Readings

• Process Management: pp. 130-141 of Nutt text
• File descriptor manipulation
• Intro to Pipes: pp. 243-246 of Nutt text
• More on Pipes

Simple example of using pipe

#define MSG "hello, world"
#define MSG_LEN 13  /* number of characters plus 1 */

int main () {
	int pfd[2];	/* pipe file descriptors */
	char inbuf[MSG_LEN], outbuf[MSG_LEN];
	int nbytes;

	if (-1 == pipe(pfd)) {
		perror ("pipe");
		exit(1);
	}

	strcpy (outbuf, MSG, MSG_LEN);
	nbytes = write (pfd[1], outbuf, MSG_LEN);
	if (MSG_LEN != nbytes) {
		perror ("write did not send message properly");
		exit(1);
	}

	nbytes = read (pfd[0], inbuf, MSG_LEN);
	if (MSG_LEN != nbytes) {
		perror ("read did not receive message properly");
		exit(1);
	}

	printf ("sent message to myself: %s\n", inbuf);
	close (pfd[0]);
	close (pfd[1]);
	return 0;
}

• this is silly; process doesn't need to send itself a message
• but very useful for two processes to communicate with each other
• strategy: parent creates pipe, then forks child, which execs new program
• both parent and child share the pipe so both can use it to communicate!
• before the exec of the new program, however, the child may wish to do some housekeeping of file descriptors -- this will be made clear in the reading