Hi Gary,
Until the Sink does not call pull() automatically, and it will not receive
an onPush without explicitly pulling its upstream first - this is the
backpressure part.
You can simply call pull(in) by overriding preStart() and calling it from
there. This is not done automatically by the frame
The reference doc shows custom Sources and Flows but not Sinks. I wrote a
custom Sink with an InHandler that overrides onPush but it is never called.
I assumed that calling runWith would cause the SinkShape to pull by
default. An upstream custom Flow doesn't receive either onPush or onPull.
Are
