def shutdown(force=false)
      status(:closed)
      args = []
      args.push(:force) if force
      @logger.info("Pool is now shutting down #{force ? 'using force' : ''}")
      @queue.clear if force
      @queue.wait_empty
      while(t = @threads.pop) do
        t.stop(*args)
      end
      unless(force)
        flush
        @threads.each{|x|x.join}
      end
      nil
    end
def shutdown(force=false)
      status(:closed)
      args = []
      args.push(:force) if force
      @logger.info("Pool is now shutting down #{force ? 'using force' : ''}")
      @queue.clear if force
      @queue.wait_empty
      while(t = @threads.pop) do
        t.stop(*args)
      end
      unless(force)
        flush
        @threads.each{|x|x.join}
      end
      nil
    end
force:: force immediate stop
 Stop the pool