source: trip-planner-front/node_modules/webpack/lib/util/Semaphore.js

/*
        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;