SetThreadDesktop keeps returning "Resource in Use"

[Frank Perry]

I have a utility that monitors whether certain third party GU
applications are running and if not, it starts them up. I would lik
to get rid of this utility and instead just have a Windows Service tha
performs that same function. Because Windows Services don't run in th
interactive Windows Station and C# has nothing to do this sort o
thing, I am being forced to use unmanaged function calls from my C
code. I first obtain the access token for the current logged in use
by enumerating all processes using EnumProcesses(), callin
OpenProcess() on each pid, calling EnumProcessModules() to enumerat
the process modules, searching for explorer.exe usin
GetModuleBaseName() and getting it's token with OpenProcessToken() i
found. If not I call CloseHandle() and move on. Once found,
duplicate the token to make an impersonation token, us
ImpersonateLoggedOnUser() and Close the handle. Next I cal
OpenWindowStation() for WinSta0 the OpenDesktop() for the Defaul
desktop.

The problem occurs when I call SetThreadDesktop() with the handl
returned from OpenDesktop(). SetThreadDesktop() is generating erro
170 "resource in use". What could cause this? I mean, I'm closin
handles that I'm not using, am I not able to call this function if
have *any* handles open? If so, how does one use this properly in C
code?

FYI, I'm on WinXP, but will need this to run on win2k if it's eve
possible. I can post some source code if you want, but it's kinda jus
thrown together at the moment because I've just been experimenting wit
various ways of doing what I'm trying to do.

Thanks
Fran

--
Frank Perr
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[Frank Perry]

For clarity, here is what the function I'm using currently looks like:

private void LaunchApp()
{
GetDesktopWindow();
IntPtr hwinstaSave = GetProcessWindowStation();
UInt32 ThreadID = GetCurrentThreadId();
IntPtr hDeskSave = GetThreadDesktop(ThreadID);

UInt32 [] procIDs = new UInt32[2048];
UInt32 [] cbNeeded = new UInt32[1];
UInt32 procarrsize = UInt32.Parse(procIDs.Length.ToString());
Int32 error;
RevertToSelf();
if (!EnumProcesses(procIDs, procarrsize, cbNeeded))
{
error = Marshal.GetLastWin32Error();
return;
}

IntPtr tokenhandle = IntPtr.Zero;
IntPtr prochandle = IntPtr.Zero;
bool pidfound = false;

foreach (UInt32 pid in procIDs)
{
if ((pid != 0) && (pid != 4))
{
prochandle = OpenProcess(0x0400 | 0x0010, false, pid);

if (!prochandle.Equals(null))
{
IntPtr[] mod = new IntPtr[2048];

if (EnumProcessModules(prochandle, mod
UInt32.Parse(mod.Length.ToString()), cbNeeded))
{
foreach(IntPtr modnum in mod)
{
if (modnum.ToInt32() > 0)
{
StringBuilder exename = new StringBuilder(256);

if (GetModuleBaseName(prochandle, modnum, exename
exename.Capacity) != 0)
{
if (String.Compare(exename.ToString().ToLower()
"explorer.exe") == 0)
{
if (OpenProcessToken(prochandle, 0x0002, ref tokenhandle) !
0)
{
pidfound = true;
break;
}
else
{
error = Marshal.GetLastWin32Error();
CloseHandle(prochandle);
return;
}
}
}
else
{
error = Marshal.GetLastWin32Error();
continue;
}
}
}

if (pidfound)
{
CloseHandle(prochandle);
break;
}
}
else
{
CloseHandle(prochandle);
LogError(Marshal.GetLastWin32Error());
continue;
}
}

CloseHandle(prochandle);

}
}

IntPtr duptok = IntPtr.Zero;
if (!DuplicateTokenEx(tokenhandle, 0x0004 | 0x0008 |0x0020
IntPtr.Zero, 2, 2, ref duptok))
{
error = Marshal.GetLastWin32Error();
CloseHandle(prochandle);
return;
}

if (ImpersonateLoggedOnUser(duptok) != 0)
{
CloseHandle(prochandle);
}
else
{
error = Marshal.GetLastWin32Error();
CloseHandle(prochandle);
return;
}

IntPtr hWinStaUser = IntPtr.Zero;
hWinStaUser = OpenWindowStation("WinSta0", false, MAXIMUM_ALLOWED);
if (!SetProcessWindowStation(hWinStaUser))
{
RevertToSelf();
LogError(Marshal.GetLastWin32Error());
return;
}

IntPtr hDeskUser = OpenDesktop("Default", 0, false, MAXIMUM_ALLOWED);
RevertToSelf();

// The error occurs on the next line.
if (!SetThreadDesktop(hDeskUser))
{
RevertToSelf();
LogError(Marshal.GetLastWin32Error());
return;
}

...
...
--
Frank Perr
-----------------------------------------------------------------------
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