feat: add "alloc" feature

Cargo.toml

@@ -7,29 +7,31 @@ description = "A buffering MPSC queue."
 homepage = "https://github.com/wyfo/swap-buffer-queue"
 readme = "README.md"
 keywords = [
-    "atomic",
-    "lock-free",
-    "no-std",
-    "mpsc",
-    "async",
+  "atomic",
+  "lock-free",
+  "no-std",
+  "mpsc",
+  "async",
 ]
 categories = [
-    "concurrency",
-    "data-structures",
-    "no-std",
+  "concurrency",
+  "data-structures",
+  "no-std",
 ]
 license = "MIT"
 repository = "https://github.com/wyfo/swap-buffer-queue"
 
 [features]
-default = ["stream"]
-std = []
-stream = ["std", "dep:futures"]
+default = ["std"]
+alloc = []
+std = ["alloc"]
+stream = ["dep:futures-core", "dep:futures-util"]
 write = []
 
 [dependencies]
 crossbeam-utils = { version = "0.8", default-features = false }
-futures = { version = "0.3", optional = true }
+futures-core = { version = "0.3", default-features = false, optional = true }
+futures-util = { version = "0.3", default-features = false, optional = true }
 
 [dev-dependencies]
 tokio-test = "0.4"
@@ -45,6 +47,6 @@ unexpected_cfgs = { level = "warn", check-cfg = ['cfg(loom)'] }
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = [
-    "--cfg",
-    "docsrs",
+  "--cfg",
+  "docsrs",
 ]

src/buffer.rs

@@ -1,6 +1,6 @@
 //! [`Buffer`] definition and simple implementations.
 
-use std::{
+use core::{
     fmt,
     iter::FusedIterator,
     marker::PhantomData,
@@ -12,12 +12,11 @@ use std::{
 use crate::queue::Queue;
 
 mod array;
-#[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+#[cfg(feature = "alloc")]
 mod vec;
 
 pub use array::ArrayBuffer;
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 pub use vec::VecBuffer;
 
 /// [`Queue`] buffer. It is used together with [`InsertIntoBuffer`].
@@ -114,8 +113,9 @@ where
         // don't loop on iterator, because `ExactSizeIterator` is not a sufficient guarantee
         // for unsafe code
         for i in index..(index + self.0.len()) {
+            const ERROR: &str = "iterator exhausted before reaching its exact size";
             // SAFETY: function contract encompass `CellBuffer::insert` one
-            unsafe { buffer.insert(i, self.0.next().unwrap()) };
+            unsafe { buffer.insert(i, self.0.next().expect(ERROR)) };
         }
     }
 }

src/buffer/array.rs

@@ -1,4 +1,4 @@
-use std::{cell::Cell, mem::MaybeUninit, ops::Range};
+use core::{cell::Cell, mem::MaybeUninit, ops::Range};
 
 use crate::{
     buffer::{Buffer, CellBuffer, Drain},

src/buffer/vec.rs

@@ -1,4 +1,5 @@
-use std::{cell::Cell, mem::MaybeUninit, ops::Range};
+use alloc::boxed::Box;
+use core::{cell::Cell, mem::MaybeUninit, ops::Range};
 
 use crate::buffer::{Buffer, CellBuffer, Drain, Resize};
 

src/error.rs

@@ -1,6 +1,6 @@
 //! Queue error types.
 
-use std::fmt;
+use core::fmt;
 
 /// Error returned by [`Queue::try_enqueue`](crate::Queue::try_enqueue).
 ///

src/lib.rs

@@ -3,7 +3,7 @@
 #![forbid(missing_docs)]
 #![forbid(unsafe_op_in_unsafe_fn)]
 #![forbid(clippy::undocumented_unsafe_blocks)]
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![cfg_attr(not(feature = "std"), no_std)]
 //! # swap-buffer-queue
 //! A buffering MPSC queue.
@@ -41,28 +41,23 @@
 //! assert_eq!(slice.into_iter().collect::<Vec<_>>(), vec![0, 1, 2, 3, 4]);
 //! ```
 
-#[cfg(not(feature = "std"))]
-extern crate core as std;
+#[cfg(feature = "alloc")]
+extern crate alloc;
 
 pub mod buffer;
 pub mod error;
 mod loom;
 pub mod notify;
 mod queue;
 #[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 mod synchronized;
 mod utils;
 #[cfg(feature = "write")]
-#[cfg_attr(docsrs, doc(cfg(feature = "write")))]
 pub mod write;
 #[cfg(feature = "write")]
-#[cfg_attr(docsrs, doc(cfg(feature = "write")))]
 #[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub mod write_vectored;
 
 pub use queue::Queue;
 #[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub use synchronized::{SynchronizedNotifier, SynchronizedQueue};

src/queue.rs

@@ -1,4 +1,4 @@
-use std::{fmt, num::NonZeroUsize, ops::Range};
+use core::{fmt, num::NonZeroUsize, ops::Range};
 
 use crossbeam_utils::CachePadded;
 
@@ -281,6 +281,7 @@ where
     /// queue.try_enqueue([0]).unwrap();
     /// assert_eq!(queue.len(), 1);
     /// ```
+    #[inline]
     pub fn len(&self) -> usize {
         let enqueuing =
             EnqueuingCapacity::from_atomic(self.enqueuing_capacity.load(Ordering::Relaxed));
@@ -406,7 +407,7 @@ where
             // Spin in case of concurrent modifications, except when the buffer is full ofc.
             if enqueuing.remaining_capacity() != 0 {
                 for _ in 0..1 << backoff {
-                    std::hint::spin_loop();
+                    hint::spin_loop();
                 }
                 if backoff < BACKOFF_LIMIT {
                     backoff += 1;
@@ -467,7 +468,7 @@ where
                     .with_mut(|buf| unsafe { (*buf).slice(range.clone()) });
                 return Some(BufferSlice::new(self, buffer_index, range, slice));
             }
-            std::hint::spin_loop();
+            hint::spin_loop();
         }
         // If the enqueuing are still ongoing, just save the dequeuing state in order to retry.
         self.dequeuing_length.store(
@@ -564,7 +565,7 @@ where
             };
             if let Some(ref mut backoff) = backoff {
                 for _ in 0..1 << *backoff {
-                    std::hint::spin_loop();
+                    hint::spin_loop();
                 }
                 if *backoff < BACKOFF_LIMIT {
                     *backoff += 1;

src/synchronized.rs

@@ -1,3 +1,23 @@
+//! Synchronization primitives for [`Queue`].
+//!
+//! It supports both synchronous and asynchronous API. [`SynchronizedQueue`] is just an alias
+//! for a [`Queue`] using [`SynchronizedNotifier`].
+//!
+//! # Examples
+//! ```rust
+//! # use std::sync::Arc;
+//! # use swap_buffer_queue::SynchronizedQueue;
+//! # use swap_buffer_queue::buffer::VecBuffer;
+//! let queue: Arc<SynchronizedQueue<VecBuffer<usize>>> =
+//!     Arc::new(SynchronizedQueue::with_capacity(1));
+//! let queue_clone = queue.clone();
+//! std::thread::spawn(move || {
+//!     queue_clone.enqueue([0]).unwrap();
+//!     queue_clone.enqueue([1]).unwrap();
+//! });
+//! assert_eq!(queue.dequeue().unwrap()[0], 0);
+//! assert_eq!(queue.dequeue().unwrap()[0], 1);
+//! ```
 use std::{
     fmt,
     future::poll_fn,
@@ -380,12 +400,11 @@ where
     }
 
     #[cfg(feature = "stream")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
     /// Returns an stream over the element of the queue (see [`BufferIter`](crate::buffer::BufferIter)).
     ///
     /// # Examples
     /// ```
-    /// # use futures::StreamExt;
+    /// # use futures_util::StreamExt;
     /// # use swap_buffer_queue::SynchronizedQueue;
     /// # use swap_buffer_queue::buffer::VecBuffer;
     /// # tokio_test::block_on(async {
@@ -402,8 +421,8 @@ where
     /// assert_eq!(stream.next().await, None);
     /// # })
     /// ```
-    pub fn stream(&self) -> impl futures::Stream<Item = B::Value> + '_ {
-        use futures::{stream, StreamExt};
+    pub fn stream(&self) -> impl futures_core::Stream<Item = B::Value> + '_ {
+        use futures_util::{stream, StreamExt};
         stream::repeat_with(|| stream::once(self.dequeue_async()))
             .flatten()
             .take_while(|res| {

src/utils.rs

@@ -1,4 +1,4 @@
-use std::{
+use core::{
     mem,
     mem::MaybeUninit,
     ops::{Deref, DerefMut},

src/write.rs

@@ -29,12 +29,11 @@
 use std::ops::{Deref, DerefMut};
 
 mod array;
-#[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+#[cfg(feature = "alloc")]
 mod vec;
 
 pub use array::WriteArrayBuffer;
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 pub use vec::WriteVecBuffer;
 
 /// A bytes slice with a `HEADER_SIZE`-bytes header and a `TRAILER_SIZE`-bytes trailer.

src/write/vec.rs

@@ -1,4 +1,5 @@
-use std::{
+use alloc::boxed::Box;
+use core::{
     cell::{Cell, UnsafeCell},
     ops::Range,
 };