queue.js

import queue from './internal/queue';
import wrapAsync from './internal/wrapAsync';

/**
 * 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 {Function} 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 {Function} unshift - add a new task to the front of the `queue`.
 * Invoke with `queue.unshift(task, [callback])`.
 * @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 = aync.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);
}