RFR: 8255596: Mutex safepoint checking options and flags should be scoped enums [v2]

[Kim Barrett]

> Please review this change to some enums in the Mutex class.
> SafepointCheckFlag and SafepointCheckRequired are changed to scoped
> enums.  Also removed the anonymous enum defining _allow_vm_block_flag
> and _as_suspend_equivalent_flag, instead defining those as bool
> constants.
> 
> To avoid changing all references to the SafepointCheckXXX enumerators
> (due to the additional scoping introduced by using scoped enums), same
> named constants are defined at Mutex class scope.  Some renaming might
> be preferable in the long term, but I didn't want to do that just to
> get the improved type checking.  An X-macro approach to defining the
> enumerators and hoisting them into class scope could have been taken,
> but the number of enumerators here doesn't seem to warrant the additional
> infrastructure to do so.
> 
> Changing the enum types uncovered a few places in the implementation
> of Mutex and MutexLocker where enum values were being implicitly
> converted to bool, with associated assumptions about the order or
> values of the enumerators.  Those have been fixed.
> 
> Testing:
> tier1

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into strong_mutex_flags
 - fix assert messages
 - use scoped enums

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/957/files
  - new: https://git.openjdk.java.net/jdk/pull/957/files/caa0c162..a4ea5df5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=957&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=957&range=00-01

  Stats: 1971 lines in 87 files changed: 1004 ins; 420 del; 547 mod
  Patch: https://git.openjdk.java.net/jdk/pull/957.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/957/head:pull/957

PR: https://git.openjdk.java.net/jdk/pull/957