Function std::intrinsics::atomic_xchg_relaxed

pub unsafe extern "rust-intrinsic" fn atomic_xchg_relaxed<T>(dst: *mut T,                                                             src: T)                                                             -> T

Stores the value at the specified memory location, returning the old value. The stabilized version of this intrinsic is available on the std::sync::atomic types via the swap method by passing Ordering::Relaxed as the order. For example, AtomicBool::swap.