[iOS] Deadlock: measureContent dispatch_syncs to main while holding the shadow tree lock
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評価
- 難易度
- 4/5
- 見積もり時間
- 3〜5日
- 初心者へのやさしさ
- 48/100
- issue の種類
- バグ
- 明瞭さ
- おおむね明確
- 活発さ
- 活発
- 技術スタック
- objective-c, react-native
- 領域
- mobile
調査の方向性
Start with EnrichedTextInputViewShadowNode::measureContent and EnrichedTextViewShadowNode to trace the synchronous main-queue measurement described in the report; then inspect EnrichedTextInputView and its measureSize: path. Reproduce by swiping back from a native-stack screen containing an EnrichedTextInput while the header is visible. Done when measurement avoids the described lock cycle and the reported freeze no longer reproduces.
索引モデルが issue の本文から書いたものです。
説明
Before submitting a new issue
- I tested using the latest version of the library, as the bug might be already fixed.
- I tested using a supported version of react native.
- I checked for possible duplicate issues, with possible answers.
Bug summary
On iOS, EnrichedTextInputViewShadowNode::measureContent can deadlock the app. When it runs off the main thread it does a dispatch_sync to the main queue to call measureSize: on the component view. But measureContent runs during a commit while that thread holds the shadow tree lock. If the main thread is meanwhile committing state of its own, it waits on the same lock, and neither side can proceed:
- Layout thread: holds the shadow tree commit lock →
measureContent→dispatch_sync(main)→ waits for main. - Main thread: react-native-screens'
RNSScreenStackHeaderConfigcommits header state from-viewDidLayoutSubviews→ waits for the shadow tree lock.
The app hangs until the watchdog kills it (0x8BADF00D).
In our app this reproduces reliably by swiping back (the interactive pop gesture) from any native-stack screen that contains an EnrichedTextInput. During the gesture both screens are mounted and the header config commits from viewDidLayoutSubviews almost every frame, so a measurement of the input soon collides with it.
EnrichedTextViewShadowNode uses the same dispatch_sync pattern, so EnrichedText is likely affected too, though we have only hit it with the input.
Proposed fix
We patch this locally and have shipped it to production. The mounted path measures without ever blocking on the main thread:
EnrichedTextInputViewkeeps an immutableNSAttributedStringsnapshot of its text storage, built with the same mock-character handlingmeasureSize:uses. It's guarded by anos_unfair_lockand refreshed on the main thread intryUpdatingHeight, just before the state update that triggers the re-measure.measureContentmeasures that snapshot on the layout thread (NSAttributedString's measuring APIs are thread safe, and the snapshot is immutable and unshared). If no snapshot exists yet, it returns a zero height instead of blocking. The view pushes a state update as soon as it has content, which forces a re-measure.
Unlike #339 (reverted in #417), this doesn't commit a fixed size through state, so the measurement follows width changes.
Library version
1.2.0 (also reproduced on 1.1.1)
Environment info
- React Native 0.88.0, New Architecture (Fabric)
- Expo SDK 58
- react-native-screens 4.30.0 (native stack)
- iOS 26 and 27, physical devices and simulator
Steps to reproduce
- Render an
EnrichedTextInputinside a screen of a native-stack navigator (react-native-screens) that shows a header. - Push that screen on top of another screen.
- Swipe back slowly with the interactive pop gesture, release, and repeat a few times.
- The app freezes; after several seconds iOS kills it with
0x8BADF00D. Pausing in the debugger shows the main thread waiting on the shadow tree mutex and the JS/layout thread insidedispatch_syncfromEnrichedTextInputViewShadowNode::measureContent.
Reproducible example repository
We don't have a standalone reproduction repo yet; We can put one together if the steps above aren't enough to reproduce it.
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