Abstract the state type for futexes

In the same way that we expose SmallAtomic and SmallPrimitive to allow
Windows to use a value other than an AtomicU32 for its futex state, this
patch switches the primary futex state type from AtomicU32 to
futex::Atomic.  The futex::Atomic type should be usable as an atomic
value with underlying primitive type equal to futex::Primitive.

This allows supporting the futex API on systems where the underlying
kernel futex implementation requires more state than simply an
AtomicU32.

All in-tree futex implementations simply define {Atomic,Primitive}
directly as {AtomicU32,u32}.

1 files changed, 3 insertions, 3 deletions

diff --git a/library/std/src/sys/sync/mutex/futex.rs b/library/std/src/sys/sync/mutex/futex.rs
index 81afa94b147..ce9b2daa5f8 100644
--- a/library/std/src/sys/sync/mutex/futex.rs
+++ b/library/std/src/sys/sync/mutex/futex.rs
@@ -1,11 +1,11 @@
 use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
 use crate::sys::futex::{self, futex_wait, futex_wake};
 
-type Atomic = futex::SmallAtomic;
+type Futex = futex::SmallFutex;
 type State = futex::SmallPrimitive;
 
 pub struct Mutex {
-    futex: Atomic,
+    futex: Futex,
 }
 
 const UNLOCKED: State = 0;
@@ -15,7 +15,7 @@ const CONTENDED: State = 2; // locked, and other threads waiting (contended)
 impl Mutex {
     #[inline]
     pub const fn new() -> Self {
-        Self { futex: Atomic::new(UNLOCKED) }
+        Self { futex: Futex::new(UNLOCKED) }
     }
 
     #[inline]