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.

1Queue.configure(require('vow').Promise);

Or use old-style promises approach:

1Queue.configure(function (handler) {
2    var dfd = $.Deferred();
3    try {
4        handler(dfd.resolve, dfd.reject, dfd.notify);
5    } catch (e) {
6        dfd.reject(e);
7    }
8    return dfd.promise();
9});

Queue one by one example

1var maxConcurrent = 1;
2var maxQueue = Infinity;
3var queue = new Queue(maxConcurrent, maxQueue);
4
5app.get('/version/:user/:repo', function (req, res, next) {
6    queue.add(function () {
7        // Assume that this action is a way too expensive
8        // Call of this function will be delayed on second request
9        return downloadTarballFromGithub(req.params);
10    })
11    .then(parseJson('package.json'))
12    .then(function (package) {
13        res.send(package.version);
14    })
15    .catch(next);
16});

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

1var maxConcurrent = 1;
2var maxQueue = 1;
3var queue = new Queue(maxConcurrent, maxQueue);
4
5queue.add(function () {
6    queue.getQueueLength() === 0;
7    queue.getPendingLength() === 1;
8    return somePromise();
9});
10
11queue.add(function () {
12    queue.getQueueLength() === 0;
13    queue.getPendingLength() === 0;
14    return somePromise();
15});
16
17queue.getQueueLength() === 1;
18queue.getPendingLength() === 1;

Live example