MPI_Iprobe is the non-blocking version of MPI_Probe. Unlike classic non-blocking operations, this routine does not work with an MPI_Request. Instead, it tells whether a message corresponding to the filters passed is waiting for reception or not, via a flag that it sets. If no such message has arrived yet, it does not wait like MPI_Probe, instead it sets the flag to false and returns. Otherwise, it sets the flag to true as well as setting the status.