[lworld] RFR: 8368333: [lworld] Add preview mode to ImageReader and JRT file-system [v7]

[Roger Riggs]

On Wed, 22 Oct 2025 19:38:45 GMT, David Beaumont <duke at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/jimage/ImageReader.java line 282:
>> 
>>> 280:         // preview-only nodes. This is used to add preview-only content to
>>> 281:         // directories as they are completed.
>>> 282:         private final HashMap<String, Directory> previewDirectoriesToMerge;
>> 
>> Can this be cleared or freed after the ImageReader is open. Its no longer needed.
>
> It's used when directories are completed (as stated in the comment):
> 
> 
>     List<Node> previewOnlyNodes = getPreviewNodesToMerge(dir);
>     ...
>     children.addAll(previewOnlyNodes);
> 
> 
> This is so that a preview only directory (and all its content) appears correctly in its parent's child list.

So it is no longer needed after that.  
Since it is a field of a SharedImageReader that will be kept open for a while, it could be cleared to free the entries and make it clear the map is no longer used.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1619#discussion_r2471012817