Unloading classes may require a walk of unreachable oops. For this reason, it is not safe to recycle memory before class unloading is complete.

Note that the behavior of the load reference barrier to accommodate this requirement for class unloading, may interfere with the DeadCounterClosure when visiting weak oop storage. However, it does not seem to be a problem in practice because the dead count callbacks do not care about the precise number of dead objects (only that there are dead objects).