[jdk11u-dev] RFR: JDK-8215889 assert(!_unloading) failed: This oop is not available to unloading class loader data with ZGC [v2]

[Peter Zhelezniakov]

> Almost clean backport. I've just changed the type of `PrepareExtraDataClosure::_safepoint_counter` from `uint64_t` to `int` to match the type of `SafepointSynchronize::_safepoint_counter` and thus avoid a compiler warning.
> 
> This fix had a flaw that was later identified and corrected under JDK-8231501, so this latter fix will also be backported.

Peter Zhelezniakov has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Backport f08eeac278b0785c0bdff0bddf46b66f65822357

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Changes:
  - all: https://git.openjdk.java.net/jdk11u-dev/pull/19/files
  - new: https://git.openjdk.java.net/jdk11u-dev/pull/19/files/46e8359b..7bcb3745

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=19&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=19&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/19.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/19/head:pull/19

PR: https://git.openjdk.java.net/jdk11u-dev/pull/19