#6437 Fix Signal crash and improve signal code

* The crash fix is ensuring we don't loop through m_disconnectCallbacks
  in DeleteSignal::send()
* This is because the callback will end up calling disconnect
  which in turn erases the entry from m_disconnectCallbacks,
  invalidating the iterators used in the loop.

Fwk/AppFwk/cafProjectDataModel/cafPdmCore/CMakeLists.txt

@@ -50,6 +50,7 @@ set( PROJECT_FILES
     cafNotificationCenter.h
 
     cafSignal.h
+    cafSignal.cpp
 
     cafTristate.cpp
     cafTristate.h

Fwk/AppFwk/cafProjectDataModel/cafPdmCore/cafPdmObjectHandle.cpp

@@ -119,6 +119,8 @@ void PdmObjectHandle::objectsWithReferringPtrFields( std::vector<PdmObjectHandle
 //--------------------------------------------------------------------------------------------------
 void PdmObjectHandle::prepareForDelete()
 {
+    this->sendDeleteSignal();
+
     m_parentField = nullptr;
 
     for ( size_t i = 0; i < m_capabilities.size(); ++i )

Fwk/AppFwk/cafProjectDataModel/cafPdmCore/cafSignal.cpp

@@ -0,0 +1,96 @@
+//##################################################################################################
+//
+//   Custom Visualization Core library
+//   Copyright (C) 2020- Ceetron Solutions AS
+//
+//   This library may be used under the terms of either the GNU General Public License or
+//   the GNU Lesser General Public License as follows:
+//
+//   GNU General Public License Usage
+//   This library is free software: you can redistribute it and/or modify
+//   it under the terms of the GNU General Public License as published by
+//   the Free Software Foundation, either version 3 of the License, or
+//   (at your option) any later version.
+//
+//   This library 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 General Public License at <<http://www.gnu.org/licenses/gpl.html>>
+//   for more details.
+//
+//   GNU Lesser General Public License Usage
+//   This library is free software; you can redistribute it and/or modify
+//   it under the terms of the GNU Lesser General Public License as published by
+//   the Free Software Foundation; either version 2.1 of the License, or
+//   (at your option) any later version.
+//
+//   This library 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 Lesser General Public License at <<http://www.gnu.org/licenses/lgpl-2.1.html>>
+//   for more details.
+//
+//##################################################################################################
+#include "cafSignal.h"
+
+using namespace caf;
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+DeleteSignal::DeleteSignal( SignalObserver* observer )
+    : m_observer( observer )
+{
+}
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+void DeleteSignal::disconnect( SignalObserver* observer )
+{
+    // Remove the observer from the call back list
+    m_disconnectCallbacks.erase( observer );
+}
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+void DeleteSignal::send()
+{
+    // Make sure we swap out the disconnect signals to avoid
+    // erasing from the signal-map while looping through it.
+    std::map<SignalObserver*, DisconnectCallback> disconnectCallbacks;
+    disconnectCallbacks.swap( m_disconnectCallbacks );
+
+    for ( auto signalCallbackPair : disconnectCallbacks )
+    {
+        signalCallbackPair.second( m_observer );
+    }
+}
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+SignalObserver::SignalObserver()
+    : beingDeleted( this )
+{
+}
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+void SignalObserver::sendDeleteSignal()
+{
+    // Make sure we
+    beingDeleted.send();
+}
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+SignalObserver::~SignalObserver()
+{
+    sendDeleteSignal();
+}

Fwk/AppFwk/cafProjectDataModel/cafPdmCore/cafSignal.h

@@ -56,10 +56,7 @@ class DeleteSignal
 public:
     using DisconnectCallback = std::function<void( SignalObserver* )>;
 
-    DeleteSignal( SignalObserver* observer )
-        : m_observer( observer )
-    {
-    }
+    DeleteSignal( SignalObserver* observer );
 
     template <typename ClassType>
     void connect( ClassType* signal )
@@ -72,14 +69,8 @@ public:
 
         if ( signalCasted ) m_disconnectCallbacks[signalCasted] = disconnectCallback;
     }
-    void disconnect( SignalObserver* observer ) { m_disconnectCallbacks.erase( observer ); }
-    void send()
-    {
-        for ( auto signalCallbackPair : m_disconnectCallbacks )
-        {
-            signalCallbackPair.second( m_observer );
-        }
-    }
+    void disconnect( SignalObserver* observer );
+    void send();
 
 private:
     std::map<SignalObserver*, DisconnectCallback> m_disconnectCallbacks;
@@ -107,11 +98,9 @@ public:
     DeleteSignal beingDeleted;
 
 public:
-    SignalObserver()
-        : beingDeleted( this )
-    {
-    }
-    virtual ~SignalObserver() { beingDeleted.send(); }
+    SignalObserver();
+    void sendDeleteSignal();
+    virtual ~SignalObserver();
 
 }; // namespace caf
 
@@ -170,6 +159,7 @@ public:
         };
         connect( observer, lambda );
     }
+
     template <typename ClassType>
     void connect( ClassType* observer, const MemberCallback& callback )
     {
@@ -187,6 +177,7 @@ public:
         m_observerCallbacks.erase( observer );
         observer->beingDeleted.disconnect( this );
     }
+
     void send( Args... args )
     {
         for ( auto observerCallbackPair : m_observerCallbacks )
@@ -197,12 +188,14 @@ public:
             }
         }
     }
+
     void block( SignalObserver* observer )
     {
         auto it = m_observerCallbacks.find( observer );
         CAF_ASSERT( it != m_observerCallbacks.end() );
         it->second.second = false;
     }
+
     void unblock( SignalObserver* observer )
     {
         auto it = m_observerCallbacks.find( observer );