Dining_philosopher/DiningPhilosopher.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include "din_ph.h"


#define N_PHILOSOPHER 5

static phil_t phil[N_PHILOSOPHER];
static spoon_t spoon[N_PHILOSOPHER];

static spoon_t* phil_get_right_spoon(phil_t* phil) {

	int phil_id = phil->phil_id;

	if (phil_id == 0) {
		return &spoon[N_PHILOSOPHER-1];
	}

	return &spoon[phil_id - 1];
}

static spoon_t* phil_get_left_spoon(phil_t* phil) {

	int phil_id = phil->phil_id;
	return &spoon[phil_id];
}

void
phil_eat(phil_t* phil) {

	spoon_t* left_spoon = phil_get_left_spoon(phil);
	spoon_t* right_spoon = phil_get_right_spoon(phil);

	/*
		Check condition that Phil is eating with right set of spoons
	*/

	assert(left_spoon->phil == phil);
	assert(right_spoon->phil == phil);
	assert(left_spoon->is_used == true);
	assert(right_spoon->is_used == true);

	phil->eat_count++;

	printf("Phil %d eats with spoon [%d , %d] for %d times\n",
		phil->phil_id, left_spoon->spoon_id, right_spoon->spoon_id,
		phil->eat_count);
	sleep(1); /* let the philosopher eat the cake for 1 second. */

}

bool
philosopher_release_both_spoons(phil_t* phil) {

	spoon_t* left_spoon = phil_get_left_spoon(phil);
	spoon_t* right_spoon = phil_get_right_spoon(phil);

	/* . . . */

	pthread_mutex_lock(&left_spoon->mutex);
	pthread_mutex_lock(&right_spoon->mutex);

	assert(left_spoon->phil == phil);
	assert(left_spoon->is_used == true);

	assert(right_spoon->phil == phil);
	assert(right_spoon->is_used == true);

	printf("phil %d releasing the left spoon %d\n", phil->phil_id, left_spoon->spoon_id);

	left_spoon->phil = NULL;
	left_spoon->is_used = false;

	pthread_cond_signal(&left_spoon->cv);
	printf("phil %d signalled the phil waiting for left spoon %d\n",
		phil->phil_id, left_spoon->spoon_id);

	pthread_mutex_unlock(&left_spoon->mutex);

	printf("phil %d releasing the right spoon %d\n",
		phil->phil_id, right_spoon->spoon_id);

	right_spoon->phil = NULL;
	right_spoon->is_used = false;
	pthread_cond_signal(&right_spoon->cv);

	printf("phil %d signalled the phil waiting for right spoon %d\n",
		phil->phil_id, right_spoon->spoon_id);

	pthread_mutex_unlock(&right_spoon->mutex);
}

bool
philosopher_access_both_spoons(phil_t* phil) {

	spoon_t* left_spoon = phil_get_left_spoon(phil);
	spoon_t* right_spoon = phil_get_right_spoon(phil);

	/* before checking status of the spoon, lock it, While one
	philosopher is inspecting the state of the spoon, no
	other phil must change it */

	printf("Phil %d waiting for lock on left spoon %d\n",
		phil->phil_id, left_spoon->spoon_id);

	pthread_mutex_lock(&left_spoon->mutex);
	printf("Phil %d inspecting left spoon %d state\n",
		phil->phil_id, left_spoon->spoon_id);

	/* Case 1 : if spoon is begin used by some other phil, then wait */
	while (left_spoon->is_used &&
		left_spoon->phil != phil) {

		printf("phil %d blocks as left spoon %d is not available\n",
			phil->phil_id, left_spoon->spoon_id);

		pthread_cond_wait(&left_spoon->cv, &left_spoon->mutex);

		printf("phil %d recvs signal to grab spoon %d\n",
			phil->phil_id, left_spoon->spoon_id);
	}


	/* Case 2 : if spoon is available, grab it and try for another spoon */

	printf("phil %d finds left spoon %d available, trying to grab it\n",
		phil->phil_id, left_spoon->spoon_id);
	left_spoon->is_used = true;
	left_spoon->phil = phil;
	printf("phil %d has successfully grabbed the left spoon %d\n",
		phil->phil_id, left_spoon->spoon_id);
	pthread_mutex_unlock(&left_spoon->mutex);

	/* Case 2.1 : Trying to grab the right spoon now */
	printf("phil %d now making an attempt to grab the right spoon %d\n",
		phil->phil_id, right_spoon->spoon_id);

	/* lock the right spoon before inspecting its state */
	printf("phil %d waiting for lock on right spoon %d\n",
		phil->phil_id, right_spoon->spoon_id);

	pthread_mutex_lock(&right_spoon->mutex);

	printf("phil %d inspecting right spoon %d state\n",
		phil->phil_id, right_spoon->spoon_id);

	if (right_spoon->is_used == false) {
		/* right spoon is also available, grab it and eat */
		right_spoon->is_used = true;
		right_spoon->phil = phil;
		pthread_mutex_unlock(&right_spoon->mutex);
		return true;
	}
	else if (right_spoon->is_used == true) {

		if (right_spoon->phil != phil) {
			printf("phil %d finds right spoon %d is already used by phil %d"
				" realeasing the left spoon as well\n",
				phil->phil_id, right_spoon->spoon_id, right_spoon->phil->phil_id);

			pthread_mutex_lock(&left_spoon->mutex);
			assert(left_spoon->is_used == true);

			assert(left_spoon->is_used == true);

			left_spoon->is_used = false;
			left_spoon->phil = NULL;

			printf("phil %d release the left spoon %d\n",
				phil->phil_id, left_spoon->spoon_id);

			pthread_mutex_unlock(&left_spoon->mutex);
			pthread_mutex_unlock(&right_spoon->mutex);
			return false;
		}
		else {
			printf("phil %d already has right spoon %d in hand\n",
				phil->phil_id, right_spoon->spoon_id);
			pthread_mutex_unlock(&right_spoon->mutex);
			return true;
		}
	}

	assert(0); /* should be dead code */
	return false;
}

void*
philosopher_fn(void* arg) {

	/* Start implementation of core logic from here */

	phil_t* phil = (phil_t*)arg;

	while (1) {

		if (philosopher_access_both_spoons(phil)) {

			phil_eat(phil);
			philosopher_release_both_spoons(phil);
			sleep(1); /* Phil wait for 1 sec to again attempt to get the spoon */
		}
	}

}

int
main(int argv, char* argc[]) {

	int i = 0;
	pthread_attr_t attr;

	/*Initialize all spoons*/
	for (i = 0; i < N_PHILOSOPHER; i++) {

		spoon[i].spoon_id = i;
		spoon[i].is_used = false;
		spoon[i].phil = NULL;
		pthread_mutex_init(&spoon[i].mutex, NULL);
		pthread_cond_init(&spoon[i].cv, NULL);

	}

	/* Default attributes of all Philosopher threads */
	pthread_attr_init(&attr);
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

	/* create philosopher threads */
	for (i = 0; i < N_PHILOSOPHER; i++) {

		phil[i].phil_id = i;
		phil[i].eat_count = 0;
		pthread_create(&phil[i].thread_handle, &attr, philosopher_fn, &phil[i]);

	}

	pthread_exit(0);
	return 0;
}