1 //! Temporal quantification.
6 //! use std::time::Duration;
8 //! let five_seconds = Duration::new(5, 0);
9 //! // both declarations are equivalent
10 //! assert_eq!(Duration::new(5, 0), Duration::from_secs(5));
13 #![stable(feature = "time", since = "1.3.0")]
16 use crate::error::Error;
18 use crate::ops::{Add, AddAssign, Sub, SubAssign};
20 use crate::sys_common::mutex::Mutex;
21 use crate::sys_common::FromInner;
23 #[stable(feature = "time", since = "1.3.0")]
24 pub use core::time::Duration;
26 /// A measurement of a monotonically nondecreasing clock.
27 /// Opaque and useful only with `Duration`.
29 /// Instants are always guaranteed to be no less than any previously measured
30 /// instant when created, and are often useful for tasks such as measuring
31 /// benchmarks or timing how long an operation takes.
33 /// Note, however, that instants are not guaranteed to be **steady**. In other
34 /// words, each tick of the underlying clock may not be the same length (e.g.
35 /// some seconds may be longer than others). An instant may jump forwards or
36 /// experience time dilation (slow down or speed up), but it will never go
39 /// Instants are opaque types that can only be compared to one another. There is
40 /// no method to get "the number of seconds" from an instant. Instead, it only
41 /// allows measuring the duration between two instants (or comparing two
44 /// The size of an `Instant` struct may vary depending on the target operating
50 /// use std::time::{Duration, Instant};
51 /// use std::thread::sleep;
54 /// let now = Instant::now();
56 /// // we sleep for 2 seconds
57 /// sleep(Duration::new(2, 0));
59 /// println!("{}", now.elapsed().as_secs());
63 /// # Underlying System calls
64 /// Currently, the following system calls are being used to get the current time using `now()`:
66 /// | Platform | System call |
67 /// |:---------:|:--------------------------------------------------------------------:|
68 /// | CloudABI | [clock_time_get (Monotonic Clock)] |
69 /// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
70 /// | UNIX | [clock_gettime (Monotonic Clock)] |
71 /// | Darwin | [mach_absolute_time] |
72 /// | VXWorks | [clock_gettime (Monotonic Clock)] |
73 /// | WASI | [__wasi_clock_time_get (Monotonic Clock)] |
74 /// | Windows | [QueryPerformanceCounter] |
76 /// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
77 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
78 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
79 /// [__wasi_clock_time_get (Monotonic Clock)]: https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-api.md#clock_time_get
80 /// [clock_gettime (Monotonic Clock)]: https://linux.die.net/man/3/clock_gettime
81 /// [mach_absolute_time]: https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/services/services.html
82 /// [clock_time_get (Monotonic Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
84 /// **Disclaimer:** These system calls might change over time.
86 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
87 #[stable(feature = "time2", since = "1.8.0")]
88 pub struct Instant(time::Instant);
90 /// A measurement of the system clock, useful for talking to
91 /// external entities like the file system or other processes.
93 /// Distinct from the [`Instant`] type, this time measurement **is not
94 /// monotonic**. This means that you can save a file to the file system, then
95 /// save another file to the file system, **and the second file has a
96 /// `SystemTime` measurement earlier than the first**. In other words, an
97 /// operation that happens after another operation in real time may have an
98 /// earlier `SystemTime`!
100 /// Consequently, comparing two `SystemTime` instances to learn about the
101 /// duration between them returns a [`Result`] instead of an infallible [`Duration`]
102 /// to indicate that this sort of time drift may happen and needs to be handled.
104 /// Although a `SystemTime` cannot be directly inspected, the [`UNIX_EPOCH`]
105 /// constant is provided in this module as an anchor in time to learn
106 /// information about a `SystemTime`. By calculating the duration from this
107 /// fixed point in time, a `SystemTime` can be converted to a human-readable time,
108 /// or perhaps some other string representation.
110 /// The size of a `SystemTime` struct may vary depending on the target operating
113 /// [`Instant`]: ../../std/time/struct.Instant.html
114 /// [`Result`]: ../../std/result/enum.Result.html
115 /// [`Duration`]: ../../std/time/struct.Duration.html
116 /// [`UNIX_EPOCH`]: ../../std/time/constant.UNIX_EPOCH.html
121 /// use std::time::{Duration, SystemTime};
122 /// use std::thread::sleep;
125 /// let now = SystemTime::now();
127 /// // we sleep for 2 seconds
128 /// sleep(Duration::new(2, 0));
129 /// match now.elapsed() {
132 /// println!("{}", elapsed.as_secs());
135 /// // an error occurred!
136 /// println!("Error: {:?}", e);
142 /// # Underlying System calls
143 /// Currently, the following system calls are being used to get the current time using `now()`:
145 /// | Platform | System call |
146 /// |:---------:|:--------------------------------------------------------------------:|
147 /// | CloudABI | [clock_time_get (Realtime Clock)] |
148 /// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
149 /// | UNIX | [clock_gettime (Realtime Clock)] |
150 /// | DARWIN | [gettimeofday] |
151 /// | VXWorks | [clock_gettime (Realtime Clock)] |
152 /// | WASI | [__wasi_clock_time_get (Realtime Clock)] |
153 /// | Windows | [GetSystemTimeAsFileTime] |
155 /// [clock_time_get (Realtime Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
156 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
157 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
158 /// [gettimeofday]: http://man7.org/linux/man-pages/man2/gettimeofday.2.html
159 /// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
160 /// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-api.md#clock_time_get
161 /// [GetSystemTimeAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime
163 /// **Disclaimer:** These system calls might change over time.
165 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
166 #[stable(feature = "time2", since = "1.8.0")]
167 pub struct SystemTime(time::SystemTime);
169 /// An error returned from the `duration_since` and `elapsed` methods on
170 /// `SystemTime`, used to learn how far in the opposite direction a system time
176 /// use std::thread::sleep;
177 /// use std::time::{Duration, SystemTime};
179 /// let sys_time = SystemTime::now();
180 /// sleep(Duration::from_secs(1));
181 /// let new_sys_time = SystemTime::now();
182 /// match sys_time.duration_since(new_sys_time) {
184 /// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
187 #[derive(Clone, Debug)]
188 #[stable(feature = "time2", since = "1.8.0")]
189 pub struct SystemTimeError(Duration);
192 /// Returns an instant corresponding to "now".
197 /// use std::time::Instant;
199 /// let now = Instant::now();
201 #[stable(feature = "time2", since = "1.8.0")]
202 pub fn now() -> Instant {
203 let os_now = time::Instant::now();
205 // And here we come upon a sad state of affairs. The whole point of
206 // `Instant` is that it's monotonically increasing. We've found in the
207 // wild, however, that it's not actually monotonically increasing for
208 // one reason or another. These appear to be OS and hardware level bugs,
209 // and there's not really a whole lot we can do about them. Here's a
210 // taste of what we've found:
212 // * #48514 - OpenBSD, x86_64
213 // * #49281 - linux arm64 and s390x
214 // * #51648 - windows, x86
215 // * #56560 - windows, x86_64, AWS
216 // * #56612 - windows, x86, vm (?)
217 // * #56940 - linux, arm64
218 // * https://bugzilla.mozilla.org/show_bug.cgi?id=1487778 - a similar
221 // It seems that this just happens a lot in the wild.
222 // We're seeing panics across various platforms where consecutive calls
223 // to `Instant::now`, such as via the `elapsed` function, are panicking
224 // as they're going backwards. Placed here is a last-ditch effort to try
225 // to fix things up. We keep a global "latest now" instance which is
226 // returned instead of what the OS says if the OS goes backwards.
228 // To hopefully mitigate the impact of this, a few platforms are
229 // whitelisted as "these at least haven't gone backwards yet".
230 if time::Instant::actually_monotonic() {
231 return Instant(os_now);
234 static LOCK: Mutex = Mutex::new();
235 static mut LAST_NOW: time::Instant = time::Instant::zero();
237 let _lock = LOCK.lock();
238 let now = cmp::max(LAST_NOW, os_now);
244 /// Returns the amount of time elapsed from another instant to this one.
248 /// This function will panic if `earlier` is later than `self`.
253 /// use std::time::{Duration, Instant};
254 /// use std::thread::sleep;
256 /// let now = Instant::now();
257 /// sleep(Duration::new(1, 0));
258 /// let new_now = Instant::now();
259 /// println!("{:?}", new_now.duration_since(now));
261 #[stable(feature = "time2", since = "1.8.0")]
262 pub fn duration_since(&self, earlier: Instant) -> Duration {
263 self.0.checked_sub_instant(&earlier.0).expect("supplied instant is later than self")
266 /// Returns the amount of time elapsed from another instant to this one,
267 /// or None if that instant is later than this one.
272 /// use std::time::{Duration, Instant};
273 /// use std::thread::sleep;
275 /// let now = Instant::now();
276 /// sleep(Duration::new(1, 0));
277 /// let new_now = Instant::now();
278 /// println!("{:?}", new_now.checked_duration_since(now));
279 /// println!("{:?}", now.checked_duration_since(new_now)); // None
281 #[stable(feature = "checked_duration_since", since = "1.39.0")]
282 pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
283 self.0.checked_sub_instant(&earlier.0)
286 /// Returns the amount of time elapsed from another instant to this one,
287 /// or zero duration if that instant is earlier than this one.
292 /// use std::time::{Duration, Instant};
293 /// use std::thread::sleep;
295 /// let now = Instant::now();
296 /// sleep(Duration::new(1, 0));
297 /// let new_now = Instant::now();
298 /// println!("{:?}", new_now.saturating_duration_since(now));
299 /// println!("{:?}", now.saturating_duration_since(new_now)); // 0ns
301 #[stable(feature = "checked_duration_since", since = "1.39.0")]
302 pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
303 self.checked_duration_since(earlier).unwrap_or(Duration::new(0, 0))
306 /// Returns the amount of time elapsed since this instant was created.
310 /// This function may panic if the current time is earlier than this
311 /// instant, which is something that can happen if an `Instant` is
312 /// produced synthetically.
317 /// use std::thread::sleep;
318 /// use std::time::{Duration, Instant};
320 /// let instant = Instant::now();
321 /// let three_secs = Duration::from_secs(3);
322 /// sleep(three_secs);
323 /// assert!(instant.elapsed() >= three_secs);
325 #[stable(feature = "time2", since = "1.8.0")]
326 pub fn elapsed(&self) -> Duration {
327 Instant::now() - *self
330 /// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be represented as
331 /// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
333 #[stable(feature = "time_checked_add", since = "1.34.0")]
334 pub fn checked_add(&self, duration: Duration) -> Option<Instant> {
335 self.0.checked_add_duration(&duration).map(Instant)
338 /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
339 /// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
341 #[stable(feature = "time_checked_add", since = "1.34.0")]
342 pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
343 self.0.checked_sub_duration(&duration).map(Instant)
347 #[stable(feature = "time2", since = "1.8.0")]
348 impl Add<Duration> for Instant {
349 type Output = Instant;
353 /// This function may panic if the resulting point in time cannot be represented by the
354 /// underlying data structure. See [`checked_add`] for a version without panic.
356 /// [`checked_add`]: ../../std/time/struct.Instant.html#method.checked_add
357 fn add(self, other: Duration) -> Instant {
358 self.checked_add(other).expect("overflow when adding duration to instant")
362 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
363 impl AddAssign<Duration> for Instant {
364 fn add_assign(&mut self, other: Duration) {
365 *self = *self + other;
369 #[stable(feature = "time2", since = "1.8.0")]
370 impl Sub<Duration> for Instant {
371 type Output = Instant;
373 fn sub(self, other: Duration) -> Instant {
374 self.checked_sub(other).expect("overflow when subtracting duration from instant")
378 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
379 impl SubAssign<Duration> for Instant {
380 fn sub_assign(&mut self, other: Duration) {
381 *self = *self - other;
385 #[stable(feature = "time2", since = "1.8.0")]
386 impl Sub<Instant> for Instant {
387 type Output = Duration;
389 fn sub(self, other: Instant) -> Duration {
390 self.duration_since(other)
394 #[stable(feature = "time2", since = "1.8.0")]
395 impl fmt::Debug for Instant {
396 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
402 /// An anchor in time which can be used to create new `SystemTime` instances or
403 /// learn about where in time a `SystemTime` lies.
405 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
406 /// respect to the system clock. Using `duration_since` on an existing
407 /// `SystemTime` instance can tell how far away from this point in time a
408 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
409 /// `SystemTime` instance to represent another fixed point in time.
414 /// use std::time::SystemTime;
416 /// match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
417 /// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
418 /// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
421 #[stable(feature = "assoc_unix_epoch", since = "1.28.0")]
422 pub const UNIX_EPOCH: SystemTime = UNIX_EPOCH;
424 /// Returns the system time corresponding to "now".
429 /// use std::time::SystemTime;
431 /// let sys_time = SystemTime::now();
433 #[stable(feature = "time2", since = "1.8.0")]
434 pub fn now() -> SystemTime {
435 SystemTime(time::SystemTime::now())
438 /// Returns the amount of time elapsed from an earlier point in time.
440 /// This function may fail because measurements taken earlier are not
441 /// guaranteed to always be before later measurements (due to anomalies such
442 /// as the system clock being adjusted either forwards or backwards).
443 /// [`Instant`] can be used to measure elapsed time without this risk of failure.
445 /// If successful, [`Ok`]`(`[`Duration`]`)` is returned where the duration represents
446 /// the amount of time elapsed from the specified measurement to this one.
448 /// Returns an [`Err`] if `earlier` is later than `self`, and the error
449 /// contains how far from `self` the time is.
451 /// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
452 /// [`Duration`]: ../../std/time/struct.Duration.html
453 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
454 /// [`Instant`]: ../../std/time/struct.Instant.html
459 /// use std::time::SystemTime;
461 /// let sys_time = SystemTime::now();
462 /// let difference = sys_time.duration_since(sys_time)
463 /// .expect("Clock may have gone backwards");
464 /// println!("{:?}", difference);
466 #[stable(feature = "time2", since = "1.8.0")]
467 pub fn duration_since(&self, earlier: SystemTime) -> Result<Duration, SystemTimeError> {
468 self.0.sub_time(&earlier.0).map_err(SystemTimeError)
471 /// Returns the difference between the clock time when this
472 /// system time was created, and the current clock time.
474 /// This function may fail as the underlying system clock is susceptible to
475 /// drift and updates (e.g., the system clock could go backwards), so this
476 /// function may not always succeed. If successful, [`Ok`]`(`[`Duration`]`)` is
477 /// returned where the duration represents the amount of time elapsed from
478 /// this time measurement to the current time.
480 /// To measure elapsed time reliably, use [`Instant`] instead.
482 /// Returns an [`Err`] if `self` is later than the current system time, and
483 /// the error contains how far from the current system time `self` is.
485 /// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
486 /// [`Duration`]: ../../std/time/struct.Duration.html
487 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
488 /// [`Instant`]: ../../std/time/struct.Instant.html
493 /// use std::thread::sleep;
494 /// use std::time::{Duration, SystemTime};
496 /// let sys_time = SystemTime::now();
497 /// let one_sec = Duration::from_secs(1);
499 /// assert!(sys_time.elapsed().unwrap() >= one_sec);
501 #[stable(feature = "time2", since = "1.8.0")]
502 pub fn elapsed(&self) -> Result<Duration, SystemTimeError> {
503 SystemTime::now().duration_since(*self)
506 /// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be represented as
507 /// `SystemTime` (which means it's inside the bounds of the underlying data structure), `None`
509 #[stable(feature = "time_checked_add", since = "1.34.0")]
510 pub fn checked_add(&self, duration: Duration) -> Option<SystemTime> {
511 self.0.checked_add_duration(&duration).map(SystemTime)
514 /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
515 /// `SystemTime` (which means it's inside the bounds of the underlying data structure), `None`
517 #[stable(feature = "time_checked_add", since = "1.34.0")]
518 pub fn checked_sub(&self, duration: Duration) -> Option<SystemTime> {
519 self.0.checked_sub_duration(&duration).map(SystemTime)
523 #[stable(feature = "time2", since = "1.8.0")]
524 impl Add<Duration> for SystemTime {
525 type Output = SystemTime;
529 /// This function may panic if the resulting point in time cannot be represented by the
530 /// underlying data structure. See [`checked_add`] for a version without panic.
532 /// [`checked_add`]: ../../std/time/struct.SystemTime.html#method.checked_add
533 fn add(self, dur: Duration) -> SystemTime {
534 self.checked_add(dur).expect("overflow when adding duration to instant")
538 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
539 impl AddAssign<Duration> for SystemTime {
540 fn add_assign(&mut self, other: Duration) {
541 *self = *self + other;
545 #[stable(feature = "time2", since = "1.8.0")]
546 impl Sub<Duration> for SystemTime {
547 type Output = SystemTime;
549 fn sub(self, dur: Duration) -> SystemTime {
550 self.checked_sub(dur).expect("overflow when subtracting duration from instant")
554 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
555 impl SubAssign<Duration> for SystemTime {
556 fn sub_assign(&mut self, other: Duration) {
557 *self = *self - other;
561 #[stable(feature = "time2", since = "1.8.0")]
562 impl fmt::Debug for SystemTime {
563 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
568 /// An anchor in time which can be used to create new `SystemTime` instances or
569 /// learn about where in time a `SystemTime` lies.
571 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
572 /// respect to the system clock. Using `duration_since` on an existing
573 /// [`SystemTime`] instance can tell how far away from this point in time a
574 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
575 /// [`SystemTime`] instance to represent another fixed point in time.
577 /// [`SystemTime`]: ../../std/time/struct.SystemTime.html
582 /// use std::time::{SystemTime, UNIX_EPOCH};
584 /// match SystemTime::now().duration_since(UNIX_EPOCH) {
585 /// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
586 /// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
589 #[stable(feature = "time2", since = "1.8.0")]
590 pub const UNIX_EPOCH: SystemTime = SystemTime(time::UNIX_EPOCH);
592 impl SystemTimeError {
593 /// Returns the positive duration which represents how far forward the
594 /// second system time was from the first.
596 /// A `SystemTimeError` is returned from the [`duration_since`] and [`elapsed`]
597 /// methods of [`SystemTime`] whenever the second system time represents a point later
598 /// in time than the `self` of the method call.
600 /// [`duration_since`]: ../../std/time/struct.SystemTime.html#method.duration_since
601 /// [`elapsed`]: ../../std/time/struct.SystemTime.html#method.elapsed
602 /// [`SystemTime`]: ../../std/time/struct.SystemTime.html
607 /// use std::thread::sleep;
608 /// use std::time::{Duration, SystemTime};
610 /// let sys_time = SystemTime::now();
611 /// sleep(Duration::from_secs(1));
612 /// let new_sys_time = SystemTime::now();
613 /// match sys_time.duration_since(new_sys_time) {
615 /// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
618 #[stable(feature = "time2", since = "1.8.0")]
619 pub fn duration(&self) -> Duration {
624 #[stable(feature = "time2", since = "1.8.0")]
625 impl Error for SystemTimeError {
627 fn description(&self) -> &str {
628 "other time was not earlier than self"
632 #[stable(feature = "time2", since = "1.8.0")]
633 impl fmt::Display for SystemTimeError {
634 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
635 write!(f, "second time provided was later than self")
639 impl FromInner<time::SystemTime> for SystemTime {
640 fn from_inner(time: time::SystemTime) -> SystemTime {
647 use super::{Duration, Instant, SystemTime, UNIX_EPOCH};
649 macro_rules! assert_almost_eq {
650 ($a:expr, $b:expr) => {{
651 let (a, b) = ($a, $b);
653 let (a, b) = if a > b { (a, b) } else { (b, a) };
654 assert!(a - Duration::new(0, 1000) <= b, "{:?} is not almost equal to {:?}", a, b);
660 fn instant_monotonic() {
661 let a = Instant::now();
662 let b = Instant::now();
667 fn instant_elapsed() {
668 let a = Instant::now();
674 let a = Instant::now();
675 let b = Instant::now();
676 println!("a: {:?}", a);
677 println!("b: {:?}", b);
678 let dur = b.duration_since(a);
679 println!("dur: {:?}", dur);
680 assert_almost_eq!(b - dur, a);
681 assert_almost_eq!(a + dur, b);
683 let second = Duration::new(1, 0);
684 assert_almost_eq!(a - second + second, a);
685 assert_almost_eq!(a.checked_sub(second).unwrap().checked_add(second).unwrap(), a);
687 // checked_add_duration will not panic on overflow
688 let mut maybe_t = Some(Instant::now());
689 let max_duration = Duration::from_secs(u64::max_value());
690 // in case `Instant` can store `>= now + max_duration`.
692 maybe_t = maybe_t.and_then(|t| t.checked_add(max_duration));
694 assert_eq!(maybe_t, None);
696 // checked_add_duration calculates the right time and will work for another year
697 let year = Duration::from_secs(60 * 60 * 24 * 365);
698 assert_eq!(a + year, a.checked_add(year).unwrap());
702 fn instant_math_is_associative() {
703 let now = Instant::now();
704 let offset = Duration::from_millis(5);
705 // Changing the order of instant math shouldn't change the results,
706 // especially when the expression reduces to X + identity.
707 assert_eq!((now + offset) - now, (now - now) + offset);
712 fn instant_duration_since_panic() {
713 let a = Instant::now();
714 (a - Duration::new(1, 0)).duration_since(a);
718 fn instant_checked_duration_since_nopanic() {
719 let now = Instant::now();
720 let earlier = now - Duration::new(1, 0);
721 let later = now + Duration::new(1, 0);
722 assert_eq!(earlier.checked_duration_since(now), None);
723 assert_eq!(later.checked_duration_since(now), Some(Duration::new(1, 0)));
724 assert_eq!(now.checked_duration_since(now), Some(Duration::new(0, 0)));
728 fn instant_saturating_duration_since_nopanic() {
729 let a = Instant::now();
730 let ret = (a - Duration::new(1, 0)).saturating_duration_since(a);
731 assert_eq!(ret, Duration::new(0, 0));
735 fn system_time_math() {
736 let a = SystemTime::now();
737 let b = SystemTime::now();
738 match b.duration_since(a) {
739 Ok(dur) if dur == Duration::new(0, 0) => {
740 assert_almost_eq!(a, b);
744 assert_almost_eq!(b - dur, a);
745 assert_almost_eq!(a + dur, b);
748 let dur = dur.duration();
750 assert_almost_eq!(b + dur, a);
751 assert_almost_eq!(a - dur, b);
755 let second = Duration::new(1, 0);
756 assert_almost_eq!(a.duration_since(a - second).unwrap(), second);
757 assert_almost_eq!(a.duration_since(a + second).unwrap_err().duration(), second);
759 assert_almost_eq!(a - second + second, a);
760 assert_almost_eq!(a.checked_sub(second).unwrap().checked_add(second).unwrap(), a);
762 let one_second_from_epoch = UNIX_EPOCH + Duration::new(1, 0);
763 let one_second_from_epoch2 =
764 UNIX_EPOCH + Duration::new(0, 500_000_000) + Duration::new(0, 500_000_000);
765 assert_eq!(one_second_from_epoch, one_second_from_epoch2);
767 // checked_add_duration will not panic on overflow
768 let mut maybe_t = Some(SystemTime::UNIX_EPOCH);
769 let max_duration = Duration::from_secs(u64::max_value());
770 // in case `SystemTime` can store `>= UNIX_EPOCH + max_duration`.
772 maybe_t = maybe_t.and_then(|t| t.checked_add(max_duration));
774 assert_eq!(maybe_t, None);
776 // checked_add_duration calculates the right time and will work for another year
777 let year = Duration::from_secs(60 * 60 * 24 * 365);
778 assert_eq!(a + year, a.checked_add(year).unwrap());
782 fn system_time_elapsed() {
783 let a = SystemTime::now();
789 let ts = SystemTime::now();
790 let a = ts.duration_since(UNIX_EPOCH + Duration::new(1, 0)).unwrap();
791 let b = ts.duration_since(UNIX_EPOCH).unwrap();
793 assert_eq!(b - a, Duration::new(1, 0));
795 let thirty_years = Duration::new(1, 0) * 60 * 60 * 24 * 365 * 30;
797 // Right now for CI this test is run in an emulator, and apparently the
798 // aarch64 emulator's sense of time is that we're still living in the
801 // Otherwise let's assume that we're all running computers later than
803 if !cfg!(target_arch = "aarch64") {
804 assert!(a > thirty_years);
807 // let's assume that we're all running computers earlier than 2090.
808 // Should give us ~70 years to fix this!
809 let hundred_twenty_years = thirty_years * 4;
810 assert!(a < hundred_twenty_years);