Shared node bookkeeping

Any time a property references a QNode there is a risk that the node gets
destroyed and then the property is left pointing to a dangling pointer.

To handle such cases, setters of such properties are able to use a helper
that internally connect QObject::destroyed signal to a setter removal method.

Change-Id: I42428c851d0e3d2d88ab0cf6a5b75605334ec648
Task-number: QTBUG-53456
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/core/nodes/qnode_p.h b/src/core/nodes/qnode_p.h
index e290ffe32..8f48dd728 100644
--- a/src/core/nodes/qnode_p.h
+++ b/src/core/nodes/qnode_p.h
@@ -57,6 +57,7 @@
 #include <Qt3DCore/private/qchangearbiter_p.h>
 #include <Qt3DCore/private/qt3dcore_global_p.h>
 #include "propertychangehandler_p.h"
+#include <functional>
 
 QT_BEGIN_NAMESPACE
 
@@ -100,6 +101,33 @@ public:
     static QNodePrivate *get(QNode *q);
     static void nodePtrDeleter(QNode *q);
 
+    template<typename Caller, typename NodeType>
+    using DestructionFunction = void (Caller::*)(NodeType *);
+
+    template<typename Caller, typename NodeType, typename PropertyType>
+    void registerDestructionHelper(NodeType *, DestructionFunction<Caller, NodeType>, PropertyType);
+
+    template<typename Caller, typename NodeType>
+    void registerDestructionHelper(NodeType *node, DestructionFunction<Caller, NodeType> func, NodeType *&)
+    {
+        // If the node is destoyed, we make sure not to keep a dangling pointer to it
+        auto f = std::bind(func, static_cast<Caller *>(q_func()), nullptr);
+        m_destructionConnections.insert(node, QObject::connect(node, &QNode::nodeDestroyed, f));
+    }
+
+    template<typename Caller, typename NodeType>
+    void registerDestructionHelper(NodeType *node, DestructionFunction<Caller, NodeType> func, QVector<NodeType*> &)
+    {
+        // If the node is destoyed, we make sure not to keep a dangling pointer to it
+        auto f = std::bind(func, static_cast<Caller *>(q_func()), node);
+        m_destructionConnections.insert(node, QObject::connect(node, &QNode::nodeDestroyed, f));
+    }
+
+    void unregisterDestructionHelper(QNode *node)
+    {
+        QObject::disconnect(m_destructionConnections.take(node));
+    }
+
 private:
     void notifyCreationChange();
     void notifyDestructionChangesAndRemoveFromScene();
@@ -118,6 +146,7 @@ private:
     friend class PropertyChangeHandler<QNodePrivate>;
     bool m_propertyChangesSetup;
     PropertyChangeHandler<QNodePrivate> m_signals;
+    QHash<QNode *, QMetaObject::Connection> m_destructionConnections;
 };
 
 } // namespace Qt3DCore