1 files changed, 187 insertions, 0 deletions
diff --git a/third_party/rust/ringbuf/src/ring_buffer.rs b/third_party/rust/ringbuf/src/ring_buffer.rs
new file mode 100644
index 0000000000..8ae68afa51
--- /dev/null
+++ b/third_party/rust/ringbuf/src/ring_buffer.rs
@@ -0,0 +1,187 @@
+use std::{
+    cell::UnsafeCell,
+    cmp::min,
+    mem::{self, MaybeUninit},
+    ptr::{self, copy},
+    sync::{
+        atomic::{AtomicUsize, Ordering},
+        Arc,
+    },
+};
+
+use crate::{consumer::Consumer, producer::Producer};
+
+pub(crate) struct SharedVec<T: Sized> {
+    cell: UnsafeCell<Vec<T>>,
+}
+
+unsafe impl<T: Sized> Sync for SharedVec<T> {}
+
+impl<T: Sized> SharedVec<T> {
+    pub fn new(data: Vec<T>) -> Self {
+        Self {
+            cell: UnsafeCell::new(data),
+        }
+    }
+    pub unsafe fn get_ref(&self) -> &Vec<T> {
+        &*self.cell.get()
+    }
+    #[allow(clippy::mut_from_ref)]
+    pub unsafe fn get_mut(&self) -> &mut Vec<T> {
+        &mut *self.cell.get()
+    }
+}
+
+/// Ring buffer itself.
+pub struct RingBuffer<T: Sized> {
+    pub(crate) data: SharedVec<MaybeUninit<T>>,
+    pub(crate) head: AtomicUsize,
+    pub(crate) tail: AtomicUsize,
+}
+
+impl<T: Sized> RingBuffer<T> {
+    /// Creates a new instance of a ring buffer.
+    pub fn new(capacity: usize) -> Self {
+        let mut data = Vec::new();
+        data.resize_with(capacity + 1, MaybeUninit::uninit);
+        Self {
+            data: SharedVec::new(data),
+            head: AtomicUsize::new(0),
+            tail: AtomicUsize::new(0),
+        }
+    }
+
+    /// Splits ring buffer into producer and consumer.
+    pub fn split(self) -> (Producer<T>, Consumer<T>) {
+        let arc = Arc::new(self);
+        (Producer { rb: arc.clone() }, Consumer { rb: arc })
+    }
+
+    /// Returns capacity of the ring buffer.
+    pub fn capacity(&self) -> usize {
+        unsafe { self.data.get_ref() }.len() - 1
+    }
+
+    /// Checks if the ring buffer is empty.
+    pub fn is_empty(&self) -> bool {
+        let head = self.head.load(Ordering::Acquire);
+        let tail = self.tail.load(Ordering::Acquire);
+        head == tail
+    }
+
+    /// Checks if the ring buffer is full.
+    pub fn is_full(&self) -> bool {
+        let head = self.head.load(Ordering::Acquire);
+        let tail = self.tail.load(Ordering::Acquire);
+        (tail + 1) % (self.capacity() + 1) == head
+    }
+
+    /// The length of the data in the buffer.
+    pub fn len(&self) -> usize {
+        let head = self.head.load(Ordering::Acquire);
+        let tail = self.tail.load(Ordering::Acquire);
+        (tail + self.capacity() + 1 - head) % (self.capacity() + 1)
+    }
+
+    /// The remaining space in the buffer.
+    pub fn remaining(&self) -> usize {
+        self.capacity() - self.len()
+    }
+}
+
+impl<T: Sized> Drop for RingBuffer<T> {
+    fn drop(&mut self) {
+        let data = unsafe { self.data.get_mut() };
+
+        let head = self.head.load(Ordering::Acquire);
+        let tail = self.tail.load(Ordering::Acquire);
+        let len = data.len();
+
+        let slices = if head <= tail {
+            (head..tail, 0..0)
+        } else {
+            (head..len, 0..tail)
+        };
+
+        let drop = |elem_ref: &mut MaybeUninit<T>| unsafe {
+            mem::replace(elem_ref, MaybeUninit::uninit()).assume_init();
+        };
+        for elem in data[slices.0].iter_mut() {
+            drop(elem);
+        }
+        for elem in data[slices.1].iter_mut() {
+            drop(elem);
+        }
+    }
+}
+
+struct SlicePtr<T: Sized> {
+    pub ptr: *mut T,
+    pub len: usize,
+}
+
+impl<T> SlicePtr<T> {
+    fn null() -> Self {
+        Self {
+            ptr: ptr::null_mut(),
+            len: 0,
+        }
+    }
+    fn new(slice: &mut [T]) -> Self {
+        Self {
+            ptr: slice.as_mut_ptr(),
+            len: slice.len(),
+        }
+    }
+    unsafe fn shift(&mut self, count: usize) {
+        self.ptr = self.ptr.add(count);
+        self.len -= count;
+    }
+}
+
+/// Moves at most `count` items from the `src` consumer to the `dst` producer.
+/// Consumer and producer may be of different buffers as well as of the same one.
+///
+/// `count` is the number of items being moved, if `None` - as much as possible items will be moved.
+///
+/// Returns number of items been moved.
+pub fn move_items<T>(src: &mut Consumer<T>, dst: &mut Producer<T>, count: Option<usize>) -> usize {
+    unsafe {
+        src.pop_access(|src_left, src_right| -> usize {
+            dst.push_access(|dst_left, dst_right| -> usize {
+                let n = count.unwrap_or_else(|| {
+                    min(
+                        src_left.len() + src_right.len(),
+                        dst_left.len() + dst_right.len(),
+                    )
+                });
+                let mut m = 0;
+                let mut src = (SlicePtr::new(src_left), SlicePtr::new(src_right));
+                let mut dst = (SlicePtr::new(dst_left), SlicePtr::new(dst_right));
+
+                loop {
+                    let k = min(n - m, min(src.0.len, dst.0.len));
+                    if k == 0 {
+                        break;
+                    }
+                    copy(src.0.ptr, dst.0.ptr, k);
+                    if src.0.len == k {
+                        src.0 = src.1;
+                        src.1 = SlicePtr::null();
+                    } else {
+                        src.0.shift(k);
+                    }
+                    if dst.0.len == k {
+                        dst.0 = dst.1;
+                        dst.1 = SlicePtr::null();
+                    } else {
+                        dst.0.shift(k);
+                    }
+                    m += k
+                }
+
+                m
+            })
+        })
+    }
+}