scratch_12.rs

struct AppState {
    config: Arc<Mutext<Vec<String>>>
}

///
/// these handlers can be running on any number of threads
///
fn handler(req: &HttpRequest<AppState>) -> Box<Future<Item = HttpResponse, Error = ()>> {

    // clone the Arc here so it can be safely moved into the closure
    let arc = req.state().config.clone();

    req.payload()
        .concat2()
        .from_err()
        .and_then(move |body| {

            // now we can access the mutex here to lock it
            // & write to it
            let m = arc.lock().unwrap();
            m.config.push(body.to_string());

            // return json response
            HttpResponse::Ok()
                .content_type("application/json")
                .body("yo!")
        })
        .responder()
}