On Mon, 30 Mar 2026 16:15:07 GMT, David Beaumont <[email protected]> wrote:
>> Implementation of preview-mode support for jimage modules file, migrated >> from Valhalla related work (see JDK-8352750). >> >> This PR (the first of several) migrates work from Valhalla (lworld) to the >> JDK mainline repository in relation to "preview mode" support. It affects >> the creation and reading of the jimage file, both in Java >> (BasicImageReader/ImageReader) and C++ (imageFile.xpp/jimage.xpp). >> >> Preview mode is a mechanism by which alternate version of JDK class files >> and resources can be made available for class loading and reflection when >> the '--enable-preview' flag is passed to the runtime. >> >> Alternate classes/resource appear in each module under the: >> >> /<module>/META-INF/preview/<path-to>/<resource-or-class> >> >> and replace the original: >> >> /<module>/<path-to>/<resource-or-class> >> >> files when preview mode is enabled. >> >> While initially useful for Valhalla work, this mechanism will be used for >> other cases where preview features (in the JEP 12 sense) require alternate >> classes/resources to be provided. None of the changes in this (or the >> follow-up PRs) are Valhalla specific. >> >> In this PR: >> * the writing of jimage files is modified to recognize and handle preview >> mode paths >> * flags in the jimage file are added or modified to support preview mode >> efficiently >> * (C++) the class loader is modified to permit reading preview versions of >> classes >> * (Java) the image reader and associated JRT file-system classes are >> modified to permit reading preview files >> * unit tests are added to ensure preview mode works as expected when enabled >> * (temporary) any code calling into the affected API (other than tests) >> specifies that preview mode is disabled >> >> Future PRs will add the plumbing to enable preview mode correctly, but with >> the PR there should be no observable change in behaviour (especially since >> no preview classes or resources are being supplied at this point). >> >> --------- >> - [ ] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > David Beaumont has updated the pull request incrementally with two additional > commits since the last revision: > > - Rename ModuleReference to ModuleLink > - tweak comments src/java.base/share/classes/jdk/internal/jimage/PreviewMode.java line 80: > 78: InvocationTargetException e) { > 79: // But if the class exists, the method must exist and > be callable. > 80: throw new InternalError(e); I'm wondering if InternalError is possible if the tool/IDE is on JDK 21 or 25, targeting JDK 27+. jdk.internal.misc.PreviewFeatures will be visible in these cases (Class.forName will succeed) but not accessible (so the invoke will fail with IllegalAccessException). I think it would be better to do the same as existing BasicImageReader and check if the defining class loader is the boot loader (null) to distinguish the "current image" from the remote case using jrt-fs.jar. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/29414#discussion_r3098999153
