# sandbox/bugs/automatic.c

The following example illustrates a scenerio where not all MPI treads try to set (automatic) boundary conditions. It may wait forever or crashes occur when other threads continue to set boundary conditions in other contexts.

Stéphane Popinet replies:

As soon as you “branch” execution depending on process number, i.e. here

if (pid() == 0)
do_something();

you need to be sure that “do_something();” is completely independent from what is happening in other processes (otherwise this thread will get stuck forever waiting for other processes).

This is not specific to Basilisk.
int main() {
init_grid(N);
scalar s[];
foreach()
s[] = x;
if (pid() == 0)
interpolate (s,  0.1, 0.1);
printf ("%d\n", pid());
}