std::hardware_destructive_interference_size, std::hardware_constructive_interference_size

 

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Technical Specifications

 

Thread support library

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thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
this_thread namespace
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Defined in header <new>
inline constexpr std::size_t     hardware_destructive_interference_size = /*implementation-defined*/;	(1)	(since C++17)
inline 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(std::max_align_t)

struct together {
  std::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.

See also

hardware_concurrency [static]

returns the number of concurrent threads supported by the implementation (public static member function of std::thread)