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use self::Kind::*; use std::error; use std::fmt; /// Errors encountered by the timer implementation. /// /// Currently, there are two different errors that can occur: /// /// * `shutdown` occurs when a timer operation is attempted, but the timer /// instance has been dropped. In this case, the operation will never be able /// to complete and the `shutdown` error is returned. This is a permanent /// error, i.e., once this error is observed, timer operations will never /// succeed in the future. /// /// * `at_capacity` occurs when a timer operation is attempted, but the timer /// instance is currently handling its maximum number of outstanding delays. /// In this case, the operation is not able to be performed at the current /// moment, and `at_capacity` is returned. This is a transient error, i.e., at /// some point in the future, if the operation is attempted again, it might /// succeed. Callers that observe this error should attempt to [shed load]. One /// way to do this would be dropping the future that issued the timer operation. /// /// [shed load]: https://en.wikipedia.org/wiki/Load_Shedding #[derive(Debug)] pub struct Error(Kind); #[derive(Debug)] enum Kind { Shutdown, AtCapacity, } impl Error { /// Creates an error representing a shutdown timer. pub fn shutdown() -> Error { Error(Shutdown) } /// Returns `true` if the error was caused by the timer being shutdown. pub fn is_shutdown(&self) -> bool { match self.0 { Kind::Shutdown => true, _ => false, } } /// Creates an error representing a timer at capacity. pub fn at_capacity() -> Error { Error(AtCapacity) } /// Returns `true` if the error was caused by the timer being at capacity. pub fn is_at_capacity(&self) -> bool { match self.0 { Kind::AtCapacity => true, _ => false, } } } impl error::Error for Error {} impl fmt::Display for Error { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { use self::Kind::*; let descr = match self.0 { Shutdown => "the timer is shutdown, must be called from the context of Tokio runtime", AtCapacity => "timer is at capacity and cannot create a new entry", }; write!(fmt, "{}", descr) } }