Thread: fork with shared memory

Hello!

I created two processes thanks fork. Now I would like to send 10 int values from the child process to the father process.

Something like that:
son writes int in shared memory
father reads int from shared memory
son writes int in shared memory
father reads int from shared memory

and so on.

Code:

  
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

/*============================================================================*/

int main(int argc, char **argv)
{
  int shmid, shmflg, permflg, res, son;
  volatile int*data;
  void *map_adr;
    
  permflg = (SHM_R|SHM_W) | ((SHM_R|SHM_W)>>3) | ((SHM_R|SHM_W)>>6);

  shmflg = IPC_CREAT | IPC_EXCL | permflg;

  shmid = shmget(IPC_PRIVATE, 8*1024, shmflg);

  map_adr = shmat(shmid, NULL, 0);

  data = (int *)map_adr;
  *data = 1;

  if((son = (fork() == 0))) { 
    map_adr = shmat(shmid, NULL, 0);
    while(*data != 0);
    *data = *data + 1;
     //printf("value is %d\n", *data);
    //*data = 1;
}
  
  else {
    while(*data != 10) {

    printf("value is %d\n", *data);
  }
}

  res = shmdt(map_adr);

  if(!son)
  
    res = shmctl(shmid, IPC_RMID, NULL);

  return 0;
}

I think my problem is my while-loop because it stops after data reaches 1. I don't know how to fix it.


Thanks for your help!