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Subject: [OMPI users] A question on MPI_Probe
From: devendra rai (rai.devendra_at_[hidden])
Date: 2012-09-21 18:32:59

Hello, 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. Devendra Rai.