#! perl -slw
use strict;
use threads qw[ async yield ];
use Thread::Queue;

my $Qrv = new Thread::Queue;

my @work = qw[ C: D: P: Q: T: U: V: W: Z: ];

for ( 1 .. 2 ) {
	my $cmd = join ' ', 'dir /s', shift( @work ),  '>nul';
	async( sub{ $Qrv->enqueue( "$_: " . system( $cmd ) ); } )->detach;
}

while( @work ) {
	my( $threadNo, $rv ) = split ': ', $Qrv->dequeue();
	my $cmd = join ' ', 'dir /s', shift( @work ),  '>nul';
	async( sub{ $Qrv->enqueue( "$threadNo: " . system( $cmd ) ); } )->detach;
}

sleep 2;