Merge pull request #1119 from cuviper/fetch_update

Use `fetch_update` instead of `compare_exchange_weak`

Author: cuviper

src/iter/find_first_last/mod.rs

@@ -181,25 +181,17 @@ impl<'p, P: 'p + Fn(&T) -> bool, T> Folder<T> for FindFolder<'p, T, P> {
         };
 
         if !found_best_in_range && (self.find_op)(&item) {
-            // Continuously try to set best_found until we succeed or we
-            // discover a better match was already found.
-            let mut current = self.best_found.load(Ordering::Relaxed);
-            loop {
-                if better_position(current, self.boundary, self.match_position) {
-                    break;
-                }
-                match self.best_found.compare_exchange_weak(
-                    current,
-                    self.boundary,
-                    Ordering::Relaxed,
-                    Ordering::Relaxed,
-                ) {
-                    Ok(_) => {
-                        self.item = Some(item);
-                        break;
-                    }
-                    Err(v) => current = v,
-                }
+            // Update the best found index if ours is better.
+            let update =
+                self.best_found
+                    .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |current| {
+                        better_position(self.boundary, current, self.match_position)
+                            .then_some(self.boundary)
+                    });
+
+            // Save this item if our index was better or equal.
+            if update.is_ok() || update == Err(self.boundary) {
+                self.item = Some(item);
             }
         }
         self

src/iter/par_bridge.rs

@@ -109,24 +109,11 @@ impl<Iter: Iterator + Send> UnindexedProducer for &IterParallelProducer<'_, Iter
     type Item = Iter::Item;
 
     fn split(self) -> (Self, Option<Self>) {
-        let mut count = self.split_count.load(Ordering::SeqCst);
-
-        loop {
-            // Check if the iterator is exhausted
-            if let Some(new_count) = count.checked_sub(1) {
-                match self.split_count.compare_exchange_weak(
-                    count,
-                    new_count,
-                    Ordering::SeqCst,
-                    Ordering::SeqCst,
-                ) {
-                    Ok(_) => return (self, Some(self)),
-                    Err(last_count) => count = last_count,
-                }
-            } else {
-                return (self, None);
-            }
-        }
+        // Check if the iterator is exhausted
+        let update = self
+            .split_count
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |c| c.checked_sub(1));
+        (self, update.is_ok().then_some(self))
     }
 
     fn fold_with<F>(self, mut folder: F) -> F