public boolean isEmpty() {
    return topAddr == 0L;
  }
A "stack" of addresses of OffHeapStoredObject instances. The stored objects are not kept in java
object form but instead each one is just an off-heap address. This class is used for each "tiny"
free-list of the FreeListManager. This class is thread safe.
geode-core/src/main/java/org/apache/geode/internal/offheap/OffHeapStoredObjectAddressStack.java