[Bug Report] SendEventAsync() never returns when DeviceClient gets disposed

[Werner-Prbk]

Context

• OS, version, SKU and CPU architecture used: Windows 10 Desktop x64 (also on linux arm32)
• Application's .NET Target Framework : .netcoreapp 3.1
• Device: Laptop (also on arm32 device with custom linux)
• SDK version used: 1.38.0

Issue description

SendEventAsync() never returns when DeviceClient gets disposed in ConnectionStatusChangesHandler.

Following the reconnection sample the DeviceClient is disposed and newly created when ConnectionStatusChangesHandler is called with (Disconnected, Retry_Expired). If another task is still busy with SendEventAsync() on the old (already disposed) DeviceClient, the method never returns.

Internet connection was cut off at 15:38:20. SendEventAsync() hangs forever:

Code sample exhibiting the issue

static async Task Main()
{
	deviceClient = DeviceClient.CreateFromConnectionString(connectionString, TransportType.Mqtt);

	// IoT-Hub connection retry policy before exception is thrown.
	// This should result in disconnected/retry_expired after a few seconds.
	deviceClient.SetRetryPolicy(
		new ExponentialBackoff(
			6,   // retry counter
			TimeSpan.FromSeconds(1),
			TimeSpan.FromSeconds(10),
			TimeSpan.FromSeconds(1)));

	deviceClient.SetConnectionStatusChangesHandler((status, reason) =>
	{
		Print($"Connection status changed: {status}, {reason}");
		if (reason == ConnectionStatusChangeReason.Retry_Expired)
		{
                        Print("Dispose Device Client");
			deviceClient.Dispose();
		}
	});

	await deviceClient.OpenAsync();
	Print("Connected");

	try
	{
		while (true)
		{
			await Task.Delay(TimeSpan.FromSeconds(5));
			Print("Send message ... start");
			await deviceClient.SendEventAsync(new Message());
			Print("Send message ... OK");
		}
	}
	catch (Exception e)
	{
		Print($"Periodic sender exception: {e.Message}. Exit.");
	}
}

Logs

dispose_logs.txt

[azabbasi]

Thank you for reporting this issue, We are working on the fix and will publish it on the next nuget release.

[azabbasi]

The SendEventAsync should throw an ObjectDisposedException and moving forward it will be.

[azabbasi]

We have checked-in the fix and will publish it on the next release.
Thank you for being a valuable contributor to the quality of the SDK.