[petsc-dev] Bug in MatShift_MPIAIJ ?

[Patrick Lacasse]

I have a dead lock in MatAssemblyEnd_MPIAIJ.
It uses nonew as collective :
if (!((Mat_SeqAIJ*)aij->B->data)->nonew) {
    ierr = MPI_Allreduce( ...

this is a good optimization for me, however this value is set by
MatSetOptions(,MAT_NEW_NONZERO_ALLOCATION_ERR,)
and this enum is negative
MAT_NEW_NONZERO_ALLOCATION_ERR = -2
thus it is not asserted as collective by MatSetOption.

Some of my procs have nonew==0 and one has nonew==-2.
I'm not sure why adding new nonzero should be an error only for some procs?
I suggest that this error flag should be set collectively, so changing the
value of the enum to positive (patch 0001).

My reel problem was caused by MatShift_MPIAIJ and the way it determine if
the matrix need to be preallocated :
if (!aij->nz && !bij->nz)
the results can be true for some procs (with no local lines)
and false for other procs.
I suggest to use Y->preallocated instead (patch 0002).

thanks,

Patrick Lacasse
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