std::atomic_ref<T>::is_lock_free (3) - Linux Manuals
bool is_lock_free() const noexcept; (since C++20)
Checks whether the atomic operations on this object are lock-free.
true if the atomic operations on this object 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.
This section is incomplete
Reason: no example
is_always_lock_free indicates that the type is always lock-free