Q106253: Program Priority and Multithreaded Applications
Article: Q106253
Product(s): Microsoft Windows NT
Version(s): 3.1 4.0
Operating System(s):
Keyword(s): kbenv
Last Modified: 08-AUG-2001
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The information in this article applies to:
- Microsoft Windows NT Server version 3.1
- Microsoft Windows NT Workstation version 3.1
- Microsoft Windows NT Advanced Server, version 3.1
- Microsoft Windows NT Server version 4.0
- Microsoft Windows NT Workstation version 4.0
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SUMMARY
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When a program is started under Windows NT, it will have a priority class that
is either normal or equal to the priority class specified in the command line
when using the START command (Idle, Normal, High, or Realtime). The priority
class determines at which priority (from 1 to 31) the program will run. In a
multithreaded application, threads spawned by the program can be lower or higher
than the current priority class of the program; however, all thread priorities
will be relative to the priority class of the parent program. While a program
can change its priority class after starting, all of its threads will still have
the same relative priority.
MORE INFORMATION
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When a process spawns a thread, one of the parameters in the function call sets
the thread priority relative to the priority of the parent process. This
parameter can have one of the following values: Idle, Lowest, Below Normal,
Normal, Above Normal, Highest and Time Critical. The starting priority set for
the thread will be based upon that parameter and the current priority of the
process starting the thread. The priorities are as follows:
RELATIVE PROCESS PRIORITY CLASS
THREAD Normal, in Normal, in
PRIORITY Idle Background Foreground High Realtime
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Time Critical 15 15 15 15 31
Highest 6 9 11 15 26
Above Normal 5 8 10 14 25
Normal 4 7 9 13 24
Below Normal 3 6 8 12 23
Lowest 2 5 7 11 22
Idle 1 1 1 1 16
The table above lists the base priority of a thread, which is set by calling the
function SetThreadPriority; however, a thread's priority can change as the
thread executes. The system can boost a thread's priority higher as time goes on
and then reduce the priority back down to the base, though Windows NT will never
reduce a thread lower than its base priority. The system will boost a thread's
priority when a user interacts directly with a thread, including mouse and
keyboard input or simply bringing the thread to the foreground.
For more information on process priorities, query on the following key words in
the WINNT Knowledge Base:
priority and process
Additional query words: prodnt
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Keywords : kbenv
Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTW310 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS310 kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNTS310search kbWinNT310Search kbWinNTW310Search
Version : 3.1 4.0
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