Stream parallel() / sequential() question.

[Brian Goetz]

Parallel is clearly needed because, for many stream generators (such as 
intRange), they are created sequential and have to be explicitly flipped 
to parallel if you want parallel.  The alternative to this was the API 
bloat of having 2x as many methods everywhere streams are generated. 
Saying generator().parallel() is pretty efficient at this point; it just 
flips a bit and returns the underlying stream.  Collection is the 
notable exception, with two methods; this was a common enough case that 
the small additional API surface area (one new method) aided 
discoverability of parallel stream capability enough to warrant the 
additional method.

Sequential is somewhat less essential, but again costs little to 
include, and provides a way of saying "force this stream to execute 
sequentially", which is still useful.

On 4/4/2013 4:20 PM, Peter Levart wrote:
>
> On 04/04/2013 04:05 PM, Brian Goetz 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.)
>
> Hi Brian,
>
> So why are sequential()/parallel() methods needed then after all? We
> have the Collection.stream() and Collection.parallelStream() where the
> shape is pre-determined at the begining by the user. Is there an API
> that constructs a Stream where the shape is chosen automatically?
>
> Regards, Peter
>
>> 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)");
>>>           }
>>>       }
>>>
>