Constructing parallel streams

[Remi Forax]

On 12/10/2012 04:50 PM, Brian Goetz wrote:
>> I don't like users being able to call parallel in the middle of the
>> stream construction.
>
> I don't love it either.  The semantics are perfectly tractible, and 
> the implementation is perfectly straightforward, but the performance 
> is unlikely to be a win in most cases.  (I mentioned earlier we would 
> doc that this really should only be done at the head of the pipeline.)
>
>> I propose to have an interface ParallelizableStream that allows to
>> choose if the user want the sequential or the parallel stream upfront.
>
> Yeah, we investigated this direction first.  Combinatorial explosion: 
> IntParallelizableStream, etc.

combinatorial exposion = 4, ParallelizableStream, 
IntParallelizableStream, LongParallelizableStream, 
DoubleParallelizableStream

>
> However, this could trivially become a dynamic property of streams 
> (fits easily into the existing stream flags mechanism).  Then only the 
> head streams would have the property, and if you tried to do 
> parallel() farther down the stream, we could ignore it or even throw ISE.
>

see my answer to Joe, switching from sequential to parallel and vice 
versa doesn't really require adhoc methods.

One another problem of sequential and parallel is that their semantics 
is ambiguous, the semantics of all other methods of Stream is once the 
method is called the previous stream is not valid anymore but if 
parallel or sequential can return this as you suggest, it's not true 
anymore.

cheers,
Rémi