From 5e706a0a59011441dea6f619fab314d7e9d60b9a Mon Sep 17 00:00:00 2001
From: Ibraheem Ahmed <ibraheem@ibraheem.ca>
Date: Mon, 26 Feb 2024 08:24:26 -0500
Subject: [PATCH] Fix race between block initialization and receiver
 disconnection (#1084)

---
 crossbeam-channel/src/flavors/list.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crossbeam-channel/src/flavors/list.rs b/crossbeam-channel/src/flavors/list.rs
index f6a79f719..6d7ba7ebf 100644
--- a/crossbeam-channel/src/flavors/list.rs
+++ b/crossbeam-channel/src/flavors/list.rs
@@ -583,7 +583,7 @@ impl<T> Channel<T> {
         }
 
         let mut head = self.head.index.load(Ordering::Acquire);
-        let mut block = self.head.block.load(Ordering::Acquire);
+        let mut block = self.head.block.swap(ptr::null_mut(), Ordering::AcqRel);
 
         // If we're going to be dropping messages we need to synchronize with initialization
         if head >> SHIFT != tail >> SHIFT {
@@ -596,6 +596,7 @@ impl<T> Channel<T> {
                 block = self.head.block.load(Ordering::Acquire);
             }
         }
+
         unsafe {
             // Drop all messages between head and tail and deallocate the heap-allocated blocks.
             while head >> SHIFT != tail >> SHIFT {
@@ -623,7 +624,6 @@ impl<T> Channel<T> {
             }
         }
         head &= !MARK_BIT;
-        self.head.block.store(ptr::null_mut(), Ordering::Release);
         self.head.index.store(head, Ordering::Release);
     }