root/sysv-ipc/dining.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 semkeys[5]={0,0,0,0,0};
const struct sembuf  up = {0,1,SEM_UNDO};
const struct sembuf  down = {0,-1,SEM_UNDO};

void clearandexit(int r)
{
        int i;
        for (i=0;i<5;i++)
                semctl(semkeys[i],1,IPC_RMID);
        exit(r);
}

void philosopher(int i,int s1, int s2) 
{
        struct sembuf sb1, sb2;
        srand(i+time(NULL));
        while (1) {
                sleep(rand()%3);
                sb1=down; semop(s1,&sb1,1);
                sb2=down; semop(s2,&sb2,1);
                printf("Philosopher %d is eating\n",i);
                sleep(rand()%10);
                printf("Philosopher %d finished eating\n",i);
                sb1=up; semop(s1,&sb1,1);
                sb2=up; semop(s2,&sb2,1);
        }
}
int main() 
{
        int i,n;
        struct sembuf sb;
        for (i=0;i<5;i++) {
                semkeys[i]=semget(IPC_PRIVATE,1,IPC_CREAT|0600);
                if (semkeys[i]<=0) {
                        perror("Creating semaphore");
                        clearandexit(-2);
                }
                sb=up; 
                semop(semkeys[i],&sb,1);
        }
        for (i=0;i<5;i++) {
                if (!fork()) {
                        philosopher(i,semkeys[i],semkeys[(i+1)%5]);
                        return 0;
                }
        }
        signal(SIGINT,clearandexit); sleep(1000);
        clearandexit(0);
}