Rust rayon example

rust_rayon.rs

// Parallel iterator over a contiguous array of i32 values given a raw pointer and size;
use rayon::prelude::*;


fn var_1(ptr: *mut i32, len: usize) {
    // With a stdlib slice
    let data_sl = unsafe { std::slice::from_raw_parts_mut(ptr, len) };
    data_sl.into_par_iter().for_each(|i| *i *= *i);
}

fn var_2(ptr: *mut i32, len: usize) {
    // With pointer arithmetic. We have to wrap the raw pointer in a Sync'able struct.
    #[derive(Debug)]
    struct Wrap(*mut i32);
    unsafe impl std::marker::Sync for Wrap{}
    let w = Wrap(ptr);

    (0..len).into_par_iter().for_each(|i|{
        unsafe {
            let cp = (&w).0.add(i);
            *cp *= *cp;
        }
    });
}

fn main() {
    let args:Vec<String> = std::env::args().collect();
    let len = args.get(1).and_then(|v| v.parse::<i32>().ok()).expect("Must provide data size");

    let mut data: Vec<i32> = (0..len).collect();
    let ptr = data.as_mut_ptr();
    let start = std::time::Instant::now();
    var_1(ptr, len as usize);
    var_2(ptr, len as usize);

    println!("Time: {}ms", method, start.elapsed().as_millis());

}