Detailed explanation of the working principle of Scheduler in React scheduling system

Introduction

React is one of the most popular JavaScript libraries available today, providing a component-based development method that makes it easy to build complex web applications. In React, there is a very important component, which is the scheduler system - Scheduler. This article will explore the concept, working principle and application scenarios of React scheduling system-Scheduler in depth.

What is Scheduler?

Scheduler is a module inside React, which is the core responsible for scheduling and coordinating tasks. The purpose of the scheduler is to ensure the performance and responsiveness of the React application while minimizing the burden on the browser as much as possible. Scheduler works similar to the task scheduler of the operating system, but it is based on JavaScript, so it can better adapt to React's needs.

How Scheduler works

Scheduler controls the update of React applications by prioritizing tasks. Each task has a priority, and Scheduler will determine which task should be executed first based on the priority. Scheduler implements task scheduling through the requestAnimationFrame API, which assigns tasks to different batches to be executed according to the priority of the task. The advantage of this is that it can avoid performing too many tasks within one frame, thereby reducing page lag.

Specifically, Scheduler classifies all tasks by priority and adds them to the task queue. When the browser is idle, Scheduler will take out a batch of tasks from the task queue for execution. When executing a task, if the task is executed for too long, Scheduler pauses the task and returns control to the browser. When the browser is idle again, Scheduler will continue to execute the suspended tasks until all tasks are executed.

Scenarios using Scheduler

In a React application, if there are some tasks that need to be executed at some point in the future, then consider using Scheduler for scheduling. For example, if you need to do some calculations after user input, but don't want the calculation process to affect the user experience, you can use Scheduler to delay the calculation task until the browser is idle. Doing this ensures that users can see the calculation results in a timely manner without affecting the user's interactive experience.

In addition to the above usage scenarios, there are some other situations that you can also consider using Scheduler. For example, when you need to share state among React components, you can use Scheduler to delay the state update to the next frame, thus avoiding too many state updates within one frame causing page stuttering.

Code Example

Here are some code examples using Scheduler:

1. Delayed execution of tasks

import { unstable_scheduleCallback as scheduleCallback } from 'scheduler';
function handleClick() {
  scheduleCallback(() => {
    // Execute the task in the next frame    ('Hello World');
  });
}
function App() {
  return (
    <div>
      <button onClick={handleClick}>Click Me</button>
    </div>
  );
}

In the above example, we used Scheduler'sunstable_scheduleCallbackMethod: Delay execution of a task in the button click event. This task is performed in the next frame, which can avoid performing too many tasks within one frame, thereby improving page performance and responsiveness.

2. Adjust the priority of tasks

import { unstable_scheduleCallback as scheduleCallback } from 'scheduler';
// Define two tasks with different prioritiesconst lowPriorityTask = { priority: 1, message: 'Low Priority Task' };
const highPriorityTask = { priority: 10, message: 'High Priority Task' };
// Start executing tasksscheduleCallback(() => {
  ();
}, lowPriorityTask);
scheduleCallback(() => {
  ();
}, highPriorityTask);

In the example above, we define two tasks with different priorities and then use Scheduler'sunstable_scheduleCallbackThe method begins to perform these tasks. Because the high priority task has higher priority, it will be executed first, while the low priority task will be executed after the high priority task is executed.

3. Batch update status

import { unstable_batchedUpdates as batchedUpdates } from 'react-dom';
// Batch update statusbatchedUpdates(() => {
  setState({ name: 'John' });
  setState({ age: 30 });
});

In the above example, we used the React providedunstable_batchedUpdatesMethod to batch update component status. Doing this will prevent too many updates from being performed within one frame, thereby reducing page stuttering.

Summarize

Scheduler is a very important component within React. It ensures the performance and responsiveness of React applications by prioritizing scheduling tasks. Scheduler is a very good choice if you need to schedule tasks in a React application. In actual development, the appropriate Scheduler API can be selected according to the specific scenario, thereby achieving more efficient and optimized task scheduling.

If you are interested, you can try the underlying implementation principle of Scheduler, or how to implement a Scheduler yourself.

The above is a detailed explanation of the working principle of Scheduler in the React Scheduler system. For more information about the React Scheduler scheduling system, please pay attention to my other related articles!