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Add conditional JDK caching (#1201)

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* Add JDK caching

Cache resolved JDK tool-cache entries by exact platform and release identity, with a default-on cache-jdk input and explicit opt-out.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Apply batched suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Fix JDK cache CI validation

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Update brace-expansion security fix

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refresh brace-expansion license metadata

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refine JDK cache semantics

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refine JDK cache documentation

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Simplify JDK cache identity

Use one normalized runner OS dimension, reset the internal cache key schema for the unreleased feature, and align documentation, tests, and bundles.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Align JDK cache OS identity

Use the established RUNNER_OS value directly and retain process.platform only as a non-Actions fallback.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Harden JDK cache saves and document tool-cache reuse

Bind each JDK cache key to the installation identity it was computed for,
keep post-job saves best-effort per entry, and state the real reuse and
verification guarantee in the documentation.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: restructure README caching section

Rename '## Caching dependencies' to '## Caching' and add a what-gets-cached
overview table covering the dependency, wrapper, and JDK caches. Lead with the
common 'cache: maven' example and the dependency-cache material, and demote JDK
caching into its own subsection.

Also corrects the IMPORTANT callout, which implied JDK caching required an
explicit opt-in; it is enabled implicitly whenever 'cache' is set.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: fix caching documentation defects

- Remove pull-request framing that compared behavior to `main`; state the
  tool-cache and `jdkfile` behavior directly and unconditionally.
- Clarify that the JDK cache is a separate cache *entry* from the dependency
  and wrapper caches, while its *enablement* is coupled to `cache`, so the
  opening paragraph agrees with the enablement matrix.
- Cite the actions/setup-java-benchmarks repository instead of an open PR and
  a self-referential PR comment, keeping the measured figures and caveats.
- Keep the `cache`/`cache-jdk` matrix only in docs/advanced-usage.md and
  summarize the rules in prose in README.md to avoid divergence.
- Describe the guarantee that a cache key is only saved with the installation
  it was computed for, instead of documenting inode/size/timestamp internals.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: add V6 what's new entry for JDK caching

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: e2755464-4e83-47b6-ba71-731bb481b418

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Copilot-Session: e2755464-4e83-47b6-ba71-731bb481b418
This commit is contained in:
Bruno Borges
2026-08-04 21:54:10 -04:00
committed by GitHub
parent 7a9a8b1dcc
commit 955f34f16f
26 changed files with 2756 additions and 827 deletions
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docs/advanced-usage.md
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@@ -17,6 +17,7 @@
- [Package compatibility](#Package-compatibility)
- [JavaFX Maven project](#JavaFX-Maven-project)
- [Ensuring the Maven cache is complete (plugin dependencies)](#ensuring-the-maven-cache-is-complete-plugin-dependencies)
- [Caching JDK installations](#caching-jdk-installations)
- [Installing custom Java architecture](#Installing-custom-Java-architecture)
- [Installing JDK without setting as default](#Installing-JDK-without-setting-as-default)
- [Installing custom Java distribution from local file](#Installing-Java-from-local-file)
@@ -468,6 +469,93 @@ jobs:
> which provides purpose-built caching (see the
> [setup-gradle documentation](https://github.com/gradle/actions/blob/main/docs/setup-gradle.md)).
## Caching JDK installations
`cache-jdk` controls caching for downloaded JDK installations. The JDK cache is
stored and restored as its own cache entry, separate from the dependency and
build-tool wrapper caches selected by `cache`. Whether it is *enabled*, however,
is coupled to `cache`: setting `cache` turns JDK caching on as well, unless
`cache-jdk` is set explicitly.
| `cache` | `cache-jdk` | Dependency and wrapper caches | JDK cache |
| --- | --- | --- | --- |
| Omitted | Omitted | Disabled | Disabled |
| Omitted | `true` | Disabled | Enabled |
| Omitted | `false` | Disabled | Disabled |
| Set | Omitted | Enabled | Enabled |
| Set | `true` | Enabled | Enabled |
| Set | `false` | Enabled | Disabled |
JDK entries are specific to the runner operating system and normalized
architecture. They are additionally separated by distribution, package type,
exact resolved Java version, release identity, and signature-verification
identity. The release identity is the authoritative checksum when available and
otherwise the download URL without its query string. These dimensions prevent
incompatible JDKs from sharing an entry. They also mean that a matrix or workflow
using multiple JDK versions, distributions, package types, architectures, or
operating systems stores a separate JDK entry for each identity and consumes
cache storage for each one.
For `distribution: jdkfile`, the release source is a SHA-256 hash of the local
`jdk-file` contents, streamed so the archive is not held in memory. Changing the
archive therefore creates a different JDK cache entry, even when its path and
requested version are unchanged. The archive is only read when the runner tool
cache holds no installation satisfying the requested version: a matching
tool-cache installation short-circuits setup, so a changed `jdk-file` is not
re-extracted for a version that is already installed. Use
`force-download: true` when the archive contents change but the version does not.
The verification identity separates unverified downloads from packages verified
with the distribution's bundled signing key and from packages verified with each
custom key. Custom public keys are represented by a SHA-256 fingerprint of
normalized key material; the key itself is not placed in the cache key, the logs,
or action state. A verified exact-key hit reuses content that was
signature-verified when it was downloaded by the run that saved the entry,
instead of downloading and verifying it again.
> [!IMPORTANT]
> The JDK cache **key** is what isolates verification modes and release
> identity: a JDK cache entry created by an unverified download can never be
> restored for a request that sets `verify-signature: true`, and vice versa.
> `cache-jdk` does not change how the runner tool cache is used. setup-java
> first looks for an installation in the runner tool cache — a preinstalled
> JDK, or one installed by an earlier step of the same job — and uses it as-is. Such an installation is not downloaded again, and its checksum
> and signature are not reverified, even when `verify-signature: true` is set,
> because its verification history is not recorded in the tool cache. Use
> `force-download: true` for a request that must download and verify the archive
> itself.
`check-latest: true` and `java-version: latest` resolve remote metadata before
looking up the exact resolved JDK entry. `force-download: true` bypasses both the
runner tool cache and JDK cache restore, but an enabled JDK cache still records
the downloaded installation for a post-job save. `cache-read-only: true` allows
restores but suppresses post-job saves for JDK, dependency, and wrapper caches.
If the cache service fails to restore an entry, or the restored entry lacks the
expected completed tool-cache path, setup continues by downloading the JDK.
Post-job saves are best-effort and do not fail the job: cache keys are immutable,
so an existing key or a concurrent job winning the save race is left unchanged,
and a failure to save one JDK entry is reported as a warning without preventing
the remaining entries from being saved.
A key is only ever populated with the installation it was computed for. Because
tool-cache paths are shared per version and architecture, a later step — for
example one using `force-download: true` — can replace the installation an
earlier step registered. setup-java detects that replacement in the post-job
step and skips the save with a warning, so a key is never saved with content
other than the installation it identifies. This guarantee holds without
rehashing hundreds of megabytes of JDK content on every job.
JDK caching trades cache storage and cold-run save work for faster warm setup.
In a five-run Ubuntu benchmark using Microsoft OpenJDK 17.0.19, the median warm
`setup-java` time fell from 7 seconds to 3 seconds and median warm job time fell
from 24 seconds to 18 seconds. The JDK entry added 175.3 MiB for that single
identity. Results vary by runner, distribution, JDK size, network, and cache
eviction pressure; short jobs may improve latency without changing billed
minutes. The benchmark harness and methodology, along with results from later
runs, live in
[actions/setup-java-benchmarks](https://github.com/actions/setup-java-benchmarks).
## Platform and architecture compatibility
The `architecture` input is normalized before setup-java checks the tool cache