boolean containsValue(Object value) {
            if (count != 0) { // read-volatile
                HashEntry<K,V>[] tab = table;
                int len = tab.length;
                for (int i = 0 ; i < len; i++) {
                    for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
                        V v = e.value;
                        if (v == null) // recheck
                            v = readValueUnderLock(e);
                        if (value.equals(v))
                            return true;
                    }
                }
            }
            return false;
        }
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.
commons-profiler/src/main/java/com/navercorp/pinpoint/common/profiler/concurrent/jsr166/ConcurrentWeakHashMap.java