Make storage Send + Sync if item is only Send, bump version

Cargo.toml

@@ -7,14 +7,14 @@ readme = "README.md"
 license = "MIT/Apache-2.0"
 
 [workspace.dependencies]
-ringbuf = { path = ".", version = "0.4.0" }
+ringbuf = { path = ".", version = "0.4.1" }
 
 [workspace]
 members = ["async", "blocking"]
 
 [package]
 name = "ringbuf"
-version = "0.4.0"
+version = "0.4.1"
 edition.workspace = true
 authors.workspace = true
 description = "Lock-free SPSC FIFO ring buffer with direct access to inner data"

async/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "async-ringbuf"
-version = "0.2.0"
+version = "0.2.1"
 edition.workspace = true
 authors.workspace = true
 description = "Async SPSC FIFO ring buffer"

src/storage.rs

@@ -38,6 +38,8 @@ pub unsafe trait Storage {
     /// # Safety
     ///
     /// Slice must not overlab with existing mutable slices.
+    ///
+    /// Non-`Sync` items must not be accessed concurrently.
     unsafe fn slice(&self, range: Range<usize>) -> &[MaybeUninit<Self::Item>] {
         slice::from_raw_parts(self.as_ptr().add(range.start), range.len())
     }
@@ -57,8 +59,8 @@ pub struct Ref<'a, T> {
     ptr: *mut MaybeUninit<T>,
     len: usize,
 }
-unsafe impl<'a, T> Send for Ref<'a, T> where T: Sync {}
-unsafe impl<'a, T> Sync for Ref<'a, T> where T: Sync {}
+unsafe impl<'a, T> Send for Ref<'a, T> where T: Send {}
+unsafe impl<'a, T> Sync for Ref<'a, T> where T: Send {}
 unsafe impl<'a, T> Storage for Ref<'a, T> {
     type Item = T;
     #[inline]
@@ -88,7 +90,7 @@ impl<'a, T> From<Ref<'a, T>> for &'a mut [MaybeUninit<T>] {
 pub struct Owning<T: ?Sized> {
     data: UnsafeCell<T>,
 }
-unsafe impl<T: ?Sized> Sync for Owning<T> where T: Sync {}
+unsafe impl<T: ?Sized> Sync for Owning<T> where T: Send {}
 impl<T> From<T> for Owning<T> {
     fn from(value: T) -> Self {
         Self {
@@ -136,7 +138,7 @@ pub struct Heap<T> {
 #[cfg(feature = "alloc")]
 unsafe impl<T> Send for Heap<T> where T: Send {}
 #[cfg(feature = "alloc")]
-unsafe impl<T> Sync for Heap<T> where T: Sync {}
+unsafe impl<T> Sync for Heap<T> where T: Send {}
 #[cfg(feature = "alloc")]
 unsafe impl<T> Storage for Heap<T> {
     type Item = T;
@@ -188,3 +190,19 @@ impl<T> Drop for Heap<T> {
         drop(unsafe { Box::from_raw(ptr::slice_from_raw_parts_mut(self.ptr, self.len)) });
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use core::{cell::Cell, marker::PhantomData};
+
+    struct Check<S: Storage + Send + Sync + ?Sized>(PhantomData<S>);
+
+    #[allow(dead_code)]
+    fn check_send_sync() {
+        let _: Check<Ref<Cell<i32>>>;
+        let _: Check<Array<Cell<i32>, 4>>;
+        let _: Check<Slice<Cell<i32>>>;
+        let _: Check<Heap<Cell<i32>>>;
+    }
+}

src/tests/shared.rs

@@ -1,13 +1,12 @@
 use crate::{storage::Heap, traits::*, SharedRb};
-use std::{thread, thread::sleep, time::Duration, vec::Vec};
+use std::{cell::Cell, thread, thread::sleep, time::Duration, vec::Vec};
+
+fn yield_() {
+    sleep(Duration::from_millis(1));
+}
 
-#[cfg(feature = "std")]
 #[test]
 fn concurrent() {
-    fn yield_() {
-        sleep(Duration::from_millis(1));
-    }
-
     const MSG: &[u8] = b"The quick brown fox jumps over the lazy dog\0";
     let rb = SharedRb::<Heap<u8>>::new(4);
     let (mut prod, mut cons) = rb.split();
@@ -34,3 +33,38 @@ fn concurrent() {
     pjh.join().unwrap();
     assert_eq!(cjh.join().unwrap(), MSG);
 }
+
+#[test]
+fn non_sync() {
+    const N: i32 = 256;
+
+    let rb = SharedRb::<Heap<Cell<i32>>>::new(4);
+    let (mut prod, mut cons) = rb.split();
+
+    let pjh = thread::spawn({
+        move || {
+            for i in 0..N {
+                while prod.try_push(Cell::new(i)).is_err() {
+                    yield_();
+                }
+            }
+        }
+    });
+
+    let cjh = thread::spawn(move || {
+        for i in 0..N {
+            assert_eq!(
+                i,
+                loop {
+                    match cons.try_pop() {
+                        Some(i) => break i.get(),
+                        None => yield_(),
+                    }
+                }
+            );
+        }
+    });
+
+    pjh.join().unwrap();
+    cjh.join().unwrap();
+}

src/traits/observer.rs

@@ -26,6 +26,8 @@ pub trait Observer {
     /// # Safety
     ///
     /// Slice must not overlap with any mutable slice existing at the same time.
+    ///
+    /// Non-`Sync` items must not be accessed from multiple threads at the same time.
     unsafe fn unsafe_slices(&self, start: usize, end: usize) -> (&[MaybeUninit<Self::Item>], &[MaybeUninit<Self::Item>]);
 
     /// Get mutable slice between `start` and `end` indices.