Fwd: Should final fields in records be trusted or not trusted in 16?

[Remi Forax]

forwarded to amber-spec-experts

Rémi

----- Mail transféré -----
De: "mandy chung" <mandy.chung at oracle.com>
À: "amber-dev" <amber-dev at openjdk.java.net>
Envoyé: Mercredi 9 Décembre 2020 05:00:03
Objet: Should final fields in records be trusted or not trusted in 16?

I need your help, amber experts, in understanding the conclusion on the 
amber-spec-experts discussion [1].  It isn't clear to me what it's 
agreed to do in Java SE 16. Remi raised in PR for JDK-8257596 [2] and so 
your clarification would help.  PR #1706 intends to fix the regression 
introduced by JDK-8255342 that removes non-specified JVM checks on 
classes with RecordComponents attributes.  This does not conflict with 
the work to implement the true TNSFF for all classes like JDK-8233873.

One way I read [1] is that it's agreed to revisit the current approach 
[3] that makes final fields in record classes "read-only" by reflection 
and JIT optimization to trust final fields in records (note that JIT 
optimization is implementation-specific). Instead all final field values 
should be trusted as a constant (see JDK-8233873).

If this is the agreement, I see two options for JDK 16:
1. Keep JDK-8247444 and fix the regression as proposed by PR #1706 [2]
2. Backout JDK-8247444 [4].  This involves spec change and we shall act 
on it quickly.

Making all final field values trusted as a constant will be a separate 
enhancement regardless of which option it goes.

Please clarify.

Mandy
[1] 
https://mail.openjdk.java.net/pipermail/amber-spec-experts/2020-November/002630.html
[2] https://github.com/openjdk/jdk/pull/1706
[3] https://bugs.openjdk.java.net/browse/JDK-8247444
[4] https://github.com/openjdk/jdk/compare/master...mlchung:backout-8247444