Linux-IPC-Shared-memory

Ex06-Linux IPC-Shared-memory

AIM:

To Write a C program that illustrates two processes communicating using shared memory.

DESIGN STEPS:

Step 1:

Navigate to any Linux environment installed on the system or installed inside a virtual environment like virtual box/vmware or online linux JSLinux (https://bellard.org/jslinux/vm.html?url=alpine-x86.cfg&mem=192) or docker.

Step 2:

Write the C Program using Linux Process API - Shared Memory

Step 3:

Execute the C Program for the desired output.

PROGRAM:

Write a C program that illustrates two processes communicating using shared memory.

//shmry1.c

#include<unistd.h> 
#include<stdlib.h> 
#include<stdio.h> 
#include<string.h> 
#include<sys/shm.h>
#define TEXT_SZ 2048 
struct shared_use_st
{
int written_by_you;
char some_text[TEXT_SZ];
};
int main()
{
int running = 1;
void *shared_memory = (void *)0; 
struct shared_use_st *shared_stuff; 
int shmid;
srand( (unsigned int)getpid() ); 
shmid = shmget( (key_t)1234, sizeof(struct shared_use_st), 0666 |IPC_CREAT );
printf("Shared memory id is %d \n",shmid);
if (shmid == -1)
{
fprintf(stderr, "shmget failed\n");
exit(EXIT_FAILURE);
}
shared_memory = shmat(shmid,(void *)0, 0); if (shared_memory == (void *)-1)
{
fprintf(stderr,	"shmat	failed\n"); exit(EXIT_FAILURE);
}
printf("Memory Attached at %x\n", (int)shared_memory);
shared_stuff = (struct shared_use_st *) shared_memory;
shared_stuff->written_by_you	=	0;
 while(running)
{
if(shared_stuff->written_by_you)
{
printf("You Wrote: %s", shared_stuff->some_text);
sleep( rand() %4 );
shared_stuff->written_by_you = 0;
if (strncmp(shared_stuff->some_text, "end", 3)== 0){
running = 0;}}
}
if (shmdt(shared_memory) == -1)

{
fprintf(stderr, "shmdt failed\n"); exit(EXIT_FAILURE);
}
if (shmctl(shmid, IPC_RMID, 0) == -1)
{
fprintf(stderr, "failed to delete\n");
exit(EXIT_FAILURE);
} exit(EXIT_SUCCESS);
}

//shmry2.c

#include<unistd.h> 
#include<stdlib.h> 
#include<stdio.h> 
#include<string.h>
#include<sys/shm.h>
#define TEXT_SZ 2048 
struct shared_use_st{
int written_by_you;
char some_text[TEXT_SZ];
};
int main()
{
int running =1;
void *shared_memory = (void *)0; 
struct shared_use_st *shared_stuff; 
char buffer[BUFSIZ];
int shmid;
shmid	=shmget(	(key_t)1234,	sizeof(struct shared_use_st), 0666 | IPC_CREAT);
printf("Shared memory id = %d \n",shmid);
if (shmid == -1)
{
fprintf(stderr, "shmget failed\n"); exit(EXIT_FAILURE);
}
shared_memory=shmat(shmid, (void *)0, 0);
if (shared_memory == (void *)-1){
fprintf(stderr,	"shmat	failed\n"); exit(EXIT_FAILURE);}
printf("Memory Attached at %x\n", (int) shared_memory); 
shared_stuff = (struct shared_use_st *)shared_memory; 
while(running)
{
while(shared_stuff->written_by_you== 1)
{
sleep(1);
printf("waiting for client.	\n");
}
printf("Enter Some Text: "); fgets (buffer, BUFSIZ, stdin);
strncpy(shared_stuff->some_text, buffer, TEXT_SZ);
shared_stuff->written_by_you = 1;
if(strncmp(buffer, "end", 3) == 0){
running = 0;}}
if (shmdt(shared_memory) == -1)
{
fprintf(stderr, "shmdt failed\n"); exit(EXIT_FAILURE);
} exit(EXIT_SUCCESS);
}

OUTPUT

$ ./shm2 
Shared memory id = 44 
Memory Attached at 12088000
waiting for client.
waiting for client.
waiting for client.
waiting for client.
Enter Some Text: hello
waiting for client.
waiting for client.
Enter Some Text: world
waiting for client.
waiting for client.
Enter Some Text: end

$ ./shm1 
Shared memory id is 44 
Memory Attached at 6467f000
You Wrote: hello
You Wrote: world
You Wrote: end

$ ipcs

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status     
 
0x00000000 6          sec        600        524288     2          dest       
  
0x00000000 9          sec        600        524288     2          dest       
  
0x00000000 12         sec        600        524288     2          dest       
  
0x00000000 15         sec        600        524288     2          dest       
  
0x00000000 22         sec        600        524288     2          dest       
  
0x00000000 31         sec        600        524288     2          dest       
  

------ Semaphore Arrays --------
key        semid      owner      perms      nsems     

RESULT:

The program is executed successfully.