Allow only 3 instances of an application using semaphores

Question

I am trying to implement a simple routine using semaphores that will allow me to run only 3 instances of the application. I could use 3 mutexes but that is not a nice approach i

Answer 1

1. You must try to see if it was created
2. You must use one of the wait function to see if you can get a count
3. At the end, you must release the lock & handle so that it can work the next time user close and open your app

Cheers

var
  hSem: THandle;
begin
  hSem := OpenSemaphore(nil, SEMAPHORE_ALL_ACCESS, True, 'MySemp3');
  if hSem = 0 then
    hSem := CreateSemaphore(nil, 3, 3,'MySemp3');

  if hSem = 0 then
  begin
    ShowMessage('... show the error');
    Halt(1);
    Exit;     
  end;

  if WaitForSingleObject(hSem, 0) <> WAIT_OBJECT_0 then
  begin
    CloseHandle(hSem);
    ShowMessage('Application can be runed only 3 times at once');
    Halt(1);
    Exit; 
  end;

  try   
    your application.run codes..

  finally
    ReleaseSemaphore(hSem, 1, nil);
    CloseHandle(hSem);
  end;