RFR: 8342283: CDS cannot handle a large number of classes [v2]

[Aleksey Shipilev]

On Mon, 28 Apr 2025 09:20:38 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> CDS cannot handle large number of classes, because `ClassLoader` data structures get too large for CDS archival. The new test captures such an occasion. We do `clear()`-s, but that is not enough to trim the backing storages for the affected collections.
>> 
>> In contrast with previous attempts to fix this (https://github.com/openjdk/jdk/pull/21797 and my VM-side field overwrite), we can just reinitialize the fields using `Unsafe`, which bypasses normal `final` field write restriction. `ClassLoader` already does a similar thing nearby! This allows us to stay fully in Java, and makes the patch fairly straightforward.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, new test reliably fails without the fix, passes with it
>>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>
> Aleksey Shipilev 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 four additional commits since the last revision:
> 
>  - Minor touchup
>  - Merge branch 'master' into JDK-8342283-cds-many-classes
>  - Adjust TEST.groups
>  - Fix

Testing is green. I am integrating.

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PR Comment: https://git.openjdk.org/jdk/pull/24877#issuecomment-2839760107