grpc-rust FAQ

Q: I get an error when I try to make mutable service

Parameters in service are immutable intentionally because operations can be executed concurrently, so self should be protected against access from multiple threads. For example, mutable value can be wrapped in Arc<Mutex<T>>.

...

use std::sync::{Arc, Mutex};

struct CounterServiceImpl {
    requests: Arc<Mutex<u64>>,
}

impl CounterServiceImpl {
    fn new() -> CounterServiceImpl {
        CounterServiceImpl { requests: Arc::new(Mutex::new(0)) }
    }
}

impl CounterService for CounterServiceImpl {
    fn Count(&self, req: Request) -> grpc::Result<Reply> {
        println!("Request url: {}", req.get_url());
        *self.requests.lock().unwrap() += 1;
        Ok(Reply::new())
    }
}