Setting a thread priority in a service

Question

Hello all,

In my service I have a few threads that each call the CreateProcess() function to launch an external application. I would like to adjust thread (or process) priorities to normal or lower, depending on some other factors. The problem is that SetThreadPriority() function fails with an error 6 (invalid handle?). I'm passing in a handle obtained from PROCESS_INFORMATION::hThread (after calling the CreateProcess() of course).

I've also tried setting the priority on the processes using the SetPriorityClass() function, which also fails.

Is there something special that I need to do to set priorities in a service? The service is logged on as a local user.

Thanks in advance for your thoughts.

Answer 1

If the processes you are launching are windowed applications you may need to have the services "Allow services to interact with desktop" checkbox selected (look in the services properties dialog, "Log On" tab).

Answer 2

Maybe you don't have the correct access rights? MSDN on SetThreadPriority says:

hThread [in] A handle to the thread whose priority value is to be set.

The handle must have the THREAD_SET_INFORMATION or THREAD_SET_LIMITED_INFORMATION access right. For more information, see Thread Security and Access Rights.

Windows Server 2003 and Windows XP/2000: The handle must have the THREAD_SET_INFORMATION access right.