event-loop-spinner

What is event-loop-spinner?

The event-loop-spinner npm package is designed to help developers manage and monitor the event loop in Node.js applications. It provides utilities to prevent the event loop from being blocked by long-running synchronous code, ensuring that the application remains responsive.

What are event-loop-spinner's main functionalities?

Check if the event loop is blocked

This feature allows you to check if the event loop is currently blocked. It can be useful for monitoring the performance of your application and ensuring that it remains responsive.

const { isEventLoopBlocked } = require('event-loop-spinner');

if (isEventLoopBlocked()) {
  console.log('The event loop is currently blocked.');
} else {
  console.log('The event loop is running smoothly.');
}

Spin the event loop

This feature allows you to yield control to the event loop during long-running synchronous tasks. By calling `spin()`, you can ensure that the event loop remains responsive and can handle other tasks while your long-running task is in progress.

const { spin } = require('event-loop-spinner');

async function longRunningTask() {
  for (let i = 0; i < 1000000; i++) {
    // Simulate a long-running task
    if (i % 1000 === 0) {
      await spin(); // Yield control to the event loop
    }
  }
  console.log('Task completed');
}

longRunningTask();

Other packages similar to event-loop-spinner

deasync

The deasync package allows you to turn asynchronous functions into synchronous ones. It can be used to prevent the event loop from being blocked by asynchronous operations. However, unlike event-loop-spinner, deasync focuses on converting async functions to sync rather than managing the event loop directly.

blocking-proxy

The blocking-proxy package is used to manage and control the event loop in end-to-end testing scenarios. It ensures that the event loop is not blocked by long-running tasks during tests. While it shares some similarities with event-loop-spinner, it is more specialized for testing environments.

async-hook

The async-hook package provides a way to track asynchronous resources in Node.js. It can be used to monitor the event loop and detect when it is blocked. However, it is more focused on tracking async resources rather than providing utilities to manage the event loop like event-loop-spinner.

README

event-loop-spinner

Tiny helper to prevent blocking Node.js event loop.

Example

import { eventLoopSpinner } from 'event-loop-spinner';
async function cpuIntensiveOperationHandler(hugeArray) {
  for (const item of hugeArray) {
    // ...
    if (eventLoopSpinner.isStarving()) {
      await eventLoopSpinner.spin();
    }
  }
}

Reading

Node.js: How even quick async functions can block the Event-Loop, starve I/O

How does this help?

Node can only run one bit of JS at a time. While it is running this bit of JS, it does nothing else. It doesn't fire timers. It doesn't accept TCP connections from clients.

In fact, Node doesn't even do these things when it finishes running one bit of JS. It prefers to immediately run the next bit of JS. It does this for "a while".

This gives you two amazingly powerful ways to shoot yourself in the foot; it's great! Just like C++.

That is, if some node process either:

• contains some JS code which runs for "too long", or
• handles too many concurrent work items, resulting in lots of JS to run,

..then it won't handle network requests, or let anyone else do any JS. This can result in the application appearing unresponsive for seconds or minutes. (Yes, we really see minutes.)

event-loop-spinner masks this problem. The spin() method allows Node to stop running this JS function, and its friends, and do some other JS, or do some IO. This significantly shortens the time before more networking is done (i.e. a response is sent to a client), and/or other people's JS is run, improving responsiveness.