Channels

A channel lets threads talk by sending messages instead of sharing data.

mpsc channels

mpsc::channel() returns a pair: a sender (tx) and a receiver (rx). mpsc means "many producers, single consumer". You can have many senders, but only one receiver.

1use std::sync::mpsc;2use std::thread;3let (tx, rx) = mpsc::channel();4thread::spawn(move || {5    tx.send(7).unwrap();6});7println!("{}", rx.recv().unwrap()); // 7

send moves the value

tx.send(v) moves v into the channel. The receiver becomes the new owner. Using v after sending is error E0382. Copy types like i32 are copied, so they stay usable.

1let s = String::from("hi");2tx.send(s).unwrap();3// println!("{s}"); // error E0382

Receiving

rx.recv() waits until a message arrives. It returns Err once every sender is gone and the channel is empty.

A for loop reads messages one by one, in the order they were sent. The loop ends when all senders have been dropped.

1drop(tx);2for msg in rx {3    println!("{msg}");4}

If a sender is still alive, the loop keeps waiting for more.

Many producers

Clone the sender to give each thread its own:

1for id in 0..3 {2    let tx = tx.clone();3    thread::spawn(move || {4        tx.send(id).unwrap();5    });6}7drop(tx); // drop the original too

Messages from different threads can arrive in any order. To get a fixed order, collect them in a Vec and call v.sort(), which puts the Vec in order from small to big.

Remember

• send moves the value; use it after and you get E0382.
• recv waits for one message.
• for msg in rx ends only when every sender is dropped.
• Clone tx for more producers; the receiver can't be cloned.