This method is called when upstream has signaled that the stream is successfully completed. Here you cannot call Push(Object), because there might not be any demand from downstream. To emit additional elements before terminating you can use AbsorbTermination and push final elements from OnPull(TContext). The stage will then be in finishing state, which can be checked with IsFinishing.

By default the finish signal is immediately propagated with Finish.

IMPORTANT NOTICE: this signal is not back-pressured, it might arrive from upstream even though the last action by this stage was a "push".