public OperationContext(CountdownEvent countdownEvent, ConcurrentOperationManager manager)
 {
     _countdownEvent = countdownEvent;
     _countdownEvent.AddCount();
     manager.OnOperationContextCreated(EventArgs.Empty);
     if(manager._isDisposed)
     {
         Dispose();
         throw new ObjectDisposedException(manager._owningType);
     }
 }