[mpich-discuss] problem with collective on sub-communicator

[Miguel Oliveira]

Hi,

Sorry, sent the version with the only correction I found that makes it work. Remove the MPI_Barrier(world) in both the master and the slaves and you should be able to reproduce the problem.

Cheers,

MAO 

On Nov 11, 2011, at 03:31 , Pavan Balaji wrote:

> 
> The test code you sent seems to work fine for me. I don't see any such problem.
> 
> -- Pavan
> 
> On 11/10/2011 03:14 PM, Miguel Oliveira wrote:
>> Hi all,
>> 
>> I wrote a very simple master/slave code in MPI and I'm having problems with MPI_Reduce, or even, MPI_Barrier, inside a subset of the world communicator.
>> These operations don't seem to be waiting for all the processes in the subgroup.
>> 
>> The code is a straightforward master/slave case where the master generates random numbers when requested and then retrieves a reduction of the sum of these
>> done on the slaves.
>> 
>> When run on more than three processes sometimes it happens that the message after the reduction, done from one of the slaves to inform the master of the final
>> result gets to the master before some of the requests for random numbers... This ought to be impossible with a blocking reduction...
>> 
>> Am I missing something?
>> 
>> Code is attached.
>> 
>> Help is appreciated.
>> 
>> Cheers,
>> 
>> MAO
>> 
>> 
>> 
>> 
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> 
> -- 
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji

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