while ( 1 ){
        {
            lock ${$self->{working threads}};
            my $pending;
            {
                lock ${$self->{poolcount}};
                $pending = ${$self->{poolcount}};
            }
            if ( ${$self->{working threads}} + $pending > 0 ){
                cond_wait ${$self->{workingthreads}};
            } else {
                return;
            }
        }
    }