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/Monitor.h

@@ -0,0 +1,67 @@
+/********************************************************************************
+ *    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"                       *
+ ********************************************************************************/
+#ifndef FAIR_MQ_SHMEM_MONITOR_H_
+#define FAIR_MQ_SHMEM_MONITOR_H_
+
+#include <boost/interprocess/managed_shared_memory.hpp>
+
+#include <thread>
+#include <chrono>
+#include <atomic>
+#include <string>
+
+namespace fair
+{
+namespace mq
+{
+namespace shmem
+{
+
+class Monitor
+{
+  public:
+    Monitor(const std::string& segmentName, bool selfDestruct, bool interactive, unsigned int timeoutInMS);
+
+    Monitor(const Monitor&) = delete;
+    Monitor operator=(const Monitor&) = delete;
+
+    void CatchSignals();
+    void Run();
+
+    virtual ~Monitor();
+
+    static void Cleanup(const std::string& segmentName);
+    static void RemoveObject(const std::string&);
+    static void RemoveQueue(const std::string&);
+
+  private:
+    void PrintHeader();
+    void PrintHelp();
+    void PrintQueues();
+    void MonitorHeartbeats();
+    void CheckSegment();
+    void Interactive();
+    void SignalMonitor();
+
+    bool fSelfDestruct; // will self-destruct after the memory has been closed
+    bool fInteractive; // running in interactive mode
+    bool fSeenOnce; // true is segment has been opened successfully at least once
+    unsigned int fTimeoutInMS;
+    std::string fSegmentName;
+    std::atomic<bool> fTerminating;
+    std::atomic<bool> fHeartbeatTriggered;
+    std::chrono::high_resolution_clock::time_point fLastHeartbeat;
+    std::thread fSignalThread;
+    boost::interprocess::managed_shared_memory fManagementSegment;
+};
+
+} // namespace shmem
+} // namespace mq
+} // namespace fair
+
+#endif /* FAIR_MQ_SHMEM_MONITOR_H_ */