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updraftcentral / js / queue.js

queue.js in UpdraftCentral Dashboard 0.8.30, at js/queue.js

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1	// @codingStandardsIgnoreStart
2	/*
3
4	Adapted and extended from the work of Stephen Morley - http://code.stephenmorley.org/javascript/queues/
5
6	Queue.js
7
8	A function to represent a queue
9
10	Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
11	the terms of the CC0 1.0 Universal legal code:
12
13	http://creativecommons.org/publicdomain/zero/1.0/legalcode
14
15	*/
16	// @codingStandardsIgnoreEnd
17	/**
18	* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
19	* items are added to the end of the queue and removed from the front.
20	*
21	* @returns {void}
22	*/
23	function UpdraftCentral_Queue() {
24
25	// initialise the queue and offset
26	var queue = [];
27	var offset = 0;
28	var locked = false;
29
30	/**
31	* Returns the length of the queue.
32	*
33	* @returns {number} - the length of the queue
34	*/
35	this.get_length = function() {
36	return (queue.length - offset);
37	}
38
39	/**
40	* Query whether the queue is empty or not
41	*
42	* @returns {boolean} - returns true if the queue is empty, and false otherwise.
43	*/
44	this.is_empty = function() {
45	return (queue.length == 0);
46	}
47
48	/**
49	* Enqueues the specified item. The parameter is:
50	*
51	* @param {*} item - the item to enqueue
52	* @returns {void}
53	*/
54	this.enqueue = function(item) {
55	queue.push(item);
56	}
57
58	/**
59	* Returns the queue lock status
60	*
61	* @returns {boolean} - whether the queue is locked or not
62	*/
63	this.is_locked = function() {
64	return locked;
65	}
66
67	/**
68	* Attempt to get the queue lock
69	*
70	* @returns {boolean} - whether the attempt succeeded or not
71	*/
72	this.get_lock = function() {
73	if (locked) { return false; }
74	this.lock();
75	return true;
76	}
77
78	/**
79	* Dequeues an item and returns it. If the queue is empty, the value
80	* 'undefined' is returned.
81	*
82	* @returns {*} - returns and removes the item at the front of the queue, or undefined if the queue is empty
83	*/
84	this.dequeue = function() {
85
86	// if the queue is empty, return immediately
87	if (queue.length == 0) return undefined;
88
89	// store the item at the front of the queue
90	var item = queue[offset];
91
92	// increment the offset and remove the free space if necessary
93	if (++ offset * 2 >= queue.length) {
94	queue = queue.slice(offset);
95	offset = 0;
96	}
97
98	// return the dequeued item
99	return item;
100
101	}
102
103	/**
104	* Lock the queue
105	*
106	* @returns {void}
107	*/
108	this.lock = function() {
109	locked = true;
110	}
111
112	/**
113	* Unlock the queue
114	*
115	* @returns {void}
116	*/
117	this.unlock = function() {
118	locked = false;
119	}
120
121	/**
122	* Returns the item at the front of the queue (without dequeuing it). If the
123	* queue is empty then undefined is returned.
124	*
125	* @returns {*} - returns the item at the front of the queue, or undefined if the queue is empty
126	*/
127	this.peek = function() {
128	return (queue.length > 0 ? queue[offset] : undefined);
129	}
130
131	/**
132	* Replaces the item at the front of the queue (if any)
133	*
134	* @param {*} item - the item to put at the front of the queue
135	*
136	* @returns {boolean} - whether or not the item was successfully replaced
137	*/
138	this.replace_front = function(item) {
139	if (queue.length < 1) { return false; }
140	queue[offset] = item;
141	return true;
142	}
143
144	}
145