add atomic_waker

Author: chaoyuepan

special/Cargo.toml

@@ -11,6 +11,7 @@ async-lock = "2.5.0"
 async-oneshot = "0.5.0"
 async-weighted-semaphore = "0.2.1"
 async_singleflight = "0.5.0"
+atomic-waker = "1.1.2"
 atomic_float = "0.1.0"
 atomicbox = "0.4.0"
 atomig = "0.4.0"

special/src/main.rs

@@ -61,6 +61,7 @@ fn main() {
     sync_cow_example().unwrap();
     arc_swap_example();
 
+    atomic_waker_example();
 }
 
 

special/src/primitive/atomic_waker_examples.rs

@@ -0,0 +1,64 @@
+use futures::future::Future;
+use futures::task::{Context, Poll, AtomicWaker};
+use std::sync::Arc;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering::Relaxed;
+use std::pin::Pin;
+
+struct Inner {
+    waker: AtomicWaker,
+    set: AtomicBool,
+}
+
+#[derive(Clone)]
+struct Flag(Arc<Inner>);
+
+impl Flag {
+    pub fn new() -> Self {
+        Flag(Arc::new(Inner {
+            waker: AtomicWaker::new(),
+            set: AtomicBool::new(false),
+        }))
+    }
+
+    pub fn signal(&self) {
+        self.0.set.store(true, Relaxed);
+        self.0.waker.wake();
+    }
+}
+
+impl Future for Flag {
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<bool> {
+        // quick check to avoid registration if already done.
+        if self.0.set.load(Relaxed) {
+            return Poll::Ready(true);
+        }
+
+        self.0.waker.register(cx.waker());
+
+        // Need to check condition **after** `register` to avoid a race
+        // condition that would result in lost notifications.
+        if self.0.set.load(Relaxed) {
+            Poll::Ready(true)
+        } else {
+            Poll::Pending
+        }
+    }
+}
+
+pub fn atomic_waker_example() {
+    smol::block_on(async {
+        let flag = Flag::new();
+        let flag2 = flag.clone();
+
+        smol::spawn(async move {
+            smol::Timer::after(std::time::Duration::from_secs(1)).await;
+            flag2.signal();
+        })
+        .detach();
+
+        println!("Waiting for flag: {}", flag.await);
+    });
+}

special/src/primitive/mod.rs

@@ -12,11 +12,13 @@ mod async_lock_examples;
 mod atomic_examples;
 mod simple_mutex_examples;
 mod waitgroup_examples;
+mod atomic_waker_examples;
 
 pub use try_lock_examples::*;
 pub use sharded_slab_example::*;
 pub use async_lock_examples::*;
 pub use atomic_examples::*; 
 pub use simple_mutex_examples::*;
 pub use waitgroup_examples::*;
+pub use atomic_waker_examples::*;