and wait for events: first you remember the	458	current coro and wait for events: first you remember the current
194	current coroutine in a variable, then arrange for some callback of	459	coro in a variable, then arrange for some callback of yours to call
195	yours to call "->ready" on that once some event happens, and last	460	"->ready" on that once some event happens, and last you call
196	you call "schedule" to put yourself to sleep. Note that a lot of	461	"schedule" to put yourself to sleep. Note that a lot of things can
197	things can wake your coroutine up, so you need to check whether the	462	wake your coro up, so you need to check whether the event indeed
198	event indeed happened, e.g. by storing the status in a variable.	463	happened, e.g. by storing the status in a variable.
199		464
200	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for	465	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
201	callbacks.	466	callbacks.
202		467
203	cede	468	cede
204	"Cede" to other coroutines. This function puts the current coroutine	469	"Cede" to other coros. This function puts the current coro into the
205	into the ready queue and calls "schedule", which has the effect of	470	ready queue and calls "schedule", which has the effect of giving up
206	giving up the current "timeslice" to other coroutines of the same or	471	the current "timeslice" to other coros of the same or higher
207	higher priority. Once your coroutine gets its turn again it will	472	priority. Once your coro gets its turn again it will automatically
208	automatically be resumed.	473	be resumed.
209		474
210	This function is often called "yield" in other languages.	475	This function is often called "yield" in other languages.
211		476
212	Coro::cede_notself	477	Coro::cede_notself
213	Works like cede, but is not exported by default and will cede to	478	Works like cede, but is not exported by default and will cede to
214	any coroutine, regardless of priority. This is useful sometimes to	479	any coro, regardless of priority. This is useful sometimes to
215	ensure progress is made.	480	ensure progress is made.
216		481
217	terminate [arg...]	482	terminate [arg...]
218	Terminates the current coroutine with the given status values (see	483	Terminates the current coro with the given status values (see
219	cancel).	484	cancel). The values will not be copied, but referenced directly.
		485
		486	Coro::on_enter BLOCK, Coro::on_leave BLOCK
		487	These function install enter and leave winders in the current scope.
		488	The enter block will be executed when on_enter is called and
		489	whenever the current coro is re-entered by the scheduler, while the
		490	leave block is executed whenever the current coro is blocked by the
		491	scheduler, and also when the containing scope is exited (by whatever
		492	means, be it exit, die, last etc.).
		493
		494	*Neither invoking the scheduler, nor exceptions, are allowed within
		495	those BLOCKs*. That means: do not even think about calling "die"
		496	without an eval, and do not even think of entering the scheduler in
		497	any way.
		498
		499	Since both BLOCKs are tied to the current scope, they will
		500	automatically be removed when the current scope exits.
		501
		502	These functions implement the same concept as "dynamic-wind" in
		503	scheme does, and are useful when you want to localise some resource
		504	to a specific coro.
		505
		506	They slow down thread switching considerably for coros that use them
		507	(about 40% for a BLOCK with a single assignment, so thread switching
		508	is still reasonably fast if the handlers are fast).
		509
		510	These functions are best understood by an example: The following
		511	function will change the current timezone to
		512	"Antarctica/South_Pole", which requires a call to "tzset", but by
		513	using "on_enter" and "on_leave", which remember/change the current
		514	timezone and restore the previous value, respectively, the timezone
		515	is only changed for the coro that installed those handlers.
		516
		517	use POSIX qw(tzset);
		518
		519	async {
		520	my $old_tz; # store outside TZ value here
		521
		522	Coro::on_enter {
		523	$old_tz = $ENV{TZ}; # remember the old value
		524
		525	$ENV{TZ} = "Antarctica/South_Pole";
		526	tzset; # enable new value
		527	};
		528
		529	Coro::on_leave {
		530	$ENV{TZ} = $old_tz;
		531	tzset; # restore old value
		532	};
		533
		534	# at this place, the timezone is Antarctica/South_Pole,
		535	# without disturbing the TZ of any other coro.
		536	};
		537
		538	This can be used to localise about any resource (locale, uid,
		539	current working directory etc.) to a block, despite the existence of
		540	other coros.
		541
		542	Another interesting example implements time-sliced multitasking
		543	using interval timers (this could obviously be optimised, but does
		544	the job):
		545
		546	# "timeslice" the given block
		547	sub timeslice(&) {
		548	use Time::HiRes ();
		549
		550	Coro::on_enter {
		551	# on entering the thread, we set an VTALRM handler to cede
		552	$SIG{VTALRM} = sub { cede };
		553	# and then start the interval timer
		554	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		555	};
		556	Coro::on_leave {
		557	# on leaving the thread, we stop the interval timer again
		558	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		559	};
		560
		561	&{+shift};
		562	}
		563
		564	# use like this:
		565	timeslice {
		566	# The following is an endless loop that would normally
		567	# monopolise the process. Since it runs in a timesliced
		568	# environment, it will regularly cede to other threads.
		569	while () { }
		570	};
220		571
221	killall	572	killall
222	Kills/terminates/cancels all coroutines except the currently running	573	Kills/terminates/cancels all coros except the currently running one.
223	one. This is useful after a fork, either in the child or the parent,
224	as usually only one of them should inherit the running coroutines.
225		574
226	Note that while this will try to free some of the main programs	575	Note that while this will try to free some of the main interpreter
227	resources, you cannot free all of them, so if a coroutine that is	576	resources if the calling coro isn't the main coro, but one cannot
228	not the main program calls this function, there will be some	577	free all of them, so if a coro that is not the main coro calls this
229	one-time resource leak.	578	function, there will be some one-time resource leak.
230		579
231	COROUTINE OBJECT METHODS	580	CORO OBJECT METHODS
232	These are the methods you can call on coroutine objects (or to create	581	These are the methods you can call on coro objects (or to create them).
233	them).
234		582
235	new Coro \&sub [, @args...]	583	new Coro \&sub [, @args...]
236	Create a new coroutine and return it. When the sub returns, the	584	Create a new coro and return it. When the sub returns, the coro
237	coroutine automatically terminates as if "terminate" with the	585	automatically terminates as if "terminate" with the returned values
238	returned values were called. To make the coroutine run you must	586	were called. To make the coro run you must first put it into the
239	first put it into the ready queue by calling the ready method.	587	ready queue by calling the ready method.
240		588
241	See "async" and "Coro::State::new" for additional info about the	589	See "async" and "Coro::State::new" for additional info about the
242	coroutine environment.	590	coro environment.
243		591
244	$success = $coroutine->ready	592	$success = $coro->ready
245	Put the given coroutine into the end of its ready queue (there is	593	Put the given coro into the end of its ready queue (there is one
246	one queue for each priority) and return true. If the coroutine is	594	queue for each priority) and return true. If the coro is already in
247	already in the ready queue, do nothing and return false.	595	the ready queue, do nothing and return false.
248		596
249	This ensures that the scheduler will resume this coroutine	597	This ensures that the scheduler will resume this coro automatically
250	automatically once all the coroutines of higher priority and all	598	once all the coro of higher priority and all coro of the same
251	coroutines of the same priority that were put into the ready queue	599	priority that were put into the ready queue earlier have been
252	earlier have been resumed.	600	resumed.
253		601
		602	$coro->suspend
		603	Suspends the specified coro. A suspended coro works just like any
		604	other coro, except that the scheduler will not select a suspended
		605	coro for execution.
		606
		607	Suspending a coro can be useful when you want to keep the coro from
		608	running, but you don't want to destroy it, or when you want to
		609	temporarily freeze a coro (e.g. for debugging) to resume it later.
		610
		611	A scenario for the former would be to suspend all (other) coros
		612	after a fork and keep them alive, so their destructors aren't
		613	called, but new coros can be created.
		614
		615	$coro->resume
		616	If the specified coro was suspended, it will be resumed. Note that
		617	when the coro was in the ready queue when it was suspended, it might
		618	have been unreadied by the scheduler, so an activation might have
		619	been lost.
		620
		621	To avoid this, it is best to put a suspended coro into the ready
		622	queue unconditionally, as every synchronisation mechanism must
		623	protect itself against spurious wakeups, and the one in the Coro
		624	family certainly do that.
		625
		626	$state->is_new
		627	Returns true iff this Coro object is "new", i.e. has never been run
		628	yet. Those states basically consist of only the code reference to
		629	call and the arguments, but consumes very little other resources.
		630	New states will automatically get assigned a perl interpreter when
		631	they are transferred to.
		632
		633	$state->is_zombie
		634	Returns true iff the Coro object has been cancelled, i.e. it's
		635	resources freed because they were "cancel"'ed, "terminate"'d,
		636	"safe_cancel"'ed or simply went out of scope.
		637
		638	The name "zombie" stems from UNIX culture, where a process that has
		639	exited and only stores and exit status and no other resources is
		640	called a "zombie".
		641
254	$is_ready = $coroutine->is_ready	642	$is_ready = $coro->is_ready
255	Return whether the coroutine is currently the ready queue or not,	643	Returns true iff the Coro object is in the ready queue. Unless the
		644	Coro object gets destroyed, it will eventually be scheduled by the
		645	scheduler.
256		646
		647	$is_running = $coro->is_running
		648	Returns true iff the Coro object is currently running. Only one Coro
		649	object can ever be in the running state (but it currently is
		650	possible to have multiple running Coro::States).
		651
		652	$is_suspended = $coro->is_suspended
		653	Returns true iff this Coro object has been suspended. Suspended
		654	Coros will not ever be scheduled.
		655
257	$coroutine->cancel (arg...)	656	$coro->cancel (arg...)
258	Terminates the given coroutine and makes it return the given	657	Terminates the given Coro thread and makes it return the given
259	arguments as status (default: the empty list). Never returns if the	658	arguments as status (default: an empty list). Never returns if the
260	coroutine is the current coroutine.	659	Coro is the current Coro.
261		660
		661	This is a rather brutal way to free a coro, with some limitations -
		662	if the thread is inside a C callback that doesn't expect to be
		663	canceled, bad things can happen, or if the cancelled thread insists
		664	on running complicated cleanup handlers that rely on its thread
		665	context, things will not work.
		666
		667	Any cleanup code being run (e.g. from "guard" blocks, destructors
		668	and so on) will be run without a thread context, and is not allowed
		669	to switch to other threads. A common mistake is to call "->cancel"
		670	from a destructor called by die'ing inside the thread to be
		671	cancelled for example.
		672
		673	On the plus side, "->cancel" will always clean up the thread, no
		674	matter what. If your cleanup code is complex or you want to avoid
		675	cancelling a C-thread that doesn't know how to clean up itself, it
		676	can be better to "->throw" an exception, or use "->safe_cancel".
		677
		678	The arguments to "->cancel" are not copied, but instead will be
		679	referenced directly (e.g. if you pass $var and after the call change
		680	that variable, then you might change the return values passed to
		681	e.g. "join", so don't do that).
		682
		683	The resources of the Coro are usually freed (or destructed) before
		684	this call returns, but this can be delayed for an indefinite amount
		685	of time, as in some cases the manager thread has to run first to
		686	actually destruct the Coro object.
		687
		688	$coro->safe_cancel ($arg...)
		689	Works mostly like "->cancel", but is inherently "safer", and
		690	consequently, can fail with an exception in cases the thread is not
		691	in a cancellable state. Essentially, "->safe_cancel" is a "->cancel"
		692	with extra checks before canceling.
		693
		694	It works a bit like throwing an exception that cannot be caught -
		695	specifically, it will clean up the thread from within itself, so all
		696	cleanup handlers (e.g. "guard" blocks) are run with full thread
		697	context and can block if they wish. The downside is that there is no
		698	guarantee that the thread can be cancelled when you call this
		699	method, and therefore, it might fail. It is also considerably slower
		700	than "cancel" or "terminate".
		701
		702	A thread is in a safe-cancellable state if it either hasn't been run
		703	yet, or it has no C context attached and is inside an SLF function.
		704
		705	The latter two basically mean that the thread isn't currently inside
		706	a perl callback called from some C function (usually via some XS
		707	modules) and isn't currently executing inside some C function itself
		708	(via Coro's XS API).
		709
		710	This call returns true when it could cancel the thread, or croaks
		711	with an error otherwise (i.e. it either returns true or doesn't
		712	return at all).
		713
		714	Why the weird interface? Well, there are two common models on how
		715	and when to cancel things. In the first, you have the expectation
		716	that your coro thread can be cancelled when you want to cancel it -
		717	if the thread isn't cancellable, this would be a bug somewhere, so
		718	"->safe_cancel" croaks to notify of the bug.
		719
		720	In the second model you sometimes want to ask nicely to cancel a
		721	thread, but if it's not a good time, well, then don't cancel. This
		722	can be done relatively easy like this:
		723
		724	if (! eval { $coro->safe_cancel }) {
		725	warn "unable to cancel thread: $@";
		726	}
		727
		728	However, what you never should do is first try to cancel "safely"
		729	and if that fails, cancel the "hard" way with "->cancel". That makes
		730	no sense: either you rely on being able to execute cleanup code in
		731	your thread context, or you don't. If you do, then "->safe_cancel"
		732	is the only way, and if you don't, then "->cancel" is always faster
		733	and more direct.
		734
262	$coroutine->schedule_to	735	$coro->schedule_to
263	Puts the current coroutine to sleep (like "Coro::schedule"), but	736	Puts the current coro to sleep (like "Coro::schedule"), but instead
264	instead of continuing with the next coro from the ready queue,	737	of continuing with the next coro from the ready queue, always switch
265	always switch to the given coroutine object (regardless of priority	738	to the given coro object (regardless of priority etc.). The
266	etc.). The readyness state of that coroutine isn't changed.	739	readyness state of that coro isn't changed.
267		740
268	This is an advanced method for special cases - I'd love to hear	741	This is an advanced method for special cases - I'd love to hear
269	about any uses for this one.	742	about any uses for this one.
270		743
271	$coroutine->cede_to	744	$coro->cede_to
272	Like "schedule_to", but puts the current coroutine into the ready	745	Like "schedule_to", but puts the current coro into the ready queue.
273	queue. This has the effect of temporarily switching to the given	746	This has the effect of temporarily switching to the given coro, and
274	coroutine, and continuing some time later.	747	continuing some time later.
275		748
276	This is an advanced method for special cases - I'd love to hear	749	This is an advanced method for special cases - I'd love to hear
277	about any uses for this one.	750	about any uses for this one.
278		751
279	$coroutine->throw ([$scalar])	752	$coro->throw ([$scalar])
280	If $throw is specified and defined, it will be thrown as an	753	If $throw is specified and defined, it will be thrown as an
281	exception inside the coroutine at the next convenient point in time.	754	exception inside the coro at the next convenient point in time.
282	Otherwise clears the exception object.	755	Otherwise clears the exception object.
283		756
284	Coro will check for the exception each time a schedule-like-function	757	Coro will check for the exception each time a schedule-like-function
285	returns, i.e. after each "schedule", "cede",	758	returns, i.e. after each "schedule", "cede",
286	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of	759	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
287	these functions detect this case and return early in case an	760	those functions (all that are part of Coro itself) detect this case
288	exception is pending.	761	and return early in case an exception is pending.
289		762
290	The exception object will be thrown "as is" with the specified	763	The exception object will be thrown "as is" with the specified
291	scalar in $@, i.e. if it is a string, no line number or newline will	764	scalar in $@, i.e. if it is a string, no line number or newline will
292	be appended (unlike with "die").	765	be appended (unlike with "die").
293		766
294	This can be used as a softer means than "cancel" to ask a coroutine	767	This can be used as a softer means than either "cancel" or
295	to end itself, although there is no guarantee that the exception	768	"safe_cancel "to ask a coro to end itself, although there is no
296	will lead to termination, and if the exception isn't caught it might	769	guarantee that the exception will lead to termination, and if the
297	well end the whole program.	770	exception isn't caught it might well end the whole program.
298		771
299	You might also think of "throw" as being the moral equivalent of	772	You might also think of "throw" as being the moral equivalent of
300	"kill"ing a coroutine with a signal (in this case, a scalar).	773	"kill"ing a coro with a signal (in this case, a scalar).
301		774
302	$coroutine->join	775	$coro->join
303	Wait until the coroutine terminates and return any values given to	776	Wait until the coro terminates and return any values given to the
304	the "terminate" or "cancel" functions. "join" can be called	777	"terminate" or "cancel" functions. "join" can be called concurrently
305	concurrently from multiple coroutines, and all will be resumed and	778	from multiple threads, and all will be resumed and given the status
306	given the status return once the $coroutine terminates.	779	return once the $coro terminates.
307		780
308	$coroutine->on_destroy (\&cb)	781	$coro->on_destroy (\&cb)
309	Registers a callback that is called when this coroutine gets	782	Registers a callback that is called when this coro thread gets
310	destroyed, but before it is joined. The callback gets passed the	783	destroyed, that is, after it's resources have been freed but before
		784	it is joined. The callback gets passed the terminate/cancel
311	terminate arguments, if any, and must not die, under any	785	arguments, if any, and must not die, under any circumstances.
312	circumstances.
313		786
		787	There can be any number of "on_destroy" callbacks per coro, and
		788	there is currently no way to remove a callback once added.
		789
314	$oldprio = $coroutine->prio ($newprio)	790	$oldprio = $coro->prio ($newprio)
315	Sets (or gets, if the argument is missing) the priority of the	791	Sets (or gets, if the argument is missing) the priority of the coro
316	coroutine. Higher priority coroutines get run before lower priority	792	thread. Higher priority coro get run before lower priority coros.
317	coroutines. Priorities are small signed integers (currently -4 ..	793	Priorities are small signed integers (currently -4 .. +3), that you
318	+3), that you can refer to using PRIO_xxx constants (use the import	794	can refer to using PRIO_xxx constants (use the import tag :prio to
319	tag :prio to get then):	795	get then):
320		796
321	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	797	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
322	3 > 1 > 0 > -1 > -3 > -4	798	3 > 1 > 0 > -1 > -3 > -4
323		799
324	# set priority to HIGH	800	# set priority to HIGH
325	current->prio(PRIO_HIGH);	801	current->prio (PRIO_HIGH);
326		802
327	The idle coroutine ($Coro::idle) always has a lower priority than	803	The idle coro thread ($Coro::idle) always has a lower priority than
328	any existing coroutine.	804	any existing coro.
329		805
330	Changing the priority of the current coroutine will take effect	806	Changing the priority of the current coro will take effect
331	immediately, but changing the priority of coroutines in the ready	807	immediately, but changing the priority of a coro in the ready queue
332	queue (but not running) will only take effect after the next	808	(but not running) will only take effect after the next schedule (of
333	schedule (of that coroutine). This is a bug that will be fixed in	809	that coro). This is a bug that will be fixed in some future version.
334	some future version.
335		810
336	$newprio = $coroutine->nice ($change)	811	$newprio = $coro->nice ($change)
337	Similar to "prio", but subtract the given value from the priority	812	Similar to "prio", but subtract the given value from the priority
338	(i.e. higher values mean lower priority, just as in unix).	813	(i.e. higher values mean lower priority, just as in UNIX's nice
		814	command).
339		815
340	$olddesc = $coroutine->desc ($newdesc)	816	$olddesc = $coro->desc ($newdesc)
341	Sets (or gets in case the argument is missing) the description for	817	Sets (or gets in case the argument is missing) the description for
342	this coroutine. This is just a free-form string you can associate	818	this coro thread. This is just a free-form string you can associate
343	with a coroutine.	819	with a coro.
344		820
345	This method simply sets the "$coroutine->{desc}" member to the given	821	This method simply sets the "$coro->{desc}" member to the given
346	string. You can modify this member directly if you wish.	822	string. You can modify this member directly if you wish, and in
		823	fact, this is often preferred to indicate major processing states
		824	that can then be seen for example in a Coro::Debug session:
		825
		826	sub my_long_function {
		827	local $Coro::current->{desc} = "now in my_long_function";
		828	...
		829	$Coro::current->{desc} = "my_long_function: phase 1";
		830	...
		831	$Coro::current->{desc} = "my_long_function: phase 2";
		832	...
		833	}
347		834
348	GLOBAL FUNCTIONS	835	GLOBAL FUNCTIONS
349	Coro::nready	836	Coro::nready
350	Returns the number of coroutines that are currently in the ready	837	Returns the number of coro that are currently in the ready state,
351	state, i.e. that can be switched to by calling "schedule" directory	838	i.e. that can be switched to by calling "schedule" directory or
352	or indirectly. The value 0 means that the only runnable coroutine is	839	indirectly. The value 0 means that the only runnable coro is the
353	the currently running one, so "cede" would have no effect, and	840	currently running one, so "cede" would have no effect, and
354	"schedule" would cause a deadlock unless there is an idle handler	841	"schedule" would cause a deadlock unless there is an idle handler
355	that wakes up some coroutines.	842	that wakes up some coro.
356		843
357	my $guard = Coro::guard { ... }	844	my $guard = Coro::guard { ... }
358	This creates and returns a guard object. Nothing happens until the	845	This function still exists, but is deprecated. Please use the
359	object gets destroyed, in which case the codeblock given as argument	846	"Guard::guard" function instead.
360	will be executed. This is useful to free locks or other resources in
361	case of a runtime error or when the coroutine gets canceled, as in
362	both cases the guard block will be executed. The guard object
363	supports only one method, "->cancel", which will keep the codeblock
364	from being executed.
365
366	Example: set some flag and clear it again when the coroutine gets
367	canceled or the function returns:
368
369	sub do_something {
370	my $guard = Coro::guard { $busy = 0 };
371	$busy = 1;
372
373	# do something that requires $busy to be true
374	}
375		847
376	unblock_sub { ... }	848	unblock_sub { ... }
377	This utility function takes a BLOCK or code reference and "unblocks"	849	This utility function takes a BLOCK or code reference and "unblocks"
378	it, returning a new coderef. Unblocking means that calling the new	850	it, returning a new coderef. Unblocking means that calling the new
379	coderef will return immediately without blocking, returning nothing,	851	coderef will return immediately without blocking, returning nothing,
380	while the original code ref will be called (with parameters) from	852	while the original code ref will be called (with parameters) from
381	within another coroutine.	853	within another coro.
382		854
383	The reason this function exists is that many event libraries (such	855	The reason this function exists is that many event libraries (such
384	as the venerable Event module) are not coroutine-safe (a weaker form	856	as the venerable Event module) are not thread-safe (a weaker form of
385	of reentrancy). This means you must not block within event	857	reentrancy). This means you must not block within event callbacks,
386	callbacks, otherwise you might suffer from crashes or worse. The	858	otherwise you might suffer from crashes or worse. The only event
387	only event library currently known that is safe to use without	859	library currently known that is safe to use without "unblock_sub" is
388	"unblock_sub" is EV.	860	EV (but you might still run into deadlocks if all event loops are
		861	blocked).
		862
		863	Coro will try to catch you when you block in the event loop ("FATAL:
		864	$Coro::idle blocked itself"), but this is just best effort and only
		865	works when you do not run your own event loop.
389		866
390	This function allows your callbacks to block by executing them in	867	This function allows your callbacks to block by executing them in
391	another coroutine where it is safe to block. One example where	868	another coro where it is safe to block. One example where blocking
392	blocking is handy is when you use the Coro::AIO functions to save	869	is handy is when you use the Coro::AIO functions to save results to
393	results to disk, for example.	870	disk, for example.
394		871
395	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	872	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
396	when creating event callbacks that want to block.	873	when creating event callbacks that want to block.
397		874
398	If your handler does not plan to block (e.g. simply sends a message	875	If your handler does not plan to block (e.g. simply sends a message
399	to another coroutine, or puts some other coroutine into the ready	876	to another coro, or puts some other coro into the ready queue),
400	queue), there is no reason to use "unblock_sub".	877	there is no reason to use "unblock_sub".
401		878
402	Note that you also need to use "unblock_sub" for any other callbacks	879	Note that you also need to use "unblock_sub" for any other callbacks
403	that are indirectly executed by any C-based event loop. For example,	880	that are indirectly executed by any C-based event loop. For example,
404	when you use a module that uses AnyEvent (and you use	881	when you use a module that uses AnyEvent (and you use
405	Coro::AnyEvent) and it provides callbacks that are the result of	882	Coro::AnyEvent) and it provides callbacks that are the result of
406	some event callback, then you must not block either, or use	883	some event callback, then you must not block either, or use
407	"unblock_sub".	884	"unblock_sub".
408		885
409	$cb = Coro::rouse_cb	886	$cb = rouse_cb
410	Create and return a "rouse callback". That's a code reference that,	887	Create and return a "rouse callback". That's a code reference that,
411	when called, will remember a copy of its arguments and notify the	888	when called, will remember a copy of its arguments and notify the
412	owner coroutine of the callback.	889	owner coro of the callback.
413		890
414	See the next function.	891	See the next function.
415		892
416	@args = Coro::rouse_wait [$cb]	893	@args = rouse_wait [$cb]
417	Wait for the specified rouse callback (or the last one that was	894	Wait for the specified rouse callback (or the last one that was
418	created in this coroutine).	895	created in this coro).
419		896
420	As soon as the callback is invoked (or when the callback was invoked	897	As soon as the callback is invoked (or when the callback was invoked
421	before "rouse_wait"), it will return the arguments originally passed	898	before "rouse_wait"), it will return the arguments originally passed
422	to the rouse callback.	899	to the rouse callback. In scalar context, that means you get the
		900	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		901	$a3...)" statement at the end.
423		902
424	See the section HOW TO WAIT FOR A CALLBACK for an actual usage	903	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
425	example.	904	example.
426		905
427	HOW TO WAIT FOR A CALLBACK	906	HOW TO WAIT FOR A CALLBACK
428	It is very common for a coroutine to wait for some callback to be	907	It is very common for a coro to wait for some callback to be called.
429	called. This occurs naturally when you use coroutines in an otherwise	908	This occurs naturally when you use coro in an otherwise event-based
430	event-based program, or when you use event-based libraries.	909	program, or when you use event-based libraries.
431		910
432	These typically register a callback for some event, and call that	911	These typically register a callback for some event, and call that
433	callback when the event occured. In a coroutine, however, you typically	912	callback when the event occurred. In a coro, however, you typically want
434	want to just wait for the event, simplyifying things.	913	to just wait for the event, simplyifying things.
435		914
436	For example "AnyEvent->child" registers a callback to be called when a	915	For example "AnyEvent->child" registers a callback to be called when a
437	specific child has exited:	916	specific child has exited:
438		917
439	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	918	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
440		919
441	But from withina coroutine, you often just want to write this:	920	But from within a coro, you often just want to write this:
442		921
443	my $status = wait_for_child $pid;	922	my $status = wait_for_child $pid;
444		923
445	Coro offers two functions specifically designed to make this easy,	924	Coro offers two functions specifically designed to make this easy,
446	"Coro::rouse_cb" and "Coro::rouse_wait".	925	"rouse_cb" and "rouse_wait".
447		926
448	The first function, "rouse_cb", generates and returns a callback that,	927	The first function, "rouse_cb", generates and returns a callback that,
449	when invoked, will save it's arguments and notify the coroutine that	928	when invoked, will save its arguments and notify the coro that created
450	created the callback.	929	the callback.
451		930
452	The second function, "rouse_wait", waits for the callback to be called	931	The second function, "rouse_wait", waits for the callback to be called
453	(by calling "schedule" to go to sleep) and returns the arguments	932	(by calling "schedule" to go to sleep) and returns the arguments
454	originally passed to the callback.	933	originally passed to the callback.
455		934
457	function mentioned above:	936	function mentioned above:
458		937
459	sub wait_for_child($) {	938	sub wait_for_child($) {
460	my ($pid) = @_;	939	my ($pid) = @_;
461		940
462	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);	941	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
463		942
464	my ($rpid, $rstatus) = Coro::rouse_wait;	943	my ($rpid, $rstatus) = rouse_wait;
465	$rstatus	944	$rstatus
466	}	945	}
467		946
468	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,	947	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
469	you can roll your own, using "schedule":	948	you can roll your own, using "schedule" and "ready":
470		949
471	sub wait_for_child($) {	950	sub wait_for_child($) {
472	my ($pid) = @_;	951	my ($pid) = @_;
473		952
474	# store the current coroutine in $current,	953	# store the current coro in $current,
475	# and provide result variables for the closure passed to ->child	954	# and provide result variables for the closure passed to ->child
476	my $current = $Coro::current;	955	my $current = $Coro::current;
477	my ($done, $rstatus);	956	my ($done, $rstatus);
478		957
479	# pass a closure to ->child	958	# pass a closure to ->child
480	my $watcher = AnyEvent->child (pid => $pid, cb => sub {	959	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
481	$rstatus = $_[1]; # remember rstatus	960	$rstatus = $_[1]; # remember rstatus
482	$done = 1; # mark $rstatus as valud	961	$done = 1; # mark $rstatus as valid
		962	$current->ready; # wake up the waiting thread
483	});	963	});
484		964
485	# wait until the closure has been called	965	# wait until the closure has been called
486	schedule while !$done;	966	schedule while !$done;
487		967
…		…
490		970
491	BUGS/LIMITATIONS	971	BUGS/LIMITATIONS
492	fork with pthread backend	972	fork with pthread backend
493	When Coro is compiled using the pthread backend (which isn't	973	When Coro is compiled using the pthread backend (which isn't
494	recommended but required on many BSDs as their libcs are completely	974	recommended but required on many BSDs as their libcs are completely
495	broken), then coroutines will not survive a fork. There is no known	975	broken), then coro will not survive a fork. There is no known
496	workaround except to fix your libc and use a saner backend.	976	workaround except to fix your libc and use a saner backend.
497		977
498	perl process emulation ("threads")	978	perl process emulation ("threads")
499	This module is not perl-pseudo-thread-safe. You should only ever use	979	This module is not perl-pseudo-thread-safe. You should only ever use
500	this module from the first thread (this requirement might be removed	980	this module from the first thread (this requirement might be removed
501	in the future to allow per-thread schedulers, but Coro::State does	981	in the future to allow per-thread schedulers, but Coro::State does
502	not yet allow this). I recommend disabling thread support and using	982	not yet allow this). I recommend disabling thread support and using
503	processes, as having the windows process emulation enabled under	983	processes, as having the windows process emulation enabled under
504	unix roughly halves perl performance, even when not used.	984	unix roughly halves perl performance, even when not used.
505		985
		986	Attempts to use threads created in another emulated process will
		987	crash ("cleanly", with a null pointer exception).
		988
506	coroutine switching not signal safe	989	coro switching is not signal safe
507	You must not switch to another coroutine from within a signal	990	You must not switch to another coro from within a signal handler
508	handler (only relevant with %SIG - most event libraries provide safe	991	(only relevant with %SIG - most event libraries provide safe
509	signals).	992	signals), unless you are sure you are not interrupting a Coro
		993	function.
510		994
511	That means you MUST NOT call any function that might "block" the	995	That means you MUST NOT call any function that might "block" the
512	current coroutine - "cede", "schedule" "Coro::Semaphore->down" or	996	current coro - "cede", "schedule" "Coro::Semaphore->down" or
513	anything that calls those. Everything else, including calling	997	anything that calls those. Everything else, including calling
514	"ready", works.	998	"ready", works.
		999
		1000	WINDOWS PROCESS EMULATION
		1001	A great many people seem to be confused about ithreads (for example,
		1002	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		1003	while in the same mail making rather confused statements about perl
		1004	ithreads (for example, that memory or files would be shared), showing
		1005	his lack of understanding of this area - if it is hard to understand for
		1006	Chip, it is probably not obvious to everybody).
		1007
		1008	What follows is an ultra-condensed version of my talk about threads in
		1009	scripting languages given on the perl workshop 2009:
		1010
		1011	The so-called "ithreads" were originally implemented for two reasons:
		1012	first, to (badly) emulate unix processes on native win32 perls, and
		1013	secondly, to replace the older, real thread model ("5.005-threads").
		1014
		1015	It does that by using threads instead of OS processes. The difference
		1016	between processes and threads is that threads share memory (and other
		1017	state, such as files) between threads within a single process, while
		1018	processes do not share anything (at least not semantically). That means
		1019	that modifications done by one thread are seen by others, while
		1020	modifications by one process are not seen by other processes.
		1021
		1022	The "ithreads" work exactly like that: when creating a new ithreads
		1023	process, all state is copied (memory is copied physically, files and
		1024	code is copied logically). Afterwards, it isolates all modifications. On
		1025	UNIX, the same behaviour can be achieved by using operating system
		1026	processes, except that UNIX typically uses hardware built into the
		1027	system to do this efficiently, while the windows process emulation
		1028	emulates this hardware in software (rather efficiently, but of course it
		1029	is still much slower than dedicated hardware).
		1030
		1031	As mentioned before, loading code, modifying code, modifying data
		1032	structures and so on is only visible in the ithreads process doing the
		1033	modification, not in other ithread processes within the same OS process.
		1034
		1035	This is why "ithreads" do not implement threads for perl at all, only
		1036	processes. What makes it so bad is that on non-windows platforms, you
		1037	can actually take advantage of custom hardware for this purpose (as
		1038	evidenced by the forks module, which gives you the (i-) threads API,
		1039	just much faster).
		1040
		1041	Sharing data is in the i-threads model is done by transferring data
		1042	structures between threads using copying semantics, which is very slow -
		1043	shared data simply does not exist. Benchmarks using i-threads which are
		1044	communication-intensive show extremely bad behaviour with i-threads (in
		1045	fact, so bad that Coro, which cannot take direct advantage of multiple
		1046	CPUs, is often orders of magnitude faster because it shares data using
		1047	real threads, refer to my talk for details).
		1048
		1049	As summary, i-threads use threads to implement processes, while the
		1050	compatible forks module uses processes to emulate, uhm, processes.
		1051	I-threads slow down every perl program when enabled, and outside of
		1052	windows, serve no (or little) practical purpose, but disadvantages every
		1053	single-threaded Perl program.
		1054
		1055	This is the reason that I try to avoid the name "ithreads", as it is
		1056	misleading as it implies that it implements some kind of thread model
		1057	for perl, and prefer the name "windows process emulation", which
		1058	describes the actual use and behaviour of it much better.
515		1059
516	SEE ALSO	1060	SEE ALSO
517	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	1061	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
518		1062
519	Debugging: Coro::Debug.	1063	Debugging: Coro::Debug.
…		…
531		1075
532	XS API: Coro::MakeMaker.	1076	XS API: Coro::MakeMaker.
533		1077
534	Low level Configuration, Thread Environment, Continuations: Coro::State.	1078	Low level Configuration, Thread Environment, Continuations: Coro::State.
535		1079
536	AUTHOR	1080	AUTHOR/SUPPORT/CONTACT
537	Marc Lehmann <schmorp@schmorp.de>	1081	Marc A. Lehmann <schmorp@schmorp.de>
538	http://home.schmorp.de/	1082	http://software.schmorp.de/pkg/Coro.html
539		1083

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