feat: Create Listener trait

This commit creates the Listener trait and moves most of EventListener's
functionality to that trait.

Signed-off-by: John Nunley <dev@notgull.net>

benches/bench.rs

@@ -1,7 +1,7 @@
 use std::iter;
 
 use criterion::{criterion_group, criterion_main, Criterion};
-use event_listener::Event;
+use event_listener::{prelude::*, Event};
 
 const COUNT: usize = 8000;
 

examples/mutex.rs

@@ -13,7 +13,7 @@ mod example {
     use std::thread;
     use std::time::{Duration, Instant};
 
-    use event_listener::Event;
+    use event_listener::{Event, Listener};
 
     /// A simple mutex.
     struct Mutex<T> {

src/lib.rs

@@ -19,7 +19,7 @@
 //! use std::thread;
 //! use std::time::Duration;
 //! use std::usize;
-//! use event_listener::Event;
+//! use event_listener::{Event, prelude::*};
 //!
 //! let flag = Arc::new(AtomicBool::new(false));
 //! let event = Arc::new(Event::new());
@@ -108,7 +108,7 @@ pub use notify::{IntoNotification, Notification};
 
 /// Useful traits for notifications.
 pub mod prelude {
-    pub use crate::{IntoNotification, Notification};
+    pub use crate::{IntoNotification, Listener, Notification};
 }
 
 /// Inner state of [`Event`].
@@ -213,7 +213,7 @@ impl<T> Event<T> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::<usize>::with_tag();
     /// ```
@@ -230,7 +230,7 @@ impl<T> Event<T> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let listener = event.listen();
@@ -254,7 +254,7 @@ impl<T> Event<T> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let listener = event.listen();
@@ -283,7 +283,7 @@ impl<T> Event<T> {
         let inner = ManuallyDrop::new(unsafe { Arc::from_raw(self.inner()) });
 
         // Allocate the listener on the heap and insert it.
-        let mut listener = Box::pin(Listener {
+        let mut listener = Box::pin(InnerListener {
             event: Arc::clone(&inner),
             listener: None,
         });
@@ -322,7 +322,7 @@ impl<T> Event<T> {
     /// Use the default notification strategy:
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     ///
@@ -539,7 +539,7 @@ impl Event<()> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// ```
@@ -576,7 +576,7 @@ impl Event<()> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     /// use std::sync::atomic::{self, Ordering};
     ///
     /// let event = Event::new();
@@ -628,7 +628,7 @@ impl Event<()> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     ///
@@ -678,7 +678,7 @@ impl Event<()> {
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     /// use std::sync::atomic::{self, Ordering};
     ///
     /// let event = Event::new();
@@ -720,47 +720,17 @@ impl<T> Drop for Event<T> {
     }
 }
 
-/// A guard waiting for a notification from an [`Event`].
-///
-/// There are two ways for a listener to wait for a notification:
-///
-/// 1. In an asynchronous manner using `.await`.
-/// 2. In a blocking manner by calling [`EventListener::wait()`] on it.
+/// A handle that is listening to an [`Event`].
 ///
-/// If a notified listener is dropped without receiving a notification, dropping will notify
-/// another active listener. Whether one *additional* listener will be notified depends on what
-/// kind of notification was delivered.
-///
-/// The listener is not registered into the linked list inside of the [`Event`] by default if
-/// it is created via the `new()` method. It needs to be pinned first before being inserted
-/// using the `listen()` method. After the listener has begun `listen`ing, the user can
-/// `await` it like a future or call `wait()` to block the current thread until it is notified.
-///
-/// This structure allocates the listener on the heap.
-pub struct EventListener<T = ()> {
-    listener: Pin<Box<Listener<T, Arc<Inner<T>>>>>,
-}
-
-unsafe impl<T: Send> Send for EventListener<T> {}
-unsafe impl<T: Send> Sync for EventListener<T> {}
-
-impl<T> core::panic::UnwindSafe for EventListener<T> {}
-impl<T> core::panic::RefUnwindSafe for EventListener<T> {}
-impl<T> Unpin for EventListener<T> {}
-
-impl<T> fmt::Debug for EventListener<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("EventListener").finish_non_exhaustive()
-    }
-}
-
-impl<T> EventListener<T> {
+/// This trait represents a type waiting for a notification from an [`Event`]. See the
+/// [`EventListener`] type for more documentation on this trait's usage.
+pub trait Listener<T>: Future<Output = T> + __private::Sealed {
     /// Blocks until a notification is received.
     ///
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let mut listener = event.listen();
@@ -772,9 +742,7 @@ impl<T> EventListener<T> {
     /// listener.wait();
     /// ```
     #[cfg(all(feature = "std", not(target_family = "wasm")))]
-    pub fn wait(mut self) -> T {
-        self.listener.as_mut().wait_internal(None).unwrap()
-    }
+    fn wait(self) -> T;
 
     /// Blocks until a notification is received or a timeout is reached.
     ///
@@ -784,7 +752,7 @@ impl<T> EventListener<T> {
     ///
     /// ```
     /// use std::time::Duration;
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let mut listener = event.listen();
@@ -793,11 +761,7 @@ impl<T> EventListener<T> {
     /// assert!(listener.wait_timeout(Duration::from_secs(1)).is_none());
     /// ```
     #[cfg(all(feature = "std", not(target_family = "wasm")))]
-    pub fn wait_timeout(mut self, timeout: Duration) -> Option<T> {
-        self.listener
-            .as_mut()
-            .wait_internal(Instant::now().checked_add(timeout))
-    }
+    fn wait_timeout(self, timeout: Duration) -> Option<T>;
 
     /// Blocks until a notification is received or a deadline is reached.
     ///
@@ -807,7 +771,7 @@ impl<T> EventListener<T> {
     ///
     /// ```
     /// use std::time::{Duration, Instant};
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let mut listener = event.listen();
@@ -816,19 +780,17 @@ impl<T> EventListener<T> {
     /// assert!(listener.wait_deadline(Instant::now() + Duration::from_secs(1)).is_none());
     /// ```
     #[cfg(all(feature = "std", not(target_family = "wasm")))]
-    pub fn wait_deadline(mut self, deadline: Instant) -> Option<T> {
-        self.listener.as_mut().wait_internal(Some(deadline))
-    }
+    fn wait_deadline(self, deadline: Instant) -> Option<T>;
 
     /// Drops this listener and discards its notification (if any) without notifying another
     /// active listener.
     ///
     /// Returns `true` if a notification was discarded.
     ///
     /// # Examples
-    /// 
+    ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let mut listener1 = event.listen();
@@ -839,41 +801,103 @@ impl<T> EventListener<T> {
     /// assert!(listener1.discard());
     /// assert!(!listener2.discard());
     /// ```
-    pub fn discard(mut self) -> bool {
-        self.listener.as_mut().discard()
-    }
+    fn discard(self) -> bool;
 
     /// Returns `true` if this listener listens to the given `Event`.
     ///
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let listener = event.listen();
     ///
     /// assert!(listener.listens_to(&event));
     /// ```
-    #[inline]
-    pub fn listens_to(&self, event: &Event<T>) -> bool {
-        ptr::eq::<Inner<T>>(&*self.listener.event, event.inner.load(Ordering::Acquire))
-    }
+    fn listens_to(&self, event: &Event<T>) -> bool;
 
     /// Returns `true` if both listeners listen to the same `Event`.
     ///
     /// # Examples
     ///
     /// ```
-    /// use event_listener::Event;
+    /// use event_listener::{Event, prelude::*};
     ///
     /// let event = Event::new();
     /// let listener1 = event.listen();
     /// let listener2 = event.listen();
     ///
     /// assert!(listener1.same_event(&listener2));
     /// ```
-    pub fn same_event(&self, other: &EventListener<T>) -> bool {
+    fn same_event(&self, other: &Self) -> bool;
+}
+
+/// A guard waiting for a notification from an [`Event`].
+///
+/// There are two ways for a listener to wait for a notification:
+///
+/// 1. In an asynchronous manner using `.await`.
+/// 2. In a blocking manner by calling [`EventListener::wait()`] on it.
+///
+/// If a notified listener is dropped without receiving a notification, dropping will notify
+/// another active listener. Whether one *additional* listener will be notified depends on what
+/// kind of notification was delivered.
+///
+/// See the [`Listener`] trait for the functionality exposed by this type.
+///
+/// The listener is not registered into the linked list inside of the [`Event`] by default if
+/// it is created via the `new()` method. It needs to be pinned first before being inserted
+/// using the `listen()` method. After the listener has begun `listen`ing, the user can
+/// `await` it like a future or call `wait()` to block the current thread until it is notified.
+///
+/// This structure allocates the listener on the heap.
+pub struct EventListener<T = ()> {
+    listener: Pin<Box<InnerListener<T, Arc<Inner<T>>>>>,
+}
+
+unsafe impl<T: Send> Send for EventListener<T> {}
+unsafe impl<T: Send> Sync for EventListener<T> {}
+
+impl<T> core::panic::UnwindSafe for EventListener<T> {}
+impl<T> core::panic::RefUnwindSafe for EventListener<T> {}
+impl<T> Unpin for EventListener<T> {}
+
+impl<T> fmt::Debug for EventListener<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("EventListener").finish_non_exhaustive()
+    }
+}
+
+impl<T> Listener<T> for EventListener<T> {
+    #[cfg(all(feature = "std", not(target_family = "wasm")))]
+    fn wait(mut self) -> T {
+        self.listener.as_mut().wait_internal(None).unwrap()
+    }
+
+    #[cfg(all(feature = "std", not(target_family = "wasm")))]
+    fn wait_timeout(mut self, timeout: Duration) -> Option<T> {
+        self.listener
+            .as_mut()
+            .wait_internal(Instant::now().checked_add(timeout))
+    }
+
+    #[cfg(all(feature = "std", not(target_family = "wasm")))]
+    fn wait_deadline(mut self, deadline: Instant) -> Option<T> {
+        self.listener.as_mut().wait_internal(Some(deadline))
+    }
+
+    fn discard(mut self) -> bool {
+        self.listener.as_mut().discard()
+    }
+
+    #[inline]
+    fn listens_to(&self, event: &Event<T>) -> bool {
+        ptr::eq::<Inner<T>>(&*self.listener.event, event.inner.load(Ordering::Acquire))
+    }
+
+    #[inline]
+    fn same_event(&self, other: &EventListener<T>) -> bool {
         ptr::eq::<Inner<T>>(&*self.listener.event, &*other.listener.event)
     }
 }
@@ -889,7 +913,7 @@ impl<T> Future for EventListener<T> {
 pin_project_lite::pin_project! {
     #[project(!Unpin)]
     #[project = ListenerProject]
-    struct Listener<T, B: Borrow<Inner<T>>>
+    struct InnerListener<T, B: Borrow<Inner<T>>>
     where
         B: Unpin,
     {
@@ -904,7 +928,7 @@ pin_project_lite::pin_project! {
         listener: Option<sys::Listener<T>>,
     }
 
-    impl<T, B: Borrow<Inner<T>>> PinnedDrop for Listener<T, B>
+    impl<T, B: Borrow<Inner<T>>> PinnedDrop for InnerListener<T, B>
     where
         B: Unpin,
     {
@@ -916,10 +940,10 @@ pin_project_lite::pin_project! {
     }
 }
 
-unsafe impl<T: Send, B: Borrow<Inner<T>> + Unpin + Send> Send for Listener<T, B> {}
-unsafe impl<T: Send, B: Borrow<Inner<T>> + Unpin + Sync> Sync for Listener<T, B> {}
+unsafe impl<T: Send, B: Borrow<Inner<T>> + Unpin + Send> Send for InnerListener<T, B> {}
+unsafe impl<T: Send, B: Borrow<Inner<T>> + Unpin + Sync> Sync for InnerListener<T, B> {}
 
-impl<T, B: Borrow<Inner<T>> + Unpin> Listener<T, B> {
+impl<T, B: Borrow<Inner<T>> + Unpin> InnerListener<T, B> {
     /// Wait until the provided deadline.
     #[cfg(all(feature = "std", not(target_family = "wasm")))]
     fn wait_internal(mut self: Pin<&mut Self>, deadline: Option<Instant>) -> Option<T> {
@@ -1225,3 +1249,11 @@ fn __test_send_and_sync() {
     _assert_send::<EventListener<()>>();
     _assert_sync::<EventListener<()>>();
 }
+
+#[doc(hidden)]
+mod __private {
+    use super::EventListener;
+
+    pub trait Sealed {}
+    impl<T> Sealed for EventListener<T> {}
+}