[GitHub] [zookeeper] maoling commented on a change in pull request #1004: ZOOKEEPER-3445 ReferenceCountedACLCache.aclIndex should be volatile

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maoling commented on a change in pull request #1004: ZOOKEEPER-3445 ReferenceCountedACLCache.aclIndex should be volatile
URL: https://github.com/apache/zookeeper/pull/1004#discussion_r297570094
 
 

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 File path: zookeeper-server/src/main/java/org/apache/zookeeper/server/ReferenceCountedACLCache.java
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 @@ -51,7 +51,7 @@
     /**
      * these are the number of acls that we have in the datatree
      */
-    long aclIndex = 0;
+    volatile long aclIndex = 0;
 
 
 Review comment:
   @jhalterman 
   Look at the call chain:
   ```
   [1]FileTxnSnapLog#restore--->FileSnap#deserialize--->SerializeUtils.deserializeSnapshot---dt.deserialize--aclCache.deserialize(ia);
   [2]Learner#syncWithLeader-->ZKDatabase#deserializeSnapshot[2]--->SerializeUtils.deserializeSnapshot---dt.deserialize--aclCache.deserialize(ia);
   ```
   [1] is for restoring from the snapshot when server start/restart; [2] is for the learner to sync with leader with snap cmd;
   the aclIndex is unlikely to be read by multiple threads? Am I right?

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