trheadz.rs

threadz.rs

use std::hint::black_box;
use std::thread;

use clap::Parser;

/// Simple program to test spawning many threads
#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
struct Args {
    /// Number of threads to spawn
    #[arg(short, long, default_value_t = 10_000)]
    num_threads: u64,

    /// Stack depth(in numer of stack frames) to generate for each thread
    #[arg(short, long, default_value_t = 1000)]
    stack_depth: u64,
}

fn main() {
    let Args {
        num_threads,
        stack_depth,
    } = Args::parse();

    let handles = (0..num_threads).map(|_| thread::spawn(move || run_thread(stack_depth)));

    let mut sum = 0;
    for handle in handles {
        let s = handle.join().expect("to join thread");
        sum += s;
    }

    println!("Sum: {sum}");
}

fn run_thread(count_to: u64) -> u64 {
    // Stop the optimizer
    return black_box(count(black_box(0), black_box(count_to)));
}

#[inline(never)]
fn count(cur: u64, to: u64) -> u64 {
    let a = black_box([1; 1_00]);
    if cur >= to {
        return to;
    }

    return cur + count(cur + 1 + a[40], to);
}