332 lines
10 KiB
Rust
332 lines
10 KiB
Rust
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use core::slice;
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use core::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
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/// Atomic reusable ringbuffer
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///
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/// This ringbuffer implementation is designed to be stored in a `static`,
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/// therefore all methods take `&self` and not `&mut self`.
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///
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/// It is "reusable": when created it has no backing buffer, you can give it
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/// one with `init` and take it back with `deinit`, and init it again in the
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/// future if needed. This is very non-idiomatic, but helps a lot when storing
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/// it in a `static`.
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///
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/// One concurrent writer and one concurrent reader are supported, even at
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/// different execution priorities (like main and irq).
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pub struct RingBuffer {
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buf: AtomicPtr<u8>,
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len: AtomicUsize,
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start: AtomicUsize,
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end: AtomicUsize,
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}
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pub struct Reader<'a>(&'a RingBuffer);
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pub struct Writer<'a>(&'a RingBuffer);
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impl RingBuffer {
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/// Create a new empty ringbuffer.
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pub const fn new() -> Self {
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Self {
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buf: AtomicPtr::new(core::ptr::null_mut()),
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len: AtomicUsize::new(0),
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start: AtomicUsize::new(0),
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end: AtomicUsize::new(0),
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}
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}
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/// Initialize the ring buffer with a buffer.
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///
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/// # Safety
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/// - The buffer (`buf .. buf+len`) must be valid memory until `deinit` is called.
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/// - Must not be called concurrently with any other methods.
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pub unsafe fn init(&self, buf: *mut u8, len: usize) {
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// Ordering: it's OK to use `Relaxed` because this is not called
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// concurrently with other methods.
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self.buf.store(buf, Ordering::Relaxed);
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self.len.store(len, Ordering::Relaxed);
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self.start.store(0, Ordering::Relaxed);
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self.end.store(0, Ordering::Relaxed);
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}
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/// Deinitialize the ringbuffer.
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///
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/// After calling this, the ringbuffer becomes empty, as if it was
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/// just created with `new()`.
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///
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/// # Safety
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/// - Must not be called concurrently with any other methods.
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pub unsafe fn deinit(&self) {
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// Ordering: it's OK to use `Relaxed` because this is not called
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// concurrently with other methods.
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self.len.store(0, Ordering::Relaxed);
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self.start.store(0, Ordering::Relaxed);
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self.end.store(0, Ordering::Relaxed);
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}
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/// Create a reader.
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///
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/// # Safety
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///
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/// Only one reader can exist at a time.
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pub unsafe fn reader(&self) -> Reader<'_> {
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Reader(self)
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}
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/// Create a writer.
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///
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/// # Safety
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///
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/// Only one writer can exist at a time.
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pub unsafe fn writer(&self) -> Writer<'_> {
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Writer(self)
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}
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pub fn is_full(&self) -> bool {
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let start = self.start.load(Ordering::Relaxed);
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let end = self.end.load(Ordering::Relaxed);
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self.wrap(end + 1) == start
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}
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pub fn is_empty(&self) -> bool {
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let start = self.start.load(Ordering::Relaxed);
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let end = self.end.load(Ordering::Relaxed);
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start == end
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}
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fn wrap(&self, n: usize) -> usize {
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let len = self.len.load(Ordering::Relaxed);
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assert!(n <= len);
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if n == len {
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0
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} else {
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n
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}
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}
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}
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impl<'a> Writer<'a> {
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/// Push data into the buffer in-place.
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///
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/// The closure `f` is called with a free part of the buffer, it must write
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/// some data to it and return the amount of bytes written.
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pub fn push(&mut self, f: impl FnOnce(&mut [u8]) -> usize) -> usize {
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let (p, n) = self.push_buf();
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let buf = unsafe { slice::from_raw_parts_mut(p, n) };
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let n = f(buf);
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self.push_done(n);
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n
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}
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/// Push one data byte.
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///
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/// Returns true if pushed succesfully.
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pub fn push_one(&mut self, val: u8) -> bool {
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let n = self.push(|f| match f {
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[] => 0,
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[x, ..] => {
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*x = val;
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1
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}
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});
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n != 0
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}
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/// Get a buffer where data can be pushed to.
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///
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/// Write data to the start of the buffer, then call `push_done` with
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/// however many bytes you've pushed.
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///
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/// The buffer is suitable to DMA to.
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///
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/// If the ringbuf is full, size=0 will be returned.
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///
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/// The buffer stays valid as long as no other `Writer` method is called
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/// and `init`/`deinit` aren't called on the ringbuf.
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pub fn push_buf(&mut self) -> (*mut u8, usize) {
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// Ordering: popping writes `start` last, so we read `start` first.
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// Read it with Acquire ordering, so that the next accesses can't be reordered up past it.
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let start = self.0.start.load(Ordering::Acquire);
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let buf = self.0.buf.load(Ordering::Relaxed);
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let len = self.0.len.load(Ordering::Relaxed);
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let end = self.0.end.load(Ordering::Relaxed);
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let n = if start <= end {
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len - end - (start == 0) as usize
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} else {
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start - end - 1
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};
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trace!(" ringbuf: push_buf {:?}..{:?}", end, end + n);
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(unsafe { buf.add(end) }, n)
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}
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pub fn push_done(&mut self, n: usize) {
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trace!(" ringbuf: push {:?}", n);
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let end = self.0.end.load(Ordering::Relaxed);
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// Ordering: write `end` last, with Release ordering.
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// The ordering ensures no preceding memory accesses (such as writing
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// the actual data in the buffer) can be reordered down past it, which
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// will guarantee the reader sees them after reading from `end`.
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self.0.end.store(self.0.wrap(end + n), Ordering::Release);
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}
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}
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impl<'a> Reader<'a> {
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/// Pop data from the buffer in-place.
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///
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/// The closure `f` is called with the next data, it must process
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/// some data from it and return the amount of bytes processed.
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pub fn pop(&mut self, f: impl FnOnce(&[u8]) -> usize) -> usize {
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let (p, n) = self.pop_buf();
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let buf = unsafe { slice::from_raw_parts(p, n) };
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let n = f(buf);
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self.pop_done(n);
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n
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}
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/// Pop one data byte.
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///
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/// Returns true if popped succesfully.
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pub fn pop_one(&mut self) -> Option<u8> {
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let mut res = None;
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self.pop(|f| match f {
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&[] => 0,
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&[x, ..] => {
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res = Some(x);
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1
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}
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});
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res
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}
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/// Get a buffer where data can be popped from.
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///
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/// Read data from the start of the buffer, then call `pop_done` with
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/// however many bytes you've processed.
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///
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/// The buffer is suitable to DMA from.
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///
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/// If the ringbuf is empty, size=0 will be returned.
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///
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/// The buffer stays valid as long as no other `Reader` method is called
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/// and `init`/`deinit` aren't called on the ringbuf.
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pub fn pop_buf(&mut self) -> (*mut u8, usize) {
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// Ordering: pushing writes `end` last, so we read `end` first.
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// Read it with Acquire ordering, so that the next accesses can't be reordered up past it.
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// This is needed to guarantee we "see" the data written by the writer.
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let end = self.0.end.load(Ordering::Acquire);
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let buf = self.0.buf.load(Ordering::Relaxed);
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let len = self.0.len.load(Ordering::Relaxed);
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let start = self.0.start.load(Ordering::Relaxed);
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let n = if end < start { len - start } else { end - start };
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trace!(" ringbuf: pop_buf {:?}..{:?}", start, start + n);
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(unsafe { buf.add(start) }, n)
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}
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pub fn pop_done(&mut self, n: usize) {
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trace!(" ringbuf: pop {:?}", n);
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let start = self.0.start.load(Ordering::Relaxed);
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// Ordering: write `start` last, with Release ordering.
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// The ordering ensures no preceding memory accesses (such as reading
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// the actual data) can be reordered down past it. This is necessary
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// because writing to `start` is effectively freeing the read part of the
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// buffer, which "gives permission" to the writer to write to it again.
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// Therefore, all buffer accesses must be completed before this.
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self.0.start.store(self.0.wrap(start + n), Ordering::Release);
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn push_pop() {
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let mut b = [0; 4];
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let rb = RingBuffer::new();
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unsafe {
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rb.init(b.as_mut_ptr(), 4);
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assert_eq!(rb.is_empty(), true);
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assert_eq!(rb.is_full(), false);
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rb.writer().push(|buf| {
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// If capacity is 4, we can fill it up to 3.
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assert_eq!(3, buf.len());
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buf[0] = 1;
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buf[1] = 2;
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buf[2] = 3;
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3
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});
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assert_eq!(rb.is_empty(), false);
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assert_eq!(rb.is_full(), true);
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rb.writer().push(|buf| {
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// If it's full, we can push 0 bytes.
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assert_eq!(0, buf.len());
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0
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});
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assert_eq!(rb.is_empty(), false);
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assert_eq!(rb.is_full(), true);
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rb.reader().pop(|buf| {
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assert_eq!(3, buf.len());
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assert_eq!(1, buf[0]);
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1
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});
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assert_eq!(rb.is_empty(), false);
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assert_eq!(rb.is_full(), false);
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rb.reader().pop(|buf| {
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assert_eq!(2, buf.len());
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0
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});
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assert_eq!(rb.is_empty(), false);
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assert_eq!(rb.is_full(), false);
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rb.reader().pop(|buf| {
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assert_eq!(2, buf.len());
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assert_eq!(2, buf[0]);
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assert_eq!(3, buf[1]);
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2
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});
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assert_eq!(rb.is_empty(), true);
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assert_eq!(rb.is_full(), false);
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rb.reader().pop(|buf| {
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assert_eq!(0, buf.len());
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0
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});
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rb.writer().push(|buf| {
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assert_eq!(1, buf.len());
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buf[0] = 10;
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1
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});
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rb.writer().push(|buf| {
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assert_eq!(2, buf.len());
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buf[0] = 11;
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buf[1] = 12;
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2
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});
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assert_eq!(rb.is_empty(), false);
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assert_eq!(rb.is_full(), true);
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}
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}
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}
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