Re: [Boost-users] [MPI] lifetime of data sent through communicator::isend()

Subject: Re: [Boost-users] [MPI] lifetime of data sent through communicator::isend()
From: Matthias Troyer (troyer_at_[hidden])
Date: 2010-11-21 15:48:57

On 21 Nov 2010, at 10:18, Riccardo Murri wrote:

> Hi Heiko and Noel,
> 
> On Sun, Nov 21, 2010 at 9:27 AM, Heiko Bauke <heiko.bauke_at_[hidden]> wrote:
>> Riccardo Murri <riccardo.murri_at_[hidden]> wrote:
>>> I'm using mpi::communicator::isend where the payload data comes from a
>>> pointer (e.g., "req = comm_.isend(dest, tag. *data)").
>>> When am I free to "delete" the pointer?  Immediately after isend()
>>> returns?  Or should I wait until the request is completed?
>> 
>> yes, you have to wait before you can free your memory. See
>> http://www.mpi-forum.org/docs/mpi22-report/node57.htm
>> and the following pages.
>> 
> 
> Thanks for the answers.  However, I think I didn't make myself clear:
> I know what I should do with the C-level MPI_ISend() calls, I'm not
> sure what I can do after an Boost.MPI's communicator::isend().
> 
> My reading of the docs is that Boost.MPI creates an instance of
> boost::mpi::packed_oarchive archive and sends *that* one with
> MPI_ISend().  So the question is: can I "delete data;" immediately
> after I do "communicator::isend(..., *data);", or does the Boost.MPI
> archive hold a reference to the "*data" buffer?  In other words, does
> Boost.MPI *copy* data into the archive or does it just reference it
> somehow?

Hi Riccardo,

It actually does not even create the packed_oarchive until you wait on the request.

Matthias