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

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

NAME

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