Can the BackgroundService support a &mut self reference?

[aniaan]

What is the problem your feature solves, or the need it fulfills?

The current signature of the start method in the BackgroundService trait is as follows.:

pingora/pingora-core/src/services/background.rs

Lines 31 to 37 in bdb13a7

	#[async_trait]
	pub trait BackgroundService {
	/// This function is called when the pingora server tries to start all the
	/// services. The background service can return at anytime or wait for the
	/// `shutdown` signal.
	async fn start(&self, mut shutdown: ShutdownWatch);
	}

The self parameter is immutable. Currently, I have a function that needs to run in the background and requires &mut self. The scenario is quite simple: it involves consuming from a channel, but because self is immutable, it cannot perform recv. Here’s an example of the code:

#[async_trait]
impl BackgroundService for Observer {
    async fn start(&self, mut shutdown: pingora::server::ShutdownWatch) {
        let mut traces = Vec::with_capacity(self.batch_size);
        let mut interval = tokio::time::interval(self.flush_interval);

        loop {
            tokio::select! {
                _ = interval.tick() => {
                    if !traces.is_empty() {
                        // self.flush(&traces).await;
                        traces.clear();
                    }
                }
                trace = self.rx.recv() => {
                    if let Some(trace) = trace {
                        traces.push(trace);
                        if traces.len() >= self.batch_size {
                            // self.flush(&traces).await;
                            traces.clear();
                        }
                    }
                }
                _ = shutdown.changed() => {
                    if !traces.is_empty() {
                        // self.flush(&traces).await;
                    }
                    break;
                }
            }
        }

        todo!()
    }
}

The following code shows that when the upper method calls start, self is &mut self. However, when it comes to the start method, self becomes &self, and these two signatures are not quite consistent. Is there a specific reason for this? I hope you can help clarify this for me. Thank you very much.

pingora/pingora-core/src/services/background.rs

Lines 66 to 76 in bdb13a7

	impl<A> Service for GenBackgroundService<A>
	where
	A: BackgroundService + Send + Sync + 'static,
	{
	async fn start_service(
	&mut self,
	#[cfg(unix)] _fds: Option<ListenFds>,
	shutdown: ShutdownWatch,
	) {
	self.task.start(shutdown).await;
	}

Describe the solution you'd like

Is it possible to change the method signature from &self to &mut self?