RFR: 8212155: Race condition when posting dynamic_code_generated event leads to JVM crash

[Leonid Mesnik]

Fixed a race condition between posting and enabling DynamicCodeGenerated event.

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Commit messages:
 - 8212155: Race condition when posting dynamic_code_generated event leads to JVM crash

Changes: https://git.openjdk.java.net/jdk/pull/4331/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4331&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8212155
  Stats: 122 lines in 3 files changed: 116 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4331.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4331/head:pull/4331

PR: https://git.openjdk.java.net/jdk/pull/4331