--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Framework/Messages/MessageBroker.h	Mon Jul 02 16:36:17 2018 +0200
@@ -0,0 +1,61 @@
+/**
+ * Stone of Orthanc
+ * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ * Copyright (C) 2017-2018 Osimis S.A., Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Affero General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+
+#pragma once
+
+#include "../StoneEnumerations.h"
+
+#include "boost/noncopyable.hpp"
+#include <map>
+#include <list>
+#include <set>
+namespace OrthancStone
+{
+  class IObserver;
+  class IObservable;
+  class IMessage;
+
+  /*
+   * This is a central message broker.  It keeps track of all observers and knows
+   * when an observer is deleted.
+   * This way, it can prevent an observable to send a message to a dead observer.
+   */
+  class MessageBroker : public boost::noncopyable
+  {
+
+    std::set<IObserver*> activeObservers_;  // the list of observers that are currently alive (that have not been deleted)
+
+  public:
+
+    void Register(IObserver& observer)
+    {
+      activeObservers_.insert(&observer);
+    }
+
+    void Unregister(IObserver& observer)
+    {
+      activeObservers_.erase(&observer);
+    }
+
+    void Emit(IObservable& from, std::set<IObserver*> observers, const IMessage& message);
+  };
+
+}