#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>
#define N 5			//No. of philosophers
#define LEFT (N+id-1)%(N)	//index of id's left neighbour
#define RIGHT (id+1)%(N)	//index of id's right neighbour
#define THINKING 0		//Symbolic constant to indicate thinking
#define HUNGRY 1		//Symbolic constant to indicate hungry state i.e. trying to get the forks
#define EATING 2		//Symbolic constant to indicate eating state
int state[N]={0,0,0,0,0};	//Array to keep track of everyone's state, initially owner thinking
int semid[5];			//One semaphore per philosopher
pthread_mutex_t mutex;
struct sembuf op[2]={{0,-1,0},{0,1,0}};
void take_forks(int);
void put_forks(int);
void * philosopher(void *);
void up(int);
void down(int);
void test(int);
void think(int id)
   {
 	printf("Philosopher %d Thinking\n",id+1);
	sleep(1);
   }
void eat(int id)
   {
	printf("Philosopher %d Eating \n",id+1);
	sleep(1);
   }
void down(int id)
  {
   if(semop(id,&op[0],1))
    {
     printf("semaphore down error\n");
     exit(1);
    }
  }
void up(int id)
  {
   if(semop(id,&op[1],1))
    {
     printf("semaphore up error\n");
     exit(1);
    }
  }
void * philosopher (void *i)
 {
  while(1)
    {
        int id=*(int *)i;
	think(id);
	take_forks(id);
	eat(id);
	put_forks(id);
    }
  }
void take_forks(int id)
 {
  printf("Philosopher %d trying to take forks\n",id+1);
  if(pthread_mutex_lock(&mutex))
       {
       printf("mutex lock error\n");
       exit(1);
       }
  state[id]=HUNGRY;
  test(id);
  if(pthread_mutex_unlock(&mutex))
    {
     printf("mutex unlock error\n");
     exit(1);
    }
   down(semid[id]);
  //sleep(3);
 }
void test(int id)
 {
   if(state[id]==HUNGRY && state[LEFT]!=EATING && state[RIGHT]!=EATING)
    {
         state[id]=EATING;
         up(semid[id]);
    }
 }
void put_forks(int id)
 {
  printf("Philosopher %d has put down forks\n",id+1);
  if(pthread_mutex_lock(&mutex))
  {
   printf("mutex lock error\n");
   exit(1);
  }
state[id]=THINKING;
test(LEFT);
test(RIGHT);
  if(pthread_mutex_unlock(&mutex))
  {
   printf("mutex unlock error\n");
   exit(1);
  }
//sleep(3);
 }
main() 
 {
   int k,i,key;
   char a;
   int phid[5]={0,1,2,3,4};
   pthread_t ph[5];
   pthread_mutex_init(&mutex,NULL);
   for(i=0,a='A';i<5;i++,a++)
    {
      if((key=ftok("dine.c",a))<0)
        {
            printf("Error in generatin key for s[%d]\n",i+1);
            exit(0);
        }
        semid[i]=semget(key,1,IPC_CREAT|0666);      //create a semaphore for each philosopher
        if(semid[i]<0)
        {
            printf("Error in creating semaphore s[%d]\n",i);
            exit(0);
        }
     }
  for(i=0;i<5;i++)
     {
      if(pthread_create(&ph[i],NULL,philosopher,(void *)&phid[i]))
         {
          printf("thread creation error\n");
          exit(1);
         }
      printf("created the semaphore for philosopher %d with id %d\n",i+1,semid[i]);
     }
  for(i=0;i<5;i++)
    {
      pthread_join(ph[i],NULL);
    }
  }