RFR: 8247281: migrate ObjectMonitor::_object to OopStorage

[Daniel D.Daugherty]

On Fri, 11 Sep 2020 19:18:26 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> This RFE is to migrate the following field to OopStorage:
>> 
>> class ObjectMonitor {
>> <snip>
>>   void* volatile _object; // backward object pointer - strong root
>> 
>> Unlike the previous patches in this series, there are a lot of collateral
>> changes so this is not a trivial review. Sorry for the tedious parts of
>> the review. Since Erik and I are both contributors to this patch, we
>> would like at least 1 GC team reviewer and 1 Runtime team reviewer.
>> 
>> This changeset was tested with Mach5 Tier[1-3],4,5,6,7,8 testing
>> along with JDK-8252980 and JDK-8252981. I also ran it through my
>> inflation stress kit for 48 hours on my Linux-X64 machine.
>
> This looks great Dan. I like your addition of is_chainmarker() - it makes this step a lot better, without having any
> special oops that are not oops. Thanks for sorting this out!

@fisk - Thanks for the blinding fast review! (Pretty easy when you wrote almost
all of the code).

Re: is_chainmarker()
I figured you would appreciate getting rid of one more "special" oop value!
And its use just fits in with the whole AllocationState model. It also gets
removed quite easily with the part3 patch... Oh yeah, I gotta file a new RFE
for that one.

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PR: https://git.openjdk.java.net/jdk/pull/135