Atomic operations library

 

C

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Variadic function support

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Concurrency support (C11)

Technical Specifications

Symbol index

 

Atomic operations library

Types

memory_order

atomic_flag

Macros

ATOMIC_***_LOCK_FREE

ATOMIC_FLAG_INIT

ATOMIC_VAR_INIT

kill_dependency

Functions

atomic_flag_test_and_set

atomic_flag_clear

atomic_init

atomic_is_lock_free

atomic_store

atomic_load

atomic_exchange

atomic_compare_exchange

atomic_fetch_add

atomic_fetch_sub

atomic_fetch_or

atomic_fetch_xor

atomic_fetch_and

atomic_thread_fence

atomic_signal_fence

 

If the macro constant __STDC_NO_ATOMICS__(C11) is defined by the compiler, the header <stdatomic.h>, the keyword _Atomic, and all of the names listed here are not provided.

Types

Defined in header <stdatomic.h>
memory_order (C11)	defines memory ordering constraints (enum)
atomic_flag (C11)	lock-free atomic boolean flag (struct)

Macros

Defined in header <stdatomic.h>
ATOMIC_BOOL_LOCK_FREEATOMIC_CHAR_LOCK_FREEATOMIC_CHAR16_T_LOCK_FREEATOMIC_CHAR32_T_LOCK_FREEATOMIC_WCHAR_T_LOCK_FREEATOMIC_SHORT_LOCK_FREEATOMIC_INT_LOCK_FREEATOMIC_LONG_LOCK_FREEATOMIC_LLONG_LOCK_FREEATOMIC_POINTER_LOCK_FREE (C11)	indicates that the given atomic type is lock-free (macro constant)
ATOMIC_FLAG_INIT (C11)	initializes a new atomic_flag (macro constant)
ATOMIC_VAR_INIT (C11)(deprecated in C17)(removed in C23)	initializes a new atomic object (function macro)
kill_dependency (C11)	breaks a dependency chain for memory_order_consume (function macro)

Functions

Defined in header <stdatomic.h>
atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C11)	sets an atomic_flag to true and returns the old value (function)
atomic_flag_clearatomic_flag_clear_explicit (C11)	sets an atomic_flag to false (function)
atomic_init (C11)	initializes an existing atomic object (function)
atomic_is_lock_free (C11)	indicates whether the atomic object is lock-free (function)
atomic_storeatomic_store_explicit (C11)	stores a value in an atomic object (function)
atomic_loadatomic_load_explicit (C11)	reads a value from an atomic object (function)
atomic_exchangeatomic_exchange_explicit (C11)	swaps a value with the value of an atomic object (function)
atomic_compare_exchange_strongatomic_compare_exchange_strong_explicitatomic_compare_exchange_weakatomic_compare_exchange_weak_explicit (C11)	swaps a value with an atomic object if the old value is what is expected, otherwise reads the old value (function)
atomic_fetch_addatomic_fetch_add_explicit (C11)	atomic addition (function)
atomic_fetch_subatomic_fetch_sub_explicit (C11)	atomic subtraction (function)
atomic_fetch_oratomic_fetch_or_explicit (C11)	atomic bitwise OR (function)
atomic_fetch_xoratomic_fetch_xor_explicit (C11)	atomic bitwise exclusive OR (function)
atomic_fetch_andatomic_fetch_and_explicit (C11)	atomic bitwise AND (function)
atomic_thread_fence (C11)	generic memory order-dependent fence synchronization primitive (function)
atomic_signal_fence (C11)	fence between a thread and a signal handler executed in the same thread (function)

Types

The standard library offers convenience typedefs for the core language atomic types.

Typedef name	Full type name
atomic_bool	_Atomic _Bool
atomic_char	_Atomic char
atomic_schar	_Atomic signed char
atomic_uchar	_Atomic unsigned char
atomic_short	_Atomic short
atomic_ushort	_Atomic unsigned short
atomic_int	_Atomic int
atomic_uint	_Atomic unsigned int
atomic_long	_Atomic long
atomic_ulong	_Atomic unsigned long
atomic_llong	_Atomic long long
atomic_ullong	_Atomic unsigned long long
atomic_char8_t (C23)	_Atomic char8_t
atomic_char16_t	_Atomic char16_t
atomic_char32_t	_Atomic char32_t
atomic_wchar_t	_Atomic wchar_t
atomic_int_least8_t	_Atomic int_least8_t
atomic_uint_least8_t	_Atomic uint_least8_t
atomic_int_least16_t	_Atomic int_least16_t
atomic_uint_least16_t	_Atomic uint_least16_t
atomic_int_least32_t	_Atomic int_least32_t
atomic_uint_least32_t	_Atomic uint_least32_t
atomic_int_least64_t	_Atomic int_least64_t
atomic_uint_least64_t	_Atomic uint_least64_t
atomic_int_fast8_t	_Atomic int_fast8_t
atomic_uint_fast8_t	_Atomic uint_fast8_t
atomic_int_fast16_t	_Atomic int_fast16_t
atomic_uint_fast16_t	_Atomic uint_fast16_t
atomic_int_fast32_t	_Atomic int_fast32_t
atomic_uint_fast32_t	_Atomic uint_fast32_t
atomic_int_fast64_t	_Atomic int_fast64_t
atomic_uint_fast64_t	_Atomic uint_fast64_t
atomic_intptr_t	_Atomic intptr_t
atomic_uintptr_t	_Atomic uintptr_t
atomic_size_t	_Atomic size_t
atomic_ptrdiff_t	_Atomic ptrdiff_t
atomic_intmax_t	_Atomic intmax_t
atomic_uintmax_t	_Atomic uintmax_t

References

• C23 standard (ISO/IEC 9899:2024):

• 7.17 Atomics <stdatomic.h> (p: TBD)

• 7.31.8 Atomics <stdatomic.h> (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.17 Atomics <stdatomic.h> (p: TBD)

• 7.31.8 Atomics <stdatomic.h> (p: TBD)

• C11 standard (ISO/IEC 9899:2011):

• 7.17 Atomics <stdatomic.h> (p: 273-286)

• 7.31.8 Atomics <stdatomic.h> (p: 455-456)

See also

C++ documentation for Atomic operations library