Async Download with ThreadPool

async_download_with_thread_pool.rs

#![feature(result_map_or_else)]

extern crate num_cpus;
extern crate reqwest;
extern crate threadpool;

use std::error::Error;
use std::thread;
use threadpool::ThreadPool;

fn main() {
    let urls = [
        "http://(wrong)www.google.com/",
        "http://microsoft.com/",
        "http://www.wordpress.com/",
        "http://www.peta.org",
        "https://www.rust-lang.org/",
        "https://www.haskell.org/",
        "https://fsharp.org/",
        "https://(wrong)ocaml.org/",
        "https://reasonml.github.io/",
        "https://www.erlang.org/",
        "https://elixir-lang.org/",
        "https://github.com/alpaca-lang",
    ];

    urls.iter().for_each(|url| download_async(url));
    THREADPOOL.with(|pool| pool.join());
}

thread_local!(static THREADPOOL: ThreadPool = ThreadPool::new(num_cpus::get()));

fn bind<F, G, T>(input: F, rest: G)
where
    F: (Fn() -> T) + Sync + Send + 'static,
    G: Fn(T) + Sync + Send + 'static,
{
    THREADPOOL.with(|pool| pool.execute(move || rest(input())));
}

fn download_async(url: &'static str) {
    bind(
        move || {
            print_msg("Downloading Url...", url);
            reqwest::get(url).and_then(|mut r| r.text())
        },
        move |result| {
            result.map_or_else(
                |_| print_msg("Error occured!", url),
                |html| {
                    print_msg("Displaying...", url);
                    println!("Total {:?}", html.len());
                },
            );
        },
    );
}

fn print_msg(msg: &'static str, url: &'static str) {
    println!("{:?}, Url = {}, {}", thread::current().id(), url, msg)
}