[Boost-mpi] Collective Operations for Serialized Types

Subject: [Boost-mpi] Collective Operations for Serialized Types
From: Lorenz Hübschle-Schneider (huebschle_at_[hidden])
Date: 2015-08-26 05:32:07

Hello,

as I understand the Boost.MPI code, collective operations on types that 
need to be serialized always use point-to-point operations, e.g.
> https://github.com/boostorg/mpi/blob/772337fa4749d5de7699842b6dae603f83d70db5/include/boost/mpi/collectives/broadcast.hpp#L102
> https://github.com/boostorg/mpi/blob/772337fa4749d5de7699842b6dae603f83d70db5/src/broadcast.cpp#L18

This is vastly inefficient, and frankly the claim that MPI_Bcast cannot 
be used in this case does not make sense to me. Is there a case where 
something like
> https://gist.github.com/lorenzhs/79dab54552fd1f9381da
would not work?

I used the same idea to implement an Allgatherv operation on vectors 
(including size exchanges) and have been using it without issues. 
However, that requires a bit of awfulness, and I severely doubt that 
such ugly code would ever make it into Boost.MPI ;) For the curious, it 
(along with some other wacky things which I do not recommend anyone use) 
can be found at
> https://gist.github.com/lorenzhs/0ad22028cf6b68a91f3f#file-unsafe_mpi-hpp-L88

Cheers,
Lorenz

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Lorenz Hübschle-Schneider
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