[MOAB-dev] problem with exchange_ghost_cells

[Lorenzo Alessio Botti]

Dear all,
I’m writing to inform you all of a problem with MOAB in parallel that bothers me a lot.
Sometimes after reading a parallel .h5m mesh file and resolving shared entities the execution hangs while exchanging ghost cells.
The issue arises randomly but I noticed a clear tendency to occur when the number of elements in each partition decreases, that is, given the same mesh, when the number of partition increases.
Here attached is a simple code that should allow you to reproduce the issue (I tried to run both with 4.6.0 and trunk and obtain the same behavior).
mesh.h5m and mesh_ok.h5m are two different 16 part partitions of the same mesh (a 3D tetrahedral elements mesh). 
While with mesh_ok.h5m the code works perfectly, using mesh.h5m it hangs, meaning that the process with rank 1 does not return from exchange_ghost_cells if the code is executed in parallel with 16 processors (mpiexec -n 16 <reader_exec_name>). 
The weird thing is that the code works if executed on less that 16 processors  

Any help is appreciated. Thanks in advance.
Lorenzo

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