Remove raw typing in dummy pool classes (#18785)

* Dummy blocking pool generics
* DummyBlockingPool
* Test cases
* Use integers to avoid imports

Author: GWphua

processing/src/main/java/org/apache/druid/collections/DummyBlockingPool.java

@@ -22,16 +22,16 @@
 import java.util.List;
 
 /**
- * BlockingPool with 0 maxSize, all take*() methods immediately throw {@link UnsupportedOperationException}.
+ * BlockingPool with 0 maxSize, all {@code takeBatch} methods immediately throw {@link UnsupportedOperationException}.
  */
-public final class DummyBlockingPool<T> implements BlockingPool<T>
+public final class DummyBlockingPool implements BlockingPool<Object>
 {
   private static final DummyBlockingPool INSTANCE = new DummyBlockingPool();
 
   @SuppressWarnings("unchecked")
   public static <T> BlockingPool<T> instance()
   {
-    return INSTANCE;
+    return (BlockingPool<T>) INSTANCE;
   }
 
   private DummyBlockingPool()
@@ -45,13 +45,13 @@ public int maxSize()
   }
 
   @Override
-  public List<ReferenceCountingResourceHolder<T>> takeBatch(int elementNum, long timeoutMs)
+  public List<ReferenceCountingResourceHolder<Object>> takeBatch(int elementNum, long timeoutMs)
   {
     throw new UnsupportedOperationException();
   }
 
   @Override
-  public List<ReferenceCountingResourceHolder<T>> takeBatch(int elementNum)
+  public List<ReferenceCountingResourceHolder<Object>> takeBatch(int elementNum)
   {
     throw new UnsupportedOperationException();
   }

processing/src/main/java/org/apache/druid/collections/DummyNonBlockingPool.java

@@ -20,24 +20,24 @@
 package org.apache.druid.collections;
 
 /**
- * NonBlockingPool which is not able to allocate objects, {@link #take()} throws {@link UnsupportedOperationException}.
+ * NonBlockingPool that cannot allocate objects, {@link #take()} throws {@link UnsupportedOperationException}.
  */
-public final class DummyNonBlockingPool<T> implements NonBlockingPool<T>
+public final class DummyNonBlockingPool implements NonBlockingPool<Object>
 {
   private static final DummyNonBlockingPool INSTANCE = new DummyNonBlockingPool();
 
   @SuppressWarnings("unchecked")
   public static <T> NonBlockingPool<T> instance()
   {
-    return INSTANCE;
+    return (NonBlockingPool<T>) INSTANCE;
   }
 
   private DummyNonBlockingPool()
   {
   }
 
   @Override
-  public ResourceHolder<T> take()
+  public ResourceHolder<Object> take()
   {
     throw new UnsupportedOperationException();
   }

processing/src/test/java/org/apache/druid/collections/DummyBlockingPoolTest.java

@@ -0,0 +1,51 @@
+/*
+ * 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.druid.collections;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class DummyBlockingPoolTest
+{
+  @Test
+  public void testSingletonInstance()
+  {
+    final BlockingPool<Object> p1 = DummyBlockingPool.instance();
+    final BlockingPool<Integer> p2 = DummyBlockingPool.instance();
+    Assertions.assertSame(p1, p2);
+  }
+
+  @Test
+  public void testMaxSizeAndMetricsAreZero()
+  {
+    final BlockingPool<Integer> pool = DummyBlockingPool.instance();
+    Assertions.assertEquals(0, pool.maxSize());
+    Assertions.assertEquals(0, pool.getPendingRequests());
+    Assertions.assertEquals(0, pool.getUsedResourcesCount());
+  }
+
+  @Test
+  public void testTakeBatchThrows()
+  {
+    final BlockingPool<Integer> pool = DummyBlockingPool.instance();
+    Assertions.assertThrows(UnsupportedOperationException.class, () -> pool.takeBatch(1));
+    Assertions.assertThrows(UnsupportedOperationException.class, () -> pool.takeBatch(1, 10L));
+  }
+}

processing/src/test/java/org/apache/druid/collections/DummyNonBlockingPoolTest.java

@@ -0,0 +1,43 @@
+/*
+ * 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.druid.collections;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class DummyNonBlockingPoolTest
+{
+  @Test
+  public void testSingletonInstance()
+  {
+    final NonBlockingPool<Object> p1 = DummyNonBlockingPool.instance();
+    final NonBlockingPool<Integer> p2 = DummyNonBlockingPool.instance();
+    Assertions.assertSame(p1, p2);
+  }
+
+  @Test
+  public void testTakeThrows()
+  {
+    final NonBlockingPool<Integer> pool = DummyNonBlockingPool.instance();
+    Assertions.assertThrows(UnsupportedOperationException.class, pool::take);
+  }
+}
+
+