Step by step

Folks,

For evebody who wants to control how the application’s threads and processes will consume the CPU I wrote this function to provide an easy way to do this.

 Delphi | 
 copy code |
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uses Windows;
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type
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  TWorkOnProcessorUseMode = (cpuNum, cpuPerc, cpuIndex);
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procedure WorkOnProcessor(AUse: Cardinal; AMode: TWorkOnProcessorUseMode);
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var
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  Mask: integer;
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  lpSystemInfo: TSystemInfo;
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  function ToMask(m: integer): integer;
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  var
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    i: integer;
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  begin
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    Result := 0;
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    for i := 0 to m - 1 do
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      Result := Result + (1 shl i);
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  end;
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begin
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  GetSystemInfo(lpSystemInfo);
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  with lpSystemInfo do
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  begin
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    case AMode of
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      cpuNum: begin
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        if AUse > dwNumberOfProcessors then
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          AUse := dwNumberOfProcessors;
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      end;
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      cpuPerc: begin
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        if AUse > 100 then AUse := 100;
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        AUse := Round(dwNumberOfProcessors / 100 * AUse);
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      end;
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    end;
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    if AMode <> cpuIndex then
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    begin
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      Mask := ToMask(dwNumberOfProcessors);
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      Mask := Mask xor ToMask(dwNumberOfProcessors - AUse);
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    end else
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      Mask := (1 shl (AUse - 1));
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    SetProcessAffinityMask(GetCurrentProcess, Mask);
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  end;    
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end;

You’ll have three ways to put your application running only on the processor(s) you want.

cpuNum mode:
With this mode you’ll be able to specify the number of processors you want to use. The logical structure will count from the first processor.

cpuPerc mode:
With this mode you’ll be able to specify a percentage to use of all processors on the machine. If the machine have four processors and you specify 50 (50%) on the first param, your application will use 2 cores. If 2 cores and 50% will use 1 core.

cpuIndex mode:
With this mode you’ll be able to specify the processor you want to use. If you have 4 cores and you want to use only the third core, specify 3 on the first param and your application will use only the 3º core and no one more.

A little detail:
Your application starts without a setting about what processor will be used and all threads and processes created before the use of the function above can be not modified and so the process can keep on an unspecified core.
The best way to use this function is declaring it on the DPR and using it before Application.Initialize;
Ex:

 Delphi | 
 copy code |
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// on the .DPR of the project
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begin
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  WorkOnProcessor(50, cpuPerc);
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  Application.Initialize;
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  Application.CreateForm(TForm1, Form1);
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  Application.Run;
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end.

Tags: Delphi, SetProcessAffinityMask, Usefull Funciton, WorkOnProcessor

This entry was posted on Thursday, July 3rd, 2008 at 7:19 pm and is filed under articles. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.