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Subject: Re: [Boost-users] [Boost.MPI] SendingReceiving an array "view"
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2009-05-11 08:34:07

Joel Falcou wrote:
> I have a small class view<T> that containes a T* and a size. When I
> send/receive view using Boost.MPI, I want transfert the actual n data
> pointed by the view pointer and send the size. On receiving, i will
> receive the size, checks if they are compatible and receive the data
> into the zone pointed by the pointer of the receiving view. Of course,
> I may do something more complex than send/Receive, like all_2_all etc.
> So i was thinking to give view<T> a proper serialize function so
> boost.serialization may kick in. As the behavior of sending and
> receiving is different, I use the load/save idiom to separate the
> behavior. The question is then, how to serialize the n elements
> poitned by a raw pointer to those data in an efficient way ?
Back to this issue, now here is my use case.

On my N MPI process, I have an array of float (let's say any fundamental
types if we want).
All processor build a few "view" of this array to map a small subset of
contiguous data.

float tab[]= {1,2,3,4,5,6,7,8,9,10};
view<float> v0(&tab[0],5);
view<float> v1(&tab[5],5);

Then I have an array of optional<view<T>> that will contain v0 and v1.

optionall< view<float> > data[2] = {v0,v1};

What I want next is to use mpi::all_to_all to send those data across.


In this example, what I want to have is that the data from v1 to be send
from P0 to P1 and data
from v0 to be send from P1 to P0 *without copies if possible* by hoping
that the serialization will
forward the data through the view pointer. view serialization is done
using make_array.

If I won't use optional, it works. Once I put those in optional, the
serialization of optional actually overwrite the data
by calling the in-place default constructor of view, which reset the
pointer to 0 and prevent proper serialization (no error but, at runtime,
the data just aren't transfered).

Is there anything I missed or should I abandon the idea to use
make_array and roll on my own serialization routine ?


Joel Falcou - Assistant Professor
PARALL Team - LRI - Universite Paris Sud XI
Tel : (+33)1 69 15 66 35

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