use rayon::prelude::*; // 1.1.0
use parking_lot::Mutex; // 0.9.0

fn main() {

    let vecs = vec![
        Mutex::new(vec![1, 2, 3]),
        Mutex::new(vec![1, 2, 3]),
        Mutex::new(vec![1, 2, 3]),
        Mutex::new(vec![1, 2, 3]),
        Mutex::new(vec![1, 2, 3]),
        Mutex::new(vec![1, 2, 3]),
    ];

    let mut indices = vec![4, 3, 1];

    // Ensure all indices are unique to ensure safety:
    indices.sort_unstable();
    let len = indices.len();
    indices.dedup();
    assert!(indices.len() == len);

    indices.par_iter().for_each(|index| {
         vecs[*index].try_lock().unwrap().push(4);
    });

    println!("vecs: {:?}", vecs);
}