[Octave-bug-tracker] [bug #45294] octave-forge-mpi issues with struct (with test case and patch)

[Alexander Barth]

Follow-up Comment #3, bug #45294 (project octave):

Yes, I have noticed also problems with non-scalar structures.
When you send to multiple nodes at once (using a vector of ranks), to current
code can hang. I think that this has to do with the handling of the tag
parameter which is a bit simplified in the attached patch.

For instance I did not increment the tag by the capacity of the cell. I
presume that in the original code, this is to avoid the reuse of the same tag
number. This is a good idea, but it assumes that each individual cells can be
send with a single MPI_send call (which is not the case if the individual
element is a struct for instance).

A better approach, in my opinion, would be to pass the tag parameter by
reference to the send_class/send_cell (and similar) functions and increment
the tag by the actual calls to MPI_Send/MPI_Recv.

But as this is a quite large change. Here I wanted to limit the extend of the
patch.



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