[mpas-developers] proposed fix in src/registry/gen_inc.c

[Todd D. Ringler]

Hi Michael,

I think that the fix is appropriate.

We might want to consider making an init after every allocation a standard
practice.

Cheers,
Todd


> Hi, All.
>
> Jeff Painter at LLNL has found a problem related to the use of
> unitialized grid metadata fields in the hydrostatic MPAS core, and
> his fix involves the shared registry code src/registry/gen_inc.c.
> Since the bug fix is to common code, and since other cores might
> be affected by similar bugs, I'd like to propose the changes in
> the attached gen_inc.c (search for "initialize field") for
> inclusion in the trunk.
>
> An example of where we would be caught by uninitialized fields is
> given in the loop below, where either cell1 or cell2 may equal
> nCells+1 when iEdge is at the boundary of a block, and the
> nCells+1 element of nEdgesOnCell could take on any value:
>
>    do iEdge=1,nEdges
>       cell1 = cellsOnEdge(1,iEdge)
>       cell2 = cellsOnEdge(2,iEdge)
>
>       do k=1,grid % nVertLevels
>
>          d2fdx2_cell1 = deriv_two(1,1,iEdge) * theta(k,cell1)
>          d2fdx2_cell2 = deriv_two(1,2,iEdge) * theta(k,cell2)
>          do i=1, grid % nEdgesOnCell % array (cell1)
>             d2fdx2_cell1 = d2fdx2_cell1 + deriv_two(i+1,1,iEdge) *
> theta(k,grid % CellsOnCell % array (i,cell1))
>          end do
>
>          ...
>
>       end do
>    end do
>
> Although there are other ways that we could handle the
> uninitialized nCells+1/nEdges+1/nVertices elements of grid
> indexing arrays, Jeff's fix is simple, and adds a only very small
> overhead during model startup. The change to gen_inc.c adds lines
> like those marked below in src/inc/grid_meta_allocs.inc:
>
>       allocate(g % latCell)
>       allocate(g % latCell % ioinfo)
>       allocate(g % latCell % array(nCells + 1))
>       g % latCell % array = 0                   <- additional code
>       g % latCell % ioinfo % input = .true.
>       g % latCell % ioinfo % restart = .true.
>       g % latCell % ioinfo % output = .true.
>
>       allocate(g % lonCell)
>       allocate(g % lonCell % ioinfo)
>       allocate(g % lonCell % array(nCells + 1))
>       g % lonCell % array = 0                   <- additional code
>       g % lonCell % ioinfo % input = .true.
>       g % lonCell % ioinfo % restart = .true.
>       g % lonCell % ioinfo % output = .true.
>
>
> If anyone has any thoughts or concerns, I'd be glad to hear them.
> Otherwise, unless there are any objections, I'd like to commit the
> attached version of gen_inc.c to the repository trunk.
>
> Cheers,
> Michael
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