79cc1468bc
Summary:
This diff fixes a race condition that was detected on "Marketplace You" production test for Android.
The race condition happens when the method ShadowTree::complete is executed concurrently from two threads (in this case this is called from Scheduller::constraintSurfaceLayout and Scheduler::uiManagerDidFinishTransaction), based on the order of execution this bug makes MountViewItems to be dispatched to the UI in the wrong order.
The root cause of the bug is in the method:
```
bool ShadowTree::complete(
const SharedRootShadowNode &oldRootShadowNode,
const UnsharedRootShadowNode &newRootShadowNode) const {
newRootShadowNode->layout();
newRootShadowNode->sealRecursive();
auto mutations =
calculateShadowViewMutations(*oldRootShadowNode, *newRootShadowNode);
if (!commit(oldRootShadowNode, newRootShadowNode, mutations)) {
return false;
}
emitLayoutEvents(mutations);
if (delegate_) {
delegate_->shadowTreeDidCommit(*this, mutations);
}
return true;
}
```
Notes:
- the commit method is guarded by the commitMutex_
- the shadowTreeDidCommit() method dispatches mutations instructions to the platform side.
- If there are two threads running concurrently, there is no guarantee that the shadowTreeDidCommit() is going to be called in the correct order.
The solution is to include the execution to shadowTreeDidCommit() in the same commitMutex_
Possible solutions:
1 - move the commitMutex_ out of the commit method (to the completeMethod)
2 - synchronize the call to complete method() - this is the implemented solution.
I chose this solution to make it consistent with the way Scheduler::constraintSurfaceLayout is implemented (https://fburl.com/8l49no5x)
This mechanism is very likely to change in the refactor of threading mechanism that Valentin Shergin is going to be working on January.
I would like to land this, so we can fix this bug and run another experiment in production as soon as possible.
Reviewed By: sahrens
Differential Revision: D13535587
fbshipit-source-id: bedd4d85f5569ab3733c302d1328aa48017bcaad
React Native · 
Learn once, write anywhere: Build mobile apps with React.
See the official React Native website for an introduction to React Native.
Requirements
Supported target operating systems are >= Android 4.1 (API 16) and >= iOS 9.0. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS by default (tools like Expo can be used to get around this).
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How React Native works
React Native lets you build mobile apps using JavaScript. It uses the same design as React, letting you compose a rich mobile UI from declarative components.
With React Native, you don't build a "mobile web app", an "HTML5 app", or a "hybrid app". You build a real mobile app that's indistinguishable from an app built using Objective-C, Java, Kotlin, or Swift. React Native uses the same fundamental UI building blocks as regular iOS and Android apps. You just put those building blocks together using JavaScript and React.
React Native lets you build your app faster. Instead of recompiling, you can reload your app instantly. With hot reloading, you can even run new code while retaining your application state.
React Native combines smoothly with components written in Objective-C, Java, Kotlin, or Swift. It's simple to drop down to native code if you need to optimize a few aspects of your application. It's also easy to build part of your app in React Native, and part of your app using native code directly - that's how the Facebook app works.
The focus of React Native is on developer efficiency across all the platforms you care about - learn once, write anywhere. Facebook uses React Native in multiple production apps and will continue investing in React Native. You can learn more about our open source roadmap in this blog post: Open Source Roadmap.
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