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

Comparing Coro/Coro.pm (file contents):
Revision 1.20 by root, Sat Jul 21 18:21:45 2001 UTC vs.
Revision 1.145 by root, Wed Oct 3 16:03:17 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	yield;	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 used in this module also
		26	guarantees 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	=cut	40	=cut
34		41
35	package Coro;	42	package Coro;
36		43
		44	use strict;
		45	no warnings "uninitialized";
		46
37	use Coro::State;	47	use Coro::State;
38		48
39	use base Exporter;	49	use base qw(Coro::State Exporter);
40		50
41	$VERSION = 0.10;	51	our $idle; # idle handler
		52	our $main; # main coroutine
		53	our $current; # current coroutine
42		54
		55	our $VERSION = '4.0';
		56
43	@EXPORT = qw(async yield schedule terminate current);	57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
44	@EXPORT_OK = qw($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));
45		62
46	{	63	{
47	my @async;	64	my @async;
		65	my $init;
48		66
49	# this way of handling attributes simply is NOT scalable ;()	67	# this way of handling attributes simply is NOT scalable ;()
50	sub import {	68	sub import {
		69	no strict 'refs';
		70
51	Coro->export_to_level(1, @_);	71	Coro->export_to_level (1, @_);
		72
52	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};	73	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
53	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {	74	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
54	my ($package, $ref) = (shift, shift);	75	my ($package, $ref) = (shift, shift);
55	my @attrs;	76	my @attrs;
56	for (@_) {	77	for (@_) {
57	if ($_ eq "Coro") {	78	if ($_ eq "Coro") {
58	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	}
59	} else {	87	} else {
60	push @attrs, $_;	88	push @attrs, $_;
61	}	89	}
62	}	90	}
63	return $old ? $old->($package, $ref, @attrs) : @attrs;	91	return $old ? $old->($package, $ref, @attrs) : @attrs;
64	};	92	};
65	}	93	}
66		94
67	sub INIT {
68	&async(pop @async) while @async;
69	}
70	}	95	}
		96
		97	=over 4
71		98
72	=item $main	99	=item $main
73		100
74	This coroutine represents the main program.	101	This coroutine represents the main program.
75		102
76	=cut	103	=cut
77		104
78	our $main = new Coro;	105	$main = new Coro;
79		106
80	=item $current (or as function: current)	107	=item $current (or as function: current)
81		108
82	The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course).	109	The current coroutine (the last coroutine switched to). The initial value
		110	is C<$main> (of course).
83		111
		112	This variable is B<strictly> I<read-only>. It is provided for performance
		113	reasons. If performance is not essential you are encouraged to use the
		114	C<Coro::current> function instead.
		115
84	=cut	116	=cut
		117
		118	$main->{desc} = "[main::]";
85		119
86	# maybe some other module used Coro::Specific before...	120	# maybe some other module used Coro::Specific before...
87	if ($current) {
88	$main->{specific} = $current->{specific};	121	$main->{_specific} = $current->{_specific}
89	}	122	if $current;
90		123
91	our $current = $main;	124	_set_current $main;
92		125
93	sub current() { $current }	126	sub current() { $current }
94		127
95	=item $idle	128	=item $idle
96		129
97	The coroutine to switch to when no other coroutine is running. The default	130	A callback that is called whenever the scheduler finds no ready coroutines
98	implementation prints "FATAL: deadlock detected" and exits.	131	to run. The default implementation prints "FATAL: deadlock detected" and
		132	exits, because the program has no other way to continue.
99		133
100	=cut	134	This hook is overwritten by modules such as C<Coro::Timer> and
		135	C<Coro::Event> to wait on an external event that hopefully wake up a
		136	coroutine so the scheduler can run it.
101		137
102	# should be done using priorities :(	138	Please note that if your callback recursively invokes perl (e.g. for event
103	our $idle = new Coro sub {	139	handlers), then it must be prepared to be called recursively.
104	print STDERR "FATAL: deadlock detected\n";	140
105	exit(51);	141	=cut
		142
		143	$idle = sub {
		144	require Carp;
		145	Carp::croak ("FATAL: deadlock detected");
106	};	146	};
107		147
108	# we really need priorities...	148	sub _cancel {
109	my @ready; # the ready queue. hehe, rather broken ;)	149	my ($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
		161	# cannot destroy itself.
		162	my @destroy;
		163	my $manager;
		164
		165	$manager = new Coro sub {
		166	while () {
		167	(shift @destroy)->_cancel
		168	while @destroy;
		169
		170	&schedule;
		171	}
		172	};
		173	$manager->desc ("[coro manager]");
		174	$manager->prio (PRIO_MAX);
110		175
111	# static methods. not really.	176	# static methods. not really.
112		177
		178	=back
		179
113	=head2 STATIC METHODS	180	=head2 STATIC METHODS
114		181
115	Static methods are actually functions that operate on the current process only.	182	Static methods are actually functions that operate on the current coroutine only.
116		183
117	=over 4	184	=over 4
118		185
119	=item async { ... } [@args...]	186	=item async { ... } [@args...]
120		187
121	Create a new asynchronous process and return it's process object	188	Create a new asynchronous coroutine and return it's coroutine object
122	(usually unused). When the sub returns the new process is automatically	189	(usually unused). When the sub returns the new coroutine is automatically
123	terminated.	190	terminated.
		191
		192	See the C<Coro::State::new> constructor for info about the coroutine
		193	environment.
		194
		195	Calling C<exit> in a coroutine will do the same as calling exit outside
		196	the coroutine. Likewise, when the coroutine dies, the program will exit,
		197	just as it would in the main program.
124		198
125	# create a new coroutine that just prints its arguments	199	# create a new coroutine that just prints its arguments
126	async {	200	async {
127	print "@_\n";	201	print "@_\n";
128	} 1,2,3,4;	202	} 1,2,3,4;
129		203
130	The coderef you submit MUST NOT be a closure that refers to variables
131	in an outer scope. This does NOT work. Pass arguments into it instead.
132
133	=cut	204	=cut
134		205
135	sub async(&@) {	206	sub async(&@) {
136	my $pid = new Coro @_;	207	my $coro = new Coro @_;
137	$pid->ready;	208	$coro->ready;
138	$pid;	209	$coro
		210	}
		211
		212	=item async_pool { ... } [@args...]
		213
		214	Similar to C<async>, but uses a coroutine pool, so you should not call
		215	terminate or join (although you are allowed to), and you get a coroutine
		216	that might have executed other code already (which can be good or bad :).
		217
		218	Also, the block is executed in an C<eval> context and a warning will be
		219	issued in case of an exception instead of terminating the program, as
		220	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
		221	will not work in the expected way, unless you call terminate or cancel,
		222	which somehow defeats the purpose of pooling.
		223
		224	The priority will be reset to C<0> after each job, otherwise the coroutine
		225	will be re-used "as-is".
		226
		227	The pool size is limited to 8 idle coroutines (this can be adjusted by
		228	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
		229	required.
		230
		231	If you are concerned about pooled coroutines growing a lot because a
		232	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
		233	{ terminate }> once per second or so to slowly replenish the pool. In
		234	addition to that, when the stacks used by a handler grows larger than 16kb
		235	(adjustable with $Coro::POOL_RSS) it will also exit.
		236
		237	=cut
		238
		239	our $POOL_SIZE = 8;
		240	our $POOL_RSS = 16 * 1024;
		241	our @async_pool;
		242
		243	sub pool_handler {
		244	my $cb;
		245
		246	while () {
		247	eval {
		248	while () {
		249	_pool_1 $cb;
		250	&$cb;
		251	_pool_2 $cb;
		252	&schedule;
		253	}
		254	};
		255
		256	last if $@ eq "\3terminate\2\n";
		257	warn $@ if $@;
		258	}
		259	}
		260
		261	sub async_pool(&@) {
		262	# this is also inlined into the unlock_scheduler
		263	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
		264
		265	$coro->{_invoke} = [@_];
		266	$coro->ready;
		267
		268	$coro
139	}	269	}
140		270
141	=item schedule	271	=item schedule
142		272
143	Calls the scheduler. Please note that the current process will not be put	273	Calls the scheduler. Please note that the current coroutine will not be put
144	into the ready queue, so calling this function usually means you will	274	into the ready queue, so calling this function usually means you will
145	never be called again.	275	never be called again unless something else (e.g. an event handler) calls
		276	ready.
146		277
147	=cut	278	The canonical way to wait on external events is this:
148		279
149	my $prev;	280	{
		281	# remember current coroutine
		282	my $current = $Coro::current;
150		283
151	sub schedule {	284	# register a hypothetical event handler
152	# should be done using priorities :(	285	on_event_invoke sub {
153	($prev, $current) = ($current, shift @ready \|\| $idle);	286	# wake up sleeping coroutine
154	Coro::State::transfer($prev, $current);
155	}
156
157	=item yield
158
159	Yield to other processes. This function puts the current process into the
160	ready queue and calls C<schedule>.
161
162	=cut
163
164	sub yield {
165	$current->ready;	287	$current->ready;
166	&schedule;	288	undef $current;
167	}	289	};
168		290
		291	# call schedule until event occurred.
		292	# in case we are woken up for other reasons
		293	# (current still defined), loop.
		294	Coro::schedule while $current;
		295	}
		296
		297	=item cede
		298
		299	"Cede" to other coroutines. This function puts the current coroutine into the
		300	ready queue and calls C<schedule>, which has the effect of giving up the
		301	current "timeslice" to other coroutines of the same or higher priority.
		302
		303	Returns true if at least one coroutine switch has happened.
		304
		305	=item Coro::cede_notself
		306
		307	Works like cede, but is not exported by default and will cede to any
		308	coroutine, regardless of priority, once.
		309
		310	Returns true if at least one coroutine switch has happened.
		311
169	=item terminate	312	=item terminate [arg...]
170		313
171	Terminates the current process.	314	Terminates the current coroutine with the given status values (see L<cancel>).
172		315
173	Future versions of this function will allow result arguments.	316	=item killall
		317
		318	Kills/terminates/cancels all coroutines except the currently running
		319	one. This is useful after a fork, either in the child or the parent, as
		320	usually only one of them should inherit the running coroutines.
174		321
175	=cut	322	=cut
176		323
177	sub terminate {	324	sub terminate {
178	$current->{_results} = [@_];	325	$current->cancel (@_);
179	&schedule;	326	}
		327
		328	sub killall {
		329	for (Coro::State::list) {
		330	$_->cancel
		331	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		332	}
180	}	333	}
181		334
182	=back	335	=back
183		336
184	# dynamic methods	337	# dynamic methods
185		338
186	=head2 PROCESS METHODS	339	=head2 COROUTINE METHODS
187		340
188	These are the methods you can call on process objects.	341	These are the methods you can call on coroutine objects.
189		342
190	=over 4	343	=over 4
191		344
192	=item new Coro \&sub [, @args...]	345	=item new Coro \&sub [, @args...]
193		346
194	Create a new process and return it. When the sub returns the process	347	Create a new coroutine and return it. When the sub returns the coroutine
195	automatically terminates. To start the process you must first put it into	348	automatically terminates as if C<terminate> with the returned values were
		349	called. To make the coroutine run you must first put it into the ready queue
196	the ready queue by calling the ready method.	350	by calling the ready method.
197		351
198	The coderef you submit MUST NOT be a closure that refers to variables	352	See C<async> and C<Coro::State::new> for additional info about the
199	in an outer scope. This does NOT work. Pass arguments into it instead.	353	coroutine environment.
200		354
201	=cut	355	=cut
202		356
203	sub _newcoro {	357	sub _run_coro {
204	terminate &{+shift};	358	terminate &{+shift};
205	}	359	}
206		360
207	sub new {	361	sub new {
208	my $class = shift;	362	my $class = shift;
209	bless {
210	_coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
211	}, $class;
212	}
213		363
214	=item $process->ready	364	$class->SUPER::new (\&_run_coro, @_)
		365	}
215		366
216	Put the current process into the ready queue.	367	=item $success = $coroutine->ready
217		368
218	=cut	369	Put the given coroutine into the ready queue (according to it's priority)
		370	and return true. If the coroutine is already in the ready queue, do nothing
		371	and return false.
219		372
220	sub ready {	373	=item $is_ready = $coroutine->is_ready
221	push @ready, $_[0];	374
		375	Return wether the coroutine is currently the ready queue or not,
		376
		377	=item $coroutine->cancel (arg...)
		378
		379	Terminates the given coroutine and makes it return the given arguments as
		380	status (default: the empty list). Never returns if the coroutine is the
		381	current coroutine.
		382
		383	=cut
		384
		385	sub cancel {
		386	my $self = shift;
		387	$self->{_status} = [@_];
		388
		389	if ($current == $self) {
		390	push @destroy, $self;
		391	$manager->ready;
		392	&schedule while 1;
		393	} else {
		394	$self->_cancel;
		395	}
		396	}
		397
		398	=item $coroutine->join
		399
		400	Wait until the coroutine terminates and return any values given to the
		401	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		402	from multiple coroutines.
		403
		404	=cut
		405
		406	sub join {
		407	my $self = shift;
		408
		409	unless ($self->{_status}) {
		410	my $current = $current;
		411
		412	push @{$self->{_on_destroy}}, sub {
		413	$current->ready;
		414	undef $current;
		415	};
		416
		417	&schedule while $current;
		418	}
		419
		420	wantarray ? @{$self->{_status}} : $self->{_status}[0];
		421	}
		422
		423	=item $coroutine->on_destroy (\&cb)
		424
		425	Registers a callback that is called when this coroutine gets destroyed,
		426	but before it is joined. The callback gets passed the terminate arguments,
		427	if any.
		428
		429	=cut
		430
		431	sub on_destroy {
		432	my ($self, $cb) = @_;
		433
		434	push @{ $self->{_on_destroy} }, $cb;
		435	}
		436
		437	=item $oldprio = $coroutine->prio ($newprio)
		438
		439	Sets (or gets, if the argument is missing) the priority of the
		440	coroutine. Higher priority coroutines get run before lower priority
		441	coroutines. Priorities are small signed integers (currently -4 .. +3),
		442	that you can refer to using PRIO_xxx constants (use the import tag :prio
		443	to get then):
		444
		445	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
		446	3 > 1 > 0 > -1 > -3 > -4
		447
		448	# set priority to HIGH
		449	current->prio(PRIO_HIGH);
		450
		451	The idle coroutine ($Coro::idle) always has a lower priority than any
		452	existing coroutine.
		453
		454	Changing the priority of the current coroutine will take effect immediately,
		455	but changing the priority of coroutines in the ready queue (but not
		456	running) will only take effect after the next schedule (of that
		457	coroutine). This is a bug that will be fixed in some future version.
		458
		459	=item $newprio = $coroutine->nice ($change)
		460
		461	Similar to C<prio>, but subtract the given value from the priority (i.e.
		462	higher values mean lower priority, just as in unix).
		463
		464	=item $olddesc = $coroutine->desc ($newdesc)
		465
		466	Sets (or gets in case the argument is missing) the description for this
		467	coroutine. This is just a free-form string you can associate with a coroutine.
		468
		469	This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
		470	can modify this member directly if you wish.
		471
		472	=cut
		473
		474	sub desc {
		475	my $old = $_[0]{desc};
		476	$_[0]{desc} = $_[1] if @_ > 1;
		477	$old;
222	}	478	}
223		479
224	=back	480	=back
225		481
		482	=head2 GLOBAL FUNCTIONS
		483
		484	=over 4
		485
		486	=item Coro::nready
		487
		488	Returns the number of coroutines that are currently in the ready state,
		489	i.e. that can be switched to. The value C<0> means that the only runnable
		490	coroutine is the currently running one, so C<cede> would have no effect,
		491	and C<schedule> would cause a deadlock unless there is an idle handler
		492	that wakes up some coroutines.
		493
		494	=item my $guard = Coro::guard { ... }
		495
		496	This creates and returns a guard object. Nothing happens until the object
		497	gets destroyed, in which case the codeblock given as argument will be
		498	executed. This is useful to free locks or other resources in case of a
		499	runtime error or when the coroutine gets canceled, as in both cases the
		500	guard block will be executed. The guard object supports only one method,
		501	C<< ->cancel >>, which will keep the codeblock from being executed.
		502
		503	Example: set some flag and clear it again when the coroutine gets canceled
		504	or the function returns:
		505
		506	sub do_something {
		507	my $guard = Coro::guard { $busy = 0 };
		508	$busy = 1;
		509
		510	# do something that requires $busy to be true
		511	}
		512
		513	=cut
		514
		515	sub guard(&) {
		516	bless \(my $cb = $_[0]), "Coro::guard"
		517	}
		518
		519	sub Coro::guard::cancel {
		520	${$_[0]} = sub { };
		521	}
		522
		523	sub Coro::guard::DESTROY {
		524	${$_[0]}->();
		525	}
		526
		527
		528	=item unblock_sub { ... }
		529
		530	This utility function takes a BLOCK or code reference and "unblocks" it,
		531	returning the new coderef. This means that the new coderef will return
		532	immediately without blocking, returning nothing, while the original code
		533	ref will be called (with parameters) from within its own coroutine.
		534
		535	The reason this function exists is that many event libraries (such as the
		536	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
		537	of thread-safety). This means you must not block within event callbacks,
		538	otherwise you might suffer from crashes or worse.
		539
		540	This function allows your callbacks to block by executing them in another
		541	coroutine where it is safe to block. One example where blocking is handy
		542	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
		543	disk.
		544
		545	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
		546	creating event callbacks that want to block.
		547
		548	=cut
		549
		550	our @unblock_queue;
		551
		552	# we create a special coro because we want to cede,
		553	# to reduce pressure on the coro pool (because most callbacks
		554	# return immediately and can be reused) and because we cannot cede
		555	# inside an event callback.
		556	our $unblock_scheduler = new Coro sub {
		557	while () {
		558	while (my $cb = pop @unblock_queue) {
		559	# this is an inlined copy of async_pool
		560	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
		561
		562	$coro->{_invoke} = $cb;
		563	$coro->ready;
		564	cede; # for short-lived callbacks, this reduces pressure on the coro pool
		565	}
		566	schedule; # sleep well
		567	}
		568	};
		569	$unblock_scheduler->desc ("[unblock_sub scheduler]");
		570
		571	sub unblock_sub(&) {
		572	my $cb = shift;
		573
		574	sub {
		575	unshift @unblock_queue, [$cb, @_];
		576	$unblock_scheduler->ready;
		577	}
		578	}
		579
		580	=back
		581
226	=cut	582	=cut
227		583
228	1;	584	1;
229		585
230	=head1 BUGS/LIMITATIONS	586	=head1 BUGS/LIMITATIONS
231		587
232	- could be faster, especially when the core would introduce special	588	- you must make very sure that no coro is still active on global
233	support for coroutines (like it does for threads).	589	destruction. very bad things might happen otherwise (usually segfaults).
234	- there is still a memleak on coroutine termination that I could not	590
235	identify. Could be as small as a single SV.
236	- this module is not well-tested.
237	- if variables or arguments "disappear" (become undef) or become
238	corrupted please contact the author so he cen iron out the
239	remaining bugs.
240	- this module is not thread-safe. You must only ever use this module from	591	- this module is not thread-safe. You should only ever use this module
241	the same thread (this requirement might be loosened in the future to	592	from the same thread (this requirement might be loosened in the future
242	allow per-thread schedulers, but Coro::State does not yet allow this).	593	to allow per-thread schedulers, but Coro::State does not yet allow
		594	this).
243		595
244	=head1 SEE ALSO	596	=head1 SEE ALSO
245		597
246	L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>,	598	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
247	L<Coro::Signal>, L<Coro::State>, L<Coro::Event>.	599
		600	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
		601
		602	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
		603
		604	Embedding: L<Coro:MakeMaker>
248		605
249	=head1 AUTHOR	606	=head1 AUTHOR
250		607
251	Marc Lehmann <pcg@goof.com>	608	Marc Lehmann <schmorp@schmorp.de>
252	http://www.goof.com/pcg/marc/	609	http://home.schmorp.de/
253		610
254	=cut	611	=cut
255		612

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Comparing Coro/Coro.pm (file contents): Revision 1.20 by root, Sat Jul 21 18:21:45 2001 UTC vs. Revision 1.145 by root, Wed Oct 3 16:03:17 2007 UTC

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Comparing Coro/Coro.pm (file contents):
Revision 1.20 by root, Sat Jul 21 18:21:45 2001 UTC vs.
Revision 1.145 by root, Wed Oct 3 16:03:17 2007 UTC