def worker_pids(cls):
        """Returns an array of all pids (as strings) of the workers on
        this machine.  Used when pruning dead workers."""
        cmd = "ps -A -o pid,command | grep pyres_worker | grep -v grep"
        output = commands.getoutput(cmd)
        if output:
            return map(lambda l: l.strip().split(' ')[0], output.split("\n"))
        else:
            return []