FairMQ: Introduce callbacks for the FairMQUnmanagedRegion.

Callbacks are called when the data buffer of the message assiciated
with the corresponding region is no longer needed by the transport.
Example in examples/advanced/Region/

fairmq/shmem/Region.h

@@ -0,0 +1,68 @@
+/********************************************************************************
+*    Copyright (C) 2014 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    *
+*                                                                              *
+*              This software is distributed under the terms of the             *
+*         GNU Lesser General Public Licence version 3 (LGPL) version 3,        *
+*                  copied verbatim in the file "LICENSE"                       *
+********************************************************************************/
+/**
+* FairMQShmManager.h
+*
+* @since 2016-04-08
+* @author A. Rybalchenko
+*/
+
+#ifndef FAIR_MQ_SHMEM_REGION_H_
+#define FAIR_MQ_SHMEM_REGION_H_
+
+#include "FairMQLogger.h"
+#include "FairMQUnmanagedRegion.h"
+#include "fairmq/Tools.h"
+
+#include <boost/interprocess/managed_shared_memory.hpp>
+#include <boost/interprocess/ipc/message_queue.hpp>
+
+#include <thread>
+#include <queue>
+#include <unordered_map>
+
+namespace fair
+{
+namespace mq
+{
+namespace shmem
+{
+
+class Manager;
+
+struct Region
+{
+    Region(Manager& manager, uint64_t id, uint64_t size, bool remote, FairMQRegionCallback callback = nullptr);
+
+    Region() = delete;
+
+    Region(const Region&) = default;
+    Region(Region&&) = default;
+
+    void StartReceivingAcks();
+    void ReceiveAcks();
+
+    ~Region();
+
+    Manager& fManager;
+    bool fRemote;
+    bool fStop;
+    std::string fName;
+    std::string fQueueName;
+    boost::interprocess::shared_memory_object fShmemObject;
+    boost::interprocess::mapped_region fRegion;
+    std::unique_ptr<boost::interprocess::message_queue> fQueue;
+    std::thread fWorker;
+    FairMQRegionCallback fCallback;
+};
+
+} // namespace shmem
+} // namespace mq
+} // namespace fair
+
+#endif /* FAIR_MQ_SHMEM_REGION_H_ */