HDFS-15792. ClasscastException while loading FSImage. Contributed by Renukaprasad C.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/ReferenceCountMap.java

@@ -46,7 +46,7 @@ public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> {
    * @param key Key to put in reference map
    * @return Referenced instance
    */
-  public E put(E key) {
+  public synchronized E put(E key) {
     E value = referenceMap.get(key);
     if (value == null) {
       value = key;
@@ -62,7 +62,7 @@ public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> {
    * 
    * @param key Key to remove the reference.
    */
-  public void remove(E key) {
+  public synchronized void remove(E key) {
     E value = referenceMap.get(key);
     if (value != null && value.decrementAndGetRefCount() == 0) {
       referenceMap.remove(key);
@@ -75,14 +75,14 @@ public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> {
    * @return
    */
   @VisibleForTesting
-  public ImmutableList<E> getEntries() {
+  public synchronized ImmutableList<E> getEntries() {
     return new ImmutableList.Builder<E>().addAll(referenceMap.keySet()).build();
   }
 
   /**
    * Get the reference count for the key
    */
-  public long getReferenceCount(E key) {
+  public synchronized long getReferenceCount(E key) {
     ReferenceCounter counter = referenceMap.get(key);
     if (counter != null) {
       return counter.getRefCount();
@@ -93,7 +93,7 @@ public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> {
   /**
    * Get the number of unique elements
    */
-  public int getUniqueElementsSize() {
+  public synchronized int getUniqueElementsSize() {
     return referenceMap.size();
   }
 
@@ -101,7 +101,7 @@ public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> {
    * Clear the contents
    */
   @VisibleForTesting
-  public void clear() {
+  public synchronized void clear() {
     referenceMap.clear();
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestReferenceCountMap.java

@@ -0,0 +1,116 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.util;
+
+import org.apache.hadoop.hdfs.server.namenode.AclFeature;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Verify ReferenceCount map in concurrent scenarios.
+ */
+public class TestReferenceCountMap {
+  //Add these number of references in loop
+  public static final int LOOP_COUNTER = 10000;
+  //Use 2 global features
+  private AclFeature aclFeature1 = new AclFeature(new int[]{1});
+  private AclFeature aclFeature2 = new AclFeature(new int[]{2});
+
+  @Test
+  public void testReferenceCountMap() throws Exception {
+    ReferenceCountMap<AclFeature> countMap =
+            new ReferenceCountMap<AclFeature>();
+    countMap.put(aclFeature1);
+    countMap.put(aclFeature2);
+    Assert.assertEquals(1, countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(1, countMap.getReferenceCount(aclFeature2));
+
+    countMap.put(aclFeature1);
+    countMap.put(aclFeature2);
+    Assert.assertEquals(2, countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(2, countMap.getReferenceCount(aclFeature2));
+
+    countMap.put(aclFeature1);
+    Assert.assertEquals(3, countMap.getReferenceCount(aclFeature1));
+    countMap.put(aclFeature1);
+    Assert.assertEquals(4, countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(2, countMap.getReferenceCount(aclFeature2));
+
+    //Delete operations:
+    countMap.remove(aclFeature1);
+    countMap.remove(aclFeature2);
+    Assert.assertEquals(3, countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(1, countMap.getReferenceCount(aclFeature2));
+
+    //Verify unique elements in map
+    Assert.assertEquals(2, countMap.getUniqueElementsSize());
+  }
+
+  @Test
+  public void testRefCountMapConcurrently() throws Exception {
+    ReferenceCountMap<AclFeature> countMap =
+            new ReferenceCountMap<AclFeature>();
+
+    PutThread putThread1 = new PutThread(countMap);
+    putThread1.start();
+    PutThread putThread2 = new PutThread(countMap);
+    putThread2.start();
+    RemoveThread removeThread1 = new RemoveThread(countMap);
+
+    putThread1.join();
+    putThread2.join();
+    Assert.assertEquals(2 * LOOP_COUNTER,
+            countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(2 * LOOP_COUNTER,
+            countMap.getReferenceCount(aclFeature2));
+
+    removeThread1.start();
+    removeThread1.join();
+    Assert.assertEquals(LOOP_COUNTER, countMap.getReferenceCount(aclFeature1));
+    Assert.assertEquals(LOOP_COUNTER, countMap.getReferenceCount(aclFeature2));
+  }
+
+  class PutThread extends Thread {
+    private ReferenceCountMap<AclFeature> referenceCountMap;
+    PutThread(ReferenceCountMap<AclFeature> referenceCountMap) {
+      this.referenceCountMap = referenceCountMap;
+    }
+    @Override
+    public void run() {
+      for (int i = 0; i < LOOP_COUNTER; i++) {
+        referenceCountMap.put(aclFeature1);
+        referenceCountMap.put(aclFeature2);
+      }
+    }
+  }
+
+  class RemoveThread extends Thread {
+    private ReferenceCountMap<AclFeature> referenceCountMap;
+    RemoveThread(ReferenceCountMap<AclFeature> referenceCountMap) {
+      this.referenceCountMap = referenceCountMap;
+    }
+    @Override
+    public void run() {
+      for (int i = 0; i < LOOP_COUNTER; i++) {
+        referenceCountMap.remove(aclFeature1);
+        referenceCountMap.remove(aclFeature2);
+      }
+    }
+  }
+}