RFR: 8352066: JVM.commit() and JVM.flush() exhibit race conditions against JFR epochs

Greetings, This change set removes some race conditions involving JFR epochs. For details, please see the JIRA issue. Testing: jdk_jfr, TestChunkIntegrity testing Thanks Markus ------------- Commit messages: - 8352066 Changes: https://git.openjdk.org/jdk/pull/24061/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24061&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352066 Stats: 64 lines in 9 files changed: 5 ins; 36 del; 23 mod Patch: https://git.openjdk.org/jdk/pull/24061.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/24061/head:pull/24061 PR: https://git.openjdk.org/jdk/pull/24061