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How To Avoid Long Main-thread Tasks?


Threads are often used to improve the performance of an application by allowing multiple tasks to be executed concurrently. A thread is a unit of execution that an operating system can schedule. It contains a program counter, a stack, and a set of registers. For example, a web browser may use one thread to handle user input, another to download web page content, and another to display the content.

Threads can also be used to improve the responsiveness of an application by allowing a task to be interrupted if it takes too long to complete. For example, a word processor may use one thread for user input and another for spell-checking. If the spell-checking task is too long, the user input thread can run so the user can continue typing.

How to avoid long main-thread tasks?

Most applications have a main thread responsible for handling UI events and other tasks. When a task takes too long to complete, it can cause the main thread to freeze and become unresponsive. This can happen when an app performs a long-running computation, such as encoding a video or downloading a large file. It can also occur when an app is waiting for a response from a network request. You may have encountered this recommendation while testing your website on PageSpeed tool.

PageSpeed long thread recommendation

There are several ways to avoid long main-thread tasks:

1. Use asynchronous methods.

2. Offload work to a background thread.

3. Use a worker thread pool.

4. Use reactive programming techniques.

The benefits of multi-threading

Multi-threading can help you avoid long main-thread tasks in a few different ways:

  1. Using multiple threads, you can break up a long task into smaller pieces that can be worked on in parallel. This can drastically reduce the overall time it takes to complete the task.
  2. Multi-threading can give you more control over how your program uses resources like CPU and memory. By carefully managing your threads, you can ensure that your program uses these resources as efficiently as possible.
  3. Multi-threading can help you improve the responsiveness of your program by allowing you to perform background tasks while the user can still interact with the program.

How to minimize main thread work in WordPress?

In WordPress, here are the ways to void long thread & get improved Page Speed score:

  • Remove unused JavaScript & CSS – Use plugins like Asset Cleanup & Perfmatters.
  • Minify and defer CSS – Use a caching plugin such as WPRocket, WP Fastest Cache to execute this.
  • Reduce impact of third-party code by optimizing fonts & preloading.
  • Use fast page builders like Gutenburg or Beaver.


Long main-thread tasks can cause your app to become unresponsive and, if not avoided, can lead to crashes. You can prevent long main-thread tasks using threading and asynchronous programming and keep your app running smoothly. If you’re unsure how to implement these techniques, we recommend seeking a professional developer to help you get started.

Learn more about performance related terms on Website Speed Glossary.

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