From 51a2b0ac91d462efde1bcba432123723f74ed95f Mon Sep 17 00:00:00 2001
From: Ian Douglas Scott <idscott@system76.com>
Date: Wed, 17 Dec 2025 12:39:49 -0800
Subject: [PATCH 1/2] sources/channel: Use a `PingOnDrop` helper

I believe previous there is a theoretically possible race, since the
`.ping()` call would have happened before the `mpsc::Sender` was
dropped.
---
 src/sources/channel.rs | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/src/sources/channel.rs b/src/sources/channel.rs
index 49f439ea..4ceee041 100644
--- a/src/sources/channel.rs
+++ b/src/sources/channel.rs
@@ -10,6 +10,7 @@
 
 use std::cmp;
 use std::fmt;
+use std::ops;
 use std::sync::mpsc;
 
 use crate::{EventSource, Poll, PostAction, Readiness, Token, TokenFactory};
@@ -30,13 +31,32 @@ pub enum Event<T> {
     Closed,
 }
 
+#[derive(Debug)]
+struct PingOnDrop(Ping);
+
+impl ops::Deref for PingOnDrop {
+    type Target = Ping;
+
+    fn deref(&self) -> &Ping {
+        &self.0
+    }
+}
+
+impl Drop for PingOnDrop {
+    fn drop(&mut self) {
+        self.0.ping();
+    }
+}
+
 /// The sender end of a channel
 ///
 /// It can be cloned and sent accross threads (if `T` is).
 #[derive(Debug)]
 pub struct Sender<T> {
     sender: mpsc::Sender<T>,
-    ping: Ping,
+    // Dropped after `sender` so receiver is guaranteed to get `Disconnected`
+    // after ping.
+    ping: PingOnDrop,
 }
 
 impl<T> Clone for Sender<T> {
@@ -44,7 +64,7 @@ impl<T> Clone for Sender<T> {
     fn clone(&self) -> Sender<T> {
         Sender {
             sender: self.sender.clone(),
-            ping: self.ping.clone(),
+            ping: PingOnDrop(self.ping.clone()),
         }
     }
 }
@@ -59,13 +79,6 @@ impl<T> Sender<T> {
     }
 }
 
-impl<T> Drop for Sender<T> {
-    fn drop(&mut self) {
-        // ping on drop, to notify about channel closure
-        self.ping.ping();
-    }
-}
-
 /// The sender end of a synchronous channel
 ///
 /// It can be cloned and sent accross threads (if `T` is).
@@ -164,7 +177,7 @@ pub fn channel<T>() -> (Sender<T>, Channel<T>) {
     (
         Sender {
             sender,
-            ping: ping.clone(),
+            ping: PingOnDrop(ping.clone()),
         },
         Channel {
             receiver,

From a885a07209f554ff725588be4912c6615ced0e08 Mon Sep 17 00:00:00 2001
From: Ian Douglas Scott <idscott@system76.com>
Date: Wed, 17 Dec 2025 12:41:51 -0800
Subject: [PATCH 2/2] sources/channel: Ping on drop of last instance of
 `SyncSender`

Presumably this should behave like `Sender`, but only ping once all
clones have been dropped. This should achieve that.
---
 src/sources/channel.rs | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/sources/channel.rs b/src/sources/channel.rs
index 4ceee041..fc84fea6 100644
--- a/src/sources/channel.rs
+++ b/src/sources/channel.rs
@@ -11,7 +11,7 @@
 use std::cmp;
 use std::fmt;
 use std::ops;
-use std::sync::mpsc;
+use std::sync::{mpsc, Arc};
 
 use crate::{EventSource, Poll, PostAction, Readiness, Token, TokenFactory};
 
@@ -85,7 +85,9 @@ impl<T> Sender<T> {
 #[derive(Debug)]
 pub struct SyncSender<T> {
     sender: mpsc::SyncSender<T>,
-    ping: Ping,
+    // Dropped after `sender` so receiver is guaranteed to get `Disconnected`
+    // after ping.
+    ping: Arc<PingOnDrop>,
 }
 
 impl<T> Clone for SyncSender<T> {
@@ -195,7 +197,7 @@ pub fn sync_channel<T>(bound: usize) -> (SyncSender<T>, Channel<T>) {
     (
         SyncSender {
             sender,
-            ping: ping.clone(),
+            ping: Arc::new(PingOnDrop(ping.clone())),
         },
         Channel {
             receiver,