Function atomic_cxchg 

pub const unsafe fn atomic_cxchg<T: Copy, const ORD_SUCC: AtomicOrdering, const ORD_FAIL: AtomicOrdering>(
    dst: *mut T,
    old: T,
    src: T,
) -> (T, bool)

🔬This is a nightly-only experimental API. (core_intrinsics)

Stores a value if the current value is the same as the old value, with the returned T being the previous value and the returned bool being whether the exchange was successful. T must be an integer or pointer type.

Safety

• If T is an integer type, this is equivalent to Atomic<T>::from_ptr followed by Atomic<T>::compare_exchange. Refer to the documentation of Atomic<T>::from_ptr for safety requirements.

• If T is a pointer type, this is equivalent to AtomicPtr<P>::from_ptr followed by AtomicPtr<P>::compare_exchange, where P is the pointee type of the pointer. Refer to the documentation of AtomicPtr<P>::from_ptr for safety requirements.

The stabilized version of this intrinsic is available on the atomic types via the compare_exchange method. For example, AtomicBool::compare_exchange.