Std::atomic_is_lock_free,ATOMIC_xxx_LOCK_FREE (3) Linux Manual Page

std::atomic_is_lock_free,ATOMIC_xxx_LOCK_FREE – std::atomic_is_lock_free,ATOMIC_xxx_LOCK_FREE

Synopsis

Defined in header<atomic>

    template <class T>

    bool atomic_is_lock_free(const volatile std::atomic<T> *obj) noexcept;

template <class T>

bool atomic_is_lock_free(const std::atomic<T> *obj) noexcept;

#define ATOMIC_BOOL_LOCK_FREE /* unspecified */

#define ATOMIC_CHAR_LOCK_FREE /* unspecified */

#define ATOMIC_CHAR16_T_LOCK_FREE /* unspecified */

#define ATOMIC_CHAR32_T_LOCK_FREE /* unspecified */ (1)(since C++ 11)

#define ATOMIC_WCHAR_T_LOCK_FREE /* unspecified */ (2)(since C++ 11)

#define ATOMIC_SHORT_LOCK_FREE /* unspecified */

#define ATOMIC_INT_LOCK_FREE /* unspecified */

#define ATOMIC_LONG_LOCK_FREE /* unspecified */

#define ATOMIC_LLONG_LOCK_FREE /* unspecified */

#define ATOMIC_POINTER_LOCK_FREE /* unspecified */

#define ATOMIC_CHAR8_T_LOCK_FREE /* unspecified */ (3)(since C++ 20)

1) Determines if the atomic object pointed to by obj is implemented lock-free, as if by calling obj->is_lock_free(). In any given program execution, the result of the lock-free query is the same for all pointers of the same type.
2,3) Expands to an integer constant expression with value
* 0 for the built-in atomic types that are never lock-free
* 1 for the built-in atomic types that are sometimes lock-free
* 2 for the built-in atomic types that are always lock-free.

Parameters

obj – pointer to the atomic object to examine

Return value

true if *obj is a lock-free atomic, false otherwise.

Notes

All atomic types except for std::atomic_flag may be implemented using mutexes or other locking operations, rather than using the lock-free atomic CPU instructions. Atomic types are also allowed to be sometimes lock-free: for example, if only some subarchitectures support lock-free atomic access for a given type (such as the CMPXCHG16B instruction on x86-64), whether atomics are lock-free may not be known until runtime.
The C++ standard recommends (but does not require) that lock-free atomic operations are also address-free, that is, suitable for communication between processes using shared memory.

Example

// Run this code

#include <iostream>

#include <utility>

#include <atomic>
struct A {
    int a[100];
};

struct B {
    int x, y;
};

int main()

{
    std::atomic<A> a;
    std::atomic<B> b;
    std::cout << std::boolalpha
              << "std::atomic<A> is lock free? "
              << std::atomic_is_lock_free(&a) << '\n'
              << "std::atomic<B> is lock free? "
              << std::atomic_is_lock_free(&b) << '\n';
}

Possible output:

std::atomic<A> is lock free? false
std::atomic<B> is lock free? true

std::atomic_is_lock_free,ATOMIC_xxx_LOCK_FREE (3) Linux Manual Page