--- a/Applications/Generic/GuiAdapter.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/GuiAdapter.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -792,7 +792,7 @@
     while (!stop)
     {
       {
-        LockingEmitter::WriterLock lock(lockingEmitter_);
+        Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
         if(func != NULL)
           (*func)(cookie);
         OnAnimationFrame(); // in SDL we must call it
@@ -802,7 +802,7 @@
 
       while (!stop && SDL_PollEvent(&event))
       {
-        LockingEmitter::WriterLock lock(lockingEmitter_);
+        Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
 
         if (event.type == SDL_QUIT)
         {

--- a/Applications/Generic/GuiAdapter.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/GuiAdapter.h	Fri Nov 29 11:03:41 2019 +0100
@@ -95,7 +95,10 @@
   struct GuiAdapterWheelEvent;
   struct GuiAdapterKeyboardEvent;
 
-  class LockingEmitter;
+  namespace Deprecated
+  {
+    class LockingEmitter;
+  }
     
 #if 1
   typedef bool (*OnMouseEventFunc)(std::string canvasId, const GuiAdapterMouseEvent* mouseEvent, void* userData);
@@ -225,7 +228,7 @@
   {
   public:
 #if ORTHANC_ENABLE_THREADS == 1
-    GuiAdapter(LockingEmitter& lockingEmitter) : lockingEmitter_(lockingEmitter)
+    GuiAdapter(Deprecated::LockingEmitter& lockingEmitter) : lockingEmitter_(lockingEmitter)
 #else
     GuiAdapter()
 #endif
@@ -301,7 +304,7 @@
     This object is used by the multithreaded Oracle to serialize access to
     shared data. We need to use it as soon as we access the state.
     */
-    LockingEmitter& lockingEmitter_;
+    Deprecated::LockingEmitter& lockingEmitter_;
 #endif
 
     /**

--- a/Applications/Generic/NativeStoneApplicationContext.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/NativeStoneApplicationContext.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -24,10 +24,10 @@
 
 namespace OrthancStone
 {
-  Deprecated::IWidget& NativeStoneApplicationContext::GlobalMutexLocker::SetCentralWidget(Deprecated::IWidget* widget)
+  void NativeStoneApplicationContext::GlobalMutexLocker::SetCentralWidget(
+    boost::shared_ptr<Deprecated::IWidget> widget)
   {
     that_.centralViewport_.SetCentralWidget(widget);
-    return *widget;
   }
 
 
@@ -45,9 +45,7 @@
   }
   
 
-  NativeStoneApplicationContext::NativeStoneApplicationContext(MessageBroker& broker) :
-    StoneApplicationContext(broker),
-    centralViewport_(broker),
+  NativeStoneApplicationContext::NativeStoneApplicationContext() :
     stopped_(true),
     updateDelayInMs_(100)   // By default, 100ms between each refresh of the content
   {

--- a/Applications/Generic/NativeStoneApplicationContext.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/NativeStoneApplicationContext.h	Fri Nov 29 11:03:41 2019 +0100
@@ -56,7 +56,7 @@
       {
       }
 
-      Deprecated::IWidget& SetCentralWidget(Deprecated::IWidget* widget);   // Takes ownership
+      void SetCentralWidget(boost::shared_ptr<Deprecated::IWidget> widget);
 
       Deprecated::IViewport& GetCentralViewport() 
       {
@@ -67,14 +67,9 @@
       {
         that_.updateDelayInMs_ = delayInMs;
       }
-
-      MessageBroker& GetMessageBroker()
-      {
-        return that_.GetMessageBroker();
-      }
     };
 
-    NativeStoneApplicationContext(MessageBroker& broker);
+    NativeStoneApplicationContext();
 
     void Start();
 

--- a/Applications/Generic/NativeStoneApplicationRunner.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/NativeStoneApplicationRunner.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -97,7 +97,7 @@
     DeclareCommandLineOptions(options);
     
     // application specific options
-    application_.DeclareStartupOptions(options);
+    application_->DeclareStartupOptions(options);
 
     boost::program_options::variables_map parameters;
     bool error = false;
@@ -197,7 +197,7 @@
 
       LogStatusBar statusBar;
 
-      NativeStoneApplicationContext context(broker_);
+      NativeStoneApplicationContext context;
 
       {
         // use multiple threads to execute asynchronous tasks like 
@@ -206,24 +206,23 @@
         oracle.Start();
 
         {
-          Deprecated::OracleWebService webService(
-            broker_, oracle, webServiceParameters, context);
-          
+          boost::shared_ptr<Deprecated::OracleWebService> webService
+            (new Deprecated::OracleWebService(oracle, webServiceParameters, context));
           context.SetWebService(webService);
           context.SetOrthancBaseUrl(webServiceParameters.GetUrl());
 
-          Deprecated::OracleDelayedCallExecutor delayedExecutor(broker_, oracle, context);
+          Deprecated::OracleDelayedCallExecutor delayedExecutor(oracle, context);
           context.SetDelayedCallExecutor(delayedExecutor);
 
-          application_.Initialize(&context, statusBar, parameters);
+          application_->Initialize(&context, statusBar, parameters);
 
           {
             NativeStoneApplicationContext::GlobalMutexLocker locker(context);
-            locker.SetCentralWidget(application_.GetCentralWidget());
+            locker.SetCentralWidget(application_->GetCentralWidget());
             locker.GetCentralViewport().SetStatusBar(statusBar);
           }
 
-          std::string title = application_.GetTitle();
+          std::string title = application_->GetTitle();
           if (title.empty())
           {
             title = "Stone of Orthanc";
@@ -244,7 +243,7 @@
       }
 
       LOG(WARNING) << "The application is stopping";
-      application_.Finalize();
+      application_->Finalize();
     }
     catch (Orthanc::OrthancException& e)
     {

--- a/Applications/Generic/NativeStoneApplicationRunner.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Generic/NativeStoneApplicationRunner.h	Fri Nov 29 11:03:41 2019 +0100
@@ -34,14 +34,11 @@
   class NativeStoneApplicationRunner
   {
   protected:
-    MessageBroker&      broker_;
-    IStoneApplication&  application_;
+    boost::shared_ptr<IStoneApplication>  application_;
+    
   public:
-
-    NativeStoneApplicationRunner(MessageBroker& broker,
-                                 IStoneApplication& application)
-      : broker_(broker),
-        application_(application)
+    NativeStoneApplicationRunner(boost::shared_ptr<IStoneApplication> application)
+      : application_(application)
     {
     }
     int Execute(int argc,

--- a/Applications/IStoneApplication.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/IStoneApplication.h	Fri Nov 29 11:03:41 2019 +0100
@@ -64,7 +64,11 @@
 #endif
 
     virtual std::string GetTitle() const = 0;
-    virtual Deprecated::IWidget* GetCentralWidget() = 0;
+    
+    virtual void SetCentralWidget(boost::shared_ptr<Deprecated::IWidget> widget) = 0;
+    
+    virtual boost::shared_ptr<Deprecated::IWidget> GetCentralWidget() = 0;
+    
     virtual void Finalize() = 0;
   };
 }

--- a/Applications/Samples/SampleApplicationBase.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Samples/SampleApplicationBase.h	Fri Nov 29 11:03:41 2019 +0100
@@ -40,9 +40,8 @@
   {
     class SampleApplicationBase : public IStoneApplication
     {
-    protected:
-      // ownership is transferred to the application context
-      Deprecated::WorldSceneWidget*  mainWidget_;
+    private:
+      boost::shared_ptr<Deprecated::IWidget>  mainWidget_;
 
     public:
       virtual void Initialize(StoneApplicationContext* context,
@@ -64,7 +63,16 @@
 
 
       virtual void Finalize() ORTHANC_OVERRIDE {}
-      virtual Deprecated::IWidget* GetCentralWidget() ORTHANC_OVERRIDE {return mainWidget_;}
+
+      virtual void SetCentralWidget(boost::shared_ptr<Deprecated::IWidget> widget) ORTHANC_OVERRIDE
+      {
+        mainWidget_ = widget;
+      }
+
+      virtual boost::shared_ptr<Deprecated::IWidget> GetCentralWidget() ORTHANC_OVERRIDE
+      {
+        return mainWidget_;
+      }
 
 #if ORTHANC_ENABLE_WASM==1
       // default implementations for a single canvas named "canvas" in the HTML and an emtpy WasmApplicationAdapter

--- a/Applications/Samples/SampleMainNative.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Samples/SampleMainNative.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -26,19 +26,18 @@
 #if ORTHANC_ENABLE_QT==1
 #include "Qt/SampleQtApplicationRunner.h"
 #endif
-#include "../../Framework/Messages/MessageBroker.h"
 
 int main(int argc, char* argv[]) 
 {
-  OrthancStone::MessageBroker broker;
-  SampleApplication sampleStoneApplication(broker);
+  boost::shared_ptr<SampleApplication> sampleStoneApplication(new SampleApplication);
 
 #if ORTHANC_ENABLE_SDL==1
-  OrthancStone::SdlStoneApplicationRunner sdlApplicationRunner(broker, sampleStoneApplication);
+  OrthancStone::SdlStoneApplicationRunner sdlApplicationRunner(sampleStoneApplication);
   return sdlApplicationRunner.Execute(argc, argv);
 #endif
+  
 #if ORTHANC_ENABLE_QT==1
-  OrthancStone::Samples::SampleQtApplicationRunner qtAppRunner(broker, sampleStoneApplication);
+  OrthancStone::Samples::SampleQtApplicationRunner qtAppRunner(sampleStoneApplication);
   return qtAppRunner.Execute(argc, argv);
 #endif
 }

--- a/Applications/Samples/SimpleViewerApplicationSingleFile.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Samples/SimpleViewerApplicationSingleFile.h	Fri Nov 29 11:03:41 2019 +0100
@@ -44,7 +44,7 @@
   {
     class SimpleViewerApplication :
       public SampleSingleCanvasWithButtonsApplicationBase,
-      public IObserver
+      public ObserverBase<SimpleViewerApplication>
     {
     private:
       class ThumbnailInteractor : public Deprecated::IWorldSceneInteractor
@@ -199,8 +199,8 @@
         SimpleViewerApplication&  viewerApplication_;
 
       public:
-        SimpleViewerApplicationAdapter(MessageBroker& broker, SimpleViewerApplication& application)
-          : WasmPlatformApplicationAdapter(broker, application),
+        SimpleViewerApplicationAdapter(SimpleViewerApplication& application)
+          : WasmPlatformApplicationAdapter(application),
             viewerApplication_(application)
         {
         }
@@ -243,7 +243,7 @@
       std::auto_ptr<ThumbnailInteractor>   thumbnailInteractor_;
       Deprecated::LayoutWidget*                        mainLayout_;
       Deprecated::LayoutWidget*                        thumbnailsLayout_;
-      std::vector<Deprecated::SliceViewerWidget*>      thumbnails_;
+      std::vector<boost::shared_ptr<Deprecated::SliceViewerWidget> >      thumbnails_;
 
       std::map<std::string, std::vector<std::string> > instancesIdsPerSeriesId_;
       std::map<std::string, Json::Value> seriesTags_;
@@ -258,8 +258,7 @@
       Orthanc::Font                        font_;
 
     public:
-      SimpleViewerApplication(MessageBroker& broker) :
-        IObserver(broker),
+      SimpleViewerApplication() :
         currentTool_(Tool_LineMeasure),
         mainLayout_(NULL),
         currentInstanceIndex_(0),
@@ -297,26 +296,28 @@
           mainLayout_->SetBackgroundColor(0, 0, 0);
           mainLayout_->SetHorizontal();
 
-          thumbnailsLayout_ = new Deprecated::LayoutWidget("thumbnail-layout");
+          boost::shared_ptr<Deprecated::LayoutWidget> thumbnailsLayout_(new Deprecated::LayoutWidget("thumbnail-layout"));
           thumbnailsLayout_->SetPadding(10);
           thumbnailsLayout_->SetBackgroundCleared(true);
           thumbnailsLayout_->SetBackgroundColor(50, 50, 50);
           thumbnailsLayout_->SetVertical();
 
-          mainWidget_ = new Deprecated::SliceViewerWidget(GetBroker(), "main-viewport");
+          boost::shared_ptr<Deprecated::SliceViewerWidget> widget
+            (new Deprecated::SliceViewerWidget("main-viewport"));
+          SetCentralWidget(widget);
           //mainWidget_->RegisterObserver(*this);
 
           // hierarchy
           mainLayout_->AddWidget(thumbnailsLayout_);
-          mainLayout_->AddWidget(mainWidget_);
+          mainLayout_->AddWidget(widget);
 
           // sources
-          smartLoader_.reset(new Deprecated::SmartLoader(GetBroker(), context->GetOrthancApiClient()));
+          smartLoader_.reset(new Deprecated::SmartLoader(context->GetOrthancApiClient()));
           smartLoader_->SetImageQuality(Deprecated::SliceImageQuality_FullPam);
 
           mainLayout_->SetTransmitMouseOver(true);
           mainWidgetInteractor_.reset(new MainWidgetInteractor(*this));
-          mainWidget_->SetInteractor(*mainWidgetInteractor_);
+          widget->SetInteractor(*mainWidgetInteractor_);
           thumbnailInteractor_.reset(new ThumbnailInteractor(*this));
         }
 
@@ -327,10 +328,10 @@
         if (parameters.count("studyId") < 1)
         {
           LOG(WARNING) << "The study ID is missing, will take the first studyId found in Orthanc";
-          context->GetOrthancApiClient().GetJsonAsync(
+          context->GetOrthancApiClient()->GetJsonAsync(
             "/studies",
             new Callable<SimpleViewerApplication, Deprecated::OrthancApiClient::JsonResponseReadyMessage>
-            (*this, &SimpleViewerApplication::OnStudyListReceived));
+            (GetSharedObserver(), &SimpleViewerApplication::OnStudyListReceived));
         }
         else
         {
@@ -357,10 +358,10 @@
         {
           for (size_t i=0; i < response["Series"].size(); i++)
           {
-            context_->GetOrthancApiClient().GetJsonAsync(
+            context_->GetOrthancApiClient()->GetJsonAsync(
               "/series/" + response["Series"][(int)i].asString(),
               new Callable<SimpleViewerApplication, Deprecated::OrthancApiClient::JsonResponseReadyMessage>
-              (*this, &SimpleViewerApplication::OnSeriesReceived));
+              (GetSharedObserver(), &SimpleViewerApplication::OnSeriesReceived));
           }
         }
       }
@@ -387,7 +388,7 @@
           LoadThumbnailForSeries(seriesId, instancesIdsPerSeriesId_[seriesId][0]);
 
           // if this is the first thumbnail loaded, load the first instance in the mainWidget
-          Deprecated::SliceViewerWidget& widget = *dynamic_cast<Deprecated::SliceViewerWidget*>(mainWidget_);
+          Deprecated::SliceViewerWidget& widget = dynamic_cast<Deprecated::SliceViewerWidget&>(*GetCentralWidget());
           if (widget.GetLayerCount() == 0)
           {
             smartLoader_->SetFrameInWidget(widget, 0, instancesIdsPerSeriesId_[seriesId][0], 0);
@@ -398,10 +399,10 @@
       void LoadThumbnailForSeries(const std::string& seriesId, const std::string& instanceId)
       {
         LOG(INFO) << "Loading thumbnail for series " << seriesId;
-        Deprecated::SliceViewerWidget* thumbnailWidget = new Deprecated::SliceViewerWidget(GetBroker(), "thumbnail-series-" + seriesId);
+        boost::shared_ptr<Deprecated::SliceViewerWidget> thumbnailWidget(new Deprecated::SliceViewerWidget("thumbnail-series-" + seriesId));
         thumbnails_.push_back(thumbnailWidget);
         thumbnailsLayout_->AddWidget(thumbnailWidget);
-        thumbnailWidget->RegisterObserverCallback(new Callable<SimpleViewerApplication, Deprecated::SliceViewerWidget::GeometryChangedMessage>(*this, &SimpleViewerApplication::OnWidgetGeometryChanged));
+        Register<Deprecated::SliceViewerWidget::GeometryChangedMessage>(*thumbnailWidget, &SimpleViewerApplication::OnWidgetGeometryChanged);
         smartLoader_->SetFrameInWidget(*thumbnailWidget, 0, instanceId, 0);
         thumbnailWidget->SetInteractor(*thumbnailInteractor_);
       }
@@ -409,9 +410,9 @@
       void SelectStudy(const std::string& studyId)
       {
         LOG(INFO) << "Selecting study: " << studyId;
-        context_->GetOrthancApiClient().GetJsonAsync(
+        context_->GetOrthancApiClient()->GetJsonAsync(
           "/studies/" + studyId, new Callable<SimpleViewerApplication, Deprecated::OrthancApiClient::JsonResponseReadyMessage>
-          (*this, &SimpleViewerApplication::OnStudyReceived));
+          (GetSharedObserver(), &SimpleViewerApplication::OnStudyReceived));
       }
 
       void OnWidgetGeometryChanged(const Deprecated::SliceViewerWidget::GeometryChangedMessage& message)
@@ -422,7 +423,7 @@
 
       void SelectSeriesInMainViewport(const std::string& seriesId)
       {
-        Deprecated::SliceViewerWidget& widget = *dynamic_cast<Deprecated::SliceViewerWidget*>(mainWidget_);
+        Deprecated::SliceViewerWidget& widget = dynamic_cast<Deprecated::SliceViewerWidget&>(*GetCentralWidget());
         smartLoader_->SetFrameInWidget(widget, 0, instancesIdsPerSeriesId_[seriesId][0], 0);
       }
 
@@ -451,7 +452,7 @@
       virtual void InitializeWasm()
       {
         AttachWidgetToWasmViewport("canvas", thumbnailsLayout_);
-        AttachWidgetToWasmViewport("canvas2", mainWidget_);
+        AttachWidgetToWasmViewport("canvas2", widget);
       }
 #endif
 

--- a/Applications/Samples/SingleFrameApplication.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Samples/SingleFrameApplication.h	Fri Nov 29 11:03:41 2019 +0100
@@ -38,7 +38,7 @@
   {
     class SingleFrameApplication :
       public SampleSingleCanvasApplicationBase,
-      public IObserver
+      public ObserverBase<SingleFrameApplication>
     {
     private:
       class Interactor : public Deprecated::IWorldSceneInteractor
@@ -127,7 +127,7 @@
 
       void OffsetSlice(int offset)
       {
-        if (source_ != NULL)
+        if (source_)
         {
           int slice = static_cast<int>(slice_) + offset;
 
@@ -149,21 +149,15 @@
       }
 
 
-      Deprecated::SliceViewerWidget& GetMainWidget()
-      {
-        return *dynamic_cast<Deprecated::SliceViewerWidget*>(mainWidget_);
-      }
-      
-
       void SetSlice(size_t index)
       {
-        if (source_ != NULL &&
+        if (source_ &&
             index < source_->GetSlicesCount())
         {
           slice_ = static_cast<unsigned int>(index);
           
 #if 1
-          GetMainWidget().SetSlice(source_->GetSlice(slice_).GetGeometry());
+          widget_->SetSlice(source_->GetSlice(slice_).GetGeometry());
 #else
           // TEST for scene extents - Rotate the axes
           double a = 15.0 / 180.0 * boost::math::constants::pi<double>();
@@ -189,22 +183,22 @@
         // Once the geometry of the series is downloaded from Orthanc,
         // display its middle slice, and adapt the viewport to fit this
         // slice
-        if (source_ == &message.GetOrigin())
+        if (source_ &&
+            source_.get() == &message.GetOrigin())
         {
           SetSlice(source_->GetSlicesCount() / 2);
         }
 
-        GetMainWidget().FitContent();
+        widget_->FitContent();
       }
-      
+
+      boost::shared_ptr<Deprecated::SliceViewerWidget>  widget_;
       std::auto_ptr<Interactor>         mainWidgetInteractor_;
-      const Deprecated::DicomSeriesVolumeSlicer*    source_;
+      boost::shared_ptr<Deprecated::DicomSeriesVolumeSlicer> source_;
       unsigned int                      slice_;
 
     public:
-      SingleFrameApplication(MessageBroker& broker) :
-        IObserver(broker),
-        source_(NULL),
+      SingleFrameApplication() :
         slice_(0)
       {
       }
@@ -243,13 +237,15 @@
         std::string instance = parameters["instance"].as<std::string>();
         int frame = parameters["frame"].as<unsigned int>();
 
-        mainWidget_ = new Deprecated::SliceViewerWidget(GetBroker(), "main-widget");
+        widget_.reset(new Deprecated::SliceViewerWidget("main-widget"));
+        SetCentralWidget(widget_);
 
-        std::auto_ptr<Deprecated::DicomSeriesVolumeSlicer> layer(new Deprecated::DicomSeriesVolumeSlicer(GetBroker(), context->GetOrthancApiClient()));
-        source_ = layer.get();
+        boost::shared_ptr<Deprecated::DicomSeriesVolumeSlicer> layer(new Deprecated::DicomSeriesVolumeSlicer);
+        layer->Connect(context->GetOrthancApiClient());
+        source_ = layer;
         layer->LoadFrame(instance, frame);
-        layer->RegisterObserverCallback(new Callable<SingleFrameApplication, Deprecated::IVolumeSlicer::GeometryReadyMessage>(*this, &SingleFrameApplication::OnMainWidgetGeometryReady));
-        GetMainWidget().AddLayer(layer.release());
+        Register<Deprecated::IVolumeSlicer::GeometryReadyMessage>(*layer, &SingleFrameApplication::OnMainWidgetGeometryReady);
+        widget_->AddLayer(layer);
 
         Deprecated::RenderStyle s;
 
@@ -258,11 +254,11 @@
           s.interpolation_ = ImageInterpolation_Bilinear;
         }
 
-        GetMainWidget().SetLayerStyle(0, s);
-        GetMainWidget().SetTransmitMouseOver(true);
+        widget_->SetLayerStyle(0, s);
+        widget_->SetTransmitMouseOver(true);
 
         mainWidgetInteractor_.reset(new Interactor(*this));
-        GetMainWidget().SetInteractor(*mainWidgetInteractor_);
+        widget_->SetInteractor(*mainWidgetInteractor_);
       }
     };
 

--- a/Applications/Samples/SingleFrameEditorApplication.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Samples/SingleFrameEditorApplication.h	Fri Nov 29 11:03:41 2019 +0100
@@ -28,13 +28,13 @@
 #include "../../Framework/Radiography/RadiographyLayerMoveTracker.h"
 #include "../../Framework/Radiography/RadiographyLayerResizeTracker.h"
 #include "../../Framework/Radiography/RadiographyLayerRotateTracker.h"
+#include "../../Framework/Radiography/RadiographyMaskLayer.h"
 #include "../../Framework/Radiography/RadiographyScene.h"
 #include "../../Framework/Radiography/RadiographySceneCommand.h"
+#include "../../Framework/Radiography/RadiographySceneReader.h"
+#include "../../Framework/Radiography/RadiographySceneWriter.h"
 #include "../../Framework/Radiography/RadiographyWidget.h"
 #include "../../Framework/Radiography/RadiographyWindowingTracker.h"
-#include "../../Framework/Radiography/RadiographySceneWriter.h"
-#include "../../Framework/Radiography/RadiographySceneReader.h"
-#include "../../Framework/Radiography/RadiographyMaskLayer.h"
 #include "../../Framework/Toolbox/TextRenderer.h"
 
 #include <Core/HttpClient.h>
@@ -55,7 +55,7 @@
   {
     class RadiographyEditorInteractor :
         public Deprecated::IWorldSceneInteractor,
-        public IObserver
+        public ObserverBase<RadiographyEditorInteractor>
     {
     private:
       enum Tool
@@ -82,8 +82,7 @@
 
 
     public:
-      RadiographyEditorInteractor(MessageBroker& broker) :
-        IObserver(broker),
+      RadiographyEditorInteractor() :
         context_(NULL),
         tool_(Tool_Move),
         maskLayer_(NULL)
@@ -315,7 +314,7 @@
           LOG(INFO) << "JSON export was successful: "
                     << snapshot.toStyledString();
 
-          boost::shared_ptr<RadiographyScene> scene(new RadiographyScene(GetBroker()));
+          boost::shared_ptr<RadiographyScene> scene(new RadiographyScene);
           RadiographySceneReader reader(*scene, context_->GetOrthancApiClient());
           reader.Read(snapshot);
 
@@ -346,7 +345,7 @@
 
           if (context_ != NULL)
           {
-            widget.GetScene().ExportDicom(context_->GetOrthancApiClient(),
+            widget.GetScene().ExportDicom(*context_->GetOrthancApiClient(),
                                           tags, std::string(), 0.1, 0.1, widget.IsInverted(),
                                           widget.GetInterpolation(), EXPORT_USING_PAM);
           }
@@ -426,16 +425,9 @@
     private:
       boost::shared_ptr<RadiographyScene>   scene_;
       RadiographyEditorInteractor           interactor_;
-      Orthanc::FontRegistry                 fontRegistry_;
       RadiographyMaskLayer*                 maskLayer_;
 
     public:
-      SingleFrameEditorApplication(MessageBroker& broker) :
-        IObserver(broker),
-        interactor_(broker)
-      {
-      }
-
       virtual ~SingleFrameEditorApplication()
       {
         LOG(WARNING) << "Destroying the application";
@@ -487,9 +479,9 @@
         std::string instance = parameters["instance"].as<std::string>();
         //int frame = parameters["frame"].as<unsigned int>();
 
-        scene_.reset(new RadiographyScene(GetBroker()));
+        scene_.reset(new RadiographyScene);
         
-        RadiographyLayer& dicomLayer = scene_->LoadDicomFrame(context->GetOrthancApiClient(), instance, 0, false, NULL);
+        RadiographyLayer& dicomLayer = scene_->LoadDicomFrame(*context->GetOrthancApiClient(), instance, 0, false, NULL);
         //scene_->LoadDicomFrame(instance, frame, false); //.SetPan(200, 0);
         // = scene_->LoadDicomFrame(context->GetOrthancApiClient(), "61f3143e-96f34791-ad6bbb8d-62559e75-45943e1b", 0, false, NULL);
 
@@ -527,10 +519,10 @@
           layer.SetPan(0, 200);
         }
         
-        
-        mainWidget_ = new RadiographyWidget(GetBroker(), scene_, "main-widget");
-        mainWidget_->SetTransmitMouseOver(true);
-        mainWidget_->SetInteractor(interactor_);
+        boost::shared_ptr<RadiographyWidget> widget(new RadiographyWidget(scene_, "main-widget"));
+        widget->SetTransmitMouseOver(true);
+        widget->SetInteractor(interactor_);
+        SetCentralWidget(widget);
 
         //scene_->SetWindowing(128, 256);
       }

--- a/Applications/Sdl/SdlCairoSurface.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlCairoSurface.h	Fri Nov 29 11:03:41 2019 +0100
@@ -27,6 +27,8 @@
 #include "../../Framework/Wrappers/CairoSurface.h"
 #include "../../Framework/Deprecated/Viewport/IViewport.h"
 
+#include <SDL_render.h>
+
 #include <boost/thread/mutex.hpp>
 
 namespace OrthancStone

--- a/Applications/Sdl/SdlEngine.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlEngine.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -99,9 +99,7 @@
 
 
   SdlEngine::SdlEngine(SdlWindow& window,
-                       NativeStoneApplicationContext& context,
-                       MessageBroker& broker) :
-    IObserver(broker),
+                       NativeStoneApplicationContext& context) :
     window_(window),
     context_(context),
     surface_(window),

--- a/Applications/Sdl/SdlEngine.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlEngine.h	Fri Nov 29 11:03:41 2019 +0100
@@ -23,12 +23,13 @@
 
 #if ORTHANC_ENABLE_SDL == 1
 
+#include "../../Framework/Messages/ObserverBase.h"
+#include "../Generic/NativeStoneApplicationContext.h"
 #include "SdlCairoSurface.h"
-#include "../Generic/NativeStoneApplicationContext.h"
 
 namespace OrthancStone
 {
-  class SdlEngine : public IObserver
+  class SdlEngine : public ObserverBase<SdlEngine>
   {
   private:
     SdlWindow&                window_;
@@ -46,8 +47,7 @@
 
   public:
     SdlEngine(SdlWindow& window,
-              NativeStoneApplicationContext& context,
-              MessageBroker& broker);
+              NativeStoneApplicationContext& context);
   
     void OnViewportChanged(const Deprecated::IViewport::ViewportChangedMessage& message)
     {

--- a/Applications/Sdl/SdlOrthancSurface.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlOrthancSurface.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -27,6 +27,8 @@
 #include <Core/OrthancException.h>
 #include <Core/Images/Image.h>
 
+#include <SDL_render.h>
+
 namespace OrthancStone
 {
   SdlOrthancSurface::SdlOrthancSurface(SdlWindow& window) :

--- a/Applications/Sdl/SdlStoneApplicationRunner.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlStoneApplicationRunner.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -103,20 +103,19 @@
     LOG(WARNING) << "Starting the application";
 
     SdlWindow window(title.c_str(), width_, height_, enableOpenGl_);
-    SdlEngine sdl(window, context, broker_);
+    boost::shared_ptr<SdlEngine> sdl(new SdlEngine(window, context));
 
     {
       NativeStoneApplicationContext::GlobalMutexLocker locker(context);
 
-      locker.GetCentralViewport().RegisterObserverCallback(
-        new Callable<SdlEngine, Deprecated::IViewport::ViewportChangedMessage>
-        (sdl, &SdlEngine::OnViewportChanged));
+      sdl->Register<Deprecated::IViewport::ViewportChangedMessage>
+        (locker.GetCentralViewport(), &SdlEngine::OnViewportChanged);
 
       //context.GetCentralViewport().Register(sdl);  // (*)
     }
 
     context.Start();
-    sdl.Run();
+    sdl->Run();
 
     LOG(WARNING) << "Stopping the application";
 

--- a/Applications/Sdl/SdlStoneApplicationRunner.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/Sdl/SdlStoneApplicationRunner.h	Fri Nov 29 11:03:41 2019 +0100
@@ -39,9 +39,8 @@
     bool          enableOpenGl_;
     
   public:
-    SdlStoneApplicationRunner(MessageBroker& broker,
-                              IStoneApplication& application) :
-      NativeStoneApplicationRunner(broker, application)
+    SdlStoneApplicationRunner(boost::shared_ptr<IStoneApplication> application) :
+      NativeStoneApplicationRunner(application)
     {
     }
 

--- a/Applications/StoneApplicationContext.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/StoneApplicationContext.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -32,35 +32,35 @@
       throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
     }
 
-    orthanc_.reset(new Deprecated::OrthancApiClient(broker_, *webService_, orthancBaseUrl_));
+    orthanc_.reset(new Deprecated::OrthancApiClient(*webService_, orthancBaseUrl_));
   }
 
 
-  Deprecated::IWebService& StoneApplicationContext::GetWebService()
+  boost::shared_ptr<Deprecated::IWebService> StoneApplicationContext::GetWebService()
   {
     if (webService_ == NULL)
     {
       throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
     }
     
-    return *webService_;
+    return webService_;
   }
 
   
-  Deprecated::OrthancApiClient& StoneApplicationContext::GetOrthancApiClient()
+  boost::shared_ptr<Deprecated::OrthancApiClient> StoneApplicationContext::GetOrthancApiClient()
   {
     if (orthanc_.get() == NULL)
     {
       throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
     }
     
-    return *orthanc_;
+    return orthanc_;
   }
 
   
-  void StoneApplicationContext::SetWebService(Deprecated::IWebService& webService)
+  void StoneApplicationContext::SetWebService(boost::shared_ptr<Deprecated::IWebService> webService)
   {
-    webService_ = &webService;
+    webService_ = webService;
     InitializeOrthanc();
   }
 

--- a/Applications/StoneApplicationContext.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Applications/StoneApplicationContext.h	Fri Nov 29 11:03:41 2019 +0100
@@ -59,18 +59,15 @@
   class StoneApplicationContext : public boost::noncopyable
   {
   private:
-    MessageBroker&                   broker_;
-    Deprecated::IWebService*         webService_;
-    Deprecated::IDelayedCallExecutor*            delayedCallExecutor_;
-    std::auto_ptr<Deprecated::OrthancApiClient>  orthanc_;
+    boost::shared_ptr<Deprecated::IWebService>     webService_;
+    Deprecated::IDelayedCallExecutor*  delayedCallExecutor_;   // TODO => shared_ptr ??
+    boost::shared_ptr<Deprecated::OrthancApiClient>  orthanc_;
     std::string                      orthancBaseUrl_;
 
     void InitializeOrthanc();
 
   public:
-    StoneApplicationContext(MessageBroker& broker) :
-      broker_(broker),
-      webService_(NULL),
+    StoneApplicationContext() :
       delayedCallExecutor_(NULL)
     {
     }
@@ -79,21 +76,11 @@
     {
     }
 
-    MessageBroker& GetMessageBroker()
-    {
-      return broker_;
-    }
+    boost::shared_ptr<Deprecated::IWebService> GetWebService();
 
-    bool HasWebService() const
-    {
-      return webService_ != NULL;
-    }
+    boost::shared_ptr<Deprecated::OrthancApiClient> GetOrthancApiClient();
 
-    Deprecated::IWebService& GetWebService();
-
-    Deprecated::OrthancApiClient& GetOrthancApiClient();
-
-    void SetWebService(Deprecated::IWebService& webService);
+    void SetWebService(boost::shared_ptr<Deprecated::IWebService> webService);
 
     void SetOrthancBaseUrl(const std::string& baseUrl);
 

--- a/Framework/Deprecated/Layers/DicomSeriesVolumeSlicer.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Layers/DicomSeriesVolumeSlicer.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -87,59 +87,73 @@
   }
 
 
-  DicomSeriesVolumeSlicer::DicomSeriesVolumeSlicer(OrthancStone::MessageBroker& broker,
-                                                   OrthancApiClient& orthanc) :
-    IVolumeSlicer(broker),
-    IObserver(broker),
-    loader_(broker, orthanc),
+  DicomSeriesVolumeSlicer::DicomSeriesVolumeSlicer() :
     quality_(SliceImageQuality_FullPng)
   {
-    loader_.RegisterObserverCallback(
-      new OrthancStone::Callable<DicomSeriesVolumeSlicer, OrthancSlicesLoader::SliceGeometryReadyMessage>
-        (*this, &DicomSeriesVolumeSlicer::OnSliceGeometryReady));
-
-    loader_.RegisterObserverCallback(
-      new OrthancStone::Callable<DicomSeriesVolumeSlicer, OrthancSlicesLoader::SliceGeometryErrorMessage>
-      (*this, &DicomSeriesVolumeSlicer::OnSliceGeometryError));
+  }
 
-    loader_.RegisterObserverCallback(
-      new OrthancStone::Callable<DicomSeriesVolumeSlicer, OrthancSlicesLoader::SliceImageReadyMessage>
-        (*this, &DicomSeriesVolumeSlicer::OnSliceImageReady));
-
-    loader_.RegisterObserverCallback(
-      new OrthancStone::Callable<DicomSeriesVolumeSlicer, OrthancSlicesLoader::SliceImageErrorMessage>
-      (*this, &DicomSeriesVolumeSlicer::OnSliceImageError));
+  void DicomSeriesVolumeSlicer::Connect(boost::shared_ptr<OrthancApiClient> orthanc)
+  {
+    loader_.reset(new OrthancSlicesLoader(orthanc));
+    Register<OrthancSlicesLoader::SliceGeometryReadyMessage>(*loader_, &DicomSeriesVolumeSlicer::OnSliceGeometryReady);
+    Register<OrthancSlicesLoader::SliceGeometryErrorMessage>(*loader_, &DicomSeriesVolumeSlicer::OnSliceGeometryError);
+    Register<OrthancSlicesLoader::SliceImageReadyMessage>(*loader_, &DicomSeriesVolumeSlicer::OnSliceImageReady);
+    Register<OrthancSlicesLoader::SliceImageErrorMessage>(*loader_, &DicomSeriesVolumeSlicer::OnSliceImageError);
   }
 
   
   void DicomSeriesVolumeSlicer::LoadSeries(const std::string& seriesId)
   {
-    loader_.ScheduleLoadSeries(seriesId);
+    if (loader_.get() == NULL)
+    {
+      // Should have called "Connect()"
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
+    }
+    
+    loader_->ScheduleLoadSeries(seriesId);
   }
 
 
   void DicomSeriesVolumeSlicer::LoadInstance(const std::string& instanceId)
   {
-    loader_.ScheduleLoadInstance(instanceId);
+    if (loader_.get() == NULL)
+    {
+      // Should have called "Connect()"
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
+    }
+    
+    loader_->ScheduleLoadInstance(instanceId);
   }
 
 
   void DicomSeriesVolumeSlicer::LoadFrame(const std::string& instanceId,
                                           unsigned int frame)
   {
-    loader_.ScheduleLoadFrame(instanceId, frame);
+    if (loader_.get() == NULL)
+    {
+      // Should have called "Connect()"
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
+    }
+    
+    loader_->ScheduleLoadFrame(instanceId, frame);
   }
 
 
   bool DicomSeriesVolumeSlicer::GetExtent(std::vector<OrthancStone::Vector>& points,
                                           const OrthancStone::CoordinateSystem3D& viewportSlice)
   {
+    if (loader_.get() == NULL)
+    {
+      // Should have called "Connect()"
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
+    }
+    
     size_t index;
 
-    if (loader_.IsGeometryReady() &&
-        loader_.LookupSlice(index, viewportSlice))
+    if (loader_->IsGeometryReady() &&
+        loader_->LookupSlice(index, viewportSlice))
     {
-      loader_.GetSlice(index).GetExtent(points);
+      loader_->GetSlice(index).GetExtent(points);
       return true;
     }
     else
@@ -151,12 +165,18 @@
   
   void DicomSeriesVolumeSlicer::ScheduleLayerCreation(const OrthancStone::CoordinateSystem3D& viewportSlice)
   {
+    if (loader_.get() == NULL)
+    {
+      // Should have called "Connect()"
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
+    }
+    
     size_t index;
 
-    if (loader_.IsGeometryReady() &&
-        loader_.LookupSlice(index, viewportSlice))
+    if (loader_->IsGeometryReady() &&
+        loader_->LookupSlice(index, viewportSlice))
     {
-      loader_.ScheduleLoadSliceImage(index, quality_);
+      loader_->ScheduleLoadSliceImage(index, quality_);
     }
   }
 }

--- a/Framework/Deprecated/Layers/DicomSeriesVolumeSlicer.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Layers/DicomSeriesVolumeSlicer.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,6 +22,7 @@
 #pragma once
 
 #include "IVolumeSlicer.h"
+#include "../../Messages/ObserverBase.h"
 #include "../Toolbox/IWebService.h"
 #include "../Toolbox/OrthancSlicesLoader.h"
 #include "../Toolbox/OrthancApiClient.h"
@@ -33,7 +34,7 @@
   // messages are sent to observers so they can use it
   class DicomSeriesVolumeSlicer :
     public IVolumeSlicer,
-    public OrthancStone::IObserver
+    public OrthancStone::ObserverBase<DicomSeriesVolumeSlicer>
     //private OrthancSlicesLoader::ISliceLoaderObserver
   {
   public:
@@ -79,13 +80,14 @@
   private:
     class RendererFactory;
     
-    OrthancSlicesLoader  loader_;
+    boost::shared_ptr<OrthancSlicesLoader> loader_;
     SliceImageQuality    quality_;
 
   public:
-    DicomSeriesVolumeSlicer(OrthancStone::MessageBroker& broker,
-                            OrthancApiClient& orthanc);
+    DicomSeriesVolumeSlicer();
 
+    void Connect(boost::shared_ptr<OrthancApiClient> orthanc);
+    
     void LoadSeries(const std::string& seriesId);
 
     void LoadInstance(const std::string& instanceId);
@@ -105,12 +107,12 @@
 
     size_t GetSlicesCount() const
     {
-      return loader_.GetSlicesCount();
+      return loader_->GetSlicesCount();
     }
 
     const Slice& GetSlice(size_t slice) const 
     {
-      return loader_.GetSlice(slice);
+      return loader_->GetSlice(slice);
     }
 
     virtual bool GetExtent(std::vector<OrthancStone::Vector>& points,

--- a/Framework/Deprecated/Layers/DicomStructureSetSlicer.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Layers/DicomStructureSetSlicer.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -20,6 +20,8 @@
 
 #include "DicomStructureSetSlicer.h"
 
+#include "../../Toolbox/DicomStructureSet.h"
+
 namespace Deprecated
 {
   class DicomStructureSetSlicer::Renderer : public ILayerRenderer
@@ -28,13 +30,18 @@
     class Structure
     {
     private:
-      bool                                                                   visible_;
-      uint8_t                                                                red_;
-      uint8_t                                                                green_;
-      uint8_t                                                                blue_;
-      std::string                                                            name_;
+      bool         visible_;
+      uint8_t      red_;
+      uint8_t      green_;
+      uint8_t      blue_;
+      std::string  name_;
+
+#if USE_BOOST_UNION_FOR_POLYGONS == 1
+      std::vector< std::vector<OrthancStone::Point2D> > polygons_;
+#else
       std::vector< std::pair<OrthancStone::Point2D, OrthancStone::Point2D> > segments_;
-
+#endif
+      
     public:
       Structure(OrthancStone::DicomStructureSet& structureSet,
                 const OrthancStone::CoordinateSystem3D& plane,
@@ -42,7 +49,12 @@
         name_(structureSet.GetStructureName(index))
       {
         structureSet.GetStructureColor(red_, green_, blue_, index);
+
+#if USE_BOOST_UNION_FOR_POLYGONS == 1
+        visible_ = structureSet.ProjectStructure(polygons_, index, plane);
+#else
         visible_ = structureSet.ProjectStructure(segments_, index, plane);
+#endif
       }
 
       void Render(OrthancStone::CairoContext& context)
@@ -53,12 +65,25 @@
         
           context.SetSourceColor(red_, green_, blue_);
 
+#if USE_BOOST_UNION_FOR_POLYGONS == 1
+          for (size_t i = 0; i < polygons_.size(); i++)
+          {
+            cairo_move_to(cr, polygons_[i][0].x, polygons_[i][0].y);
+            for (size_t j = 0; j < polygons_[i].size(); j++)
+            {
+              cairo_line_to(cr, polygons_[i][j].x, polygons_[i][j].y);
+            }
+            cairo_line_to(cr, polygons_[i][0].x, polygons_[i][0].y);
+            cairo_stroke(cr);
+          }
+#else
           for (size_t i = 0; i < segments_.size(); i++)
           {
             cairo_move_to(cr, segments_[i].first.x, segments_[i].first.y);
-            cairo_move_to(cr, segments_[i].second.x, segments_[i].second.y);
+            cairo_line_to(cr, segments_[i].second.x, segments_[i].second.y);
             cairo_stroke(cr);
           }
+#endif
         }
       }
     };
@@ -140,15 +165,10 @@
   };
   
 
-  DicomStructureSetSlicer::DicomStructureSetSlicer(OrthancStone::MessageBroker& broker,
-                                                   StructureSetLoader& loader) :
-    IVolumeSlicer(broker),
-    IObserver(broker),
+  DicomStructureSetSlicer::DicomStructureSetSlicer(StructureSetLoader& loader) :
     loader_(loader)
   {
-    loader_.RegisterObserverCallback(
-      new OrthancStone::Callable<DicomStructureSetSlicer, StructureSetLoader::ContentChangedMessage>
-      (*this, &DicomStructureSetSlicer::OnStructureSetLoaded));
+    Register<StructureSetLoader::ContentChangedMessage>(loader_, &DicomStructureSetSlicer::OnStructureSetLoaded);
   }
 
 

--- a/Framework/Deprecated/Layers/DicomStructureSetSlicer.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Layers/DicomStructureSetSlicer.h	Fri Nov 29 11:03:41 2019 +0100
@@ -28,7 +28,7 @@
 {
   class DicomStructureSetSlicer :
     public IVolumeSlicer,
-    public OrthancStone::IObserver
+    public OrthancStone::ObserverBase<DicomStructureSetSlicer>
   {
   private:
     class Renderer;
@@ -42,8 +42,7 @@
     }
 
   public:
-    DicomStructureSetSlicer(OrthancStone::MessageBroker& broker,
-                            StructureSetLoader& loader);
+    DicomStructureSetSlicer(StructureSetLoader& loader);
 
     virtual bool GetExtent(std::vector<OrthancStone::Vector>& points,
                            const OrthancStone::CoordinateSystem3D& viewportPlane)

--- a/Framework/Deprecated/Layers/IVolumeSlicer.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Layers/IVolumeSlicer.h	Fri Nov 29 11:03:41 2019 +0100
@@ -122,11 +122,6 @@
     };
 
 
-    IVolumeSlicer(OrthancStone::MessageBroker& broker) :
-      IObservable(broker)
-    {
-    }
-    
     virtual ~IVolumeSlicer()
     {
     }

--- a/Framework/Deprecated/SmartLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/SmartLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -21,7 +21,6 @@
 
 #include "SmartLoader.h"
 
-#include "../Messages/MessageForwarder.h"
 #include "../StoneException.h"
 #include "Core/Images/Image.h"
 #include "Core/Logging.h"
@@ -68,11 +67,6 @@
     CachedSliceStatus               status_;
 
   public:
-    CachedSlice(OrthancStone::MessageBroker& broker) :
-    IVolumeSlicer(broker)
-    {
-    }
-
     virtual ~CachedSlice()
     {
     }
@@ -106,7 +100,7 @@
 
     CachedSlice* Clone() const
     {
-      CachedSlice* output = new CachedSlice(GetBroker());
+      CachedSlice* output = new CachedSlice;
       output->sliceIndex_ = sliceIndex_;
       output->slice_.reset(slice_->Clone());
       output->image_ = image_;
@@ -119,10 +113,7 @@
   };
 
 
-  SmartLoader::SmartLoader(OrthancStone::MessageBroker& broker,  
-                           OrthancApiClient& orthancApiClient) :
-    IObservable(broker),
-    IObserver(broker),
+  SmartLoader::SmartLoader(boost::shared_ptr<OrthancApiClient> orthancApiClient) :
     imageQuality_(SliceImageQuality_FullPam),
     orthancApiClient_(orthancApiClient)
   {
@@ -140,7 +131,7 @@
     //   the messages to its observables
     // in both cases, we must be carefull about objects lifecycle !!!
 
-    std::auto_ptr<IVolumeSlicer> layerSource;
+    boost::shared_ptr<IVolumeSlicer> layerSource;
     std::string sliceKeyId = instanceId + ":" + boost::lexical_cast<std::string>(frame);
     SmartLoader::CachedSlice* cachedSlice = NULL;
 
@@ -151,22 +142,23 @@
     }
     else
     {
-      layerSource.reset(new DicomSeriesVolumeSlicer(IObserver::GetBroker(), orthancApiClient_));
+      layerSource.reset(new DicomSeriesVolumeSlicer);
+      dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->Connect(orthancApiClient_);
       dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->SetImageQuality(imageQuality_);
-      layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, IVolumeSlicer::GeometryReadyMessage>(*this, &SmartLoader::OnLayerGeometryReady));
-      layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, DicomSeriesVolumeSlicer::FrameReadyMessage>(*this, &SmartLoader::OnFrameReady));
-      layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, IVolumeSlicer::LayerReadyMessage>(*this, &SmartLoader::OnLayerReady));
+      Register<IVolumeSlicer::GeometryReadyMessage>(*layerSource, &SmartLoader::OnLayerGeometryReady);
+      Register<DicomSeriesVolumeSlicer::FrameReadyMessage>(*layerSource, &SmartLoader::OnFrameReady);
+      Register<IVolumeSlicer::LayerReadyMessage>(*layerSource, &SmartLoader::OnLayerReady);
       dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->LoadFrame(instanceId, frame);
     }
 
     // make sure that the widget registers the events before we trigger them
     if (sliceViewer.GetLayerCount() == layerIndex)
     {
-      sliceViewer.AddLayer(layerSource.release());
+      sliceViewer.AddLayer(layerSource);
     }
     else if (sliceViewer.GetLayerCount() > layerIndex)
     {
-      sliceViewer.ReplaceLayer(layerIndex, layerSource.release());
+      sliceViewer.ReplaceLayer(layerIndex, layerSource);
     }
     else
     {
@@ -190,7 +182,7 @@
 
 
     // create the slice in the cache with "empty" data
-    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice(IObserver::GetBroker()));
+    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice);
     cachedSlice->slice_.reset(new Slice(instanceId, frame));
     cachedSlice->status_ = CachedSliceStatus_ScheduledToLoad;
     std::string sliceKeyId = instanceId + ":" + boost::lexical_cast<std::string>(frame);
@@ -199,12 +191,12 @@
 
     cachedSlices_[sliceKeyId] = boost::shared_ptr<CachedSlice>(cachedSlice);
 
-    std::auto_ptr<IVolumeSlicer> layerSource(new DicomSeriesVolumeSlicer(IObserver::GetBroker(), orthancApiClient_));
-
+    std::auto_ptr<IVolumeSlicer> layerSource(new DicomSeriesVolumeSlicer);
+    dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->Connect(orthancApiClient_);
     dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->SetImageQuality(imageQuality_);
-    layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, IVolumeSlicer::GeometryReadyMessage>(*this, &SmartLoader::OnLayerGeometryReady));
-    layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, DicomSeriesVolumeSlicer::FrameReadyMessage>(*this, &SmartLoader::OnFrameReady));
-    layerSource->RegisterObserverCallback(new OrthancStone::Callable<SmartLoader, IVolumeSlicer::LayerReadyMessage>(*this, &SmartLoader::OnLayerReady));
+    Register<IVolumeSlicer::GeometryReadyMessage>(*layerSource, &SmartLoader::OnLayerGeometryReady);
+    Register<DicomSeriesVolumeSlicer::FrameReadyMessage>(*layerSource, &SmartLoader::OnFrameReady);
+    Register<IVolumeSlicer::LayerReadyMessage>(*layerSource, &SmartLoader::OnLayerReady);
     dynamic_cast<DicomSeriesVolumeSlicer*>(layerSource.get())->LoadFrame(instanceId, frame);
 
     // keep a ref to the VolumeSlicer until the slice is fully loaded and saved to cache
@@ -235,7 +227,7 @@
 
     LOG(WARNING) << "Geometry ready: " << sliceKeyId;
 
-    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice(IObserver::GetBroker()));
+    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice);
     cachedSlice->slice_.reset(slice.Clone());
     cachedSlice->effectiveQuality_ = source.GetImageQuality();
     cachedSlice->status_ = CachedSliceStatus_GeometryLoaded;
@@ -256,7 +248,7 @@
 
     LOG(WARNING) << "Image ready: " << sliceKeyId;
 
-    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice(IObserver::GetBroker()));
+    boost::shared_ptr<CachedSlice> cachedSlice(new CachedSlice);
     cachedSlice->image_.reset(Orthanc::Image::Clone(message.GetFrame()));
     cachedSlice->effectiveQuality_ = message.GetImageQuality();
     cachedSlice->slice_.reset(message.GetSlice().Clone());

--- a/Framework/Deprecated/SmartLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/SmartLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -30,7 +30,7 @@
 {
   class SliceViewerWidget;
 
-  class SmartLoader : public OrthancStone::IObservable, public OrthancStone::IObserver
+  class SmartLoader : public OrthancStone::IObservable, public OrthancStone::ObserverBase<SmartLoader>
   {
     class CachedSlice;
 
@@ -42,10 +42,10 @@
     PreloadingInstances preloadingInstances_;
 
     SliceImageQuality     imageQuality_;
-    OrthancApiClient&     orthancApiClient_;
+    boost::shared_ptr<OrthancApiClient>  orthancApiClient_;
 
   public:
-    SmartLoader(OrthancStone::MessageBroker& broker, OrthancApiClient& orthancApiClient);  // TODO: add maxPreloadStorageSizeInBytes
+    SmartLoader(boost::shared_ptr<OrthancApiClient> orthancApiClient);  // TODO: add maxPreloadStorageSizeInBytes
 
 //    void PreloadStudy(const std::string studyId);
 //    void PreloadSeries(const std::string seriesId);

--- a/Framework/Deprecated/Toolbox/BaseWebService.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/BaseWebService.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -97,9 +97,9 @@
       GetAsyncInternal(uri, headers,
                        new BaseWebService::BaseWebServicePayload(successCallback, failureCallback, payload), // ownership is transfered
                        new OrthancStone::Callable<BaseWebService, IWebService::HttpRequestSuccessMessage>
-                       (*this, &BaseWebService::CacheAndNotifyHttpSuccess),
+                       (GetSharedObserver(), &BaseWebService::CacheAndNotifyHttpSuccess),
                        new OrthancStone::Callable<BaseWebService, IWebService::HttpRequestErrorMessage>
-                       (*this, &BaseWebService::NotifyHttpError),
+                       (GetSharedObserver(), &BaseWebService::NotifyHttpError),
                        timeoutInSeconds);
     }
     else

--- a/Framework/Deprecated/Toolbox/BaseWebService.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/BaseWebService.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,6 +22,7 @@
 #pragma once
 
 #include "IWebService.h"
+#include "../../Messages/ObserverBase.h"
 
 #include <string>
 #include <map>
@@ -31,7 +32,7 @@
 {
   // This is an intermediate of IWebService that implements some caching on
   // the HTTP GET requests
-  class BaseWebService : public IWebService, public OrthancStone::IObserver
+  class BaseWebService : public IWebService, public OrthancStone::ObserverBase<BaseWebService>
   {
   public:
     class CachedHttpRequestSuccessMessage
@@ -90,10 +91,7 @@
     std::deque<std::string> orderedCacheKeys_;
 
   public:
-
-    BaseWebService(OrthancStone::MessageBroker& broker) :
-      IWebService(broker),
-      IObserver(broker),
+    BaseWebService() :
       cacheEnabled_(false),
       cacheCurrentSize_(0),
       cacheMaxSize_(100*1024*1024)

--- a/Framework/Deprecated/Toolbox/IDelayedCallExecutor.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/IDelayedCallExecutor.h	Fri Nov 29 11:03:41 2019 +0100
@@ -35,22 +35,12 @@
   // The IDelayedCall executes a callback after a delay (equivalent to timeout() function in javascript).
   class IDelayedCallExecutor : public boost::noncopyable
   {
-  protected:
-    OrthancStone::MessageBroker& broker_;
-    
   public:
     ORTHANC_STONE_DEFINE_EMPTY_MESSAGE(__FILE__, __LINE__, TimeoutMessage);
 
-    IDelayedCallExecutor(OrthancStone::MessageBroker& broker) :
-      broker_(broker)
-    {
-    }
-
-    
     virtual ~IDelayedCallExecutor()
     {
     }
-
     
     virtual void Schedule(OrthancStone::MessageHandler<IDelayedCallExecutor::TimeoutMessage>* callback,
                           unsigned int timeoutInMs = 1000) = 0;

--- a/Framework/Deprecated/Toolbox/IWebService.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/IWebService.h	Fri Nov 29 11:03:41 2019 +0100
@@ -40,9 +40,6 @@
   // and you'll be notified when the response/error is ready.
   class IWebService : public boost::noncopyable
   {
-  protected:
-    OrthancStone::MessageBroker& broker_;
-    
   public:
     typedef std::map<std::string, std::string> HttpHeaders;
 
@@ -138,12 +135,6 @@
     };
 
 
-    IWebService(OrthancStone::MessageBroker& broker) :
-      broker_(broker)
-    {
-    }
-
-    
     virtual ~IWebService()
     {
     }

--- a/Framework/Deprecated/Toolbox/OrthancApiClient.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/OrthancApiClient.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -73,7 +73,6 @@
     std::auto_ptr< OrthancStone::MessageHandler<BinaryResponseReadyMessage> >            binaryHandler_;
     std::auto_ptr< OrthancStone::MessageHandler<IWebService::HttpRequestErrorMessage> >  failureHandler_;
     std::auto_ptr< Orthanc::IDynamicObject >                               userPayload_;
-    OrthancStone::MessageBroker&                                                         broker_;
     void NotifyConversionError(const IWebService::HttpRequestSuccessMessage& message) const
     {
       if (failureHandler_.get() != NULL)
@@ -84,14 +83,12 @@
     }
     
   public:
-    WebServicePayload(OrthancStone::MessageBroker& broker,
-                      OrthancStone::MessageHandler<EmptyResponseReadyMessage>* handler,
+    WebServicePayload(OrthancStone::MessageHandler<EmptyResponseReadyMessage>* handler,
                       OrthancStone::MessageHandler<IWebService::HttpRequestErrorMessage>* failureHandler,
                       Orthanc::IDynamicObject* userPayload) :
       emptyHandler_(handler),
       failureHandler_(failureHandler),
-      userPayload_(userPayload),
-      broker_(broker)
+      userPayload_(userPayload)
 
     {
       if (handler == NULL)
@@ -100,14 +97,12 @@
       }
     }
 
-    WebServicePayload(OrthancStone::MessageBroker& broker,
-                      OrthancStone::MessageHandler<BinaryResponseReadyMessage>* handler,
+    WebServicePayload(OrthancStone::MessageHandler<BinaryResponseReadyMessage>* handler,
                       OrthancStone::MessageHandler<IWebService::HttpRequestErrorMessage>* failureHandler,
                       Orthanc::IDynamicObject* userPayload) :
       binaryHandler_(handler),
       failureHandler_(failureHandler),
-      userPayload_(userPayload),
-      broker_(broker)
+      userPayload_(userPayload)
     {
       if (handler == NULL)
       {
@@ -115,14 +110,12 @@
       }
     }
 
-    WebServicePayload(OrthancStone::MessageBroker& broker,
-                      OrthancStone::MessageHandler<JsonResponseReadyMessage>* handler,
+    WebServicePayload(OrthancStone::MessageHandler<JsonResponseReadyMessage>* handler,
                       OrthancStone::MessageHandler<IWebService::HttpRequestErrorMessage>* failureHandler,
                       Orthanc::IDynamicObject* userPayload) :
       jsonHandler_(handler),
       failureHandler_(failureHandler),
-      userPayload_(userPayload),
-      broker_(broker)
+      userPayload_(userPayload)
     {
       if (handler == NULL)
       {
@@ -134,35 +127,26 @@
     {
       if (emptyHandler_.get() != NULL)
       {
-        if (broker_.IsActive(*(emptyHandler_->GetObserver())))
-        {
-          emptyHandler_->Apply(OrthancApiClient::EmptyResponseReadyMessage
-                               (message.GetUri(), userPayload_.get()));
-        }
+        emptyHandler_->Apply(OrthancApiClient::EmptyResponseReadyMessage
+                             (message.GetUri(), userPayload_.get()));
       }
       else if (binaryHandler_.get() != NULL)
       {
-        if (broker_.IsActive(*(binaryHandler_->GetObserver())))
-        {
-          binaryHandler_->Apply(OrthancApiClient::BinaryResponseReadyMessage
-                                (message.GetUri(), message.GetAnswer(),
-                                 message.GetAnswerSize(), userPayload_.get()));
-        }
+        binaryHandler_->Apply(OrthancApiClient::BinaryResponseReadyMessage
+                              (message.GetUri(), message.GetAnswer(),
+                               message.GetAnswerSize(), userPayload_.get()));
       }
       else if (jsonHandler_.get() != NULL)
       {
-        if (broker_.IsActive(*(jsonHandler_->GetObserver())))
+        Json::Value response;
+        if (MessagingToolbox::ParseJson(response, message.GetAnswer(), message.GetAnswerSize()))
         {
-          Json::Value response;
-          if (MessagingToolbox::ParseJson(response, message.GetAnswer(), message.GetAnswerSize()))
-          {
-            jsonHandler_->Apply(OrthancApiClient::JsonResponseReadyMessage
-                                (message.GetUri(), response, userPayload_.get()));
-          }
-          else
-          {
-            NotifyConversionError(message);
-          }
+          jsonHandler_->Apply(OrthancApiClient::JsonResponseReadyMessage
+                              (message.GetUri(), response, userPayload_.get()));
+        }
+        else
+        {
+          NotifyConversionError(message);
         }
       }
       else
@@ -182,11 +166,8 @@
   };
 
 
-  OrthancApiClient::OrthancApiClient(OrthancStone::MessageBroker& broker,
-                                     IWebService& web,
+  OrthancApiClient::OrthancApiClient(IWebService& web,
                                      const std::string& baseUrl) :
-    IObservable(broker),
-    IObserver(broker),
     web_(web),
     baseUrl_(baseUrl)
   {
@@ -202,11 +183,11 @@
     IWebService::HttpHeaders emptyHeaders;
     web_.GetAsync(baseUrl_ + uri,
                   emptyHeaders,
-                  new WebServicePayload(IObservable::GetBroker(), successCallback, failureCallback, payload),
+                  new WebServicePayload(successCallback, failureCallback, payload),
                   new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestSuccessMessage>
-                  (*this, &OrthancApiClient::NotifyHttpSuccess),
+                  (GetSharedObserver(), &OrthancApiClient::NotifyHttpSuccess),
                   new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestErrorMessage>
-                  (*this, &OrthancApiClient::NotifyHttpError));
+                  (GetSharedObserver(), &OrthancApiClient::NotifyHttpError));
   }
 
 
@@ -232,11 +213,11 @@
     // printf("GET [%s] [%s]\n", baseUrl_.c_str(), uri.c_str());
 
     web_.GetAsync(baseUrl_ + uri, headers,
-                  new WebServicePayload(IObservable::GetBroker(), successCallback, failureCallback, payload),
+                  new WebServicePayload(successCallback, failureCallback, payload),
                   new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestSuccessMessage>
-                  (*this, &OrthancApiClient::NotifyHttpSuccess),
+                  (GetSharedObserver(), &OrthancApiClient::NotifyHttpSuccess),
                   new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestErrorMessage>
-                  (*this, &OrthancApiClient::NotifyHttpError));
+                  (GetSharedObserver(), &OrthancApiClient::NotifyHttpError));
   }
 
   
@@ -248,11 +229,11 @@
       Orthanc::IDynamicObject* payload)
   {
     web_.PostAsync(baseUrl_ + uri, IWebService::HttpHeaders(), body,
-                   new WebServicePayload(IObservable::GetBroker(), successCallback, failureCallback, payload),
+                   new WebServicePayload(successCallback, failureCallback, payload),
                    new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestSuccessMessage>
-                   (*this, &OrthancApiClient::NotifyHttpSuccess),
+                   (GetSharedObserver(), &OrthancApiClient::NotifyHttpSuccess),
                    new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestErrorMessage>
-                   (*this, &OrthancApiClient::NotifyHttpError));
+                   (GetSharedObserver(), &OrthancApiClient::NotifyHttpError));
 
   }
 
@@ -271,11 +252,11 @@
       Orthanc::IDynamicObject* payload   /* takes ownership */)
   {
     web_.PostAsync(baseUrl_ + uri, IWebService::HttpHeaders(), body,
-                   new WebServicePayload(IObservable::GetBroker(), successCallback, failureCallback, payload),
+                   new WebServicePayload(successCallback, failureCallback, payload),
                    new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestSuccessMessage>
-                   (*this, &OrthancApiClient::NotifyHttpSuccess),
+                   (GetSharedObserver(), &OrthancApiClient::NotifyHttpSuccess),
                    new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestErrorMessage>
-                   (*this, &OrthancApiClient::NotifyHttpError));
+                   (GetSharedObserver(), &OrthancApiClient::NotifyHttpError));
   }
 
   void OrthancApiClient::PostJsonAsyncExpectJson(
@@ -318,11 +299,11 @@
       Orthanc::IDynamicObject* payload)
   {
     web_.DeleteAsync(baseUrl_ + uri, IWebService::HttpHeaders(),
-                     new WebServicePayload(IObservable::GetBroker(), successCallback, failureCallback, payload),
+                     new WebServicePayload(successCallback, failureCallback, payload),
                      new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestSuccessMessage>
-                     (*this, &OrthancApiClient::NotifyHttpSuccess),
+                     (GetSharedObserver(), &OrthancApiClient::NotifyHttpSuccess),
                      new OrthancStone::Callable<OrthancApiClient, IWebService::HttpRequestErrorMessage>
-                     (*this, &OrthancApiClient::NotifyHttpError));
+                     (GetSharedObserver(), &OrthancApiClient::NotifyHttpError));
   }
 
 

--- a/Framework/Deprecated/Toolbox/OrthancApiClient.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/OrthancApiClient.h	Fri Nov 29 11:03:41 2019 +0100
@@ -25,13 +25,13 @@
 #include <json/json.h>
 
 #include "IWebService.h"
-#include "../../Messages/IObservable.h"
+#include "../../Messages/ObserverBase.h"
 
 namespace Deprecated
 {
   class OrthancApiClient :
       public OrthancStone::IObservable,
-      public OrthancStone::IObserver
+      public OrthancStone::ObserverBase<OrthancApiClient>
   {
   public:
     class JsonResponseReadyMessage : public OrthancStone::IMessage
@@ -157,8 +157,7 @@
     std::string   baseUrl_;
 
   public:
-    OrthancApiClient(OrthancStone::MessageBroker& broker,
-                     IWebService& web,
+    OrthancApiClient(IWebService& web,
                      const std::string& baseUrl);
     
     virtual ~OrthancApiClient()

--- a/Framework/Deprecated/Toolbox/OrthancSlicesLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/OrthancSlicesLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -639,10 +639,7 @@
   }
   
   
-  OrthancSlicesLoader::OrthancSlicesLoader(OrthancStone::MessageBroker& broker,
-                                           OrthancApiClient& orthanc) :
-    OrthancStone::IObservable(broker),
-    OrthancStone::IObserver(broker),
+  OrthancSlicesLoader::OrthancSlicesLoader(boost::shared_ptr<OrthancApiClient> orthanc) :
     orthanc_(orthanc),
     state_(State_Initialization)
   {
@@ -658,10 +655,10 @@
     else
     {
       state_ = State_LoadingGeometry;
-      orthanc_.GetJsonAsync("/series/" + seriesId + "/instances-tags",
-                            new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &OrthancSlicesLoader::ParseSeriesGeometry),
-                            new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(*this, &OrthancSlicesLoader::OnGeometryError),
-                            NULL);
+      orthanc_->GetJsonAsync("/series/" + seriesId + "/instances-tags",
+                             new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &OrthancSlicesLoader::ParseSeriesGeometry),
+                             new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(GetSharedObserver(), &OrthancSlicesLoader::OnGeometryError),
+                             NULL);
     }
   }
   
@@ -677,10 +674,10 @@
       
       // Tag "3004-000c" is "Grid Frame Offset Vector", which is
       // mandatory to read RT DOSE, but is too long to be returned by default
-      orthanc_.GetJsonAsync("/instances/" + instanceId + "/tags?ignore-length=3004-000c",
-                            new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &OrthancSlicesLoader::ParseInstanceGeometry),
-                            new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(*this, &OrthancSlicesLoader::OnGeometryError),
-                            Operation::DownloadInstanceGeometry(instanceId));
+      orthanc_->GetJsonAsync("/instances/" + instanceId + "/tags?ignore-length=3004-000c",
+                             new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &OrthancSlicesLoader::ParseInstanceGeometry),
+                             new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(GetSharedObserver(), &OrthancSlicesLoader::OnGeometryError),
+                             Operation::DownloadInstanceGeometry(instanceId));
     }
   }
   
@@ -696,10 +693,10 @@
     {
       state_ = State_LoadingGeometry;
 
-      orthanc_.GetJsonAsync("/instances/" + instanceId + "/tags",
-                            new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &OrthancSlicesLoader::ParseFrameGeometry),
-                            new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(*this, &OrthancSlicesLoader::OnGeometryError),
-                            Operation::DownloadFrameGeometry(instanceId, frame));
+      orthanc_->GetJsonAsync("/instances/" + instanceId + "/tags",
+                             new OrthancStone::Callable<OrthancSlicesLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &OrthancSlicesLoader::ParseFrameGeometry),
+                             new OrthancStone::Callable<OrthancSlicesLoader, IWebService::HttpRequestErrorMessage>(GetSharedObserver(), &OrthancSlicesLoader::OnGeometryError),
+                             Operation::DownloadFrameGeometry(instanceId, frame));
     }
   }
   
@@ -770,23 +767,23 @@
         throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
     }
     
-    orthanc_.GetBinaryAsync(uri, "image/png",
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        OrthancApiClient::BinaryResponseReadyMessage>
-          (*this, &OrthancSlicesLoader::ParseSliceImagePng),
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        IWebService::HttpRequestErrorMessage>
-          (*this, &OrthancSlicesLoader::OnSliceImageError),
-      Operation::DownloadSliceImage(
-        static_cast<unsigned int>(index), slice, SliceImageQuality_FullPng));
-}
+    orthanc_->GetBinaryAsync(uri, "image/png",
+                             new OrthancStone::Callable<OrthancSlicesLoader, 
+                             OrthancApiClient::BinaryResponseReadyMessage>
+                             (GetSharedObserver(), &OrthancSlicesLoader::ParseSliceImagePng),
+                             new OrthancStone::Callable<OrthancSlicesLoader, 
+                             IWebService::HttpRequestErrorMessage>
+                             (GetSharedObserver(), &OrthancSlicesLoader::OnSliceImageError),
+                             Operation::DownloadSliceImage(
+                               static_cast<unsigned int>(index), slice, SliceImageQuality_FullPng));
+  }
   
   void OrthancSlicesLoader::ScheduleSliceImagePam(const Slice& slice,
                                                   size_t index)
   {
     std::string uri = 
       ("/instances/" + slice.GetOrthancInstanceId() + "/frames/" +
-      boost::lexical_cast<std::string>(slice.GetFrame()));
+       boost::lexical_cast<std::string>(slice.GetFrame()));
 
     switch (slice.GetConverter().GetExpectedPixelFormat())
     {
@@ -806,15 +803,15 @@
         throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
     }
 
-    orthanc_.GetBinaryAsync(uri, "image/x-portable-arbitrarymap",
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        OrthancApiClient::BinaryResponseReadyMessage>
-          (*this, &OrthancSlicesLoader::ParseSliceImagePam),
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        IWebService::HttpRequestErrorMessage>
-          (*this, &OrthancSlicesLoader::OnSliceImageError),
-      Operation::DownloadSliceImage(static_cast<unsigned int>(index), 
-                                    slice, SliceImageQuality_FullPam));
+    orthanc_->GetBinaryAsync(uri, "image/x-portable-arbitrarymap",
+                             new OrthancStone::Callable<OrthancSlicesLoader, 
+                             OrthancApiClient::BinaryResponseReadyMessage>
+                             (GetSharedObserver(), &OrthancSlicesLoader::ParseSliceImagePam),
+                             new OrthancStone::Callable<OrthancSlicesLoader, 
+                             IWebService::HttpRequestErrorMessage>
+                             (GetSharedObserver(), &OrthancSlicesLoader::OnSliceImageError),
+                             Operation::DownloadSliceImage(static_cast<unsigned int>(index), 
+                                                           slice, SliceImageQuality_FullPam));
   }
 
 
@@ -849,15 +846,15 @@
                        "-" + slice.GetOrthancInstanceId() + "_" +
                        boost::lexical_cast<std::string>(slice.GetFrame()));
 
-    orthanc_.GetJsonAsync(uri,
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        OrthancApiClient::JsonResponseReadyMessage>
-          (*this, &OrthancSlicesLoader::ParseSliceImageJpeg),
-      new OrthancStone::Callable<OrthancSlicesLoader, 
-        IWebService::HttpRequestErrorMessage>
-          (*this, &OrthancSlicesLoader::OnSliceImageError),
-        Operation::DownloadSliceImage(
-          static_cast<unsigned int>(index), slice, quality));
+    orthanc_->GetJsonAsync(uri,
+                           new OrthancStone::Callable<OrthancSlicesLoader, 
+                           OrthancApiClient::JsonResponseReadyMessage>
+                           (GetSharedObserver(), &OrthancSlicesLoader::ParseSliceImageJpeg),
+                           new OrthancStone::Callable<OrthancSlicesLoader, 
+                           IWebService::HttpRequestErrorMessage>
+                           (GetSharedObserver(), &OrthancSlicesLoader::OnSliceImageError),
+                           Operation::DownloadSliceImage(
+                             static_cast<unsigned int>(index), slice, quality));
   }
   
   
@@ -890,15 +887,15 @@
     {
       std::string uri = ("/instances/" + slice.GetOrthancInstanceId() + "/frames/" +
                          boost::lexical_cast<std::string>(slice.GetFrame()) + "/raw.gz");
-      orthanc_.GetBinaryAsync(uri, IWebService::HttpHeaders(),
-        new OrthancStone::Callable<OrthancSlicesLoader, 
-          OrthancApiClient::BinaryResponseReadyMessage>
-            (*this, &OrthancSlicesLoader::ParseSliceRawImage),
-        new OrthancStone::Callable<OrthancSlicesLoader,
-          IWebService::HttpRequestErrorMessage>
-            (*this, &OrthancSlicesLoader::OnSliceImageError),
-        Operation::DownloadSliceRawImage(
-          static_cast<unsigned int>(index), slice));
+      orthanc_->GetBinaryAsync(uri, IWebService::HttpHeaders(),
+                               new OrthancStone::Callable<OrthancSlicesLoader, 
+                               OrthancApiClient::BinaryResponseReadyMessage>
+                               (GetSharedObserver(), &OrthancSlicesLoader::ParseSliceRawImage),
+                               new OrthancStone::Callable<OrthancSlicesLoader,
+                               IWebService::HttpRequestErrorMessage>
+                               (GetSharedObserver(), &OrthancSlicesLoader::OnSliceImageError),
+                               Operation::DownloadSliceRawImage(
+                                 static_cast<unsigned int>(index), slice));
     }
   }
 }

--- a/Framework/Deprecated/Toolbox/OrthancSlicesLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Toolbox/OrthancSlicesLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,6 +22,7 @@
 #pragma once
 
 #include "../../Messages/IObservable.h"
+#include "../../Messages/ObserverBase.h"
 #include "../../StoneEnumerations.h"
 #include "../../Toolbox/SlicesSorter.h"
 #include "IWebService.h"
@@ -33,7 +34,9 @@
 
 namespace Deprecated
 {
-  class OrthancSlicesLoader : public OrthancStone::IObservable, public OrthancStone::IObserver
+  class OrthancSlicesLoader :
+    public OrthancStone::IObservable,
+    public OrthancStone::ObserverBase<OrthancSlicesLoader>
   {
   public:
     ORTHANC_STONE_DEFINE_ORIGIN_MESSAGE(__FILE__, __LINE__, SliceGeometryReadyMessage, OrthancSlicesLoader);
@@ -143,7 +146,7 @@
 
     class Operation;
 
-    OrthancApiClient&  orthanc_;
+    boost::shared_ptr<OrthancApiClient>  orthanc_;
     State         state_;
     OrthancStone::SlicesSorter  slices_;
 
@@ -183,9 +186,8 @@
     void SortAndFinalizeSlices();
     
   public:
-    OrthancSlicesLoader(OrthancStone::MessageBroker& broker,
-                        //ISliceLoaderObserver& callback,
-                        OrthancApiClient& orthancApi);
+    OrthancSlicesLoader(//ISliceLoaderObserver& callback,
+      boost::shared_ptr<OrthancApiClient> orthancApi);
 
     void ScheduleLoadSeries(const std::string& seriesId);
 

--- a/Framework/Deprecated/Viewport/IViewport.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Viewport/IViewport.h	Fri Nov 29 11:03:41 2019 +0100
@@ -37,15 +37,6 @@
   public:
     ORTHANC_STONE_DEFINE_ORIGIN_MESSAGE(__FILE__, __LINE__, ViewportChangedMessage, IViewport);
 
-    IViewport(OrthancStone::MessageBroker& broker) :
-      IObservable(broker)
-    {
-    }
-    
-    virtual ~IViewport()
-    {
-    }
-
     virtual void FitContent() = 0;
 
     virtual void SetStatusBar(IStatusBar& statusBar) = 0;

--- a/Framework/Deprecated/Viewport/WidgetViewport.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Viewport/WidgetViewport.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -26,8 +26,7 @@
 
 namespace Deprecated
 {
-  WidgetViewport::WidgetViewport(OrthancStone::MessageBroker& broker) :
-    IViewport(broker),
+  WidgetViewport::WidgetViewport() :
     statusBar_(NULL),
     isMouseOver_(false),
     lastMouseX_(0),
@@ -57,7 +56,7 @@
   }
 
 
-  IWidget& WidgetViewport::SetCentralWidget(IWidget* widget)
+  void WidgetViewport::SetCentralWidget(boost::shared_ptr<IWidget> widget)
   {
     if (widget == NULL)
     {
@@ -66,7 +65,7 @@
 
     mouseTracker_.reset(NULL);
 
-    centralWidget_.reset(widget);
+    centralWidget_ = widget;
     centralWidget_->SetViewport(*this);
 
     if (statusBar_ != NULL)
@@ -75,8 +74,6 @@
     }
 
     NotifyBackgroundChanged();
-
-    return *widget;
   }
 
 

--- a/Framework/Deprecated/Viewport/WidgetViewport.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Viewport/WidgetViewport.h	Fri Nov 29 11:03:41 2019 +0100
@@ -31,7 +31,7 @@
   class WidgetViewport : public IViewport
   {
   private:
-    std::auto_ptr<IWidget>        centralWidget_;
+    boost::shared_ptr<IWidget>    centralWidget_;
     IStatusBar*                   statusBar_;
     std::auto_ptr<IMouseTracker>  mouseTracker_;
     bool                          isMouseOver_;
@@ -41,13 +41,13 @@
     bool                          backgroundChanged_;
 
   public:
-    WidgetViewport(OrthancStone::MessageBroker& broker);
+    WidgetViewport();
 
     virtual void FitContent();
 
     virtual void SetStatusBar(IStatusBar& statusBar);
 
-    IWidget& SetCentralWidget(IWidget* widget);  // Takes ownership
+    void SetCentralWidget(boost::shared_ptr<IWidget> widget);
 
     virtual void NotifyBackgroundChanged();
 

--- a/Framework/Deprecated/Volumes/ISlicedVolume.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Volumes/ISlicedVolume.h	Fri Nov 29 11:03:41 2019 +0100
@@ -65,11 +65,6 @@
     };
 
 
-    ISlicedVolume(OrthancStone::MessageBroker& broker) :
-      IObservable(broker)
-    {
-    }
-    
     virtual size_t GetSliceCount() const = 0;
 
     virtual const Slice& GetSlice(size_t slice) const = 0;

--- a/Framework/Deprecated/Volumes/IVolumeLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Volumes/IVolumeLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -31,10 +31,5 @@
     ORTHANC_STONE_DEFINE_ORIGIN_MESSAGE(__FILE__, __LINE__, GeometryReadyMessage, IVolumeLoader);
     ORTHANC_STONE_DEFINE_ORIGIN_MESSAGE(__FILE__, __LINE__, GeometryErrorMessage, IVolumeLoader);
     ORTHANC_STONE_DEFINE_ORIGIN_MESSAGE(__FILE__, __LINE__, ContentChangedMessage, IVolumeLoader);
-
-    IVolumeLoader(OrthancStone::MessageBroker& broker) :
-      IObservable(broker)
-    {
-    }
   };
 }

--- a/Framework/Deprecated/Volumes/StructureSetLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Volumes/StructureSetLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -27,10 +27,7 @@
 
 namespace Deprecated
 {
-  StructureSetLoader::StructureSetLoader(OrthancStone::MessageBroker& broker,
-                                         OrthancApiClient& orthanc) :
-    IVolumeLoader(broker),
-    IObserver(broker),
+  StructureSetLoader::StructureSetLoader(OrthancApiClient& orthanc) :
     orthanc_(orthanc)
   {
   }
@@ -60,7 +57,7 @@
          it != instances.end(); ++it)
     {
       orthanc_.PostBinaryAsyncExpectJson("/tools/lookup", *it,
-                                         new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &StructureSetLoader::OnLookupCompleted));
+                                         new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &StructureSetLoader::OnLookupCompleted));
     }
 
     BroadcastMessage(GeometryReadyMessage(*this));
@@ -84,7 +81,7 @@
 
     const std::string& instance = lookup[0]["ID"].asString();
     orthanc_.GetJsonAsync("/instances/" + instance + "/tags",
-                          new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &StructureSetLoader::OnReferencedSliceLoaded));
+                          new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &StructureSetLoader::OnReferencedSliceLoaded));
   }
 
   
@@ -97,7 +94,7 @@
     else
     {
       orthanc_.GetJsonAsync("/instances/" + instance + "/tags?ignore-length=3006-0050",
-                            new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(*this, &StructureSetLoader::OnStructureSetLoaded));
+                            new OrthancStone::Callable<StructureSetLoader, OrthancApiClient::JsonResponseReadyMessage>(GetSharedObserver(), &StructureSetLoader::OnStructureSetLoaded));
     }
   }
 

--- a/Framework/Deprecated/Volumes/StructureSetLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Volumes/StructureSetLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include "../../Messages/ObserverBase.h"
 #include "../../Toolbox/DicomStructureSet.h"
 #include "../Toolbox/OrthancApiClient.h"
 #include "IVolumeLoader.h"
@@ -29,7 +30,7 @@
 {
   class StructureSetLoader :
     public IVolumeLoader,
-    public OrthancStone::IObserver
+    public OrthancStone::ObserverBase<StructureSetLoader>
   {
   private:
     OrthancApiClient&                 orthanc_;
@@ -42,8 +43,7 @@
     void OnLookupCompleted(const OrthancApiClient::JsonResponseReadyMessage& message);
 
   public:
-    StructureSetLoader(OrthancStone::MessageBroker& broker,
-                       OrthancApiClient& orthanc);
+    StructureSetLoader(OrthancApiClient& orthanc);
 
     void ScheduleLoadInstance(const std::string& instance);
 

--- a/Framework/Deprecated/Widgets/LayoutWidget.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Widgets/LayoutWidget.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -85,14 +85,14 @@
   class LayoutWidget::ChildWidget : public boost::noncopyable
   {
   private:
-    std::auto_ptr<IWidget>  widget_;
+    boost::shared_ptr<IWidget>  widget_;
     int                     left_;
     int                     top_;
     unsigned int            width_;
     unsigned int            height_;
 
   public:
-    ChildWidget(IWidget* widget) :
+    ChildWidget(boost::shared_ptr<IWidget> widget) :
       widget_(widget)
     {
       assert(widget != NULL);
@@ -354,7 +354,7 @@
   }
 
 
-  IWidget& LayoutWidget::AddWidget(IWidget* widget)  // Takes ownership
+  void LayoutWidget::AddWidget(boost::shared_ptr<IWidget> widget)  // Takes ownership
   {
     if (widget == NULL)
     {
@@ -375,8 +375,6 @@
     {
       hasAnimation_ = true;
     }
-
-    return *widget;
   }
 
 

--- a/Framework/Deprecated/Widgets/LayoutWidget.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Widgets/LayoutWidget.h	Fri Nov 29 11:03:41 2019 +0100
@@ -94,7 +94,7 @@
       return paddingInternal_;
     }
 
-    IWidget& AddWidget(IWidget* widget);  // Takes ownership
+    void AddWidget(boost::shared_ptr<IWidget> widget);
 
     virtual void SetStatusBar(IStatusBar& statusBar);
 

--- a/Framework/Deprecated/Widgets/SliceViewerWidget.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Widgets/SliceViewerWidget.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -250,7 +250,7 @@
     {
       index = found->second;
       assert(index < layers_.size() &&
-             layers_[index] == &layer);
+             layers_[index].get() == &layer);
       return true;
     }
   }
@@ -364,42 +364,27 @@
   }
 
   
-  SliceViewerWidget::SliceViewerWidget(OrthancStone::MessageBroker& broker, 
-                                       const std::string& name) :
+  SliceViewerWidget::SliceViewerWidget(const std::string& name) :
     WorldSceneWidget(name),
-    IObserver(broker),
-    IObservable(broker),
     started_(false)
   {
     SetBackgroundCleared(true);
   }
   
   
-  SliceViewerWidget::~SliceViewerWidget()
-  {
-    for (size_t i = 0; i < layers_.size(); i++)
-    {
-      delete layers_[i];
-    }
-  }
-  
   void SliceViewerWidget::ObserveLayer(IVolumeSlicer& layer)
   {
-    layer.RegisterObserverCallback(new OrthancStone::Callable<SliceViewerWidget, IVolumeSlicer::GeometryReadyMessage>
-                                   (*this, &SliceViewerWidget::OnGeometryReady));
-    // currently ignore errors layer->RegisterObserverCallback(new Callable<SliceViewerWidget, IVolumeSlicer::GeometryErrorMessage>(*this, &SliceViewerWidget::...));
-    layer.RegisterObserverCallback(new OrthancStone::Callable<SliceViewerWidget, IVolumeSlicer::SliceContentChangedMessage>
-                                   (*this, &SliceViewerWidget::OnSliceChanged));
-    layer.RegisterObserverCallback(new OrthancStone::Callable<SliceViewerWidget, IVolumeSlicer::ContentChangedMessage>
-                                   (*this, &SliceViewerWidget::OnContentChanged));
-    layer.RegisterObserverCallback(new OrthancStone::Callable<SliceViewerWidget, IVolumeSlicer::LayerReadyMessage>
-                                   (*this, &SliceViewerWidget::OnLayerReady));
-    layer.RegisterObserverCallback(new OrthancStone::Callable<SliceViewerWidget, IVolumeSlicer::LayerErrorMessage>
-                                   (*this, &SliceViewerWidget::OnLayerError));
+    // currently ignoring errors of type IVolumeSlicer::GeometryErrorMessage
+
+    Register<IVolumeSlicer::GeometryReadyMessage>(layer, &SliceViewerWidget::OnGeometryReady);
+    Register<IVolumeSlicer::SliceContentChangedMessage>(layer, &SliceViewerWidget::OnSliceChanged);
+    Register<IVolumeSlicer::ContentChangedMessage>(layer, &SliceViewerWidget::OnContentChanged);
+    Register<IVolumeSlicer::LayerReadyMessage>(layer, &SliceViewerWidget::OnLayerReady);
+    Register<IVolumeSlicer::LayerErrorMessage>(layer, &SliceViewerWidget::OnLayerError);
   }
 
 
-  size_t SliceViewerWidget::AddLayer(IVolumeSlicer* layer)  // Takes ownership
+  size_t SliceViewerWidget::AddLayer(boost::shared_ptr<IVolumeSlicer> layer)
   {
     if (layer == NULL)
     {
@@ -409,7 +394,7 @@
     size_t index = layers_.size();
     layers_.push_back(layer);
     styles_.push_back(RenderStyle());
-    layersIndex_[layer] = index;
+    layersIndex_[layer.get()] = index;
 
     ResetPendingScene();
 
@@ -421,7 +406,8 @@
   }
 
 
-  void SliceViewerWidget::ReplaceLayer(size_t index, IVolumeSlicer* layer)  // Takes ownership
+  void SliceViewerWidget::ReplaceLayer(size_t index,
+                                       boost::shared_ptr<IVolumeSlicer> layer)
   {
     if (layer == NULL)
     {
@@ -433,9 +419,8 @@
       throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
     }
 
-    delete layers_[index];
     layers_[index] = layer;
-    layersIndex_[layer] = index;
+    layersIndex_[layer.get()] = index;
 
     ResetPendingScene();
 
@@ -452,13 +437,13 @@
       throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
     }
 
-    IVolumeSlicer* previousLayer = layers_[index];
+    IVolumeSlicer* previousLayer = layers_[index].get();
     layersIndex_.erase(layersIndex_.find(previousLayer));
     layers_.erase(layers_.begin() + index);
     changedLayers_.erase(changedLayers_.begin() + index);
     styles_.erase(styles_.begin() + index);
 
-    delete layers_[index];
+    layers_[index].reset();
 
     currentScene_->DeleteLayer(index);
     ResetPendingScene();

--- a/Framework/Deprecated/Widgets/SliceViewerWidget.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Deprecated/Widgets/SliceViewerWidget.h	Fri Nov 29 11:03:41 2019 +0100
@@ -24,7 +24,7 @@
 #include "WorldSceneWidget.h"
 #include "../Layers/IVolumeSlicer.h"
 #include "../../Toolbox/Extent2D.h"
-#include "../../Messages/IObserver.h"
+#include "../../Messages/ObserverBase.h"
 
 #include <map>
 
@@ -32,7 +32,7 @@
 {
   class SliceViewerWidget :
     public WorldSceneWidget,
-    public OrthancStone::IObserver,
+    public OrthancStone::ObserverBase<SliceViewerWidget>,
     public OrthancStone::IObservable
   {
   public:
@@ -72,7 +72,7 @@
 
     bool                         started_;
     LayersIndex                  layersIndex_;
-    std::vector<IVolumeSlicer*>  layers_;
+    std::vector<boost::shared_ptr<IVolumeSlicer> >  layers_;
     std::vector<RenderStyle>     styles_;
     OrthancStone::CoordinateSystem3D           plane_;
     std::auto_ptr<Scene>         currentScene_;
@@ -100,8 +100,7 @@
     void ResetChangedLayers();
 
   public:
-    SliceViewerWidget(OrthancStone::MessageBroker& broker, 
-                      const std::string& name);
+    SliceViewerWidget(const std::string& name);
 
     virtual OrthancStone::Extent2D GetSceneExtent();
 
@@ -120,11 +119,13 @@
     void InvalidateLayer(size_t layer);
     
   public:
-    virtual ~SliceViewerWidget();
+    virtual ~SliceViewerWidget()
+    {
+    }
 
-    size_t AddLayer(IVolumeSlicer* layer);  // Takes ownership
+    size_t AddLayer(boost::shared_ptr<IVolumeSlicer> layer);
 
-    void ReplaceLayer(size_t layerIndex, IVolumeSlicer* layer); // Takes ownership
+    void ReplaceLayer(size_t layerIndex, boost::shared_ptr<IVolumeSlicer> layer); // Takes ownership
 
     void RemoveLayer(size_t layerIndex);
 

--- a/Framework/Loaders/DicomStructureSetLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/DicomStructureSetLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -144,7 +144,7 @@
         command->SetHttpHeader("Accept-Encoding", "gzip");
         std::string uri = "/instances/" + instanceId + "/tags";
         command->SetUri(uri);
-        command->SetPayload(new AddReferencedInstance(loader, instanceId));
+        command->AcquirePayload(new AddReferencedInstance(loader, instanceId));
         Schedule(command.release());
       }
     }
@@ -231,7 +231,7 @@
         command->SetUri("/tools/lookup");
         command->SetMethod(Orthanc::HttpMethod_Post);
         command->SetBody(*it);
-        command->SetPayload(new LookupInstance(loader, *it));
+        command->AcquirePayload(new LookupInstance(loader, *it));
         Schedule(command.release());
       }
     }
@@ -347,7 +347,6 @@
   DicomStructureSetLoader::DicomStructureSetLoader(IOracle& oracle,
                                                    IObservable& oracleObservable) :
     LoaderStateMachine(oracle, oracleObservable),
-    IObservable(oracleObservable.GetBroker()),
     revision_(0),
     countProcessedInstances_(0),
     countReferencedInstances_(0),
@@ -383,7 +382,7 @@
       std::string uri = "/instances/" + instanceId + "/tags?ignore-length=3006-0050";
 
       command->SetUri(uri);
-      command->SetPayload(new LoadStructure(*this));
+      command->AcquirePayload(new LoadStructure(*this));
       Schedule(command.release());
     }
   }

--- a/Framework/Loaders/LoaderCache.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/LoaderCache.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -65,7 +65,7 @@
 
   }
 #else
-  LoaderCache::LoaderCache(ThreadedOracle& oracle, LockingEmitter& lockingEmitter)
+  LoaderCache::LoaderCache(ThreadedOracle& oracle, Deprecated::LockingEmitter& lockingEmitter)
     : oracle_(oracle)
     , lockingEmitter_(lockingEmitter)
   {
@@ -98,7 +98,7 @@
 #if ORTHANC_ENABLE_WASM == 1
           loader.reset(new OrthancSeriesVolumeProgressiveLoader(volumeImage, oracle_, oracle_));
 #else
-          LockingEmitter::WriterLock lock(lockingEmitter_);
+          Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
           loader.reset(new OrthancSeriesVolumeProgressiveLoader(volumeImage, oracle_, lock.GetOracleObservable()));
 #endif
 //          LOG(TRACE) << "LoaderCache::GetSeriesVolumeProgressiveLoader : loader = " << loader.get();
@@ -167,10 +167,8 @@
 #if ORTHANC_ENABLE_WASM == 1
           loader.reset(new OrthancMultiframeVolumeLoader(volumeImage, oracle_, oracle_));
 #else
-          LockingEmitter::WriterLock lock(lockingEmitter_);
-          loader.reset(new OrthancMultiframeVolumeLoader(volumeImage, 
-            oracle_, 
-            lock.GetOracleObservable()));
+          Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
+          loader.reset(new OrthancMultiframeVolumeLoader(volumeImage, oracle_, lock.GetOracleObservable()));
 #endif
           loader->LoadInstance(instanceUuid);
         }
@@ -270,7 +268,7 @@
 #if ORTHANC_ENABLE_WASM == 1
           loader.reset(new DicomStructureSetLoader(oracle_, oracle_));
 #else
-          LockingEmitter::WriterLock lock(lockingEmitter_);
+          Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
           loader.reset(new DicomStructureSetLoader(oracle_, lock.GetOracleObservable()));
 #endif
           loader->LoadInstance(inInstanceUuid, initiallyVisibleStructures);
@@ -366,7 +364,7 @@
   void LoaderCache::ClearCache()
   {
 #if ORTHANC_ENABLE_WASM != 1
-    LockingEmitter::WriterLock lock(lockingEmitter_);
+    Deprecated::LockingEmitter::WriterLock lock(lockingEmitter_);
 #endif
     
 //#ifndef NDEBUG

--- a/Framework/Loaders/LoaderCache.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/LoaderCache.h	Fri Nov 29 11:03:41 2019 +0100
@@ -43,7 +43,10 @@
   class WebAssemblyOracle;
 #else
   class ThreadedOracle;
-  class LockingEmitter;
+  namespace Deprecated
+  {
+    class LockingEmitter;
+  }
 #endif
 
   class LoaderCache
@@ -52,7 +55,7 @@
 #if ORTHANC_ENABLE_WASM == 1
     LoaderCache(WebAssemblyOracle& oracle);
 #else
-    LoaderCache(ThreadedOracle& oracle, LockingEmitter& lockingEmitter);
+    LoaderCache(ThreadedOracle& oracle, Deprecated::LockingEmitter& lockingEmitter);
 #endif
 
     boost::shared_ptr<OrthancSeriesVolumeProgressiveLoader>
@@ -87,7 +90,7 @@
     WebAssemblyOracle& oracle_;
 #else
     ThreadedOracle& oracle_;
-    LockingEmitter& lockingEmitter_;
+    Deprecated::LockingEmitter& lockingEmitter_;
 #endif
 
     std::map<std::string, boost::shared_ptr<OrthancSeriesVolumeProgressiveLoader> >

--- a/Framework/Loaders/LoaderStateMachine.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/LoaderStateMachine.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -43,11 +43,11 @@
   }
 
 
-  void LoaderStateMachine::Schedule(OracleCommandWithPayload* command)
+  void LoaderStateMachine::Schedule(OracleCommandBase* command)
   {
     LOG(TRACE) << "LoaderStateMachine(" << std::hex << this << std::dec << ")::Schedule()";
 
-    std::auto_ptr<OracleCommandWithPayload> protection(command);
+    std::auto_ptr<OracleCommandBase> protection(command);
 
     if (command == NULL)
     {
@@ -97,7 +97,8 @@
         ") < simultaneousDownloads_ (" << simultaneousDownloads_ << 
         ") --> will Schedule command addr " << std::hex << nextCommand << std::dec;
 
-      oracle_.Schedule(*this, nextCommand);
+      boost::shared_ptr<IObserver> observer(GetSharedObserver());
+      oracle_.Schedule(observer, nextCommand);
       pendingCommands_.pop_front();
 
       activeCommands_++;
@@ -136,7 +137,6 @@
   template <typename T>
   void LoaderStateMachine::HandleSuccessMessage(const T& message)
   {
-    LOG(TRACE) << "LoaderStateMachine(" << std::hex << this << std::dec << ")::HandleSuccessMessage(). Receiver fingerprint = " << GetFingerprint();
     if (activeCommands_ <= 0) {
       LOG(ERROR) << "LoaderStateMachine(" << std::hex << this << std::dec << ")::HandleSuccessMessage : activeCommands_ should be > 0 but is: " << activeCommands_;
     }
@@ -159,35 +159,22 @@
 
   LoaderStateMachine::LoaderStateMachine(IOracle& oracle,
                                          IObservable& oracleObservable) :
-    IObserver(oracleObservable.GetBroker()),
     oracle_(oracle),
-    oracleObservable_(oracleObservable),
     active_(false),
     simultaneousDownloads_(4),
     activeCommands_(0)
   {
     LOG(TRACE) << "LoaderStateMachine(" << std::hex << this << std::dec << ")::LoaderStateMachine()";
 
-    oracleObservable.RegisterObserverCallback(
-      new Callable<LoaderStateMachine, OrthancRestApiCommand::SuccessMessage>
-      (*this, &LoaderStateMachine::HandleSuccessMessage));
-
-    oracleObservable.RegisterObserverCallback(
-      new Callable<LoaderStateMachine, GetOrthancImageCommand::SuccessMessage>
-      (*this, &LoaderStateMachine::HandleSuccessMessage));
-
-    oracleObservable.RegisterObserverCallback(
-      new Callable<LoaderStateMachine, GetOrthancWebViewerJpegCommand::SuccessMessage>
-      (*this, &LoaderStateMachine::HandleSuccessMessage));
-
-    oracleObservable.RegisterObserverCallback(
-      new Callable<LoaderStateMachine, OracleCommandExceptionMessage>
-      (*this, &LoaderStateMachine::HandleExceptionMessage));
+    // TODO => Move this out of constructor
+    Register<OrthancRestApiCommand::SuccessMessage>(oracleObservable, &LoaderStateMachine::HandleSuccessMessage);
+    Register<GetOrthancImageCommand::SuccessMessage>(oracleObservable, &LoaderStateMachine::HandleSuccessMessage);
+    Register<GetOrthancWebViewerJpegCommand::SuccessMessage>(oracleObservable, &LoaderStateMachine::HandleSuccessMessage);
+    Register<OracleCommandExceptionMessage>(oracleObservable, &LoaderStateMachine::HandleExceptionMessage);
   }
 
   LoaderStateMachine::~LoaderStateMachine()
   {
-    oracleObservable_.Unregister(this);
     LOG(TRACE) << "LoaderStateMachine(" << std::hex << this << std::dec << ")::~LoaderStateMachine()";
     Clear();
   }

--- a/Framework/Loaders/LoaderStateMachine.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/LoaderStateMachine.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,7 +22,7 @@
 #pragma once
 
 #include "../Messages/IObservable.h"
-#include "../Messages/IObserver.h"
+#include "../Messages/ObserverBase.h"
 #include "../Oracle/GetOrthancImageCommand.h"
 #include "../Oracle/GetOrthancWebViewerJpegCommand.h"
 #include "../Oracle/IOracle.h"
@@ -41,7 +41,7 @@
      rest once slots become available. It is used, a.o., by the 
      OrtancMultiframeVolumeLoader class.
   */
-  class LoaderStateMachine : public IObserver
+  class LoaderStateMachine : public ObserverBase<LoaderStateMachine>
   {
   protected:
     class State : public Orthanc::IDynamicObject
@@ -60,7 +60,7 @@
       {
       }
 
-      void Schedule(OracleCommandWithPayload* command) const
+      void Schedule(OracleCommandBase* command) const
       {
         that_.Schedule(command);
       }
@@ -78,7 +78,7 @@
       virtual void Handle(const GetOrthancWebViewerJpegCommand::SuccessMessage& message);
     };
 
-    void Schedule(OracleCommandWithPayload* command);
+    void Schedule(OracleCommandBase* command);
 
     void Start();
 
@@ -95,7 +95,6 @@
     typedef std::list<IOracleCommand*>  PendingCommands;
 
     IOracle&         oracle_;
-    IObservable&     oracleObservable_;
     bool             active_;
     unsigned int     simultaneousDownloads_;
     PendingCommands  pendingCommands_;

--- a/Framework/Loaders/OrthancMultiframeVolumeLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/OrthancMultiframeVolumeLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -101,7 +101,7 @@
         std::auto_ptr<OrthancRestApiCommand> command(new OrthancRestApiCommand);
         command->SetUri("/instances/" + loader.GetInstanceId() + "/content/" +
                         Orthanc::DICOM_TAG_GRID_FRAME_OFFSET_VECTOR.Format());
-        command->SetPayload(new LoadRTDoseGeometry(loader, dicom.release()));
+        command->AcquirePayload(new LoadRTDoseGeometry(loader, dicom.release()));
 
         Schedule(command.release());
       }
@@ -175,7 +175,7 @@
       command->SetHttpHeader("Accept-Encoding", "gzip");
       command->SetUri("/instances/" + instanceId_ + "/content/" +
                       Orthanc::DICOM_TAG_PIXEL_DATA.Format() + "/0");
-      command->SetPayload(new LoadUncompressedPixelData(*this));
+      command->AcquirePayload(new LoadUncompressedPixelData(*this));
       Schedule(command.release());
     }
     else
@@ -345,7 +345,6 @@
                                                                IOracle& oracle,
                                                                IObservable& oracleObservable) :
     LoaderStateMachine(oracle, oracleObservable),
-    IObservable(oracleObservable.GetBroker()),
     volume_(volume),
     pixelDataLoaded_(false)
   {
@@ -370,14 +369,14 @@
       std::auto_ptr<OrthancRestApiCommand> command(new OrthancRestApiCommand);
       command->SetHttpHeader("Accept-Encoding", "gzip");
       command->SetUri("/instances/" + instanceId + "/tags");
-      command->SetPayload(new LoadGeometry(*this));
+      command->AcquirePayload(new LoadGeometry(*this));
       Schedule(command.release());
     }
 
     {
       std::auto_ptr<OrthancRestApiCommand> command(new OrthancRestApiCommand);
       command->SetUri("/instances/" + instanceId + "/metadata/TransferSyntax");
-      command->SetPayload(new LoadTransferSyntax(*this));
+      command->AcquirePayload(new LoadTransferSyntax(*this));
       Schedule(command.release());
     }
   }

--- a/Framework/Loaders/OrthancMultiframeVolumeLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/OrthancMultiframeVolumeLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -30,8 +30,7 @@
 {
   class OrthancMultiframeVolumeLoader :
     public LoaderStateMachine,
-    public IObservable,
-    public IGeometryProvider
+    public IObservable
   {
   private:
     class LoadRTDoseGeometry;
@@ -57,8 +56,8 @@
 
     void SetUncompressedPixelData(const std::string& pixelData);
 
-    virtual bool HasGeometry() const ORTHANC_OVERRIDE;
-    virtual const VolumeImageGeometry& GetImageGeometry() const ORTHANC_OVERRIDE;
+    bool HasGeometry() const;
+    const VolumeImageGeometry& GetImageGeometry() const;
 
   public:
     OrthancMultiframeVolumeLoader(boost::shared_ptr<DicomVolumeImage> volume,

--- a/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -185,18 +185,27 @@
 
       CheckVolume();
 
-      const double spacingZ = slices.ComputeSpacingBetweenSlices();
-      LOG(INFO) << "Computed spacing between slices: " << spacingZ << "mm";
+      double spacingZ;
+
+      if (slices.ComputeSpacingBetweenSlices(spacingZ))
+      {
+        LOG(INFO) << "Computed spacing between slices: " << spacingZ << "mm";
       
-      const DicomInstanceParameters& parameters = *slices_[0];
+        const DicomInstanceParameters& parameters = *slices_[0];
 
-      geometry_.reset(new VolumeImageGeometry);
-      geometry_->SetSizeInVoxels(parameters.GetImageInformation().GetWidth(),
-                         parameters.GetImageInformation().GetHeight(),
-                         static_cast<unsigned int>(slices.GetSlicesCount()));
-      geometry_->SetAxialGeometry(slices.GetSliceGeometry(0));
-      geometry_->SetVoxelDimensions(parameters.GetPixelSpacingX(),
-                                    parameters.GetPixelSpacingY(), spacingZ);
+        geometry_.reset(new VolumeImageGeometry);
+        geometry_->SetSizeInVoxels(parameters.GetImageInformation().GetWidth(),
+                                   parameters.GetImageInformation().GetHeight(),
+                                   static_cast<unsigned int>(slices.GetSlicesCount()));
+        geometry_->SetAxialGeometry(slices.GetSliceGeometry(0));
+        geometry_->SetVoxelDimensions(parameters.GetPixelSpacingX(),
+                                      parameters.GetPixelSpacingY(), spacingZ);
+      }
+      else
+      {
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_BadGeometry,
+                                        "The origins of the slices of a volume image are not regularly spaced");
+     }
     }
   }
 
@@ -237,8 +246,9 @@
   }
 
 
-  static unsigned int GetSliceIndexPayload(const OracleCommandWithPayload& command)
+  static unsigned int GetSliceIndexPayload(const OracleCommandBase& command)
   {
+    assert(command.HasPayload());
     return dynamic_cast< const Orthanc::SingleValueObject<unsigned int>& >(command.GetPayload()).GetValue();
   }
 
@@ -261,7 +271,7 @@
         throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
       }
 
-      std::auto_ptr<OracleCommandWithPayload> command;
+      std::auto_ptr<OracleCommandBase> command;
         
       if (quality == BEST_QUALITY)
       {
@@ -291,8 +301,10 @@
         command.reset(tmp.release());
       }
 
-      command->SetPayload(new Orthanc::SingleValueObject<unsigned int>(sliceIndex));
-      oracle_.Schedule(*this, command.release());
+      command->AcquirePayload(new Orthanc::SingleValueObject<unsigned int>(sliceIndex));
+
+      boost::shared_ptr<IObserver> observer(GetSharedObserver());
+      oracle_.Schedule(observer, command.release());
     }
     else
     {
@@ -400,7 +412,7 @@
   {
     unsigned int quality;
       
-    switch (message.GetOrigin().GetQuality())
+    switch (dynamic_cast<const GetOrthancWebViewerJpegCommand&>(message.GetOrigin()).GetQuality())
     {
       case 50:
         quality = LOW_QUALITY;
@@ -421,32 +433,26 @@
   OrthancSeriesVolumeProgressiveLoader::OrthancSeriesVolumeProgressiveLoader(const boost::shared_ptr<DicomVolumeImage>& volume,
                                                                              IOracle& oracle,
                                                                              IObservable& oracleObservable) :
-    IObserver(oracleObservable.GetBroker()),
-    IObservable(oracleObservable.GetBroker()),
     oracle_(oracle),
-    oracleObservable_(oracleObservable),
     active_(false),
     simultaneousDownloads_(4),
     volume_(volume),
     sorter_(new BasicFetchingItemsSorter::Factory),
     volumeImageReadyInHighQuality_(false)
   {
-    oracleObservable.RegisterObserverCallback(
-      new Callable<OrthancSeriesVolumeProgressiveLoader, OrthancRestApiCommand::SuccessMessage>
-      (*this, &OrthancSeriesVolumeProgressiveLoader::LoadGeometry));
+    // TODO => Move this out of constructor
+    Register<OrthancRestApiCommand::SuccessMessage>
+      (oracleObservable, &OrthancSeriesVolumeProgressiveLoader::LoadGeometry);
 
-    oracleObservable.RegisterObserverCallback(
-      new Callable<OrthancSeriesVolumeProgressiveLoader, GetOrthancImageCommand::SuccessMessage>
-      (*this, &OrthancSeriesVolumeProgressiveLoader::LoadBestQualitySliceContent));
+    Register<GetOrthancImageCommand::SuccessMessage>
+      (oracleObservable, &OrthancSeriesVolumeProgressiveLoader::LoadBestQualitySliceContent);
 
-    oracleObservable.RegisterObserverCallback(
-      new Callable<OrthancSeriesVolumeProgressiveLoader, GetOrthancWebViewerJpegCommand::SuccessMessage>
-      (*this, &OrthancSeriesVolumeProgressiveLoader::LoadJpegSliceContent));
+    Register<GetOrthancWebViewerJpegCommand::SuccessMessage>
+      (oracleObservable, &OrthancSeriesVolumeProgressiveLoader::LoadJpegSliceContent);
   }
 
   OrthancSeriesVolumeProgressiveLoader::~OrthancSeriesVolumeProgressiveLoader()
   {
-    oracleObservable_.Unregister(this);
     LOG(TRACE) << "OrthancSeriesVolumeProgressiveLoader::~OrthancSeriesVolumeProgressiveLoader()";
   }
 
@@ -485,7 +491,8 @@
       command->SetUri("/series/" + seriesId + "/instances-tags");
 
 //      LOG(TRACE) << "OrthancSeriesVolumeProgressiveLoader::LoadSeries about to call oracle_.Schedule";
-      oracle_.Schedule(*this, command.release());
+      boost::shared_ptr<IObserver> observer(GetSharedObserver());
+      oracle_.Schedule(observer, command.release());
 //      LOG(TRACE) << "OrthancSeriesVolumeProgressiveLoader::LoadSeries called oracle_.Schedule";
     }
   }

--- a/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Loaders/OrthancSeriesVolumeProgressiveLoader.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,7 +22,7 @@
 #pragma once
 
 #include "../Messages/IObservable.h"
-#include "../Messages/IObserver.h"
+#include "../Messages/ObserverBase.h"
 #include "../Oracle/GetOrthancImageCommand.h"
 #include "../Oracle/GetOrthancWebViewerJpegCommand.h"
 #include "../Oracle/IOracle.h"
@@ -42,10 +42,9 @@
     is stored in a Dicom series.
   */
   class OrthancSeriesVolumeProgressiveLoader : 
-    public IObserver,
+    public ObserverBase<OrthancSeriesVolumeProgressiveLoader>,
     public IObservable,
-    public IVolumeSlicer,
-    public IGeometryProvider
+    public IVolumeSlicer
   {
   private:
     static const unsigned int LOW_QUALITY = 0;
@@ -106,7 +105,6 @@
     void LoadJpegSliceContent(const GetOrthancWebViewerJpegCommand::SuccessMessage& message);
 
     IOracle&                                      oracle_;
-    IObservable&                                  oracleObservable_;
     bool                                          active_;
     unsigned int                                  simultaneousDownloads_;
     SeriesGeometry                                seriesGeometry_;
@@ -141,7 +139,7 @@
     subscribing, for instance if they are created or listening only AFTER the
     "geometry loaded" message is broadcast 
     */
-    bool HasGeometry() const ORTHANC_OVERRIDE
+    bool HasGeometry() const
     {
       return seriesGeometry_.HasGeometry();
     }
@@ -149,7 +147,7 @@
     /**
     Same remark as HasGeometry
     */
-    const VolumeImageGeometry& GetImageGeometry() const ORTHANC_OVERRIDE
+    const VolumeImageGeometry& GetImageGeometry() const
     {
       return seriesGeometry_.GetImageGeometry();
     }

--- a/Framework/Messages/ICallable.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/ICallable.h	Fri Nov 29 11:03:41 2019 +0100
@@ -22,20 +22,20 @@
 #pragma once
 
 #include "IMessage.h"
+#include "IObserver.h"
 
 #include <Core/Logging.h>
 
 #include <boost/noncopyable.hpp>
+#include <boost/weak_ptr.hpp>
 
 #include <string>
 
-namespace OrthancStone {
-
-  class IObserver;
-
+namespace OrthancStone 
+{
   // This is referencing an object and member function that can be notified
   // by an IObservable.  The object must derive from IO
-  // The member functions must be of type "void Function(const IMessage& message)" or reference a derived class of IMessage
+  // The member functions must be of type "void Method(const IMessage& message)" or reference a derived class of IMessage
   class ICallable : public boost::noncopyable
   {
   public:
@@ -47,11 +47,14 @@
 
     virtual const MessageIdentifier& GetMessageIdentifier() = 0;
 
-    virtual IObserver* GetObserver() const = 0;
+    // TODO - Is this needed?
+    virtual boost::weak_ptr<IObserver> GetObserver() const = 0;
   };
 
+
+  // TODO - Remove this class
   template <typename TMessage>
-  class MessageHandler: public ICallable
+  class MessageHandler : public ICallable
   {
   };
 
@@ -61,47 +64,28 @@
   class Callable : public MessageHandler<TMessage>
   {
   private:
-    typedef void (TObserver::* MemberFunction) (const TMessage&);
+    typedef void (TObserver::* MemberMethod) (const TMessage&);
 
-    TObserver&         observer_;
-    MemberFunction     function_;
-    std::string        observerFingerprint_;
+    boost::weak_ptr<IObserver>  observer_;
+    MemberMethod                function_;
 
   public:
-    Callable(TObserver& observer,
-             MemberFunction function) :
+    Callable(boost::shared_ptr<TObserver> observer,
+             MemberMethod function) :
       observer_(observer),
-      function_(function),
-      observerFingerprint_(observer.GetFingerprint())
-    {
-    }
-
-    void ApplyInternal(const TMessage& message)
+      function_(function)
     {
-      std::string currentFingerprint(observer_.GetFingerprint());
-      if (observerFingerprint_ != currentFingerprint)
-      {
-        LOG(TRACE) << "The observer at address " << 
-          std::hex << &observer_ << std::dec << 
-          ") has a different fingerprint than the one recorded at callback " <<
-          "registration time. This means that it is not the same object as " <<
-          "the one recorded, even though their addresses are the same. " <<
-          "Callback will NOT be sent!";
-        LOG(TRACE) << " recorded fingerprint = " << observerFingerprint_ << 
-          " current fingerprint = " << currentFingerprint;
-      }
-      else
-      {
-        LOG(TRACE) << "The recorded fingerprint is " << observerFingerprint_
-          << " and the current fingerprint is " << currentFingerprint
-          << " -- callable will be called.";
-        (observer_.*function_) (message);
-      }
     }
 
     virtual void Apply(const IMessage& message)
     {
-      ApplyInternal(dynamic_cast<const TMessage&>(message));
+      boost::shared_ptr<IObserver> lock(observer_);
+      if (lock)
+      {
+        TObserver& observer = dynamic_cast<TObserver&>(*lock);
+        const TMessage& typedMessage = dynamic_cast<const TMessage&>(message);
+        (observer.*function_) (typedMessage);
+      }
     }
 
     virtual const MessageIdentifier& GetMessageIdentifier()
@@ -109,41 +93,9 @@
       return TMessage::GetStaticIdentifier();
     }
 
-    virtual IObserver* GetObserver() const
+    virtual boost::weak_ptr<IObserver> GetObserver() const
     {
-      return &observer_;
+      return observer_;
     }
   };
-
-#if 0 /* __cplusplus >= 201103L*/
-
-#include <functional>
-
-  template <typename TMessage>
-  class LambdaCallable : public MessageHandler<TMessage>
-  {
-  private:
-
-    IObserver&      observer_;
-    std::function<void (const TMessage&)> lambda_;
-
-  public:
-    LambdaCallable(IObserver& observer,
-                    std::function<void (const TMessage&)> lambdaFunction) :
-             observer_(observer),
-             lambda_(lambdaFunction)
-    {
-    }
-
-    virtual void Apply(const IMessage& message)
-    {
-      lambda_(dynamic_cast<const TMessage&>(message));
-    }
-
-    virtual IObserver* GetObserver() const
-    {
-      return &observer_;
-    }
-  };
-#endif //__cplusplus >= 201103L
 }

--- a/Framework/Messages/IMessage.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/IMessage.h	Fri Nov 29 11:03:41 2019 +0100
@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include <boost/lexical_cast.hpp>
 #include <boost/noncopyable.hpp>
 
 #include <string.h>
@@ -33,6 +34,12 @@
     const char*  file_;
     int          line_;
 
+    bool IsEqual(const MessageIdentifier& other) const
+    {
+      return (line_ == other.line_ &&
+              strcmp(file_, other.file_) == 0);
+    }
+
   public:
     MessageIdentifier(const char* file,
                       int line) :
@@ -47,6 +54,11 @@
     {
     }
 
+    std::string AsString() const
+    {
+      return std::string(file_) + ":" + boost::lexical_cast<std::string>(line_);
+    }
+
     bool operator< (const MessageIdentifier& other) const
     {
       if (file_ == NULL)
@@ -62,6 +74,16 @@
         return strcmp(file_, other.file_) < 0;
       }
     }
+
+    bool operator== (const MessageIdentifier& other) const
+    {
+      return IsEqual(other);
+    }
+
+    bool operator!= (const MessageIdentifier& other) const
+    {
+      return !IsEqual(other);
+    }
   };
 
     

--- a/Framework/Messages/IMessageEmitter.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/IMessageEmitter.h	Fri Nov 29 11:03:41 2019 +0100
@@ -24,6 +24,8 @@
 #include "IObserver.h"
 #include "IMessage.h"
 
+#include <boost/weak_ptr.hpp>
+
 namespace OrthancStone
 {
   /**
@@ -39,7 +41,7 @@
     {
     }
 
-    virtual void EmitMessage(const IObserver& observer,
+    virtual void EmitMessage(boost::weak_ptr<IObserver> observer,
                              const IMessage& message) = 0;
   };
 }

--- a/Framework/Messages/IObservable.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/IObservable.cpp	Fri Nov 29 11:03:41 2019 +0100
@@ -21,8 +21,9 @@
 
 #include "IObservable.h"
 
+#include "../StoneException.h"
+
 #include <Core/Logging.h>
-#include <Core/OrthancException.h>
 
 #include <cassert>
 
@@ -40,20 +41,10 @@
         delete *it2;
       }
     }
-
-    // unregister the forwarders but don't delete them (they'll be
-    // deleted by the observable they are observing as any other
-    // callable)
-    for (Forwarders::iterator it = forwarders_.begin();
-         it != forwarders_.end(); ++it)
-    {
-      IMessageForwarder* fw = *it;
-      broker_.Unregister(dynamic_cast<IObserver&>(*fw));
-    }
   }
   
 
-  void IObservable::RegisterObserverCallback(ICallable* callable)
+  void IObservable::RegisterCallable(ICallable* callable)
   {
     if (callable == NULL)
     {
@@ -64,35 +55,10 @@
     callables_[id].insert(callable);
   }
 
-  void IObservable::Unregister(IObserver *observer)
-  {
-    LOG(TRACE) << "IObservable::Unregister for IObserver at addr: "
-      << std::hex << observer << std::dec;
-    // delete all callables from this observer
-    for (Callables::iterator itCallableSet = callables_.begin();
-         itCallableSet != callables_.end(); ++itCallableSet)
-    {
-      for (std::set<ICallable*>::const_iterator
-             itCallable = itCallableSet->second.begin(); itCallable != itCallableSet->second.end(); )
-      {
-        if ((*itCallable)->GetObserver() == observer)
-        {
-          LOG(TRACE) << "  ** IObservable::Unregister : deleting callable: "
-            << std::hex << (*itCallable) << std::dec;
-          delete *itCallable;
-          itCallableSet->second.erase(itCallable++);
-        }
-        else
-          ++itCallable;
-      }
-    }
-  }
-  
   void IObservable::EmitMessageInternal(const IObserver* receiver,
                                         const IMessage& message)
   {
-    LOG(TRACE) << "IObservable::EmitMessageInternal receiver = "
-      << std::hex << receiver << std::dec;
+    //LOG(TRACE) << "IObservable::EmitMessageInternal receiver = " << std::hex << receiver << std::dec;
     Callables::const_iterator found = callables_.find(message.GetIdentifier());
 
     if (found != callables_.end())
@@ -102,15 +68,36 @@
       {
         assert(*it != NULL);
 
-        const IObserver* observer = (*it)->GetObserver();
-        if (broker_.IsActive(*observer))
+        boost::shared_ptr<IObserver> observer((*it)->GetObserver().lock());
+
+        if (observer)
         {
           if (receiver == NULL ||    // Are we broadcasting?
-              observer == receiver)  // Not broadcasting, but this is the receiver
+              observer.get() == receiver)  // Not broadcasting, but this is the receiver
           {
-            (*it)->Apply(message);
+            try
+            {
+              (*it)->Apply(message);
+            }
+            catch (Orthanc::OrthancException& e)
+            {
+              LOG(ERROR) << "Exception on callable: " << e.What();
+            }
+            catch (StoneException& e)
+            {
+              LOG(ERROR) << "Exception on callable: " << e.What();
+            }
+            catch (...)
+            {
+              LOG(ERROR) << "Native exception on callable";
+            }
           }
         }
+        else
+        {
+          // TODO => Remove "it" from the list of callables => This
+          // allows to suppress the need for "Unregister()"
+        }
       }
     }
   }
@@ -122,21 +109,15 @@
   }
 
   
-  void IObservable::EmitMessage(const IObserver& observer,
+  void IObservable::EmitMessage(boost::weak_ptr<IObserver> observer,
                                 const IMessage& message)
   {
-    LOG(TRACE) << "IObservable::EmitMessage observer = "
-      << std::hex << &observer << std::dec;
-    EmitMessageInternal(&observer, message);
-  }
-  
-  void IObservable::RegisterForwarder(IMessageForwarder* forwarder)
-  {
-    if (forwarder == NULL)
+    //LOG(TRACE) << "IObservable::EmitMessage observer = " << std::hex << &observer << std::dec;
+
+    boost::shared_ptr<IObserver> lock(observer.lock());
+    if (lock)
     {
-      throw Orthanc::OrthancException(Orthanc::ErrorCode_NullPointer);
+      EmitMessageInternal(lock.get(), message);
     }
-    
-    forwarders_.insert(forwarder);
   }
 }

--- a/Framework/Messages/IObservable.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/IObservable.h	Fri Nov 29 11:03:41 2019 +0100
@@ -24,8 +24,6 @@
 #include "../StoneEnumerations.h"
 #include "ICallable.h"
 #include "IObserver.h"
-#include "MessageBroker.h"
-#include "MessageForwarder.h"
 
 #include <set>
 #include <map>
@@ -37,39 +35,20 @@
   private:
     typedef std::map<MessageIdentifier, std::set<ICallable*> >  Callables;
 
-    typedef std::set<IMessageForwarder*>     Forwarders;
-
-    MessageBroker&  broker_;
     Callables       callables_;
-    Forwarders      forwarders_;
 
     void EmitMessageInternal(const IObserver* receiver,
                              const IMessage& message);
 
   public:
-    IObservable(MessageBroker& broker) :
-      broker_(broker)
-    {
-    }
-
     virtual ~IObservable();
 
-    MessageBroker& GetBroker() const
-    {
-      return broker_;
-    }
-
-    // Takes ownsership
-    void RegisterObserverCallback(ICallable* callable);
-
-    void Unregister(IObserver* observer);
+    // Takes ownsership of the callable
+    void RegisterCallable(ICallable* callable);
 
     void BroadcastMessage(const IMessage& message);
 
-    void EmitMessage(const IObserver& observer,
+    void EmitMessage(boost::weak_ptr<IObserver> observer,
                      const IMessage& message);
-
-    // Takes ownsership
-    void RegisterForwarder(IMessageForwarder* forwarder);
   };
 }

--- a/Framework/Messages/IObserver.cpp	Thu Nov 28 18:28:15 2019 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,93 +0,0 @@
-/**
- * Stone of Orthanc
- * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics
- * Department, University Hospital of Liege, Belgium
- * Copyright (C) 2017-2019 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/>.
- **/
-
-
-#include "IObserver.h"
-
-#include "IMessage.h"
-#include "../StoneException.h"
-
-#include <Core/Logging.h>
-#include <Core/Toolbox.h>
-
-namespace OrthancStone 
-{
-  IObserver::IObserver(MessageBroker& broker)
-    : broker_(broker)
-    , fingerprint_()
-  {
-    // we store the fingerprint_ as a char array to avoid problems when
-    // reading it in a deceased object.
-    // remember this is panic-level code to track zombie object usage
-    std::string fingerprint = Orthanc::Toolbox::GenerateUuid();
-    const char* fingerprintRaw = fingerprint.c_str();
-    memcpy(fingerprint_, fingerprintRaw, 37);
-    broker_.Register(*this);
-  }
-
-
-  IObserver::~IObserver()
-  {
-    try
-    {
-      LOG(TRACE) << "IObserver(" << std::hex << this << std::dec << ")::~IObserver : fingerprint_ == " << fingerprint_;
-      const char* deadMarker = "deadbeef-dead-dead-0000-0000deadbeef";
-      ORTHANC_ASSERT(strlen(deadMarker) == 36);
-      memcpy(fingerprint_, deadMarker, 37);
-      broker_.Unregister(*this);
-    }
-    catch (const Orthanc::OrthancException& e)
-    {
-      if (e.HasDetails())
-      {
-        LOG(ERROR) << "OrthancException in ~IObserver: " << e.What() << " Details: " << e.GetDetails();
-      }
-      else
-      {
-        LOG(ERROR) << "OrthancException in ~IObserver: " << e.What();
-      }
-    }
-    catch (const std::exception& e)
-    {
-      LOG(ERROR) << "std::exception in ~IObserver: " << e.what();
-    }
-    catch (...)
-    {
-      LOG(ERROR) << "Unknown exception in ~IObserver";
-    }
-  }
-
-
-  bool IObserver::DoesFingerprintLookGood() const
-  {
-    for (size_t i = 0; i < 36; ++i) {
-      bool ok = false;
-      if (fingerprint_[i] >= 'a' && fingerprint_[i] <= 'f')
-        ok = true;
-      if (fingerprint_[i] >= '0' && fingerprint_[i] <= '9')
-        ok = true;
-      if (fingerprint_[i] == '-')
-        ok = true;
-      if (!ok)
-        return false;
-    }
-    return fingerprint_[36] == 0;
-  }
-}

--- a/Framework/Messages/IObserver.h	Thu Nov 28 18:28:15 2019 +0100
+++ b/Framework/Messages/IObserver.h	Fri Nov 29 11:03:41 2019 +0100
@@ -21,33 +21,19 @@
 
 #pragma once
 
-#include "MessageBroker.h"
+#include <boost/noncopyable.hpp>
 
 namespace OrthancStone 
 {
   class IObserver : public boost::noncopyable
   {
-  private:
-    MessageBroker&  broker_;
-    // the following is a UUID that is used to disambiguate different observers
-    // that may have the same address
-    char     fingerprint_[37];
-
   public:
-    IObserver(MessageBroker& broker);
-
-    virtual ~IObserver();
-
-    const char* GetFingerprint() const
+    IObserver()
     {
-      return fingerprint_;
     }
 
-    bool DoesFingerprintLookGood() const;
-
-    MessageBroker& GetBroker() const
+    virtual ~IObserver()
     {
-      return broker_;
     }
   };
 }