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auto.js

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  • auto.js 11.58 KiB
    'use strict';
    
    Object.defineProperty(exports, "__esModule", {
        value: true
    });
    exports.default = auto;
    
    var _once = require('./internal/once.js');
    
    var _once2 = _interopRequireDefault(_once);
    
    var _onlyOnce = require('./internal/onlyOnce.js');
    
    var _onlyOnce2 = _interopRequireDefault(_onlyOnce);
    
    var _wrapAsync = require('./internal/wrapAsync.js');
    
    var _wrapAsync2 = _interopRequireDefault(_wrapAsync);
    
    var _promiseCallback = require('./internal/promiseCallback.js');
    
    function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
    
    /**
     * Determines the best order for running the {@link AsyncFunction}s in `tasks`, based on
     * their requirements. Each function can optionally depend on other functions
     * being completed first, and each function is run as soon as its requirements
     * are satisfied.
     *
     * If any of the {@link AsyncFunction}s pass an error to their callback, the `auto` sequence
     * will stop. Further tasks will not execute (so any other functions depending
     * on it will not run), and the main `callback` is immediately called with the
     * error.
     *
     * {@link AsyncFunction}s also receive an object containing the results of functions which
     * have completed so far as the first argument, if they have dependencies. If a
     * task function has no dependencies, it will only be passed a callback.
     *
     * @name auto
     * @static
     * @memberOf module:ControlFlow
     * @method
     * @category Control Flow
     * @param {Object} tasks - An object. Each of its properties is either a
     * function or an array of requirements, with the {@link AsyncFunction} itself the last item
     * in the array. The object's key of a property serves as the name of the task
     * defined by that property, i.e. can be used when specifying requirements for
     * other tasks. The function receives one or two arguments:
     * * a `results` object, containing the results of the previously executed
     *   functions, only passed if the task has any dependencies,
     * * a `callback(err, result)` function, which must be called when finished,
     *   passing an `error` (which can be `null`) and the result of the function's
     *   execution.
     * @param {number} [concurrency=Infinity] - An optional `integer` for
     * determining the maximum number of tasks that can be run in parallel. By
     * default, as many as possible.
     * @param {Function} [callback] - An optional callback which is called when all
     * the tasks have been completed. It receives the `err` argument if any `tasks`
     * pass an error to their callback. Results are always returned; however, if an
     * error occurs, no further `tasks` will be performed, and the results object
     * will only contain partial results. Invoked with (err, results).
     * @returns {Promise} a promise, if a callback is not passed
     * @example
     *
     * //Using Callbacks
     * async.auto({
     *     get_data: function(callback) {
     *         // async code to get some data
     *         callback(null, 'data', 'converted to array');
     *     },
     *     make_folder: function(callback) {
     *         // async code to create a directory to store a file in
     *         // this is run at the same time as getting the data
     *         callback(null, 'folder');
     *     },
     *     write_file: ['get_data', 'make_folder', function(results, callback) {
     *         // once there is some data and the directory exists,
     *         // write the data to a file in the directory
     *         callback(null, 'filename');
     *     }],
     *     email_link: ['write_file', function(results, callback) {
     *         // once the file is written let's email a link to it...
     *         callback(null, {'file':results.write_file, 'email':'user@example.com'});
     *     }]
     * }, function(err, results) {
     *     if (err) {
     *         console.log('err = ', err);
     *     }
     *     console.log('results = ', results);
     *     // results = {
     *     //     get_data: ['data', 'converted to array']
     *     //     make_folder; 'folder',
     *     //     write_file: 'filename'
     *     //     email_link: { file: 'filename', email: 'user@example.com' }
     *     // }
     * });
     *
     * //Using Promises
     * async.auto({
     *     get_data: function(callback) {
     *         console.log('in get_data');
     *         // async code to get some data
     *         callback(null, 'data', 'converted to array');
     *     },
     *     make_folder: function(callback) {
     *         console.log('in make_folder');
     *         // async code to create a directory to store a file in
     *         // this is run at the same time as getting the data
     *         callback(null, 'folder');
     *     },
     *     write_file: ['get_data', 'make_folder', function(results, callback) {
     *         // once there is some data and the directory exists,
     *         // write the data to a file in the directory
     *         callback(null, 'filename');
     *     }],
     *     email_link: ['write_file', function(results, callback) {
     *         // once the file is written let's email a link to it...
     *         callback(null, {'file':results.write_file, 'email':'user@example.com'});
     *     }]
     * }).then(results => {
     *     console.log('results = ', results);
     *     // results = {
     *     //     get_data: ['data', 'converted to array']
     *     //     make_folder; 'folder',
     *     //     write_file: 'filename'
     *     //     email_link: { file: 'filename', email: 'user@example.com' }
     *     // }
     * }).catch(err => {
     *     console.log('err = ', err);
     * });
     *
     * //Using async/await
     * async () => {
     *     try {
     *         let results = await async.auto({
     *             get_data: function(callback) {
     *                 // async code to get some data
     *                 callback(null, 'data', 'converted to array');
     *             },
     *             make_folder: function(callback) {
     *                 // async code to create a directory to store a file in
     *                 // this is run at the same time as getting the data
     *                 callback(null, 'folder');
     *             },
     *             write_file: ['get_data', 'make_folder', function(results, callback) {
     *                 // once there is some data and the directory exists,
     *                 // write the data to a file in the directory
     *                 callback(null, 'filename');
     *             }],
     *             email_link: ['write_file', function(results, callback) {
     *                 // once the file is written let's email a link to it...
     *                 callback(null, {'file':results.write_file, 'email':'user@example.com'});
     *             }]
     *         });
     *         console.log('results = ', results);
     *         // results = {
     *         //     get_data: ['data', 'converted to array']
     *         //     make_folder; 'folder',
     *         //     write_file: 'filename'
     *         //     email_link: { file: 'filename', email: 'user@example.com' }
     *         // }
     *     }
     *     catch (err) {
     *         console.log(err);
     *     }
     * }
     *
     */
    function auto(tasks, concurrency, callback) {
        if (typeof concurrency !== 'number') {
            // concurrency is optional, shift the args.
            callback = concurrency;
            concurrency = null;
        }
        callback = (0, _once2.default)(callback || (0, _promiseCallback.promiseCallback)());
        var numTasks = Object.keys(tasks).length;
        if (!numTasks) {
            return callback(null);
        }
        if (!concurrency) {
            concurrency = numTasks;
        }
    
        var results = {};
        var runningTasks = 0;
        var canceled = false;
        var hasError = false;
    
        var listeners = Object.create(null);
    
        var readyTasks = [];
    
        // for cycle detection:
        var readyToCheck = []; // tasks that have been identified as reachable
        // without the possibility of returning to an ancestor task
        var uncheckedDependencies = {};
    
        Object.keys(tasks).forEach(key => {
            var task = tasks[key];
            if (!Array.isArray(task)) {
                // no dependencies
                enqueueTask(key, [task]);
                readyToCheck.push(key);
                return;
            }
    
            var dependencies = task.slice(0, task.length - 1);
            var remainingDependencies = dependencies.length;
            if (remainingDependencies === 0) {
                enqueueTask(key, task);
                readyToCheck.push(key);
                return;
            }
            uncheckedDependencies[key] = remainingDependencies;
    
            dependencies.forEach(dependencyName => {
                if (!tasks[dependencyName]) {
                    throw new Error('async.auto task `' + key + '` has a non-existent dependency `' + dependencyName + '` in ' + dependencies.join(', '));
                }
                addListener(dependencyName, () => {
                    remainingDependencies--;
                    if (remainingDependencies === 0) {
                        enqueueTask(key, task);
                    }
                });
            });
        });
    
        checkForDeadlocks();
        processQueue();
    
        function enqueueTask(key, task) {
            readyTasks.push(() => runTask(key, task));
        }
    
        function processQueue() {
            if (canceled) return;
            if (readyTasks.length === 0 && runningTasks === 0) {
                return callback(null, results);
            }
            while (readyTasks.length && runningTasks < concurrency) {
                var run = readyTasks.shift();
                run();
            }
        }
    
        function addListener(taskName, fn) {
            var taskListeners = listeners[taskName];
            if (!taskListeners) {
                taskListeners = listeners[taskName] = [];
            }
    
            taskListeners.push(fn);
        }
    
        function taskComplete(taskName) {
            var taskListeners = listeners[taskName] || [];
            taskListeners.forEach(fn => fn());
            processQueue();
        }
    
        function runTask(key, task) {
            if (hasError) return;
    
            var taskCallback = (0, _onlyOnce2.default)((err, ...result) => {
                runningTasks--;
                if (err === false) {
                    canceled = true;
                    return;
                }
                if (result.length < 2) {
                    [result] = result;
                }
                if (err) {
                    var safeResults = {};
                    Object.keys(results).forEach(rkey => {
                        safeResults[rkey] = results[rkey];
                    });
                    safeResults[key] = result;
                    hasError = true;
                    listeners = Object.create(null);
                    if (canceled) return;
                    callback(err, safeResults);
                } else {
                    results[key] = result;
                    taskComplete(key);
                }
            });
    
            runningTasks++;
            var taskFn = (0, _wrapAsync2.default)(task[task.length - 1]);
            if (task.length > 1) {
                taskFn(results, taskCallback);
            } else {
                taskFn(taskCallback);
            }
        }
    
        function checkForDeadlocks() {
            // Kahn's algorithm
            // https://en.wikipedia.org/wiki/Topological_sorting#Kahn.27s_algorithm
            // http://connalle.blogspot.com/2013/10/topological-sortingkahn-algorithm.html
            var currentTask;
            var counter = 0;
            while (readyToCheck.length) {
                currentTask = readyToCheck.pop();
                counter++;
                getDependents(currentTask).forEach(dependent => {
                    if (--uncheckedDependencies[dependent] === 0) {
                        readyToCheck.push(dependent);
                    }
                });
            }
    
            if (counter !== numTasks) {
                throw new Error('async.auto cannot execute tasks due to a recursive dependency');
            }
        }
    
        function getDependents(taskName) {
            var result = [];
            Object.keys(tasks).forEach(key => {
                const task = tasks[key];
                if (Array.isArray(task) && task.indexOf(taskName) >= 0) {
                    result.push(key);
                }
            });
            return result;
        }
    
        return callback[_promiseCallback.PROMISE_SYMBOL];
    }
    module.exports = exports.default;