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<!DOCTYPE html>
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<h1 class="page-title">queue.js</h1>
<section>
<article>
<pre class="prettyprint source linenums"><code>import queue from './internal/queue.js'
import wrapAsync from './internal/wrapAsync.js'
/**
* A queue of tasks for the worker function to complete.
* @typedef {Iterable} QueueObject
* @memberOf module:ControlFlow
* @property {Function} length - a function returning the number of items
* waiting to be processed. Invoke with `queue.length()`.
* @property {boolean} started - a boolean indicating whether or not any
* items have been pushed and processed by the queue.
* @property {Function} running - a function returning the number of items
* currently being processed. Invoke with `queue.running()`.
* @property {Function} workersList - a function returning the array of items
* currently being processed. Invoke with `queue.workersList()`.
* @property {Function} idle - a function returning false if there are items
* waiting or being processed, or true if not. Invoke with `queue.idle()`.
* @property {number} concurrency - an integer for determining how many `worker`
* functions should be run in parallel. This property can be changed after a
* `queue` is created to alter the concurrency on-the-fly.
* @property {number} payload - an integer that specifies how many items are
* passed to the worker function at a time. only applies if this is a
* [cargo]{@link module:ControlFlow.cargo} object
* @property {AsyncFunction} push - add a new task to the `queue`. Calls `callback`
* once the `worker` has finished processing the task. Instead of a single task,
* a `tasks` array can be submitted. The respective callback is used for every
* task in the list. Invoke with `queue.push(task, [callback])`,
* @property {AsyncFunction} unshift - add a new task to the front of the `queue`.
* Invoke with `queue.unshift(task, [callback])`.
* @property {AsyncFunction} pushAsync - the same as `q.push`, except this returns
* a promise that rejects if an error occurs.
* @property {AsyncFunction} unshiftAsync - the same as `q.unshift`, except this returns
* a promise that rejects if an error occurs.
* @property {Function} remove - remove items from the queue that match a test
* function. The test function will be passed an object with a `data` property,
* and a `priority` property, if this is a
* [priorityQueue]{@link module:ControlFlow.priorityQueue} object.
* Invoked with `queue.remove(testFn)`, where `testFn` is of the form
* `function ({data, priority}) {}` and returns a Boolean.
* @property {Function} saturated - a function that sets a callback that is
* called when the number of running workers hits the `concurrency` limit, and
* further tasks will be queued. If the callback is omitted, `q.saturated()`
* returns a promise for the next occurrence.
* @property {Function} unsaturated - a function that sets a callback that is
* called when the number of running workers is less than the `concurrency` &
* `buffer` limits, and further tasks will not be queued. If the callback is
* omitted, `q.unsaturated()` returns a promise for the next occurrence.
* @property {number} buffer - A minimum threshold buffer in order to say that
* the `queue` is `unsaturated`.
* @property {Function} empty - a function that sets a callback that is called
* when the last item from the `queue` is given to a `worker`. If the callback
* is omitted, `q.empty()` returns a promise for the next occurrence.
* @property {Function} drain - a function that sets a callback that is called
* when the last item from the `queue` has returned from the `worker`. If the
* callback is omitted, `q.drain()` returns a promise for the next occurrence.
* @property {Function} error - a function that sets a callback that is called
* when a task errors. Has the signature `function(error, task)`. If the
* callback is omitted, `error()` returns a promise that rejects on the next
* error.
* @property {boolean} paused - a boolean for determining whether the queue is
* in a paused state.
* @property {Function} pause - a function that pauses the processing of tasks
* until `resume()` is called. Invoke with `queue.pause()`.
* @property {Function} resume - a function that resumes the processing of
* queued tasks when the queue is paused. Invoke with `queue.resume()`.
* @property {Function} kill - a function that removes the `drain` callback and
* empties remaining tasks from the queue forcing it to go idle. No more tasks
* should be pushed to the queue after calling this function. Invoke with `queue.kill()`.
*
* @example
* const q = async.queue(worker, 2)
* q.push(item1)
* q.push(item2)
* q.push(item3)
* // queues are iterable, spread into an array to inspect
* const items = [...q] // [item1, item2, item3]
* // or use for of
* for (let item of q) {
* console.log(item)
* }
*
* q.drain(() => {
* console.log('all done')
* })
* // or
* await q.drain()
*/
/**
* Creates a `queue` object with the specified `concurrency`. Tasks added to the
* `queue` are processed in parallel (up to the `concurrency` limit). If all
* `worker`s are in progress, the task is queued until one becomes available.
* Once a `worker` completes a `task`, that `task`'s callback is called.
*
* @name queue
* @static
* @memberOf module:ControlFlow
* @method
* @category Control Flow
* @param {AsyncFunction} worker - An async function for processing a queued task.
* If you want to handle errors from an individual task, pass a callback to
* `q.push()`. Invoked with (task, callback).
* @param {number} [concurrency=1] - An `integer` for determining how many
* `worker` functions should be run in parallel. If omitted, the concurrency
* defaults to `1`. If the concurrency is `0`, an error is thrown.
* @returns {module:ControlFlow.QueueObject} A queue object to manage the tasks. Callbacks can be
* attached as certain properties to listen for specific events during the
* lifecycle of the queue.
* @example
*
* // create a queue object with concurrency 2
* var q = async.queue(function(task, callback) {
* console.log('hello ' + task.name);
* callback();
* }, 2);
*
* // assign a callback
* q.drain(function() {
* console.log('all items have been processed');
* });
* // or await the end
* await q.drain()
*
* // assign an error callback
* q.error(function(err, task) {
* console.error('task experienced an error');
* });
*
* // add some items to the queue
* q.push({name: 'foo'}, function(err) {
* console.log('finished processing foo');
* });
* // callback is optional
* q.push({name: 'bar'});
*
* // add some items to the queue (batch-wise)
* q.push([{name: 'baz'},{name: 'bay'},{name: 'bax'}], function(err) {
* console.log('finished processing item');
* });
*
* // add some items to the front of the queue
* q.unshift({name: 'bar'}, function (err) {
* console.log('finished processing bar');
* });
*/
export default function (worker, concurrency) {
var _worker = wrapAsync(worker);
return queue((items, cb) => {
_worker(items[0], cb);
}, concurrency, 1);
}
</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 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