I believe my understanding of MPI_Probe is not correct. Here's what I have as a setup:
Two MPI processes, A and B. Process A sends a large message, M1 using tag T1, and a small message, M2 using tag T2. The recepient of both messages is B.
The order of sending the messages is M1 and then M2.
The process B however executes MPI_Probe to test if the message with tag T2 is available. B will accept M1 after it has received M2 first.
I am under the impression that using information gained from MPI_Probe, I can choose not to receive message M1, and instead look for M2.
However, I see that M2 is never received by B (although A confirms that both M1 and M2 have been sent).
I am little confused. Can someone explain why B cannot receive M2? At least, does MPI allow receiving messages in the order that I have just described?
Thanks a lot.