feat(rt): add downcast on Sleep trait (#3125)

This commit allows downcasting pinned `Sleep` object to support
implementations of `Timer::reset`.

One example where this is useful is when using `TokioSleep`, i.e.
`Sleep` provided by tokio.

Closes #3027

Author: dswij

benches/support/tokiort.rs

@@ -41,6 +41,12 @@ impl Timer for TokioTimer {
             inner: tokio::time::sleep_until(deadline.into()),
         })
     }
+
+    fn reset(&self, sleep: &mut Pin<Box<dyn Sleep>>, new_deadline: Instant) {
+        if let Some(sleep) = sleep.as_mut().downcast_mut_pin::<TokioSleep>() {
+            sleep.reset(new_deadline.into())
+        }
+    }
 }
 
 struct TokioTimeout<T> {
@@ -75,7 +81,10 @@ impl Future for TokioSleep {
     }
 }
 
-// Use HasSleep to get tokio::time::Sleep to implement Unpin.
-// see https://docs.rs/tokio/latest/tokio/time/struct.Sleep.html
-
 impl Sleep for TokioSleep {}
+
+impl TokioSleep {
+    pub fn reset(self: Pin<&mut Self>, deadline: Instant) {
+        self.project().inner.as_mut().reset(deadline.into());
+    }
+}

src/rt/mod.rs

@@ -6,12 +6,9 @@
 //! to plug in other runtimes.
 
 pub mod bounds;
+mod timer;
 
-use std::{
-    future::Future,
-    pin::Pin,
-    time::{Duration, Instant},
-};
+pub use timer::{Sleep, Timer};
 
 /// An executor of futures.
 ///
@@ -39,20 +36,3 @@ pub trait Executor<Fut> {
     /// Place the future into the executor to be run.
     fn execute(&self, fut: Fut);
 }
-
-/// A timer which provides timer-like functions.
-pub trait Timer {
-    /// Return a future that resolves in `duration` time.
-    fn sleep(&self, duration: Duration) -> Pin<Box<dyn Sleep>>;
-
-    /// Return a future that resolves at `deadline`.
-    fn sleep_until(&self, deadline: Instant) -> Pin<Box<dyn Sleep>>;
-
-    /// Reset a future to resolve at `new_deadline` instead.
-    fn reset(&self, sleep: &mut Pin<Box<dyn Sleep>>, new_deadline: Instant) {
-        *sleep = self.sleep_until(new_deadline);
-    }
-}
-
-/// A future returned by a `Timer`.
-pub trait Sleep: Send + Sync + Future<Output = ()> {}

src/rt/timer.rs

@@ -0,0 +1,127 @@
+//! Provides a timer trait with timer-like functions
+//!
+//! Example using tokio timer:
+//! ```rust
+//! use std::{
+//!     pin::Pin,
+//!     task::{Context, Poll},
+//!     time::{Duration, Instant},
+//! };
+//!
+//! use futures_util::Future;
+//! use pin_project_lite::pin_project;
+//! use hyper::rt::{Timer, Sleep};
+//!
+//! #[derive(Clone, Debug)]
+//! pub struct TokioTimer;
+//!
+//! impl Timer for TokioTimer {
+//!     fn sleep(&self, duration: Duration) -> Pin<Box<dyn Sleep>> {
+//!         Box::pin(TokioSleep {
+//!             inner: tokio::time::sleep(duration),
+//!         })
+//!     }
+//!
+//!     fn sleep_until(&self, deadline: Instant) -> Pin<Box<dyn Sleep>> {
+//!         Box::pin(TokioSleep {
+//!             inner: tokio::time::sleep_until(deadline.into()),
+//!         })
+//!     }
+//!
+//!     fn reset(&self, sleep: &mut Pin<Box<dyn Sleep>>, new_deadline: Instant) {
+//!         if let Some(sleep) = sleep.as_mut().downcast_mut_pin::<TokioSleep>() {
+//!             sleep.reset(new_deadline.into())
+//!         }
+//!     }
+//! }
+//!
+//! pin_project! {
+//!     pub(crate) struct TokioSleep {
+//!         #[pin]
+//!         pub(crate) inner: tokio::time::Sleep,
+//!     }
+//! }
+//!
+//! impl Future for TokioSleep {
+//!     type Output = ();
+//!
+//!     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+//!         self.project().inner.poll(cx)
+//!     }
+//! }
+//!
+//! impl Sleep for TokioSleep {}
+//!
+//! impl TokioSleep {
+//!     pub fn reset(self: Pin<&mut Self>, deadline: Instant) {
+//!         self.project().inner.as_mut().reset(deadline.into());
+//!     }
+//! }
+//! ````
+
+use std::{
+    any::TypeId,
+    future::Future,
+    pin::Pin,
+    time::{Duration, Instant},
+};
+
+/// A timer which provides timer-like functions.
+pub trait Timer {
+    /// Return a future that resolves in `duration` time.
+    fn sleep(&self, duration: Duration) -> Pin<Box<dyn Sleep>>;
+
+    /// Return a future that resolves at `deadline`.
+    fn sleep_until(&self, deadline: Instant) -> Pin<Box<dyn Sleep>>;
+
+    /// Reset a future to resolve at `new_deadline` instead.
+    fn reset(&self, sleep: &mut Pin<Box<dyn Sleep>>, new_deadline: Instant) {
+        *sleep = self.sleep_until(new_deadline);
+    }
+}
+
+/// A future returned by a `Timer`.
+pub trait Sleep: Send + Sync + Future<Output = ()> {
+    #[doc(hidden)]
+    /// This method is private and can not be implemented by downstream crate
+    fn __type_id(&self, _: private::Sealed) -> TypeId
+    where
+        Self: 'static,
+    {
+        TypeId::of::<Self>()
+    }
+}
+
+impl dyn Sleep {
+    //! This is a re-implementation of downcast methods from std::any::Any
+
+    /// Check whether the type is the same as `T`
+    pub fn is<T>(&self) -> bool
+    where
+        T: Sleep + 'static,
+    {
+        self.__type_id(private::Sealed {}) == TypeId::of::<T>()
+    }
+
+    /// Downcast a pinned &mut Sleep object to its original type
+    pub fn downcast_mut_pin<T>(self: Pin<&mut Self>) -> Option<Pin<&'static mut T>>
+    where
+        T: Sleep + 'static,
+    {
+        if self.is::<T>() {
+            unsafe {
+                let inner = Pin::into_inner_unchecked(self);
+                Some(Pin::new_unchecked(
+                    &mut *(&mut *inner as *mut dyn Sleep as *mut T),
+                ))
+            }
+        } else {
+            None
+        }
+    }
+}
+
+mod private {
+    #![allow(missing_debug_implementations)]
+    pub struct Sealed {}
+}