RFR: 8309688: Data race on java.io.ClassCache$CacheRef.strongReferent [v5]

[Man Cao]

On Thu, 15 Jun 2023 08:23:58 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Man Cao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
>> 
>>  - Merge branch 'master' into JDK8309688
>>  - Removed volatile and comment about the benign race
>>  - Switch to using volatile instead of AtomicReference
>>  - Merge branch 'master' into JDK8309688
>>  - 8309688: Data race on java.io.ClassCache.strongReferent
>
> src/java.base/share/classes/java/io/ClassCache.java line 93:
> 
>> 91:             // multiple threads calls get() with the same Class parameter.
>> 92:             // Fixing this race could introduce noticeable performance penalty.
>> 93:             // See the review thread for JDK-8309688 for details.
> 
> Feels like this comment belongs near `strongReferent` declaration. I suggest:
> 
> 
> // This field is deliberately accessed without sychronization. ClassValue
> // provides synchronization when CacheRef is published. However, when
> // a thread reads this field, while another thread is clearing the field, it 
> // would formally constitute a data race. But that data race is benign, and
> // fixing it could introduce noticeable performance penalty, see JDK-8309688.
> private T strongReferent;

Thank you. Updated.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14386#discussion_r1231381928