feedback review.

Author: zhangshuyan0

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/SequentialBlockGroupIdGenerator.java

@@ -51,7 +51,7 @@ public class SequentialBlockGroupIdGenerator extends SequentialNumber {
   }
 
   @Override // NumberGenerator
-  synchronized public long nextValue() {
+  public synchronized long nextValue() {
     skipTo((getCurrentValue() & ~BLOCK_GROUP_INDEX_MASK) + MAX_BLOCKS_IN_GROUP);
     // Make sure there's no conflict with existing random block IDs
     final Block b = new Block(getCurrentValue());

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestSequentialBlockGroupId.java

@@ -203,10 +203,9 @@ public void testBlockGroupIdThreadSafety() throws Exception {
     Set<Long> allBlockIds = new HashSet<>();
     for (List<Long> set : blockIds) {
       for (long id : set) {
-        if (allBlockIds.contains(id)) {
+        if (!allBlockIds.add(id)) {
           fail("Same block group id is generated!");
         }
-        allBlockIds.add(id);
       }
     }
   }