Delphi – Timer queue in Windows service

MyTimerID := SetTimer(0, 0, 3333, @MyTimerProc); 

procedure TMyServiceThread.Execute;
var
 AMessage: TMsg ;
begin
 repeat
 // Some calls
 if PeekMessage(AMessage, -1, WM_TIMER, WM_TIMER, PM_REMOVE) then begin
 TranslateMessage(AMessage);
 DispatchMessage(AMessage);
 end;
 // Some more calls
 TerminateEventObject.WaitFor(1000);
 until Terminated;
end;

KillTimer(0, MyTimerID)

while not Terminated do
begin
 case TerminateEventObject.WaitFor(Interval) of
 wrSignaled:
 break;
 wrTimeout:
 // your periodic work goes here
 wrError:
 RaiseLastOSError;
 end;
end; 

For Windows services, I need one Timers are used to periodically perform a certain task. Of course, there are many options that seem to be superior to timers (multi-threaded, calling methods directly from the main thread of the service), but they all have their disadvantages in this particular case.

However, for obvious reasons, SetTimer() will not work without GUI message queue. What I did (in Free Pascal) is the following:

Create Timer:

MyTimerID := SetTimer(0, 0, 3333, @MyTimerProc);

In the main loop of the service, run the timer queue :

procedure TMyServiceThread.Execute;
var
 AMessage: TMsg;
begin
 repeat
 // Some calls
 if PeekMessage(AMessage, -1, WM_TIMER, WM_TIMER, PM_REMOVE) the n begin
 TranslateMessage(AMessage);
 DispatchMessage(AMessage);
 end;
 // Some more calls
 TerminateEventObject.WaitFor(1000);
 until Terminated;
end;

Finally, kill the timer:

KillTimer(0, MyTimerID)

Except that KillTimer always returns False, this works as expected.

I am interested in your feedback, but if my implementation is correct-I just want to avoid messing up other applications And other side effects that I don’t know about because I’m inexperienced in message handling.

Thank you!

As discussed in the comments, you may not need a timer at all. You can simply use the timeout of the event wait to create a regular pulse:

while not Terminated do
begin
 case TerminateEventObject.WaitFor(Interval) of
 wrSignaled:
 break;
 wrTimeout:
 // your periodic work goes here
 wrError:
 RaiseLastOSError;
 end;
end;

The period of the pulse will be The interval plus the time required to complete the work. If you need a specific interval and the work takes a long time, then Remy recommends using a wait timer.

At all costs, you don’t really want to What I did was to use a timer based on a message loop. This is not suitable for services.