code: void registerCallback(AsynchConsumerCallback callback)
    {
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
        SibTr.entry(tc, "registerCallback", callback);
  
      asynchConsumerCallback = callback;
  
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
        SibTr.exit(tc, "registerCallback");
    }
docs: Register the AsynchConsumerCallback. If callback is null then
  this is the equivalent of deregister, i.e. callbackRegistered
  is set to false.
  
  @param callback