Currently, CallbackInvoker in jvmtiTagMap.cpp is an all-static class with several global fields. It looks like it's only used in VM_HeapWalkOperation, and can probably be refactored to be local to this, and only be allocated on-demand. This would also solve the current cleanup-problem that this class suffers: after its use in the heap-walk, its state does not get cleaned up, and thus has dangling pointers and such.