promise-dequeue

This is fork of promise-queue, promise-based queue. Main difference from original project is that Javascript array replaced by double-ended queue. It increases perfomance on highload queues, this test shows difference with big amount of queued promises. Look at using this package instead of the original, if performance is critical for you.

Installation

promise-dequeue can be installed using npm:

npm install promise-dequeue

Interface

new Queue(Number maxConcurrent, Number maxQueued): Queue
Queue#add(Function generator): Promise - adds function argument that generates a promise to the queue
Queue#getQueueLength(): Number - returns current length of buffer(added but not started promise generators) it <= maxQueued
Queue#getPendingLength(): Number - returns number of pending(concurrently running) promises it <= maxConcurrent

Example

Configure queue

By default Queue tries to use global Promises, but you can specify your own promises.

Queue.configure(require('vow').Promise);

Or use old-style promises approach:

Queue.configure(function (handler) {
    var dfd = $.Deferred();
    try {
        handler(dfd.resolve, dfd.reject, dfd.notify);
    } catch (e) {
        dfd.reject(e);
    }
    return dfd.promise();
});

Queue one by one example

var maxConcurrent = 1;
var maxQueue = Infinity;
var queue = new Queue(maxConcurrent, maxQueue);

app.get('/version/:user/:repo', function (req, res, next) {
    queue.add(function () {
        // Assume that this action is a way too expensive
        // Call of this function will be delayed on second request
        return downloadTarballFromGithub(req.params);
    })
    .then(parseJson('package.json'))
    .then(function (package) {
        res.send(package.version);
    })
    .catch(next);
});

Getting number of pending promises and queue(buffered promises) length

var maxConcurrent = 1;
var maxQueue = 1;
var queue = new Queue(maxConcurrent, maxQueue);

queue.add(function () {
    queue.getQueueLength() === 0;
    queue.getPendingLength() === 1;
    return somePromise();
});

queue.add(function () {
    queue.getQueueLength() === 0;
    queue.getPendingLength() === 0;
    return somePromise();
});

queue.getQueueLength() === 1;
queue.getPendingLength() === 1;

Live example