fn generate_sin(
    samples: &mut [f32],
    dt: f32,
    freq: f32,
) {
    for (i, s) in samples.iter_mut().enumerate() {
        let t = i as f32 * dt;
        *s += (2.0 * std::f32::consts::PI * t * freq).sin();
    }
}

fn main() {
    let start = std::time::Instant::now();
    let dt = 1.0 / 44100.0;
    let mut samples = vec![0.0; 50_000_000];
    for f in 1..=5 {
        let freq = f as f32 * 100.0;
        generate_sin(&mut samples, dt, freq);
    }
    let duration = start.elapsed();
    println!("duration: {:?}", duration);
}

sudo apt update
sudo apt install linux-tools-generic linux-tools-`uname -r`

sudo dnf install perf

sudo pacman -S perf

echo 'kernel.perf_event_paranoid = 0' | sudo sh -c 'tee -a /etc/sysctl.conf | sysctl -q -f -'

/// Approximates sine of 2π·x with paraboloids
fn unit_sine(x: f32) -> f32 {
    let x = x - x.floor();
    let mut y = x - 0.5;
    y *= 16.0 * (y.abs() - 0.5);
    // y += 0.225 * y * (y.abs() - 1.0); // increase precision
    y
}

        // *s += (2.0 * std::f32::consts::PI * t * freq).sin();
        *s += unit_sine(t * freq);

fn thread_task(
    title: String,
    delay_ms: u64,
) {
    for i in 0..10 {
        std::thread::sleep(std::time::Duration::from_millis(delay_ms));
        println!("{} counting {}", title, i);
    }
    println!("leaving {}", title);
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // spawn a thread computing something in parallel
    let thread_title = String::from("thread task");
    let thread_delay_ms = 100;
    let consumer_thread = std::thread::spawn(move || {
        thread_task(thread_title, thread_delay_ms);
    });

    // compute something in the main thread
    for i in 0..5 {
        std::thread::sleep(std::time::Duration::from_millis(200));
        println!("main program counting {}", i);
    }

    // wait for the thread to terminate
    if let Err(e) = consumer_thread.join() {
        Err(format!("{:?}", e))?;
    }

    println!("leaving main program");
    Ok(())
}
/*
thread task counting 0
main program counting 0
thread task counting 1
thread task counting 2
main program counting 1
thread task counting 3
thread task counting 4
main program counting 2
thread task counting 5
thread task counting 6
main program counting 3
thread task counting 7
thread task counting 8
main program counting 4
thread task counting 9
leaving thread task
leaving main program
*/

fn consumer_task(
    channel_receiver: std::sync::mpsc::Receiver<String>
) -> Result<(), Box<dyn std::error::Error>> {
    let start_time = std::time::SystemTime::now();
    while let Ok(msg) = channel_receiver.recv() {
        // consume each incoming data
        let elapsed = start_time.elapsed()?;
        println!("consumer task received {:?} after {:?}", msg, elapsed);
    }
    println!("no more messages for consumer task");
    Ok(())
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // prepare a channel in order to provide the thread with some data
    let (channel_sender, channel_receiver) = std::sync::mpsc::channel();

    // spawn a thread consuming data from this channel
    let consumer_thread = std::thread::spawn(move || {
        if let Err(e) = consumer_task(channel_receiver) {
            eprintln!("ERROR: {:?}", e);
        }
    });

    // send data to the thread whenever we want
    channel_sender.send(String::from("first message"))?;
    for i in 0..5 {
        std::thread::sleep(std::time::Duration::from_millis(500));
        let msg = format!("counting {}", i);
        channel_sender.send(msg)?;
    }
    channel_sender.send(String::from("last message"))?;

    // close the channel
    drop(channel_sender);

    // wait for the thread to terminate
    if let Err(e) = consumer_thread.join() {
        Err(format!("{:?}", e))?;
    }

    Ok(())
}
/*
consumer task received "first message" after 784ns
consumer task received "counting 0" after 500.130009ms
consumer task received "counting 1" after 1.000132368s
consumer task received "counting 2" after 1.500230532s
consumer task received "counting 3" after 2.00035814s
consumer task received "counting 4" after 2.500384809s
consumer task received "last message" after 2.500390231s
no more messages for consumer task
*/

use std::sync::{
    atomic::{AtomicUsize, Ordering},
    Arc, Mutex,
};

#[derive(Debug, Default)]
struct SharedState {
    next_n: AtomicUsize,
    elements: Mutex<Vec<(char, usize)>>,
}

fn fibonacci(n: usize) -> usize {
    if n < 2 {
        n
    } else {
        fibonacci(n - 2) + fibonacci(n - 1)
    }
}

fn compute_task(
    letter: char,
    limit: usize,
    state: &SharedState,
) -> Result<(), Box<dyn std::error::Error>> {
    loop {
        // atomic increment
        let n = state.next_n.fetch_add(1, Ordering::Relaxed);

        // compute
        let fib_n = fibonacci(n);
        if fib_n > limit {
            break;
        }

        // exclusively access the shared storage
        let mut elements = state.elements.lock().unwrap();
        if elements.len() <= n {
            elements.resize(1 + n, (letter, 0));
        }
        elements[n] = (letter, fib_n);
    }
    Ok(())
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // prepare a shared state
    let state = Arc::new(SharedState::default());
    let limit = 100_000_000;

    // start many threads working with the shared state
    let mut threads = Vec::new();
    for letter in "ABCD".chars() {
        threads.push(std::thread::spawn({
            // clone the reference, not the state!
            let state = Arc::clone(&state);
            move || {
                if let Err(e) = compute_task(letter, limit, state.as_ref()) {
                    eprintln!("ERROR: {:?}", e);
                }
            }
        }));
    }

    // wait for all threads to terminate
    for th in threads {
        if let Err(e) = th.join() {
            Err(format!("{:?}", e))?;
        }
    }

    // obtain the global result
    println!("{:?}", state.elements.lock().unwrap());

    Ok(())
}
/*
[('B', 0), ('B', 1), ('B', 1), ('B', 2), ('B', 3), ('B', 5), ('B', 8), ('B', 13), ('B', 21), ('B', 34), ('B', 55), ('B', 89), ('B', 144), ('B', 233), ('B', 377), ('B', 610), ('B', 987), ('B', 1597), ('B', 2584), ('B', 4181), ('B', 6765), ('B', 10946), ('D', 17711), ('A', 28657), ('C', 46368), ('B', 75025), ('D', 121393), ('A', 196418), ('C', 317811), ('B', 514229), ('D', 832040), ('A', 1346269), ('C', 2178309), ('B', 3524578), ('D', 5702887), ('A', 9227465), ('C', 14930352), ('B', 24157817), ('D', 39088169), ('A', 63245986)]
*/