modify MembershipState comparator

Author: KeeProMise

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/impl/MembershipStoreImpl.java

@@ -279,30 +279,30 @@ private MembershipState getRepresentativeQuorum(
       Collection<MembershipState> records) {
 
     // Collate objects by field value: field value -> order set of records
-    Map<FederationNamenodeServiceState, Set<MembershipState>> occurenceMap =
+    Map<FederationNamenodeServiceState, TreeSet<MembershipState>> occurenceMap =
         new HashMap<>();
     for (MembershipState record : records) {
       FederationNamenodeServiceState state = record.getState();
-      Set<MembershipState> matchingSet = occurenceMap.get(state);
+      TreeSet<MembershipState> matchingSet = occurenceMap.get(state);
       if (matchingSet == null) {
-        matchingSet = new HashSet<>();
+        // TreeSet orders elements by descending date via comparators
+        matchingSet = new TreeSet<>();
         occurenceMap.put(state, matchingSet);
       }
       matchingSet.add(record);
     }
 
     // Select largest group
-    Set<MembershipState> largestSet = new HashSet<>();
-    for (Set<MembershipState> matchingSet : occurenceMap.values()) {
+    TreeSet<MembershipState> largestSet = new TreeSet<>();
+    for (TreeSet<MembershipState> matchingSet : occurenceMap.values()) {
       if (largestSet.size() < matchingSet.size()) {
         largestSet = matchingSet;
       }
     }
 
     // If quorum, use the newest element here
     if (largestSet.size() > records.size() / 2) {
-      TreeSet<MembershipState> sortedList = new TreeSet<>(largestSet);
-      return sortedList.first();
+      return largestSet.first();
       // Otherwise, return most recent by class comparator
     } else if (records.size() > 0) {
       TreeSet<MembershipState> sortedList = new TreeSet<>(records);

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/MembershipState.java

@@ -358,4 +358,23 @@ public long getDeletionMs() {
   public static void setDeletionMs(long time) {
     MembershipState.deletionMs = time;
   }
+
+  /**
+   * First use the comparator of the BaseRecord to compare the date modified.
+   * If they are equal, use {@link MembershipState#NAME_COMPARATOR} to continue the comparison
+   * to ensure that MembershipStates with the same date modified but reported by different routers
+   * will not be judged as equal.
+   *
+   * @param record the MembershipState object to be compared.
+   * @return a negative integer, zero, or a positive integer as this object
+   *         is less than, equal to, or greater than the specified object.
+   */
+  @Override
+  public int compareTo(BaseRecord record) {
+    int order = super.compareTo(record);
+    if (order == 0) {
+      return NAME_COMPARATOR.compare(this, (MembershipState) record);
+    }
+    return order;
+  }
 }