RFR: 8311302: Implement JEP 493: Linking Run-Time Images without JMODs [v40]

[Severin Gehwolf]

> 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 b
 eing 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.internal.vm.compiler.manage...

Severin Gehwolf has updated the pull request incrementally with five additional commits since the last revision:

 - Better handle patched modules
   
   Also add a test which ensures that module patching (if present), will
   get an appropriate error message.
 - Add /othervm to some langtools tier1 tests
   
   Those tests are using module patches from JTREG. Since the run-time
   image based link uses ModuleFinder.ofSystem(), which will see the extra
   classes comming from the module patch. Then the size look-up using the
   JRT FS provider fails, since that only looks in the module image
   (lib/modules) and NOT also in the patch. Thus, we get a
   NoSuchFileException and the link fails.
   
   Run the tests with othervm so that the JTREG patch'ed module isn't
   visible to the test.
 - Fix tests for builds with --enable-linable-runtime
   
   Those builds don't include the packaged modules, `jmods` directory.
   However, some tests assume that they're there. Add appropriate requires
   tag.
 - Fix provider verification when some JMODs are present
   
   In some configurations, e.g. when java.base is missing from the packaged
   modules, but another JDK module is present as JMOD that is linked into
   an image, then provider verification can fail. Thus, the run-time image
   link fails. Verify that this doesn't happen.
   
   The fix is to return Platform.runtime() for run-time image based links
   as well. Otherwise this code would return the wrong result.
 - Show run-time image based capability in help
   
   Also add a test for it when it's turned on and off.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14787/files
  - new: https://git.openjdk.org/jdk/pull/14787/files/22eb4b89..83a86d06

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14787&range=39
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14787&range=38-39

  Stats: 501 lines in 13 files changed: 434 ins; 28 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/14787.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14787/head:pull/14787

PR: https://git.openjdk.org/jdk/pull/14787