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diff --git a/qpid/cpp/src/qpid/ha/QueueSnapshot.h b/qpid/cpp/src/qpid/ha/QueueSnapshot.h
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+++ b/qpid/cpp/src/qpid/ha/QueueSnapshot.h
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+#ifndef QPID_HA_IDSETOBSERVER_H
+#define QPID_HA_IDSETOBSERVER_H
+
+/*
+ *
+ * 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.
+ *
+ */
+
+#include "qpid/broker/Message.h"
+#include "qpid/broker/QueueObserver.h"
+#include "qpid/sys/Mutex.h"
+
+namespace qpid {
+namespace ha {
+
+/**
+ * A QueueObserver that maintains a ReplicationIdSet of the ReplicationIds of
+ * the messages on the queue.
+ *
+ * THREAD SAFE: Note that QueueObserver methods are called under the Queues messageLock.
+ *
+ */
+class  QueueSnapshot : public broker::QueueObserver
+{
+  public:
+    void enqueued(const broker::Message& m) {
+        sys::Mutex::ScopedLock l(lock);
+        set += m.getReplicationId();
+    }
+
+    void dequeued(const broker::Message& m) {
+        sys::Mutex::ScopedLock l(lock);
+        set -= m.getReplicationId();
+    }
+
+    void acquired(const broker::Message&) {}
+
+    void requeued(const broker::Message&) {}
+
+    ReplicationIdSet getSnapshot() {
+        sys::Mutex::ScopedLock l(lock);
+        return set;
+    }
+
+  private:
+    sys::Mutex lock;
+    ReplicationIdSet set;
+};
+
+}} // namespace qpid::ha
+
+#endif  /*!QPID_HA_IDSETOBSERVER_H*/