Using MPI_Isend doesn't guarantee asynchronous progress. As you might be aware, the non-blocking communications are guaranteed to progress only when the application is in the MPI library. Currently very few MPI implementations progress asynchronously (and unfortunately Open MPI is not one of them).
On Nov 23, 2010, at 17:17 , Sébastien Boisvert wrote:
> I now use MPI_Isend, so the problem is no more.