std::atomic::is_always_lock_free
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | static constexpr bool is_always_lock_free = /*implementation-defined*/; | (since C++17) | |
Equals true if this atomic type is always lock-free and false if it is never or sometimes lock-free.
The value of this constant is consistent with both the macro ATOMIC_xxx_LOCK_FREE, where defined, with the member function is_lock_free and non-member function std::atomic_is_lock_free.
[edit] Notes
There is no non-member function equivalent of this static member constant because non-member functions take pointers to atomic types, and therefore aren't as useful in constant expressions.
[edit] See also
| checks if the atomic object is lock-free (public member function) | |
| (C++11) | checks if the atomic type's operations are lock-free (function template) | 
|  is_always_lock_free [static] (C++17) | indicates that the type is always lock-free (public static member constant) | 


