RFR: 8212107: VMThread issues and cleanup [v6]

[Daniel D.Daugherty]

On Thu, 24 Sep 2020 20:36:08 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Removed assert as suggested by David
>
> Changes requested by dcubed (Reviewer).

Most of my comments this round are not critical. The only real issue
that I found was the change in behavior for the SafepointALot flag.
The refactoring will make future code maintenance much, much easier,
but it made reviewing vmThread.cpp an adventure.

-------------

PR: https://git.openjdk.java.net/jdk/pull/228