src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnError(@NonNull Consumer<Throwable> onError) {
        ObjectHelper.requireNonNull(onError, "onError is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                onError,
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                Functions.emptyConsumer(),
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnError(@NonNull Consumer<Throwable> onError) {
        ObjectHelper.requireNonNull(onError, "onError is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                onError,
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                Functions.emptyConsumer(),
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
Call the specified consumer with the exception passing through any 'rail'.

@param onError the callback
@return the new ParallelFlowable instance