Niall, is your non-allocating future promise going to borrow from my C++Now slides, or are you trying a different direction? Tony Sent from my portable Analytical Engine ------------------------------ *From:* "Niall Douglas" <s_sourceforge@nedprod.com> *To:* "boost@lists.boost.org" <boost@lists.boost.org> *Sent:* 4 July, 2014 7:46 AM *Subject:* Re: [boost] ASIO into the standard (was: Re: C++ committee meeting report) On 4 Jul 2014 at 11:46, Neil Groves wrote:
I would hope Allocators would be added to ASIO in the standard. It is difficult to limit memory usage without Allocators in embedded systems.
I hate this recurring theme of "let's take something that works well today and then fsck it up by insisting it has allocator support"
Since I am far less familiar with these issues than you are the solution to avoiding detriment to designs by having allocator support is not obvious to me. What should we do instead of adding allocator support? Should we be improving the standard allocator like the implementations in Boost.Container, or are you suggesting that any standardisation of the allocator Concept would lead to a deterioration of the design? My own view is that the standard allocator is clearly suboptimal even for standard containers. This is evident from the performance improvements obtained in Boost.Container. I have noticed though that the improved allocators do not provide superior performance on Linux systems over the standard implementations. ITMm very interested in your proposed solutions as I suspect there is much to learn from your experience working on the standard library implementations.
There are lots of things going on here. STL allocators were always half baked because they were never finished - John Lakos is but one of many who took them to all sorts of interesting new places, indeed Stepanov's original design had enormous potential. Unfortunately, we've ended up stuck with these half finished things, and now they are creating slow path performance with std::vector> because STL containers can't have a noexcept move constructor due to allocators! Allocators are getting patched for C++17 right now, but ultimately the problem remains the same one as why they were never finished and left half baked - to take them further in any direction will benefit some uses but penalise others, so we've collectively decided that's as good as it gets for now and left it alone: no one is seriously proposing replacing STL allocators completely with something totally different. Regarding ASIO and allocators, ideally ASIO doesn't allocate nor deallocate any memory at all during its normal course of execution, thus removing much need for allocators and keeping latency low. Achieving that is probably hard - just look at promise/future, in there is an implied unavoidable malloc/free. And allocator support for promise/future really is a mess, indeed Boost.Thread still doesn't support that, and if I have my way it never will because promise/future under C++11 or later is going to become malloc-free, thereby sidestepping the problem. Niall -- ned Productions Limited Consultinghttp://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/