RFR (XS): 7114303: G1: assert(_g1->mark_in_progress()) failed: shouldn't be here otherwise

[Tony Printezis]

John,

Ship it.

Tony

On 11/22/2011 03:45 PM, John Cuthbertson wrote:
> Hi Everyone,
>
> Can I have a couple of volunteers review this small change? The webrev 
> can be found at: http://cr.openjdk.java.net/~johnc/7114303/webrev.0/
>
> Summary:
> There is a race between the concurrent mark thread updating the mark 
> in progress flag and it being read by the VM thread during an 
> evacuation pause. This is because, at the time the concurrent mark 
> thread updates the flag, it is not part of the suspendible thread set 
> and so is not blocked. The solution is to have the concurrent mark 
> thread join the STS just before updating the flag.
>
> The race was confirmed by inserting a small delay immediately before 
> calling G1CollectorPolicy::record_satb_drain_time(). The delay 
> increased failure rate to 1/5 for a 20ms delay and 4/5 for a 50ms delay.
>
> Testing: a few thousand iterations of the failing test case with a JVM 
> that included both fix and delay.
>
> Thanks,
>
> JohnC