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

Comparing Coro/Coro.pm (file contents):
Revision 1.11 by root, Sun Jul 15 03:24:18 2001 UTC vs.
Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
9	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
		11	print "2\n";
		12	cede; # yield back to main
		13	print "4\n";
11	};	14	};
12		15	print "1\n";
13	# alternatively create an async process like this:	16	cede; # yield to coro
14		17	print "3\n";
15	sub some_func : Coro {	18	cede; # and again
16	# some more async code	19
17	}	20	# use locking
18		21	use Coro::Semaphore;
19	yield;	22	my $lock = new Coro::Semaphore;
		23	my $locked;
		24
		25	$lock->down;
		26	$locked = 1;
		27	$lock->up;
20		28
21	=head1 DESCRIPTION	29	=head1 DESCRIPTION
22		30
		31	For a tutorial-style introduction, please read the L<Coro::Intro>
		32	manpage. This manpage mainly contains reference information.
		33
		34	This module collection manages continuations in general, most often in
		35	the form of cooperative threads (also called coros, or simply "coro"
		36	in the documentation). They are similar to kernel threads but don't (in
		37	general) run in parallel at the same time even on SMP machines. The
		38	specific flavor of thread offered by this module also guarantees you that
		39	it will not switch between threads unless necessary, at easily-identified
		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
		42	thread models.
		43
		44	Unlike the so-called "Perl threads" (which are not actually real threads
		45	but only the windows process emulation (see section of same name for more
		46	details) ported to unix, and as such act as processes), Coro provides
		47	a full shared address space, which makes communication between threads
		48	very easy. And Coro's threads are fast, too: disabling the Windows
		49	process emulation code in your perl and using Coro can easily result in
		50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark runs over 300 times faster on a single core than
		52	perl's pseudo-threads on a quad core using all four cores.
		53
		54	Coro achieves that by supporting multiple running interpreters that share
		55	data, which is especially useful to code pseudo-parallel processes and
		56	for event-based programming, such as multiple HTTP-GET requests running
		57	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		58	into an event-based environment.
		59
		60	In this module, a thread is defined as "callchain + lexical variables +
		61	some package variables + C stack), that is, a thread has its own callchain,
		62	its own set of lexicals and its own set of perls most important global
		63	variables (see L<Coro::State> for more configuration and background info).
		64
		65	See also the C<SEE ALSO> section at the end of this document - the Coro
		66	module family is quite large.
		67
23	=cut	68	=cut
24		69
25	package Coro;	70	package Coro;
26		71
		72	use common::sense;
		73
		74	use Carp ();
		75
		76	use Guard ();
		77
27	use Coro::State;	78	use Coro::State;
28		79
29	use base Exporter;	80	use base qw(Coro::State Exporter);
30		81
31	$VERSION = 0.04;	82	our $idle; # idle handler
		83	our $main; # main coro
		84	our $current; # current coro
32		85
33	@EXPORT = qw(async yield schedule);	86	our $VERSION = 5.21;
34	@EXPORT_OK = qw($current);
35		87
36	{	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
37	use subs 'async';	89	our %EXPORT_TAGS = (
		90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		91	);
		92	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
38		93
39	my @async;	94	=head1 GLOBAL VARIABLES
40		95
41	# this way of handling attributes simply is NOT scalable ;()	96	=over 4
42	sub import {	97
43	Coro->export_to_level(1, @_);	98	=item $Coro::main
44	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};	99
45	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {	100	This variable stores the Coro object that represents the main
46	my ($package, $ref) = (shift, shift);	101	program. While you cna C<ready> it and do most other things you can do to
47	my @attrs;	102	coro, it is mainly useful to compare again C<$Coro::current>, to see
48	for (@_) {	103	whether you are running in the main program or not.
49	if ($_ eq "Coro") {	104
50	push @async, $ref;	105	=cut
51	} else {	106
52	push @attrs, @_;	107	# $main is now being initialised by Coro::State
53	}	108
54	}	109	=item $Coro::current
55	return $old ? $old->($package, $name, @attrs) : @attrs;	110
		111	The Coro object representing the current coro (the last
		112	coro that the Coro scheduler switched to). The initial value is
		113	C<$Coro::main> (of course).
		114
		115	This variable is B<strictly> I<read-only>. You can take copies of the
		116	value stored in it and use it as any other Coro object, but you must
		117	not otherwise modify the variable itself.
		118
		119	=cut
		120
		121	sub current() { $current } # [DEPRECATED]
		122
		123	=item $Coro::idle
		124
		125	This variable is mainly useful to integrate Coro into event loops. It is
		126	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		127	pretty low-level functionality.
		128
		129	This variable stores a Coro object that is put into the ready queue when
		130	there are no other ready threads (without invoking any ready hooks).
		131
		132	The default implementation dies with "FATAL: deadlock detected.", followed
		133	by a thread listing, because the program has no other way to continue.
		134
		135	This hook is overwritten by modules such as C<Coro::EV> and
		136	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
		137	coro so the scheduler can run it.
		138
		139	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
		140
		141	=cut
		142
		143	# \|\|= because other modules could have provided their own by now
		144	$idle \|\|= new Coro sub {
		145	require Coro::Debug;
		146	die "FATAL: deadlock detected.\n"
		147	. Coro::Debug::ps_listing ();
		148	};
		149
		150	# this coro is necessary because a coro
		151	# cannot destroy itself.
		152	our @destroy;
		153	our $manager;
		154
		155	$manager = new Coro sub {
		156	while () {
		157	Coro::State::cancel shift @destroy
		158	while @destroy;
		159
		160	&schedule;
		161	}
		162	};
		163	$manager->{desc} = "[coro manager]";
		164	$manager->prio (PRIO_MAX);
		165
		166	=back
		167
		168	=head1 SIMPLE CORO CREATION
		169
		170	=over 4
		171
		172	=item async { ... } [@args...]
		173
		174	Create a new coro and return its Coro object (usually
		175	unused). The coro will be put into the ready queue, so
		176	it will start running automatically on the next scheduler run.
		177
		178	The first argument is a codeblock/closure that should be executed in the
		179	coro. When it returns argument returns the coro is automatically
		180	terminated.
		181
		182	The remaining arguments are passed as arguments to the closure.
		183
		184	See the C<Coro::State::new> constructor for info about the coro
		185	environment in which coro are executed.
		186
		187	Calling C<exit> in a coro will do the same as calling exit outside
		188	the coro. Likewise, when the coro dies, the program will exit,
		189	just as it would in the main program.
		190
		191	If you do not want that, you can provide a default C<die> handler, or
		192	simply avoid dieing (by use of C<eval>).
		193
		194	Example: Create a new coro that just prints its arguments.
		195
		196	async {
		197	print "@_\n";
		198	} 1,2,3,4;
		199
		200	=item async_pool { ... } [@args...]
		201
		202	Similar to C<async>, but uses a coro pool, so you should not call
		203	terminate or join on it (although you are allowed to), and you get a
		204	coro that might have executed other code already (which can be good
		205	or bad :).
		206
		207	On the plus side, this function is about twice as fast as creating (and
		208	destroying) a completely new coro, so if you need a lot of generic
		209	coros in quick successsion, use C<async_pool>, not C<async>.
		210
		211	The code block is executed in an C<eval> context and a warning will be
		212	issued in case of an exception instead of terminating the program, as
		213	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		214	will not work in the expected way, unless you call terminate or cancel,
		215	which somehow defeats the purpose of pooling (but is fine in the
		216	exceptional case).
		217
		218	The priority will be reset to C<0> after each run, tracing will be
		219	disabled, the description will be reset and the default output filehandle
		220	gets restored, so you can change all these. Otherwise the coro will
		221	be re-used "as-is": most notably if you change other per-coro global
		222	stuff such as C<$/> you I<must needs> revert that change, which is most
		223	simply done by using local as in: C<< local $/ >>.
		224
		225	The idle pool size is limited to C<8> idle coros (this can be
		226	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		227	coros as required.
		228
		229	If you are concerned about pooled coros growing a lot because a
		230	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		231	{ terminate }> once per second or so to slowly replenish the pool. In
		232	addition to that, when the stacks used by a handler grows larger than 32kb
		233	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		234
		235	=cut
		236
		237	our $POOL_SIZE = 8;
		238	our $POOL_RSS = 32 * 1024;
		239	our @async_pool;
		240
		241	sub pool_handler {
		242	while () {
		243	eval {
		244	&{&_pool_handler} while 1;
56	};	245	};
57	}
58		246
59	sub INIT {	247	warn $@ if $@;
60	async pop @async while @async;
61	}	248	}
62	}	249	}
63		250
64	=item $main	251	=back
65		252
66	This coroutine represents the main program.	253	=head1 STATIC METHODS
67		254
68	=cut	255	Static methods are actually functions that implicitly operate on the
		256	current coro.
69		257
70	our $main = new Coro;	258	=over 4
71		259
72	=item $current	260	=item schedule
73		261
74	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	262	Calls the scheduler. The scheduler will find the next coro that is
		263	to be run from the ready queue and switches to it. The next coro
		264	to be run is simply the one with the highest priority that is longest
		265	in its ready queue. If there is no coro ready, it will call the
		266	C<$Coro::idle> hook.
75		267
76	=cut	268	Please note that the current coro will I<not> be put into the ready
		269	queue, so calling this function usually means you will never be called
		270	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		271	thus waking you up.
77		272
78	# maybe some other module used Coro::Specific before...	273	This makes C<schedule> I<the> generic method to use to block the current
79	if ($current) {	274	coro and wait for events: first you remember the current coro in
80	$main->{specific} = $current->{specific};	275	a variable, then arrange for some callback of yours to call C<< ->ready
		276	>> on that once some event happens, and last you call C<schedule> to put
		277	yourself to sleep. Note that a lot of things can wake your coro up,
		278	so you need to check whether the event indeed happened, e.g. by storing the
		279	status in a variable.
		280
		281	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
		282
		283	=item cede
		284
		285	"Cede" to other coros. This function puts the current coro into
		286	the ready queue and calls C<schedule>, which has the effect of giving
		287	up the current "timeslice" to other coros of the same or higher
		288	priority. Once your coro gets its turn again it will automatically be
		289	resumed.
		290
		291	This function is often called C<yield> in other languages.
		292
		293	=item Coro::cede_notself
		294
		295	Works like cede, but is not exported by default and will cede to I<any>
		296	coro, regardless of priority. This is useful sometimes to ensure
		297	progress is made.
		298
		299	=item terminate [arg...]
		300
		301	Terminates the current coro with the given status values (see L<cancel>).
		302
		303	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		304
		305	These function install enter and leave winders in the current scope. The
		306	enter block will be executed when on_enter is called and whenever the
		307	current coro is re-entered by the scheduler, while the leave block is
		308	executed whenever the current coro is blocked by the scheduler, and
		309	also when the containing scope is exited (by whatever means, be it exit,
		310	die, last etc.).
		311
		312	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		313	BLOCKs>. That means: do not even think about calling C<die> without an
		314	eval, and do not even think of entering the scheduler in any way.
		315
		316	Since both BLOCKs are tied to the current scope, they will automatically
		317	be removed when the current scope exits.
		318
		319	These functions implement the same concept as C<dynamic-wind> in scheme
		320	does, and are useful when you want to localise some resource to a specific
		321	coro.
		322
		323	They slow down thread switching considerably for coros that use them
		324	(about 40% for a BLOCK with a single assignment, so thread switching is
		325	still reasonably fast if the handlers are fast).
		326
		327	These functions are best understood by an example: The following function
		328	will change the current timezone to "Antarctica/South_Pole", which
		329	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		330	which remember/change the current timezone and restore the previous
		331	value, respectively, the timezone is only changed for the coro that
		332	installed those handlers.
		333
		334	use POSIX qw(tzset);
		335
		336	async {
		337	my $old_tz; # store outside TZ value here
		338
		339	Coro::on_enter {
		340	$old_tz = $ENV{TZ}; # remember the old value
		341
		342	$ENV{TZ} = "Antarctica/South_Pole";
		343	tzset; # enable new value
		344	};
		345
		346	Coro::on_leave {
		347	$ENV{TZ} = $old_tz;
		348	tzset; # restore old value
		349	};
		350
		351	# at this place, the timezone is Antarctica/South_Pole,
		352	# without disturbing the TZ of any other coro.
		353	};
		354
		355	This can be used to localise about any resource (locale, uid, current
		356	working directory etc.) to a block, despite the existance of other
		357	coros.
		358
		359	Another interesting example implements time-sliced multitasking using
		360	interval timers (this could obviously be optimised, but does the job):
		361
		362	# "timeslice" the given block
		363	sub timeslice(&) {
		364	use Time::HiRes ();
		365
		366	Coro::on_enter {
		367	# on entering the thread, we set an VTALRM handler to cede
		368	$SIG{VTALRM} = sub { cede };
		369	# and then start the interval timer
		370	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		371	};
		372	Coro::on_leave {
		373	# on leaving the thread, we stop the interval timer again
		374	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		375	};
		376
		377	&{+shift};
		378	}
		379
		380	# use like this:
		381	timeslice {
		382	# The following is an endless loop that would normally
		383	# monopolise the process. Since it runs in a timesliced
		384	# environment, it will regularly cede to other threads.
		385	while () { }
		386	};
		387
		388
		389	=item killall
		390
		391	Kills/terminates/cancels all coros except the currently running one.
		392
		393	Note that while this will try to free some of the main interpreter
		394	resources if the calling coro isn't the main coro, but one
		395	cannot free all of them, so if a coro that is not the main coro
		396	calls this function, there will be some one-time resource leak.
		397
		398	=cut
		399
		400	sub killall {
		401	for (Coro::State::list) {
		402	$_->cancel
		403	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		404	}
81	}	405	}
82		406
83	our $current = $main;	407	=back
84		408
85	=item $idle	409	=head1 CORO OBJECT METHODS
86		410
87	The coroutine to switch to when no other coroutine is running. The default	411	These are the methods you can call on coro objects (or to create
88	implementation prints "FATAL: deadlock detected" and exits.	412	them).
89		413
90	=cut	414	=over 4
91		415
92	# should be done using priorities :(	416	=item new Coro \&sub [, @args...]
		417
		418	Create a new coro and return it. When the sub returns, the coro
		419	automatically terminates as if C<terminate> with the returned values were
		420	called. To make the coro run you must first put it into the ready
		421	queue by calling the ready method.
		422
		423	See C<async> and C<Coro::State::new> for additional info about the
		424	coro environment.
		425
		426	=cut
		427
		428	sub _coro_run {
		429	terminate &{+shift};
		430	}
		431
		432	=item $success = $coro->ready
		433
		434	Put the given coro into the end of its ready queue (there is one
		435	queue for each priority) and return true. If the coro is already in
		436	the ready queue, do nothing and return false.
		437
		438	This ensures that the scheduler will resume this coro automatically
		439	once all the coro of higher priority and all coro of the same
		440	priority that were put into the ready queue earlier have been resumed.
		441
		442	=item $coro->suspend
		443
		444	Suspends the specified coro. A suspended coro works just like any other
		445	coro, except that the scheduler will not select a suspended coro for
		446	execution.
		447
		448	Suspending a coro can be useful when you want to keep the coro from
		449	running, but you don't want to destroy it, or when you want to temporarily
		450	freeze a coro (e.g. for debugging) to resume it later.
		451
		452	A scenario for the former would be to suspend all (other) coros after a
		453	fork and keep them alive, so their destructors aren't called, but new
		454	coros can be created.
		455
		456	=item $coro->resume
		457
		458	If the specified coro was suspended, it will be resumed. Note that when
		459	the coro was in the ready queue when it was suspended, it might have been
		460	unreadied by the scheduler, so an activation might have been lost.
		461
		462	To avoid this, it is best to put a suspended coro into the ready queue
		463	unconditionally, as every synchronisation mechanism must protect itself
		464	against spurious wakeups, and the one in the Coro family certainly do
		465	that.
		466
		467	=item $is_ready = $coro->is_ready
		468
		469	Returns true iff the Coro object is in the ready queue. Unless the Coro
		470	object gets destroyed, it will eventually be scheduled by the scheduler.
		471
		472	=item $is_running = $coro->is_running
		473
		474	Returns true iff the Coro object is currently running. Only one Coro object
		475	can ever be in the running state (but it currently is possible to have
		476	multiple running Coro::States).
		477
		478	=item $is_suspended = $coro->is_suspended
		479
		480	Returns true iff this Coro object has been suspended. Suspended Coros will
		481	not ever be scheduled.
		482
		483	=item $coro->cancel (arg...)
		484
		485	Terminates the given Coro and makes it return the given arguments as
		486	status (default: the empty list). Never returns if the Coro is the
		487	current Coro.
		488
		489	=cut
		490
		491	sub cancel {
		492	my $self = shift;
		493
		494	if ($current == $self) {
		495	terminate @_;
		496	} else {
		497	$self->{_status} = [@_];
		498	Coro::State::cancel $self;
		499	}
		500	}
		501
		502	=item $coro->schedule_to
		503
		504	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		505	of continuing with the next coro from the ready queue, always switch to
		506	the given coro object (regardless of priority etc.). The readyness
		507	state of that coro isn't changed.
		508
		509	This is an advanced method for special cases - I'd love to hear about any
		510	uses for this one.
		511
		512	=item $coro->cede_to
		513
		514	Like C<schedule_to>, but puts the current coro into the ready
		515	queue. This has the effect of temporarily switching to the given
		516	coro, and continuing some time later.
		517
		518	This is an advanced method for special cases - I'd love to hear about any
		519	uses for this one.
		520
		521	=item $coro->throw ([$scalar])
		522
		523	If C<$throw> is specified and defined, it will be thrown as an exception
		524	inside the coro at the next convenient point in time. Otherwise
		525	clears the exception object.
		526
		527	Coro will check for the exception each time a schedule-like-function
		528	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		529	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		530	detect this case and return early in case an exception is pending.
		531
		532	The exception object will be thrown "as is" with the specified scalar in
		533	C<$@>, i.e. if it is a string, no line number or newline will be appended
		534	(unlike with C<die>).
		535
		536	This can be used as a softer means than C<cancel> to ask a coro to
		537	end itself, although there is no guarantee that the exception will lead to
		538	termination, and if the exception isn't caught it might well end the whole
		539	program.
		540
		541	You might also think of C<throw> as being the moral equivalent of
		542	C<kill>ing a coro with a signal (in this case, a scalar).
		543
		544	=item $coro->join
		545
		546	Wait until the coro terminates and return any values given to the
		547	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		548	from multiple coro, and all will be resumed and given the status
		549	return once the C<$coro> terminates.
		550
		551	=cut
		552
		553	sub join {
		554	my $self = shift;
		555
		556	unless ($self->{_status}) {
		557	my $current = $current;
		558
		559	push @{$self->{_on_destroy}}, sub {
		560	$current->ready;
		561	undef $current;
		562	};
		563
		564	&schedule while $current;
		565	}
		566
		567	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		568	}
		569
		570	=item $coro->on_destroy (\&cb)
		571
		572	Registers a callback that is called when this coro gets destroyed,
		573	but before it is joined. The callback gets passed the terminate arguments,
		574	if any, and I<must not> die, under any circumstances.
		575
		576	=cut
		577
		578	sub on_destroy {
		579	my ($self, $cb) = @_;
		580
		581	push @{ $self->{_on_destroy} }, $cb;
		582	}
		583
		584	=item $oldprio = $coro->prio ($newprio)
		585
		586	Sets (or gets, if the argument is missing) the priority of the
		587	coro. Higher priority coro get run before lower priority
		588	coro. Priorities are small signed integers (currently -4 .. +3),
		589	that you can refer to using PRIO_xxx constants (use the import tag :prio
		590	to get then):
		591
		592	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		593	3 > 1 > 0 > -1 > -3 > -4
		594
		595	# set priority to HIGH
		596	current->prio (PRIO_HIGH);
		597
		598	The idle coro ($Coro::idle) always has a lower priority than any
		599	existing coro.
		600
		601	Changing the priority of the current coro will take effect immediately,
		602	but changing the priority of coro in the ready queue (but not
		603	running) will only take effect after the next schedule (of that
		604	coro). This is a bug that will be fixed in some future version.
		605
		606	=item $newprio = $coro->nice ($change)
		607
		608	Similar to C<prio>, but subtract the given value from the priority (i.e.
		609	higher values mean lower priority, just as in unix).
		610
		611	=item $olddesc = $coro->desc ($newdesc)
		612
		613	Sets (or gets in case the argument is missing) the description for this
		614	coro. This is just a free-form string you can associate with a
		615	coro.
		616
		617	This method simply sets the C<< $coro->{desc} >> member to the given
		618	string. You can modify this member directly if you wish.
		619
		620	=cut
		621
		622	sub desc {
		623	my $old = $_[0]{desc};
		624	$_[0]{desc} = $_[1] if @_ > 1;
		625	$old;
		626	}
		627
		628	sub transfer {
		629	require Carp;
		630	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		631	}
		632
		633	=back
		634
		635	=head1 GLOBAL FUNCTIONS
		636
		637	=over 4
		638
		639	=item Coro::nready
		640
		641	Returns the number of coro that are currently in the ready state,
		642	i.e. that can be switched to by calling C<schedule> directory or
		643	indirectly. The value C<0> means that the only runnable coro is the
		644	currently running one, so C<cede> would have no effect, and C<schedule>
		645	would cause a deadlock unless there is an idle handler that wakes up some
		646	coro.
		647
		648	=item my $guard = Coro::guard { ... }
		649
		650	This function still exists, but is deprecated. Please use the
		651	C<Guard::guard> function instead.
		652
		653	=cut
		654
		655	BEGIN { *guard = \&Guard::guard }
		656
		657	=item unblock_sub { ... }
		658
		659	This utility function takes a BLOCK or code reference and "unblocks" it,
		660	returning a new coderef. Unblocking means that calling the new coderef
		661	will return immediately without blocking, returning nothing, while the
		662	original code ref will be called (with parameters) from within another
		663	coro.
		664
		665	The reason this function exists is that many event libraries (such as the
		666	venerable L<Event\|Event> module) are not thread-safe (a weaker form
		667	of reentrancy). This means you must not block within event callbacks,
		668	otherwise you might suffer from crashes or worse. The only event library
		669	currently known that is safe to use without C<unblock_sub> is L<EV>.
		670
		671	Coro will try to catch you when you block in the event loop
		672	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		673	only works when you do not run your own event loop.
		674
		675	This function allows your callbacks to block by executing them in another
		676	coro where it is safe to block. One example where blocking is handy
		677	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		678	disk, for example.
		679
		680	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		681	creating event callbacks that want to block.
		682
		683	If your handler does not plan to block (e.g. simply sends a message to
		684	another coro, or puts some other coro into the ready queue), there is
		685	no reason to use C<unblock_sub>.
		686
		687	Note that you also need to use C<unblock_sub> for any other callbacks that
		688	are indirectly executed by any C-based event loop. For example, when you
		689	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		690	provides callbacks that are the result of some event callback, then you
		691	must not block either, or use C<unblock_sub>.
		692
		693	=cut
		694
		695	our @unblock_queue;
		696
		697	# we create a special coro because we want to cede,
		698	# to reduce pressure on the coro pool (because most callbacks
		699	# return immediately and can be reused) and because we cannot cede
		700	# inside an event callback.
93	our $idle = new Coro sub {	701	our $unblock_scheduler = new Coro sub {
94	print STDERR "FATAL: deadlock detected\n";	702	while () {
95	exit(51);	703	while (my $cb = pop @unblock_queue) {
		704	&async_pool (@$cb);
		705
		706	# for short-lived callbacks, this reduces pressure on the coro pool
		707	# as the chance is very high that the async_poll coro will be back
		708	# in the idle state when cede returns
		709	cede;
		710	}
		711	schedule; # sleep well
		712	}
96	};	713	};
		714	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
97		715
98	# we really need priorities...	716	sub unblock_sub(&) {
99	my @ready = (); # the ready queue. hehe, rather broken ;)	717	my $cb = shift;
100		718
101	# static methods. not really.	719	sub {
		720	unshift @unblock_queue, [$cb, @_];
		721	$unblock_scheduler->ready;
		722	}
		723	}
102		724
103	=head2 STATIC METHODS	725	=item $cb = rouse_cb
104		726
105	Static methods are actually functions that operate on the current process only.	727	Create and return a "rouse callback". That's a code reference that,
		728	when called, will remember a copy of its arguments and notify the owner
		729	coro of the callback.
		730
		731	See the next function.
		732
		733	=item @args = rouse_wait [$cb]
		734
		735	Wait for the specified rouse callback (or the last one that was created in
		736	this coro).
		737
		738	As soon as the callback is invoked (or when the callback was invoked
		739	before C<rouse_wait>), it will return the arguments originally passed to
		740	the rouse callback. In scalar context, that means you get the I<last>
		741	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		742	statement at the end.
		743
		744	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		745
		746	=back
		747
		748	=cut
		749
		750	1;
		751
		752	=head1 HOW TO WAIT FOR A CALLBACK
		753
		754	It is very common for a coro to wait for some callback to be
		755	called. This occurs naturally when you use coro in an otherwise
		756	event-based program, or when you use event-based libraries.
		757
		758	These typically register a callback for some event, and call that callback
		759	when the event occured. In a coro, however, you typically want to
		760	just wait for the event, simplyifying things.
		761
		762	For example C<< AnyEvent->child >> registers a callback to be called when
		763	a specific child has exited:
		764
		765	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		766
		767	But from within a coro, you often just want to write this:
		768
		769	my $status = wait_for_child $pid;
		770
		771	Coro offers two functions specifically designed to make this easy,
		772	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		773
		774	The first function, C<rouse_cb>, generates and returns a callback that,
		775	when invoked, will save its arguments and notify the coro that
		776	created the callback.
		777
		778	The second function, C<rouse_wait>, waits for the callback to be called
		779	(by calling C<schedule> to go to sleep) and returns the arguments
		780	originally passed to the callback.
		781
		782	Using these functions, it becomes easy to write the C<wait_for_child>
		783	function mentioned above:
		784
		785	sub wait_for_child($) {
		786	my ($pid) = @_;
		787
		788	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		789
		790	my ($rpid, $rstatus) = Coro::rouse_wait;
		791	$rstatus
		792	}
		793
		794	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		795	you can roll your own, using C<schedule>:
		796
		797	sub wait_for_child($) {
		798	my ($pid) = @_;
		799
		800	# store the current coro in $current,
		801	# and provide result variables for the closure passed to ->child
		802	my $current = $Coro::current;
		803	my ($done, $rstatus);
		804
		805	# pass a closure to ->child
		806	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		807	$rstatus = $_[1]; # remember rstatus
		808	$done = 1; # mark $rstatus as valud
		809	});
		810
		811	# wait until the closure has been called
		812	schedule while !$done;
		813
		814	$rstatus
		815	}
		816
		817
		818	=head1 BUGS/LIMITATIONS
106		819
107	=over 4	820	=over 4
108		821
109	=item async { ... };	822	=item fork with pthread backend
110		823
111	Create a new asynchronous process and return it's process object	824	When Coro is compiled using the pthread backend (which isn't recommended
112	(usually unused). When the sub returns the new process is automatically	825	but required on many BSDs as their libcs are completely broken), then
113	terminated.	826	coro will not survive a fork. There is no known workaround except to
		827	fix your libc and use a saner backend.
114		828
115	=cut	829	=item perl process emulation ("threads")
116		830
117	sub async(&) {	831	This module is not perl-pseudo-thread-safe. You should only ever use this
118	my $pid = new Coro $_[0];	832	module from the first thread (this requirement might be removed in the
119	$pid->ready;	833	future to allow per-thread schedulers, but Coro::State does not yet allow
120	$pid;	834	this). I recommend disabling thread support and using processes, as having
121	}	835	the windows process emulation enabled under unix roughly halves perl
		836	performance, even when not used.
122		837
123	=item schedule	838	=item coro switching is not signal safe
124		839
125	Calls the scheduler. Please note that the current process will not be put	840	You must not switch to another coro from within a signal handler (only
126	into the ready queue, so calling this function usually means you will	841	relevant with %SIG - most event libraries provide safe signals), I<unless>
127	never be called again.	842	you are sure you are not interrupting a Coro function.
128		843
129	=cut	844	That means you I<MUST NOT> call any function that might "block" the
130		845	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
131	my $prev;	846	anything that calls those. Everything else, including calling C<ready>,
132		847	works.
133	sub schedule {
134	# should be done using priorities :(
135	($prev, $current) = ($current, shift @ready \|\| $idle);
136	Coro::State::transfer($prev, $current);
137	}
138
139	=item yield
140
141	Yield to other processes. This function puts the current process into the
142	ready queue and calls C<schedule>.
143
144	=cut
145
146	sub yield {
147	$current->ready;
148	&schedule;
149	}
150
151	=item terminate
152
153	Terminates the current process.
154
155	=cut
156
157	sub terminate {
158	&schedule;
159	}
160		848
161	=back	849	=back
162		850
163	# dynamic methods
164		851
165	=head2 PROCESS METHODS	852	=head1 WINDOWS PROCESS EMULATION
166		853
167	These are the methods you can call on process objects.	854	A great many people seem to be confused about ithreads (for example, Chip
		855	Salzenberg called me unintelligent, incapable, stupid and gullible,
		856	while in the same mail making rather confused statements about perl
		857	ithreads (for example, that memory or files would be shared), showing his
		858	lack of understanding of this area - if it is hard to understand for Chip,
		859	it is probably not obvious to everybody).
168		860
169	=over 4	861	What follows is an ultra-condensed version of my talk about threads in
		862	scripting languages given onthe perl workshop 2009:
170		863
171	=item new Coro \⊂	864	The so-called "ithreads" were originally implemented for two reasons:
		865	first, to (badly) emulate unix processes on native win32 perls, and
		866	secondly, to replace the older, real thread model ("5.005-threads").
172		867
173	Create a new process and return it. When the sub returns the process	868	It does that by using threads instead of OS processes. The difference
174	automatically terminates. To start the process you must first put it into	869	between processes and threads is that threads share memory (and other
175	the ready queue by calling the ready method.	870	state, such as files) between threads within a single process, while
		871	processes do not share anything (at least not semantically). That
		872	means that modifications done by one thread are seen by others, while
		873	modifications by one process are not seen by other processes.
176		874
177	=cut	875	The "ithreads" work exactly like that: when creating a new ithreads
		876	process, all state is copied (memory is copied physically, files and code
		877	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		878	the same behaviour can be achieved by using operating system processes,
		879	except that UNIX typically uses hardware built into the system to do this
		880	efficiently, while the windows process emulation emulates this hardware in
		881	software (rather efficiently, but of course it is still much slower than
		882	dedicated hardware).
178		883
179	sub new {	884	As mentioned before, loading code, modifying code, modifying data
180	my $class = shift;	885	structures and so on is only visible in the ithreads process doing the
181	my $proc = $_[0];	886	modification, not in other ithread processes within the same OS process.
182	bless {
183	_coro_state => new Coro::State ($proc ? sub { &$proc; &terminate } : $proc),
184	}, $class;
185	}
186		887
187	=item $process->ready	888	This is why "ithreads" do not implement threads for perl at all, only
		889	processes. What makes it so bad is that on non-windows platforms, you can
		890	actually take advantage of custom hardware for this purpose (as evidenced
		891	by the forks module, which gives you the (i-) threads API, just much
		892	faster).
188		893
189	Put the current process into the ready queue.	894	Sharing data is in the i-threads model is done by transfering data
		895	structures between threads using copying semantics, which is very slow -
		896	shared data simply does not exist. Benchmarks using i-threads which are
		897	communication-intensive show extremely bad behaviour with i-threads (in
		898	fact, so bad that Coro, which cannot take direct advantage of multiple
		899	CPUs, is often orders of magnitude faster because it shares data using
		900	real threads, refer to my talk for details).
190		901
191	=cut	902	As summary, i-threads use threads to implement processes, while
		903	the compatible forks module uses processes to emulate, uhm,
		904	processes. I-threads slow down every perl program when enabled, and
		905	outside of windows, serve no (or little) practical purpose, but
		906	disadvantages every single-threaded Perl program.
192		907
193	sub ready {	908	This is the reason that I try to avoid the name "ithreads", as it is
194	push @ready, $_[0];	909	misleading as it implies that it implements some kind of thread model for
195	}	910	perl, and prefer the name "windows process emulation", which describes the
196		911	actual use and behaviour of it much better.
197	=back
198
199	=cut
200
201	1;
202		912
203	=head1 SEE ALSO	913	=head1 SEE ALSO
204		914
205	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	915	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
206	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	916
		917	Debugging: L<Coro::Debug>.
		918
		919	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		920
		921	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		922	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		923
		924	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		925
		926	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		927	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		928	L<Coro::Select>.
		929
		930	XS API: L<Coro::MakeMaker>.
		931
		932	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
207		933
208	=head1 AUTHOR	934	=head1 AUTHOR
209		935
210	Marc Lehmann <pcg@goof.com>	936	Marc Lehmann <schmorp@schmorp.de>
211	http://www.goof.com/pcg/marc/	937	http://home.schmorp.de/
212		938
213	=cut	939	=cut
214		940

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Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC