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 = '3.56';

our @EXPORT = qw(async async_pool 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");
};

sub _cancel {
   my ($self) = @_;

   # free coroutine data and mark as destructed
   $self->_destroy
      or return;

   # call all destruction callbacks
   $_->(@{$self->{status}})
      for @{(delete $self->{destroy_cb}) || []};
}

# this coroutine is necessary because a coroutine
# cannot destroy itself.
my @destroy;
my $manager;

$manager = new Coro sub {
   while () {
      (shift @destroy)->_cancel
         while @destroy;

      &schedule;
   }
};

$manager->prio (PRIO_MAX);

# 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 try to do the same as calling exit
outside the coroutine, but this is experimental. It is best not to rely on
exit doing any cleanups or even not crashing.

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 $coro = new Coro @_;
   $coro->ready;
   $coro
}

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

Similar to C<async>, but uses a coroutine pool, so you should not call
terminate or join (although you are allowed to), and you get a coroutine
that might have executed other code already (which can be good or bad :).

Also, the block is executed in an C<eval> context and a warning will be
issued in case of an exception instead of terminating the program, as
C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
will not work in the expected way, unless you call terminate or cancel,
which somehow defeats the purpose of pooling.

The priority will be reset to C<0> after each job, otherwise the coroutine
will be re-used "as-is".

The pool size is limited to 8 idle coroutines (this can be adjusted by
changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
required.

If you are concerned about pooled coroutines growing a lot because a
single C<async_pool> used a lot of stackspace you can e.g. C<async_pool {
terminate }> once per second or so to slowly replenish the pool.

=cut

our $POOL_SIZE = 8;
our @pool;

sub pool_handler {
   while () {
      eval {
         my ($cb, @arg) = @{ delete $current->{_invoke} or return };
         $cb->(@arg);
      };
      warn $@ if $@;

      last if @pool >= $POOL_SIZE;
      push @pool, $current;

      $current->save (Coro::State::SAVE_DEF);
      $current->prio (0);
      schedule;
   }
}

sub async_pool(&@) {
   # this is also inlined into the unlock_scheduler
   my $coro = (pop @pool or new Coro \&pool_handler);

   $coro->{_invoke} = [@_];
   $coro->ready;

   $coro
}

=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.

Returns true if at least one coroutine switch has happened.

=item Coro::cede_notself

Works like cede, but is not exported by default and will cede to any
coroutine, regardless of priority, once.

Returns true if at least one coroutine switch has happened.

=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.

See C<async> for additional discussion.

=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). Never returns if the coroutine is the
current coroutine.

=cut

sub cancel {
   my $self = shift;
   $self->{status} = [@_];

   if ($current == $self) {
      push @destroy, $self;
      $manager->ready;
      &schedule while 1;
   } else {
      $self->_cancel;
   }
}

=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}) {
      my $current = $current;

      push @{$self->{destroy_cb}}, sub {
         $current->ready;
         undef $current;
      };

      &schedule while $current;
   }

   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 my $guard = Coro::guard { ... }

This creates and returns a guard object. Nothing happens until the object
gets destroyed, in which case the codeblock given as argument will be
executed. This is useful to free locks or other resources in case of a
runtime error or when the coroutine gets canceled, as in both cases the
guard block will be executed. The guard object supports only one method,
C<< ->cancel >>, which will keep the codeblock from being executed.

Example: set some flag and clear it again when the coroutine gets canceled
or the function returns:

   sub do_something {
      my $guard = Coro::guard { $busy = 0 };
      $busy = 1;

      # do something that requires $busy to be true
   }

=cut

sub guard(&) {
   bless \(my $cb = $_[0]), "Coro::guard"
}

sub Coro::guard::cancel {
   ${$_[0]} = sub { };
}

sub Coro::guard::DESTROY {
   ${$_[0]}->();
}


=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_queue;

# we create a special coro because we want to cede,
# to reduce pressure on the coro pool (because most callbacks
# return immediately and can be reused) and because we cannot cede
# inside an event callback.
our $unblock_scheduler = async {
   while () {
      while (my $cb = pop @unblock_queue) {
         # this is an inlined copy of async_pool
         my $coro = (pop @pool or new Coro \&pool_handler);

         $coro->{_invoke} = $cb;
         $coro->ready;
         cede; # for short-lived callbacks, this reduces pressure on the coro pool
      }
      schedule; # sleep well
   }
};

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

   sub {
      unshift @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:	1.121
Committed:	Fri Apr 13 12:56:55 2007 UTC (17 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.120:	+4 -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 $VERSION = '3.56';
56
57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
58	our %EXPORT_TAGS = (
59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60	);
61	our @EXPORT_OK = (@{$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	$idle = sub {
142	require Carp;
143	Carp::croak ("FATAL: deadlock detected");
144	};
145
146	sub _cancel {
147	my ($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);
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 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.
196
197	# create a new coroutine that just prints its arguments
198	async {
199	print "@_\n";
200	} 1,2,3,4;
201
202	=cut
203
204	sub async(&@) {
205	my $coro = new Coro @_;
206	$coro->ready;
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
263	}
264
265	=item schedule
266
267	Calls the scheduler. Please note that the current coroutine will not be put
268	into the ready queue, so calling this function usually means you will
269	never be called again unless something else (e.g. an event handler) calls
270	ready.
271
272	The canonical way to wait on external events is this:
273
274	{
275	# remember current coroutine
276	my $current = $Coro::current;
277
278	# register a hypothetical event handler
279	on_event_invoke sub {
280	# wake up sleeping coroutine
281	$current->ready;
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	}
290
291	=item cede
292
293	"Cede" to other coroutines. This function puts the current coroutine into the
294	ready queue and calls C<schedule>, which has the effect of giving up the
295	current "timeslice" to other coroutines of the same or higher priority.
296
297	Returns true if at least one coroutine switch has happened.
298
299	=item Coro::cede_notself
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
306	=item terminate [arg...]
307
308	Terminates the current coroutine with the given status values (see L<cancel>).
309
310	=cut
311
312	sub terminate {
313	$current->cancel (@_);
314	}
315
316	=back
317
318	# dynamic methods
319
320	=head2 COROUTINE METHODS
321
322	These are the methods you can call on coroutine objects.
323
324	=over 4
325
326	=item new Coro \&sub [, @args...]
327
328	Create a new coroutine and return it. When the sub returns the coroutine
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
331	by calling the ready method.
332
333	See C<async> for additional discussion.
334
335	=cut
336
337	sub _run_coro {
338	terminate &{+shift};
339	}
340
341	sub new {
342	my $class = shift;
343
344	$class->SUPER::new (\&_run_coro, @_)
345	}
346
347	=item $success = $coroutine->ready
348
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.
352
353	=item $is_ready = $coroutine->is_ready
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;
455	}
456
457	=back
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
558	=cut
559
560	1;
561
562	=head1 BUGS/LIMITATIONS
563
564	- you must make very sure that no coro is still active on global
565	destruction. very bad things might happen otherwise (usually segfaults).
566
567	- this module is not thread-safe. You should only ever use this module
568	from the same thread (this requirement might be losened in the future
569	to allow per-thread schedulers, but Coro::State does not yet allow
570	this).
571
572	=head1 SEE ALSO
573
574	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
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>
581
582	=head1 AUTHOR
583
584	Marc Lehmann <schmorp@schmorp.de>
585	http://home.schmorp.de/
586
587	=cut
588