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//! Writing and reading multiple items at once into and from a [`RingBuffer`].
//!
//! Multiple items at once can be moved from an iterator into the ring buffer by using
//! [`Producer::write_chunk_uninit()`] followed by [`WriteChunkUninit::fill_from_iter()`].
//! Alternatively, mutable access to the (uninitialized) slots of the chunk can be obtained with
//! [`WriteChunkUninit::as_mut_slices()`], which requires writing some `unsafe` code.
//! To avoid that, [`Producer::write_chunk()`] can be used,
//! which initializes all slots with their [`Default`] value
//! and provides mutable access by means of [`WriteChunk::as_mut_slices()`].
//!
//! Multiple items at once can be moved out of the ring buffer by using
//! [`Consumer::read_chunk()`] and iterating over the returned [`ReadChunk`]
//! (or by explicitly calling [`ReadChunk::into_iter()`]).
//! Immutable access to the slots of the chunk can be obtained with [`ReadChunk::as_slices()`].
//!
//! # Examples
//!
//! This example uses a single thread for simplicity, but in a real application,
//! `producer` and `consumer` would of course live on different threads:
//!
//! ```
//! use rtrb::RingBuffer;
//!
//! let (mut producer, mut consumer) = RingBuffer::new(5);
//!
//! if let Ok(chunk) = producer.write_chunk_uninit(4) {
//! chunk.fill_from_iter([10, 11, 12]);
//! // Note that we requested 4 slots but we've only written to 3 of them!
//! } else {
//! unreachable!();
//! }
//!
//! assert_eq!(producer.slots(), 2);
//! assert_eq!(consumer.slots(), 3);
//!
//! if let Ok(chunk) = consumer.read_chunk(2) {
//! assert_eq!(chunk.into_iter().collect::<Vec<_>>(), [10, 11]);
//! } else {
//! unreachable!();
//! }
//!
//! // One element is still in the queue:
//! assert_eq!(consumer.peek(), Ok(&12));
//!
//! let data = vec![20, 21, 22, 23];
//! // NB: write_chunk_uninit() could be used for possibly better performance:
//! if let Ok(mut chunk) = producer.write_chunk(4) {
//! let (first, second) = chunk.as_mut_slices();
//! let mid = first.len();
//! first.copy_from_slice(&data[..mid]);
//! second.copy_from_slice(&data[mid..]);
//! chunk.commit_all();
//! } else {
//! unreachable!();
//! }
//!
//! assert!(producer.is_full());
//! assert_eq!(consumer.slots(), 5);
//!
//! let mut v = Vec::<i32>::with_capacity(5);
//! if let Ok(chunk) = consumer.read_chunk(5) {
//! let (first, second) = chunk.as_slices();
//! v.extend(first);
//! v.extend(second);
//! chunk.commit_all();
//! } else {
//! unreachable!();
//! }
//! assert_eq!(v, [12, 20, 21, 22, 23]);
//! assert!(consumer.is_empty());
//! ```
//!
//! The iterator API can be used to move items from one ring buffer to another:
//!
//! ```
//! use rtrb::{Consumer, Producer};
//!
//! fn move_items<T>(src: &mut Consumer<T>, dst: &mut Producer<T>) -> usize {
//! let n = src.slots().min(dst.slots());
//! dst.write_chunk_uninit(n).unwrap().fill_from_iter(src.read_chunk(n).unwrap())
//! }
//! ```
//!
//! ## Common Access Patterns
//!
//! The following examples show the [`Producer`] side;
//! similar patterns can of course be used with [`Consumer::read_chunk()`] as well.
//! Furthermore, the examples use [`Producer::write_chunk_uninit()`],
//! along with a bit of `unsafe` code.
//! To avoid this, you can use [`Producer::write_chunk()`] instead,
//! which requires the trait bound `T: Default` and will lead to a small runtime overhead.
//!
//! Copy a whole slice of items into the ring buffer, but only if space permits
//! (if not, the entire input slice is returned as an error):
//!
//! ```
//! use rtrb::{Producer, CopyToUninit};
//!
//! fn push_entire_slice<'a, T>(queue: &mut Producer<T>, slice: &'a [T]) -> Result<(), &'a [T]>
//! where
//! T: Copy,
//! {
//! if let Ok(mut chunk) = queue.write_chunk_uninit(slice.len()) {
//! let (first, second) = chunk.as_mut_slices();
//! let mid = first.len();
//! slice[..mid].copy_to_uninit(first);
//! slice[mid..].copy_to_uninit(second);
//! // SAFETY: All slots have been initialized
//! unsafe {
//! chunk.commit_all();
//! }
//! Ok(())
//! } else {
//! Err(slice)
//! }
//! }
//! ```
//!
//! Copy as many items as possible from a given slice, returning the number of copied items:
//!
//! ```
//! use rtrb::{Producer, CopyToUninit, chunks::ChunkError::TooFewSlots};
//!
//! fn push_partial_slice<T>(queue: &mut Producer<T>, slice: &[T]) -> usize
//! where
//! T: Copy,
//! {
//! let mut chunk = match queue.write_chunk_uninit(slice.len()) {
//! Ok(chunk) => chunk,
//! // Remaining slots are returned, this will always succeed:
//! Err(TooFewSlots(n)) => queue.write_chunk_uninit(n).unwrap(),
//! };
//! let end = chunk.len();
//! let (first, second) = chunk.as_mut_slices();
//! let mid = first.len();
//! slice[..mid].copy_to_uninit(first);
//! slice[mid..end].copy_to_uninit(second);
//! // SAFETY: All slots have been initialized
//! unsafe {
//! chunk.commit_all();
//! }
//! end
//! }
//! ```
//!
//! Write as many slots as possible, given an iterator
//! (and return the number of written slots):
//!
//! ```
//! use rtrb::{Producer, chunks::ChunkError::TooFewSlots};
//!
//! fn push_from_iter<T, I>(queue: &mut Producer<T>, iter: I) -> usize
//! where
//! T: Default,
//! I: IntoIterator<Item = T>,
//! {
//! let iter = iter.into_iter();
//! let n = match iter.size_hint() {
//! (_, None) => queue.slots(),
//! (_, Some(n)) => n,
//! };
//! let chunk = match queue.write_chunk_uninit(n) {
//! Ok(chunk) => chunk,
//! // Remaining slots are returned, this will always succeed:
//! Err(TooFewSlots(n)) => queue.write_chunk_uninit(n).unwrap(),
//! };
//! chunk.fill_from_iter(iter)
//! }
//! ```
use core::fmt;
use core::mem::MaybeUninit;
use core::sync::atomic::Ordering;
use crate::{Consumer, CopyToUninit, Producer};
// This is used in the documentation.
#[allow(unused_imports)]
use crate::RingBuffer;
impl<T> Producer<T> {
/// Returns `n` slots (initially containing their [`Default`] value) for writing.
///
/// [`WriteChunk::as_mut_slices()`] provides mutable access to the slots.
/// After writing to those slots, they explicitly have to be made available
/// to be read by the [`Consumer`] by calling [`WriteChunk::commit()`]
/// or [`WriteChunk::commit_all()`].
///
/// For an alternative that does not require the trait bound [`Default`],
/// see [`Producer::write_chunk_uninit()`].
///
/// If items are supposed to be moved from an iterator into the ring buffer,
/// [`Producer::write_chunk_uninit()`] followed by [`WriteChunkUninit::fill_from_iter()`]
/// can be used.
///
/// # Errors
///
/// If not enough slots are available, an error
/// (containing the number of available slots) is returned.
/// Use [`Producer::slots()`] to obtain the number of available slots beforehand.
///
/// # Examples
///
/// See the documentation of the [`chunks`](crate::chunks#examples) module.
pub fn write_chunk(&mut self, n: usize) -> Result<WriteChunk<'_, T>, ChunkError>
where
T: Default,
{
self.write_chunk_uninit(n).map(WriteChunk::from)
}
/// Returns `n` (uninitialized) slots for writing.
///
/// [`WriteChunkUninit::as_mut_slices()`] provides mutable access
/// to the uninitialized slots.
/// After writing to those slots, they explicitly have to be made available
/// to be read by the [`Consumer`] by calling [`WriteChunkUninit::commit()`]
/// or [`WriteChunkUninit::commit_all()`].
///
/// Alternatively, [`WriteChunkUninit::fill_from_iter()`] can be used
/// to move items from an iterator into the available slots.
/// All moved items are automatically made available to be read by the [`Consumer`].
///
/// # Errors
///
/// If not enough slots are available, an error
/// (containing the number of available slots) is returned.
/// Use [`Producer::slots()`] to obtain the number of available slots beforehand.
///
/// # Safety
///
/// This function itself is safe, as is [`WriteChunkUninit::fill_from_iter()`].
/// However, when using [`WriteChunkUninit::as_mut_slices()`],
/// the user has to make sure that the relevant slots have been initialized
/// before calling [`WriteChunkUninit::commit()`] or [`WriteChunkUninit::commit_all()`].
///
/// For a safe alternative that provides mutable slices of [`Default`]-initialized slots,
/// see [`Producer::write_chunk()`].
pub fn write_chunk_uninit(&mut self, n: usize) -> Result<WriteChunkUninit<'_, T>, ChunkError> {
let tail = self.tail.get();
// Check if the queue has *possibly* not enough slots.
if self.buffer.capacity - self.buffer.distance(self.head.get(), tail) < n {
// Refresh the head ...
let head = self.buffer.head.load(Ordering::Acquire);
self.head.set(head);
// ... and check if there *really* are not enough slots.
let slots = self.buffer.capacity - self.buffer.distance(head, tail);
if slots < n {
return Err(ChunkError::TooFewSlots(slots));
}
}
let tail = self.buffer.collapse_position(tail);
let first_len = n.min(self.buffer.capacity - tail);
Ok(WriteChunkUninit {
first_ptr: unsafe { self.buffer.data_ptr.add(tail) },
first_len,
second_ptr: self.buffer.data_ptr,
second_len: n - first_len,
producer: self,
})
}
}
impl<T> Consumer<T> {
/// Returns `n` slots for reading.
///
/// [`ReadChunk::as_slices()`] provides immutable access to the slots.
/// After reading from those slots, they explicitly have to be made available
/// to be written again by the [`Producer`] by calling [`ReadChunk::commit()`]
/// or [`ReadChunk::commit_all()`].
///
/// Alternatively, items can be moved out of the [`ReadChunk`] using iteration
/// because it implements [`IntoIterator`]
/// ([`ReadChunk::into_iter()`] can be used to explicitly turn it into an [`Iterator`]).
/// All moved items are automatically made available to be written again by the [`Producer`].
///
/// # Errors
///
/// If not enough slots are available, an error
/// (containing the number of available slots) is returned.
/// Use [`Consumer::slots()`] to obtain the number of available slots beforehand.
///
/// # Examples
///
/// See the documentation of the [`chunks`](crate::chunks#examples) module.
pub fn read_chunk(&mut self, n: usize) -> Result<ReadChunk<'_, T>, ChunkError> {
let head = self.head.get();
// Check if the queue has *possibly* not enough slots.
if self.buffer.distance(head, self.tail.get()) < n {
// Refresh the tail ...
let tail = self.buffer.tail.load(Ordering::Acquire);
self.tail.set(tail);
// ... and check if there *really* are not enough slots.
let slots = self.buffer.distance(head, tail);
if slots < n {
return Err(ChunkError::TooFewSlots(slots));
}
}
let head = self.buffer.collapse_position(head);
let first_len = n.min(self.buffer.capacity - head);
Ok(ReadChunk {
first_ptr: unsafe { self.buffer.data_ptr.add(head) },
first_len,
second_ptr: self.buffer.data_ptr,
second_len: n - first_len,
consumer: self,
})
}
}
/// Structure for writing into multiple ([`Default`]-initialized) slots in one go.
///
/// This is returned from [`Producer::write_chunk()`].
///
/// To obtain uninitialized slots, use [`Producer::write_chunk_uninit()`] instead,
/// which also allows moving items from an iterator into the ring buffer
/// by means of [`WriteChunkUninit::fill_from_iter()`].
#[derive(Debug, PartialEq, Eq)]
pub struct WriteChunk<'a, T>(WriteChunkUninit<'a, T>);
impl<'a, T> From<WriteChunkUninit<'a, T>> for WriteChunk<'a, T>
where
T: Default,
{
/// Fills all slots with the [`Default`] value.
fn from(chunk: WriteChunkUninit<'a, T>) -> Self {
for i in 0..chunk.first_len {
unsafe {
chunk.first_ptr.add(i).write(Default::default());
}
}
for i in 0..chunk.second_len {
unsafe {
chunk.second_ptr.add(i).write(Default::default());
}
}
WriteChunk(chunk)
}
}
impl<T> WriteChunk<'_, T>
where
T: Default,
{
/// Returns two slices for writing to the requested slots.
///
/// All slots are initially filled with their [`Default`] value.
///
/// The first slice can only be empty if `0` slots have been requested.
/// If the first slice contains all requested slots, the second one is empty.
///
/// After writing to the slots, they are *not* automatically made available
/// to be read by the [`Consumer`].
/// This has to be explicitly done by calling [`commit()`](WriteChunk::commit)
/// or [`commit_all()`](WriteChunk::commit_all).
/// If items are written but *not* committed afterwards,
/// they will *not* become available for reading and
/// they will be leaked (which is only relevant if `T` implements [`Drop`]).
pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
// Safety: All slots have been initialized in From::from().
unsafe {
(
core::slice::from_raw_parts_mut(self.0.first_ptr, self.0.first_len),
core::slice::from_raw_parts_mut(self.0.second_ptr, self.0.second_len),
)
}
}
/// Makes the first `n` slots of the chunk available for reading.
///
/// # Panics
///
/// Panics if `n` is greater than the number of slots in the chunk.
pub fn commit(self, n: usize) {
// Safety: All slots have been initialized in From::from() and there are no destructors.
unsafe {
self.0.commit(n);
}
}
/// Makes the whole chunk available for reading.
pub fn commit_all(self) {
// Safety: All slots have been initialized in From::from().
unsafe {
self.0.commit_all();
}
}
/// Returns the number of slots in the chunk.
#[must_use]
pub fn len(&self) -> usize {
self.0.len()
}
/// Returns `true` if the chunk contains no slots.
#[must_use]
pub fn is_empty(&self) -> bool {
self.0.is_empty()
}
}
/// Structure for writing into multiple (uninitialized) slots in one go.
///
/// This is returned from [`Producer::write_chunk_uninit()`].
#[derive(Debug, PartialEq, Eq)]
pub struct WriteChunkUninit<'a, T> {
first_ptr: *mut T,
first_len: usize,
second_ptr: *mut T,
second_len: usize,
producer: &'a Producer<T>,
}
impl<T> WriteChunkUninit<'_, T> {
/// Returns two slices for writing to the requested slots.
///
/// The first slice can only be empty if `0` slots have been requested.
/// If the first slice contains all requested slots, the second one is empty.
///
/// The extension trait [`CopyToUninit`] can be used to safely copy data into those slices.
///
/// After writing to the slots, they are *not* automatically made available
/// to be read by the [`Consumer`].
/// This has to be explicitly done by calling [`commit()`](WriteChunkUninit::commit)
/// or [`commit_all()`](WriteChunkUninit::commit_all).
/// If items are written but *not* committed afterwards,
/// they will *not* become available for reading and
/// they will be leaked (which is only relevant if `T` implements [`Drop`]).
pub fn as_mut_slices(&mut self) -> (&mut [MaybeUninit<T>], &mut [MaybeUninit<T>]) {
unsafe {
(
core::slice::from_raw_parts_mut(self.first_ptr as *mut _, self.first_len),
core::slice::from_raw_parts_mut(self.second_ptr as *mut _, self.second_len),
)
}
}
/// Makes the first `n` slots of the chunk available for reading.
///
/// # Panics
///
/// Panics if `n` is greater than the number of slots in the chunk.
///
/// # Safety
///
/// The user must make sure that the first `n` elements have been initialized.
pub unsafe fn commit(self, n: usize) {
assert!(n <= self.len(), "cannot commit more than chunk size");
self.commit_unchecked(n);
}
/// Makes the whole chunk available for reading.
///
/// # Safety
///
/// The user must make sure that all elements have been initialized.
pub unsafe fn commit_all(self) {
let slots = self.len();
self.commit_unchecked(slots);
}
unsafe fn commit_unchecked(self, n: usize) -> usize {
let tail = self.producer.buffer.increment(self.producer.tail.get(), n);
self.producer.buffer.tail.store(tail, Ordering::Release);
self.producer.tail.set(tail);
n
}
/// Moves items from an iterator into the (uninitialized) slots of the chunk.
///
/// The number of moved items is returned.
///
/// All moved items are automatically made availabe to be read by the [`Consumer`].
///
/// # Examples
///
/// If the iterator contains too few items, only a part of the chunk
/// is made available for reading:
///
/// ```
/// use rtrb::{RingBuffer, PopError};
///
/// let (mut p, mut c) = RingBuffer::new(4);
///
/// if let Ok(chunk) = p.write_chunk_uninit(3) {
/// assert_eq!(chunk.fill_from_iter([10, 20]), 2);
/// } else {
/// unreachable!();
/// }
/// assert_eq!(p.slots(), 2);
/// assert_eq!(c.pop(), Ok(10));
/// assert_eq!(c.pop(), Ok(20));
/// assert_eq!(c.pop(), Err(PopError::Empty));
/// ```
///
/// If the chunk size is too small, some items may remain in the iterator.
/// To be able to keep using the iterator after the call,
/// `&mut` (or [`Iterator::by_ref()`]) can be used.
///
/// ```
/// use rtrb::{RingBuffer, PopError};
///
/// let (mut p, mut c) = RingBuffer::new(4);
///
/// let mut it = vec![10, 20, 30].into_iter();
/// if let Ok(chunk) = p.write_chunk_uninit(2) {
/// assert_eq!(chunk.fill_from_iter(&mut it), 2);
/// } else {
/// unreachable!();
/// }
/// assert_eq!(c.pop(), Ok(10));
/// assert_eq!(c.pop(), Ok(20));
/// assert_eq!(c.pop(), Err(PopError::Empty));
/// assert_eq!(it.next(), Some(30));
/// ```
pub fn fill_from_iter<I>(self, iter: I) -> usize
where
I: IntoIterator<Item = T>,
{
let mut iter = iter.into_iter();
let mut iterated = 0;
'outer: for &(ptr, len) in &[
(self.first_ptr, self.first_len),
(self.second_ptr, self.second_len),
] {
for i in 0..len {
match iter.next() {
Some(item) => {
// Safety: It is allowed to write to this memory slot
unsafe {
ptr.add(i).write(item);
}
iterated += 1;
}
None => break 'outer,
}
}
}
// Safety: iterated slots have been initialized above
unsafe { self.commit_unchecked(iterated) }
}
/// Returns the number of slots in the chunk.
#[must_use]
pub fn len(&self) -> usize {
self.first_len + self.second_len
}
/// Returns `true` if the chunk contains no slots.
#[must_use]
pub fn is_empty(&self) -> bool {
self.first_len == 0
}
}
/// Structure for reading from multiple slots in one go.
///
/// This is returned from [`Consumer::read_chunk()`].
#[derive(Debug, PartialEq, Eq)]
pub struct ReadChunk<'a, T> {
first_ptr: *const T,
first_len: usize,
second_ptr: *const T,
second_len: usize,
consumer: &'a mut Consumer<T>,
}
impl<T> ReadChunk<'_, T> {
/// Returns two slices for reading from the requested slots.
///
/// The first slice can only be empty if `0` slots have been requested.
/// If the first slice contains all requested slots, the second one is empty.
///
/// The provided slots are *not* automatically made available
/// to be written again by the [`Producer`].
/// This has to be explicitly done by calling [`commit()`](ReadChunk::commit)
/// or [`commit_all()`](ReadChunk::commit_all).
/// Note that this runs the destructor of the committed items (if `T` implements [`Drop`]).
/// You can "peek" at the contained values by simply not calling any of the "commit" methods.
#[must_use]
pub fn as_slices(&self) -> (&[T], &[T]) {
(
unsafe { core::slice::from_raw_parts(self.first_ptr, self.first_len) },
unsafe { core::slice::from_raw_parts(self.second_ptr, self.second_len) },
)
}
/// Drops the first `n` slots of the chunk, making the space available for writing again.
///
/// # Panics
///
/// Panics if `n` is greater than the number of slots in the chunk.
///
/// # Examples
///
/// The following example shows that items are dropped when "committed"
/// (which is only relevant if `T` implements [`Drop`]).
///
/// ```
/// use rtrb::RingBuffer;
///
/// // Static variable to count all drop() invocations
/// static mut DROP_COUNT: i32 = 0;
/// #[derive(Debug)]
/// struct Thing;
/// impl Drop for Thing {
/// fn drop(&mut self) { unsafe { DROP_COUNT += 1; } }
/// }
///
/// // Scope to limit lifetime of ring buffer
/// {
/// let (mut p, mut c) = RingBuffer::new(2);
///
/// assert!(p.push(Thing).is_ok()); // 1
/// assert!(p.push(Thing).is_ok()); // 2
/// if let Ok(thing) = c.pop() {
/// // "thing" has been *moved* out of the queue but not yet dropped
/// assert_eq!(unsafe { DROP_COUNT }, 0);
/// } else {
/// unreachable!();
/// }
/// // First Thing has been dropped when "thing" went out of scope:
/// assert_eq!(unsafe { DROP_COUNT }, 1);
/// assert!(p.push(Thing).is_ok()); // 3
///
/// if let Ok(chunk) = c.read_chunk(2) {
/// assert_eq!(chunk.len(), 2);
/// assert_eq!(unsafe { DROP_COUNT }, 1);
/// chunk.commit(1); // Drops only one of the two Things
/// assert_eq!(unsafe { DROP_COUNT }, 2);
/// } else {
/// unreachable!();
/// }
/// // The last Thing is still in the queue ...
/// assert_eq!(unsafe { DROP_COUNT }, 2);
/// }
/// // ... and it is dropped when the ring buffer goes out of scope:
/// assert_eq!(unsafe { DROP_COUNT }, 3);
/// ```
pub fn commit(self, n: usize) {
assert!(n <= self.len(), "cannot commit more than chunk size");
unsafe { self.commit_unchecked(n) };
}
/// Drops all slots of the chunk, making the space available for writing again.
pub fn commit_all(self) {
let slots = self.len();
unsafe { self.commit_unchecked(slots) };
}
unsafe fn commit_unchecked(self, n: usize) -> usize {
let head = self.consumer.head.get();
// Safety: head has not yet been incremented
let first_ptr = self.consumer.buffer.slot_ptr(head);
let first_len = self.first_len.min(n);
for i in 0..first_len {
first_ptr.add(i).drop_in_place();
}
let second_ptr = self.consumer.buffer.data_ptr;
let second_len = self.second_len.min(n - first_len);
for i in 0..second_len {
second_ptr.add(i).drop_in_place();
}
let head = self.consumer.buffer.increment(head, n);
self.consumer.buffer.head.store(head, Ordering::Release);
self.consumer.head.set(head);
n
}
/// Returns the number of slots in the chunk.
#[must_use]
pub fn len(&self) -> usize {
self.first_len + self.second_len
}
/// Returns `true` if the chunk contains no slots.
#[must_use]
pub fn is_empty(&self) -> bool {
self.first_len == 0
}
}
impl<'a, T> IntoIterator for ReadChunk<'a, T> {
type Item = T;
type IntoIter = ReadChunkIntoIter<'a, T>;
/// Turns a [`ReadChunk`] into an iterator.
///
/// When the iterator is dropped, all iterated slots are made available for writing again.
/// Non-iterated items remain in the ring buffer.
fn into_iter(self) -> Self::IntoIter {
Self::IntoIter {
chunk: self,
iterated: 0,
}
}
}
/// An iterator that moves out of a [`ReadChunk`].
///
/// This `struct` is created by the [`into_iter()`](ReadChunk::into_iter) method
/// on [`ReadChunk`] (provided by the [`IntoIterator`] trait).
///
/// When this `struct` is dropped, the iterated slots are made available for writing again.
/// Non-iterated items remain in the ring buffer.
#[derive(Debug)]
pub struct ReadChunkIntoIter<'a, T> {
chunk: ReadChunk<'a, T>,
iterated: usize,
}
impl<'a, T> Drop for ReadChunkIntoIter<'a, T> {
/// Makes all iterated slots available for writing again.
///
/// Non-iterated items remain in the ring buffer and are *not* dropped.
fn drop(&mut self) {
let consumer = &self.chunk.consumer;
let head = consumer
.buffer
.increment(consumer.head.get(), self.iterated);
consumer.buffer.head.store(head, Ordering::Release);
consumer.head.set(head);
}
}
impl<'a, T> Iterator for ReadChunkIntoIter<'a, T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
let ptr = if self.iterated < self.chunk.first_len {
unsafe { self.chunk.first_ptr.add(self.iterated) }
} else if self.iterated < self.chunk.first_len + self.chunk.second_len {
unsafe {
self.chunk
.second_ptr
.add(self.iterated - self.chunk.first_len)
}
} else {
return None;
};
self.iterated += 1;
Some(unsafe { ptr.read() })
}
fn size_hint(&self) -> (usize, Option<usize>) {
let remaining = self.chunk.first_len + self.chunk.second_len - self.iterated;
(remaining, Some(remaining))
}
}
impl<'a, T> ExactSizeIterator for ReadChunkIntoIter<'a, T> {}
impl<'a, T> core::iter::FusedIterator for ReadChunkIntoIter<'a, T> {}
#[cfg(feature = "std")]
impl std::io::Write for Producer<u8> {
#[inline]
fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
use ChunkError::TooFewSlots;
let mut chunk = match self.write_chunk_uninit(buf.len()) {
Ok(chunk) => chunk,
Err(TooFewSlots(0)) => return Err(std::io::ErrorKind::WouldBlock.into()),
Err(TooFewSlots(n)) => self.write_chunk_uninit(n).unwrap(),
};
let end = chunk.len();
let (first, second) = chunk.as_mut_slices();
let mid = first.len();
// NB: If buf.is_empty(), chunk will be empty as well and the following are no-ops:
buf[..mid].copy_to_uninit(first);
buf[mid..end].copy_to_uninit(second);
// Safety: All slots have been initialized
unsafe {
chunk.commit_all();
}
Ok(end)
}
fn flush(&mut self) -> std::io::Result<()> {
// Nothing to do here.
Ok(())
}
}
#[cfg(feature = "std")]
impl std::io::Read for Consumer<u8> {
#[inline]
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
use ChunkError::TooFewSlots;
let chunk = match self.read_chunk(buf.len()) {
Ok(chunk) => chunk,
Err(TooFewSlots(0)) => return Err(std::io::ErrorKind::WouldBlock.into()),
Err(TooFewSlots(n)) => self.read_chunk(n).unwrap(),
};
let (first, second) = chunk.as_slices();
let mid = first.len();
let end = chunk.len();
// NB: If buf.is_empty(), chunk will be empty as well and the following are no-ops:
buf[..mid].copy_from_slice(first);
buf[mid..end].copy_from_slice(second);
chunk.commit_all();
Ok(end)
}
}
/// Error type for [`Consumer::read_chunk()`], [`Producer::write_chunk()`]
/// and [`Producer::write_chunk_uninit()`].
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum ChunkError {
/// Fewer than the requested number of slots were available.
///
/// Contains the number of slots that were available.
TooFewSlots(usize),
}
#[cfg(feature = "std")]
impl std::error::Error for ChunkError {}
impl fmt::Display for ChunkError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
ChunkError::TooFewSlots(n) => {
alloc::format!("only {} slots available in ring buffer", n).fmt(f)
}
}
}
}