def signal
      synchronize do
        while(t = @threads.shift)
          if(t && t.alive? && t.stop?)
            t.wakeup
            break
          else
            next
          end
        end
      end
    end
def signal
      synchronize do
        while(t = @threads.shift)
          if(t && t.alive? && t.stop?)
            t.wakeup
            break
          else
            next
          end
        end
      end
    end
Wake up earliest thread