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import queue from './internal/queue';
/**
* A queue of tasks for the worker function to complete.
* @typedef {Object} 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 {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} saturated - a callback that is called when the number of
* running workers hits the `concurrency` limit, and further tasks will be
* queued.
* @property {Function} unsaturated - 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.
* @property {number} buffer - A minimum threshold buffer in order to say that
* the `queue` is `unsaturated`.
* @property {Function} empty - a callback that is called when the last item
* from the `queue` is given to a `worker`.
* @property {Function} drain - a callback that is called when the last item
* from the `queue` has returned from the `worker`.
* @property {Function} error - a callback that is called when a task errors.
* Has the signature `function(error, task)`.
* @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
6F1E
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. Invoke with `queue.kill()`.
*/
/**
* 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 {Function} worker - An asynchronous function for processing a queued
* task, which must call its `callback(err)` argument when finished, with an
* optional `error` as an argument. 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
* 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');
* };
*
* // add some items to the queue
* q.push({name: 'foo'}, function(err) {
* console.log('finished processing foo');
* });
* q.push({name: 'bar'}, function (err) {
* console.log('finished processing 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) {
return queue(function (items, cb) {
worker(items[0], cb);
}, concurrency, 1);
}