RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v20]

[Mandy Chung]

On Thu, 14 Mar 2024 14:24:57 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 one additional commit since the last revision:
> 
>   Fix comment in autoconf file

> The updated patch uses a **build-only** `jlink` plugin, still called `--create-linkable-runtime` which is _a)_ added only at build time with `--add-modules` and _b)_ now generates the diff and prepares the image for runtime linking as before in one step. The code for this now lives in `src/jdk.jlink/build/classes`.

This patch introduces a new module `jdk.unsupported_jlink_runtime` .   `src/jdk.jlink` should only contain one module (see JEP 201).  If it ought to have another module, its source files should be placed under `src/$MODULE`.   

I would suggest to simplify it - drop the new module `jdk.unsupported_jlink_runtime` and simply include all its classes in `jdk.jlink` module; for example in `jdk.tools.jlink.internal.runtimelink` package to follow the existing jlink package name hierarchy.   This package can only be compiled when JDK is configured to build linkable images.  The build can simply invoke `jlink --create-linkable-runtime` and avoids all the setup to add exports to this build tool.  If jlink is running from a linkable image, --create-linkable-runtime` plugin should be disabled and hidden.   What do you think?

About the configure options, 

  --enable-keep-packaged-modules
                          enable keeping of packaged modules in jdk image [enabled]
  --enable-runtime-link-image
                          enable producing an image suitable for runtime linking [disabled]


If `--enable-runtime-link-image` is enabled, the JDK image does not include the packaged modules.  If `--enable-runtime-link-image --enable-keep-packaged-modules` are both enabled, it should probably fail?   @erikj79 should it?

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PR Comment: https://git.openjdk.org/jdk/pull/14787#issuecomment-1998467918