smallring 0.2.3

//! Atomic type ring buffer with specialized trait
//!
//! 为原子类型专门设计的环形缓冲区
//!
//! This module provides ring buffer implementation optimized for atomic types like AtomicU64.
//! Unlike generic ring buffers, atomic ring buffers don't move values but operate through
//! atomic load/store operations.
//!
//! 本模块提供针对原子类型（如 AtomicU64）优化的环形缓冲区实现。
//! 与通用环形缓冲区不同，原子环形缓冲区不移动值，而是通过原子 load/store 操作进行读写。

use super::core::RingBufCore;
use super::vec::FixedVec;
use crate::shim::atomic::{AtomicUsize, Ordering};
use alloc::vec::Vec;
use core::fmt;
use core::mem::MaybeUninit;

#[cfg(feature = "loom")]
fn backoff() {
    loom::thread::yield_now();
}

#[cfg(not(feature = "loom"))]
fn backoff() {
    core::hint::spin_loop();
}

mod traits;
pub use traits::{AtomicElement, AtomicNumeric};

/// Internal trait to dispatch push behavior based on OVERWRITE
///
/// 根据 OVERWRITE 分发 push 行为的内部 trait
pub trait PushDispatch<T: AtomicElement, const N: usize, const OVERWRITE: bool> {
    /// The return type of the push operation
    ///
    /// push 操作的返回类型
    type PushOutput;

    /// The actual push implementation
    ///
    /// 实际的 push 实现
    fn push_impl(
        ringbuf: &AtomicRingBuf<T, N, OVERWRITE>,
        value: T::Primitive,
        order: Ordering,
    ) -> Self::PushOutput;
}

/// Marker struct for compile-time dispatch
///
/// 编译期分发的标记结构
pub struct PushMarker<const OVERWRITE: bool>;

impl<T: AtomicElement, const N: usize> PushDispatch<T, N, true> for PushMarker<true> {
    /// Returns `Some(T::Primitive)` if an element was overwritten, `None` otherwise
    ///
    /// 如果覆盖了元素则返回 `Some(T::Primitive)`，否则返回 `None`
    type PushOutput = Option<T::Primitive>;

    #[inline]
    fn push_impl(
        ringbuf: &AtomicRingBuf<T, N, true>,
        value: T::Primitive,
        order: Ordering,
    ) -> Self::PushOutput {
        // Reservation phase
        let write = ringbuf.core.write_idx().fetch_add(1, Ordering::Relaxed);
        let read = ringbuf.core.read_idx().load(Ordering::Acquire);

        // Check if we need to overwrite
        let mut overwritten = false;
        if write.wrapping_sub(read) >= ringbuf.core.capacity() {
            // Buffer was full - attempt to advance read index
            overwritten = ringbuf
                .core
                .read_idx()
                .compare_exchange(
                    read,
                    read.wrapping_add(1),
                    Ordering::Release,
                    Ordering::Relaxed,
                )
                .is_ok();
        }

        let index = write & ringbuf.core.mask();
        let old_value = unsafe {
            let slot = ringbuf.core.peek_at(index);
            slot.swap(value, order)
        };

        // Mark as committed for this write index
        ringbuf
            .get_commit_status(index)
            .store(write, Ordering::Release);

        if overwritten { Some(old_value) } else { None }
    }
}

impl<T: AtomicElement, const N: usize> PushDispatch<T, N, false> for PushMarker<false> {
    /// Returns `Ok(())` on success, or `Err(value)` if full
    ///
    /// 成功时返回 `Ok(())`，如果满则返回 `Err(value)`
    type PushOutput = Result<(), T::Primitive>;

    #[inline]
    fn push_impl(
        ringbuf: &AtomicRingBuf<T, N, false>,
        value: T::Primitive,
        order: Ordering,
    ) -> Self::PushOutput {
        loop {
            // Load read index first to ensure we don't see a "future" read index
            // combined with a "past" write index, which would cause false "full" detection.
            let read = ringbuf.core.read_idx().load(Ordering::Acquire);
            let write = ringbuf.core.write_idx().load(Ordering::Relaxed);

            if write.wrapping_sub(read) >= ringbuf.core.capacity() {
                return Err(value);
            }

            // Attempt to reserve a slot
            if ringbuf
                .core
                .write_idx()
                .compare_exchange_weak(
                    write,
                    write.wrapping_add(1),
                    Ordering::Relaxed,
                    Ordering::Relaxed,
                )
                .is_ok()
            {
                // Reservation successful
                let index = write & ringbuf.core.mask();
                unsafe {
                    let slot = ringbuf.core.peek_at(index);
                    slot.store(value, order);
                }

                // Mark as committed for this write index
                ringbuf
                    .get_commit_status(index)
                    .store(write, Ordering::Release);
                return Ok(());
            }
            backoff();
        }
    }
}

/// Ring buffer specialized for atomic types
///
/// 为原子类型特化的环形缓冲区
///
/// # Type Parameters
/// - `T`: Atomic type implementing AtomicElement
/// - `N`: Stack capacity threshold
/// - `OVERWRITE`: Overwrite mode (true = overwrite oldest, false = reject when full)
///
/// # 类型参数
/// - `T`: 实现 AtomicElement 的原子类型
/// - `N`: 栈容量阈值
/// - `OVERWRITE`: 覆盖模式（true = 覆盖最旧的，false = 满时拒绝）
pub struct AtomicRingBuf<T: AtomicElement, const N: usize, const OVERWRITE: bool = true> {
    core: RingBufCore<T, N>,
    commit_status: FixedVec<AtomicUsize, N>,
}

impl<T: AtomicElement, const N: usize, const OVERWRITE: bool> AtomicRingBuf<T, N, OVERWRITE> {
    /// Create a new atomic ring buffer
    ///
    /// 创建新的原子环形缓冲区
    #[inline]
    pub fn new(capacity: usize) -> Self
    where
        T: Default,
    {
        let uninit = Self::new_uninit(capacity);
        unsafe {
            for i in 0..uninit.core.capacity() {
                uninit.core.write_at(i, T::default());
            }
        }
        uninit
    }

    /// Create a new atomic ring buffer with uninitialized elements
    ///
    /// 创建新的原子环形缓冲区，元素未初始化
    #[inline]
    pub fn new_uninit(capacity: usize) -> Self {
        let actual_capacity = super::core::round_to_power_of_two(capacity);
        let mut commit_status = FixedVec::with_capacity(actual_capacity);
        unsafe {
            for i in 0..actual_capacity {
                commit_status
                    .get_unchecked_mut_ptr(i)
                    .write(MaybeUninit::new(AtomicUsize::new(usize::MAX)));
            }
            commit_status.set_len(actual_capacity);
        }
        Self {
            core: RingBufCore::new(capacity),
            commit_status,
        }
    }

    #[inline]
    fn get_commit_status(&self, index: usize) -> &AtomicUsize {
        unsafe { self.commit_status[index].assume_init_ref() }
    }

    /// Get capacity
    ///
    /// 获取容量
    #[inline]
    pub fn capacity(&self) -> usize {
        self.core.capacity()
    }

    /// Get current length
    ///
    /// 获取当前长度
    #[inline]
    pub fn len(&self) -> usize {
        let write = self.core.write_idx().load(Ordering::Acquire);
        let read = self.core.read_idx().load(Ordering::Acquire);
        write.wrapping_sub(read).min(self.core.capacity())
    }

    /// Check if empty
    ///
    /// 检查是否为空
    #[inline]
    pub fn is_empty(&self) -> bool {
        let write = self.core.write_idx().load(Ordering::Acquire);
        let read = self.core.read_idx().load(Ordering::Acquire);
        write == read
    }

    /// Check if full
    ///
    /// 检查是否已满
    #[inline]
    pub fn is_full(&self) -> bool {
        self.core.is_full()
    }

    /// Push a value into the buffer
    ///
    /// 向缓冲区推送一个值
    ///
    /// # Behavior
    ///
    /// - **Overwrite mode (OVERWRITE=true)**: Always succeeds. Returns `Some(T::Primitive)` if an element was overwritten, `None` otherwise.
    /// - **Non-overwrite mode (OVERWRITE=false)**: Returns `Err(value)` if buffer is full, `Ok(())` otherwise.
    ///
    /// # 行为
    ///
    /// - **覆盖模式 (OVERWRITE=true)**: 总是成功。如果覆盖了元素则返回 `Some(T::Primitive)`，否则返回 `None`。
    /// - **非覆盖模式 (OVERWRITE=false)**: 如果缓冲区满则返回 `Err(value)`，否则返回 `Ok(())`。
    ///
    /// # Examples
    ///
    /// ```rust
    /// use smallring::atomic::{AtomicRingBuf, AtomicElement};
    /// use std::sync::atomic::{AtomicU64, Ordering};
    ///
    /// // Overwrite mode
    /// let buf_ow: AtomicRingBuf<AtomicU64, 32, true> = AtomicRingBuf::new(2);
    /// assert_eq!(buf_ow.push(1, Ordering::Relaxed), None);
    /// assert_eq!(buf_ow.push(2, Ordering::Relaxed), None);
    /// assert_eq!(buf_ow.push(3, Ordering::Relaxed), Some(1)); // Overwrote 1
    ///
    /// // Non-overwrite mode
    /// let buf_no: AtomicRingBuf<AtomicU64, 32, false> = AtomicRingBuf::new(2);
    /// assert_eq!(buf_no.push(1, Ordering::Relaxed), Ok(()));
    /// assert_eq!(buf_no.push(2, Ordering::Relaxed), Ok(()));
    /// assert_eq!(buf_no.push(3, Ordering::Relaxed), Err(3)); // Full
    /// ```
    #[inline(always)]
    pub fn push(
        &self,
        value: T::Primitive,
        order: Ordering,
    ) -> <PushMarker<OVERWRITE> as PushDispatch<T, N, OVERWRITE>>::PushOutput
    where
        PushMarker<OVERWRITE>: PushDispatch<T, N, OVERWRITE>,
    {
        PushMarker::<OVERWRITE>::push_impl(self, value, order)
    }

    /// Pop a value from the buffer
    ///
    /// 从缓冲区弹出一个值
    #[inline]
    pub fn pop(&self, order: Ordering) -> Option<T::Primitive> {
        loop {
            let read = self.core.read_idx().load(Ordering::Acquire);
            let index = read & self.core.mask();

            let commit = self.get_commit_status(index).load(Ordering::Acquire);
            if commit != read {
                return None;
            }

            let value = unsafe {
                let slot = self.core.peek_at(index);
                slot.load(order)
            };

            if self
                .core
                .read_idx()
                .compare_exchange(
                    read,
                    read.wrapping_add(1),
                    Ordering::AcqRel,
                    Ordering::Relaxed,
                )
                .is_ok()
            {
                return Some(value);
            }
            backoff();
        }
    }

    /// Peek at the next value without removing it
    ///
    /// 查看下一个值但不移除
    #[inline]
    pub fn peek(&self, order: Ordering) -> Option<T::Primitive> {
        let read = self.core.read_idx().load(Ordering::Acquire);
        let index = read & self.core.mask();

        let commit = self.get_commit_status(index).load(Ordering::Acquire);
        if commit != read {
            return None;
        }

        unsafe {
            let slot = self.core.peek_at(index);
            Some(slot.load(order))
        }
    }

    /// Access a slot directly by offset from read position
    ///
    /// 通过从读位置的偏移直接访问槽位
    ///
    /// # Safety
    /// Caller must ensure offset < len()
    #[inline]
    pub unsafe fn get_unchecked(&self, offset: usize) -> &T {
        let read = self.core.read_idx().load(Ordering::Acquire);
        let index = read.wrapping_add(offset) & self.core.mask();
        // SAFETY: Caller guarantees offset < len(), so index is valid
        unsafe { self.core.peek_at(index) }
    }

    /// Clear all elements from the buffer
    ///
    /// 清空缓冲区中的所有元素
    ///
    /// Resets the buffer to empty state by synchronizing read and write indices.
    ///
    /// 通过同步读写索引将缓冲区重置为空状态。
    ///
    /// # Examples
    ///
    /// ```rust
    /// use smallring::atomic::AtomicRingBuf;
    /// use std::sync::atomic::{AtomicU64, Ordering};
    ///
    /// let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);
    /// buf.push(1, Ordering::Relaxed);
    /// buf.push(2, Ordering::Relaxed);
    /// assert_eq!(buf.len(), 2);
    ///
    /// buf.clear();
    /// assert_eq!(buf.len(), 0);
    /// assert!(buf.is_empty());
    /// ```
    #[inline]
    pub fn clear(&self) {
        let write = self.core.write_idx().load(Ordering::Acquire);
        self.core.read_idx().store(write, Ordering::Release);
    }

    /// Read all valid elements from the buffer
    ///
    /// 读取缓冲区中所有有效元素
    ///
    /// Returns a vector of all elements currently in the buffer, in FIFO order.
    /// This does not remove elements from the buffer.
    ///
    /// 返回缓冲区中当前所有元素的向量，按 FIFO 顺序排列。
    /// 此操作不会从缓冲区中移除元素。
    ///
    /// # Examples
    ///
    /// ```rust
    /// use smallring::atomic::AtomicRingBuf;
    /// use std::sync::atomic::{AtomicU64, Ordering};
    ///
    /// let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);
    /// buf.push(1, Ordering::Relaxed);
    /// buf.push(2, Ordering::Relaxed);
    /// buf.push(3, Ordering::Relaxed);
    ///
    /// let values = buf.read_all(Ordering::Acquire);
    /// assert_eq!(values, vec![1, 2, 3]);
    /// assert_eq!(buf.len(), 3); // Elements still in buffer
    /// ```
    #[inline]
    pub fn read_all(&self, order: Ordering) -> Vec<T::Primitive> {
        let read = self.core.read_idx().load(Ordering::Acquire);
        let write = self.core.write_idx().load(Ordering::Acquire);

        let len = write.wrapping_sub(read).min(self.core.capacity());
        let mut values = Vec::with_capacity(len);

        for i in 0..len {
            let curr_idx = read.wrapping_add(i);
            let index = curr_idx & self.core.mask();
            if self.get_commit_status(index).load(Ordering::Acquire) == curr_idx {
                let value = unsafe {
                    let slot = self.core.peek_at(index);
                    slot.load(order)
                };
                values.push(value);
            } else {
                break;
            }
        }

        values
    }

    /// Get an iterator over elements in the buffer
    ///
    /// 获取缓冲区元素的迭代器
    ///
    /// Returns an iterator that yields references to atomic elements in FIFO order.
    /// The iterator provides read-only access to the underlying atomic values.
    ///
    /// 返回一个按 FIFO 顺序产生原子元素引用的迭代器。
    /// 迭代器提供对底层原子值的只读访问。
    ///
    /// # Examples
    ///
    /// ```rust
    /// use smallring::atomic::AtomicRingBuf;
    /// use std::sync::atomic::{AtomicU64, Ordering};
    ///
    /// let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);
    /// buf.push(1, Ordering::Relaxed);
    /// buf.push(2, Ordering::Relaxed);
    /// buf.push(3, Ordering::Relaxed);
    ///
    /// let values: Vec<u64> = buf.iter()
    ///     .map(|atom| atom.load(Ordering::Acquire))
    ///     .collect();
    /// assert_eq!(values, vec![1, 2, 3]);
    /// ```
    #[inline]
    pub fn iter(&self) -> AtomicIter<'_, T, N, OVERWRITE> {
        let read = self.core.read_idx().load(Ordering::Acquire);
        let write = self.core.write_idx().load(Ordering::Acquire);
        let len = write.wrapping_sub(read).min(self.core.capacity());

        AtomicIter {
            ringbuf: self,
            start: read,
            remaining: len,
        }
    }
}

/// Iterator over atomic ring buffer elements
///
/// 原子环形缓冲区元素的迭代器
pub struct AtomicIter<'a, T: AtomicElement, const N: usize, const OVERWRITE: bool> {
    ringbuf: &'a AtomicRingBuf<T, N, OVERWRITE>,
    start: usize,
    remaining: usize,
}

impl<'a, T: AtomicElement, const N: usize, const OVERWRITE: bool> Iterator
    for AtomicIter<'a, T, N, OVERWRITE>
{
    type Item = &'a T;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.remaining == 0 {
            return None;
        }

        let index = self.start & self.ringbuf.core.mask();
        let element = unsafe { self.ringbuf.core.peek_at(index) };

        self.start = self.start.wrapping_add(1);
        self.remaining -= 1;
        Some(element)
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.remaining, Some(self.remaining))
    }
}

impl<'a, T: AtomicElement, const N: usize, const OVERWRITE: bool> ExactSizeIterator
    for AtomicIter<'a, T, N, OVERWRITE>
{
    #[inline]
    fn len(&self) -> usize {
        self.remaining
    }
}

impl<T: AtomicElement + AtomicNumeric, const N: usize, const OVERWRITE: bool>
    AtomicRingBuf<T, N, OVERWRITE>
{
    /// Atomically add to an element at the given offset from read position
    ///
    /// 原子地将值加到从读位置开始的给定偏移处的元素
    ///
    /// # Safety
    /// Caller must ensure offset < len()
    ///
    /// # Examples
    ///
    /// ```rust
    /// use smallring::atomic::AtomicRingBuf;
    /// use std::sync::atomic::{AtomicU64, Ordering};
    ///
    /// let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);
    /// buf.push(10, Ordering::Relaxed);
    /// buf.push(20, Ordering::Relaxed);
    ///
    /// // Add 5 to the first element
    /// let old = unsafe { buf.fetch_add_at(0, 5, Ordering::Relaxed) };
    /// assert_eq!(old, 10);
    /// assert_eq!(buf.peek(Ordering::Acquire).unwrap(), 15);
    /// ```
    #[inline]
    pub unsafe fn fetch_add_at(
        &self,
        offset: usize,
        val: T::Primitive,
        order: Ordering,
    ) -> T::Primitive {
        let element = unsafe { self.get_unchecked(offset) };
        element.fetch_add(val, order)
    }

    /// Atomically subtract from an element at the given offset from read position
    ///
    /// 原子地从读位置开始的给定偏移处的元素减去值
    ///
    /// # Safety
    /// Caller must ensure offset < len()
    #[inline]
    pub unsafe fn fetch_sub_at(
        &self,
        offset: usize,
        val: T::Primitive,
        order: Ordering,
    ) -> T::Primitive {
        let element = unsafe { self.get_unchecked(offset) };
        element.fetch_sub(val, order)
    }
}

impl<T: AtomicElement, const N: usize, const OVERWRITE: bool> fmt::Debug
    for AtomicRingBuf<T, N, OVERWRITE>
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("AtomicRingBuf")
            .field("capacity", &self.core.capacity())
            .field("len", &self.core.len())
            .field("is_empty", &self.core.is_empty())
            .field("is_full", &self.core.is_full())
            .field("overwrite_mode", &OVERWRITE)
            .finish()
    }
}

unsafe impl<T: AtomicElement, const N: usize, const OVERWRITE: bool> Send
    for AtomicRingBuf<T, N, OVERWRITE>
{
}
unsafe impl<T: AtomicElement, const N: usize, const OVERWRITE: bool> Sync
    for AtomicRingBuf<T, N, OVERWRITE>
{
}

#[cfg(all(test, not(feature = "loom")))]
mod tests {
    use super::*;
    use crate::shim::atomic::{AtomicBool, AtomicU32, AtomicU64};

    #[test]
    fn test_basic_push_pop() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(4);

        buf.push(1, Ordering::Relaxed);
        buf.push(2, Ordering::Relaxed);
        buf.push(3, Ordering::Relaxed);

        assert_eq!(buf.len(), 3);
        assert_eq!(buf.pop(Ordering::Relaxed), Some(1));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(2));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(3));
        assert_eq!(buf.pop(Ordering::Relaxed), None);
    }

    #[test]
    fn test_basic_overwrite_mode() {
        let buf: AtomicRingBuf<AtomicU64, 32, true> = AtomicRingBuf::new(2);

        assert_eq!(buf.push(1, Ordering::Relaxed), None);
        assert_eq!(buf.push(2, Ordering::Relaxed), None);
        assert_eq!(buf.push(3, Ordering::Relaxed), Some(1));

        assert_eq!(buf.len(), 2);
        assert_eq!(buf.pop(Ordering::Relaxed), Some(2));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(3));
    }

    #[test]
    fn test_basic_non_overwrite_mode() {
        let buf: AtomicRingBuf<AtomicU64, 32, false> = AtomicRingBuf::new(2);

        assert_eq!(buf.push(1, Ordering::Relaxed), Ok(()));
        assert_eq!(buf.push(2, Ordering::Relaxed), Ok(()));
        assert_eq!(buf.push(3, Ordering::Relaxed), Err(3));

        assert_eq!(buf.len(), 2);
        assert!(buf.is_full());
    }

    #[test]
    fn test_basic_peek() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(4);

        assert_eq!(buf.peek(Ordering::Relaxed), None);

        buf.push(42, Ordering::Relaxed);
        assert_eq!(buf.peek(Ordering::Relaxed), Some(42));
        assert_eq!(buf.len(), 1);

        buf.push(99, Ordering::Relaxed);
        assert_eq!(buf.peek(Ordering::Relaxed), Some(42));

        buf.pop(Ordering::Relaxed);
        assert_eq!(buf.peek(Ordering::Relaxed), Some(99));
    }

    #[test]
    fn test_basic_clear() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);

        buf.push(1, Ordering::Relaxed);
        buf.push(2, Ordering::Relaxed);
        buf.push(3, Ordering::Relaxed);
        assert_eq!(buf.len(), 3);

        buf.clear();
        assert_eq!(buf.len(), 0);
        assert!(buf.is_empty());

        buf.push(10, Ordering::Relaxed);
        assert_eq!(buf.pop(Ordering::Relaxed), Some(10));
    }

    #[test]
    fn test_basic_capacity() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);
        assert_eq!(buf.capacity(), 8);

        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(5);
        assert_eq!(buf.capacity(), 8);
    }

    #[test]
    fn test_basic_is_empty_full() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(2);

        assert!(buf.is_empty());
        assert!(!buf.is_full());

        buf.push(1, Ordering::Relaxed);
        assert!(!buf.is_empty());
        assert!(!buf.is_full());

        buf.push(2, Ordering::Relaxed);
        assert!(!buf.is_empty());
        assert!(buf.is_full());

        buf.pop(Ordering::Relaxed);
        assert!(!buf.is_empty());
        assert!(!buf.is_full());

        buf.pop(Ordering::Relaxed);
        assert!(buf.is_empty());
        assert!(!buf.is_full());
    }

    #[test]
    fn test_basic_read_all() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);

        buf.push(1, Ordering::Relaxed);
        buf.push(2, Ordering::Relaxed);
        buf.push(3, Ordering::Relaxed);

        let values = buf.read_all(Ordering::Acquire);
        assert_eq!(values, vec![1, 2, 3]);
        assert_eq!(buf.len(), 3);
    }

    #[test]
    fn test_basic_iter() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);

        buf.push(10, Ordering::Relaxed);
        buf.push(20, Ordering::Relaxed);
        buf.push(30, Ordering::Relaxed);

        let values: Vec<u64> = buf
            .iter()
            .map(|atom| atom.load(Ordering::Acquire))
            .collect();
        assert_eq!(values, vec![10, 20, 30]);
    }

    #[test]
    fn test_basic_atomic_u32() {
        let buf: AtomicRingBuf<AtomicU32, 32> = AtomicRingBuf::new(4);

        buf.push(100u32, Ordering::Relaxed);
        buf.push(200u32, Ordering::Relaxed);

        assert_eq!(buf.pop(Ordering::Relaxed), Some(100u32));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(200u32));
    }

    #[test]
    fn test_basic_atomic_bool() {
        let buf: AtomicRingBuf<AtomicBool, 32> = AtomicRingBuf::new(4);

        buf.push(true, Ordering::Relaxed);
        buf.push(false, Ordering::Relaxed);
        buf.push(true, Ordering::Relaxed);

        assert_eq!(buf.pop(Ordering::Relaxed), Some(true));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(false));
        assert_eq!(buf.pop(Ordering::Relaxed), Some(true));
    }

    #[test]
    fn test_basic_fetch_add_at() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);

        buf.push(10, Ordering::Relaxed);
        buf.push(20, Ordering::Relaxed);
        buf.push(30, Ordering::Relaxed);

        let old = unsafe { buf.fetch_add_at(0, 5, Ordering::Relaxed) };
        assert_eq!(old, 10);
        assert_eq!(buf.peek(Ordering::Acquire).unwrap(), 15);

        let old = unsafe { buf.fetch_add_at(1, 100, Ordering::Relaxed) };
        assert_eq!(old, 20);
    }

    #[test]
    fn test_basic_fetch_sub_at() {
        let buf: AtomicRingBuf<AtomicU64, 32> = AtomicRingBuf::new(8);

        buf.push(100, Ordering::Relaxed);
        buf.push(200, Ordering::Relaxed);

        let old = unsafe { buf.fetch_sub_at(0, 10, Ordering::Relaxed) };
        assert_eq!(old, 100);
        assert_eq!(buf.peek(Ordering::Acquire).unwrap(), 90);
    }
}