Bounded Channels

With bounded (synchronous) channels, send() can block the current thread:

rust,editable

# // Copyright 2022 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::sync::mpsc;
use std::thread;
use std::time::Duration;

fn main() {
    let (tx, rx) = mpsc::sync_channel(3);

    thread::spawn(move || {
        let thread_id = thread::current().id();
        for i in 0..10 {
            tx.send(format!("Message {i}")).unwrap();
            println!("{thread_id:?}: sent Message {i}");
        }
        println!("{thread_id:?}: done");
    });
    thread::sleep(Duration::from_millis(100));

    for msg in rx {
        println!("Main: got {msg}");
    }
}

Calling send() will block the current thread until there is space in the channel for the new message. The thread can be blocked indefinitely if there is nobody who reads from the channel.
Like unbounded channels, a call to send() will abort with an error if the channel is closed.
A bounded channel with a size of zero is called a "rendezvous channel". Every send will block the current thread until another thread calls recv().

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