=head1 NAME

Coro::Select - a (slow but coro-aware) replacement for CORE::select

=head1 SYNOPSIS

 use Coro::Select;          # replace select globally (be careful, see below)
 use Core::Select 'select'; # only in this module
 use Coro::Select ();       # use Coro::Select::select

=head1 DESCRIPTION

This module tries to create a fully working replacement for perl's
C<select> built-in, using C<AnyEvent> watchers to do the job, so other
threads can run in parallel to any select user. As many libraries that
only have a blocking API do not use global variables and often use select
(or IO::Select), this effectively makes most such libraries "somewhat"
non-blocking w.r.t. other threads.

This implementation works fastest when only very few bits are set in the
fd set(s).

To be effective globally, this module must be C<use>'d before any other
module that uses C<select>, so it should generally be the first module
C<use>'d in the main program. Note that overriding C<select> globally
might actually cause problems, as some C<AnyEvent> backends use C<select>
themselves, and asking AnyEvent to use Coro::Select, which in turn asks
AnyEvent will not quite work.

You can also invoke it from the commandline as C<perl -MCoro::Select>.

To override select only for a single module (e.g. C<Net::DBus::Reactor>),
use a code fragment like this to load it:

   {
      package Net::DBus::Reactor;
      use Coro::Select qw(select);
      use Net::DBus::Reactor;
   }

Some modules (notably L<POE::Loop::Select>) directly call
C<CORE::select>. For these modules, we need to patch the opcode table by
sandwiching it between calls to C<Coro::Select::patch_pp_sselect> and
C<Coro::Select::unpatch_pp_sselect>:

 BEGIN {
    use Coro::Select ();
    Coro::Select::patch_pp_sselect;
    require evil_poe_module_using_CORE::SELECT;
    Coro::Select::unpatch_pp_sselect;
 }

=over 4

=cut

package Coro::Select;

use common::sense;

use Errno;

use Coro ();
use Coro::State ();
use AnyEvent 4.800001 ();
use Coro::AnyEvent ();

use base Exporter::;

our $VERSION = 6.57;
our @EXPORT_OK = "select";

sub import {
   my $pkg = shift;
   if (@_) {
      $pkg->export (scalar caller 0, @_);
   } else {
      $pkg->export ("CORE::GLOBAL", "select");
   }
}

sub select(;*$$$) {
   if (@_ == 0) {
      return CORE::select
   } elsif (@_ == 1) {
      return CORE::select $_[0]
   } elsif (defined $_[3] && !$_[3]) {
      return CORE::select $_[0], $_[1], $_[2], $_[3]
   } else {
      my $nfound = 0;
      my @w;
      my $wakeup = Coro::rouse_cb;

      # AnyEvent does not do 'e', so replace it by 'r'
      for ([0, 0], [1, 1], [2, 0]) {
         my ($i, $poll) = @$_;
         if (defined $_[$i]) {
            my $rvec = \$_[$i];

            # we parse the bitmask by first expanding it into
            # a string of bits
            for (unpack "b*", $$rvec) {
               # and then repeatedly matching a regex against it
               while (/1/g) {
                  my $fd = (pos) - 1;

                  push @w,
                     AE::io $fd, $poll, sub {
                        (vec $$rvec, $fd, 1) = 1;
                        ++$nfound;
                        $wakeup->();
                     };
               }
            }

            $$rvec ^= $$rvec; # clear all bits
         }
      }

      push @w,
         AE::timer $_[3], 0, $wakeup
            if defined $_[3];

      Coro::rouse_wait;

      return $nfound
   }
}

1;

=back

=head1 BUGS

For performance reasons, Coro::Select's select function might not
properly detect bad file descriptors (but relying on EBADF is inherently
non-portable).

=head1 SEE ALSO

L<Coro::LWP>.

=head1 AUTHOR/SUPPORT/CONTACT

   Marc A. Lehmann <schmorp@schmorp.de>
   http://software.schmorp.de/pkg/Coro.html

=cut