InOutImpl

Whether all outputs are available for pushing.

Exposed from GraphStageLogic API.

Whether all input buffers are valid.

Requests the update of the canWrite status.

Invoked by Akka after processing of external events stopped because the operator is about to stop or fail. Calls stopped and then removes the node from the control.

Final so we don't accidentally place code here. In order to initialize state, use NodeHasInitImpl and implement init.

Subclasses can override this