louis-langholtz

C++: Thread Safe Initialization Requirements

Seems like this has come up for me enough in discussing C++ with others, that it might help to put together the information in this gist.

Standard C++ has since C++11 required that block-scope variables with static or thread storage duration get initialized in a thread safe way. Besides there being a StackOverflow answer - to a related question - showing some example assembly for C++11 that includes thread safe guards, there's also the C++ standard documents themselves.

What follows is the specific requirement by versions of the standard.

C++03

louis-langholtz

C++: Stateless vs. Stateful Allocators

Categorizing Allocators

All standard C++ library conforming allocators have to support the minimal interface requirements. Beyond these requirements, some examples of fully defined allocators are LLVM's latest standard C++ library implementation of std::allocator, and a custom allocator I've written called ThreadLocalAllocator. These are both examples of what's been categorized as "stateless" allocators. Alternatively, allocators can be "stateful".

louis-langholtz

C++: Minimal Allocator

From item 11 of section 16.5.3.5 Cpp17Allocator requirements of n4861.pdf:

"The following is an allocator class template supporting the minimal interface...":

template<class Tp>
struct SimpleAllocator {
 typedef Tp value_type;

louis-langholtz

C++: More Reasons To Avoid std::endl

In the realm of death by a thousand cuts, please stop using std::endl and remove it from code. Per cppreference.com, std::endl "inserts a newline character into the output sequence... and flushes it". Okay, so why exactly shouldn't it be used???

The Issues

There have been numerous articles written about endl that echo the sentiment against using it. Here's some:

• Don't use std::endl: https://accu.org/journals/overload/27/149/sharpe_2619/
• "std::endl" vs "\n": https://stackoverflow.com/questions/213907/stdendl-vs-n

louis-langholtz

C++: My Love Affair With Polymorphic Value Types

If you're developing C++ code, especially for larger projects with longer histories, "polymorphic value types" might just be the best solution to your biggest coding frustrations!

Problem

Have you worked with code with countless derived classes? Have you had to deal with lots of pointers to data structures that in turn have pointers to other data structures? Did you find yourself feeling tired from the mental hopping around you were doing in order to understand that code? If so, you're not alone.

louis-langholtz

Extend the runtime polymorphism to vistor like pattern...

namespace playrho {

template <>
void Visit(const d2::EdgeShapeConf& shape, void* userData)
{
    const auto shapeDrawer = static_cast<ShapeDrawer*>(userData);
 shapeDrawer-&gt;Visit(shape);

louis-langholtz

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