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 /// # OS-specific behaviors
65 /// An `Instant` is a wrapper around system-specific types and it may behave
66 /// differently depending on the underlying operating system. For example,
67 /// the following snippet is fine on Linux but panics on macOS:
70 /// use std::time::{Instant, Duration};
72 /// let now = Instant::now();
73 /// let max_nanoseconds = u64::MAX / 1_000_000_000;
74 /// let duration = Duration::new(max_nanoseconds, 0);
75 /// println!("{:?}", now + duration);
78 /// # Underlying System calls
79 /// Currently, the following system calls are being used to get the current time using `now()`:
81 /// | Platform | System call |
82 /// |:---------:|:--------------------------------------------------------------------:|
83 /// | CloudABI | [clock_time_get (Monotonic Clock)] |
84 /// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
85 /// | UNIX | [clock_gettime (Monotonic Clock)] |
86 /// | Darwin | [mach_absolute_time] |
87 /// | VXWorks | [clock_gettime (Monotonic Clock)] |
88 /// | WASI | [__wasi_clock_time_get (Monotonic Clock)] |
89 /// | Windows | [QueryPerformanceCounter] |
91 /// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
92 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
93 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
94 /// [__wasi_clock_time_get (Monotonic Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
95 /// [clock_gettime (Monotonic Clock)]: https://linux.die.net/man/3/clock_gettime
96 /// [mach_absolute_time]: https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/services/services.html
97 /// [clock_time_get (Monotonic Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
99 /// **Disclaimer:** These system calls might change over time.
100 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
101 #[stable(feature = "time2", since = "1.8.0")]
102 pub struct Instant(time::Instant);
104 /// A measurement of the system clock, useful for talking to
105 /// external entities like the file system or other processes.
107 /// Distinct from the [`Instant`] type, this time measurement **is not
108 /// monotonic**. This means that you can save a file to the file system, then
109 /// save another file to the file system, **and the second file has a
110 /// `SystemTime` measurement earlier than the first**. In other words, an
111 /// operation that happens after another operation in real time may have an
112 /// earlier `SystemTime`!
114 /// Consequently, comparing two `SystemTime` instances to learn about the
115 /// duration between them returns a [`Result`] instead of an infallible [`Duration`]
116 /// to indicate that this sort of time drift may happen and needs to be handled.
118 /// Although a `SystemTime` cannot be directly inspected, the [`UNIX_EPOCH`]
119 /// constant is provided in this module as an anchor in time to learn
120 /// information about a `SystemTime`. By calculating the duration from this
121 /// fixed point in time, a `SystemTime` can be converted to a human-readable time,
122 /// or perhaps some other string representation.
124 /// The size of a `SystemTime` struct may vary depending on the target operating
130 /// use std::time::{Duration, SystemTime};
131 /// use std::thread::sleep;
134 /// let now = SystemTime::now();
136 /// // we sleep for 2 seconds
137 /// sleep(Duration::new(2, 0));
138 /// match now.elapsed() {
141 /// println!("{}", elapsed.as_secs());
144 /// // an error occurred!
145 /// println!("Error: {:?}", e);
151 /// # Underlying System calls
152 /// Currently, the following system calls are being used to get the current time using `now()`:
154 /// | Platform | System call |
155 /// |:---------:|:--------------------------------------------------------------------:|
156 /// | CloudABI | [clock_time_get (Realtime Clock)] |
157 /// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
158 /// | UNIX | [clock_gettime (Realtime Clock)] |
159 /// | DARWIN | [gettimeofday] |
160 /// | VXWorks | [clock_gettime (Realtime Clock)] |
161 /// | WASI | [__wasi_clock_time_get (Realtime Clock)] |
162 /// | Windows | [GetSystemTimeAsFileTime] |
164 /// [clock_time_get (Realtime Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
165 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
166 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
167 /// [gettimeofday]: http://man7.org/linux/man-pages/man2/gettimeofday.2.html
168 /// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
169 /// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
170 /// [GetSystemTimeAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime
172 /// **Disclaimer:** These system calls might change over time.
173 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
174 #[stable(feature = "time2", since = "1.8.0")]
175 pub struct SystemTime(time::SystemTime);
177 /// An error returned from the `duration_since` and `elapsed` methods on
178 /// `SystemTime`, used to learn how far in the opposite direction a system time
184 /// use std::thread::sleep;
185 /// use std::time::{Duration, SystemTime};
187 /// let sys_time = SystemTime::now();
188 /// sleep(Duration::from_secs(1));
189 /// let new_sys_time = SystemTime::now();
190 /// match sys_time.duration_since(new_sys_time) {
192 /// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
195 #[derive(Clone, Debug)]
196 #[stable(feature = "time2", since = "1.8.0")]
197 pub struct SystemTimeError(Duration);
200 /// Returns an instant corresponding to "now".
205 /// use std::time::Instant;
207 /// let now = Instant::now();
209 #[stable(feature = "time2", since = "1.8.0")]
210 pub fn now() -> Instant {
211 let os_now = time::Instant::now();
213 // And here we come upon a sad state of affairs. The whole point of
214 // `Instant` is that it's monotonically increasing. We've found in the
215 // wild, however, that it's not actually monotonically increasing for
216 // one reason or another. These appear to be OS and hardware level bugs,
217 // and there's not really a whole lot we can do about them. Here's a
218 // taste of what we've found:
220 // * #48514 - OpenBSD, x86_64
221 // * #49281 - linux arm64 and s390x
222 // * #51648 - windows, x86
223 // * #56560 - windows, x86_64, AWS
224 // * #56612 - windows, x86, vm (?)
225 // * #56940 - linux, arm64
226 // * https://bugzilla.mozilla.org/show_bug.cgi?id=1487778 - a similar
229 // It seems that this just happens a lot in the wild.
230 // We're seeing panics across various platforms where consecutive calls
231 // to `Instant::now`, such as via the `elapsed` function, are panicking
232 // as they're going backwards. Placed here is a last-ditch effort to try
233 // to fix things up. We keep a global "latest now" instance which is
234 // returned instead of what the OS says if the OS goes backwards.
236 // To hopefully mitigate the impact of this, a few platforms are
237 // excluded as "these at least haven't gone backwards yet".
238 if time::Instant::actually_monotonic() {
239 return Instant(os_now);
242 static LOCK: Mutex = Mutex::new();
243 static mut LAST_NOW: time::Instant = time::Instant::zero();
245 let _lock = LOCK.lock();
246 let now = cmp::max(LAST_NOW, os_now);
252 /// Returns the amount of time elapsed from another instant to this one.
256 /// This function will panic if `earlier` is later than `self`.
261 /// use std::time::{Duration, Instant};
262 /// use std::thread::sleep;
264 /// let now = Instant::now();
265 /// sleep(Duration::new(1, 0));
266 /// let new_now = Instant::now();
267 /// println!("{:?}", new_now.duration_since(now));
269 #[stable(feature = "time2", since = "1.8.0")]
270 pub fn duration_since(&self, earlier: Instant) -> Duration {
271 self.0.checked_sub_instant(&earlier.0).expect("supplied instant is later than self")
274 /// Returns the amount of time elapsed from another instant to this one,
275 /// or None if that instant is later than this one.
280 /// use std::time::{Duration, Instant};
281 /// use std::thread::sleep;
283 /// let now = Instant::now();
284 /// sleep(Duration::new(1, 0));
285 /// let new_now = Instant::now();
286 /// println!("{:?}", new_now.checked_duration_since(now));
287 /// println!("{:?}", now.checked_duration_since(new_now)); // None
289 #[stable(feature = "checked_duration_since", since = "1.39.0")]
290 pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
291 self.0.checked_sub_instant(&earlier.0)
294 /// Returns the amount of time elapsed from another instant to this one,
295 /// or zero duration if that instant is later than this one.
300 /// use std::time::{Duration, Instant};
301 /// use std::thread::sleep;
303 /// let now = Instant::now();
304 /// sleep(Duration::new(1, 0));
305 /// let new_now = Instant::now();
306 /// println!("{:?}", new_now.saturating_duration_since(now));
307 /// println!("{:?}", now.saturating_duration_since(new_now)); // 0ns
309 #[stable(feature = "checked_duration_since", since = "1.39.0")]
310 pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
311 self.checked_duration_since(earlier).unwrap_or(Duration::new(0, 0))
314 /// Returns the amount of time elapsed since this instant was created.
318 /// This function may panic if the current time is earlier than this
319 /// instant, which is something that can happen if an `Instant` is
320 /// produced synthetically.
325 /// use std::thread::sleep;
326 /// use std::time::{Duration, Instant};
328 /// let instant = Instant::now();
329 /// let three_secs = Duration::from_secs(3);
330 /// sleep(three_secs);
331 /// assert!(instant.elapsed() >= three_secs);
333 #[stable(feature = "time2", since = "1.8.0")]
334 pub fn elapsed(&self) -> Duration {
335 Instant::now() - *self
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_add(&self, duration: Duration) -> Option<Instant> {
343 self.0.checked_add_duration(&duration).map(Instant)
346 /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
347 /// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
349 #[stable(feature = "time_checked_add", since = "1.34.0")]
350 pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
351 self.0.checked_sub_duration(&duration).map(Instant)
355 #[stable(feature = "time2", since = "1.8.0")]
356 impl Add<Duration> for Instant {
357 type Output = Instant;
361 /// This function may panic if the resulting point in time cannot be represented by the
362 /// underlying data structure. See [`Instant::checked_add`] for a version without panic.
363 fn add(self, other: Duration) -> Instant {
364 self.checked_add(other).expect("overflow when adding duration to instant")
368 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
369 impl AddAssign<Duration> for Instant {
370 fn add_assign(&mut self, other: Duration) {
371 *self = *self + other;
375 #[stable(feature = "time2", since = "1.8.0")]
376 impl Sub<Duration> for Instant {
377 type Output = Instant;
379 fn sub(self, other: Duration) -> Instant {
380 self.checked_sub(other).expect("overflow when subtracting duration from instant")
384 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
385 impl SubAssign<Duration> for Instant {
386 fn sub_assign(&mut self, other: Duration) {
387 *self = *self - other;
391 #[stable(feature = "time2", since = "1.8.0")]
392 impl Sub<Instant> for Instant {
393 type Output = Duration;
395 fn sub(self, other: Instant) -> Duration {
396 self.duration_since(other)
400 #[stable(feature = "time2", since = "1.8.0")]
401 impl fmt::Debug for Instant {
402 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
408 /// An anchor in time which can be used to create new `SystemTime` instances or
409 /// learn about where in time a `SystemTime` lies.
411 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
412 /// respect to the system clock. Using `duration_since` on an existing
413 /// `SystemTime` instance can tell how far away from this point in time a
414 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
415 /// `SystemTime` instance to represent another fixed point in time.
420 /// use std::time::SystemTime;
422 /// match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
423 /// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
424 /// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
427 #[stable(feature = "assoc_unix_epoch", since = "1.28.0")]
428 pub const UNIX_EPOCH: SystemTime = UNIX_EPOCH;
430 /// Returns the system time corresponding to "now".
435 /// use std::time::SystemTime;
437 /// let sys_time = SystemTime::now();
439 #[stable(feature = "time2", since = "1.8.0")]
440 pub fn now() -> SystemTime {
441 SystemTime(time::SystemTime::now())
444 /// Returns the amount of time elapsed from an earlier point in time.
446 /// This function may fail because measurements taken earlier are not
447 /// guaranteed to always be before later measurements (due to anomalies such
448 /// as the system clock being adjusted either forwards or backwards).
449 /// [`Instant`] can be used to measure elapsed time without this risk of failure.
451 /// If successful, [`Ok`]`(`[`Duration`]`)` is returned where the duration represents
452 /// the amount of time elapsed from the specified measurement to this one.
454 /// Returns an [`Err`] if `earlier` is later than `self`, and the error
455 /// contains how far from `self` the time is.
460 /// use std::time::SystemTime;
462 /// let sys_time = SystemTime::now();
463 /// let difference = sys_time.duration_since(sys_time)
464 /// .expect("Clock may have gone backwards");
465 /// println!("{:?}", difference);
467 #[stable(feature = "time2", since = "1.8.0")]
468 pub fn duration_since(&self, earlier: SystemTime) -> Result<Duration, SystemTimeError> {
469 self.0.sub_time(&earlier.0).map_err(SystemTimeError)
472 /// Returns the difference between the clock time when this
473 /// system time was created, and the current clock time.
475 /// This function may fail as the underlying system clock is susceptible to
476 /// drift and updates (e.g., the system clock could go backwards), so this
477 /// function may not always succeed. If successful, [`Ok`]`(`[`Duration`]`)` is
478 /// returned where the duration represents the amount of time elapsed from
479 /// this time measurement to the current time.
481 /// To measure elapsed time reliably, use [`Instant`] instead.
483 /// Returns an [`Err`] if `self` is later than the current system time, and
484 /// the error contains how far from the current system time `self` is.
489 /// use std::thread::sleep;
490 /// use std::time::{Duration, SystemTime};
492 /// let sys_time = SystemTime::now();
493 /// let one_sec = Duration::from_secs(1);
495 /// assert!(sys_time.elapsed().unwrap() >= one_sec);
497 #[stable(feature = "time2", since = "1.8.0")]
498 pub fn elapsed(&self) -> Result<Duration, SystemTimeError> {
499 SystemTime::now().duration_since(*self)
502 /// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be represented as
503 /// `SystemTime` (which means it's inside the bounds of the underlying data structure), `None`
505 #[stable(feature = "time_checked_add", since = "1.34.0")]
506 pub fn checked_add(&self, duration: Duration) -> Option<SystemTime> {
507 self.0.checked_add_duration(&duration).map(SystemTime)
510 /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
511 /// `SystemTime` (which means it's inside the bounds of the underlying data structure), `None`
513 #[stable(feature = "time_checked_add", since = "1.34.0")]
514 pub fn checked_sub(&self, duration: Duration) -> Option<SystemTime> {
515 self.0.checked_sub_duration(&duration).map(SystemTime)
519 #[stable(feature = "time2", since = "1.8.0")]
520 impl Add<Duration> for SystemTime {
521 type Output = SystemTime;
525 /// This function may panic if the resulting point in time cannot be represented by the
526 /// underlying data structure. See [`SystemTime::checked_add`] for a version without panic.
527 fn add(self, dur: Duration) -> SystemTime {
528 self.checked_add(dur).expect("overflow when adding duration to instant")
532 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
533 impl AddAssign<Duration> for SystemTime {
534 fn add_assign(&mut self, other: Duration) {
535 *self = *self + other;
539 #[stable(feature = "time2", since = "1.8.0")]
540 impl Sub<Duration> for SystemTime {
541 type Output = SystemTime;
543 fn sub(self, dur: Duration) -> SystemTime {
544 self.checked_sub(dur).expect("overflow when subtracting duration from instant")
548 #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
549 impl SubAssign<Duration> for SystemTime {
550 fn sub_assign(&mut self, other: Duration) {
551 *self = *self - other;
555 #[stable(feature = "time2", since = "1.8.0")]
556 impl fmt::Debug for SystemTime {
557 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
562 /// An anchor in time which can be used to create new `SystemTime` instances or
563 /// learn about where in time a `SystemTime` lies.
565 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
566 /// respect to the system clock. Using `duration_since` on an existing
567 /// [`SystemTime`] instance can tell how far away from this point in time a
568 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
569 /// [`SystemTime`] instance to represent another fixed point in time.
574 /// use std::time::{SystemTime, UNIX_EPOCH};
576 /// match SystemTime::now().duration_since(UNIX_EPOCH) {
577 /// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
578 /// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
581 #[stable(feature = "time2", since = "1.8.0")]
582 pub const UNIX_EPOCH: SystemTime = SystemTime(time::UNIX_EPOCH);
584 impl SystemTimeError {
585 /// Returns the positive duration which represents how far forward the
586 /// second system time was from the first.
588 /// A `SystemTimeError` is returned from the [`SystemTime::duration_since`]
589 /// and [`SystemTime::elapsed`] methods whenever the second system time
590 /// represents a point later in time than the `self` of the method call.
595 /// use std::thread::sleep;
596 /// use std::time::{Duration, SystemTime};
598 /// let sys_time = SystemTime::now();
599 /// sleep(Duration::from_secs(1));
600 /// let new_sys_time = SystemTime::now();
601 /// match sys_time.duration_since(new_sys_time) {
603 /// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
606 #[stable(feature = "time2", since = "1.8.0")]
607 pub fn duration(&self) -> Duration {
612 #[stable(feature = "time2", since = "1.8.0")]
613 impl Error for SystemTimeError {
615 fn description(&self) -> &str {
616 "other time was not earlier than self"
620 #[stable(feature = "time2", since = "1.8.0")]
621 impl fmt::Display for SystemTimeError {
622 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
623 write!(f, "second time provided was later than self")
627 impl FromInner<time::SystemTime> for SystemTime {
628 fn from_inner(time: time::SystemTime) -> SystemTime {
635 use super::{Duration, Instant, SystemTime, UNIX_EPOCH};
637 macro_rules! assert_almost_eq {
638 ($a:expr, $b:expr) => {{
639 let (a, b) = ($a, $b);
641 let (a, b) = if a > b { (a, b) } else { (b, a) };
642 assert!(a - Duration::new(0, 1000) <= b, "{:?} is not almost equal to {:?}", a, b);
648 fn instant_monotonic() {
649 let a = Instant::now();
650 let b = Instant::now();
655 fn instant_elapsed() {
656 let a = Instant::now();
662 let a = Instant::now();
663 let b = Instant::now();
664 println!("a: {:?}", a);
665 println!("b: {:?}", b);
666 let dur = b.duration_since(a);
667 println!("dur: {:?}", dur);
668 assert_almost_eq!(b - dur, a);
669 assert_almost_eq!(a + dur, b);
671 let second = Duration::new(1, 0);
672 assert_almost_eq!(a - second + second, a);
673 assert_almost_eq!(a.checked_sub(second).unwrap().checked_add(second).unwrap(), a);
675 // checked_add_duration will not panic on overflow
676 let mut maybe_t = Some(Instant::now());
677 let max_duration = Duration::from_secs(u64::MAX);
678 // in case `Instant` can store `>= now + max_duration`.
680 maybe_t = maybe_t.and_then(|t| t.checked_add(max_duration));
682 assert_eq!(maybe_t, None);
684 // checked_add_duration calculates the right time and will work for another year
685 let year = Duration::from_secs(60 * 60 * 24 * 365);
686 assert_eq!(a + year, a.checked_add(year).unwrap());
690 fn instant_math_is_associative() {
691 let now = Instant::now();
692 let offset = Duration::from_millis(5);
693 // Changing the order of instant math shouldn't change the results,
694 // especially when the expression reduces to X + identity.
695 assert_eq!((now + offset) - now, (now - now) + offset);
700 fn instant_duration_since_panic() {
701 let a = Instant::now();
702 (a - Duration::new(1, 0)).duration_since(a);
706 fn instant_checked_duration_since_nopanic() {
707 let now = Instant::now();
708 let earlier = now - Duration::new(1, 0);
709 let later = now + Duration::new(1, 0);
710 assert_eq!(earlier.checked_duration_since(now), None);
711 assert_eq!(later.checked_duration_since(now), Some(Duration::new(1, 0)));
712 assert_eq!(now.checked_duration_since(now), Some(Duration::new(0, 0)));
716 fn instant_saturating_duration_since_nopanic() {
717 let a = Instant::now();
718 let ret = (a - Duration::new(1, 0)).saturating_duration_since(a);
719 assert_eq!(ret, Duration::new(0, 0));
723 fn system_time_math() {
724 let a = SystemTime::now();
725 let b = SystemTime::now();
726 match b.duration_since(a) {
727 Ok(dur) if dur == Duration::new(0, 0) => {
728 assert_almost_eq!(a, b);
732 assert_almost_eq!(b - dur, a);
733 assert_almost_eq!(a + dur, b);
736 let dur = dur.duration();
738 assert_almost_eq!(b + dur, a);
739 assert_almost_eq!(a - dur, b);
743 let second = Duration::new(1, 0);
744 assert_almost_eq!(a.duration_since(a - second).unwrap(), second);
745 assert_almost_eq!(a.duration_since(a + second).unwrap_err().duration(), second);
747 assert_almost_eq!(a - second + second, a);
748 assert_almost_eq!(a.checked_sub(second).unwrap().checked_add(second).unwrap(), a);
750 let one_second_from_epoch = UNIX_EPOCH + Duration::new(1, 0);
751 let one_second_from_epoch2 =
752 UNIX_EPOCH + Duration::new(0, 500_000_000) + Duration::new(0, 500_000_000);
753 assert_eq!(one_second_from_epoch, one_second_from_epoch2);
755 // checked_add_duration will not panic on overflow
756 let mut maybe_t = Some(SystemTime::UNIX_EPOCH);
757 let max_duration = Duration::from_secs(u64::MAX);
758 // in case `SystemTime` can store `>= UNIX_EPOCH + max_duration`.
760 maybe_t = maybe_t.and_then(|t| t.checked_add(max_duration));
762 assert_eq!(maybe_t, None);
764 // checked_add_duration calculates the right time and will work for another year
765 let year = Duration::from_secs(60 * 60 * 24 * 365);
766 assert_eq!(a + year, a.checked_add(year).unwrap());
770 fn system_time_elapsed() {
771 let a = SystemTime::now();
777 let ts = SystemTime::now();
778 let a = ts.duration_since(UNIX_EPOCH + Duration::new(1, 0)).unwrap();
779 let b = ts.duration_since(UNIX_EPOCH).unwrap();
781 assert_eq!(b - a, Duration::new(1, 0));
783 let thirty_years = Duration::new(1, 0) * 60 * 60 * 24 * 365 * 30;
785 // Right now for CI this test is run in an emulator, and apparently the
786 // aarch64 emulator's sense of time is that we're still living in the
787 // 70s. This is also true for riscv (also qemu)
789 // Otherwise let's assume that we're all running computers later than
791 if !cfg!(target_arch = "aarch64") && !cfg!(target_arch = "riscv64") {
792 assert!(a > thirty_years);
795 // let's assume that we're all running computers earlier than 2090.
796 // Should give us ~70 years to fix this!
797 let hundred_twenty_years = thirty_years * 4;
798 assert!(a < hundred_twenty_years);