Struct SystemInstant 

pub struct SystemInstant(/* private fields */);

Available on crate features std only.

🕘 std A measurement of a monotonically nondecreasing clock.

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^{📍phys/time/source re-exported from std::time ::Instant as SystemInstant}

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📜
A measurement of a monotonically nondecreasing clock. Opaque and useful only with Duration.

Instants are always guaranteed, barring platform bugs, to be no less than any previously measured instant when created, and are often useful for tasks such as measuring benchmarks or timing how long an operation takes.

Note, however, that instants are not guaranteed to be steady. In other words, each tick of the underlying clock might not be the same length (e.g. some seconds may be longer than others). An instant may jump forwards or experience time dilation (slow down or speed up), but it will never go backwards. As part of this non-guarantee it is also not specified whether system suspends count as elapsed time or not. The behavior varies across platforms and Rust versions.

Instants are opaque types that can only be compared to one another. There is no method to get “the number of seconds” from an instant. Instead, it only allows measuring the duration between two instants (or comparing two instants).

The size of an Instant struct may vary depending on the target operating system.

Example:

use std::time::{Duration, Instant};
use std::thread::sleep;

fn main() {
   let now = Instant::now();

   // we sleep for 2 seconds
   sleep(Duration::new(2, 0));
   // it prints '2'
   println!("{}", now.elapsed().as_secs());
}

OS-specific behaviors

An Instant is a wrapper around system-specific types and it may behave differently depending on the underlying operating system. For example, the following snippet is fine on Linux but panics on macOS:

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

let now = Instant::now();
let days_per_10_millennia = 365_2425;
let solar_seconds_per_day = 60 * 60 * 24;
let millennium_in_solar_seconds = 31_556_952_000;
assert_eq!(millennium_in_solar_seconds, days_per_10_millennia * solar_seconds_per_day / 10);

let duration = Duration::new(millennium_in_solar_seconds, 0);
println!("{:?}", now + duration);

For cross-platform code, you can comfortably use durations of up to around one hundred years.

Underlying System calls

The following system calls are currently being used by now() to find out the current time:

Platform	System call
SGX	insecure_time usercall. More information on timekeeping in SGX
UNIX	clock_gettime with CLOCK_MONOTONIC
WASI	clock_gettime with CLOCK_MONOTONIC
Darwin	clock_gettime with CLOCK_UPTIME_RAW
VXWorks	clock_gettime with CLOCK_MONOTONIC
SOLID	get_tim
Windows	QueryPerformanceCounter

Disclaimer: These system calls might change over time.

Note: mathematical operations like add may panic if the underlying structure cannot represent the new point in time.

Monotonicity

On all platforms Instant will try to use an OS API that guarantees monotonic behavior if available, which is the case for all tier 1 platforms. In practice such guarantees are – under rare circumstances – broken by hardware, virtualization or operating system bugs. To work around these bugs and platforms not offering monotonic clocks duration_since, elapsed and sub saturate to zero. In older Rust versions this lead to a panic instead. checked_duration_since can be used to detect and handle situations where monotonicity is violated, or Instants are subtracted in the wrong order.

This workaround obscures programming errors where earlier and later instants are accidentally swapped. For this reason future Rust versions may reintroduce panics.

Implementations

impl Instant

pub fn now() -> Instant

Returns an instant corresponding to “now”.

Examples

use std::time::Instant;

let now = Instant::now();

pub fn duration_since(&self, earlier: Instant) -> Duration

Returns the amount of time elapsed from another instant to this one, or zero duration if that instant is later than this one.

Panics

Previous Rust versions panicked when earlier was later than self. Currently this method saturates. Future versions may reintroduce the panic in some circumstances. See Monotonicity.

Examples

use std::time::{Duration, Instant};
use std::thread::sleep;

let now = Instant::now();
sleep(Duration::new(1, 0));
let new_now = Instant::now();
println!("{:?}", new_now.duration_since(now));
println!("{:?}", now.duration_since(new_now)); // 0ns

pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration>

Returns the amount of time elapsed from another instant to this one, or None if that instant is later than this one.

Due to monotonicity bugs, even under correct logical ordering of the passed Instants, this method can return None.

Examples

use std::time::{Duration, Instant};
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 saturating_duration_since(&self, earlier: Instant) -> Duration

Returns the amount of time elapsed from another instant to this one, or zero duration if that instant is later than this one.

Examples

use std::time::{Duration, 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 elapsed(&self) -> Duration

Returns the amount of time elapsed since this instant.

Panics

Previous Rust versions panicked when the current time was earlier than self. Currently this method returns a Duration of zero in that case. Future versions may reintroduce the panic. See Monotonicity.

Examples

use std::thread::sleep;
use std::time::{Duration, Instant};

let instant = Instant::now();
let three_secs = Duration::from_secs(3);
sleep(three_secs);
assert!(instant.elapsed() >= three_secs);

pub fn checked_add(&self, duration: Duration) -> Option<Instant>

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>

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.

Trait Implementations

impl Add<Duration> for Instant

fn add(self, other: Duration) -> 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.

type Output = Instant

The resulting type after applying the + operator.

impl Add<TimeDelta> for SystemInstant

Shifts Instant forward or backward.

type Output = Instant

The resulting type after applying the + operator.

fn add(self, rhs: TimeDelta) -> SystemInstant

Performs the + operation.

impl AddAssign<Duration> for Instant

fn add_assign(&mut self, other: Duration)

Performs the += operation.

impl BitSized<128> for SystemInstant

const BIT_SIZE: usize = _

The bit size of this type (only the relevant data part, without padding).

const MIN_BYTE_SIZE: usize = _

The rounded up byte size for this type.

fn bit_size(&self) -> usize

Returns the bit size of this type (only the relevant data part, without padding).

fn min_byte_size(&self) -> usize

Returns the rounded up byte size for this type.

impl Clone for Instant

fn clone(&self) -> Instant

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Instant

impl Debug for Instant

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Eq for Instant

impl Hash for Instant

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Instant

fn cmp(&self, other: &Instant) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Instant

fn eq(&self, other: &Instant) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Instant

fn partial_cmp(&self, other: &Instant) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Instant

impl Sub for Instant

fn sub(self, other: Instant) -> Duration

Returns the amount of time elapsed from another instant to this one, or zero duration if that instant is later than this one.

Panics

Previous Rust versions panicked when other was later than self. Currently this method saturates. Future versions may reintroduce the panic in some circumstances. See Monotonicity.

type Output = Duration

The resulting type after applying the - operator.

impl Sub<Duration> for Instant

type Output = Instant

The resulting type after applying the - operator.

fn sub(self, other: Duration) -> Instant

Performs the - operation.

impl Sub<Instant> for TimeDelta

Returns a signed TimeDelta.

type Output = Instant

The resulting type after applying the - operator.

fn sub(self, rhs: SystemInstant) -> SystemInstant

Performs the - operation.

impl Sub<TimeDelta> for SystemInstant

Moves Instant backward or forward.

type Output = Instant

The resulting type after applying the - operator.

fn sub(self, rhs: TimeDelta) -> SystemInstant

Performs the - operation.

impl SubAssign<Duration> for Instant

fn sub_assign(&mut self, other: Duration)

Performs the -= operation.

impl TimePoint for SystemInstant

type Elapsed = Duration

The elapsed-difference type between two time points.

fn time_cmp(a: Self, b: Self) -> Ordering

Compares two time points on the same timeline.

fn time_elapsed_checked(later: Self, earlier: Self) -> Option<Self::Elapsed>

Returns the forward elapsed difference from earlier to later, or None if it is not valid or not representable.

fn time_elapsed(later: Self, earlier: Self) -> Self::Elapsed

Returns the forward elapsed difference from earlier to later.

impl TimeSource<Instant> for SystemInstant

fn time_is_monotonic() -> bool

Returns whether this source is monotonic.

fn time_is_absolute() -> bool

Returns whether this source provides an absolute civil timeline.

fn time_scale() -> TimeScale

Returns the unit used by time_point_value and time_elapsed_value.

fn time_now() -> SystemInstant

Returns the current time point in the chosen representation P.

fn time_point_value(point: SystemInstant) -> u64

Converts a time point into a u64 value in time_scale units.

fn time_elapsed_value(elapsed: Duration) -> u64

Converts an elapsed value into a u64 value in time_scale units.

fn time_now_value() -> u64

Returns the current time as a u64 value in time_scale units.

fn time_elapsed_since(point: P) -> P::Elapsed

Returns the forward elapsed value from point to now.

fn time_elapsed_since_checked(point: P) -> Option<P::Elapsed>

Returns the forward elapsed value from point to now, or None if it is not valid or not representable.

fn time_elapsed_since_value(point: P) -> u64

Returns the forward elapsed value from point to now as a u64 in time_scale units.

fn time_point_seconds(point: P) -> u64

Converts point to seconds.

fn time_point_millis(point: P) -> u64

Converts point to milliseconds.

fn time_point_micros(point: P) -> u64

Converts point to microseconds.

fn time_point_nanos(point: P) -> u64

Converts point to nanoseconds.

fn time_elapsed_seconds(elapsed: P::Elapsed) -> u64

Converts elapsed to seconds.

fn time_elapsed_millis(elapsed: P::Elapsed) -> u64

Converts elapsed to milliseconds.

fn time_elapsed_micros(elapsed: P::Elapsed) -> u64

Converts elapsed to microseconds.

fn time_elapsed_nanos(elapsed: P::Elapsed) -> u64

Converts elapsed to nanoseconds.

fn time_now_seconds() -> u64

Returns the current timestamp in seconds.

fn time_now_millis() -> u64

Returns the current timestamp in milliseconds.

fn time_now_micros() -> u64

Returns the current timestamp in microseconds.

fn time_now_nanos() -> u64

Returns the current timestamp in nanoseconds.

fn time_now_millis_f64() -> f64

Returns the current timestamp as milliseconds in f64.

impl TimeSource<u32> for SystemInstant

Process-local monotonic u32 projection of SystemInstant in microseconds.

This compact projection trades range for storage size while keeping sub-millisecond precision useful for short and medium-lived runtimes.

At microsecond resolution, u32 spans about 71.6 minutes,

fn time_is_monotonic() -> bool

Returns whether this source is monotonic.

fn time_is_absolute() -> bool

Returns whether this source provides an absolute civil timeline.

fn time_scale() -> TimeScale

Returns the unit used by time_point_value and time_elapsed_value.

fn time_now() -> u32

Returns the current time point in the chosen representation P.

fn time_point_value(point: u32) -> u64

Converts a time point into a u64 value in time_scale units.

fn time_elapsed_value(elapsed: u32) -> u64

Converts an elapsed value into a u64 value in time_scale units.

fn time_now_value() -> u64

Returns the current time as a u64 value in time_scale units.

fn time_elapsed_since(point: P) -> P::Elapsed

Returns the forward elapsed value from point to now.

fn time_elapsed_since_checked(point: P) -> Option<P::Elapsed>

Returns the forward elapsed value from point to now, or None if it is not valid or not representable.

fn time_elapsed_since_value(point: P) -> u64

Returns the forward elapsed value from point to now as a u64 in time_scale units.

fn time_point_seconds(point: P) -> u64

Converts point to seconds.

fn time_point_millis(point: P) -> u64

Converts point to milliseconds.

fn time_point_micros(point: P) -> u64

Converts point to microseconds.

fn time_point_nanos(point: P) -> u64

Converts point to nanoseconds.

fn time_elapsed_seconds(elapsed: P::Elapsed) -> u64

Converts elapsed to seconds.

fn time_elapsed_millis(elapsed: P::Elapsed) -> u64

Converts elapsed to milliseconds.

fn time_elapsed_micros(elapsed: P::Elapsed) -> u64

Converts elapsed to microseconds.

fn time_elapsed_nanos(elapsed: P::Elapsed) -> u64

Converts elapsed to nanoseconds.

fn time_now_seconds() -> u64

Returns the current timestamp in seconds.

fn time_now_millis() -> u64

Returns the current timestamp in milliseconds.

fn time_now_micros() -> u64

Returns the current timestamp in microseconds.

fn time_now_nanos() -> u64

Returns the current timestamp in nanoseconds.

fn time_now_millis_f64() -> f64

Returns the current timestamp as milliseconds in f64.

impl TimeSource<u64> for SystemInstant

Process-local monotonic u64 projection of SystemInstant in nanoseconds.

This is the canonical wide numeric projection: At nanosecond resolution, u64 spans about 584 years.

fn time_is_monotonic() -> bool

Returns whether this source is monotonic.

fn time_is_absolute() -> bool

Returns whether this source provides an absolute civil timeline.

fn time_scale() -> TimeScale

Returns the unit used by time_point_value and time_elapsed_value.

fn time_now() -> u64

Returns the current time point in the chosen representation P.

fn time_point_value(point: u64) -> u64

Converts a time point into a u64 value in time_scale units.

fn time_elapsed_value(elapsed: u64) -> u64

Converts an elapsed value into a u64 value in time_scale units.

fn time_now_value() -> u64

Returns the current time as a u64 value in time_scale units.

fn time_elapsed_since(point: P) -> P::Elapsed

Returns the forward elapsed value from point to now.

fn time_elapsed_since_checked(point: P) -> Option<P::Elapsed>

Returns the forward elapsed value from point to now, or None if it is not valid or not representable.

fn time_elapsed_since_value(point: P) -> u64

Returns the forward elapsed value from point to now as a u64 in time_scale units.

fn time_point_seconds(point: P) -> u64

Converts point to seconds.

fn time_point_millis(point: P) -> u64

Converts point to milliseconds.

fn time_point_micros(point: P) -> u64

Converts point to microseconds.

fn time_point_nanos(point: P) -> u64

Converts point to nanoseconds.

fn time_elapsed_seconds(elapsed: P::Elapsed) -> u64

Converts elapsed to seconds.

fn time_elapsed_millis(elapsed: P::Elapsed) -> u64

Converts elapsed to milliseconds.

fn time_elapsed_micros(elapsed: P::Elapsed) -> u64

Converts elapsed to microseconds.

fn time_elapsed_nanos(elapsed: P::Elapsed) -> u64

Converts elapsed to nanoseconds.

fn time_now_seconds() -> u64

Returns the current timestamp in seconds.

fn time_now_millis() -> u64

Returns the current timestamp in milliseconds.

fn time_now_micros() -> u64

Returns the current timestamp in microseconds.

fn time_now_nanos() -> u64

Returns the current timestamp in nanoseconds.

fn time_now_millis_f64() -> f64

Returns the current timestamp as milliseconds in f64.