/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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/**
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* Simple counting semaphore used to limit how many asynchronous tasks may run
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* concurrently.
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*/
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class Semaphore {
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/**
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* Initializes the semaphore with the number of permits that may be held at
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* the same time.
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* @param {number} available the amount available number of "tasks"
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* in the Semaphore
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*/
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constructor(available) {
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this.available = available;
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/** @type {(() => void)[]} */
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this.waiters = [];
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/** @private */
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this._continue = this._continue.bind(this);
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}
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/**
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* Acquires a permit for the callback immediately when one is available or
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* queues the callback until another task releases its permit.
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* @param {() => void} callback function block to capture and run
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* @returns {void}
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*/
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acquire(callback) {
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if (this.available > 0) {
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this.available--;
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callback();
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} else {
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this.waiters.push(callback);
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}
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}
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/**
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* Releases a permit and schedules the next waiting callback, if any.
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*/
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release() {
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this.available++;
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if (this.waiters.length > 0) {
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process.nextTick(this._continue);
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}
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}
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/**
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* Drains the next waiting callback after a permit becomes available.
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*/
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_continue() {
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if (this.available > 0 && this.waiters.length > 0) {
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this.available--;
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const callback = /** @type {(() => void)} */ (this.waiters.pop());
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callback();
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}
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}
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}
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module.exports = Semaphore;
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