Alternative Sleep Methods

posted 9 Mar 2010, 03:53 by Delphi Basics
It is possible for emulators to skip over sleep commands called using the Sleep API.  Therefore, alternative methods prove useful in ensuring that your commands are not skipped; for application stability as well as security. 

The advantages and disadvantages of each method are discussed.

1. Delay.
procedure Delay(dwMilliseconds: Longint);
var
  
iStart, iStop: DWORD;
begin
  
iStart := GetTickCount;
  repeat
    
iStop := GetTickCount;
    Application.ProcessMessages;
    Sleep(1); // addition from Christian Scheffler to avoid high CPU last
  
until (iStop - iStart) >= dwMilliseconds;
end;

2. Delay: with API.
procedure Delay(msecs: Longint);
var
  
targettime: Longint;
  Msg: TMsg;
begin
  
targettime := GetTickCount + msecs;
  while targettime > GetTickCount do
    if 
PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
    begin
      if 
Msg.message = WM_QUIT then
      begin
        
PostQuitMessage(Msg.wParam);
        Break;
      end;
      TranslateMessage(Msg);
      DispatchMessage(Msg);
    end;
end;
{
  Note:
  The elapsed time is stored as a DWORD value.
  Therefore, the time will wrap around to zero if the system is
  run continuously for 49.7 days.
}

3. Sleep - suspends the execution of the current thread for a specified interval.
Sleep(dwMilliseconds: Word);

4. Combined Delay
        Including the Sleep in the loop prevents the app from hogging 100% of the CPU for doing practically nothing but running around the loop.
procedure PauseFunc(delay: DWORD);
var
  
lTicks: DWORD;
begin
  
lTicks := GetTickCount + delay;
  repeat
    
Sleep(100);
    Application.ProcessMessages;
  until (lTicks <= GetTickCount) or Application.Terminated;
end;

5. Delay - more resource sparing.

procedure Delay(Milliseconds: Integer);
  {by Hagen Reddmann}
var
  
Tick: DWORD;
  Event: THandle;
begin
  
Event := CreateEvent(nil, False, False, nil);
  try
    
Tick := GetTickCount + DWORD(Milliseconds);
    while (Milliseconds > 0) and
      
(MsgWaitForMultipleObjects(1, Event, False, Milliseconds,
      QS_ALLINPUT) <> WAIT_TIMEOUT) do
    begin
      
Application.ProcessMessages;
      Milliseconds := Tick - GetTickCount;
    end;
  finally
    
CloseHandle(Event);
  end;
end;

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