src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnSubscribe(@NonNull Consumer<? super Subscription> onSubscribe) {
        ObjectHelper.requireNonNull(onSubscribe, "onSubscribe is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                onSubscribe,
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnSubscribe(@NonNull Consumer<? super Subscription> onSubscribe) {
        ObjectHelper.requireNonNull(onSubscribe, "onSubscribe is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                onSubscribe,
                Functions.EMPTY_LONG_CONSUMER,
                Functions.EMPTY_ACTION
                ));
    }
@ CheckReturnValue @ NonNull public final ParallelFlowable < T > doOnSubscribe ( @ NonNull Consumer < ? super Subscription > onSubscribe ) { ObjectHelper . requireNonNull ( onSubscribe , "onSubscribe is null" ) ; return RxJavaPlugins . onAssembly ( new ParallelPeek < T > ( this , Functions . emptyConsumer ( ) , Functions . emptyConsumer ( ) , Functions . emptyConsumer ( ) , Functions . EMPTY_ACTION , Functions . EMPTY_ACTION , onSubscribe , Functions . EMPTY_LONG_CONSUMER , Functions . EMPTY_ACTION ) ) ; }
Call the specified callback when a 'rail' receives a Subscription from its upstream.

@param onSubscribe the callback
@return the new ParallelFlowable instance
Call the specified callback when a rail receives a Subscription from its upstream .