[lworld] RFR: 8366093: [lworld] Add preview mode to C++ classloader

[Roger Riggs]

On Mon, 29 Sep 2025 01:50:01 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> C++ 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 being zero (which matches location flags for "normal" entries).
>
> src/java.base/share/native/libjimage/imageFile.hpp line 259:
> 
>> 257:         // it exists in the same module.
>> 258:         FLAGS_IS_PREVIEW_ONLY = 0x4
>> 259:     };
> 
> A refactoring of the flags can avoid conflicting states.
> FLAGS_IS_PREVIEW_VERSION = 2;   // set for preview version
> FLAGS_NO_NORMAL_VERSION = 1;    // preserving the zero value for normal and no preview.
> 
> Create static methods in ImageLocation to perform the desired tests on flags.
> The utility methods make the code easier to read.
> Also define macros/function in the native code in ImageFile and jimage.
> 
> isPreviewVersion(flags) { return (flags & FLAGS_IS_PREVIEW_VERSION) != 0)}
> isPreviewOnly(flags) { return (flags & FLAGS_IS_REVIEW_VERSION | FLAGS_NO_NORMAL_VERSION) == FLAGS_NO_NORMAL_VERSION}

Reprise:

Your name FLAGS_IS_PREVIEW_ONLY probably better than FLAGS_NO_NORMAL_VERSION and has the same semantics.

FLAGS_HAS_PREVIEW_VERSION means that there is a preview version and it will be found in the <META-INF/Preview> hierarchy. if the flag is in the preview node then this is it. If found in the normal hierarchy, the preview class is found in the <META-INF/Preview> hierarchy.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1618#discussion_r2388252261