CFD Online Discussion Forums - Boundary condition coding

Dear Forum,
I coded a boundary condition using

Code:

scalar Area = sum(patch().magSf());

to get he patch surface area.
Everything seems fine but in parallel runs the code segfaults on the threads that run on the mesh part that does not contain the patch in the following piece of code:

Code:

        if ( fabs(directions_*celerity_*xi*dimension[1]) > SMALL )

        {

            sourcevel = (directions_*celerity_*xi*dimension[1])/Area;

        }

Using the following

Code:

        if ( fabs(directions_*celerity_*xi*dimension[1]) > SMALL && fabs(Area) > SMALL )

        {

            sourcevel = (directions_*celerity_*xi*dimension[1])/Area;

        }

solves the problem but seems a bit clumsy.
Is there a better way of doing this? Why is a patch evaluated if it is not in the part of the decomposed domain?
Thanks for comments,
Have a great day,
Pal