On Wed, 11 Feb 2026 18:57:02 GMT, Rémi Forax <[email protected]> wrote:
>> What issue? This is an integral part of the performance optimization. > > Your PR proposes two optimizations, > - HashMap.putAll(HashMap) > - HashMap.putAll(UnmodifiableMap(HashMap)) > > The former have been done numerous time for other collections, the latter is > as far as as know new. > > There are several reasons to not wanting to do the latter , on top of my head: > - this is not a symmetrical transformation, > - why only have this optimization on HashMap and not ArrayList and/or > ArrayDeque ? > > So It's a separate issue that should be discussed on on the mailist list > first. Hmm, I disagree, since they are both aspects of improving performance of the target method, HashMap.putMapEntries(). They also both directly attack the underlying JDK JIT limitations described in https://bugs.openjdk.org/browse/JDK-8368292 . It's a two-piece fix to one problem, and they're covered simultaneously by a single unit test and JMH benchmark. Open to opinions from others. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/28243#discussion_r2795064430
