Hi All,

A colleague recently asked a question that I wasn't able to answer definitively. Is the following code guaranteed to make progress?

MPI_Barrier();
if rank == 1
create_file("test")
if rank == 0
while not_exists("test")
sleep(1);

That is, can rank 1 require rank 0 to make MPI calls after its return from the barrier, in order for rank 1 to complete the barrier? If the code were written as follows:

isend(..., other_rank, &req[0])
irecv(..., other_rank, &req[1])
waitall(2, req)
if rank == 1
  create_file("test")
if rank == 0
   while not_exists("test")
       sleep(1);

I think it would clearly not guarantee progress since the send data can be buffered. Is the same true for barrier?

Cheers,

~Jim.