When a synchronization context has been established, but no message loop is running and a message is sent from another thread, this will cause a deadlock as the thread that sent the message is waiting for work to be done, but there will never be a response so long no message loop is running. Though it is the responsibility of the user to ensure a message loop will start eventually, we should not block the thread in case message loop has not run yet.
In this particular repro issue presents, SystemEvents thread cannot shut down as it is waiting on WinFormsSynchronizationContext, which is waiting for another thread to respond to OnUserPreferenceChanged event
This change involves checking if a message loop is running before committing to waiting for a response to avoid blocking the thread indefinitely.
Manually tested scenarios:
Tested that message will still come through when starting the message loop after the message was sent when message loop wasn't running
Tested message will still come through as expected when message is sent while message loop is running
Related https://github.com/dotnet/winforms/issues/11944
When a synchronization context has been established, but no message loop is running and a message is sent from another thread, this will cause a deadlock as the thread that sent the message is waiting for work to be done, but there will never be a response so long no message loop is running. Though it is the responsibility of the user to ensure a message loop will start eventually, we should not block the thread in case message loop has not run yet. In this particular repro issue presents, SystemEvents thread cannot shut down as it is waiting on
WinFormsSynchronizationContext, which is waiting for another thread to respond to OnUserPreferenceChanged eventThis change involves checking if a message loop is running before committing to waiting for a response to avoid blocking the thread indefinitely.
Manually tested scenarios:
Draft for more testing.
Microsoft Reviewers: Open in CodeFlow