I don't understand stack overflow error with repeated DispatchMessageW in the call stack

Question

This is a Delphi application, but I suppose it is a general Windows programming question.

I left my application running (in the Delphi IDE) over the weekend and have just come back to find a stack overflow.

The stack starts like this...

:75c4417e kernel32.GetDriveTypeW + 0x23
:75c452ae kernel32.IsProcessorFeaturePresent + 0xa9
:75c45272 kernel32.IsProcessorFeaturePresent + 0x6d
:75c45248 kernel32.IsProcessorFeaturePresent + 0x43
:7678410b KERNELBASE.LoadStringBaseExW + 0xc7
:76678ed2 USER32.LoadStringW + 0x19
:0040c4ae LoadResString + $4A
uADStanDef.TADDefinition.Create(nil)
uADStanDef.TADDefinition.CreateTemporary
uADStanDef.TADConnectionDefTemporaryFactory.CreateObject
uADStanFactory.TADManager.CreateInterface((1050358107, 62550, 16757, (168, 100, 178, 87, 60, 74, 32, 21)),(no value),True)
uADStanFactory.ADCreateInterface((1050358107, 62550, 16757, (168, 100, 178, 87, 60, 74, 32, 21)),(no value),True)
uADCompClient.TADCustomConnection.Create($2DB7EB0)
fMainForm.TMainForm.ServerAliveTimerTimer($2E8DE38)    <========== my code
:004f1546 Winapi + $4F1546
:00461316 Winapi + $461316
:766762fa ; C:\Windows\syswow64\USER32.dll
:76676d3a USER32.GetThreadDesktop + 0xd7
:766777c4 ; C:\Windows\syswow64\USER32.dll
:7667788a USER32.DispatchMessageW + 0xf

So, a timer is expiring, I am creating a new object (of an AnyDac component) and the stack overflows. The code definitely frees the object. I have appended it below for those who want to check, but I don't think that that is my question.

The stack then continues

:7669cdfd ; C:\Windows\syswow64\USER32.dll
:7669cf5c ; C:\Windows\syswow64\USER32.dll
:766cf73c ; C:\Windows\syswow64\USER32.dll
:766cfa18 ; C:\Windows\syswow64\USER32.dll
:766cfb1f USER32.MessageBoxTimeoutW + 0x52
:766cfd15 USER32.MessageBoxExW + 0x1b
:766cfd57 USER32.MessageBoxW + 0x18
:00549986 Vcl + $549986
:00549aa2 Vcl + $549AA2
:00549873 Vcl + $549873
:00461316 Winapi + $461316
:766762fa ; C:\Windows\syswow64\USER32.dll
:76676d3a USER32.GetThreadDesktop + 0xd7
:766777c4 ; C:\Windows\syswow64\USER32.dll
:7667788a USER32.DispatchMessageW + 0xf

With that block repeated for three thoussand line (!) And I have no idea what it is or what it is doing. It then ends

StoreRoom.StoreRoom
:75c4339a kernel32.BaseThreadInitThunk + 0x12
:77eb9ef2 ntdll.RtlInitializeExceptionChain + 0x63
:77eb9ec5 ntdll.RtlInitializeExceptionChain + 0x36

I do no tunderstand all of that repeated stack - can anyone advise?

(And for the astutute of you who notice that my exception handling is showing a dialog, that is a TForm which closes when the user clicks OK)

My code:

procedure TMainForm.ServerAliveTimerTimer(Sender: TObject);
begin
   try
      ADConnection := TADConnection.Create(Self);  <======= stack overflow here
      ADConnection.DriverName := 'mysql';
      ADConnection.Params.Add('Server=' + MAIN_STOREROOM_IP_ADDRESS);  
      // other params, such as password, removed for posting
      ADConnection.Connected := True;

   except
      on E : Exception do
      begin
         ADConnection.Free();
         theDialogForm := TDialogFormForm.Create(Nil);
         theDialogForm.ShowTheForm('Database problem'+#13+#10+''+#13+#10+
                                   E.ClassName+#13+#10+E.Message);    
         StopTheApplication();   <===== just calls ExitProcess(0);
         Exit;                     as I had problems with Halt elsewhere in the code
      end;
   end;

   if isMainStoreRoom then
   begin
      CheckIfStoreRoomIsAlive(SECONDARY_STOREROOM_IP_ADDRESS);
   end
   else
   begin
      CheckIfStoreRoomIsAlive(MAIN_STOREROOM_IP_ADDRESS);
   end;

   try    // Now, update our own timestamp
      timestamp  := GetCurrentUnixTimeStamp();
      ADConnection.ExecSQL('UPDATE server_status SET alive_timestamp="' + IntToStr(timestamp) + '" WHERE ip_address="' + ipAddress + '"');

   except
      on E : Exception do
      begin
         ADConnection.Free();
         Exit;
      end;
   end;

   ADConnection.Free();
end;     // ServerAliveTimerTimer()

Answer 1

Your stack overflow is due to MessageBox() being called over and over and over in response to a repeating window message. Internally, MessageBox() runs its own message loop, which is obviously processing and dispatching the same message over and over. That might indicate a timer that has gone astray. I would strongly suggest you disable your timer when you first enter your OnTimer event handler, and then re-enable the timer before exiting.

On a separate note, StopTheApplication() should NOT be calling ExitProcess() (or even Halt()) directly. Use Application.Terminate() instead.