Hi,
Am 26.08.2025 um 17:07 schrieb Chris Hegarty:
Thanks Uwe.
There we only use it to keep track of attributes and how to construct them. In that case
it is "write-once, read-many" and items are never deleted.
This is the key information. IIUC, the JDK performance regression is only
triggered by removal - and since we don’t remove, then I would expect Lucene to
be unaffected by it.
That's also how I interpreted it. But when reading the PR that is
applied as fix for 25.0.3 and 26, the magic is done on "get". So I am
not fully sure how this behaves in reality. But I don't expect real
performance problems on plain computeValue and later gets, because most
of the lambda-related stuff (like a type cache) in the JDK also depends
on ClassValue to keep track of implementation classes. They have similar
patterns like our's: we keep track of a MethodHandle to the constructor
of an attribute implementation class (and MethodHanles use ClassValue to
lookup some MethodHandles vor varargs handling, too:
https://github.com/openjdk/jdk/blob/075ddef831f059cad1639bb6834a0923e725e15f/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java#L705-L711).
So pure computeValue with only gets() looks unaffected, otherwise they
would have seen it earlier.
I think Elasticsearch's Painless also has LambdaMetaFactory-like caches
like this and those should be unaffected, too.
I think most of the code using ClassValue won't be affected, because the
normal usage pattern is to attach something to classes for their
lifetime (like Groovy attaches its Metadata) and never remove them
again. When classes are unloaded the values are freed, too (and this is
why it was invented to not need to use Class-keyed crazy weak maps).
Uwe
-Chris.
On 26 Aug 2025, at 14:11, Uwe Schindler <[email protected]> wrote:
Hi,
We don't use ClassValue too extensively, only at one place: The only use of ClassValue is
in TokenStream's attribute management. There we only use it to keep track of attributes
and how to construct them. In that case it is "write-once, read-many" and items
are never deleted. So basically when a TokenStream is constructed and attributes are
added, we keep track of the implementations responsible for all attribute classes.
Uwe
Am 26.08.2025 um 14:19 schrieb Luca Cavanna:
Hey all,
I was wondering if anyone ran Lucene benchmarks against JDK 25 so far.
Based on another thread in this same list, I would assume that we ran
successful tests but no benchmarks yet. Would it make sense to set this up yet
or is it too early?
In particular, I have some questions about
https://bugs.openjdk.org/browse/JDK-8358535 and whether it may impact Lucene.
Cheers
Luca
--
Uwe Schindler
Achterdiek 19, D-28357 Bremen
https://www.thetaphi.de
eMail: [email protected]
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