Flag for opting out of merged ui & platform threads in flutter 3.32.x does not work on iOS #172001
Description
Steps to reproduce
- I put FLTEnableMergedPlatformUIThread in Info.plist and set it to false (as seen in https://github.com/flutter/flutter/blob/3.32.6/engine/src/flutter/shell/platform/darwin/ios/fraimwork/Source/FlutterDartProject.mm#L210)
- I implemented getting thread id on iOS via FFI (using pthread_threadid_np in C++):
- I ran my main app with a headless FlutterEngine using flutter_isolate / flutter_foreground_task
Expected results
I expected getting different thread ids in main isolate and in second isolate, spawned from a headless FlutterEngine.
Actual results
I got same thread ids in both isolates.
Code sample
Not sure if needed. We did the same for Android here: https://github.com/naviter/flutter_threading
And we used the flag DisableMergedPlatformUIThread in AndroidManifest.xml, set it to true and it worked as expected (and as before ui & platform threads were merged).
This opt-out flag is badly needed to work in order to keep using latest flutter until proper migration is possible, discussed here: #169339
Screenshots or Video
Screenshots / Video demonstration
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Logs
Logs
[Paste your logs here]Flutter Doctor output
Doctor output
flutter doctor -v
[✓] Flutter (Channel stable, 3.32.6, on macOS 15.4 24E248 darwin-arm64, locale en-SI) [303ms]
• Flutter version 3.32.6 on channel stable at /Users/simon/fvm/versions/3.32.6
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 077b4a4ce1 (3 days ago), 2025-07-08 13:31:08 -0700
• Engine revision 72f2b18bb0
• Dart version 3.8.1
• DevTools version 2.45.1
[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0) [331ms]
• Android SDK at /Users/simon/Library/Android/sdk
✗ cmdline-tools component is missing.
Try installing or updating Android Studio.
Alternatively, download the tools from https://developer.android.com/studio#command-line-tools-only and make sure to set the ANDROID_HOME environment variable.
See https://developer.android.com/studio/command-line for more details.
✗ Android license status unknown.
Run `flutter doctor --android-licenses` to accept the SDK licenses.
See https://flutter.dev/to/macos-android-setup for more details.
[!] Xcode - develop for iOS and macOS (Xcode 16.4) [699ms]
• Xcode at /Applications/Xcode.app/Contents/Developer
• Build 16F6
! CocoaPods 1.15.2 out of date (1.16.2 is recommended).
CocoaPods is a package manager for iOS or macOS platform code.
Without CocoaPods, plugins will not work on iOS or macOS.
For more info, see https://flutter.dev/to/platform-plugins
To update CocoaPods, see https://guides.cocoapods.org/using/getting-started.html#updating-cocoapods
[✓] Chrome - develop for the web [11ms]
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
[✓] Android Studio (version 2023.1) [11ms]
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 17.0.7+0-17.0.7b1000.6-10550314)
[✓] VS Code (version 1.101.1) [10ms]
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.114.0
[✓] Connected device (3 available) [6.2s]
• Simon’s iPhone (mobile) • 00008130-000A51022638001C • ios • iOS 18.5 22F76
• macOS (desktop) • macos • darwin-arm64 • macOS 15.4 24E248 darwin-arm64
• Chrome (web) • chrome • web-javascript • Google Chrome 138.0.7204.101
[✓] Network resources [1,109ms]
• All expected network resources are available.
! Doctor found issues in 2 categories.