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/**
* @file
*
* This file is a copy of queue.h from NSA's CVS repository. It has
* been modified to follow the setools naming conventions.
*
* Author : Stephen Smalley, <sds@epoch.ncsc.mil>
*
* A double-ended queue is a singly linked list of
* elements of arbitrary type that may be accessed
* at either end.
*/
#ifndef APOL_QUEUE_H
#define APOL_QUEUE_H
typedef struct apol_queue_node
{
void *element;
struct apol_queue_node *next;
} apol_queue_node_t;
typedef struct apol_queue
{
apol_queue_node_t *head;
apol_queue_node_t *tail;
} apol_queue_t;
/**
* Allocate and return a new queue. The caller is responsible for
* calling apol_queue_destroy() upon the return value.
*
* @return A newly allocated queue, or NULL upon error.
*/
apol_queue_t *apol_queue_create(void);
/**
* Adds an element to the end of a queue.
*
* @param q Queue to modify.
* @param element Element to append to the end.
*
* @return 0 on success, < 0 on error.
*/
int apol_queue_insert(apol_queue_t * q, void *element);
/**
* Adds an element to the beginning of a queue.
*
* @param q Queue to modify.
* @param element Element to prepend to the beginning.
*
* @return 0 on success, < 0 on error.
*/
int apol_queue_push(apol_queue_t * q, void *element);
/**
* Remove the first element from a queue and return the data; the
* queue is advanced afterwards. If the queue was empty then return
* NULL.
*
* @return First element of a queue, or NULL if nothing is there.
*/
void *apol_queue_remove(apol_queue_t * q);
/**
* Return the data within the first element, but do not remove it from
* the queue. If the queue was empty then return NULL.
*
* @return First element of a queue, or NULL if nothing is there.
*/
void *apol_queue_head(apol_queue_t * q);
/**
* Destroy the referenced queue, but <i>do not</i> attempt to free the
* data stored within. (The caller is responsible for doing that.)
* Afterwards set the referenced variable to NULL. If the variable is
* NULL then do nothing.
*
* @param Reference to a queue to destroy.
*/
void apol_queue_destroy(apol_queue_t ** q);
#endif
/* FLASK */
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