51 lines
1.3 KiB
Plaintext
51 lines
1.3 KiB
Plaintext
/**
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* @flow
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*/
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import ncp from 'ncp';
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export function ncpAsync(source: string, dest: string, options: any = {}) {
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return new Promise((resolve, reject) => {
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ncp(source, dest, options, err => {
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if (err) {
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reject(err);
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} else {
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resolve();
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}
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});
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});
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}
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export class Semaphore {
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queue: Array<(v: boolean) => void> = [];
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available = 1;
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async acquire(): Promise<boolean> {
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if (this.available > 0) {
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this.available -= 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 "available" is equal to one.
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return new Promise(resolver => this.queue.push(resolver));
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}
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release() {
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this.available += 1;
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if (this.available > 1 && this.queue.length > 0) {
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throw new Error('this.available should never be > 0 when there is someone waiting.');
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} else if (this.available === 1 && this.queue.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.available -= 1;
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const nextResolver = this.queue.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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