parallel.js

import eachOf from './eachOf';
import parallel from './internal/parallel';

/**
 * Run the `tasks` collection of functions in parallel, without waiting until
 * the previous function has completed. If any of the functions pass an error to
 * its callback, the main `callback` is immediately called with the value of the
 * error. Once the `tasks` have completed, the results are passed to the final
 * `callback` as an array.
 *
 * **Note:** `parallel` is about kicking-off I/O tasks in parallel, not about
 * parallel execution of code.  If your tasks do not use any timers or perform
 * any I/O, they will actually be executed in series.  Any synchronous setup
 * sections for each task will happen one after the other.  JavaScript remains
 * single-threaded.
 *
 * It is also possible to use an object instead of an array. Each property will
 * be run as a function and the results will be passed to the final `callback`
 * as an object instead of an array. This can be a more readable way of handling
 * results from {@link async.parallel}.
 *
 * @name parallel
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @category Control Flow
 * @param {Array|Iterable|Object} tasks - A collection containing functions to run.
 * Each function is passed a `callback(err, result)` which it must call on
 * completion with an error `err` (which can be `null`) and an optional `result`
 * value.
 * @param {Function} [callback] - An optional callback to run once all the
 * functions have completed successfully. This function gets a results array
 * (or object) containing all the result arguments passed to the task callbacks.
 * Invoked with (err, results).
 * @example
 * async.parallel([
 *     function(callback) {
 *         setTimeout(function() {
 *             callback(null, 'one');
 *         }, 200);
 *     },
 *     function(callback) {
 *         setTimeout(function() {
 *             callback(null, 'two');
 *         }, 100);
 *     }
 * ],
 * // optional callback
 * function(err, results) {
 *     // the results array will equal ['one','two'] even though
 *     // the second function had a shorter timeout.
 * });
 *
 * // an example using an object instead of an array
 * async.parallel({
 *     one: function(callback) {
 *         setTimeout(function() {
 *             callback(null, 1);
 *         }, 200);
 *     },
 *     two: function(callback) {
 *         setTimeout(function() {
 *             callback(null, 2);
 *         }, 100);
 *     }
 * }, function(err, results) {
 *     // results is now equals to: {one: 1, two: 2}
 * });
 */
export default function parallelLimit(tasks, callback) {
    parallel(eachOf, tasks, callback);
}