使用Java ConcurrentHashMap实现缓存

如果为要缓存的内容临时拥有多个实例是安全的，则可以执行“无锁”缓存，如下所示：

public Heavy instance(Object key) {  Heavy info = infoMap.get(key);  if ( info == null ) {    // It's OK to construct a Heavy that ends up not being used    info = new Heavy(key);    Heavy putByOtherThreadJustNow = infoMap.putIfAbsent(key, info);    if ( putByOtherThreadJustNow != null ) {      // Some other thread "won"      info = putByOtherThreadJustNow;    }    else {      // This thread was the winner    }  }  return info;}

多个线程可以“竞争”来创建和添加密钥项，但是只有一个应该“获胜”。