reactor-core/src/main/java/reactor/core/publisher/ParallelFlux.java
public final ParallelFlux<T> doOnRequest(LongConsumer onRequest) {
		Objects.requireNonNull(onRequest, "onRequest");
		return doOnSignal(this, null, null, null, null, null, null, onRequest, null);
	}
public final ParallelFlux<T> doOnRequest(LongConsumer onRequest) {
		Objects.requireNonNull(onRequest, "onRequest");
		return doOnSignal(this, null, null, null, null, null, null, onRequest, null);
	}
Call the specified consumer with the request amount if any rail receives a
request.

@param onRequest the callback

@return the new {@link ParallelFlux} instance