WPF application not terminating when using v2.9.0-beta3 or newer

[IGx89]

If you are reporting bug/issue, please provide detailed Repro instructions.

Repro Steps

1. Open Visual Studio and create a new WPF application
2. Add the "Microsoft.ApplicationInsights.WindowsServer" NuGet package, v2.9.0-beta3 or v2.9.0 (final)
3. Add the following line into MainWindow's constructor: TelemetryConfiguration.Active.InstrumentationKey = ""; (per instructions on https://docs.microsoft.com/en-us/azure/azure-monitor/app/windows-services#4-send-telemetry)
4. Press F5 to start the application, then exit it by clicking the "X" on the application window

Actual Behavior

Window closes but application doesn't terminate.

Expected Behavior

Application fully terminates.

Version Info

SDK Version : 2.9.0 beta 3 or newer (beta 2 or older, like v2.8.1, don't have this issue)
.NET Version : 4.7.2
How Application was onboarded with SDK(VisualStudio/StatusMonitor/Azure Extension) : Visual Studio
OS : Windows 10 1803
Hosting Info (IIS/Azure WebApps/ etc) : N/A

[IGx89]

Best guess is that this was caused by #1028, which creates a new non-background thread. Since the thread isn't set as Background and apparently isn't being terminated by the code, the application can't fully terminate.

CC @macrogreg

[IGx89]

I also attempted adding TelemetryConfiguration.Active.Dispose(); to Application_Exit, with no luck either.

[Dmitry-Matveev]

@IGx89 , thanks a lot for catching this. PR #1081 is to address this issue.

[Dmitry-Matveev]

@IGx89 , we shipped 2.9.1 stable with the fix. Thanks again for reporting!

[IGx89]

Thanks a lot!