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Revision 1.32 by root, Wed Mar 6 06:00:08 2013 UTC

…		…
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 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
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
…		…
181		443
182	schedule	444	schedule
183	Calls the scheduler. The scheduler will find the next coro that is	445	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	446	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	447	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	448	in its ready queue. If there is no coro ready, it will call the
187	$Coro::idle hook.	449	$Coro::idle hook.
188		450
189	Please note that the current coro will not be put into the ready	451	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	452	queue, so calling this function usually means you will never be
191	called again unless something else (e.g. an event handler) calls	453	called again unless something else (e.g. an event handler) calls
…		…
216	any coro, regardless of priority. This is useful sometimes to	478	any coro, regardless of priority. This is useful sometimes to
217	ensure progress is made.	479	ensure progress is made.
218		480
219	terminate [arg...]	481	terminate [arg...]
220	Terminates the current coro with the given status values (see	482	Terminates the current coro with the given status values (see
221	cancel).	483	cancel). The values will not be copied, but referenced directly.
222		484
223	Coro::on_enter BLOCK, Coro::on_leave BLOCK	485	Coro::on_enter BLOCK, Coro::on_leave BLOCK
224	These function install enter and leave winders in the current scope.	486	These function install enter and leave winders in the current scope.
225	The enter block will be executed when on_enter is called and	487	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	488	whenever the current coro is re-entered by the scheduler, while the
…		…
238		500
239	These functions implement the same concept as "dynamic-wind" in	501	These functions implement the same concept as "dynamic-wind" in
240	scheme does, and are useful when you want to localise some resource	502	scheme does, and are useful when you want to localise some resource
241	to a specific coro.	503	to a specific coro.
242		504
243	They slow down coro switching considerably for coros that use them	505	They slow down thread switching considerably for coros that use them
		506	(about 40% for a BLOCK with a single assignment, so thread switching
244	(But coro switching is still reasonably fast if the handlers are	507	is still reasonably fast if the handlers are fast).
245	fast).
246		508
247	These functions are best understood by an example: The following	509	These functions are best understood by an example: The following
248	function will change the current timezone to	510	function will change the current timezone to
249	"Antarctica/South_Pole", which requires a call to "tzset", but by	511	"Antarctica/South_Pole", which requires a call to "tzset", but by
250	using "on_enter" and "on_leave", which remember/change the current	512	using "on_enter" and "on_leave", which remember/change the current
251	timezone and restore the previous value, respectively, the timezone	513	timezone and restore the previous value, respectively, the timezone
252	is only changes for the coro that installed those handlers.	514	is only changed for the coro that installed those handlers.
253		515
254	use POSIX qw(tzset);	516	use POSIX qw(tzset);
255		517
256	async {	518	async {
257	my $old_tz; # store outside TZ value here	519	my $old_tz; # store outside TZ value here
…		…
273	};	535	};
274		536
275	This can be used to localise about any resource (locale, uid,	537	This can be used to localise about any resource (locale, uid,
276	current working directory etc.) to a block, despite the existance of	538	current working directory etc.) to a block, despite the existance of
277	other coros.	539	other coros.
		540
		541	Another interesting example implements time-sliced multitasking
		542	using interval timers (this could obviously be optimised, but does
		543	the job):
		544
		545	# "timeslice" the given block
		546	sub timeslice(&) {
		547	use Time::HiRes ();
		548
		549	Coro::on_enter {
		550	# on entering the thread, we set an VTALRM handler to cede
		551	$SIG{VTALRM} = sub { cede };
		552	# and then start the interval timer
		553	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		554	};
		555	Coro::on_leave {
		556	# on leaving the thread, we stop the interval timer again
		557	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		558	};
		559
		560	&{+shift};
		561	}
		562
		563	# use like this:
		564	timeslice {
		565	# The following is an endless loop that would normally
		566	# monopolise the process. Since it runs in a timesliced
		567	# environment, it will regularly cede to other threads.
		568	while () { }
		569	};
278		570
279	killall	571	killall
280	Kills/terminates/cancels all coros except the currently running one.	572	Kills/terminates/cancels all coros except the currently running one.
281		573
282	Note that while this will try to free some of the main interpreter	574	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	620	To avoid this, it is best to put a suspended coro into the ready
329	queue unconditionally, as every synchronisation mechanism must	621	queue unconditionally, as every synchronisation mechanism must
330	protect itself against spurious wakeups, and the one in the Coro	622	protect itself against spurious wakeups, and the one in the Coro
331	family certainly do that.	623	family certainly do that.
332		624
		625	$state->is_new
		626	Returns true iff this Coro object is "new", i.e. has never been run
		627	yet. Those states basically consist of only the code reference to
		628	call and the arguments, but consumes very little other resources.
		629	New states will automatically get assigned a perl interpreter when
		630	they are transfered to.
		631
		632	$state->is_zombie
		633	Returns true iff the Coro object has been cancelled, i.e. it's
		634	resources freed because they were "cancel"'ed, "terminate"'d,
		635	"safe_cancel"'ed or simply went out of scope.
		636
		637	The name "zombie" stems from UNIX culture, where a process that has
		638	exited and only stores and exit status and no other resources is
		639	called a "zombie".
		640
333	$is_ready = $coro->is_ready	641	$is_ready = $coro->is_ready
334	Returns true iff the Coro object is in the ready queue. Unless the	642	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	643	Coro object gets destroyed, it will eventually be scheduled by the
336	scheduler.	644	scheduler.
337		645
…		…
343	$is_suspended = $coro->is_suspended	651	$is_suspended = $coro->is_suspended
344	Returns true iff this Coro object has been suspended. Suspended	652	Returns true iff this Coro object has been suspended. Suspended
345	Coros will not ever be scheduled.	653	Coros will not ever be scheduled.
346		654
347	$coro->cancel (arg...)	655	$coro->cancel (arg...)
348	Terminates the given Coro and makes it return the given arguments as	656	Terminates the given Coro thread and makes it return the given
349	status (default: the empty list). Never returns if the Coro is the	657	arguments as status (default: an empty list). Never returns if the
350	current Coro.	658	Coro is the current Coro.
		659
		660	This is a rather brutal way to free a coro, with some limitations -
		661	if the thread is inside a C callback that doesn't expect to be
		662	canceled, bad things can happen, or if the cancelled thread insists
		663	on running complicated cleanup handlers that rely on its thread
		664	context, things will not work.
		665
		666	Any cleanup code being run (e.g. from "guard" blocks) will be run
		667	without a thread context, and is not allowed to switch to other
		668	threads. On the plus side, "->cancel" will always clean up the
		669	thread, no matter what. If your cleanup code is complex or you want
		670	to avoid cancelling a C-thread that doesn't know how to clean up
		671	itself, it can be better to "->throw" an exception, or use
		672	"->safe_cancel".
		673
		674	The arguments to "->cancel" are not copied, but instead will be
		675	referenced directly (e.g. if you pass $var and after the call change
		676	that variable, then you might change the return values passed to
		677	e.g. "join", so don't do that).
		678
		679	The resources of the Coro are usually freed (or destructed) before
		680	this call returns, but this can be delayed for an indefinite amount
		681	of time, as in some cases the manager thread has to run first to
		682	actually destruct the Coro object.
		683
		684	$coro->safe_cancel ($arg...)
		685	Works mostly like "->cancel", but is inherently "safer", and
		686	consequently, can fail with an exception in cases the thread is not
		687	in a cancellable state.
		688
		689	This method works a bit like throwing an exception that cannot be
		690	caught - specifically, it will clean up the thread from within
		691	itself, so all cleanup handlers (e.g. "guard" blocks) are run with
		692	full thread context and can block if they wish. The downside is that
		693	there is no guarantee that the thread can be cancelled when you call
		694	this method, and therefore, it might fail. It is also considerably
		695	slower than "cancel" or "terminate".
		696
		697	A thread is in a safe-cancellable state if it either hasn't been run
		698	yet, or it has no C context attached and is inside an SLF function.
		699
		700	The latter two basically mean that the thread isn't currently inside
		701	a perl callback called from some C function (usually via some XS
		702	modules) and isn't currently executing inside some C function itself
		703	(via Coro's XS API).
		704
		705	This call returns true when it could cancel the thread, or croaks
		706	with an error otherwise (i.e. it either returns true or doesn't
		707	return at all).
		708
		709	Why the weird interface? Well, there are two common models on how
		710	and when to cancel things. In the first, you have the expectation
		711	that your coro thread can be cancelled when you want to cancel it -
		712	if the thread isn't cancellable, this would be a bug somewhere, so
		713	"->safe_cancel" croaks to notify of the bug.
		714
		715	In the second model you sometimes want to ask nicely to cancel a
		716	thread, but if it's not a good time, well, then don't cancel. This
		717	can be done relatively easy like this:
		718
		719	if (! eval { $coro->safe_cancel }) {
		720	warn "unable to cancel thread: $@";
		721	}
		722
		723	However, what you never should do is first try to cancel "safely"
		724	and if that fails, cancel the "hard" way with "->cancel". That makes
		725	no sense: either you rely on being able to execute cleanup code in
		726	your thread context, or you don't. If you do, then "->safe_cancel"
		727	is the only way, and if you don't, then "->cancel" is always faster
		728	and more direct.
351		729
352	$coro->schedule_to	730	$coro->schedule_to
353	Puts the current coro to sleep (like "Coro::schedule"), but instead	731	Puts the current coro to sleep (like "Coro::schedule"), but instead
354	of continuing with the next coro from the ready queue, always switch	732	of continuing with the next coro from the ready queue, always switch
355	to the given coro object (regardless of priority etc.). The	733	to the given coro object (regardless of priority etc.). The
…		…
372	Otherwise clears the exception object.	750	Otherwise clears the exception object.
373		751
374	Coro will check for the exception each time a schedule-like-function	752	Coro will check for the exception each time a schedule-like-function
375	returns, i.e. after each "schedule", "cede",	753	returns, i.e. after each "schedule", "cede",
376	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of	754	"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
377	these functions detect this case and return early in case an	755	those functions (all that are part of Coro itself) detect this case
378	exception is pending.	756	and return early in case an exception is pending.
379		757
380	The exception object will be thrown "as is" with the specified	758	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	759	scalar in $@, i.e. if it is a string, no line number or newline will
382	be appended (unlike with "die").	760	be appended (unlike with "die").
383		761
384	This can be used as a softer means than "cancel" to ask a coro to	762	This can be used as a softer means than either "cancel" or
385	end itself, although there is no guarantee that the exception will	763	"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	764	guarantee that the exception will lead to termination, and if the
387	end the whole program.	765	exception isn't caught it might well end the whole program.
388		766
389	You might also think of "throw" as being the moral equivalent of	767	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).	768	"kill"ing a coro with a signal (in this case, a scalar).
391		769
392	$coro->join	770	$coro->join
393	Wait until the coro terminates and return any values given to the	771	Wait until the coro terminates and return any values given to the
394	"terminate" or "cancel" functions. "join" can be called concurrently	772	"terminate" or "cancel" functions. "join" can be called concurrently
395	from multiple coro, and all will be resumed and given the status	773	from multiple threads, and all will be resumed and given the status
396	return once the $coro terminates.	774	return once the $coro terminates.
397		775
398	$coro->on_destroy (\&cb)	776	$coro->on_destroy (\&cb)
399	Registers a callback that is called when this coro gets destroyed,	777	Registers a callback that is called when this coro thread gets
		778	destroyed, that is, after it's resources have been freed but before
400	but before it is joined. The callback gets passed the terminate	779	it is joined. The callback gets passed the terminate/cancel
401	arguments, if any, and must not die, under any circumstances.	780	arguments, if any, and must not die, under any circumstances.
402		781
		782	There can be any number of "on_destroy" callbacks per coro, and
		783	there is no way currently to remove a callback once added.
		784
403	$oldprio = $coro->prio ($newprio)	785	$oldprio = $coro->prio ($newprio)
404	Sets (or gets, if the argument is missing) the priority of the coro.	786	Sets (or gets, if the argument is missing) the priority of the coro
405	Higher priority coro get run before lower priority coro. Priorities	787	thread. Higher priority coro get run before lower priority coros.
406	are small signed integers (currently -4 .. +3), that you can refer	788	Priorities are small signed integers (currently -4 .. +3), that you
407	to using PRIO_xxx constants (use the import tag :prio to get then):	789	can refer to using PRIO_xxx constants (use the import tag :prio to
		790	get then):
408		791
409	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	792	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
410	3 > 1 > 0 > -1 > -3 > -4	793	3 > 1 > 0 > -1 > -3 > -4
411		794
412	# set priority to HIGH	795	# set priority to HIGH
413	current->prio (PRIO_HIGH);	796	current->prio (PRIO_HIGH);
414		797
415	The idle coro ($Coro::idle) always has a lower priority than any	798	The idle coro thread ($Coro::idle) always has a lower priority than
416	existing coro.	799	any existing coro.
417		800
418	Changing the priority of the current coro will take effect	801	Changing the priority of the current coro will take effect
419	immediately, but changing the priority of coro in the ready queue	802	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	803	(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.	804	that coro). This is a bug that will be fixed in some future version.
422		805
423	$newprio = $coro->nice ($change)	806	$newprio = $coro->nice ($change)
424	Similar to "prio", but subtract the given value from the priority	807	Similar to "prio", but subtract the given value from the priority
425	(i.e. higher values mean lower priority, just as in unix).	808	(i.e. higher values mean lower priority, just as in UNIX's nice
		809	command).
426		810
427	$olddesc = $coro->desc ($newdesc)	811	$olddesc = $coro->desc ($newdesc)
428	Sets (or gets in case the argument is missing) the description for	812	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	813	this coro thread. This is just a free-form string you can associate
430	coro.	814	with a coro.
431		815
432	This method simply sets the "$coro->{desc}" member to the given	816	This method simply sets the "$coro->{desc}" member to the given
433	string. You can modify this member directly if you wish.	817	string. You can modify this member directly if you wish, and in
		818	fact, this is often preferred to indicate major processing states
		819	that can then be seen for example in a Coro::Debug session:
		820
		821	sub my_long_function {
		822	local $Coro::current->{desc} = "now in my_long_function";
		823	...
		824	$Coro::current->{desc} = "my_long_function: phase 1";
		825	...
		826	$Coro::current->{desc} = "my_long_function: phase 2";
		827	...
		828	}
434		829
435	GLOBAL FUNCTIONS	830	GLOBAL FUNCTIONS
436	Coro::nready	831	Coro::nready
437	Returns the number of coro that are currently in the ready state,	832	Returns the number of coro that are currently in the ready state,
438	i.e. that can be switched to by calling "schedule" directory or	833	i.e. that can be switched to by calling "schedule" directory or
…		…
455	The reason this function exists is that many event libraries (such	850	The reason this function exists is that many event libraries (such
456	as the venerable Event module) are not thread-safe (a weaker form of	851	as the venerable Event module) are not thread-safe (a weaker form of
457	reentrancy). This means you must not block within event callbacks,	852	reentrancy). This means you must not block within event callbacks,
458	otherwise you might suffer from crashes or worse. The only event	853	otherwise you might suffer from crashes or worse. The only event
459	library currently known that is safe to use without "unblock_sub" is	854	library currently known that is safe to use without "unblock_sub" is
460	EV.	855	EV (but you might still run into deadlocks if all event loops are
		856	blocked).
		857
		858	Coro will try to catch you when you block in the event loop
		859	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort
		860	and only works when you do not run your own event loop.
461		861
462	This function allows your callbacks to block by executing them in	862	This function allows your callbacks to block by executing them in
463	another coro where it is safe to block. One example where blocking	863	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	864	is handy is when you use the Coro::AIO functions to save results to
465	disk, for example.	865	disk, for example.
…		…
476	when you use a module that uses AnyEvent (and you use	876	when you use a module that uses AnyEvent (and you use
477	Coro::AnyEvent) and it provides callbacks that are the result of	877	Coro::AnyEvent) and it provides callbacks that are the result of
478	some event callback, then you must not block either, or use	878	some event callback, then you must not block either, or use
479	"unblock_sub".	879	"unblock_sub".
480		880
481	$cb = Coro::rouse_cb	881	$cb = rouse_cb
482	Create and return a "rouse callback". That's a code reference that,	882	Create and return a "rouse callback". That's a code reference that,
483	when called, will remember a copy of its arguments and notify the	883	when called, will remember a copy of its arguments and notify the
484	owner coro of the callback.	884	owner coro of the callback.
485		885
486	See the next function.	886	See the next function.
487		887
488	@args = Coro::rouse_wait [$cb]	888	@args = rouse_wait [$cb]
489	Wait for the specified rouse callback (or the last one that was	889	Wait for the specified rouse callback (or the last one that was
490	created in this coro).	890	created in this coro).
491		891
492	As soon as the callback is invoked (or when the callback was invoked	892	As soon as the callback is invoked (or when the callback was invoked
493	before "rouse_wait"), it will return the arguments originally passed	893	before "rouse_wait"), it will return the arguments originally passed
494	to the rouse callback.	894	to the rouse callback. In scalar context, that means you get the
		895	last argument, just as if "rouse_wait" had a "return ($a1, $a2,
		896	$a3...)" statement at the end.
495		897
496	See the section HOW TO WAIT FOR A CALLBACK for an actual usage	898	See the section HOW TO WAIT FOR A CALLBACK for an actual usage
497	example.	899	example.
498		900
499	HOW TO WAIT FOR A CALLBACK	901	HOW TO WAIT FOR A CALLBACK
…		…
513	But from within a coro, you often just want to write this:	915	But from within a coro, you often just want to write this:
514		916
515	my $status = wait_for_child $pid;	917	my $status = wait_for_child $pid;
516		918
517	Coro offers two functions specifically designed to make this easy,	919	Coro offers two functions specifically designed to make this easy,
518	"Coro::rouse_cb" and "Coro::rouse_wait".	920	"rouse_cb" and "rouse_wait".
519		921
520	The first function, "rouse_cb", generates and returns a callback that,	922	The first function, "rouse_cb", generates and returns a callback that,
521	when invoked, will save its arguments and notify the coro that created	923	when invoked, will save its arguments and notify the coro that created
522	the callback.	924	the callback.
523		925
…		…
529	function mentioned above:	931	function mentioned above:
530		932
531	sub wait_for_child($) {	933	sub wait_for_child($) {
532	my ($pid) = @_;	934	my ($pid) = @_;
533		935
534	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);	936	my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb);
535		937
536	my ($rpid, $rstatus) = Coro::rouse_wait;	938	my ($rpid, $rstatus) = rouse_wait;
537	$rstatus	939	$rstatus
538	}	940	}
539		941
540	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,	942	In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
541	you can roll your own, using "schedule":	943	you can roll your own, using "schedule" and "ready":
542		944
543	sub wait_for_child($) {	945	sub wait_for_child($) {
544	my ($pid) = @_;	946	my ($pid) = @_;
545		947
546	# store the current coro in $current,	948	# store the current coro in $current,
…		…
549	my ($done, $rstatus);	951	my ($done, $rstatus);
550		952
551	# pass a closure to ->child	953	# pass a closure to ->child
552	my $watcher = AnyEvent->child (pid => $pid, cb => sub {	954	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
553	$rstatus = $_[1]; # remember rstatus	955	$rstatus = $_[1]; # remember rstatus
554	$done = 1; # mark $rstatus as valud	956	$done = 1; # mark $rstatus as valid
		957	$current->ready; # wake up the waiting thread
555	});	958	});
556		959
557	# wait until the closure has been called	960	# wait until the closure has been called
558	schedule while !$done;	961	schedule while !$done;
559		962
…		…
573	in the future to allow per-thread schedulers, but Coro::State does	976	in the future to allow per-thread schedulers, but Coro::State does
574	not yet allow this). I recommend disabling thread support and using	977	not yet allow this). I recommend disabling thread support and using
575	processes, as having the windows process emulation enabled under	978	processes, as having the windows process emulation enabled under
576	unix roughly halves perl performance, even when not used.	979	unix roughly halves perl performance, even when not used.
577		980
		981	Attempts to use threads created in another emulated process will
		982	crash ("cleanly", with a null pointer exception).
		983
578	coro switching is not signal safe	984	coro switching is not signal safe
579	You must not switch to another coro from within a signal handler	985	You must not switch to another coro from within a signal handler
580	(only relevant with %SIG - most event libraries provide safe	986	(only relevant with %SIG - most event libraries provide safe
581	signals).	987	signals), unless you are sure you are not interrupting a Coro
		988	function.
582		989
583	That means you MUST NOT call any function that might "block" the	990	That means you MUST NOT call any function that might "block" the
584	current coro - "cede", "schedule" "Coro::Semaphore->down" or	991	current coro - "cede", "schedule" "Coro::Semaphore->down" or
585	anything that calls those. Everything else, including calling	992	anything that calls those. Everything else, including calling
586	"ready", works.	993	"ready", works.
587		994
		995	WINDOWS PROCESS EMULATION
		996	A great many people seem to be confused about ithreads (for example,
		997	Chip Salzenberg called me unintelligent, incapable, stupid and gullible,
		998	while in the same mail making rather confused statements about perl
		999	ithreads (for example, that memory or files would be shared), showing
		1000	his lack of understanding of this area - if it is hard to understand for
		1001	Chip, it is probably not obvious to everybody).
		1002
		1003	What follows is an ultra-condensed version of my talk about threads in
		1004	scripting languages given on the perl workshop 2009:
		1005
		1006	The so-called "ithreads" were originally implemented for two reasons:
		1007	first, to (badly) emulate unix processes on native win32 perls, and
		1008	secondly, to replace the older, real thread model ("5.005-threads").
		1009
		1010	It does that by using threads instead of OS processes. The difference
		1011	between processes and threads is that threads share memory (and other
		1012	state, such as files) between threads within a single process, while
		1013	processes do not share anything (at least not semantically). That means
		1014	that modifications done by one thread are seen by others, while
		1015	modifications by one process are not seen by other processes.
		1016
		1017	The "ithreads" work exactly like that: when creating a new ithreads
		1018	process, all state is copied (memory is copied physically, files and
		1019	code is copied logically). Afterwards, it isolates all modifications. On
		1020	UNIX, the same behaviour can be achieved by using operating system
		1021	processes, except that UNIX typically uses hardware built into the
		1022	system to do this efficiently, while the windows process emulation
		1023	emulates this hardware in software (rather efficiently, but of course it
		1024	is still much slower than dedicated hardware).
		1025
		1026	As mentioned before, loading code, modifying code, modifying data
		1027	structures and so on is only visible in the ithreads process doing the
		1028	modification, not in other ithread processes within the same OS process.
		1029
		1030	This is why "ithreads" do not implement threads for perl at all, only
		1031	processes. What makes it so bad is that on non-windows platforms, you
		1032	can actually take advantage of custom hardware for this purpose (as
		1033	evidenced by the forks module, which gives you the (i-) threads API,
		1034	just much faster).
		1035
		1036	Sharing data is in the i-threads model is done by transfering data
		1037	structures between threads using copying semantics, which is very slow -
		1038	shared data simply does not exist. Benchmarks using i-threads which are
		1039	communication-intensive show extremely bad behaviour with i-threads (in
		1040	fact, so bad that Coro, which cannot take direct advantage of multiple
		1041	CPUs, is often orders of magnitude faster because it shares data using
		1042	real threads, refer to my talk for details).
		1043
		1044	As summary, i-threads use threads to implement processes, while the
		1045	compatible forks module uses processes to emulate, uhm, processes.
		1046	I-threads slow down every perl program when enabled, and outside of
		1047	windows, serve no (or little) practical purpose, but disadvantages every
		1048	single-threaded Perl program.
		1049
		1050	This is the reason that I try to avoid the name "ithreads", as it is
		1051	misleading as it implies that it implements some kind of thread model
		1052	for perl, and prefer the name "windows process emulation", which
		1053	describes the actual use and behaviour of it much better.
		1054
588	SEE ALSO	1055	SEE ALSO
589	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.	1056	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
590		1057
591	Debugging: Coro::Debug.	1058	Debugging: Coro::Debug.
592		1059

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Revision 1.22 by root, Mon Mar 16 22:22:12 2009 UTC vs.
Revision 1.32 by root, Wed Mar 6 06:00:08 2013 UTC