- Cookbook - Timing loops

From: [at]} <Alexander>
Date: Wed, 24 May 2006 03:30:36 +0700

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Hello, Robert!

CRDSUE> I am afraid that I did not have the time
CRDSUE> to follow the details of this discussion,
CRDSUE> but the topic seemed to be of potentially
CRDSUE> general utility.

CRDSUE> With the benefit of hindsight, can someone provide
CRDSUE> a simple explanation of the problem and the recommended
CRDSUE> solution leaving out the interesting twists & turns
CRDSUE> that got there - or was the final outcome that the problem
CRDSUE> does not have a satisfactory solution?

  Problem: a procedure Delay is required which should return execution
  not before a certain amount of time. For example:

  DoSomething1;
  Delay(10000);
  DoSomething2;

  After DoSomething1 returns execution and before DoSomething2 starts
  working there should be a gap about 10 seconds wide (not precisely).
  During Delay BlackBox should not look "frozen", background tasks
  must keep functioning, interface must be responsive.

  Services.Action is not a valid solution, because the overall task is
  to port some old code without refactoring. The solution using
  Services.Action would require DoSomething1 and DoSomething2 to be
  relocated to two different places.

  Solution:
  1. Enhance BlackBox background multitasking ability with patch
  provided by Marco Ciot.
  2. Implement message-processing loop in Delay (see below).
  3. Use with caution. (I.e.: avoid unloading module while it is in
  Delay, avoid recursive Delaying, some fixes required if Delay is to
  be used from within Services.Actions, etc.)

  PROCEDURE Delay* (delta: LONGINT); (* delta time to wait in [ms] *)
    VAR
      t: LONGINT; (* time to exit *)
      res: INTEGER;
      msg: USER32.Message;
      quit: BOOLEAN;
  BEGIN
    t := Services.Ticks() + delta;
    quit := FALSE;
    REPEAT
      res := USER32.GetMessageA(msg, 0, 0, 0);
      IF res > 0 THEN
        (* process messages *)
        IF USER32.TranslateMDISysAccel(HostWindows.client, msg) = 0 THEN
          res := USER32.TranslateMessage(msg);
          (* warning! this module may be unloaded here: *)
          res := USER32.DispatchMessageA(msg)
        END;
        (* update windows if message queue is empty *)
        IF USER32.PeekMessageA(msg, 0, 0, 0, 0) = 0 THEN
          Windows.dir.Update(NIL)
        END;
        (* process background tasks *)
        Services.actionHook.Step;
      ELSE
        quit := TRUE;
        IF res = 0 THEN (* WM_QUIT received, exit loop and repost *)
          WinApi.PostQuitMessage(0)
        ELSE (* some error occured; exit loop *)
        END
      END;
    UNTIL quit OR (Services.Ticks() >= t);
  END Delay;


  Outcome: the provided Delay does the job, but there are some issues.
  First of all - stability of resulting code. Second - shortcuts are
  not working. (Probably there are other issues.) Overall: there is no
  "legal" way to do this, but the hack is quite functional.

  
---=====---
 Alexander

--- BlackBox
--- send subject HELP or UNSUBSCRIBE to blackbox{([at]})nowhere.xy



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Received on Tue May 23 2006 - 22:30:36 UTC