ARTEMIS-2538 Removing all messages from a huge queue causes OOM

The iterQueue transaction commits are locked by the synchronization
context. So removing all messages from a huge queue causes the creation
of too locked transactions for the paged messages and so OOM.
The iteration on paged message is executed out the iterQueue
synchronization context to avoid to lock the transaction commits.

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

@@ -227,6 +227,8 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
    //This lock is used to prevent deadlocks between direct and async deliveries
    private final ReentrantLock deliverLock = new ReentrantLock();
 
+   private final ReentrantLock depageLock = new ReentrantLock();
+
    private volatile boolean depagePending = false;
 
    private final StorageManager storageManager;
@@ -1967,16 +1969,20 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
     * @return
     * @throws Exception
     */
-   private synchronized int iterQueue(final int flushLimit,
+   private int iterQueue(final int flushLimit,
                                       final Filter filter1,
                                       QueueIterateAction messageAction,
                                       final boolean remove) throws Exception {
       int count = 0;
       int txCount = 0;
 
+      depageLock.lock();
+
+      try {
          Transaction tx = new TransactionImpl(storageManager);
 
          synchronized (this) {
+
             try (LinkedListIterator<MessageReference> iter = iterator()) {
 
                while (iter.hasNext()) {
@@ -2020,6 +2026,7 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
                   txCount = 0;
                }
             }
+         }
 
          if (pageIterator != null && !queueDestroyed) {
             while (pageIterator.hasNext()) {
@@ -2052,6 +2059,8 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
          }
 
          return count;
+      } finally {
+         depageLock.unlock();
       }
    }
 
@@ -3879,10 +3888,13 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
 
       @Override
       public void run() {
+         depageLock.lock();
          try {
             depage(scheduleExpiry);
          } catch (Exception e) {
             ActiveMQServerLogger.LOGGER.errorDelivering(e);
+         } finally {
+            depageLock.unlock();
          }
       }
    }

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

@@ -0,0 +1,89 @@
+/*
+ * 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.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.Semaphore;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.activemq.artemis.api.core.Message;
+import org.apache.activemq.artemis.api.core.SimpleString;
+import org.apache.activemq.artemis.core.io.IOCallback;
+import org.apache.activemq.artemis.core.paging.cursor.PageIterator;
+import org.apache.activemq.artemis.core.paging.cursor.PagePosition;
+import org.apache.activemq.artemis.core.paging.cursor.PageSubscription;
+import org.apache.activemq.artemis.core.paging.cursor.PagedReferenceImpl;
+import org.apache.activemq.artemis.core.paging.impl.PagedMessageImpl;
+import org.apache.activemq.artemis.core.persistence.StorageManager;
+import org.apache.activemq.artemis.core.postoffice.PostOffice;
+import org.apache.activemq.artemis.core.server.ActiveMQServer;
+import org.apache.activemq.artemis.core.server.QueueFactory;
+import org.apache.activemq.artemis.utils.actors.ArtemisExecutor;
+import org.junit.Assert;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class QueueImplTest {
+
+   @Test
+   public void deleteAllPagedReferencesTest() throws Exception {
+      SimpleString address = new SimpleString("test");
+      AtomicInteger pageIteratorIndex = new AtomicInteger(0);
+      PageIterator pageIterator = Mockito.mock(PageIterator.class);
+      PageSubscription pageSubscription = Mockito.mock(PageSubscription.class);
+      ExecutorService executorService = Executors.newSingleThreadExecutor();
+      StorageManager storageManager = Mockito.mock(StorageManager.class);
+
+      final int flushLimit = 100;
+      final int pagedReferences = 5 * flushLimit;
+      Semaphore availableTransactions = new Semaphore(3);
+
+      //Mock pageIterator.
+      Mockito.doAnswer(invocationOnMock -> pageIteratorIndex.get() < pagedReferences).
+         when(pageIterator).hasNext();
+      Mockito.doAnswer(invocationOnMock -> {
+         pageIteratorIndex.incrementAndGet();
+         return new PagedReferenceImpl(Mockito.mock(PagePosition.class), new PagedMessageImpl(
+            Mockito.mock(Message.class), new long[]{0}), pageSubscription);
+      }).when(pageIterator).next();
+      Mockito.doReturn(pageIterator).when(pageSubscription).iterator();
+
+      //Mock storageManager.
+      Mockito.doAnswer(invocationOnMock -> {
+         Assert.assertTrue("Too transactions locked on afterCommit.",
+                           availableTransactions.tryAcquire(3000, TimeUnit.MILLISECONDS));
+         executorService.execute(() -> {
+            ((IOCallback) invocationOnMock.getArgument(0)).done();
+            availableTransactions.release();
+         });
+         return null;
+      }).when(storageManager).afterCompleteOperations(Mockito.any(IOCallback.class));
+
+      QueueImpl queue = new QueueImpl(0, address, address, null, pageSubscription, null, false,
+                                      false, false, Mockito.mock(ScheduledExecutorService.class),
+                                      Mockito.mock(PostOffice.class), storageManager, null,
+                                      Mockito.mock(ArtemisExecutor.class), Mockito.mock(ActiveMQServer.class),
+                                      Mockito.mock(QueueFactory.class));
+
+      Mockito.doReturn(queue).when(pageSubscription).getQueue();
+
+      Assert.assertEquals(pagedReferences, queue.deleteAllReferences(flushLimit));
+   }
+}