Marshal.StructureToPtr without boxing

问题:

Is there a way to marshal a structure (possibly stored in a TypedReference) to unmanaged memory without actually boxing it? The type of the structure isn't known at runtime, so I can't use the generic overload of StructureToPtr (.NET 4.5.1). I can get a MethodInfo of the StructureToPtr overload, but there doesn't seem to be a way to invoke it passing a generic reference or a TypedReference.

Edit: The generic StructureToPtr still boxes the structure, so trying to invoke it is useless.

回答1:

I've finally found the answer, the SafeBuffer class. It contains exactly what I wanted - structure with marshalling methods using both TypedReference and generic parameters. So, it's really simple then to make a wrapper:

public static unsafe class InteropTools
{
    private static readonly Type SafeBufferType = typeof(SafeBuffer);
    public delegate void PtrToStructureNativeDelegate(byte* ptr, TypedReference structure, uint sizeofT);
    public delegate void StructureToPtrNativeDelegate(TypedReference structure, byte* ptr, uint sizeofT);
    const BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Static;
    private static readonly MethodInfo PtrToStructureNativeMethod = SafeBufferType.GetMethod("PtrToStructureNative", flags);
    private static readonly MethodInfo StructureToPtrNativeMethod = SafeBufferType.GetMethod("StructureToPtrNative", flags);
    public static readonly PtrToStructureNativeDelegate PtrToStructureNative = (PtrToStructureNativeDelegate)Delegate.CreateDelegate(typeof(PtrToStructureNativeDelegate), PtrToStructureNativeMethod);
    public static readonly StructureToPtrNativeDelegate StructureToPtrNative = (StructureToPtrNativeDelegate)Delegate.CreateDelegate(typeof(StructureToPtrNativeDelegate), StructureToPtrNativeMethod);

    private static readonly Func<Type,bool,int> SizeOfHelper_f = (Func<Type,bool,int>)Delegate.CreateDelegate(typeof(Func<Type,bool,int>), typeof(Marshal).GetMethod("SizeOfHelper", flags));

    public static void StructureToPtrDirect(TypedReference structure, IntPtr ptr, int size)
    {
        StructureToPtrNative(structure, (byte*)ptr, unchecked((uint)size));
    }

    public static void StructureToPtrDirect(TypedReference structure, IntPtr ptr)
    {
        StructureToPtrDirect(structure, ptr, SizeOf(__reftype(structure)));
    }

    public static void PtrToStructureDirect(IntPtr ptr, TypedReference structure, int size)
    {
        PtrToStructureNative((byte*)ptr, structure, unchecked((uint)size));
    }

    public static void PtrToStructureDirect(IntPtr ptr, TypedReference structure)
    {
        PtrToStructureDirect(ptr, structure, SizeOf(__reftype(structure)));
    }

    public static void StructureToPtr<T>(ref T structure, IntPtr ptr)
    {
        StructureToPtrDirect(__makeref(structure), ptr);
    }

    public static void PtrToStructure<T>(IntPtr ptr, out T structure)
    {
        structure = default(T);
        PtrToStructureDirect(ptr, __makeref(structure));
    }

    public static T PtrToStructure<T>(IntPtr ptr)
    {
        T obj;
        PtrToStructure(ptr, out obj);
        return obj;
    }

    public static int SizeOf<T>(T structure)
    {
        return SizeOf<T>();
    }

    public static int SizeOf<T>()
    {
        return SizeOf(typeof(T));
    }

    public static int SizeOf(Type t)
    {
        return SizeOfHelper_f(t, true);
    }
}

Usage

Guid g = Guid.NewGuid();
int size = InteropTools.SizeOf(g);
IntPtr mem = Marshal.AllocHGlobal(size);
InteropTools.StructureToPtr(ref g, mem);

Guid g2 = InteropTools.PtrToStructure<Guid>(mem);

Now, does it actually have any advantages over the non-generic object-taking methods in the Marshal class? It seems the StructureToPtr takes about 80 % less time, and PtrToStructure can take almost 95 % less time. Also, these methods can handle nullable types correctly.