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Subject: Re: [OMPI users] Beginner Problem with OpenMPI (MPI_Waitall)
From: Joao Marcelo (jmarcelo.alencar_at_[hidden])
Date: 2008-06-27 11:51:27


Thanks Rainer and Matt, your suggestions solved my problem.

On Fri, Jun 27, 2008 at 11:44 AM, Matt Hughes
<matt.c.hughes+ompi_at_[hidden]> wrote:
> 2008/6/27 Joao Marcelo <jmarcelo.alencar_at_[hidden]>:
>> Hi,
>>
>> I'm starting to code with MPI and decided to use openmpi. I'm using
>> Ubuntu Linux with GCC version 4.2.3 and OpenMPI 1.2.5 (distribution
>> package). The output of "ompi_info -- all" is attached. I'm also
>> sending a copy of the source code I'm trying to run.
>
> One problem I see is that you are incorrectly indexing the reqs array:
>
> for ( i = 1; i < numtasks; ++i){
> rc = MPI_Isend(&a , 1 , MPI_INT , i , 0 , MPI_COMM_WORLD , &reqs[i]);
> }
>
> MPI_Waitall(numtasks - 1 , reqs , stats);
>
> If size = 3, you allocate enough space for two items in reqs but you
> index starting at one, so you access memory past the end of the array.
> Additional, MPI_Waitall will be looking at uninitialized memory in
> the first element of reqs. This is not immediately causing the crash,
> but it may be messing with MPI enough that Finalize crashes. Try:
>
> for ( i = 0; i < numtasks-1; ++i)
>
> Fixing that *might* fix your crash.
>
> mch
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-- 
__________________________________
João Marcelo Uchôa de Alencar
Computer Science BSc.
jmarcelo.alencar(at)gmail.com
Linux User 398939
__________________________________