RFR: 8280844: Epoch shift synchronization point for Compiler threads is inadequate [v2]

[Markus Grönlund]

> Greetings,
> 
> [JDK-8233111](https://bugs.openjdk.java.net/browse/JDK-8233111) attempted to address artefact tagging for Compiler threads, letting threads run _thread_in_native to avoid the transition. Unfortunately, that attempt proved inadequate.
> 
> The epoch race is avoided only by performing the transition to _thread_in_vm.
> 
> Testing: jdk_jfr
> 
> Thanks
> Markus

Markus Grönlund has updated the pull request incrementally with one additional commit since the last revision:

  delegate assertion

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8724/files
  - new: https://git.openjdk.java.net/jdk/pull/8724/files/9ce10130..b4e59b72

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8724&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8724&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8724.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8724/head:pull/8724

PR: https://git.openjdk.java.net/jdk/pull/8724