while( not ( $worker1Finished eq 'true' and 
             $worker2Finished eq 'true'     ) 
) {
    # ...
}

##</code><code>##

while( not $worker1Finished eq 'true' &&
           $worker2Finished eq 'true'
) {
    # ...
}

##</code><code>##

until( $worker1Finished eq 'true' and
       $worker2Finished eq 'true'
) {
    # ...
}