1 files changed, 86 insertions, 0 deletions

diff --git a/embassy-sync/src/raw_rwlock.rs b/embassy-sync/src/raw_rwlock.rs
new file mode 100644
index 000000000..de4bd1dc5
--- /dev/null
+++ b/embassy-sync/src/raw_rwlock.rs
@@ -0,0 +1,86 @@
+use core::sync::atomic::{AtomicUsize, Ordering};
+use core::task::Waker;
+use core::cell::UnsafeCell;
+
+pub trait RawRwLock {
+    fn lock_read(&self);
+    fn try_lock_read(&self) -> bool;
+    fn unlock_read(&self);
+    fn lock_write(&self);
+    fn try_lock_write(&self) -> bool;
+    fn unlock_write(&self);
+}
+
+pub struct RawRwLockImpl {
+    state: AtomicUsize,
+    waker: UnsafeCell<Option<Waker>>,
+}
+
+impl RawRwLockImpl {
+    pub const fn new() -> Self {
+        Self {
+            state: AtomicUsize::new(0),
+            waker: UnsafeCell::new(None),
+        }
+    }
+}
+
+unsafe impl Send for RawRwLockImpl {}
+unsafe impl Sync for RawRwLockImpl {}
+
+impl RawRwLock for RawRwLockImpl {
+    fn lock_read(&self) {
+        loop {
+            let state = self.state.load(Ordering::Acquire);
+            if state & 1 == 0 {
+                if self.state.compare_and_swap(state, state + 2, Ordering::AcqRel) == state {
+                    break;
+                }
+            }
+        }
+    }
+
+    fn try_lock_read(&self) -> bool {
+        let state = self.state.load(Ordering::Acquire);
+        if state & 1 == 0 {
+            if self.state.compare_and_swap(state, state + 2, Ordering::AcqRel) == state {
+                return true;
+            }
+        }
+        false
+    }
+
+    fn unlock_read(&self) {
+        self.state.fetch_sub(2, Ordering::Release);
+        if self.state.load(Ordering::Acquire) == 0 {
+            if let Some(waker) = unsafe { &*self.waker.get() } {
+                waker.wake_by_ref();
+            }
+        }
+    }
+
+    fn lock_write(&self) {
+        loop {
+            let state = self.state.load(Ordering::Acquire);
+            if state == 0 {
+                if self.state.compare_and_swap(0, 1, Ordering::AcqRel) == 0 {
+                    break;
+                }
+            }
+        }
+    }
+
+    fn try_lock_write(&self) -> bool {
+        if self.state.compare_and_swap(0, 1, Ordering::AcqRel) == 0 {
+            return true;
+        }
+        false
+    }
+
+    fn unlock_write(&self) {
+        self.state.store(0, Ordering::Release);
+        if let Some(waker) = unsafe { &*self.waker.get() } {
+            waker.wake_by_ref();
+        }
+    }
+}