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Comparing Coro/README (file contents):
Revision 1.24 by root, Tue Jun 23 23:40:06 2009 UTC vs.
Revision 1.30 by root, Wed Jun 29 17:58:52 2011 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;
…		…
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
…		…
60	important global variables (see Coro::State for more configuration and	60	important global variables (see Coro::State for more configuration and
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
		66	CORO THREAD LIFE CYCLE
		67	During the long and exciting (or not) life of a coro thread, it goes
		68	through a number of states:
		69
		70	1. Creation
		71	The first thing in the life of a coro thread is it's creation -
		72	obviously. The typical way to create a thread is to call the "async
		73	BLOCK" function:
		74
		75	async {
		76	# thread code goes here
		77	};
		78
		79	You can also pass arguments, which are put in @_:
		80
		81	async {
		82	print $_[1]; # prints 2
		83	} 1, 2, 3;
		84
		85	This creates a new coro thread and puts it into the ready queue,
		86	meaning it will run as soon as the CPU is free for it.
		87
		88	"async" will return a Coro object - you can store this for future
		89	reference or ignore it - a thread that is running, ready to run or
		90	waiting for some event is alive on it's own.
		91
		92	Another way to create a thread is to call the "new" constructor with
		93	a code-reference:
		94
		95	new Coro sub {
		96	# thread code goes here
		97	}, @optional_arguments;
		98
		99	This is quite similar to calling "async", but the important
		100	difference is that the new thread is not put into the ready queue,
		101	so the thread will not run until somebody puts it there. "async" is,
		102	therefore, identical to this sequence:
		103
		104	my $coro = new Coro sub {
		105	# thread code goes here
		106	};
		107	$coro->ready;
		108	return $coro;
		109
		110	2. Startup
		111	When a new coro thread is created, only a copy of the code reference
		112	and the arguments are stored, no extra memory for stacks and so on
		113	is allocated, keeping the coro thread in a low-memory state.
		114
		115	Only when it actually starts executing will all the resources be
		116	finally allocated.
		117
		118	The optional arguments specified at coro creation are available in
		119	@_, similar to function calls.
		120
		121	3. Running / Blocking
		122	A lot can happen after the coro thread has started running. Quite
		123	usually, it will not run to the end in one go (because you could use
		124	a function instead), but it will give up the CPU regularly because
		125	it waits for external events.
		126
		127	As long as a coro thread runs, its Coro object is available in the
		128	global variable $Coro::current.
		129
		130	The low-level way to give up the CPU is to call the scheduler, which
		131	selects a new coro thread to run:
		132
		133	Coro::schedule;
		134
		135	Since running threads are not in the ready queue, calling the
		136	scheduler without doing anything else will block the coro thread
		137	forever - you need to arrange either for the coro to put woken up
		138	(readied) by some other event or some other thread, or you can put
		139	it into the ready queue before scheduling:
		140
		141	# this is exactly what Coro::cede does
		142	$Coro::current->ready;
		143	Coro::schedule;
		144
		145	All the higher-level synchronisation methods (Coro::Semaphore,
		146	Coro::rouse_*...) are actually implemented via "->ready" and
		147	"Coro::schedule".
		148
		149	While the coro thread is running it also might get assigned a
		150	C-level thread, or the C-level thread might be unassigned from it,
		151	as the Coro runtime wishes. A C-level thread needs to be assigned
		152	when your perl thread calls into some C-level function and that
		153	function in turn calls perl and perl then wants to switch
		154	coroutines. This happens most often when you run an event loop and
		155	block in the callback, or when perl itself calls some function such
		156	as "AUTOLOAD" or methods via the "tie" mechanism.
		157
		158	4. Termination
		159	Many threads actually terminate after some time. There are a number
		160	of ways to terminate a coro thread, the simplest is returning from
		161	the top-level code reference:
		162
		163	async {
		164	# after returning from here, the coro thread is terminated
		165	};
		166
		167	async {
		168	return if 0.5 < rand; # terminate a little earlier, maybe
		169	print "got a chance to print this\n";
		170	# or here
		171	};
		172
		173	Any values returned from the coroutine can be recovered using
		174	"->join":
		175
		176	my $coro = async {
		177	"hello, world\n" # return a string
		178	};
		179
		180	my $hello_world = $coro->join;
		181
		182	print $hello_world;
		183
		184	Another way to terminate is to call "Coro::terminate", which at any
		185	subroutine call nesting level:
		186
		187	async {
		188	Coro::terminate "return value 1", "return value 2";
		189	};
		190
		191	And yet another way is to "->cancel" (or "->safe_cancel") the coro
		192	thread from another thread:
		193
		194	my $coro = async {
		195	exit 1;
		196	};
		197
		198	$coro->cancel; # also accepts values for ->join to retrieve
		199
		200	Cancellation can be dangerous - it's a bit like calling "exit"
		201	without actually exiting, and might leave C libraries and XS modules
		202	in a weird state. Unlike other thread implementations, however, Coro
		203	is exceptionally safe with regards to cancellation, as perl will
		204	always be in a consistent state, and for those cases where you want
		205	to do truly marvellous things with your coro while it is being
		206	cancelled - that is, make sure all cleanup code is executed from the
		207	thread being cancelled - there is even a "->safe_cancel" method.
		208
		209	So, cancelling a thread that runs in an XS event loop might not be
		210	the best idea, but any other combination that deals with perl only
		211	(cancelling when a thread is in a "tie" method or an "AUTOLOAD" for
		212	example) is safe.
		213
		214	Lastly, a coro thread object that isn't referenced is "->cancel"'ed
		215	automatically - just like other objects in Perl. This is not such a
		216	common case, however - a running thread is referencedy b
		217	$Coro::current, a thread ready to run is referenced by the ready
		218	queue, a thread waiting on a lock or semaphore is referenced by
		219	being in some wait list and so on. But a thread that isn't in any of
		220	those queues gets cancelled:
		221
		222	async {
		223	schedule; # cede to other coros, don't go into the ready queue
		224	};
		225
		226	cede;
		227	# now the async above is destroyed, as it is not referenced by anything.
		228
		229	5. Cleanup
		230	Threads will allocate various resources. Most but not all will be
		231	returned when a thread terminates, during clean-up.
		232
		233	Cleanup is quite similar to throwing an uncaught exception: perl
		234	will work it's way up through all subroutine calls and blocks. On
		235	it's way, it will release all "my" variables, undo all "local"'s and
		236	free any other resources truly local to the thread.
		237
		238	So, a common way to free resources is to keep them referenced only
		239	by my variables:
		240
		241	async {
		242	my $big_cache = new Cache ...;
		243	};
		244
		245	If there are no other references, then the $big_cache object will be
		246	freed when the thread terminates, regardless of how it does so.
		247
		248	What it does "NOT" do is unlock any Coro::Semaphores or similar
		249	resources, but that's where the "guard" methods come in handy:
		250
		251	my $sem = new Coro::Semaphore;
		252
		253	async {
		254	my $lock_guard = $sem->guard;
		255	# if we reutrn, or die or get cancelled, here,
		256	# then the semaphore will be "up"ed.
		257	};
		258
		259	The "Guard::guard" function comes in handy for any custom cleanup
		260	you might want to do (but you cannot switch to other coroutines form
		261	those code blocks):
		262
		263	async {
		264	my $window = new Gtk2::Window "toplevel";
		265	# The window will not be cleaned up automatically, even when $window
		266	# gets freed, so use a guard to ensure it's destruction
		267	# in case of an error:
		268	my $window_guard = Guard::guard { $window->destroy };
		269
		270	# we are safe here
		271	};
		272
		273	Last not least, "local" can often be handy, too, e.g. when
		274	temporarily replacing the coro thread description:
		275
		276	sub myfunction {
		277	local $Coro::current->{desc} = "inside myfunction(@_)";
		278
		279	# if we return or die here, the description will be restored
		280	}
		281
		282	6. Viva La Zombie Muerte
		283	Even after a thread has terminated and cleaned up its resources, the
		284	Coro object still is there and stores the return values of the
		285	thread.
		286
		287	The means the Coro object gets freed automatically when the thread
		288	has terminated and cleaned up and there arenot other references.
		289
		290	If there are, the Coro object will stay around, and you can call
		291	"->join" as many times as you wish to retrieve the result values:
		292
		293	async {
		294	print "hi\n";
		295	1
		296	};
		297
		298	# run the async above, and free everything before returning
		299	# from Coro::cede:
		300	Coro::cede;
		301
		302	{
		303	my $coro = async {
		304	print "hi\n";
		305	1
		306	};
		307
		308	# run the async above, and clean up, but do not free the coro
		309	# object:
		310	Coro::cede;
		311
		312	# optionally retrieve the result values
		313	my @results = $coro->join;
		314
		315	# now $coro goes out of scope, and presumably gets freed
		316	};
65		317
66	GLOBAL VARIABLES	318	GLOBAL VARIABLES
67	$Coro::main	319	$Coro::main
68	This variable stores the Coro object that represents the main	320	This variable stores the Coro object that represents the main
69	program. While you cna "ready" it and do most other things you can	321	program. While you cna "ready" it and do most other things you can
…		…
82	$Coro::idle	334	$Coro::idle
83	This variable is mainly useful to integrate Coro into event loops.	335	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	336	It is usually better to rely on Coro::AnyEvent or Coro::EV, as this
85	is pretty low-level functionality.	337	is pretty low-level functionality.
86		338
87	This variable stores either a Coro object or a callback.	339	This variable stores a Coro object that is put into the ready queue
		340	when there are no other ready threads (without invoking any ready
		341	hooks).
88		342
89	If it is a callback, the it is called whenever the scheduler finds	343	The default implementation dies with "FATAL: deadlock detected.",
90	no ready coros to run. The default implementation prints "FATAL:	344	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.	345	to continue.
93		346
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	347	This hook is overwritten by modules such as "Coro::EV" and
99	"Coro::AnyEvent" to wait on an external event that hopefully wake up	348	"Coro::AnyEvent" to wait on an external event that hopefully wakes
100	a coro so the scheduler can run it.	349	up a coro so the scheduler can run it.
101		350
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	351	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		352
115	SIMPLE CORO CREATION	353	SIMPLE CORO CREATION
116	async { ... } [@args...]	354	async { ... } [@args...]
117	Create a new coro and return its Coro object (usually unused). The	355	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	356	coro will be put into the ready queue, so it will start running
…		…
181		419
182	schedule	420	schedule
183	Calls the scheduler. The scheduler will find the next coro that is	421	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	422	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	423	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	424	in its ready queue. If there is no coro ready, it will call the
187	$Coro::idle hook.	425	$Coro::idle hook.
188		426
189	Please note that the current coro will not be put into the ready	427	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	428	queue, so calling this function usually means you will never be
191	called again unless something else (e.g. an event handler) calls	429	called again unless something else (e.g. an event handler) calls
…		…
216	any coro, regardless of priority. This is useful sometimes to	454	any coro, regardless of priority. This is useful sometimes to
217	ensure progress is made.	455	ensure progress is made.
218		456
219	terminate [arg...]	457	terminate [arg...]
220	Terminates the current coro with the given status values (see	458	Terminates the current coro with the given status values (see
221	cancel).	459	cancel). The values will not be copied, but referenced directly.
222		460
223	Coro::on_enter BLOCK, Coro::on_leave BLOCK	461	Coro::on_enter BLOCK, Coro::on_leave BLOCK
224	These function install enter and leave winders in the current scope.	462	These function install enter and leave winders in the current scope.
225	The enter block will be executed when on_enter is called and	463	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	464	whenever the current coro is re-entered by the scheduler, while the
…		…
358	To avoid this, it is best to put a suspended coro into the ready	596	To avoid this, it is best to put a suspended coro into the ready
359	queue unconditionally, as every synchronisation mechanism must	597	queue unconditionally, as every synchronisation mechanism must
360	protect itself against spurious wakeups, and the one in the Coro	598	protect itself against spurious wakeups, and the one in the Coro
361	family certainly do that.	599	family certainly do that.
362		600
		601	$state->is_new
		602	Returns true iff this Coro object is "new", i.e. has never been run
		603	yet. Those states basically consist of only the code reference to
		604	call and the arguments, but consumes very little other resources.
		605	New states will automatically get assigned a perl interpreter when
		606	they are transfered to.
		607
		608	$state->is_zombie
		609	Returns true iff the Coro object has been cancelled, i.e. it's
		610	resources freed because they were "cancel"'ed, "terminate"'d,
		611	"safe_cancel"'ed or simply went out of scope.
		612
		613	The name "zombie" stems from UNIX culture, where a process that has
		614	exited and only stores and exit status and no other resources is
		615	called a "zombie".
		616
363	$is_ready = $coro->is_ready	617	$is_ready = $coro->is_ready
364	Returns true iff the Coro object is in the ready queue. Unless the	618	Returns true iff the Coro object is in the ready queue. Unless the
365	Coro object gets destroyed, it will eventually be scheduled by the	619	Coro object gets destroyed, it will eventually be scheduled by the
366	scheduler.	620	scheduler.
367		621
…		…
373	$is_suspended = $coro->is_suspended	627	$is_suspended = $coro->is_suspended
374	Returns true iff this Coro object has been suspended. Suspended	628	Returns true iff this Coro object has been suspended. Suspended
375	Coros will not ever be scheduled.	629	Coros will not ever be scheduled.
376		630
377	$coro->cancel (arg...)	631	$coro->cancel (arg...)
378	Terminates the given Coro and makes it return the given arguments as	632	Terminates the given Coro thread and makes it return the given
379	status (default: the empty list). Never returns if the Coro is the	633	arguments as status (default: an empty list). Never returns if the
380	current Coro.	634	Coro is the current Coro.
		635
		636	This is a rather brutal way to free a coro, with some limitations -
		637	if the thread is inside a C callback that doesn't expect to be
		638	canceled, bad things can happen, or if the cancelled thread insists
		639	on running complicated cleanup handlers that rely on its thread
		640	context, things will not work.
		641
		642	Any cleanup code being run (e.g. from "guard" blocks) will be run
		643	without a thread context, and is not allowed to switch to other
		644	threads. On the plus side, "->cancel" will always clean up the
		645	thread, no matter what. If your cleanup code is complex or you want
		646	to avoid cancelling a C-thread that doesn't know how to clean up
		647	itself, it can be better to "->throw" an exception, or use
		648	"->safe_cancel".
		649
		650	The arguments to "->cancel" are not copied, but instead will be
		651	referenced directly (e.g. if you pass $var and after the call change
		652	that variable, then you might change the return values passed to
		653	e.g. "join", so don't do that).
		654
		655	The resources of the Coro are usually freed (or destructed) before
		656	this call returns, but this can be delayed for an indefinite amount
		657	of time, as in some cases the manager thread has to run first to
		658	actually destruct the Coro object.
		659
		660	$coro->safe_cancel ($arg...)
		661	Works mostly like "->cancel", but is inherently "safer", and
		662	consequently, can fail with an exception in cases the thread is not
		663	in a cancellable state.
		664
		665	This method works a bit like throwing an exception that cannot be
		666	caught - specifically, it will clean up the thread from within
		667	itself, so all cleanup handlers (e.g. "guard" blocks) are run with
		668	full thread context and can block if they wish. The downside is that
		669	there is no guarantee that the thread can be cancelled when you call
		670	this method, and therefore, it might fail. It is also considerably
		671	slower than "cancel" or "terminate".
		672
		673	A thread is in a safe-cancellable state if it either hasn't been run
		674	yet, or it has no C context attached and is inside an SLF function.
		675
		676	The latter two basically mean that the thread isn't currently inside
		677	a perl callback called from some C function (usually via some XS
		678	modules) and isn't currently executing inside some C function itself
		679	(via Coro's XS API).
		680
		681	This call returns true when it could cancel the thread, or croaks
		682	with an error otherwise (i.e. it either returns true or doesn't
		683	return at all).
		684
		685	Why the weird interface? Well, there are two common models on how
		686	and when to cancel things. In the first, you have the expectation
		687	that your coro thread can be cancelled when you want to cancel it -
		688	if the thread isn't cancellable, this would be a bug somewhere, so
		689	"->safe_cancel" croaks to notify of the bug.
		690
		691	In the second model you sometimes want to ask nicely to cancel a
		692	thread, but if it's not a good time, well, then don't cancel. This
		693	can be done relatively easy like this:
		694
		695	if (! eval { $coro->safe_cancel }) {
		696	warn "unable to cancel thread: $@";
		697	}
		698
		699	However, what you never should do is first try to cancel "safely"
		700	and if that fails, cancel the "hard" way with "->cancel". That makes
		701	no sense: either you rely on being able to execute cleanup code in
		702	your thread context, or you don't. If you do, then "->safe_cancel"
		703	is the only way, and if you don't, then "->cancel" is always faster
		704	and more direct.
381		705
382	$coro->schedule_to	706	$coro->schedule_to
383	Puts the current coro to sleep (like "Coro::schedule"), but instead	707	Puts the current coro to sleep (like "Coro::schedule"), but instead
384	of continuing with the next coro from the ready queue, always switch	708	of continuing with the next coro from the ready queue, always switch
385	to the given coro object (regardless of priority etc.). The	709	to the given coro object (regardless of priority etc.). The
…		…
402	Otherwise clears the exception object.	726	Otherwise clears the exception object.
403		727
404	Coro will check for the exception each time a schedule-like-function	728	Coro will check for the exception each time a schedule-like-function
405	returns, i.e. after each "schedule", "cede",	729	returns, i.e. after each "schedule", "cede",
406	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of	730	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
407	these functions detect this case and return early in case an	731	those functions (all that are part of Coro itself) detect this case
408	exception is pending.	732	and return early in case an exception is pending.
409		733
410	The exception object will be thrown "as is" with the specified	734	The exception object will be thrown "as is" with the specified
411	scalar in $@, i.e. if it is a string, no line number or newline will	735	scalar in $@, i.e. if it is a string, no line number or newline will
412	be appended (unlike with "die").	736	be appended (unlike with "die").
413		737
414	This can be used as a softer means than "cancel" to ask a coro to	738	This can be used as a softer means than either "cancel" or
415	end itself, although there is no guarantee that the exception will	739	"safe_cancel "to ask a coro to end itself, although there is no
416	lead to termination, and if the exception isn't caught it might well	740	guarantee that the exception will lead to termination, and if the
417	end the whole program.	741	exception isn't caught it might well end the whole program.
418		742
419	You might also think of "throw" as being the moral equivalent of	743	You might also think of "throw" as being the moral equivalent of
420	"kill"ing a coro with a signal (in this case, a scalar).	744	"kill"ing a coro with a signal (in this case, a scalar).
421		745
422	$coro->join	746	$coro->join
423	Wait until the coro terminates and return any values given to the	747	Wait until the coro terminates and return any values given to the
424	"terminate" or "cancel" functions. "join" can be called concurrently	748	"terminate" or "cancel" functions. "join" can be called concurrently
425	from multiple coro, and all will be resumed and given the status	749	from multiple threads, and all will be resumed and given the status
426	return once the $coro terminates.	750	return once the $coro terminates.
427		751
428	$coro->on_destroy (\&cb)	752	$coro->on_destroy (\&cb)
429	Registers a callback that is called when this coro gets destroyed,	753	Registers a callback that is called when this coro thread gets
		754	destroyed, that is, after it's resources have been freed but before
430	but before it is joined. The callback gets passed the terminate	755	it is joined. The callback gets passed the terminate/cancel
431	arguments, if any, and must not die, under any circumstances.	756	arguments, if any, and must not die, under any circumstances.
432		757
		758	There can be any number of "on_destroy" callbacks per coro, and
		759	there is no way currently to remove a callback once added.
		760
433	$oldprio = $coro->prio ($newprio)	761	$oldprio = $coro->prio ($newprio)
434	Sets (or gets, if the argument is missing) the priority of the coro.	762	Sets (or gets, if the argument is missing) the priority of the coro
435	Higher priority coro get run before lower priority coro. Priorities	763	thread. Higher priority coro get run before lower priority coros.
436	are small signed integers (currently -4 .. +3), that you can refer	764	Priorities are small signed integers (currently -4 .. +3), that you
437	to using PRIO_xxx constants (use the import tag :prio to get then):	765	can refer to using PRIO_xxx constants (use the import tag :prio to
		766	get then):
438		767
439	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	768	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
440	3 > 1 > 0 > -1 > -3 > -4	769	3 > 1 > 0 > -1 > -3 > -4
441		770
442	# set priority to HIGH	771	# set priority to HIGH
443	current->prio (PRIO_HIGH);	772	current->prio (PRIO_HIGH);
444		773
445	The idle coro ($Coro::idle) always has a lower priority than any	774	The idle coro thread ($Coro::idle) always has a lower priority than
446	existing coro.	775	any existing coro.
447		776
448	Changing the priority of the current coro will take effect	777	Changing the priority of the current coro will take effect
449	immediately, but changing the priority of coro in the ready queue	778	immediately, but changing the priority of a coro in the ready queue
450	(but not running) will only take effect after the next schedule (of	779	(but not running) will only take effect after the next schedule (of
451	that coro). This is a bug that will be fixed in some future version.	780	that coro). This is a bug that will be fixed in some future version.
452		781
453	$newprio = $coro->nice ($change)	782	$newprio = $coro->nice ($change)
454	Similar to "prio", but subtract the given value from the priority	783	Similar to "prio", but subtract the given value from the priority
455	(i.e. higher values mean lower priority, just as in unix).	784	(i.e. higher values mean lower priority, just as in UNIX's nice
		785	command).
456		786
457	$olddesc = $coro->desc ($newdesc)	787	$olddesc = $coro->desc ($newdesc)
458	Sets (or gets in case the argument is missing) the description for	788	Sets (or gets in case the argument is missing) the description for
459	this coro. This is just a free-form string you can associate with a	789	this coro thread. This is just a free-form string you can associate
460	coro.	790	with a coro.
461		791
462	This method simply sets the "$coro->{desc}" member to the given	792	This method simply sets the "$coro->{desc}" member to the given
463	string. You can modify this member directly if you wish.	793	string. You can modify this member directly if you wish, and in
		794	fact, this is often preferred to indicate major processing states
		795	that cna then be seen for example in a Coro::Debug session:
		796
		797	sub my_long_function {
		798	local $Coro::current->{desc} = "now in my_long_function";
		799	...
		800	$Coro::current->{desc} = "my_long_function: phase 1";
		801	...
		802	$Coro::current->{desc} = "my_long_function: phase 2";
		803	...
		804	}
464		805
465	GLOBAL FUNCTIONS	806	GLOBAL FUNCTIONS
466	Coro::nready	807	Coro::nready
467	Returns the number of coro that are currently in the ready state,	808	Returns the number of coro that are currently in the ready state,
468	i.e. that can be switched to by calling "schedule" directory or	809	i.e. that can be switched to by calling "schedule" directory or
…		…
485	The reason this function exists is that many event libraries (such	826	The reason this function exists is that many event libraries (such
486	as the venerable Event module) are not thread-safe (a weaker form of	827	as the venerable Event module) are not thread-safe (a weaker form of
487	reentrancy). This means you must not block within event callbacks,	828	reentrancy). This means you must not block within event callbacks,
488	otherwise you might suffer from crashes or worse. The only event	829	otherwise you might suffer from crashes or worse. The only event
489	library currently known that is safe to use without "unblock_sub" is	830	library currently known that is safe to use without "unblock_sub" is
490	EV.	831	EV (but you might still run into deadlocks if all event loops are
		832	blocked).
		833
		834	Coro will try to catch you when you block in the event loop
		835	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		836	and only works when you do not run your own event loop.
491		837
492	This function allows your callbacks to block by executing them in	838	This function allows your callbacks to block by executing them in
493	another coro where it is safe to block. One example where blocking	839	another coro where it is safe to block. One example where blocking
494	is handy is when you use the Coro::AIO functions to save results to	840	is handy is when you use the Coro::AIO functions to save results to
495	disk, for example.	841	disk, for example.
…		…
506	when you use a module that uses AnyEvent (and you use	852	when you use a module that uses AnyEvent (and you use
507	Coro::AnyEvent) and it provides callbacks that are the result of	853	Coro::AnyEvent) and it provides callbacks that are the result of
508	some event callback, then you must not block either, or use	854	some event callback, then you must not block either, or use
509	"unblock_sub".	855	"unblock_sub".
510		856
511	$cb = Coro::rouse_cb	857	$cb = rouse_cb
512	Create and return a "rouse callback". That's a code reference that,	858	Create and return a "rouse callback". That's a code reference that,
513	when called, will remember a copy of its arguments and notify the	859	when called, will remember a copy of its arguments and notify the
514	owner coro of the callback.	860	owner coro of the callback.
515		861
516	See the next function.	862	See the next function.
517		863
518	@args = Coro::rouse_wait [$cb]	864	@args = rouse_wait [$cb]
519	Wait for the specified rouse callback (or the last one that was	865	Wait for the specified rouse callback (or the last one that was
520	created in this coro).	866	created in this coro).
521		867
522	As soon as the callback is invoked (or when the callback was invoked	868	As soon as the callback is invoked (or when the callback was invoked
523	before "rouse_wait"), it will return the arguments originally passed	869	before "rouse_wait"), it will return the arguments originally passed
524	to the rouse callback.	870	to the rouse callback. In scalar context, that means you get the
		871	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		872	$a3...)" statement at the end.
525		873
526	See the section HOW TO WAIT FOR A CALLBACK for an actual usage	874	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
527	example.	875	example.
528		876
529	HOW TO WAIT FOR A CALLBACK	877	HOW TO WAIT FOR A CALLBACK
…		…
603	in the future to allow per-thread schedulers, but Coro::State does	951	in the future to allow per-thread schedulers, but Coro::State does
604	not yet allow this). I recommend disabling thread support and using	952	not yet allow this). I recommend disabling thread support and using
605	processes, as having the windows process emulation enabled under	953	processes, as having the windows process emulation enabled under
606	unix roughly halves perl performance, even when not used.	954	unix roughly halves perl performance, even when not used.
607		955
		956	Attempts to use threads created in another emulated process will
		957	crash ("cleanly", with a null pointer exception).
		958
608	coro switching is not signal safe	959	coro switching is not signal safe
609	You must not switch to another coro from within a signal handler	960	You must not switch to another coro from within a signal handler
610	(only relevant with %SIG - most event libraries provide safe	961	(only relevant with %SIG - most event libraries provide safe
611	signals).	962	signals), unless you are sure you are not interrupting a Coro
		963	function.
612		964
613	That means you MUST NOT call any function that might "block" the	965	That means you MUST NOT call any function that might "block" the
614	current coro - "cede", "schedule" "Coro::Semaphore->down" or	966	current coro - "cede", "schedule" "Coro::Semaphore->down" or
615	anything that calls those. Everything else, including calling	967	anything that calls those. Everything else, including calling
616	"ready", works.	968	"ready", works.
617		969
		970	WINDOWS PROCESS EMULATION
		971	A great many people seem to be confused about ithreads (for example,
		972	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		973	while in the same mail making rather confused statements about perl
		974	ithreads (for example, that memory or files would be shared), showing
		975	his lack of understanding of this area - if it is hard to understand for
		976	Chip, it is probably not obvious to everybody).
		977
		978	What follows is an ultra-condensed version of my talk about threads in
		979	scripting languages given on the perl workshop 2009:
		980
		981	The so-called "ithreads" were originally implemented for two reasons:
		982	first, to (badly) emulate unix processes on native win32 perls, and
		983	secondly, to replace the older, real thread model ("5.005-threads").
		984
		985	It does that by using threads instead of OS processes. The difference
		986	between processes and threads is that threads share memory (and other
		987	state, such as files) between threads within a single process, while
		988	processes do not share anything (at least not semantically). That means
		989	that modifications done by one thread are seen by others, while
		990	modifications by one process are not seen by other processes.
		991
		992	The "ithreads" work exactly like that: when creating a new ithreads
		993	process, all state is copied (memory is copied physically, files and
		994	code is copied logically). Afterwards, it isolates all modifications. On
		995	UNIX, the same behaviour can be achieved by using operating system
		996	processes, except that UNIX typically uses hardware built into the
		997	system to do this efficiently, while the windows process emulation
		998	emulates this hardware in software (rather efficiently, but of course it
		999	is still much slower than dedicated hardware).
		1000
		1001	As mentioned before, loading code, modifying code, modifying data
		1002	structures and so on is only visible in the ithreads process doing the
		1003	modification, not in other ithread processes within the same OS process.
		1004
		1005	This is why "ithreads" do not implement threads for perl at all, only
		1006	processes. What makes it so bad is that on non-windows platforms, you
		1007	can actually take advantage of custom hardware for this purpose (as
		1008	evidenced by the forks module, which gives you the (i-) threads API,
		1009	just much faster).
		1010
		1011	Sharing data is in the i-threads model is done by transfering data
		1012	structures between threads using copying semantics, which is very slow -
		1013	shared data simply does not exist. Benchmarks using i-threads which are
		1014	communication-intensive show extremely bad behaviour with i-threads (in
		1015	fact, so bad that Coro, which cannot take direct advantage of multiple
		1016	CPUs, is often orders of magnitude faster because it shares data using
		1017	real threads, refer to my talk for details).
		1018
		1019	As summary, i-threads use threads to implement processes, while the
		1020	compatible forks module uses processes to emulate, uhm, processes.
		1021	I-threads slow down every perl program when enabled, and outside of
		1022	windows, serve no (or little) practical purpose, but disadvantages every
		1023	single-threaded Perl program.
		1024
		1025	This is the reason that I try to avoid the name "ithreads", as it is
		1026	misleading as it implies that it implements some kind of thread model
		1027	for perl, and prefer the name "windows process emulation", which
		1028	describes the actual use and behaviour of it much better.
		1029
618	SEE ALSO	1030	SEE ALSO
619	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	1031	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
620		1032
621	Debugging: Coro::Debug.	1033	Debugging: Coro::Debug.
622		1034

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