On Thu, 7 Sep 2023 11:13:44 GMT, Per Minborg <pminb...@openjdk.org> wrote:
> This PR outlines a solution for making immutable maps `@ValueBased` by
> removing cacheing of certain values in `AbstractMap`.
>
> By removing these caching fields in `AbstractMap`, we can make the immutable
> maps `@ValueBased` and at the same time, performance is likely improved
> because the JVM is probably able to optimize away object creation anyway via
> escape analysis. Also, all maps will occupy less space as we get rid of a
> number of objects and references stored for each map.
>
> We need to benchmark this solution to better understand its implications.
@cl4es ran some benchmarks:
Name (size) Cnt Base Error Test Error Unit Diff%
HashMapViews.entrySetSize 1 5 1,085 ± 0,118 1,003 ± 0,053 ns/op
7,6% (p = 0,002*)
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
-0,1% (p = 0,639 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
-7,7% (p = 0,003*)
:gc.count N/A 5 0,000 0,000 counts
HashMapViews.entrySetSize 1000 5 1,001 ± 0,026 1,033 ± 0,170 ns/op
-3,3% (p = 0,173 )
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
0,6% (p = 0,012 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
3,9% (p = 0,124 )
:gc.count N/A 5 0,000 0,000 counts
HashMapViews.keySetSize 1 5 1,051 ± 0,017 0,706 ± 0,008 ns/op
32,8% (p = 0,000*)
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
0,0% (p = 0,947 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
-32,8% (p = 0,000*)
:gc.count N/A 5 0,000 0,000 counts
HashMapViews.keySetSize 1000 5 1,078 ± 0,013 0,705 ± 0,006 ns/op
34,6% (p = 0,000*)
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
-0,1% (p = 0,756 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
-34,7% (p = 0,000*)
:gc.count N/A 5 0,000 0,000 counts
HashMapViews.valuesSize 1 5 0,998 ± 0,033 0,718 ± 0,062 ns/op
28,1% (p = 0,000*)
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
0,7% (p = 0,055 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
-27,6% (p = 0,000*)
:gc.count N/A 5 0,000 0,000 counts
HashMapViews.valuesSize 1000 5 1,043 ± 0,062 0,705 ± 0,011 ns/op
32,4% (p = 0,000*)
:gc.alloc.rate N/A 5 0,013 ± 0,000 0,013 ± 0,000 MB/sec
-0,3% (p = 0,405 )
:gc.alloc.rate.norm N/A 5 0,000 ± 0,000 0,000 ± 0,000 B/op
-32,6% (p = 0,000*)
:gc.count N/A 5 0,000 0,000 counts
* = significant
Invariant parameters used by above microbenchmarks:
mapType: HashMap
src/java.base/share/classes/java/util/AbstractMap.java line 323:
> 321: return new AbstractSet<>() {
> 322: public Iterator<K> iterator() {
> 323: return new Iterator<>() {
There is another PR that proposes to refactor these anonymous classes:
https://github.com/openjdk/jdk/pull/15615/files
-------------
PR Comment: https://git.openjdk.org/jdk/pull/15614#issuecomment-1710165103
PR Review Comment: https://git.openjdk.org/jdk/pull/15614#discussion_r1329664799
