use threads       qw( async );
use Thread::Queue qw( );

my $q = Threads::Queue->new();

async { 
   while (<STDIN>) {
      $q->enqueue(...);
   }
   $q->enqueue(...);
};

async { 
   while (<$fr_child_pipe>) {
      $q->enqueue(...);
   }
   $q->enqueue(...);
};

while (defined(my $item = $q->dequeue())) {
   ...
}

##</code><code>##

use threads           qw( async );
use Win32::Socketpair qw( winsocketpair );

my ($fr_parent_sock, $fr_parent_sock_writer) = winsocketpair();
async {
   print($fr_parent_sock_writer $_) while <STDIN>;
   close($fr_parent_sock_writer);
};

my ($fr_child_sock, $fr_child_sock_writer) = winsocketpair();
async {
   print($fr_child_sock_writer $_) while <$fr_child_pipe>;
   close($fr_child_sock_writer);
};

... select $fr_parent_sock and $fr_child_sock ...