How to parallelize correctly?

Question

Multithreading

There is a function making 100 requests to the server. This takes approximately 5-10 seconds. (Although, there are times when you have to wait 16-18 seconds)

Function

const PARALLEL_REQUESTS: usize = 8;

fn task(port: u64, start: u64) {
    tokio::runtime::Runtime::new().unwrap().block_on(async move {
        let client = reqwest::Client::builder()
                            .proxy(reqwest::Proxy::all(&format!("socks5h://127.0.0.1:{}", port)).unwrap())
                            .build().unwrap();
        
        let mut offsets: Vec<u64> = vec![];                
        for i in (start..start + 1000).step_by(10) {
            offsets.push(i);
        }
    
    
        let bodies = stream::iter(offsets)
            .map(|offset| {
                let client = &client;
                let url = format!("https://site.ru/test?offset={}", offset).to_owned();
                async move {
                    let resp = client.post(&url)
                                    .header("X-Requested-With", "XMLHttpRequest")
                                    .body("_ajax=1")
                                    .send().await?;
                    resp.text().await
                }
            }).buffer_unordered(PARALLEL_REQUESTS);
        
    
        bodies
            .for_each(|b| {
                async {
                   // getting some info
                }
            })
            .await;
    });
}

But if you run this code in multiple threads, then the execution time becomes longer.

fn main() {
    let start_time = Instant::now();
    let n_workers = 4;

    let mut tasks = vec![];

    for i in 0..n_workers {
        tasks.push(thread::spawn(move || {
            task(9000 + i, 15 + (i * 1000));
        }));
    }
    for task in tasks {
        let _ = task.join();
    }
    
    let delta = Instant::now() - start_time;
    println!("Time {}s", delta.as_secs_f64());
}

// Время выполнения функции task тоже измеряю
Takes 5.694900368s
Takes 9.479882614s
Takes 10.280974229s
Takes 12.753506558s
Takes 12.755521696s

Is it normal that this is happening?
I use Tor proxy (multitor).
Is the problem that the Tor proxy is not the best solution or that it needs to be better optimized?
How can you speed this up?

Answer 1

With http requests, everything will rest on I / O, so it is very likely that the tor itself is slow - then it is better to regulate the number of simultaneous requests on the contrary.
I won’t tell you exactly how to do this, because I don’t understand rust very well.