RFR: 8306055: Add a built-in Catalog to JDK XML module [v3]

[Elliot Barlas]

On Wed, 22 Nov 2023 17:10:06 GMT, Joe Wang <joehw at openjdk.org> wrote:

>> I'm happy with the addition of the JDK built-in catalog, the inclusion of the DTD defined by Java SE, and the docs updates.
>
>> I'm happy with the addition of the JDK built-in catalog, the inclusion of the DTD defined by Java SE, and the docs updates.
> 
> Thanks again, Alan, I really appreciate it! Finally got all pieces together, a nice foundation for the next.

Hi @JoeWang-Java , I believe there is a thread-safety issue with this change.

The change to `XMLEntityManager` introduced a reference to the JDK catalog singleton. Multiple, independent entity managers can, therefore, concurrently access the shared JDK catalog, which is not thread-safe. This can result in invalid data states and unexpected exceptions within the JDK catalog instance.

I sent an email to `core-libs-dev` about this issue yesterday, as well: https://mail.openjdk.org/pipermail/core-libs-dev/2025-October/153319.html

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PR Comment: https://git.openjdk.org/jdk/pull/16719#issuecomment-3408356230