.NET : How to PInvoke UpdateProcThreadAttribute

Question

Hi All:

I am trying to PInvoke UpdateProcThreadAttribute() on Windows 7 but my attempts just keep returning FALSE with a Last Win32 Error of 50.

Function declaration (from MSDN)

BOOL WINAPI UpdateProcThreadAttribute( __inout LPPROC_THREAD_ATTRIBUTE_LIST lpAttributeList, __in DWORD dwFlags, __in DWORD_PTR Attribute, __in PVOID lpValue, __in SIZE_T cbSize, __out_opt PVOID lpPreviousValue, __in_opt PSIZE_T lpReturnSize );

Here is my attempt at the PInvoke signature:

[DllImport("kernel32.dll", CallingConvention = CallingConvention.Winapi, SetLastError = true)] public static extern bool UpdateProcThreadAttribute ( IntPtr lpAttributeList, UInt32 dwFlags, ref UInt32 Attribute, ref IntPtr lpValue, ref IntPtr cbSize, IntPtr lpPreviousValue, IntPtr lpReturnSize );

Is this declaration sensible? Thanks.

Answer 1

You have a few problems with your declaration but the one that is giving you the not supported error is the Attribute parameter. A DWORD_PTR is not a pointer but rather a pointer sized unsigned integer so rather than ref uint it should be an IntPtr.

The declaration I would use is:

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UpdateProcThreadAttribute(
        IntPtr lpAttributeList, uint dwFlags, IntPtr Attribute,
        IntPtr lpValue, IntPtr cbSize, IntPtr lpPreviousValue, 
        IntPtr lpReturnSize);

EDIT:

I tried to do this as a comment but it doesn't take to code very well.

For a process handle you need an IntPtr to hold the handle. So you would need something like:

IntPtr hProcess //previously retrieved.
IntPtr lpAttributeList //previously allocated using InitializeProcThreadAttributeList and Marshal.AllocHGlobal.

const int PROC_THREAD_ATTRIBUTE_PARENT_PROCESS = 0x00020000;
IntPtr lpValue = Marshal.AllocHGlobal(IntPtr.Size); 
Marshal.WriteIntPtr(lpValue, hProcess);
if(UpdateProcThreadAttribute(lpAttributeList, 0, (IntPtr)PROC_THREAD_ATTRIBUTE_PARENT_PROCESS, lpValue, (IntPtr)IntPtr.Size, IntPtr.Zero, IntPtr.Zero))
{
    //do something
}

//Free lpValue only after the lpAttributeList is deleted.