Joshua Gross
b6bbbf8efa
Summary: TL;DR: For applications using JS navigation, save 50-95% of CPU during mounting phase in N>2 navigations that replace ~most of screen. During investigation of performance on the UI thread of React Native applications, I noticed that the /initial/ render of an screen for an application using JS navigation is /mostly/ consumed (on the UI thread) by tearing-down the previous View hierarchy. In one 185ms segment on the UI thread in production, 95% of the CPU time was Remove/Delete instructions and only 5% of CPU time was consumed by actually displaying the new hierarchy (this is specific to Android and also assumes that View Preallocation is being used, so post-commit work consists of Insert and UpdateLayout mutations primarily). There are /some/ cases where the C++ differ knows that we are deleting an entire subtree and therefore we could communicate this to the mounting layer. All that matters is that these Views are removed from the View hierarchy immediately; and secondarily that their memory is cleaned up ASAP, but that doesn't need to happen immediately. Some additional constraints and notes: 1) As noted in the comments, we cannot simply stop producing Remove and Delete instructions. We need to produce /both/ the new RemoveDeleteTree instruction, /and/ produce all the Remove/Delete instructions, primarily because LayoutAnimations relies heavily on these Remove/Delete instructions and certain things would break if we removed those instructions entirely. However, we can mark those Remove/Delete instructions as redundant, process them only in LayoutAnimations, and not send them to the Android mounting layer. 2) We want to make sure that View Recycling is not impacted. Since Android cannot take advantage of View Recycling until /after/ the second major render (preallocation of views will happen before any views are recycled), this doesn't impact View Recycling and we'll make sure Views are recycled whenever they are deleted. Thus, we do two things: 1) Introduce a new RemoveDeleteTree operation that can delete an entire subtree recursively as part of one operation. This allows us to avoid serializing hundreds or thousands of instructions and prevents JNI traffic. 2) Besides removing the topmost View from the View hierarchy, and ensuring it's not drawn, the full teardown and recycling of the tree can happen /after/ the paint. In some flows with JS navigation this saves us 95% of CPU during the mount phase. In the general case it is probably closer to 25-50% of CPU time that is saved and/or deferred. Changelog: [Android][Changed] Significant perf optimization to Fabric Remove/Delete operations Reviewed By: ryancat Differential Revision: D37257864 fbshipit-source-id: a7d33fc74683939965cfb98be4db7890644110b2
React Native
Learn once, write anywhere:
Build mobile apps with React.
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React Native brings React's declarative UI framework to iOS and Android. With React Native, you use native UI controls and have full access to the native platform.
- Declarative. React makes it painless to create interactive UIs. Declarative views make your code more predictable and easier to debug.
- Component-Based. Build encapsulated components that manage their state, then compose them to make complex UIs.
- Developer Velocity. See local changes in seconds. Changes to JavaScript code can be live reloaded without rebuilding the native app.
- Portability. Reuse code across iOS, Android, and other platforms.
React Native is developed and supported by many companies and individual core contributors. Find out more in our ecosystem overview.
Contents
- Requirements
- Building your first React Native app
- Documentation
- Upgrading
- How to Contribute
- Code of Conduct
- License
📋 Requirements
React Native apps may target iOS 11.0 and Android 5.0 (API 21) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like Expo can be used to work around this.
🎉 Building your first React Native app
Follow the Getting Started guide. The recommended way to install React Native depends on your project. Here you can find short guides for the most common scenarios:
📖 Documentation
The full documentation for React Native can be found on our website.
The React Native documentation discusses components, APIs, and topics that are specific to React Native. For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
The source for the React Native documentation and website is hosted on a separate repo, @facebook/react-native-website.
🚀 Upgrading
Upgrading to new versions of React Native may give you access to more APIs, views, developer tools, and other goodies. See the Upgrading Guide for instructions.
React Native releases are discussed in this discussion repo.
👏 How to Contribute
The main purpose of this repository is to continue evolving React Native core. We want to make contributing to this project as easy and transparent as possible, and we are grateful to the community for contributing bug fixes and improvements. Read below to learn how you can take part in improving React Native.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our Contributing Guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React Native.
Open Source Roadmap
You can learn more about our vision for React Native in the Roadmap.
Good First Issues
We have a list of good first issues that contain bugs which have a relatively limited scope. This is a great place to get started, gain experience, and get familiar with our contribution process.
Discussions
Larger discussions and proposals are discussed in @react-native-community/discussions-and-proposals.
📄 License
React Native is MIT licensed, as found in the LICENSE file.
React Native documentation is Creative Commons licensed, as found in the LICENSE-docs file.