[GitHub] [hbase] Apache9 commented on a change in pull request #242: HBASE-22422 Retain an ByteBuff with refCnt=0 when getBlock from LRUCache

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Apache9 commented on a change in pull request #242: HBASE-22422 Retain an ByteBuff with refCnt=0 when getBlock from LRUCache
URL: https://github.com/apache/hbase/pull/242#discussion_r284723788
 
 

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 File path: hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java
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 @@ -611,6 +609,10 @@ protected long evictBlock(LruCachedBlock block, boolean evictedByEvictionProcess
         victimHandler.cacheBlock(block.getCacheKey(), block.getBuffer());
       }
     }
+    // Decrease the block's reference count, and if refCount is 0, then it'll auto-deallocate. DO
+    // NOT move this up because if do that then the victimHandler may access the buffer with
+    // refCnt = 0 which is disallowed.
+    previous.getBuffer().release();
 
 Review comment:
   So this is the problem. Mind explaining more? Why in victimHandler we will access the previous? And is it possible to add a UT?

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