Struct SystemTime 

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

Available on crate features std only.

🕘 std A measurement of the system clock.

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

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📜
A measurement of the system clock, useful for talking to external entities like the file system or other processes.

Distinct from the Instant type, this time measurement is not monotonic. This means that you can save a file to the file system, then save another file to the file system, and the second file has a SystemTime measurement earlier than the first. In other words, an operation that happens after another operation in real time may have an earlier SystemTime!

Consequently, comparing two SystemTime instances to learn about the duration between them returns a Result instead of an infallible Duration to indicate that this sort of time drift may happen and needs to be handled.

Although a SystemTime cannot be directly inspected, the UNIX_EPOCH constant is provided in this module as an anchor in time to learn information about a SystemTime. By calculating the duration from this fixed point in time, a SystemTime can be converted to a human-readable time, or perhaps some other string representation.

The size of a SystemTime struct may vary depending on the target operating system.

A SystemTime does not count leap seconds. SystemTime::now()’s behavior around a leap second is the same as the operating system’s wall clock. The precise behavior near a leap second (e.g. whether the clock appears to run slow or fast, or stop, or jump) depends on platform and configuration, so should not be relied on.

Example:

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

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

   // we sleep for 2 seconds
   sleep(Duration::new(2, 0));
   match now.elapsed() {
       Ok(elapsed) => {
           // it prints '2'
           println!("{}", elapsed.as_secs());
       }
       Err(e) => {
           // the system clock went backwards!
           println!("Great Scott! {e:?}");
       }
   }
}

Platform-specific behavior

The precision of SystemTime can depend on the underlying OS-specific time format. For example, on Windows the time is represented in 100 nanosecond intervals whereas Linux can represent nanosecond intervals.

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 (Realtime Clock)
WASI	clock_gettime (Realtime Clock)
Darwin	clock_gettime (Realtime Clock)
VXWorks	clock_gettime (Realtime Clock)
SOLID	SOLID_RTC_ReadTime
Windows	GetSystemTimePreciseAsFileTime / GetSystemTimeAsFileTime

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.

Implementations

impl SystemTime

pub const UNIX_EPOCH: SystemTime = UNIX_EPOCH

An anchor in time which can be used to create new SystemTime instances or learn about where in time a SystemTime lies.

This constant is defined to be “1970-01-01 00:00:00 UTC” on all systems with respect to the system clock. Using duration_since on an existing SystemTime instance can tell how far away from this point in time a measurement lies, and using UNIX_EPOCH + duration can be used to create a SystemTime instance to represent another fixed point in time.

duration_since(UNIX_EPOCH).unwrap().as_secs() returns the number of non-leap seconds since the start of 1970 UTC. This is a POSIX time_t (as a u64), and is the same time representation as used in many Internet protocols.

Examples

use std::time::SystemTime;

match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
    Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
    Err(_) => panic!("SystemTime before UNIX EPOCH!"),
}

pub const MAX: SystemTime

🔬This is a nightly-only experimental API. (time_systemtime_limits)

Represents the maximum value representable by SystemTime on this platform.

This value differs a lot between platforms, but it is always the case that any positive addition of a Duration, whose value is greater than or equal to the time precision of the operating system, to SystemTime::MAX will fail.

Examples

#![feature(time_systemtime_limits)]
use std::time::{Duration, SystemTime};

// Adding zero will change nothing.
assert_eq!(SystemTime::MAX.checked_add(Duration::ZERO), Some(SystemTime::MAX));

// But adding just one second will already fail ...
//
// Keep in mind that this in fact may succeed, if the Duration is
// smaller than the time precision of the operating system, which
// happens to be 1ns on most operating systems, with Windows being the
// notable exception by using 100ns, hence why this example uses 1s.
assert_eq!(SystemTime::MAX.checked_add(Duration::new(1, 0)), None);

// Utilize this for saturating arithmetic to improve error handling.
// In this case, we will use a certificate with a timestamp in the
// future as a practical example.
let configured_offset = Duration::from_secs(60 * 60 * 24);
let valid_after =
    SystemTime::now()
        .checked_add(configured_offset)
        .unwrap_or(SystemTime::MAX);

pub const MIN: SystemTime

🔬This is a nightly-only experimental API. (time_systemtime_limits)

Represents the minimum value representable by SystemTime on this platform.

This value differs a lot between platforms, but it is always the case that any positive subtraction of a Duration from, whose value is greater than or equal to the time precision of the operating system, to SystemTime::MIN will fail.

Depending on the platform, this may be either less than or equal to SystemTime::UNIX_EPOCH, depending on whether the operating system supports the representation of timestamps before the Unix epoch or not. However, it is always guaranteed that a SystemTime::UNIX_EPOCH fits between a SystemTime::MIN and SystemTime::MAX.

Examples

#![feature(time_systemtime_limits)]
use std::time::{Duration, SystemTime};

// Subtracting zero will change nothing.
assert_eq!(SystemTime::MIN.checked_sub(Duration::ZERO), Some(SystemTime::MIN));

// But subtracting just one second will already fail.
//
// Keep in mind that this in fact may succeed, if the Duration is
// smaller than the time precision of the operating system, which
// happens to be 1ns on most operating systems, with Windows being the
// notable exception by using 100ns, hence why this example uses 1s.
assert_eq!(SystemTime::MIN.checked_sub(Duration::new(1, 0)), None);

// Utilize this for saturating arithmetic to improve error handling.
// In this case, we will use a cache expiry as a practical example.
let configured_expiry = Duration::from_secs(60 * 3);
let expiry_threshold =
    SystemTime::now()
        .checked_sub(configured_expiry)
        .unwrap_or(SystemTime::MIN);

pub fn now() -> SystemTime

Returns the system time corresponding to “now”.

Examples

use std::time::SystemTime;

let sys_time = SystemTime::now();

pub fn duration_since( &self, earlier: SystemTime, ) -> Result<Duration, SystemTimeError>

Returns the amount of time elapsed from an earlier point in time.

This function may fail because measurements taken earlier are not guaranteed to always be before later measurements (due to anomalies such as the system clock being adjusted either forwards or backwards). Instant can be used to measure elapsed time without this risk of failure.

If successful, Ok(Duration) is returned where the duration represents the amount of time elapsed from the specified measurement to this one.

Returns an Err if earlier is later than self, and the error contains how far from self the time is.

Examples

use std::time::SystemTime;

let sys_time = SystemTime::now();
let new_sys_time = SystemTime::now();
let difference = new_sys_time.duration_since(sys_time)
    .expect("Clock may have gone backwards");
println!("{difference:?}");

pub fn elapsed(&self) -> Result<Duration, SystemTimeError>

Returns the difference from this system time to the current clock time.

This function may fail as the underlying system clock is susceptible to drift and updates (e.g., the system clock could go backwards), so this function might not always succeed. If successful, Ok(Duration) is returned where the duration represents the amount of time elapsed from this time measurement to the current time.

To measure elapsed time reliably, use Instant instead.

Returns an Err if self is later than the current system time, and the error contains how far from the current system time self is.

Examples

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

let sys_time = SystemTime::now();
let one_sec = Duration::from_secs(1);
sleep(one_sec);
assert!(sys_time.elapsed().unwrap() >= one_sec);

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

Returns Some(t) where t is the time self + duration if t can be represented as SystemTime (which means it’s inside the bounds of the underlying data structure), None otherwise.

In the case that the duration is smaller than the time precision of the operating system, Some(self) will be returned.

pub fn checked_sub(&self, duration: Duration) -> Option<SystemTime>

Returns Some(t) where t is the time self - duration if t can be represented as SystemTime (which means it’s inside the bounds of the underlying data structure), None otherwise.

In the case that the duration is smaller than the time precision of the operating system, Some(self) will be returned.

pub fn saturating_add(&self, duration: Duration) -> SystemTime

🔬This is a nightly-only experimental API. (time_saturating_systemtime)

Saturating SystemTime addition, computing self + duration, returning SystemTime::MAX if overflow occurred.

In the case that the duration is smaller than the time precision of the operating system, self will be returned.

pub fn saturating_sub(&self, duration: Duration) -> SystemTime

🔬This is a nightly-only experimental API. (time_saturating_systemtime)

Saturating SystemTime subtraction, computing self - duration, returning SystemTime::MIN if overflow occurred.

In the case that the duration is smaller than the time precision of the operating system, self will be returned.

pub fn saturating_duration_since(&self, earlier: SystemTime) -> Duration

🔬This is a nightly-only experimental API. (time_saturating_systemtime)

Saturating computation of time elapsed from an earlier point in time, returning Duration::ZERO in the case that earlier is later or equal to self.

Examples

#![feature(time_saturating_systemtime)]
use std::time::{Duration, SystemTime};

let now = SystemTime::now();
let prev = now.saturating_sub(Duration::new(1, 0));

// now - prev should return non-zero.
assert_eq!(now.saturating_duration_since(prev), Duration::new(1, 0));
assert!(now.duration_since(prev).is_ok());

// prev - now should return zero (and fail with the non-saturating).
assert_eq!(prev.saturating_duration_since(now), Duration::ZERO);
assert!(prev.duration_since(now).is_err());

// now - now should return zero (and work with the non-saturating).
assert_eq!(now.saturating_duration_since(now), Duration::ZERO);
assert!(now.duration_since(now).is_ok());

Trait Implementations

impl Add<Duration> for SystemTime

fn add(self, dur: Duration) -> SystemTime

Panics

This function may panic if the resulting point in time cannot be represented by the underlying data structure. See SystemTime::checked_add for a version without panic.

type Output = SystemTime

The resulting type after applying the + operator.

impl AddAssign<Duration> for SystemTime

fn add_assign(&mut self, other: Duration)

Performs the += operation.

impl BitSized<128> for SystemTime

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 SystemTime

fn clone(&self) -> SystemTime

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for SystemTime

impl Debug for SystemTime

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

Formats the value using the given formatter.

impl Eq for SystemTime

impl<'a> From<&'a Zoned> for SystemTime

fn from(time: &'a Zoned) -> SystemTime

Converts to this type from the input type.

impl From<Timestamp> for SystemTime

fn from(time: Timestamp) -> SystemTime

Converts to this type from the input type.

impl From<Zoned> for SystemTime

fn from(time: Zoned) -> SystemTime

Converts to this type from the input type.

impl Hash for SystemTime

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 SystemTime

fn cmp(&self, other: &SystemTime) -> 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 SystemTime

fn eq(&self, other: &SystemTime) -> 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 SystemTime

fn partial_cmp(&self, other: &SystemTime) -> 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 SystemTime

impl Sub<Duration> for SystemTime

type Output = SystemTime

The resulting type after applying the - operator.

fn sub(self, dur: Duration) -> SystemTime

Performs the - operation.

impl SubAssign<Duration> for SystemTime

fn sub_assign(&mut self, other: Duration)

Performs the -= operation.

impl TimePoint for SystemTime

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<SystemTime> for SystemTime

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() -> SystemTime

Returns the current time point in the chosen representation P.

fn time_point_value(point: SystemTime) -> 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 SystemTime

Unix-time u32 projection of SystemTime in seconds.

This gives a compact absolute projection with a range of about 136 years from the Unix epoch, so it remains valid until February 2106.

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 SystemTime

Unix-time u64 projection of SystemTime 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.

impl TryFrom<SystemTime> for Timestamp

type Error = Error

The type returned in the event of a conversion error.

fn try_from(system_time: SystemTime) -> Result<Timestamp, Error>

Performs the conversion.

impl TryFrom<SystemTime> for Zoned

type Error = Error

The type returned in the event of a conversion error.

fn try_from(system_time: SystemTime) -> Result<Zoned, Error>

Performs the conversion.

impl TryFrom<SystemTime> for TimeUnixI64

type Error = SystemTimeError

The type returned in the event of a conversion error.

fn try_from(time: SystemTime) -> Result<Self, Self::Error>

Performs the conversion.

impl TryFrom<SystemTime> for TimeUnixU32

type Error = TimeError

The type returned in the event of a conversion error.

fn try_from(time: SystemTime) -> Result<Self, Self::Error>

Performs the conversion.