Re: [boost] Serialisation: Is is_trivial<T> a sufficient precondition to bypass serialisation?

On 4 Feb 2015 at 21:46, Thomas Heller wrote:

...

Basically, AFIO v1.3 has new pre-serialisation metaprogramming in response to Robert's comments on his Incubator about it being too hard to serialise and deserialise data with AFIO. AFIO will now consume any STL container and will implicitly auto expand to ASIO scatter gather buffers any:

1. Trivial type T 2. C array of trivial type T 3. STL container of trivial type T, including initializer_list.

So you generate a list of N scatter/gather buffers for a container with the size of N? That sounds a tad too much. Doesn't that create a immense overhead for the network interface?

Firstly AFIO does file i/o, not network i/o. You'd use ASIO for network i/o. If the user feeds std::list<int>(1000) to AFIO write(), I don't think you get a choice here: a gather write of 1000 individual items is requested and that is what is issued. If the user feeds std::vector<int>(1000) to AFIO write(), there is already a specialisation of to_asio_buffers() for vector, array, string and C arrays which recognises the fact they guarantee contiguous storage of their contents. In that situation AFIO issues a single gather buffer for the entire contents at once. If the user feeds std::vector(100), then AFIO will create an ASIO gather buffer sequence of 100 buffers, each pointing at a region of 1000 ints. You can nest your STL containers to any arbitrary length - AFIO understands. AFIO also understands you can gather write a const value_type container like unordered_map, but cannot scatter read into a const value_type and a static assert is thrown if you try. In other words, const containers or value_types always turn into asio::const_buffer, as indeed they should. As with network sockets, most DMA engines for disk i/o have hard limits on scatter gather buffer size. That isn't AFIO's problem. POSIX also imposes a limit of IOV_MAX scatter gather buffers which is AFIO's problem, and AFIO correctly issues blocks of IOV_MAX until the input is fully dispatched. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/