RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v30]

[Alan Bateman]

On Tue, 4 Jun 2024 16:23:19 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 113 commits:
> 
>  - Mark some tests with requiring packaged modules
>  - Correctly set packaged modules default
>  - Merge branch 'master' into jdk-8311302-jmodless-link
>  - Merge branch 'master' into jdk-8311302-jmodless-link
>  - Fix new line in jlink.properties
>  - Merge branch 'master' into jdk-8311302-jmodless-link
>  - Simplify JLINK_JDK_EXTRA_OPTS var handling
>  - Only add runtime track files for linkable runtimes
>  - 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
>  - ... and 103 more: https://git.openjdk.org/jdk/compare/64bbae75...0eb1e48d

test/jdk/tools/lib/tests/JImageHelper.java line 38:

> 36:  * JDK Modular image iterator
> 37:  */
> 38: public class JImageHelper {

This is only usable in tests that use `@modules` to open jdk.internal.jimage.*. It might be better  co-locate this with the jlink tests for now. It may be that we do have test infra structure for jimage in the future but starting out with the supporting test lib in the jlink test tree should be okay.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14787#discussion_r1627780757