blob: 107287f3b5ecf9fe4c495c1297bd5791a38470f0 (
about) (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
|
/**
* Myext lock (aka binary semaphore aka mutex)
*
* Copyright (C) 2021 Wojtek Kosior
*
* Dual-licensed under:
* - 0BSD license
* - GPLv3 or (at your option) any later version
*/
/*
* Javascript runs single-threaded, with an event loop. Because of that,
* explicit synchronization is often not needed. An exception is when we use
* an API function that must wait. Ajax is an example. Callback passed to ajax
* call doesn't get called immediately, but after some time. In the meantime
* some other piece of code might get to execute and modify some variables.
* Access to WebExtension local storage is another situation where this problem
* can occur.
*
* This is a solution. A lock object, that can be used to delay execution of
* some code until other code finishes its critical work. Locking is wrapped
* in a promise.
*/
"use strict";
(() => {
function make_lock() {
return {free: true, queue: []};
}
function _lock(lock, cb) {
if (lock.free) {
lock.free = false;
setTimeout(cb);
} else {
lock.queue.push(cb);
}
}
function lock(lock) {
return new Promise((resolve, reject) => _lock(lock, resolve));
}
function unlock(lock) {
if (lock.free)
throw new Exception("Attempting to release a free lock");
if (lock.queue.length === 0) {
lock.free = true;
} else {
let cb = lock.queue[0];
lock.queue.splice(0, 1);
setTimeout(cb);
}
}
window.make_lock = make_lock;
window.lock = lock;
window.unlock = unlock;
})();
|
