On Tue, 24 Mar 2026 12:04:18 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). > > David Beaumont has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains 12 commits: > > - Merge branch 'master' into jimage_preview_mode > - rename jimage_exists to jimage_is_open > - Feedback tweaks > - Feedback tweaks > - More feedback tweaks > - Updated copyright > - Feedback changes > - Merge branch 'master' into jimage_preview_mode > - Merge branch 'master' into jimage_preview_mode > - undo exploded image changes for now > - ... and 2 more: https://git.openjdk.org/jdk/compare/7695b1f9...0e802079 src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java line 79: > 77: */ > 78: private static final int FLAGS_HAS_PREVIEW_VERSION = 0x1; > 79: /** Would it be possible to put a blank line after each flag so it's easier to read the comment on each flag in isolation? src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java line 132: > 130: * is present. > 131: * @return flags for the ATTRIBUTE_PREVIEW_FLAGS attribute. > 132: */ getPreviewFlags looks very strange. Is this motivated by tests? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/29414#discussion_r3001818814 PR Review Comment: https://git.openjdk.org/jdk/pull/29414#discussion_r3001863391
