=head1 NAME

Coro::Multicore - make coro threads on multiple cores with specially supported modules

=head1 SYNOPSIS

 use Coro::Multicore;

 # or, if you want it disabled by default (e.g. to use it from a module)
 use Coro::Multicore ();

=head1 DESCRIPTION

While L<Coro> threads (unlike ithreads) provide real threads similar to
pthreads, python threads and so on, they do not run in parallel to each
other even on machines with multiple CPUs or multiple CPU cores.

This module lifts this restriction under two very specific but useful
conditions: firstly, the coro thread executes in XS code and does not
touch any perl data structures, and secondly, the XS code is specially
prepared to allow this.

This means that, when you call an XS function of a module prepared for it,
this XS function can execute in parallel to any other Coro threads.

The mechanism to support this is easily added to existing modules
and is independent of L<Coro> or L<Coro::Multicore>, and therefore
could be used, without changes, with other, similar, modules, or even
the perl core, should it gain real thread support anytime soon. See
L<http://perlmulticore.schmorp.de/> for more info on how to prepare a
module to allow parallel execution. Preparing an existing module is easy,
doesn't add much overhead and no dependencies.

This module is an L<AnyEvent> user (and also, if not obvious, uses
L<Coro>).

=head1 HOW TO USE IT

It could hardly be simpler - if you use coro threads, and before you call
a supported lengthy operation implemented in XS, use this module and other
coro threads can run in parallel:

   use Coro::Multicore;

This module has no important API functions to learn or remember. All you
need to do is I<load> it before you can take advantage of it.

=head2 EXPORTS

This module does not (at the moment) export any symbols. It does, however,
export "behaviour" - if you use the default import, then Coro::Multicore
will be enabled for all threads and all callers in the whole program:

   use Coro::Multicore;

In a module where you don't control what else might be loaded and run, you
might want to be more conservative, and not import anything. This has the
effect of not enabling the functionality by default, so you have to enable
it per scope:

   use Coro::Multicore ();

   sub myfunc {
      Coro::Multicore::scoped_enable;

      # from here to the end of this function, and in any functions
      # called from this function, tasks will be executed asynchronously.
   }

=head1 API FUNCTIONS

=over 4

=item $previous = Coro::Multicore::enable [$enable]

This function enables (if C<$enable> is true) or disables (if C<$enable>
is false) the multicore functionality globally. By default, it is enabled.

This can be used to effectively disable this module's functionality by
default, and enable it only for selected threads or scopes, by calling
C<Coro::Multicore::scope_enable>.

The function returns the previous value of the enable flag.

=item Coro::Multicore::scoped_enable

This function instructs Coro::Multicore to handle all requests executed
in the current coro thread, from the call to the end of the current scope.

Calls to C<scoped_enable> and C<scoped_disable> don't nest very well at
the moment, so don't nest them.

=item Coro::Multicore::scoped_disable

The opposite of C<Coro::Multicore::scope_disable>: instructs Coro::Multicore to
I<not> handle the next multicore-enabled request.

=back

=cut

package Coro::Multicore;

use Coro ();
use AnyEvent ();

BEGIN {
   our $VERSION = 0.02;

   use XSLoader;
   XSLoader::load __PACKAGE__, $VERSION;
}


sub import {
   if (@_ > 1) {
      require Carp;
      Carp::croak ("Coro::Multicore does not export any symbols");
   }

   enable 1;
}

our $WATCHER = AE::io fd, 0, \&poll;

=head1 INTERACTION WITH OTHER SOFTWARE

TODO

=head1 BUGS

=over 4

=item (OS-) threads are never released

At the moment, threads that were created once will never be freed. They
will be reused for asynchronous requests, though, so a slong as you limit
the maximum number of concurrent asynchronous tasks, this will also limit
the maximum number of threads created.

Future versions will likely lift this limitation.

=item AnyEvent is initalised on module load

AnyEvent is initialised on module load, as opposed to at a later time.

Future versions will likely change this.

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/AnyEvent-XSThreadPool.html

Additional thanks to Zsbán Ambrus, who gave considerable desing input for
this module and the perl multicore specification.

=cut

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