Uttarayan Mondal
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163 lines
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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="An implementation of asynchronous process management for Tokio."><meta name="keywords" content="rust, rustlang, rust-lang, process"><title>tokio::process - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><style type="text/css">#crate-search{background-image:url("../../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../tokio/index.html'><div class='logo-container rust-logo'><img src='../../rust-logo.png' alt='logo'></div></a><p class="location">Module process</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class="location"><a href="../index.html">tokio</a></p><div id="sidebar-vars" data-name="process" data-ty="mod" data-relpath="../"></div><script defer src="../sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" class="help-button">?</button>
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<a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class="fqn"><span class="in-band">Module <a href="../index.html">tokio</a>::<wbr><a class="mod" href="">process</a></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../../src/tokio/process/mod.rs.html#1-1384" title="goto source code">[src]</a></span></h1><div class="docblock"><p>An implementation of asynchronous process management for Tokio.</p>
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<p>This module provides a <a href="../../tokio/process/struct.Command.html"><code>Command</code></a> struct that imitates the interface of the
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<a href="https://doc.rust-lang.org/nightly/std/process/struct.Command.html"><code>std::process::Command</code></a> type in the standard library, but provides asynchronous versions of
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functions that create processes. These functions (<code>spawn</code>, <code>status</code>, <code>output</code> and their
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variants) return “future aware” types that interoperate with Tokio. The asynchronous process
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support is provided through signal handling on Unix and system APIs on Windows.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Here’s an example program which will spawn <code>echo hello world</code> and then wait
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for it complete.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">process</span>::<span class="ident">Command</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span><span class="op">></span> {
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<span class="comment">// The usage is similar as with the standard library's `Command` type</span>
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">child</span> <span class="op">=</span> <span class="ident">Command</span>::<span class="ident">new</span>(<span class="string">"echo"</span>)
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.<span class="ident">arg</span>(<span class="string">"hello"</span>)
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.<span class="ident">arg</span>(<span class="string">"world"</span>)
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.<span class="ident">spawn</span>()
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.<span class="ident">expect</span>(<span class="string">"failed to spawn"</span>);
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<span class="comment">// Await until the command completes</span>
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<span class="kw">let</span> <span class="ident">status</span> <span class="op">=</span> <span class="ident">child</span>.<span class="ident">wait</span>().<span class="kw">await</span><span class="question-mark">?</span>;
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"the command exited with: {}"</span>, <span class="ident">status</span>);
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<span class="prelude-val">Ok</span>(())
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}</pre></div>
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<p>Next, let’s take a look at an example where we not only spawn <code>echo hello world</code> but we also capture its output.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">process</span>::<span class="ident">Command</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span><span class="op">></span> {
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<span class="comment">// Like above, but use `output` which returns a future instead of</span>
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<span class="comment">// immediately returning the `Child`.</span>
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<span class="kw">let</span> <span class="ident">output</span> <span class="op">=</span> <span class="ident">Command</span>::<span class="ident">new</span>(<span class="string">"echo"</span>).<span class="ident">arg</span>(<span class="string">"hello"</span>).<span class="ident">arg</span>(<span class="string">"world"</span>)
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.<span class="ident">output</span>();
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<span class="kw">let</span> <span class="ident">output</span> <span class="op">=</span> <span class="ident">output</span>.<span class="kw">await</span><span class="question-mark">?</span>;
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<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">output</span>.<span class="ident">status</span>.<span class="ident">success</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">output</span>.<span class="ident">stdout</span>, <span class="string">b"hello world\n"</span>);
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<span class="prelude-val">Ok</span>(())
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}</pre></div>
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<p>We can also read input line by line.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">io</span>::{<span class="ident">BufReader</span>, <span class="ident">AsyncBufReadExt</span>};
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">process</span>::<span class="ident">Command</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">process</span>::<span class="ident">Stdio</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span><span class="op">></span> {
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cmd</span> <span class="op">=</span> <span class="ident">Command</span>::<span class="ident">new</span>(<span class="string">"cat"</span>);
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<span class="comment">// Specify that we want the command's standard output piped back to us.</span>
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<span class="comment">// By default, standard input/output/error will be inherited from the</span>
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<span class="comment">// current process (for example, this means that standard input will</span>
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<span class="comment">// come from the keyboard and standard output/error will go directly to</span>
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<span class="comment">// the terminal if this process is invoked from the command line).</span>
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<span class="ident">cmd</span>.<span class="ident">stdout</span>(<span class="ident">Stdio</span>::<span class="ident">piped</span>());
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">child</span> <span class="op">=</span> <span class="ident">cmd</span>.<span class="ident">spawn</span>()
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.<span class="ident">expect</span>(<span class="string">"failed to spawn command"</span>);
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<span class="kw">let</span> <span class="ident">stdout</span> <span class="op">=</span> <span class="ident">child</span>.<span class="ident">stdout</span>.<span class="ident">take</span>()
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.<span class="ident">expect</span>(<span class="string">"child did not have a handle to stdout"</span>);
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">reader</span> <span class="op">=</span> <span class="ident">BufReader</span>::<span class="ident">new</span>(<span class="ident">stdout</span>).<span class="ident">lines</span>();
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<span class="comment">// Ensure the child process is spawned in the runtime so it can</span>
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<span class="comment">// make progress on its own while we await for any output.</span>
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<span class="ident">tokio</span>::<span class="ident">spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="kw">let</span> <span class="ident">status</span> <span class="op">=</span> <span class="ident">child</span>.<span class="ident">wait</span>().<span class="kw">await</span>
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.<span class="ident">expect</span>(<span class="string">"child process encountered an error"</span>);
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"child status was: {}"</span>, <span class="ident">status</span>);
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});
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<span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">line</span>) <span class="op">=</span> <span class="ident">reader</span>.<span class="ident">next_line</span>().<span class="kw">await</span><span class="question-mark">?</span> {
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Line: {}"</span>, <span class="ident">line</span>);
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}
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<span class="prelude-val">Ok</span>(())
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}</pre></div>
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<p>With some coordination, we can also pipe the output of one command into
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another.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">join</span>;
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<span class="kw">use</span> <span class="ident">tokio</span>::<span class="ident">process</span>::<span class="ident">Command</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">convert</span>::<span class="ident">TryInto</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">process</span>::<span class="ident">Stdio</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span><span class="op">></span> {
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">echo</span> <span class="op">=</span> <span class="ident">Command</span>::<span class="ident">new</span>(<span class="string">"echo"</span>)
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.<span class="ident">arg</span>(<span class="string">"hello world!"</span>)
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.<span class="ident">stdout</span>(<span class="ident">Stdio</span>::<span class="ident">piped</span>())
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.<span class="ident">spawn</span>()
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.<span class="ident">expect</span>(<span class="string">"failed to spawn echo"</span>);
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<span class="kw">let</span> <span class="ident">tr_stdin</span>: <span class="ident">Stdio</span> <span class="op">=</span> <span class="ident">echo</span>
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.<span class="ident">stdout</span>
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.<span class="ident">take</span>()
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.<span class="ident">unwrap</span>()
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.<span class="ident">try_into</span>()
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.<span class="ident">expect</span>(<span class="string">"failed to convert to Stdio"</span>);
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<span class="kw">let</span> <span class="ident">tr</span> <span class="op">=</span> <span class="ident">Command</span>::<span class="ident">new</span>(<span class="string">"tr"</span>)
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.<span class="ident">arg</span>(<span class="string">"a-z"</span>)
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.<span class="ident">arg</span>(<span class="string">"A-Z"</span>)
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.<span class="ident">stdin</span>(<span class="ident">tr_stdin</span>)
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.<span class="ident">stdout</span>(<span class="ident">Stdio</span>::<span class="ident">piped</span>())
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.<span class="ident">spawn</span>()
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.<span class="ident">expect</span>(<span class="string">"failed to spawn tr"</span>);
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<span class="kw">let</span> (<span class="ident">echo_result</span>, <span class="ident">tr_output</span>) <span class="op">=</span> <span class="macro">join</span><span class="macro">!</span>(<span class="ident">echo</span>.<span class="ident">wait</span>(), <span class="ident">tr</span>.<span class="ident">wait_with_output</span>());
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<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">echo_result</span>.<span class="ident">unwrap</span>().<span class="ident">success</span>());
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<span class="kw">let</span> <span class="ident">tr_output</span> <span class="op">=</span> <span class="ident">tr_output</span>.<span class="ident">expect</span>(<span class="string">"failed to await tr"</span>);
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<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">tr_output</span>.<span class="ident">status</span>.<span class="ident">success</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">tr_output</span>.<span class="ident">stdout</span>, <span class="string">b"HELLO WORLD!\n"</span>);
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<span class="prelude-val">Ok</span>(())
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}</pre></div>
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<h1 id="caveats" class="section-header"><a href="#caveats">Caveats</a></h1><h2 id="droppingcancellation" class="section-header"><a href="#droppingcancellation">Dropping/Cancellation</a></h2>
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<p>Similar to the behavior to the standard library, and unlike the futures
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paradigm of dropping-implies-cancellation, a spawned process will, by
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default, continue to execute even after the <code>Child</code> handle has been dropped.</p>
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<p>The <a href="../../tokio/process/struct.Command.html#method.kill_on_drop"><code>Command::kill_on_drop</code></a> method can be used to modify this behavior
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and kill the child process if the <code>Child</code> wrapper is dropped before it
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has exited.</p>
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<h2 id="unix-processes" class="section-header"><a href="#unix-processes">Unix Processes</a></h2>
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<p>On Unix platforms processes must be “reaped” by their parent process after
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they have exited in order to release all OS resources. A child process which
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has exited, but has not yet been reaped by its parent is considered a “zombie”
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process. Such processes continue to count against limits imposed by the system,
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and having too many zombie processes present can prevent additional processes
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from being spawned.</p>
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<p>The tokio runtime will, on a best-effort basis, attempt to reap and clean up
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any process which it has spawned. No additional guarantees are made with regards
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how quickly or how often this procedure will take place.</p>
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<p>It is recommended to avoid dropping a <a href="../../tokio/process/struct.Child.html"><code>Child</code></a> process handle before it has been
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fully <code>await</code>ed if stricter cleanup guarantees are required.</p>
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</div><h2 id="structs" class="section-header"><a href="#structs">Structs</a></h2>
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<table><tr class="module-item"><td><a class="struct" href="struct.Child.html" title="tokio::process::Child struct">Child</a></td><td class="docblock-short"><p>Representation of a child process spawned onto an event loop.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.ChildStderr.html" title="tokio::process::ChildStderr struct">ChildStderr</a></td><td class="docblock-short"><p>The standard error stream for spawned children.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.ChildStdin.html" title="tokio::process::ChildStdin struct">ChildStdin</a></td><td class="docblock-short"><p>The standard input stream for spawned children.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.ChildStdout.html" title="tokio::process::ChildStdout struct">ChildStdout</a></td><td class="docblock-short"><p>The standard output stream for spawned children.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.Command.html" title="tokio::process::Command struct">Command</a></td><td class="docblock-short"><p>This structure mimics the API of <a href="https://doc.rust-lang.org/nightly/std/process/struct.Command.html"><code>std::process::Command</code></a> found in the standard library, but
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replaces functions that create a process with an asynchronous variant. The main provided
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asynchronous functions are <a href="../../tokio/process/struct.Command.html#method.spawn">spawn</a>, <a href="../../tokio/process/struct.Command.html#method.status">status</a>, and
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<a href="../../tokio/process/struct.Command.html#method.output">output</a>.</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tokio"></div>
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