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/**
Adapted and extended from the work of Stephen Morley - http://code.stephenmorley.org/javascript/queues/
Queue.js
A function to represent a queue
Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
the terms of the CC0 1.0 Universal legal code:
http://creativecommons.org/publicdomain/zero/1.0/legalcode
*/
/**
* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
* items are added to the end of the queue and removed from the front.
*
* @return {void}
*/
function Updraft_Queue() {
// Initialise the queue and offset.
var queue = [];
var offset = 0;
var locked = false;
/**
* Returns the length of the queue.
*
* @returns {number} - the length of the queue
*/
this.get_length = function () {
return (queue.length - offset);
}
/**
* Query whether the queue is empty or not
*
* @returns {boolean} - returns true if the queue is empty, and false otherwise.
*/
this.is_empty = function () {
return (queue.length == 0);
}
/**
* Enqueues the specified item. The parameter is:
*
* @param {*} item The item to enqueue
*
* @return {void}
*/
this.enqueue = function (item) {
queue.push(item);
}
/**
* Returns the queue lock status
*
* @returns {boolean} - whether the queue is locked or not
*/
this.is_locked = function () {
return locked;
}
/**
* Attempt to get the queue lock
*
* @returns {boolean} - whether the attempt succeeded or not
*/
this.get_lock = function () {
if (locked) { return false; }
this.lock();
return true;
}
/**
* Dequeues an item and returns it. If the queue is empty, the value
* 'undefined' is returned.
*
* @returns {*} - returns and removes the item at the front of the queue, or undefined if the queue is empty
*/
this.dequeue = function () {
// If the queue is empty, return immediately.
if (queue.length == 0) return undefined;
// Store the item at the front of the queue.
var item = queue[offset];
// Increment the offset and remove the free space if necessary.
if ((++offset * 2) >= queue.length) {
queue = queue.slice(offset);
offset = 0;
}
// Return the dequeued item.
return item;
}
/**
* Lock the queue
*
* @returns {void}
*/
this.lock = function () {
locked = true;
}
/**
* Unlock the queue
*
* @returns {void}
*/
this.unlock = function () {
locked = false;
}
/**
* Returns the item at the front of the queue (without dequeuing it). If the
* queue is empty then undefined is returned.
*
* @returns {*} - returns the item at the front of the queue, or undefined if the queue is empty
*/
this.peek = function () {
return (queue.length > 0 ? queue[offset] : undefined);
}
/**
* Replaces the item at the front of the queue (if any)
*
* @param {*} item The item to put at the front of the queue.
*
* @return {boolean} Whether or not the item was successfully replaced.
*/
this.replace_front = function (item) {
if (queue.length < 1) { return false; }
queue[offset] = item;
return true;
}
}