Nonblocking IO (ITS8020)

Allikas: Kursused
Mine navigeerimisribale Mine otsikasti

Practice with nonblocking IO.

1. Nonblocking reads from a FIFO

Goal: To write a program which prints a '.' character every half-a second unless some input is provided on a fifo file.


  • Try to put the terminal into noncanonical mode (you want to turn off line buffering) and remove terminal echo See 'man termios' or Google "noncanonical mode" for that.
  • Note that you should restore the terminal mode before quitting since otherwise the terminal might get messed up (no echo).
  • Working with bits:
flags &= ~NEWFLAG   // Clears the bit NEWFLAG on flags
flags |= NEWFLAG    // Set the bit NEWFLAG on flags
flags ^= NEWFLAG    // Toggle NEWLAG

2. Reading from stidin

Goal: To write a program which echoes characters on screen while typed until button 'q' is pressed. Then it quits and prints a newline.


  • Use open() with O_NONBLOCK flag.
  • If read() does not have anything to read, it returns with -1 and sets errno to constant EAGAIN - you can check that or try messing around with select() function.
  • FIFO can be made with a 'mkfifo fifoname' command and written to using 'cat > fifoname'.
  • You have to open fifo before reading (open two terminal windows).
  • Write your output with write() function to bypass line buffering (or turn it off).
  • Function usleep() can be used for half-a second pause here.