std: use queue-based RwLock on Xous

library/std/src/sys/sync/rwlock/xous.rs

@@ -1,74 +0,0 @@
-use crate::sync::atomic::{AtomicIsize, Ordering::Acquire};
-use crate::thread::yield_now;
-
-pub struct RwLock {
-    /// The "mode" value indicates how many threads are waiting on this
-    /// Mutex. Possible values are:
-    ///    -1: The lock is locked for writing
-    ///     0: The lock is unlocked
-    ///   >=1: The lock is locked for reading
-    ///
-    /// This currently spins waiting for the lock to be freed. An
-    /// optimization would be to involve the ticktimer server to
-    /// coordinate unlocks.
-    mode: AtomicIsize,
-}
-
-const RWLOCK_WRITING: isize = -1;
-const RWLOCK_FREE: isize = 0;
-
-unsafe impl Send for RwLock {}
-unsafe impl Sync for RwLock {}
-
-impl RwLock {
-    #[inline]
-    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
-    pub const fn new() -> RwLock {
-        RwLock { mode: AtomicIsize::new(RWLOCK_FREE) }
-    }
-
-    #[inline]
-    pub unsafe fn read(&self) {
-        while !unsafe { self.try_read() } {
-            yield_now();
-        }
-    }
-
-    #[inline]
-    pub unsafe fn try_read(&self) -> bool {
-        self.mode
-            .fetch_update(
-                Acquire,
-                Acquire,
-                |v| if v == RWLOCK_WRITING { None } else { Some(v + 1) },
-            )
-            .is_ok()
-    }
-
-    #[inline]
-    pub unsafe fn write(&self) {
-        while !unsafe { self.try_write() } {
-            yield_now();
-        }
-    }
-
-    #[inline]
-    pub unsafe fn try_write(&self) -> bool {
-        self.mode.compare_exchange(RWLOCK_FREE, RWLOCK_WRITING, Acquire, Acquire).is_ok()
-    }
-
-    #[inline]
-    pub unsafe fn read_unlock(&self) {
-        let previous = self.mode.fetch_sub(1, Acquire);
-        assert!(previous != RWLOCK_FREE);
-        assert!(previous != RWLOCK_WRITING);
-    }
-
-    #[inline]
-    pub unsafe fn write_unlock(&self) {
-        assert_eq!(
-            self.mode.compare_exchange(RWLOCK_WRITING, RWLOCK_FREE, Acquire, Acquire),
-            Ok(RWLOCK_WRITING)
-        );
-    }
-}