Support Advisory 49138: Instrumenting an async method results in System.Runtime.InteropServices.SEHException

This document describes the support advisory for an AppDynamics product.

Summary

AppDynamics has discovered an issue triggered when the .NET agent attempts to instrument any async method encapsulated in a generic class or method. In most cases this will result in a System.Runtime.InteropServices.SEHException. In rare cases, an application hang could result.

Affected Software


Product	Component	Version
AppDynamics .NET APM	.NET Agent	4.1 versions below 4.1.3

Impact

Application Exception : Instrumentation of a method described in the Summary will result in an SEHException.

Examples

// An async method called inside of a generic class will trigger the exception.
class GenericClass<T>
{
   async Task AsyncMethod()
   {
   //Do work...  

   }
}

// An async method called inside of a generic method will also trigger the exception.
class MyClass
{
   public async void MyMethod<T>(T input)
   {
      await AsyncMethod();
   }
}

Workaround

Customers running version 4.1.0 – 4.1.2 versions of the agent are advised to upgrade to 4.1.3 or later, or
Edit the .NET Agent Configuration file to disable the AsyncStateMachineInstrumentor, as described in the following steps.

To disable AsyncStateMachineInstrumentor:

Open the following file, depending on your version of Windows:
- Windows Server 2008 and later: %ProgramData%\AppDynamics\DotNetAgent\Config\config.xml
- Windows Server 2003: %AllUsersProfile%\Application Data\AppDynamics\DotNetAgent\Config\config.xml

Replace or update the <machine-agent> node to include:

<machine-agent>
   <instrumentation>
      <instrumentor name="AsyncStateMachineInstrumentor" enabled="false" />
   </instrumentation>
</machine-agent>

Restart the AppDynamics.Agent.Coordinator service and then all instrumented processes.

Documentation