Hi Baker, It really couldn't say whether this might be an new OSG bug or just co-incidence that changing OSG version reveavlled a bug in your code that has be lingering for a while just waiting for the right time to ruin your day - threading bugs have a habit of doing!
As I don't know your code there isn't much directly I can do. The only thing I'd suggest that might be an area to look at is to always use ref_ptr<> in all your code. The read*File() methods doing pass C pointers which does open one to possibility of problems if other codes are retaining a ref_ptr<> to it but that ref_ptr<> itself could be deleted by another thread. The solution to this is to use readRef*File() methods that all pass be a ref_ptr<>, or to do the read call directly from the Registry where you get back a ReadResult that holds a ref_ptr<> to the object. If you have a look at the OpenSceneGraph/src/osgDB/DatabasePager.cpp usage of read*File() you'll see that it gets the ReadResult. The advantage it has it you can also get more information about failures as well as it being thread safe. Robert. On 19 November 2013 19:46, Bradley Baker Searles <bakersear...@gmail.com>wrote: > Hello, > > Summary: > > Since upgrading to OSG 3.2, our application will crash during render while > loading a legacy .OSG file on a worker thread. The legacy/deprecated OSG > code will load objects that are put into the object cache, but then use > "takeImage" to get a raw pointer to a ref-counted object. If the threads > are serviced in a particular order the main thread will do cache cleanup > and delete this object that looks like it has no references while the load > thread is pre-empted. > > More Detail: > > In this use case, the rendered scene graph is empty, and the loaded assets > are not introduced into the scene graph until the worker thread returns. > Let me map out the basic flow of the error case (not that freezing the > worker thread when it has the raw pointer can trigger this crash every > time): > > > Code: > > WORKER THREAD: > * Texture2D_readLocalData > (src/OsgWrappers/deprecated-dotosg/osg/Texture2D.cpp) calls: > * Input::readImage(), which calls > * osgDB::readImageFile(), which uses rr.takeImage() to return a raw > pointer. > * NOTE: the only reference count to the Image at this point is from the > cache object. > > MAIN THREAD: > * Registry::updateTimeStampOfObjectsInCacheWithExternalReferences() > *** timestamp is not updated because there are no counted external > references! > * Registry::removeExpiredObjectsInCache() > *** this deletes the object because the timestamp was not updated above. > > WORKER THREAD: > * raw Image pointer is added to the texture, but it's not valid at this > point. Crash ensues. > > > > > There are several fixes I can think of offhand, some seem more proper than > others. I'm not sure why the raw pointer usage is there, it would seem to > violate the principle of the smart pointers. > > POSSIBLE FIXES: > > 1. Remove code that "sort of" uses ref counting, or remove ref-counting > along entire speed critical paths. This would seem most correct at a glance. > 2. Do not render while loading. We've done this as a temporary fix, but > the drawbacks are obvious. Heck, maybe this is not a supported feature and > I have just somehow missed this along the way. > 3. Introduce an "UNDEFINED TIME" to initialize cache objects to when > they're added (instead of the 0.0 that the parameter currently defaults > to). This would allow the problem to be masked to not happen as long as the > objects are re-ref-counted within the timeframe alotted to the object > cache. I implemented this as well, and it works in our situation, although > if I were to freeze the load thread long enough in the right spots I could > get it to fail, implying it's not proper in my mind. > 4. Don't use old style OSG files. This is not really a good option for > us, we've been using OpenSceneGraph for years, and we have a lot of > customers with legacy OSG data out there. Our typical use has a mixture of > OSG and OBJ files, the OBJ load paths seem to use refcounted pointers > throughout. > > I would have supplied a patch with this post, but not fully understanding > the intentions of this code prevents me from creating something that I'm > sure is "correct". > > Build/Test Environment: > OSG 3.2, using wxWidgets 2.9.5 for windowing > Windows 8.1, 64-bit > Visual Studio 2010 > > Input, insight, or better solutions would be greatly appreciated. > > Thanks > Baker > [/code] > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=57327#57327 > > > > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >
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