pub struct Instant(_);
Expand description
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.
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());
}
RunOS-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 max_nanoseconds = u64::MAX / 1_000_000_000;
let duration = Duration::new(max_nanoseconds, 0);
println!("{:?}", now + duration);
RunUnderlying 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 (Monotonic Clock) |
Darwin | mach_absolute_time |
VXWorks | clock_gettime (Monotonic Clock) |
SOLID | get_tim |
WASI | __wasi_clock_time_get (Monotonic Clock) |
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 Instant
s 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
sourceimpl Instant
impl Instant
sourcepub fn duration_since(&self, earlier: Instant) -> Duration
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
Run1.39.0 · sourcepub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration>
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 Instant
s,
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
Run1.39.0 · sourcepub fn saturating_duration_since(&self, earlier: Instant) -> Duration
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
Runsourcepub fn elapsed(&self) -> Duration
pub fn elapsed(&self) -> Duration
Returns the amount of time elapsed since this instant was created.
Panics
Previous rust versions panicked when self was earlier than the current time. 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);
Run1.34.0 · sourcepub fn checked_add(&self, duration: Duration) -> Option<Instant>
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.
1.34.0 · sourcepub fn checked_sub(&self, duration: Duration) -> Option<Instant>
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
1.9.0 · sourceimpl AddAssign<Duration> for Instant
impl AddAssign<Duration> for Instant
sourcefn add_assign(&mut self, other: Duration)
fn add_assign(&mut self, other: Duration)
Performs the +=
operation. Read more
sourceimpl Ord for Instant
impl Ord for Instant
sourceimpl PartialOrd<Instant> for Instant
impl PartialOrd<Instant> for Instant
sourcefn partial_cmp(&self, other: &Instant) -> Option<Ordering>
fn partial_cmp(&self, other: &Instant) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
1.0.0 · sourcefn lt(&self, other: &Rhs) -> bool
fn lt(&self, other: &Rhs) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
sourceimpl Sub<Instant> for Instant
impl Sub<Instant> for Instant
sourcefn sub(self, other: Instant) -> Duration
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.
1.9.0 · sourceimpl SubAssign<Duration> for Instant
impl SubAssign<Duration> for Instant
sourcefn sub_assign(&mut self, other: Duration)
fn sub_assign(&mut self, other: Duration)
Performs the -=
operation. Read more
impl Copy for Instant
impl Eq for Instant
impl StructuralEq for Instant
impl StructuralPartialEq for Instant
Auto Trait Implementations
impl RefUnwindSafe for Instant
impl Send for Instant
impl Sync for Instant
impl Unpin for Instant
impl UnwindSafe for Instant
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
Uses borrowed data to replace owned data, usually by cloning. Read more