KeeProMise commented on code in PR #5990:
URL: https://github.com/apache/hadoop/pull/5990#discussion_r1306648529


##########
hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MembershipNamenodeResolver.java:
##########
@@ -478,4 +476,27 @@ private List<MembershipState> 
getRecentRegistrationForQuery(
   public void setRouterId(String router) {
     this.routerId = router;
   }
+
+  /**
+   * Shuffle cache, to ensure that the current nn will not be accessed first 
next time.
+   *
+   *
+   * @param nsId name service id
+   * @param namenode namenode contexts
+   */
+  @Override
+  public synchronized void shuffleCache(String nsId, FederationNamenodeContext 
namenode) {
+    cacheNS.compute(Pair.of(nsId, false), (ns, namenodeContexts) -> {
+      if (namenodeContexts != null
+              && namenodeContexts.size() > 0

Review Comment:
   Guaranteed atomicity can ensure that the above 2 and 3 are recognized before 
modifying the cache



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