Coro/Coro.pm

=head1 NAME

Coro - coroutine process abstraction

=head1 SYNOPSIS

 use Coro;

 async {
    # some asynchronous thread of execution
    print "2\n";
    cede; # yield back to main
    print "4\n";
 };
 print "1\n";
 cede; # yield to coroutine
 print "3\n";
 cede; # and again

 # use locking
 my $lock = new Coro::Semaphore;
 my $locked;

 $lock->down;
 $locked = 1;
 $lock->up;

=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 (see L<Coro::State> for more configuration).

=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 = '4.31';

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 itself.

=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.

See the C<Coro::State::new> constructor for info about the coroutine
environment in which coroutines run.

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, tracing will be
disabled, the description will be reset and the default output filehandle
gets restored, so you can change alkl these. Otherwise the coroutine will
be re-used "as-is": most notably if you change other per-coroutine global
stuff such as C<$/> you need to revert that change, which is most simply
done by using local as in C< local $/ >.

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 "\3async_pool terminate\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.

=item Coro::cede_notself

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

=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> and C<Coro::State::new> for additional info about the
coroutine environment.

=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.

=item $coroutine->throw ([$scalar])

If C<$throw> is specified and defined, it will be thrown as an exception
inside the coroutine at the next convinient point in time (usually after
it gains control at the next schedule/transfer/cede). Otherwise clears the
exception object.

The exception object will be thrown "as is" with the specified scalar in
C<$@>, i.e. if it is a string, no line number or newline will be appended
(unlike with C<die>).

This can be used as a softer means than C<cancel> to ask a coroutine to
end itself, although there is no guarentee that the exception will lead to
termination, and if the exception isn't caught it might well end the whole
program.

=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

Lower level Configuration, Coroutine Environment: L<Coro::State>.

Debugging: L<Coro::Debug>.

Support/Utility: L<Coro::Specific>, 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>.

Compatibility: L<Coro::LWP>, L<Coro::Storable>, L<Coro::Select>.

Embedding: L<Coro:MakeMaker>.

=head1 AUTHOR

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

=cut

Revision:	1.161
Committed:	Wed Dec 5 11:32:58 2007 UTC (18 years, 1 month ago) by root
Branch:	MAIN
CVS Tags:	rel-4_31
Changes since 1.160:	+1 -1 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	print "2\n";
12	cede; # yield back to main
13	print "4\n";
14	};
15	print "1\n";
16	cede; # yield to coroutine
17	print "3\n";
18	cede; # and again
19
20	# use locking
21	my $lock = new Coro::Semaphore;
22	my $locked;
23
24	$lock->down;
25	$locked = 1;
26	$lock->up;
27
28	=head1 DESCRIPTION
29
30	This module collection manages coroutines. Coroutines are similar
31	to threads but don't run in parallel at the same time even on SMP
32	machines. The specific flavor of coroutine used in this module also
33	guarantees you that it will not switch between coroutines unless
34	necessary, at easily-identified points in your program, so locking and
35	parallel access are rarely an issue, making coroutine programming much
36	safer than threads programming.
37
38	(Perl, however, does not natively support real threads but instead does a
39	very slow and memory-intensive emulation of processes using threads. This
40	is a performance win on Windows machines, and a loss everywhere else).
41
42	In this module, coroutines are defined as "callchain + lexical variables +
43	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
44	its own set of lexicals and its own set of perls most important global
45	variables (see L<Coro::State> for more configuration).
46
47	=cut
48
49	package Coro;
50
51	use strict;
52	no warnings "uninitialized";
53
54	use Coro::State;
55
56	use base qw(Coro::State Exporter);
57
58	our $idle; # idle handler
59	our $main; # main coroutine
60	our $current; # current coroutine
61
62	our $VERSION = '4.31';
63
64	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
65	our %EXPORT_TAGS = (
66	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
67	);
68	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
69
70	{
71	my @async;
72	my $init;
73
74	# this way of handling attributes simply is NOT scalable ;()
75	sub import {
76	no strict 'refs';
77
78	Coro->export_to_level (1, @_);
79
80	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
81	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
82	my ($package, $ref) = (shift, shift);
83	my @attrs;
84	for (@_) {
85	if ($_ eq "Coro") {
86	push @async, $ref;
87	unless ($init++) {
88	eval q{
89	sub INIT {
90	&async(pop @async) while @async;
91	}
92	};
93	}
94	} else {
95	push @attrs, $_;
96	}
97	}
98	return $old ? $old->($package, $ref, @attrs) : @attrs;
99	};
100	}
101
102	}
103
104	=over 4
105
106	=item $main
107
108	This coroutine represents the main program.
109
110	=cut
111
112	$main = new Coro;
113
114	=item $current (or as function: current)
115
116	The current coroutine (the last coroutine switched to). The initial value
117	is C<$main> (of course).
118
119	This variable is B<strictly> I<read-only>. It is provided for performance
120	reasons. If performance is not essential you are encouraged to use the
121	C<Coro::current> function instead.
122
123	=cut
124
125	$main->{desc} = "[main::]";
126
127	# maybe some other module used Coro::Specific before...
128	$main->{_specific} = $current->{_specific}
129	if $current;
130
131	_set_current $main;
132
133	sub current() { $current }
134
135	=item $idle
136
137	A callback that is called whenever the scheduler finds no ready coroutines
138	to run. The default implementation prints "FATAL: deadlock detected" and
139	exits, because the program has no other way to continue.
140
141	This hook is overwritten by modules such as C<Coro::Timer> and
142	C<Coro::Event> to wait on an external event that hopefully wake up a
143	coroutine so the scheduler can run it.
144
145	Please note that if your callback recursively invokes perl (e.g. for event
146	handlers), then it must be prepared to be called recursively itself.
147
148	=cut
149
150	$idle = sub {
151	require Carp;
152	Carp::croak ("FATAL: deadlock detected");
153	};
154
155	sub _cancel {
156	my ($self) = @_;
157
158	# free coroutine data and mark as destructed
159	$self->_destroy
160	or return;
161
162	# call all destruction callbacks
163	$_->(@{$self->{_status}})
164	for @{(delete $self->{_on_destroy}) \|\| []};
165	}
166
167	# this coroutine is necessary because a coroutine
168	# cannot destroy itself.
169	my @destroy;
170	my $manager;
171
172	$manager = new Coro sub {
173	while () {
174	(shift @destroy)->_cancel
175	while @destroy;
176
177	&schedule;
178	}
179	};
180	$manager->desc ("[coro manager]");
181	$manager->prio (PRIO_MAX);
182
183	# static methods. not really.
184
185	=back
186
187	=head2 STATIC METHODS
188
189	Static methods are actually functions that operate on the current coroutine only.
190
191	=over 4
192
193	=item async { ... } [@args...]
194
195	Create a new asynchronous coroutine and return it's coroutine object
196	(usually unused). When the sub returns the new coroutine is automatically
197	terminated.
198
199	See the C<Coro::State::new> constructor for info about the coroutine
200	environment in which coroutines run.
201
202	Calling C<exit> in a coroutine will do the same as calling exit outside
203	the coroutine. Likewise, when the coroutine dies, the program will exit,
204	just as it would in the main program.
205
206	# create a new coroutine that just prints its arguments
207	async {
208	print "@_\n";
209	} 1,2,3,4;
210
211	=cut
212
213	sub async(&@) {
214	my $coro = new Coro @_;
215	$coro->ready;
216	$coro
217	}
218
219	=item async_pool { ... } [@args...]
220
221	Similar to C<async>, but uses a coroutine pool, so you should not call
222	terminate or join (although you are allowed to), and you get a coroutine
223	that might have executed other code already (which can be good or bad :).
224
225	Also, the block is executed in an C<eval> context and a warning will be
226	issued in case of an exception instead of terminating the program, as
227	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
228	will not work in the expected way, unless you call terminate or cancel,
229	which somehow defeats the purpose of pooling.
230
231	The priority will be reset to C<0> after each job, tracing will be
232	disabled, the description will be reset and the default output filehandle
233	gets restored, so you can change alkl these. Otherwise the coroutine will
234	be re-used "as-is": most notably if you change other per-coroutine global
235	stuff such as C<$/> you need to revert that change, which is most simply
236	done by using local as in C< local $/ >.
237
238	The pool size is limited to 8 idle coroutines (this can be adjusted by
239	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
240	required.
241
242	If you are concerned about pooled coroutines growing a lot because a
243	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
244	{ terminate }> once per second or so to slowly replenish the pool. In
245	addition to that, when the stacks used by a handler grows larger than 16kb
246	(adjustable with $Coro::POOL_RSS) it will also exit.
247
248	=cut
249
250	our $POOL_SIZE = 8;
251	our $POOL_RSS = 16 * 1024;
252	our @async_pool;
253
254	sub pool_handler {
255	my $cb;
256
257	while () {
258	eval {
259	while () {
260	_pool_1 $cb;
261	&$cb;
262	_pool_2 $cb;
263	&schedule;
264	}
265	};
266
267	last if $@ eq "\3async_pool terminate\2\n";
268	warn $@ if $@;
269	}
270	}
271
272	sub async_pool(&@) {
273	# this is also inlined into the unlock_scheduler
274	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
275
276	$coro->{_invoke} = [@_];
277	$coro->ready;
278
279	$coro
280	}
281
282	=item schedule
283
284	Calls the scheduler. Please note that the current coroutine will not be put
285	into the ready queue, so calling this function usually means you will
286	never be called again unless something else (e.g. an event handler) calls
287	ready.
288
289	The canonical way to wait on external events is this:
290
291	{
292	# remember current coroutine
293	my $current = $Coro::current;
294
295	# register a hypothetical event handler
296	on_event_invoke sub {
297	# wake up sleeping coroutine
298	$current->ready;
299	undef $current;
300	};
301
302	# call schedule until event occurred.
303	# in case we are woken up for other reasons
304	# (current still defined), loop.
305	Coro::schedule while $current;
306	}
307
308	=item cede
309
310	"Cede" to other coroutines. This function puts the current coroutine into the
311	ready queue and calls C<schedule>, which has the effect of giving up the
312	current "timeslice" to other coroutines of the same or higher priority.
313
314	=item Coro::cede_notself
315
316	Works like cede, but is not exported by default and will cede to any
317	coroutine, regardless of priority, once.
318
319	=item terminate [arg...]
320
321	Terminates the current coroutine with the given status values (see L<cancel>).
322
323	=item killall
324
325	Kills/terminates/cancels all coroutines except the currently running
326	one. This is useful after a fork, either in the child or the parent, as
327	usually only one of them should inherit the running coroutines.
328
329	=cut
330
331	sub terminate {
332	$current->cancel (@_);
333	}
334
335	sub killall {
336	for (Coro::State::list) {
337	$_->cancel
338	if $_ != $current && UNIVERSAL::isa $_, "Coro";
339	}
340	}
341
342	=back
343
344	# dynamic methods
345
346	=head2 COROUTINE METHODS
347
348	These are the methods you can call on coroutine objects.
349
350	=over 4
351
352	=item new Coro \&sub [, @args...]
353
354	Create a new coroutine and return it. When the sub returns the coroutine
355	automatically terminates as if C<terminate> with the returned values were
356	called. To make the coroutine run you must first put it into the ready queue
357	by calling the ready method.
358
359	See C<async> and C<Coro::State::new> for additional info about the
360	coroutine environment.
361
362	=cut
363
364	sub _run_coro {
365	terminate &{+shift};
366	}
367
368	sub new {
369	my $class = shift;
370
371	$class->SUPER::new (\&_run_coro, @_)
372	}
373
374	=item $success = $coroutine->ready
375
376	Put the given coroutine into the ready queue (according to it's priority)
377	and return true. If the coroutine is already in the ready queue, do nothing
378	and return false.
379
380	=item $is_ready = $coroutine->is_ready
381
382	Return wether the coroutine is currently the ready queue or not,
383
384	=item $coroutine->cancel (arg...)
385
386	Terminates the given coroutine and makes it return the given arguments as
387	status (default: the empty list). Never returns if the coroutine is the
388	current coroutine.
389
390	=cut
391
392	sub cancel {
393	my $self = shift;
394	$self->{_status} = [@_];
395
396	if ($current == $self) {
397	push @destroy, $self;
398	$manager->ready;
399	&schedule while 1;
400	} else {
401	$self->_cancel;
402	}
403	}
404
405	=item $coroutine->join
406
407	Wait until the coroutine terminates and return any values given to the
408	C<terminate> or C<cancel> functions. C<join> can be called concurrently
409	from multiple coroutines.
410
411	=cut
412
413	sub join {
414	my $self = shift;
415
416	unless ($self->{_status}) {
417	my $current = $current;
418
419	push @{$self->{_on_destroy}}, sub {
420	$current->ready;
421	undef $current;
422	};
423
424	&schedule while $current;
425	}
426
427	wantarray ? @{$self->{_status}} : $self->{_status}[0];
428	}
429
430	=item $coroutine->on_destroy (\&cb)
431
432	Registers a callback that is called when this coroutine gets destroyed,
433	but before it is joined. The callback gets passed the terminate arguments,
434	if any.
435
436	=cut
437
438	sub on_destroy {
439	my ($self, $cb) = @_;
440
441	push @{ $self->{_on_destroy} }, $cb;
442	}
443
444	=item $oldprio = $coroutine->prio ($newprio)
445
446	Sets (or gets, if the argument is missing) the priority of the
447	coroutine. Higher priority coroutines get run before lower priority
448	coroutines. Priorities are small signed integers (currently -4 .. +3),
449	that you can refer to using PRIO_xxx constants (use the import tag :prio
450	to get then):
451
452	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
453	3 > 1 > 0 > -1 > -3 > -4
454
455	# set priority to HIGH
456	current->prio(PRIO_HIGH);
457
458	The idle coroutine ($Coro::idle) always has a lower priority than any
459	existing coroutine.
460
461	Changing the priority of the current coroutine will take effect immediately,
462	but changing the priority of coroutines in the ready queue (but not
463	running) will only take effect after the next schedule (of that
464	coroutine). This is a bug that will be fixed in some future version.
465
466	=item $newprio = $coroutine->nice ($change)
467
468	Similar to C<prio>, but subtract the given value from the priority (i.e.
469	higher values mean lower priority, just as in unix).
470
471	=item $olddesc = $coroutine->desc ($newdesc)
472
473	Sets (or gets in case the argument is missing) the description for this
474	coroutine. This is just a free-form string you can associate with a coroutine.
475
476	This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
477	can modify this member directly if you wish.
478
479	=item $coroutine->throw ([$scalar])
480
481	If C<$throw> is specified and defined, it will be thrown as an exception
482	inside the coroutine at the next convinient point in time (usually after
483	it gains control at the next schedule/transfer/cede). Otherwise clears the
484	exception object.
485
486	The exception object will be thrown "as is" with the specified scalar in
487	C<$@>, i.e. if it is a string, no line number or newline will be appended
488	(unlike with C<die>).
489
490	This can be used as a softer means than C<cancel> to ask a coroutine to
491	end itself, although there is no guarentee that the exception will lead to
492	termination, and if the exception isn't caught it might well end the whole
493	program.
494
495	=cut
496
497	sub desc {
498	my $old = $_[0]{desc};
499	$_[0]{desc} = $_[1] if @_ > 1;
500	$old;
501	}
502
503	=back
504
505	=head2 GLOBAL FUNCTIONS
506
507	=over 4
508
509	=item Coro::nready
510
511	Returns the number of coroutines that are currently in the ready state,
512	i.e. that can be switched to. The value C<0> means that the only runnable
513	coroutine is the currently running one, so C<cede> would have no effect,
514	and C<schedule> would cause a deadlock unless there is an idle handler
515	that wakes up some coroutines.
516
517	=item my $guard = Coro::guard { ... }
518
519	This creates and returns a guard object. Nothing happens until the object
520	gets destroyed, in which case the codeblock given as argument will be
521	executed. This is useful to free locks or other resources in case of a
522	runtime error or when the coroutine gets canceled, as in both cases the
523	guard block will be executed. The guard object supports only one method,
524	C<< ->cancel >>, which will keep the codeblock from being executed.
525
526	Example: set some flag and clear it again when the coroutine gets canceled
527	or the function returns:
528
529	sub do_something {
530	my $guard = Coro::guard { $busy = 0 };
531	$busy = 1;
532
533	# do something that requires $busy to be true
534	}
535
536	=cut
537
538	sub guard(&) {
539	bless \(my $cb = $_[0]), "Coro::guard"
540	}
541
542	sub Coro::guard::cancel {
543	${$_[0]} = sub { };
544	}
545
546	sub Coro::guard::DESTROY {
547	${$_[0]}->();
548	}
549
550
551	=item unblock_sub { ... }
552
553	This utility function takes a BLOCK or code reference and "unblocks" it,
554	returning the new coderef. This means that the new coderef will return
555	immediately without blocking, returning nothing, while the original code
556	ref will be called (with parameters) from within its own coroutine.
557
558	The reason this function exists is that many event libraries (such as the
559	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form
560	of thread-safety). This means you must not block within event callbacks,
561	otherwise you might suffer from crashes or worse.
562
563	This function allows your callbacks to block by executing them in another
564	coroutine where it is safe to block. One example where blocking is handy
565	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
566	disk.
567
568	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
569	creating event callbacks that want to block.
570
571	=cut
572
573	our @unblock_queue;
574
575	# we create a special coro because we want to cede,
576	# to reduce pressure on the coro pool (because most callbacks
577	# return immediately and can be reused) and because we cannot cede
578	# inside an event callback.
579	our $unblock_scheduler = new Coro sub {
580	while () {
581	while (my $cb = pop @unblock_queue) {
582	# this is an inlined copy of async_pool
583	my $coro = (pop @async_pool) \|\| new Coro \&pool_handler;
584
585	$coro->{_invoke} = $cb;
586	$coro->ready;
587	cede; # for short-lived callbacks, this reduces pressure on the coro pool
588	}
589	schedule; # sleep well
590	}
591	};
592	$unblock_scheduler->desc ("[unblock_sub scheduler]");
593
594	sub unblock_sub(&) {
595	my $cb = shift;
596
597	sub {
598	unshift @unblock_queue, [$cb, @_];
599	$unblock_scheduler->ready;
600	}
601	}
602
603	=back
604
605	=cut
606
607	1;
608
609	=head1 BUGS/LIMITATIONS
610
611	- you must make very sure that no coro is still active on global
612	destruction. very bad things might happen otherwise (usually segfaults).
613
614	- this module is not thread-safe. You should only ever use this module
615	from the same thread (this requirement might be loosened in the future
616	to allow per-thread schedulers, but Coro::State does not yet allow
617	this).
618
619	=head1 SEE ALSO
620
621	Lower level Configuration, Coroutine Environment: L<Coro::State>.
622
623	Debugging: L<Coro::Debug>.
624
625	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
626
627	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
628
629	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>.
630
631	Compatibility: L<Coro::LWP>, L<Coro::Storable>, L<Coro::Select>.
632
633	Embedding: L<Coro:MakeMaker>.
634
635	=head1 AUTHOR
636
637	Marc Lehmann <schmorp@schmorp.de>
638	http://home.schmorp.de/
639
640	=cut
641