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+[atomics.lockfree]
+
+# 32 Concurrency support library [[thread]](./#thread)
+
+## 32.5 Atomic operations [[atomics]](atomics#lockfree)
+
+### 32.5.5 Lock-free property [atomics.lockfree]
+
+[ð](#:values_of_various_ATOMIC_..._LOCK_FREE_macros)
+
+#define ATOMIC_BOOL_LOCK_FREE *unspecified*#define ATOMIC_CHAR_LOCK_FREE *unspecified*#define ATOMIC_CHAR8_T_LOCK_FREE *unspecified*#define ATOMIC_CHAR16_T_LOCK_FREE *unspecified*#define ATOMIC_CHAR32_T_LOCK_FREE *unspecified*#define ATOMIC_WCHAR_T_LOCK_FREE *unspecified*#define ATOMIC_SHORT_LOCK_FREE *unspecified*#define ATOMIC_INT_LOCK_FREE *unspecified*#define ATOMIC_LONG_LOCK_FREE *unspecified*#define ATOMIC_LLONG_LOCK_FREE *unspecified*#define ATOMIC_POINTER_LOCK_FREE *unspecified*
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L3101)
+
+The ATOMIC_..._LOCK_FREE macros indicate the lock-free property of the
+corresponding atomic types, with the signed and unsigned variants grouped
+together[.](#1.sentence-1)
+
+The properties also apply to the corresponding (partial) specializations of theatomic template[.](#1.sentence-2)
+
+A value of 0 indicates that the types are never
+lock-free[.](#1.sentence-3)
+
+A value of 1 indicates that the types are sometimes lock-free[.](#1.sentence-4)
+
+A
+value of 2 indicates that the types are always lock-free[.](#1.sentence-5)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L3109)
+
+On a hosted implementation ([[compliance]](compliance "16.4.2.5 Freestanding implementations")),
+at least one signed integral specialization of the atomic template,
+along with the specialization
+for the corresponding unsigned type ([[basic.fundamental]](basic.fundamental "6.9.2 Fundamental types")),
+is always lock-free[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L3116)
+
+The functions atomic<T>::is_lock_free andatomic_is_lock_free ([[atomics.types.operations]](atomics.types.operations "32.5.8.2 Operations on atomic types"))
+indicate whether the object is lock-free[.](#3.sentence-1)
+
+In any given program execution, the
+result of the lock-free query
+is the same for all atomic objects of the same type[.](#3.sentence-2)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L3123)
+
+Atomic operations that are not lock-free are considered to potentially
+block ([[intro.progress]](intro.progress "6.10.2.3 Forward progress"))[.](#4.sentence-1)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L3127)
+
+*Recommended practice*: Operations that are lock-free should also be address-free[.](#5.sentence-1)[294](#footnote-294 "That is, atomic operations on the same memory location via two different addresses will communicate atomically.")
+
+The implementation of these operations should not depend on any per-process state[.](#5.sentence-2)
+
+[*Note [1](#note-1)*:
+
+This restriction enables communication by memory that is
+mapped into a process more than once and by memory that is shared between two
+processes[.](#5.sentence-3)
+
+â *end note*]
+
+[294)](#footnote-294)[294)](#footnoteref-294)
+
+That is,
+atomic operations on the same memory location via two different addresses will
+communicate atomically[.](#footnote-294.sentence-1)