SwitchDesktop works momentarily but switches back after a moment - c++

Question

I've got some code to create a new desktop and launch a process into that desktop.
One a few select Windows XP machines, when this code runs, I can see it switch to the new desktop and start the process, but almost immediately, the desktop switches back to the normal desktop.
This code works fine on about 98% of machines, and I can't seem to isolate any reason for this not working on the others.
Should SwitchDesktop be reliable? Can I hook calls to SwitchDesktop that might be called from another application?
My code:
int DLL_EXP_IMP WINAPI Process_Desktop(char *szDesktopName, char *szPath)
{
HDESK hOriginalThread;
HDESK hOriginalInput;
HDESK hNewDesktop;
int procSuccess;
// Save original ...
hOriginalThread = GetThreadDesktop(GetCurrentThreadId());
hOriginalInput = OpenInputDesktop(0, FALSE, DESKTOP_SWITCHDESKTOP);
// Create a new Desktop and switch to it
hNewDesktop = CreateDesktop(szDesktopName, NULL, NULL, DF_ALLOWOTHERACCOUNTHOOK, GENERIC_ALL, NULL);
SetThreadDesktop(hNewDesktop);
SwitchDesktop(hNewDesktop);
// This call blocks until the process exits, and is confirmed to work on the affected machines
procSuccess = StartProcess(szDesktopName, szPath);
// Restore original ...
SwitchDesktop(hOriginalInput);
SetThreadDesktop(hOriginalThread);
// Close the Desktop
CloseDesktop(hNewDesktop);
if (procSuccess != 0)
{
return procSuccess;
}
else
{
return 0;
}
}

Answer 1

My guess is that SetThreadDesktop() fails.
From MSDN:
"The SetThreadDesktop function will fail if the calling thread has any windows or hooks on its current desktop (unless the hDesktop parameter is a handle to the current desktop)."
You mentioned that StartProcess() blocks until the process terminated.
So then there is nobody referencing the new desktop and thus the desktop will go away.
You may want to consider wrapping fallible system calls in C++
-- throwing an exception in case of they fail.
And certainly the pair CreateDesktop/CloseDesktop belongs into a C++ resource wrapper.
This is 2013!

Answer 2

Either SwitchDesktop is failing (most of the time is access denies, or error 170 because of existing handles in another desktop), or there is another program that switches back to the default desktop.
I know for a fact that Yahoo toolbar did this (versions 5-6-7, perhaps they fixed now); KABE4.exe (I don't know what this is), an Acronis program (backup scheduler, AFAIK), and more. All of these are calling SwitchDesktop without any user intervention (a big no-no).
I proved this for Yahoo toolbar; hooking the SwitchDesktop by injecting another dll into yt.dll (loaded by IE) and returning FALSE from the hooked call solved my problem.
The proof of concept sent almost 2 years ago to Yahoo remained unanswered to this day.

Answer 3

In your posted code, there is that part:
// Create a new Desktop and switch to it
hNewDesktop = CreateDesktop(szDesktopName, NULL, NULL, DF_ALLOWOTHERACCOUNTHOOK, GENERIC_ALL, NULL);
SetThreadDesktop(hNewDesktop);
SwitchDesktop(hNewDesktop);
// This call blocks until the process exits, and is confirmed to work on the affected machines
procSuccess = StartProcess(szDesktopName, szPath);
// Restore original ...
SwitchDesktop(hOriginalInput);
SetThreadDesktop(hOriginalThread);
Your call to StartProcess function is between two calls to SwitchDesktop.
No function in this code stop (pause) or delay the running code, thread or process, so as you switch to hNewDesktop, you immediately switch back to hOriginalInput. You should add a while loop with end condition, after the call to StartProcess, and before the second call to SwitchDesktop. I don't know what will be the end condition for the while loop, but you do know, you will choose, after all it is your program.
For example you can use either GetKeyState or GetAsyncKeyState function to check which key is pressed on the keyboard, and make it as the end condition for the while loop, so when you will press that key, you will return immediately to your original desktop!