Gijs Weterings
c467843ed0
Summary: Pull Request resolved: https://github.com/react/react-native/pull/57975 `HighResDuration::fromDOMHighResTimeStamp` and `HighResTimeStamp::fromDOMHighResTimeStamp` converted milliseconds back to nanoseconds with `static_cast<int64_t>(units * 1e6)`, which truncates toward zero. `toDOMHighResTimeStamp()` divides the nanosecond count by 1e6 (one rounding) and multiplying back by 1e6 rounds again, so the product frequently lands a hair below the original integer (e.g. `537648854729249.97`). Truncation then chops off a whole nanosecond, so `fromDOMHighResTimeStamp(toDOMHighResTimeStamp(x)) != x` for roughly 2% of random `now()` values. That is the source of an intermittent `BridgingTest/highResTimeStampTest` failure, which reported: ``` Expected equality of these values: timestamp Which is: 8-byte object <22-02 00-21 FD-E8 01-00> bridging::fromJs<HighResTimeStamp>( rt, bridging::toJs(rt, timestamp), invoker) Which is: 8-byte object <21-02 00-21 FD-E8 01-00> ``` Round to the nearest nanosecond instead of truncating. Nanosecond values below 2^53 are exactly representable in a double, so the round trip is now exact for every value below 2.25e15 ns (26 days of monotonic clock); beyond that the double's ULP exceeds 0.5 ns and residual error is at most 2 ns, which is a floor of the DOM representation itself. Rounding is also the correct semantic independently of the round trip — truncation gives a systematic downward bias and is asymmetric across zero, which affects the other callers (`RCTHighResTimeStampFromSeconds` for touch timestamps, `RuntimeTargetConsole` `console.timeStamp`, and `PerformanceTracer`). The rounding is `std::llround`, which costs both overloads their `constexpr`: `<cmath>` rounding functions do not become usable in a constant expression until C++23 (P0533), and this header is compiled as C++20 everywhere (`-std=c++20` in `rn_defs.bzl`, `react-native-flags.cmake`, the podspecs and `Package.swift`). Both carry a `TODO` to restore `constexpr` once the C++23 rollout reaches them. Dropping it is safe here. All 14 call sites are plain runtime calls — none is in a constant-expression context, none assigns to a `constexpr` variable or feeds a `static_assert` — and both functions are defined inside the class body, so they stay implicitly `inline` and neither linkage nor ABI changes. `fromDOMHighResTimeStamp` converts a `double` arriving from JS, so constant-evaluating it was never meaningful in the first place. This does narrow the published API surface, so the C++ API snapshots are regenerated: the only change across all nine `.api` files is the `constexpr` keyword dropping off these two declarations, 18 lines in total. `HighResTimeStamp::fromDOMHighResTimeStamp` now delegates to `HighResDuration`'s so there is a single implementation. `highResTimeStampTest` previously asserted on `HighResTimeStamp::now()`, whose magnitude is host-uptime-dependent, so it only tripped the bug on about 2% of runs. It now round-trips five fixed nanosecond values (including the exact value from the failing run), which exercises the bug on every run. No test was skipped, disabled, or loosened. Changelog: [General][Fixed] - Round instead of truncate when converting a `DOMHighResTimeStamp` back to nanoseconds, so `HighResTimeStamp` and `HighResDuration` round trips are exact Reviewed By: javache Differential Revision: D116286868 fbshipit-source-id: 1adafd1b57b1185f51f08fa4dc55d96b88c176cd
React Native
Learn once, write anywhere:
Build mobile apps with React.
Getting Started · Learn the Basics · Showcase · Contribute · Community · Support
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 15.1 and Android 7.0 (API 24) 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 repository, @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.
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.