Vtables

[upretyrohan]

What is the use of SetupVTables() method generated for each class during C++ conversion to C#. What does protected void[] __OriginalVTables; private static void[] _Thunks; private static void*[] __ManagedVTables; store

[tritao]

Those members provide the machinery necessary to allow overriding the C++ virtual methods from C#.

They store the original virtual tables setup by C++, which we then manipulate to contain pointers to the thunks created by the .NET runtime that provide the transitions between the native and managed world.

[upretyrohan]

Thanks, I want to understand more. Here SetObject and SetObject1 are virtual methods in unmanaged world. __OriginalVTables stores vtable pointer, right? What is the use of _SetObjectDelegateHook and _SetObject1DelegateHook . There are never invoked as per what i found while debugging

        private void SetupVTables(bool destructorOnly = false)
        {
            if (__OriginalVTables != null)
                return;
            __OriginalVTables = new void*[] { *(void**) (__Instance + 0) };

            if (destructorOnly)
                return;
            if (_Thunks == null)
            {
                _Thunks = new void*[2];
                _SetObjectDelegateInstance += _SetObjectDelegateHook;
                _Thunks[0] = Marshal.GetFunctionPointerForDelegate(_SetObjectDelegateInstance).ToPointer();
                _SetObject1DelegateInstance += _SetObject1DelegateHook;
                _Thunks[1] = Marshal.GetFunctionPointerForDelegate(_SetObject1DelegateInstance).ToPointer();
            }

            if (__ManagedVTables == null)
            {
                __ManagedVTables = new void*[1];
                var vfptr0 = Marshal.AllocHGlobal(2 * 4);
                __ManagedVTables[0] = vfptr0.ToPointer();
                *(void**) (vfptr0 + 0) = _Thunks[0];
                *(void**) (vfptr0 + 4) = _Thunks[1];
            }

            *(void**) (__Instance + 0) = __ManagedVTables[0];
        }