pdns/noinitvector.hh

   1 #pragma once
   2
   3 #include <memory>
   4 #include <new>
   5 #include <utility>
   6 #include <vector>
   7
   8 // based on boost::core::noinit_adaptor
   9 // The goal is to avoid initialization of the content of a container,
  10 // because setting several kB of uint8_t to 0 has a real cost if you
  11 // do 100k times per second.
  12 template<class Allocator>
  13 struct noinit_adaptor: Allocator
  14 {
  15   template<class U>
  16   struct rebind {
  17     typedef noinit_adaptor<typename std::allocator_traits<Allocator>::template
  18                            rebind_alloc<U> > other;
  19     };
  20
  21   noinit_adaptor(): Allocator() { }
  22
  23   template<class U>
  24   noinit_adaptor(U&& u) noexcept : Allocator(std::forward<U>(u)) { }
  25
  26   template<class U>
  27   noinit_adaptor(const noinit_adaptor<U>& u) noexcept : Allocator(static_cast<const U&>(u)) { }
  28
  29   template<class U>
  30   void construct(U* p) {
  31     ::new((void*)p) U;
  32   }
  33
  34   template<class U, class V, class... Args>
  35   void construct(U* p, V&& v, Args&&... args) {
  36     ::new((void*)p) U(std::forward<V>(v), std::forward<Args>(args)...);
  37   }
  38
  39   template<class U>
  40   void destroy(U* p) {
  41     p->~U();
  42   }
  43 };
  44
  45 template<class T, class U>
  46 inline bool operator==(const noinit_adaptor<T>& lhs,
  47                        const noinit_adaptor<U>& rhs) noexcept
  48 {
  49   return static_cast<const T&>(lhs) == static_cast<const U&>(rhs);
  50 }
  51
  52 template<class T, class U>
  53 inline bool operator!=(const noinit_adaptor<T>& lhs,
  54                        const noinit_adaptor<U>& rhs) noexcept
  55 {
  56   return !(lhs == rhs);
  57 }
  58
  59 template<class Allocator>
  60 inline noinit_adaptor<Allocator> noinit_adapt(const Allocator& a) noexcept
  61 {
  62   return noinit_adaptor<Allocator>(a);
  63 }
  64
  65 template<class T> using NoInitVector = std::vector<T, noinit_adaptor<std::allocator<T>>>;
  66
  67 using PacketBuffer = NoInitVector<uint8_t>;