CppCon
7 HN recommenders · recommended in 15 months, 2017–2025
1:12:27 · 196K views · Oct 13, 2015
Andrei Alexandrescu's CppCon 2015 talk argues that std::allocator is badly designed. He proposes building high-performance allocators from small composable, templated pieces.
HN repeatedly recommends it as an entertaining, mind-opening talk on allocator design and composable generic programming.
16 comments from Hacker News
> The issue with this approach is that the more you can control, the less the compiler can assume. That's absolutely true, but there's a workaround, albeit a complicated one. The compiler internals need the same kind of constraints or traits that abstract code such as language interfaces or template parameters can have. These can then be used to constrain the internals in a way that then would allow assumptions to be safely "plumbed through" the various layers. The (big!) challenge here is that these abstractions haven't been well-developed in the industry. Certainly nowhere near as well as the typical runtime "type theory" as seen in modern languages. > some very basic ones like allocating heap memory. Well... this is sort-of my point! For example, what's the fundamental difference between allocating memory in some heap[1] structure at runtime and a compiler allocating members in a struct/record/class for optimal packing? IMHO, not much. E.g.: Watch this talk by Andrei Alexandrescu titled "std::allocator Is to Allocation what std::vector Is to Vexation": this video It really opened my eyes to how one could very elegantly make a very complex and high-performance heap allocator from trivial parts composed at compile-time. There's no reason that a nearly identical abstraction couldn't also be used to efficiently "bin pack" variables into a struct. E.g.: accounting for alignment, collecting like-sized items into contiguous sections, extra padding for "lock" objects to prevent cache
Not exactly a lecture series, but Andrei Alexandrescu has had some fantastic keynote presentations at CppCon. I don't even program in C++ any more, but I've watched these more than once, they're entertaining, approachable, and inspiring: Speed Is Found In The Minds of People [LINK] std::allocator Is to Allocation what std::vector Is to Vexation this video An actual lecture series I've enjoyed watching is "The WE-Heraeus International Winter School on Gravity and Light", which covers General Relativity using modern mathematical approaches: [LINK] Again, I haven't done physics in 20 years, but I've found it surprisingly easy to follow because it is so clearly presented.
Actually it is C's malloc and free that is "broken". malloc() takes a size parameter, but free() doesn't. This imbalance means it can never be maximally efficient. Whatever GNU stdlibc++ is doing is probably, on balance, a net win for most programs. It's not exactly roses in C++ either of course. You can do better than the standard library facilities. Andrei Alexandrescu gave a great, entertaining, and technically elegant talk on memory allocation in C and C++ at Cppcon 2015 that is well worth watching this video
> I would have liked to hear more about what exactly made D so great This WIP article explains very well the USP of D: [LINK] (section 3) This article highlight the value of "design-by-introspection" applied to a particular problem space: [LINK] This talk present a concrete example of such: this video (mind bending stuff) You might not understand what is new about it, but soon your competitors will understand it.
A bit unrelated, but if anyone is interested, I recently watched Andrei Alexandrescu's 2015 talk about a composable allocator design in C++ and it was really interesting. And Andrei's presentation style was fantastic, per usual. Note that this talk is about a std::allocator-like type, potentially on top of one of malloc/jemalloc/etc. this video