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

Comparing Coro/Coro.pm (file contents):
Revision 1.14 by root, Tue Jul 17 02:21:56 2001 UTC vs.
Revision 1.269 by root, Thu Oct 1 23:25:03 2009 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
23	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
24	Threads but don't run in parallel.	32	manpage. This manpage mainly contains reference information.
25		33
26	This module is still experimental, see the BUGS section below.	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.
27		67
28	=cut	68	=cut
29		69
30	package Coro;	70	package Coro;
31		71
		72	use common::sense;
		73
		74	use Carp ();
		75
		76	use Guard ();
		77
32	use Coro::State;	78	use Coro::State;
33		79
34	use base Exporter;	80	use base qw(Coro::State Exporter);
35		81
36	$VERSION = 0.05;	82	our $idle; # idle handler
		83	our $main; # main coro
		84	our $current; # current coro
37		85
38	@EXPORT = qw(async yield schedule terminate);	86	our $VERSION = 5.17;
39	@EXPORT_OK = qw($current);
40		87
41	{	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
42	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));
43		93
44	my @async;	94	=head1 GLOBAL VARIABLES
45		95
46	# this way of handling attributes simply is NOT scalable ;()	96	=over 4
47	sub import {	97
48	Coro->export_to_level(1, @_);	98	=item $Coro::main
49	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};	99
50	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {	100	This variable stores the Coro object that represents the main
51	my ($package, $ref) = (shift, shift);	101	program. While you cna C<ready> it and do most other things you can do to
52	my @attrs;	102	coro, it is mainly useful to compare again C<$Coro::current>, to see
53	for (@_) {	103	whether you are running in the main program or not.
54	if ($_ eq "Coro") {	104
55	push @async, $ref;	105	=cut
56	} else {	106
57	push @attrs, @_;	107	# $main is now being initialised by Coro::State
58	}	108
59	}	109	=item $Coro::current
60	return $old ? $old->($package, $name, @attrs) : @attrs;	110
61	};	111	The Coro object representing the current coro (the last
		112	coro that the Coro scheduler switched to). The initial value is
		113	C<$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 either a Coro object or a callback.
		130
		131	If it is a callback, the it is called whenever the scheduler finds no
		132	ready coros to run. The default implementation prints "FATAL:
		133	deadlock detected" and exits, because the program has no other way to
		134	continue.
		135
		136	If it is a coro object, then this object will be readied (without
		137	invoking any ready hooks, however) when the scheduler finds no other ready
		138	coros to run.
		139
		140	This hook is overwritten by modules such as C<Coro::EV> and
		141	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
		142	coro so the scheduler can run it.
		143
		144	Note that the callback I<must not>, under any circumstances, block
		145	the current coro. Normally, this is achieved by having an "idle
		146	coro" that calls the event loop and then blocks again, and then
		147	readying that coro in the idle handler, or by simply placing the idle
		148	coro in this variable.
		149
		150	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
		151	technique.
		152
		153	Please note that if your callback recursively invokes perl (e.g. for event
		154	handlers), then it must be prepared to be called recursively itself.
		155
		156	=cut
		157
		158	$idle = sub {
		159	Carp::confess ("FATAL: deadlock detected");
		160	};
		161
		162	# this coro is necessary because a coro
		163	# cannot destroy itself.
		164	our @destroy;
		165	our $manager;
		166
		167	$manager = new Coro sub {
		168	while () {
		169	Coro::State::cancel shift @destroy
		170	while @destroy;
		171
		172	&schedule;
62	}	173	}
63
64	sub INIT {
65	async pop @async while @async;
66	}
67	}
68
69	=item $main
70
71	This coroutine represents the main program.
72
73	=cut
74
75	our $main = new Coro;
76
77	=item $current
78
79	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).
80
81	=cut
82
83	# maybe some other module used Coro::Specific before...
84	if ($current) {
85	$main->{specific} = $current->{specific};
86	}
87
88	our $current = $main;
89
90	=item $idle
91
92	The coroutine to switch to when no other coroutine is running. The default
93	implementation prints "FATAL: deadlock detected" and exits.
94
95	=cut
96
97	# should be done using priorities :(
98	our $idle = new Coro sub {
99	print STDERR "FATAL: deadlock detected\n";
100	exit(51);
101	};	174	};
		175	$manager->{desc} = "[coro manager]";
		176	$manager->prio (PRIO_MAX);
102		177
103	# we really need priorities...	178	=back
104	## my @ready; #d#
105	our @ready = (); # the ready queue. hehe, rather broken ;)
106		179
107	# static methods. not really.	180	=head1 SIMPLE CORO CREATION
108
109	=head2 STATIC METHODS
110
111	Static methods are actually functions that operate on the current process only.
112		181
113	=over 4	182	=over 4
114		183
115	=item async { ... } [@args...]	184	=item async { ... } [@args...]
116		185
117	Create a new asynchronous process and return it's process object	186	Create a new coro and return its Coro object (usually
118	(usually unused). When the sub returns the new process is automatically	187	unused). The coro will be put into the ready queue, so
		188	it will start running automatically on the next scheduler run.
		189
		190	The first argument is a codeblock/closure that should be executed in the
		191	coro. When it returns argument returns the coro is automatically
119	terminated.	192	terminated.
120		193
		194	The remaining arguments are passed as arguments to the closure.
		195
		196	See the C<Coro::State::new> constructor for info about the coro
		197	environment in which coro are executed.
		198
		199	Calling C<exit> in a coro will do the same as calling exit outside
		200	the coro. Likewise, when the coro dies, the program will exit,
		201	just as it would in the main program.
		202
		203	If you do not want that, you can provide a default C<die> handler, or
		204	simply avoid dieing (by use of C<eval>).
		205
121	# create a new coroutine that just prints its arguments	206	Example: Create a new coro that just prints its arguments.
		207
122	async {	208	async {
123	print "@_\n";	209	print "@_\n";
124	} 1,2,3,4;	210	} 1,2,3,4;
125		211
126	The coderef you submit MUST NOT be a closure that refers to variables	212	=item async_pool { ... } [@args...]
127	in an outer scope. This does NOT work. Pass arguments into it instead.
128		213
129	=cut	214	Similar to C<async>, but uses a coro pool, so you should not call
		215	terminate or join on it (although you are allowed to), and you get a
		216	coro that might have executed other code already (which can be good
		217	or bad :).
130		218
131	sub async(&@) {	219	On the plus side, this function is about twice as fast as creating (and
132	my $pid = new Coro @_;	220	destroying) a completely new coro, so if you need a lot of generic
133	$pid->ready;	221	coros in quick successsion, use C<async_pool>, not C<async>.
134	$pid;	222
		223	The code block is executed in an C<eval> context and a warning will be
		224	issued in case of an exception instead of terminating the program, as
		225	C<async> does. As the coro is being reused, stuff like C<on_destroy>
		226	will not work in the expected way, unless you call terminate or cancel,
		227	which somehow defeats the purpose of pooling (but is fine in the
		228	exceptional case).
		229
		230	The priority will be reset to C<0> after each run, tracing will be
		231	disabled, the description will be reset and the default output filehandle
		232	gets restored, so you can change all these. Otherwise the coro will
		233	be re-used "as-is": most notably if you change other per-coro global
		234	stuff such as C<$/> you I<must needs> revert that change, which is most
		235	simply done by using local as in: C<< local $/ >>.
		236
		237	The idle pool size is limited to C<8> idle coros (this can be
		238	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
		239	coros as required.
		240
		241	If you are concerned about pooled coros growing a lot because a
		242	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		243	{ terminate }> once per second or so to slowly replenish the pool. In
		244	addition to that, when the stacks used by a handler grows larger than 32kb
		245	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
		246
		247	=cut
		248
		249	our $POOL_SIZE = 8;
		250	our $POOL_RSS = 32 * 1024;
		251	our @async_pool;
		252
		253	sub pool_handler {
		254	while () {
		255	eval {
		256	&{&_pool_handler} while 1;
		257	};
		258
		259	warn $@ if $@;
		260	}
135	}	261	}
136		262
		263	=back
		264
		265	=head1 STATIC METHODS
		266
		267	Static methods are actually functions that implicitly operate on the
		268	current coro.
		269
		270	=over 4
		271
137	=item schedule	272	=item schedule
138		273
139	Calls the scheduler. Please note that the current process will not be put	274	Calls the scheduler. The scheduler will find the next coro that is
		275	to be run from the ready queue and switches to it. The next coro
		276	to be run is simply the one with the highest priority that is longest
		277	in its ready queue. If there is no coro ready, it will clal the
		278	C<$Coro::idle> hook.
		279
		280	Please note that the current coro will I<not> be put into the ready
140	into the ready queue, so calling this function usually means you will	281	queue, so calling this function usually means you will never be called
141	never be called again.	282	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		283	thus waking you up.
142		284
143	=cut	285	This makes C<schedule> I<the> generic method to use to block the current
		286	coro and wait for events: first you remember the current coro in
		287	a variable, then arrange for some callback of yours to call C<< ->ready
		288	>> on that once some event happens, and last you call C<schedule> to put
		289	yourself to sleep. Note that a lot of things can wake your coro up,
		290	so you need to check whether the event indeed happened, e.g. by storing the
		291	status in a variable.
144		292
145	my $prev;	293	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
146		294
147	sub schedule {	295	=item cede
148	# should be done using priorities :(	296
149	($prev, $current) = ($current, shift @ready \|\| $idle);	297	"Cede" to other coros. This function puts the current coro into
150	Coro::State::transfer($prev, $current);	298	the ready queue and calls C<schedule>, which has the effect of giving
		299	up the current "timeslice" to other coros of the same or higher
		300	priority. Once your coro gets its turn again it will automatically be
		301	resumed.
		302
		303	This function is often called C<yield> in other languages.
		304
		305	=item Coro::cede_notself
		306
		307	Works like cede, but is not exported by default and will cede to I<any>
		308	coro, regardless of priority. This is useful sometimes to ensure
		309	progress is made.
		310
		311	=item terminate [arg...]
		312
		313	Terminates the current coro with the given status values (see L<cancel>).
		314
		315	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		316
		317	These function install enter and leave winders in the current scope. The
		318	enter block will be executed when on_enter is called and whenever the
		319	current coro is re-entered by the scheduler, while the leave block is
		320	executed whenever the current coro is blocked by the scheduler, and
		321	also when the containing scope is exited (by whatever means, be it exit,
		322	die, last etc.).
		323
		324	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		325	BLOCKs>. That means: do not even think about calling C<die> without an
		326	eval, and do not even think of entering the scheduler in any way.
		327
		328	Since both BLOCKs are tied to the current scope, they will automatically
		329	be removed when the current scope exits.
		330
		331	These functions implement the same concept as C<dynamic-wind> in scheme
		332	does, and are useful when you want to localise some resource to a specific
		333	coro.
		334
		335	They slow down thread switching considerably for coros that use them
		336	(about 40% for a BLOCK with a single assignment, so thread switching is
		337	still reasonably fast if the handlers are fast).
		338
		339	These functions are best understood by an example: The following function
		340	will change the current timezone to "Antarctica/South_Pole", which
		341	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		342	which remember/change the current timezone and restore the previous
		343	value, respectively, the timezone is only changed for the coro that
		344	installed those handlers.
		345
		346	use POSIX qw(tzset);
		347
		348	async {
		349	my $old_tz; # store outside TZ value here
		350
		351	Coro::on_enter {
		352	$old_tz = $ENV{TZ}; # remember the old value
		353
		354	$ENV{TZ} = "Antarctica/South_Pole";
		355	tzset; # enable new value
		356	};
		357
		358	Coro::on_leave {
		359	$ENV{TZ} = $old_tz;
		360	tzset; # restore old value
		361	};
		362
		363	# at this place, the timezone is Antarctica/South_Pole,
		364	# without disturbing the TZ of any other coro.
		365	};
		366
		367	This can be used to localise about any resource (locale, uid, current
		368	working directory etc.) to a block, despite the existance of other
		369	coros.
		370
		371	Another interesting example implements time-sliced multitasking using
		372	interval timers (this could obviously be optimised, but does the job):
		373
		374	# "timeslice" the given block
		375	sub timeslice(&) {
		376	use Time::HiRes ();
		377
		378	Coro::on_enter {
		379	# on entering the thread, we set an VTALRM handler to cede
		380	$SIG{VTALRM} = sub { cede };
		381	# and then start the interval timer
		382	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		383	};
		384	Coro::on_leave {
		385	# on leaving the thread, we stop the interval timer again
		386	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		387	};
		388
		389	&{+shift};
		390	}
		391
		392	# use like this:
		393	timeslice {
		394	# The following is an endless loop that would normally
		395	# monopolise the process. Since it runs in a timesliced
		396	# environment, it will regularly cede to other threads.
		397	while () { }
		398	};
		399
		400
		401	=item killall
		402
		403	Kills/terminates/cancels all coros except the currently running one.
		404
		405	Note that while this will try to free some of the main interpreter
		406	resources if the calling coro isn't the main coro, but one
		407	cannot free all of them, so if a coro that is not the main coro
		408	calls this function, there will be some one-time resource leak.
		409
		410	=cut
		411
		412	sub killall {
		413	for (Coro::State::list) {
		414	$_->cancel
		415	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		416	}
151	}	417	}
152		418
153	=item yield
154
155	Yield to other processes. This function puts the current process into the
156	ready queue and calls C<schedule>.
157
158	=cut
159
160	sub yield {
161	$current->ready;
162	&schedule;
163	}
164
165	=item terminate
166
167	Terminates the current process.
168
169	Future versions of this function will allow result arguments.
170
171	=cut
172
173	sub terminate {
174	$current->{_results} = [@_];
175	&schedule;
176	}
177
178	=back	419	=back
179		420
180	# dynamic methods	421	=head1 CORO OBJECT METHODS
181		422
182	=head2 PROCESS METHODS
183
184	These are the methods you can call on process objects.	423	These are the methods you can call on coro objects (or to create
		424	them).
185		425
186	=over 4	426	=over 4
187		427
188	=item new Coro \&sub [, @args...]	428	=item new Coro \&sub [, @args...]
189		429
190	Create a new process and return it. When the sub returns the process	430	Create a new coro and return it. When the sub returns, the coro
191	automatically terminates. To start the process you must first put it into	431	automatically terminates as if C<terminate> with the returned values were
		432	called. To make the coro run you must first put it into the ready
192	the ready queue by calling the ready method.	433	queue by calling the ready method.
193		434
194	The coderef you submit MUST NOT be a closure that refers to variables	435	See C<async> and C<Coro::State::new> for additional info about the
195	in an outer scope. This does NOT work. Pass arguments into it instead.	436	coro environment.
196		437
197	=cut	438	=cut
198		439
199	sub _newcoro {	440	sub _coro_run {
200	terminate &{+shift};	441	terminate &{+shift};
201	}	442	}
202		443
		444	=item $success = $coro->ready
		445
		446	Put the given coro into the end of its ready queue (there is one
		447	queue for each priority) and return true. If the coro is already in
		448	the ready queue, do nothing and return false.
		449
		450	This ensures that the scheduler will resume this coro automatically
		451	once all the coro of higher priority and all coro of the same
		452	priority that were put into the ready queue earlier have been resumed.
		453
		454	=item $coro->suspend
		455
		456	Suspends the specified coro. A suspended coro works just like any other
		457	coro, except that the scheduler will not select a suspended coro for
		458	execution.
		459
		460	Suspending a coro can be useful when you want to keep the coro from
		461	running, but you don't want to destroy it, or when you want to temporarily
		462	freeze a coro (e.g. for debugging) to resume it later.
		463
		464	A scenario for the former would be to suspend all (other) coros after a
		465	fork and keep them alive, so their destructors aren't called, but new
		466	coros can be created.
		467
		468	=item $coro->resume
		469
		470	If the specified coro was suspended, it will be resumed. Note that when
		471	the coro was in the ready queue when it was suspended, it might have been
		472	unreadied by the scheduler, so an activation might have been lost.
		473
		474	To avoid this, it is best to put a suspended coro into the ready queue
		475	unconditionally, as every synchronisation mechanism must protect itself
		476	against spurious wakeups, and the one in the Coro family certainly do
		477	that.
		478
		479	=item $is_ready = $coro->is_ready
		480
		481	Returns true iff the Coro object is in the ready queue. Unless the Coro
		482	object gets destroyed, it will eventually be scheduled by the scheduler.
		483
		484	=item $is_running = $coro->is_running
		485
		486	Returns true iff the Coro object is currently running. Only one Coro object
		487	can ever be in the running state (but it currently is possible to have
		488	multiple running Coro::States).
		489
		490	=item $is_suspended = $coro->is_suspended
		491
		492	Returns true iff this Coro object has been suspended. Suspended Coros will
		493	not ever be scheduled.
		494
		495	=item $coro->cancel (arg...)
		496
		497	Terminates the given Coro and makes it return the given arguments as
		498	status (default: the empty list). Never returns if the Coro is the
		499	current Coro.
		500
		501	=cut
		502
203	sub new {	503	sub cancel {
204	my $class = shift;	504	my $self = shift;
205	bless {	505
206	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),	506	if ($current == $self) {
207	}, $class;	507	terminate @_;
		508	} else {
		509	$self->{_status} = [@_];
		510	Coro::State::cancel $self;
		511	}
208	}	512	}
209		513
210	=item $process->ready	514	=item $coro->schedule_to
211		515
212	Put the current process into the ready queue.	516	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		517	of continuing with the next coro from the ready queue, always switch to
		518	the given coro object (regardless of priority etc.). The readyness
		519	state of that coro isn't changed.
213		520
214	=cut	521	This is an advanced method for special cases - I'd love to hear about any
		522	uses for this one.
215		523
216	sub ready {	524	=item $coro->cede_to
217	push @ready, $_[0];	525
		526	Like C<schedule_to>, but puts the current coro into the ready
		527	queue. This has the effect of temporarily switching to the given
		528	coro, and continuing some time later.
		529
		530	This is an advanced method for special cases - I'd love to hear about any
		531	uses for this one.
		532
		533	=item $coro->throw ([$scalar])
		534
		535	If C<$throw> is specified and defined, it will be thrown as an exception
		536	inside the coro at the next convenient point in time. Otherwise
		537	clears the exception object.
		538
		539	Coro will check for the exception each time a schedule-like-function
		540	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		541	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		542	detect this case and return early in case an exception is pending.
		543
		544	The exception object will be thrown "as is" with the specified scalar in
		545	C<$@>, i.e. if it is a string, no line number or newline will be appended
		546	(unlike with C<die>).
		547
		548	This can be used as a softer means than C<cancel> to ask a coro to
		549	end itself, although there is no guarantee that the exception will lead to
		550	termination, and if the exception isn't caught it might well end the whole
		551	program.
		552
		553	You might also think of C<throw> as being the moral equivalent of
		554	C<kill>ing a coro with a signal (in this case, a scalar).
		555
		556	=item $coro->join
		557
		558	Wait until the coro terminates and return any values given to the
		559	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		560	from multiple coro, and all will be resumed and given the status
		561	return once the C<$coro> terminates.
		562
		563	=cut
		564
		565	sub join {
		566	my $self = shift;
		567
		568	unless ($self->{_status}) {
		569	my $current = $current;
		570
		571	push @{$self->{_on_destroy}}, sub {
		572	$current->ready;
		573	undef $current;
		574	};
		575
		576	&schedule while $current;
		577	}
		578
		579	wantarray ? @{$self->{_status}} : $self->{_status}[0];
218	}	580	}
219		581
		582	=item $coro->on_destroy (\&cb)
		583
		584	Registers a callback that is called when this coro gets destroyed,
		585	but before it is joined. The callback gets passed the terminate arguments,
		586	if any, and I<must not> die, under any circumstances.
		587
		588	=cut
		589
		590	sub on_destroy {
		591	my ($self, $cb) = @_;
		592
		593	push @{ $self->{_on_destroy} }, $cb;
		594	}
		595
		596	=item $oldprio = $coro->prio ($newprio)
		597
		598	Sets (or gets, if the argument is missing) the priority of the
		599	coro. Higher priority coro get run before lower priority
		600	coro. Priorities are small signed integers (currently -4 .. +3),
		601	that you can refer to using PRIO_xxx constants (use the import tag :prio
		602	to get then):
		603
		604	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		605	3 > 1 > 0 > -1 > -3 > -4
		606
		607	# set priority to HIGH
		608	current->prio (PRIO_HIGH);
		609
		610	The idle coro ($Coro::idle) always has a lower priority than any
		611	existing coro.
		612
		613	Changing the priority of the current coro will take effect immediately,
		614	but changing the priority of coro in the ready queue (but not
		615	running) will only take effect after the next schedule (of that
		616	coro). This is a bug that will be fixed in some future version.
		617
		618	=item $newprio = $coro->nice ($change)
		619
		620	Similar to C<prio>, but subtract the given value from the priority (i.e.
		621	higher values mean lower priority, just as in unix).
		622
		623	=item $olddesc = $coro->desc ($newdesc)
		624
		625	Sets (or gets in case the argument is missing) the description for this
		626	coro. This is just a free-form string you can associate with a
		627	coro.
		628
		629	This method simply sets the C<< $coro->{desc} >> member to the given
		630	string. You can modify this member directly if you wish.
		631
		632	=cut
		633
		634	sub desc {
		635	my $old = $_[0]{desc};
		636	$_[0]{desc} = $_[1] if @_ > 1;
		637	$old;
		638	}
		639
		640	sub transfer {
		641	require Carp;
		642	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		643	}
		644
220	=back	645	=back
221		646
		647	=head1 GLOBAL FUNCTIONS
		648
		649	=over 4
		650
		651	=item Coro::nready
		652
		653	Returns the number of coro that are currently in the ready state,
		654	i.e. that can be switched to by calling C<schedule> directory or
		655	indirectly. The value C<0> means that the only runnable coro is the
		656	currently running one, so C<cede> would have no effect, and C<schedule>
		657	would cause a deadlock unless there is an idle handler that wakes up some
		658	coro.
		659
		660	=item my $guard = Coro::guard { ... }
		661
		662	This function still exists, but is deprecated. Please use the
		663	C<Guard::guard> function instead.
		664
		665	=cut
		666
		667	BEGIN { *guard = \&Guard::guard }
		668
		669	=item unblock_sub { ... }
		670
		671	This utility function takes a BLOCK or code reference and "unblocks" it,
		672	returning a new coderef. Unblocking means that calling the new coderef
		673	will return immediately without blocking, returning nothing, while the
		674	original code ref will be called (with parameters) from within another
		675	coro.
		676
		677	The reason this function exists is that many event libraries (such as the
		678	venerable L<Event\|Event> module) are not thread-safe (a weaker form
		679	of reentrancy). This means you must not block within event callbacks,
		680	otherwise you might suffer from crashes or worse. The only event library
		681	currently known that is safe to use without C<unblock_sub> is L<EV>.
		682
		683	This function allows your callbacks to block by executing them in another
		684	coro where it is safe to block. One example where blocking is handy
		685	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		686	disk, for example.
		687
		688	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		689	creating event callbacks that want to block.
		690
		691	If your handler does not plan to block (e.g. simply sends a message to
		692	another coro, or puts some other coro into the ready queue), there is
		693	no reason to use C<unblock_sub>.
		694
		695	Note that you also need to use C<unblock_sub> for any other callbacks that
		696	are indirectly executed by any C-based event loop. For example, when you
		697	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		698	provides callbacks that are the result of some event callback, then you
		699	must not block either, or use C<unblock_sub>.
		700
		701	=cut
		702
		703	our @unblock_queue;
		704
		705	# we create a special coro because we want to cede,
		706	# to reduce pressure on the coro pool (because most callbacks
		707	# return immediately and can be reused) and because we cannot cede
		708	# inside an event callback.
		709	our $unblock_scheduler = new Coro sub {
		710	while () {
		711	while (my $cb = pop @unblock_queue) {
		712	&async_pool (@$cb);
		713
		714	# for short-lived callbacks, this reduces pressure on the coro pool
		715	# as the chance is very high that the async_poll coro will be back
		716	# in the idle state when cede returns
		717	cede;
		718	}
		719	schedule; # sleep well
		720	}
		721	};
		722	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
		723
		724	sub unblock_sub(&) {
		725	my $cb = shift;
		726
		727	sub {
		728	unshift @unblock_queue, [$cb, @_];
		729	$unblock_scheduler->ready;
		730	}
		731	}
		732
		733	=item $cb = Coro::rouse_cb
		734
		735	Create and return a "rouse callback". That's a code reference that,
		736	when called, will remember a copy of its arguments and notify the owner
		737	coro of the callback.
		738
		739	See the next function.
		740
		741	=item @args = Coro::rouse_wait [$cb]
		742
		743	Wait for the specified rouse callback (or the last one that was created in
		744	this coro).
		745
		746	As soon as the callback is invoked (or when the callback was invoked
		747	before C<rouse_wait>), it will return the arguments originally passed to
		748	the rouse callback. In scalar context, that means you get the I<last>
		749	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		750	statement at the end.
		751
		752	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		753
		754	=back
		755
222	=cut	756	=cut
223		757
224	1;	758	1;
225		759
226	=head1 BUGS	760	=head1 HOW TO WAIT FOR A CALLBACK
227		761
228	- could be faster, especially when the core would introduce special	762	It is very common for a coro to wait for some callback to be
229	support for coroutines (like it does for threads).	763	called. This occurs naturally when you use coro in an otherwise
230	- there is still a memleak on coroutine termination that I could not	764	event-based program, or when you use event-based libraries.
231	identify. Could be as small as a single SV.	765
232	- this module is not well-tested.	766	These typically register a callback for some event, and call that callback
		767	when the event occured. In a coro, however, you typically want to
		768	just wait for the event, simplyifying things.
		769
		770	For example C<< AnyEvent->child >> registers a callback to be called when
		771	a specific child has exited:
		772
		773	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		774
		775	But from within a coro, you often just want to write this:
		776
		777	my $status = wait_for_child $pid;
		778
		779	Coro offers two functions specifically designed to make this easy,
		780	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		781
		782	The first function, C<rouse_cb>, generates and returns a callback that,
		783	when invoked, will save its arguments and notify the coro that
		784	created the callback.
		785
		786	The second function, C<rouse_wait>, waits for the callback to be called
		787	(by calling C<schedule> to go to sleep) and returns the arguments
		788	originally passed to the callback.
		789
		790	Using these functions, it becomes easy to write the C<wait_for_child>
		791	function mentioned above:
		792
		793	sub wait_for_child($) {
		794	my ($pid) = @_;
		795
		796	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		797
		798	my ($rpid, $rstatus) = Coro::rouse_wait;
		799	$rstatus
		800	}
		801
		802	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		803	you can roll your own, using C<schedule>:
		804
		805	sub wait_for_child($) {
		806	my ($pid) = @_;
		807
		808	# store the current coro in $current,
		809	# and provide result variables for the closure passed to ->child
		810	my $current = $Coro::current;
		811	my ($done, $rstatus);
		812
		813	# pass a closure to ->child
		814	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		815	$rstatus = $_[1]; # remember rstatus
		816	$done = 1; # mark $rstatus as valud
		817	});
		818
		819	# wait until the closure has been called
		820	schedule while !$done;
		821
		822	$rstatus
		823	}
		824
		825
		826	=head1 BUGS/LIMITATIONS
		827
		828	=over 4
		829
		830	=item fork with pthread backend
		831
		832	When Coro is compiled using the pthread backend (which isn't recommended
		833	but required on many BSDs as their libcs are completely broken), then
		834	coro will not survive a fork. There is no known workaround except to
		835	fix your libc and use a saner backend.
		836
		837	=item perl process emulation ("threads")
		838
		839	This module is not perl-pseudo-thread-safe. You should only ever use this
		840	module from the first thread (this requirement might be removed in the
		841	future to allow per-thread schedulers, but Coro::State does not yet allow
		842	this). I recommend disabling thread support and using processes, as having
		843	the windows process emulation enabled under unix roughly halves perl
		844	performance, even when not used.
		845
		846	=item coro switching is not signal safe
		847
		848	You must not switch to another coro from within a signal handler
		849	(only relevant with %SIG - most event libraries provide safe signals).
		850
		851	That means you I<MUST NOT> call any function that might "block" the
		852	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		853	anything that calls those. Everything else, including calling C<ready>,
		854	works.
		855
		856	=back
		857
		858
		859	=head1 WINDOWS PROCESS EMULATION
		860
		861	A great many people seem to be confused about ithreads (for example, Chip
		862	Salzenberg called me unintelligent, incapable, stupid and gullible,
		863	while in the same mail making rather confused statements about perl
		864	ithreads (for example, that memory or files would be shared), showing his
		865	lack of understanding of this area - if it is hard to understand for Chip,
		866	it is probably not obvious to everybody).
		867
		868	What follows is an ultra-condensed version of my talk about threads in
		869	scripting languages given onthe perl workshop 2009:
		870
		871	The so-called "ithreads" were originally implemented for two reasons:
		872	first, to (badly) emulate unix processes on native win32 perls, and
		873	secondly, to replace the older, real thread model ("5.005-threads").
		874
		875	It does that by using threads instead of OS processes. The difference
		876	between processes and threads is that threads share memory (and other
		877	state, such as files) between threads within a single process, while
		878	processes do not share anything (at least not semantically). That
		879	means that modifications done by one thread are seen by others, while
		880	modifications by one process are not seen by other processes.
		881
		882	The "ithreads" work exactly like that: when creating a new ithreads
		883	process, all state is copied (memory is copied physically, files and code
		884	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		885	the same behaviour can be achieved by using operating system processes,
		886	except that UNIX typically uses hardware built into the system to do this
		887	efficiently, while the windows process emulation emulates this hardware in
		888	software (rather efficiently, but of course it is still much slower than
		889	dedicated hardware).
		890
		891	As mentioned before, loading code, modifying code, modifying data
		892	structures and so on is only visible in the ithreads process doing the
		893	modification, not in other ithread processes within the same OS process.
		894
		895	This is why "ithreads" do not implement threads for perl at all, only
		896	processes. What makes it so bad is that on non-windows platforms, you can
		897	actually take advantage of custom hardware for this purpose (as evidenced
		898	by the forks module, which gives you the (i-) threads API, just much
		899	faster).
		900
		901	Sharing data is in the i-threads model is done by transfering data
		902	structures between threads using copying semantics, which is very slow -
		903	shared data simply does not exist. Benchmarks using i-threads which are
		904	communication-intensive show extremely bad behaviour with i-threads (in
		905	fact, so bad that Coro, which cannot take direct advantage of multiple
		906	CPUs, is often orders of magnitude faster because it shares data using
		907	real threads, refer to my talk for details).
		908
		909	As summary, i-threads use threads to implement processes, while
		910	the compatible forks module uses processes to emulate, uhm,
		911	processes. I-threads slow down every perl program when enabled, and
		912	outside of windows, serve no (or little) practical purpose, but
		913	disadvantages every single-threaded Perl program.
		914
		915	This is the reason that I try to avoid the name "ithreads", as it is
		916	misleading as it implies that it implements some kind of thread model for
		917	perl, and prefer the name "windows process emulation", which describes the
		918	actual use and behaviour of it much better.
233		919
234	=head1 SEE ALSO	920	=head1 SEE ALSO
235		921
236	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	922	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
237	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	923
		924	Debugging: L<Coro::Debug>.
		925
		926	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
		927
		928	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		929	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		930
		931	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
		932
		933	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		934	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		935	L<Coro::Select>.
		936
		937	XS API: L<Coro::MakeMaker>.
		938
		939	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
238		940
239	=head1 AUTHOR	941	=head1 AUTHOR
240		942
241	Marc Lehmann <pcg@goof.com>	943	Marc Lehmann <schmorp@schmorp.de>
242	http://www.goof.com/pcg/marc/	944	http://home.schmorp.de/
243		945
244	=cut	946	=cut
245		947

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