StreamOpFlag.* and OutOfMemoryError when going parall

[Remi Forax]

On 12/05/2012 07:18 PM, Christian Mallwitz wrote:
> Hi,
>
> Using lambda-8-b67-linux-i586-03_dec_2012 I'm trying to compute n (not
> necessarily the first n) prime numbers:
>
> import java.util.*;
> import java.util.function.*;
> import java.util.stream.*;
>
> public class LambdaExample3 {
>
>      public static boolean isPrime(long n) {
>          if (n <= 1) { return false; }
>          if (n == 2) { return true; }
>          for (int i = 2; i <= Math.sqrt(n) + 1; i++) { if (n % i == 0)
> return false; }
>          return true;
>      }
>
>      public static void main(String[] args) {
>
>          Stream<Long> stream =
> Streams.parallel(Streams.spliteratorUnknownSize(new Iterator<Long>() {
>                  private long n = 0;
>                  @Override public boolean hasNext() { return true; }
>                  @Override public Long next() { return ++n; }
>                  }),
>              // fails with OutOfMemoryError
>              // StreamOpFlag.toStreamFlags(StreamOpFlag.NOT_SIZED,
> StreamOpFlag.INITIAL_OPS_VALUE)
>              // fails with OutOfMemoryError
>              // StreamOpFlag.NOT_SIZED
>              // works, but no speed-up to non-parallel version
>              StreamOpFlag.INITIAL_OPS_VALUE
>              );
>
>          stream
>              .filter(LambdaExample3::isPrime)
>              .limit(300000)
>              .forEach(l -> { /*System.out.println(l);*/ });
>      }
> }
>
> I'm struggling with the StreamOpFlag parameter. What should I pick?
> INITIAL_OPS_VALUE seems to work but isn't running anything in parallel
> (at least it is not faster than the serial version). NOT_SIZED isn't
> working but failing miserably with an  OutOfMemoryError. IS_PARALLEL
> is not needed because I already use parallel() - should specifying
> IS_PARALLEL and using Streams.stream() supposed to go parallel as
> well?
>
> Is the OutOfMemoryError caused by a bug? The OutOfMemoryError is
> reported from a fork/join pool thread so at least it is going
> parallel? Am I missing something?

I've trouble to understand how you expect that your code work in parallel.

>
> Thanks
> Christian
>

Rémi