I’ve been using Howard Hinnant’s stack allocator and it works like a charm, but some details of the implementation are a little unclear to me. Glad it’s been working for you. 1. Why are global operators new and delete used? The allocate() and deallocate() member functions use ::operator new and ::operator delete respectively. Similarly, the … Read more
A quoted text from Foundations of Algorithms in C++11, Volume 1, chap 4, p. 35 : template <typename T> struct allocator { template <typename U> using rebind = allocator<U>; }; sample usage : allocator<int>::rebind<char> x; In The C++ Programming Language, 4th edition, section 34.4.1, p. 998, commenting the ‘classical’ rebind member in default allocator class … Read more
You wrote […] copy itself to a new location […] which is not the way a vector works. The vector data is copied to a new location, not the vector itself. My answer should give you an idea of how a vector is designed. The common std::vector layout* Note: The std::allocator is actually likely to … Read more
Choice quote from cppreference: This runtime polymorphism allows objects using polymorphic_allocator to behave as if they used different allocator types at run time despite the identical static allocator type The issue with “regular” allocators is that they change the type of the container. If you want a vector with a specific allocator, you can make … Read more
When std::vector<T> runs out of capacity it has to allocate a new block. You have correctly covered the reasons. IMO it would make sense to augment the allocator interface. Two of us tried to for C++11 and we were unable to gain support for it: [1] [2] I became convinced that in order to make … Read more
C++ standard requires allocation functions (malloc() and operator new()) to allocate memory suitably aligned for any standard type. As these functions don’t receive the alignment requirement as an argument, in practice it means that the alignment for all allocations is the same, and is that of a standard type with the largest alignment requirement, which … Read more
It’s definitely possible to create a fully C++11/C++14 conforming stack allocator*. But you need to consider some of the ramifications about the implementation and the semantics of stack allocation and how they interact with standard containers. Here’s a fully C++11/C++14 conforming stack allocator (also hosted on my github): #include <functional> #include <memory> template <class T, … Read more
Edit: I removed the inheritance of std::allocator as suggested by GManNickG and made the alignment parameter a compile time thing. I recently wrote this piece of code. It’s not tested as much as I would like it so go on and report errors. 🙂 enum class Alignment : size_t { Normal = sizeof(void*), SSE = … Read more
As I mention here, I’ve seen Intel TBB’s custom STL allocator significantly improve performance of a multithreaded app simply by changing a single std::vector<T> to std::vector<T,tbb::scalable_allocator<T> > (this is a quick and convenient way of switching the allocator to use TBB’s nifty thread-private heaps; see page 7 in this document)