Nonblocking IO (ITI8510)

Real-Time Operating Systems and Systems Programming

Basic Linux command-line and utilities for accessing it Standard Streams Stack Exploration Exploring Debugger Signals Threads Processes File Attributes Reading Binary Files LAB: Hufmann Encoder Network Sockets Optimization (mmap() helps here)

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We have two tasks today. Both with practicing nonblocking IO.

1. Canonical mode

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

Hints:

• Try to put the terminal into noncanonical mode and remove terminal echo See 'man termios' or Google 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. 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.

Hints:

• 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 buffering.
• Function usleep() can be used for half-a second pause here.