code: public boolean tryAdd(final Agent agent)
      {
          Objects.requireNonNull(agent, "agent cannot be null");
  
          if (Status.ACTIVE != status)
          {
              throw new IllegalStateException("add called when not active");
          }
  
          return addAgent.compareAndSet(null, agent);
      }
docs: Try and add a new {@link Agent} to the composite. This method does not block and will return false if another
  concurrent attempt to add is in progress.
  <p>
  The agent will be added during the next invocation of {@link #doWork()} if this operation is successful.
  If the {@link Agent#onStart()} method throws an exception then it will not be added and {@link Agent#onClose()}
  will be called.
  
  @param agent to be added to the composite.
  @return true is a successful add request is pending otherwise false if another concurrent add request is in
  progress.
  @see #hasAddAgentCompleted()