On Mon, 24 May 2021 04:35:42 GMT, Tagir F. Valeev <tval...@openjdk.org> wrote:
>> With the introduction of `toList()`, preserving the SIZED characteristics in
>> more cases becomes more important. This patch preserves SIZED on `skip()`
>> and `limit()` operations, so now every combination of
>> `map/mapToX/boxed/asXyzStream/skip/limit/sorted` preserves size, and
>> `toList()`, `toArray()` and `count()` may benefit from this. E. g.,
>> `LongStream.range(0, 10_000_000_000L).skip(1).count()` returns result
>> instantly with this patch.
>>
>> Some microbenchmarks added that confirm the reduced memory allocation in
>> `toList()` and `toArray()` cases. Before patch:
>>
>> ref.SliceToList.seq_baseline:·gc.alloc.rate.norm 10000
>> thrpt 10 40235,534 ± 0,984 B/op
>> ref.SliceToList.seq_limit:·gc.alloc.rate.norm 10000
>> thrpt 10 106431,101 ± 0,198 B/op
>> ref.SliceToList.seq_skipLimit:·gc.alloc.rate.norm 10000
>> thrpt 10 106544,977 ± 1,983 B/op
>> value.SliceToArray.seq_baseline:·gc.alloc.rate.norm 10000
>> thrpt 10 40121,878 ± 0,247 B/op
>> value.SliceToArray.seq_limit:·gc.alloc.rate.norm 10000
>> thrpt 10 106317,693 ± 1,083 B/op
>> value.SliceToArray.seq_skipLimit:·gc.alloc.rate.norm 10000
>> thrpt 10 106430,954 ± 0,136 B/op
>>
>>
>> After patch:
>>
>> ref.SliceToList.seq_baseline:·gc.alloc.rate.norm 10000
>> thrpt 10 40235,648 ± 1,354 B/op
>> ref.SliceToList.seq_limit:·gc.alloc.rate.norm 10000
>> thrpt 10 40355,784 ± 1,288 B/op
>> ref.SliceToList.seq_skipLimit:·gc.alloc.rate.norm 10000
>> thrpt 10 40476,032 ± 2,855 B/op
>> value.SliceToArray.seq_baseline:·gc.alloc.rate.norm 10000
>> thrpt 10 40121,830 ± 0,308 B/op
>> value.SliceToArray.seq_limit:·gc.alloc.rate.norm 10000
>> thrpt 10 40242,554 ± 0,443 B/op
>> value.SliceToArray.seq_skipLimit:·gc.alloc.rate.norm 10000
>> thrpt 10 40363,674 ± 1,576 B/op
>>
>>
>> Time improvements are less exciting. It's likely that inlining and
>> vectorizing dominate in these tests over array allocations and unnecessary
>> copying. Still, I notice a significant improvement in SliceToArray.seq_limit
>> case (2x) and mild improvement (+12..16%) in other slice tests. No
>> significant change in parallel execution time, though its performance is
>> much less stable and I didn't run enough tests.
>>
>> Before patch:
>>
>> Benchmark (size) Mode Cnt Score Error
>> Units
>> ref.SliceToList.par_baseline 10000 thrpt 30 14876,723 ± 99,770
>> ops/s
>> ref.SliceToList.par_limit 10000 thrpt 30 14856,841 ± 215,089
>> ops/s
>> ref.SliceToList.par_skipLimit 10000 thrpt 30 9555,818 ± 991,335
>> ops/s
>> ref.SliceToList.seq_baseline 10000 thrpt 30 23732,290 ± 444,162
>> ops/s
>> ref.SliceToList.seq_limit 10000 thrpt 30 14894,040 ± 176,496
>> ops/s
>> ref.SliceToList.seq_skipLimit 10000 thrpt 30 10646,929 ± 36,469
>> ops/s
>> value.SliceToArray.par_baseline 10000 thrpt 30 25093,141 ± 376,402
>> ops/s
>> value.SliceToArray.par_limit 10000 thrpt 30 24798,889 ± 760,762
>> ops/s
>> value.SliceToArray.par_skipLimit 10000 thrpt 30 16456,310 ± 926,882
>> ops/s
>> value.SliceToArray.seq_baseline 10000 thrpt 30 69669,787 ± 494,562
>> ops/s
>> value.SliceToArray.seq_limit 10000 thrpt 30 21097,081 ± 117,338
>> ops/s
>> value.SliceToArray.seq_skipLimit 10000 thrpt 30 15522,871 ± 112,557
>> ops/s
>>
>>
>> After patch:
>>
>> Benchmark (size) Mode Cnt Score Error
>> Units
>> ref.SliceToList.par_baseline 10000 thrpt 30 14793,373 ± 64,905
>> ops/s
>> ref.SliceToList.par_limit 10000 thrpt 30 13301,024 ± 1300,431
>> ops/s
>> ref.SliceToList.par_skipLimit 10000 thrpt 30 11131,698 ± 1769,932
>> ops/s
>> ref.SliceToList.seq_baseline 10000 thrpt 30 24101,048 ± 263,528
>> ops/s
>> ref.SliceToList.seq_limit 10000 thrpt 30 16872,168 ± 76,696
>> ops/s
>> ref.SliceToList.seq_skipLimit 10000 thrpt 30 11953,253 ± 105,231
>> ops/s
>> value.SliceToArray.par_baseline 10000 thrpt 30 25442,442 ± 455,554
>> ops/s
>> value.SliceToArray.par_limit 10000 thrpt 30 23111,730 ± 2246,086
>> ops/s
>> value.SliceToArray.par_skipLimit 10000 thrpt 30 17980,750 ± 2329,077
>> ops/s
>> value.SliceToArray.seq_baseline 10000 thrpt 30 66512,898 ± 1001,042
>> ops/s
>> value.SliceToArray.seq_limit 10000 thrpt 30 41792,549 ± 1085,547
>> ops/s
>> value.SliceToArray.seq_skipLimit 10000 thrpt 30 18007,613 ± 141,716
>> ops/s
>>
>>
>> I also modernized SliceOps a little bit, using switch expression (with no
>> explicit default!) and diamonds on anonymous classes.
>
> Tagir F. Valeev has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Trailing whitespace removed
Very good. Thanks making the adjustments. Architecturally, i think we are in a
better place. Just have some comments, mostly around code comments.
src/java.base/share/classes/java/util/stream/AbstractPipeline.java line 471:
> 469: int flags = getStreamAndOpFlags();
> 470: long size = StreamOpFlag.SIZED.isKnown(flags) ?
> spliterator.getExactSizeIfKnown() : -1;
> 471: if (size != -1 && StreamOpFlag.SIZE_ADJUSTING.isKnown(flags) &&
> !isParallel()) {
Very nice. It's a good compromise to support only for sequential streams, since
we have no size adjusting intermediate stateless op. If that was the case we
would need to step back through the pipeline until the depth was zero, then
step forward. I think it worth a comment here to inform our future selves if we
ever add such an operation.
Strictly speaking we only need to call `exactOutputSize` if the stage is size
adjusting. Not sure it really matters perf-wise. If we leave as is maybe add a
comment.
src/java.base/share/classes/java/util/stream/StreamOpFlag.java line 331:
> 329:
> 330: /**
> 331: * Characteristic value signifying that an operation may adjust the
I think we need to add two additional constraints to the documentation:
1. The flag, if present, is only valid when SIZED is present; and
2. The flag is only valid for sequential streams.
The latter is a good compromise given we currently have no size adjusting
stateless intermediate op.
-------------
PR: https://git.openjdk.java.net/jdk/pull/3427
