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Subject: Re: [OMPI users] Best way to reduce 3D array
From: Ricardo Reis (rreis_at_[hidden])
Date: 2010-04-05 15:20:16


On Mon, 5 Apr 2010, Rob Latham wrote:

> On Tue, Mar 30, 2010 at 11:51:39PM +0100, Ricardo Reis wrote:
>>
>> If using the master/slace IO model, would it be better to cicle
>> through all the process and each one would write it's part of the
>> array into the file. This file would be open in "stream" mode...
>>
>> like
>>
>> do p=0,nprocs-1
>>
>> if(my_rank.eq.i)then
>>
>> openfile (append mode)
>> write_to_file
>> closefile
>>
>> endif
>>
>> call MPI_Barrier(world,ierr)
>>
>> enddo
>
> Note that there's no guarantee of the order here, though. Nothing
> prevents rank 30 from hitting that loop before rank 2 does. To ensure

don't they all have to hit the same Barrier? I think that will ensure
order in this business... or am I being blind to something?

I will agree, though, this is not the best solution to do it. I use this
kind of arrangment when I'm desperate to do some prinf kind of debugging
and want it ordered by process. Never had a problem with it.

I mean, I assume there is some sort of sync before the do cycle starts.

  cheers!

  Ricardo Reis

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