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<h1 class="page-title">auto.js</h1>
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<article>
<pre class="prettyprint source linenums"><code>import once from './internal/once.js'
import onlyOnce from './internal/onlyOnce.js'
import wrapAsync from './internal/wrapAsync.js'
import { promiseCallback, PROMISE_SYMBOL } from './internal/promiseCallback.js'
/**
* 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);
* }
* }
*
*/
export default function auto(tasks, concurrency, callback) {
if (typeof concurrency !== 'number') {
// concurrency is optional, shift the args.
callback = concurrency;
concurrency = null;
}
callback = once(callback || 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 = onlyOnce((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 = wrapAsync(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[PROMISE_SYMBOL]
}
</code></pre>
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<h3>Methods:</h3><ul class="nav methods"><li class="toc-header"><a href="docs.html#collections">Collections</a></li><li data-type="method" class="toc-method"><a href="docs.html#concat">concat</a></li><li data-type="method" class="toc-method"><a href="docs.html#concatLimit">concatLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#concatSeries">concatSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#detect">detect</a></li><li data-type="method" class="toc-method"><a href="docs.html#detectLimit">detectLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#detectSeries">detectSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#each">each</a></li><li data-type="method" class="toc-method"><a href="docs.html#eachLimit">eachLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#eachOf">eachOf</a></li><li data-type="method" class="toc-method"><a href="docs.html#eachOfLimit">eachOfLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#eachOfSeries">eachOfSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#eachSeries">eachSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#every">every</a></li><li data-type="method" class="toc-method"><a href="docs.html#everyLimit">everyLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#everySeries">everySeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#filter">filter</a></li><li data-type="method" class="toc-method"><a href="docs.html#filterLimit">filterLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#filterSeries">filterSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#groupBy">groupBy</a></li><li data-type="method" class="toc-method"><a href="docs.html#groupByLimit">groupByLimit</a></li><li data-type="method" 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data-type="method" class="toc-method"><a href="docs.html#rejectSeries">rejectSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#some">some</a></li><li data-type="method" class="toc-method"><a href="docs.html#someLimit">someLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#someSeries">someSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#sortBy">sortBy</a></li><li data-type="method" class="toc-method"><a href="docs.html#transform">transform</a></li><li class="toc-header"><a href="docs.html#controlflow">Control Flow</a></li><li data-type="method" class="toc-method"><a href="docs.html#applyEach">applyEach</a></li><li data-type="method" class="toc-method"><a href="docs.html#applyEachSeries">applyEachSeries</a></li><li data-type="method" class="toc-method active"><a href="docs.html#auto">auto</a></li><li data-type="method" class="toc-method"><a href="docs.html#autoInject">autoInject</a></li><li data-type="method" class="toc-method"><a href="docs.html#cargo">cargo</a></li><li data-type="method" class="toc-method"><a href="docs.html#cargoQueue">cargoQueue</a></li><li data-type="method" class="toc-method"><a href="docs.html#compose">compose</a></li><li data-type="method" class="toc-method"><a href="docs.html#doUntil">doUntil</a></li><li data-type="method" class="toc-method"><a href="docs.html#doWhilst">doWhilst</a></li><li data-type="method" class="toc-method"><a href="docs.html#forever">forever</a></li><li data-type="method" class="toc-method"><a href="docs.html#parallel">parallel</a></li><li data-type="method" class="toc-method"><a href="docs.html#parallelLimit">parallelLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#priorityQueue">priorityQueue</a></li><li data-type="method" class="toc-method"><a href="docs.html#queue">queue</a></li><li data-type="method" class="toc-method"><a href="docs.html#race">race</a></li><li data-type="method" class="toc-method"><a href="docs.html#retry">retry</a></li><li data-type="method" class="toc-method"><a href="docs.html#retryable">retryable</a></li><li data-type="method" class="toc-method"><a href="docs.html#seq">seq</a></li><li data-type="method" class="toc-method"><a href="docs.html#series">series</a></li><li data-type="method" class="toc-method"><a href="docs.html#times">times</a></li><li data-type="method" class="toc-method"><a href="docs.html#timesLimit">timesLimit</a></li><li data-type="method" class="toc-method"><a href="docs.html#timesSeries">timesSeries</a></li><li data-type="method" class="toc-method"><a href="docs.html#tryEach">tryEach</a></li><li data-type="method" class="toc-method"><a href="docs.html#until">until</a></li><li data-type="method" class="toc-method"><a href="docs.html#waterfall">waterfall</a></li><li data-type="method" class="toc-method"><a href="docs.html#whilst">whilst</a></li><li class="toc-header"><a href="docs.html#utils">Utils</a></li><li data-type="method" class="toc-method"><a href="docs.html#apply">apply</a></li><li data-type="method" class="toc-method"><a href="docs.html#asyncify">asyncify</a></li><li data-type="method" class="toc-method"><a href="docs.html#constant">constant</a></li><li data-type="method" class="toc-method"><a href="docs.html#dir">dir</a></li><li data-type="method" class="toc-method"><a href="docs.html#ensureAsync">ensureAsync</a></li><li data-type="method" class="toc-method"><a href="docs.html#log">log</a></li><li data-type="method" class="toc-method"><a href="docs.html#memoize">memoize</a></li><li data-type="method" class="toc-method"><a href="docs.html#nextTick">nextTick</a></li><li data-type="method" class="toc-method"><a href="docs.html#reflect">reflect</a></li><li data-type="method" class="toc-method"><a href="docs.html#reflectAll">reflectAll</a></li><li data-type="method" class="toc-method"><a href="docs.html#setImmediate">setImmediate</a></li><li data-type="method" class="toc-method"><a href="docs.html#timeout">timeout</a></li><li data-type="method" class="toc-method"><a href="docs.html#unmemoize">unmemoize</a></li></ul><h3>Methods:</h3>
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