#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <mqueue.h>
#include <sys/wait.h>
#include <fcntl.h>

#define MSG_QNAME    "/msgq_example_name"
#define MSG_MAXMSGS  5
#define MSG_MAXMSGSZ 20

#define MSG_MSGSZ MSG_MAXMSGSZ /* must be at least MSG_MAXMSGSZ */

int producer ()
{
	mqd_t mqdes;
	struct mq_attr attr;
	char msg_ptr[] = "example message";
	size_t msg_len = strlen (msg_ptr) + 1;
	unsigned msg_prio = 10;

	attr.mq_flags = 0;
	attr.mq_maxmsg = MSG_MAXMSGS;
	attr.mq_msgsize = MSG_MAXMSGSZ;
	mqdes = mq_open ( MSG_QNAME, O_WRONLY | O_CREAT, 00600, &attr );
	if ( mqdes == (mqd_t) -1 ) {
		perror ( "producer:mq_open" );
		return -1;
	}
	if ( mq_send ( mqdes, msg_ptr, msg_len, msg_prio ) ) {
		perror ( "mq_send" );
		return -1;
	}
	printf ( "Sent: %s [prio=%d]\n", msg_ptr, msg_prio );

	return 0;
}

int consumer ()
{
	mqd_t mqdes;
	char msg_ptr[MSG_MSGSZ];
	size_t msg_len;
	unsigned msg_prio;

	mqdes = mq_open ( MSG_QNAME, O_RDONLY );
	if ( mqdes == (mqd_t) -1 ) {
		perror ( "consumer:mq_open" );
		return -1;
	}
	msg_len = mq_receive ( mqdes, msg_ptr, MSG_MSGSZ, &msg_prio );
	if ( msg_len < 0 ) {
		perror ( "mq_receive" );
		return -1;
	}
	printf ( "Received: %s [prio=%d]\n", msg_ptr, msg_prio );

	return 0;
}

int main ( void )
{
	producer ();

	sleep (1);
	if ( !fork() ) {
		consumer ();
		exit (0);
	}
	wait (NULL);

	mq_unlink ( MSG_QNAME );

	return 0;
}