| Platform SDK: DLLs, Processes, and Threads |
The GetPriorityClass function retrieves the priority class for the specified process. This value, together with the priority value of each thread of the process, determines each thread's base priority level.
DWORD GetPriorityClass( HANDLE hProcess // handle to process );
Windows NT/2000: The handle must have PROCESS_QUERY_INFORMATION access. For more information, see Process Security and Access Rights.
If the function succeeds, the return value is the priority class of the specified process.
If the function fails, the return value is zero. To get extended error information, call GetLastError.
The process's priority class is one of the following values.
| Priority | Meaning |
|---|---|
| ABOVE_NORMAL_PRIORITY_CLASS | Windows 2000: Indicates a process that has priority above NORMAL_PRIORITY_CLASS but below HIGH_PRIORITY_CLASS. |
| BELOW_NORMAL_PRIORITY_CLASS | Windows 2000: Indicates a process that has priority above IDLE_PRIORITY_CLASS but below NORMAL_PRIORITY_CLASS. |
| HIGH_PRIORITY_CLASS | Indicates a process that performs time-critical tasks that must be executed immediately for it to run correctly. The threads of a high-priority class process preempt the threads of normal or idle priority class processes. An example is the Task List, which must respond quickly when called by the user, regardless of the load on the operating system. Use extreme care when using the high-priority class, because a high-priority class CPU-bound application can use nearly all available cycles. |
| IDLE_PRIORITY_CLASS | Indicates a process whose threads run only when the system is idle and are preempted by the threads of any process running in a higher priority class. An example is a screen saver. The idle priority class is inherited by child processes. |
| NORMAL_PRIORITY_CLASS | Indicates a normal process with no special scheduling needs. |
| REALTIME_PRIORITY_CLASS | Indicates a process that has the highest possible priority. The threads of a real-time priority class process preempt the threads of all other processes, including operating system processes performing important tasks. For example, a real-time process that executes for more than a very brief interval can cause disk caches not to flush or cause the mouse to be unresponsive. |
Every thread has a base priority level determined by the thread's priority value and the priority class of its process. The operating system uses the base priority level of all executable threads to determine which thread gets the next slice of CPU time. Threads are scheduled in a round-robin fashion at each priority level, and only when there are no executable threads at a higher level will scheduling of threads at a lower level take place.
For a table that shows the base priority levels for each combination of priority class and thread priority value, see the SetPriorityClass function.
Windows NT 4.0 and earlier: Priority class is maintained by the Windows subsystem (csrss), so only Windows-based application have a priority class that can be queried.
Windows 2000: Priority class is maintained by the executive, so all processes have a priority class that can be queried.
Windows NT/2000: Requires Windows NT 3.1 or later.
Windows 95/98: Requires Windows 95 or later.
Header: Declared in Winbase.h; include Windows.h.
Library: Use Kernel32.lib.
Processes and Threads Overview, Process and Thread Functions, GetThreadPriority, SetPriorityClass, SetThreadPriority