This closes #2726

artemis-server/src/main/java/org/apache/activemq/artemis/core/server/ActiveMQServerLogger.java

@@ -2021,4 +2021,8 @@ public interface ActiveMQServerLogger extends BasicLogger {
    @Message(id = 224100, value = "Timed out waiting for large messages deletion with IDs {0}, might not be deleted if broker crashes atm",
       format = Message.Format.MESSAGE_FORMAT)
    void timedOutWaitingForLargeMessagesDeletion(List<Long> largeMessageIds);
+
+   @LogMessage(level = Logger.Level.WARN)
+   @Message(id = 224101, value = "Apache ActiveMQ Artemis is using a scheduled pool without remove on cancel policy, so a cancelled task could be not automatically removed from the work queue, it may also cause unbounded retention of cancelled tasks.", format = Message.Format.MESSAGE_FORMAT)
+   void scheduledPoolWithNoRemoveOnCancelPolicy();
 }

artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/ActiveMQServerImpl.java

@@ -2707,10 +2707,18 @@ public class ActiveMQServerImpl implements ActiveMQServer {
                return new ActiveMQThreadFactory("ActiveMQ-scheduled-threads", false, ClientSessionFactoryImpl.class.getClassLoader());
             }
          });
-         scheduledPool = new ScheduledThreadPoolExecutor(configuration.getScheduledThreadPoolMaxSize(), tFactory);
+
+         ScheduledThreadPoolExecutor scheduledPoolExecutor = new ScheduledThreadPoolExecutor(configuration.getScheduledThreadPoolMaxSize(), tFactory);
+         scheduledPoolExecutor.setRemoveOnCancelPolicy(true);
+         scheduledPool = scheduledPoolExecutor;
       } else {
          this.scheduledPoolSupplied = true;
          this.scheduledPool = serviceRegistry.getScheduledExecutorService();
+
+         if (!(scheduledPool instanceof ScheduledThreadPoolExecutor) ||
+            !((ScheduledThreadPoolExecutor)scheduledPool).getRemoveOnCancelPolicy()) {
+            ActiveMQServerLogger.LOGGER.scheduledPoolWithNoRemoveOnCancelPolicy();
+         }
       }
    }
 

artemis-server/src/test/java/org/apache/activemq/artemis/core/server/impl/ActiveMQServerImplTest.java

@@ -0,0 +1,63 @@
+/*
+ * 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.activemq.artemis.core.server.impl;
+
+import java.lang.ref.WeakReference;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.activemq.artemis.core.server.ActiveMQServer;
+import org.apache.activemq.artemis.tests.util.ActiveMQTestBase;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class ActiveMQServerImplTest extends ActiveMQTestBase {
+
+   @Test
+   public void testScheduledPoolGC() throws Exception {
+      ActiveMQServer server = createServer(false);
+
+      server.start();
+
+      Runnable scheduledRunnable = new Runnable() {
+         @Override
+         public void run() {
+            Assert.fail();
+         }
+      };
+      WeakReference<Runnable> scheduledRunnableRef = new WeakReference<>(scheduledRunnable);
+
+      ScheduledExecutorService scheduledPool = server.getScheduledPool();
+      ScheduledFuture scheduledFuture = scheduledPool.schedule(scheduledRunnable, 5000, TimeUnit.MILLISECONDS);
+
+      Assert.assertFalse(scheduledFuture.isCancelled());
+      Assert.assertTrue(scheduledFuture.cancel(true));
+      Assert.assertTrue(scheduledFuture.isCancelled());
+
+      Assert.assertNotEquals(null, scheduledRunnableRef.get());
+
+      scheduledRunnable = null;
+
+      forceGC();
+
+      Assert.assertEquals(null, scheduledRunnableRef.get());
+
+      server.stop();
+   }
+
+}