MessageBox.Show sporadically don't show on catching exception

Question

I am writing a Visual Studio extension in C# and I get a strange behavior on managing exception and displaying error messages. Basically, I just want to add some details to the exception message to help me investigate in case of a problem.

It all starts from a command on a context menu item and I suspect it may be related to threads management behind the async/await mechanism. But I am not sure I guess correctly and I am not able to find any solution. HELP!

It starts from my menu item callback:

internal sealed class My_RunAnalysis
{
    //...
    public static async Task InitializeAsync(AsyncPackage package)
    {
        // Switch to the main thread - the call to AddCommand in PS_RunAnalysis's constructor requires
        // the UI thread.
        await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(package.DisposalToken);

        OleMenuCommandService commandService = await package.GetServiceAsync((typeof(IMenuCommandService))) as OleMenuCommandService;
        Instance = new My_RunAnalysis(package, commandService);
    }

    //...
    private async void ExecuteAsync(object sender, EventArgs e)
    {
        try
        {
            await My_ViewModel.RunAnalysisAsync();
        }
        catch (Exception exc)
        {
            await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(package.DisposalToken);

            MessageBox.Show(exc.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Warning);
        }
    }
}

//...

class My_ViewModel
{
    async public static Task RunAnalysisAsync()
    {
        await My_Model.GetResultsListAsync();
    }
}

//...

class My_Model
    async public static Task GetResultsListAsync()
    {
        ResultsList = new My_ResultsList();

        var rawResultsList = await QueryServerAsync<RawResultsListResponse>("GET", My_Request.GetResults());

        //...
    }

    async public static Task<JsonResponse> QueryServerAsync<JsonResponse>(string method, 
        string request)
    {
        try
        {
            HttpResponseMessage response;

            switch (method)
            {
                case "GET":
                    response = await _httpClient.GetAsync(request);
                    break;
                case "POST":
                default:
                    StringContent httpContent = new StringContent("", Encoding.UTF8, "application/json");
                    response = await _httpClient.PostAsync(request, httpContent);
                    break;
            }

            if (!response.IsSuccessStatusCode) //<<<<<<CASE #1
            {
                throw new My_Exception(
                response.ReasonPhrase,
                "Exception while querying server for " + request);
            }

            string serializedJson = await response.Content.ReadAsStringAsync();
            // CASE #2>>>>>
            var jsonResponse = serializer.Deserialize<JsonResponse>(serializedJson); 

            return jsonResponse;
        }
        catch (Exception e)
        {
            throw new My_Exception(
                e.Message,
                "Exception while querying server for " + request);
        }
    }

The strange thing is that:

• When an error occurs in case #1 and I create a custom exception (my server responded but there was an internal error and I have a clean error code), the MessageBox in the catch of My_ViewModel::RunAnalysisAsync() will show correctly and immediately.

• When a native exception occurs in case #2 (my server responded with malformed json and I get an exception from serializer.Deserialize), the MessageBox in the catch of My_ViewModel::RunAnalysisAsync() will not show, the IDE will hang for around 15s before restarting (and still not show the MessageBox).

Any idea what's wrong?

Thanks!

EDIT:

Seeing that the template for my custom command initializes also with SwitchToMainThreadAsync, I have tried to do the same with the Execute method. I updated the code above but it still does not work: an exception thrown by serializer.Deserialize will still freeze the UI for 10 to 15s and the MessageBox will not show!

Also note that the debugger can step immediately on "await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(package.DisposalToken);" and go on next step to MessageBox. I would tend to suppose it means that the switch to the main thread is immediate but there is still something wrong...

Any idea what's wrong? I really need to capture exceptions a reliable way...

Answer 1

I could not find any explanation to the MessageBox working on a case and not on the other one. I ended up going to some log solution using FileStream.WriteAsync. Hence everything keeps async and I don't have to use MessageBox anymore.