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>

3 files changed, 22 insertions, 0 deletions

diff --git a/src/render/geometry/qattribute.cpp b/src/render/geometry/qattribute.cpp
index 1e9348567..671179f20 100644
--- a/src/render/geometry/qattribute.cpp
+++ b/src/render/geometry/qattribute.cpp
@@ -258,6 +258,9 @@ void QAttribute::setBuffer(QBuffer *buffer)
     if (d->m_buffer == buffer)
         return;
 
+    if (d->m_buffer)
+        d->unregisterDestructionHelper(d->m_buffer);
+
     // We need to add it as a child of the current node if it has been declared inline
     // Or not previously added as a child of the current node so that
     // 1) The backend gets notified about it's creation
@@ -266,6 +269,11 @@ void QAttribute::setBuffer(QBuffer *buffer)
         buffer->setParent(this);
 
     d->m_buffer = buffer;
+
+    // Ensures proper bookkeeping
+    if (d->m_buffer)
+        d->registerDestructionHelper(d->m_buffer, &QAttribute::setBuffer, d->m_buffer);
+
     emit bufferChanged(buffer);
 }
 
diff --git a/src/render/geometry/qgeometry.cpp b/src/render/geometry/qgeometry.cpp
index 57222a364..9b6b9a8e7 100644
--- a/src/render/geometry/qgeometry.cpp
+++ b/src/render/geometry/qgeometry.cpp
@@ -124,6 +124,9 @@ void QGeometry::addAttribute(QAttribute *attribute)
     if (!d->m_attributes.contains(attribute)) {
         d->m_attributes.append(attribute);
 
+        // Ensures proper bookkeeping
+        d->registerDestructionHelper(attribute, &QGeometry::removeAttribute, d->m_attributes);
+
         // We need to add it as a child of the current node if it has been declared inline
         // Or not previously added as a child of the current node so that
         // 1) The backend gets notified about it's creation
@@ -152,6 +155,8 @@ void QGeometry::removeAttribute(QAttribute *attribute)
         d->notifyObservers(change);
     }
     d->m_attributes.removeOne(attribute);
+    // Remove bookkeeping connection
+    d->unregisterDestructionHelper(attribute);
 }
 
 void QGeometry::setBoundingVolumePositionAttribute(QAttribute *boundingVolumePositionAttribute)
diff --git a/src/render/geometry/qgeometryrenderer.cpp b/src/render/geometry/qgeometryrenderer.cpp
index a714c3155..db59f04a6 100644
--- a/src/render/geometry/qgeometryrenderer.cpp
+++ b/src/render/geometry/qgeometryrenderer.cpp
@@ -398,10 +398,19 @@ void QGeometryRenderer::setGeometry(QGeometry *geometry)
         d->notifyObservers(change);
     }
 
+    if (d->m_geometry)
+        d->unregisterDestructionHelper(d->m_geometry);
+
     if (geometry && !geometry->parent())
         geometry->setParent(this);
 
     d->m_geometry = geometry;
+
+
+    // Ensures proper bookkeeping
+    if (d->m_geometry)
+        d->registerDestructionHelper(d->m_geometry, &QGeometryRenderer::setGeometry, d->m_geometry);
+
     const bool blocked = blockNotifications(true);
     emit geometryChanged(geometry);
     blockNotifications(blocked);