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