Hi Hartwig, As far as I can tell the code and comment is correct, the unref afterwards is to catch cases like:
osg::Group* parent = new osg::Group; osg::Node* child = new osg::Geode; parent->addChild(child); osg::ref_ptr<osg::Node> ptr = parent; // takes a reference to pararent ptr = parent->getChild(0); // should take a references to child and then unref the parent deleting it Now think what would happen if you unref first... it would delete the parent and it's child, then you'd assign a dangling pointer. If the compiler's optimizer is breaking this then... it's a terrible compiler. It does highlight how subtle ref counting can be, and how much optimizers can't just blindly do certain types of optimization like re-ordering. Robert. On 24 October 2017 at 23:34, Hartwig Wiesmann <[email protected]> wrote: > Hi, > > in ref_ptr you find the following code: > > > Code: > > template<class Other> void assign(const ref_ptr<Other>& rp) > { > if (_ptr==rp._ptr) return; > T* tmp_ptr = _ptr; > _ptr = rp._ptr; > if (_ptr) _ptr->ref(); > // unref second to prevent any deletion of any object which > might > // be referenced by the other object. i.e rp is child of the > // original _ptr. > if (tmp_ptr) tmp_ptr->unref(); > } > > > > > I was puzzled by the comment: actually, there is nothing that prevents an > optimiser to re-write the code to > > Code: > > if (tmp_ptr) tmp_ptr->unref(); > if (_ptr) _ptr->ref(); > > > > > or > > > Code: > > _ptr->unref(); > _ptr = rp._ptr; > if (_ptr) _ptr->ref(); > > > > > It seems to be that it has not happened, yet, respectively the scenario > described in the comment did not occur, but this does not mean that it > cannot happen, or? > Actually, I do not see a solution for the described scenario, so probably > the comment should be removed or changed? But in this case the code can be > simplified, too. > > Cheers, > Hartwig[/code] > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=72242#72242 > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >
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