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cppdraft/hardware/interference.md

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+[hardware.interference]
+
+# 17 Language support library [[support]](./#support)
+
+## 17.6 Dynamic memory management [[support.dynamic]](support.dynamic#hardware.interference)
+
+### 17.6.6 Hardware interference size [hardware.interference]
+
+[🔗](#lib:hardware_destructive_interference_size)
+
+`inline constexpr size_t hardware_destructive_interference_size = implementation-defined;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L3217)
+
+This number is the minimum recommended offset
+between two concurrently-accessed objects
+to avoid additional performance degradation due to contention
+introduced by the implementation[.](#1.sentence-1)
+
+It shall be at least alignof(max_align_t)[.](#1.sentence-2)
+
+[*Example [1](#example-1)*: struct keep_apart {alignas(hardware_destructive_interference_size) atomic<int> cat; alignas(hardware_destructive_interference_size) atomic<int> dog;}; — *end example*]
+
+[🔗](#lib:hardware_constructive_interference_size)
+
+`inline constexpr size_t hardware_constructive_interference_size = implementation-defined;
+`
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L3239)
+
+This number is the maximum recommended size of contiguous memory
+occupied by two objects accessed with temporal locality by concurrent threads[.](#2.sentence-1)
+
+It shall be at least alignof(max_align_t)[.](#2.sentence-2)
+
+[*Example [2](#example-2)*: struct together { atomic<int> dog; int puppy;};struct kennel {// Other data members...alignas(sizeof(together)) together pack; // Other data members...};static_assert(sizeof(together) <= hardware_constructive_interference_size); — *end example*]