On Sat, 10 Apr 2021 06:30:33 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.
src/java.base/share/classes/java/util/stream/SliceOps.java line 238:
> 236: long adjustSize(long size) {
> 237: return isParallel() ? super.adjustSize(size)
> 238: : calcSize(super.adjustSize(size), skip,
> adjustedLimit);
Do you think it is worth adding a comment that clarifies why serial and
parallel cases are different?
-------------
PR: https://git.openjdk.java.net/jdk/pull/3427
