Non-block Socket:select()

• What 's socket
• §Socket is a file descriptor associated with an opened file.
• Blocking or non-blocking socket:
• Blocking socket
• The program is "blocked" until the request for data has been satisfied Socket default behavior

§

• Non-blocking socket
• Synchronous I/O Multiplexing
• select() 

• Select()
• select() monitor readfds, writefds, and exceptfds.
• fd: file descriptor
• Use socket descriptor for file descriptor.
• Provide the ability to monitor a set of sockets at the same time
• Which socket is ready for read
• Which socket is ready for write
• Provide multiple sessions 
• Several clients can access server at the same time
• Non-blocking
• Return to process if timer expires

• Parameters in select()

int select(

int nfds, 

fd_set_t *readSet, 

fd_set_t *writeSet, 

fd_set_t *exSet, 

timeval_t *timeVal

) 

• nfds
• Be the highest file descriptor plus one
• readSet
• Reflect which file descriptor your selected is ready for reading.
• writeSet
• Reflect which file descriptor your selected is ready for writing.
• exSet
• timeVal

• Macro for select()

• Bind() : FD_ZERO(), FD_SET()
• Select(): FD_ISSET()
• Close(): FD_CLR()

• Sample code for select()

Reference:

Beej’s Guide to Network Programming Using Internet Sockets