Hi,

I am trying to call the Tool Help API (
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/perfmon/base/to
ol_help_functions.asp
) from C# using interop.

I have declared:

       [DllImport("Kernel32.dll")]
       private static extern IntPtr CreateToolhelp32Snapshot(UInt32
dwFlags, UInt32 th32ProcessID);

       [DllImport("Kernel32.dll")]
       private static extern bool Thread32First(IntPtr hSnapshot, ref
THREADENTRY32 lpte);

The THREADENTRY32 struct is declared as:

       [StructLayout(LayoutKind.Sequential)]
       public class THREADENTRY32
       {
           public UInt32 dwSize;
           public UInt32 cntUsage;
           public UInt32 th32ThreadID;
           public UInt32 th32OwnerProcessID;
           public Int32 tpBasePri;
           public Int32 tpDeltaPri;
           public UInt32 dwFlags;
       }

On the C side its:
typedef struct tagTHREADENTRY32 {
 DWORD dwSize;
 DWORD cntUsage;
 DWORD th32ThreadID;
 DWORD th32OwnerProcessID;
 LONG tpBasePri;
 LONG tpDeltaPri;
 DWORD dwFlags;
} THREADENTRY32,
*PTHREADENTRY32;

I call CreateToolhelp32Snapshot with the current process ID and
TH32CS_SNAPTHREAD (=0x4) and get something which appears correct(ie the
handle returned is not equal to INVALID_HANDLE_VALUE(=-1) and
GetLastError returns 0).

However when i then call:
           THREADENTRY32 te = new THREADENTRY32();
           Int32 size =
System.Runtime.InteropServices.Marshal.SizeOf(te);
           te.dwSize = (uint)size;
           bool ok = Thread32First(h, ref te); // h is return value of
CreateToolhelp32Snapshot

ok is false and GetLastError is 24 which translates to:
ERROR_BAD_LENGTH ("The program issued a command but the command length
is incorrect.").

Im guessing something is wrong with the struct i am passing in, but
what? I have checked that dwSize is set to 28 which is correct as far
as i can tell. Any help is appreciated.