queue

What is queue?

The 'queue' npm package is a fast, robust, and extensible queue implementation for managing a list of tasks in a sequential manner. It allows for asynchronous task processing, concurrency control, timeout for tasks, and pausing/resuming the queue. This package is particularly useful for rate-limiting tasks or operations that need to be executed in order but might have asynchronous results, such as API calls, file processing, or any task that requires throttling.

What are queue's main functionalities?

Basic Queue Functionality

This demonstrates how to create a basic queue, add tasks to it, and start processing. Each task is a function that accepts a callback, which must be called upon completion.

const queue = require('queue');
const q = queue();
q.push(function(cb) {
  console.log('Hello');
cb();
});
q.push(function(cb) {
  console.log('World');
cb();
});
q.start(function(err) {
  console.log('All tasks finished.');
});

Concurrency Control

This example shows how to set a concurrency limit, allowing up to 2 tasks to be processed simultaneously.

const q = queue({concurrency: 2});
// Add tasks to q
q.start(function(err) {
  console.log('All tasks processed with a maximum of 2 tasks concurrently.');
});

Timeout for Tasks

This code sets a timeout for each task in the queue. If a task does not call its callback within the specified timeout, the queue will move on to the next task.

const q = queue();
q.timeout = 1000; // 1 second timeout for each task
q.push(function(cb) {
  setTimeout(function() {
    console.log('This task will timeout');
    cb();
  }, 1500); // This task takes longer than the timeout
});
q.start();

Other packages similar to queue

async

The 'async' package provides a wide array of functionalities for working with asynchronous JavaScript, including queue management. Compared to 'queue', 'async' offers more comprehensive control over asynchronous flow control but might be more complex for simple queue needs.

bull

Bull is a Redis-backed queue package for handling distributed jobs and messages in Node.js. It's more suited for scenarios requiring robustness, such as background processing or job scheduling, and offers features like prioritization, repeatable jobs, and event listeners. It's more complex and feature-rich compared to 'queue', which is simpler and doesn't require Redis.

p-queue

p-queue is a promise-based queue with concurrency control, similar to 'queue' but leveraging Promises for task handling. It provides an easy-to-use API for managing asynchronous tasks with more modern JavaScript syntax. It's a good alternative if you prefer working with Promises over callbacks.

README

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 | / \|| | |||  \  | | |||  \  
 | \_\|| \_/||  /_ | \_/||  /_ 
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An async job queue with adjustable concurrency.

Why

Wanted something more flexible than async's queue.

How

The module exports a class named Queue that implements most of the Array api. Pass async functions (ones that accept a callback) to an instance's push() method. Processing begins automatically on process.nextTick().

Install

npm install queue

Properties

• concurrency maximum number of jobs that the queue should process concurrently - the default is 1
• timeout milliseconds to wait for a job to execute its callback

Methods

• push(job) add a job to the queue

Events

• 'processed' when jobs finish
• 'timeout' when queue.timeout milliseconds have elapsed and a job has not executed its callback
• 'drain' when the queue finishes processing all its jobs

Usage

var Queue = require('queue');

var q = new Queue({
  timeout: 100,
  concurrency: 100
});

var results = [];


// listen for events

q.on('processed', function(job) {
  console.log('job finished processing:', job.toString().replace(/\n/g, ''));
});

q.on('drain', function() {
  console.log('all done:', results);
});


// add jobs using familiar Array api

q.push(function(cb) {
  results.push('two');
  cb();
});

q.push(
  function(cb) {
    results.push('four');
    cb();
  },
  function(cb) {
    results.push('five');
    cb();
  }
);

q.unshift(function(cb) {
  results.push('one');
  cb();
});

q.splice(2, 0, function(cb) {
  results.push('three');
  cb();
});


// use the timeout feature to deal with jobs that 
// take too long or forget to execute a callback

q.on('timeout', function(job, next) {
  console.log('job timed out:', job.toString().replace(/\n/g, ''));
  next();
})

q.push(function(cb) {
  setTimeout(function() {
    console.log('slow job finished');
    cb();
  }, 200);
});

q.push(function(cb) {
  console.log('forgot to execute callback');
});

Note

Version 1.0 introduces api changes and is NOT backwards compatible with 0.0.2

License

WTFPL