How can I restart a Windows service application wr

Question

I have a Windows service written in Delphi. One of the third-party resources it uses occasionally gets corrupted, and the only way I've found to fix the situation is to exit and restart the program. I can detect when the resource is corrupted from within the program, and I can tell Windows to restart the service after it stops, but I can't figure out how to have the service tell itself to stop.

The program is pretty simple. I created a service application in what seems to be the normal way. I have a subclass of TService to manage the service, while all of the functionality occurs in a separate thread. The TService subclass pretty much just manages the execution of the subthread, and it's in the subthread that I would be detecting the corruption.

For reference, here's the header info for the service and subthread.

type
  TScannerThread = class(TThread)
   private     
    Scanner    : TScanner;
    DefaultDir : String;
    ImageDir   : String;
    procedure CheckScanner;
   public      
    Parent     : TComponent;
    procedure Execute; override;
  end;         
  
  TCardScanSvc   = class(TService)
    procedure ServiceCreate(Sender: TObject);
    procedure ServiceExecute(Sender: TService);
    procedure ServiceStart(Sender: TService; var Started: Boolean);
    procedure ServiceStop(Sender: TService; var Stopped: Boolean);
    procedure ServicePause(Sender: TService; var Paused: Boolean);
    procedure ServiceContinue(Sender: TService; var Continued: Boolean);
   private        
    ScannerThread : TScannerThread;
   public         
    function GetServiceController: TServiceController; override;
  end;            

var
  CardScanSvc : TCardScanSvc;

In a GUI application, I'd call Application.Terminate, but TServiceApplication doesn't seem to have that method. I can terminate the subthread, but the main thread never notices, and Windows thinks the service is still running. I can't really think of much else to try.

The program was originally created in Delphi 5, and I'm currently using Delphi 2007, in case that makes a difference.

---

Edit:

With mghie's code, I can stop the service, but Windows will only restart the service if it fails unexpectedly, not if it's stopped normally. What I'm going to do is make a separate service application, have the first signal the second if it has problems, and then have the second restart the first.

Answer 1

You should be able to use WMI (Windows Management Instrumentation) to restart a service, even from within the service itself. Don't know if this would cause any strange problems but it should work. Here's an article on doing WMI with Delphi.

UPDATE: Well well, I assumed (my mistake) that there is a single WMI service restart command, such as the button you can click in the services maangement listing. Apparently not.
You could instead write a console app that the service starts when the data is corrupted. The console app would restart the service from a separate process.

Answer 2

There is no problem having the service stop itself - I just tried with one of my own services, written with Delphi 4 (without using the TService class). The following routine works for me:

procedure TTestService.StopService;
var
  Scm, Svc: SC_Handle;
  Status: SERVICE_STATUS;
begin
  Scm := OpenSCManager(nil, nil, SC_MANAGER_ALL_ACCESS);
  if Scm <> 0 then begin
    Svc := OpenService(Scm, PChar(ServiceName), SERVICE_ALL_ACCESS);
    if Svc <> 0 then begin
      ControlService(Svc, SERVICE_CONTROL_STOP, Status);
      // handle Status....
      CloseServiceHandle(Svc);
    end;
    CloseServiceHandle(Scm);
  end;
end;

You need to check whether it will also work from your worker thread.

Answer 3

I have found a simpler alternative that should work. You can add a method to your TService subclass:

procedure TSomeService.StopService;
begin
  Controller(SERVICE_CONTROL_STOP);
end;

I am using the same setup as the OP - specifically, a TService descendant that simply starts a worker thread and then does nothing but process Windows messages. Unfortunately, you cannot call Controller from the worker thread because it is protected. Of course the simple way around it is to create a public method as I showed above. To use this from the worker thread you will need a reference to the TService object accessible from within the worker thread. I do this by passing my TService object into my worker thread in the thread's constructor.