1. In the src/bin folder, create a file called parallelism.rs

2. Add the following code and run it with cargo run --bin parallelism

1   use std::thread;
2
3   fn main() {
4     // Spawning a thread lets it execute a lambda
5     let child = thread::spawn(|| println!("Hello from a new
      thread!"));
6     println!("Hello from the main thread!");
7     // Joining a child thread with the main thread means
8     // that the main thread waits until the child has
9     // finished it's work
10    child.join().expect("Failed to join the child thread");
11 
12    let sum = parallel_sum(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
13    println!("The sum of the numbers 1 to 10 is {}", sum);
14  }
15 
16  // We are going to write a function that
17  // sums the numbers in a slice in parallel
18  fn parallel_sum(range: &[i32]) -> i32 {
19    // We are going to use exactly 4 threads to sum the numbers
20    const NUM_THREADS: usize = 4;
21     
22    // If we have less numbers than threads,
23    // there's no point in multithreading them
24    if range.len() < NUM_THREADS {
25      sum_bucket(range)
26    } else {
27        // We define "bucket" as the amount of numbers
28        // we sum in a single thread
29        let bucket_size = range.len() / NUM_THREADS;
30        let mut count = 0;
31        // This vector will keep track of our threads
32        let mut threads = Vec::new();
33        // We try to sum as much as possible in other threads
34        while count + bucket_size < range.len() {
35          let bucket = range[count..count +
                               bucket_size].to_vec();
36          let thread = thread::Builder::new()
37            .name("calculation".to_string())
38            .spawn(move || sum_bucket(&bucket))
39            .expect("Failed to create the thread");
40          threads.push(thread);
41             
42          count += bucket_size
43    }
44    // We are going to sum the rest in the main thread
45    let mut sum = sum_bucket(&range[count..]);
46         
47    // Time to add the results up
48    for thread in threads {
49      sum += thread.join().expect("Failed to join thread");
50    }
51    sum
52  }
53 }
54 
55  // This is the function that will be executed in the threads
56  fn sum_bucket(range: &[i32]) -> i32 {
57    let mut sum = 0;
58    for num in range {
59      sum += *num;
60    }
61     sum
62  }