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// Copyright 2020 Quentin De Coninck // // Distributed under MIT license. //! A minimal crate to play with Instant based on UNIX epoch. //! //! The standard library provides Instant and Duration structures to measure //! elapsed time. This is fine for most use cases, but the Instant structure //! voluntary hides its implementation to keep its semantics. This crate exposes //! its time base to the UNIX Epoch (1st January 1970 at 0:00). //! //! The exposed API tries to mimic as much as possible the `std::time` one for //! the related `Instant` structures, such that passing from these to the ones //! of this crate would be as seamless as possible (as it actually uses //! `std::time` under the hood). //! //! This crate should only be used to compute local time. It is thus not //! appropriate for timezone computations, playing with dates,... use std::time::SystemTime; use std::time::Duration; use std::ops::{Add, AddAssign, Sub, SubAssign}; /// An precise instant relative to the UNIX epoch, with nanosecond precision. #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)] pub struct Instant { secs: u64, nanos: u32, } impl Instant { /// Creates an `Instant` at the specified seconds and nanoseconds after the /// UNIX epoch. pub fn at(secs: u64, nanos: u32) -> Self { Self { secs, nanos } } /// Returns an instant corresponding to "now". pub fn now() -> Self { let since_epoch = SystemTime::now() .duration_since(SystemTime::UNIX_EPOCH) .expect("SystemTime before UNIX epoch?!?"); Self::at(since_epoch.as_secs(), since_epoch.subsec_nanos()) } /// Returns the number of _whole_ seconds that spaces `self` from the UNIX /// epoch. /// /// The returned value does not include the fractional (nanosecond) part of /// the duration, which can be obtained using [`subsec_nanos`]. /// /// # Examples /// /// ``` /// use unix_time::Instant; /// /// let duration = Instant::at(5, 730023852); /// assert_eq!(duration.secs(), 5); /// ``` /// /// To determine the total number of seconds represented by the `Duration`, /// use `secs` in combination with [`subsec_nanos`]: /// /// ``` /// use unix_time::Instant; /// /// let instant = Instant::at(5, 730023852); /// /// assert_eq!(5.730023852, /// instant.secs() as f64 /// + instant.subsec_nanos() as f64 * 1e-9); /// ``` /// /// [`subsec_nanos`]: Instant::subsec_nanos pub fn secs(&self) -> u64 { self.secs } /// Returns the fractional part that spaces `self` from the UNIX epoch in /// nanoseconds. /// /// This method does _not_ return the total duration since the UNIX epoch in /// nanoseconds. The returned number always represents a fractional portion /// of a second (i.e., it is less than one billion). /// /// # Examples /// /// ``` /// use unix_time::Instant; /// /// let instant = Instant::at(5, 10_000_000); /// assert_eq!(instant.secs(), 5); /// assert_eq!(instant.subsec_nanos(), 10_000_000); /// ``` pub fn subsec_nanos(&self) -> u32 { self.nanos } /// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be /// represented as `Instant` (which means it's inside the bounds of the /// underlying data structure), `None` otherwise. pub fn checked_add(&self, duration: Duration) -> Option<Instant> { let d: Duration = (*self).into(); d.checked_add(duration).map(|x| x.into()) } /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be /// represented as `Instant` (which means it's inside the bounds of the /// underlying data structure), `None` otherwise. pub fn checked_sub(&self, duration: Duration) -> Option<Instant> { let d: Duration = (*self).into(); d.checked_sub(duration).map(|x| x.into()) } /// Returns the amount of time elapsed from another instant to this one, /// or None if that instant is later than this one. /// /// # Examples /// /// ```no_run /// use unix_time::Instant; /// use std::time::Duration; /// use std::thread::sleep; /// /// let now = Instant::now(); /// sleep(Duration::new(1, 0)); /// let new_now = Instant::now(); /// println!("{:?}", new_now.checked_duration_since(now)); /// println!("{:?}", now.checked_duration_since(new_now)); // None /// ``` pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> { let d: Duration = (*self).into(); d.checked_sub(earlier.into()) } /// Returns the amount of time elapsed from another instant to this one. /// /// # Panics /// /// This function will panic if `earlier` is later than `self`. /// /// # Examples /// /// ```no_run /// use std::time::Duration; /// use unix_time::Instant; /// use std::thread::sleep; /// /// let now = Instant::now(); /// sleep(Duration::new(1, 0).into()); /// let new_now = Instant::now(); /// println!("{:?}", new_now.duration_since(now)); /// ``` pub fn duration_since(&self, earlier: Instant) -> Duration { self.checked_duration_since(earlier).expect("supplied instant is later than self") } /// Returns the amount of time elapsed from another instant to this one, /// or zero duration if that instant is later than this one. /// /// # Examples /// /// ```no_run /// use std::time::Duration; /// use unix_time::Instant; /// use std::thread::sleep; /// /// let now = Instant::now(); /// sleep(Duration::new(1, 0)); /// let new_now = Instant::now(); /// println!("{:?}", new_now.saturating_duration_since(now)); /// println!("{:?}", now.saturating_duration_since(new_now)); // 0ns /// ``` pub fn saturating_duration_since(&self, earlier: Instant) -> Duration { self.checked_duration_since(earlier).unwrap_or(Duration::new(0, 0)) } /// Returns the amount of time elapsed since this instant was created. /// /// # Panics /// /// This function may panic if the current time is earlier than this /// instant, which is something that can happen if an `Instant` is /// produced synthetically. /// /// # Examples /// /// ```no_run /// use std::thread::sleep; /// use std::time::Duration; /// use unix_time::Instant; /// /// let instant = Instant::now(); /// let three_secs = Duration::from_secs(3); /// sleep(three_secs); /// assert!(instant.elapsed() >= three_secs); /// ``` pub fn elapsed(&self) -> Duration { Instant::now() - *self } } impl From<Instant> for Duration { fn from(i: Instant) -> Duration { Duration::new(i.secs, i.nanos) } } impl From<Duration> for Instant { fn from(d: Duration) -> Instant { Instant::at(d.as_secs(), d.subsec_nanos()) } } impl Add<Duration> for Instant { type Output = Instant; /// # Panics /// /// This function may panic if the resulting point in time cannot be represented by the /// underlying data structure. See [`Instant::checked_add`] for a version without panic. fn add(self, other: Duration) -> Instant { self.checked_add(other).expect("overflow when adding duration to instant") } } impl AddAssign<Duration> for Instant { fn add_assign(&mut self, other: Duration) { *self = *self + other; } } impl Sub<Duration> for Instant { type Output = Instant; fn sub(self, other: Duration) -> Instant { self.checked_sub(other).expect("overflow when subtracting duration from instant") } } impl SubAssign<Duration> for Instant { fn sub_assign(&mut self, other: Duration) { *self = *self - other; } } impl Sub<Instant> for Instant { type Output = Duration; fn sub(self, other: Instant) -> Duration { self.duration_since(other) } }