hs25 review request: 8008511 JSR 292: MemberName vmtarget refs to methods must be updated at class redefinition (original) (raw)

David Holmes david.holmes at oracle.com
Tue Mar 26 02:17:33 PDT 2013

Hi Serguei,

The removal of the NoSafepointVerifier could be problematic. If that method is never meant to be on the stack when you block for a safepoint then the method is atomic with respect to the safepoint - and so can not suffer interference from actions that occur at a safepoint (like class unloading (?) ). Now I presume that somewhere from that method you end up taking the mutex and so can block at a safepoint (or block on the lock and so still allow a safepoint to occur) - which might invalidate assumptions the method has about "safepoint atomicity".

You need to understand why the NSV was put there in the first place.

David

On 26/03/2013 6:37 PM, serguei.spitsyn at oracle.com wrote:

Please, review the following fix. The fix was preliminarily reviewed by Coleen, Christian and John but still a final and open jdk review is needed. So that, everyone is welcome to review the fix! This is open webrev: http://cr.openjdk.java.net/~sspitsyn/webrevs/2013/hotspot/8008511-JVMTI-JSR292.1/ The CR is: http://bugs.sun.com/bugdatabase/viewbug.do?bugid=8008511 https://jbs.oracle.com/bugs/browse/JDK-8008511

The problem is that the old version of the bootstrap method is re-invoked after a popframe from the bootstrap method execution. It is because the MemberName keeps a stale reference to the old method version. The solution (suggested by John Rose) is to lazily create and keep up-to-date a MemberNameTable which plays a role of MemberName cache assosiated with the InstanceKlass. Then, at the Class redefinition, this cache is used to replace the old method references in the MemberName's with the new method references. The MemberNameTable is based on the GrowableArray. A CHEAP array is allocated at the first call to InstanceKlass::addmembername(). It is released in the InstanceKlass::releaseCheapstructures(). A global week reference to member name oop is stored in the MemberNameTable. It allowed to avoid having the oopsdo() in the MemberNameTable. Also, the MemberNameTable won't hold member name oops in memory. The MemberNameTablelock mutex is added to serialize MemberNameTable's updates. The following NoSafepointVerifier has been disabled: * src/share/vm/prims/methodHandles.cpp*: 799 int MethodHandles::findMemberNames(Klass* k, . . . 803 DEBUGONLY(NoSafepointVerifier nsv); It is probably Ok, but, please, let me know if it is not. The assert related to locking is fired if it is not disabled. Test coverage: vm.mlvm, nsk.jvmti, nsk.jdi tests on multiple platforms (32 vs 64-bit too). The testing looks good so far. Thanks, Serguei

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