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

Comparing Coro/Coro.pm (file contents):
Revision 1.219 by root, Sun Nov 16 00:55:41 2008 UTC vs.
Revision 1.268 by root, Thu Oct 1 23:16:27 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 $VERSION = 5.17;
73		87
74	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
75	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
76	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77	);	91	);
78	our @EXPORT_OK = (@{$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 = new Coro;	107	# $main is now being initialised by Coro::State
92		108
93	=item $Coro::current	109	=item $Coro::current
94		110
95	The coroutine object representing the current coroutine (the last	111	The Coro object representing the current coro (the last
96	coroutine that the Coro scheduler switched to). The initial value is	112	coro that the Coro scheduler switched to). The initial value is
97	C<$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	$main->{desc} = "[main::]";
106
107	# maybe some other module used Coro::Specific before...
108	$main->{_specific} = $current->{_specific}
109	if $current;
110
111	_set_current $main;
112
113	sub current() { $current } # [DEPRECATED]	121	sub current() { $current } # [DEPRECATED]
114		122
115	=item $Coro::idle	123	=item $Coro::idle
116		124
117	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
118	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
119	pretty low-level functionality.	127	pretty low-level functionality.
120		128
121	This variable stores a callback that is called whenever the scheduler	129	This variable stores either a Coro object or a callback.
		130
		131	If it is a callback, the it is called whenever the scheduler finds no
122	finds no ready coroutines to run. The default implementation prints	132	ready coros to run. The default implementation prints "FATAL:
123	"FATAL: deadlock detected" and exits, because the program has no other way	133	deadlock detected" and exits, because the program has no other way to
124	to continue.	134	continue.
125		135
		136	If it is a coro object, then this object will be readied (without
		137	invoking any ready hooks, however) when the scheduler finds no other ready
		138	coros to run.
		139
126	This hook is overwritten by modules such as C<Coro::Timer> and	140	This hook is overwritten by modules such as C<Coro::EV> and
127	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a	141	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
128	coroutine so the scheduler can run it.	142	coro so the scheduler can run it.
129		143
130	Note that the callback I<must not>, under any circumstances, block	144	Note that the callback I<must not>, under any circumstances, block
131	the current coroutine. Normally, this is achieved by having an "idle	145	the current coro. Normally, this is achieved by having an "idle
132	coroutine" that calls the event loop and then blocks again, and then	146	coro" that calls the event loop and then blocks again, and then
133	readying that coroutine in the idle handler.	147	readying that coro in the idle handler, or by simply placing the idle
		148	coro in this variable.
134		149
135	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this	150	See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
136	technique.	151	technique.
137		152
138	Please note that if your callback recursively invokes perl (e.g. for event	153	Please note that if your callback recursively invokes perl (e.g. for event
139	handlers), then it must be prepared to be called recursively itself.	154	handlers), then it must be prepared to be called recursively itself.
140		155
141	=cut	156	=cut
142		157
143	$idle = sub {	158	$idle = sub {
144	require Carp;	159	warn "oi\n";#d#
145	Carp::croak ("FATAL: deadlock detected");	160	Carp::confess ("FATAL: deadlock detected");
146	};	161	};
147		162
148	sub _cancel {
149	my ($self) = @_;
150
151	# free coroutine data and mark as destructed
152	$self->_destroy
153	or return;
154
155	# call all destruction callbacks
156	$_->(@{$self->{_status}})
157	for @{ delete $self->{_on_destroy} \|\| [] };
158	}
159
160	# this coroutine is necessary because a coroutine	163	# this coro is necessary because a coro
161	# cannot destroy itself.	164	# cannot destroy itself.
162	my @destroy;	165	our @destroy;
163	my $manager;	166	our $manager;
164		167
165	$manager = new Coro sub {	168	$manager = new Coro sub {
166	while () {	169	while () {
167	(shift @destroy)->_cancel	170	Coro::State::cancel shift @destroy
168	while @destroy;	171	while @destroy;
169		172
170	&schedule;	173	&schedule;
171	}	174	}
172	};	175	};
173	$manager->{desc} = "[coro manager]";	176	$manager->{desc} = "[coro manager]";
174	$manager->prio (PRIO_MAX);	177	$manager->prio (PRIO_MAX);
175		178
176	=back	179	=back
177		180
178	=head2 SIMPLE COROUTINE CREATION	181	=head1 SIMPLE CORO CREATION
179		182
180	=over 4	183	=over 4
181		184
182	=item async { ... } [@args...]	185	=item async { ... } [@args...]
183		186
184	Create a new coroutine and return it's coroutine object (usually	187	Create a new coro and return its Coro object (usually
185	unused). The coroutine will be put into the ready queue, so	188	unused). The coro will be put into the ready queue, so
186	it will start running automatically on the next scheduler run.	189	it will start running automatically on the next scheduler run.
187		190
188	The first argument is a codeblock/closure that should be executed in the	191	The first argument is a codeblock/closure that should be executed in the
189	coroutine. When it returns argument returns the coroutine is automatically	192	coro. When it returns argument returns the coro is automatically
190	terminated.	193	terminated.
191		194
192	The remaining arguments are passed as arguments to the closure.	195	The remaining arguments are passed as arguments to the closure.
193		196
194	See the C<Coro::State::new> constructor for info about the coroutine	197	See the C<Coro::State::new> constructor for info about the coro
195	environment in which coroutines are executed.	198	environment in which coro are executed.
196		199
197	Calling C<exit> in a coroutine will do the same as calling exit outside	200	Calling C<exit> in a coro will do the same as calling exit outside
198	the coroutine. Likewise, when the coroutine dies, the program will exit,	201	the coro. Likewise, when the coro dies, the program will exit,
199	just as it would in the main program.	202	just as it would in the main program.
200		203
201	If you do not want that, you can provide a default C<die> handler, or	204	If you do not want that, you can provide a default C<die> handler, or
202	simply avoid dieing (by use of C<eval>).	205	simply avoid dieing (by use of C<eval>).
203		206
204	Example: Create a new coroutine that just prints its arguments.	207	Example: Create a new coro that just prints its arguments.
205		208
206	async {	209	async {
207	print "@_\n";	210	print "@_\n";
208	} 1,2,3,4;	211	} 1,2,3,4;
209		212
210	=cut
211
212	sub async(&@) {
213	my $coro = new Coro @_;
214	$coro->ready;
215	$coro
216	}
217
218	=item async_pool { ... } [@args...]	213	=item async_pool { ... } [@args...]
219		214
220	Similar to C<async>, but uses a coroutine pool, so you should not call	215	Similar to C<async>, but uses a coro pool, so you should not call
221	terminate or join on it (although you are allowed to), and you get a	216	terminate or join on it (although you are allowed to), and you get a
222	coroutine that might have executed other code already (which can be good	217	coro that might have executed other code already (which can be good
223	or bad :).	218	or bad :).
224		219
225	On the plus side, this function is faster than creating (and destroying)	220	On the plus side, this function is about twice as fast as creating (and
226	a completly new coroutine, so if you need a lot of generic coroutines in	221	destroying) a completely new coro, so if you need a lot of generic
227	quick successsion, use C<async_pool>, not C<async>.	222	coros in quick successsion, use C<async_pool>, not C<async>.
228		223
229	The code block is executed in an C<eval> context and a warning will be	224	The code block is executed in an C<eval> context and a warning will be
230	issued in case of an exception instead of terminating the program, as	225	issued in case of an exception instead of terminating the program, as
231	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	226	C<async> does. As the coro is being reused, stuff like C<on_destroy>
232	will not work in the expected way, unless you call terminate or cancel,	227	will not work in the expected way, unless you call terminate or cancel,
233	which somehow defeats the purpose of pooling (but is fine in the	228	which somehow defeats the purpose of pooling (but is fine in the
234	exceptional case).	229	exceptional case).
235		230
236	The priority will be reset to C<0> after each run, tracing will be	231	The priority will be reset to C<0> after each run, tracing will be
237	disabled, the description will be reset and the default output filehandle	232	disabled, the description will be reset and the default output filehandle
238	gets restored, so you can change all these. Otherwise the coroutine will	233	gets restored, so you can change all these. Otherwise the coro will
239	be re-used "as-is": most notably if you change other per-coroutine global	234	be re-used "as-is": most notably if you change other per-coro global
240	stuff such as C<$/> you I<must needs> revert that change, which is most	235	stuff such as C<$/> you I<must needs> revert that change, which is most
241	simply done by using local as in: C<< local $/ >>.	236	simply done by using local as in: C<< local $/ >>.
242		237
243	The idle pool size is limited to C<8> idle coroutines (this can be	238	The idle pool size is limited to C<8> idle coros (this can be
244	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle	239	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
245	coros as required.	240	coros as required.
246		241
247	If you are concerned about pooled coroutines growing a lot because a	242	If you are concerned about pooled coros growing a lot because a
248	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool	243	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
249	{ terminate }> once per second or so to slowly replenish the pool. In	244	{ terminate }> once per second or so to slowly replenish the pool. In
250	addition to that, when the stacks used by a handler grows larger than 16kb	245	addition to that, when the stacks used by a handler grows larger than 32kb
251	(adjustable via $Coro::POOL_RSS) it will also be destroyed.	246	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
252		247
253	=cut	248	=cut
254		249
255	our $POOL_SIZE = 8;	250	our $POOL_SIZE = 8;
256	our $POOL_RSS = 16 * 1024;	251	our $POOL_RSS = 32 * 1024;
257	our @async_pool;	252	our @async_pool;
258		253
259	sub pool_handler {	254	sub pool_handler {
260	my $cb;
261
262	while () {	255	while () {
263	eval {	256	eval {
264	while () {	257	&{&_pool_handler} while 1;
265	_pool_1 $cb;
266	&$cb;
267	_pool_2 $cb;
268	&schedule;
269	}
270	};	258	};
271		259
272	if ($@) {
273	last if $@ eq "\3async_pool terminate\2\n";
274	warn $@;	260	warn $@ if $@;
275	}
276	}	261	}
277	}	262	}
278		263
279	sub async_pool(&@) {
280	# this is also inlined into the unblock_scheduler
281	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
282
283	$coro->{_invoke} = [@_];
284	$coro->ready;
285
286	$coro
287	}
288
289	=back	264	=back
290		265
291	=head2 STATIC METHODS	266	=head1 STATIC METHODS
292		267
293	Static methods are actually functions that operate on the current coroutine.	268	Static methods are actually functions that implicitly operate on the
		269	current coro.
294		270
295	=over 4	271	=over 4
296		272
297	=item schedule	273	=item schedule
298		274
299	Calls the scheduler. The scheduler will find the next coroutine that is	275	Calls the scheduler. The scheduler will find the next coro that is
300	to be run from the ready queue and switches to it. The next coroutine	276	to be run from the ready queue and switches to it. The next coro
301	to be run is simply the one with the highest priority that is longest	277	to be run is simply the one with the highest priority that is longest
302	in its ready queue. If there is no coroutine ready, it will clal the	278	in its ready queue. If there is no coro ready, it will clal the
303	C<$Coro::idle> hook.	279	C<$Coro::idle> hook.
304		280
305	Please note that the current coroutine will I<not> be put into the ready	281	Please note that the current coro will I<not> be put into the ready
306	queue, so calling this function usually means you will never be called	282	queue, so calling this function usually means you will never be called
307	again unless something else (e.g. an event handler) calls C<< ->ready >>,	283	again unless something else (e.g. an event handler) calls C<< ->ready >>,
308	thus waking you up.	284	thus waking you up.
309		285
310	This makes C<schedule> I<the> generic method to use to block the current	286	This makes C<schedule> I<the> generic method to use to block the current
311	coroutine and wait for events: first you remember the current coroutine in	287	coro and wait for events: first you remember the current coro in
312	a variable, then arrange for some callback of yours to call C<< ->ready	288	a variable, then arrange for some callback of yours to call C<< ->ready
313	>> on that once some event happens, and last you call C<schedule> to put	289	>> on that once some event happens, and last you call C<schedule> to put
314	yourself to sleep. Note that a lot of things can wake your coroutine up,	290	yourself to sleep. Note that a lot of things can wake your coro up,
315	so you need to check whether the event indeed happened, e.g. by storing the	291	so you need to check whether the event indeed happened, e.g. by storing the
316	status in a variable.	292	status in a variable.
317		293
318	The canonical way to wait on external events is this:	294	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
319		295
320	{	296	=item cede
321	# remember current coroutine
322	my $current = $Coro::current;
323		297
324	# register a hypothetical event handler	298	"Cede" to other coros. This function puts the current coro into
325	on_event_invoke sub {	299	the ready queue and calls C<schedule>, which has the effect of giving
326	# wake up sleeping coroutine	300	up the current "timeslice" to other coros of the same or higher
327	$current->ready;	301	priority. Once your coro gets its turn again it will automatically be
328	undef $current;	302	resumed.
		303
		304	This function is often called C<yield> in other languages.
		305
		306	=item Coro::cede_notself
		307
		308	Works like cede, but is not exported by default and will cede to I<any>
		309	coro, regardless of priority. This is useful sometimes to ensure
		310	progress is made.
		311
		312	=item terminate [arg...]
		313
		314	Terminates the current coro with the given status values (see L<cancel>).
		315
		316	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		317
		318	These function install enter and leave winders in the current scope. The
		319	enter block will be executed when on_enter is called and whenever the
		320	current coro is re-entered by the scheduler, while the leave block is
		321	executed whenever the current coro is blocked by the scheduler, and
		322	also when the containing scope is exited (by whatever means, be it exit,
		323	die, last etc.).
		324
		325	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		326	BLOCKs>. That means: do not even think about calling C<die> without an
		327	eval, and do not even think of entering the scheduler in any way.
		328
		329	Since both BLOCKs are tied to the current scope, they will automatically
		330	be removed when the current scope exits.
		331
		332	These functions implement the same concept as C<dynamic-wind> in scheme
		333	does, and are useful when you want to localise some resource to a specific
		334	coro.
		335
		336	They slow down thread switching considerably for coros that use them
		337	(about 40% for a BLOCK with a single assignment, so thread switching is
		338	still reasonably fast if the handlers are fast).
		339
		340	These functions are best understood by an example: The following function
		341	will change the current timezone to "Antarctica/South_Pole", which
		342	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		343	which remember/change the current timezone and restore the previous
		344	value, respectively, the timezone is only changed for the coro that
		345	installed those handlers.
		346
		347	use POSIX qw(tzset);
		348
		349	async {
		350	my $old_tz; # store outside TZ value here
		351
		352	Coro::on_enter {
		353	$old_tz = $ENV{TZ}; # remember the old value
		354
		355	$ENV{TZ} = "Antarctica/South_Pole";
		356	tzset; # enable new value
329	};	357	};
330		358
331	# call schedule until event occurred.	359	Coro::on_leave {
332	# in case we are woken up for other reasons	360	$ENV{TZ} = $old_tz;
333	# (current still defined), loop.	361	tzset; # restore old value
334	Coro::schedule while $current;	362	};
		363
		364	# at this place, the timezone is Antarctica/South_Pole,
		365	# without disturbing the TZ of any other coro.
335	}	366	};
336		367
337	=item cede	368	This can be used to localise about any resource (locale, uid, current
		369	working directory etc.) to a block, despite the existance of other
		370	coros.
338		371
339	"Cede" to other coroutines. This function puts the current coroutine into	372	Another interesting example implements time-sliced multitasking using
340	the ready queue and calls C<schedule>, which has the effect of giving	373	interval timers (this could obviously be optimised, but does the job):
341	up the current "timeslice" to other coroutines of the same or higher
342	priority. Once your coroutine gets its turn again it will automatically be
343	resumed.
344		374
345	This function is often called C<yield> in other languages.	375	# "timeslice" the given block
		376	sub timeslice(&) {
		377	use Time::HiRes ();
346		378
347	=item Coro::cede_notself	379	Coro::on_enter {
		380	# on entering the thread, we set an VTALRM handler to cede
		381	$SIG{VTALRM} = sub { cede };
		382	# and then start the interval timer
		383	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		384	};
		385	Coro::on_leave {
		386	# on leaving the thread, we stop the interval timer again
		387	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		388	};
348		389
349	Works like cede, but is not exported by default and will cede to I<any>	390	&{+shift};
350	coroutine, regardless of priority. This is useful sometimes to ensure	391	}
351	progress is made.
352		392
353	=item terminate [arg...]	393	# use like this:
		394	timeslice {
		395	# The following is an endless loop that would normally
		396	# monopolise the process. Since it runs in a timesliced
		397	# environment, it will regularly cede to other threads.
		398	while () { }
		399	};
354		400
355	Terminates the current coroutine with the given status values (see L<cancel>).
356		401
357	=item killall	402	=item killall
358		403
359	Kills/terminates/cancels all coroutines except the currently running	404	Kills/terminates/cancels all coros except the currently running one.
360	one. This is useful after a fork, either in the child or the parent, as
361	usually only one of them should inherit the running coroutines.
362		405
363	Note that while this will try to free some of the main programs resources,	406	Note that while this will try to free some of the main interpreter
		407	resources if the calling coro isn't the main coro, but one
364	you cannot free all of them, so if a coroutine that is not the main	408	cannot free all of them, so if a coro that is not the main coro
365	program calls this function, there will be some one-time resource leak.	409	calls this function, there will be some one-time resource leak.
366		410
367	=cut	411	=cut
368
369	sub terminate {
370	$current->cancel (@_);
371	}
372		412
373	sub killall {	413	sub killall {
374	for (Coro::State::list) {	414	for (Coro::State::list) {
375	$_->cancel	415	$_->cancel
376	if $_ != $current && UNIVERSAL::isa $_, "Coro";	416	if $_ != $current && UNIVERSAL::isa $_, "Coro";
377	}	417	}
378	}	418	}
379		419
380	=back	420	=back
381		421
382	=head2 COROUTINE METHODS	422	=head1 CORO OBJECT METHODS
383		423
384	These are the methods you can call on coroutine objects (or to create	424	These are the methods you can call on coro objects (or to create
385	them).	425	them).
386		426
387	=over 4	427	=over 4
388		428
389	=item new Coro \&sub [, @args...]	429	=item new Coro \&sub [, @args...]
390		430
391	Create a new coroutine and return it. When the sub returns, the coroutine	431	Create a new coro and return it. When the sub returns, the coro
392	automatically terminates as if C<terminate> with the returned values were	432	automatically terminates as if C<terminate> with the returned values were
393	called. To make the coroutine run you must first put it into the ready	433	called. To make the coro run you must first put it into the ready
394	queue by calling the ready method.	434	queue by calling the ready method.
395		435
396	See C<async> and C<Coro::State::new> for additional info about the	436	See C<async> and C<Coro::State::new> for additional info about the
397	coroutine environment.	437	coro environment.
398		438
399	=cut	439	=cut
400		440
401	sub _run_coro {	441	sub _coro_run {
402	terminate &{+shift};	442	terminate &{+shift};
403	}	443	}
404		444
405	sub new {
406	my $class = shift;
407
408	$class->SUPER::new (\&_run_coro, @_)
409	}
410
411	=item $success = $coroutine->ready	445	=item $success = $coro->ready
412		446
413	Put the given coroutine into the end of its ready queue (there is one	447	Put the given coro into the end of its ready queue (there is one
414	queue for each priority) and return true. If the coroutine is already in	448	queue for each priority) and return true. If the coro is already in
415	the ready queue, do nothing and return false.	449	the ready queue, do nothing and return false.
416		450
417	This ensures that the scheduler will resume this coroutine automatically	451	This ensures that the scheduler will resume this coro automatically
418	once all the coroutines of higher priority and all coroutines of the same	452	once all the coro of higher priority and all coro of the same
419	priority that were put into the ready queue earlier have been resumed.	453	priority that were put into the ready queue earlier have been resumed.
420		454
		455	=item $coro->suspend
		456
		457	Suspends the specified coro. A suspended coro works just like any other
		458	coro, except that the scheduler will not select a suspended coro for
		459	execution.
		460
		461	Suspending a coro can be useful when you want to keep the coro from
		462	running, but you don't want to destroy it, or when you want to temporarily
		463	freeze a coro (e.g. for debugging) to resume it later.
		464
		465	A scenario for the former would be to suspend all (other) coros after a
		466	fork and keep them alive, so their destructors aren't called, but new
		467	coros can be created.
		468
		469	=item $coro->resume
		470
		471	If the specified coro was suspended, it will be resumed. Note that when
		472	the coro was in the ready queue when it was suspended, it might have been
		473	unreadied by the scheduler, so an activation might have been lost.
		474
		475	To avoid this, it is best to put a suspended coro into the ready queue
		476	unconditionally, as every synchronisation mechanism must protect itself
		477	against spurious wakeups, and the one in the Coro family certainly do
		478	that.
		479
421	=item $is_ready = $coroutine->is_ready	480	=item $is_ready = $coro->is_ready
422		481
423	Return whether the coroutine is currently the ready queue or not,	482	Returns true iff the Coro object is in the ready queue. Unless the Coro
		483	object gets destroyed, it will eventually be scheduled by the scheduler.
424		484
		485	=item $is_running = $coro->is_running
		486
		487	Returns true iff the Coro object is currently running. Only one Coro object
		488	can ever be in the running state (but it currently is possible to have
		489	multiple running Coro::States).
		490
		491	=item $is_suspended = $coro->is_suspended
		492
		493	Returns true iff this Coro object has been suspended. Suspended Coros will
		494	not ever be scheduled.
		495
425	=item $coroutine->cancel (arg...)	496	=item $coro->cancel (arg...)
426		497
427	Terminates the given coroutine and makes it return the given arguments as	498	Terminates the given Coro and makes it return the given arguments as
428	status (default: the empty list). Never returns if the coroutine is the	499	status (default: the empty list). Never returns if the Coro is the
429	current coroutine.	500	current Coro.
430		501
431	=cut	502	=cut
432		503
433	sub cancel {	504	sub cancel {
434	my $self = shift;	505	my $self = shift;
435	$self->{_status} = [@_];
436		506
437	if ($current == $self) {	507	if ($current == $self) {
438	push @destroy, $self;	508	terminate @_;
439	$manager->ready;
440	&schedule while 1;
441	} else {	509	} else {
442	$self->_cancel;	510	$self->{_status} = [@_];
		511	Coro::State::cancel $self;
443	}	512	}
444	}	513	}
445		514
		515	=item $coro->schedule_to
		516
		517	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		518	of continuing with the next coro from the ready queue, always switch to
		519	the given coro object (regardless of priority etc.). The readyness
		520	state of that coro isn't changed.
		521
		522	This is an advanced method for special cases - I'd love to hear about any
		523	uses for this one.
		524
		525	=item $coro->cede_to
		526
		527	Like C<schedule_to>, but puts the current coro into the ready
		528	queue. This has the effect of temporarily switching to the given
		529	coro, and continuing some time later.
		530
		531	This is an advanced method for special cases - I'd love to hear about any
		532	uses for this one.
		533
446	=item $coroutine->throw ([$scalar])	534	=item $coro->throw ([$scalar])
447		535
448	If C<$throw> is specified and defined, it will be thrown as an exception	536	If C<$throw> is specified and defined, it will be thrown as an exception
449	inside the coroutine at the next convenient point in time (usually after	537	inside the coro at the next convenient point in time. Otherwise
450	it gains control at the next schedule/transfer/cede). Otherwise clears the
451	exception object.	538	clears the exception object.
		539
		540	Coro will check for the exception each time a schedule-like-function
		541	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		542	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		543	detect this case and return early in case an exception is pending.
452		544
453	The exception object will be thrown "as is" with the specified scalar in	545	The exception object will be thrown "as is" with the specified scalar in
454	C<$@>, i.e. if it is a string, no line number or newline will be appended	546	C<$@>, i.e. if it is a string, no line number or newline will be appended
455	(unlike with C<die>).	547	(unlike with C<die>).
456		548
457	This can be used as a softer means than C<cancel> to ask a coroutine to	549	This can be used as a softer means than C<cancel> to ask a coro to
458	end itself, although there is no guarantee that the exception will lead to	550	end itself, although there is no guarantee that the exception will lead to
459	termination, and if the exception isn't caught it might well end the whole	551	termination, and if the exception isn't caught it might well end the whole
460	program.	552	program.
461		553
462	You might also think of C<throw> as being the moral equivalent of	554	You might also think of C<throw> as being the moral equivalent of
463	C<kill>ing a coroutine with a signal (in this case, a scalar).	555	C<kill>ing a coro with a signal (in this case, a scalar).
464		556
465	=item $coroutine->join	557	=item $coro->join
466		558
467	Wait until the coroutine terminates and return any values given to the	559	Wait until the coro terminates and return any values given to the
468	C<terminate> or C<cancel> functions. C<join> can be called concurrently	560	C<terminate> or C<cancel> functions. C<join> can be called concurrently
469	from multiple coroutines, and all will be resumed and given the status	561	from multiple coro, and all will be resumed and given the status
470	return once the C<$coroutine> terminates.	562	return once the C<$coro> terminates.
471		563
472	=cut	564	=cut
473		565
474	sub join {	566	sub join {
475	my $self = shift;	567	my $self = shift;
…		…
486	}	578	}
487		579
488	wantarray ? @{$self->{_status}} : $self->{_status}[0];	580	wantarray ? @{$self->{_status}} : $self->{_status}[0];
489	}	581	}
490		582
491	=item $coroutine->on_destroy (\&cb)	583	=item $coro->on_destroy (\&cb)
492		584
493	Registers a callback that is called when this coroutine gets destroyed,	585	Registers a callback that is called when this coro gets destroyed,
494	but before it is joined. The callback gets passed the terminate arguments,	586	but before it is joined. The callback gets passed the terminate arguments,
495	if any, and I<must not> die, under any circumstances.	587	if any, and I<must not> die, under any circumstances.
496		588
497	=cut	589	=cut
498		590
…		…
500	my ($self, $cb) = @_;	592	my ($self, $cb) = @_;
501		593
502	push @{ $self->{_on_destroy} }, $cb;	594	push @{ $self->{_on_destroy} }, $cb;
503	}	595	}
504		596
505	=item $oldprio = $coroutine->prio ($newprio)	597	=item $oldprio = $coro->prio ($newprio)
506		598
507	Sets (or gets, if the argument is missing) the priority of the	599	Sets (or gets, if the argument is missing) the priority of the
508	coroutine. Higher priority coroutines get run before lower priority	600	coro. Higher priority coro get run before lower priority
509	coroutines. Priorities are small signed integers (currently -4 .. +3),	601	coro. Priorities are small signed integers (currently -4 .. +3),
510	that you can refer to using PRIO_xxx constants (use the import tag :prio	602	that you can refer to using PRIO_xxx constants (use the import tag :prio
511	to get then):	603	to get then):
512		604
513	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	605	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
514	3 > 1 > 0 > -1 > -3 > -4	606	3 > 1 > 0 > -1 > -3 > -4
515		607
516	# set priority to HIGH	608	# set priority to HIGH
517	current->prio(PRIO_HIGH);	609	current->prio (PRIO_HIGH);
518		610
519	The idle coroutine ($Coro::idle) always has a lower priority than any	611	The idle coro ($Coro::idle) always has a lower priority than any
520	existing coroutine.	612	existing coro.
521		613
522	Changing the priority of the current coroutine will take effect immediately,	614	Changing the priority of the current coro will take effect immediately,
523	but changing the priority of coroutines in the ready queue (but not	615	but changing the priority of coro in the ready queue (but not
524	running) will only take effect after the next schedule (of that	616	running) will only take effect after the next schedule (of that
525	coroutine). This is a bug that will be fixed in some future version.	617	coro). This is a bug that will be fixed in some future version.
526		618
527	=item $newprio = $coroutine->nice ($change)	619	=item $newprio = $coro->nice ($change)
528		620
529	Similar to C<prio>, but subtract the given value from the priority (i.e.	621	Similar to C<prio>, but subtract the given value from the priority (i.e.
530	higher values mean lower priority, just as in unix).	622	higher values mean lower priority, just as in unix).
531		623
532	=item $olddesc = $coroutine->desc ($newdesc)	624	=item $olddesc = $coro->desc ($newdesc)
533		625
534	Sets (or gets in case the argument is missing) the description for this	626	Sets (or gets in case the argument is missing) the description for this
535	coroutine. This is just a free-form string you can associate with a	627	coro. This is just a free-form string you can associate with a
536	coroutine.	628	coro.
537		629
538	This method simply sets the C<< $coroutine->{desc} >> member to the given	630	This method simply sets the C<< $coro->{desc} >> member to the given
539	string. You can modify this member directly if you wish.	631	string. You can modify this member directly if you wish.
540		632
541	=cut	633	=cut
542		634
543	sub desc {	635	sub desc {
544	my $old = $_[0]{desc};	636	my $old = $_[0]{desc};
545	$_[0]{desc} = $_[1] if @_ > 1;	637	$_[0]{desc} = $_[1] if @_ > 1;
546	$old;	638	$old;
547	}	639	}
548		640
		641	sub transfer {
		642	require Carp;
		643	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		644	}
		645
549	=back	646	=back
550		647
551	=head2 GLOBAL FUNCTIONS	648	=head1 GLOBAL FUNCTIONS
552		649
553	=over 4	650	=over 4
554		651
555	=item Coro::nready	652	=item Coro::nready
556		653
557	Returns the number of coroutines that are currently in the ready state,	654	Returns the number of coro that are currently in the ready state,
558	i.e. that can be switched to by calling C<schedule> directory or	655	i.e. that can be switched to by calling C<schedule> directory or
559	indirectly. The value C<0> means that the only runnable coroutine is the	656	indirectly. The value C<0> means that the only runnable coro is the
560	currently running one, so C<cede> would have no effect, and C<schedule>	657	currently running one, so C<cede> would have no effect, and C<schedule>
561	would cause a deadlock unless there is an idle handler that wakes up some	658	would cause a deadlock unless there is an idle handler that wakes up some
562	coroutines.	659	coro.
563		660
564	=item my $guard = Coro::guard { ... }	661	=item my $guard = Coro::guard { ... }
565		662
566	This creates and returns a guard object. Nothing happens until the object	663	This function still exists, but is deprecated. Please use the
567	gets destroyed, in which case the codeblock given as argument will be	664	C<Guard::guard> function instead.
568	executed. This is useful to free locks or other resources in case of a
569	runtime error or when the coroutine gets canceled, as in both cases the
570	guard block will be executed. The guard object supports only one method,
571	C<< ->cancel >>, which will keep the codeblock from being executed.
572		665
573	Example: set some flag and clear it again when the coroutine gets canceled
574	or the function returns:
575
576	sub do_something {
577	my $guard = Coro::guard { $busy = 0 };
578	$busy = 1;
579
580	# do something that requires $busy to be true
581	}
582
583	=cut	666	=cut
584		667
585	sub guard(&) {	668	BEGIN { *guard = \&Guard::guard }
586	bless \(my $cb = $_[0]), "Coro::guard"
587	}
588
589	sub Coro::guard::cancel {
590	${$_[0]} = sub { };
591	}
592
593	sub Coro::guard::DESTROY {
594	${$_[0]}->();
595	}
596
597		669
598	=item unblock_sub { ... }	670	=item unblock_sub { ... }
599		671
600	This utility function takes a BLOCK or code reference and "unblocks" it,	672	This utility function takes a BLOCK or code reference and "unblocks" it,
601	returning a new coderef. Unblocking means that calling the new coderef	673	returning a new coderef. Unblocking means that calling the new coderef
602	will return immediately without blocking, returning nothing, while the	674	will return immediately without blocking, returning nothing, while the
603	original code ref will be called (with parameters) from within another	675	original code ref will be called (with parameters) from within another
604	coroutine.	676	coro.
605		677
606	The reason this function exists is that many event libraries (such as the	678	The reason this function exists is that many event libraries (such as the
607	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	679	venerable L<Event\|Event> module) are not thread-safe (a weaker form
608	of thread-safety). This means you must not block within event callbacks,	680	of reentrancy). This means you must not block within event callbacks,
609	otherwise you might suffer from crashes or worse. The only event library	681	otherwise you might suffer from crashes or worse. The only event library
610	currently known that is safe to use without C<unblock_sub> is L<EV>.	682	currently known that is safe to use without C<unblock_sub> is L<EV>.
611		683
612	This function allows your callbacks to block by executing them in another	684	This function allows your callbacks to block by executing them in another
613	coroutine where it is safe to block. One example where blocking is handy	685	coro where it is safe to block. One example where blocking is handy
614	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	686	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
615	disk, for example.	687	disk, for example.
616		688
617	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	689	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
618	creating event callbacks that want to block.	690	creating event callbacks that want to block.
619		691
620	If your handler does not plan to block (e.g. simply sends a message to	692	If your handler does not plan to block (e.g. simply sends a message to
621	another coroutine, or puts some other coroutine into the ready queue),	693	another coro, or puts some other coro into the ready queue), there is
622	there is no reason to use C<unblock_sub>.	694	no reason to use C<unblock_sub>.
623		695
624	Note that you also need to use C<unblock_sub> for any other callbacks that	696	Note that you also need to use C<unblock_sub> for any other callbacks that
625	are indirectly executed by any C-based event loop. For example, when you	697	are indirectly executed by any C-based event loop. For example, when you
626	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it	698	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
627	provides callbacks that are the result of some event callback, then you	699	provides callbacks that are the result of some event callback, then you
…		…
636	# return immediately and can be reused) and because we cannot cede	708	# return immediately and can be reused) and because we cannot cede
637	# inside an event callback.	709	# inside an event callback.
638	our $unblock_scheduler = new Coro sub {	710	our $unblock_scheduler = new Coro sub {
639	while () {	711	while () {
640	while (my $cb = pop @unblock_queue) {	712	while (my $cb = pop @unblock_queue) {
641	# this is an inlined copy of async_pool	713	&async_pool (@$cb);
642	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
643		714
644	$coro->{_invoke} = $cb;
645	$coro->ready;
646	cede; # for short-lived callbacks, this reduces pressure on the coro pool	715	# for short-lived callbacks, this reduces pressure on the coro pool
		716	# as the chance is very high that the async_poll coro will be back
		717	# in the idle state when cede returns
		718	cede;
647	}	719	}
648	schedule; # sleep well	720	schedule; # sleep well
649	}	721	}
650	};	722	};
651	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";	723	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
…		…
657	unshift @unblock_queue, [$cb, @_];	729	unshift @unblock_queue, [$cb, @_];
658	$unblock_scheduler->ready;	730	$unblock_scheduler->ready;
659	}	731	}
660	}	732	}
661		733
		734	=item $cb = Coro::rouse_cb
		735
		736	Create and return a "rouse callback". That's a code reference that,
		737	when called, will remember a copy of its arguments and notify the owner
		738	coro of the callback.
		739
		740	See the next function.
		741
		742	=item @args = Coro::rouse_wait [$cb]
		743
		744	Wait for the specified rouse callback (or the last one that was created in
		745	this coro).
		746
		747	As soon as the callback is invoked (or when the callback was invoked
		748	before C<rouse_wait>), it will return the arguments originally passed to
		749	the rouse callback. In scalar context, that means you get the I<last>
		750	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		751	statement at the end.
		752
		753	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		754
662	=back	755	=back
663		756
664	=cut	757	=cut
665		758
666	1;	759	1;
		760
		761	=head1 HOW TO WAIT FOR A CALLBACK
		762
		763	It is very common for a coro to wait for some callback to be
		764	called. This occurs naturally when you use coro in an otherwise
		765	event-based program, or when you use event-based libraries.
		766
		767	These typically register a callback for some event, and call that callback
		768	when the event occured. In a coro, however, you typically want to
		769	just wait for the event, simplyifying things.
		770
		771	For example C<< AnyEvent->child >> registers a callback to be called when
		772	a specific child has exited:
		773
		774	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		775
		776	But from within a coro, you often just want to write this:
		777
		778	my $status = wait_for_child $pid;
		779
		780	Coro offers two functions specifically designed to make this easy,
		781	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		782
		783	The first function, C<rouse_cb>, generates and returns a callback that,
		784	when invoked, will save its arguments and notify the coro that
		785	created the callback.
		786
		787	The second function, C<rouse_wait>, waits for the callback to be called
		788	(by calling C<schedule> to go to sleep) and returns the arguments
		789	originally passed to the callback.
		790
		791	Using these functions, it becomes easy to write the C<wait_for_child>
		792	function mentioned above:
		793
		794	sub wait_for_child($) {
		795	my ($pid) = @_;
		796
		797	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		798
		799	my ($rpid, $rstatus) = Coro::rouse_wait;
		800	$rstatus
		801	}
		802
		803	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		804	you can roll your own, using C<schedule>:
		805
		806	sub wait_for_child($) {
		807	my ($pid) = @_;
		808
		809	# store the current coro in $current,
		810	# and provide result variables for the closure passed to ->child
		811	my $current = $Coro::current;
		812	my ($done, $rstatus);
		813
		814	# pass a closure to ->child
		815	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		816	$rstatus = $_[1]; # remember rstatus
		817	$done = 1; # mark $rstatus as valud
		818	});
		819
		820	# wait until the closure has been called
		821	schedule while !$done;
		822
		823	$rstatus
		824	}
		825
667		826
668	=head1 BUGS/LIMITATIONS	827	=head1 BUGS/LIMITATIONS
669		828
670	=over 4	829	=over 4
671		830
672	=item fork with pthread backend	831	=item fork with pthread backend
673		832
674	When Coro is compiled using the pthread backend (which isn't recommended	833	When Coro is compiled using the pthread backend (which isn't recommended
675	but required on many BSDs as their libcs are completely broken), then	834	but required on many BSDs as their libcs are completely broken), then
676	coroutines will not survive a fork. There is no known workaround except to	835	coro will not survive a fork. There is no known workaround except to
677	fix your libc and use a saner backend.	836	fix your libc and use a saner backend.
678		837
679	=item perl process emulation ("threads")	838	=item perl process emulation ("threads")
680		839
681	This module is not perl-pseudo-thread-safe. You should only ever use this	840	This module is not perl-pseudo-thread-safe. You should only ever use this
682	module from the same thread (this requirement might be removed in the	841	module from the first thread (this requirement might be removed in the
683	future to allow per-thread schedulers, but Coro::State does not yet allow	842	future to allow per-thread schedulers, but Coro::State does not yet allow
684	this). I recommend disabling thread support and using processes, as having	843	this). I recommend disabling thread support and using processes, as having
685	the windows process emulation enabled under unix roughly halves perl	844	the windows process emulation enabled under unix roughly halves perl
686	performance, even when not used.	845	performance, even when not used.
687		846
688	=item coroutine switching not signal safe	847	=item coro switching is not signal safe
689		848
690	You must not switch to another coroutine from within a signal handler	849	You must not switch to another coro from within a signal handler
691	(only relevant with %SIG - most event libraries provide safe signals).	850	(only relevant with %SIG - most event libraries provide safe signals).
692		851
693	That means you I<MUST NOT> call any fucntion that might "block" the	852	That means you I<MUST NOT> call any function that might "block" the
694	current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or	853	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
695	anything that calls those. Everything else, including calling C<ready>,	854	anything that calls those. Everything else, including calling C<ready>,
696	works.	855	works.
697		856
698	=back	857	=back
699		858
700		859
		860	=head1 WINDOWS PROCESS EMULATION
		861
		862	A great many people seem to be confused about ithreads (for example, Chip
		863	Salzenberg called me unintelligent, incapable, stupid and gullible,
		864	while in the same mail making rather confused statements about perl
		865	ithreads (for example, that memory or files would be shared), showing his
		866	lack of understanding of this area - if it is hard to understand for Chip,
		867	it is probably not obvious to everybody).
		868
		869	What follows is an ultra-condensed version of my talk about threads in
		870	scripting languages given onthe perl workshop 2009:
		871
		872	The so-called "ithreads" were originally implemented for two reasons:
		873	first, to (badly) emulate unix processes on native win32 perls, and
		874	secondly, to replace the older, real thread model ("5.005-threads").
		875
		876	It does that by using threads instead of OS processes. The difference
		877	between processes and threads is that threads share memory (and other
		878	state, such as files) between threads within a single process, while
		879	processes do not share anything (at least not semantically). That
		880	means that modifications done by one thread are seen by others, while
		881	modifications by one process are not seen by other processes.
		882
		883	The "ithreads" work exactly like that: when creating a new ithreads
		884	process, all state is copied (memory is copied physically, files and code
		885	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		886	the same behaviour can be achieved by using operating system processes,
		887	except that UNIX typically uses hardware built into the system to do this
		888	efficiently, while the windows process emulation emulates this hardware in
		889	software (rather efficiently, but of course it is still much slower than
		890	dedicated hardware).
		891
		892	As mentioned before, loading code, modifying code, modifying data
		893	structures and so on is only visible in the ithreads process doing the
		894	modification, not in other ithread processes within the same OS process.
		895
		896	This is why "ithreads" do not implement threads for perl at all, only
		897	processes. What makes it so bad is that on non-windows platforms, you can
		898	actually take advantage of custom hardware for this purpose (as evidenced
		899	by the forks module, which gives you the (i-) threads API, just much
		900	faster).
		901
		902	Sharing data is in the i-threads model is done by transfering data
		903	structures between threads using copying semantics, which is very slow -
		904	shared data simply does not exist. Benchmarks using i-threads which are
		905	communication-intensive show extremely bad behaviour with i-threads (in
		906	fact, so bad that Coro, which cannot take direct advantage of multiple
		907	CPUs, is often orders of magnitude faster because it shares data using
		908	real threads, refer to my talk for details).
		909
		910	As summary, i-threads use threads to implement processes, while
		911	the compatible forks module uses processes to emulate, uhm,
		912	processes. I-threads slow down every perl program when enabled, and
		913	outside of windows, serve no (or little) practical purpose, but
		914	disadvantages every single-threaded Perl program.
		915
		916	This is the reason that I try to avoid the name "ithreads", as it is
		917	misleading as it implies that it implements some kind of thread model for
		918	perl, and prefer the name "windows process emulation", which describes the
		919	actual use and behaviour of it much better.
		920
701	=head1 SEE ALSO	921	=head1 SEE ALSO
702		922
703	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.	923	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
704		924
705	Debugging: L<Coro::Debug>.	925	Debugging: L<Coro::Debug>.
706		926
707	Support/Utility: L<Coro::Specific>, L<Coro::Util>.	927	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
708		928
709	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	929	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		930	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
710		931
711	IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.	932	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
712		933
713	Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.	934	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		935	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		936	L<Coro::Select>.
714		937
715	XS API: L<Coro::MakeMaker>.	938	XS API: L<Coro::MakeMaker>.
716		939
717	Low level Configuration, Coroutine Environment: L<Coro::State>.	940	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
718		941
719	=head1 AUTHOR	942	=head1 AUTHOR
720		943
721	Marc Lehmann <schmorp@schmorp.de>	944	Marc Lehmann <schmorp@schmorp.de>
722	http://home.schmorp.de/	945	http://home.schmorp.de/

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Revision 1.268 by root, Thu Oct 1 23:16:27 2009 UTC