[ViewVC] Diff of: cvs/cvsroot/Coro/Coro.pm

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.248 by root, Mon Dec 15 15:03:31 2008 UTC vs.
Revision 1.297 by root, Thu May 12 23:55:39 2011 UTC

…		…
40	points in your program, so locking and parallel access are rarely an	40	points in your program, so locking and parallel access are rarely an
41	issue, making thread programming much safer and easier than using other	41	issue, making thread programming much safer and easier than using other
42	thread models.	42	thread models.
43		43
44	Unlike the so-called "Perl threads" (which are not actually real threads	44	Unlike the so-called "Perl threads" (which are not actually real threads
45	but only the windows process emulation ported to unix), Coro provides a	45	but only the windows process emulation (see section of same name for
		46	more details) ported to UNIX, and as such act as processes), Coro
46	full shared address space, which makes communication between threads	47	provides a full shared address space, which makes communication between
47	very easy. And threads are fast, too: disabling the Windows process	48	threads very easy. And coro threads are fast, too: disabling the Windows
48	emulation code in your perl and using Coro can easily result in a two to	49	process emulation code in your perl and using Coro can easily result in
49	four times speed increase for your programs.	50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark (very communication-intensive) runs over 300
		52	times faster on a single core than perls pseudo-threads on a quad core
		53	using all four cores.
50		54
51	Coro achieves that by supporting multiple running interpreters that share	55	Coro achieves that by supporting multiple running interpreters that share
52	data, which is especially useful to code pseudo-parallel processes and	56	data, which is especially useful to code pseudo-parallel processes and
53	for event-based programming, such as multiple HTTP-GET requests running	57	for event-based programming, such as multiple HTTP-GET requests running
54	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro	58	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
55	into an event-based environment.	59	into an event-based environment.
56		60
57	In this module, a thread is defined as "callchain + lexical variables +	61	In this module, a thread is defined as "callchain + lexical variables +
58	@_ + $_ + $@ + $/ + C stack), that is, a thread has its own callchain,	62	some package variables + C stack), that is, a thread has its own callchain,
59	its own set of lexicals and its own set of perls most important global	63	its own set of lexicals and its own set of perls most important global
60	variables (see L<Coro::State> for more configuration and background info).	64	variables (see L<Coro::State> for more configuration and background info).
61		65
62	See also the C<SEE ALSO> section at the end of this document - the Coro	66	See also the C<SEE ALSO> section at the end of this document - the Coro
63	module family is quite large.	67	module family is quite large.
64		68
		69	=head1 CORO THREAD LIFE CYCLE
		70
		71	During the long and exciting (or not) life of a coro thread, it goes
		72	through a number of states:
		73
		74	=over 4
		75
		76	=item 1. Creation
		77
		78	The first thing in the life of a coro thread is it's creation -
		79	obviously. The typical way to create a thread is to call the C<async
		80	BLOCK> function:
		81
		82	async {
		83	# thread code goes here
		84	};
		85
		86	You can also pass arguments, which are put in C<@_>:
		87
		88	async {
		89	print $_[1]; # prints 2
		90	} 1, 2, 3;
		91
		92	This creates a new coro thread and puts it into the ready queue, meaning
		93	it will run as soon as the CPU is free for it.
		94
		95	C<async> will return a Coro object - you can store this for future
		96	reference or ignore it - a thread that is running, ready to run or waiting
		97	for some event is alive on it's own.
		98
		99	Another way to create a thread is to call the C<new> constructor with a
		100	code-reference:
		101
		102	new Coro sub {
		103	# thread code goes here
		104	}, @optional_arguments;
		105
		106	This is quite similar to calling C<async>, but the important difference is
		107	that the new thread is not put into the ready queue, so the thread will
		108	not run until somebody puts it there. C<async> is, therefore, identical to
		109	this sequence:
		110
		111	my $coro = new Coro sub {
		112	# thread code goes here
		113	};
		114	$coro->ready;
		115	return $coro;
		116
		117	=item 2. Startup
		118
		119	When a new coro thread is created, only a copy of the code reference
		120	and the arguments are stored, no extra memory for stacks and so on is
		121	allocated, keeping the coro thread in a low-memory state.
		122
		123	Only when it actually starts executing will all the resources be finally
		124	allocated.
		125
		126	The optional arguments specified at coro creation are available in C<@_>,
		127	similar to function calls.
		128
		129	=item 3. Running / Blocking
		130
		131	A lot can happen after the coro thread has started running. Quite usually,
		132	it will not run to the end in one go (because you could use a function
		133	instead), but it will give up the CPU regularly because it waits for
		134	external events.
		135
		136	As long as a coro thread runs, its Coro object is available in the global
		137	variable C<$Coro::current>.
		138
		139	The low-level way to give up the CPU is to call the scheduler, which
		140	selects a new coro thread to run:
		141
		142	Coro::schedule;
		143
		144	Since running threads are not in the ready queue, calling the scheduler
		145	without doing anything else will block the coro thread forever - you need
		146	to arrange either for the coro to put woken up (readied) by some other
		147	event or some other thread, or you can put it into the ready queue before
		148	scheduling:
		149
		150	# this is exactly what Coro::cede does
		151	$Coro::current->ready;
		152	Coro::schedule;
		153
		154	All the higher-level synchronisation methods (Coro::Semaphore,
		155	Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
		156	Coro::schedule >>.
		157
		158	While the coro thread is running it also might get assigned a C-level
		159	thread, or the C-level thread might be unassigned from it, as the Coro
		160	runtime wishes. A C-level thread needs to be assigned when your perl
		161	thread calls into some C-level function and that function in turn calls
		162	perl and perl then wants to switch coroutines. This happens most often
		163	when you run an event loop and block in the callback, or when perl
		164	itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
		165	mechanism.
		166
		167	=item 4. Termination
		168
		169	Many threads actually terminate after some time. There are a number of
		170	ways to terminate a coro thread, the simplest is returning from the
		171	top-level code reference:
		172
		173	async {
		174	# after returning from here, the coro thread is terminated
		175	};
		176
		177	async {
		178	return if 0.5 < rand; # terminate a little earlier, maybe
		179	print "got a chance to print this\n";
		180	# or here
		181	};
		182
		183	Any values returned from the coroutine can be recovered using C<< ->join
		184	>>:
		185
		186	my $coro = async {
		187	"hello, world\n" # return a string
		188	};
		189
		190	my $hello_world = $coro->join;
		191
		192	print $hello_world;
		193
		194	Another way to terminate is to call C<< Coro::terminate >>, which at any
		195	subroutine call nesting level:
		196
		197	async {
		198	Coro::terminate "return value 1", "return value 2";
		199	};
		200
		201	And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
		202	coro thread from another thread:
		203
		204	my $coro = async {
		205	exit 1;
		206	};
		207
		208	$coro->cancel; # also accepts values for ->join to retrieve
		209
		210	Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
		211	actually exiting, and might leave C libraries and XS modules in a weird
		212	state. Unlike other thread implementations, however, Coro is exceptionally
		213	safe with regards to cancellation, as perl will always be in a consistent
		214	state, and for those cases where you want to do truly marvellous things
		215	with your coro while it is being cancelled - that is, make sure all
		216	cleanup code is executed from the thread being cancelled - there is even a
		217	C<< ->safe_cancel >> method.
		218
		219	So, cancelling a thread that runs in an XS event loop might not be the
		220	best idea, but any other combination that deals with perl only (cancelling
		221	when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
		222	safe.
		223
		224	Lastly, a coro thread object that isn't referenced is C<< ->cancel >>'ed
		225	automatically - just like other objects in Perl. This is not such a common
		226	case, however - a running thread is referencedy b C<$Coro::current>, a
		227	thread ready to run is referenced by the ready queue, a thread waiting
		228	on a lock or semaphore is referenced by being in some wait list and so
		229	on. But a thread that isn't in any of those queues gets cancelled:
		230
		231	async {
		232	schedule; # cede to other coros, don't go into the ready queue
		233	};
		234
		235	cede;
		236	# now the async above is destroyed, as it is not referenced by anything.
		237
		238	=item 5. Cleanup
		239
		240	Threads will allocate various resources. Most but not all will be returned
		241	when a thread terminates, during clean-up.
		242
		243	Cleanup is quite similar to throwing an uncaught exception: perl will
		244	work it's way up through all subroutine calls and blocks. On it's way, it
		245	will release all C<my> variables, undo all C<local>'s and free any other
		246	resources truly local to the thread.
		247
		248	So, a common way to free resources is to keep them referenced only by my
		249	variables:
		250
		251	async {
		252	my $big_cache = new Cache ...;
		253	};
		254
		255	If there are no other references, then the C<$big_cache> object will be
		256	freed when the thread terminates, regardless of how it does so.
		257
		258	What it does C<NOT> do is unlock any Coro::Semaphores or similar
		259	resources, but that's where the C<guard> methods come in handy:
		260
		261	my $sem = new Coro::Semaphore;
		262
		263	async {
		264	my $lock_guard = $sem->guard;
		265	# if we reutrn, or die or get cancelled, here,
		266	# then the semaphore will be "up"ed.
		267	};
		268
		269	The C<Guard::guard> function comes in handy for any custom cleanup you
		270	might want to do (but you cannot switch to other coroutines form those
		271	code blocks):
		272
		273	async {
		274	my $window = new Gtk2::Window "toplevel";
		275	# The window will not be cleaned up automatically, even when $window
		276	# gets freed, so use a guard to ensure it's destruction
		277	# in case of an error:
		278	my $window_guard = Guard::guard { $window->destroy };
		279
		280	# we are safe here
		281	};
		282
		283	Last not least, C<local> can often be handy, too, e.g. when temporarily
		284	replacing the coro thread description:
		285
		286	sub myfunction {
		287	local $Coro::current->{desc} = "inside myfunction(@_)";
		288
		289	# if we return or die here, the description will be restored
		290	}
		291
		292	=item 6. Viva La Zombie Muerte
		293
		294	Even after a thread has terminated and cleaned up its resources, the Coro
		295	object still is there and stores the return values of the thread.
		296
		297	The means the Coro object gets freed automatically when the thread has
		298	terminated and cleaned up and there arenot other references.
		299
		300	If there are, the Coro object will stay around, and you can call C<<
		301	->join >> as many times as you wish to retrieve the result values:
		302
		303	async {
		304	print "hi\n";
		305	1
		306	};
		307
		308	# run the async above, and free everything before returning
		309	# from Coro::cede:
		310	Coro::cede;
		311
		312	{
		313	my $coro = async {
		314	print "hi\n";
		315	1
		316	};
		317
		318	# run the async above, and clean up, but do not free the coro
		319	# object:
		320	Coro::cede;
		321
		322	# optionally retrieve the result values
		323	my @results = $coro->join;
		324
		325	# now $coro goes out of scope, and presumably gets freed
		326	};
		327
		328	=back
		329
65	=cut	330	=cut
66		331
67	package Coro;	332	package Coro;
68		333
69	use strict qw(vars subs);	334	use common::sense;
70	no warnings "uninitialized";	335
		336	use Carp ();
71		337
72	use Guard ();	338	use Guard ();
73		339
74	use Coro::State;	340	use Coro::State;
75		341
…		…
77		343
78	our $idle; # idle handler	344	our $idle; # idle handler
79	our $main; # main coro	345	our $main; # main coro
80	our $current; # current coro	346	our $current; # current coro
81		347
82	our $VERSION = 5.13;	348	our $VERSION = 5.372;
83		349
84	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	350	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
85	our %EXPORT_TAGS = (	351	our %EXPORT_TAGS = (
86	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	352	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
87	);	353	);
88	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	354	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
89		355
…		…
120		386
121	This variable is mainly useful to integrate Coro into event loops. It is	387	This variable is mainly useful to integrate Coro into event loops. It is
122	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is	388	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
123	pretty low-level functionality.	389	pretty low-level functionality.
124		390
125	This variable stores either a Coro object or a callback.	391	This variable stores a Coro object that is put into the ready queue when
		392	there are no other ready threads (without invoking any ready hooks).
126		393
127	If it is a callback, the it is called whenever the scheduler finds no	394	The default implementation dies with "FATAL: deadlock detected.", followed
128	ready coros to run. The default implementation prints "FATAL:	395	by a thread listing, because the program has no other way to continue.
129	deadlock detected" and exits, because the program has no other way to
130	continue.
131
132	If it is a coro object, then this object will be readied (without
133	invoking any ready hooks, however) when the scheduler finds no other ready
134	coros to run.
135		396
136	This hook is overwritten by modules such as C<Coro::EV> and	397	This hook is overwritten by modules such as C<Coro::EV> and
137	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	398	C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
138	coro so the scheduler can run it.	399	coro so the scheduler can run it.
139		400
140	Note that the callback I<must not>, under any circumstances, block
141	the current coro. Normally, this is achieved by having an "idle
142	coro" that calls the event loop and then blocks again, and then
143	readying that coro in the idle handler, or by simply placing the idle
144	coro in this variable.
145
146	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this	401	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
147	technique.
148
149	Please note that if your callback recursively invokes perl (e.g. for event
150	handlers), then it must be prepared to be called recursively itself.
151		402
152	=cut	403	=cut
153		404
154	$idle = sub {	405	# \|\|= because other modules could have provided their own by now
155	require Carp;	406	$idle \|\|= new Coro sub {
156	Carp::croak ("FATAL: deadlock detected");	407	require Coro::Debug;
		408	die "FATAL: deadlock detected.\n"
		409	. Coro::Debug::ps_listing ();
157	};	410	};
158		411
159	# this coro is necessary because a coro	412	# this coro is necessary because a coro
160	# cannot destroy itself.	413	# cannot destroy itself.
161	our @destroy;	414	our @destroy;
162	our $manager;	415	our $manager;
163		416
164	$manager = new Coro sub {	417	$manager = new Coro sub {
165	while () {	418	while () {
166	Coro::State::cancel shift @destroy	419	_destroy shift @destroy
167	while @destroy;	420	while @destroy;
168		421
169	&schedule;	422	&schedule;
170	}	423	}
171	};	424	};
…		…
203	Example: Create a new coro that just prints its arguments.	456	Example: Create a new coro that just prints its arguments.
204		457
205	async {	458	async {
206	print "@_\n";	459	print "@_\n";
207	} 1,2,3,4;	460	} 1,2,3,4;
208
209	=cut
210
211	sub async(&@) {
212	my $coro = new Coro @_;
213	$coro->ready;
214	$coro
215	}
216		461
217	=item async_pool { ... } [@args...]	462	=item async_pool { ... } [@args...]
218		463
219	Similar to C<async>, but uses a coro pool, so you should not call	464	Similar to C<async>, but uses a coro pool, so you should not call
220	terminate or join on it (although you are allowed to), and you get a	465	terminate or join on it (although you are allowed to), and you get a
…		…
277	=item schedule	522	=item schedule
278		523
279	Calls the scheduler. The scheduler will find the next coro that is	524	Calls the scheduler. The scheduler will find the next coro that is
280	to be run from the ready queue and switches to it. The next coro	525	to be run from the ready queue and switches to it. The next coro
281	to be run is simply the one with the highest priority that is longest	526	to be run is simply the one with the highest priority that is longest
282	in its ready queue. If there is no coro ready, it will clal the	527	in its ready queue. If there is no coro ready, it will call the
283	C<$Coro::idle> hook.	528	C<$Coro::idle> hook.
284		529
285	Please note that the current coro will I<not> be put into the ready	530	Please note that the current coro will I<not> be put into the ready
286	queue, so calling this function usually means you will never be called	531	queue, so calling this function usually means you will never be called
287	again unless something else (e.g. an event handler) calls C<< ->ready >>,	532	again unless something else (e.g. an event handler) calls C<< ->ready >>,
…		…
313	coro, regardless of priority. This is useful sometimes to ensure	558	coro, regardless of priority. This is useful sometimes to ensure
314	progress is made.	559	progress is made.
315		560
316	=item terminate [arg...]	561	=item terminate [arg...]
317		562
318	Terminates the current coro with the given status values (see L<cancel>).	563	Terminates the current coro with the given status values (see
		564	L<cancel>). The values will not be copied, but referenced directly.
319		565
320	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK	566	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
321		567
322	These function install enter and leave winders in the current scope. The	568	These function install enter and leave winders in the current scope. The
323	enter block will be executed when on_enter is called and whenever the	569	enter block will be executed when on_enter is called and whenever the
…		…
335		581
336	These functions implement the same concept as C<dynamic-wind> in scheme	582	These functions implement the same concept as C<dynamic-wind> in scheme
337	does, and are useful when you want to localise some resource to a specific	583	does, and are useful when you want to localise some resource to a specific
338	coro.	584	coro.
339		585
340	They slow down coro switching considerably for coros that use	586	They slow down thread switching considerably for coros that use them
341	them (But coro switching is still reasonably fast if the handlers are	587	(about 40% for a BLOCK with a single assignment, so thread switching is
342	fast).	588	still reasonably fast if the handlers are fast).
343		589
344	These functions are best understood by an example: The following function	590	These functions are best understood by an example: The following function
345	will change the current timezone to "Antarctica/South_Pole", which	591	will change the current timezone to "Antarctica/South_Pole", which
346	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,	592	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
347	which remember/change the current timezone and restore the previous	593	which remember/change the current timezone and restore the previous
348	value, respectively, the timezone is only changes for the coro that	594	value, respectively, the timezone is only changed for the coro that
349	installed those handlers.	595	installed those handlers.
350		596
351	use POSIX qw(tzset);	597	use POSIX qw(tzset);
352		598
353	async {	599	async {
…		…
370	};	616	};
371		617
372	This can be used to localise about any resource (locale, uid, current	618	This can be used to localise about any resource (locale, uid, current
373	working directory etc.) to a block, despite the existance of other	619	working directory etc.) to a block, despite the existance of other
374	coros.	620	coros.
		621
		622	Another interesting example implements time-sliced multitasking using
		623	interval timers (this could obviously be optimised, but does the job):
		624
		625	# "timeslice" the given block
		626	sub timeslice(&) {
		627	use Time::HiRes ();
		628
		629	Coro::on_enter {
		630	# on entering the thread, we set an VTALRM handler to cede
		631	$SIG{VTALRM} = sub { cede };
		632	# and then start the interval timer
		633	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		634	};
		635	Coro::on_leave {
		636	# on leaving the thread, we stop the interval timer again
		637	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		638	};
		639
		640	&{+shift};
		641	}
		642
		643	# use like this:
		644	timeslice {
		645	# The following is an endless loop that would normally
		646	# monopolise the process. Since it runs in a timesliced
		647	# environment, it will regularly cede to other threads.
		648	while () { }
		649	};
		650
375		651
376	=item killall	652	=item killall
377		653
378	Kills/terminates/cancels all coros except the currently running one.	654	Kills/terminates/cancels all coros except the currently running one.
379		655
…		…
424		700
425	This ensures that the scheduler will resume this coro automatically	701	This ensures that the scheduler will resume this coro automatically
426	once all the coro of higher priority and all coro of the same	702	once all the coro of higher priority and all coro of the same
427	priority that were put into the ready queue earlier have been resumed.	703	priority that were put into the ready queue earlier have been resumed.
428		704
		705	=item $coro->suspend
		706
		707	Suspends the specified coro. A suspended coro works just like any other
		708	coro, except that the scheduler will not select a suspended coro for
		709	execution.
		710
		711	Suspending a coro can be useful when you want to keep the coro from
		712	running, but you don't want to destroy it, or when you want to temporarily
		713	freeze a coro (e.g. for debugging) to resume it later.
		714
		715	A scenario for the former would be to suspend all (other) coros after a
		716	fork and keep them alive, so their destructors aren't called, but new
		717	coros can be created.
		718
		719	=item $coro->resume
		720
		721	If the specified coro was suspended, it will be resumed. Note that when
		722	the coro was in the ready queue when it was suspended, it might have been
		723	unreadied by the scheduler, so an activation might have been lost.
		724
		725	To avoid this, it is best to put a suspended coro into the ready queue
		726	unconditionally, as every synchronisation mechanism must protect itself
		727	against spurious wakeups, and the one in the Coro family certainly do
		728	that.
		729
		730	=item $state->is_new
		731
		732	Returns true iff this Coro object is "new", i.e. has never been run
		733	yet. Those states basically consist of only the code reference to call and
		734	the arguments, but consumes very little other resources. New states will
		735	automatically get assigned a perl interpreter when they are transfered to.
		736
		737	=item $state->is_zombie
		738
		739	Returns true iff the Coro object has been cancelled, i.e.
		740	it's resources freed because they were C<cancel>'ed, C<terminate>'d,
		741	C<safe_cancel>'ed or simply went out of scope.
		742
		743	The name "zombie" stems from UNIX culture, where a process that has
		744	exited and only stores and exit status and no other resources is called a
		745	"zombie".
		746
429	=item $is_ready = $coro->is_ready	747	=item $is_ready = $coro->is_ready
430		748
431	Returns true iff the Coro object is in the ready queue. Unless the Coro	749	Returns true iff the Coro object is in the ready queue. Unless the Coro
432	object gets destroyed, it will eventually be scheduled by the scheduler.	750	object gets destroyed, it will eventually be scheduled by the scheduler.
433		751
…		…
442	Returns true iff this Coro object has been suspended. Suspended Coros will	760	Returns true iff this Coro object has been suspended. Suspended Coros will
443	not ever be scheduled.	761	not ever be scheduled.
444		762
445	=item $coro->cancel (arg...)	763	=item $coro->cancel (arg...)
446		764
447	Terminates the given Coro and makes it return the given arguments as	765	Terminates the given Coro thread and makes it return the given arguments as
448	status (default: the empty list). Never returns if the Coro is the	766	status (default: an empty list). Never returns if the Coro is the
449	current Coro.	767	current Coro.
450		768
451	=cut	769	This is a rather brutal way to free a coro, with some limitations - if
		770	the thread is inside a C callback that doesn't expect to be canceled,
		771	bad things can happen, or if the cancelled thread insists on running
		772	complicated cleanup handlers that rely on it'S thread context, things will
		773	not work.
452		774
453	sub cancel {	775	Any cleanup code being run (e.g. from C<guard> blocks) will be run without
454	my $self = shift;	776	a thread context, and is not allowed to switch to other threads. On the
		777	plus side, C<< ->cancel >> will always clean up the thread, no matter
		778	what. If your cleanup code is complex or you want to avoid cancelling a
		779	C-thread that doesn't know how to clean up itself, it can be better to C<<
		780	->throw >> an exception, or use C<< ->safe_cancel >>.
455		781
456	if ($current == $self) {	782	The arguments to C<< ->cancel >> are not copied, but instead will
457	terminate @_;	783	be referenced directly (e.g. if you pass C<$var> and after the call
458	} else {	784	change that variable, then you might change the return values passed to
459	$self->{_status} = [@_];	785	e.g. C<join>, so don't do that).
460	Coro::State::cancel $self;	786
		787	The resources of the Coro are usually freed (or destructed) before this
		788	call returns, but this can be delayed for an indefinite amount of time, as
		789	in some cases the manager thread has to run first to actually destruct the
		790	Coro object.
		791
		792	=item $coro->safe_cancel ($arg...)
		793
		794	Works mostly like C<< ->cancel >>, but is inherently "safer", and
		795	consequently, can fail with an exception in cases the thread is not in a
		796	cancellable state.
		797
		798	This method works a bit like throwing an exception that cannot be caught
		799	- specifically, it will clean up the thread from within itself, so
		800	all cleanup handlers (e.g. C<guard> blocks) are run with full thread
		801	context and can block if they wish. The downside is that there is no
		802	guarantee that the thread can be cancelled when you call this method, and
		803	therefore, it might fail. It is also considerably slower than C<cancel> or
		804	C<terminate>.
		805
		806	A thread is in a safe-cancellable state if it either hasn't been run yet,
		807	or it has no C context attached and is inside an SLF function.
		808
		809	The latter two basically mean that the thread isn't currently inside a
		810	perl callback called from some C function (usually via some XS modules)
		811	and isn't currently executing inside some C function itself (via Coro's XS
		812	API).
		813
		814	This call returns true when it could cancel the thread, or croaks with an
		815	error otherwise (i.e. it either returns true or doesn't return at all).
		816
		817	Why the weird interface? Well, there are two common models on how and
		818	when to cancel things. In the first, you have the expectation that your
		819	coro thread can be cancelled when you want to cancel it - if the thread
		820	isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
		821	croaks to notify of the bug.
		822
		823	In the second model you sometimes want to ask nicely to cancel a thread,
		824	but if it's not a good time, well, then don't cancel. This can be done
		825	relatively easy like this:
		826
		827	if (! eval { $coro->safe_cancel }) {
		828	warn "unable to cancel thread: $@";
461	}	829	}
462	}	830
		831	However, what you never should do is first try to cancel "safely" and
		832	if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
		833	no sense: either you rely on being able to execute cleanup code in your
		834	thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
		835	only way, and if you don't, then C<< ->cancel >> is always faster and more
		836	direct.
463		837
464	=item $coro->schedule_to	838	=item $coro->schedule_to
465		839
466	Puts the current coro to sleep (like C<Coro::schedule>), but instead	840	Puts the current coro to sleep (like C<Coro::schedule>), but instead
467	of continuing with the next coro from the ready queue, always switch to	841	of continuing with the next coro from the ready queue, always switch to
…		…
486	inside the coro at the next convenient point in time. Otherwise	860	inside the coro at the next convenient point in time. Otherwise
487	clears the exception object.	861	clears the exception object.
488		862
489	Coro will check for the exception each time a schedule-like-function	863	Coro will check for the exception each time a schedule-like-function
490	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down	864	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
491	>>, C<< Coro::Handle->readable >> and so on. Most of these functions	865	>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
492	detect this case and return early in case an exception is pending.	866	that are part of Coro itself) detect this case and return early in case an
		867	exception is pending.
493		868
494	The exception object will be thrown "as is" with the specified scalar in	869	The exception object will be thrown "as is" with the specified scalar in
495	C<$@>, i.e. if it is a string, no line number or newline will be appended	870	C<$@>, i.e. if it is a string, no line number or newline will be appended
496	(unlike with C<die>).	871	(unlike with C<die>).
497		872
498	This can be used as a softer means than C<cancel> to ask a coro to	873	This can be used as a softer means than either C<cancel> or C<safe_cancel
499	end itself, although there is no guarantee that the exception will lead to	874	>to ask a coro to end itself, although there is no guarantee that the
500	termination, and if the exception isn't caught it might well end the whole	875	exception will lead to termination, and if the exception isn't caught it
501	program.	876	might well end the whole program.
502		877
503	You might also think of C<throw> as being the moral equivalent of	878	You might also think of C<throw> as being the moral equivalent of
504	C<kill>ing a coro with a signal (in this case, a scalar).	879	C<kill>ing a coro with a signal (in this case, a scalar).
505		880
506	=item $coro->join	881	=item $coro->join
507		882
508	Wait until the coro terminates and return any values given to the	883	Wait until the coro terminates and return any values given to the
509	C<terminate> or C<cancel> functions. C<join> can be called concurrently	884	C<terminate> or C<cancel> functions. C<join> can be called concurrently
510	from multiple coro, and all will be resumed and given the status	885	from multiple threads, and all will be resumed and given the status
511	return once the C<$coro> terminates.	886	return once the C<$coro> terminates.
512		887
513	=cut
514
515	sub join {
516	my $self = shift;
517
518	unless ($self->{_status}) {
519	my $current = $current;
520
521	push @{$self->{_on_destroy}}, sub {
522	$current->ready;
523	undef $current;
524	};
525
526	&schedule while $current;
527	}
528
529	wantarray ? @{$self->{_status}} : $self->{_status}[0];
530	}
531
532	=item $coro->on_destroy (\&cb)	888	=item $coro->on_destroy (\&cb)
533		889
534	Registers a callback that is called when this coro gets destroyed,	890	Registers a callback that is called when this coro thread gets destroyed,
535	but before it is joined. The callback gets passed the terminate arguments,	891	that is, after it's resources have been freed but before it is joined. The
		892	callback gets passed the terminate/cancel arguments, if any, and I<must
536	if any, and I<must not> die, under any circumstances.	893	not> die, under any circumstances.
537		894
538	=cut	895	There can be any number of C<on_destroy> callbacks per coro, and there is
539		896	no way currently to remove a callback once added.
540	sub on_destroy {
541	my ($self, $cb) = @_;
542
543	push @{ $self->{_on_destroy} }, $cb;
544	}
545		897
546	=item $oldprio = $coro->prio ($newprio)	898	=item $oldprio = $coro->prio ($newprio)
547		899
548	Sets (or gets, if the argument is missing) the priority of the	900	Sets (or gets, if the argument is missing) the priority of the
549	coro. Higher priority coro get run before lower priority	901	coro thread. Higher priority coro get run before lower priority
550	coro. Priorities are small signed integers (currently -4 .. +3),	902	coros. Priorities are small signed integers (currently -4 .. +3),
551	that you can refer to using PRIO_xxx constants (use the import tag :prio	903	that you can refer to using PRIO_xxx constants (use the import tag :prio
552	to get then):	904	to get then):
553		905
554	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	906	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
555	3 > 1 > 0 > -1 > -3 > -4	907	3 > 1 > 0 > -1 > -3 > -4
556		908
557	# set priority to HIGH	909	# set priority to HIGH
558	current->prio (PRIO_HIGH);	910	current->prio (PRIO_HIGH);
559		911
560	The idle coro ($Coro::idle) always has a lower priority than any	912	The idle coro thread ($Coro::idle) always has a lower priority than any
561	existing coro.	913	existing coro.
562		914
563	Changing the priority of the current coro will take effect immediately,	915	Changing the priority of the current coro will take effect immediately,
564	but changing the priority of coro in the ready queue (but not	916	but changing the priority of a coro in the ready queue (but not running)
565	running) will only take effect after the next schedule (of that	917	will only take effect after the next schedule (of that coro). This is a
566	coro). This is a bug that will be fixed in some future version.	918	bug that will be fixed in some future version.
567		919
568	=item $newprio = $coro->nice ($change)	920	=item $newprio = $coro->nice ($change)
569		921
570	Similar to C<prio>, but subtract the given value from the priority (i.e.	922	Similar to C<prio>, but subtract the given value from the priority (i.e.
571	higher values mean lower priority, just as in unix).	923	higher values mean lower priority, just as in UNIX's nice command).
572		924
573	=item $olddesc = $coro->desc ($newdesc)	925	=item $olddesc = $coro->desc ($newdesc)
574		926
575	Sets (or gets in case the argument is missing) the description for this	927	Sets (or gets in case the argument is missing) the description for this
576	coro. This is just a free-form string you can associate with a	928	coro thread. This is just a free-form string you can associate with a
577	coro.	929	coro.
578		930
579	This method simply sets the C<< $coro->{desc} >> member to the given	931	This method simply sets the C<< $coro->{desc} >> member to the given
580	string. You can modify this member directly if you wish.	932	string. You can modify this member directly if you wish, and in fact, this
		933	is often preferred to indicate major processing states that cna then be
		934	seen for example in a L<Coro::Debug> session:
		935
		936	sub my_long_function {
		937	local $Coro::current->{desc} = "now in my_long_function";
		938	...
		939	$Coro::current->{desc} = "my_long_function: phase 1";
		940	...
		941	$Coro::current->{desc} = "my_long_function: phase 2";
		942	...
		943	}
581		944
582	=cut	945	=cut
583		946
584	sub desc {	947	sub desc {
585	my $old = $_[0]{desc};	948	my $old = $_[0]{desc};
…		…
622	returning a new coderef. Unblocking means that calling the new coderef	985	returning a new coderef. Unblocking means that calling the new coderef
623	will return immediately without blocking, returning nothing, while the	986	will return immediately without blocking, returning nothing, while the
624	original code ref will be called (with parameters) from within another	987	original code ref will be called (with parameters) from within another
625	coro.	988	coro.
626		989
627	The reason this function exists is that many event libraries (such as the	990	The reason this function exists is that many event libraries (such as
628	venerable L<Event\|Event> module) are not thread-safe (a weaker form	991	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
629	of reentrancy). This means you must not block within event callbacks,	992	of reentrancy). This means you must not block within event callbacks,
630	otherwise you might suffer from crashes or worse. The only event library	993	otherwise you might suffer from crashes or worse. The only event library
631	currently known that is safe to use without C<unblock_sub> is L<EV>.	994	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		995	you might still run into deadlocks if all event loops are blocked).
		996
		997	Coro will try to catch you when you block in the event loop
		998	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		999	only works when you do not run your own event loop.
632		1000
633	This function allows your callbacks to block by executing them in another	1001	This function allows your callbacks to block by executing them in another
634	coro where it is safe to block. One example where blocking is handy	1002	coro where it is safe to block. One example where blocking is handy
635	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	1003	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
636	disk, for example.	1004	disk, for example.
…		…
678	unshift @unblock_queue, [$cb, @_];	1046	unshift @unblock_queue, [$cb, @_];
679	$unblock_scheduler->ready;	1047	$unblock_scheduler->ready;
680	}	1048	}
681	}	1049	}
682		1050
683	=item $cb = Coro::rouse_cb	1051	=item $cb = rouse_cb
684		1052
685	Create and return a "rouse callback". That's a code reference that,	1053	Create and return a "rouse callback". That's a code reference that,
686	when called, will remember a copy of its arguments and notify the owner	1054	when called, will remember a copy of its arguments and notify the owner
687	coro of the callback.	1055	coro of the callback.
688		1056
689	See the next function.	1057	See the next function.
690		1058
691	=item @args = Coro::rouse_wait [$cb]	1059	=item @args = rouse_wait [$cb]
692		1060
693	Wait for the specified rouse callback (or the last one that was created in	1061	Wait for the specified rouse callback (or the last one that was created in
694	this coro).	1062	this coro).
695		1063
696	As soon as the callback is invoked (or when the callback was invoked	1064	As soon as the callback is invoked (or when the callback was invoked
697	before C<rouse_wait>), it will return the arguments originally passed to	1065	before C<rouse_wait>), it will return the arguments originally passed to
698	the rouse callback.	1066	the rouse callback. In scalar context, that means you get the I<last>
		1067	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		1068	statement at the end.
699		1069
700	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	1070	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
701		1071
702	=back	1072	=back
703		1073
704	=cut	1074	=cut
		1075
		1076	for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
		1077	my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
		1078
		1079	*{"Coro::$module\::new"} = sub {
		1080	require "Coro/$module.pm";
		1081
		1082	# some modules have their new predefined in State.xs, some don't
		1083	*{"Coro::$module\::new"} = $old
		1084	if $old;
		1085
		1086	goto &{"Coro::$module\::new"};
		1087	};
		1088	}
705		1089
706	1;	1090	1;
707		1091
708	=head1 HOW TO WAIT FOR A CALLBACK	1092	=head1 HOW TO WAIT FOR A CALLBACK
709		1093
…		…
789	future to allow per-thread schedulers, but Coro::State does not yet allow	1173	future to allow per-thread schedulers, but Coro::State does not yet allow
790	this). I recommend disabling thread support and using processes, as having	1174	this). I recommend disabling thread support and using processes, as having
791	the windows process emulation enabled under unix roughly halves perl	1175	the windows process emulation enabled under unix roughly halves perl
792	performance, even when not used.	1176	performance, even when not used.
793		1177
		1178	Attempts to use threads created in another emulated process will crash
		1179	("cleanly", with a null pointer exception).
		1180
794	=item coro switching is not signal safe	1181	=item coro switching is not signal safe
795		1182
796	You must not switch to another coro from within a signal handler	1183	You must not switch to another coro from within a signal handler (only
797	(only relevant with %SIG - most event libraries provide safe signals).	1184	relevant with %SIG - most event libraries provide safe signals), I<unless>
		1185	you are sure you are not interrupting a Coro function.
798		1186
799	That means you I<MUST NOT> call any function that might "block" the	1187	That means you I<MUST NOT> call any function that might "block" the
800	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	1188	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
801	anything that calls those. Everything else, including calling C<ready>,	1189	anything that calls those. Everything else, including calling C<ready>,
802	works.	1190	works.
803		1191
804	=back	1192	=back
805		1193
806		1194
		1195	=head1 WINDOWS PROCESS EMULATION
		1196
		1197	A great many people seem to be confused about ithreads (for example, Chip
		1198	Salzenberg called me unintelligent, incapable, stupid and gullible,
		1199	while in the same mail making rather confused statements about perl
		1200	ithreads (for example, that memory or files would be shared), showing his
		1201	lack of understanding of this area - if it is hard to understand for Chip,
		1202	it is probably not obvious to everybody).
		1203
		1204	What follows is an ultra-condensed version of my talk about threads in
		1205	scripting languages given on the perl workshop 2009:
		1206
		1207	The so-called "ithreads" were originally implemented for two reasons:
		1208	first, to (badly) emulate unix processes on native win32 perls, and
		1209	secondly, to replace the older, real thread model ("5.005-threads").
		1210
		1211	It does that by using threads instead of OS processes. The difference
		1212	between processes and threads is that threads share memory (and other
		1213	state, such as files) between threads within a single process, while
		1214	processes do not share anything (at least not semantically). That
		1215	means that modifications done by one thread are seen by others, while
		1216	modifications by one process are not seen by other processes.
		1217
		1218	The "ithreads" work exactly like that: when creating a new ithreads
		1219	process, all state is copied (memory is copied physically, files and code
		1220	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		1221	the same behaviour can be achieved by using operating system processes,
		1222	except that UNIX typically uses hardware built into the system to do this
		1223	efficiently, while the windows process emulation emulates this hardware in
		1224	software (rather efficiently, but of course it is still much slower than
		1225	dedicated hardware).
		1226
		1227	As mentioned before, loading code, modifying code, modifying data
		1228	structures and so on is only visible in the ithreads process doing the
		1229	modification, not in other ithread processes within the same OS process.
		1230
		1231	This is why "ithreads" do not implement threads for perl at all, only
		1232	processes. What makes it so bad is that on non-windows platforms, you can
		1233	actually take advantage of custom hardware for this purpose (as evidenced
		1234	by the forks module, which gives you the (i-) threads API, just much
		1235	faster).
		1236
		1237	Sharing data is in the i-threads model is done by transfering data
		1238	structures between threads using copying semantics, which is very slow -
		1239	shared data simply does not exist. Benchmarks using i-threads which are
		1240	communication-intensive show extremely bad behaviour with i-threads (in
		1241	fact, so bad that Coro, which cannot take direct advantage of multiple
		1242	CPUs, is often orders of magnitude faster because it shares data using
		1243	real threads, refer to my talk for details).
		1244
		1245	As summary, i-threads use threads to implement processes, while
		1246	the compatible forks module uses processes to emulate, uhm,
		1247	processes. I-threads slow down every perl program when enabled, and
		1248	outside of windows, serve no (or little) practical purpose, but
		1249	disadvantages every single-threaded Perl program.
		1250
		1251	This is the reason that I try to avoid the name "ithreads", as it is
		1252	misleading as it implies that it implements some kind of thread model for
		1253	perl, and prefer the name "windows process emulation", which describes the
		1254	actual use and behaviour of it much better.
		1255
807	=head1 SEE ALSO	1256	=head1 SEE ALSO
808		1257
809	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	1258	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
810		1259
811	Debugging: L<Coro::Debug>.	1260	Debugging: L<Coro::Debug>.

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Revision 1.297 by root, Thu May 12 23:55:39 2011 UTC