Delphi Clinic

C++Builder Gate

Training & Consultancy

Delphi Notes Weblog

Dr.Bob's Webshop

Under The Hood #8 - Time to Sleep See Also:  Delphi Papers and Dr.Bob's Examines Columns

This time, we will create a delay/sleep function in an ObjectPascal unit that does not have a form. Of course, we could decide to use a TTimer for this problem, but it's not always practical to (dynamically if needed) create a TTimer and set up the response event, so let's go for the non-timer approach.
In order to ensure portablility of our solution, it's good to know that both Windows 3.x and Win32 (Win95/NT) support the GetTickCount API.
The GetTickCount API gives us the number of milliseconds since Windows was started. The accuracy of this API, however, is only 55 ms, as it is updated 18.2 times each second (just like the real mode system clock). Hence, we should use GetTickCount only for very rough measurements. But it's accurate enough to be used in a while loop that does nothing until the GetTickCount is the StartingTime + the amount of milliseconds we wanted to wait:

  StartTime := GetTickCount;
  while (GetTickCount < (StartTime + MilliSecondsToWait)) do

  while (GetTickCount >= StartTime) ...

  program Hood8;
  uses
    WinProcs, Forms, WinCrt;

    procedure Sleep(MilliSecondsToWait: LongInt);
    var StartTime: LongInt;
    begin
      StartTime := GetTickCount;
      while (GetTickCount >= StartTime) and
            (GetTickCount < (StartTime + MilliSecondsToWait)) do
        Application.ProcessMessages
    end {Sleep};

  var i: Integer;
  begin
    writeln(GetTickCount);
    for i:=1 to 10 do
    begin
      Sleep(i * 1000);
      writeln(GetTickCount);
    end
  end.