2020-12-25 14:16:02 +00:00
<!DOCTYPE HTML>
< html lang = "en" class = "sidebar-visible no-js light" >
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
2021-02-09 09:07:07 +00:00
< title > Channels - Easy Rust< / title >
2020-12-25 14:16:02 +00:00
<!-- Custom HTML head -->
< meta content = "text/html; charset=utf-8" http-equiv = "Content-Type" >
< meta name = "description" content = "" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" / >
< link rel = "icon" href = "favicon.svg" >
< link rel = "shortcut icon" href = "favicon.png" >
< link rel = "stylesheet" href = "css/variables.css" >
< link rel = "stylesheet" href = "css/general.css" >
< link rel = "stylesheet" href = "css/chrome.css" >
< link rel = "stylesheet" href = "css/print.css" media = "print" >
<!-- Fonts -->
< link rel = "stylesheet" href = "FontAwesome/css/font-awesome.css" >
< link rel = "stylesheet" href = "fonts/fonts.css" >
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" href = "highlight.css" >
< link rel = "stylesheet" href = "tomorrow-night.css" >
< link rel = "stylesheet" href = "ayu-highlight.css" >
<!-- Custom theme stylesheets -->
< / head >
< body >
<!-- Provide site root to javascript -->
< script type = "text/javascript" >
var path_to_root = "";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
< / script >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script type = "text/javascript" >
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script type = "text/javascript" >
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('light')
html.classList.add(theme);
html.classList.add('js');
< / script >
<!-- Hide / unhide sidebar before it is displayed -->
< script type = "text/javascript" >
var html = document.querySelector('html');
var sidebar = 'hidden';
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
}
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
< / script >
< nav id = "sidebar" class = "sidebar" aria-label = "Table of contents" >
< div class = "sidebar-scrollbox" >
2021-02-09 09:07:07 +00:00
< 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
2020-12-25 14:16:02 +00:00
< / div >
< div id = "sidebar-resize-handle" class = "sidebar-resize-handle" > < / div >
< / nav >
< div id = "page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "menu-bar-hover-placeholder" > < / div >
< div id = "menu-bar" class = "menu-bar sticky bordered" >
< div class = "left-buttons" >
< button id = "sidebar-toggle" class = "icon-button" type = "button" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "sidebar" >
< i class = "fa fa-bars" > < / i >
< / button >
< button id = "theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "theme-list" >
< i class = "fa fa-paint-brush" > < / i >
< / button >
< ul id = "theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "light" > Light (default)< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "ayu" > Ayu< / button > < / li >
< / ul >
< button id = "search-toggle" class = "icon-button" type = "button" title = "Search. (Shortkey: s)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "S" aria-controls = "searchbar" >
< i class = "fa fa-search" > < / i >
< / button >
< / div >
< h1 class = "menu-title" > Easy Rust< / h1 >
< div class = "right-buttons" >
< a href = "print.html" title = "Print this book" aria-label = "Print this book" >
< i id = "print-button" class = "fa fa-print" > < / i >
< / a >
< / div >
< / div >
< div id = "search-wrapper" class = "hidden" >
< form id = "searchbar-outer" class = "searchbar-outer" >
< input type = "search" name = "search" id = "searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "searchresults-outer" aria-describedby = "searchresults-header" >
< / form >
< div id = "searchresults-outer" class = "searchresults-outer hidden" >
< div id = "searchresults-header" class = "searchresults-header" > < / div >
< ul id = "searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script type = "text/javascript" >
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "content" class = "content" >
< main >
2021-02-24 06:13:19 +00:00
< h2 id = "channels" > < a class = "header" href = "#channels" > Channels< / a > < / h2 >
2021-02-09 09:07:07 +00:00
< 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 " multiple producer, single consumer" , so " many threads sending to one place" . 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 >
2020-12-25 14:16:02 +00:00
< pre > < pre class = "playground" > < code class = "language-rust" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
2021-02-09 09:07:07 +00:00
< / span > // 🚧
pub fn channel< T> () -> (Sender< T> , Receiver< T> )
2020-12-25 14:16:02 +00:00
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
2021-02-09 09:07:07 +00:00
< 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;
2020-12-25 14:16:02 +00:00
fn main() {
2021-02-09 09:07:07 +00:00
let (sender, receiver) = channel(); // ⚠️
2020-12-25 14:16:02 +00:00
}
< / code > < / pre > < / pre >
2021-02-09 09:07:07 +00:00
< p > The compiler says:< / p >
< pre > < code class = "language-text" > error[E0282]: type annotations needed for `(std::sync::mpsc::Sender< T> , std::sync::mpsc::Receiver< T> )`
--> 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< T> , std::sync::mpsc::Receiver< T> )`, 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< i32> , Receiver< i32> ) = channel();
2020-12-25 14:16:02 +00:00
}
2021-02-09 09:07:07 +00:00
< / 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;
2020-12-25 14:16:02 +00:00
2021-02-09 09:07:07 +00:00
fn main() {
let (sender, receiver) = channel();
2020-12-25 14:16:02 +00:00
2021-02-09 09:07:07 +00:00
sender.send(5);
receiver.recv(); // recv = receive, not " rec v"
}
< / code > < / pre > < / pre >
< p > Now the compiler knows the type. < code > sender< / code > is a < code > Result< (), SendError< i32> > < / code > and < code > receiver< / code > is a < code > Result< i32, RecvError> < / 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;
2020-12-25 14:16:02 +00:00
2021-02-09 09:07:07 +00:00
fn main() {
let (sender, receiver) = channel();
2020-12-25 14:16:02 +00:00
2021-02-09 09:07:07 +00:00
sender.send(5).unwrap();
println!(" {}" , receiver.recv().unwrap());
2020-12-25 14:16:02 +00:00
}
2021-02-09 09:07:07 +00:00
< / 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;
2020-12-25 14:16:02 +00:00
fn main() {
2021-02-09 09:07:07 +00:00
let (sender, receiver) = channel();
let sender_clone = sender.clone();
2020-12-25 14:16:02 +00:00
2021-02-09 09:07:07 +00:00
std::thread::spawn(move|| { // move sender in
sender.send(" Send a & str this time" ).unwrap();
2020-12-25 14:16:02 +00:00
});
2021-02-09 09:07:07 +00:00
std::thread::spawn(move|| { // move sender_clone in
sender_clone.send(" And here is another & str" ).unwrap();
2020-12-25 14:16:02 +00:00
});
2021-02-09 09:07:07 +00:00
println!(" {}" , receiver.recv().unwrap());
}
< / code > < / pre > < / pre >
< p > The two threads start sending, and then we < code > println!< / code > . It might say < code > Send a & str this time< / code > or < code > And here is another & 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(" Send a & str this time" ).unwrap();
}));
handle_vec.push(std::thread::spawn(move|| { // and push this into the vec
sender_clone.send(" And here is another & str" ).unwrap();
}));
for _ in handle_vec { // now handle_vec has 2 items. Let's print them
println!(" {:?}" , receiver.recv().unwrap());
}
2020-12-25 14:16:02 +00:00
}
< / code > < / pre > < / pre >
2021-02-09 09:07:07 +00:00
< p > This prints:< / p >
< pre > < code class = "language-text" > " Send a & str this time"
" And here is another & str"
2020-12-25 14:16:02 +00:00
< / code > < / pre >
2021-02-09 09:07:07 +00:00
< 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(" Send a & str this time" ).unwrap();
}));
handle_vec.push(std::thread::spawn(move|| {
sender_clone.send(" And here is another & str" ).unwrap();
}));
for _ in handle_vec {
results_vec.push(receiver.recv().unwrap());
}
println!(" {:?}" , results_vec);
}
< / code > < / pre > < / pre >
< p > Now the results are in our vec: < code > [" Send a & str this time" , " And here is another & str" ]< / 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;
2021-03-16 07:58:31 +00:00
use std::thread::spawn;
2021-02-09 09:07:07 +00:00
fn main() {
let (sender, receiver) = channel();
2021-03-16 07:58:31 +00:00
let hugevec = vec![0; 1_000_000];
2021-02-09 09:07:07 +00:00
let mut newvec = vec![];
2021-03-16 07:58:31 +00:00
let mut handle_vec = vec![];
2021-02-09 09:07:07 +00:00
for i in 0..10 {
let sender_clone = sender.clone();
let mut work: Vec< u8> = Vec::with_capacity(hugevec.len() / 10); // new vec to put the work in. 1/10th the size
2021-03-16 07:58:31 +00:00
work.extend(& hugevec[i*100_000..(i+1)*100_000]); // first part gets 0..100_000, next gets 100_000..200_000, etc.
let handle =spawn(move || { // make a handle
2021-02-09 09:07:07 +00:00
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
});
2021-03-16 07:58:31 +00:00
handle_vec.push(handle);
}
for handle in handle_vec { // stop until the threads are done
handle.join().unwrap();
}
while let Ok(results) = receiver.try_recv() {
newvec.push(results); // push the results from receiver.recv() into the vec
2021-02-09 09:07:07 +00:00
}
// Now we have a Vec< Vec< u8> > . To put it together we can use .flatten()
2021-03-16 07:58:31 +00:00
let newvec = newvec.into_iter().flatten().collect::< Vec< u8> > (); // Now it's one vec of 1_000_000 u8 numbers
println!(" {:?}, {:?}, total length: {}" , // Let's print out some numbers to make sure they are all 1
& newvec[0..10], & newvec[newvec.len()-10..newvec.len()], newvec.len() // And show that the length is 1_000_000 items
);
for number in newvec { // And let's tell Rust that it can panic if even one number is not 1
if number != 1 {
panic!();
}
}
2021-02-09 09:07:07 +00:00
}
< / code > < / pre > < / pre >
2020-12-25 14:16:02 +00:00
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "Chapter_49.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
< a rel = "next" href = "Chapter_51.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< i class = "fa fa-angle-right" > < / i >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
< a rel = "prev" href = "Chapter_49.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< i class = "fa fa-angle-left" > < / i >
< / a >
< a rel = "next" href = "Chapter_51.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< i class = "fa fa-angle-right" > < / i >
< / a >
< / nav >
< / div >
< script type = "text/javascript" >
window.playground_copyable = true;
< / script >
< script src = "elasticlunr.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "mark.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "searcher.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "clipboard.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "highlight.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "book.js" type = "text/javascript" charset = "utf-8" > < / script >
<!-- Custom JS scripts -->
< / body >
< / html >
