HDFS-17049. EC: Fix duplicate block group IDs generated by SequentialBlockGroupIdGenerator.

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
-  public long nextValue() {
+  synchronized public 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

@@ -22,11 +22,15 @@
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.not;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.spy;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -172,6 +176,41 @@ public void testTriggerBlockGroupIdCollision() throws IOException {
     }
   }
 
+  /**
+   * Test that the values generated by blockGroup ID generator are unique,
+   * even if they are generated concurrently.
+   * @throws Exception
+   */
+  @Test
+  public void testBlockGroupIdThreadSafety() throws Exception {
+    List<List<Long>> blockIds = new ArrayList<>();
+    List<Thread> threads = new ArrayList<>();
+    for (int i = 0; i < 20; i++) {
+      blockIds.add(new ArrayList<>());
+      threads.add(new Thread(() -> {
+        for (int j = 0; j < 1000; j++) {
+          long next = blockGrpIdGenerator.nextValue();
+          blockIds.get(j).add(next);
+        }
+      }));
+    }
+    for (Thread t : threads) {
+      t.start();
+    }
+    for (Thread t : threads) {
+      t.join();
+    }
+    Set<Long> allBlockIds = new HashSet<>();
+    for (List<Long> set : blockIds) {
+      for (long id : set) {
+        if (allBlockIds.contains(id)) {
+          fail("Same block group id is generated!");
+        }
+        allBlockIds.add(id);
+      }
+    }
+  }
+
   /**
    * Test that collisions in the blockGroup ID when the id is occupied by legacy
    * block.