45 lines
1.8 KiB
JavaScript
45 lines
1.8 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.Lock = void 0;
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// Based on https://github.com/jsoendermann/semaphore-async-await/blob/master/src/Semaphore.ts
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class Lock {
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constructor() {
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this.permits = 1;
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this.promiseResolverQueue = [];
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}
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/**
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* Returns a promise used to wait for a permit to become available. This method should be awaited on.
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* @returns A promise that gets resolved when execution is allowed to proceed.
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*/
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async acquire() {
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if (this.permits > 0) {
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this.permits -= 1;
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return Promise.resolve(true);
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}
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// If there is no permit available, we return a promise that resolves once the semaphore gets
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// signaled enough times that permits is equal to one.
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return new Promise((resolver) => this.promiseResolverQueue.push(resolver));
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}
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/**
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* Increases the number of permits by one. If there are other functions waiting, one of them will
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* continue to execute in a future iteration of the event loop.
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*/
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release() {
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this.permits += 1;
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if (this.permits > 1 && this.promiseResolverQueue.length > 0) {
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// eslint-disable-next-line no-console
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console.warn('Lock.permits should never be > 0 when there is someone waiting.');
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}
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else if (this.permits === 1 && this.promiseResolverQueue.length > 0) {
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// If there is someone else waiting, immediately consume the permit that was released
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// at the beginning of this function and let the waiting function resume.
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this.permits -= 1;
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const nextResolver = this.promiseResolverQueue.shift();
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if (nextResolver) {
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nextResolver(true);
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}
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}
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}
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}
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exports.Lock = Lock;
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//# sourceMappingURL=lock.js.map
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