Rollup merge of #91176 - hermitcore:spin, r=kennytm

If the thread does not get the lock in the short term, yield the CPU Reduces on [RustyHermit](https://github.com/hermitcore/rusty-hermit) the amount of wasted processor cycles
rust-lang · Nov 26, 2021 · fdc305d · fdc305d
2 parents 324b4bc + 6911af9
commit fdc305d
Showing 1 changed file with 10 additions and 1 deletion.
diff --git a/library/std/src/sys/hermit/mutex.rs b/library/std/src/sys/hermit/mutex.rs
@@ -46,8 +46,17 @@ impl<T> Spinlock<T> {
     #[inline]
     fn obtain_lock(&self) {
         let ticket = self.queue.fetch_add(1, Ordering::SeqCst) + 1;
+        let mut counter: u16 = 0;
         while self.dequeue.load(Ordering::SeqCst) != ticket {
-            hint::spin_loop();
+            counter += 1;
+            if counter < 100 {
+                hint::spin_loop();
+            } else {
+                counter = 0;
+                unsafe {
+                    abi::yield_now();
+                }
+            }
         }
     }