[HBASE-27991] fixing ClassCastException in multithread client run

Author: nikita15p

hbase-examples/src/main/java/org/apache/hadoop/hbase/client/example/MultiThreadedClientExample.java

@@ -24,6 +24,8 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.Future;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.ThreadLocalRandom;
@@ -129,7 +131,14 @@ public int run(String[] args) throws Exception {
     //
     // We don't want to mix hbase and business logic.
     //
-    ExecutorService service = new ForkJoinPool(threads * 2);
+    ThreadPoolExecutor service = new ThreadPoolExecutor(
+      threads * 2,
+      threads * 2,
+      60L,
+      TimeUnit.SECONDS,
+      new LinkedBlockingQueue<>()
+    );
+
 
     // Create two different connections showing how it's possible to
     // separate different types of requests onto different connections

hbase-examples/src/test/java/org/apache/hadoop/hbase/client/example/TestMultiThreadedClientExample.java

@@ -0,0 +1,88 @@
+/*
+ * 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.hbase.client.example;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+import java.io.IOException;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HBaseTestingUtility;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.Result;
+import org.apache.hadoop.hbase.client.ResultScanner;
+import org.apache.hadoop.hbase.client.Scan;
+import org.apache.hadoop.hbase.client.Table;
+import org.apache.hadoop.hbase.testclassification.ClientTests;
+import org.apache.hadoop.hbase.testclassification.MediumTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category({ ClientTests.class, MediumTests.class })
+public class TestMultiThreadedClientExample {
+
+  private final static HBaseTestingUtility TEST_UTIL = new HBaseTestingUtility();
+  private static String tableName = "test_mt_table";
+  private static Table table;
+  static final TableName MY_TABLE_NAME = TableName.valueOf(tableName);
+  private static byte[] familyName = Bytes.toBytes("d");
+  private static byte[] columnName = Bytes.toBytes("col");
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestMultiThreadedClientExample.class);
+
+  @BeforeClass
+  public static void setup() throws Exception {
+    TEST_UTIL.startMiniCluster(1);
+    table = TEST_UTIL.createTable(MY_TABLE_NAME, familyName);
+  }
+
+  @AfterClass
+  public static void tearDown() throws Exception {
+    TEST_UTIL.deleteTable(MY_TABLE_NAME);
+    TEST_UTIL.shutdownMiniCluster();
+  }
+
+  @Test
+  public void testMultiThreadedClientExample() throws Exception {
+    MultiThreadedClientExample example = new MultiThreadedClientExample();
+    example.setConf(TEST_UTIL.getConfiguration());
+    String[] args = { tableName, "200" };
+    // Define assertions to check the returned data here
+    assertEquals(0, example.run(args));
+    // Define assertions to check the row count of the table
+    assertNotEquals(0, getRowCountFromTable(table));
+  }
+
+  // getRowCountFromTable takes table as input and return the number of rows
+  private static int getRowCountFromTable(Table t) throws IOException {
+    Scan scan = new Scan();
+    // Scan the table and get the scan result
+    ResultScanner scanner = t.getScanner(scan);
+    int rowCount = 0;
+    for (Result result : scanner) {
+      rowCount++;
+    }
+    return rowCount;
+  }
+}