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

Comparing Coro/Coro.pm (file contents):
Revision 1.22 by root, Mon Jul 23 02:14:19 2001 UTC vs.
Revision 1.121 by root, Fri Apr 13 12:56:55 2007 UTC

…		…
8		8
9	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
11	};	11	};
12		12
13	# alternatively create an async process like this:	13	# alternatively create an async coroutine like this:
14		14
15	sub some_func : Coro {	15	sub some_func : Coro {
16	# some more async code	16	# some more async code
17	}	17	}
18		18
19	cede;	19	cede;
20		20
21	=head1 DESCRIPTION	21	=head1 DESCRIPTION
22		22
23	This module collection manages coroutines. Coroutines are similar to	23	This module collection manages coroutines. Coroutines are similar
24	Threads but don't run in parallel.	24	to threads but don't run in parallel at the same time even on SMP
		25	machines. The specific flavor of coroutine use din this module also
		26	guarentees you that it will not switch between coroutines unless
		27	necessary, at easily-identified points in your program, so locking and
		28	parallel access are rarely an issue, making coroutine programming much
		29	safer than threads programming.
25		30
26	This module is still experimental, see the BUGS section below.	31	(Perl, however, does not natively support real threads but instead does a
		32	very slow and memory-intensive emulation of processes using threads. This
		33	is a performance win on Windows machines, and a loss everywhere else).
27		34
28	In this module, coroutines are defined as "callchain + lexical variables	35	In this module, coroutines are defined as "callchain + lexical variables +
29	+ @_ + $_ + $@ + $^W), that is, a coroutine has it's own callchain, it's	36	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
30	own set of lexicals and it's own set of perl's most important global	37	its own set of lexicals and its own set of perls most important global
31	variables.	38	variables.
32		39
33	WARNING: When using this module, make sure that, at program end, no
34	coroutines are still running OR just call exit before falling off the
35	end. The reason for this is that some coroutine of yours might have called
36	into a C function, and falling off the end of main:: results in returning
37	to that C function instead if to the main C interpreter.
38
39	WARNING: Unless you really know what you are doing, do NOT do context
40	switches inside callbacks from the XS level. The reason for this is
41	similar to the reason above: A callback calls a perl function, this
42	perl function does a context switch, some other callback is called, the
43	original function returns from it - to what? To the wrong XS function,
44	with totally different return values. Unfortunately, this includes
45	callbacks done by perl itself (tie'd variables!).
46
47	The only workaround for this is to do coroutines on C level.
48
49	=cut	40	=cut
50		41
51	package Coro;	42	package Coro;
52		43
		44	use strict;
		45	no warnings "uninitialized";
		46
53	use Coro::State;	47	use Coro::State;
54		48
55	use base Exporter;	49	use base qw(Coro::State Exporter);
56		50
57	$VERSION = 0.10;	51	our $idle; # idle handler
		52	our $main; # main coroutine
		53	our $current; # current coroutine
58		54
		55	our $VERSION = '3.56';
		56
59	@EXPORT = qw(async cede schedule terminate current);	57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
60	@EXPORT_OK = qw($current);	58	our %EXPORT_TAGS = (
		59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
		60	);
		61	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
61		62
62	{	63	{
63	my @async;	64	my @async;
		65	my $init;
64		66
65	# this way of handling attributes simply is NOT scalable ;()	67	# this way of handling attributes simply is NOT scalable ;()
66	sub import {	68	sub import {
		69	no strict 'refs';
		70
67	Coro->export_to_level(1, @_);	71	Coro->export_to_level (1, @_);
		72
68	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};	73	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
69	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {	74	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
70	my ($package, $ref) = (shift, shift);	75	my ($package, $ref) = (shift, shift);
71	my @attrs;	76	my @attrs;
72	for (@_) {	77	for (@_) {
73	if ($_ eq "Coro") {	78	if ($_ eq "Coro") {
74	push @async, $ref;	79	push @async, $ref;
		80	unless ($init++) {
		81	eval q{
		82	sub INIT {
		83	&async(pop @async) while @async;
		84	}
		85	};
		86	}
75	} else {	87	} else {
76	push @attrs, $_;	88	push @attrs, $_;
77	}	89	}
78	}	90	}
79	return $old ? $old->($package, $ref, @attrs) : @attrs;	91	return $old ? $old->($package, $ref, @attrs) : @attrs;
80	};	92	};
81	}	93	}
82		94
83	sub INIT {
84	&async(pop @async) while @async;
85	}
86	}	95	}
		96
		97	=over 4
87		98
88	=item $main	99	=item $main
89		100
90	This coroutine represents the main program.	101	This coroutine represents the main program.
91		102
92	=cut	103	=cut
93		104
94	our $main = new Coro;	105	$main = new Coro;
95		106
96	=item $current (or as function: current)	107	=item $current (or as function: current)
97		108
98	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	109	The current coroutine (the last coroutine switched to). The initial value
		110	is C<$main> (of course).
		111
		112	This variable is B<strictly> I<read-only>. It is provided for performance
		113	reasons. If performance is not essentiel you are encouraged to use the
		114	C<Coro::current> function instead.
99		115
100	=cut	116	=cut
101		117
102	# maybe some other module used Coro::Specific before...	118	# maybe some other module used Coro::Specific before...
103	if ($current) {
104	$main->{specific} = $current->{specific};	119	$main->{specific} = $current->{specific}
105	}	120	if $current;
106		121
107	our $current = $main;	122	_set_current $main;
108		123
109	sub current() { $current }	124	sub current() { $current }
110		125
111	=item $idle	126	=item $idle
112		127
113	The coroutine to switch to when no other coroutine is running. The default	128	A callback that is called whenever the scheduler finds no ready coroutines
114	implementation prints "FATAL: deadlock detected" and exits.	129	to run. The default implementation prints "FATAL: deadlock detected" and
		130	exits, because the program has no other way to continue.
115		131
116	=cut	132	This hook is overwritten by modules such as C<Coro::Timer> and
		133	C<Coro::Event> to wait on an external event that hopefully wake up a
		134	coroutine so the scheduler can run it.
117		135
118	# should be done using priorities :(	136	Please note that if your callback recursively invokes perl (e.g. for event
119	our $idle = new Coro sub {	137	handlers), then it must be prepared to be called recursively.
120	print STDERR "FATAL: deadlock detected\n";	138
121	exit(51);	139	=cut
		140
		141	$idle = sub {
		142	require Carp;
		143	Carp::croak ("FATAL: deadlock detected");
122	};	144	};
123		145
124	# we really need priorities...	146	sub _cancel {
125	my @ready; # the ready queue. hehe, rather broken ;)	147	my ($self) = @_;
		148
		149	# free coroutine data and mark as destructed
		150	$self->_destroy
		151	or return;
		152
		153	# call all destruction callbacks
		154	$_->(@{$self->{status}})
		155	for @{(delete $self->{destroy_cb}) \|\| []};
		156	}
		157
		158	# this coroutine is necessary because a coroutine
		159	# cannot destroy itself.
		160	my @destroy;
		161	my $manager;
		162
		163	$manager = new Coro sub {
		164	while () {
		165	(shift @destroy)->_cancel
		166	while @destroy;
		167
		168	&schedule;
		169	}
		170	};
		171
		172	$manager->prio (PRIO_MAX);
126		173
127	# static methods. not really.	174	# static methods. not really.
128		175
		176	=back
		177
129	=head2 STATIC METHODS	178	=head2 STATIC METHODS
130		179
131	Static methods are actually functions that operate on the current process only.	180	Static methods are actually functions that operate on the current coroutine only.
132		181
133	=over 4	182	=over 4
134		183
135	=item async { ... } [@args...]	184	=item async { ... } [@args...]
136		185
137	Create a new asynchronous process and return it's process object	186	Create a new asynchronous coroutine and return it's coroutine object
138	(usually unused). When the sub returns the new process is automatically	187	(usually unused). When the sub returns the new coroutine is automatically
139	terminated.	188	terminated.
		189
		190	Calling C<exit> in a coroutine will try to do the same as calling exit
		191	outside the coroutine, but this is experimental. It is best not to rely on
		192	exit doing any cleanups or even not crashing.
		193
		194	When the coroutine dies, the program will exit, just as in the main
		195	program.
140		196
141	# create a new coroutine that just prints its arguments	197	# create a new coroutine that just prints its arguments
142	async {	198	async {
143	print "@_\n";	199	print "@_\n";
144	} 1,2,3,4;	200	} 1,2,3,4;
145		201
146	The coderef you submit MUST NOT be a closure that refers to variables
147	in an outer scope. This does NOT work. Pass arguments into it instead.
148
149	=cut	202	=cut
150		203
151	sub async(&@) {	204	sub async(&@) {
152	my $pid = new Coro @_;	205	my $coro = new Coro @_;
153	$pid->ready;	206	$coro->ready;
154	$pid;	207	$coro
		208	}
		209
		210	=item async_pool { ... } [@args...]
		211
		212	Similar to C<async>, but uses a coroutine pool, so you should not call
		213	terminate or join (although you are allowed to), and you get a coroutine
		214	that might have executed other code already (which can be good or bad :).
		215
		216	Also, the block is executed in an C<eval> context and a warning will be
		217	issued in case of an exception instead of terminating the program, as
		218	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		219	will not work in the expected way, unless you call terminate or cancel,
		220	which somehow defeats the purpose of pooling.
		221
		222	The priority will be reset to C<0> after each job, otherwise the coroutine
		223	will be re-used "as-is".
		224
		225	The pool size is limited to 8 idle coroutines (this can be adjusted by
		226	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
		227	required.
		228
		229	If you are concerned about pooled coroutines growing a lot because a
		230	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool {
		231	terminate }> once per second or so to slowly replenish the pool.
		232
		233	=cut
		234
		235	our $POOL_SIZE = 8;
		236	our @pool;
		237
		238	sub pool_handler {
		239	while () {
		240	eval {
		241	my ($cb, @arg) = @{ delete $current->{_invoke} or return };
		242	$cb->(@arg);
		243	};
		244	warn $@ if $@;
		245
		246	last if @pool >= $POOL_SIZE;
		247	push @pool, $current;
		248
		249	$current->save (Coro::State::SAVE_DEF);
		250	$current->prio (0);
		251	schedule;
		252	}
		253	}
		254
		255	sub async_pool(&@) {
		256	# this is also inlined into the unlock_scheduler
		257	my $coro = (pop @pool or new Coro \&pool_handler);
		258
		259	$coro->{_invoke} = [@_];
		260	$coro->ready;
		261
		262	$coro
155	}	263	}
156		264
157	=item schedule	265	=item schedule
158		266
159	Calls the scheduler. Please note that the current process will not be put	267	Calls the scheduler. Please note that the current coroutine will not be put
160	into the ready queue, so calling this function usually means you will	268	into the ready queue, so calling this function usually means you will
161	never be called again.	269	never be called again unless something else (e.g. an event handler) calls
		270	ready.
162		271
163	=cut	272	The canonical way to wait on external events is this:
164		273
165	my $prev;	274	{
		275	# remember current coroutine
		276	my $current = $Coro::current;
166		277
167	sub schedule {	278	# register a hypothetical event handler
168	# should be done using priorities :(	279	on_event_invoke sub {
169	($prev, $current) = ($current, shift @ready \|\| $idle);	280	# wake up sleeping coroutine
170	Coro::State::transfer($prev, $current);	281	$current->ready;
171	}	282	undef $current;
		283	};
		284
		285	# call schedule until event occured.
		286	# in case we are woken up for other reasons
		287	# (current still defined), loop.
		288	Coro::schedule while $current;
		289	}
172		290
173	=item cede	291	=item cede
174		292
175	"Cede" to other processes. This function puts the current process into the	293	"Cede" to other coroutines. This function puts the current coroutine into the
176	ready queue and calls C<schedule>, which has the effect of giving up the	294	ready queue and calls C<schedule>, which has the effect of giving up the
177	current "timeslice" to other coroutines of the same or higher priority.	295	current "timeslice" to other coroutines of the same or higher priority.
178		296
179	=cut	297	Returns true if at least one coroutine switch has happened.
180		298
181	sub cede {	299	=item Coro::cede_notself
182	$current->ready;
183	&schedule;
184	}
185		300
		301	Works like cede, but is not exported by default and will cede to any
		302	coroutine, regardless of priority, once.
		303
		304	Returns true if at least one coroutine switch has happened.
		305
186	=item terminate	306	=item terminate [arg...]
187		307
188	Terminates the current process.	308	Terminates the current coroutine with the given status values (see L<cancel>).
189
190	Future versions of this function will allow result arguments.
191		309
192	=cut	310	=cut
193		311
194	sub terminate {	312	sub terminate {
195	my $self = $current;	313	$current->cancel (@_);
196	$self->{_results} = [@_];
197	$current = shift @ready \|\| $idle;
198	Coro::State::transfer(delete $self->{_coro_state}, $current);
199	# cannot return
200	die;
201	}	314	}
202		315
203	=back	316	=back
204		317
205	# dynamic methods	318	# dynamic methods
206		319
207	=head2 PROCESS METHODS	320	=head2 COROUTINE METHODS
208		321
209	These are the methods you can call on process objects.	322	These are the methods you can call on coroutine objects.
210		323
211	=over 4	324	=over 4
212		325
213	=item new Coro \&sub [, @args...]	326	=item new Coro \&sub [, @args...]
214		327
215	Create a new process and return it. When the sub returns the process	328	Create a new coroutine and return it. When the sub returns the coroutine
216	automatically terminates. To start the process you must first put it into	329	automatically terminates as if C<terminate> with the returned values were
		330	called. To make the coroutine run you must first put it into the ready queue
217	the ready queue by calling the ready method.	331	by calling the ready method.
218		332
219	The coderef you submit MUST NOT be a closure that refers to variables	333	See C<async> for additional discussion.
220	in an outer scope. This does NOT work. Pass arguments into it instead.
221		334
222	=cut	335	=cut
223		336
224	sub _newcoro {	337	sub _run_coro {
225	terminate &{+shift};	338	terminate &{+shift};
226	}	339	}
227		340
228	sub new {	341	sub new {
229	my $class = shift;	342	my $class = shift;
230	bless {
231	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
232	}, $class;
233	}
234		343
235	=item $process->ready	344	$class->SUPER::new (\&_run_coro, @_)
		345	}
236		346
237	Put the current process into the ready queue.	347	=item $success = $coroutine->ready
238		348
239	=cut	349	Put the given coroutine into the ready queue (according to it's priority)
		350	and return true. If the coroutine is already in the ready queue, do nothing
		351	and return false.
240		352
241	sub ready {	353	=item $is_ready = $coroutine->is_ready
242	push @ready, $_[0];	354
		355	Return wether the coroutine is currently the ready queue or not,
		356
		357	=item $coroutine->cancel (arg...)
		358
		359	Terminates the given coroutine and makes it return the given arguments as
		360	status (default: the empty list). Never returns if the coroutine is the
		361	current coroutine.
		362
		363	=cut
		364
		365	sub cancel {
		366	my $self = shift;
		367	$self->{status} = [@_];
		368
		369	if ($current == $self) {
		370	push @destroy, $self;
		371	$manager->ready;
		372	&schedule while 1;
		373	} else {
		374	$self->_cancel;
		375	}
		376	}
		377
		378	=item $coroutine->join
		379
		380	Wait until the coroutine terminates and return any values given to the
		381	C<terminate> or C<cancel> functions. C<join> can be called multiple times
		382	from multiple coroutine.
		383
		384	=cut
		385
		386	sub join {
		387	my $self = shift;
		388
		389	unless ($self->{status}) {
		390	my $current = $current;
		391
		392	push @{$self->{destroy_cb}}, sub {
		393	$current->ready;
		394	undef $current;
		395	};
		396
		397	&schedule while $current;
		398	}
		399
		400	wantarray ? @{$self->{status}} : $self->{status}[0];
		401	}
		402
		403	=item $coroutine->on_destroy (\&cb)
		404
		405	Registers a callback that is called when this coroutine gets destroyed,
		406	but before it is joined. The callback gets passed the terminate arguments,
		407	if any.
		408
		409	=cut
		410
		411	sub on_destroy {
		412	my ($self, $cb) = @_;
		413
		414	push @{ $self->{destroy_cb} }, $cb;
		415	}
		416
		417	=item $oldprio = $coroutine->prio ($newprio)
		418
		419	Sets (or gets, if the argument is missing) the priority of the
		420	coroutine. Higher priority coroutines get run before lower priority
		421	coroutines. Priorities are small signed integers (currently -4 .. +3),
		422	that you can refer to using PRIO_xxx constants (use the import tag :prio
		423	to get then):
		424
		425	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		426	3 > 1 > 0 > -1 > -3 > -4
		427
		428	# set priority to HIGH
		429	current->prio(PRIO_HIGH);
		430
		431	The idle coroutine ($Coro::idle) always has a lower priority than any
		432	existing coroutine.
		433
		434	Changing the priority of the current coroutine will take effect immediately,
		435	but changing the priority of coroutines in the ready queue (but not
		436	running) will only take effect after the next schedule (of that
		437	coroutine). This is a bug that will be fixed in some future version.
		438
		439	=item $newprio = $coroutine->nice ($change)
		440
		441	Similar to C<prio>, but subtract the given value from the priority (i.e.
		442	higher values mean lower priority, just as in unix).
		443
		444	=item $olddesc = $coroutine->desc ($newdesc)
		445
		446	Sets (or gets in case the argument is missing) the description for this
		447	coroutine. This is just a free-form string you can associate with a coroutine.
		448
		449	=cut
		450
		451	sub desc {
		452	my $old = $_[0]{desc};
		453	$_[0]{desc} = $_[1] if @_ > 1;
		454	$old;
243	}	455	}
244		456
245	=back	457	=back
246		458
		459	=head2 GLOBAL FUNCTIONS
		460
		461	=over 4
		462
		463	=item Coro::nready
		464
		465	Returns the number of coroutines that are currently in the ready state,
		466	i.e. that can be swicthed to. The value C<0> means that the only runnable
		467	coroutine is the currently running one, so C<cede> would have no effect,
		468	and C<schedule> would cause a deadlock unless there is an idle handler
		469	that wakes up some coroutines.
		470
		471	=item my $guard = Coro::guard { ... }
		472
		473	This creates and returns a guard object. Nothing happens until the object
		474	gets destroyed, in which case the codeblock given as argument will be
		475	executed. This is useful to free locks or other resources in case of a
		476	runtime error or when the coroutine gets canceled, as in both cases the
		477	guard block will be executed. The guard object supports only one method,
		478	C<< ->cancel >>, which will keep the codeblock from being executed.
		479
		480	Example: set some flag and clear it again when the coroutine gets canceled
		481	or the function returns:
		482
		483	sub do_something {
		484	my $guard = Coro::guard { $busy = 0 };
		485	$busy = 1;
		486
		487	# do something that requires $busy to be true
		488	}
		489
		490	=cut
		491
		492	sub guard(&) {
		493	bless \(my $cb = $_[0]), "Coro::guard"
		494	}
		495
		496	sub Coro::guard::cancel {
		497	${$_[0]} = sub { };
		498	}
		499
		500	sub Coro::guard::DESTROY {
		501	${$_[0]}->();
		502	}
		503
		504
		505	=item unblock_sub { ... }
		506
		507	This utility function takes a BLOCK or code reference and "unblocks" it,
		508	returning the new coderef. This means that the new coderef will return
		509	immediately without blocking, returning nothing, while the original code
		510	ref will be called (with parameters) from within its own coroutine.
		511
		512	The reason this fucntion exists is that many event libraries (such as the
		513	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		514	of thread-safety). This means you must not block within event callbacks,
		515	otherwise you might suffer from crashes or worse.
		516
		517	This function allows your callbacks to block by executing them in another
		518	coroutine where it is safe to block. One example where blocking is handy
		519	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		520	disk.
		521
		522	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		523	creating event callbacks that want to block.
		524
		525	=cut
		526
		527	our @unblock_queue;
		528
		529	# we create a special coro because we want to cede,
		530	# to reduce pressure on the coro pool (because most callbacks
		531	# return immediately and can be reused) and because we cannot cede
		532	# inside an event callback.
		533	our $unblock_scheduler = async {
		534	while () {
		535	while (my $cb = pop @unblock_queue) {
		536	# this is an inlined copy of async_pool
		537	my $coro = (pop @pool or new Coro \&pool_handler);
		538
		539	$coro->{_invoke} = $cb;
		540	$coro->ready;
		541	cede; # for short-lived callbacks, this reduces pressure on the coro pool
		542	}
		543	schedule; # sleep well
		544	}
		545	};
		546
		547	sub unblock_sub(&) {
		548	my $cb = shift;
		549
		550	sub {
		551	unshift @unblock_queue, [$cb, @_];
		552	$unblock_scheduler->ready;
		553	}
		554	}
		555
		556	=back
		557
247	=cut	558	=cut
248		559
249	1;	560	1;
250		561
251	=head1 BUGS/LIMITATIONS	562	=head1 BUGS/LIMITATIONS
252		563
253	- could be faster, especially when the core would introduce special	564	- you must make very sure that no coro is still active on global
254	support for coroutines (like it does for threads).	565	destruction. very bad things might happen otherwise (usually segfaults).
255	- there is still a memleak on coroutine termination that I could not	566
256	identify. Could be as small as a single SV.
257	- this module is not well-tested.
258	- if variables or arguments "disappear" (become undef) or become
259	corrupted please contact the author so he cen iron out the
260	remaining bugs.
261	- this module is not thread-safe. You must only ever use this module from	567	- this module is not thread-safe. You should only ever use this module
262	the same thread (this requirement might be loosened in the future to	568	from the same thread (this requirement might be losened in the future
263	allow per-thread schedulers, but Coro::State does not yet allow this).	569	to allow per-thread schedulers, but Coro::State does not yet allow
		570	this).
264		571
265	=head1 SEE ALSO	572	=head1 SEE ALSO
266		573
267	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	574	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
268	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	575
		576	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		577
		578	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
		579
		580	Embedding: L<Coro:MakeMaker>
269		581
270	=head1 AUTHOR	582	=head1 AUTHOR
271		583
272	Marc Lehmann <pcg@goof.com>	584	Marc Lehmann <schmorp@schmorp.de>
273	http://www.goof.com/pcg/marc/	585	http://home.schmorp.de/
274		586
275	=cut	587	=cut
276		588

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Comparing Coro/Coro.pm (file contents): Revision 1.22 by root, Mon Jul 23 02:14:19 2001 UTC vs. Revision 1.121 by root, Fri Apr 13 12:56:55 2007 UTC

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Comparing Coro/Coro.pm (file contents):
Revision 1.22 by root, Mon Jul 23 02:14:19 2001 UTC vs.
Revision 1.121 by root, Fri Apr 13 12:56:55 2007 UTC