Loading x86 or x64 assembly

Question

I have two versions of System.Data.SQLite.DLL - for x86 and x64 platform. The x86 version keeps in application folder and x64 version keeps in appFolder\x64 folder. The application compiled as AnyCPU. How can i load needed version of SQLite according to windows platform?

Answer 1

If you are using SQLite from http://system.data.sqlite.org, the System.Data.SQLite.DLL is completely managed. There is an underlying native DLL, SQLite.Interop.DLL, that needs to change depending on the process (32- or 64-bit).

I deploy the native libraries in ".\Native\X64" for 64-bit and ".\Native\X86" for 32-bit. At runtime P/Invoke SetDllDirectory to set the DLL load directory pointing at the correct path for the process. http://msdn.microsoft.com/en-us/library/ms686203(v=vs.85).aspx

(Note that I'm not familiar with the architecture of the legacy System.Data.SQLite.DLL version from http://sqlite.phxsoftware.com)

private static class NativeMethods
{
    [DllImport("kernel32.dll", CallingConvention = CallingConvention.Cdecl)]
    internal static extern bool SetDllDirectory(string pathName);
}

... 

    // Underlying SQLite libraries are native. 
    // Manually set the DLL load path depending on the process.
    var path = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "Native");
    if(IntPtr.Size == 8) // or: if(Environment.Is64BitProcess) // .NET 4.0
    {
        path = Path.Combine(path, "X64");
    }
    else
    {
        // X32
        path = Path.Combine(path, "X86");
    }
    NativeMethods.SetDllDirectory(path);

Answer 2

Some antivir progs prevent SetDllDirectory() - took me a long time to realize that. We are using

System.Reflection.Assembly myass = System.Reflection.Assembly.GetExecutingAssembly();
FileInfo fi = new FileInfo(myass.Location);
System.IntPtr moduleHandle = LoadLibraryEx(fi.Directory.FullName + "\\x64\\SQLite.Interop.DLL", IntPtr.Zero, 0);

to load the x64 DLL with explicit path. It is loaded at that point and the .NET Runtime will use the in-memory DLL instead of searching the disk for it.