8368333: [lworld] Add preview mode to ImageReader and JRT file-system #1619

david-beaumont · 2025-09-23T19:15:43Z

Java changes for supporting preview mode when preview mode resources (with new location flags) are available.

At the moment, this code will operate on non-preview jimage files (1.0) and act as if no preview resources are available by virtue of the default value for missing attributes and package flags being zero (which matches jimage 1.0).

This should be reviewed on top of #1618

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Change must not contain extraneous whitespace

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⚠️ Dependency #1618 must be integrated first

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JDK-8368333: [lworld] Add preview mode to ImageReader and JRT file-system (Sub-task - P4)

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$ git fetch https://git.openjdk.org/valhalla.git pull/1619/head:pull/1619
$ git checkout pull/1619

Update a local copy of the PR:
$ git checkout pull/1619
$ git pull https://git.openjdk.org/valhalla.git pull/1619/head

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$ git pr checkout 1619

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https://git.openjdk.org/valhalla/pull/1619.diff

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david-beaumont · 2025-09-23T19:16:47Z

This is a new version of #1613, re-created so there's now a pr/xxx branch for use by dependent PRs.

bridgekeeper · 2025-09-23T19:17:55Z

👋 Welcome back david-beaumont! A progress list of the required criteria for merging this PR into lworld will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-09-23T19:19:25Z

@david-beaumont This change is no longer ready for integration - check the PR body for details.

mlbridge · 2025-09-23T19:23:16Z

Webrevs

RogerRiggs · 2025-09-24T18:20:58Z

src/java.base/share/classes/jdk/internal/jimage/ImageHeader.java

+ * <p>Known jimage file code which needs updating on version change:
+ * <ul>
+ *     <li>src/java.base/share/native/libjimage/imageFile.hpp
+ * </ul>


Are there any java source files that have to be updated on a version change?

RogerRiggs · 2025-09-24T18:22:48Z

src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java

+    /**
+     * Set on all locations in the {@code /modules/xxx/META-INF/preview/...}
+     * namespace.
+     *
+     * <p>This flag is mutually exclusive with {@link #FLAGS_HAS_PREVIEW_VERSION}.
+     */
+    public static final int FLAGS_IS_PREVIEW_VERSION = 0x2;


Seems to be redundant with HAS_PREVIEW_VERSION when seen in a preview location.

RogerRiggs · 2025-09-24T18:23:16Z

src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java

+    /**
+     * Indicates that a location only exists due to preview resources.
+     *
+     * <p>This can apply to both resources and directories in the
+     * {@code /modules/xxx/...} namespace, as well as {@code /packages/xxx}
+     * directories.
+     *
+     * <p>For {@code /packages/xxx} directories it indicates that, for every
+     * module in which the package exists, it is preview only.
+     *
+     * <p>This flag is mutually exclusive with {@link #FLAGS_HAS_PREVIEW_VERSION}
+     * and need not imply that {@link #FLAGS_IS_PREVIEW_VERSION} is set (i.e.
+     * for {@code /packages/xxx} directories).
+     */
+    public static final int FLAGS_IS_PREVIEW_ONLY = 0x4;


The preview-only case is expected to be the empty set. There seems to be a lot of code dedicated to it.

RogerRiggs · 2025-09-24T18:24:52Z

src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java

+     * Helper function to calculate preview flags (ATTRIBUTE_PREVIEW_FLAGS).
+     *


A summary of what gets what flags might be easier to read than the code.
Or list the flags and refer to their descriptions (that would describe the paths where the flags would be found)

RogerRiggs · 2025-09-24T18:26:07Z

src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java

+     * Indicates that a non-preview location is associated with preview
+     * resources.


This comment would read better saying that preview resources exist related to this location.
More like FLAGS_HAS_PREVIEW_VERSION.

RogerRiggs · 2025-09-24T18:54:57Z

src/java.base/share/classes/jdk/internal/jimage/ImageReader.java

+import static jdk.internal.jimage.ImageLocation.FLAGS_HAS_PREVIEW_VERSION;
+import static jdk.internal.jimage.ImageLocation.FLAGS_IS_PREVIEW_ONLY;


Import utility methods not flags.

RogerRiggs · 2025-09-24T20:56:14Z

src/java.base/share/classes/jdk/internal/jimage/ImageReader.java

+            return ensureCachedIfNonNull(
+                    loc != null && loc.getType() == RESOURCE ? newResource(name, loc) : null);


It seems odd to test loc and type to produce a null and them pass it to a method that will do nothing.
The non-productive test can be done and return immediately.

RogerRiggs · 2025-09-24T21:14:34Z

src/java.base/share/classes/jdk/internal/jrtfs/JrtFileSystemProvider.java

+        if (envValue instanceof Boolean && (Boolean) envValue) {
+            return PreviewMode.ENABLED;
+        } else if (envValue instanceof String && Boolean.parseBoolean((String) envValue)) {
+            return PreviewMode.ENABLED;
        }


This kind of ambiguous type for the environment variable should not be supported.
Pick a type and stick to it.
Whereever the jrt: file system is specified will need a description for enablePreview to be added to the spec.

RogerRiggs · 2025-09-24T21:22:34Z

src/java.base/share/classes/jdk/internal/jrtfs/SystemImage.java

+        // TODO: Maybe throw if enablePreview attempted for exploded image?
+


Exploded image is useful for debugging, it could support preview mode using the same META-INF directory structure.

RogerRiggs · 2025-09-26T01:35:01Z

test/jdk/jdk/internal/jimage/ModuleReferenceTest.java

+    }
+
+    // Encodes strings sequentially starting from index 100.
+    private static Function<String, Integer> testEncoder() {


The method name testEncoder gives the impression of being a test, but it is just a utility function used by a test.

david-beaumont added 4 commits September 23, 2025 21:02

Java ImageReader changes for preview mode

cc8d109

Clarifying flag docs for /packages/xxx case

96ee008

Add workaround until new image writing code is in

924698e

Word smithing flags definitions.

629ba8c

openjdk bot added ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 23, 2025

david-beaumont changed the base branch from lworld to pr/1618 September 23, 2025 19:22

openjdk bot removed the ready Pull request is ready to be integrated label Sep 23, 2025

david-beaumont mentioned this pull request Sep 23, 2025

8368467: [lworld] Add new flag generation for jimage to support preview mode #1621

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Manually deleting ImageReaderFactory (it returned somehow)

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RogerRiggs reviewed Sep 29, 2025

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8368333: [lworld] Add preview mode to ImageReader and JRT file-system #1619

8368333: [lworld] Add preview mode to ImageReader and JRT file-system #1619

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		* Helper function to calculate preview flags (ATTRIBUTE_PREVIEW_FLAGS).
		*

		* Indicates that a non-preview location is associated with preview
		* resources.

		import static jdk.internal.jimage.ImageLocation.FLAGS_HAS_PREVIEW_VERSION;
		import static jdk.internal.jimage.ImageLocation.FLAGS_IS_PREVIEW_ONLY;

		return ensureCachedIfNonNull(
		loc != null && loc.getType() == RESOURCE ? newResource(name, loc) : null);

		// TODO: Maybe throw if enablePreview attempted for exploded image?

8368333: [lworld] Add preview mode to ImageReader and JRT file-system #1619

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8368333: [lworld] Add preview mode to ImageReader and JRT file-system #1619

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david-beaumont commented Sep 23, 2025 •

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