Keep reference to generic server function delegates so they don't get GCed and crash the application

[campersau]

Extracted the fix from #53

Fixes #56

[tom-j-irvine]

I'm looking forward to this making it into the library as I currently have it manually implemented in my code. I've run into one small thing while using it though and want to mention it. In my application, I need to be able to Stop/Start the RFC Server.

I can do a _server.Shutdown() and _server.Launch(), but if I fully dispose my ISapServer and re-create it, I run into the GC issue after launching my new instance. Generally, I think this is OK and works for my current purposes. However, it seems like the only way to really destroy the server and delegates is to fully recycle the application.

[campersau]

@tom-j-irvine can you please show some code where you would run into the GC issue? Or are you referring to the implementation in #53 ?

[tom-j-irvine]

Here is what works:

private ISapServer _sapServer;

// ... lots of other code

private void StartRfcServer()
{
    // force shutdown if already running
    StopRfcServer(false);
    
    // start
    _logger.LogInformation("Starting RFC server");
    try
    {
        if (_sapServer == null) 
        {

            _sapServer = SapServer.Create(_config.GetRfcServerParameters());

            SapServer.InstallGenericServerFunctionHandler(
                _config.GetRfcDestinationParameters(),
                (connection, function) => HandleFunction(function)
                );
        }

        _sapServer.Launch();

        _logger.LogInformation("RFC server started");
    }
    catch (Exception ex)
    {
        _logger.LogError("Exception starting RFC server: {message}", ex.Message);
    }
    
}

private void StopRfcServer(bool logShutdown = true)
{
    if (_sapServer != null)
    {
        if (logShutdown) _logger.LogInformation("Stopping RFC server");
        try
        {
            _sapServer.Shutdown(2000);
            if (logShutdown) _logger.LogInformation("RFC server stopped");
        }
        catch (Exception ex)
        {
            _logger.LogWarning("Exception shutting down RFC server: {message}", ex.Message);
        }
    }
}

As I said, this works for my purposes. However, I had a version of the code where during shutdown, I would completely dispose the _sapServer and assign null back to it. Then, after starting it back up with Create and InstallGenericServerFunctionHandler, I would run into the GC issue.

I'm really not sure this matters, but there does seem to be something lingering if you create a server and try to destroy it. I imagine things could get funky if you tried to create multiple servers too, but hopefully no one would try to do that.

[campersau]

Thanks! I will investigate it.

[campersau]

It looks like that calling RfcInstallGenericServerFunction multiple times does not work. So I changed the code that calling SapServer.InstallGenericServerFunctionHandler multiple times will only set the user delegates and RfcInstallGenericServerFunction is just called the first time. Which avoids wrapping the users methods but introduces a few more static fields.