mpsc channel
- Rust course
- Advanced
- Lesson 19/81
- 4 min
Create a channel with std::sync::mpsc.
The mpsc channel
Channels let threads communicate by messages instead of sharing data: "Don't communicate by sharing memory; share memory by communicating." mpsc (multiple producer, single consumer) gives a sender (tx) and a receiver (rx):
use std::sync::mpsc;
let (tx, rx) = mpsc::channel();
thread::spawn(move || {
for i in 1..=3 {
tx.send(format!("mesaj {i}")).unwrap();
}
});
for m in rx { // the loop ends when tx is dropped
println!("{m}");
}Ownership of the sent value passes to the receiver; the sender can no longer access it.
A channel is an iterator
for m in rx (or rx.iter()) calls recv for each message and ends when all senders are dropped. When the sender thread's closure finishes, tx is dropped automatically, so the loop ends on its own.
// message order is preserved for a single sender
// mesaj 1
// mesaj 2
// mesaj 3Practice Messages
Open a channel. Let a separate thread send the texts mesaj 1, mesaj 2 and mesaj 3; let the main thread print each with for m in rx.
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 || {
for i in 1..=3 {
tx.send(format!("mesaj {i}")).unwrap();
}
});
for m in rx {
println!("{}", m);
}
}Expected output
mesaj 1 mesaj 2 mesaj 3
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if you try to use the value after sending (<code>tx.send(s); println!("{s}")</code>)?
- It works
- Panic
- It prints empty text
- E0382: s was moved into the channel Correct answer
Explanation: The transfer of ownership makes it impossible for two threads to change the same data at once.
2 Open a channel
let (tx, rx) = mpsc::____();let (tx, rx) = mpsc::channel();Explanation: mpsc::channel returns a (sender, receiver) pair.
3 Piece and role
| Term | Meaning |
|---|---|
tx |
Sender |
rx |
Receiver |
tx.send(v) |
Transfers ownership |
for m in rx |
Until the senders close |