RFR(XS): 7074579: G1: JVM crash with JDK7 running ATG CRMDemo Fusion App

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers look at these changes? The webrev can 
be found at: http://cr.openjdk.java.net/~johnc/7074579/webrev.0/

The issue was a crash caused by an oop that was naked across a GC.  What 
was happening was that the ServiceThread was attempting to send a GC 
notification that came from the end of an evacuation pause. (Note that 
the ServiceThread is a Java thread and the GC notification is sent when 
the threads are restarted after the safepoint.) The construction of the 
first of the object arrays (used to pass before and memory pool 
information) triggered a full GC which moved the memory usage  class. 
Thus when the attempt to allocate the second object array was made, the 
variable holding the klass oop was now stale causing the crash. Although 
this issue was found when the app was run with G1, the issue is not G1 
specific.

The solution was to allocate a handle to hold the klass oop and use the 
de-referenced handle in the allocations.

Verified by inserting a full GC after the first array allocation and 
running the GC notification regression test. Fix was tested by running 
the regression test with all collectors and monitoring a KitchenSink run 
with jconsole.

Thanks,

JohnC