NAME

ATOMIC_VAR_INIT, atomic_init, atomic_load, atomic_store, atomic_exchange, atomic_compare_exchange_strong, atomic_compare_exchange_weak, atomic_fetch_add, atomic_fetch_and, atomic_fetch_or, atomic_fetch_sub, atomic_fetch_xor, atomic_is_lock_free — type-generic atomic operations

SYNOPSIS

#include <stdatomic.h>

_Atomic(T) v = ATOMIC_VAR_INIT(c);
_Atomic T v = ATOMIC_VAR_INIT(c);

void
atomic_init(_Atomic(T) *object, T value);

T
atomic_load(_Atomic(T) *object);

T
atomic_load_explicit(_Atomic(T) *object, memory_order order);

void
atomic_store(_Atomic(T) *object, T desired);

void
atomic_store_explicit(_Atomic(T) *object, T desired, memory_order order);

T
atomic_exchange(_Atomic(T) *object, T desired);

T
atomic_exchange_explicit(_Atomic(T) *object, T desired, memory_order order);

_Bool
atomic_compare_exchange_strong(_Atomic(T) *object, T *expected, T desired);

_Bool
atomic_compare_exchange_strong_explicit(_Atomic(T) *object, T *expected, T desired, memory_order success, memory_order failure);

_Bool
atomic_compare_exchange_weak(_Atomic(T) *object, T *expected, T desired);

_Bool
atomic_compare_exchange_weak_explicit(_Atomic(T) *object, T *expected, T desired, memory_order success, memory_order failure);

T
atomic_fetch_add(_Atomic(T) *object, T operand);

T
atomic_fetch_add_explicit(_Atomic(T) *object, T operand, memory_order order);

T
atomic_fetch_and(_Atomic(T) *object, T operand);

T
atomic_fetch_and_explicit(_Atomic(T) *object, T operand, memory_order order);

T
atomic_fetch_or(_Atomic(T) *object, T operand);

T
atomic_fetch_or_explicit(_Atomic(T) *object, T operand, memory_order order);

T
atomic_fetch_sub(_Atomic(T) *object, T operand);

T
atomic_fetch_sub_explicit(_Atomic(T) *object, T operand, memory_order order);

T
atomic_fetch_xor(_Atomic(T) *object, T operand);

T
atomic_fetch_xor_explicit(_Atomic(T) *object, T operand, memory_order order);

_Bool
atomic_is_lock_free(const _Atomic(T) *object);

DESCRIPTION

The header <stdatomic.h> provides type-generic operations on atomic operations.

Atomic variables are declared using the _Atomic() type specifier or the _Atomic type qualifier. Such variables are not type-compatible with their non-atomic counterparts and may have different alignment.

Operations on atomic variables that do not use the atomic_() interfaces, including compound assignment operations, will behave as if the non-_explicit() versions of those interfaces had been used.

The atomic_init() operation initializes the atomic variable object with value. Atomic variables can be initialized while being declared using ATOMIC_VAR_INIT().

The atomic_load() operation returns the value of atomic variable object. The atomic_store() operation sets the atomic variable object to the desired value.

The atomic_exchange() operation combines the behaviour of atomic_load() and atomic_store(). It sets the atomic variable object to the desired value and returns the original contents of the atomic variable.

The atomic_compare_exchange_strong() operation stores the desired value into atomic variable object, but only if the atomic variable is equal to the expected value. Upon success, the operation returns true. Upon failure, the expected value is overwritten with the contents of the atomic variable and false is returned.

The atomic_compare_exchange_weak() operation is identical to atomic_compare_exchange_strong(), but is allowed to fail even if atomic variable object is equal to the expected value. When an atomic_compare_exchange() operation is in a loop, the weak version will yield better performance on some platforms. When atomic_compare_exchange_weak() would require a loop and atomic_compare_exchange_strong() would not, the strong version is preferable.

The atomic_fetch_add() operation adds the value operand to atomic variable object and returns the original contents of the atomic variable.

The atomic_fetch_and() operation applies the and operator to atomic variable object and value operand and stores the result into object, while returning the original contents of the atomic variable.

The atomic_fetch_or() operation applies the or operator to atomic variable object and value operand and stores the result into object, while returning the original contents of the atomic variable.

The atomic_fetch_sub() operation subtracts the value operand from atomic variable object and returns the original contents of the atomic variable.

The atomic_fetch_xor() operation applies the xor operator to atomic variable object and value operand and stores the result into object, while returning the original contents of the atomic variable.

The atomic_is_lock_free() operation returns whether atomic variable object uses locks to implement atomic operations.

MEMORY ORDER

C11 defines a memory model that may allow for the reordering of operations in the absence of fences or explicit memory ordering operations. The non-_explicit() interfaces use the strictest available memory order: sequential consistency. The _explicit() interfaces allow for configuration of the memory order operation which is present. The types of available memory order operations are explained in more detail in ISO/IEC 9899:2011 (“ISO C11”).

The order parameter of the _explicit() interfaces can have one of the following values:

memory_order_relaxed

Operation does not order memory.

memory_order_consume

Performs a consume operation.

memory_order_acquire

Performs an acquire operation.

memory_order_release

Performs a release operation.

memory_order_acq_rel

Performs both an acquire and a release operation.

memory_order_seq_cst

Provides sequential consistency.

SEE ALSO

atomic(3), pthread(3)

STANDARDS

These interfaces conform to ISO/IEC 9899:2011 (“ISO C11”).