Barry Smith wrote:

I do not know a way to generate unique MPI-comm-id's. Any thoughts? Some feature of MPI I don't know?

This seems very hard. One could (the first time PETSc sees a communicator) hash the hostname+pid of every process on the communicator, start a counter on this hash, and set the communicator name to be the hash concatenated with this counter. I think this is sufficient, but it's kinda nasty. Jed