Module in JDK image as platform module or loaded by application class loader?

[Langer, Christoph]

Hi there,

for our JDK 9 image the jtreg test jdk/modules/etc/VerifyModuleDelegation has unveiled a problem.

The issue is that we introduced a few modules that are defined as a platform module. One of these modules requires jdk.attach which is neither boot nor platform. The code within the module that requires jdk.attach seems to work since the platform class loader is able to load jdk.attach classes because it delegates to the application class loader. However, VerifyModuleDelegation is not satisfied with the fact that the loader of our custom module isn't the loader of jdk.attach or one of its ancestors.

Now, for me the question is how to solve this correctly? I currently see 3 options:
1. move jdk.attach (and hence jdk.internal.jvmstat ) to the platform modules
2. remove our custom modules from the list of platform modules in order to get them under the application class loader
3. leave the class loaders of the modules alone, remove the requires statement from module-info and implement a Service (Loader) that can be implemented in our jdk.attach version

To get on the right way here I probably understand too little of the implications of a module being "Platform". I understand that platform modules don't have all permissions by default such as modules loaded by the boot loader. However, there are some differences and there were reasons why we elevated our modules to "platform", I think it had to do something with caller sensitive calls or other authentication checking mechanisms.

So, probably solution 1.) would be the easiest but I don't know if it is a good idea and we lose some compatibility with OpenJDK. 2.) I have to check again where the problems were and 3.) Seems a bit complicated and would unnecessarily break the coupling of modules via module-info.

So, I'm hoping to get some advice here :)

Thanks in advance and best regards
Christoph