Take a look at revision 4214 to src/mesh/mesh_refinement.C It's the "implicit PointLocator construction fails" bug again, but this time with no threads involved. If a problem with periodic boundaries was run under certain conditions and on the right partitioning, then some of the MPI ranks (those with partitions falling on a periodic boundary) would need to construct/update a PointLocator to do searches across the boundary, while other ranks would not. PointLocatorTree's constructor needs to run on all ranks to build a bounding box, and so fails.
The fix is the same, but I'm not sure how to make sure we catch this problem in the future. That "libmesh_assert(!Threads::in_threads)" call is a good safeguard for the "in threaded code" case, but what about the "in an ordinary local_elements loop" case? The library is fixed for now, but it's an easy mistake to repeat. I'm going to Cc: Derek since his people are probably the most likely to get bitten by this in user code too. The problem: point_locator(), and topological_neighbor(), and perhaps an expanding range of future functions, should not be used inside element loops unless the loop is preceded by an explicit PointLocator construction. The only solutions I can think of: 1. The default: we accept that code with this problem may work fine on N processors but then die horribly on N+1. 2. We could create a convoluted functor-class-based paradigm similar to Threads::/TBB to enable a similar test... but if we go through that much trouble we might as well just make every single local_elements loop multithreaded. 3. We could wait for the neat lambda function support in C++0x... or was that C++1x? 4. We always generate a PointLocatorTree when preparing an updated Mesh. This is too expensive for users who don't need the tree, and it won't fix things when (as was just the case) the problem is in a class like MeshRefinement that's in the middle of the Mesh-updating process. --- Roy ------------------------------------------------------------------------------ Free Software Download: Index, Search & Analyze Logs and other IT data in Real-Time with Splunk. Collect, index and harness all the fast moving IT data generated by your applications, servers and devices whether physical, virtual or in the cloud. Deliver compliance at lower cost and gain new business insights. http://p.sf.net/sfu/splunk-dev2dev _______________________________________________ Libmesh-devel mailing list Libmesh-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-devel
