remove one notify_unless call (#9)

* remove one notify_unless call

* update comments

* Update src/join_handle.rs

Co-Authored-By: Stjepan Glavina <stjepang@gmail.com>

Author: laizy

src/join_handle.rs

@@ -206,11 +206,10 @@ impl<R, T> Future for JoinHandle<R, T> {
                     // completed or closed just before registration so we need to check for that.
                     state = (*header).state.load(Ordering::Acquire);
 
-                    // If the task has been closed, notify the awaiter and return `None`.
+                    // If the task has been closed, return `None`. We do not need to notify the
+                    // awaiter here, since we have replaced the waker above, and the executor can
+                    // only set it back to `None`.
                     if state & CLOSED != 0 {
-                        // Even though the awaiter is most likely the current task, it could also
-                        // be another task.
-                        (*header).notify_unless(cx.waker());
                         return Poll::Ready(None);
                     }