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

[Robbin Ehn]

On Fri, 30 Oct 2020 14:20:25 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> 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

+1

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Marked as reviewed by rehn (Reviewer).

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