Combined Send/Receive
Suppose task 0 sends data to task 1 and at the
same time receives data from task 2.This can be
achieved through a combined send/receive call.
Technically this sends a message and posts a
receive before blocking.
It will block till the sending application buffer is
free for reuse and the receiving application
buffer contains the sent message.
MPI_SENDRECV (sendbuf, sendcount,
sendtype, dest, sendtag, recvbuf, recvcount,
recvtype, source, recvtag, comm, status,ierr)