Inter Process Communication
Shared Memory
SYSTEM CALL:
shmget() – Used to create a new message queue, or access an existing queue.
Prototype: int shmget ( key_t key, int size, int shmflg );
Returns: shared memory segment identifier on success (or) -1 on error
shmat() – attaches the shared memory segment identified by shmid to the address space of the calling process.
Prototype: int shmat ( int shmid, char *shmaddr, int shmflg);
Returns: address at which segment was attached to the process, (or) -1 on error
Program :
// 1. IPC Using Shared Memory – Server Program
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 27
void die(char *s)
{
perror(s);
exit(1);
}
int main()
{
char c;
int shmid;
key_t key;
char *shm, *s;
key = 5678;
if ((shmid = shmget(key, MAXSIZE, IPC_CREAT | 0666)) < 0)
die(“shmget”);
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1)
die(“shmat”);
s = shm;
for (c = ‘a’; c <= ‘z’; c++)
*s++ = c;
while (*shm != ‘*’)
sleep(1);
exit(0);
}
// 1. IPC Using Shared Memory – Client Program
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 27
void die(char *s)
{
perror(s);
exit(1);
}
int main()
{
int shmid;
key_t key;
char *shm, *s;
key = 5678;
if ((shmid = shmget(key, MAXSIZE, 0666)) < 0)
die(“shmget”);
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1)
die(“shmat”);
for (s = shm; *s != ‘\0’; s++)
putchar(*s);
putchar(‘\n’);
*shm = ‘*’;
exit(0);
}