tokio::sync
- Rust course
- Advanced
- Lesson 9/81
- 4 min
Learn async synchronization primitives from tokio::sync.
tokio::sync
tokio::sync offers synchronization tools between tasks: Mutex, RwLock (they don't block the thread while waiting for the lock), mpsc, broadcast, watch and oneshot for a one-time reply:
let (tx, rx) = tokio::sync::oneshot::channel();
tokio::spawn(async move {
tx.send(6 * 7).unwrap();
});
println!("{}", rx.await.unwrap()); // 42oneshot is ideal for the "give a task some work, get its result in a single message" pattern.
std counterpart: a one-message channel
The standard library has no separate oneshot, but an mpsc channel used for a single message does the same job:
use std::sync::mpsc;
use std::thread;
let (tx, rx) = mpsc::channel();
thread::spawn(move || {
tx.send(6 * 7).unwrap();
});
println!("{}", rx.recv().unwrap());recv waits until a message arrives; if the sender is dropped without sending, it returns Err.
Practice One-time reply
Open a channel with mpsc::channel. Let a separate thread send the result of 6 * 7; let the main thread receive it with recv and print it.
Starter code
use std::sync::mpsc;
use std::thread;
fn main() {
// buraya yaz
}Sample solution
use std::sync::mpsc;
use std::thread;
fn main() {
let (tx, rx) = mpsc::channel();
thread::spawn(move || {
tx.send(6 * 7).unwrap();
});
println!("{}", rx.recv().unwrap());
}Expected output
42
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 When is <code>std::sync::Mutex</code> acceptable in async code?
- Never
- Always
- Only on a single thread
- When the lock is held briefly and not across an .await Correct answer
Explanation: Holding a std mutex across .await can block and also makes the future non-Send; in that case tokio::sync::Mutex is needed.
2 Wait for the message
let (tx, rx) = mpsc::channel();
thread::spawn(move || tx.send(42).unwrap());
let n = rx.____().unwrap();let (tx, rx) = mpsc::channel();
thread::spawn(move || tx.send(42).unwrap());
let n = rx.recv().unwrap();Explanation: recv waits until a message arrives.
3 Tool and use
| Term | Meaning |
|---|---|
oneshot |
Single reply |
mpsc |
Many producers, one consumer |
broadcast |
Broadcast to all |
watch |
Watch the latest value |