RFR 8022887: Assertion hit while using class and redefining it with RedefineClasses s,imultaneously

[Coleen Phillimore]

Dan,
Thank you for looking at this so quickly.   You are right, we are not 
only getting public methods, whose number cannot change right now with 
redefine classes.
I have to rework this change.
Thanks,
Coleen

On 9/5/2013 12:23 PM, Daniel D. Daugherty wrote:
> On 9/5/13 9:33 AM, Coleen Phillimore wrote:
>> Summary: Need to refetch the methods array from InstanceKlass after 
>> safepoint.
>>
>> open webrev at http://cr.openjdk.java.net/~coleenp/8022887/
>
> The "frames" links are broken in this webrev. I had to
> write down the changed line numbers for jvm.cpp and then
> use the "new" link to see the context of the changes.
>
> src/share/vm/oops/instanceKlass.cpp
>     Nice catch. The old code could return an 'm' value that
>     referred to a method that wasn't a match. Ouch.
>

yes, it was a bit of a red herring for a while.

> src/share/vm/prims/jvm.cpp
>     Nice catch of the use of potentially stale method array, but I
>     think there might be more issues here.
>
>     In JVM_GetClassDeclaredMethods:
>
>     line 1865: ++num_methods;
>
> <snip>
>
>     line 1871: objArrayOop r = 
> oopFactory::new_objArray(SystemDictionary::reflect_Method_klass(), 
> num_methods, CHECK_NULL);
>
> <snip>
>
>     line 1876: methods = k->methods();
>     line 1877: methods_length = methods->length();
>
> <snip>
>
>     line 1885: result->obj_at_put(out_idx, m);
>
> <snip>
>
>     line 1890:  assert(out_idx == num_methods, "just checking");
>
>         So num_methods is computed before the new_objArray() call that
>         can result in a safepoint which can permit a RedefineClasses()
>         operation to complete. You refresh methods and methods_length,
>         but num_methods still has its pre-RedefineClasses value and
>         the size of the result array is also at the pre-RedefineClasses
>         size. Isn't it possible that we could overflow the result array
>         here? And maybe fire that assert() on line 1890.
>
>
>     In JVM_GetClassDeclaredConstructors(), similar concerns for these
>     lines:
>
>     line 1922: ++num_constructors;
>
> <snip>
>
>     line 1928: objArrayOop r = 
> oopFactory::new_objArray(SystemDictionary::reflect_Constructor_klass(), num_constructors, 
> CHECK_NULL);
>
> <snip>
>
>     line 1942: result->obj_at_put(out_idx, m);
>
> <snip>
>
>     line 1947: assert(out_idx == num_constructors, "just checking");
>
>
>     Yes, this RedefineClasses() stuff is a serious pain in the butt
>     because it can change your assumed invariants in the middle of
>     your function.
>
> Dan
>
>> bug link at http://bugs.sun.com/view_bug.do?bug_id=8022887
>>
>> Tested with the test cases in the bug, and with internal SQE tests 
>> (nsk.quick.testlist).
>>
>> thanks,
>> Coleen
>