Barrier Synchronization for async/await

[ytakano]

Implement a barrier synchronization for async/await.

I implemented a barrier synchronization as follows.

awkernel/applications/measure_channel/src/lib.rs

Lines 30 to 63 in 7b7e050

	#[derive(Clone)]
	struct Barrier {
	count: Arc<AtomicUsize>,
	tx: Arc<Publisher<()>>,
	rx: Subscriber<()>,
	}
	impl Barrier {
	fn new(count: usize) -> Self {
	let attr = Attribute {
	queue_size: 1,
	..Attribute::default()
	};
	let (tx, rx) = pubsub::create_pubsub(attr);
	Self {
	count: Arc::new(AtomicUsize::new(count)),
	tx: Arc::new(tx),
	rx,
	}
	}
	async fn wait(&mut self) {
	if self
	.count
	.fetch_sub(1, core::sync::atomic::Ordering::Relaxed)
	== 1
	{
	self.tx.send(()).await;
	} else {
	self.rx.recv().await;
	}
	}
	}

However, the APIs are not compatible with other libraries like Tokio.

• https://docs.rs/tokio/latest/tokio/sync/struct.Barrier.html
• https://doc.rust-lang.org/beta/std/sync/struct.Barrier.html