using message queues in Linux

simple message queue program writes a phrase into a message queue and fork to another process read it then exit
with signal supporting and clearing after

كود PHP:


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

struct msgbuf
{
        long mtype;
        char mtext[1];
};

void sig_chld(int signo)
{
        pid_t cdeath;

        signal(SIGCHLD , sig_chld);
        printf("CHILD IS DEAD\n");

        wait(&cdeath);
}

int main()
{
        int id;
        int rc;
        int len;
        pid_t child;
        struct msgbuf *send;
        struct msgbuf *recv;

        char *msg = " Hello Bitchs";
        char shell_cmd[50];

        len = strlen(msg);

        id = msgget( IPC_PRIVATE , IPC_CREAT | IPC_EXCL);

        signal( SIGCHLD , sig_chld);

        if(id < 0)
        {
                perror("msgget");
                _exit(1);
        }

        send = malloc(sizeof(struct msgbuf) + len);

        strncpy( send->mtext , msg , len );

        send->mtype = 1;

        rc = msgsnd( id , send , len , 0);

        if(rc < 0)
        {
                perror("msgsnd");
                _exit(1);
        }

        child = fork();

        switch(child)
        {
                case -1:
                        perror("fork");
                        _exit(1);
                        break;
                case 0:
                        recv = malloc(sizeof(struct msgbuf) + len);

                        rc = msgrcv(id , recv , len , 1 , 0);

                        if(rc < 0)
                        {
                                perror("msgrcv");
                                _exit(1);
                        }
                        printf("recived msg %s\n",recv->mtext);
                        free(recv);
                        _exit(0);

                        break;
                default:
                        sleep(2);
                        break;
        }


        printf("DONE clearing messages queues\n");
        sprintf(shell_cmd , "ipcrm -q %d", id);

        return 0;
}

using message queues is better than using a pipe or named pipes
pipe and named pipes are FIFO means first in first out
so if you wanna read a particular type of a message you have to read it all to reach your goal !
reading from a message queue could be blocked if there is no current messages is there unless
there is a message placed
or queue was removed
or receiving a signal

or it could not be wait or block at all
if you summery IPC_NOWAIT to the fourth parameter of msgrecv(); system call

so as a summery for this code creating a message queue and using it requires
1-creating a message queue
2-setting up a message queue structure and filling it
3-send this message
4- receiving it or not to it's your choice ;)

are you one of those curious people ?
man msgrcv , msgget , msgsnd

إعـــــــلان

اترك تعليق:

using message queues in Linux