ATOMIC_*_LOCK_FREE

Defined in header <stdatomic.h> 
#define ATOMIC_BOOL_LOCK_FREE     /* implementation-defined */
#define ATOMIC_CHAR_LOCK_FREE     /* implementation-defined */
#define ATOMIC_CHAR16_T_LOCK_FREE /* implementation-defined */
#define ATOMIC_CHAR32_T_LOCK_FREE /* implementation-defined */
#define ATOMIC_WCHAR_T_LOCK_FREE  /* implementation-defined */
#define ATOMIC_SHORT_LOCK_FREE    /* implementation-defined */
#define ATOMIC_INT_LOCK_FREE      /* implementation-defined */
#define ATOMIC_LONG_LOCK_FREE     /* implementation-defined */
#define ATOMIC_LLONG_LOCK_FREE    /* implementation-defined */
#define ATOMIC_POINTER_LOCK_FREE  /* implementation-defined */
 (since C11) 
#define ATOMIC_CHAR8_T_LOCK_FREE  /* implementation-defined */
 (since C23)

Expands to preprocessor constant expressions that evaluate to either 0, 1, or 2 which indicate the lock-free property of the corresponding atomic types (both signed and unsigned).

Value Explanation
0 The atomic type is never lock-free
1 The atomic type is sometimes lock-free
2 The atomic type is always lock-free

References

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