concurrency-queue

A lightweight, minimalist FIFO queue that holds jobs, releasing only a fixed number for concurrent processing.

Usage

Install

    npm install concurrency-queue

Use

Use .createInstance() to setup a concurrency queue with maxConcurrency parameter.

var cQ = require('concurrent-queue')
            .createInstance({
                'maxConcurrency': 3
            });

Then push a job into the queue:

    var jobId = cQ.push(job)    

The queue generates a unique jobId for each job instance pushed into the queue.

Events

Ready Event

The 'ready' event is fired when a job is released to be processed based on the maxConcurrency rules.

cQ.on('ready', function (job, jobId, status) {
    //Do some job processing here
    
    //when complete, drain the queue of the job
    cQ.drain(jobId); 
});

The status field shows current state of the queue: { maxConcurrency: xx, processing: xx, queued: xx }.

When job processing is completed, use .drain(jobId) to drain queue of job, releasing next job in queue, if one exists.

Queued Event

The 'queued' event is fired when a job is queued i.e, max number of concurrent jobs already being processed.

cQ.on('queued', function (job, jobId, status) {
    //job with jobId has been queued
});

Drained Event

The 'drained' event is fired when a job is drained from the queue. This releases the next queued job, if any are available.

cQ.on('drained', function (job, jobId, status) {
    //job with jobId has been drained from the queue
});

Empty Event

Finally an 'empty' event is fired when the last job is drained from the queue.

For examples see the /examples/ folder.

License:

MIT - See LICENSE file.