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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;
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	This module collection manages coroutines. Coroutines are similar to	27	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	28	This manpage mainly contains reference information.
30	SMP machines. The specific flavor of coroutine used in this module also	29
31	guarantees you that it will not switch between coroutines unless	30	This module collection manages continuations in general, most often in
		31	the form of cooperative threads (also called coros, or simply "coro" in
		32	the documentation). They are similar to kernel threads but don't (in
		33	general) run in parallel at the same time even on SMP machines. The
		34	specific flavor of thread offered by this module also guarantees you
		35	that it will not switch between threads unless necessary, at
32	necessary, at easily-identified points in your program, so locking and	36	easily-identified points in your program, so locking and parallel access
33	parallel access are rarely an issue, making coroutine programming much	37	are rarely an issue, making thread programming much safer and easier
34	safer and easier than threads programming.	38	than using other thread models.
35		39
36	Unlike a normal perl program, however, coroutines allow you to have	40	Unlike the so-called "Perl threads" (which are not actually real threads
37	multiple running interpreters that share data, which is especially	41	but only the windows process emulation (see section of same name for
38	useful to code pseudo-parallel processes and for event-based	42	more details) ported to UNIX, and as such act as processes), Coro
39	programming, such as multiple HTTP-GET requests running concurrently.	43	provides a full shared address space, which makes communication between
40	See Coro::AnyEvent to learn more.	44	threads very easy. And coro threads are fast, too: disabling the Windows
		45	process emulation code in your perl and using Coro can easily result in
		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.
41		50
42	Coroutines are also useful because Perl has no support for threads (the	51	Coro achieves that by supporting multiple running interpreters that
43	so called "threads" that perl offers are nothing more than the (bad)	52	share data, which is especially useful to code pseudo-parallel processes
44	process emulation coming from the Windows platform: On standard	53	and for event-based programming, such as multiple HTTP-GET requests
45	operating systems they serve no purpose whatsoever, except by making	54	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	55	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		56
50	In this module, coroutines are defined as "callchain + lexical variables	57	In this module, a thread is defined as "callchain + lexical variables +
51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	58	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	59	callchain, its own set of lexicals and its own set of perls most
53	important global variables (see Coro::State for more configuration).	60	important global variables (see Coro::State for more configuration and
		61	background info).
54		62
		63	See also the "SEE ALSO" section at the end of this document - the Coro
		64	module family is quite large.
		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	And 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	Lastly, a coro thread object that isn't referenced is "->cancel"'ed
		215	automatically - just like other objects in Perl. This is not such a
		216	common case, however - a running thread is referencedy b
		217	$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	5. Cleanup
		230	Threads will allocate various resources. Most but not all will be
		231	returned when a thread terminates, during clean-up.
		232
		233	Cleanup is quite similar to throwing an uncaught exception: perl
		234	will work it's way up through all subroutine calls and blocks. On
		235	it's way, it will release all "my" variables, undo all "local"'s and
		236	free any other resources truly local to the thread.
		237
		238	So, a common way to free resources is to keep them referenced only
		239	by my variables:
		240
		241	async {
		242	my $big_cache = new Cache ...;
		243	};
		244
		245	If there are no other references, then the $big_cache object will be
		246	freed when the thread terminates, regardless of how it does so.
		247
		248	What it does "NOT" do is unlock any Coro::Semaphores or similar
		249	resources, but that's where the "guard" methods come in handy:
		250
		251	my $sem = new Coro::Semaphore;
		252
		253	async {
		254	my $lock_guard = $sem->guard;
		255	# if we reutrn, or die or get cancelled, here,
		256	# then the semaphore will be "up"ed.
		257	};
		258
		259	The "Guard::guard" function comes in handy for any custom cleanup
		260	you might want to do (but you cannot switch to other coroutines form
		261	those code blocks):
		262
		263	async {
		264	my $window = new Gtk2::Window "toplevel";
		265	# The window will not be cleaned up automatically, even when $window
		266	# gets freed, so use a guard to ensure it's destruction
		267	# in case of an error:
		268	my $window_guard = Guard::guard { $window->destroy };
		269
		270	# we are safe here
		271	};
		272
		273	Last not least, "local" can often be handy, too, e.g. when
		274	temporarily replacing the coro thread description:
		275
		276	sub myfunction {
		277	local $Coro::current->{desc} = "inside myfunction(@_)";
		278
		279	# if we return or die here, the description will be restored
		280	}
		281
		282	6. Viva La Zombie Muerte
		283	Even after a thread has terminated and cleaned up its resources, the
		284	Coro object still is there and stores the return values of the
		285	thread.
		286
		287	The means the Coro object gets freed automatically when the thread
		288	has terminated and cleaned up and there arenot other references.
		289
		290	If there are, the Coro object will stay around, and you can call
		291	"->join" as many times as you wish to retrieve the result values:
		292
		293	async {
		294	print "hi\n";
		295	1
		296	};
		297
		298	# run the async above, and free everything before returning
		299	# from Coro::cede:
		300	Coro::cede;
		301
		302	{
		303	my $coro = async {
		304	print "hi\n";
		305	1
		306	};
		307
		308	# run the async above, and clean up, but do not free the coro
		309	# object:
		310	Coro::cede;
		311
		312	# optionally retrieve the result values
		313	my @results = $coro->join;
		314
		315	# now $coro goes out of scope, and presumably gets freed
		316	};
		317
		318	GLOBAL VARIABLES
55	$Coro::main	319	$Coro::main
56	This variable stores the coroutine object that represents the main	320	This variable stores the Coro object that represents the main
57	program. While you cna "ready" it and do most other things you can	321	program. While you can "ready" it and do most other things you can
58	do to coroutines, it is mainly useful to compare again	322	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	323	see whether you are running in the main program or not.
60	or not.
61		324
62	$Coro::current	325	$Coro::current
63	The coroutine object representing the current coroutine (the last	326	The Coro object representing the current coro (the last coro that
64	coroutine that the Coro scheduler switched to). The initial value is	327	the Coro scheduler switched to). The initial value is $Coro::main
65	$main (of course).	328	(of course).
66		329
67	This variable is strictly read-only. You can take copies of the	330	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	331	value stored in it and use it as any other Coro object, but you must
69	must not otherwise modify the variable itself.	332	not otherwise modify the variable itself.
70		333
71	$Coro::idle	334	$Coro::idle
72	This variable is mainly useful to integrate Coro into event loops.	335	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	336	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
74	this is pretty low-level functionality.	337	is pretty low-level functionality.
75		338
76	This variable stores a callback that is called whenever the	339	This variable stores a Coro object that is put into the ready queue
77	scheduler finds no ready coroutines to run. The default	340	when there are no other ready threads (without invoking any ready
78	implementation prints "FATAL: deadlock detected" and exits, because	341	hooks).
79	the program has no other way to continue.
80		342
		343	The default implementation dies with "FATAL: deadlock detected.",
		344	followed by a thread listing, because the program has no other way
		345	to continue.
		346
81	This hook is overwritten by modules such as "Coro::Timer" and	347	This hook is overwritten by modules such as "Coro::EV" and
82	"Coro::AnyEvent" to wait on an external event that hopefully wake up	348	"Coro::AnyEvent" to wait on an external event that hopefully wakes
83	a coroutine so the scheduler can run it.	349	up a coro so the scheduler can run it.
84		350
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	351	See Coro::EV or Coro::AnyEvent for examples of using this technique.
91	technique.
92		352
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	353	SIMPLE CORO CREATION
98	async { ... } [@args...]	354	async { ... } [@args...]
99	Create a new coroutine and return it's coroutine object (usually	355	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	356	coro will be put into the ready queue, so it will start running
101	start running automatically on the next scheduler run.	357	automatically on the next scheduler run.
102		358
103	The first argument is a codeblock/closure that should be executed in	359	The first argument is a codeblock/closure that should be executed in
104	the coroutine. When it returns argument returns the coroutine is	360	the coro. When it returns argument returns the coro is automatically
105	automatically terminated.	361	terminated.
106		362
107	The remaining arguments are passed as arguments to the closure.	363	The remaining arguments are passed as arguments to the closure.
108		364
109	See the "Coro::State::new" constructor for info about the coroutine	365	See the "Coro::State::new" constructor for info about the coro
110	environment in which coroutines are executed.	366	environment in which coro are executed.
111		367
112	Calling "exit" in a coroutine will do the same as calling exit	368	Calling "exit" in a coro will do the same as calling exit outside
113	outside the coroutine. Likewise, when the coroutine dies, the	369	the coro. Likewise, when the coro dies, the program will exit, just
114	program will exit, just as it would in the main program.	370	as it would in the main program.
115		371
116	If you do not want that, you can provide a default "die" handler, or	372	If you do not want that, you can provide a default "die" handler, or
117	simply avoid dieing (by use of "eval").	373	simply avoid dieing (by use of "eval").
118		374
119	Example: Create a new coroutine that just prints its arguments.	375	Example: Create a new coro that just prints its arguments.
120		376
121	async {	377	async {
122	print "@_\n";	378	print "@_\n";
123	} 1,2,3,4;	379	} 1,2,3,4;
124		380
125	async_pool { ... } [@args...]	381	async_pool { ... } [@args...]
126	Similar to "async", but uses a coroutine pool, so you should not	382	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	383	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	384	coro that might have executed other code already (which can be good
129	can be good or bad :).	385	or bad :).
130		386
131	On the plus side, this function is faster than creating (and	387	On the plus side, this function is about twice as fast as creating
132	destroying) a completly new coroutine, so if you need a lot of	388	(and destroying) a completely new coro, so if you need a lot of
133	generic coroutines in quick successsion, use "async_pool", not	389	generic coros in quick successsion, use "async_pool", not "async".
134	"async".
135		390
136	The code block is executed in an "eval" context and a warning will	391	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	392	be issued in case of an exception instead of terminating the
138	program, as "async" does. As the coroutine is being reused, stuff	393	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	394	"on_destroy" will not work in the expected way, unless you call
140	terminate or cancel, which somehow defeats the purpose of pooling	395	terminate or cancel, which somehow defeats the purpose of pooling
141	(but is fine in the exceptional case).	396	(but is fine in the exceptional case).
142		397
143	The priority will be reset to 0 after each run, tracing will be	398	The priority will be reset to 0 after each run, tracing will be
144	disabled, the description will be reset and the default output	399	disabled, the description will be reset and the default output
145	filehandle gets restored, so you can change all these. Otherwise the	400	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	401	coro will be re-used "as-is": most notably if you change other
147	per-coroutine global stuff such as $/ you must needs revert that	402	per-coro global stuff such as $/ you must needs revert that
148	change, which is most simply done by using local as in: "local $/".	403	change, which is most simply done by using local as in: "local $/".
149		404
150	The idle pool size is limited to 8 idle coroutines (this can be	405	The idle pool size is limited to 8 idle coros (this can be adjusted
151	adjusted by changing $Coro::POOL_SIZE), but there can be as many	406	by changing $Coro::POOL_SIZE), but there can be as many non-idle
152	non-idle coros as required.	407	coros as required.
153		408
154	If you are concerned about pooled coroutines growing a lot because a	409	If you are concerned about pooled coros growing a lot because a
155	single "async_pool" used a lot of stackspace you can e.g.	410	single "async_pool" used a lot of stackspace you can e.g.
156	"async_pool { terminate }" once per second or so to slowly replenish	411	"async_pool { terminate }" once per second or so to slowly replenish
157	the pool. In addition to that, when the stacks used by a handler	412	the pool. In addition to that, when the stacks used by a handler
158	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also	413	grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also
159	be destroyed.	414	be destroyed.
160		415
161	STATIC METHODS	416	STATIC METHODS
162	Static methods are actually functions that operate on the current	417	Static methods are actually functions that implicitly operate on the
163	coroutine.	418	current coro.
164		419
165	schedule	420	schedule
166	Calls the scheduler. The scheduler will find the next coroutine that	421	Calls the scheduler. The scheduler will find the next coro that is
167	is to be run from the ready queue and switches to it. The next	422	to be run from the ready queue and switches to it. The next coro to
168	coroutine to be run is simply the one with the highest priority that	423	be run is simply the one with the highest priority that is longest
169	is longest in its ready queue. If there is no coroutine ready, it	424	in its ready queue. If there is no coro ready, it will call the
170	will clal the $Coro::idle hook.	425	$Coro::idle hook.
171		426
172	Please note that the current coroutine will not be put into the	427	Please note that the current coro will not be put into the ready
173	ready queue, so calling this function usually means you will never	428	queue, so calling this function usually means you will never be
174	be called again unless something else (e.g. an event handler) calls	429	called again unless something else (e.g. an event handler) calls
175	"->ready", thus waking you up.	430	"->ready", thus waking you up.
176		431
177	This makes "schedule" the generic method to use to block the	432	This makes "schedule" the generic method to use to block the
178	current coroutine and wait for events: first you remember the	433	current coro and wait for events: first you remember the current
179	current coroutine in a variable, then arrange for some callback of	434	coro in a variable, then arrange for some callback of yours to call
180	yours to call "->ready" on that once some event happens, and last	435	"->ready" on that once some event happens, and last you call
181	you call "schedule" to put yourself to sleep. Note that a lot of	436	"schedule" to put yourself to sleep. Note that a lot of things can
182	things can wake your coroutine up, so you need to check whether the	437	wake your coro up, so you need to check whether the event indeed
183	event indeed happened, e.g. by storing the status in a variable.	438	happened, e.g. by storing the status in a variable.
184		439
185	The canonical way to wait on external events is this:	440	See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
186		441	callbacks.
187	{
188	# remember current coroutine
189	my $current = $Coro::current;
190
191	# register a hypothetical event handler
192	on_event_invoke sub {
193	# wake up sleeping coroutine
194	$current->ready;
195	undef $current;
196	};
197
198	# call schedule until event occurred.
199	# in case we are woken up for other reasons
200	# (current still defined), loop.
201	Coro::schedule while $current;
202	}
203		442
204	cede	443	cede
205	"Cede" to other coroutines. This function puts the current coroutine	444	"Cede" to other coros. This function puts the current coro into the
206	into the ready queue and calls "schedule", which has the effect of	445	ready queue and calls "schedule", which has the effect of giving up
207	giving up the current "timeslice" to other coroutines of the same or	446	the current "timeslice" to other coros of the same or higher
208	higher priority. Once your coroutine gets its turn again it will	447	priority. Once your coro gets its turn again it will automatically
209	automatically be resumed.	448	be resumed.
210		449
211	This function is often called "yield" in other languages.	450	This function is often called "yield" in other languages.
212		451
213	Coro::cede_notself	452	Coro::cede_notself
214	Works like cede, but is not exported by default and will cede to	453	Works like cede, but is not exported by default and will cede to
215	any coroutine, regardless of priority. This is useful sometimes to	454	any coro, regardless of priority. This is useful sometimes to
216	ensure progress is made.	455	ensure progress is made.
217		456
218	terminate [arg...]	457	terminate [arg...]
219	Terminates the current coroutine with the given status values (see	458	Terminates the current coro with the given status values (see
220	cancel).	459	cancel). The values will not be copied, but referenced directly.
		460
		461	Coro::on_enter BLOCK, Coro::on_leave BLOCK
		462	These function install enter and leave winders in the current scope.
		463	The enter block will be executed when on_enter is called and
		464	whenever the current coro is re-entered by the scheduler, while the
		465	leave block is executed whenever the current coro is blocked by the
		466	scheduler, and also when the containing scope is exited (by whatever
		467	means, be it exit, die, last etc.).
		468
		469	*Neither invoking the scheduler, nor exceptions, are allowed within
		470	those BLOCKs*. That means: do not even think about calling "die"
		471	without an eval, and do not even think of entering the scheduler in
		472	any way.
		473
		474	Since both BLOCKs are tied to the current scope, they will
		475	automatically be removed when the current scope exits.
		476
		477	These functions implement the same concept as "dynamic-wind" in
		478	scheme does, and are useful when you want to localise some resource
		479	to a specific coro.
		480
		481	They slow down thread switching considerably for coros that use them
		482	(about 40% for a BLOCK with a single assignment, so thread switching
		483	is still reasonably fast if the handlers are fast).
		484
		485	These functions are best understood by an example: The following
		486	function will change the current timezone to
		487	"Antarctica/South_Pole", which requires a call to "tzset", but by
		488	using "on_enter" and "on_leave", which remember/change the current
		489	timezone and restore the previous value, respectively, the timezone
		490	is only changed for the coro that installed those handlers.
		491
		492	use POSIX qw(tzset);
		493
		494	async {
		495	my $old_tz; # store outside TZ value here
		496
		497	Coro::on_enter {
		498	$old_tz = $ENV{TZ}; # remember the old value
		499
		500	$ENV{TZ} = "Antarctica/South_Pole";
		501	tzset; # enable new value
		502	};
		503
		504	Coro::on_leave {
		505	$ENV{TZ} = $old_tz;
		506	tzset; # restore old value
		507	};
		508
		509	# at this place, the timezone is Antarctica/South_Pole,
		510	# without disturbing the TZ of any other coro.
		511	};
		512
		513	This can be used to localise about any resource (locale, uid,
		514	current working directory etc.) to a block, despite the existance of
		515	other coros.
		516
		517	Another interesting example implements time-sliced multitasking
		518	using interval timers (this could obviously be optimised, but does
		519	the job):
		520
		521	# "timeslice" the given block
		522	sub timeslice(&) {
		523	use Time::HiRes ();
		524
		525	Coro::on_enter {
		526	# on entering the thread, we set an VTALRM handler to cede
		527	$SIG{VTALRM} = sub { cede };
		528	# and then start the interval timer
		529	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		530	};
		531	Coro::on_leave {
		532	# on leaving the thread, we stop the interval timer again
		533	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		534	};
		535
		536	&{+shift};
		537	}
		538
		539	# use like this:
		540	timeslice {
		541	# The following is an endless loop that would normally
		542	# monopolise the process. Since it runs in a timesliced
		543	# environment, it will regularly cede to other threads.
		544	while () { }
		545	};
221		546
222	killall	547	killall
223	Kills/terminates/cancels all coroutines except the currently running	548	Kills/terminates/cancels all coros except the currently running one.
224	one. This is useful after a fork, either in the child or the parent,
225	as usually only one of them should inherit the running coroutines.
226		549
227	Note that while this will try to free some of the main programs	550	Note that while this will try to free some of the main interpreter
228	resources, you cannot free all of them, so if a coroutine that is	551	resources if the calling coro isn't the main coro, but one cannot
229	not the main program calls this function, there will be some	552	free all of them, so if a coro that is not the main coro calls this
230	one-time resource leak.	553	function, there will be some one-time resource leak.
231		554
232	COROUTINE METHODS	555	CORO OBJECT METHODS
233	These are the methods you can call on coroutine objects (or to create	556	These are the methods you can call on coro objects (or to create them).
234	them).
235		557
236	new Coro \&sub [, @args...]	558	new Coro \&sub [, @args...]
237	Create a new coroutine and return it. When the sub returns, the	559	Create a new coro and return it. When the sub returns, the coro
238	coroutine automatically terminates as if "terminate" with the	560	automatically terminates as if "terminate" with the returned values
239	returned values were called. To make the coroutine run you must	561	were called. To make the coro run you must first put it into the
240	first put it into the ready queue by calling the ready method.	562	ready queue by calling the ready method.
241		563
242	See "async" and "Coro::State::new" for additional info about the	564	See "async" and "Coro::State::new" for additional info about the
243	coroutine environment.	565	coro environment.
244		566
245	$success = $coroutine->ready	567	$success = $coro->ready
246	Put the given coroutine into the end of its ready queue (there is	568	Put the given coro into the end of its ready queue (there is one
247	one queue for each priority) and return true. If the coroutine is	569	queue for each priority) and return true. If the coro is already in
248	already in the ready queue, do nothing and return false.	570	the ready queue, do nothing and return false.
249		571
250	This ensures that the scheduler will resume this coroutine	572	This ensures that the scheduler will resume this coro automatically
251	automatically once all the coroutines of higher priority and all	573	once all the coro of higher priority and all coro of the same
252	coroutines of the same priority that were put into the ready queue	574	priority that were put into the ready queue earlier have been
253	earlier have been resumed.	575	resumed.
254		576
		577	$coro->suspend
		578	Suspends the specified coro. A suspended coro works just like any
		579	other coro, except that the scheduler will not select a suspended
		580	coro for execution.
		581
		582	Suspending a coro can be useful when you want to keep the coro from
		583	running, but you don't want to destroy it, or when you want to
		584	temporarily freeze a coro (e.g. for debugging) to resume it later.
		585
		586	A scenario for the former would be to suspend all (other) coros
		587	after a fork and keep them alive, so their destructors aren't
		588	called, but new coros can be created.
		589
		590	$coro->resume
		591	If the specified coro was suspended, it will be resumed. Note that
		592	when the coro was in the ready queue when it was suspended, it might
		593	have been unreadied by the scheduler, so an activation might have
		594	been lost.
		595
		596	To avoid this, it is best to put a suspended coro into the ready
		597	queue unconditionally, as every synchronisation mechanism must
		598	protect itself against spurious wakeups, and the one in the Coro
		599	family certainly do that.
		600
		601	$state->is_new
		602	Returns true iff this Coro object is "new", i.e. has never been run
		603	yet. Those states basically consist of only the code reference to
		604	call and the arguments, but consumes very little other resources.
		605	New states will automatically get assigned a perl interpreter when
		606	they are transfered to.
		607
		608	$state->is_zombie
		609	Returns true iff the Coro object has been cancelled, i.e. it's
		610	resources freed because they were "cancel"'ed, "terminate"'d,
		611	"safe_cancel"'ed or simply went out of scope.
		612
		613	The name "zombie" stems from UNIX culture, where a process that has
		614	exited and only stores and exit status and no other resources is
		615	called a "zombie".
		616
255	$is_ready = $coroutine->is_ready	617	$is_ready = $coro->is_ready
256	Return whether the coroutine is currently the ready queue or not,	618	Returns true iff the Coro object is in the ready queue. Unless the
		619	Coro object gets destroyed, it will eventually be scheduled by the
		620	scheduler.
257		621
		622	$is_running = $coro->is_running
		623	Returns true iff the Coro object is currently running. Only one Coro
		624	object can ever be in the running state (but it currently is
		625	possible to have multiple running Coro::States).
		626
		627	$is_suspended = $coro->is_suspended
		628	Returns true iff this Coro object has been suspended. Suspended
		629	Coros will not ever be scheduled.
		630
258	$coroutine->cancel (arg...)	631	$coro->cancel (arg...)
259	Terminates the given coroutine and makes it return the given	632	Terminates the given Coro thread and makes it return the given
260	arguments as status (default: the empty list). Never returns if the	633	arguments as status (default: an empty list). Never returns if the
261	coroutine is the current coroutine.	634	Coro is the current Coro.
262		635
		636	This is a rather brutal way to free a coro, with some limitations -
		637	if the thread is inside a C callback that doesn't expect to be
		638	canceled, bad things can happen, or if the cancelled thread insists
		639	on running complicated cleanup handlers that rely on its thread
		640	context, things will not work.
		641
		642	Any cleanup code being run (e.g. from "guard" blocks) will be run
		643	without a thread context, and is not allowed to switch to other
		644	threads. On the plus side, "->cancel" will always clean up the
		645	thread, no matter what. If your cleanup code is complex or you want
		646	to avoid cancelling a C-thread that doesn't know how to clean up
		647	itself, it can be better to "->throw" an exception, or use
		648	"->safe_cancel".
		649
		650	The arguments to "->cancel" are not copied, but instead will be
		651	referenced directly (e.g. if you pass $var and after the call change
		652	that variable, then you might change the return values passed to
		653	e.g. "join", so don't do that).
		654
		655	The resources of the Coro are usually freed (or destructed) before
		656	this call returns, but this can be delayed for an indefinite amount
		657	of time, as in some cases the manager thread has to run first to
		658	actually destruct the Coro object.
		659
		660	$coro->safe_cancel ($arg...)
		661	Works mostly like "->cancel", but is inherently "safer", and
		662	consequently, can fail with an exception in cases the thread is not
		663	in a cancellable state.
		664
		665	This method works a bit like throwing an exception that cannot be
		666	caught - specifically, it will clean up the thread from within
		667	itself, so all cleanup handlers (e.g. "guard" blocks) are run with
		668	full thread context and can block if they wish. The downside is that
		669	there is no guarantee that the thread can be cancelled when you call
		670	this method, and therefore, it might fail. It is also considerably
		671	slower than "cancel" or "terminate".
		672
		673	A thread is in a safe-cancellable state if it either hasn't been run
		674	yet, or it has no C context attached and is inside an SLF function.
		675
		676	The latter two basically mean that the thread isn't currently inside
		677	a perl callback called from some C function (usually via some XS
		678	modules) and isn't currently executing inside some C function itself
		679	(via Coro's XS API).
		680
		681	This call returns true when it could cancel the thread, or croaks
		682	with an error otherwise (i.e. it either returns true or doesn't
		683	return at all).
		684
		685	Why the weird interface? Well, there are two common models on how
		686	and when to cancel things. In the first, you have the expectation
		687	that your coro thread can be cancelled when you want to cancel it -
		688	if the thread isn't cancellable, this would be a bug somewhere, so
		689	"->safe_cancel" croaks to notify of the bug.
		690
		691	In the second model you sometimes want to ask nicely to cancel a
		692	thread, but if it's not a good time, well, then don't cancel. This
		693	can be done relatively easy like this:
		694
		695	if (! eval { $coro->safe_cancel }) {
		696	warn "unable to cancel thread: $@";
		697	}
		698
		699	However, what you never should do is first try to cancel "safely"
		700	and if that fails, cancel the "hard" way with "->cancel". That makes
		701	no sense: either you rely on being able to execute cleanup code in
		702	your thread context, or you don't. If you do, then "->safe_cancel"
		703	is the only way, and if you don't, then "->cancel" is always faster
		704	and more direct.
		705
		706	$coro->schedule_to
		707	Puts the current coro to sleep (like "Coro::schedule"), but instead
		708	of continuing with the next coro from the ready queue, always switch
		709	to the given coro object (regardless of priority etc.). The
		710	readyness state of that coro isn't changed.
		711
		712	This is an advanced method for special cases - I'd love to hear
		713	about any uses for this one.
		714
		715	$coro->cede_to
		716	Like "schedule_to", but puts the current coro into the ready queue.
		717	This has the effect of temporarily switching to the given coro, and
		718	continuing some time later.
		719
		720	This is an advanced method for special cases - I'd love to hear
		721	about any uses for this one.
		722
263	$coroutine->throw ([$scalar])	723	$coro->throw ([$scalar])
264	If $throw is specified and defined, it will be thrown as an	724	If $throw is specified and defined, it will be thrown as an
265	exception inside the coroutine at the next convenient point in time	725	exception inside the coro at the next convenient point in time.
266	(usually after it gains control at the next schedule/transfer/cede).
267	Otherwise clears the exception object.	726	Otherwise clears the exception object.
		727
		728	Coro will check for the exception each time a schedule-like-function
		729	returns, i.e. after each "schedule", "cede",
		730	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
		731	those functions (all that are part of Coro itself) detect this case
		732	and return early in case an exception is pending.
268		733
269	The exception object will be thrown "as is" with the specified	734	The exception object will be thrown "as is" with the specified
270	scalar in $@, i.e. if it is a string, no line number or newline will	735	scalar in $@, i.e. if it is a string, no line number or newline will
271	be appended (unlike with "die").	736	be appended (unlike with "die").
272		737
273	This can be used as a softer means than "cancel" to ask a coroutine	738	This can be used as a softer means than either "cancel" or
274	to end itself, although there is no guarantee that the exception	739	"safe_cancel "to ask a coro to end itself, although there is no
275	will lead to termination, and if the exception isn't caught it might	740	guarantee that the exception will lead to termination, and if the
276	well end the whole program.	741	exception isn't caught it might well end the whole program.
277		742
278	You might also think of "throw" as being the moral equivalent of	743	You might also think of "throw" as being the moral equivalent of
279	"kill"ing a coroutine with a signal (in this case, a scalar).	744	"kill"ing a coro with a signal (in this case, a scalar).
280		745
281	$coroutine->join	746	$coro->join
282	Wait until the coroutine terminates and return any values given to	747	Wait until the coro terminates and return any values given to the
283	the "terminate" or "cancel" functions. "join" can be called	748	"terminate" or "cancel" functions. "join" can be called concurrently
284	concurrently from multiple coroutines, and all will be resumed and	749	from multiple threads, and all will be resumed and given the status
285	given the status return once the $coroutine terminates.	750	return once the $coro terminates.
286		751
287	$coroutine->on_destroy (\&cb)	752	$coro->on_destroy (\&cb)
288	Registers a callback that is called when this coroutine gets	753	Registers a callback that is called when this coro thread gets
289	destroyed, but before it is joined. The callback gets passed the	754	destroyed, that is, after it's resources have been freed but before
		755	it is joined. The callback gets passed the terminate/cancel
290	terminate arguments, if any, and must not die, under any	756	arguments, if any, and must not die, under any circumstances.
291	circumstances.
292		757
		758	There can be any number of "on_destroy" callbacks per coro, and
		759	there is no way currently to remove a callback once added.
		760
293	$oldprio = $coroutine->prio ($newprio)	761	$oldprio = $coro->prio ($newprio)
294	Sets (or gets, if the argument is missing) the priority of the	762	Sets (or gets, if the argument is missing) the priority of the coro
295	coroutine. Higher priority coroutines get run before lower priority	763	thread. Higher priority coro get run before lower priority coros.
296	coroutines. Priorities are small signed integers (currently -4 ..	764	Priorities are small signed integers (currently -4 .. +3), that you
297	+3), that you can refer to using PRIO_xxx constants (use the import	765	can refer to using PRIO_xxx constants (use the import tag :prio to
298	tag :prio to get then):	766	get then):
299		767
300	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	768	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
301	3 > 1 > 0 > -1 > -3 > -4	769	3 > 1 > 0 > -1 > -3 > -4
302		770
303	# set priority to HIGH	771	# set priority to HIGH
304	current->prio(PRIO_HIGH);	772	current->prio (PRIO_HIGH);
305		773
306	The idle coroutine ($Coro::idle) always has a lower priority than	774	The idle coro thread ($Coro::idle) always has a lower priority than
307	any existing coroutine.	775	any existing coro.
308		776
309	Changing the priority of the current coroutine will take effect	777	Changing the priority of the current coro will take effect
310	immediately, but changing the priority of coroutines in the ready	778	immediately, but changing the priority of a coro in the ready queue
311	queue (but not running) will only take effect after the next	779	(but not running) will only take effect after the next schedule (of
312	schedule (of that coroutine). This is a bug that will be fixed in	780	that coro). This is a bug that will be fixed in some future version.
313	some future version.
314		781
315	$newprio = $coroutine->nice ($change)	782	$newprio = $coro->nice ($change)
316	Similar to "prio", but subtract the given value from the priority	783	Similar to "prio", but subtract the given value from the priority
317	(i.e. higher values mean lower priority, just as in unix).	784	(i.e. higher values mean lower priority, just as in UNIX's nice
		785	command).
318		786
319	$olddesc = $coroutine->desc ($newdesc)	787	$olddesc = $coro->desc ($newdesc)
320	Sets (or gets in case the argument is missing) the description for	788	Sets (or gets in case the argument is missing) the description for
321	this coroutine. This is just a free-form string you can associate	789	this coro thread. This is just a free-form string you can associate
322	with a coroutine.	790	with a coro.
323		791
324	This method simply sets the "$coroutine->{desc}" member to the given	792	This method simply sets the "$coro->{desc}" member to the given
325	string. You can modify this member directly if you wish.	793	string. You can modify this member directly if you wish, and in
		794	fact, this is often preferred to indicate major processing states
		795	that can then be seen for example in a Coro::Debug session:
326		796
		797	sub my_long_function {
		798	local $Coro::current->{desc} = "now in my_long_function";
		799	...
		800	$Coro::current->{desc} = "my_long_function: phase 1";
		801	...
		802	$Coro::current->{desc} = "my_long_function: phase 2";
		803	...
		804	}
		805
327	GLOBAL FUNCTIONS	806	GLOBAL FUNCTIONS
328	Coro::nready	807	Coro::nready
329	Returns the number of coroutines that are currently in the ready	808	Returns the number of coro that are currently in the ready state,
330	state, i.e. that can be switched to by calling "schedule" directory	809	i.e. that can be switched to by calling "schedule" directory or
331	or indirectly. The value 0 means that the only runnable coroutine is	810	indirectly. The value 0 means that the only runnable coro is the
332	the currently running one, so "cede" would have no effect, and	811	currently running one, so "cede" would have no effect, and
333	"schedule" would cause a deadlock unless there is an idle handler	812	"schedule" would cause a deadlock unless there is an idle handler
334	that wakes up some coroutines.	813	that wakes up some coro.
335		814
336	my $guard = Coro::guard { ... }	815	my $guard = Coro::guard { ... }
337	This creates and returns a guard object. Nothing happens until the	816	This function still exists, but is deprecated. Please use the
338	object gets destroyed, in which case the codeblock given as argument	817	"Guard::guard" function instead.
339	will be executed. This is useful to free locks or other resources in
340	case of a runtime error or when the coroutine gets canceled, as in
341	both cases the guard block will be executed. The guard object
342	supports only one method, "->cancel", which will keep the codeblock
343	from being executed.
344
345	Example: set some flag and clear it again when the coroutine gets
346	canceled or the function returns:
347
348	sub do_something {
349	my $guard = Coro::guard { $busy = 0 };
350	$busy = 1;
351
352	# do something that requires $busy to be true
353	}
354		818
355	unblock_sub { ... }	819	unblock_sub { ... }
356	This utility function takes a BLOCK or code reference and "unblocks"	820	This utility function takes a BLOCK or code reference and "unblocks"
357	it, returning a new coderef. Unblocking means that calling the new	821	it, returning a new coderef. Unblocking means that calling the new
358	coderef will return immediately without blocking, returning nothing,	822	coderef will return immediately without blocking, returning nothing,
359	while the original code ref will be called (with parameters) from	823	while the original code ref will be called (with parameters) from
360	within another coroutine.	824	within another coro.
361		825
362	The reason this function exists is that many event libraries (such	826	The reason this function exists is that many event libraries (such
363	as the venerable Event module) are not coroutine-safe (a weaker form	827	as the venerable Event module) are not thread-safe (a weaker form of
364	of thread-safety). This means you must not block within event	828	reentrancy). This means you must not block within event callbacks,
365	callbacks, otherwise you might suffer from crashes or worse. The	829	otherwise you might suffer from crashes or worse. The only event
366	only event library currently known that is safe to use without	830	library currently known that is safe to use without "unblock_sub" is
367	"unblock_sub" is EV.	831	EV (but you might still run into deadlocks if all event loops are
		832	blocked).
		833
		834	Coro will try to catch you when you block in the event loop
		835	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		836	and only works when you do not run your own event loop.
368		837
369	This function allows your callbacks to block by executing them in	838	This function allows your callbacks to block by executing them in
370	another coroutine where it is safe to block. One example where	839	another coro where it is safe to block. One example where blocking
371	blocking is handy is when you use the Coro::AIO functions to save	840	is handy is when you use the Coro::AIO functions to save results to
372	results to disk, for example.	841	disk, for example.
373		842
374	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	843	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
375	when creating event callbacks that want to block.	844	when creating event callbacks that want to block.
376		845
377	If your handler does not plan to block (e.g. simply sends a message	846	If your handler does not plan to block (e.g. simply sends a message
378	to another coroutine, or puts some other coroutine into the ready	847	to another coro, or puts some other coro into the ready queue),
379	queue), there is no reason to use "unblock_sub".	848	there is no reason to use "unblock_sub".
380		849
381	Note that you also need to use "unblock_sub" for any other callbacks	850	Note that you also need to use "unblock_sub" for any other callbacks
382	that are indirectly executed by any C-based event loop. For example,	851	that are indirectly executed by any C-based event loop. For example,
383	when you use a module that uses AnyEvent (and you use	852	when you use a module that uses AnyEvent (and you use
384	Coro::AnyEvent) and it provides callbacks that are the result of	853	Coro::AnyEvent) and it provides callbacks that are the result of
385	some event callback, then you must not block either, or use	854	some event callback, then you must not block either, or use
386	"unblock_sub".	855	"unblock_sub".
387		856
		857	$cb = rouse_cb
		858	Create and return a "rouse callback". That's a code reference that,
		859	when called, will remember a copy of its arguments and notify the
		860	owner coro of the callback.
		861
		862	See the next function.
		863
		864	@args = rouse_wait [$cb]
		865	Wait for the specified rouse callback (or the last one that was
		866	created in this coro).
		867
		868	As soon as the callback is invoked (or when the callback was invoked
		869	before "rouse_wait"), it will return the arguments originally passed
		870	to the rouse callback. In scalar context, that means you get the
		871	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		872	$a3...)" statement at the end.
		873
		874	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
		875	example.
		876
		877	HOW TO WAIT FOR A CALLBACK
		878	It is very common for a coro to wait for some callback to be called.
		879	This occurs naturally when you use coro in an otherwise event-based
		880	program, or when you use event-based libraries.
		881
		882	These typically register a callback for some event, and call that
		883	callback when the event occured. In a coro, however, you typically want
		884	to just wait for the event, simplyifying things.
		885
		886	For example "AnyEvent->child" registers a callback to be called when a
		887	specific child has exited:
		888
		889	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		890
		891	But from within a coro, you often just want to write this:
		892
		893	my $status = wait_for_child $pid;
		894
		895	Coro offers two functions specifically designed to make this easy,
		896	"Coro::rouse_cb" and "Coro::rouse_wait".
		897
		898	The first function, "rouse_cb", generates and returns a callback that,
		899	when invoked, will save its arguments and notify the coro that created
		900	the callback.
		901
		902	The second function, "rouse_wait", waits for the callback to be called
		903	(by calling "schedule" to go to sleep) and returns the arguments
		904	originally passed to the callback.
		905
		906	Using these functions, it becomes easy to write the "wait_for_child"
		907	function mentioned above:
		908
		909	sub wait_for_child($) {
		910	my ($pid) = @_;
		911
		912	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		913
		914	my ($rpid, $rstatus) = Coro::rouse_wait;
		915	$rstatus
		916	}
		917
		918	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
		919	you can roll your own, using "schedule" and "ready":
		920
		921	sub wait_for_child($) {
		922	my ($pid) = @_;
		923
		924	# store the current coro in $current,
		925	# and provide result variables for the closure passed to ->child
		926	my $current = $Coro::current;
		927	my ($done, $rstatus);
		928
		929	# pass a closure to ->child
		930	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		931	$rstatus = $_[1]; # remember rstatus
		932	$done = 1; # mark $rstatus as valid
		933	$current->ready; # wake up the waiting thread
		934	});
		935
		936	# wait until the closure has been called
		937	schedule while !$done;
		938
		939	$rstatus
		940	}
		941
388	BUGS/LIMITATIONS	942	BUGS/LIMITATIONS
		943	fork with pthread backend
		944	When Coro is compiled using the pthread backend (which isn't
		945	recommended but required on many BSDs as their libcs are completely
		946	broken), then coro will not survive a fork. There is no known
		947	workaround except to fix your libc and use a saner backend.
		948
		949	perl process emulation ("threads")
389	This module is not perl-pseudo-thread-safe. You should only ever use	950	This module is not perl-pseudo-thread-safe. You should only ever use
390	this module from the same thread (this requirement might be removed in	951	this module from the first thread (this requirement might be removed
391	the future to allow per-thread schedulers, but Coro::State does not yet	952	in the future to allow per-thread schedulers, but Coro::State does
392	allow this). I recommend disabling thread support and using processes,	953	not yet allow this). I recommend disabling thread support and using
393	as this is much faster and uses less memory.	954	processes, as having the windows process emulation enabled under
		955	unix roughly halves perl performance, even when not used.
		956
		957	Attempts to use threads created in another emulated process will
		958	crash ("cleanly", with a null pointer exception).
		959
		960	coro switching is not signal safe
		961	You must not switch to another coro from within a signal handler
		962	(only relevant with %SIG - most event libraries provide safe
		963	signals), unless you are sure you are not interrupting a Coro
		964	function.
		965
		966	That means you MUST NOT call any function that might "block" the
		967	current coro - "cede", "schedule" "Coro::Semaphore->down" or
		968	anything that calls those. Everything else, including calling
		969	"ready", works.
		970
		971	WINDOWS PROCESS EMULATION
		972	A great many people seem to be confused about ithreads (for example,
		973	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		974	while in the same mail making rather confused statements about perl
		975	ithreads (for example, that memory or files would be shared), showing
		976	his lack of understanding of this area - if it is hard to understand for
		977	Chip, it is probably not obvious to everybody).
		978
		979	What follows is an ultra-condensed version of my talk about threads in
		980	scripting languages given on the perl workshop 2009:
		981
		982	The so-called "ithreads" were originally implemented for two reasons:
		983	first, to (badly) emulate unix processes on native win32 perls, and
		984	secondly, to replace the older, real thread model ("5.005-threads").
		985
		986	It does that by using threads instead of OS processes. The difference
		987	between processes and threads is that threads share memory (and other
		988	state, such as files) between threads within a single process, while
		989	processes do not share anything (at least not semantically). That means
		990	that modifications done by one thread are seen by others, while
		991	modifications by one process are not seen by other processes.
		992
		993	The "ithreads" work exactly like that: when creating a new ithreads
		994	process, all state is copied (memory is copied physically, files and
		995	code is copied logically). Afterwards, it isolates all modifications. On
		996	UNIX, the same behaviour can be achieved by using operating system
		997	processes, except that UNIX typically uses hardware built into the
		998	system to do this efficiently, while the windows process emulation
		999	emulates this hardware in software (rather efficiently, but of course it
		1000	is still much slower than dedicated hardware).
		1001
		1002	As mentioned before, loading code, modifying code, modifying data
		1003	structures and so on is only visible in the ithreads process doing the
		1004	modification, not in other ithread processes within the same OS process.
		1005
		1006	This is why "ithreads" do not implement threads for perl at all, only
		1007	processes. What makes it so bad is that on non-windows platforms, you
		1008	can actually take advantage of custom hardware for this purpose (as
		1009	evidenced by the forks module, which gives you the (i-) threads API,
		1010	just much faster).
		1011
		1012	Sharing data is in the i-threads model is done by transfering data
		1013	structures between threads using copying semantics, which is very slow -
		1014	shared data simply does not exist. Benchmarks using i-threads which are
		1015	communication-intensive show extremely bad behaviour with i-threads (in
		1016	fact, so bad that Coro, which cannot take direct advantage of multiple
		1017	CPUs, is often orders of magnitude faster because it shares data using
		1018	real threads, refer to my talk for details).
		1019
		1020	As summary, i-threads use threads to implement processes, while the
		1021	compatible forks module uses processes to emulate, uhm, processes.
		1022	I-threads slow down every perl program when enabled, and outside of
		1023	windows, serve no (or little) practical purpose, but disadvantages every
		1024	single-threaded Perl program.
		1025
		1026	This is the reason that I try to avoid the name "ithreads", as it is
		1027	misleading as it implies that it implements some kind of thread model
		1028	for perl, and prefer the name "windows process emulation", which
		1029	describes the actual use and behaviour of it much better.
394		1030
395	SEE ALSO	1031	SEE ALSO
396	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	1032	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
397		1033
398	Debugging: Coro::Debug.	1034	Debugging: Coro::Debug.
399		1035
400	Support/Utility: Coro::Specific, Coro::Util.	1036	Support/Utility: Coro::Specific, Coro::Util.
401		1037
402	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	1038	Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
403	Coro::SemaphoreSet, Coro::RWLock.	1039	Coro::SemaphoreSet, Coro::RWLock.
404		1040
405	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.	1041	I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
406		1042
407	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.	1043	Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP
		1044	for a better-working alternative), Coro::BDB, Coro::Storable,
		1045	Coro::Select.
408		1046
409	XS API: Coro::MakeMaker.	1047	XS API: Coro::MakeMaker.
410		1048
411	Low level Configuration, Coroutine Environment: Coro::State.	1049	Low level Configuration, Thread Environment, Continuations: Coro::State.
412		1050
413	AUTHOR	1051	AUTHOR
414	Marc Lehmann <schmorp@schmorp.de>	1052	Marc Lehmann <schmorp@schmorp.de>
415	http://home.schmorp.de/	1053	http://home.schmorp.de/
416		1054

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