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Showing content from http://en.cppreference.com/w/cpp/ranges/../utility/program/../../atomic/atomic/is_lock_free.html below:

std::atomic<T>::is_lock_free - cppreference.com

bool is_lock_free() const noexcept;

bool is_lock_free() const volatile noexcept;

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

(none)

true if the atomic operations on the objects of this type are lock-free, false otherwise.

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.

#include <atomic>
#include <iostream>
#include <utility>
 
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

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