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updraftcentral / js / queue.js

queue.js in UpdraftCentral Dashboard 0.6.0, at js/queue.js

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1	/*
2
3	Adapted and extended from the work of Stephen Morley - http://code.stephenmorley.org/javascript/queues/
4
5	Queue.js
6
7	A function to represent a queue
8
9	Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
10	the terms of the CC0 1.0 Universal legal code:
11
12	http://creativecommons.org/publicdomain/zero/1.0/legalcode
13
14	*/
15
16	/**
17	* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
18	* items are added to the end of the queue and removed from the front.
19	* @returns {void}
20	*/
21	function UpdraftCentral_Queue() {
22
23	// initialise the queue and offset
24	var queue = [];
25	var offset = 0;
26	var locked = false;
27
28	/**
29	* Returns the length of the queue.
30	*
31	* @returns {number} - the length of the queue
32	*/
33	this.get_length = function() {
34	return (queue.length - offset);
35	}
36
37	/**
38	* Query whether the queue is empty or not
39	*
40	* @returns {boolean} - returns true if the queue is empty, and false otherwise.
41	*/
42	this.is_empty = function() {
43	return (queue.length == 0);
44	}
45
46	/**
47	*
48	* Enqueues the specified item. The parameter is:
49	*
50	* @param {*} item - the item to enqueue
51	* @returns {void}
52	*/
53	this.enqueue = function(item) {
54	queue.push(item);
55	}
56
57	/**
58	* Returns the queue lock status
59	*
60	* @returns {boolean} - whether the queue is locked or not
61	*/
62	this.is_locked = function() {
63	return locked;
64	}
65
66	/**
67	* Attempt to get the queue lock
68	*
69	* @returns {boolean} - whether the attempt succeeded or not
70	*/
71	this.get_lock = function() {
72	if (locked) { return false; }
73	this.lock();
74	return true;
75	}
76
77	/**
78	* Dequeues an item and returns it. If the queue is empty, the value
79	* 'undefined' is returned.
80	*
81	* @returns {*} - returns and removes the item at the front of the queue, or undefined if the queue is empty
82	*/
83	this.dequeue = function() {
84
85	// if the queue is empty, return immediately
86	if (queue.length == 0) return undefined;
87
88	// store the item at the front of the queue
89	var item = queue[offset];
90
91	// increment the offset and remove the free space if necessary
92	if (++ offset * 2 >= queue.length) {
93	queue = queue.slice(offset);
94	offset = 0;
95	}
96
97	// return the dequeued item
98	return item;
99
100	}
101
102	/**
103	* Lock the queue
104	* @returns {void}
105	*/
106	this.lock = function() {
107	locked = true;
108	}
109
110	/**
111	* Unlock the queue
112	* @returns {void}
113	*/
114	this.unlock = function() {
115	locked = false;
116	}
117
118	/**
119	* Returns the item at the front of the queue (without dequeuing it). If the
120	* queue is empty then undefined is returned.
121	*
122	* @returns {*} - returns the item at the front of the queue, or undefined if the queue is empty
123	*/
124	this.peek = function() {
125	return (queue.length > 0 ? queue[offset] : undefined);
126	}
127
128	/**
129	* Replaces the item at the front of the queue (if any)
130	*
131	* @param {*} item - the item to put at the front of the queue
132	*
133	* @returns {boolean} - whether or not the item was successfully replaced
134	*/
135	this.replace_front = function(item) {
136	if (queue.length < 1) { return false; }
137	queue[offset] = item;
138	return true;
139	}
140
141	}
142