Determine if operations on
*this are lock free.
std::experimental::atomic_weak_ptr are lock-free
if the target CPU supports double-word-compare-and-swap. This is true
for all supported 32-bit CPUs, and for 64-bit CPUs that support the
This determination is done at runtime, since it depends on the model
of the CPU rather than the OS or compiler.
bool is_lock_free() const noexcept;
true if operations
are lock free,