webpack/lib/util/processAsyncTree.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

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

"use strict";

/**
 * @template T
 * @template {Error} E
 * @param {Iterable<T>} items initial items
 * @param {number} concurrency number of items running in parallel
 * @param {function(T, function(T): void, function(E=): void): void} processor worker which pushes more items
 * @param {function(E=): void} callback all items processed
 * @returns {void}
 */
const processAsyncTree = (items, concurrency, processor, callback) => {
	const queue = Array.from(items);
	if (queue.length === 0) return callback();
	let processing = 0;
	let finished = false;
	let processScheduled = true;

	const push = item => {
		queue.push(item);
		if (!processScheduled && processing < concurrency) {
			processScheduled = true;
			process.nextTick(processQueue);
		}
	};

	const processorCallback = err => {
		processing--;
		if (err && !finished) {
			finished = true;
			callback(err);
			return;
		}
		if (!processScheduled) {
			processScheduled = true;
			process.nextTick(processQueue);
		}
	};

	const processQueue = () => {
		if (finished) return;
		while (processing < concurrency && queue.length > 0) {
			processing++;
			const item = queue.pop();
			processor(item, push, processorCallback);
		}
		processScheduled = false;
		if (queue.length === 0 && processing === 0 && !finished) {
			finished = true;
			callback();
		}
	};

	processQueue();
};

module.exports = processAsyncTree;