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use std::cell::UnsafeCell;
use std::ops::{Deref, DerefMut};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
type AtomicFlag = AtomicUsize;
#[repr(align(64))]
struct AlignedData<T>(T);
struct TripleBuffer<T> {
buffers: UnsafeCell<[AlignedData<T>; 3]>,
flags: AtomicFlag,
}
unsafe impl<T> Sync for TripleBuffer<T> {}
impl<T: Default> TripleBuffer<T> {
pub fn new() -> TripleBuffer<T> {
TripleBuffer {
buffers: UnsafeCell::new([
AlignedData(Default::default()),
AlignedData(Default::default()),
AlignedData(Default::default()),
]),
flags: AtomicFlag::new(0x6),
}
}
}
impl<T> TripleBuffer<T> {
fn get_produce_index(&self) -> usize {
(self.flags.load(Ordering::SeqCst) & 0x30) >> 4
}
fn try_get_consume_index(&self) -> Result<usize, ()> {
let mut old_flags = self.flags.load(Ordering::Acquire);
let mut new_flags: usize;
loop {
if (old_flags & 0x40) == 0 {
return Err(());
}
new_flags = (old_flags & 0x30) | ((old_flags & 0x3) << 2) | ((old_flags & 0xC) >> 2);
match self
.flags
.compare_exchange(old_flags, new_flags, Ordering::SeqCst, Ordering::Relaxed)
{
Ok(_) => break,
Err(x) => old_flags = x,
}
}
Ok(new_flags & 0x3)
}
fn set_produce(&self) {
let mut old_flags = self.flags.load(Ordering::Acquire);
loop {
let new_flags = 0x40 | ((old_flags & 0xC) << 2) | ((old_flags & 0x30) >> 2) | (old_flags & 0x3);
match self
.flags
.compare_exchange(old_flags, new_flags, Ordering::SeqCst, Ordering::Relaxed)
{
Ok(_) => break,
Err(x) => old_flags = x,
}
}
}
}
pub struct Sender<T>(Arc<TripleBuffer<T>>);
unsafe impl<T: Send> Send for Sender<T> {}
impl<T> Sender<T> {
fn new(owner: &Arc<TripleBuffer<T>>) -> Sender<T> {
Sender(owner.clone())
}
pub fn send_buffer(&self) -> Result<RefSendBuffer<T>, ()> {
Ok(RefSendBuffer(&self.0, self.0.get_produce_index()))
}
}
impl<T: Copy> Sender<T> {
pub fn send(&self, value: T) -> Result<(), ()> {
match self.send_buffer() {
Ok(mut b) => {
*b = value;
Ok(())
}
Err(_) => Err(()),
}
}
}
pub struct RefSendBuffer<'a, T: 'a>(&'a TripleBuffer<T>, usize);
impl<'a, T> Drop for RefSendBuffer<'a, T> {
fn drop(&mut self) {
self.0.set_produce();
}
}
impl<'a, T> Deref for RefSendBuffer<'a, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &(*self.0.buffers.get())[self.1].0 }
}
}
impl<'a, T> DerefMut for RefSendBuffer<'a, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut (*self.0.buffers.get())[self.1].0 }
}
}
pub struct Receiver<T>(Arc<TripleBuffer<T>>);
unsafe impl<T: Send> Send for Receiver<T> {}
impl<T> Receiver<T> {
fn new(owner: &Arc<TripleBuffer<T>>) -> Receiver<T> {
Receiver(owner.clone())
}
pub fn receive_buffer(&self) -> Result<RefReceiveBuffer<T>, ()> {
match self.0.try_get_consume_index() {
Ok(idx) => Ok(RefReceiveBuffer(&self.0, idx)),
Err(_) => Err(()),
}
}
}
impl<T: Copy> Receiver<T> {
pub fn receive(&self) -> Result<T, ()> {
match self.receive_buffer() {
Ok(b) => Ok(*b),
Err(_) => Err(()),
}
}
}
pub struct RefReceiveBuffer<'a, T: 'a>(&'a TripleBuffer<T>, usize);
impl<'a, T> Deref for RefReceiveBuffer<'a, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &(*self.0.buffers.get())[self.1].0 }
}
}
impl<'a, T> DerefMut for RefReceiveBuffer<'a, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut (*self.0.buffers.get())[self.1].0 }
}
}
pub fn state_channel<T: Default>() -> (Sender<T>, Receiver<T>) {
let a = Arc::new(TripleBuffer::new());
(Sender::new(&a), Receiver::new(&a))
}