[jdk13u-dev] RFR: 8264640: CMS ParScanClosure misses a barrier

[Anton Kozlov]

Hi, please review an original fix for a GC crash. The jdk13u is the latest supported version that still has buggy code, it was deleted in jdk14 as a part of   JEP 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector. So I'm proposing it here.

The fix is low-risk, on x86-64 it just introduces a compiler barrier to prevent two reads to be reordered as intended by surrounding comments. On CPUs with weaker memory models it introduces CPU barriers as well.

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Commit messages:
 - Add missing barriers

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/165/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=165&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264640
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/165.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/165/head:pull/165

PR: https://git.openjdk.java.net/jdk13u-dev/pull/165