Using Select for Data-driven Processing

• A process calls select to wait for one (or more) of a collection of open files (or sockets) to be ready for I/O.

  int select(int n, fd_set *readfds, fd_set *writefds,
      fd_set *exceptfds, struct timeval *timeout);
  
  FD_CLR(int fd, fd_set *set);
  FD_ISSET(int fd, fd_set *set);
  FD_SET(int fd, fd_set *set);
  FD_ZERO(fd_set *set);
  

• select returns the number of fd's ready for I/O

• FD_ISSET is used to determine which fd's are ready

• select returns 0 if the timer expires

• select returns -1 if there is an error