reactor-core/src/main/java/reactor/core/publisher/Mono.java
public static Mono<Void> when(final Iterable<? extends Publisher<?>> sources) {
		return onAssembly(new MonoWhen(false, sources));
	}
public static Mono<Void> when(final Iterable<? extends Publisher<?>> sources) {
		return onAssembly(new MonoWhen(false, sources));
	}
Aggregate given publishers into a new {@literal Mono} that will be
fulfilled when all of the given {@literal Publishers} have completed.
An error will cause pending results to be cancelled and immediate error emission
to the returned {@link Mono}.

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

@param sources The sources to use.

@return a {@link Mono}.