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 *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.8	Coro - coroutine process abstraction
4	root	1.1
5			=head1 SYNOPSIS
6
7			use Coro;
8
9	root	1.8	async {
10			# some asynchronous thread of execution
11	root	1.2	};
12
13	root	1.92	# alternatively create an async coroutine like this:
14	root	1.6
15	root	1.8	sub some_func : Coro {
16			# some more async code
17			}
18
19	root	1.22	cede;
20	root	1.2
21	root	1.1	=head1 DESCRIPTION
22
23	root	1.98	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	root	1.22
40	root	1.8	=cut
41
42			package Coro;
43
44	root	1.71	use strict;
45			no warnings "uninitialized";
46	root	1.36
47	root	1.8	use Coro::State;
48
49	root	1.83	use base qw(Coro::State Exporter);
50	pcg	1.55
51	root	1.83	our $idle; # idle handler
52	root	1.71	our $main; # main coroutine
53			our $current; # current coroutine
54	root	1.8
55	root	1.101	our $VERSION = '3.3';
56	root	1.8
57	root	1.92	our @EXPORT = qw(async cede schedule terminate current unblock_sub);
58	root	1.71	our %EXPORT_TAGS = (
59	root	1.31	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60			);
61	root	1.97	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
62	root	1.8
63			{
64			my @async;
65	root	1.26	my $init;
66	root	1.8
67			# this way of handling attributes simply is NOT scalable ;()
68			sub import {
69	root	1.71	no strict 'refs';
70
71	root	1.93	Coro->export_to_level (1, @_);
72	root	1.71
73	root	1.8	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, $ref;
80	root	1.26	unless ($init++) {
81			eval q{
82			sub INIT {
83			&async(pop @async) while @async;
84			}
85			};
86			}
87	root	1.8	} else {
88	root	1.17	push @attrs, $_;
89	root	1.8	}
90			}
91	root	1.17	return $old ? $old->($package, $ref, @attrs) : @attrs;
92	root	1.8	};
93			}
94
95			}
96
97	root	1.43	=over 4
98
99	root	1.8	=item $main
100	root	1.2
101	root	1.8	This coroutine represents the main program.
102	root	1.1
103			=cut
104
105	pcg	1.55	$main = new Coro;
106	root	1.8
107	root	1.19	=item $current (or as function: current)
108	root	1.1
109	root	1.83	The current coroutine (the last coroutine switched to). The initial value
110			is C<$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	root	1.1
116	root	1.8	=cut
117
118			# maybe some other module used Coro::Specific before...
119	root	1.93	$main->{specific} = $current->{specific}
120			if $current;
121	root	1.1
122	root	1.93	_set_current $main;
123	root	1.19
124			sub current() { $current }
125	root	1.9
126			=item $idle
127
128	root	1.83	A callback that is called whenever the scheduler finds no ready coroutines
129			to run. The default implementation prints "FATAL: deadlock detected" and
130	root	1.91	exits, because the program has no other way to continue.
131	root	1.83
132			This hook is overwritten by modules such as C<Coro::Timer> and
133	root	1.91	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	root	1.9
139			=cut
140
141	root	1.83	$idle = sub {
142	root	1.96	require Carp;
143			Carp::croak ("FATAL: deadlock detected");
144	root	1.9	};
145	root	1.8
146	root	1.24	# this coroutine is necessary because a coroutine
147			# cannot destroy itself.
148			my @destroy;
149	root	1.86	my $manager; $manager = new Coro sub {
150	pcg	1.57	while () {
151	root	1.37	# 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	root	1.40	while (@destroy) {
157			my $coro = pop @destroy;
158	root	1.101
159	root	1.40	$coro->{status} \|\|= [];
160	root	1.101
161			$_->ready for @{(delete $coro->{join} ) \|\| []};
162			$_->(@{$coro->{status}}) for @{(delete $coro->{destroy_cb}) \|\| []};
163	pcg	1.59
164	root	1.83	# the next line destroys the coro state, but keeps the
165	root	1.92	# 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	root	1.83	$coro->_clone_state_from ($manager);
169	root	1.40	}
170	root	1.24	&schedule;
171			}
172			};
173
174	root	1.8	# static methods. not really.
175	root	1.43
176			=back
177	root	1.8
178			=head2 STATIC METHODS
179
180	root	1.92	Static methods are actually functions that operate on the current coroutine only.
181	root	1.8
182			=over 4
183
184	root	1.13	=item async { ... } [@args...]
185	root	1.8
186	root	1.92	Create a new asynchronous coroutine and return it's coroutine object
187			(usually unused). When the sub returns the new coroutine is automatically
188	root	1.8	terminated.
189
190	root	1.89	Calling C<exit> in a coroutine will not work correctly, so do not do that.
191
192	root	1.79	When the coroutine dies, the program will exit, just as in the main
193			program.
194
195	root	1.13	# create a new coroutine that just prints its arguments
196			async {
197			print "@_\n";
198			} 1,2,3,4;
199
200	root	1.8	=cut
201
202	root	1.13	sub async(&@) {
203			my $pid = new Coro @_;
204	root	1.11	$pid->ready;
205	root	1.85	$pid
206	root	1.8	}
207	root	1.1
208	root	1.8	=item schedule
209	root	1.6
210	root	1.92	Calls the scheduler. Please note that the current coroutine will not be put
211	root	1.8	into the ready queue, so calling this function usually means you will
212	root	1.91	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	root	1.92	# remember current coroutine
219	root	1.91	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	root	1.1
234	root	1.22	=item cede
235	root	1.1
236	root	1.92	"Cede" to other coroutines. This function puts the current coroutine into the
237	root	1.22	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	root	1.7
240	root	1.40	=item terminate [arg...]
241	root	1.7
242	root	1.92	Terminates the current coroutine with the given status values (see L<cancel>).
243	root	1.13
244	root	1.1	=cut
245
246	root	1.8	sub terminate {
247	pcg	1.59	$current->cancel (@_);
248	root	1.1	}
249	root	1.6
250	root	1.8	=back
251
252			# dynamic methods
253
254	root	1.92	=head2 COROUTINE METHODS
255	root	1.8
256	root	1.92	These are the methods you can call on coroutine objects.
257	root	1.6
258	root	1.8	=over 4
259
260	root	1.13	=item new Coro \&sub [, @args...]
261	root	1.8
262	root	1.92	Create a new coroutine and return it. When the sub returns the coroutine
263	root	1.40	automatically terminates as if C<terminate> with the returned values were
264	root	1.92	called. To make the coroutine run you must first put it into the ready queue
265	root	1.41	by calling the ready method.
266	root	1.13
267	root	1.89	Calling C<exit> in a coroutine will not work correctly, so do not do that.
268
269	root	1.6	=cut
270
271	root	1.94	sub _run_coro {
272	root	1.13	terminate &{+shift};
273			}
274
275	root	1.8	sub new {
276			my $class = shift;
277	root	1.83
278	root	1.94	$class->SUPER::new (\&_run_coro, @_)
279	root	1.8	}
280	root	1.6
281	root	1.92	=item $success = $coroutine->ready
282	root	1.1
283	root	1.92	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	root	1.90	and return false.
286	root	1.1
287	root	1.92	=item $is_ready = $coroutine->is_ready
288	root	1.90
289	root	1.92	Return wether the coroutine is currently the ready queue or not,
290	root	1.28
291	root	1.92	=item $coroutine->cancel (arg...)
292	root	1.28
293	root	1.92	Terminates the given coroutine and makes it return the given arguments as
294	pcg	1.59	status (default: the empty list).
295	root	1.28
296			=cut
297
298			sub cancel {
299	pcg	1.59	my $self = shift;
300			$self->{status} = [@_];
301			push @destroy, $self;
302	root	1.28	$manager->ready;
303	pcg	1.59	&schedule if $current == $self;
304	root	1.40	}
305
306	root	1.92	=item $coroutine->join
307	root	1.40
308			Wait until the coroutine terminates and return any values given to the
309	pcg	1.59	C<terminate> or C<cancel> functions. C<join> can be called multiple times
310	root	1.92	from multiple coroutine.
311	root	1.40
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	root	1.31	}
322
323	root	1.101	=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	root	1.92	=item $oldprio = $coroutine->prio ($newprio)
338	root	1.31
339	root	1.41	Sets (or gets, if the argument is missing) the priority of the
340	root	1.92	coroutine. Higher priority coroutines get run before lower priority
341			coroutines. Priorities are small signed integers (currently -4 .. +3),
342	root	1.41	that you can refer to using PRIO_xxx constants (use the import tag :prio
343			to get then):
344	root	1.31
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	root	1.92	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	root	1.31	running) will only take effect after the next schedule (of that
357	root	1.92	coroutine). This is a bug that will be fixed in some future version.
358	root	1.31
359	root	1.92	=item $newprio = $coroutine->nice ($change)
360	root	1.31
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	root	1.92	=item $olddesc = $coroutine->desc ($newdesc)
365	root	1.41
366			Sets (or gets in case the argument is missing) the description for this
367	root	1.92	coroutine. This is just a free-form string you can associate with a coroutine.
368	root	1.41
369			=cut
370
371			sub desc {
372			my $old = $_[0]{desc};
373			$_[0]{desc} = $_[1] if @_ > 1;
374			$old;
375	root	1.8	}
376	root	1.1
377	root	1.8	=back
378	root	1.2
379	root	1.97	=head2 GLOBAL FUNCTIONS
380	root	1.92
381			=over 4
382
383	root	1.97	=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	root	1.92	=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	root	1.8	=cut
453	root	1.2
454	root	1.8	1;
455	root	1.14
456	root	1.17	=head1 BUGS/LIMITATIONS
457	root	1.14
458	root	1.52	- you must make very sure that no coro is still active on global
459	root	1.53	destruction. very bad things might happen otherwise (usually segfaults).
460	root	1.52
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	root	1.9
466			=head1 SEE ALSO
467
468	root	1.67	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	root	1.1
476			=head1 AUTHOR
477
478	root	1.66	Marc Lehmann <schmorp@schmorp.de>
479	root	1.64	http://home.schmorp.de/
480	root	1.1
481			=cut
482