Fan-out the stream to several streams.
Fan-out the stream to several streams. Each upstream element is emitted to the first available downstream consumer.
Reactive Streams semantics
emits when any of the outputs stops backpressuring; emits the element to the first available output
backpressures when all of the outputs backpressure
completes when upstream completes
cancels depends on the
eagerCancel flag. If it is true, when any downstream cancels, if false, when all downstreams cancel.