Hello Carsten, "Carsten Neumann" <carsten_neum...@gmx.net> schrieb im Newsbeitrag news:4f4fa2b3.3030...@gmx.net... > On 03/01/2012 05:16 AM, Johannes Brunen wrote: >> I have another problem/misunderstanding with respect to deep cloning. >> >> I have a ChunkMaterial which I need to clone. The material has embedded >> ClipPlaneChunks with properly initialized beacon fields. Now, I have >> discovered that the ClipPaneChunks of the deep copied ChunkMaterial >> still has initialized beacon fields, but on calling getBeacon() on them, >> I got a Null pointer. Inspection revealed that the _iRefCount is zero >> which prevents returning the beacon object in the following code: > > the beacons are only held with weak pointers so that you can use an > ancestor node as beacon without generating loops of ref counted objects > - which then would not destroy properly.
yes... > A weak pointer will prevent the destructor of the pointed-to object from > running, but only so that the weak pointer has a chance to actually > notice that it's pointed-to object is actually dead. That is what the > code below handles: My understanding of a weak pointer is different. It should not prevent destruction of the pointed-to object, but give means to test, if it is still available. Isn't that the way the boost shared_ptr weak_ptr are designed, for instance? >From the boost documentation: The weak_ptr class template stores a "weak reference" to an object that's already managed by a shared_ptr. To access the object, a weak_ptr can be converted to a shared_ptr using the shared_ptr constructor or the member function lock. When the last shared_ptr to the object goes away and the object is deleted, the attempt to obtain a shared_ptr from the weak_ptr instances that refer to the deleted object will fail: the constructor will throw an exception of type boost::bad_weak_ptr, and weak_ptr::lock will return an empty shared_ptr. So, this is another kind of weak pointer, with different semantics, I guess? > > well, it wasn't explicitly designed to behave in this somewhat > unexpected way, but I don't think there is much the generic deepClone() > can do to handle this better - for starters it would have to return a > sequence of parent-less nodes (the root of the tree you clone and > parent-less beacons in the tree). > That means, that deep cloning is quite a dangerous operation! Generally, you don't know about the details (beacons) of the tree you are cloning... Howerver, I have understood, that my design is flawed at this point, and I will look for a proper solution. Best, Johannes ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Opensg-users mailing list Opensg-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/opensg-users
