free_request_id

# File lib/resolv.rb, line 639
    def self.free_request_id(host, port, id) # :nodoc:
      RequestIDMutex.synchronize {
        key = [host, port]
        if h = RequestID[key]
          h.delete id
          if h.empty?
            RequestID.delete key
          end
        end
      }
    end