int para_select(int n, fd_set *readfds, fd_set *writefds,
struct timeval *timeout_tv);
__must_check int mark_fd_nonblocking(int fd);
int para_select(int n, fd_set *readfds, fd_set *writefds,
struct timeval *timeout_tv);
__must_check int mark_fd_nonblocking(int fd);