Integrated: 8254598: StringDedupTable should use OopStorage

[Kim Barrett]

On Fri, 23 Apr 2021 19:48:47 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to the String Deduplication facility.  It is being
> changed to use OopStorage to hold weak references to relevant objects,
> rather than bespoke data structures requiring dedicated processing phases by
> supporting GCs.
> 
> (The Shenandoah update was contributed by Zhengyu Gu.)
> 
> This change significantly simplifies the interface between a given GC and
> the String Deduplication facility, which should make it much easier for
> other GCs to opt in.  However, this change does not alter the set of GCs
> providing support; currently only G1 and Shenandoah support string
> deduplication.  Adding support by other GCs will be in followup RFEs.
> 
> Reviewing via the diffs might not be all that useful for some parts, as
> several files have been essentially completely replaced, and a number of
> files have been added or eliminated.  The full webrev might be a better
> place to look.
> 
> The major changes are in gc/shared/stringdedup/* and in the supporting
> collectors, but there are also some smaller changes in other places, most
> notably classfile/{stringTable,javaClasses}.
> 
> This change is additionally labeled for review by core-libs, although there
> are no source changes there.  This change injects a byte field of bits into
> java.lang.String, using one of the previously unused padding bytes in that
> class.  (There were two unused bytes, now only one.)
> 
> Testing:
> mach5 tier1-2 with and without -XX:+UseStringDeduplication
> 
> Locally (linux-x64) ran all of the existing tests that use string
> deduplication with both G1 and Shenandoah.  Note that
> TestStringDeduplicationInterned.java is disabled for shenandoah, as it
> currently fails, for reasons I haven't figured out but suspect are test
> related.
> 
> - gc/stringdedup/   -- these used to be in gc/g1
> - runtime/cds/SharedStringsDedup.java
> - runtime/cds/appcds/cacheObject/DifferentHeapSizes.java
> - runtime/cds/appcds/sharedStrings/*
> 
> shenandoah-only:
> - gc/shenandoah/jvmti/TestHeapDump.java
> - gc/shenandoah/TestStringDedup.java
> - gc/shenandoah/TestStringDedupStress.java
> 
> Performance tested baseline, baseline + stringdedup, new with stringdedup,
> finding no significant differences.

This pull request has now been integrated.

Changeset: be0a6552
Author:    Kim Barrett <kbarrett at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/be0a655208f64e076e9e0141fe5dadc862cba981
Stats:     6192 lines in 105 files changed: 2369 ins; 3204 del; 619 mod

8254598: StringDedupTable should use OopStorage

Co-authored-by: Kim Barrett <kbarrett at openjdk.org>
Co-authored-by: Zhengyu Gu <zgu at openjdk.org>
Reviewed-by: coleenp, iklam, tschatzl, ayang

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PR: https://git.openjdk.java.net/jdk/pull/3662