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<h1 id="cargo-缓存"><a class="header" href="#cargo-缓存">Cargo 缓存</a></h1>
<p>Cargo 使用了缓存的方式提升构建效率当构建时Cargo 会将已下载的依赖包放在 <code>CARGO_HOME</code> 目录下,下面一起来看看。</p>
<h2 id="cargo-home"><a class="header" href="#cargo-home">Cargo Home</a></h2>
<p>默认情况下Cargo Home 所在的目录是 <code>$HOME/.cargo/</code>,例如在 <code>macos</code> ,对应的目录是:</p>
<pre><code class="language-shell">$ echo $HOME/.cargo/
/Users/sunfei/.cargo/
</code></pre>
<p>我们也可以通过修改 <code>CARGO_HOME</code> 环境变量的方式来重新设定该目录的位置。若你需要在项目中通过代码的方式来获取 <code>CARGO_HOME</code> <a href="https://crates.io/crates/home"><code>home</code></a> 包提供了相应的 API。</p>
<blockquote>
<p>注意! Cargo Home 目录的内部结构并没有稳定化,在未来可能会发生变化</p>
</blockquote>
<h2 id="文件"><a class="header" href="#文件">文件</a></h2>
<ul>
<li><code>config.toml</code> 是 Cargo 的全局配置文件,具体请查看<a href="https://course.rs/cargo/reference/configuration.html">这里</a></li>
<li><code>credentials.toml</code><code>cargo login</code> 提供私有化登录证书,用于登录 <code>package</code> 注册中心,例如 <code>crates.io</code></li>
<li><code>.crates.toml</code>, <code>.crates2.json</code> 这两个是隐藏文件,包含了通过 <code>cargo install</code> 安装的包的 <code>package</code> 信息,<strong>请不要手动修改!</strong></li>
</ul>
<h2 id="目录"><a class="header" href="#目录">目录</a></h2>
<ul>
<li><code>bin</code> 目录包含了通过 <code>cargo install</code><code>rustup</code> 下载的包编译出的可执行文件。你可以将该目录加入到 <code>$PATH</code> 环境变量中,以实现对这些可执行文件的直接访问</li>
<li><code>git</code> 中存储了 <code>Git</code> 的资源文件:
<ul>
<li><code>git/db</code>,当一个包依赖某个 <code>git</code> 仓库时,<code>Cargo</code> 会将该仓库克隆到 <code>git/db</code> 目录下,如果未来需要还会对其进行更新</li>
<li><code>git/checkouts</code>,若指定了 <code>git</code> 源和 <code>commit</code>,那相应的仓库就会从 <code>git/db</code><code>checkout</code> 到该目录下,因此同一个仓库的不同 <code>checkout</code> 共存成为了可能性</li>
</ul>
</li>
<li><code>registry</code> 包含了注册中心( 例如 <code>crates.io</code> )的元数据 和 <code>packages</code>
<ul>
<li><code>registry/index</code> 是一个 git 仓库,包含了注册中心中所有可用包的元数据( 版本、依赖等 )</li>
<li><code>registry/cache</code> 中保存了已下载的依赖,这些依赖包以 <code>gzip</code> 的压缩档案形式保存,后缀名为 <code>.crate</code></li>
<li><code>registry/src</code>,若一个已下载的 <code>.crate</code> 档案被一个 <code>package</code> 所需要,该档案会被解压缩到 <code>registry/src</code> 文件夹下,最终 <code>rustc</code> 可以在其中找到所需的 <code>.rs</code> 文件</li>
</ul>
</li>
</ul>
<h2 id="在-ci-时缓存-cargo-home"><a class="header" href="#在-ci-时缓存-cargo-home">在 CI 时缓存 Cargo Home</a></h2>
<p>为了避免持续集成时重复下载所有的包依赖,我们可以将 <code>$CARGO_HOME</code> 目录进行缓存,但缓存整个目录是效率低下的,原因是源文件可能会被缓存两次。</p>
<p>例如我们依赖一个包 <code>serde 1.0.92</code>,如果将整个 <code>$CACHE_HOME</code> 目录缓存,那么<code>serde</code> 的源文件就会被缓存两次:在 <code>registry/cache</code> 中的 <code>serde-1.0.92.crate</code> 以及 <code>registry/src</code> 下被解压缩的 <code>.rs</code> 文件。</p>
<p>因此,在 CI 构建时,出于效率的考虑,我们仅应该缓存以下目录:</p>
<ul>
<li><code>bin/</code></li>
<li><code>registry/index/</code></li>
<li><code>registry/cache/</code></li>
<li><code>git/db/</code></li>
</ul>
<h2 id="清除缓存"><a class="header" href="#清除缓存">清除缓存</a></h2>
<p>理论上,我们可以手动移除缓存中的任何一部分,当后续有包需要时 <code>Cargo</code> 会尽可能去恢复这些资源:</p>
<ul>
<li>解压缩 <code>registry/cache</code> 下的 <code>.crate</code> 档案</li>
<li><code>.git</code><code>checkout</code> 缓存的仓库</li>
<li>如果以上都没了,会从网络上重新下载</li>
</ul>
<p>你也可以使用 <a href="https://crates.io/crates/cargo-cache">cargo-cache</a> 包来选择性的清除 <code>cache</code> 中指定的部分,当然,它还可以用来查看缓存中的组件大小。</p>
<h2 id="构建时卡住blocking-waiting-for-file-lock-"><a class="header" href="#构建时卡住blocking-waiting-for-file-lock-">构建时卡住Blocking waiting for file lock ..</a></h2>
<p>在开发过程中,或多或少我们都会碰到这种问题,例如你同时打开了 VSCode IDE 和终端,然后在 <code>Cargo.toml</code> 中刚添加了一个新的依赖。</p>
<p>此时 IDE 会捕捉到这个修改然后自动去重新下载依赖(这个过程可能还会更新 <code>crates.io</code> 使用的索引列表),在此过程中, Cargo 会将相关信息写入到 <code>$HOME/.cargo/.package_cache</code> 下,并将其锁住。</p>
<p>如果你试图在另一个地方(例如终端)对同一个项目进行构建,就会报错: <code>Blocking waiting for file lock on package cache</code></p>
<p>解决办法很简单:</p>
<ul>
<li>既然下载慢,那就使用<a href="https://course.rs/cargo/reference/specify-deps.html#%E4%BB%8E%E5%85%B6%E5%AE%83%E6%B3%A8%E5%86%8C%E6%9C%8D%E5%8A%A1%E5%BC%95%E5%85%A5%E4%BE%9D%E8%B5%96%E5%8C%85">国内的注册服务</a>,不再使用 crates.io</li>
<li>耐心等待持有锁的用户构建完成</li>
<li>强行停止正在构建的进程,例如杀掉 IDE 使用的 rust-analyer 插件进程,然后删除 <code>$HOME/.cargo/.package_cache</code> 目录</li>
</ul>
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