On Wed, 16 Jul 2025 15:31:07 GMT, David Beaumont <[email protected]> wrote:
>> Refactoring `ImageReader` to make it easy to add preview mode functionality
>> for Valhalla.
>>
>> This PR is a large change to `ImageReader` (effectively a rewrite) but
>> reduces the surface area of the API significantly, reduces code complexity
>> and increases performance/memory efficiency. The need for this sort of
>> change comes from the need to support "preview mode" in Valhalla for classes
>> loaded from core modules.
>>
>> ### Preview Mode
>>
>> In the proposed preview mode support for Valhalla, a resource with the name
>> `/modules/<module>/<path>` may come from one of two locations in the
>> underlying jimage file; `/<module>/<path>` or
>> `/<module>/META-INF/preview/<path>`. Furthermore, directories (represented
>> as directory nodes via the API) will have a potentially different number of
>> child nodes depending on whether preview mode is in effect, and some
>> directories may only exist at all in preview mode.
>>
>> Furthermore, the directories and symbolic link nodes in `/packages/...` will
>> also be affected by the existence of new package directories. To retain
>> consistency and avoid "surprises" later, all of this needs to be taken into
>> account.
>>
>> Below is a summary of the main changes for mainline JDK to better support
>> preview mode later:
>>
>> ### 1: Improved encapsulation for preview mode
>>
>> The current `ImageReader` code exposes the data from the jimage file in
>> several ways; via the `Node` abstraction, but also with methods which return
>> an `ImageLocation` instance directly. In preview mode it would not be
>> acceptable to return the `ImageLocation`, since that would leak the
>> existence of resources in the `META-INF/preview` namespace and lets users
>> see resource nodes with names that don't match the underlying
>> `ImageLocation` from which their contents come.
>>
>> As such, the PR removes all methods which can leak `ImageLocation` or other
>> "underlying" semantics about the jimage file. Luckily most of these are
>> either used minimally and easily migrated to using nodes, or they were not
>> being used at all. This PR also removes any methods which were already
>> unused across the OpenJDK codebase (if I discover any issues with
>> over-trimming of the API during full CI testing, it will be easy to address).
>>
>> ### 2. Simplification of directory child node handling
>>
>> The current `ImageReader` code attempts to create parent directories "on
>> demand" for any child nodes it creates. This results in parent directories
>> having a non-empty but incomplete set of child nodes present. This is re...
>
> David Beaumont has updated the pull request with a new target base due to a
> merge or a rebase. The pull request now contains one commit:
>
> Resync after benchmark.
src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 28:
> 26:
> 27: import java.io.IOException;
> 28: import java.io.UncheckedIOException;
Unused, can be removed
src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 279:
> 277: }
> 278:
> 279: /// Returns a node in the JRT filesystem namespace, or null if
> no resource or
Using the standard javadoc tags for @param, @return can give some consistency
and readability even for internal methods.
src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 532:
> 530: public abstract static class Node {
> 531: private final String name;
> 532: private final BasicFileAttributes fileAttrs;
It seems a bit wasteful to cache the same attributes in every Node.
But its no more expensive (size-wise) than a referernce to the ImageReader and
the indirection.
src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 543:
> 541: // As such, non-directory nodes are always complete.
> 542: boolean isCompleted() {
> 543: return true;
Seems like a risky default to have this be a concrete method/default that is
not required to be overridden.
A subclass (not that many here) could forget to override and have a default
wrong answer. YMMV.
src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 611:
> 609: *
> 610: * <p>If this node is not a directory ({@code isDirectory() ==
> false})
> 611: * then this method will throw {@link IllegalStateException}.
A mismatch in overriding could give inconsistent results (since the impl does
not call `isDirectory()`.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/26054#discussion_r2216403082
PR Review Comment: https://git.openjdk.org/jdk/pull/26054#discussion_r2216447991
PR Review Comment: https://git.openjdk.org/jdk/pull/26054#discussion_r2216510819
PR Review Comment: https://git.openjdk.org/jdk/pull/26054#discussion_r2216472104
PR Review Comment: https://git.openjdk.org/jdk/pull/26054#discussion_r2216478048
