case 2: return null; // new CliffWrapHerlihy(); // was a non-blocking HashSet implementation from Maurice Herlihy
case 3: return new ConcurrentHashMap<String,String>(_table_size,0.75f, 16); // force to 16 striping
case 4: return new ConcurrentHashMap<String,String>(_table_size,0.75f, 256); // force to 256 striping
case 5: return new ConcurrentHashMap<String,String>(_table_size,0.75f,4096); // force to 4096 striping
case 6: return new NonBlockingHashMap<String,String>();
case 7: return new CacheBuilder().maximumCapacity(Integer.MAX_VALUE).makeCache(Cache.LinkedHashMap_Lru_Sync);
case 8:
return new ConcurrentLinkedHashMap.Builder<String, String>()
.concurrencyLevel(16) // force to 16 striping
.initialCapacity(_table_size)
.maximumWeightedCapacity(Integer.MAX_VALUE)