RFR: 8317542: Specjvm::xml have scalability issue for high vCPU numbers

[Vladimir Ivanov]

The synchronization block may be substituted by the 'volatile' variable smaller synchronization block.
It reduce the total blocking time for the specjvm2008::xml.validation workload and improve the reported score.
Scores for the 112vCPU on the with 28GB heap increased from 17915.83 to 22943.2.
Unit tests was not affected:
Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR
   jtreg:test/jaxp                                     516   516     0     0
   jtreg:test/jdk/javax/xml                             70    70     0     0
==============================
TEST SUCCESS

The tier1 is OK too.

-------------

Commit messages:
 - 8317542: Specjvm::xml have scalability issue for high vCPU numbers
 - 8317542 Specjvm::xml have scalability issue for high vCPU numbers

Changes: https://git.openjdk.org/jdk/pull/21815/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21815&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317542
  Stats: 57 lines in 1 file changed: 23 ins; 4 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/21815.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21815/head:pull/21815

PR: https://git.openjdk.org/jdk/pull/21815