Hello, I have a program that include two processes, one is doing a lot of MPI_Isend, the other one loops, receives the messages using MPI_Irecv and treats them. I'd like to know what the MPI-2 standard says, and what Mpich2 does, if the first process is too fast and the second process cannot keep up with the number of messages sent. Is the first process supposed to eventually block, waiting for the messages to be received, or will the application crashes? Thanks Matthieu Dorier PhD student at ENS Cachan Brittany and IRISA http://people.irisa.fr/Matthieu.Dorier