Fix Microsoft.Owin.Hosting.WebApp throws 'System.ObjectDisposedException'

Question

We have our own SignalR server in our WPF application. WebApp starts when the application starts. When the application exits, we remove WebApp.

public void Start() { myWebApp = WebApp.Start<MyApp>(url); } private void Dispose(bool isDisposing) { if (disposed) return; if (isDisposing) myWebApp.Dispose(); disposed = true; } 

A call to myWebApp.Dispose () throws a "System.ObjectDisposedException". Am I doing something wrong? Microsoft.Owin libraries. * There is version 2.1.0 and the SignalR 2.0.3 host itself

UPDATE It turns out that this is the first random exception that I see in visual studio, because the parameter "break on clr exceptions" is active. This exception is apparently handled internally and does not turn into our code

Answer 1

After studying the source code of Katana, I found the cause of this problem. This is the Microsoft.Owin.Host.HttpListener.OwinHttpListener.ProcessRequestsAsync() method. It starts a while loop containing a call to _listener.GetContextAsync() private HttpListener instance in the try-catch section.

The class also implements IDisposable and contains the Dispose() method. This method provides a private HttpListener instance.

When you call WebApp.Start() , it returns an instance of IDisposable , which has only the Dispose() method, which has an OwinHttpListener .

So, when you destroy it, you call its Dispose() OwinHttpListener , which provides a private HttpListener .

But at the same time, ProcessRequestsAsync() throws _listener.GetContextAsync() , but _listener already placed and throws an ObjectDisposedException . catch locks the exception record and returns from ProcessRequestsAsync() .

I think double check lock in ProcessRequestsAsync() might be a good option.

 private async void ProcessRequestsAsync() { while (_listener.IsListening && CanAcceptMoreRequests) { Interlocked.Increment(ref _currentOutstandingAccepts); HttpListenerContext context; try { context = await _listener.GetContextAsync(); } (SOME_OTHER_CATCHES) catch (ObjectDisposedException ode) { // These happen if HttpListener has been disposed Interlocked.Decrement(ref _currentOutstandingAccepts); LogHelper.LogException(_logger, "Accept", ode); return; } (SOME_OTHER_CODE) } } public void Dispose() { if (_listener.IsListening) { _listener.Stop(); } ((IDisposable)_listener).Dispose(); }