RFR: 8265029: Preserve SIZED characteristics on slice operations (skip, limit) [v6]
Tagir F.Valeev
tvaleev at openjdk.java.net
Sun May 23 11:33:49 UTC 2021
On Sun, 23 May 2021 11:24:12 GMT, Tagir F. Valeev <tvaleev at 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:
>
> SIZE_ADJUSTING flag; exactOutputSize is pure
src/java.base/share/classes/java/util/stream/AbstractPipeline.java line 482:
> 480: * Returns the exact output size of the pipeline given the exact size reported by the previous stage.
> 481: *
> 482: * @param previousSize the exact size reported by the previous stage
I renamed `sourceSize` parameter to `previousSize`, as `source` could be associated with `sourceStage` which is misleading here.
src/java.base/share/classes/java/util/stream/StreamOpFlag.java line 340:
> 338: set(Type.OP));
> 339:
> 340: // The following 2 flags are currently undefined and a free for any further
For some reason, the comment says 'The following 2 flags', while we had three, so it was incorrect before but correct now.
-------------
PR: https://git.openjdk.java.net/jdk/pull/3427
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