libasync/smoltcp/mod: prevent duplicated wakers

libasync/src/smoltcp/mod.rs

@@ -81,7 +81,14 @@ impl Sockets {
     /// TODO: this was called through eg. TcpStream, another poll()
     /// might want to send packets before sleeping for an interrupt.
     pub(crate) fn register_waker(waker: Waker) {
-        Self::instance().wakers.borrow_mut()
-            .push(waker);
+        let mut wakers = Self::instance().wakers.borrow_mut();
+        for (i, w) in wakers.iter().enumerate() {
+            if w.will_wake(&waker) {
+                let last = wakers.len() - 1;
+                wakers.swap(i, last);
+                return;
+            }
+        }
+        wakers.push(waker);
     }
 }