RequestDataAsync causes two TransferData calls

[Giorgi]

When debugging my extension I have noticed that sometimes a single call to RequestDataAsync results in two calls of TransferData. Is there anything I can do to avoid the second call?

[mpeyrotc]

Hello @Giorgi could I bother you with the call stacks for the two calls into TransferData so that I can investigate further? Thanks!

[Giorgi]

@mpeyrotc I'm unsure how to attach a debugger to the class that inherits from VisualizerObjectSource so I added a few Debug.WriteLine calls.

Here is how TransferData looks: https://github.com/Giorgi/EFCore.Visualizer/blob/c2ee2156f438b0edd29b42558dd5cb327a2faa73/src/IQueryableObjectSource/EFCoreQueryableObjectSource.cs#L15

var operationType = ReadOperationType(incomingData);

Debug.WriteLine($"TransferData called for {operationType}. Stacktrace: ");
Debug.WriteLine(Environment.StackTrace);

switch (operationType)
{
    case OperationType.GetQuery:
        GetQuery(queryable, outgoingData);
        break;
    case OperationType.GetQueryPlan:
        GetQueryPlan(queryable, outgoingData);
        break;
    case OperationType.Unknown:
    default:
        outgoingData.WriteError("Unknown operation type");
        break;
}

The visualizer part makes two calls to the RequestDataAsync but I get three hits at TransferData. GetQueryAsync and GetQueryPlanAsync call RequestDataAsync internally. I have noticed that only the call to GetQueryPlanAsync causes two calls of TransferData

(var _, var _, filePath) = await GetQueryAsync();

var (isError, error, planFilePath) = await GetQueryPlanAsync();

TransferData called for GetQuery. Stacktrace:
at System.Environment.get_StackTrace()
at IQueryableObjectSource.EFCoreQueryableObjectSource.TransferData(Object target, Stream incomingData, Stream outgoingData)
at Microsoft.VisualStudio.DebuggerVisualizers.DebuggeeSide.Impl.ClrCustomVisualizerDebuggeeHost.TransferData(Object visualizedObject, Byte[] uiSideData)
at MySqlEFCoreDemo.Program.Main(String[] args) in S:\src\ConsoleApp2\MySqlEFCoreDemo\Program.cs:line 14

TransferData called for GetQueryPlan. Stacktrace:
at System.Environment.get_StackTrace()
at IQueryableObjectSource.EFCoreQueryableObjectSource.TransferData(Object target, Stream incomingData, Stream outgoingData)
at Microsoft.VisualStudio.DebuggerVisualizers.DebuggeeSide.Impl.ClrCustomVisualizerDebuggeeHost.TransferData(Object visualizedObject, Byte[] uiSideData)
at MySqlEFCoreDemo.Program.Main(String[] args) in S:\src\ConsoleApp2\MySqlEFCoreDemo\Program.cs:line 14

TransferData called for GetQueryPlan. Stacktrace:
at System.Environment.get_StackTrace()
at IQueryableObjectSource.EFCoreQueryableObjectSource.TransferData(Object target, Stream incomingData, Stream outgoingData)
at Microsoft.VisualStudio.DebuggerVisualizers.DebuggeeSide.Impl.ClrCustomVisualizerDebuggeeHost.TransferData(Object visualizedObject, Byte[] uiSideData)
at MySqlEFCoreDemo.Program.Main(String[] args) in S:\src\ConsoleApp2\MySqlEFCoreDemo\Program.cs:line 14

I have also noticed that this happens only during the first hit of the breakpoint. When another breakpoint is hit, and I inspect some variable with my visualizer, I don't get duplicated hits.