Function record 

pub fn record(
    kind: &str,
    name: &str,
    args: &[String],
    ms: u128,
    outcome: &str,
    slowest: Option<(String, u128)>,
    caller: impl FnOnce() -> Option<String>,
) -> bool

One line, when ms is above the bound. caller is asked only then (resolving a caller reads the process table). Answers whether a line was written.