RFR: 8252981: ObjectMonitor::object() cleanup changes extracted from JDK-8247281 [v2]

[Daniel D.Daugherty]

On Thu, 10 Sep 2020 20:01:54 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove left over setting of GVars.stw_random; fixed separately via JDK-8252126.
>
> src/hotspot/share/runtime/objectMonitor.inline.hpp line 95:
> 
>> 93:   assert(_waiters == 0, "must be 0: waiters=%d", _waiters);
>> 94:   assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions);
>> 95:   assert(object() != NULL, "must be non-NULL");
> 
> In your next changeset, you'll want object to peek not resolve when it's an OopHandle here.

Actually that assert is gone in JDK-8247281. Since the _object field becomes
a weak handle, we cannot assert that object() is not NULL there.

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PR: https://git.openjdk.java.net/jdk/pull/114