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[assignments.git] / homework / assgn9 / queue.c

#include "queue.h"
#include <stdlib.h>
#include <pthread.h>

/* Requirements 4 & 5 for Homework 09 indicate that you should modify the add
 * and pop methods for the queue to provide for thread safety.  If you modify
 * the producer and consumer methods instead you will not receive full credit
 * for the solution.  Additionally, the due date for the homework is now
 * Thursday to provide for the necessary modifications to fulfill requirements
 * 4 & 5.  Please note that you should NOT be using a global mutex.  Any
 * structures you use to protect the queue should be associated with the
 * particular queue that is being used (the one given to the add/pop methods).
 * */

/* private methods */

static void clear_node(queue_node_t* node)
{
   if (node != NULL)
   {
      clear_node(node->next);
      free(node);
   }
}

static queue_node_t* create_node(int value)
{
   queue_node_t* node = malloc(sizeof(queue_node_t));
   node->value = value;
   node->next = NULL;
   return node;
}

/* public methods */

void queue_init(queue_t* queue)
{
   queue->root = NULL;

   queue->mx_pop    = (pthread_mutex_t *) calloc(1, sizeof(pthread_mutex_t));
   queue->mx_push   = (pthread_mutex_t *) calloc(1, sizeof(pthread_mutex_t));
   queue->mx_valid_root = (pthread_mutex_t *) calloc(1, sizeof(pthread_mutex_t));
   queue->valid_root = (pthread_cond_t *) calloc(1, sizeof(pthread_cond_t));

   pthread_mutex_init(queue->mx_pop,  NULL);
   pthread_mutex_init(queue->mx_push, NULL);
   pthread_mutex_init(queue->mx_valid_root, NULL);

   pthread_cond_init(queue->valid_root, NULL); 

   return;
}

void queue_clear(queue_t* queue)
{
   clear_node(queue->root);
   free(queue->mx_pop);
   free(queue->mx_push);
   free(queue->valid_root);
   return;
}

/* edit */
void queue_add(queue_t* queue, int value)
{
   pthread_mutex_lock(queue->mx_push);
   pthread_mutex_lock(queue->mx_valid_root);

   if (queue->root == NULL)
   {
      queue->root = create_node(value);
      pthread_cond_signal(queue->valid_root);
      pthread_mutex_unlock(queue->mx_valid_root);
   }
   else
   {
      pthread_cond_signal(queue->valid_root);
      pthread_mutex_unlock(queue->mx_valid_root);

      queue_node_t* last = queue->root;
      while (last->next != NULL)
      {
         last = last->next;
      }
      last->next = create_node(value);
   }
   pthread_mutex_unlock(queue->mx_push);
   return;
}

/* edit */
int queue_pop(queue_t* queue) 
{
   if(queue->root == NULL) {

      pthread_mutex_lock(queue->mx_valid_root);
      pthread_cond_wait(queue->valid_root, queue->mx_valid_root);
      pthread_mutex_unlock(queue->mx_valid_root);
	}
   pthread_mutex_lock(queue->mx_pop);   
   queue_node_t* temp = queue->root->next;
   int value = queue->root->value;
   free(queue->root);
   queue->root = temp;
   pthread_mutex_unlock(queue->mx_pop);
   return value;
}