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

Comparing Coro/Coro.pm (file contents):
Revision 1.226 by root, Wed Nov 19 16:01:32 2008 UTC vs.
Revision 1.271 by root, Fri Oct 2 19:55:59 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
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 $VERSION = 5.2;
73		87
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	91	);
78	our @EXPORT_OK = (@{$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	$idle = new Coro sub {
136	require Carp;	144	require Coro::Debug;
137	Carp::croak ("FATAL: deadlock detected");	145	die "FATAL: deadlock detected.\n"
		146	. Coro::Debug::ps_listing ();
138	};	147	};
139		148
140	sub _cancel {
141	my ($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	149	# this coro is necessary because a coro
153	# cannot destroy itself.	150	# cannot destroy itself.
154	our @destroy;	151	our @destroy;
155	our $manager;	152	our $manager;
156		153
157	$manager = new Coro sub {	154	$manager = new Coro sub {
158	while () {	155	while () {
159	(shift @destroy)->_cancel	156	Coro::State::cancel shift @destroy
160	while @destroy;	157	while @destroy;
161		158
162	&schedule;	159	&schedule;
163	}	160	}
164	};	161	};
165	$manager->{desc} = "[coro manager]";	162	$manager->{desc} = "[coro manager]";
166	$manager->prio (PRIO_MAX);	163	$manager->prio (PRIO_MAX);
167		164
168	=back	165	=back
169		166
170	=head2 SIMPLE COROUTINE CREATION	167	=head1 SIMPLE CORO CREATION
171		168
172	=over 4	169	=over 4
173		170
174	=item async { ... } [@args...]	171	=item async { ... } [@args...]
175		172
176	Create a new coroutine and return it's coroutine object (usually	173	Create a new coro and return its Coro object (usually
177	unused). The coroutine will be put into the ready queue, so	174	unused). The coro will be put into the ready queue, so
178	it will start running automatically on the next scheduler run.	175	it will start running automatically on the next scheduler run.
179		176
180	The first argument is a codeblock/closure that should be executed in the	177	The first argument is a codeblock/closure that should be executed in the
181	coroutine. When it returns argument returns the coroutine is automatically	178	coro. When it returns argument returns the coro is automatically
182	terminated.	179	terminated.
183		180
184	The remaining arguments are passed as arguments to the closure.	181	The remaining arguments are passed as arguments to the closure.
185		182
186	See the C<Coro::State::new> constructor for info about the coroutine	183	See the C<Coro::State::new> constructor for info about the coro
187	environment in which coroutines are executed.	184	environment in which coro are executed.
188		185
189	Calling C<exit> in a coroutine will do the same as calling exit outside	186	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,	187	the coro. Likewise, when the coro dies, the program will exit,
191	just as it would in the main program.	188	just as it would in the main program.
192		189
193	If you do not want that, you can provide a default C<die> handler, or	190	If you do not want that, you can provide a default C<die> handler, or
194	simply avoid dieing (by use of C<eval>).	191	simply avoid dieing (by use of C<eval>).
195		192
196	Example: Create a new coroutine that just prints its arguments.	193	Example: Create a new coro that just prints its arguments.
197		194
198	async {	195	async {
199	print "@_\n";	196	print "@_\n";
200	} 1,2,3,4;	197	} 1,2,3,4;
201		198
202	=cut
203
204	sub async(&@) {
205	my $coro = new Coro @_;
206	$coro->ready;
207	$coro
208	}
209
210	=item async_pool { ... } [@args...]	199	=item async_pool { ... } [@args...]
211		200
212	Similar to C<async>, but uses a coroutine pool, so you should not call	201	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	202	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	203	coro that might have executed other code already (which can be good
215	or bad :).	204	or bad :).
216		205
217	On the plus side, this function is faster than creating (and destroying)	206	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	207	destroying) a completely new coro, so if you need a lot of generic
219	quick successsion, use C<async_pool>, not C<async>.	208	coros in quick successsion, use C<async_pool>, not C<async>.
220		209
221	The code block is executed in an C<eval> context and a warning will be	210	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	211	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>	212	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,	213	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	214	which somehow defeats the purpose of pooling (but is fine in the
226	exceptional case).	215	exceptional case).
227		216
228	The priority will be reset to C<0> after each run, tracing will be	217	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	218	disabled, the description will be reset and the default output filehandle
230	gets restored, so you can change all these. Otherwise the coroutine will	219	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	220	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	221	stuff such as C<$/> you I<must needs> revert that change, which is most
233	simply done by using local as in: C<< local $/ >>.	222	simply done by using local as in: C<< local $/ >>.
234		223
235	The idle pool size is limited to C<8> idle coroutines (this can be	224	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	225	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
237	coros as required.	226	coros as required.
238		227
239	If you are concerned about pooled coroutines growing a lot because a	228	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	229	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	230	{ 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	231	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.	232	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
244		233
245	=cut	234	=cut
246		235
247	our $POOL_SIZE = 8;	236	our $POOL_SIZE = 8;
248	our $POOL_RSS = 16 * 1024;	237	our $POOL_RSS = 32 * 1024;
249	our @async_pool;	238	our @async_pool;
250		239
251	sub pool_handler {	240	sub pool_handler {
252	my $cb;
253
254	while () {	241	while () {
255	eval {	242	eval {
256	while () {	243	&{&_pool_handler} while 1;
257	_pool_1 $cb;
258	&$cb;
259	_pool_2 $cb;
260	&schedule;
261	}
262	};	244	};
263		245
264	if ($@) {
265	last if $@ eq "\3async_pool terminate\2\n";
266	warn $@;	246	warn $@ if $@;
267	}
268	}	247	}
269	}	248	}
270		249
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	$coro
279	}
280
281	=back	250	=back
282		251
283	=head2 STATIC METHODS	252	=head1 STATIC METHODS
284		253
285	Static methods are actually functions that operate on the current coroutine.	254	Static methods are actually functions that implicitly operate on the
		255	current coro.
286		256
287	=over 4	257	=over 4
288		258
289	=item schedule	259	=item schedule
290		260
291	Calls the scheduler. The scheduler will find the next coroutine that is	261	Calls the scheduler. The scheduler will find the next coro that is
292	to be run from the ready queue and switches to it. The next coroutine	262	to be run from the ready queue and switches to it. The next coro
293	to be run is simply the one with the highest priority that is longest	263	to be run is simply the one with the highest priority that is longest
294	in its ready queue. If there is no coroutine ready, it will clal the	264	in its ready queue. If there is no coro ready, it will call the
295	C<$Coro::idle> hook.	265	C<$Coro::idle> hook.
296		266
297	Please note that the current coroutine will I<not> be put into the ready	267	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	268	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 >>,	269	again unless something else (e.g. an event handler) calls C<< ->ready >>,
300	thus waking you up.	270	thus waking you up.
301		271
302	This makes C<schedule> I<the> generic method to use to block the current	272	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	273	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	274	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	275	>> 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,	276	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	277	so you need to check whether the event indeed happened, e.g. by storing the
308	status in a variable.	278	status in a variable.
309		279
310	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	280	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
311		281
312	=item cede	282	=item cede
313		283
314	"Cede" to other coroutines. This function puts the current coroutine into	284	"Cede" to other coros. This function puts the current coro into
315	the ready queue and calls C<schedule>, which has the effect of giving	285	the ready queue and calls C<schedule>, which has the effect of giving
316	up the current "timeslice" to other coroutines of the same or higher	286	up the current "timeslice" to other coros of the same or higher
317	priority. Once your coroutine gets its turn again it will automatically be	287	priority. Once your coro gets its turn again it will automatically be
318	resumed.	288	resumed.
319		289
320	This function is often called C<yield> in other languages.	290	This function is often called C<yield> in other languages.
321		291
322	=item Coro::cede_notself	292	=item Coro::cede_notself
323		293
324	Works like cede, but is not exported by default and will cede to I<any>	294	Works like cede, but is not exported by default and will cede to I<any>
325	coroutine, regardless of priority. This is useful sometimes to ensure	295	coro, regardless of priority. This is useful sometimes to ensure
326	progress is made.	296	progress is made.
327		297
328	=item terminate [arg...]	298	=item terminate [arg...]
329		299
330	Terminates the current coroutine with the given status values (see L<cancel>).	300	Terminates the current coro with the given status values (see L<cancel>).
		301
		302	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		303
		304	These function install enter and leave winders in the current scope. The
		305	enter block will be executed when on_enter is called and whenever the
		306	current coro is re-entered by the scheduler, while the leave block is
		307	executed whenever the current coro is blocked by the scheduler, and
		308	also when the containing scope is exited (by whatever means, be it exit,
		309	die, last etc.).
		310
		311	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		312	BLOCKs>. That means: do not even think about calling C<die> without an
		313	eval, and do not even think of entering the scheduler in any way.
		314
		315	Since both BLOCKs are tied to the current scope, they will automatically
		316	be removed when the current scope exits.
		317
		318	These functions implement the same concept as C<dynamic-wind> in scheme
		319	does, and are useful when you want to localise some resource to a specific
		320	coro.
		321
		322	They slow down thread switching considerably for coros that use them
		323	(about 40% for a BLOCK with a single assignment, so thread switching is
		324	still reasonably fast if the handlers are fast).
		325
		326	These functions are best understood by an example: The following function
		327	will change the current timezone to "Antarctica/South_Pole", which
		328	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		329	which remember/change the current timezone and restore the previous
		330	value, respectively, the timezone is only changed for the coro that
		331	installed those handlers.
		332
		333	use POSIX qw(tzset);
		334
		335	async {
		336	my $old_tz; # store outside TZ value here
		337
		338	Coro::on_enter {
		339	$old_tz = $ENV{TZ}; # remember the old value
		340
		341	$ENV{TZ} = "Antarctica/South_Pole";
		342	tzset; # enable new value
		343	};
		344
		345	Coro::on_leave {
		346	$ENV{TZ} = $old_tz;
		347	tzset; # restore old value
		348	};
		349
		350	# at this place, the timezone is Antarctica/South_Pole,
		351	# without disturbing the TZ of any other coro.
		352	};
		353
		354	This can be used to localise about any resource (locale, uid, current
		355	working directory etc.) to a block, despite the existance of other
		356	coros.
		357
		358	Another interesting example implements time-sliced multitasking using
		359	interval timers (this could obviously be optimised, but does the job):
		360
		361	# "timeslice" the given block
		362	sub timeslice(&) {
		363	use Time::HiRes ();
		364
		365	Coro::on_enter {
		366	# on entering the thread, we set an VTALRM handler to cede
		367	$SIG{VTALRM} = sub { cede };
		368	# and then start the interval timer
		369	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		370	};
		371	Coro::on_leave {
		372	# on leaving the thread, we stop the interval timer again
		373	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		374	};
		375
		376	&{+shift};
		377	}
		378
		379	# use like this:
		380	timeslice {
		381	# The following is an endless loop that would normally
		382	# monopolise the process. Since it runs in a timesliced
		383	# environment, it will regularly cede to other threads.
		384	while () { }
		385	};
		386
331		387
332	=item killall	388	=item killall
333		389
334	Kills/terminates/cancels all coroutines except the currently running	390	Kills/terminates/cancels all coros except the currently running one.
335	one. This is useful after a fork, either in the child or the parent, as
336	usually only one of them should inherit the running coroutines.
337		391
338	Note that while this will try to free some of the main programs resources,	392	Note that while this will try to free some of the main interpreter
		393	resources if the calling coro isn't the main coro, but one
339	you cannot free all of them, so if a coroutine that is not the main	394	cannot free all of them, so if a coro that is not the main coro
340	program calls this function, there will be some one-time resource leak.	395	calls this function, there will be some one-time resource leak.
341		396
342	=cut	397	=cut
343
344	sub terminate {
345	$current->{_status} = [@_];
346	push @destroy, $current;
347	$manager->ready;
348	do { &schedule } while 1;
349	}
350		398
351	sub killall {	399	sub killall {
352	for (Coro::State::list) {	400	for (Coro::State::list) {
353	$_->cancel	401	$_->cancel
354	if $_ != $current && UNIVERSAL::isa $_, "Coro";	402	if $_ != $current && UNIVERSAL::isa $_, "Coro";
355	}	403	}
356	}	404	}
357		405
358	=back	406	=back
359		407
360	=head2 COROUTINE METHODS	408	=head1 CORO OBJECT METHODS
361		409
362	These are the methods you can call on coroutine objects (or to create	410	These are the methods you can call on coro objects (or to create
363	them).	411	them).
364		412
365	=over 4	413	=over 4
366		414
367	=item new Coro \&sub [, @args...]	415	=item new Coro \&sub [, @args...]
368		416
369	Create a new coroutine and return it. When the sub returns, the coroutine	417	Create a new coro and return it. When the sub returns, the coro
370	automatically terminates as if C<terminate> with the returned values were	418	automatically terminates as if C<terminate> with the returned values were
371	called. To make the coroutine run you must first put it into the ready	419	called. To make the coro run you must first put it into the ready
372	queue by calling the ready method.	420	queue by calling the ready method.
373		421
374	See C<async> and C<Coro::State::new> for additional info about the	422	See C<async> and C<Coro::State::new> for additional info about the
375	coroutine environment.	423	coro environment.
376		424
377	=cut	425	=cut
378		426
379	sub _terminate {	427	sub _coro_run {
380	terminate &{+shift};	428	terminate &{+shift};
381	}	429	}
382		430
383	=item $success = $coroutine->ready	431	=item $success = $coro->ready
384		432
385	Put the given coroutine into the end of its ready queue (there is one	433	Put the given coro into the end of its ready queue (there is one
386	queue for each priority) and return true. If the coroutine is already in	434	queue for each priority) and return true. If the coro is already in
387	the ready queue, do nothing and return false.	435	the ready queue, do nothing and return false.
388		436
389	This ensures that the scheduler will resume this coroutine automatically	437	This ensures that the scheduler will resume this coro automatically
390	once all the coroutines of higher priority and all coroutines of the same	438	once all the coro of higher priority and all coro of the same
391	priority that were put into the ready queue earlier have been resumed.	439	priority that were put into the ready queue earlier have been resumed.
392		440
		441	=item $coro->suspend
		442
		443	Suspends the specified coro. A suspended coro works just like any other
		444	coro, except that the scheduler will not select a suspended coro for
		445	execution.
		446
		447	Suspending a coro can be useful when you want to keep the coro from
		448	running, but you don't want to destroy it, or when you want to temporarily
		449	freeze a coro (e.g. for debugging) to resume it later.
		450
		451	A scenario for the former would be to suspend all (other) coros after a
		452	fork and keep them alive, so their destructors aren't called, but new
		453	coros can be created.
		454
		455	=item $coro->resume
		456
		457	If the specified coro was suspended, it will be resumed. Note that when
		458	the coro was in the ready queue when it was suspended, it might have been
		459	unreadied by the scheduler, so an activation might have been lost.
		460
		461	To avoid this, it is best to put a suspended coro into the ready queue
		462	unconditionally, as every synchronisation mechanism must protect itself
		463	against spurious wakeups, and the one in the Coro family certainly do
		464	that.
		465
393	=item $is_ready = $coroutine->is_ready	466	=item $is_ready = $coro->is_ready
394		467
395	Return whether the coroutine is currently the ready queue or not,	468	Returns true iff the Coro object is in the ready queue. Unless the Coro
		469	object gets destroyed, it will eventually be scheduled by the scheduler.
396		470
		471	=item $is_running = $coro->is_running
		472
		473	Returns true iff the Coro object is currently running. Only one Coro object
		474	can ever be in the running state (but it currently is possible to have
		475	multiple running Coro::States).
		476
		477	=item $is_suspended = $coro->is_suspended
		478
		479	Returns true iff this Coro object has been suspended. Suspended Coros will
		480	not ever be scheduled.
		481
397	=item $coroutine->cancel (arg...)	482	=item $coro->cancel (arg...)
398		483
399	Terminates the given coroutine and makes it return the given arguments as	484	Terminates the given Coro and makes it return the given arguments as
400	status (default: the empty list). Never returns if the coroutine is the	485	status (default: the empty list). Never returns if the Coro is the
401	current coroutine.	486	current Coro.
402		487
403	=cut	488	=cut
404		489
405	sub cancel {	490	sub cancel {
406	my $self = shift;	491	my $self = shift;
407		492
408	if ($current == $self) {	493	if ($current == $self) {
409	terminate @_;	494	terminate @_;
410	} else {	495	} else {
411	$self->{_status} = [@_];	496	$self->{_status} = [@_];
412	$self->_cancel;	497	Coro::State::cancel $self;
413	}	498	}
414	}	499	}
415		500
		501	=item $coro->schedule_to
		502
		503	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		504	of continuing with the next coro from the ready queue, always switch to
		505	the given coro object (regardless of priority etc.). The readyness
		506	state of that coro isn't changed.
		507
		508	This is an advanced method for special cases - I'd love to hear about any
		509	uses for this one.
		510
		511	=item $coro->cede_to
		512
		513	Like C<schedule_to>, but puts the current coro into the ready
		514	queue. This has the effect of temporarily switching to the given
		515	coro, and continuing some time later.
		516
		517	This is an advanced method for special cases - I'd love to hear about any
		518	uses for this one.
		519
416	=item $coroutine->throw ([$scalar])	520	=item $coro->throw ([$scalar])
417		521
418	If C<$throw> is specified and defined, it will be thrown as an exception	522	If C<$throw> is specified and defined, it will be thrown as an exception
419	inside the coroutine at the next convenient point in time. Otherwise	523	inside the coro at the next convenient point in time. Otherwise
420	clears the exception object.	524	clears the exception object.
421		525
422	Coro will check for the exception each time a schedule-like-function	526	Coro will check for the exception each time a schedule-like-function
423	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down	527	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
424	>>, C<< Coro::Handle->readable >> and so on. Most of these functions	528	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
…		…
426		530
427	The exception object will be thrown "as is" with the specified scalar in	531	The exception object will be thrown "as is" with the specified scalar in
428	C<$@>, i.e. if it is a string, no line number or newline will be appended	532	C<$@>, i.e. if it is a string, no line number or newline will be appended
429	(unlike with C<die>).	533	(unlike with C<die>).
430		534
431	This can be used as a softer means than C<cancel> to ask a coroutine to	535	This can be used as a softer means than C<cancel> to ask a coro to
432	end itself, although there is no guarantee that the exception will lead to	536	end itself, although there is no guarantee that the exception will lead to
433	termination, and if the exception isn't caught it might well end the whole	537	termination, and if the exception isn't caught it might well end the whole
434	program.	538	program.
435		539
436	You might also think of C<throw> as being the moral equivalent of	540	You might also think of C<throw> as being the moral equivalent of
437	C<kill>ing a coroutine with a signal (in this case, a scalar).	541	C<kill>ing a coro with a signal (in this case, a scalar).
438		542
439	=item $coroutine->join	543	=item $coro->join
440		544
441	Wait until the coroutine terminates and return any values given to the	545	Wait until the coro terminates and return any values given to the
442	C<terminate> or C<cancel> functions. C<join> can be called concurrently	546	C<terminate> or C<cancel> functions. C<join> can be called concurrently
443	from multiple coroutines, and all will be resumed and given the status	547	from multiple coro, and all will be resumed and given the status
444	return once the C<$coroutine> terminates.	548	return once the C<$coro> terminates.
445		549
446	=cut	550	=cut
447		551
448	sub join {	552	sub join {
449	my $self = shift;	553	my $self = shift;
…		…
460	}	564	}
461		565
462	wantarray ? @{$self->{_status}} : $self->{_status}[0];	566	wantarray ? @{$self->{_status}} : $self->{_status}[0];
463	}	567	}
464		568
465	=item $coroutine->on_destroy (\&cb)	569	=item $coro->on_destroy (\&cb)
466		570
467	Registers a callback that is called when this coroutine gets destroyed,	571	Registers a callback that is called when this coro gets destroyed,
468	but before it is joined. The callback gets passed the terminate arguments,	572	but before it is joined. The callback gets passed the terminate arguments,
469	if any, and I<must not> die, under any circumstances.	573	if any, and I<must not> die, under any circumstances.
470		574
471	=cut	575	=cut
472		576
…		…
474	my ($self, $cb) = @_;	578	my ($self, $cb) = @_;
475		579
476	push @{ $self->{_on_destroy} }, $cb;	580	push @{ $self->{_on_destroy} }, $cb;
477	}	581	}
478		582
479	=item $oldprio = $coroutine->prio ($newprio)	583	=item $oldprio = $coro->prio ($newprio)
480		584
481	Sets (or gets, if the argument is missing) the priority of the	585	Sets (or gets, if the argument is missing) the priority of the
482	coroutine. Higher priority coroutines get run before lower priority	586	coro. Higher priority coro get run before lower priority
483	coroutines. Priorities are small signed integers (currently -4 .. +3),	587	coro. Priorities are small signed integers (currently -4 .. +3),
484	that you can refer to using PRIO_xxx constants (use the import tag :prio	588	that you can refer to using PRIO_xxx constants (use the import tag :prio
485	to get then):	589	to get then):
486		590
487	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	591	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
488	3 > 1 > 0 > -1 > -3 > -4	592	3 > 1 > 0 > -1 > -3 > -4
489		593
490	# set priority to HIGH	594	# set priority to HIGH
491	current->prio(PRIO_HIGH);	595	current->prio (PRIO_HIGH);
492		596
493	The idle coroutine ($Coro::idle) always has a lower priority than any	597	The idle coro ($Coro::idle) always has a lower priority than any
494	existing coroutine.	598	existing coro.
495		599
496	Changing the priority of the current coroutine will take effect immediately,	600	Changing the priority of the current coro will take effect immediately,
497	but changing the priority of coroutines in the ready queue (but not	601	but changing the priority of coro in the ready queue (but not
498	running) will only take effect after the next schedule (of that	602	running) will only take effect after the next schedule (of that
499	coroutine). This is a bug that will be fixed in some future version.	603	coro). This is a bug that will be fixed in some future version.
500		604
501	=item $newprio = $coroutine->nice ($change)	605	=item $newprio = $coro->nice ($change)
502		606
503	Similar to C<prio>, but subtract the given value from the priority (i.e.	607	Similar to C<prio>, but subtract the given value from the priority (i.e.
504	higher values mean lower priority, just as in unix).	608	higher values mean lower priority, just as in unix).
505		609
506	=item $olddesc = $coroutine->desc ($newdesc)	610	=item $olddesc = $coro->desc ($newdesc)
507		611
508	Sets (or gets in case the argument is missing) the description for this	612	Sets (or gets in case the argument is missing) the description for this
509	coroutine. This is just a free-form string you can associate with a	613	coro. This is just a free-form string you can associate with a
510	coroutine.	614	coro.
511		615
512	This method simply sets the C<< $coroutine->{desc} >> member to the given	616	This method simply sets the C<< $coro->{desc} >> member to the given
513	string. You can modify this member directly if you wish.	617	string. You can modify this member directly if you wish.
514		618
515	=cut	619	=cut
516		620
517	sub desc {	621	sub desc {
518	my $old = $_[0]{desc};	622	my $old = $_[0]{desc};
519	$_[0]{desc} = $_[1] if @_ > 1;	623	$_[0]{desc} = $_[1] if @_ > 1;
520	$old;	624	$old;
521	}	625	}
522		626
		627	sub transfer {
		628	require Carp;
		629	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		630	}
		631
523	=back	632	=back
524		633
525	=head2 GLOBAL FUNCTIONS	634	=head1 GLOBAL FUNCTIONS
526		635
527	=over 4	636	=over 4
528		637
529	=item Coro::nready	638	=item Coro::nready
530		639
531	Returns the number of coroutines that are currently in the ready state,	640	Returns the number of coro that are currently in the ready state,
532	i.e. that can be switched to by calling C<schedule> directory or	641	i.e. that can be switched to by calling C<schedule> directory or
533	indirectly. The value C<0> means that the only runnable coroutine is the	642	indirectly. The value C<0> means that the only runnable coro is the
534	currently running one, so C<cede> would have no effect, and C<schedule>	643	currently running one, so C<cede> would have no effect, and C<schedule>
535	would cause a deadlock unless there is an idle handler that wakes up some	644	would cause a deadlock unless there is an idle handler that wakes up some
536	coroutines.	645	coro.
537		646
538	=item my $guard = Coro::guard { ... }	647	=item my $guard = Coro::guard { ... }
539		648
540	This creates and returns a guard object. Nothing happens until the object	649	This function still exists, but is deprecated. Please use the
541	gets destroyed, in which case the codeblock given as argument will be	650	C<Guard::guard> function instead.
542	executed. This is useful to free locks or other resources in case of a
543	runtime error or when the coroutine gets canceled, as in both cases the
544	guard block will be executed. The guard object supports only one method,
545	C<< ->cancel >>, which will keep the codeblock from being executed.
546		651
547	Example: set some flag and clear it again when the coroutine gets canceled
548	or the function returns:
549
550	sub do_something {
551	my $guard = Coro::guard { $busy = 0 };
552	$busy = 1;
553
554	# do something that requires $busy to be true
555	}
556
557	=cut	652	=cut
558		653
559	sub guard(&) {	654	BEGIN { *guard = \&Guard::guard }
560	bless \(my $cb = $_[0]), "Coro::guard"
561	}
562
563	sub Coro::guard::cancel {
564	${$_[0]} = sub { };
565	}
566
567	sub Coro::guard::DESTROY {
568	${$_[0]}->();
569	}
570
571		655
572	=item unblock_sub { ... }	656	=item unblock_sub { ... }
573		657
574	This utility function takes a BLOCK or code reference and "unblocks" it,	658	This utility function takes a BLOCK or code reference and "unblocks" it,
575	returning a new coderef. Unblocking means that calling the new coderef	659	returning a new coderef. Unblocking means that calling the new coderef
576	will return immediately without blocking, returning nothing, while the	660	will return immediately without blocking, returning nothing, while the
577	original code ref will be called (with parameters) from within another	661	original code ref will be called (with parameters) from within another
578	coroutine.	662	coro.
579		663
580	The reason this function exists is that many event libraries (such as the	664	The reason this function exists is that many event libraries (such as the
581	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	665	venerable L<Event\|Event> module) are not thread-safe (a weaker form
582	of thread-safety). This means you must not block within event callbacks,	666	of reentrancy). This means you must not block within event callbacks,
583	otherwise you might suffer from crashes or worse. The only event library	667	otherwise you might suffer from crashes or worse. The only event library
584	currently known that is safe to use without C<unblock_sub> is L<EV>.	668	currently known that is safe to use without C<unblock_sub> is L<EV>.
585		669
586	This function allows your callbacks to block by executing them in another	670	This function allows your callbacks to block by executing them in another
587	coroutine where it is safe to block. One example where blocking is handy	671	coro where it is safe to block. One example where blocking is handy
588	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	672	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
589	disk, for example.	673	disk, for example.
590		674
591	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	675	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
592	creating event callbacks that want to block.	676	creating event callbacks that want to block.
593		677
594	If your handler does not plan to block (e.g. simply sends a message to	678	If your handler does not plan to block (e.g. simply sends a message to
595	another coroutine, or puts some other coroutine into the ready queue),	679	another coro, or puts some other coro into the ready queue), there is
596	there is no reason to use C<unblock_sub>.	680	no reason to use C<unblock_sub>.
597		681
598	Note that you also need to use C<unblock_sub> for any other callbacks that	682	Note that you also need to use C<unblock_sub> for any other callbacks that
599	are indirectly executed by any C-based event loop. For example, when you	683	are indirectly executed by any C-based event loop. For example, when you
600	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	684	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
601	provides callbacks that are the result of some event callback, then you	685	provides callbacks that are the result of some event callback, then you
…		…
610	# return immediately and can be reused) and because we cannot cede	694	# return immediately and can be reused) and because we cannot cede
611	# inside an event callback.	695	# inside an event callback.
612	our $unblock_scheduler = new Coro sub {	696	our $unblock_scheduler = new Coro sub {
613	while () {	697	while () {
614	while (my $cb = pop @unblock_queue) {	698	while (my $cb = pop @unblock_queue) {
615	# this is an inlined copy of async_pool	699	&async_pool (@$cb);
616	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
617		700
618	$coro->{_invoke} = $cb;
619	$coro->ready;
620	cede; # for short-lived callbacks, this reduces pressure on the coro pool	701	# for short-lived callbacks, this reduces pressure on the coro pool
		702	# as the chance is very high that the async_poll coro will be back
		703	# in the idle state when cede returns
		704	cede;
621	}	705	}
622	schedule; # sleep well	706	schedule; # sleep well
623	}	707	}
624	};	708	};
625	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	709	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
631	unshift @unblock_queue, [$cb, @_];	715	unshift @unblock_queue, [$cb, @_];
632	$unblock_scheduler->ready;	716	$unblock_scheduler->ready;
633	}	717	}
634	}	718	}
635		719
636	=item $cb = Coro::rouse_cb	720	=item $cb = rouse_cb
637		721
638	Create and return a "rouse callback". That's a code reference that, when	722	Create and return a "rouse callback". That's a code reference that,
639	called, will save its arguments and notify the owner coroutine of the	723	when called, will remember a copy of its arguments and notify the owner
640	callback.	724	coro of the callback.
641		725
642	See the next function.	726	See the next function.
643		727
644	=item @args = Coro::rouse_wait [$cb]	728	=item @args = rouse_wait [$cb]
645		729
646	Wait for the specified rouse callback (or the last one tht was created in	730	Wait for the specified rouse callback (or the last one that was created in
647	this coroutine).	731	this coro).
648		732
649	As soon as the callback is invoked (or when the calback was invoked before	733	As soon as the callback is invoked (or when the callback was invoked
650	C<rouse_wait>), it will return a copy of the arguments originally passed	734	before C<rouse_wait>), it will return the arguments originally passed to
651	to the rouse callback.	735	the rouse callback. In scalar context, that means you get the I<last>
		736	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		737	statement at the end.
652		738
653	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	739	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
654		740
655	=back	741	=back
656		742
…		…
658		744
659	1;	745	1;
660		746
661	=head1 HOW TO WAIT FOR A CALLBACK	747	=head1 HOW TO WAIT FOR A CALLBACK
662		748
663	It is very common for a coroutine to wait for some callback to be	749	It is very common for a coro to wait for some callback to be
664	called. This occurs naturally when you use coroutines in an otherwise	750	called. This occurs naturally when you use coro in an otherwise
665	event-based program, or when you use event-based libraries.	751	event-based program, or when you use event-based libraries.
666		752
667	These typically register a callback for some event, and call that callback	753	These typically register a callback for some event, and call that callback
668	when the event occured. In a coroutine, however, you typically want to	754	when the event occured. In a coro, however, you typically want to
669	just wait for the event, simplyifying things.	755	just wait for the event, simplyifying things.
670		756
671	For example C<< AnyEvent->child >> registers a callback to be called when	757	For example C<< AnyEvent->child >> registers a callback to be called when
672	a specific child has exited:	758	a specific child has exited:
673		759
674	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	760	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
675		761
676	But from withina coroutine, you often just want to write this:	762	But from within a coro, you often just want to write this:
677		763
678	my $status = wait_for_child $pid;	764	my $status = wait_for_child $pid;
679		765
680	Coro offers two functions specifically designed to make this easy,	766	Coro offers two functions specifically designed to make this easy,
681	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	767	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
682		768
683	The first function, C<rouse_cb>, generates and returns a callback that,	769	The first function, C<rouse_cb>, generates and returns a callback that,
684	when invoked, will save it's arguments and notify the coroutine that	770	when invoked, will save its arguments and notify the coro that
685	created the callback.	771	created the callback.
686		772
687	The second function, C<rouse_wait>, waits for the callback to be called	773	The second function, C<rouse_wait>, waits for the callback to be called
688	(by calling C<schedule> to go to sleep) and returns the arguments	774	(by calling C<schedule> to go to sleep) and returns the arguments
689	originally passed to the callback.	775	originally passed to the callback.
…		…
704	you can roll your own, using C<schedule>:	790	you can roll your own, using C<schedule>:
705		791
706	sub wait_for_child($) {	792	sub wait_for_child($) {
707	my ($pid) = @_;	793	my ($pid) = @_;
708		794
709	# store the current coroutine in $current,	795	# store the current coro in $current,
710	# and provide result variables for the closure passed to ->child	796	# and provide result variables for the closure passed to ->child
711	my $current = $Coro::current;	797	my $current = $Coro::current;
712	my ($done, $rstatus);	798	my ($done, $rstatus);
713		799
714	# pass a closure to ->child	800	# pass a closure to ->child
…		…
730		816
731	=item fork with pthread backend	817	=item fork with pthread backend
732		818
733	When Coro is compiled using the pthread backend (which isn't recommended	819	When Coro is compiled using the pthread backend (which isn't recommended
734	but required on many BSDs as their libcs are completely broken), then	820	but required on many BSDs as their libcs are completely broken), then
735	coroutines will not survive a fork. There is no known workaround except to	821	coro will not survive a fork. There is no known workaround except to
736	fix your libc and use a saner backend.	822	fix your libc and use a saner backend.
737		823
738	=item perl process emulation ("threads")	824	=item perl process emulation ("threads")
739		825
740	This module is not perl-pseudo-thread-safe. You should only ever use this	826	This module is not perl-pseudo-thread-safe. You should only ever use this
741	module from the same thread (this requirement might be removed in the	827	module from the first thread (this requirement might be removed in the
742	future to allow per-thread schedulers, but Coro::State does not yet allow	828	future to allow per-thread schedulers, but Coro::State does not yet allow
743	this). I recommend disabling thread support and using processes, as having	829	this). I recommend disabling thread support and using processes, as having
744	the windows process emulation enabled under unix roughly halves perl	830	the windows process emulation enabled under unix roughly halves perl
745	performance, even when not used.	831	performance, even when not used.
746		832
747	=item coroutine switching not signal safe	833	=item coro switching is not signal safe
748		834
749	You must not switch to another coroutine from within a signal handler	835	You must not switch to another coro from within a signal handler
750	(only relevant with %SIG - most event libraries provide safe signals).	836	(only relevant with %SIG - most event libraries provide safe signals).
751		837
752	That means you I<MUST NOT> call any function that might "block" the	838	That means you I<MUST NOT> call any function that might "block" the
753	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	839	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
754	anything that calls those. Everything else, including calling C<ready>,	840	anything that calls those. Everything else, including calling C<ready>,
755	works.	841	works.
756		842
757	=back	843	=back
758		844
759		845
		846	=head1 WINDOWS PROCESS EMULATION
		847
		848	A great many people seem to be confused about ithreads (for example, Chip
		849	Salzenberg called me unintelligent, incapable, stupid and gullible,
		850	while in the same mail making rather confused statements about perl
		851	ithreads (for example, that memory or files would be shared), showing his
		852	lack of understanding of this area - if it is hard to understand for Chip,
		853	it is probably not obvious to everybody).
		854
		855	What follows is an ultra-condensed version of my talk about threads in
		856	scripting languages given onthe perl workshop 2009:
		857
		858	The so-called "ithreads" were originally implemented for two reasons:
		859	first, to (badly) emulate unix processes on native win32 perls, and
		860	secondly, to replace the older, real thread model ("5.005-threads").
		861
		862	It does that by using threads instead of OS processes. The difference
		863	between processes and threads is that threads share memory (and other
		864	state, such as files) between threads within a single process, while
		865	processes do not share anything (at least not semantically). That
		866	means that modifications done by one thread are seen by others, while
		867	modifications by one process are not seen by other processes.
		868
		869	The "ithreads" work exactly like that: when creating a new ithreads
		870	process, all state is copied (memory is copied physically, files and code
		871	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		872	the same behaviour can be achieved by using operating system processes,
		873	except that UNIX typically uses hardware built into the system to do this
		874	efficiently, while the windows process emulation emulates this hardware in
		875	software (rather efficiently, but of course it is still much slower than
		876	dedicated hardware).
		877
		878	As mentioned before, loading code, modifying code, modifying data
		879	structures and so on is only visible in the ithreads process doing the
		880	modification, not in other ithread processes within the same OS process.
		881
		882	This is why "ithreads" do not implement threads for perl at all, only
		883	processes. What makes it so bad is that on non-windows platforms, you can
		884	actually take advantage of custom hardware for this purpose (as evidenced
		885	by the forks module, which gives you the (i-) threads API, just much
		886	faster).
		887
		888	Sharing data is in the i-threads model is done by transfering data
		889	structures between threads using copying semantics, which is very slow -
		890	shared data simply does not exist. Benchmarks using i-threads which are
		891	communication-intensive show extremely bad behaviour with i-threads (in
		892	fact, so bad that Coro, which cannot take direct advantage of multiple
		893	CPUs, is often orders of magnitude faster because it shares data using
		894	real threads, refer to my talk for details).
		895
		896	As summary, i-threads use threads to implement processes, while
		897	the compatible forks module uses processes to emulate, uhm,
		898	processes. I-threads slow down every perl program when enabled, and
		899	outside of windows, serve no (or little) practical purpose, but
		900	disadvantages every single-threaded Perl program.
		901
		902	This is the reason that I try to avoid the name "ithreads", as it is
		903	misleading as it implies that it implements some kind of thread model for
		904	perl, and prefer the name "windows process emulation", which describes the
		905	actual use and behaviour of it much better.
		906
760	=head1 SEE ALSO	907	=head1 SEE ALSO
761		908
762	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	909	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
763		910
764	Debugging: L<Coro::Debug>.	911	Debugging: L<Coro::Debug>.
765		912
766	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	913	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
767		914
768	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	915	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		916	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
769		917
770	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	918	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
771		919
772	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	920	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		921	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		922	L<Coro::Select>.
773		923
774	XS API: L<Coro::MakeMaker>.	924	XS API: L<Coro::MakeMaker>.
775		925
776	Low level Configuration, Coroutine Environment: L<Coro::State>.	926	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
777		927
778	=head1 AUTHOR	928	=head1 AUTHOR
779		929
780	Marc Lehmann <schmorp@schmorp.de>	930	Marc Lehmann <schmorp@schmorp.de>
781	http://home.schmorp.de/	931	http://home.schmorp.de/

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Revision 1.271 by root, Fri Oct 2 19:55:59 2009 UTC