sync::mpsc: reload state after spinning on CAS failure

Author: ibraheemdev

library/std/src/sync/mpmc/array.rs

@@ -167,9 +167,9 @@ impl<T> Channel<T> {
                         token.array.stamp = tail + 1;
                         return true;
                     }
-                    Err(t) => {
-                        tail = t;
+                    Err(_) => {
                         backoff.spin();
+                        tail = self.load(Ordering::Relaxed);
                     }
                 }
             } else if stamp.wrapping_add(self.one_lap) == tail + 1 {
@@ -251,8 +251,8 @@ impl<T> Channel<T> {
                         return true;
                     }
                     Err(h) => {
-                        head = h;
                         backoff.spin();
+                        head = self.head.load(Ordering::Relaxed);
                     }
                 }
             } else if stamp == head {

library/std/src/sync/mpmc/list.rs

@@ -246,10 +246,10 @@ impl<T> Channel<T> {
                     token.list.offset = offset;
                     return true;
                 },
-                Err(t) => {
-                    tail = t;
-                    block = self.tail.block.load(Ordering::Acquire);
+                Err(_) => {
                     backoff.spin();
+                    tail = self.tail.index.load(Ordering::Acquire);
+                    block = self.tail.block.load(Ordering::Acquire);
                 }
             }
         }
@@ -351,9 +351,9 @@ impl<T> Channel<T> {
                     return true;
                 },
                 Err(h) => {
-                    head = h;
-                    block = self.head.block.load(Ordering::Acquire);
                     backoff.spin();
+                    head = self.head.index.load(Ordering::Acquire);
+                    block = self.head.block.load(Ordering::Acquire);
                 }
             }
         }