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

src/jdk.jlink/share/classes/jdk/tools/jlink/resources/jlink.properties line 119:

> 117: 
> 118: err.runtime.link.not.linkable.runtime=The current run-time image does not support run-time linking.
> 119: err.runtime.link.jdk.jlink.prohibited=Including jdk.jlink module for run-time image based links is not allowed.

The phrase "run-time image based links" in this error message (and in the value of err.runtime.link.packaged.mods) is a bit unusual. As developers will see this message then maybe it could say that this jlink in the current run-time image doesn't contain packaged modules and cannot be used to create another run-time image that include the jdk.jlink module.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14787#discussion_r1627820124