virtual void watch_fd(int fd, poll_flag flag) = 0;
virtual bool unwatch_fd(int fd, poll_flag flag) = 0;
virtual void wait_ready(vector<int> & readable, vector<int> & writable) = 0;
virtual void watch_fd(int fd, poll_flag flag) = 0;
virtual bool unwatch_fd(int fd, poll_flag flag) = 0;
virtual void wait_ready(vector<int> & readable, vector<int> & writable) = 0;