8338931: ZipEntry.flag could be made internal to ZipOutputStream

[eirbjo]

Please review this refactoring PR which moves the ZipEntry.flag field back to ZipOutputStream.XEntry.

Moving this field will save four bytes from the ZipEntry object size and also saves an unneccessary read in ZipFile.getZipEntry.

Testing:

This PR is a refactoring of existing code and does not update any tests. I added the label noreg-cleanup to the JBS issue.

The following runs clean:

make test TEST="test/jdk/java/util/zip"
make test TEST="test/jdk/java/util/jar"

Performance:

The JMH benchmark java.util.zip.ZipFileGetEntry.getEntryHit show a small but consistent improvement (2-3%).

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Progress

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Issue

• JDK-8338931: ZipEntry.flag could be made internal to ZipOutputStream (Enhancement - P4)

Reviewing

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/20702/head

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$ git pr checkout 20702

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https://git.openjdk.org/jdk/pull/20702.diff

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[mlbridge]

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• 01: Full - Incremental (97eec65d)
• 00: Full (4ac3abfd)

[LanceAndersen]

I need to spend some more time thinking about this, but I can ask what made you decide to look at this?

Changing the field name from flag -> flags then becomes a bit confusing as for example its usage in initCEN and the name of CENFLG. The field is also used via ZipInputStream (not via ZipEntry but flag). So some thought needs to be given to the naming

Similar comment for ZipFileSystem as if we move forward, then we need to be consistent in naming otherwise it becomes (or can be) confusing for future maintainers.

Also the Zip Spec refers to the field as "general purpose bit flag" and the zlib repository includes a minzip, which also references this field as flag which might be another reason to keep the field name as is regardless of it moving to XEntry

[eirbjo]

Sorry, the renaming was just an accident, It was “flags” in my head, but that was wrong.

Will revert the rename once I’m in front of a keyboard again in a few days.

The reason I’m looking at this is that ZipEntry is 88 bytes, and allocation is a significant cost when enumerating and looking up entries. So it would be beneficial to move unused or optional parts out of these common read paths. This seemed like a small but obvious win.

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