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

Hi Riccardo, On Nov 21, 2010, at 2:18 AM, Riccardo Murri wrote:

On Sun, Nov 21, 2010 at 9:27 AM, Heiko Bauke wrote:

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Riccardo Murri wrote:

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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?

It seems you're asking what the Boost.MPI implementation does and, to me, you shouldn't depend on an implementation detail of Boost.MPI for the correct operation of your code. I'd stick to the documented behavior and either use a blocking form of send so that you know you're free to release the data once send returns, or use iSend and correctly interrogate or wait on the returned request object. -- Noel