dine.c

Dining Philosopher s Problem

#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);

    }


  }