RFR: JDK-8319123 : Implementation of JEP-461: Stream Gatherers (Preview) [v2]

[Tagir F. Valeev]

On Wed, 8 Nov 2023 21:08:03 GMT, Viktor Klang <vklang at openjdk.org> wrote:

>> This Pull-Request implements [JEP-461](https://openjdk.org/jeps/461)
>
> Viktor Klang has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Addressing review feedback
>  - Make Gatherer.andThen take a wildcard for the rhs Gatherer state type

src/java.base/share/classes/java/util/stream/GathererOp.java line 301:

> 299:      * the output.  This is highly beneficial in the parallel case as stateful
> 300:      * operations cannot be pipelined in the ReferencePipeline implementation.
> 301:      * Overriding collect-operations overcomes this limitation.

Does this mean that .parallel().gather(myGatherer).map(smth).collect(..) will be slower than .parallel().gather(myGatherer.andThen(mappingGatherer(smth))).collect(..)? Also, what about other terminals (e.g. reduce())? Will they require processing all the upstream before reduction?

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PR Review Comment: https://git.openjdk.org/jdk/pull/16420#discussion_r1389147792