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[ios] Crash in VsyncWaiter when running ios platform view integration test using local engine #182108
Description
Steps to reproduce
- Build local engine targeting iOS device
et build -c ios_debug_unopt && et build -c host_debug_unopt_arm64 - Use local engine for
/Users/huanlin/Desktop/flutter/flutter/dev/integration_tests/ios_platform_view_testsby runningflutter build ios --debug --local-engine ios_debug_unopt --local-engine-host host_debug_unopt_arm64 --local-engine-src-path ~/Desktop/flutter/flutter/engine/src --config-only - Open in Xcode, hit CMD+U to run unit test
- Observe the crash
Thread 1 Queue : com.apple.main-thread (serial)
#0 0x00000002409a90cc in __pthread_kill ()
#1 0x00000001f24ce810 in pthread_kill ()
#2 0x00000001a149ff64 in abort ()
#3 0x00000001099937f4 in fml::KillProcess at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/fml/logging.cc:199
#4 0x0000000109993750 in fml::LogMessage::~LogMessage at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/fml/logging.cc:186
#5 0x0000000109993810 in fml::LogMessage::~LogMessage at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/fml/logging.cc:113
#6 0x000000010af2d530 in flutter::VsyncWaiter::FireCallback at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/shell/common/vsync_waiter.cc:90
#7 0x00000001098a8ee0 in flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0::operator()(std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>) const at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/shell/platform/darwin/ios/framework/Source/vsync_waiter_ios.mm:37
#8 0x00000001098a8e2c in std::__fl::__invoke[abi:nn210000]<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0&, std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>> at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__type_traits/invoke.h:179
#9 0x00000001098a8de8 in std::__fl::__invoke_void_return_wrapper<void, true>::__call[abi:nn210000]<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0&, std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>> at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__type_traits/invoke.h:251
#10 0x00000001098a8dbc in std::__fl::__invoke_r[abi:nn210000]<void, flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0&, std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>> at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__type_traits/invoke.h:273
#11 0x00000001098a8d90 in std::__fl::__function::__alloc_func<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0, std::__fl::allocator<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0>, void (std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>)>::operator()[abi:nn210000] at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__functional/function.h:167
#12 0x00000001098a8688 in std::__fl::__function::__func<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0, std::__fl::allocator<flutter::VsyncWaiterIOS::VsyncWaiterIOS(flutter::TaskRunners const&)::$_0>, void (std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>)>::operator() at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__functional/function.h:319
#13 0x00000001098aa108 in std::__fl::__function::__value_func<void (std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>)>::operator()[abi:nn210000] at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__functional/function.h:436
#14 0x00000001098a7b84 in std::__fl::function<void (std::__fl::unique_ptr<flutter::FrameTimingsRecorder, std::__fl::default_delete<flutter::FrameTimingsRecorder>>)>::operator() at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/third_party/libcxx/include/__functional/function.h:995
#15 0x00000001098a796c in -[VSyncClient onDisplayLink:] at /Users/huanlin/Desktop/flutter/flutter/engine/src/flutter/shell/platform/darwin/ios/framework/Source/vsync_waiter_ios.mm:136
#16 0x0000000196662924 in CA::Display::DisplayLinkItem::dispatch_ ()
#17 0x000000019663ff38 in CA::Display::DisplayLink::dispatch_items ()
#18 0x0000000196653770 in CA::Display::DisplayLink::dispatch_deferred_display_links ()
#19 0x000000019b5b6ee4 in _UIUpdateSequenceRunNext ()
#20 0x000000019b5b6374 in schedulerStepScheduledMainSectionContinue ()
#21 0x0000000284a2d560 in UC::DriverCore::continueProcessing ()
#22 0x0000000195c47f10 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#23 0x0000000195c47e84 in __CFRunLoopDoSource0 ()
#24 0x0000000195c25acc in __CFRunLoopDoSources0 ()
#25 0x0000000195bfc6d8 in __CFRunLoopRun ()
#26 0x0000000195bfba6c in _CFRunLoopRunSpecificWithOptions ()
#27 0x0000000237830498 in GSEventRunModal ()
#28 0x000000019b5d6df8 in -[UIApplication _run] ()
#29 0x000000019b57fe54 in UIApplicationMain ()
#30 0x0000000102bfc63c in main at /Users/huanlin/Desktop/flutter/flutter/dev/integration_tests/ios_platform_view_tests/ios/Runner/main.m:11
#31 0x0000000192c0ee28 in start ()
Expected results
Should not crash
Actual results
Crash
Code sample
NA
Screenshots or Video
No response
Logs
No response
Flutter Doctor output
huanlin@huanlin-mac ios_platform_view_tests % flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[!] Flutter (Channel [user-branch], 3.40.0-1.0.pre-987, on macOS 15.7.3 24G419 darwin-arm64, locale en)
! Flutter version 3.40.0-1.0.pre-987 on channel [user-branch] at /Users/huanlin/Desktop/flutter/flutter
Currently on an unknown channel. Run flutter channel to switch to an official channel.
If that doesn't fix the issue, reinstall Flutter by following instructions at https://flutter.dev/setup.
! Upstream repository unknown source is not a standard remote.
Set environment variable "FLUTTER_GIT_URL" to unknown source to dismiss this error.
[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
✗ Flutter requires Android SDK 36 and the Android BuildTools 28.0.3
To update the Android SDK visit https://flutter.dev/to/macos-android-setup for detailed instructions.
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 26.2)
[✓] Chrome - develop for the web
[✓] Connected device (6 available)
! Error: Browsing on the local area network for Huan’s Work iPhone. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this
Mac.
The device must be opted into Developer Mode to connect wirelessly. (code -27)
! Error: Browsing on the local area network for iPhone 13 Mini. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this Mac.
The device must be opted into Developer Mode to connect wirelessly. (code -27)
! Error: Browsing on the local area network for iPad Pro 11 Inch. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this Mac.
The device must be opted into Developer Mode to connect wirelessly. (code -27)
! Error: Browsing on the local area network for Huan’s iPad. Ensure the device is unlocked and attached with a cable or associated with the same local area network as this Mac.
The device must be opted into Developer Mode to connect wirelessly. (code -27)
[✓] Network resources
! Doctor found issues in 2 categories.
huanlin@huanlin-mac ios_platform_view_tests %
Activity
hellohuanlin commentedon Feb 9, 2026
As a workaround, I simply commented out
KillProcess.vashworth commentedon Feb 12, 2026
Crashing on:
flutter/engine/src/flutter/shell/common/vsync_waiter.cc
Line 90 in 7bafe12
FML_DCHECK will crash with local engine but not pre-built engines
hellohuanlin commentedon Feb 13, 2026
It also reproduces on latest master (pulled today).
hellohuanlin commentedon Feb 23, 2026
I wonder if any insights from team-engine? thank you
gaaclarke commentedon Feb 23, 2026
So, this is for scheduling callbacks tied to vsync. I poked around with gemini and it seems to think this could be related to apple's ProMotion displays where
CACurrentMediaTime()can return a time slightly earlier than the callback. This is what it proposed as a fix.I'm not sure if we want to do that since it may be working against some of the ProMotion display's attempts at reducing latency. This could also explain why it wasn't noticed before if the behavior is tied to a new piece of hardware.