V readValueUnderLock(final HashEntry<K, V> e) {
      final ReentrantReadWriteLock.ReadLock readLock = super.readLock();
      readLock.lock();
      final V v = e.getMapValue();
      readLock.unlock();
      return v;
    }
Reads value field of an entry under lock. Called if value field ever appears to be null. This
is possible only if a compiler happens to reorder a HashEntry initialization with its table
assignment, which is legal under memory model but is not known to ever occur.
geode-core/src/main/java/org/apache/geode/internal/util/concurrent/CustomEntryConcurrentHashMap.java