> 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 > referred to as the directory being "incomple...
David Beaumont has updated the pull request incrementally with one additional commit since the last revision: Small feedback related tweaks. ------------- Changes: - all: https://git.openjdk.org/jdk/pull/26054/files - new: https://git.openjdk.org/jdk/pull/26054/files/9d9e62ba..a8b68c7b Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=26054&range=03 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26054&range=02-03 Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/26054.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/26054/head:pull/26054 PR: https://git.openjdk.org/jdk/pull/26054
