RFR: 8274715: Implement forEach in Collections.CopiesList [v2]

[Martin Buchholz]

On Tue, 5 Oct 2021 09:18:57 GMT, Сергей Цыпанов <github.com+10835776+stsypanov at openjdk.org> wrote:

>> Originally was proposed by Zheka Kozlov here: http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-December/057192.html
>> 
>> Just a tiny optimization: we can use for-i loop instead of `Iterable.forEach()` which is relying on iterator.
>> 
>> Simple benchmark demonstrates slight improvement:
>> 
>> @State(Scope.Thread)
>> @BenchmarkMode(Mode.AverageTime)
>> @OutputTimeUnit(TimeUnit.NANOSECONDS)
>> public class NCopiesBenchmarks {
>>   @Param({"10", "50", "100"})
>>   int size;
>> 
>>   private List<Object> list;
>> 
>>   @Setup
>>   public void prepare() {
>>     list = Collections.nCopies(size, new Object());
>>   }
>> 
>>   @Benchmark
>>   public void forEach(Blackhole bh) {
>>     list.forEach(bh::consume);
>>   }
>> }
>> 
>> 
>> 
>> before
>> 
>> Benchmark                                      (size)  Mode  Cnt    Score    Error   Units
>> NCopiesBenchmarks.forEach                          10  avgt   50   40.737 ±  1.854   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate           10  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm      10  avgt   50   ≈ 10⁻⁴             B/op
>> NCopiesBenchmarks.forEach:·gc.count                10  avgt   50      ≈ 0           counts
>> NCopiesBenchmarks.forEach                          50  avgt   50  213.324 ±  3.784   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate           50  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm      50  avgt   50   ≈ 10⁻³             B/op
>> NCopiesBenchmarks.forEach:·gc.count                50  avgt   50      ≈ 0           counts
>> NCopiesBenchmarks.forEach                         100  avgt   50  443.171 ± 17.919   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate          100  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm     100  avgt   50    0.001 ±  0.001    B/op
>> NCopiesBenchmarks.forEach:·gc.count               100  avgt   50      ≈ 0           counts
>> 
>> after
>> 
>> Benchmark                                      (size)  Mode  Cnt    Score    Error   Units
>> NCopiesBenchmarks.forEach                          10  avgt   50   36.838 ±  0.065   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate           10  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm      10  avgt   50   ≈ 10⁻⁴             B/op
>> NCopiesBenchmarks.forEach:·gc.count                10  avgt   50      ≈ 0           counts
>> NCopiesBenchmarks.forEach                          50  avgt   50  191.173 ±  0.570   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate           50  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm      50  avgt   50   ≈ 10⁻⁴             B/op
>> NCopiesBenchmarks.forEach:·gc.count                50  avgt   50      ≈ 0           counts
>> NCopiesBenchmarks.forEach                         100  avgt   50  376.675 ±  2.476   ns/op
>> NCopiesBenchmarks.forEach:·gc.alloc.rate          100  avgt   50    0.001 ±  0.001  MB/sec
>> NCopiesBenchmarks.forEach:·gc.alloc.rate.norm     100  avgt   50    0.001 ±  0.001    B/op
>> NCopiesBenchmarks.forEach:·gc.count               100  avgt   50      ≈ 0           counts
>
> Сергей Цыпанов has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:
> 
>  - Merge branch 'master' into ncopies
>  - 8274715: Add NCopiesBenchmarks.java
>  - 8274715: Revert some irrelevant changes
>  - 8274715: Implement forEach in Collections.CopiesList

Thanks - TIL about Blackhole::consume .

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Changes requested by martin (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2524