Rust/rocket pass variable to endpoints

Not to my preference but I'm forced to write some Rust today so I'm trying to create a Rocket instance with only one endpoint but, on that endpoint I need to access a variable that is being created during main. The variable takes a long time to be instantiated so that's why I do it there.

My problem is that I can;t find a way to pass it safely. Whatever I do, the compiler complaints about thread safety even though the library appears to be thread safe: https://github.com/brave/adblock-rust/pull/130 (commited code is found on my local instance)

This is the error tat I get:

   |
18 | / lazy_static! {
19 | |     static ref rules_engine: Mutex<Vec<Engine>> = Mutex::new(vec![]);
20 | | }
   | |_^ `std::rc::Rc<std::cell::RefCell<lifeguard::CappedCollection<std::vec::Vec<u64>>>>` cannot be sent between threads safely
   |

...and this is my code:

#![feature(proc_macro_hygiene, decl_macro)]

#[macro_use]
extern crate rocket;

use std::fs::File;
use std::io::{self, BufRead};
use std::path::Path;

use lazy_static::lazy_static;
use std::sync::Mutex;

use adblock::engine::Engine;
use adblock::lists::FilterFormat;

use rocket::request::{Form, FormError, FormDataError};

lazy_static! {
    static ref rules_engine: Mutex<Vec<Engine>> = Mutex::new(vec![]);
}

fn main() {
    if !Path::new("./rules.txt").exists() {
        println!("rules file does not exist")
    } else {
        println!("loading rules");

        let mut rules = vec![];

        if let Ok(lines) = read_lines("./rules.txt") {
            for line in lines {
                if let Ok(ip) = line {
                    rules.insert(0, ip)
                }
            }

            let eng = Engine::from_rules(&rules, FilterFormat::Standard);
            rules_engine.lock().unwrap().push(eng);
            rocket().launch();
        }
    }
}

#[derive(Debug, FromForm)]
struct FormInput<> {
    #[form(field = "textarea")]
    text_area: String
}

#[post("/", data = "<sink>")]
fn sink(sink: Result<Form<FormInput>, FormError>) -> String {
    match sink {
        Ok(form) => {
            format!("{:?}", &*form)
        }
        Err(FormDataError::Io(_)) => format!("Form input was invalid UTF-8."),
        Err(FormDataError::Malformed(f)) | Err(FormDataError::Parse(_, f)) => {
            format!("Invalid form input: {}", f)
        }
    }
}

fn rocket() -> rocket::Rocket {
    rocket::ignite().mount("/", routes![sink])
}

fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
    where P: AsRef<Path>, {
    let file = File::open(filename)?;
    Ok(io::BufReader::new(file).lines())
}

Any way of having the eng available inside the sink endpoint method?

Solution

Rc is not thread safe, even behind a mutex. It looks like Rc is used in eng.blocker.pool.pool which is a lifeguard::Pool. So no, the Engine is not thread safe (at least by default).

Fortunately, it appears that the adblock crate has a feature called "object-pooling", which enables that specific functionality. Removing that feature will (hopefully) make it thread safe.