How To Implement IPC Using Shared Memory - c

Question

I have the following problem to solve:
implement IPC between 3 processes in a way that the first process create the shared memory and then sends a signal to the second and third processes so they can get attached to that shared memory, now make the second process write something to the shared memory and then make it send a signal to the third process so that the third process reads what the second process had written.
this is what I've came up with so far
First_Process.c
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
struct memory {
char msg[100];
int status, pid1, pid2, pid3;
};
struct memory* shmptr;
int main()
{
// First_Process Process Id
int pid = getpid();
// Key Of The Shared Memory
key_t key = ftok("/tmp", 'a');
// Shared Memory Creation
int shmid = shmget(key, sizeof(struct memory), IPC_CREAT | 0666);
// Attaching First_Process To The Shared Memory
shmptr = (struct memory*)shmat(shmid, NULL, 0);
// Store The First_Process Process Id In The Shared Memory
shmptr->pid1 = pid;
while (1) {
// Waiting For Second_Process And Third_Process To Get Attached To The Shared Memory
while (shmptr->status != 1)
continue;
sleep(1);
// Sending The Notification to Second_Process And Third_Process Using The Kill Command
//kill(shmptr->pid2, SIGUSR1);
//kill(shmptr->pid3, SIGUSR1);
}
// Detaching First_Process From The Shared Memory
shmdt((void*)shmptr);
}
Second_Process.c
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
struct memory {
char msg[100];
int status, pid1, pid2, pid3;
};
struct memory* shmptr;
int main()
{
// Second_Process Process Id
int pid = getpid();
// Key Of The Shared Memory
key_t key = ftok("/tmp", 'a');
// Shared Memory Id Fetching
int shmid = shmget(key, sizeof(struct memory), IPC_CREAT | 0666);
// Attaching Second_Process To The Shared Memory
shmptr = (struct memory*)shmat(shmid, NULL, 0);
// Store The Second_Process Process Id In The Shared Memory
shmptr->pid2 = pid;
while (1) {
// Waiting For Third_Process To Get Attached To The Shared Memory
while (shmptr->status != 1)
continue;
sleep(1);
// Writing A Message To The Shared Memory
printf("Enter A Message To Send To Third_Process: \n");
fgets(shmptr->msg, 100, stdin);
// Sending The Message To Third_Process Using The Kill Command
kill(shmptr->pid3, SIGUSR2);
}
// Detaching Second_Process From The Shared Memory
shmdt((void*)shmptr);
}
Third_Process.c
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
struct memory {
char msg[100];
int status, pid1, pid2, pid3;
};
struct memory* shmptr;
// Handler Function To Read From The Shared Memory
void handler(int signum)
{
// if signum is SIGUSR2, then user 2 is receiving a message from user1
if (signum == SIGUSR2) {
printf("Received From Second: ");
puts(shmptr->msg);
kill(shmptr->pid1, SIGINT);
kill(shmptr->pid2, SIGINT);
kill(shmptr->pid3, SIGINT);
}
}
int main()
{
// Third_Process Process Id
int pid = getpid();
// Key of The Shared Memory
key_t key = ftok("/tmp", 'a');
// Shared Memory Id Fetching
int shmid = shmget(key, sizeof(struct memory), IPC_CREAT | 0666);
// Attaching Third_Process to The Shared Memory
shmptr = (struct memory*)shmat(shmid, NULL, 0);
// Store The Third_Process Process Id In The Shared Memory
shmptr->pid3 = pid;
// Telling Second_Process And First_Process That Third_Process Got Attached To The Shared Memory
shmptr->status = 1;
// Attaching Handler Function To Signal SIGUSR1 And SIGUSR2
signal(SIGUSR1, handler);
signal(SIGUSR2, handler);
while(1){}
// Detaching Third_Process From The Shared Memory
shmdt((void*)shmptr);
}
Is there something wrong with the code?
thanks in advance.
EDIT: it was working well then it started to give the segmentation fault error i don't know why