RFR: 8368174: Proactive initialization of @AOTSafeClassInitializer classes [v2]
Ioi Lam
iklam at openjdk.org
Tue Sep 23 22:10:53 UTC 2025
> This is an alternative to https://github.com/openjdk/jdk/pull/27024. Thanks to @ashu-mehra for the suggestion.
>
> ### Background:
>
> The AOT Assembly Phase is in essence a small Java program that executes a limited set of Java bytecodes. This program bootstraps the module system, loads classes, and performs certain ahead-of-time optimizations such as resolving `invokedynamic` call sites.
>
> As a side effect of Java program execution, a small set of Java classes are initialized in the Assembly Phase.
>
> Since [JDK-8360163](https://bugs.openjdk.org/browse/JDK-8360163), if a class `X` is annotated with `@AOTSafeClassInitializer` *and* is initialized in the Assembly Phase, then `X` will be stored in the AOT cache in the "initialized" state. When the AOT cache is used in the Production Run, `X::<clinit>` will not be executed, and the static variables of `X` will be available upon JVM bootstrap.
>
> ### Problem:
>
> The Assembly Phase doesn't touch many classes that may benefit from `@AOTSafeClassInitializer`. For example, `jdk.internal.math.MathUtils::<clinit>` creates a few large tables. Caching `MathUtils` in the "initialized" state will improve start-up time. However, since no bytecodes executed by the Assembly Phase use `MathUtils`. it will not be initialized.
>
> ### Fix:
>
> If a class `X` has the `@AOTSafeClassInitializer` annotation *and* was initialized in the AOT Training Run, the JVM will proactively initialize `X` in the Assembly Phase. This will ensure that `X` will be cached in the "initialized" state.
>
> As a proof of concept, `@AOTSafeClassInitializer` is added to `MathUtils`. `@AOTSafeClassInitializer` will be added to more classes in future RFEs.
Ioi Lam 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 six additional commits since the last revision:
- Exclude new test from hotspot_aot_classlinking and hotspot_appcds_dynamic test groups
- @adinn and @liach comments
- Merge branch 'master' into 8368174-proactive-init-aot-safe-class-initializer
- updated javadoc for AOTSafeClassInitializer.java
- Fix
- imported
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/27402/files
- new: https://git.openjdk.org/jdk/pull/27402/files/1fa2b1ec..774fe0ee
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=27402&range=01
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=27402&range=00-01
Stats: 123813 lines in 925 files changed: 112515 ins; 7470 del; 3828 mod
Patch: https://git.openjdk.org/jdk/pull/27402.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/27402/head:pull/27402
PR: https://git.openjdk.org/jdk/pull/27402
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