33 Concurrency support library [thread]

33.5 Atomic operations [atomics]

33.5.8 Class template atomic [atomics.types.generic]

33.5.8.3 Specializations for integers [atomics.types.int]

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There are specializations of the atomic class template for the integral types char, signed char, unsigned char, short, unsigned short, int, unsigned int, long, unsigned long, long long, unsigned long long, char8_t, char16_t, char32_t, wchar_t, and any other types needed by the typedefs in the header <cstdint>.
For each such type integral-type, the specialization atomic<integral-type> provides additional atomic operations appropriate to integral types.
[Note 1: 
The specialization atomic<bool> uses the primary template ([atomics.types.generic]).
— end note]
namespace std { template<> struct atomic<integral-type> { using value_type = integral-type; using difference_type = value_type; static constexpr bool is_always_lock_free = implementation-defined; bool is_lock_free() const volatile noexcept; bool is_lock_free() const noexcept; constexpr atomic() noexcept; constexpr atomic(integral-type) noexcept; atomic(const atomic&) = delete; atomic& operator=(const atomic&) = delete; atomic& operator=(const atomic&) volatile = delete; void store(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; void store(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type operator=(integral-type) volatile noexcept; integral-type operator=(integral-type) noexcept; integral-type load(memory_order = memory_order::seq_cst) const volatile noexcept; integral-type load(memory_order = memory_order::seq_cst) const noexcept; operator integral-type() const volatile noexcept; operator integral-type() const noexcept; integral-type exchange(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type exchange(integral-type, memory_order = memory_order::seq_cst) noexcept; bool compare_exchange_weak(integral-type&, integral-type, memory_order, memory_order) volatile noexcept; bool compare_exchange_weak(integral-type&, integral-type, memory_order, memory_order) noexcept; bool compare_exchange_strong(integral-type&, integral-type, memory_order, memory_order) volatile noexcept; bool compare_exchange_strong(integral-type&, integral-type, memory_order, memory_order) noexcept; bool compare_exchange_weak(integral-type&, integral-type, memory_order = memory_order::seq_cst) volatile noexcept; bool compare_exchange_weak(integral-type&, integral-type, memory_order = memory_order::seq_cst) noexcept; bool compare_exchange_strong(integral-type&, integral-type, memory_order = memory_order::seq_cst) volatile noexcept; bool compare_exchange_strong(integral-type&, integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type fetch_add(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type fetch_add(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type fetch_sub(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type fetch_sub(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type fetch_and(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type fetch_and(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type fetch_or(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type fetch_or(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type fetch_xor(integral-type, memory_order = memory_order::seq_cst) volatile noexcept; integral-type fetch_xor(integral-type, memory_order = memory_order::seq_cst) noexcept; integral-type operator++(int) volatile noexcept; integral-type operator++(int) noexcept; integral-type operator--(int) volatile noexcept; integral-type operator--(int) noexcept; integral-type operator++() volatile noexcept; integral-type operator++() noexcept; integral-type operator--() volatile noexcept; integral-type operator--() noexcept; integral-type operator+=(integral-type) volatile noexcept; integral-type operator+=(integral-type) noexcept; integral-type operator-=(integral-type) volatile noexcept; integral-type operator-=(integral-type) noexcept; integral-type operator&=(integral-type) volatile noexcept; integral-type operator&=(integral-type) noexcept; integral-type operator|=(integral-type) volatile noexcept; integral-type operator|=(integral-type) noexcept; integral-type operator^=(integral-type) volatile noexcept; integral-type operator^=(integral-type) noexcept; void wait(integral-type, memory_order = memory_order::seq_cst) const volatile noexcept; void wait(integral-type, memory_order = memory_order::seq_cst) const noexcept; void notify_one() volatile noexcept; void notify_one() noexcept; void notify_all() volatile noexcept; void notify_all() noexcept; }; }
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The atomic integral specializations are standard-layout structs.
They each have a trivial destructor.
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Descriptions are provided below only for members that differ from the primary template.
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The following operations perform arithmetic computations.
The correspondence among key, operator, and computation is specified in Table 145.
Table 145: Atomic arithmetic computations [tab:atomic.types.int.comp]
key
Op
Computation
key
Op
Computation
add
+
addition
sub
-
subtraction
or
|
bitwise inclusive or
xor
^
bitwise exclusive or
and
&
bitwise and
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T fetch_key(T operand, memory_order order = memory_order::seq_cst) volatile noexcept; T fetch_key(T operand, memory_order order = memory_order::seq_cst) noexcept;
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Constraints: For the volatile overload of this function, is_always_lock_free is true.
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Effects: Atomically replaces the value pointed to by this with the result of the computation applied to the value pointed to by this and the given operand.
Memory is affected according to the value of order.
These operations are atomic read-modify-write operations ([intro.multithread]).
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Returns: Atomically, the value pointed to by this immediately before the effects.
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Remarks: For signed integer types, the result is as if the object value and parameters were converted to their corresponding unsigned types, the computation performed on those types, and the result converted back to the signed type.
[Note 2: 
There are no undefined results arising from the computation.
— end note]
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T operator op=(T operand) volatile noexcept; T operator op=(T operand) noexcept;
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Constraints: For the volatile overload of this function, is_always_lock_free is true.
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Effects: Equivalent to: return fetch_key(operand) op operand;