Stream parallel() / sequential() question.

[Boaz Nahum]

Suppose I wrote a method:

<T> Stream<T>  foo(Stream<T> source ) {

   return s.sequential().map(nonThreadSafeMapper);

}

I which I used a non-thread-safe-mapper. To protect my self I
'sequential()' it.

Now, somewhere else somebody:

foo().parallel() ....


So, My non-thread-safe-mapper is running concurrently ?

Thanks
Boaz






On Thu, Apr 4, 2013 at 5:39 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

> Let me make a real world analogy.
>
> Replace "stream" with "package".
> Replace "non thread safe mapper" with "bomb".
>
> Boaz concludes: "Don't send packages in the mail, someone could get hurt
> because the package might have a bomb in it."
>
> Brian logic: "Don't send packages in the mail that have bombs in them."
>
> Seriously, streams with non-thread-safe lambdas are like bombs.  Don't
> make bombs, and no one blows up, no matter how many packages we send each
> other!
>
> Now, let's rewind and bring this conversation back to the list -- can you
> summarize your question on-list so everyone can see the answer? Knowing in
> advance that I will poke some fun at you :)
>
>
> On 4/4/2013 10:30 AM, Boaz Nahum wrote:
>
>> Becuase, if
>>
>> Me:
>> ----
>>
>> Stream<T>  foo() {
>>
>>    return s.sequential().map(**nonThreadSafeMapper);
>>
>> }
>>
>>
>> You:
>> ------
>> foo().parallel(). .....
>>
>> Then my non thread safe mapper will be run concurrently !
>>
>> Thanks
>> Boaz
>>
>>
>>
>>
>>
>> On Thu, Apr 4, 2013 at 5:16 PM, Brian Goetz <brian.goetz at oracle.com
>> <mailto:brian.goetz at oracle.com**>> wrote:
>>
>>     Exactly the opposite!
>>
>>     All streams should be usable and produce correct results under
>>     either sequential or parallel execution.  Why would this advice make
>>     you think we were telling you not to return streams?
>>
>>
>>     On 4/4/2013 10:14 AM, Boaz Nahum wrote:
>>
>>         I understand. But still don't know how to solve my problem ?
>>
>>         If I understood right, You are telling me don't write libraries
>> that
>>         return a Stream ? Because you never know how your stream will be
>>         used ?
>>
>>         Thank
>>         Boaz
>>
>>
>>
>>
>>
>>
>>
>>         On Thu, Apr 4, 2013 at 5:05 PM, Brian Goetz
>>         <brian.goetz at oracle.com <mailto:brian.goetz at oracle.com**>
>>         <mailto:brian.goetz at oracle.com
>>
>>         <mailto:brian.goetz at oracle.com**>__>> wrote:
>>
>>              This was simplified recently.
>>
>>              There is *one* sequential/parallel bit for the whole
>>         pipeline.  The
>>              stream starts off with it set one way or the other.  These
>>         calls
>>              overwrite it.  The bit is only acted on when you actually
>>         start the
>>              computation (invoke the terminal operation.)
>>
>>
>>              On 4/4/2013 9:21 AM, Boaz Nahum wrote:
>>
>>                  When I invoked parallel() or sequential() how backward
>>         it goes ?
>>
>>                  Let me explain, I wrote a simple Consumer that report
>>         how many
>>                  different
>>                  threads used to run it:
>>
>>                  source.
>>                                parallel().peek(new
>>         ThreadReporter("Segement 1
>>                  parallel")).
>>                                sequential().peek(new
>>         ThreadReporter("Segement 2
>>                  sequential")).
>>                                parallel().peek(new
>>         ThreadReporter("Segement 3
>>                  parallel")).
>>                                sequential().peek(new
>>         ThreadReporter("Segement 4
>>                  sequential")).forEach((t) -> {});
>>
>>
>>
>>                     private static class ThreadReporter implements
>>                  Consumer<Integer> {
>>
>>
>>                            @Override
>>                            public void accept(Integer integer) {
>>                                threads.put(Thread.____**currentThread(),
>>
>>         true);
>>
>>                            }
>>
>>                            public void report() {
>>                                System.out.println("Name +'" + name + "':
>> " +
>>                  threads.size() +
>>                  " Thread(s)");
>>                            }
>>                        }
>>
>>
>>
>>