Detecting cross-thread marshaling by COM RCW objects in C#
You should be able to accomplish this by testing whether you can get to the IMarshal interface, which should be aggregated into the proxy if the call is a cross-apartment call. First, you will need to declare IMarshal somewhere in your project:
[System.Runtime.InteropServices.InterfaceTypeAttribute(1)] [System.Runtime.InteropServices.Guid("00000003-0000-0000-C000-000000000046")] public interface IMarshal { // no methods needed, just querying for the interface }Then, you can test for the interface like so.
if (suspiciousComInterface is IMarshal) // cross-apartment call else // direct call