On Tue, 19 Sep 2023 18:38:06 GMT, ExE Boss <d...@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.
>
> src/java.base/share/classes/java/util/AbstractMap.java line 375:
>
>> 373: */
>> 374: public Collection<V> values() {
>> 375: return new AbstractCollection<>() {
>
> Note that this causes `m.values().equals(m.values())` to no longer return
> `true`, as base `Collection::equals` is defined using reference equality.
Looking at the specification above:
> No synchronization is performed, so there is a slight chance that multiple
> calls to this method will not all return the same collection.
This should be an acceptable change to behavior.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/15614#discussion_r1330809662
