.NET : How to PInvoke UpdateProcThreadAttribute

Question

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.

it is always worth checking http://www.pinvoke.net/ for these type of problems. — Ian Ringrose, Sep 21 '09 at 14:18

Stephen Martin · Accepted Answer · 2009-09-15T16:51:19.870

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.

Thanks for this. I updated the signature but still get 50. How do you recommend setting up, say, lpValue to hold the handle of a process. I have it as an IntPtr (pHandle, say) so do I just pass that straight through and for cbSize do something like: IntPtr pSize = (System.IntPtr)(Marshal.SizeOf(pHandle)); ? Normally my pinvokes are OK, but this one seems particular fiendish. I am very grateful for your response. Thank you. — mrbouffant, Sep 15 '09 at 14:57
Thanks so much. You have helped me nearly get there.. Now I get error 24 (bad length). In your example above you talked about pass IntPtr.Size as the cbSize parameter, whereas in your original post you had this as an IntPtr. I tried IntPtr lpSize = Marshal.AllocHGlobal(IntPtr.Size); Marshal.WriteInt32(lpSize, IntPtr.Size) and passing that through. Clearly it is wrong but I can't work out what the correct usage should be. Any ideas? Thanks. — mrbouffant, Sep 15 '09 at 16:35
Sorry, I left out the conversion. It should be (IntPtr)IntPtr.Size. I've corrected the post. — Stephen Martin, Sep 15 '09 at 16:50

.NET : How to PInvoke UpdateProcThreadAttribute

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