RFR: 8234773: Fix ThreadsSMRSupport::_bootstrap_list [v2]

[Daniel D.Daugherty]

On Mon, 4 Jan 2021 12:19:14 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Please review this change to ThreadsList and the singleton _bootstrap_list.
>> ThreadsList is made noncopyable, with _bootstrap_list changed to be direct
>> initialized to avoid referencing the copy constructor.  The ThreadsList
>> constructor now uses a static array for the 0-entry case, so that static
>> ctor/dtor of _bootstrap_list doesn't involve C-heap allocation.
>> 
>> Testing:
>> mach5 tier1
>> 
>> Local (linux-x64) build with -fno-elide-constructors and ran hotspot:tier1.
>> This has a failure unrelated to this change:
>> compiler/intrinsics/klass/CastNullCheckDroppingsTest.java fails with
>> #  Internal Error (../../src/hotspot/share/jfr/utilities/jfrVersionSystem.inline.hpp:98), pid=31086, tid=31713
>> #  assert(node->_live) failed: invariant
>> Filed new bug: https://bugs.openjdk.java.net/browse/JDK-8259036
>
> Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make ThreadsList constructor explicit.

Thumbs up.
Like @dholmes-ora, I'm not familiar with this "explicit" stuff.

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Marked as reviewed by dcubed (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1921