Robert Ramey wrote:

David Abrahams wrote:

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And since Boost.MPI and Boost.Serialization are so closely related, I think it's especially important that *you* underestand.

I disagree. Boost MPI depends upon Boost.Serialization but not the other way around.

I didn't say they were interdependent, just that they were closely-related. But anyway, I think you're being shortsighted: The success of tools built on top of Boost.Serialization is an important indicator of the correctness and genericity of its design.

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Boost.Serialization *is* dependent on Boost.MPI for a portion of its userbase,

<off topic> what portion of the user base? (This is a rhetorical question please don't spend any time answering it.) It's always bothered me that we have no per library data/feedback on the interest/usage on a library by library basis. I've spoken about this before and I know you agree with me about it. But until this get's addressed I think we just have to set these questions aside and recognize that the answers are anyone's guess.

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You can't be a generic serialization library without reference to real applications. Maybe you still haven't really decided whether serving Boost.MPI and its users is something you want to do.

I think that

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might account for a good deal of the recurring friction we experience. It would be a good idea to settle on an answer to that question, along with the question of what other applications you're willing to support.

I am acutely aware of this aspect of "generic library design". Every post on this list reminds me of it.

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I only really have few observations/suggestions at this point.

a) It would be helpful if there were a way to test the serialization of the archive classes in boost MPI without having MPI installed. If this is not possible, it would seem to me that the serialization is intertwined with the data transport - rather than be separated as it is in the stream/streambuf io/stream design. This would look like a design flaw to me.

Helpful to whom? I agree this is all a good idea, but I'm not sure how this relates to anything else we're discussing.

It would permit me to use the MPI serialization as a use case to verify that I hadn't broken anything. I know what your going to say - concepts - but that is going to be a while before that happens.

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b) user experience seems to show that archive construction/destruction is a significant performance issue when a new archive is made for each data transmission. On the other hand, one has to do this since the current archive implemenation track addresses of serialized obects so the same archive can't be use send the same structure (maybe with changed data) multiple times.

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I can't understand how you reach that conclusion. In my long explanation I thought I made it clear that Boost.MPI and its database get a great deal of its performance advantage from exactly that: sending the same structure multiple times with the same MPI type map.

hmm - what about tracked objects? I suggested turning off tracking and Matthias told me that it was needed to send pointers. But for this to work an archive has to be reconstructed everytime to re-initialize the tracking lists. I don't want to spend a lot of time on this as that means I have to delve into the MPI serialization and I don't want to do this.

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Given that MPI has a focus on performance, I wonder if this has been considered. I looked a the documentation, code and examples and it wasn't obvious to me how this is question was addressed - if at all.

We've obviously misunderstood one another somewhere along the way. It would be good if we could get that cleared up.

I think it would take too much time for me to understand. And if I did come to understand it, I might have something to say about it. If I said it, then it might start a thread which would cost even more time which I don't have right now.

Robert Ramey

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