When to use MPI_BUFFER_ATTACH?

Question

As far as I know, MPI_BUFFER_ATTACH must be called by a process if it is going to do buffered communication. But does this include the standard MPI_SEND as well? We know that MPI_SEND may behave either as a synchronous send or as a buffered send.

Answer 1

You need to call MPI_Buffer_attach() only if you plan to perform (explicitly) buffered sends via MPI_Bsend().

If you only plan to MPI_Send() or MPI_Isend(), then you do not need to invoke MPI_Buffer_attach().

FWIW, buffered sends are error prone and I strongly encourage you not to use them.