Request for reviews (S): 6987703 iCMS: Intermittent hang with gc/gctests/CallGC/CallGC01 and +ExplicitGCInvokesConcurrent

John Coomes John.Coomes at
Mon Mar 14 18:15:39 PDT 2011

Y. Srinivas Ramakrishna (y.s.ramakrishna at wrote:
> Summary: In the existing implementation of ExplicitGCInvokesConcurrent
> two concurrent System.gc()'s could intefere when using CMSIncremetalMode,
> leaving the CMS thread stranded in incremental mode with no foreground
> allocation happening to act as a trigger to get the (i)CMS thread going.
> Solution: enable_icms() and disable_icms(), which respectively enable and
> disable the incremental mode of CMS, should be counting requests
> so as not to intefere. Also added some related asserts.
> (Removed the obsolete and unused _next field in the CMST class.)
> webrev:
> Testing: The failing test (and JPRT) with
>     +/-ExplicitGCInvokesConcurrent +/-ExplicitGCInvokesConcurrent
> Prior to the fix, on a specific machine, the test would
> hang about once in three runs or so. After the fix it's been
> running without hanging for a whole day (many thousands of iterations).

Looks good to me.


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