If this method returns true when all ports had been closed then the stage is not stopped until CompleteStage or FailStage(Exception) are explicitly called

The IMaterializer that has set this GraphStage in motion.

TBD

An IMaterializer that may run fusable parts of the graphs that it materializes within the same actor as the current GraphStage(if fusing is available). This materializer must not be shared outside of the GraphStage.