A6

Aim:     Deadlock Avoidance Using Semaphores: Implement the deadlock-free solution to Dining Philosophers problem to illustrate the problem of deadlock and/or starvation that can occur when many synchronized threads are competing for limited resources.

#include<stdio.h>

#include<semaphore.h>

#include<pthread.h>

#include<unistd.h>

#define N 5

#define               THINKING 0

#define               HUNGRY 1

#define               EATING 2          

#define               Left (ph_num+4)%N

#define               Right (ph_num+1)%N

sem_t room;

sem_t chopst[N];

void *philospher(void *num);

void take_chopst(int);

void put_chopst(int);

void test(int);

int state[N];

int phil_num[N]={0,1,2,3,4};

int main()

{

int i;

pthread_t thread_id[N];

sem_init(&room,0,1);

for(i=0;i<N;i++)

sem_init(&chopst[i],0,0);

for(i=0;i<N;i++)

{

pthread_create(&thread_id[i],NULL,philospher,&phil_num[i]);

printf("philospher %d is thinking \n ",i+1);

}

for(i=0;i<N;i++)

{

pthread_join(thread_id[i],NULL);

sem_destroy(&chopst[N]);

sem_destroy(&room);

pthread_exit(0);                            

}

}

void *philospher(void *num)

{

int x=1;

while(x<5)

{

int *i=num;

usleep(1);

take_chopst(*i);

usleep(1);

put_chopst(*i);

x++;

}

}

void take_chopst(int ph_num)

{

sem_wait(&room);

state[ph_num]=HUNGRY;

printf("philospher %d is hungry \n",ph_num+1);

test(ph_num);

sem_post(&room);

sem_wait(&chopst[ph_num]);

}

void test(int ph_num)

               {

if(state[ph_num]==HUNGRY && state[Left]!=EATING && state[Right]!=EATING)

{

state[ph_num]=EATING;

usleep(1);

printf("philospher %d takes left chopst %d and right chopst %d\n",ph_num+1,Left+1,ph_num+1);

printf("philospher %d is Eating \n",ph_num+1);

sem_post(&chopst[ph_num]);

}

}

void put_chopst(int ph_num)

{

               sem_wait(&room);

               state[ph_num]=THINKING;

               printf("philospher %d is putting left chopst %d and right chopst %d down\n",ph_num+1,Left+1,ph_num+1);

               printf("Philospher %d is thinking \n",ph_num+1);

               test(Left);

               test(Right);

               sem_post(&room);

}