tokio-timer-segfault

This repo shows a minimal setup where a segmentation fault is obtained when running the program with the nightly toolchain with optimizations turned on.

Tested setup where the segfault occurs:

Toolchains:

• beta-x86_64-apple-darwin
• nightly-x86_64-apple-darwin

Cargo command: cargo run --release

System:

• macOS 10.13.3

While debugging I found out that the error can be avoided when inserting a print!-statement after line 248 in the file tokio-timer/src/wheel.rs. By inserting println!s I also found out that the segfault occurs somewhere within the loop.

    /// Returns the instant in time that corresponds to the next timeout
    /// scheduled in this wheel.
    pub fn next_timeout(&self) -> Option<Instant> {
        // TODO: can this be optimized to not look at the whole array?
        let mut min = None;
        for a in self.wheel.iter().filter_map(|s| s.next_timeout.as_ref()) {
            if let Some(b) = min {
                if b < a {
                    print!("");  // FIXME: optimization bug here
                    continue
                }
            }
            min = Some(a);
        }

        min.map(|t| *t)
    }