ServiceLoader based on module-info.java not working

[codepitbull]

Describe the issue
I am currently experimenting with JPMS on Java 21 and GraalVM.

I discovered using services defined in a different module than the main one aren't picked up.

Steps to reproduce the issue
Clone the reproducer: git clone --depth 1 https://github.com/codepitbull/graalvm-bug-java21.git

There is an app module with a dependency on the dependency module defined:

module javatest.app.main {
    requires javatest.dependency.main;
    uses MyService;
}

The dependency defines the interface and the service implementation:

module javatest.dependency.main {
    exports de.codepitbull.module.example;
    provides MyService with de.codepitbull.module.example.MyServiceImpl;
}

The expctation would be that the app sees the defined service when a native image is built.

Build java only

• Run ./gradlew :app:build
• Run the application: `java --module-path ./app/build/libs/app.jar:./dependency/build/libs/dependency.jar -m javatest.app.main/java21.App``

Output:

Found a service: MyService!
Called Dependency.hello()

This shows the service is discovered running regular Java.

Build with native-image

• Run ./gradlew :app:nativeBuild
• Run the app app/build/native/nativeBuild/app

Output:

Called Dependency.hello()

This shows that the service is not discovered when using the native build.

Build image natively (to avoid possible Gradle-plugin issues)

• Run `native-image --module-path ./app/build/libs/app.jar:./dependency/build/libs/dependency.jar --module javatest.dependency.main -m javatest.app.main/java21.App``
• Run app `java21.app``

Output:

Called Dependency.hello()

Again, service not resolved.

Describe GraalVM and your environment:

• GraalVM version:

native-image 21 2023-09-19
GraalVM Runtime Environment GraalVM CE 21+35.1 (build 21+35-jvmci-23.1-b15)
Substrate VM GraalVM CE 21+35.1 (build 21+35, serial gc)

• JDK major version:

openjdk version "21" 2023-09-19
OpenJDK Runtime Environment GraalVM CE 21+35.1 (build 21+35-jvmci-23.1-b15)
OpenJDK 64-Bit Server VM GraalVM CE 21+35.1 (build 21+35-jvmci-23.1-b15, mixed mode, sharing)

• OS: 13.5.1 (22G90)
• Architecture: Applie Silicon M2

[hamzaGhaissi]

Hi @codepitbull ,
You need to register the service interface so that the ServiceLoader can identify and load them. The configuration files need to be created in the folder META-INF/services.
In order to resolve the issue create a sub directories inside the dependency folder like this
dependency/src/main/resources/META-INF/services
and inside the services folder create a file named de.codepitbull.module.example.MyService, that file will have all the implementation of that service (one in each line) in this case only 1 like this
de.codepitbull.module.example.MyServiceImpl

[codepitbull]

Thanks for your answer!

I am aware of the old way, but I was looking at doing this using JPMS.
According to this issue it is supposed to work: #4141

So, is JPMS not fully supported on Graal?
Do you have any pointers where this might be documented?

[hamzaGhaissi]

Thanks, Issue reproduced and we are looking into it

[PeteSL]

With 21.0.2, even if the META-INF/services files are there, they are not recognized and ServiceLoader does not work. JVMs work fine, native-image only works using classpath instead of module-path.