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140 lines
7.7 KiB
140 lines
7.7 KiB
11 months ago
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<div class="sidebar-about">
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<a href="https://blog.juliobiason.me"><h1>Julio Biason .Me 4.3</h1></a>
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<p class="lead">Old school dev living in a 2.0 dev world</p>
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<div class="content container">
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<div class="post">
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<h1 class="post-title">Timeout With Command in Tokio</h1>
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<span class="post-date">
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2023-08-31
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<a href="https://blog.juliobiason.me/tags/random/">#random</a>
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<a href="https://blog.juliobiason.me/tags/rust/">#rust</a>
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<a href="https://blog.juliobiason.me/tags/tokio/">#tokio</a>
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<a href="https://blog.juliobiason.me/tags/spawn/">#spawn</a>
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<a href="https://blog.juliobiason.me/tags/process/">#process</a>
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<a href="https://blog.juliobiason.me/tags/command/">#command</a>
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<a href="https://blog.juliobiason.me/tags/timeout/">#timeout</a>
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</span>
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<p>How to spawn an external command and give it a timeout in Rust, with Tokio</p>
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<span id="continue-reading"></span>
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<p>The entry point for running external applications in Rust is the
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<a href="https://doc.rust-lang.org/std/process/struct.Command.html">Command</a> structure,
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in the process module. This whole structure is duplicated <a href="https://docs.rs/tokio/latest/tokio/process/struct.Command.html">on Tokio, with
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async</a>.</p>
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<p>But there is one thing that exist in other languages (like Python) that Rust
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doesn't have: Having a timeout for the command (and killing it if it runs over
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the timeout). The usual solution is to run the command on a specialized thread
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and, with another thread, make sure to kill the first if the second finishes
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first.</p>
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<p>But Tokio have a funcionality that saves a lot of code when dealing with this:
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<a href="https://docs.rs/tokio/latest/tokio/time/fn.timeout.html">timeout</a>. While it
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doesn't apply to the Command itself, it applies to Futures, and waiting for a
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command is an async function, which means it is wrapped around a Future, and we
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can leverage this.</p>
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<pre data-lang="rust" style="background-color:#2b303b;color:#c0c5ce;" class="language-rust "><code class="language-rust" data-lang="rust"><span style="color:#b48ead;">use </span><span>std::time::Duration;
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</span><span>
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</span><span style="color:#b48ead;">use </span><span>tokio::process::Command;
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</span><span style="color:#b48ead;">use </span><span>tokio::time::timeout;
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</span><span>
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</span><span>#[</span><span style="color:#bf616a;">tokio</span><span>::</span><span style="color:#bf616a;">main</span><span>(flavor = "</span><span style="color:#a3be8c;">current_thread</span><span>")]
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</span><span>async </span><span style="color:#b48ead;">fn </span><span style="color:#8fa1b3;">main</span><span>() {
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</span><span> </span><span style="color:#b48ead;">let</span><span> sleep = "</span><span style="color:#a3be8c;">sleep</span><span>";
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</span><span>
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</span><span> println!("</span><span style="color:#a3be8c;">Run 3 secs</span><span>");
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</span><span> </span><span style="color:#b48ead;">let mut</span><span> cmd = Command::new(&sleep).</span><span style="color:#96b5b4;">arg</span><span>("</span><span style="color:#a3be8c;">3s</span><span>").</span><span style="color:#96b5b4;">spawn</span><span>().</span><span style="color:#96b5b4;">unwrap</span><span>();
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</span><span> </span><span style="color:#b48ead;">if let </span><span>Err(_) = </span><span style="color:#96b5b4;">timeout</span><span>(Duration::from_secs(</span><span style="color:#d08770;">4</span><span>), cmd.</span><span style="color:#96b5b4;">wait</span><span>()).await {
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</span><span> println!("</span><span style="color:#a3be8c;">Got timeout!</span><span>");
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</span><span> cmd.</span><span style="color:#96b5b4;">kill</span><span>().await.</span><span style="color:#96b5b4;">unwrap</span><span>();
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</span><span> } </span><span style="color:#b48ead;">else </span><span>{
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</span><span> println!("</span><span style="color:#a3be8c;">No timeout</span><span>");
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</span><span> }
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</span><span>
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</span><span> println!("</span><span style="color:#a3be8c;">Run 25 secs</span><span>");
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</span><span> </span><span style="color:#b48ead;">let mut</span><span> cmd = Command::new(&sleep).</span><span style="color:#96b5b4;">arg</span><span>("</span><span style="color:#a3be8c;">25s</span><span>").</span><span style="color:#96b5b4;">spawn</span><span>().</span><span style="color:#96b5b4;">unwrap</span><span>();
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</span><span> </span><span style="color:#b48ead;">if let </span><span>Err(_) = </span><span style="color:#96b5b4;">timeout</span><span>(Duration::from_secs(</span><span style="color:#d08770;">4</span><span>), cmd.</span><span style="color:#96b5b4;">wait</span><span>()).await {
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</span><span> println!("</span><span style="color:#a3be8c;">Got timeout</span><span>");
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</span><span> cmd.</span><span style="color:#96b5b4;">kill</span><span>().await.</span><span style="color:#96b5b4;">unwrap</span><span>();
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</span><span> } </span><span style="color:#b48ead;">else </span><span>{
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</span><span> println!("</span><span style="color:#a3be8c;">No timeout</span><span>");
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</span><span> }
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</span><span>}
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</span></code></pre>
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<p>The thing here is <code>.wait()</code>. That's when Tokio wraps the command call into a
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Future. But, because the task is dead, it doesn't actually kill the command,
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and that's why we need to call <code>.kill()</code> in case of timeout -- otherwise the
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command will still run (you can check this by removing the <code>.kill()</code> call on
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the 25s block, and calling <code>ps</code> after the application finishes).</p>
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<p>Just note that the <code>if let Err(_)</code> is for timeout; <code>.wait()</code> also returns a
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<code>Result</code>, and that's the one that needs to be checked for the actual success of
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the execution.</p>
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</div>
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</div>
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</body>
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</html>
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