Handle disposed AsyncWaitHandle during BeginInvoke completion

[jaywang-cn]

Summary

• tolerate ObjectDisposedException when ThreadMethodEntry.Complete signals an AsyncWaitHandle disposed by its consumer
• add a regression test that verifies the callback runs and the async result completes

Fixes #14996

Testing

• dotnet test src/test/unit/System.Windows.Forms/System.Windows.Forms.Tests.csproj --no-restore -- --filter-method System.Windows.Forms.Tests.ControlTests.Control_BeginInvoke_DisposedAsyncWaitHandle_CompletesCallback (1 passed)

Microsoft Reviewers: Open in CodeFlow

[KlausLoeffelmann]

Thanks for the excellent report and focused fix.
FWIW, the lifetime-analysis (WaitHandle) and picking up the runtime precedent was technically sharp, sound, helpful and made this straightforward to assess!

[KlausLoeffelmann]

LGTM!
Thanks for your contribution!

[Copilot]

🟢 Approval recommended

Pull request overview

This PR hardens WinForms Control.BeginInvoke completion so that a consumer-disposed IAsyncResult.AsyncWaitHandle no longer causes an ObjectDisposedException on the UI thread during marshaled callback completion.

Changes:

• Catch and tolerate ObjectDisposedException when ThreadMethodEntry.Complete() signals the internal ManualResetEvent.
• Add a regression test ensuring the marshaled callback still runs and the returned IAsyncResult reports completion even if AsyncWaitHandle is disposed.

File summaries

File	Description
src/System.Windows.Forms/System/Windows/Forms/Control.ThreadMethodEntry.cs	Wraps completion signaling (_resetEvent?.Set()) in an ObjectDisposedException handler to prevent UI-thread crashes when the wait handle is externally disposed.
src/test/unit/System.Windows.Forms/System/Windows/Forms/ControlTests.Methods.cs	Adds a regression test that disposes AsyncWaitHandle before invoking marshaled callbacks and verifies callback execution and IsCompleted.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[Shyam-Gupta]

Instead of catching an exception, can we check: if(!_marshaler.IsDisposed)

[KlausLoeffelmann]

No. We could have the waitHandle disposed ...

IAsyncResult result = control.BeginInvoke(callback);
result.AsyncWaitHandle.Dispose();

... but not the marshaling control.

[Copilot]

🟢 Approval recommended

The change matches the issue’s acceptance criteria and the added regression test validates the previously failing scenario.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

[KlausLoeffelmann]

Merging this, as this is a bug fix of an existing feature, and not a contribution of a new feature.

@jaywang-cn - for contribution other than bug fixes, please take a look at the contributor licence agreement, which we would need to take respective PRs. Thanks for you help on this matter!