presto-array/src/main/java/io/prestosql/array/ReferenceCountMap.java/ReferenceCountMap/decrementAndGet
class ReferenceCountMap:    public int decrementAndGet(Object key)
    {
        long hashCode = getHashCode(key);
        int previousCount = addTo(hashCode, -1);
        if (previousCount == 1) {
            remove(hashCode);
        }
        return previousCount - 1;
    }