[CI] Flaky: MonoTouchFixtures.CategoryTest.NavigationControllerOverride — NSAsyncActionDispatcher marshalling race condition

[rolfbjarne]

Flaky Test Report (automated)

Test: MonoTouchFixtures.CategoryTest.NavigationControllerOverride
Platform: iOS (simulator, Debug)
Category: Flaky
Period: June 29, 2026

Occurrence Summary

PR	Build	Configuration	Bot	Direct Link
#25856	14516627	monotouch-test/iOS - simulator/Debug	AcesShared 20	Run tests (attempt 1)

Total: Failed in 1 build; rerun (attempt 2) was triggered, confirming suspected flakiness.

Error Details

ObjCRuntime.RuntimeException : Failed to lookup the required marshalling information.
Additional information:
    Selector: xamarinApplySelector
    Type: __MonoMac_NSAsyncActionDispatcher
  Code: 8034
  Error: True
  ----> ObjCRuntime.RuntimeException : Failed to get the 'this' instance in a method call to Foundation.NSAsyncActionDispatcher.Apply.
  Code: 8035
  Error: True
  ----> ObjCRuntime.RuntimeException : Failed to marshal the Objective-C object 0x128759080 (type: __MonoMac_NSAsyncActionDispatcher). Could not find an existing managed instance for this object, nor was it possible to create a new managed instance (because the type 'Foundation.NSAsyncActionDispatcher' does not have a constructor that takes one NativeHandle argument).
  Code: 8027
  Error: True

Stack trace:

at ObjCRuntime.Runtime.RethrowManagedException(IntPtr exception_gchandle)
at ObjCRuntime.Runtime.rethrow_managed_exception(...)
at Foundation.NSRunLoop.RunUntil(NSDate date)
at AppDelegate.PresentModalViewController(UIViewController vc, Double duration) in SceneDelegate.cs:line 40
at MonoTouchFixtures.CategoryTest.NavigationControllerOverride()

Analysis

This is a GC race condition: NSAsyncActionDispatcher gets garbage-collected while native code still holds a reference to it. When NSRunLoop.RunUntil() delivers the async callback via xamarinApplySelector, the managed instance is gone and cannot be recreated because Foundation.NSAsyncActionDispatcher lacks a NativeHandle constructor.

The test itself (CategoryTest.NavigationControllerOverride) is about Objective-C category overrides on UINavigationController. The marshalling failure in NSAsyncActionDispatcher is a side effect — an unrelated async dispatch races with the GC during the modal presentation loop.

Classification

This failure was identified as flaky because:

• The PR ([tools] Honor the 'ProductException.Warning' field if nothing has been configured for an exception. #25856) only modifies build-tool warning/error classification code (tools/common/ErrorHelper.tools.cs, tools/common/error.cs) — completely unrelated to runtime marshalling
• A rerun was triggered (attempt 2), indicating the CI system also flagged it as potentially transient
• The error pattern (GC race in async dispatch) is inherently non-deterministic

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This issue was automatically generated by CI post-mortem analysis.