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

[kimbarrett]

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

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8255596: Mutex safepoint checking options and flags should be scoped enums

Reviewers

• Thomas Schatzl (@tschatzl - Reviewer) ⚠️ Review applies to caa0c16
• Robbin Ehn (@robehn - Reviewer) ⚠️ Review applies to caa0c16

Download

$ git fetch https://git.openjdk.java.net/jdk pull/957/head:pull/957
$ git checkout pull/957

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[mlbridge]

Webrevs

• 01: Full - Incremental (a4ea5df)
• 00: Full (caa0c16)

[tschatzl]

Lgtm.

[openjdk]

@kimbarrett This change now passes all automated pre-integration checks.

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

Reviewed-by: tschatzl, rehn

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[robehn]

+1

[kimbarrett]

Thanks @tschatzl and @robehn for reviews.

[kimbarrett]

/integrate

[openjdk]

@kimbarrett Since your change was applied there has been 1 commit pushed to the master branch:

• d05df7c: 8236842: Surprising 'multiple elements' behaviour from getTypeElement when cross-compiling with --release

Your commit was automatically rebased without conflicts.

Pushed as commit 69f5235.

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