RFR: JDK-8287671: Adjust ForceGC to invoke System::gc fewer times for negative case

[Mandy Chung]

On Fri, 3 Jun 2022 18:05:52 GMT, Mandy Chung <mchung at openjdk.org> wrote:

> This reapplies JDK-8287384 and adjust the number of GCs for negative case, i.e. the condition is never met that is used to verify a reference is not GC'ed.

JDK-8287384 affects the tests using ForceGC for negative cases only.  It will return with a fewer GC cycles of a shortened wait time between each cycle.  It will be okay since a strongly reachable reference will never be GC'ed.

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PR: https://git.openjdk.java.net/jdk/pull/9021