Function std::intrinsics::atomic_cxchg_acq

pub unsafe extern "rust-intrinsic" fn atomic_cxchg_acq<T>(    dst: *mut T,     old: T,     src: T) -> (T, bool) where    T: Copy, 

Stores a value if the current value is the same as the old value.

The stabilized version of this intrinsic is available on the atomic types via the compare_exchange method by passing Ordering::Acquire as both the success and failure parameters. For example, AtomicBool::compare_exchange.