#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>

/*
use the pthread flag with gcc to compile this code
~$ gcc -pthread dining_philosophers.c -o dining_philosophers
*/

pthread_t *philosophers;
pthread_mutex_t *forks;

int philosophers_count;


void eat(int i){

	printf("Philosopher %d is eating\n",i+1);

	sleep(1 + rand()%10);
}

void* philosopher(void* args){
	int i = 0,first,second;
	while(!pthread_equal(*(philosophers+i),pthread_self()) && i < philosophers_count){
		i++;
	}

	while(1){

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

		sleep(1 + rand()%10);

		first = i;
		second = (i+1)%philosophers_count;

		pthread_mutex_lock(forks + (first>second?second:first));
		pthread_mutex_lock(forks + (first<second?second:first));
		eat(i);
		pthread_mutex_unlock(forks+first);
		pthread_mutex_unlock(forks+second);
	}

	return NULL;
}


int main(void){
	int i,err;

	srand(time(NULL));

	printf("Enter number of philosophers:");
	scanf("%d",&philosophers_count);
	philosophers = (pthread_t*) malloc(philosophers_count*sizeof(pthread_t));
	forks = (pthread_mutex_t*) malloc(philosophers_count*sizeof(pthread_mutex_t));

	for(i=0;i<philosophers_count;++i)
		if(pthread_mutex_init(forks+i,NULL) != 0){
			printf("Failed initializing fork %d\n",i+1);
			return 1;
		}

	for(i=0;i<philosophers_count;++i){
		err = pthread_create(philosophers+i,NULL,&philosopher,NULL);

		if(err != 0){
			printf("Error creating philosopher: %s\n",strerror(err));
		}else{
			printf("Successfully created philosopher %d\n",i+1);
		}
	}

	for(i=0;i<philosophers_count;++i)
		pthread_join(*(philosophers+i),NULL);

	free(philosophers);
	free(forks);

	return 0;
}