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

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:

1. 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

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

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

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