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std::atomic

From cppreference.com
< cpp‎ | atomic
 
 
 
 
Defined in header <atomic>
template< class T >
struct atomic;
(1) (since C++11)
template<>
struct atomic<Integral>;
(2) (since C++11)
template< class T >
struct atomic<T*>;
(3) (since C++11)

Each instantiation and full specialization of the std::atomic template defines an atomic type. Objects of atomic types are the only C++ objects that are free from data races; that is, if one thread writes to an atomic object while another thread reads from it, the behavior is well-defined.

In addition, accesses to atomic objects may establish inter-thread synchronization and order non-atomic memory accesses as specified by std::memory_order.

std::atomic may be instantiated with any TriviallyCopyable type T.

The standard library provides specializations of the std::atomic template for the following types:

1) One full specialization for the type bool and its typedef name is defined that is treated as a non-specialized std::atomic<T> except that it has standard layout, trivial default constructor, trivial destructors, and supports aggregate initialization syntax:

Typedef name Full specialization
std::atomic_bool std::atomic<bool>

2) Full specializations and typedefs for integral types, as follows:

Typedef name Full specialization
std::atomic_char std::atomic<char>
std::atomic_schar std::atomic<signed char>
std::atomic_uchar std::atomic<unsigned char>
std::atomic_short std::atomic<short>
std::atomic_ushort std::atomic<unsigned short>
std::atomic_int std::atomic<int>
std::atomic_uint std::atomic<unsigned int>
std::atomic_long std::atomic<long>
std::atomic_ulong std::atomic<unsigned long>
std::atomic_llong std::atomic<long long>
std::atomic_ullong std::atomic<unsigned long long>
std::atomic_char16_t std::atomic<char16_t>
std::atomic_char32_t std::atomic<char32_t>
std::atomic_wchar_t std::atomic<wchar_t>
std::atomic_int_least8_t std::atomic<std::int_least8_t>
std::atomic_uint_least8_t std::atomic<std::uint_least8_t>
std::atomic_int_least16_t std::atomic<std::int_least16_t>
std::atomic_uint_least16_t std::atomic<std::uint_least16_t>
std::atomic_int_least32_t std::atomic<std::int_least32_t>
std::atomic_uint_least32_t std::atomic<std::uint_least32_t>
std::atomic_int_least64_t std::atomic<std::int_least64_t>
std::atomic_uint_least64_t std::atomic<std::uint_least64_t>
std::atomic_int_fast8_t std::atomic<std::int_fast8_t>
std::atomic_uint_fast8_t std::atomic<std::uint_fast8_t>
std::atomic_int_fast16_t std::atomic<std::int_fast16_t>
std::atomic_uint_fast16_t std::atomic<std::uint_fast16_t>
std::atomic_int_fast32_t std::atomic<std::int_fast32_t>
std::atomic_uint_fast32_t std::atomic<std::uint_fast32_t>
std::atomic_int_fast64_t std::atomic<std::int_fast64_t>
std::atomic_uint_fast64_t std::atomic<std::uint_fast64_t>
std::atomic_intptr_t std::atomic<std::intptr_t>
std::atomic_uintptr_t std::atomic<std::uintptr_t>
std::atomic_size_t std::atomic<std::size_t>
std::atomic_ptrdiff_t std::atomic<std::ptrdiff_t>
std::atomic_intmax_t std::atomic<std::intmax_t>
std::atomic_uintmax_t std::atomic<std::uintmax_t>

These specializations have standard layout, trivial default constructors, and trivial destructors. They support aggregate initialization syntax. Besides the operations provided for all atomic types, these specializations have additional atomic operations appropriate to integer types such as fetch_add, fetch_sub, fetch_and, fetch_or, fetch_xor.

3) Partial specializations std::atomic<T*> for all pointer types. These specializations have standard layout, trivial default constructors, and trivial destructors. They support aggregate initialization syntax. Besides the operations provided for all atomic types, these specializations additionally support atomic arithmetic operations appropriate to pointer types, such as fetch_add, fetch_sub.

Contents

[edit] Member functions

constructs an atomic object
(public member function) [edit]
stores a value into an atomic object
(public member function) [edit]
checks if the atomic object is lock-free
(public member function) [edit]
(C++11)
atomically replaces the value of the atomic object with a non-atomic argument
(public member function) [edit]
(C++11)
atomically obtains the value of the atomic object
(public member function) [edit]
loads a value from an atomic object
(public member function) [edit]
(C++11)
atomically replaces the value of the atomic object and obtains the value held previously
(public member function) [edit]
atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not
(public member function) [edit]

[edit] Specialized member functions

(C++11)
atomically adds the argument to the value stored in the atomic object and obtains the value held previously
(public member function) [edit]
(C++11)
atomically subtracts the argument from the value stored in the atomic object and obtains the value held previously
(public member function) [edit]
(C++11)
atomically performs bitwise AND between the argument and the value of the atomic object and obtains the value held previously
(public member function) [edit]
(C++11)
atomically performs bitwise OR between the argument and the value of the atomic object and obtains the value held previously
(public member function) [edit]
(C++11)
atomically performs bitwise XOR between the argument and the value of the atomic object and obtains the value held previously
(public member function) [edit]
increments or decrements the atomic value by one
(public member function) [edit]
adds, subtracts, or performs bitwise AND, OR, XOR with the atomic value
(public member function) [edit]

[edit] Notes

There are non-member function template equivalents for all member functions of std::atomic. Those non-member functions may be additionally overloaded for types that are not specializations of std::atomic, but are able to guarantee atomicity. The only such type in the standard library is std::shared_ptr<T>.

[edit] See also

the lock-free boolean atomic type
(class) [edit]

[edit] References

  • C++11 standard (ISO/IEC 14882:2011):
  • 29.5 Atomic types [atomics.types.generic]