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CreateProcess with priority class

// Delphi 2007 and XE3
// Create form 'TForm1', place 1 Edit, 1 ComboBox, 1 Button.
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    ComboBox1: TComboBox;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{$WARN SYMBOL_PLATFORM OFF}

{$IF RTLVersion < 24}
const
  BELOW_NORMAL_PRIORITY_CLASS = $00004000;
  {$EXTERNALSYM ABOVE_NORMAL_PRIORITY_CLASS}
  ABOVE_NORMAL_PRIORITY_CLASS = $00008000;
  {$EXTERNALSYM ABOVE_NORMAL_PRIORITY_CLASS}
{$IFEND}

procedure TForm1.FormCreate(Sender: TObject);
begin

  Edit1.Text := '%windir%\notepad.exe';

  with ComboBox1.Items do
  begin
    BeginUpdate;
    try
      Clear;
      AddObject(Format('%s (0x%8.8X)',['IDLE',IDLE_PRIORITY_CLASS]),
                TObject(IDLE_PRIORITY_CLASS));
      AddObject(Format('%s (0x%8.8X)',['BELOW_NORMAL',BELOW_NORMAL_PRIORITY_CLASS]),
                TObject(BELOW_NORMAL_PRIORITY_CLASS));
      AddObject(Format('%s (0x%8.8X)',['NORMAL',NORMAL_PRIORITY_CLASS]),
                TObject(NORMAL_PRIORITY_CLASS));
      AddObject(Format('%s (0x%8.8X)',['ABOVE_NORMAL',ABOVE_NORMAL_PRIORITY_CLASS]),
                TObject(ABOVE_NORMAL_PRIORITY_CLASS));
      AddObject(Format('%s (0x%8.8X)',['HIGH',HIGH_PRIORITY_CLASS]),
                TObject(HIGH_PRIORITY_CLASS));
      AddObject(Format('%s (0x%8.8X)',['REALTIME',REALTIME_PRIORITY_CLASS]),
                TObject(REALTIME_PRIORITY_CLASS));

    finally
      EndUpdate;
    end;
  end;

  with ComboBox1 do
  begin
    ItemIndex := Items.IndexOfObject(TObject(NORMAL_PRIORITY_CLASS));
  end;

end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ApplicationName: String;
  CreationFlags: DWORD;
  StartupInfo: TStartupInfo;
  ProcessInformation: TProcessInformation;
  Length: Integer;
begin

  Length := ExpandEnvironmentStrings(PChar(Edit1.Text),nil,0);
  SetLength(ApplicationName,Length);
  ExpandEnvironmentStrings(PChar(Edit1.Text),PChar(ApplicationName),Length);
  UniqueString(ApplicationName);

  with ComboBox1 do
  begin
    if ItemIndex < 0 then
    begin
      Exit;
    end;

    CreationFlags := DWORD(Items.Objects[ItemIndex]);
  end;

  FillChar(StartupInfo,SizeOf(StartupInfo),0);
  StartupInfo.cb := SizeOf(StartupInfo);

  FillChar(ProcessInformation,SizeOf(ProcessInformation),0);

  Win32Check(CreateProcess(PChar(ApplicationName),nil,nil,nil,False,
             CreationFlags,nil,nil,StartupInfo,ProcessInformation));

  CloseHandle(ProcessInformation.hProcess);
  CloseHandle(ProcessInformation.hThread);

end;

end.