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use std::sync::{Arc, Weak};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::fmt;
use std::mem;
use std::marker::PhantomData;
pub struct ArcCell<T> {
inner: AtomicUsize,
_marker: PhantomData<T>,
}
impl<T> ArcCell<T> {
pub fn new(value: Arc<T>) -> ArcCell<T> {
ArcCell {
inner: AtomicUsize::new(unsafe { mem::transmute(value) }),
_marker: PhantomData,
}
}
fn take(&self) -> Arc<T> {
loop {
let ptr = self.inner.swap(0, Ordering::Acquire);
if ptr != 0 {
return unsafe { mem::transmute(ptr) };
}
}
}
fn put(&self, ptr: Arc<T>) {
self.inner.store(unsafe { mem::transmute(ptr) }, Ordering::Release);
}
pub fn get(&self) -> Arc<T> {
let ptr = self.take();
let res = ptr.clone();
self.put(ptr);
res
}
pub fn set(&self, value: Arc<T>) -> Arc<T> {
let old = self.take();
self.put(value);
old
}
}
impl<T: fmt::Debug> fmt::Debug for ArcCell<T> {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
self.get().fmt(fmt)
}
}
pub struct WeakCell<T> {
inner: AtomicUsize,
_marker: PhantomData<T>,
}
impl<T> WeakCell<T> {
pub fn new(value: Weak<T>) -> WeakCell<T> {
WeakCell {
inner: AtomicUsize::new(unsafe { mem::transmute(value) }),
_marker: PhantomData,
}
}
pub fn empty() -> WeakCell<T> {
WeakCell::new(Weak::new())
}
fn take(&self) -> Weak<T> {
loop {
let ptr = self.inner.swap(0, Ordering::Acquire);
if ptr != 0 {
return unsafe { mem::transmute(ptr) };
}
}
}
fn put(&self, ptr: Weak<T>) {
self.inner.store(unsafe { mem::transmute(ptr) }, Ordering::Release);
}
pub fn get(&self) -> Weak<T> {
let ptr = self.take();
let res = ptr.clone();
self.put(ptr);
res
}
pub fn upgrade(&self) -> Option<Arc<T>> {
self.get().upgrade()
}
pub fn set(&self, value: Weak<T>) -> Weak<T> {
let old = self.take();
self.put(value);
old
}
pub fn store(&self, value: &Arc<T>) {
self.set(Arc::downgrade(&value));
}
pub fn reset(&self) -> Weak<T> {
self.set(Weak::new())
}
}
impl<T: fmt::Debug> fmt::Debug for WeakCell<T> {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
self.upgrade().fmt(fmt)
}
}
#[cfg(test)]
mod tests {
use std::sync::Arc;
use {ArcCell, WeakCell};
#[test]
fn arc_cell() {
let data1 = Arc::new(5);
let data2 = Arc::new(6);
let cell = ArcCell::new(data1);
assert_eq!(*cell.get(), 5);
cell.set(data2);
assert_eq!(*cell.get(), 6);
}
#[test]
fn weak_cell() {
let data = Arc::new(5);
let cell = WeakCell::empty();
cell.store(&data);
assert_eq!(cell.upgrade(), Some(data.clone()));
drop(data);
assert_eq!(cell.upgrade(), None);
}
}