RFR: 8272579: G1: remove unnecesary null check for G1ParScanThreadStateSet::_states slots

[Albert Mingkun Yang]

On Tue, 17 Aug 2021 14:38:09 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of replacing a null-check with an assertion.
> 
> Test: hotspot_gc

I updated the JBS ticket description/title as well to reflect the new patch.

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PR: https://git.openjdk.java.net/jdk/pull/5145