promise-queue

Promise-based queue

Installation

promise-queue can be installed using npm:

npm install promise-queue

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