Two techniques to prevent blocking the Event Loop when handling CPU-intensive tasks

Two techniques to prevent blocking the Event Loop when handling CPU-intensive tasks

Daily short news for you
  • Now everything is so modern that people can come up with anything. ferretdb.com is an open-source project that transforms the PostgreSQL database into... MongoDB. That's right, you heard it correctly. If you still want to use Postgres but prefer the Mongo query syntax, then ferretdb is for you.

    Oh, besides PostgreSQL, it can also connect to SQLite. Awesome!!! 🙏

    » Read more
  • Dedicating this to those of you using Cursor. PatrickJS/awesome-cursorrules gathers some .cursorrules files to optimize prompts for Cursor. Imagine these files as the System Prompt for Cursor, controlling it according to your wishes in each project.

    The usage is really simple, just copy the appropriate .cursorrules file and place it in the root folder of the project 🥳

    » Read more
  • Gemini 2.5 has just been released, everyone. This is the most advanced model from Google to date, with top-notch reasoning and coding capabilities - as they introduce it.

    Everyone, take a look at the benchmark table; the metrics are all superior to the other competitors. We don't know the price yet, but you can try it for free in Google AI Studio. I guess we’ll wait for it to be integrated into Cursor to see how its coding abilities measure up 😁

    » Read more

Issue

Complex calculations can often cause the Event Loop to become blocked, resulting in unresponsiveness of the server until the computation is complete.

Does this mean Node.js struggles with such calculations? In today's article, I will present two techniques to address this issue.

Partitioning

Also known as "chunking," this technique is based on the principle of dividing the calculation into smaller parts to ensure the interleaving of the Event Loop.

For example, consider an average calculation of numbers from 1 to n with a complexity of O(n):

for (let i = 0; i < n; i++)
  sum += i;
let avg = sum / n;
console.log('avg: ' + avg);

The complexity and CPU usage increases as n increases. However, by applying the Partitioning technique, the calculation can be divided into n asynchronous steps with a constant performance cost of O(1):

function asyncAvg(n, avgCB) {
  var sum = 0;
  function help(i, cb) {
    sum += i;
    if (i == n) {
      cb(sum);
      return;
    }

    setImmediate(help.bind(null, i+1, cb));
  }

  help(1, function(sum){
      var avg = sum/n;
      avgCB(avg);
  });
}

asyncAvg(n, function(avg){
  console.log('avg: ' + avg);
});

Partitioning utilizes setImmediate to perform each step of the loop asynchronously, ensuring that the Event Loop is not blocked since setImmediate is executed during the "Check" phase. To learn more, I recommend reading the article Understanding the Event Loop in Node.js (in Vietnamese). In simple terms, calculations are performed on each iteration of the Event Loop.

Offloading

If your task is more complex, Partitioning might not be sufficient. The Event Loop is responsible for ordering the execution of tasks, not directly executing them. To take advantage of multi-core processors, offload the tasks from the Event Loop.

There are two ways to apply Offloading:

To learn more about Worker Thread implementations, you can refer to the article What are Worker threads? Do you know when to use Worker threads in node.js? (in Vietnamese).

Conclusion

For simple tasks, such as iterating over elements of an arbitrarily long array, Partitioning can be a good choice. If your computational logic is more complex, Offloading is a better approach.

The Offloading technique incurs some overhead due to the communication between the serialized objects of the Event Loop and the Worker Pool. However, it can utilize the CPU's multiple cores.

However, if your server primarily performs heavy CPU computations, you should consider whether Node.js is the best fit. Node.js excels with asynchronous I/O tasks but may not be the optimal choice for CPU-intensive tasks.

References:

Premium
Hello

Me & the desire to "play with words"

Have you tried writing? And then failed or not satisfied? At 2coffee.dev we have had a hard time with writing. Don't be discouraged, because now we have a way to help you. Click to become a member now!

Have you tried writing? And then failed or not satisfied? At 2coffee.dev we have had a hard time with writing. Don't be discouraged, because now we have a way to help you. Click to become a member now!

View all

Subscribe to receive new article notifications

or
* The summary newsletter is sent every 1-2 weeks, cancel anytime.

Comments (1)

Leave a comment...
Avatar
Gin Na2 years ago
Phép tính đc thực hiện trên mỗi lần lặp là sao ạ?
Reply
Avatar
Gin Na2 years ago
@gif [3o6Zt6KHxJTbXCnSvu] Cảm ơn ad
Avatar
Xuân Hoài Tống2 years ago
Bạn đọc lại bài viết&nbsp;https://2coffee.dev/bai-viet/tim-hieu-ve-vong-lap-su-kien-event-loop-trong-nodejs-8 này để biết thêm các event loop hoạt động nhé