CODEWITHSUNDEEP
parallel-processingmpi
cpp_noname
cpp_noname

Reputation: 2071

Can I use MPI_Probe to probe messages sent by a collective operation?

In my code I have a server process repeatedly probing for incoming messages, which come in two types. One type of the two will be sent once by each process to give hint to the server process about its termination.

I was wondering if it is valid to use MPI_Broadcast to broadcast these termination messages and use MPI_Probe to probe their arrivals.

I tried using this combination but it failed. This failure might have been caused by some other things. So I would like anyone who knows about this to confirm.

Upvotes: 0

Views: 610

Answers (2)

Jonathan Dursi
Jonathan Dursi

Reputation: 50927

No, you can only use MPI_Probe for testing for point-to-point communications. For collective communications, the only way to participate at all is to actively make the collective call. From the definition of MPI_Probe in the standard, "The call matches the same message that would have been received by a call to MPI_RECV(..., source, tag, comm, status) executed at the same point in the program" -- eg, it only matches point-to-point stuff like Recv would.

With the new nonblocking collectives coming in MPI3, you would however be able to use MPI_Test (or MPI_Wait) to check to see the status of the nonblocking request, just as you would with a nonblocking send/recv, although I haven't been following that WGs work too closely so I don't know the details.

Upvotes: 5

High Performance Mark
High Performance Mark

Reputation: 78334

I'm not sure that the MPI standard excludes this, but I don't see how it would be useful if it is possible. On the (rare) occasions when I've used mpi_probe I've used it to find out the size of an incoming message; it can, of course, get other information about messages 'in flight' too. But mpi_bcast is a collective operation so all the processes in a communicator know everything about a message that you could use mpi_probe to find out. I think ?

Upvotes: 1

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