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[iOS] Deadlock: measureContent dispatch_syncs to main while holding the shadow tree lock

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Đánh giá

Độ khó
4/5
Thời gian dự kiến
3-5 ngày
Mức phù hợp với người mới
48/100
Loại issue
Lỗi
Độ rõ ràng
Khá rõ ràng
Mức độ hoạt động
Sôi nổi
Công nghệ
objective-c, react-native
Lĩnh vực
mobile

Hướng nghiên cứu

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.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.

Mô tả

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' RNSScreenStackHeaderConfig commits 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:

  1. EnrichedTextInputView keeps an immutable NSAttributedString snapshot of its text storage, built with the same mock-character handling measureSize: uses. It's guarded by an os_unfair_lock and refreshed on the main thread in tryUpdatingHeight, just before the state update that triggers the re-measure.
  2. measureContent measures 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
  1. Render an EnrichedTextInput inside a screen of a native-stack navigator (react-native-screens) that shows a header.
  2. Push that screen on top of another screen.
  3. Swipe back slowly with the interactive pop gesture, release, and repeat a few times.
  4. 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 inside dispatch_sync from EnrichedTextInputViewShadowNode::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.

Ngôn ngữ chính
C
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Issue khác của software-mansion/react-native-enriched-html

Tất cả issue của software-mansion/react-native-enriched-html

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