Message Queue

Message Queue - README

1. Fire up the command prompt.
2.1. Execute: gcc send.c -o send
2.2. Execute: gcc recv.c -o recv
3. Execute: ./send <<< "Message."
4. Execute: ./recv

recv.c

#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>

#define MSGSZ    255
#define KEY 10

typedef struct msgbuf
{
    long mtype;
    char mtext[MSGSZ+1];
} message_buf;

static void INThandler(int);

int main(void)
{
    key_t key = KEY;
    int msgflg = 0644;
    message_buf rbuf;

    int msqid = msgget(key, msgflg);

    if (msqid < 0)
    {
        perror("msgget");
        exit(1);
    }

    signal(SIGINT, INThandler);

    rbuf.mtype = 1;
    for ( ; ; )
    {
        printf("Waiting...\n");
        ssize_t nbytes = msgrcv(msqid, &rbuf, MSGSZ, 0, 0);
        if (nbytes < 0)
        {
            perror("msgrcv");
            exit(1);
        }
        printf("PID - %ld : Message (%d) - %s", rbuf.mtype, (int)nbytes, rbuf.mtext);
    }

    return 0;
}

static void  INThandler(int sig)
{
    signal(sig, SIG_IGN);
    int mask, msgid;
    key_t key = KEY;
    mask = 0644;
    msgid = msgget(key, mask);

    if (msgid == -1)
    {
        printf("Message queue does not exist.\n");
        exit(EXIT_SUCCESS);
    }

    if (msgctl(msgid, IPC_RMID, NULL) == -1)
    {
        fprintf(stderr, "Message queue could not be deleted.\n");
        exit(EXIT_FAILURE);
    }
    else
        printf("Message queue was deleted.\n");
    exit(0);
}

send.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>

#define MSGSZ   255
#define KEY     10

typedef struct msgbuf
{
    long mtype;
    char mtext[MSGSZ+1];
} message_buf;

int main(void)
{
    message_buf sbuf;
    sbuf.mtype = getpid();

    printf("The PID is %ld\n", sbuf.mtype);

    printf("Enter word(s) (Limit: %d characters):\n", MSGSZ+1);
    if (fgets(sbuf.mtext, sizeof(sbuf.mtext), stdin) == 0)
    {
        printf("End-of-File detected!\n");
        exit(EXIT_FAILURE);
    }

    printf("\n");

    key_t key = KEY;
    int mask = 0644 | IPC_CREAT;
    int msgid = msgget(key, mask);
    if (msgid < 0)
    {
        fprintf(stderr, "Failed to create message key %d.\n", key);
        exit(EXIT_FAILURE);
    }

    if (msgsnd(msgid, &sbuf, strlen(sbuf.mtext)+1, IPC_NOWAIT) < 0)
    {
        perror("msgsnd");
        exit(EXIT_FAILURE);
    }

    printf("id - %ld : message - %s\n", sbuf.mtype, sbuf.mtext);

    return 0;
}