/* philosophers.c
 * Simulate the dining philosophers problem with POSIX threads.
 * This uses asymmetry to make a deadlock-free solution.
 * gcc -o philosophers -lpthread philosophers.c
 */
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h> // has pthreads types
#include "pthread.h"



// constants
#define NUM_PHILOSOPHERS 5

// global variables
int err;
int phil_ids[NUM_PHILOSOPHERS];
pthread_mutex_t chopsticks[NUM_PHILOSOPHERS];

// thread's main function
void *philosopher(void *arg)
{	
	int i;
	int id = *(int *)arg;
	int first = id-1;
	if (first < 0) first = NUM_PHILOSOPHERS-1;
	int second = id;
	
	// Break the symmetry. If this is commented out, then the simulation
	// is subject to deadlock. We are more likely to encounter the deadlock
	// if the sleep commands are commented out.
// 	if (id==0)
// 	{
// 		// I'm the odd philosopher out
// 		first = id;
// 		second = NUM_PHILOSOPHERS-1;
// 	}

	for (i = 0; i < 1000; i++) // lots of meals :)
	{
		// sleep to simulate thinking
// 		sleep(1*(rand()%4+1)); // think between 1 and 4 seconds
		// eat
		pthread_mutex_lock(&chopsticks[first]);
		pthread_mutex_lock(&chopsticks[second]);
		printf("Philosopher %i dining\n",id);
		// sleep to simulate eating
// 		sleep(1*(rand()%3+1)); // eat between 1 and 3 seconds
		pthread_mutex_unlock(&chopsticks[first]);
		pthread_mutex_unlock(&chopsticks[second]);
	} // end for loop
	return NULL;
} // end philospoher function

// main function
int main(int argc, char *argv[])
{
	pthread_t tid[NUM_PHILOSOPHERS];
	int i;		
	for (i = 0; i < NUM_PHILOSOPHERS; i++)
		pthread_mutex_init(&chopsticks[i],NULL);
	
	for (i = 0; i < NUM_PHILOSOPHERS; i++)
	{
		phil_ids[i] = i;
		err = pthread_create(&tid[i],NULL,philosopher,&phil_ids[i]);
	}
	for (i = 0; i < NUM_PHILOSOPHERS; i++)
	{
		err = pthread_join(tid[i], NULL);
	}
	
	for (i = 0; i < NUM_PHILOSOPHERS; i++)
		pthread_mutex_destroy(&chopsticks[i]);
}