ARTEMIS-1140 Avoid lock on queue for message counts

(cherry picked from commit 33f2ad65c9)

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

@@ -208,6 +208,8 @@ public class QueueImpl implements Queue {
 
    // We cache the consumers here since we don't want to include the redistributor
 
+   private final AtomicInteger consumersCount = new AtomicInteger();
+
    private final Set<Consumer> consumerSet = new HashSet<>();
 
    private final Map<SimpleString, Consumer> groups = new HashMap<>();
@@ -717,7 +719,9 @@ public class QueueImpl implements Queue {
 
          consumerList.add(new ConsumerHolder(consumer));
 
-         consumerSet.add(consumer);
+         if (consumerSet.add(consumer)) {
+            consumersCount.incrementAndGet();
+         }
 
          if (refCountForConsumers != null) {
             refCountForConsumers.increment();
@@ -745,7 +749,9 @@ public class QueueImpl implements Queue {
             pos = consumerList.size() - 1;
          }
 
-         consumerSet.remove(consumer);
+         if (consumerSet.remove(consumer)) {
+            consumersCount.decrementAndGet();
+         }
 
          LinkedList<SimpleString> groupsToRemove = null;
 
@@ -830,8 +836,8 @@ public class QueueImpl implements Queue {
    }
 
    @Override
-   public synchronized int getConsumerCount() {
-      return consumerSet.size();
+   public int getConsumerCount() {
+      return consumersCount.get();
    }
 
    @Override
@@ -917,16 +923,14 @@ public class QueueImpl implements Queue {
 
    @Override
    public long getMessageCount() {
-      synchronized (this) {
-         if (pageSubscription != null) {
-            // messageReferences will have depaged messages which we need to discount from the counter as they are
-            // counted on the pageSubscription as well
-            return messageReferences.size() + getScheduledCount() +
-               deliveringCount.get() +
-               pageSubscription.getMessageCount();
-         } else {
-            return messageReferences.size() + getScheduledCount() + deliveringCount.get();
-         }
+      if (pageSubscription != null) {
+         // messageReferences will have depaged messages which we need to discount from the counter as they are
+         // counted on the pageSubscription as well
+         return messageReferences.size() + getScheduledCount() +
+            deliveringCount.get() +
+            pageSubscription.getMessageCount();
+      } else {
+         return messageReferences.size() + getScheduledCount() + deliveringCount.get();
       }
    }