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101 lines
3.2 KiB
Rust
101 lines
3.2 KiB
Rust
use parking_lot::RwLock;
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use std::sync::Arc;
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pub type SharedDraft<T> = Arc<T>;
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type DraftInner<T> = (SharedDraft<T>, Option<SharedDraft<T>>);
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/// Draft 管理：committed 与 optional draft 都以 Arc<Box<T>> 存储，
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// (committed_snapshot, optional_draft_snapshot)
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#[derive(Debug)]
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pub struct Draft<T> {
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inner: Arc<RwLock<DraftInner<T>>>,
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}
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impl<T: Clone> Draft<T> {
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#[inline]
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pub fn new(data: T) -> Self {
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Self {
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inner: Arc::new(RwLock::new((Arc::new(data), None))),
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}
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}
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/// 以 Arc<Box<T>> 的形式获取当前“已提交（正式）”数据的快照（零拷贝，仅 clone Arc）
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#[inline]
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pub fn data_arc(&self) -> SharedDraft<T> {
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let guard = self.inner.read();
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Arc::clone(&guard.0)
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}
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/// 获取当前（草稿若存在则返回草稿，否则返回已提交）的快照
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/// 这也是零拷贝：只 clone Arc，不 clone T
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#[inline]
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pub fn latest_arc(&self) -> SharedDraft<T> {
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let guard = self.inner.read();
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guard.1.clone().unwrap_or_else(|| Arc::clone(&guard.0))
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}
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/// 通过闭包以可变方式编辑草稿（在闭包中我们给出 &mut T）
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/// - 延迟拷贝：如果只有这一个 Arc 引用，则直接修改，不会克隆 T；
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/// - 若草稿被其他读者共享，Arc::make_mut 会做一次 T.clone（最小必要拷贝）。
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#[inline]
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pub fn edit_draft<F, R>(&self, f: F) -> R
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where
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F: FnOnce(&mut T) -> R,
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{
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let mut guard = self.inner.write();
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let mut draft_arc = guard.1.take().unwrap_or_else(|| Arc::clone(&guard.0));
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let data_mut = Arc::make_mut(&mut draft_arc);
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let result = f(data_mut);
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guard.1 = Some(draft_arc);
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result
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}
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/// 将草稿提交到已提交位置（替换），并清除草稿
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#[inline]
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pub fn apply(&self) {
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let mut guard = self.inner.write();
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if let Some(d) = guard.1.take() {
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guard.0 = d;
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}
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}
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/// 丢弃草稿（如果存在）
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#[inline]
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pub fn discard(&self) {
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let mut guard = self.inner.write();
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guard.1 = None;
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}
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/// 异步地以拥有 Box<T> 的方式修改已提交数据：将克隆一次已提交数据到本地，
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/// 异步闭包返回新的 Box<T>（替换已提交数据）和业务返回值 R。
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#[inline]
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pub async fn with_data_modify<F, Fut, R>(&self, f: F) -> Result<R, anyhow::Error>
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where
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T: Send + Sync + 'static,
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F: FnOnce(T) -> Fut + Send,
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Fut: std::future::Future<Output = Result<(T, R), anyhow::Error>> + Send,
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{
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let (local, original_arc) = {
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let guard = self.inner.read();
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let arc = Arc::clone(&guard.0);
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((*arc).clone(), arc)
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};
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let (new_local, res) = f(local).await?;
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let mut guard = self.inner.write();
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if !Arc::ptr_eq(&guard.0, &original_arc) {
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return Err(anyhow::anyhow!(
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"Optimistic lock failed: Committed data has changed during async operation"
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));
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}
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guard.0 = Arc::from(new_local);
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Ok(res)
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}
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}
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impl<T: Clone> Clone for Draft<T> {
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fn clone(&self) -> Self {
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Self {
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inner: Arc::clone(&self.inner),
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}
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}
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}
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