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

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.226 by root, Wed Nov 19 16:01:32 2008 UTC vs.
Revision 1.275 by root, Wed Mar 31 17:41:07 2010 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
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 $VERSION = 5.21;
73		87
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
75	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	91	);
78	our @EXPORT_OK = (@{$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	our @destroy;	152	our @destroy;
155	our $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	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.	281	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
311		282
312	=item cede	283	=item cede
313		284
314	"Cede" to other coroutines. This function puts the current coroutine into	285	"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	286	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	287	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	288	priority. Once your coro gets its turn again it will automatically be
318	resumed.	289	resumed.
319		290
320	This function is often called C<yield> in other languages.	291	This function is often called C<yield> in other languages.
321		292
322	=item Coro::cede_notself	293	=item Coro::cede_notself
323		294
324	Works like cede, but is not exported by default and will cede to I<any>	295	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	296	coro, regardless of priority. This is useful sometimes to ensure
326	progress is made.	297	progress is made.
327		298
328	=item terminate [arg...]	299	=item terminate [arg...]
329		300
330	Terminates the current coroutine with the given status values (see L<cancel>).	301	Terminates the current coro with the given status values (see L<cancel>).
		302
		303	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		304
		305	These function install enter and leave winders in the current scope. The
		306	enter block will be executed when on_enter is called and whenever the
		307	current coro is re-entered by the scheduler, while the leave block is
		308	executed whenever the current coro is blocked by the scheduler, and
		309	also when the containing scope is exited (by whatever means, be it exit,
		310	die, last etc.).
		311
		312	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		313	BLOCKs>. That means: do not even think about calling C<die> without an
		314	eval, and do not even think of entering the scheduler in any way.
		315
		316	Since both BLOCKs are tied to the current scope, they will automatically
		317	be removed when the current scope exits.
		318
		319	These functions implement the same concept as C<dynamic-wind> in scheme
		320	does, and are useful when you want to localise some resource to a specific
		321	coro.
		322
		323	They slow down thread switching considerably for coros that use them
		324	(about 40% for a BLOCK with a single assignment, so thread switching is
		325	still reasonably fast if the handlers are fast).
		326
		327	These functions are best understood by an example: The following function
		328	will change the current timezone to "Antarctica/South_Pole", which
		329	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		330	which remember/change the current timezone and restore the previous
		331	value, respectively, the timezone is only changed for the coro that
		332	installed those handlers.
		333
		334	use POSIX qw(tzset);
		335
		336	async {
		337	my $old_tz; # store outside TZ value here
		338
		339	Coro::on_enter {
		340	$old_tz = $ENV{TZ}; # remember the old value
		341
		342	$ENV{TZ} = "Antarctica/South_Pole";
		343	tzset; # enable new value
		344	};
		345
		346	Coro::on_leave {
		347	$ENV{TZ} = $old_tz;
		348	tzset; # restore old value
		349	};
		350
		351	# at this place, the timezone is Antarctica/South_Pole,
		352	# without disturbing the TZ of any other coro.
		353	};
		354
		355	This can be used to localise about any resource (locale, uid, current
		356	working directory etc.) to a block, despite the existance of other
		357	coros.
		358
		359	Another interesting example implements time-sliced multitasking using
		360	interval timers (this could obviously be optimised, but does the job):
		361
		362	# "timeslice" the given block
		363	sub timeslice(&) {
		364	use Time::HiRes ();
		365
		366	Coro::on_enter {
		367	# on entering the thread, we set an VTALRM handler to cede
		368	$SIG{VTALRM} = sub { cede };
		369	# and then start the interval timer
		370	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		371	};
		372	Coro::on_leave {
		373	# on leaving the thread, we stop the interval timer again
		374	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		375	};
		376
		377	&{+shift};
		378	}
		379
		380	# use like this:
		381	timeslice {
		382	# The following is an endless loop that would normally
		383	# monopolise the process. Since it runs in a timesliced
		384	# environment, it will regularly cede to other threads.
		385	while () { }
		386	};
		387
331		388
332	=item killall	389	=item killall
333		390
334	Kills/terminates/cancels all coroutines except the currently running	391	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		392
338	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
339	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
340	program calls this function, there will be some one-time resource leak.	396	calls this function, there will be some one-time resource leak.
341		397
342	=cut	398	=cut
343
344	sub terminate {
345	$current->{_status} = [@_];
346	push @destroy, $current;
347	$manager->ready;
348	do { &schedule } while 1;
349	}
350		399
351	sub killall {	400	sub killall {
352	for (Coro::State::list) {	401	for (Coro::State::list) {
353	$_->cancel	402	$_->cancel
354	if $_ != $current && UNIVERSAL::isa $_, "Coro";	403	if $_ != $current && UNIVERSAL::isa $_, "Coro";
355	}	404	}
356	}	405	}
357		406
358	=back	407	=back
359		408
360	=head2 COROUTINE METHODS	409	=head1 CORO OBJECT METHODS
361		410
362	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
363	them).	412	them).
364		413
365	=over 4	414	=over 4
366		415
367	=item new Coro \&sub [, @args...]	416	=item new Coro \&sub [, @args...]
368		417
369	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
370	automatically terminates as if C<terminate> with the returned values were	419	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	420	called. To make the coro run you must first put it into the ready
372	queue by calling the ready method.	421	queue by calling the ready method.
373		422
374	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
375	coroutine environment.	424	coro environment.
376		425
377	=cut	426	=cut
378		427
379	sub _terminate {	428	sub _coro_run {
380	terminate &{+shift};	429	terminate &{+shift};
381	}	430	}
382		431
383	=item $success = $coroutine->ready	432	=item $success = $coro->ready
384		433
385	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
386	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
387	the ready queue, do nothing and return false.	436	the ready queue, do nothing and return false.
388		437
389	This ensures that the scheduler will resume this coroutine automatically	438	This ensures that the scheduler will resume this coro automatically
390	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
391	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.
392		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
393	=item $is_ready = $coroutine->is_ready	467	=item $is_ready = $coro->is_ready
394		468
395	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.
396		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
397	=item $coroutine->cancel (arg...)	483	=item $coro->cancel (arg...)
398		484
399	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
400	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
401	current coroutine.	487	current Coro.
402		488
403	=cut	489	=cut
404		490
405	sub cancel {	491	sub cancel {
406	my $self = shift;	492	my $self = shift;
407		493
408	if ($current == $self) {	494	if ($current == $self) {
409	terminate @_;	495	terminate @_;
410	} else {	496	} else {
411	$self->{_status} = [@_];	497	$self->{_status} = [@_];
412	$self->_cancel;	498	Coro::State::cancel $self;
413	}	499	}
414	}	500	}
415		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
416	=item $coroutine->throw ([$scalar])	521	=item $coro->throw ([$scalar])
417		522
418	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
419	inside the coroutine at the next convenient point in time. Otherwise	524	inside the coro at the next convenient point in time. Otherwise
420	clears the exception object.	525	clears the exception object.
421		526
422	Coro will check for the exception each time a schedule-like-function	527	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	528	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	529	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
…		…
426		531
427	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
428	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
429	(unlike with C<die>).	534	(unlike with C<die>).
430		535
431	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
432	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
433	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
434	program.	539	program.
435		540
436	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
437	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).
438		543
439	=item $coroutine->join	544	=item $coro->join
440		545
441	Wait until the coroutine terminates and return any values given to the	546	Wait until the coro terminates and return any values given to the
442	C<terminate> or C<cancel> functions. C<join> can be called concurrently	547	C<terminate> or C<cancel> functions. C<join> can be called concurrently
443	from multiple coroutines, and all will be resumed and given the status	548	from multiple coro, and all will be resumed and given the status
444	return once the C<$coroutine> terminates.	549	return once the C<$coro> terminates.
445		550
446	=cut	551	=cut
447		552
448	sub join {	553	sub join {
449	my $self = shift;	554	my $self = shift;
…		…
460	}	565	}
461		566
462	wantarray ? @{$self->{_status}} : $self->{_status}[0];	567	wantarray ? @{$self->{_status}} : $self->{_status}[0];
463	}	568	}
464		569
465	=item $coroutine->on_destroy (\&cb)	570	=item $coro->on_destroy (\&cb)
466		571
467	Registers a callback that is called when this coroutine gets destroyed,	572	Registers a callback that is called when this coro gets destroyed,
468	but before it is joined. The callback gets passed the terminate arguments,	573	but before it is joined. The callback gets passed the terminate arguments,
469	if any, and I<must not> die, under any circumstances.	574	if any, and I<must not> die, under any circumstances.
470		575
471	=cut	576	=cut
472		577
…		…
474	my ($self, $cb) = @_;	579	my ($self, $cb) = @_;
475		580
476	push @{ $self->{_on_destroy} }, $cb;	581	push @{ $self->{_on_destroy} }, $cb;
477	}	582	}
478		583
479	=item $oldprio = $coroutine->prio ($newprio)	584	=item $oldprio = $coro->prio ($newprio)
480		585
481	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
482	coroutine. Higher priority coroutines get run before lower priority	587	coro. Higher priority coro get run before lower priority
483	coroutines. Priorities are small signed integers (currently -4 .. +3),	588	coro. Priorities are small signed integers (currently -4 .. +3),
484	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
485	to get then):	590	to get then):
486		591
487	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
488	3 > 1 > 0 > -1 > -3 > -4	593	3 > 1 > 0 > -1 > -3 > -4
489		594
490	# set priority to HIGH	595	# set priority to HIGH
491	current->prio(PRIO_HIGH);	596	current->prio (PRIO_HIGH);
492		597
493	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
494	existing coroutine.	599	existing coro.
495		600
496	Changing the priority of the current coroutine will take effect immediately,	601	Changing the priority of the current coro will take effect immediately,
497	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
498	running) will only take effect after the next schedule (of that	603	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.	604	coro). This is a bug that will be fixed in some future version.
500		605
501	=item $newprio = $coroutine->nice ($change)	606	=item $newprio = $coro->nice ($change)
502		607
503	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.
504	higher values mean lower priority, just as in unix).	609	higher values mean lower priority, just as in unix).
505		610
506	=item $olddesc = $coroutine->desc ($newdesc)	611	=item $olddesc = $coro->desc ($newdesc)
507		612
508	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
509	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
510	coroutine.	615	coro.
511		616
512	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
513	string. You can modify this member directly if you wish.	618	string. You can modify this member directly if you wish.
514		619
515	=cut	620	=cut
516		621
517	sub desc {	622	sub desc {
518	my $old = $_[0]{desc};	623	my $old = $_[0]{desc};
519	$_[0]{desc} = $_[1] if @_ > 1;	624	$_[0]{desc} = $_[1] if @_ > 1;
520	$old;	625	$old;
521	}	626	}
522		627
		628	sub transfer {
		629	require Carp;
		630	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		631	}
		632
523	=back	633	=back
524		634
525	=head2 GLOBAL FUNCTIONS	635	=head1 GLOBAL FUNCTIONS
526		636
527	=over 4	637	=over 4
528		638
529	=item Coro::nready	639	=item Coro::nready
530		640
531	Returns the number of coroutines that are currently in the ready state,	641	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	642	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	643	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>	644	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	645	would cause a deadlock unless there is an idle handler that wakes up some
536	coroutines.	646	coro.
537		647
538	=item my $guard = Coro::guard { ... }	648	=item my $guard = Coro::guard { ... }
539		649
540	This creates and returns a guard object. Nothing happens until the object	650	This function still exists, but is deprecated. Please use the
541	gets destroyed, in which case the codeblock given as argument will be	651	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		652
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	653	=cut
558		654
559	sub guard(&) {	655	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		656
572	=item unblock_sub { ... }	657	=item unblock_sub { ... }
573		658
574	This utility function takes a BLOCK or code reference and "unblocks" it,	659	This utility function takes a BLOCK or code reference and "unblocks" it,
575	returning a new coderef. Unblocking means that calling the new coderef	660	returning a new coderef. Unblocking means that calling the new coderef
576	will return immediately without blocking, returning nothing, while the	661	will return immediately without blocking, returning nothing, while the
577	original code ref will be called (with parameters) from within another	662	original code ref will be called (with parameters) from within another
578	coroutine.	663	coro.
579		664
580	The reason this function exists is that many event libraries (such as the	665	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	666	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,	667	of reentrancy). This means you must not block within event callbacks,
583	otherwise you might suffer from crashes or worse. The only event library	668	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>.	669	currently known that is safe to use without C<unblock_sub> is L<EV>.
585		670
		671	Coro will try to catch you when you block in the event loop
		672	("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
		673	only works when you do not run your own event loop.
		674
586	This function allows your callbacks to block by executing them in another	675	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	676	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	677	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
589	disk, for example.	678	disk, for example.
590		679
591	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	680	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
592	creating event callbacks that want to block.	681	creating event callbacks that want to block.
593		682
594	If your handler does not plan to block (e.g. simply sends a message to	683	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),	684	another coro, or puts some other coro into the ready queue), there is
596	there is no reason to use C<unblock_sub>.	685	no reason to use C<unblock_sub>.
597		686
598	Note that you also need to use C<unblock_sub> for any other callbacks that	687	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	688	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	689	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	690	provides callbacks that are the result of some event callback, then you
…		…
610	# return immediately and can be reused) and because we cannot cede	699	# return immediately and can be reused) and because we cannot cede
611	# inside an event callback.	700	# inside an event callback.
612	our $unblock_scheduler = new Coro sub {	701	our $unblock_scheduler = new Coro sub {
613	while () {	702	while () {
614	while (my $cb = pop @unblock_queue) {	703	while (my $cb = pop @unblock_queue) {
615	# this is an inlined copy of async_pool	704	&async_pool (@$cb);
616	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
617		705
618	$coro->{_invoke} = $cb;
619	$coro->ready;
620	cede; # for short-lived callbacks, this reduces pressure on the coro pool	706	# for short-lived callbacks, this reduces pressure on the coro pool
		707	# as the chance is very high that the async_poll coro will be back
		708	# in the idle state when cede returns
		709	cede;
621	}	710	}
622	schedule; # sleep well	711	schedule; # sleep well
623	}	712	}
624	};	713	};
625	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	714	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
631	unshift @unblock_queue, [$cb, @_];	720	unshift @unblock_queue, [$cb, @_];
632	$unblock_scheduler->ready;	721	$unblock_scheduler->ready;
633	}	722	}
634	}	723	}
635		724
636	=item $cb = Coro::rouse_cb	725	=item $cb = rouse_cb
637		726
638	Create and return a "rouse callback". That's a code reference that, when	727	Create and return a "rouse callback". That's a code reference that,
639	called, will save its arguments and notify the owner coroutine of the	728	when called, will remember a copy of its arguments and notify the owner
640	callback.	729	coro of the callback.
641		730
642	See the next function.	731	See the next function.
643		732
644	=item @args = Coro::rouse_wait [$cb]	733	=item @args = rouse_wait [$cb]
645		734
646	Wait for the specified rouse callback (or the last one tht was created in	735	Wait for the specified rouse callback (or the last one that was created in
647	this coroutine).	736	this coro).
648		737
649	As soon as the callback is invoked (or when the calback was invoked before	738	As soon as the callback is invoked (or when the callback was invoked
650	C<rouse_wait>), it will return a copy of the arguments originally passed	739	before C<rouse_wait>), it will return the arguments originally passed to
651	to the rouse callback.	740	the rouse callback. In scalar context, that means you get the I<last>
		741	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		742	statement at the end.
652		743
653	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.	744	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
654		745
655	=back	746	=back
656		747
…		…
658		749
659	1;	750	1;
660		751
661	=head1 HOW TO WAIT FOR A CALLBACK	752	=head1 HOW TO WAIT FOR A CALLBACK
662		753
663	It is very common for a coroutine to wait for some callback to be	754	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	755	called. This occurs naturally when you use coro in an otherwise
665	event-based program, or when you use event-based libraries.	756	event-based program, or when you use event-based libraries.
666		757
667	These typically register a callback for some event, and call that callback	758	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	759	when the event occured. In a coro, however, you typically want to
669	just wait for the event, simplyifying things.	760	just wait for the event, simplyifying things.
670		761
671	For example C<< AnyEvent->child >> registers a callback to be called when	762	For example C<< AnyEvent->child >> registers a callback to be called when
672	a specific child has exited:	763	a specific child has exited:
673		764
674	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });	765	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
675		766
676	But from withina coroutine, you often just want to write this:	767	But from within a coro, you often just want to write this:
677		768
678	my $status = wait_for_child $pid;	769	my $status = wait_for_child $pid;
679		770
680	Coro offers two functions specifically designed to make this easy,	771	Coro offers two functions specifically designed to make this easy,
681	C<Coro::rouse_cb> and C<Coro::rouse_wait>.	772	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
682		773
683	The first function, C<rouse_cb>, generates and returns a callback that,	774	The first function, C<rouse_cb>, generates and returns a callback that,
684	when invoked, will save it's arguments and notify the coroutine that	775	when invoked, will save its arguments and notify the coro that
685	created the callback.	776	created the callback.
686		777
687	The second function, C<rouse_wait>, waits for the callback to be called	778	The second function, C<rouse_wait>, waits for the callback to be called
688	(by calling C<schedule> to go to sleep) and returns the arguments	779	(by calling C<schedule> to go to sleep) and returns the arguments
689	originally passed to the callback.	780	originally passed to the callback.
…		…
704	you can roll your own, using C<schedule>:	795	you can roll your own, using C<schedule>:
705		796
706	sub wait_for_child($) {	797	sub wait_for_child($) {
707	my ($pid) = @_;	798	my ($pid) = @_;
708		799
709	# store the current coroutine in $current,	800	# store the current coro in $current,
710	# and provide result variables for the closure passed to ->child	801	# and provide result variables for the closure passed to ->child
711	my $current = $Coro::current;	802	my $current = $Coro::current;
712	my ($done, $rstatus);	803	my ($done, $rstatus);
713		804
714	# pass a closure to ->child	805	# pass a closure to ->child
…		…
730		821
731	=item fork with pthread backend	822	=item fork with pthread backend
732		823
733	When Coro is compiled using the pthread backend (which isn't recommended	824	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	825	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	826	coro will not survive a fork. There is no known workaround except to
736	fix your libc and use a saner backend.	827	fix your libc and use a saner backend.
737		828
738	=item perl process emulation ("threads")	829	=item perl process emulation ("threads")
739		830
740	This module is not perl-pseudo-thread-safe. You should only ever use this	831	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	832	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	833	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	834	this). I recommend disabling thread support and using processes, as having
744	the windows process emulation enabled under unix roughly halves perl	835	the windows process emulation enabled under unix roughly halves perl
745	performance, even when not used.	836	performance, even when not used.
746		837
747	=item coroutine switching not signal safe	838	=item coro switching is not signal safe
748		839
749	You must not switch to another coroutine from within a signal handler	840	You must not switch to another coro from within a signal handler (only
750	(only relevant with %SIG - most event libraries provide safe signals).	841	relevant with %SIG - most event libraries provide safe signals), I<unless>
		842	you are sure you are not interrupting a Coro function.
751		843
752	That means you I<MUST NOT> call any function that might "block" the	844	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	845	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
754	anything that calls those. Everything else, including calling C<ready>,	846	anything that calls those. Everything else, including calling C<ready>,
755	works.	847	works.
756		848
757	=back	849	=back
758		850
759		851
		852	=head1 WINDOWS PROCESS EMULATION
		853
		854	A great many people seem to be confused about ithreads (for example, Chip
		855	Salzenberg called me unintelligent, incapable, stupid and gullible,
		856	while in the same mail making rather confused statements about perl
		857	ithreads (for example, that memory or files would be shared), showing his
		858	lack of understanding of this area - if it is hard to understand for Chip,
		859	it is probably not obvious to everybody).
		860
		861	What follows is an ultra-condensed version of my talk about threads in
		862	scripting languages given onthe perl workshop 2009:
		863
		864	The so-called "ithreads" were originally implemented for two reasons:
		865	first, to (badly) emulate unix processes on native win32 perls, and
		866	secondly, to replace the older, real thread model ("5.005-threads").
		867
		868	It does that by using threads instead of OS processes. The difference
		869	between processes and threads is that threads share memory (and other
		870	state, such as files) between threads within a single process, while
		871	processes do not share anything (at least not semantically). That
		872	means that modifications done by one thread are seen by others, while
		873	modifications by one process are not seen by other processes.
		874
		875	The "ithreads" work exactly like that: when creating a new ithreads
		876	process, all state is copied (memory is copied physically, files and code
		877	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		878	the same behaviour can be achieved by using operating system processes,
		879	except that UNIX typically uses hardware built into the system to do this
		880	efficiently, while the windows process emulation emulates this hardware in
		881	software (rather efficiently, but of course it is still much slower than
		882	dedicated hardware).
		883
		884	As mentioned before, loading code, modifying code, modifying data
		885	structures and so on is only visible in the ithreads process doing the
		886	modification, not in other ithread processes within the same OS process.
		887
		888	This is why "ithreads" do not implement threads for perl at all, only
		889	processes. What makes it so bad is that on non-windows platforms, you can
		890	actually take advantage of custom hardware for this purpose (as evidenced
		891	by the forks module, which gives you the (i-) threads API, just much
		892	faster).
		893
		894	Sharing data is in the i-threads model is done by transfering data
		895	structures between threads using copying semantics, which is very slow -
		896	shared data simply does not exist. Benchmarks using i-threads which are
		897	communication-intensive show extremely bad behaviour with i-threads (in
		898	fact, so bad that Coro, which cannot take direct advantage of multiple
		899	CPUs, is often orders of magnitude faster because it shares data using
		900	real threads, refer to my talk for details).
		901
		902	As summary, i-threads use threads to implement processes, while
		903	the compatible forks module uses processes to emulate, uhm,
		904	processes. I-threads slow down every perl program when enabled, and
		905	outside of windows, serve no (or little) practical purpose, but
		906	disadvantages every single-threaded Perl program.
		907
		908	This is the reason that I try to avoid the name "ithreads", as it is
		909	misleading as it implies that it implements some kind of thread model for
		910	perl, and prefer the name "windows process emulation", which describes the
		911	actual use and behaviour of it much better.
		912
760	=head1 SEE ALSO	913	=head1 SEE ALSO
761		914
762	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	915	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
763		916
764	Debugging: L<Coro::Debug>.	917	Debugging: L<Coro::Debug>.
765		918
766	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	919	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
767		920
768	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	921	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		922	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
769		923
770	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	924	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
771		925
772	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	926	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		927	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		928	L<Coro::Select>.
773		929
774	XS API: L<Coro::MakeMaker>.	930	XS API: L<Coro::MakeMaker>.
775		931
776	Low level Configuration, Coroutine Environment: L<Coro::State>.	932	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
777		933
778	=head1 AUTHOR	934	=head1 AUTHOR
779		935
780	Marc Lehmann <schmorp@schmorp.de>	936	Marc Lehmann <schmorp@schmorp.de>
781	http://home.schmorp.de/	937	http://home.schmorp.de/

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