pipe()

int pipe(int pfd[2]);

• Purpose: Creates an anonymous pipe for Inter-Process Communication (IPC).
• Usage: Typically used between a parent and child process after fork().
• Parameters:
  • pfd[2]: An integer array storing two file descriptors:
    • pfd[0] → Read end (used for reading from the pipe)
    • pfd[1] → Write end (used for writing to the pipe)
• Return Value:
  • 0 on success (for pipe only).
  • -1 on failure (sets errno).
• Common Errors:
  • EMFILE: Too many file descriptors open.
  • ENFILE: System-wide file descriptor limit reached.
  • EFAULT: pfd points to an invalid memory address.

Pipe Communication Flow & Behavior

1. Parent writes to pipe (write(pfd[1], ...)).
2. Child reads from pipe (read(pfd[0], ...)).
3. Data is transferred in a unidirectional manner (one writes, the other reads).
4. read() blocks if no data is available.
5. write() blocks if the pipe buffer is full.
6. If all write ends are closed → read() returns 0 (EOF).
7. If all read ends are closed → write() triggers SIGPIPE, terminating the process.
8. Processes exit using exit(0) after completing communication.

Pipe Buffer & Non-Blocking Mode

• Pipes have a fixed-size buffer (OS-dependent, typically 4KB - 64KB).
• When the pipe buffer is full, write() blocks unless in non-blocking mode.
• When the pipe buffer is empty, read() blocks unless in non-blocking mode.