Coro/Coro.pm

=head1 NAME

Coro - coroutine process abstraction

=head1 SYNOPSIS

 use Coro;

 async {
    # some asynchronous thread of execution
 };

 # alternatively create an async coroutine like this:

 sub some_func : Coro {
    # some more async code
 }

 cede;

=head1 DESCRIPTION

This module collection manages coroutines. Coroutines are similar
to threads but don't run in parallel at the same time even on SMP
machines. The specific flavor of coroutine use din this module also
guarentees you that it will not switch between coroutines unless
necessary, at easily-identified points in your program, so locking and
parallel access are rarely an issue, making coroutine programming much
safer than threads programming.

(Perl, however, does not natively support real threads but instead does a
very slow and memory-intensive emulation of processes using threads. This
is a performance win on Windows machines, and a loss everywhere else).

In this module, coroutines are defined as "callchain + lexical variables +
@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
its own set of lexicals and its own set of perls most important global
variables.

=cut

package Coro;

use strict;
no warnings "uninitialized";

use Coro::State;

use base qw(Coro::State Exporter);

our $idle;    # idle handler
our $main;    # main coroutine
our $current; # current coroutine

our $VERSION = '3.3';

our @EXPORT = qw(async cede schedule terminate current unblock_sub);
our %EXPORT_TAGS = (
      prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
);
our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));

{
   my @async;
   my $init;

   # this way of handling attributes simply is NOT scalable ;()
   sub import {
      no strict 'refs';

      Coro->export_to_level (1, @_);

      my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
      *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
         my ($package, $ref) = (shift, shift);
         my @attrs;
         for (@_) {
            if ($_ eq "Coro") {
               push @async, $ref;
               unless ($init++) {
                  eval q{
                     sub INIT {
                        &async(pop @async) while @async;
                     }
                  };
               }
            } else {
               push @attrs, $_;
            }
         }
         return $old ? $old->($package, $ref, @attrs) : @attrs;
      };
   }

}

=over 4

=item $main

This coroutine represents the main program.

=cut

$main = new Coro;

=item $current (or as function: current)

The current coroutine (the last coroutine switched to). The initial value
is C<$main> (of course).

This variable is B<strictly> I<read-only>. It is provided for performance
reasons. If performance is not essentiel you are encouraged to use the
C<Coro::current> function instead.

=cut

# maybe some other module used Coro::Specific before...
$main->{specific} = $current->{specific}
   if $current;

_set_current $main;

sub current() { $current }

=item $idle

A callback that is called whenever the scheduler finds no ready coroutines
to run. The default implementation prints "FATAL: deadlock detected" and
exits, because the program has no other way to continue.

This hook is overwritten by modules such as C<Coro::Timer> and
C<Coro::Event> to wait on an external event that hopefully wake up a
coroutine so the scheduler can run it.

Please note that if your callback recursively invokes perl (e.g. for event
handlers), then it must be prepared to be called recursively.

=cut

$idle = sub {
   require Carp;
   Carp::croak ("FATAL: deadlock detected");
};

# this coroutine is necessary because a coroutine
# cannot destroy itself.
my @destroy;
my $manager; $manager = new Coro sub {
   while () {
      # by overwriting the state object with the manager we destroy it
      # while still being able to schedule this coroutine (in case it has
      # been readied multiple times. this is harmless since the manager
      # can be called as many times as neccessary and will always
      # remove itself from the runqueue
      while (@destroy) {
         my $coro = pop @destroy;

         $coro->{status} ||= [];

         $_->ready                for @{(delete $coro->{join}      ) || []};
         $_->(@{$coro->{status}}) for @{(delete $coro->{destroy_cb}) || []};

         # the next line destroys the coro state, but keeps the
         # coroutine itself intact (we basically make it a zombie
         # coroutine that always runs the manager thread, so it's possible
         # to transfer() to this coroutine).
         $coro->_clone_state_from ($manager);
      }
      &schedule;
   }
};

# static methods. not really.

=back

=head2 STATIC METHODS

Static methods are actually functions that operate on the current coroutine only.

=over 4

=item async { ... } [@args...]

Create a new asynchronous coroutine and return it's coroutine object
(usually unused). When the sub returns the new coroutine is automatically
terminated.

Calling C<exit> in a coroutine will not work correctly, so do not do that.

When the coroutine dies, the program will exit, just as in the main
program.

   # create a new coroutine that just prints its arguments
   async {
      print "@_\n";
   } 1,2,3,4;

=cut

sub async(&@) {
   my $pid = new Coro @_;
   $pid->ready;
   $pid
}

=item schedule

Calls the scheduler. Please note that the current coroutine will not be put
into the ready queue, so calling this function usually means you will
never be called again unless something else (e.g. an event handler) calls
ready.

The canonical way to wait on external events is this:

   {
      # remember current coroutine
      my $current = $Coro::current;

      # register a hypothetical event handler
      on_event_invoke sub {
         # wake up sleeping coroutine
         $current->ready;
         undef $current;
      };

      # call schedule until event occured.
      # in case we are woken up for other reasons
      # (current still defined), loop.
      Coro::schedule while $current;
   }

=item cede

"Cede" to other coroutines. This function puts the current coroutine into the
ready queue and calls C<schedule>, which has the effect of giving up the
current "timeslice" to other coroutines of the same or higher priority.

=item terminate [arg...]

Terminates the current coroutine with the given status values (see L<cancel>).

=cut

sub terminate {
   $current->cancel (@_);
}

=back

# dynamic methods

=head2 COROUTINE METHODS

These are the methods you can call on coroutine objects.

=over 4

=item new Coro \&sub [, @args...]

Create a new coroutine and return it. When the sub returns the coroutine
automatically terminates as if C<terminate> with the returned values were
called. To make the coroutine run you must first put it into the ready queue
by calling the ready method.

Calling C<exit> in a coroutine will not work correctly, so do not do that.

=cut

sub _run_coro {
   terminate &{+shift};
}

sub new {
   my $class = shift;

   $class->SUPER::new (\&_run_coro, @_)
}

=item $success = $coroutine->ready

Put the given coroutine into the ready queue (according to it's priority)
and return true. If the coroutine is already in the ready queue, do nothing
and return false.

=item $is_ready = $coroutine->is_ready

Return wether the coroutine is currently the ready queue or not,

=item $coroutine->cancel (arg...)

Terminates the given coroutine and makes it return the given arguments as
status (default: the empty list).

=cut

sub cancel {
   my $self = shift;
   $self->{status} = [@_];
   push @destroy, $self;
   $manager->ready;
   &schedule if $current == $self;
}

=item $coroutine->join

Wait until the coroutine terminates and return any values given to the
C<terminate> or C<cancel> functions. C<join> can be called multiple times
from multiple coroutine.

=cut

sub join {
   my $self = shift;
   unless ($self->{status}) {
      push @{$self->{join}}, $current;
      &schedule;
   }
   wantarray ? @{$self->{status}} : $self->{status}[0];
}

=item $coroutine->on_destroy (\&cb)

Registers a callback that is called when this coroutine gets destroyed,
but before it is joined. The callback gets passed the terminate arguments,
if any.

=cut

sub on_destroy {
   my ($self, $cb) = @_;

   push @{ $self->{destroy_cb} }, $cb;
}

=item $oldprio = $coroutine->prio ($newprio)

Sets (or gets, if the argument is missing) the priority of the
coroutine. Higher priority coroutines get run before lower priority
coroutines. Priorities are small signed integers (currently -4 .. +3),
that you can refer to using PRIO_xxx constants (use the import tag :prio
to get then):

   PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
       3    >     1     >      0      >    -1    >    -3     >    -4

   # set priority to HIGH
   current->prio(PRIO_HIGH);

The idle coroutine ($Coro::idle) always has a lower priority than any
existing coroutine.

Changing the priority of the current coroutine will take effect immediately,
but changing the priority of coroutines in the ready queue (but not
running) will only take effect after the next schedule (of that
coroutine). This is a bug that will be fixed in some future version.

=item $newprio = $coroutine->nice ($change)

Similar to C<prio>, but subtract the given value from the priority (i.e.
higher values mean lower priority, just as in unix).

=item $olddesc = $coroutine->desc ($newdesc)

Sets (or gets in case the argument is missing) the description for this
coroutine. This is just a free-form string you can associate with a coroutine.

=cut

sub desc {
   my $old = $_[0]{desc};
   $_[0]{desc} = $_[1] if @_ > 1;
   $old;
}

=back

=head2 GLOBAL FUNCTIONS

=over 4

=item Coro::nready

Returns the number of coroutines that are currently in the ready state,
i.e. that can be swicthed to. The value C<0> means that the only runnable
coroutine is the currently running one, so C<cede> would have no effect,
and C<schedule> would cause a deadlock unless there is an idle handler
that wakes up some coroutines.

=item unblock_sub { ... }

This utility function takes a BLOCK or code reference and "unblocks" it,
returning the new coderef. This means that the new coderef will return
immediately without blocking, returning nothing, while the original code
ref will be called (with parameters) from within its own coroutine.

The reason this fucntion exists is that many event libraries (such as the
venerable L<Event|Event> module) are not coroutine-safe (a weaker form
of thread-safety). This means you must not block within event callbacks,
otherwise you might suffer from crashes or worse.

This function allows your callbacks to block by executing them in another
coroutine where it is safe to block. One example where blocking is handy
is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
disk.

In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
creating event callbacks that want to block.

=cut

our @unblock_pool;
our @unblock_queue;
our $UNBLOCK_POOL_SIZE = 2;

sub unblock_handler_ {
   while () {
      my ($cb, @arg) = @{ delete $Coro::current->{arg} };
      $cb->(@arg);

      last if @unblock_pool >= $UNBLOCK_POOL_SIZE;
      push @unblock_pool, $Coro::current;
      schedule;
   }        
}           

our $unblock_scheduler = async {
   while () {
      while (my $cb = pop @unblock_queue) {
         my $handler = (pop @unblock_pool or new Coro \&unblock_handler_);
         $handler->{arg} = $cb;
         $handler->ready;
         cede;
      }

      schedule;
   }
};

sub unblock_sub(&) {
   my $cb = shift;

   sub {
      push @unblock_queue, [$cb, @_];
      $unblock_scheduler->ready;
   }
}

=back

=cut

1;

=head1 BUGS/LIMITATIONS

 - you must make very sure that no coro is still active on global
   destruction. very bad things might happen otherwise (usually segfaults).

 - this module is not thread-safe. You should only ever use this module
   from the same thread (this requirement might be losened in the future
   to allow per-thread schedulers, but Coro::State does not yet allow
   this).

=head1 SEE ALSO

Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.

Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.

Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.

Embedding: L<Coro:MakeMaker>

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.101
Committed:	Fri Dec 29 08:36:34 2006 UTC (17 years, 5 months ago) by root
Branch:	MAIN
Changes since 1.100:	+19 -2 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Coro - coroutine process abstraction
4
5	=head1 SYNOPSIS
6
7	use Coro;
8
9	async {
10	# some asynchronous thread of execution
11	};
12
13	# alternatively create an async coroutine like this:
14
15	sub some_func : Coro {
16	# some more async code
17	}
18
19	cede;
20
21	=head1 DESCRIPTION
22
23	This module collection manages coroutines. Coroutines are similar
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.
30
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).
34
35	In this module, coroutines are defined as "callchain + lexical variables +
36	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
37	its own set of lexicals and its own set of perls most important global
38	variables.
39
40	=cut
41
42	package Coro;
43
44	use strict;
45	no warnings "uninitialized";
46
47	use Coro::State;
48
49	use base qw(Coro::State Exporter);
50
51	our $idle; # idle handler
52	our $main; # main coroutine
53	our $current; # current coroutine
54
55	our $VERSION = '3.3';
56
57	our @EXPORT = qw(async cede schedule terminate current unblock_sub);
58	our %EXPORT_TAGS = (
59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60	);
61	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
62
63	{
64	my @async;
65	my $init;
66
67	# this way of handling attributes simply is NOT scalable ;()
68	sub import {
69	no strict 'refs';
70
71	Coro->export_to_level (1, @_);
72
73	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
74	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
75	my ($package, $ref) = (shift, shift);
76	my @attrs;
77	for (@_) {
78	if ($_ eq "Coro") {
79	push @async, $ref;
80	unless ($init++) {
81	eval q{
82	sub INIT {
83	&async(pop @async) while @async;
84	}
85	};
86	}
87	} else {
88	push @attrs, $_;
89	}
90	}
91	return $old ? $old->($package, $ref, @attrs) : @attrs;
92	};
93	}
94
95	}
96
97	=over 4
98
99	=item $main
100
101	This coroutine represents the main program.
102
103	=cut
104
105	$main = new Coro;
106
107	=item $current (or as function: current)
108
109	The current coroutine (the last coroutine switched to). The initial value
110	is C<$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.
115
116	=cut
117
118	# maybe some other module used Coro::Specific before...
119	$main->{specific} = $current->{specific}
120	if $current;
121
122	_set_current $main;
123
124	sub current() { $current }
125
126	=item $idle
127
128	A callback that is called whenever the scheduler finds no ready coroutines
129	to run. The default implementation prints "FATAL: deadlock detected" and
130	exits, because the program has no other way to continue.
131
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.
135
136	Please note that if your callback recursively invokes perl (e.g. for event
137	handlers), then it must be prepared to be called recursively.
138
139	=cut
140
141	$idle = sub {
142	require Carp;
143	Carp::croak ("FATAL: deadlock detected");
144	};
145
146	# this coroutine is necessary because a coroutine
147	# cannot destroy itself.
148	my @destroy;
149	my $manager; $manager = new Coro sub {
150	while () {
151	# by overwriting the state object with the manager we destroy it
152	# while still being able to schedule this coroutine (in case it has
153	# been readied multiple times. this is harmless since the manager
154	# can be called as many times as neccessary and will always
155	# remove itself from the runqueue
156	while (@destroy) {
157	my $coro = pop @destroy;
158
159	$coro->{status} \|\|= [];
160
161	$_->ready for @{(delete $coro->{join} ) \|\| []};
162	$_->(@{$coro->{status}}) for @{(delete $coro->{destroy_cb}) \|\| []};
163
164	# the next line destroys the coro state, but keeps the
165	# coroutine itself intact (we basically make it a zombie
166	# coroutine that always runs the manager thread, so it's possible
167	# to transfer() to this coroutine).
168	$coro->_clone_state_from ($manager);
169	}
170	&schedule;
171	}
172	};
173
174	# static methods. not really.
175
176	=back
177
178	=head2 STATIC METHODS
179
180	Static methods are actually functions that operate on the current coroutine only.
181
182	=over 4
183
184	=item async { ... } [@args...]
185
186	Create a new asynchronous coroutine and return it's coroutine object
187	(usually unused). When the sub returns the new coroutine is automatically
188	terminated.
189
190	Calling C<exit> in a coroutine will not work correctly, so do not do that.
191
192	When the coroutine dies, the program will exit, just as in the main
193	program.
194
195	# create a new coroutine that just prints its arguments
196	async {
197	print "@_\n";
198	} 1,2,3,4;
199
200	=cut
201
202	sub async(&@) {
203	my $pid = new Coro @_;
204	$pid->ready;
205	$pid
206	}
207
208	=item schedule
209
210	Calls the scheduler. Please note that the current coroutine will not be put
211	into the ready queue, so calling this function usually means you will
212	never be called again unless something else (e.g. an event handler) calls
213	ready.
214
215	The canonical way to wait on external events is this:
216
217	{
218	# remember current coroutine
219	my $current = $Coro::current;
220
221	# register a hypothetical event handler
222	on_event_invoke sub {
223	# wake up sleeping coroutine
224	$current->ready;
225	undef $current;
226	};
227
228	# call schedule until event occured.
229	# in case we are woken up for other reasons
230	# (current still defined), loop.
231	Coro::schedule while $current;
232	}
233
234	=item cede
235
236	"Cede" to other coroutines. This function puts the current coroutine into the
237	ready queue and calls C<schedule>, which has the effect of giving up the
238	current "timeslice" to other coroutines of the same or higher priority.
239
240	=item terminate [arg...]
241
242	Terminates the current coroutine with the given status values (see L<cancel>).
243
244	=cut
245
246	sub terminate {
247	$current->cancel (@_);
248	}
249
250	=back
251
252	# dynamic methods
253
254	=head2 COROUTINE METHODS
255
256	These are the methods you can call on coroutine objects.
257
258	=over 4
259
260	=item new Coro \&sub [, @args...]
261
262	Create a new coroutine and return it. When the sub returns the coroutine
263	automatically terminates as if C<terminate> with the returned values were
264	called. To make the coroutine run you must first put it into the ready queue
265	by calling the ready method.
266
267	Calling C<exit> in a coroutine will not work correctly, so do not do that.
268
269	=cut
270
271	sub _run_coro {
272	terminate &{+shift};
273	}
274
275	sub new {
276	my $class = shift;
277
278	$class->SUPER::new (\&_run_coro, @_)
279	}
280
281	=item $success = $coroutine->ready
282
283	Put the given coroutine into the ready queue (according to it's priority)
284	and return true. If the coroutine is already in the ready queue, do nothing
285	and return false.
286
287	=item $is_ready = $coroutine->is_ready
288
289	Return wether the coroutine is currently the ready queue or not,
290
291	=item $coroutine->cancel (arg...)
292
293	Terminates the given coroutine and makes it return the given arguments as
294	status (default: the empty list).
295
296	=cut
297
298	sub cancel {
299	my $self = shift;
300	$self->{status} = [@_];
301	push @destroy, $self;
302	$manager->ready;
303	&schedule if $current == $self;
304	}
305
306	=item $coroutine->join
307
308	Wait until the coroutine terminates and return any values given to the
309	C<terminate> or C<cancel> functions. C<join> can be called multiple times
310	from multiple coroutine.
311
312	=cut
313
314	sub join {
315	my $self = shift;
316	unless ($self->{status}) {
317	push @{$self->{join}}, $current;
318	&schedule;
319	}
320	wantarray ? @{$self->{status}} : $self->{status}[0];
321	}
322
323	=item $coroutine->on_destroy (\&cb)
324
325	Registers a callback that is called when this coroutine gets destroyed,
326	but before it is joined. The callback gets passed the terminate arguments,
327	if any.
328
329	=cut
330
331	sub on_destroy {
332	my ($self, $cb) = @_;
333
334	push @{ $self->{destroy_cb} }, $cb;
335	}
336
337	=item $oldprio = $coroutine->prio ($newprio)
338
339	Sets (or gets, if the argument is missing) the priority of the
340	coroutine. Higher priority coroutines get run before lower priority
341	coroutines. Priorities are small signed integers (currently -4 .. +3),
342	that you can refer to using PRIO_xxx constants (use the import tag :prio
343	to get then):
344
345	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
346	3 > 1 > 0 > -1 > -3 > -4
347
348	# set priority to HIGH
349	current->prio(PRIO_HIGH);
350
351	The idle coroutine ($Coro::idle) always has a lower priority than any
352	existing coroutine.
353
354	Changing the priority of the current coroutine will take effect immediately,
355	but changing the priority of coroutines in the ready queue (but not
356	running) will only take effect after the next schedule (of that
357	coroutine). This is a bug that will be fixed in some future version.
358
359	=item $newprio = $coroutine->nice ($change)
360
361	Similar to C<prio>, but subtract the given value from the priority (i.e.
362	higher values mean lower priority, just as in unix).
363
364	=item $olddesc = $coroutine->desc ($newdesc)
365
366	Sets (or gets in case the argument is missing) the description for this
367	coroutine. This is just a free-form string you can associate with a coroutine.
368
369	=cut
370
371	sub desc {
372	my $old = $_[0]{desc};
373	$_[0]{desc} = $_[1] if @_ > 1;
374	$old;
375	}
376
377	=back
378
379	=head2 GLOBAL FUNCTIONS
380
381	=over 4
382
383	=item Coro::nready
384
385	Returns the number of coroutines that are currently in the ready state,
386	i.e. that can be swicthed to. The value C<0> means that the only runnable
387	coroutine is the currently running one, so C<cede> would have no effect,
388	and C<schedule> would cause a deadlock unless there is an idle handler
389	that wakes up some coroutines.
390
391	=item unblock_sub { ... }
392
393	This utility function takes a BLOCK or code reference and "unblocks" it,
394	returning the new coderef. This means that the new coderef will return
395	immediately without blocking, returning nothing, while the original code
396	ref will be called (with parameters) from within its own coroutine.
397
398	The reason this fucntion exists is that many event libraries (such as the
399	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
400	of thread-safety). This means you must not block within event callbacks,
401	otherwise you might suffer from crashes or worse.
402
403	This function allows your callbacks to block by executing them in another
404	coroutine where it is safe to block. One example where blocking is handy
405	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
406	disk.
407
408	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
409	creating event callbacks that want to block.
410
411	=cut
412
413	our @unblock_pool;
414	our @unblock_queue;
415	our $UNBLOCK_POOL_SIZE = 2;
416
417	sub unblock_handler_ {
418	while () {
419	my ($cb, @arg) = @{ delete $Coro::current->{arg} };
420	$cb->(@arg);
421
422	last if @unblock_pool >= $UNBLOCK_POOL_SIZE;
423	push @unblock_pool, $Coro::current;
424	schedule;
425	}
426	}
427
428	our $unblock_scheduler = async {
429	while () {
430	while (my $cb = pop @unblock_queue) {
431	my $handler = (pop @unblock_pool or new Coro \&unblock_handler_);
432	$handler->{arg} = $cb;
433	$handler->ready;
434	cede;
435	}
436
437	schedule;
438	}
439	};
440
441	sub unblock_sub(&) {
442	my $cb = shift;
443
444	sub {
445	push @unblock_queue, [$cb, @_];
446	$unblock_scheduler->ready;
447	}
448	}
449
450	=back
451
452	=cut
453
454	1;
455
456	=head1 BUGS/LIMITATIONS
457
458	- you must make very sure that no coro is still active on global
459	destruction. very bad things might happen otherwise (usually segfaults).
460
461	- this module is not thread-safe. You should only ever use this module
462	from the same thread (this requirement might be losened in the future
463	to allow per-thread schedulers, but Coro::State does not yet allow
464	this).
465
466	=head1 SEE ALSO
467
468	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
469
470	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
471
472	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
473
474	Embedding: L<Coro:MakeMaker>
475
476	=head1 AUTHOR
477
478	Marc Lehmann <schmorp@schmorp.de>
479	http://home.schmorp.de/
480
481	=cut
482