Prevent Delphi Service from not responding

Question

my problem is the following: I implemented a Windows Service with Delphi Tokyo but imho this is no version problem rather than a design problem. I use the following code to pause my service and be responsive in that state.

procedure TMyService.ServiceExecute(Sender: TService);
begin
    while not Terminated do
    begin
      MyProductiveFunction;
      Delay(10000);
    end;
end;

procedure TMyService.Delay(Milliseconds: integer);
var
  Tick: DWord;
  Event: THandle;
begin
  LogOnLevel(clogger, CAS_LOGGER.Debug, '', ['Delay', 'ENTER', 'Delayed for ' + Milliseconds.ToString]);
  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
      ServiceThread.ProcessRequests(False);
      if Terminated then
        exit;
      Milliseconds := Tick - GetTickCount;
    end;
  finally
    CloseHandle(Event);
  end;
end;

The Function I run sometimes is very time consuming. When I try to Stop the Service while it is in the Delay procedure it stops and everything is fine. But when I try to stop the Service while running "MyProductiveFunction" it will say Service is not responding and after that there is no other way to terminate the Service than killing it by Taskmanager. Is there a better way to implement that so the Service will be responding independently from its actual state?

Do not use Service.OnExecute! spawn a new thread in Service.OnStart and terminate that thread in Service.OnStop. Look [here](https://stackoverflow.com/questions/10537267/delphi-windows-service-design/10538102#10538102) if you want a code skeleton. — whosrdaddy, Nov 05 '20 at 11:42
And signal that thread to pause its work in the `Service.OnPause` event, and resume the work in the `Service.OnContinue` event. — Remy Lebeau, Nov 05 '20 at 17:39
Also, your `Event` is completely useless, since nobody has access to it to signal it. You don't need an `Event` just to use `MsgWaitForMultipleObjects()`, you can set its `nCount` parameter to `0` and `pHandles` to `nil` to wait only on the calling thread's message queue. Though, I would suggest using a [waitable timer](https://learn.microsoft.com/en-us/windows/win32/sync/waitable-timer-objects) instead of counting ticks manually. — Remy Lebeau, Nov 05 '20 at 17:42

score 1 · Answer 1 · answered Nov 05 '20 at 08:44

1

You have to write MyProductiveFunction like you programmed your Delay function: periodically process requests and terminate the function if the service is asked to terminate.

Instead, you may also create another thread to execute MyProductiveFunction and from the ServiceExecute call ProcessRequest and check for termination. When termination is requested, you have to terminate the other thread. The best is to have this other thread check something shared such a TEvent for terminating, or ServiceExecute may kill/abort that thread.

answered Nov 05 '20 at 08:44

fpiette

11,983
1
24
46

1

If you use a separate thread, preferably started in the `OnStart` event and terminated in the `OnStop`/`OnShutdown` events, then you shouldn't use the `OnExecute` event at all, don't even assign a handler to it. `TService` will process SCM requests just fine on its own without an `OnExecute` handler, but if you assign `OnExecute` then you become responsible for processing SCM requests. – Remy Lebeau Nov 05 '20 at 17:44

score 1 · Accepted Answer · answered Mar 01 '21 at 15:51

1

Thanks for your Support.

I used the code skeleton from Remys post here:

Delphi Windows Service Design

Works great. Thx to that great community and thx to Remy

answered Mar 01 '21 at 15:51

fisi-pjm

378
2
16

Prevent Delphi Service from not responding

2 Answers2