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<ol class="chapter"><li class="chapter-item expanded "><a href="Chapter_0.html"><strong aria-hidden="true">1.</strong> Update</a></li><li class="chapter-item expanded "><a href="Chapter_1.html"><strong aria-hidden="true">2.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="Chapter_2.html"><strong aria-hidden="true">3.</strong> Who am I?</a></li><li class="chapter-item expanded "><a href="Chapter_3.html"><strong aria-hidden="true">4.</strong> Writing Rust in Easy English</a></li><li class="chapter-item expanded "><a href="Chapter_4.html"><strong aria-hidden="true">5.</strong> Rust Playground</a></li><li class="chapter-item expanded "><a href="Chapter_5.html"><strong aria-hidden="true">6.</strong> 🚧 and ⚠️</a></li><li class="chapter-item expanded "><a href="Chapter_6.html"><strong aria-hidden="true">7.</strong> Comments</a></li><li class="chapter-item expanded "><a href="Chapter_7.html"><strong aria-hidden="true">8.</strong> Types</a></li><li class="chapter-item expanded "><a href="Chapter_8.html"><strong aria-hidden="true">9.</strong> Type inference</a></li><li class="chapter-item expanded "><a href="Chapter_9.html"><strong aria-hidden="true">10.</strong> Printing 'hello, world!'</a></li><li class="chapter-item expanded "><a href="Chapter_10.html"><strong aria-hidden="true">11.</strong> Display and debug</a></li><li class="chapter-item expanded "><a href="Chapter_11.html"><strong aria-hidden="true">12.</strong> Mutability (changing)</a></li><li class="chapter-item expanded "><a href="Chapter_12.html"><strong aria-hidden="true">13.</strong> The stack, the heap, and pointers</a></li><li class="chapter-item expanded "><a href="Chapter_13.html"><strong aria-hidden="true">14.</strong> More about printing</a></li><li class="chapter-item expanded "><a href="Chapter_14.html"><strong aria-hidden="true">15.</strong> Strings</a></li><li class="chapter-item expanded "><a href="Chapter_15.html"><strong aria-hidden="true">16.</strong> const and static</a></li><li class="chapter-item expanded "><a href="Chapter_16.html"><strong aria-hidden="true">17.</strong> More on references</a></li><li class="chapter-item expanded "><a href="Chapter_17.html"><strong aria-hidden="true">18.</strong> Mutable references</a></li><li class="chapter-item expanded "><a href="Chapter_18.html"><strong aria-hidden="true">19.</strong> Giving references to functions</a></li><li class="chapter-item expanded "><a href="Chapter_19.html"><strong aria-hidden="true">20.</strong> Copy types</a></li><li class="chapter-item expanded "><a href="Chapter_20.html"><strong aria-hidden="true">21.</strong> Collection types</a></li><li class="chapter-item expanded "><a href="Chapter_21.html"><strong aria-hidden="true">22.</strong> Vectors</a></li><li class="chapter-item expanded "><a href="Chapter_22.html"><strong aria-hidden="true">23.</strong> Tuples</a></li><li class="chapter-item expanded "><a href="Chapter_23.html"><strong aria-hidden="true">24.</strong> Control flow</a></li><li class="chapter-item expanded "><a href="Chapter_24.html"><strong aria-hidden="true">25.</strong> Structs</a></li><li class="chapter-item expanded "><a href="Chapter_25.html"><strong aria-hidden="true">26.</strong> Enums</a></li><li class="chapter-item expanded "><a href="Chapter_26.html"><strong aria-hidden="true">27.</strong> Loops</a></li><li class="chapter-item expanded "><a href="Chapter_27.html"><strong aria-hidden="true">28.</strong> Implementing structs and enums</a></li><li class="chapter-item expanded "><a href="Chapter_28.html"><strong aria-hidden="true">29.</strong> Destructuring</a></li><li class="chapter-item expanded "><a href="Chapter_29.html"><strong aria-hidden="true">30.</strong> References and the dot operator</a></li><li class="chapter-item expanded "><a href="Chapter_30.html"><strong aria-hidden="true">31.</strong> Generics</a></li><li class="chapter-item expanded "><a href="Chapter_31.html"><strong aria-hidden="true">32.</strong> Option and Result</a></li><li class="chapter-item expanded "><a href="Chapter_32.html"><strong aria-hi
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<h1 class="menu-title">Easy Rust</h1>
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<h2><a class="header" href="#channels" id="channels">Channels</a></h2>
<p>A channel is an easy way to use many threads that send to one place. They are fairly popular because they are pretty simple to put together. You can create a channel in Rust with <code>std::sync::mpsc</code>. <code>mpsc</code> means &quot;multiple producer, single consumer&quot;, so &quot;many threads sending to one place&quot;. To start a channel, you use <code>channel()</code>. This creates a <code>Sender</code> and a <code>Receiver</code> that are tied together. You can see this in the function signature:</p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// 🚧
pub fn channel&lt;T&gt;() -&gt; (Sender&lt;T&gt;, Receiver&lt;T&gt;)
<span class="boring">}
</span></code></pre></pre>
<p>So you have to choose one name for the sender and one for the receiver. Usually you see something like <code>let (sender, receiver) = channel();</code> to start. Because it's generic, Rust won't know the type if that is all you write:</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel(); // ⚠️
}
</code></pre></pre>
<p>The compiler says:</p>
<pre><code class="language-text">error[E0282]: type annotations needed for `(std::sync::mpsc::Sender&lt;T&gt;, std::sync::mpsc::Receiver&lt;T&gt;)`
--&gt; src\main.rs:30:30
|
30 | let (sender, receiver) = channel();
| ------------------ ^^^^^^^ cannot infer type for type parameter `T` declared on the function `channel`
| |
| consider giving this pattern the explicit type `(std::sync::mpsc::Sender&lt;T&gt;, std::sync::mpsc::Receiver&lt;T&gt;)`, where
the type parameter `T` is specified
</code></pre>
<p>It suggests adding a type for the <code>Sender</code> and <code>Receiver</code>. You can do that if you want:</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::{channel, Sender, Receiver}; // Added Sender and Receiver here
fn main() {
let (sender, receiver): (Sender&lt;i32&gt;, Receiver&lt;i32&gt;) = channel();
}
</code></pre></pre>
<p>but you don't have to. Once you start using the <code>Sender</code> and <code>Receiver</code>, Rust can guess the type.</p>
<p>So let's look at the simplest way to use a channel.</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
sender.send(5);
receiver.recv(); // recv = receive, not &quot;rec v&quot;
}
</code></pre></pre>
<p>Now the compiler knows the type. <code>sender</code> is a <code>Result&lt;(), SendError&lt;i32&gt;&gt;</code> and <code>receiver</code> is a <code>Result&lt;i32, RecvError&gt;</code>. So you can use <code>.unwrap()</code> to see if the sending works, or use better error handling. Let's add <code>.unwrap()</code> and also <code>println!</code> to see what we get:</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
sender.send(5).unwrap();
println!(&quot;{}&quot;, receiver.recv().unwrap());
}
</code></pre></pre>
<p>This prints <code>5</code>.</p>
<p>A <code>channel</code> is like an <code>Arc</code> because you can clone it and send the clones into other threads. Let's make two threads and send values to <code>receiver</code>. This code will work, but it is not exactly what we want.</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
let sender_clone = sender.clone();
std::thread::spawn(move|| { // move sender in
sender.send(&quot;Send a &amp;str this time&quot;).unwrap();
});
std::thread::spawn(move|| { // move sender_clone in
sender_clone.send(&quot;And here is another &amp;str&quot;).unwrap();
});
println!(&quot;{}&quot;, receiver.recv().unwrap());
}
</code></pre></pre>
<p>The two threads start sending, and then we <code>println!</code>. It might say <code>Send a &amp;str this time</code> or <code>And here is another &amp;str</code>, depending on which thread finished first. Let's make a join handle to make them wait.</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
let sender_clone = sender.clone();
let mut handle_vec = vec![]; // Put our handles in here
handle_vec.push(std::thread::spawn(move|| { // push this into the vec
sender.send(&quot;Send a &amp;str this time&quot;).unwrap();
}));
handle_vec.push(std::thread::spawn(move|| { // and push this into the vec
sender_clone.send(&quot;And here is another &amp;str&quot;).unwrap();
}));
for _ in handle_vec { // now handle_vec has 2 items. Let's print them
println!(&quot;{:?}&quot;, receiver.recv().unwrap());
}
}
</code></pre></pre>
<p>This prints:</p>
<pre><code class="language-text">&quot;Send a &amp;str this time&quot;
&quot;And here is another &amp;str&quot;
</code></pre>
<p>Now let's make a <code>results_vec</code> instead of printing.</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
let sender_clone = sender.clone();
let mut handle_vec = vec![];
let mut results_vec = vec![];
handle_vec.push(std::thread::spawn(move|| {
sender.send(&quot;Send a &amp;str this time&quot;).unwrap();
}));
handle_vec.push(std::thread::spawn(move|| {
sender_clone.send(&quot;And here is another &amp;str&quot;).unwrap();
}));
for _ in handle_vec {
results_vec.push(receiver.recv().unwrap());
}
println!(&quot;{:?}&quot;, results_vec);
}
</code></pre></pre>
<p>Now the results are in our vec: <code>[&quot;Send a &amp;str this time&quot;, &quot;And here is another &amp;str&quot;]</code>.</p>
<p>Now let's pretend that we have a lot of work to do, and want to use threads. We have a big vec with 1000 items, all 0. We want to change each 0 to a 1. We will use ten threads, and each thread will do one tenth of the work. We will create a new vec and use <code>.extend()</code> to put the work in.</p>
<pre><pre class="playground"><code class="language-rust">use std::sync::mpsc::channel;
fn main() {
let (sender, receiver) = channel();
let hugevec = vec![0; 1000];
let mut newvec = vec![];
for i in 0..10 {
let sender_clone = sender.clone();
let mut work: Vec&lt;u8&gt; = Vec::with_capacity(hugevec.len() / 10); // new vec to put the work in. 1/10th the size
work.extend(&amp;hugevec[i*100..(i+1)*100]); // first part gets 0..100, next gets 100..200, etc.
let handle = std::thread::spawn(move || { // make a handle
for number in work.iter_mut() { // do the actual work
*number += 1;
};
sender_clone.send(work).unwrap(); // use the sender_clone to send the work to the receiver
});
handle.join().unwrap(); // stop the thread until it's done
newvec.push(receiver.recv().unwrap()); // push the results from receiver.recv() into the vec
}
// Now we have a Vec&lt;Vec&lt;u8&gt;&gt;. To put it together we can use .flatten()
let newvec = newvec.into_iter().flatten().collect::&lt;Vec&lt;u8&gt;&gt;(); // Now it's one vec of 1000 u8 numbers
}
</code></pre></pre>
<p>If you print this you can see 1000 number 1s.</p>
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