breeze-queue

Throttled parallel function invocation.

Installation

Node.js

breeze-queue is available on npm.

$ npm install breeze-queue

Component

breeze-queue is available as a component.

$ component install qualiancy/breeze-queue

Usage

Queue (iterator, concurrency)

• @param {Function} iterator
• @param {Number} concurrency (defaults to 10)
• @return {Object} queue api

The queue mechanism allows for a any number of data objects to be processed by an iterator when they become available. The queue will processes items in parellel, up to a given concurrently value, then will wait until an item has finished until beginning to process the next. The items queued can have a callback executed when it has completed its iterator.

In addition, a queue may also have functions attached to listen for specific events. On such event is an error. Should any item in the queue fail to process and provide an error to it's next callback, no further items will be processed.

var Queue = require('breeze-queue');

var queue = Queue(function (obj, next) {
  setTimeout(next, 10);
}, 5);

.length

• @return {Number} count of queued items

Property indicating the number of items current in the queue. An item is removed from this list prior to being processed.

.push (items[, callback[, autostart]])

• @param {Array} item or items to be added to the queue
• @param {Function} callback for completion of each item
• @param {Boolean} autostart process (defaults to false)

You can push an item or an array of items into the queue for processing. The callback will be called for the completion of each item if the queue has not entered into an error state. A autostart boolean my also be provided if you wish to start processing the queue with this push of items. If no pushes provide the autostart, then the queue must be started manually with .process().

Note that if the queue has already been started but has been drained of items, it will not start again with another push unless the autostart toggle is present.

// single item
queue.push({ hello: 'universe' });

// multiple items
queue.push([
    { hello: 'world' }
  , { hello: 'universe' }
]);

// notify callback
queue.push({ hello: 'universe' }, notify);

// autostart
queue.push({ hello: 'universe' }, true);

// notify + autostart
queue.push({ hello: 'univeerse' }, notify, true);

.process ()

Begin the queue processing cycle. Has no impact if the queue is already processing.

queue.process();

.onerror

• @cb {Error} object that was passed as error during iteration

Setting this to a function will provide a listener should an error occur. It will not be executed otherwise.

queue.onerror = function (err) {
  console.error(err.message);
};

.saturated

This listener will be executed when the number of queued items exceeds the current concurrency value. This will be executed directly after the push of said items.

queue.saturated = function () {
  console.log('the queue is saturated');
};

.empty

This listener will be executed when the queue is empty. In other words, prior to the last item in the queue being processed.

queue.empty = function () {
  console.log('the queue is on the last item');
};

.drain

This listener will be executed when all queued items have been executed through the iterator.

queue.drain = function () {
  console.log('the queue has processed all tiems');
};

License

(The MIT License)

Copyright (c) 2012 Jake Luer [email protected] (http://qualiancy.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.