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

[Hiatt, Dave M]

Thanks, yes I took it initially that way, but then I read too closely I guess.

So if Bcasts' and Recvs' are intermingled, is MPICH2 completely thread safe so that I can have both a Bcast and a Recv outstanding on two different threads for the same process (rank) or do I need to make communicators for the Recvs' that are different than for the Bcasts', what's the best approach?

-----Original Message-----
From: mpich-discuss-bounces at mcs.anl.gov
[mailto:mpich-discuss-bounces at mcs.anl.gov]On Behalf Of Rajeev Thakur
Sent: Wednesday, August 26, 2009 4:34 PM
To: mpich-discuss at mcs.anl.gov
Subject: Re: [mpich-discuss] A bit of clarification on Bcast - Send -
Recv


No you cannot match a broadcast with a receive. Note that the text you
mention in Using MPI comes under the section "Common Errors and
Misunderstandings", one of which is "Matching MPI_Bcast with MPI_Recv."

Rajeev

> -----Original Message-----
> From: mpich-discuss-bounces at mcs.anl.gov
> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of Hiatt, Dave M
> Sent: Wednesday, August 26, 2009 4:19 PM
> To: mpich-discuss at mcs.anl.gov
> Subject: [mpich-discuss] A bit of clarification on Bcast - Send - Recv
>
> 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.
> 1000 Technology Dr.
> Third Floor East, M.S. 55
> O'Fallon, MO 63368-2240
>
> Phone:  636-261-1408
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> Email:     Dave.M.Hiatt at citigroup.com
>
>
>
>
>