[GitHub] [rocketmq] leeyiyu opened a new issue, #6879: [Bug] ConcurrentHashMapUtils fails to solve the loop bug in JDK8.

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

leeyiyu opened a new issue, #6879:
URL: https://github.com/apache/rocketmq/issues/6879

   ### Before Creating the Bug Report
   
   - [X] I found a bug, not just asking a question, which should be created in [GitHub Discussions](https://github.com/apache/rocketmq/discussions).
   
   - [X] I have searched the [GitHub Issues](https://github.com/apache/rocketmq/issues) and [GitHub Discussions](https://github.com/apache/rocketmq/discussions)  of this repository and believe that this is not a duplicate.
   
   - [X] I have confirmed that this bug belongs to the current repository, not other repositories of RocketMQ.
   
   
   ### Runtime platform environment
   
   Mac  OS 13.0
   
   ### RocketMQ version
   
   develop
   
   ### JDK Version
   
   jdk8
   
   ### Describe the Bug
   
   [ConcurrentHashMapUtils](https://github.com/apache/rocketmq/blob/develop/common/src/main/java/org/apache/rocketmq/common/utils/ConcurrentHashMapUtils.java) 中提供的computeIfAbsent方法没有解决jdk8的循环问题，复现代码如下
   
   ```
   ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
   map.computeIfAbsent("AaAa", key->map.computeIfAbsent("BBBB",key2->"42"));
   ```
   
   解决方案
   ```
   public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Function<? super K, ? extends V> func) {
           Objects.requireNonNull(func);
           if (isJdk8) {
               V v = map.get(key);
               if (null == v) {
   //                v = map.computeIfAbsent(key, func);
   
                   // this bug fix methods maybe cause `func.apply` multiple calls.
                   v = func.apply(key);
                   if (null == v) {
                       return null;
                   }
                   final V res = map.putIfAbsent(key, v);
                   if (null != res) {
                       // if pre value present, means other thread put value already, and putIfAbsent not effect
                       // return exist value
                       return res;
                   }
               }
               return v;
           } else {
               return map.computeIfAbsent(key, func);
           }
       }
   ```
   
   
   ### Steps to Reproduce
   
   ```
   ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
   map.computeIfAbsent("AaAa", key->map.computeIfAbsent("BBBB",key2->"42"));
   ```
   
   ### What Did You Expect to See?
   
   死循环
   
   ### What Did You See Instead?
   
   符合原先预期
   
   ### Additional Context
   
   _No response_


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[GitHub] [rocketmq] dingshuangxi888 commented on issue #6879: [Bug] ConcurrentHashMapUtils fails to solve the loop bug in JDK8.

["dingshuangxi888 (via GitHub)" <gi...@apache.org>]

dingshuangxi888 commented on issue #6879:
URL: https://github.com/apache/rocketmq/issues/6879#issuecomment-1635494730

   I understand that it's not necessary to use it that way, and there aren't any use cases for it currently.


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[GitHub] [rocketmq] yuz10 closed issue #6879: [Bug] ConcurrentHashMapUtils fails to solve the loop bug in JDK8.

["yuz10 (via GitHub)" <gi...@apache.org>]

yuz10 closed issue #6879: [Bug] ConcurrentHashMapUtils fails to solve the loop bug in JDK8.
URL: https://github.com/apache/rocketmq/issues/6879


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