/* A simple program to illustrate the use of Message Queues.
 * Note that message queues continue to exist after all processes have
 * terminated; messages continue to remain in the queues as well.  This is
 * desired, but requires that processes clean up after themselves when
 * they are done using the queues.
 *
 * Note that in this example we manually specify the key instead of using
 * ftok(2).
 *
 * Use this tool to create/send messages, then run msgrecv.c to retrieve
 * them (in order).
 *
 * Use ipcs(1) to inspect the usage.
 *
 * Derived from:
 * http://www.cs.cf.ac.uk/Dave/C/node25.html
 */

#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define MSGSZ     128

typedef struct msgbuf {
	long mtype;
	char mtext[MSGSZ];
} message_buf;

int
main(int argc, char **argv) {
	int msqid;
	int msgflg = IPC_CREAT | 0666;
	key_t key;
	message_buf sbuf;
	size_t buf_length;

	if (argc != 2) {
		fprintf(stderr, "Usage: msgsend key\n");
		exit(EXIT_FAILURE);
	}

	if ((key = atoi(argv[1])) < 1) {
		fprintf(stderr, "Invalid key: %s\n", argv[1]);
		exit(EXIT_FAILURE);
	}

	if ((msqid = msgget(key, msgflg )) < 0) {
		perror("msgget");
		exit(EXIT_FAILURE);
	}

	sbuf.mtype = 1;

	strncpy(sbuf.mtext, "Did you get this?", MSGSZ);

	buf_length = strlen(sbuf.mtext) + 1 ;

	if (msgsnd(msqid, &sbuf, buf_length, IPC_NOWAIT) < 0) {
		fprintf (stderr, "%d, %ld, %s, %d\n",
				msqid, sbuf.mtype, sbuf.mtext, (int)buf_length);
		perror("msgsnd");
		exit(EXIT_FAILURE);
	}

	exit(0);
}