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Using C++17 Parallel Algorithms for Better Performance--Billy O’Neal

By Adrien Hamelin | Sep 13, 2018 12:36 PM | Tags: performance c++17

Are you using the parallel capacities of the std?

Using C++17 Parallel Algorithms for Better Performance

by Billy O’Neal

From the article:

C++17 added support for parallel algorithms to the standard library, to help programs take advantage of parallel execution for improved performance. MSVC first added experimental support for some algorithms in 15.5, and the experimental tag was removed in 15.7.

The interface described in the standard for the parallel algorithms doesn’t say exactly how a given workload is to be parallelized. In particular, the interface is intended to express parallelism in a general form that works for heterogeneous machines, allowing SIMD parallelism like that exposed by SSE, AVX, or NEON, vector “lanes” like that exposed in GPU programming models, and traditional threaded parallelism.

Our parallel algorithms implementation currently relies entirely on library support, not on special support from the compiler. This means our implementation will work with any tool currently consuming our standard library, not just MSVC’s compiler. In particular, we test that it works with Clang/LLVM and the version of EDG that powers Intellisense...

How To Use std::visit With Multiple Variants--Bartlomiej Filipek

By Adrien Hamelin | Sep 13, 2018 12:33 PM | Tags: intermediate c++17

Variant utility.

How To Use std::visit With Multiple Variants

by Bartlomiej Filipek

From the article:

std::visit is a powerful utility that allows you to call a function over a currently active type in std::variant. It does some magic to select the proper overload, and what’s more, it can support many variants at once.

Let’s have a look at a few examples of how to use this functionality...

CppCon 2017: Fantastic Algorithms and Where To Find Them--Nicholas Ormrod

By Adrien Hamelin | Sep 12, 2018 12:23 PM | Tags: community

Have you registered for CppCon 2018 in September? Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2017 for you to enjoy. Here is today’s feature:

Fantastic Algorithms and Where To Find Them

by Nicholas Ormrod

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Come dive into some exciting algorithms — tools rare enough to be novel, but useful enough to be found in practice. Want to learn about "heavy hitters" to prevent DOS attacks? Come to this talk. Want to avoid smashing your stack during tree destruction? Come to this talk. Want to hear war stories about how a new algorithm saved the day? Come to this talk! We'll dive into the finest of algorithms and see them in use — Fantastic Algorithms, and Where To Find Them.

Quick Q: C++ constexpr - Value can be evaluated at compile time?

By Adrien Hamelin | Sep 12, 2018 12:20 PM | Tags: intermediate c++11

Quick A: if parameter are not known at compile time, it is like a normal function

Recently on SO:

C++ constexpr - Value can be evaluated at compile time?

The quoted wording is a little misleading in a sense. If you just take PlusOne in isolation, and observe its logic, and assume that the inputs are known at compile-time, then the calculations therein can also be performed at compile-time. Slapping the constexpr keyword on it ensures that we maintain this lovely state and everything's fine.

But if the input isn't known at compile-time then it's still just a normal function and will be called at runtime.

So the constexpr is a property of the function ("possible to evaluate at compile time" for some input, not for all input) not of your function/input combination in this specific case (so not for this particular input either).

It's a bit like how a function could take a const int& but that doesn't mean the original object had to be const. Here, similarly, constexpr adds constraints onto the function, without adding constraints onto the function's input.

Admittedly it's all a giant, confusing, nebulous mess (C++! Yay!). Just remember, your code describes the meaning of a program! It's not a direct recipe for machine instructions at different phases of compilation.

(To really enforce this you'd have the integer be a template argument.)

C++ Links #1--Bartlomiej Filipek

By Adrien Hamelin | Sep 12, 2018 12:15 PM | Tags: community

Things to look at.

C++ Links #1

by Bartlomiej Filipek

From the article:

I'd like to make an experiment on the blog and introduce a new simple series. Each Friday you'll see a summary with valuable links and resources from the C++ World. The links and annotations are coming from a guest author - Wojciech Razik - one of the co-author of cpp-polska.pl.

Stack Factory Puzzle -- Alex Marmer

By Alex Marmer | Sep 11, 2018 01:41 PM | Tags: None

When instances of classes derived from the same class need to be created based on certain conditions, they are created on the heap. The puzzle is about how to do it on the stack.

Stack Factory Puzzle

By Alex Marmer

 

CppCon 2017: Boost Your Program’s Health by Adding Fibers to your Coroutine

By Adrien Hamelin | Sep 7, 2018 12:03 PM | Tags: community

Have you registered for CppCon 2018 in September? Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2017 for you to enjoy. Here is today’s feature:

Boost Your Program’s Health by Adding Fibers to your Coroutine

by David Sackstein

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

This session is intended to help the advanced programmer to understand what coroutines and fibers are, what problems they solve and how they should be applied in practice.
The session begins with an overview of these concepts, comparing them with threads, and demonstrating how they are exposed by the Boost libraries.
Apart from being clean and succinct as Boost libraries typically are, the authors of these libraries have gone to great lengths to ensure that fibers and coroutines expose a programming model consistent with that of threads. This will make them seem very familiar.
During the session I will demonstrate how fibers and coroutines can be used together with the powerful Boost.Asio library to solve some commonly occurring problems.
To conclude, I will provide some practical tips and guidelines for those who are adding fibers and coroutines to their programming diet.

Mathematics behind Comparison #4: Three-Way Comparison--Jonathan Müller

By Adrien Hamelin | Sep 7, 2018 11:59 AM | Tags: experimental advanced

Everything you need to know!

Mathematics behind Comparison #4: Three-Way Comparison

by Jonathan Müller

From the article:

In order to sort a collection of elements you need to provide a sorting predicate that determines when one element is less than the other. This predicate must “induce a strict total ordering on the equivalence classes” according to cppreference. Wait, what?

The upcoming C++ spaceship operator implements a three-way comparison, i.e. it is a single function that can return the results of <, == and > combined. But related to it are terms like “strong equality” and “weak ordering” which are somewhat confusing if you don’t have the mathematical background.

So let’s untangle it: This series will explain both the mathematics behind equality and ordering, as well as give concrete guidelines for implementing the comparison operators and the spaceship operator.

Now that we’ve covered both equivalence and ordering relations we can finally talk about the spaceship operator and three-way comparisons...

Quick Q: How to track newer C++ std documents of given topic?

By Adrien Hamelin | Sep 7, 2018 11:54 AM | Tags: advanced

Quick A: Use wg21.link

Recently on SO:

How to track newer C++ std documents of given topic?

For the newer proposals (ones that start with the letter P) you can use wg21.link redirect service to obtain the latest document:

wg21.link - WG21 redirect service.

Usage:
wg21.link/nXXXX
wg21.link/pXXXX
wg21.link/pXXXXrX Get paper.

wg21.link/standard
Get working draft.

wg21.link/cwgXXX
wg21.link/ewgXXX
wg21.link/lwgXXX
wg21.link/lewgXXX
wg21.link/fsXXX
wg21.link/editXXX
Get issue.

wg21.link/index.json
wg21.link/index.ndjson
wg21.link/index.txt
wg21.link/specref.json
Get everything.

wg21.link/
Get usage.

For example for P0476: Bit-casting object representations if we use wg21.link/P0476 we obtain the latest version which is P0476R2.

In my answer to How does the standards committee indicate the status of a paper under consideration? I go into more details of the WG21 site and what documents you can find there.

Use the everything link for Pre P proposals
If we use the wg21 redirect service Get Everything link we can do a text search for the paper title. So for your example Improvements to std::future<T> and Related APIs we can see the last document is N3857:

"N3857": {
"type": "paper",
"title": "Improvements to std::future and Related APIs",
"subgroup": "Concurrency",
"author": "N. Gustafsson, A. Laksberg, H. Sutter, S. Mithani",
"long_link": "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3857.pdf",
"link": "https://wg21.link/n3857",
"source": "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/",
"date": "2014-01-16"
},