[mpich-discuss] A bit of clarification on Bcast - Send - Recv

[Dorian Krause]

Hi Dave,

the MPI_Bcast will block unless all members of the communicator issue 
the call. Therefore there is no chance to receive the message with 
MPI_Recv. The text you are referring to explains why you *can't* do it 
with MPI_Recv (the session is titled "Common Errors and 
Misunderstandings")...

Hiatt, Dave M wrote:
> First, I apologize for "if you node", if A node, sorry I think a lot faster than I can type (thank goodness for that).
>
> My question revolves around a statement on Pg 66 of Using MPI, which led me to believe that I could use MPI::Recv to receive MPI::Bcast messages.  "An MPI::Recv does not have to check whether the message it has just received is part of a broadcast .....".  But in every attempt I have made to us MPI::Recv, it never responds to a MPI::Bcast.  I have assumed that I am making some bonehead mistake, but am now totally frustrated that I have failed to get this to work.  MPI::Bcast on the receiving node works fine as a receiver, but MPI::Recv does not for broadcast messages.  I am on 1.0.7 of MPICH2 by the way.
>
> Thanks again
> Dave
>
>
> "Premature optimization is the root of all evil" - Donald Knuth
> Dave Hiatt
> Manager, Market Risk Systems Integration
> CitiMortgage, Inc.
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>