cros_async: switch to std::hint::spin_loop

Replace the deprecated std::sync::spin_loop_hint with
std::hint::spin_loop.

Fixes this new warning from Rust 1.51:

  warning: use of deprecated function `std::sync::atomic::spin_loop_hint`:
  use hint::spin_loop instead

BUG=None
TEST=bin/clippy

Change-Id: Ic975c77ea19bcf256f73c0b3b89f85866abfe0bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2864362
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

cros_async/src/sync/cv.rs

@@ -3,8 +3,9 @@
 // found in the LICENSE file.
 
 use std::cell::UnsafeCell;
+use std::hint;
 use std::mem;
-use std::sync::atomic::{spin_loop_hint, AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 
 use crate::sync::mu::{MutexGuard, MutexReadGuard, RawMutex};
@@ -171,7 +172,7 @@ impl Condvar {
                 )
                 .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 
@@ -223,7 +224,7 @@ impl Condvar {
                 )
                 .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 
@@ -281,7 +282,7 @@ impl Condvar {
                 )
                 .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 
@@ -319,7 +320,7 @@ impl Condvar {
                 )
                 .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 

cros_async/src/sync/mu.rs

@@ -3,9 +3,10 @@
 // found in the LICENSE file.
 
 use std::cell::UnsafeCell;
+use std::hint;
 use std::mem;
 use std::ops::{Deref, DerefMut};
-use std::sync::atomic::{spin_loop_hint, AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::thread::yield_now;
 
@@ -182,7 +183,7 @@ fn get_wake_list(waiters: &mut WaiterList) -> (WaiterList, usize) {
 #[inline]
 fn cpu_relax(iterations: usize) {
     for _ in 0..iterations {
-        spin_loop_hint();
+        hint::spin_loop();
     }
 }
 
@@ -518,7 +519,7 @@ impl RawMutex {
                 )
                 .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 
@@ -593,7 +594,7 @@ impl RawMutex {
             )
             .is_err()
         {
-            spin_loop_hint();
+            hint::spin_loop();
             oldstate = self.state.load(Ordering::Relaxed);
         }
 

cros_async/src/sync/spin.rs

@@ -3,8 +3,9 @@
 // found in the LICENSE file.
 
 use std::cell::UnsafeCell;
+use std::hint;
 use std::ops::{Deref, DerefMut};
-use std::sync::atomic::{spin_loop_hint, AtomicBool, Ordering};
+use std::sync::atomic::{AtomicBool, Ordering};
 
 const UNLOCKED: bool = false;
 const LOCKED: bool = true;
@@ -64,7 +65,7 @@ impl<T: ?Sized> SpinLock<T> {
             {
                 break;
             }
-            spin_loop_hint();
+            hint::spin_loop();
         }
 
         SpinLockGuard {