HI Mikael, Thanks for the details.
Your comment about the delete not being mutexed made me think about why the ref count could get to zero and then have the thread progress to delete, and one shouldn't progress to delete as long as the ref count is non zero. This led me to wonder just how with your code this could happen and I think the crux of it is that in your test app you are creating an object using a C pointer to it, then letting different threads assign and reset ref_ptr<> independently. For the case where it crashes my guess is that the main thread creates the MyThread and this stores a C pointer to the Image, then the main thread calls startThread() which returns to main which then assigns and resets the ref_ptr<>, if this assign/reset happens before the MyThread::run() gets going and creates it's own ref to the Image then it'll be deleted before it gets a chance to increment the ref count. This isn't a bug in ref counting, it's a bug in your code - MyThread should never have been written with a C pointer in the first place, as this opens the door to the sequence I've explain and problem you are seeing. So I think this example is good one for demonstrating how dangerous it is to use C pointers and ref_ptr<>'s without taking proper care about sequencing of the creation and assignments. These types of errors are very hard to spot, even on an example as small of yours it's not obvious, so taking a full scale app it becomes very hard to spot these problems indeed. The best defence is to be very careful anytime you pass C pointers around, and especially carefully when you retain C pointers for use later. Robert. On 7 February 2012 13:50, mikael lemercier <[email protected]> wrote: > > 2012/2/7 Robert Osfield <[email protected]> >> >> Also what hardware, OS, dev environment are you working on? > > > I'm working on: > - Hardware : Intel Core i7-2600 > - OS : Windows 7 > - Dev environment : Visual 2010 > - Build config : x64 > > I also reproduced the problem on: > - Hardware : Intel Core i7-2600 > - OS : OpenSuse 11.1 > - Dev environment : Eclipse > > >> >> Could you also check whether the OSG is using atomic ref counting or >> OpenThreads::Mutex version? include/OpenThreads/Config will reveal >> which should be being used. > > > It's using atomic ref counting in my case : > _OSG_REFERENCED_USE_ATOMIC_OPERATIONS is defined. > But the problem might also exist with Mutex, since in both cases the delete > part is not locked. > >> >> Could you also outline how you are running your tests. > > > To reproduce the problem, without any interference from my work, I inserted > my test file directly in the osg solution. > I just replaced osgviewer.cpp by my test file (joined with my first > message). > As I said before, I also added a sleep() of 1s to the Referenced::unref() > function so that the created thread has time to increment the refCount > before the main thread calls the delete. > > > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
