RFR: 8277631: ZGC: CriticalMetaspaceAllocation asserts [v2]

[Erik Österlund]

> The MetaspaceCritical_lock is a non-safepoint checking lock. That implies that the allow VM block flag is true. That implies that taking that lock takes a NoSafepointVerifier. That causes an assert to fire when MetaspaceCriticalAllocation::wait_for_purge transitions to blocked with ThreadBlockInVM while holding the lock. The fix is to move the locker inside of the ThreadBlockInVM.

Erik Österlund has updated the pull request incrementally with one additional commit since the last revision:

  dholmes review comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6520/files
  - new: https://git.openjdk.java.net/jdk/pull/6520/files/ec93bede..ea651174

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6520&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6520&range=00-01

  Stats: 10 lines in 2 files changed: 2 ins; 2 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6520.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6520/head:pull/6520

PR: https://git.openjdk.java.net/jdk/pull/6520