RFR: 8302822: Method/Field/Constructor/RecordComponent::getGenericInfo() is not thread safe

[Claes Redestad]

On Mon, 20 Feb 2023 17:03:33 GMT, Peter Levart <plevart at openjdk.org> wrote:

>> We don't fear calling the factory twice for benign races, as the distinct constructor factory instances are behaviorally the same.
>> 
>> The true issue lies in the double getfield operations: Java memory model doesn't require the second read to happen-after a write reflected in the first read, so return this.genericInfo may return null while this.genericInfo == null evaluates to false, in case genericInfo is initialized lazily by another thread. See https://bugs.openjdk.org/browse/JDK-8261404
>
> Hi @liach,
> 
> I think @dholmes-ora is worried about the fields in the object being returned by the getGenericInfo() method and similar. In above case this means fields in class ConstructorRepository.
> I checked it and the entire hierarchy based on sun.reflect.generics.repository.AbstractRepository with subclasses including ConstructorRepository is modeled such that all fields are either:
> - volatile and lazily initialized; or
> - final and initialized in constructor
> 
> Such objects may be published via data race and still be seen consistent on the accepting side.

I don't have any issue with this version. Making the fields volatile is _currently_ unnecessary to ensure correctness -- thanks @plevart for double-checking that all fields in the hierarchy is either `volatile` or `final` -- but adding it is relatively benign (very minor performance cost to a likely-not-very-performance-sensitive code path), reduces fragility and might avoid extraneous allocations of under race conditions.

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PR Comment: https://git.openjdk.org/jdk/pull/12643#issuecomment-1572275936