RFR[14]: 8235751: Assertion when triggering concurrent cycle during shutdown

[Kim Barrett]

> On Jan 7, 2020, at 4:10 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
> 
> Hi Kim,
> 
> On 2019-12-31 04:01, Kim Barrett wrote:
>> Please review this change to G1's handling of requests to initiate
>> concurrent marking.
>> When such a request is made during shutdown processing, after the cm
>> thread has been stopped, the request to initiate concurrent marking is
>> ignored.  This could lead to an assertion failure for user requested
>> GCs (System.gc and via agent) by a thread that has not yet been
>> brought to a halt, because the possibility of such a request being
>> ignored was missed when the assertion was recently added by JDK-8232588.
>> We now report to the GC-invoking thread when initiation of concurrent
>> marking has been suppressed because termination of the cm thread has
>> been requested.  In that case the GC invocation is considered finished.
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8235751
>> Webrev:
>> https://cr.openjdk.java.net/~kbarrett/8235751/open.00/
>> 
> 
> Looks good,
> StefanJ
> 
>> Testing:
>> mach5 tier1-5
>> Locally (linux-x64) reproduced fairly quickly the failure using the
>> approach described in the CR; after applying the proposed chage,
>> failed to reproduce.

Thanks.