Std::atomic::is_lock_free (3) Linux Manual Page

std::atomic<T>::is_lock_free – std::atomic<T>::is_lock_free

Synopsis

bool is_lock_free() const noexcept;
(since C++ 11)

    bool is_lock_free() const volatile noexcept;

Checks whether the atomic operations on all objects of this type are lock-free.

Parameters

(none)

Return value

true if the atomic operations on the objects of this type are lock-free, 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, e.g. if only aligned memory accesses are naturally atomic on a given architecture, misaligned objects of the same type have to use locks.
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::cout << std::boolalpha
              << "std::atomic<A> is lock free? "
              << std::atomic<A>{}.is_lock_free() << '\n'
              << "std::atomic<B> is lock free? "
              << std::atomic<B>{}.is_lock_free() << '\n';
}

Possible output:

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

std::atomic::is_lock_free (3) Linux Manual Page