Rollup merge of #127807 - ChrisDenton:win-parking, r=joboet

Use futex.rs for Windows thread parking

If I'm not overlooking anything then the Windows 10+ thread parking implementation is practically the same as the futex.rs implementation. So we may as well use the same implementation for both. The old version is still kept around for Windows 7 support.

r? ````@joboet```` if you wouldn't mind double checking I've not missed something

4 files changed, 19 insertions, 26 deletions

diff --git a/library/std/src/sys/sync/mutex/futex.rs b/library/std/src/sys/sync/mutex/futex.rs
index 7427cae94d6..81afa94b147 100644
--- a/library/std/src/sys/sync/mutex/futex.rs
+++ b/library/std/src/sys/sync/mutex/futex.rs
@@ -1,19 +1,8 @@
-use crate::sync::atomic::{
-    self,
-    Ordering::{Acquire, Relaxed, Release},
-};
-use crate::sys::futex::{futex_wait, futex_wake};
-
-cfg_if::cfg_if! {
-if #[cfg(windows)] {
-    // On Windows we can have a smol futex
-    type Atomic = atomic::AtomicU8;
-    type State = u8;
-} else {
-    type Atomic = atomic::AtomicU32;
-    type State = u32;
-}
-}
+use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
+use crate::sys::futex::{self, futex_wait, futex_wake};
+
+type Atomic = futex::SmallAtomic;
+type State = futex::SmallPrimitive;
 
 pub struct Mutex {
     futex: Atomic,
diff --git a/library/std/src/sys/sync/thread_parking/futex.rs b/library/std/src/sys/sync/thread_parking/futex.rs
index 588e7b27826..034eececb2a 100644
--- a/library/std/src/sys/sync/thread_parking/futex.rs
+++ b/library/std/src/sys/sync/thread_parking/futex.rs
@@ -1,15 +1,18 @@
+#![forbid(unsafe_op_in_unsafe_fn)]
 use crate::pin::Pin;
-use crate::sync::atomic::AtomicU32;
 use crate::sync::atomic::Ordering::{Acquire, Release};
-use crate::sys::futex::{futex_wait, futex_wake};
+use crate::sys::futex::{self, futex_wait, futex_wake};
 use crate::time::Duration;
 
-const PARKED: u32 = u32::MAX;
-const EMPTY: u32 = 0;
-const NOTIFIED: u32 = 1;
+type Atomic = futex::SmallAtomic;
+type State = futex::SmallPrimitive;
+
+const PARKED: State = State::MAX;
+const EMPTY: State = 0;
+const NOTIFIED: State = 1;
 
 pub struct Parker {
-    state: AtomicU32,
+    state: Atomic,
 }
 
 // Notes about memory ordering:
@@ -36,7 +39,7 @@ impl Parker {
     /// Construct the futex parker. The UNIX parker implementation
     /// requires this to happen in-place.
     pub unsafe fn new_in_place(parker: *mut Parker) {
-        parker.write(Self { state: AtomicU32::new(EMPTY) });
+        unsafe { parker.write(Self { state: Atomic::new(EMPTY) }) };
     }
 
     // Assumes this is only called by the thread that owns the Parker,
diff --git a/library/std/src/sys/sync/thread_parking/mod.rs b/library/std/src/sys/sync/thread_parking/mod.rs
index ed1a6437faa..0ebc5e093ee 100644
--- a/library/std/src/sys/sync/thread_parking/mod.rs
+++ b/library/std/src/sys/sync/thread_parking/mod.rs
@@ -1,5 +1,6 @@
 cfg_if::cfg_if! {
     if #[cfg(any(
+        all(target_os = "windows", not(target_vendor = "win7")),
         target_os = "linux",
         target_os = "android",
         all(target_arch = "wasm32", target_feature = "atomics"),
@@ -18,9 +19,9 @@ cfg_if::cfg_if! {
     ))] {
         mod id;
         pub use id::Parker;
-    } else if #[cfg(target_os = "windows")] {
-        mod windows;
-        pub use windows::Parker;
+    } else if #[cfg(target_vendor = "win7")] {
+        mod windows7;
+        pub use windows7::Parker;
     } else if #[cfg(all(target_vendor = "apple", not(miri)))] {
         mod darwin;
         pub use darwin::Parker;
diff --git a/library/std/src/sys/sync/thread_parking/windows.rs b/library/std/src/sys/sync/thread_parking/windows7.rs
index 3a8d40dc5cf..3a8d40dc5cf 100644
--- a/library/std/src/sys/sync/thread_parking/windows.rs
+++ b/library/std/src/sys/sync/thread_parking/windows7.rs