left-right 0.11.5

#[cfg(loom)]
pub(crate) use loom::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
#[cfg(loom)]
pub(crate) use loom::sync::{Arc, Mutex, MutexGuard};
#[cfg(loom)]
pub(crate) fn fence(ord: Ordering) {
    if let Ordering::Acquire = ord {
    } else {
        // FIXME: loom only supports acquire fences at the moment.
        // https://github.com/tokio-rs/loom/issues/117
        // let's at least not panic...
        // this may generate some false positives (`SeqCst` is stronger than `Acquire`
        // for example), and some false negatives (`Relaxed` is weaker than `Acquire`),
        // but it's the best we can do for the time being.
    }
    loom::sync::atomic::fence(Ordering::Acquire)
}

#[cfg(not(loom))]
pub(crate) use std::sync::atomic::{fence, AtomicPtr, AtomicUsize, Ordering};
#[cfg(not(loom))]
pub(crate) use std::sync::{Arc, Mutex, MutexGuard};