8290223: Initialize G1CardClosure in card scanning once

[tschatzl]

Hi all,

please review this minor change to avoid repeatedly initializing G1CardClosure in card scanning.

Testing: gha, local compilation

Thanks,
Thomas

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Issue

• JDK-8290223: Initialize G1CardClosure in card scanning once

Reviewing

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[mlbridge]

Webrevs

• 00: Full (1320641c)

[kimbarrett]

The JBS issue is labled gc-performance. Is it measurable?

I'm not strongly opposed to the change, but it increases the scope of the
scan closure (which is slightly unhelpful for code understanding). It also
passes the _heap_roots_found counter (by reference) to the closure constructor
before it's value has been initialized, so have to make sure the closure
constructor doesn't access the value. So I'd like to know what the benefit
might be.

[tschatzl]

Closing after re-measuring.