log slow functions, optimized out in release, example of cancelling a thread

timing.rs

use std::{
    sync::mpsc,
    time::{Duration, Instant},
};

/// Warns on any function that is behaving slow
///
/// Useful for when your code appears to be getting stuck somewhere
/// and you want a fast "debug print" way of knowing where.
#[inline]
pub fn with_timing<F, G>(delay: Duration, mut f: F) -> G
where
    F: FnMut() -> G,
{
    if cfg!(debug_assertions) {
        let (tx, rx) = mpsc::channel();
        let span = tracing::Span::current();
        let now = Instant::now();
        std::thread::spawn(move || {
            let _span = span.entered();
            while let Err(mpsc::TryRecvError::Empty) = rx.try_recv() {
                let elapsed = now.elapsed();
                if elapsed > delay {
                    tracing::warn!(?elapsed, "SLOW");
                }
                std::thread::sleep(Duration::from_secs(1));
            }
        });
        let result = f();
        tx.send(()).ok();
        result
    } else {
        f()
    }
}