linux_programming

select() vs poll() vs epoll()

1. select() int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

2. poll()

   int poll (struct pollfd *fds, unsigned int nfds, int timeout);
   
   struct pollfd {
         int fd;
         short events; 
         short revents;
   };

3. epoll() epoll_create(), epoll_ctl(), epoll_wait()

• select() have three bitmask-based set of fds(fd-set), poll() only have signle array of fds(pollfd structure)

• select() will reconstruct the fds, so should build each set before each call; poll() has seperate events and returned events, so it don't need.

• select() and poll() manage everything in user mode and send sets each time to wait on, to add another fd we need to add it to the set and call select()/poll() again(); however epoll() use epoll_create to create context in the kernel mode, using epoll_ctl to update the context.