fix for #ARTEMIS-2476

artemis-protocols/artemis-mqtt-protocol/src/main/java/org/apache/activemq/artemis/core/protocol/mqtt/MQTTRetainMessageManager.java

@@ -52,19 +52,12 @@ public class MQTTRetainMessageManager {
          queue = session.getServer().createQueue(retainAddress, retainAddress, null, true, false);
       }
 
-      try (LinkedListIterator<MessageReference> iterator = queue.iterator()) {
+      queue.deleteAllReferences();
-         synchronized (queue) {
-            if (iterator.hasNext()) {
-               MessageReference ref = iterator.next();
-               iterator.remove();
-               queue.acknowledge(tx, ref);
-            }
 
       if (!reset) {
          sendToQueue(message.copy(session.getServer().getStorageManager().generateID()), queue, tx);
       }
-         }
+
-      }
    }
 
    // SEND to Queue.
@@ -76,18 +69,23 @@ public class MQTTRetainMessageManager {
       // Iterate over all matching retain queues and add the queue
       Transaction tx = session.getServerSession().newTransaction();
       try {
-         synchronized (queue) {
          for (SimpleString retainedQueueName : bindingQueryResult.getQueueNames()) {
             Queue retainedQueue = session.getServer().locateQueue(retainedQueueName);
             try (LinkedListIterator<MessageReference> i = retainedQueue.iterator()) {
                if (i.hasNext()) {
-                     Message message = i.next().getMessage().copy(session.getServer().getStorageManager().generateID());
+                  MessageReference ref = i.next();
+                  while (i.hasNext()) {
+                     ref = i.next();
+                     if (i.hasNext()) {
+                        i.remove();
+                     }
+                  }
+                  Message message = ref.getMessage().copy(session.getServer().getStorageManager().generateID());
                   sendToQueue(message, queue, tx);
                }
             }
          }
-         }
+      } catch (Exception t) {
-      } catch (Throwable t) {
          tx.rollback();
          throw t;
       }