Example

Let us see Arc and Mutex in action:

rust,editable,compile_fail

# // Copyright 2024 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::thread;
// use std::sync::{Arc, Mutex};

fn main() {
    let v = vec![10, 20, 30];
    let mut handles = Vec::new();
    for i in 0..5 {
        handles.push(thread::spawn(|| {
            v.push(10 * i);
            println!("v: {v:?}");
        }));
    }

    handles.into_iter().for_each(|h| h.join().unwrap());
}

Possible solution:

rust,editable

# // Copyright 2024 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::sync::{Arc, Mutex};
use std::thread;

fn main() {
    let v = Arc::new(Mutex::new(vec![10, 20, 30]));
    let mut handles = Vec::new();
    for i in 0..5 {
        let v = Arc::clone(&v);
        handles.push(thread::spawn(move || {
            let mut v = v.lock().unwrap();
            v.push(10 * i);
            println!("v: {v:?}");
        }));
    }

    handles.into_iter().for_each(|h| h.join().unwrap());
}

Notable parts:

v is wrapped in both Arc and Mutex, because their concerns are orthogonal.
- Wrapping a Mutex in an Arc is a common pattern to share mutable state between threads.
v: Arc<_> needs to be cloned to make a new reference for each new spawned thread. Note move was added to the lambda signature.
Blocks are introduced to narrow the scope of the LockGuard as much as possible.

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