fix TestDecommission#testDecommissionWithOpenfileReporting

Author: huanghaibin

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -1996,7 +1996,11 @@ public BatchedListEntries<OpenFileEntry> getFilesBlockingDecom(long prevId,
     LightWeightHashSet<Long> openFileIds = new LightWeightHashSet<>();
     for (DatanodeDescriptor dataNode :
         blockManager.getDatanodeManager().getDatanodes()) {
-      for (long ucFileId : dataNode.getLeavingServiceStatus().getOpenFiles()) {
+      // Sort open files
+      LightWeightHashSet<Long> dnOpenFiles = dataNode.getLeavingServiceStatus().getOpenFiles();
+      Long[] dnOpenFileIds = new Long[dnOpenFiles.size()];
+      Arrays.sort(dnOpenFiles.toArray(dnOpenFileIds));
+      for (Long ucFileId : dnOpenFileIds) {
         INode ucFile = getFSDirectory().getInode(ucFileId);
         if (ucFile == null || ucFileId <= prevId ||
             openFileIds.contains(ucFileId)) {