'async/await throws NullReferenceException how can we diagnose where we messed it up?

we have started using async/await in asp.net application, now we are getting the famous exception in our production

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/376/ROOT

Process ID: 3796

Exception: System.NullReferenceException

Message: Object reference not set to an instance of an object.

StackTrace: at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext) at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext) at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state) at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state) at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask) --- End of stack trace from previous location where exception was thrown --- at System.Threading.Tasks.AwaitTaskContinuation.b__1(Object s) 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()

Is there any way we can get more information about the code/task that makes problem?

Second question: we tried to reproduce the exception locally in a simple test webform application 

        protected void Page_Load(object sender, EventArgs e)
    {
        LogMessageToFile("before_task");
        var t = Test();

        tasks.Add(t);
    }
    async Task Test()
    {
        await Task.Run(() =>
       {
           LogMessageToFile("inside_task");
           Thread.Sleep(1000);
       }
            );
        this.Title = "test";
        LogMessageToFile("after_task");

        //  throw new Exception("");
    }

but we never get the exception in our test page seems that the code after await in Test function is never called and the tasks state are WaitingForActivation, why we do not get exception in this code?

c++sharpasp.netasync-awaitarmbootloadercortex-msamd21


Solution 1:[1]

I think after return back from "await", the http request process already finish, HttpContext should null at that time. https://referencesource.microsoft.com/#system.web/ThreadContext.cs,56 and then caused NullReferenceException.

Solution 2:[2]

Yes, you could implement firmware encryption on SAMD21 as well as a lot of other MCUs. The idea of firmware encryption does not depend on exact chip or even MCU architecture. The main things are:

  1. The manufacturer releases the new firmware and encrypts it.
  2. The encrypted firmware is transmitted via public domain into the target MCU.
  3. The target MCU decrypt the encrypted firmware and flashes it directly to the internal flash.
  4. The target MCU should be locked to prevent reading decrypted firmware from the internal flash.

As you can see, there is nothing here about protocols, encryption methods, or microcontroller type - all this up to you. The main thing that is needed from the microcontroller is the presence of a protection bit and a memory area for the bootloader. You could use any of the Safe and Secure Bootloader Implementation Tutorial and adopt it to SAMD21 accordingly.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 user2767141
Solution 2 Mephistt

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