[foreign-abi] RFR: Transition back to java on safepoint poll slow-path when returning from an optimized native call

[Jorn Vernee]

Hi,

Due to a bug report last week, it was found that threads do not transition back to the _thread_in_java state on the
safepoint poll slow path after returning from an optimized native call.

While I was not able to reproduce the crash in question so far, the current code is obviously wrong, since the thread
state transition back only happens on the fast path.

This patch rectifies that issue.

Thanks,
Jorn

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Commit messages:
 - Transition back to java on slow path as well

Changes: https://git.openjdk.java.net/panama-foreign/pull/356/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=356&range=00
  Stats: 5 lines in 1 file changed: 3 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/356.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/356/head:pull/356

PR: https://git.openjdk.java.net/panama-foreign/pull/356