[GitHub] [hadoop] elek commented on a change in pull request #1551: HDDS-2199 In SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host

[GitBox <gi...@apache.org>]

elek commented on a change in pull request #1551: HDDS-2199 In SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host
URL: https://github.com/apache/hadoop/pull/1551#discussion_r330472982
 
 

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 File path: hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/node/SCMNodeManager.java
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 @@ -275,6 +278,26 @@ public RegisteredCommand register(
         .build();
   }
 
+  /**
+   * Add an entry to the dnsToUuidMap, which maps hostname / IP to the DNs
+   * running on that host. As each address can have many DNs running on it,
+   * this is a one to many mapping.
+   * @param dnsName String representing the hostname or IP of the node
+   * @param uuid String representing the UUID of the registered node.
+   */
+  @SuppressFBWarnings(value="AT_OPERATION_SEQUENCE_ON_CONCURRENT_ABSTRACTION",
+      justification="The method is synchronized and this is the only place "+
+          "dnsToUuidMap is modified")
+  private synchronized void addEntryTodnsToUuidMap(
+      String dnsName, String uuid) {
+    Set<String> dnList = dnsToUuidMap.get(dnsName);
+    if (dnList == null) {
+      dnList = new HashSet<>();
 
 Review comment:
   Do we need concurrent HashSet here? dnsToUuidMap is thread safe but what about if one reader and one writer start to use the same HashSet?

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