RFR: JDK-8259983: do not use uninitialized expand_ms value in G1CollectedHeap::expand_heap_after_young_collection

[Kim Barrett]

On Tue, 19 Jan 2021 15:37:10 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> Currently we could run into an uninitialized value of expand_ms in G1CollectedHeap::expand_heap_after_young_collection() .
> This would happen in case of an early return of bool G1CollectedHeap::expand(size_t expand_bytes, WorkGang* pretouch_workers, double* expand_time_ms) . See  the special case in expand 
> 
>   if (is_maximal_no_gc()) {
>     log_debug(gc, ergo, heap)("Did not expand the heap (heap already fully expanded)");
>     return false;
>   }

I considered suggesting instead only calling record_expand_heap_time if
expand succeeds. The underlying value is reset to 0 as part of
G1GCPhaseTimes::reset.  But that assumes there aren't any time-consuming
reasons for expand to fail.  So this change looks good to me.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2148