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

[Thomas Schatzl]

Hi,

On 31.12.19 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/
> 
> 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.
> 

   looks good.

Thomas