On Fri, 2 Oct 2020 20:38:40 GMT, Paul Sandoz <psan...@openjdk.org> wrote:
>> Plumb new internal static factory method to trust the array passed in,
>> avoiding unnecessary copying. JMH results for
>> the benchmark show about 15% improvement for the cases that were optimized,
>> namely the 3 to 10 fixed arg cases.
>> # VM options: -verbose:gc -XX:+UseParallelGC -Xms4g -Xmx4g --enable-preview
>> -verbose:gc -XX:+UsePara
>> llelGC -Xms4g -Xmx4g -Xint
>> # Warmup: 5 iterations, 1 s each
>> # Measurement: 5 iterations, 2 s each
>>
>> WITHOUT varargs optimization:
>>
>> Benchmark Mode Cnt Score Error Units
>> ListArgs.list00 thrpt 15 6019.539 ± 144.040 ops/ms
>> ListArgs.list01 thrpt 15 1985.009 ± 40.606 ops/ms
>> ListArgs.list02 thrpt 15 1854.812 ± 17.488 ops/ms
>> ListArgs.list03 thrpt 15 963.866 ± 10.262 ops/ms
>> ListArgs.list04 thrpt 15 908.116 ± 6.278 ops/ms
>> ListArgs.list05 thrpt 15 848.607 ± 16.701 ops/ms
>> ListArgs.list06 thrpt 15 822.282 ± 8.905 ops/ms
>> ListArgs.list07 thrpt 15 780.057 ± 11.214 ops/ms
>> ListArgs.list08 thrpt 15 745.295 ± 19.204 ops/ms
>> ListArgs.list09 thrpt 15 704.596 ± 14.003 ops/ms
>> ListArgs.list10 thrpt 15 696.436 ± 4.914 ops/ms
>> ListArgs.list11 thrpt 15 661.908 ± 11.041 ops/ms
>>
>> WITH varargs optimization:
>>
>> Benchmark Mode Cnt Score Error Units
>> ListArgs.list00 thrpt 15 6172.298 ± 62.736 ops/ms
>> ListArgs.list01 thrpt 15 1987.724 ± 45.468 ops/ms
>> ListArgs.list02 thrpt 15 1843.419 ± 10.693 ops/ms
>> ListArgs.list03 thrpt 15 1126.946 ± 30.952 ops/ms
>> ListArgs.list04 thrpt 15 1050.440 ± 17.859 ops/ms
>> ListArgs.list05 thrpt 15 999.275 ± 23.656 ops/ms
>> ListArgs.list06 thrpt 15 948.844 ± 19.615 ops/ms
>> ListArgs.list07 thrpt 15 897.541 ± 15.531 ops/ms
>> ListArgs.list08 thrpt 15 853.359 ± 18.755 ops/ms
>> ListArgs.list09 thrpt 15 826.394 ± 8.284 ops/ms
>> ListArgs.list10 thrpt 15 779.231 ± 4.104 ops/ms
>> ListArgs.list11 thrpt 15 650.888 ± 3.948 ops/ms
>
> Looks good, i wondered why the performance results were so slow then i looked
> more closely and saw "-Xint" was used. I
> usually don't ascribe much value to micro benchmarks run in interpreter only
> mode, but hey any shaving off startup time
> is welcome. Less allocation is definitely welcome (although i do wish C2 was
> better at eliding redundant array
> initialization and allocation).
Sorry to be late to the party. I thought that all reviews labeled with
core-libs should be mirrored to core-libs-dev
mailing list but I haven't seen it there :(
Please note that the integrated implementation exposes listFromTrustedArray to
everybody. No dirty unsafe reflection is
necessary, only single unchecked cast:
static <T> List<T> untrustedArrayToList(T[] array) {
@SuppressWarnings("unchecked")
Function<List<T>, List<T>> finisher =
(Function<List<T>, List<T>>)
Collectors.<T>toUnmodifiableList().finisher();
ArrayList<T> list = new ArrayList<>() {
@Override
public Object[] toArray() {
return array;
}
};
return finisher.apply(list);
}
This might be qualified as a security issue.
-------------
PR: https://git.openjdk.java.net/jdk/pull/449
