When you've looked at all the complicated select-based work-arounds, try it the simple way :)

#! perl -sw
use strict;
use threads;
use Thread::Queue;

$|++;

our $THREADS //= 4;

my $Q = new Thread::Queue;

async {
    open my $pipe, '-|',
        q[ perl -E"$|++; sleep(1), say $$, ':', $_ for 1 .. 3" ]
        or die $!;
    $Q->enqueue( $_ ) while defined( $_ = <$pipe> );
    $Q->enqueue( undef );
}->detach for 1 .. $THREADS;

for ( 1 .. $THREADS ) {
    print while defined( $_ = $Q->dequeue );
}

__END__
c:\test>925473.pl
4648:1
4764:1
704:1
1924:1
4648:2
4764:2
704:2
1924:2
4648:3
4764:3
704:3
1924:3
[download]