RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v26]

[Magnus Ihse Bursie]

On Tue, 7 May 2024 16:52:12 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 with a new target base due to a merge or a rebase. The pull request now contains 105 commits:
> 
>  - Generate the runtime image link diff at jlink time
>    
>    But only do that once the plugin-pipeline has run. The generation is
>    enabled with the hidden option '--generate-linkable-runtime' and
>    the resource pools available at jlink time are being used to generate
>    the diff.
>  - Merge branch 'master' into jdk-8311302-jmodless-link
>  - Use shorter name for the build tool
>  - Review feedback from Erik J.
>  - Remove dependency on CDS which isn't needed anymore
>  - Fix coment
>  - Fix comment
>  - Fix typo
>  - Revert some now unneded build changes
>  - Follow build tools naming convention
>  - ... and 95 more: https://git.openjdk.org/jdk/compare/23a72a1f...67aea4ca

make/Images.gmk line 100:

> 98: 
> 99: ifeq ($(JLINK_PRODUCE_RUNTIME_LINK_JDK), true)
> 100:   JLINK_JDK_EXTRA_OPTS := $(JLINK_JDK_EXTRA_OPTS) --generate-linkable-runtime

I just noticed this slight improvement:

Suggestion:

  JLINK_JDK_EXTRA_OPTS += --generate-linkable-runtime

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14787#discussion_r1594774220