Prevent Multiple Instance of the Application

General Help
1

Hi all
I inserted the following call to the dpr file of the application to prevent the multiple instances. But did not succeeded.

function isOneInstance(): Boolean;
Var
  Handle: THandle;
  ErrCode: DWORD;
Begin
  Result:= False;
  Handle:= 0;

  try
    Handle:= CreateMutex(nil, False, 'Global\_AFB2FB05-5FA5-4C9E-9633-2353418AFF7E');
    if(Handle= 0) then exit();
    if GetLastError() = ERROR_ALREADY_EXISTS then exit();

    Result:= True;
  finally
    if(Handle<>0) then begin
      ReleaseMutex(Handle);
      CloseHandle(Handle);
    end;
    Handle:= 0;
  end;
End;


begin
  if(isOneInstance()) then begin
    Application.Initialize;
    Application.MainFormOnTaskbar := True;
    Application.CreateForm(TForm1, Form1);
    Application.Run;
  end else begin
    Application.MessageBox('Already Running', 'WARNING', MB_OK);
    Application.Terminate();
  end;
end.

What is wrong with that code did not understand. I inserted Global\ to the mutex string to have that mutex object in the global name spaces also but did not work anyway

Best Regards,

2

Even using True to request the intial ownership did not make any difference.

3

The Mutex needs to exist for the life of the program. You are closing the Mutex at the end of the isOneInstance function.

1 Like
4

Thank you for your fast response.
After your reply, I shocked that how I did that mistake.

Regards,