std::atomic<T>::is_lock_free (3) - Linux Manuals

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


std::atomic<T>::is_lock_free - std::atomic<T>::is_lock_free


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.



Return value

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.


// 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

See also

atomic_is_lock_free checks if the atomic type's operations are lock-free
                                     (function template)
                                     specializes atomic operations for std::shared_ptr
atomic_is_lock_free(std::shared_ptr) (function template)

is_always_lock_free indicates that the type is always lock-free
                                     (public static member constant)
[static] (C++17)