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 = '4.0';

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

$main->{desc} = "[main::]";

# 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->{_on_destroy}) || []};
}

# 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->desc ("[coro manager]");
$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. In
addition to that, when the stacks used by a handler grows larger than 16kb
(adjustable with $Coro::POOL_RSS) it will also exit.

=cut

our $POOL_SIZE = 8;
our $POOL_RSS  = 16 * 1024;
our @async_pool;

sub pool_handler {
   my $cb;

   while () {
      eval {
         while () {
            _pool_1 $cb;
            &$cb;
            _pool_2 $cb;
            &schedule;
         }
      };

      last if $@ eq "\3terminate\2\n";
      warn $@ if $@;
   }
}

sub async_pool(&@) {
   # this is also inlined into the unlock_scheduler
   my $coro = (pop @async_pool) || 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 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>).

=item killall

Kills/terminates/cancels all coroutines except the currently running
one. This is useful after a fork, either in the child or the parent, as
usually only one of them should inherit the running coroutines.

=cut

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

sub killall {
   for (Coro::State::list) {
      $_->cancel
         if $_ != $current && UNIVERSAL::isa $_, "Coro";
   }
}

=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 concurrently
from multiple coroutines.

=cut

sub join {
   my $self = shift;

   unless ($self->{_status}) {
      my $current = $current;

      push @{$self->{_on_destroy}}, 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->{_on_destroy} }, $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.

This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
can modify this member directly if you wish.

=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 = new Coro sub {
   while () {
      while (my $cb = pop @unblock_queue) {
         # this is an inlined copy of async_pool
         my $coro = (pop @async_pool) || new Coro \&pool_handler;

         $coro->{_invoke} = $cb;
         $coro->ready;
         cede; # for short-lived callbacks, this reduces pressure on the coro pool
      }
      schedule; # sleep well
   }
};
$unblock_scheduler->desc ("[unblock_sub scheduler]");

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:	1.144
Committed:	Wed Oct 3 01:48:05 2007 UTC (16 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.143:	+1 -1 lines
Log Message:	temporary check-in, non-working version
#	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 $VERSION = '4.0';
56
57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
58	our %EXPORT_TAGS = (
59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60	);
61	our @EXPORT_OK = (@{$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	$main->{desc} = "[main::]";
119
120	# maybe some other module used Coro::Specific before...
121	$main->{_specific} = $current->{_specific}
122	if $current;
123
124	_set_current $main;
125
126	sub current() { $current }
127
128	=item $idle
129
130	A callback that is called whenever the scheduler finds no ready coroutines
131	to run. The default implementation prints "FATAL: deadlock detected" and
132	exits, because the program has no other way to continue.
133
134	This hook is overwritten by modules such as C<Coro::Timer> and
135	C<Coro::Event> to wait on an external event that hopefully wake up a
136	coroutine so the scheduler can run it.
137
138	Please note that if your callback recursively invokes perl (e.g. for event
139	handlers), then it must be prepared to be called recursively.
140
141	=cut
142
143	$idle = sub {
144	require Carp;
145	Carp::croak ("FATAL: deadlock detected");
146	};
147
148	sub _cancel {
149	my ($self) = @_;
150
151	# free coroutine data and mark as destructed
152	$self->_destroy
153	or return;
154
155	# call all destruction callbacks
156	$_->(@{$self->{_status}})
157	for @{(delete $self->{_on_destroy}) \|\| []};
158	}
159
160	# this coroutine is necessary because a coroutine
161	# cannot destroy itself.
162	my @destroy;
163	my $manager;
164
165	$manager = new Coro sub {
166	while () {
167	(shift @destroy)->_cancel
168	while @destroy;
169
170	&schedule;
171	}
172	};
173	$manager->desc ("[coro manager]");
174	$manager->prio (PRIO_MAX);
175
176	# static methods. not really.
177
178	=back
179
180	=head2 STATIC METHODS
181
182	Static methods are actually functions that operate on the current coroutine only.
183
184	=over 4
185
186	=item async { ... } [@args...]
187
188	Create a new asynchronous coroutine and return it's coroutine object
189	(usually unused). When the sub returns the new coroutine is automatically
190	terminated.
191
192	Calling C<exit> in a coroutine will do the same as calling exit outside
193	the coroutine. Likewise, when the coroutine dies, the program will exit,
194	just as it would in the main program.
195
196	# create a new coroutine that just prints its arguments
197	async {
198	print "@_\n";
199	} 1,2,3,4;
200
201	=cut
202
203	sub async(&@) {
204	my $coro = new Coro @_;
205	$coro->ready;
206	$coro
207	}
208
209	=item async_pool { ... } [@args...]
210
211	Similar to C<async>, but uses a coroutine pool, so you should not call
212	terminate or join (although you are allowed to), and you get a coroutine
213	that might have executed other code already (which can be good or bad :).
214
215	Also, the block is executed in an C<eval> context and a warning will be
216	issued in case of an exception instead of terminating the program, as
217	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
218	will not work in the expected way, unless you call terminate or cancel,
219	which somehow defeats the purpose of pooling.
220
221	The priority will be reset to C<0> after each job, otherwise the coroutine
222	will be re-used "as-is".
223
224	The pool size is limited to 8 idle coroutines (this can be adjusted by
225	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
226	required.
227
228	If you are concerned about pooled coroutines growing a lot because a
229	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
230	{ terminate }> once per second or so to slowly replenish the pool. In
231	addition to that, when the stacks used by a handler grows larger than 16kb
232	(adjustable with $Coro::POOL_RSS) it will also exit.
233
234	=cut
235
236	our $POOL_SIZE = 8;
237	our $POOL_RSS = 16 * 1024;
238	our @async_pool;
239
240	sub pool_handler {
241	my $cb;
242
243	while () {
244	eval {
245	while () {
246	_pool_1 $cb;
247	&$cb;
248	_pool_2 $cb;
249	&schedule;
250	}
251	};
252
253	last if $@ eq "\3terminate\2\n";
254	warn $@ if $@;
255	}
256	}
257
258	sub async_pool(&@) {
259	# this is also inlined into the unlock_scheduler
260	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
261
262	$coro->{_invoke} = [@_];
263	$coro->ready;
264
265	$coro
266	}
267
268	=item schedule
269
270	Calls the scheduler. Please note that the current coroutine will not be put
271	into the ready queue, so calling this function usually means you will
272	never be called again unless something else (e.g. an event handler) calls
273	ready.
274
275	The canonical way to wait on external events is this:
276
277	{
278	# remember current coroutine
279	my $current = $Coro::current;
280
281	# register a hypothetical event handler
282	on_event_invoke sub {
283	# wake up sleeping coroutine
284	$current->ready;
285	undef $current;
286	};
287
288	# call schedule until event occurred.
289	# in case we are woken up for other reasons
290	# (current still defined), loop.
291	Coro::schedule while $current;
292	}
293
294	=item cede
295
296	"Cede" to other coroutines. This function puts the current coroutine into the
297	ready queue and calls C<schedule>, which has the effect of giving up the
298	current "timeslice" to other coroutines of the same or higher priority.
299
300	Returns true if at least one coroutine switch has happened.
301
302	=item Coro::cede_notself
303
304	Works like cede, but is not exported by default and will cede to any
305	coroutine, regardless of priority, once.
306
307	Returns true if at least one coroutine switch has happened.
308
309	=item terminate [arg...]
310
311	Terminates the current coroutine with the given status values (see L<cancel>).
312
313	=item killall
314
315	Kills/terminates/cancels all coroutines except the currently running
316	one. This is useful after a fork, either in the child or the parent, as
317	usually only one of them should inherit the running coroutines.
318
319	=cut
320
321	sub terminate {
322	$current->cancel (@_);
323	}
324
325	sub killall {
326	for (Coro::State::list) {
327	$_->cancel
328	if $_ != $current && UNIVERSAL::isa $_, "Coro";
329	}
330	}
331
332	=back
333
334	# dynamic methods
335
336	=head2 COROUTINE METHODS
337
338	These are the methods you can call on coroutine objects.
339
340	=over 4
341
342	=item new Coro \&sub [, @args...]
343
344	Create a new coroutine and return it. When the sub returns the coroutine
345	automatically terminates as if C<terminate> with the returned values were
346	called. To make the coroutine run you must first put it into the ready queue
347	by calling the ready method.
348
349	See C<async> for additional discussion.
350
351	=cut
352
353	sub _run_coro {
354	terminate &{+shift};
355	}
356
357	sub new {
358	my $class = shift;
359
360	$class->SUPER::new (\&_run_coro, @_)
361	}
362
363	=item $success = $coroutine->ready
364
365	Put the given coroutine into the ready queue (according to it's priority)
366	and return true. If the coroutine is already in the ready queue, do nothing
367	and return false.
368
369	=item $is_ready = $coroutine->is_ready
370
371	Return wether the coroutine is currently the ready queue or not,
372
373	=item $coroutine->cancel (arg...)
374
375	Terminates the given coroutine and makes it return the given arguments as
376	status (default: the empty list). Never returns if the coroutine is the
377	current coroutine.
378
379	=cut
380
381	sub cancel {
382	my $self = shift;
383	$self->{_status} = [@_];
384
385	if ($current == $self) {
386	push @destroy, $self;
387	$manager->ready;
388	&schedule while 1;
389	} else {
390	$self->_cancel;
391	}
392	}
393
394	=item $coroutine->join
395
396	Wait until the coroutine terminates and return any values given to the
397	C<terminate> or C<cancel> functions. C<join> can be called concurrently
398	from multiple coroutines.
399
400	=cut
401
402	sub join {
403	my $self = shift;
404
405	unless ($self->{_status}) {
406	my $current = $current;
407
408	push @{$self->{_on_destroy}}, sub {
409	$current->ready;
410	undef $current;
411	};
412
413	&schedule while $current;
414	}
415
416	wantarray ? @{$self->{_status}} : $self->{_status}[0];
417	}
418
419	=item $coroutine->on_destroy (\&cb)
420
421	Registers a callback that is called when this coroutine gets destroyed,
422	but before it is joined. The callback gets passed the terminate arguments,
423	if any.
424
425	=cut
426
427	sub on_destroy {
428	my ($self, $cb) = @_;
429
430	push @{ $self->{_on_destroy} }, $cb;
431	}
432
433	=item $oldprio = $coroutine->prio ($newprio)
434
435	Sets (or gets, if the argument is missing) the priority of the
436	coroutine. Higher priority coroutines get run before lower priority
437	coroutines. Priorities are small signed integers (currently -4 .. +3),
438	that you can refer to using PRIO_xxx constants (use the import tag :prio
439	to get then):
440
441	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
442	3 > 1 > 0 > -1 > -3 > -4
443
444	# set priority to HIGH
445	current->prio(PRIO_HIGH);
446
447	The idle coroutine ($Coro::idle) always has a lower priority than any
448	existing coroutine.
449
450	Changing the priority of the current coroutine will take effect immediately,
451	but changing the priority of coroutines in the ready queue (but not
452	running) will only take effect after the next schedule (of that
453	coroutine). This is a bug that will be fixed in some future version.
454
455	=item $newprio = $coroutine->nice ($change)
456
457	Similar to C<prio>, but subtract the given value from the priority (i.e.
458	higher values mean lower priority, just as in unix).
459
460	=item $olddesc = $coroutine->desc ($newdesc)
461
462	Sets (or gets in case the argument is missing) the description for this
463	coroutine. This is just a free-form string you can associate with a coroutine.
464
465	This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
466	can modify this member directly if you wish.
467
468	=cut
469
470	sub desc {
471	my $old = $_[0]{desc};
472	$_[0]{desc} = $_[1] if @_ > 1;
473	$old;
474	}
475
476	=back
477
478	=head2 GLOBAL FUNCTIONS
479
480	=over 4
481
482	=item Coro::nready
483
484	Returns the number of coroutines that are currently in the ready state,
485	i.e. that can be switched to. The value C<0> means that the only runnable
486	coroutine is the currently running one, so C<cede> would have no effect,
487	and C<schedule> would cause a deadlock unless there is an idle handler
488	that wakes up some coroutines.
489
490	=item my $guard = Coro::guard { ... }
491
492	This creates and returns a guard object. Nothing happens until the object
493	gets destroyed, in which case the codeblock given as argument will be
494	executed. This is useful to free locks or other resources in case of a
495	runtime error or when the coroutine gets canceled, as in both cases the
496	guard block will be executed. The guard object supports only one method,
497	C<< ->cancel >>, which will keep the codeblock from being executed.
498
499	Example: set some flag and clear it again when the coroutine gets canceled
500	or the function returns:
501
502	sub do_something {
503	my $guard = Coro::guard { $busy = 0 };
504	$busy = 1;
505
506	# do something that requires $busy to be true
507	}
508
509	=cut
510
511	sub guard(&) {
512	bless \(my $cb = $_[0]), "Coro::guard"
513	}
514
515	sub Coro::guard::cancel {
516	${$_[0]} = sub { };
517	}
518
519	sub Coro::guard::DESTROY {
520	${$_[0]}->();
521	}
522
523
524	=item unblock_sub { ... }
525
526	This utility function takes a BLOCK or code reference and "unblocks" it,
527	returning the new coderef. This means that the new coderef will return
528	immediately without blocking, returning nothing, while the original code
529	ref will be called (with parameters) from within its own coroutine.
530
531	The reason this function exists is that many event libraries (such as the
532	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
533	of thread-safety). This means you must not block within event callbacks,
534	otherwise you might suffer from crashes or worse.
535
536	This function allows your callbacks to block by executing them in another
537	coroutine where it is safe to block. One example where blocking is handy
538	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
539	disk.
540
541	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
542	creating event callbacks that want to block.
543
544	=cut
545
546	our @unblock_queue;
547
548	# we create a special coro because we want to cede,
549	# to reduce pressure on the coro pool (because most callbacks
550	# return immediately and can be reused) and because we cannot cede
551	# inside an event callback.
552	our $unblock_scheduler = new Coro sub {
553	while () {
554	while (my $cb = pop @unblock_queue) {
555	# this is an inlined copy of async_pool
556	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
557
558	$coro->{_invoke} = $cb;
559	$coro->ready;
560	cede; # for short-lived callbacks, this reduces pressure on the coro pool
561	}
562	schedule; # sleep well
563	}
564	};
565	$unblock_scheduler->desc ("[unblock_sub scheduler]");
566
567	sub unblock_sub(&) {
568	my $cb = shift;
569
570	sub {
571	unshift @unblock_queue, [$cb, @_];
572	$unblock_scheduler->ready;
573	}
574	}
575
576	=back
577
578	=cut
579
580	1;
581
582	=head1 BUGS/LIMITATIONS
583
584	- you must make very sure that no coro is still active on global
585	destruction. very bad things might happen otherwise (usually segfaults).
586
587	- this module is not thread-safe. You should only ever use this module
588	from the same thread (this requirement might be loosened in the future
589	to allow per-thread schedulers, but Coro::State does not yet allow
590	this).
591
592	=head1 SEE ALSO
593
594	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
595
596	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
597
598	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
599
600	Embedding: L<Coro:MakeMaker>
601
602	=head1 AUTHOR
603
604	Marc Lehmann <schmorp@schmorp.de>
605	http://home.schmorp.de/
606
607	=cut
608