If the function succeeds, it returns the priority of the thread, which is a value from zero through 255. Zero is the highest priority.
THREAD_PRIORITY_ERROR_RETURN indicates failure. To get extended error information, call GetLastError.
This function returns the base priority of the thread. If priority inheritance changes the priority of a thread, the value returned by this function might not match the original thread priority or the value assigned by SetThreadPriority.