Meeting 25 May 2017

C++ feature polls by Bryce Lelbach

C++20 C++23 C++26 C++29 C++32 C++35 C++38 C++41 C++44 C++47 C++50

What is in Ranges
What is in Ranges TS (Ranges minus the good stuff, like views or actions)
“Based on Concepts TS which was finalised, what, 2–3 years ago?” Hah!
Latest draft: http://wg21.link/N4651
C++11 implementation: https://github.com/ericniebler/range-v3
Concepts-based implementation: https://github.com/CaseyCarter/cmcstl2
This is the beginning of STLv2 (namespace std2)
Eric shows snippers of code that use the standard library and then converts them to use ranges — so nice!
“Projection” is basically a map using a unary function
SentinelsHow to convert your own algorithms to using Ranges TS
Ranges and coroutines: https://github.com/toby-allsopp/ranges-coroutines — lets you write lazy ranges which work very well with views
Async ranges based on coroutines ⇒ reactive programming! Does Eric know about RxCpp?

how not to implement network server
don’t use one thread per connection
epoll (IO completion ports): OS tells us when a connection is ready, so we don’t need threads, don’t have race conditions, and can scale well
overview of callback libraries, including Boost ASIO
live reimplementation of ASIO event loop
“futures” in event loops: no threads, but syntactic sugar around callbacks: like JavaScript promise or Python deferred
coroutines (“user-space threads”)
fibers are the same as stackful coroutines
his “coroutine” code is using Boost coroutines, not Coroutines TS
demonstrates performance degradation and scaling capabilities of all the way of implementing async code
slide 116 has a summary table at 1:26:30

discusses snippets of code, best practices, what not to do
engages the audience (a bit too much IMHO) ⇒ lots of interruptions, sometimes they see his bugs and it all gets very confusing
poor volunteer with the microphone running around like mad trying his best to catch random replies across the huge room

C++ is efficient, close to metal, you can do anything, and tooling is readily available
Soft real-time constraints, speed is king
Memory constraints for embedded encoders/decoders
C++ toolchain permits optimisations that are simply not possible in other languages
SIMD

“Libuv is a C library that provides the asynchronous I/O in Node.js. While it was explicitly designed for use by Node.js, it can be used on its own and provides a common cross-platform API, abstracting away the various platform-specific asynchronous APIs.”
“With resumable functions, you can write code that looks very sequential but executes asynchronously.”
Header-only wrappers for the main lib functions

Using coroutines with boost::future and boost::asio
Interesting techniques for adapting future/promise and callback-based APIs to using coroutines
I expect more adaptations like this coming in the near future
- awaitable_tasks — for boost::asio
- a Gist by John Bandela — a much simpler version that relies on boost::asio capability to return a future instead of using a callback.