RFR (XS): 8023004: JSR 292: java.lang.RuntimeException: Original target method was called.

[serguei.spitsyn at oracle.com]

On 10/16/13 1:28 PM, Christian Thalinger wrote:
> On Oct 14, 2013, at 12:15 PM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
>
>> http://cr.openjdk.java.net/~vlivanov/8023004/webrev.00/
>> 7 lines changed: 5 ins; 1 del; 1 mod
>>
>> Assertion code in JDK fetches info from VM using MHN.getMemberVMInfo:
>> assert(m.vminfoIsConsistent());
>>
>> After that check, class redefinition is broken - it's still possible to invoke old version of a method.
>>
>> Analysis from Serguei:
>> "The problem is here:
>> oop MethodHandles::init_method_MemberName(Handle mname, CallInfo& info) {
>>   . . . . . . . .
>>   m->method_holder()->add_member_name(m->method_idnum(), mname);
>>
>>   return mname();
>> }
>>
>> The call to add_member_name() resets the member name at the index m->method_idnum(). After that one of the two member names with the same method_idnum() is out of the MNT and is not updated when the method is redefined."
> As I understand this the problem is calling MethodHandles::init_method_MemberName which installs a new MemberName instance in the MemberNameTable.  Correct?
>
> If that's the case then there is a potential race here.
>
> +     x = m->method_holder()->get_member_name(m->method_idnum());
> +     if (x == NULL) {
> +       Handle mname2 = MethodHandles::new_MemberName(CHECK_NULL);
>          x = MethodHandles::init_method_MemberName(mname2, info);
>        }
>
> Racing threads can get back null when calling get_member_name and then install different MemberName objects in the table.

Good catch, Chris.
I do not see a way to fix it easily without some refactoring.

It is probably better to add to the InstanceKlass a helper function that 
will do
this dance with a required synchronization.
But the following line needs to be taken out of the 
init_method_MemberName() :
   m->method_holder()->add_member_name(m->method_idnum(), mname);


Thanks,
Serguei

>
>> The fix is to check whether there's already a member name associated with the before creating a new one.
>>
>> Testing: failing test.
>>
>> Contributed-by: sspitsyn, vlivanov
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> JBS: https://bugs.openjdk.java.net/browse/JDK-8023004