Enabling the Gradle configuration cache seems to cause issues with Quarkus test

[LarsSven]

Describe the bug

As of Gradle 9, it is recommended to enable the Gradle configuration cache to improve performance (You actually get notified about this). We tried to roll this out for our repositories, however we started noticing that when we enabled the Gradle configuration cache, Quarkus test things in multi-module projects started suddenly happening in parallel, causing issues around port conflicts of the started services.

Note that the gradle configuration cache will be enabled by default in Gradle 10, and users get told to enable this feature in Gradle 9, so this is something that Quarkus probably needs to support.

Expected behavior

We expect to be able to set org.gradle.configuration-cache=true without causing issues with Quarkus test

Actual behavior

When we run a Gradle task that runs tests on all of our modules, it suddenly starts failing with:

java.util.concurrent.ExecutionException: io.quarkus.runtime.QuarkusBindException: Port already bound: 8081: Address already in use

Note that we don't use org.gradle.parallel, we know inter-project parallelism doesn't work with Quarkus. It is purely adding org.gradle.configuration-cache=true that suddenly breaks Quarkus tests as if we enabled inter-project parallelism.

How to Reproduce?

1. Clone https://gitlab.com/rug-digitallab/products/themis/themis-core.git
2. Add org.gradle.configuration-cache=true to gradle.properties
3. Run ./gradlew test

Output of uname -a or ver

Ubuntu 25.04

Output of java -version

OpenJDK 21.0.8

Quarkus version or git rev

Quarkus 3.25.3

Build tool (ie. output of mvnw --version or gradlew --version)

Gradle 9.0.0

Additional information

No response

[quarkus-bot]

/cc @glefloch, @gwenneg (cache), @quarkusio/devtools, @radcortez (config)

[LarsSven]

You can also just run ./gradlew test from the branch/MR where we tried to roll this out: https://gitlab.com/rug-digitallab/products/themis/themis-core/-/merge_requests/288

[jskillin-idt]

Edit: Ignore this comment. I am dumb. I didn't see the part of the OP that said, "Note that we don't use org.gradle.parallel, we know inter-project parallelism doesn't work with Quarkus". My bad!

I don't think running tests in parallel is supported but the issue I linked may be about a different kind of parallel. The reason I am not sure it's supported is I do I remember running into an issue like this way back in the 2.x days, but I can't find an issue filed unfortunately so I only have vague emotional memories to go on. 😅