RFR: 8038925: Java 7 with G1 crashes in dump_instance_fields using jmap or jcmd without fullgc

[Mikael Gerdin]

On Friday 25 April 2014 14.53.29 Thomas Schatzl wrote:
> Hi,
> 
> On Fri, 2014-04-25 at 14:17 +0200, Andreas Eriksson wrote:
> > Hi,
> > 
> > Could I have a review for this G1 jdk7 only fix please?
> 
>   why is this change only necessary for jdk7?

The idea was that for 9 and 8u40+ we will need a separate way to handle this 
anyway due to class unloading (as previously discussed).

We may or may not want to get this fix into 8u20, I'd like to hear your input 
on that Thomas.

/Mikael

> 
> > Description:
> > When using G1 and doing a heap dump while no fullgc has been done,
> > hotspot crashes.
> > This is because G1CollectedHeap::safe_object_iterate uses
> > ContiguousSpace::object_iterate_from, which does not avoid dead objects
> > that can still be on the heap when using G1.
> > 
> > The fix adds a G1 specific safe_object_iterate code path that avoids
> > dead objects.
> > 
> > http://cr.openjdk.java.net/~aeriksso/8038925/webrev.00/
> > https://bugs.openjdk.java.net/browse/JDK-8038925
> > 
> > Thanks to Mikael Gerdin for his help with this.
> 
> Thanks,
> Thomas