1 files changed, 19 insertions, 5 deletions

diff --git a/tokio/src/io/driver/scheduled_io.rs b/tokio/src/io/driver/scheduled_io.rs
index 3aefb376..ed3adc39 100644
--- a/tokio/src/io/driver/scheduled_io.rs
+++ b/tokio/src/io/driver/scheduled_io.rs
@@ -49,6 +49,8 @@ struct Waiters {
 }
 
 cfg_io_readiness! {
+    use crate::io::Interest;
+
     #[derive(Debug)]
     struct Waiter {
         pointers: linked_list::Pointers<Waiter>,
@@ -57,7 +59,7 @@ cfg_io_readiness! {
         waker: Option<Waker>,
 
         /// The interest this waiter is waiting on
-        interest: mio::Interest,
+        interest: Interest,
 
         is_ready: bool,
 
@@ -283,7 +285,7 @@ impl ScheduledIo {
     /// These are to support `AsyncRead` and `AsyncWrite` polling methods,
     /// which cannot use the `async fn` version. This uses reserved reader
     /// and writer slots.
-    pub(in crate::io) fn poll_readiness(
+    pub(super) fn poll_readiness(
         &self,
         cx: &mut Context<'_>,
         direction: Direction,
@@ -299,7 +301,19 @@ impl ScheduledIo {
                 Direction::Read => &mut waiters.reader,
                 Direction::Write => &mut waiters.writer,
             };
-            *slot = Some(cx.waker().clone());
+
+            // Avoid cloning the waker if one is already stored that matches the
+            // current task.
+            match slot {
+                Some(existing) => {
+                    if !existing.will_wake(cx.waker()) {
+                        *existing = cx.waker().clone();
+                    }
+                }
+                None => {
+                    *slot = Some(cx.waker().clone());
+                }
+            }
 
             // Try again, in case the readiness was changed while we were
             // taking the waiters lock
@@ -348,7 +362,7 @@ unsafe impl Sync for ScheduledIo {}
 cfg_io_readiness! {
     impl ScheduledIo {
         /// An async version of `poll_readiness` which uses a linked list of wakers
-        pub(crate) async fn readiness(&self, interest: mio::Interest) -> ReadyEvent {
+        pub(crate) async fn readiness(&self, interest: Interest) -> ReadyEvent {
             self.readiness_fut(interest).await
         }
 
@@ -356,7 +370,7 @@ cfg_io_readiness! {
         // we are borrowing the `UnsafeCell` possibly over await boundaries.
         //
         // Go figure.
-        fn readiness_fut(&self, interest: mio::Interest) -> Readiness<'_> {
+        fn readiness_fut(&self, interest: Interest) -> Readiness<'_> {
             Readiness {
                 scheduled_io: self,
                 state: State::Init,