Integrated: 8342283: CDS cannot handle a large number of classes

[Aleksey Shipilev]

On Fri, 25 Apr 2025 14:49:37 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`

This pull request has now been integrated.

Changeset: ead67574
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/ead6757486fb58f35f6e93b691519673bca1a549
Stats:     166 lines in 4 files changed: 156 ins; 2 del; 8 mod

8342283: CDS cannot handle a large number of classes

Co-authored-by: Ioi Lam <iklam at openjdk.org>
Reviewed-by: iklam, lmesnik, ccheung

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PR: https://git.openjdk.org/jdk/pull/24877