Shared memory w/ unmanaged DLL

[Jeremy Johnson]

This is my first excursion into .NET development, so please forgive any novice oversights...

I'm trying to write a C# application that accesses shared memory in an unmanaged Win32 DLL.

The Win32 DLL defines the shared memory in such a fashion:

// -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// define shared memory
//
// data must be initialized!  data_seg pragma applies only to initialized data.
#pragma data_seg(".SHAREDMEMORY")

int gshared_nTest = 0;

#pragma data_seg() 

// sets linker switch for shared memory section
#pragma comment(linker, "/SECTION:.SHAREDMEMORY,RWS");

How can I get my C# application to access this shared memory? Is it even possible?

Thanks,
Jeremy

[pareshgh]

actually for unmanaged stuff !!,

so what you should do is , if you want the shared memory information then you should create a function which returns the information or array,
and later on you can access that array in C# by following. C++ array creation is your side !!!


using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Explicit)]
public struct Short2DArray
{
public const int ElementSize = 2;

[FieldOffset(0)]
private int _size0;
[FieldOffset(4)]
private int _size1;

[FieldOffset(8), MarshalAs(UnmanagedType.ByValArray)]
public readonly short[] shortArray;

[FieldOffset(8), MarshalAs(UnmanagedType.ByValArray)]
public readonly byte[] byteArray;

public Short2DArray(int size0, int size1)
{
_size0 = size0;
_size1 = size1;

shortArray = new short[size0 * size1];
byteArray = new byte[size0 * size1 * ElementSize];
}

public byte this[int index]
{
get { return byteArray[index]; }
set { byteArray[index] = value; }
}

public short this[int index0, int index1]
{
get
{
if (index0 >= _size0 || index1 >= _size1)
throw new ArgumentOutOfRangeException();

return shortArray[index0 * _size0 + index1];
}
set
{
if (index0 >= _size0 || index1 >= _size1)
throw new ArgumentOutOfRangeException();

shortArray[index0 * _size0 + index1] = value;
}
}

public int ShortSize
{
get { return _size0 * _size1; }
}

public int ShortSize0
{
get { return _size0; }
}
public int ShortSize1
{
get { return _size1; }
}

public int ByteSize
{
get { return ElementSize * _size0 * _size1; }
}

public byte[] GetSafeBytes()
{
byte[] ret = new byte[ByteSize];
Buffer.BlockCopy(byteArray, 0, ret, 0, ByteSize);
return ret;
}

public short[,] GetSafeShorts()
{
short[,] ret = new short[_size0, _size1];
Buffer.BlockCopy(byteArray, 0, ret, 0, ByteSize);
return ret;
}
}



Paresh

[Jeremy Johnson]

Thanks!!

I also received this helpful reply from MatiasN on www.gotdotnet.com:


[Begin quote from MatiasN]

Yes, you can. But you will need access to the underlying dll that contains the shared memory in order to create functions that can get/set the shared memory values ( or perform whatever action on the shared memory that you need to.

I thought this was an interesting example, so I quickly created something that should work. Its primitive, but it proves the point. The following code snippet is from a VC++ 7.0 project and this is the main cpp file.
( By the way the semi-colon you had on your original #pragma comment line was unnecessary and will cause a compiler warning ).

//================================================= 
#include "stdafx.h" 
#pragma data_seg(".SHAREDMEMORY") 
int gshared_nTest=0; 
#pragma data_seg() 
#pragma comment(linker,"/SECTION:.SHAREDMEMORY,RWS") 
BOOL APIENTRY DllMain( HANDLE hModule, 
                      DWORD  ul_reason_for_call, 
                      LPVOID lpReserved 
                              ) 
{ 
    return TRUE; 
} 
extern "C" __declspec(dllexport) int __stdcall getMyData() 
{ 
      return gshared_nTest; 
} 
extern "C" __declspec(dllexport) void __stdcall setMyData( int data ) 
{ 
      gshared_nTest = data; 
} 
//================== END OF CPP FILE ================== 

Note: You must declare it as extern "C" in order to prevent the mangling of names. This is absolutely necessary in order to import it into a c# project. 

//================================================= 
To test this you can create a simple console application with the following code snippet. I put the message box in there so I could run multiple console applications at the same time and pause them so that I could see the shared memory values changing. 

//================================================= 

using System; 
using System.Windows.Forms; 
using System.Runtime.InteropServices; 

namespace TestShared 
{ 
      class TestShared 
      { 
            [DllImport(@"C:\VS Projects\Shared\Debug\Shared.dll")] 
            public static extern int getMyData(); 
            [DllImport(@"C:\VS Projects\Shared\Debug\Shared.dll")] 
            public static extern void setMyData(int data); 

            [STAThread] 
            static void Main(string[] args) 
            { 
                  setMyData( getMyData() + 100 ); 
                  MessageBox.Show( getMyData().ToString() ); 
            } 
      } 
}

-MatiasN

[End quote from MatiasN]

[pareshgh]

good. yes I had seen that . its actually kind of tough problem when u deal with C++ specially with memory since it has to pass thru several layers to talk with memory.

Paresh

[Jeremy Johnson]

I've successfully shared Integers, but I'm running into problems when I attempt to share a simple struct.

Here's what I'm defining in the unmanaged DLL:

--------------------------------------------------------------
typedef struct
{
int vt;
int nVal;
double dVal;
} BP_SHARED_DATA;

extern "C" __declspec(dllexport) BP_SHARED_DATA ReadPipe();
--------------------------------------------------------------

ReadPipe() is just returning my shared structure (not shown).

Here's the .NET side of things:

--------------------------------------------------------------
public class BrowserPipe
{
[StructLayout( LayoutKind.Sequential)]
public class SHARED_DATA
{
public Int32 vt;
public Int32 nVal;
public Double dVal;
};

[DllImport(@"BrowserPipe.ocx")]
public static extern SHARED_DATA ReadPipe();
}

---------------------------------------------------------------

Whenever I call ReadPipe(), I get a "System.NotSupportedException". I've also tried defining "SHARED_DATA" as a struct, but it doesn't solve the problem.

Any suggestions? Oh, I should mention that I'm using the Compact Framework.

Thanks!
Jeremy

[pareshgh]

try using with another kind of Layout strucutre..

Paresh