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

Comparing Coro/Coro.pm (file contents):
Revision 1.220 by root, Sun Nov 16 11:12:57 2008 UTC vs.
Revision 1.282 by root, Sun Dec 26 16:23:51 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
11	print "2\n";	11	print "2\n";
12	cede; # yield back to main	12	cede; # yield back to main
13	print "4\n";	13	print "4\n";
14	};	14	};
15	print "1\n";	15	print "1\n";
16	cede; # yield to coroutine	16	cede; # yield to coro
17	print "3\n";	17	print "3\n";
18	cede; # and again	18	cede; # and again
19		19
20	# use locking	20	# use locking
21	use Coro::Semaphore;	21	use Coro::Semaphore;
…		…
26	$locked = 1;	26	$locked = 1;
27	$lock->up;	27	$lock->up;
28		28
29	=head1 DESCRIPTION	29	=head1 DESCRIPTION
30		30
31	This module collection manages coroutines. Coroutines are similar to	31	For a tutorial-style introduction, please read the L<Coro::Intro>
32	threads but don't (in general) run in parallel at the same time even	32	manpage. This manpage mainly contains reference information.
33	on SMP machines. The specific flavor of coroutine used in this module
34	also guarantees you that it will not switch between coroutines unless
35	necessary, at easily-identified points in your program, so locking and
36	parallel access are rarely an issue, making coroutine programming much
37	safer and easier than threads programming.
38		33
39	Unlike a normal perl program, however, coroutines allow you to have	34	This module collection manages continuations in general, most often in
40	multiple running interpreters that share data, which is especially useful	35	the form of cooperative threads (also called coros, or simply "coro"
41	to code pseudo-parallel processes and for event-based programming, such as	36	in the documentation). They are similar to kernel threads but don't (in
42	multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to	37	general) run in parallel at the same time even on SMP machines. The
43	learn more.	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.
44		43
45	Coroutines are also useful because Perl has no support for threads (the so	44	Unlike the so-called "Perl threads" (which are not actually real threads
46	called "threads" that perl offers are nothing more than the (bad) process	45	but only the windows process emulation (see section of same name for more
47	emulation coming from the Windows platform: On standard operating systems	46	details) ported to unix, and as such act as processes), Coro provides
48	they serve no purpose whatsoever, except by making your programs slow and	47	a full shared address space, which makes communication between threads
49	making them use a lot of memory. Best disable them when building perl, or	48	very easy. And Coro's threads are fast, too: disabling the Windows
50	aks your software vendor/distributor to do it for you).	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.
51		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
52	In this module, coroutines are defined as "callchain + lexical variables +	60	In this module, a thread is defined as "callchain + lexical variables +
53	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	61	some package variables + C stack), that is, a thread has its own callchain,
54	its own set of lexicals and its own set of perls most important global	62	its own set of lexicals and its own set of perls most important global
55	variables (see L<Coro::State> for more configuration).	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.
56		67
57	=cut	68	=cut
58		69
59	package Coro;	70	package Coro;
60		71
61	use strict qw(vars subs);	72	use common::sense;
62	no warnings "uninitialized";	73
		74	use Carp ();
		75
		76	use Guard ();
63		77
64	use Coro::State;	78	use Coro::State;
65		79
66	use base qw(Coro::State Exporter);	80	use base qw(Coro::State Exporter);
67		81
68	our $idle; # idle handler	82	our $idle; # idle handler
69	our $main; # main coroutine	83	our $main; # main coro
70	our $current; # current coroutine	84	our $current; # current coro
71		85
72	our $VERSION = 5.0;	86	our $VERSION = 5.25;
73		87
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	91	);
78	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	92	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
79		93
		94	=head1 GLOBAL VARIABLES
		95
80	=over 4	96	=over 4
81		97
82	=item $Coro::main	98	=item $Coro::main
83		99
84	This variable stores the coroutine object that represents the main	100	This variable stores the Coro object that represents the main
85	program. While you cna C<ready> it and do most other things you can do to	101	program. While you cna C<ready> it and do most other things you can do to
86	coroutines, it is mainly useful to compare again C<$Coro::current>, to see	102	coro, it is mainly useful to compare again C<$Coro::current>, to see
87	whether you are running in the main program or not.	103	whether you are running in the main program or not.
88		104
89	=cut	105	=cut
90		106
91	# $main is now being initialised by Coro::State	107	# $main is now being initialised by Coro::State
92		108
93	=item $Coro::current	109	=item $Coro::current
94		110
95	The coroutine object representing the current coroutine (the last	111	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	112	coro that the Coro scheduler switched to). The initial value is
97	C<$Coro::main> (of course).	113	C<$Coro::main> (of course).
98		114
99	This variable is B<strictly> I<read-only>. You can take copies of the	115	This variable is B<strictly> I<read-only>. You can take copies of the
100	value stored in it and use it as any other coroutine object, but you must	116	value stored in it and use it as any other Coro object, but you must
101	not otherwise modify the variable itself.	117	not otherwise modify the variable itself.
102		118
103	=cut	119	=cut
104		120
105	sub current() { $current } # [DEPRECATED]	121	sub current() { $current } # [DEPRECATED]
106		122
107	=item $Coro::idle	123	=item $Coro::idle
108		124
109	This variable is mainly useful to integrate Coro into event loops. It is	125	This variable is mainly useful to integrate Coro into event loops. It is
110	usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is	126	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
111	pretty low-level functionality.	127	pretty low-level functionality.
112		128
113	This variable stores a callback that is called whenever the scheduler	129	This variable stores a Coro object that is put into the ready queue when
114	finds no ready coroutines to run. The default implementation prints	130	there are no other ready threads (without invoking any ready hooks).
115	"FATAL: deadlock detected" and exits, because the program has no other way
116	to continue.
117		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
118	This hook is overwritten by modules such as C<Coro::Timer> and	135	This hook is overwritten by modules such as C<Coro::EV> and
119	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	136	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
120	coroutine so the scheduler can run it.	137	coro so the scheduler can run it.
121		138
122	Note that the callback I<must not>, under any circumstances, block
123	the current coroutine. Normally, this is achieved by having an "idle
124	coroutine" that calls the event loop and then blocks again, and then
125	readying that coroutine in the idle handler.
126
127	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this	139	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
128	technique.
129		140
130	Please note that if your callback recursively invokes perl (e.g. for event
131	handlers), then it must be prepared to be called recursively itself.
132
133	=cut	141	=cut
134		142
135	$idle = sub {	143	# \|\|= because other modules could have provided their own by now
136	require Carp;	144	$idle \|\|= new Coro sub {
137	Carp::croak ("FATAL: deadlock detected");	145	require Coro::Debug;
		146	die "FATAL: deadlock detected.\n"
		147	. Coro::Debug::ps_listing ();
138	};	148	};
139		149
140	sub _cancel {
141	my ($self) = @_;
142
143	# free coroutine data and mark as destructed
144	$self->_destroy
145	or return;
146
147	# call all destruction callbacks
148	$_->(@{$self->{_status}})
149	for @{ delete $self->{_on_destroy} \|\| [] };
150	}
151
152	# this coroutine is necessary because a coroutine	150	# this coro is necessary because a coro
153	# cannot destroy itself.	151	# cannot destroy itself.
154	my @destroy;	152	our @destroy;
155	my $manager;	153	our $manager;
156		154
157	$manager = new Coro sub {	155	$manager = new Coro sub {
158	while () {	156	while () {
159	(shift @destroy)->_cancel	157	Coro::State::cancel shift @destroy
160	while @destroy;	158	while @destroy;
161		159
162	&schedule;	160	&schedule;
163	}	161	}
164	};	162	};
165	$manager->{desc} = "[coro manager]";	163	$manager->{desc} = "[coro manager]";
166	$manager->prio (PRIO_MAX);	164	$manager->prio (PRIO_MAX);
167		165
168	=back	166	=back
169		167
170	=head2 SIMPLE COROUTINE CREATION	168	=head1 SIMPLE CORO CREATION
171		169
172	=over 4	170	=over 4
173		171
174	=item async { ... } [@args...]	172	=item async { ... } [@args...]
175		173
176	Create a new coroutine and return it's coroutine object (usually	174	Create a new coro and return its Coro object (usually
177	unused). The coroutine will be put into the ready queue, so	175	unused). The coro will be put into the ready queue, so
178	it will start running automatically on the next scheduler run.	176	it will start running automatically on the next scheduler run.
179		177
180	The first argument is a codeblock/closure that should be executed in the	178	The first argument is a codeblock/closure that should be executed in the
181	coroutine. When it returns argument returns the coroutine is automatically	179	coro. When it returns argument returns the coro is automatically
182	terminated.	180	terminated.
183		181
184	The remaining arguments are passed as arguments to the closure.	182	The remaining arguments are passed as arguments to the closure.
185		183
186	See the C<Coro::State::new> constructor for info about the coroutine	184	See the C<Coro::State::new> constructor for info about the coro
187	environment in which coroutines are executed.	185	environment in which coro are executed.
188		186
189	Calling C<exit> in a coroutine will do the same as calling exit outside	187	Calling C<exit> in a coro will do the same as calling exit outside
190	the coroutine. Likewise, when the coroutine dies, the program will exit,	188	the coro. Likewise, when the coro dies, the program will exit,
191	just as it would in the main program.	189	just as it would in the main program.
192		190
193	If you do not want that, you can provide a default C<die> handler, or	191	If you do not want that, you can provide a default C<die> handler, or
194	simply avoid dieing (by use of C<eval>).	192	simply avoid dieing (by use of C<eval>).
195		193
196	Example: Create a new coroutine that just prints its arguments.	194	Example: Create a new coro that just prints its arguments.
197		195
198	async {	196	async {
199	print "@_\n";	197	print "@_\n";
200	} 1,2,3,4;	198	} 1,2,3,4;
201		199
202	=cut
203
204	sub async(&@) {
205	my $coro = new Coro @_;
206	$coro->ready;
207	$coro
208	}
209
210	=item async_pool { ... } [@args...]	200	=item async_pool { ... } [@args...]
211		201
212	Similar to C<async>, but uses a coroutine pool, so you should not call	202	Similar to C<async>, but uses a coro pool, so you should not call
213	terminate or join on it (although you are allowed to), and you get a	203	terminate or join on it (although you are allowed to), and you get a
214	coroutine that might have executed other code already (which can be good	204	coro that might have executed other code already (which can be good
215	or bad :).	205	or bad :).
216		206
217	On the plus side, this function is faster than creating (and destroying)	207	On the plus side, this function is about twice as fast as creating (and
218	a completly new coroutine, so if you need a lot of generic coroutines in	208	destroying) a completely new coro, so if you need a lot of generic
219	quick successsion, use C<async_pool>, not C<async>.	209	coros in quick successsion, use C<async_pool>, not C<async>.
220		210
221	The code block is executed in an C<eval> context and a warning will be	211	The code block is executed in an C<eval> context and a warning will be
222	issued in case of an exception instead of terminating the program, as	212	issued in case of an exception instead of terminating the program, as
223	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	213	C<async> does. As the coro is being reused, stuff like C<on_destroy>
224	will not work in the expected way, unless you call terminate or cancel,	214	will not work in the expected way, unless you call terminate or cancel,
225	which somehow defeats the purpose of pooling (but is fine in the	215	which somehow defeats the purpose of pooling (but is fine in the
226	exceptional case).	216	exceptional case).
227		217
228	The priority will be reset to C<0> after each run, tracing will be	218	The priority will be reset to C<0> after each run, tracing will be
229	disabled, the description will be reset and the default output filehandle	219	disabled, the description will be reset and the default output filehandle
230	gets restored, so you can change all these. Otherwise the coroutine will	220	gets restored, so you can change all these. Otherwise the coro will
231	be re-used "as-is": most notably if you change other per-coroutine global	221	be re-used "as-is": most notably if you change other per-coro global
232	stuff such as C<$/> you I<must needs> revert that change, which is most	222	stuff such as C<$/> you I<must needs> revert that change, which is most
233	simply done by using local as in: C<< local $/ >>.	223	simply done by using local as in: C<< local $/ >>.
234		224
235	The idle pool size is limited to C<8> idle coroutines (this can be	225	The idle pool size is limited to C<8> idle coros (this can be
236	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle	226	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
237	coros as required.	227	coros as required.
238		228
239	If you are concerned about pooled coroutines growing a lot because a	229	If you are concerned about pooled coros growing a lot because a
240	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	230	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
241	{ terminate }> once per second or so to slowly replenish the pool. In	231	{ terminate }> once per second or so to slowly replenish the pool. In
242	addition to that, when the stacks used by a handler grows larger than 16kb	232	addition to that, when the stacks used by a handler grows larger than 32kb
243	(adjustable via $Coro::POOL_RSS) it will also be destroyed.	233	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
244		234
245	=cut	235	=cut
246		236
247	our $POOL_SIZE = 8;	237	our $POOL_SIZE = 8;
248	our $POOL_RSS = 16 * 1024;	238	our $POOL_RSS = 32 * 1024;
249	our @async_pool;	239	our @async_pool;
250		240
251	sub pool_handler {	241	sub pool_handler {
252	my $cb;
253
254	while () {	242	while () {
255	eval {	243	eval {
256	while () {	244	&{&_pool_handler} while 1;
257	_pool_1 $cb;
258	&$cb;
259	_pool_2 $cb;
260	&schedule;
261	}
262	};	245	};
263		246
264	if ($@) {
265	last if $@ eq "\3async_pool terminate\2\n";
266	warn $@;	247	warn $@ if $@;
267	}
268	}	248	}
269	}	249	}
270		250
271	sub async_pool(&@) {
272	# this is also inlined into the unblock_scheduler
273	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
274
275	$coro->{_invoke} = [@_];
276	$coro->ready;
277
278	$coro
279	}
280
281	=back	251	=back
282		252
283	=head2 STATIC METHODS	253	=head1 STATIC METHODS
284		254
285	Static methods are actually functions that operate on the current coroutine.	255	Static methods are actually functions that implicitly operate on the
		256	current coro.
286		257
287	=over 4	258	=over 4
288		259
289	=item schedule	260	=item schedule
290		261
291	Calls the scheduler. The scheduler will find the next coroutine that is	262	Calls the scheduler. The scheduler will find the next coro that is
292	to be run from the ready queue and switches to it. The next coroutine	263	to be run from the ready queue and switches to it. The next coro
293	to be run is simply the one with the highest priority that is longest	264	to be run is simply the one with the highest priority that is longest
294	in its ready queue. If there is no coroutine ready, it will clal the	265	in its ready queue. If there is no coro ready, it will call the
295	C<$Coro::idle> hook.	266	C<$Coro::idle> hook.
296		267
297	Please note that the current coroutine will I<not> be put into the ready	268	Please note that the current coro will I<not> be put into the ready
298	queue, so calling this function usually means you will never be called	269	queue, so calling this function usually means you will never be called
299	again unless something else (e.g. an event handler) calls C<< ->ready >>,	270	again unless something else (e.g. an event handler) calls C<< ->ready >>,
300	thus waking you up.	271	thus waking you up.
301		272
302	This makes C<schedule> I<the> generic method to use to block the current	273	This makes C<schedule> I<the> generic method to use to block the current
303	coroutine and wait for events: first you remember the current coroutine in	274	coro and wait for events: first you remember the current coro in
304	a variable, then arrange for some callback of yours to call C<< ->ready	275	a variable, then arrange for some callback of yours to call C<< ->ready
305	>> on that once some event happens, and last you call C<schedule> to put	276	>> on that once some event happens, and last you call C<schedule> to put
306	yourself to sleep. Note that a lot of things can wake your coroutine up,	277	yourself to sleep. Note that a lot of things can wake your coro up,
307	so you need to check whether the event indeed happened, e.g. by storing the	278	so you need to check whether the event indeed happened, e.g. by storing the
308	status in a variable.	279	status in a variable.
309		280
310	The canonical way to wait on external events is this:	281	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
311		282
312	{	283	=item cede
313	# remember current coroutine
314	my $current = $Coro::current;
315		284
316	# register a hypothetical event handler	285	"Cede" to other coros. This function puts the current coro into
317	on_event_invoke sub {	286	the ready queue and calls C<schedule>, which has the effect of giving
318	# wake up sleeping coroutine	287	up the current "timeslice" to other coros of the same or higher
319	$current->ready;	288	priority. Once your coro gets its turn again it will automatically be
320	undef $current;	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
321	};	344	};
322		345
323	# call schedule until event occurred.	346	Coro::on_leave {
324	# in case we are woken up for other reasons	347	$ENV{TZ} = $old_tz;
325	# (current still defined), loop.	348	tzset; # restore old value
326	Coro::schedule while $current;	349	};
		350
		351	# at this place, the timezone is Antarctica/South_Pole,
		352	# without disturbing the TZ of any other coro.
327	}	353	};
328		354
329	=item cede	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.
330		358
331	"Cede" to other coroutines. This function puts the current coroutine into	359	Another interesting example implements time-sliced multitasking using
332	the ready queue and calls C<schedule>, which has the effect of giving	360	interval timers (this could obviously be optimised, but does the job):
333	up the current "timeslice" to other coroutines of the same or higher
334	priority. Once your coroutine gets its turn again it will automatically be
335	resumed.
336		361
337	This function is often called C<yield> in other languages.	362	# "timeslice" the given block
		363	sub timeslice(&) {
		364	use Time::HiRes ();
338		365
339	=item Coro::cede_notself	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	};
340		376
341	Works like cede, but is not exported by default and will cede to I<any>	377	&{+shift};
342	coroutine, regardless of priority. This is useful sometimes to ensure	378	}
343	progress is made.
344		379
345	=item terminate [arg...]	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	};
346		387
347	Terminates the current coroutine with the given status values (see L<cancel>).
348		388
349	=item killall	389	=item killall
350		390
351	Kills/terminates/cancels all coroutines except the currently running	391	Kills/terminates/cancels all coros except the currently running one.
352	one. This is useful after a fork, either in the child or the parent, as
353	usually only one of them should inherit the running coroutines.
354		392
355	Note that while this will try to free some of the main programs resources,	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
356	you cannot free all of them, so if a coroutine that is not the main	395	cannot free all of them, so if a coro that is not the main coro
357	program calls this function, there will be some one-time resource leak.	396	calls this function, there will be some one-time resource leak.
358		397
359	=cut	398	=cut
360
361	sub terminate {
362	$current->cancel (@_);
363	}
364		399
365	sub killall {	400	sub killall {
366	for (Coro::State::list) {	401	for (Coro::State::list) {
367	$_->cancel	402	$_->cancel
368	if $_ != $current && UNIVERSAL::isa $_, "Coro";	403	if $_ != $current && UNIVERSAL::isa $_, "Coro";
369	}	404	}
370	}	405	}
371		406
372	=back	407	=back
373		408
374	=head2 COROUTINE METHODS	409	=head1 CORO OBJECT METHODS
375		410
376	These are the methods you can call on coroutine objects (or to create	411	These are the methods you can call on coro objects (or to create
377	them).	412	them).
378		413
379	=over 4	414	=over 4
380		415
381	=item new Coro \&sub [, @args...]	416	=item new Coro \&sub [, @args...]
382		417
383	Create a new coroutine and return it. When the sub returns, the coroutine	418	Create a new coro and return it. When the sub returns, the coro
384	automatically terminates as if C<terminate> with the returned values were	419	automatically terminates as if C<terminate> with the returned values were
385	called. To make the coroutine run you must first put it into the ready	420	called. To make the coro run you must first put it into the ready
386	queue by calling the ready method.	421	queue by calling the ready method.
387		422
388	See C<async> and C<Coro::State::new> for additional info about the	423	See C<async> and C<Coro::State::new> for additional info about the
389	coroutine environment.	424	coro environment.
390		425
391	=cut	426	=cut
392		427
393	sub _run_coro {	428	sub _coro_run {
394	terminate &{+shift};	429	terminate &{+shift};
395	}	430	}
396		431
397	sub new {
398	my $class = shift;
399
400	$class->SUPER::new (\&_run_coro, @_)
401	}
402
403	=item $success = $coroutine->ready	432	=item $success = $coro->ready
404		433
405	Put the given coroutine into the end of its ready queue (there is one	434	Put the given coro into the end of its ready queue (there is one
406	queue for each priority) and return true. If the coroutine is already in	435	queue for each priority) and return true. If the coro is already in
407	the ready queue, do nothing and return false.	436	the ready queue, do nothing and return false.
408		437
409	This ensures that the scheduler will resume this coroutine automatically	438	This ensures that the scheduler will resume this coro automatically
410	once all the coroutines of higher priority and all coroutines of the same	439	once all the coro of higher priority and all coro of the same
411	priority that were put into the ready queue earlier have been resumed.	440	priority that were put into the ready queue earlier have been resumed.
412		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
413	=item $is_ready = $coroutine->is_ready	467	=item $is_ready = $coro->is_ready
414		468
415	Return whether the coroutine is currently the ready queue or not,	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.
416		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
417	=item $coroutine->cancel (arg...)	483	=item $coro->cancel (arg...)
418		484
419	Terminates the given coroutine and makes it return the given arguments as	485	Terminates the given Coro and makes it return the given arguments as
420	status (default: the empty list). Never returns if the coroutine is the	486	status (default: the empty list). Never returns if the Coro is the
421	current coroutine.	487	current Coro.
422		488
423	=cut	489	=cut
424		490
425	sub cancel {	491	sub cancel {
426	my $self = shift;	492	my $self = shift;
427	$self->{_status} = [@_];
428		493
429	if ($current == $self) {	494	if ($current == $self) {
430	push @destroy, $self;	495	terminate @_;
431	$manager->ready;
432	&schedule while 1;
433	} else {	496	} else {
434	$self->_cancel;	497	$self->{_status} = [@_];
		498	Coro::State::cancel $self;
435	}	499	}
436	}	500	}
437		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
438	=item $coroutine->throw ([$scalar])	521	=item $coro->throw ([$scalar])
439		522
440	If C<$throw> is specified and defined, it will be thrown as an exception	523	If C<$throw> is specified and defined, it will be thrown as an exception
441	inside the coroutine at the next convenient point in time (usually after	524	inside the coro at the next convenient point in time. Otherwise
442	it gains control at the next schedule/transfer/cede). Otherwise clears the
443	exception object.	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.
444		531
445	The exception object will be thrown "as is" with the specified scalar in	532	The exception object will be thrown "as is" with the specified scalar in
446	C<$@>, i.e. if it is a string, no line number or newline will be appended	533	C<$@>, i.e. if it is a string, no line number or newline will be appended
447	(unlike with C<die>).	534	(unlike with C<die>).
448		535
449	This can be used as a softer means than C<cancel> to ask a coroutine to	536	This can be used as a softer means than C<cancel> to ask a coro to
450	end itself, although there is no guarantee that the exception will lead to	537	end itself, although there is no guarantee that the exception will lead to
451	termination, and if the exception isn't caught it might well end the whole	538	termination, and if the exception isn't caught it might well end the whole
452	program.	539	program.
453		540
454	You might also think of C<throw> as being the moral equivalent of	541	You might also think of C<throw> as being the moral equivalent of
455	C<kill>ing a coroutine with a signal (in this case, a scalar).	542	C<kill>ing a coro with a signal (in this case, a scalar).
456		543
457	=item $coroutine->join	544	=item $coro->join
458		545
459	Wait until the coroutine terminates and return any values given to the	546	Wait until the coro terminates and return any values given to the
460	C<terminate> or C<cancel> functions. C<join> can be called concurrently	547	C<terminate> or C<cancel> functions. C<join> can be called concurrently
461	from multiple coroutines, and all will be resumed and given the status	548	from multiple coro, and all will be resumed and given the status
462	return once the C<$coroutine> terminates.	549	return once the C<$coro> terminates.
463		550
464	=cut	551	=cut
465		552
466	sub join {	553	sub join {
467	my $self = shift;	554	my $self = shift;
…		…
478	}	565	}
479		566
480	wantarray ? @{$self->{_status}} : $self->{_status}[0];	567	wantarray ? @{$self->{_status}} : $self->{_status}[0];
481	}	568	}
482		569
483	=item $coroutine->on_destroy (\&cb)	570	=item $coro->on_destroy (\&cb)
484		571
485	Registers a callback that is called when this coroutine gets destroyed,	572	Registers a callback that is called when this coro gets destroyed,
486	but before it is joined. The callback gets passed the terminate arguments,	573	but before it is joined. The callback gets passed the terminate arguments,
487	if any, and I<must not> die, under any circumstances.	574	if any, and I<must not> die, under any circumstances.
488		575
489	=cut	576	=cut
490		577
…		…
492	my ($self, $cb) = @_;	579	my ($self, $cb) = @_;
493		580
494	push @{ $self->{_on_destroy} }, $cb;	581	push @{ $self->{_on_destroy} }, $cb;
495	}	582	}
496		583
497	=item $oldprio = $coroutine->prio ($newprio)	584	=item $oldprio = $coro->prio ($newprio)
498		585
499	Sets (or gets, if the argument is missing) the priority of the	586	Sets (or gets, if the argument is missing) the priority of the
500	coroutine. Higher priority coroutines get run before lower priority	587	coro. Higher priority coro get run before lower priority
501	coroutines. Priorities are small signed integers (currently -4 .. +3),	588	coro. Priorities are small signed integers (currently -4 .. +3),
502	that you can refer to using PRIO_xxx constants (use the import tag :prio	589	that you can refer to using PRIO_xxx constants (use the import tag :prio
503	to get then):	590	to get then):
504		591
505	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	592	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
506	3 > 1 > 0 > -1 > -3 > -4	593	3 > 1 > 0 > -1 > -3 > -4
507		594
508	# set priority to HIGH	595	# set priority to HIGH
509	current->prio(PRIO_HIGH);	596	current->prio (PRIO_HIGH);
510		597
511	The idle coroutine ($Coro::idle) always has a lower priority than any	598	The idle coro ($Coro::idle) always has a lower priority than any
512	existing coroutine.	599	existing coro.
513		600
514	Changing the priority of the current coroutine will take effect immediately,	601	Changing the priority of the current coro will take effect immediately,
515	but changing the priority of coroutines in the ready queue (but not	602	but changing the priority of coro in the ready queue (but not
516	running) will only take effect after the next schedule (of that	603	running) will only take effect after the next schedule (of that
517	coroutine). This is a bug that will be fixed in some future version.	604	coro). This is a bug that will be fixed in some future version.
518		605
519	=item $newprio = $coroutine->nice ($change)	606	=item $newprio = $coro->nice ($change)
520		607
521	Similar to C<prio>, but subtract the given value from the priority (i.e.	608	Similar to C<prio>, but subtract the given value from the priority (i.e.
522	higher values mean lower priority, just as in unix).	609	higher values mean lower priority, just as in unix).
523		610
524	=item $olddesc = $coroutine->desc ($newdesc)	611	=item $olddesc = $coro->desc ($newdesc)
525		612
526	Sets (or gets in case the argument is missing) the description for this	613	Sets (or gets in case the argument is missing) the description for this
527	coroutine. This is just a free-form string you can associate with a	614	coro. This is just a free-form string you can associate with a
528	coroutine.	615	coro.
529		616
530	This method simply sets the C<< $coroutine->{desc} >> member to the given	617	This method simply sets the C<< $coro->{desc} >> member to the given
531	string. You can modify this member directly if you wish.	618	string. You can modify this member directly if you wish, and in fact, this
		619	is often preferred to indicate major processing states that cna then be
		620	seen for example in a L<Coro::Debug> session:
		621
		622	sub my_long_function {
		623	local $Coro::current->{desc} = "now in my_long_function";
		624	...
		625	$Coro::current->{desc} = "my_long_function: phase 1";
		626	...
		627	$Coro::current->{desc} = "my_long_function: phase 2";
		628	...
		629	}
532		630
533	=cut	631	=cut
534		632
535	sub desc {	633	sub desc {
536	my $old = $_[0]{desc};	634	my $old = $_[0]{desc};
537	$_[0]{desc} = $_[1] if @_ > 1;	635	$_[0]{desc} = $_[1] if @_ > 1;
538	$old;	636	$old;
539	}	637	}
540		638
		639	sub transfer {
		640	require Carp;
		641	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		642	}
		643
541	=back	644	=back
542		645
543	=head2 GLOBAL FUNCTIONS	646	=head1 GLOBAL FUNCTIONS
544		647
545	=over 4	648	=over 4
546		649
547	=item Coro::nready	650	=item Coro::nready
548		651
549	Returns the number of coroutines that are currently in the ready state,	652	Returns the number of coro that are currently in the ready state,
550	i.e. that can be switched to by calling C<schedule> directory or	653	i.e. that can be switched to by calling C<schedule> directory or
551	indirectly. The value C<0> means that the only runnable coroutine is the	654	indirectly. The value C<0> means that the only runnable coro is the
552	currently running one, so C<cede> would have no effect, and C<schedule>	655	currently running one, so C<cede> would have no effect, and C<schedule>
553	would cause a deadlock unless there is an idle handler that wakes up some	656	would cause a deadlock unless there is an idle handler that wakes up some
554	coroutines.	657	coro.
555		658
556	=item my $guard = Coro::guard { ... }	659	=item my $guard = Coro::guard { ... }
557		660
558	This creates and returns a guard object. Nothing happens until the object	661	This function still exists, but is deprecated. Please use the
559	gets destroyed, in which case the codeblock given as argument will be	662	C<Guard::guard> function instead.
560	executed. This is useful to free locks or other resources in case of a
561	runtime error or when the coroutine gets canceled, as in both cases the
562	guard block will be executed. The guard object supports only one method,
563	C<< ->cancel >>, which will keep the codeblock from being executed.
564		663
565	Example: set some flag and clear it again when the coroutine gets canceled
566	or the function returns:
567
568	sub do_something {
569	my $guard = Coro::guard { $busy = 0 };
570	$busy = 1;
571
572	# do something that requires $busy to be true
573	}
574
575	=cut	664	=cut
576		665
577	sub guard(&) {	666	BEGIN { *guard = \&Guard::guard }
578	bless \(my $cb = $_[0]), "Coro::guard"
579	}
580
581	sub Coro::guard::cancel {
582	${$_[0]} = sub { };
583	}
584
585	sub Coro::guard::DESTROY {
586	${$_[0]}->();
587	}
588
589		667
590	=item unblock_sub { ... }	668	=item unblock_sub { ... }
591		669
592	This utility function takes a BLOCK or code reference and "unblocks" it,	670	This utility function takes a BLOCK or code reference and "unblocks" it,
593	returning a new coderef. Unblocking means that calling the new coderef	671	returning a new coderef. Unblocking means that calling the new coderef
594	will return immediately without blocking, returning nothing, while the	672	will return immediately without blocking, returning nothing, while the
595	original code ref will be called (with parameters) from within another	673	original code ref will be called (with parameters) from within another
596	coroutine.	674	coro.
597		675
598	The reason this function exists is that many event libraries (such as the	676	The reason this function exists is that many event libraries (such as
599	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	677	the venerable L<Event\|Event> module) are not thread-safe (a weaker form
600	of thread-safety). This means you must not block within event callbacks,	678	of reentrancy). This means you must not block within event callbacks,
601	otherwise you might suffer from crashes or worse. The only event library	679	otherwise you might suffer from crashes or worse. The only event library
602	currently known that is safe to use without C<unblock_sub> is L<EV>.	680	currently known that is safe to use without C<unblock_sub> is L<EV> (but
		681	you might still run into deadlocks if all event loops are blocked).
		682
		683	Coro will try to catch you when you block in the event loop
		684	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		685	only works when you do not run your own event loop.
603		686
604	This function allows your callbacks to block by executing them in another	687	This function allows your callbacks to block by executing them in another
605	coroutine where it is safe to block. One example where blocking is handy	688	coro where it is safe to block. One example where blocking is handy
606	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	689	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
607	disk, for example.	690	disk, for example.
608		691
609	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	692	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
610	creating event callbacks that want to block.	693	creating event callbacks that want to block.
611		694
612	If your handler does not plan to block (e.g. simply sends a message to	695	If your handler does not plan to block (e.g. simply sends a message to
613	another coroutine, or puts some other coroutine into the ready queue),	696	another coro, or puts some other coro into the ready queue), there is
614	there is no reason to use C<unblock_sub>.	697	no reason to use C<unblock_sub>.
615		698
616	Note that you also need to use C<unblock_sub> for any other callbacks that	699	Note that you also need to use C<unblock_sub> for any other callbacks that
617	are indirectly executed by any C-based event loop. For example, when you	700	are indirectly executed by any C-based event loop. For example, when you
618	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	701	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
619	provides callbacks that are the result of some event callback, then you	702	provides callbacks that are the result of some event callback, then you
…		…
628	# return immediately and can be reused) and because we cannot cede	711	# return immediately and can be reused) and because we cannot cede
629	# inside an event callback.	712	# inside an event callback.
630	our $unblock_scheduler = new Coro sub {	713	our $unblock_scheduler = new Coro sub {
631	while () {	714	while () {
632	while (my $cb = pop @unblock_queue) {	715	while (my $cb = pop @unblock_queue) {
633	# this is an inlined copy of async_pool	716	&async_pool (@$cb);
634	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
635		717
636	$coro->{_invoke} = $cb;
637	$coro->ready;
638	cede; # for short-lived callbacks, this reduces pressure on the coro pool	718	# for short-lived callbacks, this reduces pressure on the coro pool
		719	# as the chance is very high that the async_poll coro will be back
		720	# in the idle state when cede returns
		721	cede;
639	}	722	}
640	schedule; # sleep well	723	schedule; # sleep well
641	}	724	}
642	};	725	};
643	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	726	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
649	unshift @unblock_queue, [$cb, @_];	732	unshift @unblock_queue, [$cb, @_];
650	$unblock_scheduler->ready;	733	$unblock_scheduler->ready;
651	}	734	}
652	}	735	}
653		736
		737	=item $cb = rouse_cb
		738
		739	Create and return a "rouse callback". That's a code reference that,
		740	when called, will remember a copy of its arguments and notify the owner
		741	coro of the callback.
		742
		743	See the next function.
		744
		745	=item @args = rouse_wait [$cb]
		746
		747	Wait for the specified rouse callback (or the last one that was created in
		748	this coro).
		749
		750	As soon as the callback is invoked (or when the callback was invoked
		751	before C<rouse_wait>), it will return the arguments originally passed to
		752	the rouse callback. In scalar context, that means you get the I<last>
		753	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		754	statement at the end.
		755
		756	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		757
654	=back	758	=back
655		759
656	=cut	760	=cut
657		761
658	1;	762	1;
		763
		764	=head1 HOW TO WAIT FOR A CALLBACK
		765
		766	It is very common for a coro to wait for some callback to be
		767	called. This occurs naturally when you use coro in an otherwise
		768	event-based program, or when you use event-based libraries.
		769
		770	These typically register a callback for some event, and call that callback
		771	when the event occured. In a coro, however, you typically want to
		772	just wait for the event, simplyifying things.
		773
		774	For example C<< AnyEvent->child >> registers a callback to be called when
		775	a specific child has exited:
		776
		777	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		778
		779	But from within a coro, you often just want to write this:
		780
		781	my $status = wait_for_child $pid;
		782
		783	Coro offers two functions specifically designed to make this easy,
		784	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		785
		786	The first function, C<rouse_cb>, generates and returns a callback that,
		787	when invoked, will save its arguments and notify the coro that
		788	created the callback.
		789
		790	The second function, C<rouse_wait>, waits for the callback to be called
		791	(by calling C<schedule> to go to sleep) and returns the arguments
		792	originally passed to the callback.
		793
		794	Using these functions, it becomes easy to write the C<wait_for_child>
		795	function mentioned above:
		796
		797	sub wait_for_child($) {
		798	my ($pid) = @_;
		799
		800	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		801
		802	my ($rpid, $rstatus) = Coro::rouse_wait;
		803	$rstatus
		804	}
		805
		806	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		807	you can roll your own, using C<schedule>:
		808
		809	sub wait_for_child($) {
		810	my ($pid) = @_;
		811
		812	# store the current coro in $current,
		813	# and provide result variables for the closure passed to ->child
		814	my $current = $Coro::current;
		815	my ($done, $rstatus);
		816
		817	# pass a closure to ->child
		818	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		819	$rstatus = $_[1]; # remember rstatus
		820	$done = 1; # mark $rstatus as valud
		821	});
		822
		823	# wait until the closure has been called
		824	schedule while !$done;
		825
		826	$rstatus
		827	}
		828
659		829
660	=head1 BUGS/LIMITATIONS	830	=head1 BUGS/LIMITATIONS
661		831
662	=over 4	832	=over 4
663		833
664	=item fork with pthread backend	834	=item fork with pthread backend
665		835
666	When Coro is compiled using the pthread backend (which isn't recommended	836	When Coro is compiled using the pthread backend (which isn't recommended
667	but required on many BSDs as their libcs are completely broken), then	837	but required on many BSDs as their libcs are completely broken), then
668	coroutines will not survive a fork. There is no known workaround except to	838	coro will not survive a fork. There is no known workaround except to
669	fix your libc and use a saner backend.	839	fix your libc and use a saner backend.
670		840
671	=item perl process emulation ("threads")	841	=item perl process emulation ("threads")
672		842
673	This module is not perl-pseudo-thread-safe. You should only ever use this	843	This module is not perl-pseudo-thread-safe. You should only ever use this
674	module from the same thread (this requirement might be removed in the	844	module from the first thread (this requirement might be removed in the
675	future to allow per-thread schedulers, but Coro::State does not yet allow	845	future to allow per-thread schedulers, but Coro::State does not yet allow
676	this). I recommend disabling thread support and using processes, as having	846	this). I recommend disabling thread support and using processes, as having
677	the windows process emulation enabled under unix roughly halves perl	847	the windows process emulation enabled under unix roughly halves perl
678	performance, even when not used.	848	performance, even when not used.
679		849
680	=item coroutine switching not signal safe	850	=item coro switching is not signal safe
681		851
682	You must not switch to another coroutine from within a signal handler	852	You must not switch to another coro from within a signal handler (only
683	(only relevant with %SIG - most event libraries provide safe signals).	853	relevant with %SIG - most event libraries provide safe signals), I<unless>
		854	you are sure you are not interrupting a Coro function.
684		855
685	That means you I<MUST NOT> call any fucntion that might "block" the	856	That means you I<MUST NOT> call any function that might "block" the
686	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	857	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
687	anything that calls those. Everything else, including calling C<ready>,	858	anything that calls those. Everything else, including calling C<ready>,
688	works.	859	works.
689		860
690	=back	861	=back
691		862
692		863
		864	=head1 WINDOWS PROCESS EMULATION
		865
		866	A great many people seem to be confused about ithreads (for example, Chip
		867	Salzenberg called me unintelligent, incapable, stupid and gullible,
		868	while in the same mail making rather confused statements about perl
		869	ithreads (for example, that memory or files would be shared), showing his
		870	lack of understanding of this area - if it is hard to understand for Chip,
		871	it is probably not obvious to everybody).
		872
		873	What follows is an ultra-condensed version of my talk about threads in
		874	scripting languages given on the perl workshop 2009:
		875
		876	The so-called "ithreads" were originally implemented for two reasons:
		877	first, to (badly) emulate unix processes on native win32 perls, and
		878	secondly, to replace the older, real thread model ("5.005-threads").
		879
		880	It does that by using threads instead of OS processes. The difference
		881	between processes and threads is that threads share memory (and other
		882	state, such as files) between threads within a single process, while
		883	processes do not share anything (at least not semantically). That
		884	means that modifications done by one thread are seen by others, while
		885	modifications by one process are not seen by other processes.
		886
		887	The "ithreads" work exactly like that: when creating a new ithreads
		888	process, all state is copied (memory is copied physically, files and code
		889	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		890	the same behaviour can be achieved by using operating system processes,
		891	except that UNIX typically uses hardware built into the system to do this
		892	efficiently, while the windows process emulation emulates this hardware in
		893	software (rather efficiently, but of course it is still much slower than
		894	dedicated hardware).
		895
		896	As mentioned before, loading code, modifying code, modifying data
		897	structures and so on is only visible in the ithreads process doing the
		898	modification, not in other ithread processes within the same OS process.
		899
		900	This is why "ithreads" do not implement threads for perl at all, only
		901	processes. What makes it so bad is that on non-windows platforms, you can
		902	actually take advantage of custom hardware for this purpose (as evidenced
		903	by the forks module, which gives you the (i-) threads API, just much
		904	faster).
		905
		906	Sharing data is in the i-threads model is done by transfering data
		907	structures between threads using copying semantics, which is very slow -
		908	shared data simply does not exist. Benchmarks using i-threads which are
		909	communication-intensive show extremely bad behaviour with i-threads (in
		910	fact, so bad that Coro, which cannot take direct advantage of multiple
		911	CPUs, is often orders of magnitude faster because it shares data using
		912	real threads, refer to my talk for details).
		913
		914	As summary, i-threads use threads to implement processes, while
		915	the compatible forks module uses processes to emulate, uhm,
		916	processes. I-threads slow down every perl program when enabled, and
		917	outside of windows, serve no (or little) practical purpose, but
		918	disadvantages every single-threaded Perl program.
		919
		920	This is the reason that I try to avoid the name "ithreads", as it is
		921	misleading as it implies that it implements some kind of thread model for
		922	perl, and prefer the name "windows process emulation", which describes the
		923	actual use and behaviour of it much better.
		924
693	=head1 SEE ALSO	925	=head1 SEE ALSO
694		926
695	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	927	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
696		928
697	Debugging: L<Coro::Debug>.	929	Debugging: L<Coro::Debug>.
698		930
699	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	931	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
700		932
701	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	933	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		934	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
702		935
703	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	936	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
704		937
705	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	938	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		939	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		940	L<Coro::Select>.
706		941
707	XS API: L<Coro::MakeMaker>.	942	XS API: L<Coro::MakeMaker>.
708		943
709	Low level Configuration, Coroutine Environment: L<Coro::State>.	944	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
710		945
711	=head1 AUTHOR	946	=head1 AUTHOR
712		947
713	Marc Lehmann <schmorp@schmorp.de>	948	Marc Lehmann <schmorp@schmorp.de>
714	http://home.schmorp.de/	949	http://home.schmorp.de/

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Comparing Coro/Coro.pm (file contents):
Revision 1.220 by root, Sun Nov 16 11:12:57 2008 UTC vs.
Revision 1.282 by root, Sun Dec 26 16:23:51 2010 UTC