20.threads

threads1.rs

Github solution link

// threads1.rs
//
// This program spawns multiple threads that each run for at least 250ms, and
// each thread returns how much time they took to complete. The program should
// wait until all the spawned threads have finished and should collect their
// return values into a vector.
//
// Execute `rustlings hint threads1` or use the `hint` watch subcommand for a
// hint.


use std::thread;
use std::time::{Duration, Instant};

fn main() {
    let mut handles = vec![];
    for i in 0..10 {
        handles.push(thread::spawn(move || {
            let start = Instant::now();
            thread::sleep(Duration::from_millis(1));
            println!("thread {} is complete", i);
            start.elapsed().as_millis()
        }));
    }

    let mut results: Vec<u128> = vec![];
    for handle in handles {
        match handle.join() {
            Ok(x) => results.push(x),
            Err(_) => results.push(0),
        }
    }

    if results.len() != 10 {
        panic!("Oh no! All the spawned threads did not finish!");
    }

    println!();
    for (i, result) in results.into_iter().enumerate() {
        println!("thread {} took {}ms", i, result);
    }
}

threads2.rs

Github solution link

// threads2.rs
//
// Building on the last exercise, we want all of the threads to complete their
// work but this time the spawned threads need to be in charge of updating a
// shared value: JobStatus.jobs_completed
//
// Execute `rustlings hint threads2` or use the `hint` watch subcommand for a
// hint.


use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

struct JobStatus {
    jobs_completed: u32,
}

fn main() {
    let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));
    let mut handles = vec![];
    for _ in 0..10 {
        let status_shared = Arc::clone(&status);
        let handle = thread::spawn(move || {
            thread::sleep(Duration::from_millis(250));
            let mut locked_status = status_shared.lock().unwrap();
            // TODO: You must take an action before you update a shared value
            locked_status.jobs_completed += 1;
        });
        handles.push(handle);
    }
    for handle in handles {
        handle.join().unwrap();
        // TODO: Print the value of the JobStatus.jobs_completed. Did you notice
        // anything interesting in the output? Do you have to 'join' on all the
        // handles?


        // Output:
        // ====================
        // jobs completed 1
        // jobs completed 2
        // jobs completed 3
        // jobs completed 4
        // jobs completed 5
        // jobs completed 6
        // jobs completed 10
        // jobs completed 10
        // jobs completed 10
        // jobs completed 10

        // ====================
        // By the time 6th thread completes, all the other tasks are completed.

        let mut locked_read_only_status = status.lock().unwrap();
        println!("jobs completed {}", locked_read_only_status.jobs_completed);
    }
}

threads3.rs

Github solution link

// threads3.rs
//
// Execute `rustlings hint threads3` or use the `hint` watch subcommand for a
// hint.


use std::sync::mpsc;
use std::sync::Arc;
use std::thread;
use std::time::Duration;

struct Queue {
    length: u32,
    first_half: Vec<u32>,
    second_half: Vec<u32>,
}

impl Queue {
    fn new() -> Self {
        Queue {
            length: 10,
            first_half: vec![1, 2, 3, 4, 5],
            second_half: vec![6, 7, 8, 9, 10],
        }
    }
}

fn send_tx(q: Queue, tx: mpsc::Sender<u32>) -> () {
    let qc = Arc::new(q);
    let qc1 = Arc::clone(&qc);
    let qc2 = Arc::clone(&qc);

    let tx1 = tx.clone();
    let tx2 = tx.clone();

    thread::spawn(move || {
        for val in &qc1.first_half {
            println!("sending {:?}", val);
            tx1.send(*val).unwrap();
            thread::sleep(Duration::from_millis(5));
        }
    });

    thread::spawn(move || {
        for val in &qc2.second_half {
            println!("sending {:?}", val);
            tx2.send(*val).unwrap();
            thread::sleep(Duration::from_millis(5));
        }
    });
}

#[test]
fn main() {
    let (tx, rx) = mpsc::channel();
    let queue = Queue::new();
    let queue_length = queue.length;

    send_tx(queue, tx);

    let mut total_received: u32 = 0;
    for received in rx {
        println!("Got: {}", received);
        total_received += 1;
    }

    println!("total numbers received: {}", total_received);
    assert_eq!(total_received, queue_length)
}