CODEWITHSUNDEEP
clinuxparallel-processingmpiopenmpi
beasone
beasone

Reputation: 1085

Can OpenMPI guarantee order of received message come from the same process?

For example, I use mpirun -n 4 to start 4 processes. Process 0 receives messages come from process1, process2 and process3. Process 1 sends messages in the order of message0, message1, message2. When process 0 receives these messages come from process1, can it guarantee that process receives these messages in the oder of message0, message1, message2 ? I don't care about the total order of all messages come from all different processes, I only need to know whether it can guarantee the order of messages come from the same process . By the way, when I use MPI_Send() to send message, the size of message is limited, right? What about MPI_Bcast() ?

Upvotes: 2

Views: 550

Answers (1)

Hristo Iliev
Hristo Iliev

Reputation: 74395

As long as message0, message1, and message2 have the same tag and are sent within the same communicator comm, the MPI standard guarantees that MPI_Recv(..., source, tag, comm, ...) will receive the messages in exactly the same order.

The size of the message is limited by the implementation, but most modern ones support messages of more than 2 GiB of size. You have to use user defined datatypes though as MPI_Send cannot send more than 231-1 elements at a time.

Upvotes: 5

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