chore: reduce pin related unsafe code (#2613)

2 files changed, 9 insertions, 12 deletions

diff --git a/tokio/src/runtime/blocking/task.rs b/tokio/src/runtime/blocking/task.rs
index e0ae6e4e..a521af46 100644
--- a/tokio/src/runtime/blocking/task.rs
+++ b/tokio/src/runtime/blocking/task.rs
@@ -14,14 +14,17 @@ impl<T> BlockingTask<T> {
     }
 }
 
+// The closure `F` is never pinned
+impl<T> Unpin for BlockingTask<T> {}
+
 impl<T, R> Future for BlockingTask<T>
 where
     T: FnOnce() -> R,
 {
     type Output = R;
 
-    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> {
-        let me = unsafe { self.get_unchecked_mut() };
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> {
+        let me = &mut *self;
         let func = me
             .func
             .take()
diff --git a/tokio/src/runtime/enter.rs b/tokio/src/runtime/enter.rs
index ad5580cc..56a7c57b 100644
--- a/tokio/src/runtime/enter.rs
+++ b/tokio/src/runtime/enter.rs
@@ -142,12 +142,11 @@ cfg_block_on! {
     impl Enter {
         /// Blocks the thread on the specified future, returning the value with
         /// which that future completes.
-        pub(crate) fn block_on<F>(&mut self, mut f: F) -> Result<F::Output, crate::park::ParkError>
+        pub(crate) fn block_on<F>(&mut self, f: F) -> Result<F::Output, crate::park::ParkError>
         where
             F: std::future::Future,
         {
             use crate::park::{CachedParkThread, Park};
-            use std::pin::Pin;
             use std::task::Context;
             use std::task::Poll::Ready;
 
@@ -155,9 +154,7 @@ cfg_block_on! {
             let waker = park.get_unpark()?.into_waker();
             let mut cx = Context::from_waker(&waker);
 
-            // `block_on` takes ownership of `f`. Once it is pinned here, the original `f` binding can
-            // no longer be accessed, making the pinning safe.
-            let mut f = unsafe { Pin::new_unchecked(&mut f) };
+            pin!(f);
 
             loop {
                 if let Ready(v) = crate::coop::budget(|| f.as_mut().poll(&mut cx)) {
@@ -179,12 +176,11 @@ cfg_blocking_impl! {
         ///
         /// If the future completes before `timeout`, the result is returned. If
         /// `timeout` elapses, then `Err` is returned.
-        pub(crate) fn block_on_timeout<F>(&mut self, mut f: F, timeout: Duration) -> Result<F::Output, ParkError>
+        pub(crate) fn block_on_timeout<F>(&mut self, f: F, timeout: Duration) -> Result<F::Output, ParkError>
         where
             F: std::future::Future,
         {
             use crate::park::{CachedParkThread, Park};
-            use std::pin::Pin;
             use std::task::Context;
             use std::task::Poll::Ready;
             use std::time::Instant;
@@ -193,9 +189,7 @@ cfg_blocking_impl! {
             let waker = park.get_unpark()?.into_waker();
             let mut cx = Context::from_waker(&waker);
 
-            // `block_on` takes ownership of `f`. Once it is pinned here, the original `f` binding can
-            // no longer be accessed, making the pinning safe.
-            let mut f = unsafe { Pin::new_unchecked(&mut f) };
+            pin!(f);
             let when = Instant::now() + timeout;
 
             loop {