int file_exists(const char *);
int para_select(int n, fd_set *readfds, fd_set *writefds,
struct timeval *timeout);
int mark_fd_nonblock(int fd);
int file_exists(const char *);
int para_select(int n, fd_set *readfds, fd_set *writefds,
struct timeval *timeout);
int mark_fd_nonblock(int fd);