Review request (M): 8003720: NPG: Method in interpreter stack frame can be deallocated
Stefan Karlsson
stefan.karlsson at oracle.com
Thu Nov 22 06:14:34 PST 2012
http://cr.openjdk.java.net/~stefank/8003720/webrev/
Description from CR:
In virtual calls the Method pointer in the interpreter stack frame is
not kept alive by anything other than the "this" pointers to that
method. If bytecodes overwrite the "this" pointer, then call a full GC,
the class loader containing the Method* can be unloaded and the Method*
deallocated.
This is also a problem with JSR292 MethodHandle static code because the
MethodHandle containing the mirror for the interpreted method Method* is
not on the stack if a GC occurs.
Fix proposal:
The "obvious" solution to this problem would be to apply the root
scanning OopClosure to the Klass::_java_mirror field of the method in
the interpreted frame. However, doing this might cause us to scan the
same metadata oop location more than once, which is not allowed by some
of the HotSpot GCs. We currently solve similar situations by always
"claiming" and start scanning from the ClassLoaderData and then proceed
down into the Klasses of that class loader.
For this bug we do the same. All old collections, where class unloading
can occur, pass down a closure that is applied to the ClassLoaderData of
the Klass of the Method in the interpreted frame. This closure does the
claiming and proceeds to scan the class metadata. Note that during young
collections, where we don't do class unloading, all classes are already
used as strong roots and we don't have to apply this new closure in the
interpreted frame.
Testing:
The added test was initially written by John Rose. I only ported it to
JTreg and made some artistic cleanups to it.
thanks,
StefanK
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