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 used in this module also
guarantees 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 = '3.7';

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 essential 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 do the same as calling exit outside
the coroutine. Likewise, when the coroutine dies, the program will exit,
just as it would 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) || do {
      my $coro = new Coro \&pool_handler;
      $coro->{desc} = "async_pool";
      $coro
   };

   $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 occurred.
      # 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 switched 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 function 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 loosened 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:	1.128
Committed:	Wed Sep 19 21:39:15 2007 UTC (16 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.127:	+6 -2 lines
Log Message:	yeah
#	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 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.
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 $VERSION = '3.7';
56
57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
58	our %EXPORT_TAGS = (
59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60	);
61	our @EXPORT_OK = (@{$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 essential 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 do the same as calling exit outside
191	the coroutine. Likewise, when the coroutine dies, the program will exit,
192	just as it would in the main program.
193
194	# create a new coroutine that just prints its arguments
195	async {
196	print "@_\n";
197	} 1,2,3,4;
198
199	=cut
200
201	sub async(&@) {
202	my $coro = new Coro @_;
203	$coro->ready;
204	$coro
205	}
206
207	=item async_pool { ... } [@args...]
208
209	Similar to C<async>, but uses a coroutine pool, so you should not call
210	terminate or join (although you are allowed to), and you get a coroutine
211	that might have executed other code already (which can be good or bad :).
212
213	Also, the block is executed in an C<eval> context and a warning will be
214	issued in case of an exception instead of terminating the program, as
215	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
216	will not work in the expected way, unless you call terminate or cancel,
217	which somehow defeats the purpose of pooling.
218
219	The priority will be reset to C<0> after each job, otherwise the coroutine
220	will be re-used "as-is".
221
222	The pool size is limited to 8 idle coroutines (this can be adjusted by
223	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
224	required.
225
226	If you are concerned about pooled coroutines growing a lot because a
227	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool {
228	terminate }> once per second or so to slowly replenish the pool.
229
230	=cut
231
232	our $POOL_SIZE = 8;
233	our @pool;
234
235	sub pool_handler {
236	while () {
237	eval {
238	my ($cb, @arg) = @{ delete $current->{_invoke} or return };
239	$cb->(@arg);
240	};
241	warn $@ if $@;
242
243	last if @pool >= $POOL_SIZE;
244	push @pool, $current;
245
246	$current->save (Coro::State::SAVE_DEF);
247	$current->prio (0);
248	schedule;
249	}
250	}
251
252	sub async_pool(&@) {
253	# this is also inlined into the unlock_scheduler
254	my $coro = (pop @pool) \|\| do {
255	my $coro = new Coro \&pool_handler;
256	$coro->{desc} = "async_pool";
257	$coro
258	};
259
260	$coro->{_invoke} = [@_];
261	$coro->ready;
262
263	$coro
264	}
265
266	=item schedule
267
268	Calls the scheduler. Please note that the current coroutine will not be put
269	into the ready queue, so calling this function usually means you will
270	never be called again unless something else (e.g. an event handler) calls
271	ready.
272
273	The canonical way to wait on external events is this:
274
275	{
276	# remember current coroutine
277	my $current = $Coro::current;
278
279	# register a hypothetical event handler
280	on_event_invoke sub {
281	# wake up sleeping coroutine
282	$current->ready;
283	undef $current;
284	};
285
286	# call schedule until event occurred.
287	# in case we are woken up for other reasons
288	# (current still defined), loop.
289	Coro::schedule while $current;
290	}
291
292	=item cede
293
294	"Cede" to other coroutines. This function puts the current coroutine into the
295	ready queue and calls C<schedule>, which has the effect of giving up the
296	current "timeslice" to other coroutines of the same or higher priority.
297
298	Returns true if at least one coroutine switch has happened.
299
300	=item Coro::cede_notself
301
302	Works like cede, but is not exported by default and will cede to any
303	coroutine, regardless of priority, once.
304
305	Returns true if at least one coroutine switch has happened.
306
307	=item terminate [arg...]
308
309	Terminates the current coroutine with the given status values (see L<cancel>).
310
311	=cut
312
313	sub terminate {
314	$current->cancel (@_);
315	}
316
317	=back
318
319	# dynamic methods
320
321	=head2 COROUTINE METHODS
322
323	These are the methods you can call on coroutine objects.
324
325	=over 4
326
327	=item new Coro \&sub [, @args...]
328
329	Create a new coroutine and return it. When the sub returns the coroutine
330	automatically terminates as if C<terminate> with the returned values were
331	called. To make the coroutine run you must first put it into the ready queue
332	by calling the ready method.
333
334	See C<async> for additional discussion.
335
336	=cut
337
338	sub _run_coro {
339	terminate &{+shift};
340	}
341
342	sub new {
343	my $class = shift;
344
345	$class->SUPER::new (\&_run_coro, @_)
346	}
347
348	=item $success = $coroutine->ready
349
350	Put the given coroutine into the ready queue (according to it's priority)
351	and return true. If the coroutine is already in the ready queue, do nothing
352	and return false.
353
354	=item $is_ready = $coroutine->is_ready
355
356	Return wether the coroutine is currently the ready queue or not,
357
358	=item $coroutine->cancel (arg...)
359
360	Terminates the given coroutine and makes it return the given arguments as
361	status (default: the empty list). Never returns if the coroutine is the
362	current coroutine.
363
364	=cut
365
366	sub cancel {
367	my $self = shift;
368	$self->{status} = [@_];
369
370	if ($current == $self) {
371	push @destroy, $self;
372	$manager->ready;
373	&schedule while 1;
374	} else {
375	$self->_cancel;
376	}
377	}
378
379	=item $coroutine->join
380
381	Wait until the coroutine terminates and return any values given to the
382	C<terminate> or C<cancel> functions. C<join> can be called multiple times
383	from multiple coroutine.
384
385	=cut
386
387	sub join {
388	my $self = shift;
389
390	unless ($self->{status}) {
391	my $current = $current;
392
393	push @{$self->{destroy_cb}}, sub {
394	$current->ready;
395	undef $current;
396	};
397
398	&schedule while $current;
399	}
400
401	wantarray ? @{$self->{status}} : $self->{status}[0];
402	}
403
404	=item $coroutine->on_destroy (\&cb)
405
406	Registers a callback that is called when this coroutine gets destroyed,
407	but before it is joined. The callback gets passed the terminate arguments,
408	if any.
409
410	=cut
411
412	sub on_destroy {
413	my ($self, $cb) = @_;
414
415	push @{ $self->{destroy_cb} }, $cb;
416	}
417
418	=item $oldprio = $coroutine->prio ($newprio)
419
420	Sets (or gets, if the argument is missing) the priority of the
421	coroutine. Higher priority coroutines get run before lower priority
422	coroutines. Priorities are small signed integers (currently -4 .. +3),
423	that you can refer to using PRIO_xxx constants (use the import tag :prio
424	to get then):
425
426	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
427	3 > 1 > 0 > -1 > -3 > -4
428
429	# set priority to HIGH
430	current->prio(PRIO_HIGH);
431
432	The idle coroutine ($Coro::idle) always has a lower priority than any
433	existing coroutine.
434
435	Changing the priority of the current coroutine will take effect immediately,
436	but changing the priority of coroutines in the ready queue (but not
437	running) will only take effect after the next schedule (of that
438	coroutine). This is a bug that will be fixed in some future version.
439
440	=item $newprio = $coroutine->nice ($change)
441
442	Similar to C<prio>, but subtract the given value from the priority (i.e.
443	higher values mean lower priority, just as in unix).
444
445	=item $olddesc = $coroutine->desc ($newdesc)
446
447	Sets (or gets in case the argument is missing) the description for this
448	coroutine. This is just a free-form string you can associate with a coroutine.
449
450	=cut
451
452	sub desc {
453	my $old = $_[0]{desc};
454	$_[0]{desc} = $_[1] if @_ > 1;
455	$old;
456	}
457
458	=back
459
460	=head2 GLOBAL FUNCTIONS
461
462	=over 4
463
464	=item Coro::nready
465
466	Returns the number of coroutines that are currently in the ready state,
467	i.e. that can be switched to. The value C<0> means that the only runnable
468	coroutine is the currently running one, so C<cede> would have no effect,
469	and C<schedule> would cause a deadlock unless there is an idle handler
470	that wakes up some coroutines.
471
472	=item my $guard = Coro::guard { ... }
473
474	This creates and returns a guard object. Nothing happens until the object
475	gets destroyed, in which case the codeblock given as argument will be
476	executed. This is useful to free locks or other resources in case of a
477	runtime error or when the coroutine gets canceled, as in both cases the
478	guard block will be executed. The guard object supports only one method,
479	C<< ->cancel >>, which will keep the codeblock from being executed.
480
481	Example: set some flag and clear it again when the coroutine gets canceled
482	or the function returns:
483
484	sub do_something {
485	my $guard = Coro::guard { $busy = 0 };
486	$busy = 1;
487
488	# do something that requires $busy to be true
489	}
490
491	=cut
492
493	sub guard(&) {
494	bless \(my $cb = $_[0]), "Coro::guard"
495	}
496
497	sub Coro::guard::cancel {
498	${$_[0]} = sub { };
499	}
500
501	sub Coro::guard::DESTROY {
502	${$_[0]}->();
503	}
504
505
506	=item unblock_sub { ... }
507
508	This utility function takes a BLOCK or code reference and "unblocks" it,
509	returning the new coderef. This means that the new coderef will return
510	immediately without blocking, returning nothing, while the original code
511	ref will be called (with parameters) from within its own coroutine.
512
513	The reason this function exists is that many event libraries (such as the
514	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
515	of thread-safety). This means you must not block within event callbacks,
516	otherwise you might suffer from crashes or worse.
517
518	This function allows your callbacks to block by executing them in another
519	coroutine where it is safe to block. One example where blocking is handy
520	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
521	disk.
522
523	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
524	creating event callbacks that want to block.
525
526	=cut
527
528	our @unblock_queue;
529
530	# we create a special coro because we want to cede,
531	# to reduce pressure on the coro pool (because most callbacks
532	# return immediately and can be reused) and because we cannot cede
533	# inside an event callback.
534	our $unblock_scheduler = async {
535	while () {
536	while (my $cb = pop @unblock_queue) {
537	# this is an inlined copy of async_pool
538	my $coro = (pop @pool or new Coro \&pool_handler);
539
540	$coro->{_invoke} = $cb;
541	$coro->ready;
542	cede; # for short-lived callbacks, this reduces pressure on the coro pool
543	}
544	schedule; # sleep well
545	}
546	};
547
548	sub unblock_sub(&) {
549	my $cb = shift;
550
551	sub {
552	unshift @unblock_queue, [$cb, @_];
553	$unblock_scheduler->ready;
554	}
555	}
556
557	=back
558
559	=cut
560
561	1;
562
563	=head1 BUGS/LIMITATIONS
564
565	- you must make very sure that no coro is still active on global
566	destruction. very bad things might happen otherwise (usually segfaults).
567
568	- this module is not thread-safe. You should only ever use this module
569	from the same thread (this requirement might be loosened in the future
570	to allow per-thread schedulers, but Coro::State does not yet allow
571	this).
572
573	=head1 SEE ALSO
574
575	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
576
577	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
578
579	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
580
581	Embedding: L<Coro:MakeMaker>
582
583	=head1 AUTHOR
584
585	Marc Lehmann <schmorp@schmorp.de>
586	http://home.schmorp.de/
587
588	=cut
589