[GitHub] [dubbo] looly commented on issue #11986: ConcurrentHashMapUtils无法解决jdk8的循环bug

["looly (via GitHub)" <gi...@apache.org>]

looly commented on issue #11986:
URL: https://github.com/apache/dubbo/issues/11986#issuecomment-1493319150

   但是有issue反馈说这种方式获取的value有可能为null，我不确定这种写法是否存在问题。
   
   issue中提出的替代方案是：
   
   ```java
   V value = map.get(key);
   if (null == value) {
   	value = mappingFunction.apply(key);
   	final V res = map.putIfAbsent(key, mappingFunction.apply(key));
   	if(null != res){
   		// issues#I6RVMY
   		// 如果旧值存在，说明其他线程已经赋值成功，putIfAbsent没有执行，返回旧值
   		return res;
   	}
   	// 如果旧值不存在，说明赋值成功，返回当前值
   }
   return value;
   ```


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