On this step we shall add a code to the OnExecute event handler. There is only one rule that must be followed: the ProcessRequests method should be called from this event handler. This method is an analog of the Application.ProcessMessages in the regular application. The ProcessRequests method has only one boolean parameter. The false value of this parameter means that ProcessRequests should check the message queue for control messages, process it if necessary and return. The true value of parameter means that this method should not return until service terminates. So if you need to do something while service runs use the OnExecute event as shown below:

procedure TSampleService2.SampleService2Execute(Sender: TObject);
begin
    while not Terminated do
    begin
        ProcessRequests(False);
        DoWhatYouNeed; 
    end;
end;

The Terminated property indicates whether the service should be stopped or it can continue working. In this example our "necessary operation" will be sleeping again. Modify our example as shown below.

procedure TSampleService2.SampleService2Execute(Sender: TObject);
begin
    while not Terminated do
    begin
        ProcessRequests(False);
        Sleep(1000); 
    end;
end;

Warning: The final part of this step shows the problems that occur if the ProcessRequests call is lost. It is recommended to use a debug mode to perform this test. In other case you will have to restart your computer to stop uncontrollable service. In addition it is recommended to change the service start mode (StartType property) to stManual and reinstall service. It will prevent the automatic service starting after reboot.

Well, if you are ready to continue then save changes, compile your example and run it. It works and can be controlled as usually. Now try to comment the ProcessRequests call and test our service again (in debug mode or not as you wish). You will see that service starts normally but becomes uncontrollable after that. It does not stop or pause because control requests are not processed. If you started the service in debug mode just close the debug window to terminate it. In other case you will have to restart your computer.

The final conclusion is: call ProcessRequests(False) periodically from the OnExecute event handler.

The next step of this example will show how to interact with user from our service. Let's continue...