Replace deprecated compare_and_swap with compare_exchange (#2297)

Author: taiki-e

futures-channel/src/mpsc/mod.rs

@@ -923,17 +923,16 @@ impl<T> Clone for UnboundedSenderInner<T> {
             debug_assert!(curr < MAX_BUFFER);
 
             let next = curr + 1;
-            let actual = self.inner.num_senders.compare_and_swap(curr, next, SeqCst);
-
-            // The ABA problem doesn't matter here. We only care that the
-            // number of senders never exceeds the maximum.
-            if actual == curr {
-                return Self {
-                    inner: self.inner.clone(),
-                };
+            match self.inner.num_senders.compare_exchange(curr, next, SeqCst, SeqCst) {
+                Ok(_) => {
+                    // The ABA problem doesn't matter here. We only care that the
+                    // number of senders never exceeds the maximum.
+                    return Self {
+                        inner: self.inner.clone(),
+                    };
+                }
+                Err(actual) => curr = actual,
             }
-
-            curr = actual;
         }
     }
 }
@@ -954,19 +953,18 @@ impl<T> Clone for BoundedSenderInner<T> {
             debug_assert!(curr < self.inner.max_senders());
 
             let next = curr + 1;
-            let actual = self.inner.num_senders.compare_and_swap(curr, next, SeqCst);
-
-            // The ABA problem doesn't matter here. We only care that the
-            // number of senders never exceeds the maximum.
-            if actual == curr {
-                return Self {
-                    inner: self.inner.clone(),
-                    sender_task: Arc::new(Mutex::new(SenderTask::new())),
-                    maybe_parked: false,
-                };
+            match self.inner.num_senders.compare_exchange(curr, next, SeqCst, SeqCst) {
+                Ok(_) => {
+                    // The ABA problem doesn't matter here. We only care that the
+                    // number of senders never exceeds the maximum.
+                    return Self {
+                        inner: self.inner.clone(),
+                        sender_task: Arc::new(Mutex::new(SenderTask::new())),
+                        maybe_parked: false,
+                    };
+                }
+                Err(actual) => curr = actual,
             }
-
-            curr = actual;
         }
     }
 }

futures-core/src/task/__internal/atomic_waker.rs

@@ -259,7 +259,11 @@ impl AtomicWaker {
     /// }
     /// ```
     pub fn register(&self, waker: &Waker) {
-        match self.state.compare_and_swap(WAITING, REGISTERING, Acquire) {
+        match self
+            .state
+            .compare_exchange(WAITING, REGISTERING, Acquire, Acquire)
+            .unwrap_or_else(|x| x)
+        {
             WAITING => {
                 unsafe {
                     // Locked acquired, update the waker cell

futures-util/src/future/future/shared.rs

@@ -210,7 +210,12 @@ where
 
         inner.record_waker(&mut this.waker_key, cx);
 
-        match inner.notifier.state.compare_and_swap(IDLE, POLLING, SeqCst) {
+        match inner
+            .notifier
+            .state
+            .compare_exchange(IDLE, POLLING, SeqCst, SeqCst)
+            .unwrap_or_else(|x| x)
+        {
             IDLE => {
                 // Lock acquired, fall through
             }
@@ -255,14 +260,18 @@ where
 
             match future.poll(&mut cx) {
                 Poll::Pending => {
-                    match inner.notifier.state.compare_and_swap(POLLING, IDLE, SeqCst) {
-                        POLLING => {
-                            // Success
-                            drop(_reset);
-                            this.inner = Some(inner);
-                            return Poll::Pending;
-                        }
-                        _ => unreachable!(),
+                    if inner
+                        .notifier
+                        .state
+                        .compare_exchange(POLLING, IDLE, SeqCst, SeqCst)
+                        .is_ok()
+                    {
+                        // Success
+                        drop(_reset);
+                        this.inner = Some(inner);
+                        return Poll::Pending;
+                    } else {
+                        unreachable!()
                     }
                 }
                 Poll::Ready(output) => output,