In addition to routines to receive messages, MPI provides routines to
determine whether a message could be received. The corresponding ADI
functions are
MPID_Probe (blocking test) and MPID_Iprobe (nonblocking test).
Since these perform message matching in the same way as the receive
routines do, they have similar argument lists.
MPID_Probe( comm, tag, context_id, src_lrank, &error_code, &status ) MPID_Iprobe( comm, tag, context_id, src_lrank, &flag, &error_code, &status )Just as for the receive routines (both blocking and wait/test on a receive request), the status argument may be null.
Note that MPID_Probe and MPID_Iprobe may need both relative rank and global rank, depending on how the message is tested for. See the Meiko device (in mpid/meiko) for an example. However, since the communicator is passed to the device, it is as easy for the device to convert relative rank to absolute rank as it is for the MPI implementation. This is the same as for the corresponding MPID_Recvxxxx routines.