src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doAfterNext(@NonNull Consumer<? super T> onAfterNext) {
        ObjectHelper.requireNonNull(onAfterNext, "onAfterNext is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                onAfterNext,
                Functions.emptyConsumer(),
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                Functions.emptyConsumer(),
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doAfterNext(@NonNull Consumer<? super T> onAfterNext) {
        ObjectHelper.requireNonNull(onAfterNext, "onAfterNext is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                onAfterNext,
                Functions.emptyConsumer(),
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                Functions.emptyConsumer(),
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
Call the specified consumer with the current element passing through any 'rail'
after it has been delivered to downstream within the rail.

@param onAfterNext the callback
@return the new ParallelFlowable instance