Integrated: 8280915: Better parallelization for AbstractSpliterator and IteratorSpliterator when size is unknown

[Tagir F.Valeev]

On Sat, 29 Jan 2022 16:31:43 GMT, Tagir F. Valeev <tvaleev at openjdk.org> wrote:

> See the bug description for details.
> 
> I propose a simple solution. Let's allow ArraySpliterator to be non-SIZED and report artificial estimatedSize(), much bigger than the real one. This will allow AbstractSpliterator and IteratorSpliterator to produce prefix whose size is comparable to Long.MAX_VALUE (say, starting with Long.MAX_VALUE/2), and this will enable further splitting of the prefix. This change will drastically improve parallel streaming for affected streams of size <= 1024 and significantly improve for streams of size 1025..20000. The cost is higher-grained splitting for huge streams of unknown size. This might add a minor overhead for such scenarios which, I believe, is completely tolerable.
> 
> No public API changes are necessary, sequential processing should not be affected, except an extra field in ArraySpliterator which increases a footprint by 8 bytes.
> 
> I added a simple test using an artificial collector to ensure that at least two non-empty parts are created when parallelizing Stream.iterate source. More testing ideas are welcome.

This pull request has now been integrated.

Changeset: 4cc8eccf
Author:    Tagir F. Valeev <tvaleev at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/4cc8eccfcadf5d3edc31809ead2dd6554c7cca4b
Stats:     212 lines in 3 files changed: 178 ins; 0 del; 34 mod

8280915: Better parallelization for AbstractSpliterator and IteratorSpliterator when size is unknown

Reviewed-by: psandoz

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PR: https://git.openjdk.java.net/jdk/pull/7279