Semaphore.js
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	/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
	*/

	"use strict";

	class Semaphore {
	/**
	* Creates an instance of Semaphore.
	*
	* @param {number} available the amount available number of "tasks"
	* in the Semaphore
	*/
	constructor(available) {
	this.available = available;
	/** @type {(function(): void)[]} */
	this.waiters = [];
	/** @private */
	this._continue = this._continue.bind(this);
	}

	/**
	* @param {function(): void} callback function block to capture and run
	* @returns {void}
	*/
	acquire(callback) {
	if (this.available > 0) {
	this.available--;
	callback();
	} else {
	this.waiters.push(callback);
	}
	}

	release() {
	this.available++;
	if (this.waiters.length > 0) {
	process.nextTick(this._continue);
	}
	}

	_continue() {
	if (this.available > 0) {
	if (this.waiters.length > 0) {
	this.available--;
	const callback = this.waiters.pop();
	callback();
	}
	}
	}
	}

	module.exports = Semaphore;