std::hardware_destructive_interference_size, std::hardware_constructive_interference_size

 

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static constexpr std::size_t     hardware_destructive_interference_size = /*implementation-defined*/;	(1)	(since C++17)
static constexpr std::size_t     hardware_constructive_interference_size = /*implementation-defined*/;	(2)	(since C++17)

1) Minimum offset between two objects to avoid false sharing. Guaranteed to be at least alignof(std::max_align_t)

struct keep_apart {
  alignas(std::hardware_destructive_interference_size) std::atomic<int> cat;
  alignas(std::hardware_destructive_interference_size) std::atomic<int> dog;
};

2) Maximum size of contiguous memory to promote true sharing. Guaranteed to be at least alignof(max_align_t)

struct together {
  atomic<int> dog;
  int puppy;
};
struct kennel {
  // Other data members...
  alignas(sizeof(together)) together pack;
  // Other data members...
};
static_assert(sizeof(together) <= std::hardware_constructive_interference_size);

Notes

These constants provide a portable way to access the L1 data cache line size.