1 files changed, 159 insertions, 0 deletions

diff --git a/embassy-sync/src/blocking_rwlock/raw.rs b/embassy-sync/src/blocking_rwlock/raw.rs
new file mode 100644
index 000000000..85e8374b5
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+++ b/embassy-sync/src/blocking_rwlock/raw.rs
@@ -0,0 +1,159 @@
+//! Read-Write Lock primitives.
+//!
+//! This module provides a trait for read-write locks that can be used in different contexts.
+use core::marker::PhantomData;
+
+/// Raw read-write lock trait.
+///
+/// This read-write lock is "raw", which means it does not actually contain the protected data, it
+/// just implements the read-write lock mechanism. For most uses you should use [`super::RwLock`] instead,
+/// which is generic over a RawRwLock and contains the protected data.
+///
+/// Note that, unlike other read-write locks, implementations only guarantee no
+/// concurrent access from other threads: concurrent access from the current
+/// thread is allowed. For example, it's possible to lock the same read-write lock multiple times reentrantly.
+///
+/// Therefore, locking a `RawRwLock` is only enough to guarantee safe shared (`&`) access
+/// to the data, it is not enough to guarantee exclusive (`&mut`) access.
+///
+/// # Safety
+///
+/// RawRwLock implementations must ensure that, while locked, no other thread can lock
+/// the RawRwLock concurrently.
+///
+/// Unsafe code is allowed to rely on this fact, so incorrect implementations will cause undefined behavior.
+pub unsafe trait RawRwLock {
+    /// Create a new `RawRwLock` instance.
+    ///
+    /// This is a const instead of a method to allow creating instances in const context.
+    const INIT: Self;
+
+    /// Lock this `RawRwLock` for reading.
+    fn read_lock<R>(&self, f: impl FnOnce() -> R) -> R;
+
+    /// Lock this `RawRwLock` for writing.
+    fn write_lock<R>(&self, f: impl FnOnce() -> R) -> R;
+}
+
+/// A read-write lock that allows borrowing data across executors and interrupts.
+///
+/// # Safety
+///
+/// This read-write lock is safe to share between different executors and interrupts.
+pub struct CriticalSectionRawRwLock {
+    _phantom: PhantomData<()>,
+}
+unsafe impl Send for CriticalSectionRawRwLock {}
+unsafe impl Sync for CriticalSectionRawRwLock {}
+
+impl CriticalSectionRawRwLock {
+    /// Create a new `CriticalSectionRawRwLock`.
+    pub const fn new() -> Self {
+        Self { _phantom: PhantomData }
+    }
+}
+
+unsafe impl RawRwLock for CriticalSectionRawRwLock {
+    const INIT: Self = Self::new();
+
+    fn read_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+        critical_section::with(|_| f())
+    }
+
+    fn write_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+        critical_section::with(|_| f())
+    }
+}
+
+// ================
+
+/// A read-write lock that allows borrowing data in the context of a single executor.
+///
+/// # Safety
+///
+/// **This Read-Write Lock is only safe within a single executor.**
+pub struct NoopRawRwLock {
+    _phantom: PhantomData<*mut ()>,
+}
+
+unsafe impl Send for NoopRawRwLock {}
+
+impl NoopRawRwLock {
+    /// Create a new `NoopRawRwLock`.
+    pub const fn new() -> Self {
+        Self { _phantom: PhantomData }
+    }
+}
+
+unsafe impl RawRwLock for NoopRawRwLock {
+    const INIT: Self = Self::new();
+    fn read_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+        f()
+    }
+
+    fn write_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+        f()
+    }
+}
+
+// ================
+
+#[cfg(any(cortex_m, feature = "std"))]
+mod thread_mode {
+    use super::*;
+
+    /// A "read-write lock" that only allows borrowing from thread mode.
+    ///
+    /// # Safety
+    ///
+    /// **This Read-Write Lock is only safe on single-core systems.**
+    ///
+    /// On multi-core systems, a `ThreadModeRawRwLock` **is not sufficient** to ensure exclusive access.
+    pub struct ThreadModeRawRwLock {
+        _phantom: PhantomData<()>,
+    }
+
+    unsafe impl Send for ThreadModeRawRwLock {}
+    unsafe impl Sync for ThreadModeRawRwLock {}
+
+    impl ThreadModeRawRwLock {
+        /// Create a new `ThreadModeRawRwLock`.
+        pub const fn new() -> Self {
+            Self { _phantom: PhantomData }
+        }
+    }
+
+    unsafe impl RawRwLock for ThreadModeRawRwLock {
+        const INIT: Self = Self::new();
+        fn read_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+            assert!(in_thread_mode(), "ThreadModeRwLock can only be locked from thread mode.");
+
+            f()
+        }
+
+        fn write_lock<R>(&self, f: impl FnOnce() -> R) -> R {
+            assert!(in_thread_mode(), "ThreadModeRwLock can only be locked from thread mode.");
+
+            f()
+        }
+    }
+
+    impl Drop for ThreadModeRawRwLock {
+        fn drop(&mut self) {
+            assert!(
+                in_thread_mode(),
+                "ThreadModeRwLock can only be dropped from thread mode."
+            );
+        }
+    }
+
+    pub(crate) fn in_thread_mode() -> bool {
+        #[cfg(feature = "std")]
+        return Some("main") == std::thread::current().name();
+
+        #[cfg(not(feature = "std"))]
+        return unsafe { (0xE000ED04 as *const u32).read_volatile() } & 0x1FF == 0;
+    }
+}
+#[cfg(any(cortex_m, feature = "std"))]
+pub use thread_mode::*;
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