root/sysv-ipc/dining-semarr.c

DEFINITIONS

1. clearandexit
2. philosopher
3. main

#include<stdio.h>
#include<stdlib.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<sys/signal.h>
#include<sys/time.h>
int semkey;
const struct sembuf  up = {0,1,SEM_UNDO};
const struct sembuf  down = {0,-1,SEM_UNDO};

void clearandexit(int r)
{
        int i;
        semctl(semkey,5,IPC_RMID);
        exit(r);
}

void philosopher(int i,int s1, int s2) 
{
        struct sembuf sb[2];
        srand(i+time(NULL));
        while (1) {
                sleep(rand()%2+1);
                sb[0]=down;sb[1]=down;
                sb[0].sem_num=s1; sb[1].sem_num=s2;
                semop(semkey,sb,2);
                printf("Philosopher %d is eating\n",i);
                sleep(rand()%4+1);
                printf("Philosopher %d finished eating\n",i);
                sb[0]=up;sb[1]=up;
                sb[0].sem_num=s1; sb[1].sem_num=s2;
                semop(semkey,sb,2);
        }
}
int main() 
{
        int i,n;
        struct sembuf sb[5];
        
        semkey=semget(IPC_PRIVATE,5,IPC_CREAT|0600);
        if (semkey<=0) {
                perror("Creating semaphore");
                clearandexit(-2);
        }
        for (i=0;i<5;i++) {
                sb[i].sem_num=i; sb[i].sem_op=1;
                sb[i].sem_flg=SEM_UNDO;
        }
        semop(semkey,sb,5);

        for (i=0;i<5;i++) {
                if (!fork()) {
                        philosopher(i,i,(i+1)%5);
                        return 0;
                }
        }
        signal(SIGINT,clearandexit); sleep(1000);
        clearandexit(0);
}