RFR: 8369255: Assess and remedy any unsafe usage of the Semaphores used by JFR

[Markus Grönlund]

Greetings,

Please help review this change set that prevents a race in the shutdown of the VM, where the CRT is destroyed while threads might still be running JFR code. Please see the JIRA issue for an explanation.

Testing: jdk_jfr, tier 1 - 3

Thanks
Markus

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Commit messages:
 - adjustment
 - 8369255

Changes: https://git.openjdk.org/jdk/pull/27722/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27722&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369255
  Stats: 51 lines in 2 files changed: 33 ins; 13 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27722.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27722/head:pull/27722

PR: https://git.openjdk.org/jdk/pull/27722