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<h1 id="rust-新版解读--168--crates-index-优化"><a class="header" href="#rust-新版解读--168--crates-index-优化">Rust 新版解读 | 1.68 | crates index 优化</a></h1>
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<blockquote>
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<p>Rust 1.68 官方 release doc: <a href="https://blog.rust-lang.org/2023/03/09/Rust-1.68.0.html">Announcing Rust 1.68.0 | Rust Blog</a></p>
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</blockquote>
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<p>通过 <a href="https://www.rust-lang.org/tools/install">rustup</a> 安装的同学可以使用以下命令升级到 1.68 版本:</p>
|
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<pre><code class="language-shell">$ rustup update stable
|
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</code></pre>
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<h2 id="cargo-稀疏注册协议-sparse-protocol"><a class="header" href="#cargo-稀疏注册协议-sparse-protocol">Cargo 稀疏注册协议 （sparse protocol）</a></h2>
|
|
|
<p>Cargo的“稀疏”注册协议已经稳定，它是用来读取注册在 crates.io 上的 crates 的索引的基础设施。以前的 git 协议（目前仍然是默认协议）会克隆一个包括所有 crates 的索引的仓库，但这已经开始遇到扩展限制问题，在更新该仓库时会出现明显的延迟。新协议应在访问 crates.io 时提供显着的性能提升，因为它只会下载有关实际用到的 crates 的索引。</p>
|
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<p>要使用新的协议，需要设置环境变量 <code>CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse</code> ，或者编辑 <code>.cargo/config.toml</code> 文件添加：</p>
|
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<pre><code class="language-text">[registries.crates-io]
|
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|
protocol = "sparse"
|
|
|
</code></pre>
|
|
|
<p>稀疏注册协议目前计划于 1.70.0 版本成为默认的协议。更多细节可以看官方博客的 <a href="https://blog.rust-lang.org/inside-rust/2023/01/30/cargo-sparse-protocol.html">announcement</a>， <a href="https://rust-lang.github.io/rfcs/2789-sparse-index.html">RFC 2789</a>， 当前 Cargo Book 的 <a href="https://doc.rust-lang.org/stable/cargo/reference/registry-index.html#sparse-protocol">文档</a></p>
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<h2 id="局部-pin-构造"><a class="header" href="#局部-pin-构造">局部 <code>Pin</code> 构造</a></h2>
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|
<p>新增的 <code>pin!</code> 宏能够用 <code>T</code> 构造一个 <code>Pin<&mut T></code> ，从而匿名捕获在局部状态内。这通常叫做 堆栈固定（stack-pinning），同时这个堆栈也可以被 <code>async fn</code> 或者 代码块 来捕获住。这个宏和一些 crates 里提供的（比如 <code>tokio::pin!</code>）很像，但是标准库可以利用 <code>Pin</code> 的内部结构和 临时生命周期拓展(<a href="https://doc.rust-lang.org/stable/reference/destructors.html#temporary-lifetime-extension">Temporary lifetime extension</a>)来实现出更像表达式的宏。</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
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|
</span><span class="boring">fn main() {
|
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|
</span>/// Runs a future to completion.
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|
fn block_on<F: Future>(future: F) -> F::Output {
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|
|
let waker_that_unparks_thread = todo!();
|
|
|
let mut cx = Context::from_waker(&waker_that_unparks_thread);
|
|
|
// Pin the future so it can be polled.
|
|
|
let mut pinned_future = pin!(future);
|
|
|
loop {
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|
|
match pinned_future.as_mut().poll(&mut cx) {
|
|
|
Poll::Pending => thread::park(),
|
|
|
Poll::Ready(result) => return result,
|
|
|
}
|
|
|
}
|
|
|
}
|
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|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>在这个例子中，原来的 <code>future</code> 将被移动到一个临时的局部区域，由新的 <code>pinned_future</code> 引用，类型为 <code>Pin<&mut F></code>，并且该 pin 受制于正常的借用检查器以确保它不会超过局部作用域。</p>
|
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<h2 id="alloc-默认错误处理"><a class="header" href="#alloc-默认错误处理"><code>alloc</code> 默认错误处理</a></h2>
|
|
|
<p>当 Rust 内存分配失败时，类似于 <code>Box::new</code> 和 <code>Vec::push</code> 的 API 无法反映出这个错误，从而采取了一些不同的措施。当使用 <code>std</code> 时，程序会打印 <code>stderr</code> 然后中止。从 Rust 1.68.0 开始，包含 <code>std</code> 的二进制程序仍然会继续这样，而不保护 <code>std</code> 只包含 <code>alloc</code> 的二进制程序会对内存分配错误调用 <code>panic!</code>，如果需要可以再进一步通过 <code>#[panic_handler]</code> 来调整其行为。</p>
|
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<p>未来，<code>std</code> 也可能会改成这样。</p>
|
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<h2 id="others"><a class="header" href="#others">Others</a></h2>
|
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<p>其它更新细节，和稳定的API列表，参考<a href="https://blog.rust-lang.org/2023/03/09/Rust-1.68.0.html#stabilized-apis">原Blog</a></p>
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