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Remove race condition in initial layout of ReactRootView 

Summary:
There is a race condition stemming from `ReactRootView.onCreate` that occasionally causes the initial root layout calculation to never occur. In this method currently, `updateRootLayoutSpecs(...)` is called before `enableLayoutCalculation()`, meaning that it's possible for the native modules thread to reach `UIImplementation.updateViewHierarchy` before layout calculation has been enabled (i.e. before the rootViewTag is added to `UIImplementation.mMeasuredRootNodes` on the UI thread).

When this occurs, `UIImplementation.applyUpdatesRecursive` is never called. This causes the app to hang on the splash screen indefinitely, the JS never gets past the first call to `render`, and no layout events are ever sent to the JS.

This PR reverses the order of those two method calls to ensure that the rootViewTag is always added to `mMeasuredRootNodes` before `UIImplementation.updateViewHierarchy` expects it. We inspected all of the code paths of both `enableLayoutCalculation()` and `updateRootLayoutSpecs()` to ensure that in this new order, the rootViewTag will *always* be added to `mMeasuredRootNodes` before the call to `updateViewHierarchy` is dispatched, and that no other side effects would be introduced.

Tested with an app that reliably had this issue (hanging splash screen) on 1 out of every ~10 launches. Logged values to ensure that empty `mMeasuredRootNodes` was the difference between failed and successful launches. After this change, I launched the same app 50+ times without any issues.

[ANDROID][BUGFIX][ReactRootView] - remove race condition in initial layout of ReactRootView
Closes https://github.com/facebook/react-native/pull/19038

Differential Revision: D7834270

Pulled By: hramos

fbshipit-source-id: 6040da900f807dcacbc86ae2c36b4ca004f80178
This commit is contained in:
Eric Samelson 2018-05-01 13:57:58 -07:00 committed by Facebook Github Bot
parent fa25311d27
commit bf83600996
1 changed files with 2 additions and 2 deletions
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4
ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java
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@ -147,12 +147,12 @@ public class ReactRootView extends SizeMonitoringFrameLayout
// Check if we were waiting for onMeasure to attach the root view.
if (mReactInstanceManager != null && !mIsAttachedToInstance) {
attachToReactInstanceManager();
enableLayoutCalculation();
} else {
enableLayoutCalculation();
updateRootLayoutSpecs(mWidthMeasureSpec, mHeightMeasureSpec);
}
enableLayoutCalculation();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}