mtumilowicz / java11-spliterator-forkjoin

Fork-join using spliterator and parallel streams.

java11-spliterator-forkjoin

Fork-join using spliterator and parallel streams.

Reference: https://java-8-tips.readthedocs.io/en/stable/parallelization.html

For more info about spliterators please refer my other github project:

• https://github.com/mtumilowicz/java11-spliterator

Note that this project is the exact copy of my other github project: https://github.com/mtumilowicz/fork-join-find-minimum but using spliterator + parallel streams instead of fork-join API.

project description

Find minimum in the stream of ints in a parallel way with full control over splitting.

1. We have int[] arr, so we will be using Spliterator.OfInt (it removes overhead of autoboxing).
2. We implement Spliterator.OfInt in FindMinimumSpliterator in the same way like fork-join, but note that:
   • splitting tear away part of this (so this spliterator has to be mutable)
   • trySplit() returns
     • a Spliterator covering some portion of the elements
     • or null if this spliterator cannot be split
3. Used characteristics:
   • IMMUTABLE - Characteristic value signifying that the element source cannot be structurally modified; that is, elements cannot be added, replaced, or removed, so such changes cannot occur during traversal.
   • NONNULL - Characteristic value signifying that the source guarantees that encountered elements will not be null.
   • ORDERED - Characteristic value signifying that an encounter order is defined for elements.
   • SIZED - Characteristic value signifying that the value returned from estimateSize() prior to traversal or splitting represents a finite size that, in the absence of structural source modification, represents an exact count of the number of elements that would be encountered by a complete traversal.
   • SUBSIZED - Characteristic value signifying that all Spliterators resulting from trySplit() will be both SIZED and SUBSIZED (This means that all child Spliterators, whether direct or indirect, will SIZED).
4. Constructing parallel IntStream from Spliterator.OfInt:

   IntStream intStream = StreamSupport.intStream(new FindMinimumSpliterator(array, 0, array.length - 1), true);
   

5. On the IntStream we found minimum calling min() method

   OptionalInt minimum = intStream.min();
   

tests

Tested in FindMinimumTest over array of 100_000 random elements.