Concurrent Callback Queue

A simple, lightweight, zero dependencies pure JavaScript queue implementation that allows for asynchronous operations such as API calls heavy computations or large file processing to be scheduled for execution in a parallel fashion.

The project consists of a single ConcurrentCallbackQueue class that provides a simple API to manage the execution of multiple callbacks concurrently with a configurable limit on the number of concurrent executions. It also provides a retry mechanism for each callback in case of errors, and callback hooks for queue state changes and callback events.

Table of Contents

• Features
• Installation
  • NPM
  • CDN
• Usage
  • Example
  • Basic Usage
  • Configuration Options
  • Multiple Callbacks
  • Retry Mechanism
  • Queue State
  • Event Hooks
  • Queue Control
• Use Cases
• License
• Author
• Contributing
  • Commit Message Format

Features

• Concurrent Execution: Execute multiple callbacks concurrently with a configurable limit on the number of concurrent executions.
• Automatic Start: Option to automatically start the queue execution upon adding a callback.
• Retry Mechanism: Define the number of retry attempts for each callback in case of errors.
• State Management: Callbacks for different queue states (idle, busy, stopped) and events (success, error).
• Custom Callbacks: Customize behavior on callback success, error, and different queue states.

Installation

NPM

If you are using npm as your package manager, you can install the package by running:

npm install @diomeh/concurrent_callback_queue

Then you can import the ConcurrentCallbackQueue class in your project:

import { ConcurrentCallbackQueue } from "@diomeh/concurrent_callback_queue";
const queue = new ConcurrentCallbackQueue();

CDN

You can also include the script directly in your HTML file using the jsDelivr CDN:

As a module:

<script
  type="module"
  src="https://cdn.jsdelivr.net/npm/@diomeh/concurrent_callback_queue/dist/ConcurrentCallbackQueue.esm.js"
></script>

As a script:

<script src="https://cdn.jsdelivr.net/npm/@diomeh/concurrent_callback_queue/dist/ConcurrentCallbackQueue.iife.min.js"></script>

This will expose the ConcurrentCallbackQueue class globally, and you can use it in your JavaScript code:

const queue = new ConcurrentCallbackQueue();

Usage

Example

Detailed examples can be found in the tutorial page.

Here's an example of how to use the ConcurrentCallbackQueue:

const queue = new ConcurrentCallbackQueue({
  autoStart: false,
  maxConcurrent: 2,
  onCallbackError: (error) => console.error(error),
});

for (let i = 0; i < 10; i++) {
  queue.enqueue(() => {
    const uri = "https://httpstat.us/200,400?sleep=2000";
    return fetch(uri).then((response) => response.text());
  }, 3);
}

queue.start();

Basic Usage

To create and use a basic concurrent callback queue:

const queue = new ConcurrentCallbackQueue();
queue.enqueue(() => fetch("https://httpstat.us/200,400?sleep=2000"));

Configuration Options

Execution can be configured with the following options:

• autoStart (boolean): Whether to start the queue automatically when a callback is added.
• maxConcurrent (number): Maximum number of callbacks to execute concurrently.
• onCallbackError (function): Callback executed when an error occurs during callback execution.
• onCallbackSuccess (function): Callback executed after a callback is executed successfully.
• onQueueIdle (function): Callback executed when the queue becomes idle.
• onQueueBusy (function): Callback executed when the queue becomes busy.
• onQueueStop (function): Callback executed when the queue stops.

const queue = new ConcurrentCallbackQueue({
  autoStart: false,
  onCallbackError: (error) => console.error(error),
});
queue.enqueue(() => {
  throw new Error("Error");
});
queue.start();

Multiple Callbacks

To enqueue multiple callbacks at once:

const queue = new ConcurrentCallbackQueue();
queue.enqueueAll([
  () => fetch("https://httpstat.us/200,400?sleep=2000"),
  () => fetch("https://httpstat.us/200,400?sleep=2000"),
]);

Retry Mechanism

You can specify the number of retry attempts for each callback:

const queue = new ConcurrentCallbackQueue();
const retries = 3;
queue.enqueue(() => fetch("https://httpstat.us/200,400?sleep=2000"), retries);

Queue State

You can check the state of the queue at any time:

const queue = new ConcurrentCallbackQueue();
console.log(queue.getState()); // QueueState.IDLE

Possible states are:

• QueueState.IDLE: There are no pending callbacks and the queue will start processing as soon as a callback is added.
• QueueState.BUSY: Currently processing callbacks up to the maximum concurrent limit.
• QueueState.STOPPED: Processing has been stopped and no further callbacks will be executed unless the queue is started again.

Event Hooks

You can define custom event hooks to handle various queue state changes:

const queue = new ConcurrentCallbackQueue({
  onQueueIdle: () => console.log("Queue is idle"),
  onQueueBusy: () => console.log("Queue is busy"),
  onQueueStop: () => console.log("Queue has stopped"),
});

There are also hooks for individual callback events:

const queue = new ConcurrentCallbackQueue({
  onCallbackSuccess: (result) => console.log("Callback succeeded:", result),
  onCallbackError: (error) => console.error("Callback failed:", error),
});
queue.enqueueAll([
  () => fetch("https://httpstat.us/200,400?sleep=2000"),
  () => {
    throw new Error("Error");
  },
]);

Queue Control

You can start, stop, and clear the queue as needed:

const queue = new ConcurrentCallbackQueue({
  autoStart: false,
  maxConcurrent: 1,
});

queue.enqueueAll([
  () => fetch("https://httpstat.us/200,400?sleep=2000"),
  () => fetch("https://httpstat.us/200,400?sleep=2000"),
]);

queue.start(); // Will execute the first callback
queue.stop(); // Will stop the queue after the first callback
queue.clear(); // Will clear all callbacks that have not been executed yet and return them in an array

Use Cases

The ConcurrentCallbackQueue can be used in various scenarios where you need to manage multiple asynchronous operations concurrently:

• API Calls: Execute multiple API requests in parallel.
• Heavy Computations: Run CPU-intensive tasks concurrently.
• File Processing: Process multiple files simultaneously.
• Task Scheduling: Schedule and manage multiple tasks.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Author

David Urbina

Contributing

Contributions are welcome! Feel free to submit a pull request or open an issue if you have any suggestions or feedback.

This project follows the Contributor Covenant Code of Conduct and the Conventional Commits Specification.

Commit Message Format

From the Conventional Commits Specification Summary:

The commit message should be structured as follows:

{type}[optional scope]: {description}

[optional body]

[optional footer(s)]

Where type is one of the following:

For more information, refer to the Conventional Commits Specification.