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

[Hiatt, Dave M]

Thanks Dorian,

You are up late!

-----Original Message-----
From: mpich-discuss-bounces at mcs.anl.gov
[mailto:mpich-discuss-bounces at mcs.anl.gov]On Behalf Of Dorian Krause
Sent: Wednesday, August 26, 2009 4:50 PM
To: mpich-discuss at mcs.anl.gov
Subject: Re: [mpich-discuss] A bit of clarification on Bcast - Send -
Recv


Hiatt, Dave M wrote:
> 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?
>

The MPI standard guarantees that pt-2-pt communication and collective
calls do not interfer (p. 131). With a standard conforming
implementation you can use the same communicator.

> -----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
>> Mobile: 314-452-9165
>> FAX:    636-261-1312
>> Email:     Dave.M.Hiatt at citigroup.com
>>
>>
>>
>>
>>
>>