[ViewVC] Diff of: cvs/Coro/README

Comparing Coro/README (file contents):
Revision 1.26 by root, Sun Oct 4 12:55:21 2009 UTC vs.
Revision 1.39 by root, Fri Jul 14 13:14:32 2017 UTC

…		…
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;
…		…
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 (see section of same name for	41	but only the windows process emulation (see section of same name for
43	more details) ported to unix, and as such act as processes), Coro	42	more details) ported to UNIX, and as such act as processes), Coro
44	provides a full shared address space, which makes communication between	43	provides a full shared address space, which makes communication between
45	threads very easy. And Coro's threads are fast, too: disabling the	44	threads very easy. And coro threads are fast, too: disabling the Windows
46	Windows process emulation code in your perl and using Coro can easily	45	process emulation code in your perl and using Coro can easily result in
47	result in a two to four times speed increase for your programs. A	46	a two to four times speed increase for your programs. A parallel matrix
48	parallel matrix multiplication benchmark runs over 300 times faster on a	47	multiplication benchmark (very communication-intensive) runs over 300
49	single core than perl's pseudo-threads on a quad core using all four	48	times faster on a single core than perls pseudo-threads on a quad core
50	cores.	49	using all four cores.
51		50
52	Coro achieves that by supporting multiple running interpreters that	51	Coro achieves that by supporting multiple running interpreters that
53	share data, which is especially useful to code pseudo-parallel processes	52	share data, which is especially useful to code pseudo-parallel processes
54	and for event-based programming, such as multiple HTTP-GET requests	53	and for event-based programming, such as multiple HTTP-GET requests
55	running concurrently. See Coro::AnyEvent to learn more on how to	54	running concurrently. See Coro::AnyEvent to learn more on how to
…		…
62	background info).	61	background info).
63		62
64	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
65	module family is quite large.	64	module family is quite large.
66		65
		66	CORO THREAD LIFE CYCLE
		67	During the long and exciting (or not) life of a coro thread, it goes
		68	through a number of states:
		69
		70	1. Creation
		71	The first thing in the life of a coro thread is it's creation -
		72	obviously. The typical way to create a thread is to call the "async
		73	BLOCK" function:
		74
		75	async {
		76	# thread code goes here
		77	};
		78
		79	You can also pass arguments, which are put in @_:
		80
		81	async {
		82	print $_[1]; # prints 2
		83	} 1, 2, 3;
		84
		85	This creates a new coro thread and puts it into the ready queue,
		86	meaning it will run as soon as the CPU is free for it.
		87
		88	"async" will return a Coro object - you can store this for future
		89	reference or ignore it - a thread that is running, ready to run or
		90	waiting for some event is alive on it's own.
		91
		92	Another way to create a thread is to call the "new" constructor with
		93	a code-reference:
		94
		95	new Coro sub {
		96	# thread code goes here
		97	}, @optional_arguments;
		98
		99	This is quite similar to calling "async", but the important
		100	difference is that the new thread is not put into the ready queue,
		101	so the thread will not run until somebody puts it there. "async" is,
		102	therefore, identical to this sequence:
		103
		104	my $coro = new Coro sub {
		105	# thread code goes here
		106	};
		107	$coro->ready;
		108	return $coro;
		109
		110	2. Startup
		111	When a new coro thread is created, only a copy of the code reference
		112	and the arguments are stored, no extra memory for stacks and so on
		113	is allocated, keeping the coro thread in a low-memory state.
		114
		115	Only when it actually starts executing will all the resources be
		116	finally allocated.
		117
		118	The optional arguments specified at coro creation are available in
		119	@_, similar to function calls.
		120
		121	3. Running / Blocking
		122	A lot can happen after the coro thread has started running. Quite
		123	usually, it will not run to the end in one go (because you could use
		124	a function instead), but it will give up the CPU regularly because
		125	it waits for external events.
		126
		127	As long as a coro thread runs, its Coro object is available in the
		128	global variable $Coro::current.
		129
		130	The low-level way to give up the CPU is to call the scheduler, which
		131	selects a new coro thread to run:
		132
		133	Coro::schedule;
		134
		135	Since running threads are not in the ready queue, calling the
		136	scheduler without doing anything else will block the coro thread
		137	forever - you need to arrange either for the coro to put woken up
		138	(readied) by some other event or some other thread, or you can put
		139	it into the ready queue before scheduling:
		140
		141	# this is exactly what Coro::cede does
		142	$Coro::current->ready;
		143	Coro::schedule;
		144
		145	All the higher-level synchronisation methods (Coro::Semaphore,
		146	Coro::rouse_*...) are actually implemented via "->ready" and
		147	"Coro::schedule".
		148
		149	While the coro thread is running it also might get assigned a
		150	C-level thread, or the C-level thread might be unassigned from it,
		151	as the Coro runtime wishes. A C-level thread needs to be assigned
		152	when your perl thread calls into some C-level function and that
		153	function in turn calls perl and perl then wants to switch
		154	coroutines. This happens most often when you run an event loop and
		155	block in the callback, or when perl itself calls some function such
		156	as "AUTOLOAD" or methods via the "tie" mechanism.
		157
		158	4. Termination
		159	Many threads actually terminate after some time. There are a number
		160	of ways to terminate a coro thread, the simplest is returning from
		161	the top-level code reference:
		162
		163	async {
		164	# after returning from here, the coro thread is terminated
		165	};
		166
		167	async {
		168	return if 0.5 < rand; # terminate a little earlier, maybe
		169	print "got a chance to print this\n";
		170	# or here
		171	};
		172
		173	Any values returned from the coroutine can be recovered using
		174	"->join":
		175
		176	my $coro = async {
		177	"hello, world\n" # return a string
		178	};
		179
		180	my $hello_world = $coro->join;
		181
		182	print $hello_world;
		183
		184	Another way to terminate is to call "Coro::terminate", which at any
		185	subroutine call nesting level:
		186
		187	async {
		188	Coro::terminate "return value 1", "return value 2";
		189	};
		190
		191	Yet another way is to "->cancel" (or "->safe_cancel") the coro
		192	thread from another thread:
		193
		194	my $coro = async {
		195	exit 1;
		196	};
		197
		198	$coro->cancel; # also accepts values for ->join to retrieve
		199
		200	Cancellation can be dangerous - it's a bit like calling "exit"
		201	without actually exiting, and might leave C libraries and XS modules
		202	in a weird state. Unlike other thread implementations, however, Coro
		203	is exceptionally safe with regards to cancellation, as perl will
		204	always be in a consistent state, and for those cases where you want
		205	to do truly marvellous things with your coro while it is being
		206	cancelled - that is, make sure all cleanup code is executed from the
		207	thread being cancelled - there is even a "->safe_cancel" method.
		208
		209	So, cancelling a thread that runs in an XS event loop might not be
		210	the best idea, but any other combination that deals with perl only
		211	(cancelling when a thread is in a "tie" method or an "AUTOLOAD" for
		212	example) is safe.
		213
		214	Last not least, a coro thread object that isn't referenced is
		215	"->cancel"'ed automatically - just like other objects in Perl. This
		216	is not such a common case, however - a running thread is referencedy
		217	by $Coro::current, a thread ready to run is referenced by the ready
		218	queue, a thread waiting on a lock or semaphore is referenced by
		219	being in some wait list and so on. But a thread that isn't in any of
		220	those queues gets cancelled:
		221
		222	async {
		223	schedule; # cede to other coros, don't go into the ready queue
		224	};
		225
		226	cede;
		227	# now the async above is destroyed, as it is not referenced by anything.
		228
		229	A slightly embellished example might make it clearer:
		230
		231	async {
		232	my $guard = Guard::guard { print "destroyed\n" };
		233	schedule while 1;
		234	};
		235
		236	cede;
		237
		238	Superficially one might not expect any output - since the "async"
		239	implements an endless loop, the $guard will not be cleaned up.
		240	However, since the thread object returned by "async" is not stored
		241	anywhere, the thread is initially referenced because it is in the
		242	ready queue, when it runs it is referenced by $Coro::current, but
		243	when it calls "schedule", it gets "cancel"ed causing the guard
		244	object to be destroyed (see the next section), and printing it's
		245	message.
		246
		247	If this seems a bit drastic, remember that this only happens when
		248	nothing references the thread anymore, which means there is no way
		249	to further execute it, ever. The only options at this point are
		250	leaking the thread, or cleaning it up, which brings us to...
		251
		252	5. Cleanup
		253	Threads will allocate various resources. Most but not all will be
		254	returned when a thread terminates, during clean-up.
		255
		256	Cleanup is quite similar to throwing an uncaught exception: perl
		257	will work it's way up through all subroutine calls and blocks. On
		258	it's way, it will release all "my" variables, undo all "local"'s and
		259	free any other resources truly local to the thread.
		260
		261	So, a common way to free resources is to keep them referenced only
		262	by my variables:
		263
		264	async {
		265	my $big_cache = new Cache ...;
		266	};
		267
		268	If there are no other references, then the $big_cache object will be
		269	freed when the thread terminates, regardless of how it does so.
		270
		271	What it does "NOT" do is unlock any Coro::Semaphores or similar
		272	resources, but that's where the "guard" methods come in handy:
		273
		274	my $sem = new Coro::Semaphore;
		275
		276	async {
		277	my $lock_guard = $sem->guard;
		278	# if we return, or die or get cancelled, here,
		279	# then the semaphore will be "up"ed.
		280	};
		281
		282	The "Guard::guard" function comes in handy for any custom cleanup
		283	you might want to do (but you cannot switch to other coroutines from
		284	those code blocks):
		285
		286	async {
		287	my $window = new Gtk2::Window "toplevel";
		288	# The window will not be cleaned up automatically, even when $window
		289	# gets freed, so use a guard to ensure it's destruction
		290	# in case of an error:
		291	my $window_guard = Guard::guard { $window->destroy };
		292
		293	# we are safe here
		294	};
		295
		296	Last not least, "local" can often be handy, too, e.g. when
		297	temporarily replacing the coro thread description:
		298
		299	sub myfunction {
		300	local $Coro::current->{desc} = "inside myfunction(@_)";
		301
		302	# if we return or die here, the description will be restored
		303	}
		304
		305	6. Viva La Zombie Muerte
		306	Even after a thread has terminated and cleaned up its resources, the
		307	Coro object still is there and stores the return values of the
		308	thread.
		309
		310	When there are no other references, it will simply be cleaned up and
		311	freed.
		312
		313	If there areany references, the Coro object will stay around, and
		314	you can call "->join" as many times as you wish to retrieve the
		315	result values:
		316
		317	async {
		318	print "hi\n";
		319	1
		320	};
		321
		322	# run the async above, and free everything before returning
		323	# from Coro::cede:
		324	Coro::cede;
		325
		326	{
		327	my $coro = async {
		328	print "hi\n";
		329	1
		330	};
		331
		332	# run the async above, and clean up, but do not free the coro
		333	# object:
		334	Coro::cede;
		335
		336	# optionally retrieve the result values
		337	my @results = $coro->join;
		338
		339	# now $coro goes out of scope, and presumably gets freed
		340	};
		341
67	GLOBAL VARIABLES	342	GLOBAL VARIABLES
68	$Coro::main	343	$Coro::main
69	This variable stores the Coro object that represents the main	344	This variable stores the Coro object that represents the main
70	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
71	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
72	see whether you are running in the main program or not.	347	see whether you are running in the main program or not.
73		348
74	$Coro::current	349	$Coro::current
75	The Coro object representing the current coro (the last coro that	350	The Coro object representing the current coro (the last coro that
…		…
92	The default implementation dies with "FATAL: deadlock detected.",	367	The default implementation dies with "FATAL: deadlock detected.",
93	followed by a thread listing, because the program has no other way	368	followed by a thread listing, because the program has no other way
94	to continue.	369	to continue.
95		370
96	This hook is overwritten by modules such as "Coro::EV" and	371	This hook is overwritten by modules such as "Coro::EV" and
97	"Coro::AnyEvent" to wait on an external event that hopefully wake up	372	"Coro::AnyEvent" to wait on an external event that hopefully wakes
98	a coro so the scheduler can run it.	373	up a coro so the scheduler can run it.
99		374
100	See Coro::EV or Coro::AnyEvent for examples of using this technique.	375	See Coro::EV or Coro::AnyEvent for examples of using this technique.
101		376
102	SIMPLE CORO CREATION	377	SIMPLE CORO CREATION
103	async { ... } [@args...]	378	async { ... } [@args...]
…		…
142	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
143	"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
144	terminate or cancel, which somehow defeats the purpose of pooling	419	terminate or cancel, which somehow defeats the purpose of pooling
145	(but is fine in the exceptional case).	420	(but is fine in the exceptional case).
146		421
147	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
148	disabled, the description will be reset and the default output	423	will be undone, tracing will be disabled, the description will be
149	filehandle gets restored, so you can change all these. Otherwise the	424	reset and the default output filehandle gets restored, so you can
150	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
151	per-coro global stuff such as $/ you must needs revert that	426	notably if you change other per-coro global stuff such as $/ you
152	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 $/".
153		429
154	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
155	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
156	coros as required.	432	coros as required.
157		433
…		…
203	any coro, regardless of priority. This is useful sometimes to	479	any coro, regardless of priority. This is useful sometimes to
204	ensure progress is made.	480	ensure progress is made.
205		481
206	terminate [arg...]	482	terminate [arg...]
207	Terminates the current coro with the given status values (see	483	Terminates the current coro with the given status values (see
208	cancel).	484	cancel). The values will not be copied, but referenced directly.
209		485
210	Coro::on_enter BLOCK, Coro::on_leave BLOCK	486	Coro::on_enter BLOCK, Coro::on_leave BLOCK
211	These function install enter and leave winders in the current scope.	487	These function install enter and leave winders in the current scope.
212	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
213	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
…		…
258	# at this place, the timezone is Antarctica/South_Pole,	534	# at this place, the timezone is Antarctica/South_Pole,
259	# without disturbing the TZ of any other coro.	535	# without disturbing the TZ of any other coro.
260	};	536	};
261		537
262	This can be used to localise about any resource (locale, uid,	538	This can be used to localise about any resource (locale, uid,
263	current working directory etc.) to a block, despite the existance of	539	current working directory etc.) to a block, despite the existence of
264	other coros.	540	other coros.
265		541
266	Another interesting example implements time-sliced multitasking	542	Another interesting example implements time-sliced multitasking
267	using interval timers (this could obviously be optimised, but does	543	using interval timers (this could obviously be optimised, but does
268	the job):	544	the job):
…		…
274	Coro::on_enter {	550	Coro::on_enter {
275	# on entering the thread, we set an VTALRM handler to cede	551	# on entering the thread, we set an VTALRM handler to cede
276	$SIG{VTALRM} = sub { cede };	552	$SIG{VTALRM} = sub { cede };
277	# and then start the interval timer	553	# and then start the interval timer
278	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;	554	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
279	};	555	};
280	Coro::on_leave {	556	Coro::on_leave {
281	# on leaving the thread, we stop the interval timer again	557	# on leaving the thread, we stop the interval timer again
282	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;	558	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
283	};	559	};
284		560
285	&{+shift};	561	&{+shift};
286	}	562	}
287		563
288	# use like this:	564	# use like this:
289	timeslice {	565	timeslice {
290	# The following is an endless loop that would normally	566	# The following is an endless loop that would normally
291	# monopolise the process. Since it runs in a timesliced	567	# monopolise the process. Since it runs in a timesliced
…		…
345	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
346	queue unconditionally, as every synchronisation mechanism must	622	queue unconditionally, as every synchronisation mechanism must
347	protect itself against spurious wakeups, and the one in the Coro	623	protect itself against spurious wakeups, and the one in the Coro
348	family certainly do that.	624	family certainly do that.
349		625
		626	$state->is_new
		627	Returns true iff this Coro object is "new", i.e. has never been run
		628	yet. Those states basically consist of only the code reference to
		629	call and the arguments, but consumes very little other resources.
		630	New states will automatically get assigned a perl interpreter when
		631	they are transferred to.
		632
		633	$state->is_zombie
		634	Returns true iff the Coro object has been cancelled, i.e. it's
		635	resources freed because they were "cancel"'ed, "terminate"'d,
		636	"safe_cancel"'ed or simply went out of scope.
		637
		638	The name "zombie" stems from UNIX culture, where a process that has
		639	exited and only stores and exit status and no other resources is
		640	called a "zombie".
		641
350	$is_ready = $coro->is_ready	642	$is_ready = $coro->is_ready
351	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
352	Coro object gets destroyed, it will eventually be scheduled by the	644	Coro object gets destroyed, it will eventually be scheduled by the
353	scheduler.	645	scheduler.
354		646
…		…
360	$is_suspended = $coro->is_suspended	652	$is_suspended = $coro->is_suspended
361	Returns true iff this Coro object has been suspended. Suspended	653	Returns true iff this Coro object has been suspended. Suspended
362	Coros will not ever be scheduled.	654	Coros will not ever be scheduled.
363		655
364	$coro->cancel (arg...)	656	$coro->cancel (arg...)
365	Terminates the given Coro and makes it return the given arguments as	657	Terminates the given Coro thread and makes it return the given
366	status (default: the empty list). Never returns if the Coro is the	658	arguments as status (default: an empty list). Never returns if the
367	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 hasn't been run
		703	yet, or it has no C context attached and is inside an SLF function.
		704
		705	The latter two basically mean that the thread isn't currently inside
		706	a perl callback called from some C function (usually via some XS
		707	modules) and isn't currently executing inside some C function itself
		708	(via Coro's XS API).
		709
		710	This call returns true when it could cancel the thread, or croaks
		711	with an error otherwise (i.e. it either returns true or doesn't
		712	return at all).
		713
		714	Why the weird interface? Well, there are two common models on how
		715	and when to cancel things. In the first, you have the expectation
		716	that your coro thread can be cancelled when you want to cancel it -
		717	if the thread isn't cancellable, this would be a bug somewhere, so
		718	"->safe_cancel" croaks to notify of the bug.
		719
		720	In the second model you sometimes want to ask nicely to cancel a
		721	thread, but if it's not a good time, well, then don't cancel. This
		722	can be done relatively easy like this:
		723
		724	if (! eval { $coro->safe_cancel }) {
		725	warn "unable to cancel thread: $@";
		726	}
		727
		728	However, what you never should do is first try to cancel "safely"
		729	and if that fails, cancel the "hard" way with "->cancel". That makes
		730	no sense: either you rely on being able to execute cleanup code in
		731	your thread context, or you don't. If you do, then "->safe_cancel"
		732	is the only way, and if you don't, then "->cancel" is always faster
		733	and more direct.
368		734
369	$coro->schedule_to	735	$coro->schedule_to
370	Puts the current coro to sleep (like "Coro::schedule"), but instead	736	Puts the current coro to sleep (like "Coro::schedule"), but instead
371	of continuing with the next coro from the ready queue, always switch	737	of continuing with the next coro from the ready queue, always switch
372	to the given coro object (regardless of priority etc.). The	738	to the given coro object (regardless of priority etc.). The
…		…
389	Otherwise clears the exception object.	755	Otherwise clears the exception object.
390		756
391	Coro will check for the exception each time a schedule-like-function	757	Coro will check for the exception each time a schedule-like-function
392	returns, i.e. after each "schedule", "cede",	758	returns, i.e. after each "schedule", "cede",
393	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of	759	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
394	these functions detect this case and return early in case an	760	those functions (all that are part of Coro itself) detect this case
395	exception is pending.	761	and return early in case an exception is pending.
396		762
397	The exception object will be thrown "as is" with the specified	763	The exception object will be thrown "as is" with the specified
398	scalar in $@, i.e. if it is a string, no line number or newline will	764	scalar in $@, i.e. if it is a string, no line number or newline will
399	be appended (unlike with "die").	765	be appended (unlike with "die").
400		766
401	This can be used as a softer means than "cancel" to ask a coro to	767	This can be used as a softer means than either "cancel" or
402	end itself, although there is no guarantee that the exception will	768	"safe_cancel "to ask a coro to end itself, although there is no
403	lead to termination, and if the exception isn't caught it might well	769	guarantee that the exception will lead to termination, and if the
404	end the whole program.	770	exception isn't caught it might well end the whole program.
405		771
406	You might also think of "throw" as being the moral equivalent of	772	You might also think of "throw" as being the moral equivalent of
407	"kill"ing a coro with a signal (in this case, a scalar).	773	"kill"ing a coro with a signal (in this case, a scalar).
408		774
409	$coro->join	775	$coro->join
410	Wait until the coro terminates and return any values given to the	776	Wait until the coro terminates and return any values given to the
411	"terminate" or "cancel" functions. "join" can be called concurrently	777	"terminate" or "cancel" functions. "join" can be called concurrently
412	from multiple coro, and all will be resumed and given the status	778	from multiple threads, and all will be resumed and given the status
413	return once the $coro terminates.	779	return once the $coro terminates.
414		780
415	$coro->on_destroy (\&cb)	781	$coro->on_destroy (\&cb)
416	Registers a callback that is called when this coro gets destroyed,	782	Registers a callback that is called when this coro thread gets
		783	destroyed, that is, after it's resources have been freed but before
417	but before it is joined. The callback gets passed the terminate	784	it is joined. The callback gets passed the terminate/cancel
418	arguments, if any, and must not die, under any circumstances.	785	arguments, if any, and must not die, under any circumstances.
419		786
		787	There can be any number of "on_destroy" callbacks per coro, and
		788	there is currently no way to remove a callback once added.
		789
420	$oldprio = $coro->prio ($newprio)	790	$oldprio = $coro->prio ($newprio)
421	Sets (or gets, if the argument is missing) the priority of the coro.	791	Sets (or gets, if the argument is missing) the priority of the coro
422	Higher priority coro get run before lower priority coro. Priorities	792	thread. Higher priority coro get run before lower priority coros.
423	are small signed integers (currently -4 .. +3), that you can refer	793	Priorities are small signed integers (currently -4 .. +3), that you
424	to using PRIO_xxx constants (use the import tag :prio to get then):	794	can refer to using PRIO_xxx constants (use the import tag :prio to
		795	get then):
425		796
426	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	797	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
427	3 > 1 > 0 > -1 > -3 > -4	798	3 > 1 > 0 > -1 > -3 > -4
428		799
429	# set priority to HIGH	800	# set priority to HIGH
430	current->prio (PRIO_HIGH);	801	current->prio (PRIO_HIGH);
431		802
432	The idle coro ($Coro::idle) always has a lower priority than any	803	The idle coro thread ($Coro::idle) always has a lower priority than
433	existing coro.	804	any existing coro.
434		805
435	Changing the priority of the current coro will take effect	806	Changing the priority of the current coro will take effect
436	immediately, but changing the priority of coro in the ready queue	807	immediately, but changing the priority of a coro in the ready queue
437	(but not running) will only take effect after the next schedule (of	808	(but not running) will only take effect after the next schedule (of
438	that coro). This is a bug that will be fixed in some future version.	809	that coro). This is a bug that will be fixed in some future version.
439		810
440	$newprio = $coro->nice ($change)	811	$newprio = $coro->nice ($change)
441	Similar to "prio", but subtract the given value from the priority	812	Similar to "prio", but subtract the given value from the priority
442	(i.e. higher values mean lower priority, just as in unix).	813	(i.e. higher values mean lower priority, just as in UNIX's nice
		814	command).
443		815
444	$olddesc = $coro->desc ($newdesc)	816	$olddesc = $coro->desc ($newdesc)
445	Sets (or gets in case the argument is missing) the description for	817	Sets (or gets in case the argument is missing) the description for
446	this coro. This is just a free-form string you can associate with a	818	this coro thread. This is just a free-form string you can associate
447	coro.	819	with a coro.
448		820
449	This method simply sets the "$coro->{desc}" member to the given	821	This method simply sets the "$coro->{desc}" member to the given
450	string. You can modify this member directly if you wish.	822	string. You can modify this member directly if you wish, and in
		823	fact, this is often preferred to indicate major processing states
		824	that can then be seen for example in a Coro::Debug session:
		825
		826	sub my_long_function {
		827	local $Coro::current->{desc} = "now in my_long_function";
		828	...
		829	$Coro::current->{desc} = "my_long_function: phase 1";
		830	...
		831	$Coro::current->{desc} = "my_long_function: phase 2";
		832	...
		833	}
451		834
452	GLOBAL FUNCTIONS	835	GLOBAL FUNCTIONS
453	Coro::nready	836	Coro::nready
454	Returns the number of coro that are currently in the ready state,	837	Returns the number of coro that are currently in the ready state,
455	i.e. that can be switched to by calling "schedule" directory or	838	i.e. that can be switched to by calling "schedule" directory or
…		…
472	The reason this function exists is that many event libraries (such	855	The reason this function exists is that many event libraries (such
473	as the venerable Event module) are not thread-safe (a weaker form of	856	as the venerable Event module) are not thread-safe (a weaker form of
474	reentrancy). This means you must not block within event callbacks,	857	reentrancy). This means you must not block within event callbacks,
475	otherwise you might suffer from crashes or worse. The only event	858	otherwise you might suffer from crashes or worse. The only event
476	library currently known that is safe to use without "unblock_sub" is	859	library currently known that is safe to use without "unblock_sub" is
477	EV.	860	EV (but you might still run into deadlocks if all event loops are
		861	blocked).
		862
		863	Coro will try to catch you when you block in the event loop ("FATAL:
		864	$Coro::idle blocked itself"), but this is just best effort and only
		865	works when you do not run your own event loop.
478		866
479	This function allows your callbacks to block by executing them in	867	This function allows your callbacks to block by executing them in
480	another coro where it is safe to block. One example where blocking	868	another coro where it is safe to block. One example where blocking
481	is handy is when you use the Coro::AIO functions to save results to	869	is handy is when you use the Coro::AIO functions to save results to
482	disk, for example.	870	disk, for example.
…		…
519	It is very common for a coro to wait for some callback to be called.	907	It is very common for a coro to wait for some callback to be called.
520	This occurs naturally when you use coro in an otherwise event-based	908	This occurs naturally when you use coro in an otherwise event-based
521	program, or when you use event-based libraries.	909	program, or when you use event-based libraries.
522		910
523	These typically register a callback for some event, and call that	911	These typically register a callback for some event, and call that
524	callback when the event occured. In a coro, however, you typically want	912	callback when the event occurred. In a coro, however, you typically want
525	to just wait for the event, simplyifying things.	913	to just wait for the event, simplyifying things.
526		914
527	For example "AnyEvent->child" registers a callback to be called when a	915	For example "AnyEvent->child" registers a callback to be called when a
528	specific child has exited:	916	specific child has exited:
529		917
…		…
532	But from within a coro, you often just want to write this:	920	But from within a coro, you often just want to write this:
533		921
534	my $status = wait_for_child $pid;	922	my $status = wait_for_child $pid;
535		923
536	Coro offers two functions specifically designed to make this easy,	924	Coro offers two functions specifically designed to make this easy,
537	"Coro::rouse_cb" and "Coro::rouse_wait".	925	"rouse_cb" and "rouse_wait".
538		926
539	The first function, "rouse_cb", generates and returns a callback that,	927	The first function, "rouse_cb", generates and returns a callback that,
540	when invoked, will save its arguments and notify the coro that created	928	when invoked, will save its arguments and notify the coro that created
541	the callback.	929	the callback.
542		930
…		…
548	function mentioned above:	936	function mentioned above:
549		937
550	sub wait_for_child($) {	938	sub wait_for_child($) {
551	my ($pid) = @_;	939	my ($pid) = @_;
552		940
553	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);	941	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
554		942
555	my ($rpid, $rstatus) = Coro::rouse_wait;	943	my ($rpid, $rstatus) = rouse_wait;
556	$rstatus	944	$rstatus
557	}	945	}
558		946
559	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,	947	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
560	you can roll your own, using "schedule":	948	you can roll your own, using "schedule" and "ready":
561		949
562	sub wait_for_child($) {	950	sub wait_for_child($) {
563	my ($pid) = @_;	951	my ($pid) = @_;
564		952
565	# store the current coro in $current,	953	# store the current coro in $current,
…		…
568	my ($done, $rstatus);	956	my ($done, $rstatus);
569		957
570	# pass a closure to ->child	958	# pass a closure to ->child
571	my $watcher = AnyEvent->child (pid => $pid, cb => sub {	959	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
572	$rstatus = $_[1]; # remember rstatus	960	$rstatus = $_[1]; # remember rstatus
573	$done = 1; # mark $rstatus as valud	961	$done = 1; # mark $rstatus as valid
		962	$current->ready; # wake up the waiting thread
574	});	963	});
575		964
576	# wait until the closure has been called	965	# wait until the closure has been called
577	schedule while !$done;	966	schedule while !$done;
578		967
…		…
592	in the future to allow per-thread schedulers, but Coro::State does	981	in the future to allow per-thread schedulers, but Coro::State does
593	not yet allow this). I recommend disabling thread support and using	982	not yet allow this). I recommend disabling thread support and using
594	processes, as having the windows process emulation enabled under	983	processes, as having the windows process emulation enabled under
595	unix roughly halves perl performance, even when not used.	984	unix roughly halves perl performance, even when not used.
596		985
		986	Attempts to use threads created in another emulated process will
		987	crash ("cleanly", with a null pointer exception).
		988
597	coro switching is not signal safe	989	coro switching is not signal safe
598	You must not switch to another coro from within a signal handler	990	You must not switch to another coro from within a signal handler
599	(only relevant with %SIG - most event libraries provide safe	991	(only relevant with %SIG - most event libraries provide safe
600	signals).	992	signals), unless you are sure you are not interrupting a Coro
		993	function.
601		994
602	That means you MUST NOT call any function that might "block" the	995	That means you MUST NOT call any function that might "block" the
603	current coro - "cede", "schedule" "Coro::Semaphore->down" or	996	current coro - "cede", "schedule" "Coro::Semaphore->down" or
604	anything that calls those. Everything else, including calling	997	anything that calls those. Everything else, including calling
605	"ready", works.	998	"ready", works.
…		…
611	ithreads (for example, that memory or files would be shared), showing	1004	ithreads (for example, that memory or files would be shared), showing
612	his lack of understanding of this area - if it is hard to understand for	1005	his lack of understanding of this area - if it is hard to understand for
613	Chip, it is probably not obvious to everybody).	1006	Chip, it is probably not obvious to everybody).
614		1007
615	What follows is an ultra-condensed version of my talk about threads in	1008	What follows is an ultra-condensed version of my talk about threads in
616	scripting languages given onthe perl workshop 2009:	1009	scripting languages given on the perl workshop 2009:
617		1010
618	The so-called "ithreads" were originally implemented for two reasons:	1011	The so-called "ithreads" were originally implemented for two reasons:
619	first, to (badly) emulate unix processes on native win32 perls, and	1012	first, to (badly) emulate unix processes on native win32 perls, and
620	secondly, to replace the older, real thread model ("5.005-threads").	1013	secondly, to replace the older, real thread model ("5.005-threads").
621		1014
…		…
643	processes. What makes it so bad is that on non-windows platforms, you	1036	processes. What makes it so bad is that on non-windows platforms, you
644	can actually take advantage of custom hardware for this purpose (as	1037	can actually take advantage of custom hardware for this purpose (as
645	evidenced by the forks module, which gives you the (i-) threads API,	1038	evidenced by the forks module, which gives you the (i-) threads API,
646	just much faster).	1039	just much faster).
647		1040
648	Sharing data is in the i-threads model is done by transfering data	1041	Sharing data is in the i-threads model is done by transferring data
649	structures between threads using copying semantics, which is very slow -	1042	structures between threads using copying semantics, which is very slow -
650	shared data simply does not exist. Benchmarks using i-threads which are	1043	shared data simply does not exist. Benchmarks using i-threads which are
651	communication-intensive show extremely bad behaviour with i-threads (in	1044	communication-intensive show extremely bad behaviour with i-threads (in
652	fact, so bad that Coro, which cannot take direct advantage of multiple	1045	fact, so bad that Coro, which cannot take direct advantage of multiple
653	CPUs, is often orders of magnitude faster because it shares data using	1046	CPUs, is often orders of magnitude faster because it shares data using
…		…
682		1075
683	XS API: Coro::MakeMaker.	1076	XS API: Coro::MakeMaker.
684		1077
685	Low level Configuration, Thread Environment, Continuations: Coro::State.	1078	Low level Configuration, Thread Environment, Continuations: Coro::State.
686		1079
687	AUTHOR	1080	AUTHOR/SUPPORT/CONTACT
688	Marc Lehmann <schmorp@schmorp.de>	1081	Marc A. Lehmann <schmorp@schmorp.de>
689	http://home.schmorp.de/	1082	http://software.schmorp.de/pkg/Coro.html
690		1083

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Revision 1.39 by root, Fri Jul 14 13:14:32 2017 UTC