Module scc::ebr

use scc::ebr::{suspend, Arc, AtomicArc, Barrier, Ptr, Tag};
use std::sync::atomic::Ordering::Relaxed;

// `atomic_arc` holds a strong reference to `17`.
let atomic_arc: AtomicArc<usize> = AtomicArc::new(17);

// `barrier` prevents the garbage collector from dropping reachable instances.
let barrier: Barrier = Barrier::new();

// `ptr` cannot outlive `barrier`.
let mut ptr: Ptr<usize> = atomic_arc.load(Relaxed, &barrier);
assert_eq!(*ptr.as_ref().unwrap(), 17);

// `atomic_arc` can be tagged.
atomic_arc.update_tag_if(Tag::First, |p| p.tag() == Tag::None, Relaxed, Relaxed);

// `ptr` is not tagged, so CAS fails.
assert!(atomic_arc.compare_exchange(
    ptr,
    (Some(Arc::new(18)), Tag::First),
    Relaxed,
    Relaxed,
    &barrier).is_err());

// `ptr` can be tagged.
ptr.set_tag(Tag::First);

// The result of CAS is a handle to the instance that `atomic_arc` previously owned.
let prev: Arc<usize> = atomic_arc.compare_exchange(
    ptr,
    (Some(Arc::new(18)), Tag::Second),
    Relaxed,
    Relaxed,
    &barrier).unwrap().0.unwrap();
assert_eq!(*prev, 17);

// `17` will be garbage-collected later.
drop(prev);

// `ebr::AtomicArc` can be converted into `ebr::Arc`.
let arc: Arc<usize> = atomic_arc.try_into_arc(Relaxed).unwrap();
assert_eq!(*arc, 18);

// `18` will be garbage-collected later.
drop(arc);

// `17` is still valid as `barrier` keeps the garbage collector from dropping it.
assert_eq!(*ptr.as_ref().unwrap(), 17);

// Execution of a closure can be deferred until all the current readers are gone.
barrier.defer_execute(|| println!("deferred"));
drop(barrier);

// The closure will be repeatedly invoked until it returns `true`.
let barrier = Barrier::new();
let mut data = 3;
barrier.defer_incremental_execute(move || {
    if data == 0 {
        return true;
    }
    data -= 1;
    false
});
drop(barrier);

// If the thread is expected to lie dormant for a while, call `suspend()` to allow other
// threads to reclaim its own retired instances.
suspend();