RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v13]

[Severin Gehwolf]

On Mon, 11 Dec 2023 16:37:38 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this patch which adds a jlink mode to the JDK which doesn't need the packaged modules being present. A.k.a run-time image based jlink. Fundamentally this patch adds an option to use `jlink` even though your JDK install might not come with the packaged modules (directory `jmods`). This is particularly useful to further reduce the size of a jlinked runtime. After the removal of the concept of a JRE, a common distribution mechanism is still the full JDK with all modules and packaged modules. However, packaged modules can incur an additional size tax. For example in a container scenario it could be useful to have a base JDK container including all modules, but without also delivering the packaged modules. This comes at a size advantage of `~25%`. Such a base JDK container could then be used to `jlink` application specific runtimes, further reducing the size of the application runtime image (App + JDK runtime; as a single image *or* separate bundles, depending on the app 
 being modularized).
>> 
>> The basic design of this approach is to add a jlink plugin for tracking non-class and non-resource files of a JDK install. I.e. files which aren't present in the jimage (`lib/modules`). This enables producing a `JRTArchive` class which has all the info of what constitutes the final jlinked runtime.
>> 
>> Basic usage example:
>> 
>> $ diff -u <(./bin/java --list-modules --limit-modules java.se) <(../linux-x86_64-server-release/images/jdk/bin/java --list-modules --limit-modules java.se)
>> $ diff -u <(./bin/java --list-modules --limit-modules jdk.jlink) <(../linux-x86_64-server-release/images/jdk/bin/java --list-modules --limit-modules jdk.jlink)
>> $ ls ../linux-x86_64-server-release/images/jdk/jmods
>> java.base.jmod            java.net.http.jmod       java.sql.rowset.jmod      jdk.crypto.ec.jmod         jdk.internal.opt.jmod                     jdk.jdi.jmod         jdk.management.agent.jmod  jdk.security.auth.jmod
>> java.compiler.jmod        java.prefs.jmod          java.transaction.xa.jmod  jdk.dynalink.jmod          jdk.internal.vm.ci.jmod                   jdk.jdwp.agent.jmod  jdk.management.jfr.jmod    jdk.security.jgss.jmod
>> java.datatransfer.jmod    java.rmi.jmod            java.xml.crypto.jmod      jdk.editpad.jmod           jdk.internal.vm.compiler.jmod             jdk.jfr.jmod         jdk.management.jmod        jdk.unsupported.desktop.jmod
>> java.desktop.jmod         java.scripting.jmod      java.xml.jmod             jdk.hotspot.agent.jmod     jdk.i...
>
> Severin Gehwolf has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Disallow packaged modules and run-time image link
>  - Only check for existing path when not a scratch task
>    
>    When using a run-time image link and the initial build was produced with
>    the --keep-packaged-modules option, we don't need to check existing
>    paths to the location where packaged modules need to be copied. This
>    breaks the --verbose output validation.

Thanks. I'm not super happy with it either (yet). I'll do some pondering myself to try to clean this up. Basically it would be good to know if the functionality so far would be complete as far as you're concerned as I could then focus on a cleaner patch without needing to add more bits.

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PR Comment: https://git.openjdk.org/jdk/pull/14787#issuecomment-1857598537