Custom Marshallers never use stateful GetPinnableReference on struct

[jtschuster]

Even when present, and in scenarios where the stateless GetPinnableReference would be used, the stateful method will not be used.

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Issue Details

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Even when present, and in scenarios where the stateless GetPinnableReference would be used, the stateful method will not be used.

Author:	jtschuster
Assignees:	-
Labels:	area-System.Runtime.InteropServices, source-generator
Milestone:	9.0.0

[jkoritzinsky]

@jtschuster can you share the case where this occurs? I could have sworn that we have tests that validate this behavior in the LibraryImportGenerator.Tests test suite.

[jtschuster]

In IStatefulPinnedMarshalling, with a stateless GetPinnableReference on the marshaller, the by value parameter RCW looks like this:

    void global::SharedTypes.ComInterfaces.IStatefulPinnedMarshalling.Method(global::SharedTypes.ComInterfaces.StatefulPinnedType param)
    {
        var(__this, __vtable_native) = ((System.Runtime.InteropServices.Marshalling.IUnmanagedVirtualMethodTableProvider)this).GetVirtualMethodTableInfoForKey(typeof(global::SharedTypes.ComInterfaces.IStatefulPinnedMarshalling));
        int __invokeRetVal;
        // Pin - Pin data in preparation for calling the P/Invoke.
        fixed (void* __param_native = &global::SharedTypes.ComInterfaces.StatefulPinnedTypeMarshaller.GetPinnableReference(param))
        {
            __invokeRetVal = ((delegate* unmanaged[MemberFunction]<void*, nint, int> )__vtable_native[3])(__this, (nint)__param_native);
        }

        // NotifyForSuccessfulInvoke - Keep alive any managed objects that need to stay alive across the call.
        System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
        System.GC.KeepAlive(this);
    }

With only a stateful GetPinnableReference, it looks like this:

    void global::SharedTypes.ComInterfaces.IStatefulPinnedMarshalling.Method(global::SharedTypes.ComInterfaces.StatefulPinnedType param)
    {
        var(__this, __vtable_native) = ((System.Runtime.InteropServices.Marshalling.IUnmanagedVirtualMethodTableProvider)this).GetVirtualMethodTableInfoForKey(typeof(global::SharedTypes.ComInterfaces.IStatefulPinnedMarshalling));
        nint __param_native = default;
        int __invokeRetVal = default;
        // Setup - Perform required setup.
        global::SharedTypes.ComInterfaces.StatefulPinnedTypeMarshaller __param_native__marshaller = new();
        try
        {
            // Marshal - Convert managed data to native data.
            __param_native__marshaller.FromManaged(param);
            // Pin - Pin data in preparation for calling the P/Invoke.
            fixed (void* __param_native__unused = __param_native__marshaller)
            {
                // PinnedMarshal - Convert managed data to native data that requires the managed data to be pinned.
                __param_native = __param_native__marshaller.ToUnmanaged();
                __invokeRetVal = ((delegate* unmanaged[MemberFunction]<void*, nint, int> )__vtable_native[3])(__this, __param_native);
            }

            // NotifyForSuccessfulInvoke - Keep alive any managed objects that need to stay alive across the call.
            System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
            __param_native__marshaller.OnInvoked();
            System.GC.KeepAlive(this);
        }
        finally
        {
            // CleanupCallerAllocated - Perform cleanup of caller allocated resources.
            __param_native__marshaller.Free();
        }
    }

[jtschuster]

Looks like this test is supposed to, but it doesn't actually validate that GetPinnableReference was called.

[jkoritzinsky]

No, that is calling GetPinnableReference. The GetPinnableReference call is part of the fixed (void* __param_native__unused = __param_native__marshaller) statement (it's implied by the C# language).