ObjectDisposedException on shutdown

Bắt đầu với WebApiAppBuilderExtensions.cs và HttpMessageHandlerAdapter.cs tại phần đăng ký giải phóng liên quan, sau đó theo dõi luồng host.OnAppDisposing và HostingEnvironment.StopListening. Xác định cách việc giải phóng có thể tránh làm gián đoạn các request đang xử lý và sự kiện hoặc cơ chế vòng đời nào nên thực hiện việc giải phóng cuối cùng; hoàn tất khi quá trình shutdown không còn gây ra ObjectDisposedException và các tài nguyên cuối cùng được dọn dẹp.

An app running in IIS with OWIN integration gets ObjectDisposedExceptions on shutdown rather than gracefully draining requests.

Exception Details: System.ObjectDisposedException, Cannot access a disposed object.
Object name: '[Redacted].AuthenticationHandler'.,
    at System.Net.Http.DelegatingHandler.CheckDisposed()
   at System.Net.Http.DelegatingHandler.SetOperationStarted()
   at System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at [Redacted].AuthenticationHandler.<SendAsync>d__12.MoveNext()

Here's where dispose is called:

   at [Redacted].AuthenticationHandler.Dispose(Boolean disposing)
   at System.Net.Http.DelegatingHandler.Dispose(Boolean disposing)
   at System.Web.Http.HttpServer.Dispose(Boolean disposing)
   at System.Net.Http.HttpMessageInvoker.Dispose(Boolean disposing)
   at System.Web.Http.Owin.HttpMessageHandlerAdapter.OnAppDisposing()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.CancellationCallbackInfo.ExecuteCallback()
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   at System.Threading.CancellationTokenSource.NotifyCancellation(Boolean throwOnFirstException)
   at Microsoft.Owin.Host.SystemWeb.ShutdownDetector.Cancel()
   at Microsoft.Owin.Host.SystemWeb.ShutdownDetector.Stop(Boolean immediate)
   at System.Web.Hosting.HostingEnvironment.StopRegisteredObjects(Boolean immediate)
   at System.Web.Hosting.HostingEnvironment.InitiateShutdownWorkItemCallback(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()'

The root event here is HostingEnvironment.StopListening. "Occurs when the worker process or application pool associated with this host has stopped listening for new requests and will eventually shut down." The app is shutting down, but there may still be requests in flight that should be completed if possible.

Microsoft.Owin wired into the StopListening event so that SignalR could gracefully shut down long polling and WebSocket requests. WebAPI however wired up it's pipeline disposal to this event. This causes the pipeline to be disposed while request are in flight.
https://github.com/aspnet/AspNetWebStack/blob/ba26cfbfbf958d548e4c0a96e853250f13450dc6/src/System.Web.Http.Owin/WebApiAppBuilderExtensions.cs#L111
https://github.com/aspnet/AspNetWebStack/blob/ba26cfbfbf958d548e4c0a96e853250f13450dc6/src/System.Web.Http.Owin/WebApiAppBuilderExtensions.cs#L119-L128
https://github.com/aspnet/AspNetWebStack/blame/ba26cfbfbf958d548e4c0a96e853250f13450dc6/src/System.Web.Http.Owin/HttpMessageHandlerAdapter.cs#L87

There is no alternate event in IIS that fires when requests have drained.

Workaround: Remove the CancellationToken from the IAppBuilder so WebAPI cannot register with it.

appBuilder.Properties.Remove("host.OnAppDisposing");

Proposed fix: WebApi should not register for disposal with this event.
https://github.com/aspnet/AspNetWebStack/blame/ba26cfbfbf958d548e4c0a96e853250f13450dc6/src/System.Web.Http.Owin/HttpMessageHandlerAdapter.cs#L87
(When should it be disposed then?)