CLR Hosting: Call a function with an arbitrary method signature?

Question

I need to take a C++ program, load CLR and call a function in a C# library. The function I need to call takes in a COM interface as the parameter.

My problem is, the CLR hosting interface only seems to let you call a method with this signature:

int Foo(String arg)

Example, this C++ code loads CLR and runs the P.Test function in "test.exe":

ICLRRuntimeHost *pClrHost = NULL;
HRESULT hrCorBind = CorBindToRuntimeEx(NULL, L"wks", 0, CLSID_CLRRuntimeHost, IID_ICLRRuntimeHost, (PVOID*)&pClrHost);

HRESULT hrStart = pClrHost->Start();

DWORD retVal;
HRESULT hrExecute = pClrHost->ExecuteInDefaultAppDomain(L"C:\\Test.exe", L"P", L"Test", L"", &retVal);

What I need to do is call a function with this method signature (note I own the C# code, so I can change it):

void SomeFunction(IFoo interface)

Where IFoo is a com interface. I could even do what I need to if I could call a function like this:

IntPtr SomeFunction();

I could have SomeFunction construct a correct delegate then use Marshal.GetFunctionPointerForDelegate. However, I can't figure out how to make the hosting interfaces do anything other than call a function with an int func(string) signature.

Does anyone know how to call a C# function from C++ code with a different signature?

(Note I cannot use C++/CLI for this. I need to use the hosting APIs.)

Answer 1

Edit: I promised to update my answer to include the code for passing 64-bit values, so here's goes..

• I left the original answer if someone's interested in a less complicated solution for a 32-bit system.

Note: Since you're using CorBindToRuntimeEx, which is obsolete in .net 4.0, I'll assume a .net 2.0 compliant solution using good old Win32 API.

So, in order to pass data between C# and C++ (in our case - the IntPtr of a delegate), we'll create a small Win32 DLL project, named SharedMem, with two straight-forward methods.

SharedMem.h

#pragma once

#ifdef SHAREDMEM_EXPORTS
#define SHAREDMEM_API __declspec(dllexport)
#else
#define SHAREDMEM_API __declspec(dllimport)
#endif

#define SHAREDMEM_CALLING_CONV __cdecl

extern "C" {
    SHAREDMEM_API BOOL SHAREDMEM_CALLING_CONV SetSharedMem(ULONGLONG _64bitValue);
    SHAREDMEM_API BOOL SHAREDMEM_CALLING_CONV GetSharedMem(ULONGLONG* p64bitValue);
}

Now for the implementation file:

SharedMem.cpp

#include "stdafx.h"
#include "SharedMem.h"

HANDLE      hMappedFileObject = NULL;  // handle to mapped file
LPVOID      lpvSharedMem = NULL;       // pointer to shared memory
const int   SHARED_MEM_SIZE = sizeof(ULONGLONG);

BOOL CreateSharedMem()
{
    // Create a named file mapping object
    hMappedFileObject = CreateFileMapping(
                            INVALID_HANDLE_VALUE,
                            NULL,
                            PAGE_READWRITE,
                            0,
                            SHARED_MEM_SIZE,
                            TEXT("shmemfile") // Name of shared mem file
                        );

    if (hMappedFileObject == NULL) 
    {
        return FALSE;
    }

    BOOL bFirstInit = (ERROR_ALREADY_EXISTS != GetLastError());

    // Get a ptr to the shared memory
    lpvSharedMem = MapViewOfFile( hMappedFileObject, FILE_MAP_WRITE, 0, 0, 0);

    if (lpvSharedMem == NULL) 
    {
        return FALSE; 
    }

    if (bFirstInit) // First time the shared memory is accessed?
    {
        ZeroMemory(lpvSharedMem, SHARED_MEM_SIZE); 
    }

    return TRUE;
}

BOOL SetSharedMem(ULONGLONG _64bitValue) 
{ 
    BOOL bOK = CreateSharedMem();

    if ( bOK )
    {
        ULONGLONG* pSharedMem = (ULONGLONG*)lpvSharedMem;
        *pSharedMem = _64bitValue;
    }

    return bOK;
}

BOOL GetSharedMem(ULONGLONG* p64bitValue) 
{ 
    if ( p64bitValue == NULL ) return FALSE;

    BOOL bOK = CreateSharedMem();

    if ( bOK )
    {
        ULONGLONG* pSharedMem = (ULONGLONG*)lpvSharedMem;
        *p64bitValue = *pSharedMem;
    }

    return bOK;
}

• Note that for simplicity I'm just sharing a 64-bit value, but this is a general way of sharing memory between C# and C++. Feel free to enlarge SHARED_MEM_SIZE and/or add functions in order to share other data types as you see fit.

This is how we'll consume the above methods: we'll use SetSharedMem() on the C# side in order to set the delegate's IntPtr as a 64-bit value (regardless if the code runs on a 32 or a 64 bit system).

C# Code

namespace CSharpCode
{
    delegate void VoidDelegate();

    static public class COMInterfaceClass
    {
        [DllImport( "SharedMem.dll" )]
        static extern bool SetSharedMem( Int64 value );

        static GCHandle gcDelegateHandle;

        public static int EntryPoint(string ignored)
        {
            IntPtr pFunc = IntPtr.Zero;
            Delegate myFuncDelegate = new VoidDelegate( SomeMethod );
            gcDelegateHandle = GCHandle.Alloc( myFuncDelegate );
            pFunc = Marshal.GetFunctionPointerForDelegate( myFuncDelegate );
            bool bSetOK = SetSharedMem( pFunc.ToInt64() );
            return bSetOK ? 1 : 0;
        }

        public static void SomeMethod()
        {
            MessageBox.Show( "Hello from C# SomeMethod!" );
            gcDelegateHandle.Free();
        }
    }
}

• Note the use of GCHandle in order to prevent the delegate from being garbage-collected.
• For good measures, we'll use the return value as a success/failure flag.

On the C++ side we'll extract the 64-bit value using GetSharedMem(), convert it to a function pointer and invoke the C# delegate.

C++ Code

#include "SharedMem.h"
typedef void (*VOID_FUNC_PTR)();

void ExecCSharpCode()
{
    ICLRRuntimeHost *pClrHost = NULL;
    HRESULT hrCorBind = CorBindToRuntimeEx(
                                NULL,
                                L"wks",
                                0,
                                CLSID_CLRRuntimeHost,
                                IID_ICLRRuntimeHost,
                                (PVOID*)&pClrHost
                            );

    HRESULT hrStart = pClrHost->Start();

    DWORD retVal;
    HRESULT hrExecute = pClrHost->ExecuteInDefaultAppDomain(
                                szPathToAssembly,
                                L"CSharpCode.COMInterfaceClass",
                                L"EntryPoint",
                                L"",
                                &retVal // 1 for success, 0 is a failure
                            );

    if ( hrExecute == S_OK && retVal == 1 )
    {
        ULONGLONG nSharedMemValue = 0;
        BOOL bGotValue = GetSharedMem(&nSharedMemValue);
        if ( bGotValue )
        {
            VOID_FUNC_PTR CSharpFunc = (VOID_FUNC_PTR)nSharedMemValue;
            CSharpFunc();
        }
    }
}

---

The Original Answer - Good for 32-bit Systems

Here's a solution that is based on using IntPtr.ToInt32() in order to convert the delegate func. ptr. to the int which is returned from the static C# EntryPoint method.

(*) Note the use of GCHandle in order to prevent the delegate from being garbage-collected.

C# Code

namespace CSharpCode
{
    delegate void VoidDelegate();

    public class COMInterfaceClass
    {
        static GCHandle gcDelegateHandle;

        public static int EntryPoint(string ignored)
        {
            IntPtr pFunc = IntPtr.Zero;
            Delegate myFuncDelegate = new VoidDelegate( SomeMethod );
            gcDelegateHandle = GCHandle.Alloc( myFuncDelegate );
            pFunc = Marshal.GetFunctionPointerForDelegate( myFuncDelegate );
            return (int)pFunc.ToInt32();
        }

        public static void SomeMethod()
        {
            MessageBox.Show( "Hello from C# SomeMethod!" );
            gcDelegateHandle.Free();
        }
    }
}

C++ Code We'll need to convert the returned int value to a function pointer, so we'll start off by defining a void function ptr. type:

typedef void (*VOID_FUNC_PTR)();

And the rest of the code looks pretty much like your original code, with the addition of converting and executing the function ptr.

ICLRRuntimeHost *pClrHost = NULL;
HRESULT hrCorBind = CorBindToRuntimeEx(
                            NULL,
                            L"wks",
                            0,
                            CLSID_CLRRuntimeHost,
                            IID_ICLRRuntimeHost,
                            (PVOID*)&pClrHost
                        );

HRESULT hrStart = pClrHost->Start();

DWORD retVal;
HRESULT hrExecute = pClrHost->ExecuteInDefaultAppDomain(
                            szPathToAssembly,
                            L"CSharpCode.COMInterfaceClass",
                            L"EntryPoint",
                            L"",
                            &retVal
                        );

if ( hrExecute == S_OK )
{
    VOID_FUNC_PTR func = (VOID_FUNC_PTR)retVal;
    func();
}

A Little Bit of Extra

You can also make use of the string input in order to choose which method to execute:

public static int EntryPoint( string interfaceName )
{
    IntPtr pFunc = IntPtr.Zero;

    if ( interfaceName == "SomeMethod" )
    {
        Delegate myFuncDelegate = new VoidDelegate( SomeMethod );
        gcDelegateHandle = GCHandle.Alloc( myFuncDelegate );
        pFunc = Marshal.GetFunctionPointerForDelegate( myFuncDelegate );
    }

    return (int)pFunc.ToInt32();
}

• You can get even more generic by using reflection in order to find the correct method according to the given string input.