RFR: 8262087: Use atomic boolean type in G1FullGCAdjustTask

[Kim Barrett]

On Sun, 21 Feb 2021 11:30:52 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Use atomic boolean type to make the intention clear.

The change looks fine.

I would hope though that in the future this flag will be eliminated and this
can instead invoke parallel reference processing, rather than forcing it to
be done single threaded. Doing anything about that is a task for after Leo's
in-progress work on cleaning up reference processing tasking.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2664