RFR: 8373485: JFR Crash during sampling: assert(jt->has_last_Java_frame()) failed: invariant

[Markus Grönlund]

Greetings,

When sampling threads in state _thread_in_native, there is a missing memory barrier when UseSystemMemoryBarrier is used, because it must be emitted manually.

Testing: jdk_jfr

Thanks
Markus

PS "threads_lock" local variable was renamed to "lock" not to confuse with the global Threads_lock.

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

Commit messages:
 - 8373485

Changes: https://git.openjdk.org/jdk/pull/29155/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29155&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373485
  Stats: 11 lines in 1 file changed: 7 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29155.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29155/head:pull/29155

PR: https://git.openjdk.org/jdk/pull/29155