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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 coro	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.
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, and as such act	41	but only the windows process emulation (see section of same name for
43	as processes), Coro provides a full shared address space, which makes	42	more details) ported to UNIX, and as such act as processes), Coro
44	communication between threads very easy. And Coro's threads are fast,	43	provides a full shared address space, which makes communication between
45	too: disabling the Windows process emulation code in your perl and using	44	threads very easy. And coro threads are fast, too: disabling the Windows
46	Coro can easily result in a two to four times speed increase for your	45	process emulation code in your perl and using Coro can easily result in
47	programs. A parallel matrix multiplication benchmark runs over 300 times	46	a two to four times speed increase for your programs. A parallel matrix
		47	multiplication benchmark (very communication-intensive) runs over 300
48	faster on a single core than perl's pseudo-threads on a quad core using	48	times faster on a single core than perls pseudo-threads on a quad core
49	all four cores.	49	using all four cores.
50		50
51	Coro achieves that by supporting multiple running interpreters that	51	Coro achieves that by supporting multiple running interpreters that
52	share data, which is especially useful to code pseudo-parallel processes	52	share data, which is especially useful to code pseudo-parallel processes
53	and for event-based programming, such as multiple HTTP-GET requests	53	and for event-based programming, such as multiple HTTP-GET requests
54	running concurrently. See Coro::AnyEvent to learn more on how to	54	running concurrently. See Coro::AnyEvent to learn more on how to
…		…
61	background info).	61	background info).
62		62
63	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
64	module family is quite large.	64	module family is quite large.
65		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 its 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 its 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 its
		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 its way up through all subroutine calls and blocks. On its
		258	way, it will release all "my" variables, undo all "local"'s and free
		259	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 its 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
66	GLOBAL VARIABLES	342	GLOBAL VARIABLES
67	$Coro::main	343	$Coro::main
68	This variable stores the Coro object that represents the main	344	This variable stores the Coro object that represents the main
69	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
70	do to coro, it is mainly useful to compare again $Coro::current, to	346	do to coro, it is mainly useful to compare again $Coro::current, to
71	see whether you are running in the main program or not.	347	see whether you are running in the main program or not.
72		348
73	$Coro::current	349	$Coro::current
74	The Coro object representing the current coro (the last coro that	350	The Coro object representing the current coro (the last coro that
…		…
82	$Coro::idle	358	$Coro::idle
83	This variable is mainly useful to integrate Coro into event loops.	359	This variable is mainly useful to integrate Coro into event loops.
84	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
85	is pretty low-level functionality.	361	is pretty low-level functionality.
86		362
87	This variable stores either a Coro object 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).
88		366
89	If it is a callback, the it is called whenever the scheduler finds	367	The default implementation dies with "FATAL: deadlock detected.",
90	no ready coros to run. The default implementation prints "FATAL:	368	followed by a thread listing, because the program has no other way
91	deadlock detected" and exits, because the program has no other way
92	to continue.	369	to continue.
93		370
94	If it is a coro object, then this object will be readied (without
95	invoking any ready hooks, however) when the scheduler finds no other
96	ready coros to run.
97
98	This hook is overwritten by modules such as "Coro::EV" and	371	This hook is overwritten by modules such as "Coro::EV" and
99	"Coro::AnyEvent" to wait on an external event that hopefully wake up	372	"Coro::AnyEvent" to wait on an external event that hopefully wakes
100	a coro so the scheduler can run it.	373	up a coro so the scheduler can run it.
101		374
102	Note that the callback must not, under any circumstances, block
103	the current coro. Normally, this is achieved by having an "idle
104	coro" that calls the event loop and then blocks again, and then
105	readying that coro in the idle handler, or by simply placing the
106	idle coro in this variable.
107
108	See Coro::Event or Coro::AnyEvent for examples of using this	375	See Coro::EV or Coro::AnyEvent for examples of using this technique.
109	technique.
110
111	Please note that if your callback recursively invokes perl (e.g. for
112	event handlers), then it must be prepared to be called recursively
113	itself.
114		376
115	SIMPLE CORO CREATION	377	SIMPLE CORO CREATION
116	async { ... } [@args...]	378	async { ... } [@args...]
117	Create a new coro and return its Coro object (usually unused). The	379	Create a new coro and return its Coro object (usually unused). The
118	coro will be put into the ready queue, so it will start running	380	coro will be put into the ready queue, so it will start running
…		…
155	program, as "async" does. As the coro is being reused, stuff like	417	program, as "async" does. As the coro is being reused, stuff like
156	"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
157	terminate or cancel, which somehow defeats the purpose of pooling	419	terminate or cancel, which somehow defeats the purpose of pooling
158	(but is fine in the exceptional case).	420	(but is fine in the exceptional case).
159		421
160	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
161	disabled, the description will be reset and the default output	423	will be undone, tracing will be disabled, the description will be
162	filehandle gets restored, so you can change all these. Otherwise the	424	reset and the default output filehandle gets restored, so you can
163	coro 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
164	per-coro global stuff such as $/ you must needs revert that	426	notably if you change other per-coro global stuff such as $/ you
165	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 $/".
166		429
167	The idle pool size is limited to 8 idle coros (this can be adjusted	430	The idle pool size is limited to 8 idle coros (this can be adjusted
168	by changing $Coro::POOL_SIZE), but there can be as many non-idle	431	by changing $Coro::POOL_SIZE), but there can be as many non-idle
169	coros as required.	432	coros as required.
170		433
…		…
181		444
182	schedule	445	schedule
183	Calls the scheduler. The scheduler will find the next coro that is	446	Calls the scheduler. The scheduler will find the next coro that is
184	to be run from the ready queue and switches to it. The next coro to	447	to be run from the ready queue and switches to it. The next coro to
185	be run is simply the one with the highest priority that is longest	448	be run is simply the one with the highest priority that is longest
186	in its ready queue. If there is no coro ready, it will clal the	449	in its ready queue. If there is no coro ready, it will call the
187	$Coro::idle hook.	450	$Coro::idle hook.
188		451
189	Please note that the current coro will not be put into the ready	452	Please note that the current coro will not be put into the ready
190	queue, so calling this function usually means you will never be	453	queue, so calling this function usually means you will never be
191	called again unless something else (e.g. an event handler) calls	454	called again unless something else (e.g. an event handler) calls
…		…
216	any coro, regardless of priority. This is useful sometimes to	479	any coro, regardless of priority. This is useful sometimes to
217	ensure progress is made.	480	ensure progress is made.
218		481
219	terminate [arg...]	482	terminate [arg...]
220	Terminates the current coro with the given status values (see	483	Terminates the current coro with the given status values (see
221	cancel).	484	cancel). The values will not be copied, but referenced directly.
222		485
223	Coro::on_enter BLOCK, Coro::on_leave BLOCK	486	Coro::on_enter BLOCK, Coro::on_leave BLOCK
224	These function install enter and leave winders in the current scope.	487	These function install enter and leave winders in the current scope.
225	The enter block will be executed when on_enter is called and	488	The enter block will be executed when on_enter is called and
226	whenever the current coro is re-entered by the scheduler, while the	489	whenever the current coro is re-entered by the scheduler, while the
…		…
238		501
239	These functions implement the same concept as "dynamic-wind" in	502	These functions implement the same concept as "dynamic-wind" in
240	scheme does, and are useful when you want to localise some resource	503	scheme does, and are useful when you want to localise some resource
241	to a specific coro.	504	to a specific coro.
242		505
243	They slow down coro switching considerably for coros that use them	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
244	(But coro switching is still reasonably fast if the handlers are	508	is still reasonably fast if the handlers are fast).
245	fast).
246		509
247	These functions are best understood by an example: The following	510	These functions are best understood by an example: The following
248	function will change the current timezone to	511	function will change the current timezone to
249	"Antarctica/South_Pole", which requires a call to "tzset", but by	512	"Antarctica/South_Pole", which requires a call to "tzset", but by
250	using "on_enter" and "on_leave", which remember/change the current	513	using "on_enter" and "on_leave", which remember/change the current
…		…
271	# at this place, the timezone is Antarctica/South_Pole,	534	# at this place, the timezone is Antarctica/South_Pole,
272	# without disturbing the TZ of any other coro.	535	# without disturbing the TZ of any other coro.
273	};	536	};
274		537
275	This can be used to localise about any resource (locale, uid,	538	This can be used to localise about any resource (locale, uid,
276	current working directory etc.) to a block, despite the existance of	539	current working directory etc.) to a block, despite the existence of
277	other coros.	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	};
278		571
279	killall	572	killall
280	Kills/terminates/cancels all coros except the currently running one.	573	Kills/terminates/cancels all coros except the currently running one.
281		574
282	Note that while this will try to free some of the main interpreter	575	Note that while this will try to free some of the main interpreter
…		…
328	To avoid this, it is best to put a suspended coro into the ready	621	To avoid this, it is best to put a suspended coro into the ready
329	queue unconditionally, as every synchronisation mechanism must	622	queue unconditionally, as every synchronisation mechanism must
330	protect itself against spurious wakeups, and the one in the Coro	623	protect itself against spurious wakeups, and the one in the Coro
331	family certainly do that.	624	family certainly do that.
332		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. its
		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
333	$is_ready = $coro->is_ready	642	$is_ready = $coro->is_ready
334	Returns true iff the Coro object is in the ready queue. Unless the	643	Returns true iff the Coro object is in the ready queue. Unless the
335	Coro object gets destroyed, it will eventually be scheduled by the	644	Coro object gets destroyed, it will eventually be scheduled by the
336	scheduler.	645	scheduler.
337		646
…		…
342		651
343	$is_suspended = $coro->is_suspended	652	$is_suspended = $coro->is_suspended
344	Returns true iff this Coro object has been suspended. Suspended	653	Returns true iff this Coro object has been suspended. Suspended
345	Coros will not ever be scheduled.	654	Coros will not ever be scheduled.
346		655
347	$coro->cancel (arg...)	656	$coro->cancel ($arg...)
348	Terminates the given Coro and makes it return the given arguments as	657	Terminate the given Coro thread and make it return the given
349	status (default: the empty list). Never returns if the Coro is the	658	arguments as status (default: an empty list). Never returns if the
350	current Coro.	659	Coro is the current Coro.
		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 has never been
		703	run yet, has already been canceled/terminated or otherwise
		704	destroyed, or has no C context attached and is inside an SLF
		705	function.
		706
		707	The first two states are trivial - a thread that hasnot started or
		708	has already finished is safe to cancel.
		709
		710	The last state basically means that the thread isn't currently
		711	inside a perl callback called from some C function (usually via some
		712	XS modules) and isn't currently executing inside some C function
		713	itself (via Coro's XS API).
		714
		715	This call returns true when it could cancel the thread, or croaks
		716	with an error otherwise (i.e. it either returns true or doesn't
		717	return at all).
		718
		719	Why the weird interface? Well, there are two common models on how
		720	and when to cancel things. In the first, you have the expectation
		721	that your coro thread can be cancelled when you want to cancel it -
		722	if the thread isn't cancellable, this would be a bug somewhere, so
		723	"->safe_cancel" croaks to notify of the bug.
		724
		725	In the second model you sometimes want to ask nicely to cancel a
		726	thread, but if it's not a good time, well, then don't cancel. This
		727	can be done relatively easy like this:
		728
		729	if (! eval { $coro->safe_cancel }) {
		730	warn "unable to cancel thread: $@";
		731	}
		732
		733	However, what you never should do is first try to cancel "safely"
		734	and if that fails, cancel the "hard" way with "->cancel". That makes
		735	no sense: either you rely on being able to execute cleanup code in
		736	your thread context, or you don't. If you do, then "->safe_cancel"
		737	is the only way, and if you don't, then "->cancel" is always faster
		738	and more direct.
351		739
352	$coro->schedule_to	740	$coro->schedule_to
353	Puts the current coro to sleep (like "Coro::schedule"), but instead	741	Puts the current coro to sleep (like "Coro::schedule"), but instead
354	of continuing with the next coro from the ready queue, always switch	742	of continuing with the next coro from the ready queue, always switch
355	to the given coro object (regardless of priority etc.). The	743	to the given coro object (regardless of priority etc.). The
…		…
372	Otherwise clears the exception object.	760	Otherwise clears the exception object.
373		761
374	Coro will check for the exception each time a schedule-like-function	762	Coro will check for the exception each time a schedule-like-function
375	returns, i.e. after each "schedule", "cede",	763	returns, i.e. after each "schedule", "cede",
376	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of	764	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
377	these functions detect this case and return early in case an	765	those functions (all that are part of Coro itself) detect this case
378	exception is pending.	766	and return early in case an exception is pending.
379		767
380	The exception object will be thrown "as is" with the specified	768	The exception object will be thrown "as is" with the specified
381	scalar in $@, i.e. if it is a string, no line number or newline will	769	scalar in $@, i.e. if it is a string, no line number or newline will
382	be appended (unlike with "die").	770	be appended (unlike with "die").
383		771
384	This can be used as a softer means than "cancel" to ask a coro to	772	This can be used as a softer means than either "cancel" or
385	end itself, although there is no guarantee that the exception will	773	"safe_cancel "to ask a coro to end itself, although there is no
386	lead to termination, and if the exception isn't caught it might well	774	guarantee that the exception will lead to termination, and if the
387	end the whole program.	775	exception isn't caught it might well end the whole program.
388		776
389	You might also think of "throw" as being the moral equivalent of	777	You might also think of "throw" as being the moral equivalent of
390	"kill"ing a coro with a signal (in this case, a scalar).	778	"kill"ing a coro with a signal (in this case, a scalar).
391		779
392	$coro->join	780	$coro->join
393	Wait until the coro terminates and return any values given to the	781	Wait until the coro terminates and return any values given to the
394	"terminate" or "cancel" functions. "join" can be called concurrently	782	"terminate" or "cancel" functions. "join" can be called concurrently
395	from multiple coro, and all will be resumed and given the status	783	from multiple threads, and all will be resumed and given the status
396	return once the $coro terminates.	784	return once the $coro terminates.
397		785
398	$coro->on_destroy (\&cb)	786	$coro->on_destroy (\&cb)
399	Registers a callback that is called when this coro gets destroyed,	787	Registers a callback that is called when this coro thread gets
		788	destroyed, that is, after its resources have been freed but before
400	but before it is joined. The callback gets passed the terminate	789	it is joined. The callback gets passed the terminate/cancel
401	arguments, if any, and must not die, under any circumstances.	790	arguments, if any, and must not die, under any circumstances.
402		791
		792	There can be any number of "on_destroy" callbacks per coro, and
		793	there is currently no way to remove a callback once added.
		794
403	$oldprio = $coro->prio ($newprio)	795	$oldprio = $coro->prio ($newprio)
404	Sets (or gets, if the argument is missing) the priority of the coro.	796	Sets (or gets, if the argument is missing) the priority of the coro
405	Higher priority coro get run before lower priority coro. Priorities	797	thread. Higher priority coro get run before lower priority coros.
406	are small signed integers (currently -4 .. +3), that you can refer	798	Priorities are small signed integers (currently -4 .. +3), that you
407	to using PRIO_xxx constants (use the import tag :prio to get then):	799	can refer to using PRIO_xxx constants (use the import tag :prio to
		800	get then):
408		801
409	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	802	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
410	3 > 1 > 0 > -1 > -3 > -4	803	3 > 1 > 0 > -1 > -3 > -4
411		804
412	# set priority to HIGH	805	# set priority to HIGH
413	current->prio (PRIO_HIGH);	806	current->prio (PRIO_HIGH);
414		807
415	The idle coro ($Coro::idle) always has a lower priority than any	808	The idle coro thread ($Coro::idle) always has a lower priority than
416	existing coro.	809	any existing coro.
417		810
418	Changing the priority of the current coro will take effect	811	Changing the priority of the current coro will take effect
419	immediately, but changing the priority of coro in the ready queue	812	immediately, but changing the priority of a coro in the ready queue
420	(but not running) will only take effect after the next schedule (of	813	(but not running) will only take effect after the next schedule (of
421	that coro). This is a bug that will be fixed in some future version.	814	that coro). This is a bug that will be fixed in some future version.
422		815
423	$newprio = $coro->nice ($change)	816	$newprio = $coro->nice ($change)
424	Similar to "prio", but subtract the given value from the priority	817	Similar to "prio", but subtract the given value from the priority
425	(i.e. higher values mean lower priority, just as in unix).	818	(i.e. higher values mean lower priority, just as in UNIX's nice
		819	command).
426		820
427	$olddesc = $coro->desc ($newdesc)	821	$olddesc = $coro->desc ($newdesc)
428	Sets (or gets in case the argument is missing) the description for	822	Sets (or gets in case the argument is missing) the description for
429	this coro. This is just a free-form string you can associate with a	823	this coro thread. This is just a free-form string you can associate
430	coro.	824	with a coro.
431		825
432	This method simply sets the "$coro->{desc}" member to the given	826	This method simply sets the "$coro->{desc}" member to the given
433	string. You can modify this member directly if you wish.	827	string. You can modify this member directly if you wish, and in
		828	fact, this is often preferred to indicate major processing states
		829	that can then be seen for example in a Coro::Debug session:
		830
		831	sub my_long_function {
		832	local $Coro::current->{desc} = "now in my_long_function";
		833	...
		834	$Coro::current->{desc} = "my_long_function: phase 1";
		835	...
		836	$Coro::current->{desc} = "my_long_function: phase 2";
		837	...
		838	}
434		839
435	GLOBAL FUNCTIONS	840	GLOBAL FUNCTIONS
436	Coro::nready	841	Coro::nready
437	Returns the number of coro that are currently in the ready state,	842	Returns the number of coro that are currently in the ready state,
438	i.e. that can be switched to by calling "schedule" directory or	843	i.e. that can be switched to by calling "schedule" directory or
…		…
455	The reason this function exists is that many event libraries (such	860	The reason this function exists is that many event libraries (such
456	as the venerable Event module) are not thread-safe (a weaker form of	861	as the venerable Event module) are not thread-safe (a weaker form of
457	reentrancy). This means you must not block within event callbacks,	862	reentrancy). This means you must not block within event callbacks,
458	otherwise you might suffer from crashes or worse. The only event	863	otherwise you might suffer from crashes or worse. The only event
459	library currently known that is safe to use without "unblock_sub" is	864	library currently known that is safe to use without "unblock_sub" is
460	EV.	865	EV (but you might still run into deadlocks if all event loops are
		866	blocked).
		867
		868	Coro will try to catch you when you block in the event loop ("FATAL:
		869	$Coro::idle blocked itself"), but this is just best effort and only
		870	works when you do not run your own event loop.
461		871
462	This function allows your callbacks to block by executing them in	872	This function allows your callbacks to block by executing them in
463	another coro where it is safe to block. One example where blocking	873	another coro where it is safe to block. One example where blocking
464	is handy is when you use the Coro::AIO functions to save results to	874	is handy is when you use the Coro::AIO functions to save results to
465	disk, for example.	875	disk, for example.
…		…
476	when you use a module that uses AnyEvent (and you use	886	when you use a module that uses AnyEvent (and you use
477	Coro::AnyEvent) and it provides callbacks that are the result of	887	Coro::AnyEvent) and it provides callbacks that are the result of
478	some event callback, then you must not block either, or use	888	some event callback, then you must not block either, or use
479	"unblock_sub".	889	"unblock_sub".
480		890
481	$cb = Coro::rouse_cb	891	$cb = rouse_cb
482	Create and return a "rouse callback". That's a code reference that,	892	Create and return a "rouse callback". That's a code reference that,
483	when called, will remember a copy of its arguments and notify the	893	when called, will remember a copy of its arguments and notify the
484	owner coro of the callback.	894	owner coro of the callback.
485		895
		896	Only the first invocation will store agruments and signal any waiter
		897	- further calls will effectively be ignored, but it is ok to try.
		898
486	See the next function.	899	Also see the next function.
487		900
488	@args = Coro::rouse_wait [$cb]	901	@args = rouse_wait [$cb]
489	Wait for the specified rouse callback (or the last one that was	902	Wait for the specified rouse callback to be invoked (or if the
490	created in this coro).	903	argument is missing, use the most recently created callback in the
		904	current coro).
491		905
492	As soon as the callback is invoked (or when the callback was invoked	906	As soon as the callback is invoked (or when the callback was invoked
493	before "rouse_wait"), it will return the arguments originally passed	907	before "rouse_wait"), it will return the arguments originally passed
494	to the rouse callback.	908	to the rouse callback. In scalar context, that means you get the
		909	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		910	$a3...)" statement at the end.
		911
		912	You are only allowed to wait once for a given rouse callback.
495		913
496	See the section HOW TO WAIT FOR A CALLBACK for an actual usage	914	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
497	example.	915	example.
		916
		917	As of Coro 6.57, you can reliably wait for a rouse callback in a
		918	different thread than from where it was created.
498		919
499	HOW TO WAIT FOR A CALLBACK	920	HOW TO WAIT FOR A CALLBACK
500	It is very common for a coro to wait for some callback to be called.	921	It is very common for a coro to wait for some callback to be called.
501	This occurs naturally when you use coro in an otherwise event-based	922	This occurs naturally when you use coro in an otherwise event-based
502	program, or when you use event-based libraries.	923	program, or when you use event-based libraries.
503		924
504	These typically register a callback for some event, and call that	925	These typically register a callback for some event, and call that
505	callback when the event occured. In a coro, however, you typically want	926	callback when the event occurred. In a coro, however, you typically want
506	to just wait for the event, simplyifying things.	927	to just wait for the event, simplyifying things.
507		928
508	For example "AnyEvent->child" registers a callback to be called when a	929	For example "AnyEvent->child" registers a callback to be called when a
509	specific child has exited:	930	specific child has exited:
510		931
…		…
513	But from within a coro, you often just want to write this:	934	But from within a coro, you often just want to write this:
514		935
515	my $status = wait_for_child $pid;	936	my $status = wait_for_child $pid;
516		937
517	Coro offers two functions specifically designed to make this easy,	938	Coro offers two functions specifically designed to make this easy,
518	"Coro::rouse_cb" and "Coro::rouse_wait".	939	"rouse_cb" and "rouse_wait".
519		940
520	The first function, "rouse_cb", generates and returns a callback that,	941	The first function, "rouse_cb", generates and returns a callback that,
521	when invoked, will save its arguments and notify the coro that created	942	when invoked, will save its arguments and notify the coro that created
522	the callback.	943	the callback.
523		944
…		…
529	function mentioned above:	950	function mentioned above:
530		951
531	sub wait_for_child($) {	952	sub wait_for_child($) {
532	my ($pid) = @_;	953	my ($pid) = @_;
533		954
534	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);	955	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
535		956
536	my ($rpid, $rstatus) = Coro::rouse_wait;	957	my ($rpid, $rstatus) = rouse_wait;
537	$rstatus	958	$rstatus
538	}	959	}
539		960
540	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,	961	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
541	you can roll your own, using "schedule":	962	you can roll your own, using "schedule" and "ready":
542		963
543	sub wait_for_child($) {	964	sub wait_for_child($) {
544	my ($pid) = @_;	965	my ($pid) = @_;
545		966
546	# store the current coro in $current,	967	# store the current coro in $current,
…		…
549	my ($done, $rstatus);	970	my ($done, $rstatus);
550		971
551	# pass a closure to ->child	972	# pass a closure to ->child
552	my $watcher = AnyEvent->child (pid => $pid, cb => sub {	973	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
553	$rstatus = $_[1]; # remember rstatus	974	$rstatus = $_[1]; # remember rstatus
554	$done = 1; # mark $rstatus as valud	975	$done = 1; # mark $rstatus as valid
		976	$current->ready; # wake up the waiting thread
555	});	977	});
556		978
557	# wait until the closure has been called	979	# wait until the closure has been called
558	schedule while !$done;	980	schedule while !$done;
559		981
…		…
573	in the future to allow per-thread schedulers, but Coro::State does	995	in the future to allow per-thread schedulers, but Coro::State does
574	not yet allow this). I recommend disabling thread support and using	996	not yet allow this). I recommend disabling thread support and using
575	processes, as having the windows process emulation enabled under	997	processes, as having the windows process emulation enabled under
576	unix roughly halves perl performance, even when not used.	998	unix roughly halves perl performance, even when not used.
577		999
		1000	Attempts to use threads created in another emulated process will
		1001	crash ("cleanly", with a null pointer exception).
		1002
578	coro switching is not signal safe	1003	coro switching is not signal safe
579	You must not switch to another coro from within a signal handler	1004	You must not switch to another coro from within a signal handler
580	(only relevant with %SIG - most event libraries provide safe	1005	(only relevant with %SIG - most event libraries provide safe
581	signals).	1006	signals), unless you are sure you are not interrupting a Coro
		1007	function.
582		1008
583	That means you MUST NOT call any function that might "block" the	1009	That means you MUST NOT call any function that might "block" the
584	current coro - "cede", "schedule" "Coro::Semaphore->down" or	1010	current coro - "cede", "schedule" "Coro::Semaphore->down" or
585	anything that calls those. Everything else, including calling	1011	anything that calls those. Everything else, including calling
586	"ready", works.	1012	"ready", works.
587		1013
		1014	WINDOWS PROCESS EMULATION
		1015	A great many people seem to be confused about ithreads (for example,
		1016	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		1017	while in the same mail making rather confused statements about perl
		1018	ithreads (for example, that memory or files would be shared), showing
		1019	his lack of understanding of this area - if it is hard to understand for
		1020	Chip, it is probably not obvious to everybody).
		1021
		1022	What follows is an ultra-condensed version of my talk about threads in
		1023	scripting languages given on the perl workshop 2009:
		1024
		1025	The so-called "ithreads" were originally implemented for two reasons:
		1026	first, to (badly) emulate unix processes on native win32 perls, and
		1027	secondly, to replace the older, real thread model ("5.005-threads").
		1028
		1029	It does that by using threads instead of OS processes. The difference
		1030	between processes and threads is that threads share memory (and other
		1031	state, such as files) between threads within a single process, while
		1032	processes do not share anything (at least not semantically). That means
		1033	that modifications done by one thread are seen by others, while
		1034	modifications by one process are not seen by other processes.
		1035
		1036	The "ithreads" work exactly like that: when creating a new ithreads
		1037	process, all state is copied (memory is copied physically, files and
		1038	code is copied logically). Afterwards, it isolates all modifications. On
		1039	UNIX, the same behaviour can be achieved by using operating system
		1040	processes, except that UNIX typically uses hardware built into the
		1041	system to do this efficiently, while the windows process emulation
		1042	emulates this hardware in software (rather efficiently, but of course it
		1043	is still much slower than dedicated hardware).
		1044
		1045	As mentioned before, loading code, modifying code, modifying data
		1046	structures and so on is only visible in the ithreads process doing the
		1047	modification, not in other ithread processes within the same OS process.
		1048
		1049	This is why "ithreads" do not implement threads for perl at all, only
		1050	processes. What makes it so bad is that on non-windows platforms, you
		1051	can actually take advantage of custom hardware for this purpose (as
		1052	evidenced by the forks module, which gives you the (i-) threads API,
		1053	just much faster).
		1054
		1055	Sharing data is in the i-threads model is done by transferring data
		1056	structures between threads using copying semantics, which is very slow -
		1057	shared data simply does not exist. Benchmarks using i-threads which are
		1058	communication-intensive show extremely bad behaviour with i-threads (in
		1059	fact, so bad that Coro, which cannot take direct advantage of multiple
		1060	CPUs, is often orders of magnitude faster because it shares data using
		1061	real threads, refer to my talk for details).
		1062
		1063	As summary, i-threads use threads to implement processes, while the
		1064	compatible forks module uses processes to emulate, uhm, processes.
		1065	I-threads slow down every perl program when enabled, and outside of
		1066	windows, serve no (or little) practical purpose, but disadvantages every
		1067	single-threaded Perl program.
		1068
		1069	This is the reason that I try to avoid the name "ithreads", as it is
		1070	misleading as it implies that it implements some kind of thread model
		1071	for perl, and prefer the name "windows process emulation", which
		1072	describes the actual use and behaviour of it much better.
		1073
588	SEE ALSO	1074	SEE ALSO
589	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	1075	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
590		1076
591	Debugging: Coro::Debug.	1077	Debugging: Coro::Debug.
592		1078
…		…
603		1089
604	XS API: Coro::MakeMaker.	1090	XS API: Coro::MakeMaker.
605		1091
606	Low level Configuration, Thread Environment, Continuations: Coro::State.	1092	Low level Configuration, Thread Environment, Continuations: Coro::State.
607		1093
608	AUTHOR	1094	AUTHOR/SUPPORT/CONTACT
609	Marc Lehmann <schmorp@schmorp.de>	1095	Marc A. Lehmann <schmorp@schmorp.de>
610	http://home.schmorp.de/	1096	http://software.schmorp.de/pkg/Coro.html
611		1097

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Comparing Coro/README (file contents): Revision 1.23 by root, Fri May 29 07:01:18 2009 UTC vs. Revision 1.42 by root, Wed Jul 29 13:09:19 2020 UTC

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Comparing Coro/README (file contents):
Revision 1.23 by root, Fri May 29 07:01:18 2009 UTC vs.
Revision 1.42 by root, Wed Jul 29 13:09:19 2020 UTC