path: root/ntpd/ntp_prio_q.c

/* ntp_prio_q.c
 *
 * This file contains the priority queue implementation used by the
 * discrete event simulator.
 *
 * Written By:	Sachin Kamboj
 *		University of Delaware
 *		Newark, DE 19711
 * Copyright (c) 2006
 */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <ntp_stdlib.h>
#include <ntp_prio_q.h>

/* Priority Queue
 * --------------
 * Define a priority queue in which the relative priority of the elements
 * is determined by a function 'get_order' which is supplied to the
 * priority_queue
 */
queue *debug_create_priority_queue(
	q_order_func	get_order
#ifdef _CRTDBG_MAP_ALLOC
	, const char *	sourcefile
	, int		line_num
#endif	
	)
{
	queue *my_queue;

#ifndef _CRTDBG_MAP_ALLOC
	my_queue = emalloc(sizeof(queue));
#else
	/* preserve original callsite __FILE__ and __LINE__ for leak report */
	my_queue = debug_erealloc(NULL, sizeof(queue), sourcefile, line_num);
#endif
	my_queue->get_order = get_order;
	my_queue->front = NULL;
	my_queue->no_of_elements = 0;

	return my_queue;
}


/* Define a function to "destroy" a priority queue, freeing-up
 * all the allocated resources in the process 
 */

void destroy_queue(
	queue *my_queue
	)
{
    node *temp = NULL;

    /* Empty out the queue elements if they are not already empty */
    while (my_queue->front != NULL) {
        temp = my_queue->front;
        my_queue->front = my_queue->front->node_next;
        free(temp);
    }

    /* Now free the queue */
    free(my_queue);
}


/* Define a function to allocate memory for one element 
 * of the queue. The allocated memory consists of size
 * bytes plus the number of bytes needed for bookkeeping
 */

void *debug_get_node(
	size_t		size
#ifdef _CRTDBG_MAP_ALLOC
	, const char *	sourcefile
	, int		line_num
#endif
	)
{
	node *new_node;

#ifndef _CRTDBG_MAP_ALLOC
	new_node = emalloc(sizeof(*new_node) + size);
#else
	new_node = debug_erealloc(NULL, sizeof(*new_node) + size,
				  sourcefile, line_num);
#endif
	new_node->node_next = NULL; 

	return new_node + 1;
}

/* Define a function to free the allocated memory for a queue node */
void free_node(
	void *my_node
	)
{
	node *old_node = my_node;

	free(old_node - 1);
}


void *
next_node(
	void *pv
	)
{
	node *pn;

	pn = pv;
	pn--;

	if (pn->node_next == NULL)
		return NULL;

	return pn->node_next + 1;
}


/* Define a function to check if the queue is empty. */
int empty(
	queue *my_queue
	)
{
	return (!my_queue || !my_queue->front);
}


void *
queue_head(
	queue *q
	)
{
	if (NULL == q || NULL == q->front)
		return NULL;
		
	return q->front + 1;
}


/* Define a function to add an element to the priority queue.
 * The element is added according to its priority - 
 * relative priority is given by the get_order function
 */
queue *enqueue(
	queue *	my_queue,
	void *	my_node
	)
{
	node *new_node = (node *)my_node - 1;
	node *i = NULL;
	node *j = my_queue->front;

	while (j != NULL && 
	       (*my_queue->get_order)(new_node + 1, j + 1) > 0) {
		i = j;
		j = j->node_next;
	}

	if (i == NULL) {	/* Insert at beginning of the queue */
		new_node->node_next = my_queue->front;
		my_queue->front = new_node;
	} else {		/* Insert Elsewhere, including the end */
		new_node->node_next = i->node_next;
		i->node_next = new_node;
	}

	++my_queue->no_of_elements;    
	return my_queue;
}


/* Define a function to dequeue the first element from the priority
 * queue and return it
 */
void *dequeue(
	queue *my_queue
	)
{
	node *my_node = my_queue->front;

	if (my_node != NULL) {
		my_queue->front = my_node->node_next;
		--my_queue->no_of_elements;    
		return my_node + 1;
	} else
		return NULL;
}


/* Define a function that returns the number of elements in the 
 * priority queue
 */
int get_no_of_elements(
	queue *my_queue
	)
{
	return my_queue->no_of_elements;
}


/* Define a function to append a queue onto another.
 * Note: there is a faster way (O(1) as opposed to O(n))
 * to do this for simple (FIFO) queues, but we can't rely on
 * that for priority queues. (Given the current representation)
 * 
 * I don't anticipate this to be a problem. If it does turn
 * out to be a bottleneck, I will consider replacing the 
 * current implementation with a binomial or fibonacci heap.
 */
void append_queue(
	queue *q1,
	queue *q2
	) 
{
	while (!empty(q2))
		enqueue(q1, dequeue(q2));
	destroy_queue(q2);
}


/* FIFO Queue
 * ----------
 * Use the priority queue to create a traditional FIFO queue.
 * The only extra function needed is the create_queue 
 */

/* C is not Lisp and does not allow anonymous lambda functions :-(. 
 * So define a get_fifo_order function here
 */
int get_fifo_order(const void *el1, const void *el2)
{
	return 1;
}