public final <V> Flux<V> flatMap(Function<? super T, ? extends Publisher<? extends V>> mapper, int
			concurrency) {
		return flatMap(mapper, concurrency, Queues.XS_BUFFER_SIZE);
	}
public final <V> Flux<V> flatMap(Function<? super T, ? extends Publisher<? extends V>> mapper, int
			concurrency) {
		return flatMap(mapper, concurrency, Queues.XS_BUFFER_SIZE);
	}
public final < V > Flux < V > flatMap ( Function < ? super T , ? extends Publisher < ? extends V > > mapper , int concurrency ) { return flatMap ( mapper , concurrency , Queues . XS_BUFFER_SIZE ) ; }
Transform the elements emitted by this {@link Flux} asynchronously into Publishers,
then flatten these inner publishers into a single {@link Flux} through merging,
which allow them to interleave.
<p>
There are three dimensions to this operator that can be compared with
{@link #flatMapSequential(Function) flatMapSequential} and {@link #concatMap(Function) concatMap}:
<ul>
<li><b>Generation of inners and subscription</b>: this operator is eagerly
subscribing to its inners.</li>
<li><b>Ordering of the flattened values</b>: this operator does not necessarily preserve
original ordering, as inner element are flattened as they arrive.</li>
<li><b>Interleaving</b>: this operator lets values from different inners interleave
(similar to merging the inner sequences).</li>
</ul>
The concurrency argument allows to control how many {@link Publisher} can be
subscribed to and merged in parallel. In turn, that argument shows the size of
the first {@link Subscription#request} to the upstream.

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

@reactor.discard This operator discards elements internally queued for backpressure upon cancellation or error triggered by a data signal.

@param mapper the {@link Function} to transform input sequence into N sequences {@link Publisher}
@param concurrency the maximum number of in-flight inner sequences
@param <V> the merged output sequence type

@reactor.errorMode This operator supports {@link #onErrorContinue(BiConsumer) resuming on errors}
in the mapper {@link Function}. Exceptions thrown by the mapper then behave as if
it had mapped the value to an empty publisher. If the mapper does map to a scalar
publisher (an optimization in which the value can be resolved immediately without
subscribing to the publisher, e.g. a {@link Mono#fromCallable(Callable)}) but said
publisher throws, this can be resumed from in the same manner.

@return a new {@link Flux}
Transform the elements emitted by this { @link Flux } asynchronously into Publishers then flatten these inner publishers into a single { @link Flux } through merging which allow them to interleave . <p > There are three dimensions to this operator that can be compared with { @link #flatMapSequential ( Function ) flatMapSequential } and { @link #concatMap ( Function ) concatMap } : <ul > <li > <b > Generation of inners and subscription< / b > : this operator is eagerly subscribing to its inners . < / li > <li > <b > Ordering of the flattened values< / b > : this operator does not necessarily preserve original ordering as inner element are flattened as they arrive . < / li > <li > <b > Interleaving< / b > : this operator lets values from different inners interleave ( similar to merging the inner sequences ) . < / li > < / ul > The concurrency argument allows to control how many { @link Publisher } can be subscribed to and merged in parallel . In turn that argument shows the size of the first { @link Subscription#request } to the upstream .