code: def worker_pids(cls):
          
          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 []
docs: Returns an array of all pids (as strings) of the workers on
          this machine.  Used when pruning dead workers.