Hi bros! I'm confused and new to this Dining Philosophers Problem. I have read algorithms and pseudocodes about it but when it comes to coding and running it on the terminal, I can't seem to understand how it works.
Here's a code that I found from the internet:
Code:
#include<stdio.h>
#include<semaphore.h>
#include<pthread.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 mutex;
sem_t S[N];
void * philospher(void *num);
void take_fork(int);
void put_fork(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(&mutex,0,1);
for(i=0;i<N;i++)
sem_init(&S[i],0,0);
for(i=0;i<N;i++){
pthread_create(&thread_id[i],NULL,philospher,&phil_num[i]);
printf("Philosopher %d is thinking\n",i+1);
}
for(i=0;i<N;i++)
pthread_join(thread_id[i],NULL);
}
void *philospher(void *num){
while(1){
int *i = num;
sleep(1);
take_fork(*i);
sleep(0);
put_fork(*i);
}
}
void take_fork(int ph_num){
sem_wait(&mutex);
state[ph_num] = HUNGRY;
printf("Philosopher %d is Hungry\n",ph_num+1);
test(ph_num);
sem_post(&mutex);
sem_wait(&S[ph_num]);
sleep(1);
}
void test(int ph_num){
if (state[ph_num] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING){
state[ph_num] = EATING;
sleep(2);
printf("Philosopher %d takes fork %d and %d\n",ph_num+1,LEFT+1,ph_num+1);
printf("Philosopher %d is Eating\n",ph_num+1);
sem_post(&S[ph_num]);
}
}
void put_fork(int ph_num){
sem_wait(&mutex);
state[ph_num] = THINKING;
printf("Philosopher %d putting fork %d and %d down\n",ph_num+1,LEFT+1,ph_num+1);
printf("Philosopher %d is thinking\n",ph_num+1);
test(LEFT);
test(RIGHT);
sem_post(&mutex);
}
Can you guys teach me on how this code works? commenting on the code helps a lot. Sorry for the title but I don't know if this is implemented using Tannenbaum's solution, is it? And does this implementation have deadlocks and starvation?
A little help would be much appreciated.