src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final <R> ParallelFlowable<R> map(@NonNull Function<? super T, ? extends R> mapper, @NonNull ParallelFailureHandling errorHandler) {
        ObjectHelper.requireNonNull(mapper, "mapper");
        ObjectHelper.requireNonNull(errorHandler, "errorHandler is null");
        return RxJavaPlugins.onAssembly(new ParallelMapTry<T, R>(this, mapper, errorHandler));
    }
@CheckReturnValue
    @NonNull
    public final <R> ParallelFlowable<R> map(@NonNull Function<? super T, ? extends R> mapper, @NonNull ParallelFailureHandling errorHandler) {
        ObjectHelper.requireNonNull(mapper, "mapper");
        ObjectHelper.requireNonNull(errorHandler, "errorHandler is null");
        return RxJavaPlugins.onAssembly(new ParallelMapTry<T, R>(this, mapper, errorHandler));
    }
Maps the source values on each 'rail' to another value and
handles errors based on the given {@link ParallelFailureHandling} enumeration value.
<p>
Note that the same mapper function may be called from multiple threads concurrently.
<p>History: 2.0.8 - experimental
@param <R> the output value type
@param mapper the mapper function turning Ts into Us.
@param errorHandler the enumeration that defines how to handle errors thrown
from the mapper function
@return the new ParallelFlowable instance
@since 2.2