instance method with_listener

# File railties/lib/commands/ncgi/tracker, line 27
  def with_listener
    message "listener requested"

    mutex = has_lock = index = nil
    3.times do 
      @listeners.each_with_index do |mutex, index|
        has_lock = mutex.try_lock
        break if has_lock
      end
      break if has_lock
      sleep 0.05
    end

    if has_lock
      message "obtained listener #{index}"
      @active = true
      begin yield index
      ensure
        mutex.unlock
        message "released listener #{index}"
      end
    else
      message "dropping request because no listeners are available!"
    end
  end