### Summary This PR just replaces `ThreadCritical` with a lock specific to NMT. `ThreadCritical` is a big lock and is unnecessary for the purposes of NMT. I've implemented the new lock with a semaphore so that it can be used early before VM init. There is also the possibility of adding assertions in places we expect NMT to have synchronization. I haven't added assertions yet in many places because some code paths such as the (NMT tests) don't lock yet. I think it makes sense to close any gaps in locking in another PR in which I can also add more assertions.
Testing: - hotspot_nmt - gtest:VirtualSpace - tier1 ------------- Commit messages: - Replace ThreadCritical with a specific NMT lock Changes: https://git.openjdk.org/jdk/pull/20852/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20852&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8304824 Stats: 58 lines in 10 files changed: 35 ins; 4 del; 19 mod Patch: https://git.openjdk.org/jdk/pull/20852.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/20852/head:pull/20852 PR: https://git.openjdk.org/jdk/pull/20852
