reactor-core/src/main/java/reactor/core/publisher/Flux.java
public final ParallelFlux<T> parallel(int parallelism, int prefetch) {
		return ParallelFlux.from(this,
				parallelism,
				prefetch,
				Queues.get(prefetch));
	}
public final ParallelFlux<T> parallel(int parallelism, int prefetch) {
		return ParallelFlux.from(this,
				parallelism,
				prefetch,
				Queues.get(prefetch));
	}
Prepare this {@link Flux} by dividing data on a number of 'rails' matching the
provided {@code parallelism} parameter, in a round-robin fashion and using a
custom prefetch amount and queue for dealing with the source {@link Flux}'s values.
Note that to actually perform the work in parallel, you should call
{@link ParallelFlux#runOn(Scheduler)} afterward.

<p>
<img class="marble" src="doc-files/marbles/parallel.svg" alt="">

@param parallelism the number of parallel rails
@param prefetch the number of values to prefetch from the source

@return a new {@link ParallelFlux} instance