Make the Waitlist responsible for calling wake

This api is harder to misuse, as one cannot forget to call wake after
pop.

Author: espindola

src/conn/pool/mod.rs

@@ -229,9 +229,7 @@ impl Pool {
             .connection_count
             .store(exchange.exist, atomic::Ordering::Relaxed);
         // we just enabled the creation of a new connection!
-        if let Some(w) = exchange.waiting.pop() {
-            w.wake();
-        }
+        exchange.waiting.wake();
     }
 
     /// Poll the pool for an available connection.

src/conn/pool/recycler.rs

@@ -81,9 +81,7 @@ impl Recycler {
                 .metrics
                 .connections_in_pool
                 .store(exchange.available.len(), Ordering::Relaxed);
-            if let Some(w) = exchange.waiting.pop() {
-                w.wake();
-            }
+            exchange.waiting.wake();
         }
     }
 }
@@ -244,9 +242,7 @@ impl Future for Recycler {
                 .connection_count
                 .store(exchange.exist, Ordering::Relaxed);
             for _ in 0..self.discarded {
-                if let Some(w) = exchange.waiting.pop() {
-                    w.wake();
-                }
+                exchange.waiting.wake();
             }
             drop(exchange);
             self.discarded = 0;
@@ -282,9 +278,7 @@ impl Future for Recycler {
         if self.inner.closed.load(Ordering::Acquire) {
             // `DisconnectPool` might still wait to be woken up.
             let mut exchange = self.inner.exchange.lock().unwrap();
-            while let Some(w) = exchange.waiting.pop() {
-                w.wake();
-            }
+            while exchange.waiting.wake() {}
             // we're about to exit, so there better be no outstanding connections
             assert_eq!(exchange.exist, 0);
             assert_eq!(exchange.available.len(), 0);

src/conn/pool/waitlist.rs

@@ -48,15 +48,17 @@ impl Waitlist {
         !occupied
     }
 
-    pub(crate) fn pop(&mut self) -> Option<Waker> {
+    /// Returns `true` if anyone was awaken
+    pub(crate) fn wake(&mut self) -> bool {
         match self.queue.pop() {
             Some((qw, _)) => {
                 self.metrics
                     .active_wait_requests
                     .fetch_sub(1, atomic::Ordering::Relaxed);
-                Some(qw.waker)
+                qw.waker.wake();
+                true
             }
-            None => None,
+            None => false,
         }
     }