643 lines
24 KiB
Rust
643 lines
24 KiB
Rust
//! Temporal quantification.
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//!
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//! Example:
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//!
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//! ```
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//! use std::time::Duration;
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//!
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//! let five_seconds = Duration::new(5, 0);
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//! // both declarations are equivalent
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//! assert_eq!(Duration::new(5, 0), Duration::from_secs(5));
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//! ```
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#![stable(feature = "time", since = "1.3.0")]
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#[cfg(test)]
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mod tests;
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use crate::cmp;
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use crate::error::Error;
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use crate::fmt;
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use crate::ops::{Add, AddAssign, Sub, SubAssign};
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use crate::sys::time;
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use crate::sys_common::mutex::StaticMutex;
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use crate::sys_common::FromInner;
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#[stable(feature = "time", since = "1.3.0")]
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pub use core::time::Duration;
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/// A measurement of a monotonically nondecreasing clock.
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/// Opaque and useful only with `Duration`.
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///
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/// Instants are always guaranteed to be no less than any previously measured
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/// instant when created, and are often useful for tasks such as measuring
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/// benchmarks or timing how long an operation takes.
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///
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/// Note, however, that instants are not guaranteed to be **steady**. In other
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/// words, each tick of the underlying clock may not be the same length (e.g.
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/// some seconds may be longer than others). An instant may jump forwards or
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/// experience time dilation (slow down or speed up), but it will never go
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/// backwards.
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///
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/// Instants are opaque types that can only be compared to one another. There is
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/// no method to get "the number of seconds" from an instant. Instead, it only
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/// allows measuring the duration between two instants (or comparing two
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/// instants).
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///
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/// The size of an `Instant` struct may vary depending on the target operating
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/// system.
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///
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/// Example:
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///
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/// ```no_run
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/// use std::time::{Duration, Instant};
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/// use std::thread::sleep;
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///
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/// fn main() {
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/// let now = Instant::now();
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///
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/// // we sleep for 2 seconds
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/// sleep(Duration::new(2, 0));
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/// // it prints '2'
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/// println!("{}", now.elapsed().as_secs());
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/// }
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/// ```
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///
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/// # OS-specific behaviors
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///
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/// An `Instant` is a wrapper around system-specific types and it may behave
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/// differently depending on the underlying operating system. For example,
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/// the following snippet is fine on Linux but panics on macOS:
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///
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/// ```no_run
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/// use std::time::{Instant, Duration};
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///
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/// let now = Instant::now();
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/// let max_nanoseconds = u64::MAX / 1_000_000_000;
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/// let duration = Duration::new(max_nanoseconds, 0);
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/// println!("{:?}", now + duration);
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/// ```
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///
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/// # Underlying System calls
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/// Currently, the following system calls are being used to get the current time using `now()`:
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///
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/// | Platform | System call |
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/// |:---------:|:--------------------------------------------------------------------:|
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/// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
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/// | UNIX | [clock_gettime (Monotonic Clock)] |
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/// | Darwin | [mach_absolute_time] |
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/// | VXWorks | [clock_gettime (Monotonic Clock)] |
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/// | WASI | [__wasi_clock_time_get (Monotonic Clock)] |
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/// | Windows | [QueryPerformanceCounter] |
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///
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/// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
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/// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
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/// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
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/// [__wasi_clock_time_get (Monotonic Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
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/// [clock_gettime (Monotonic Clock)]: https://linux.die.net/man/3/clock_gettime
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/// [mach_absolute_time]: https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/services/services.html
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///
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/// **Disclaimer:** These system calls might change over time.
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///
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/// > Note: mathematical operations like [`add`] may panic if the underlying
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/// > structure cannot represent the new point in time.
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///
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/// [`add`]: Instant::add
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#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
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#[stable(feature = "time2", since = "1.8.0")]
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pub struct Instant(time::Instant);
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/// A measurement of the system clock, useful for talking to
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/// external entities like the file system or other processes.
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///
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/// Distinct from the [`Instant`] type, this time measurement **is not
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/// monotonic**. This means that you can save a file to the file system, then
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/// save another file to the file system, **and the second file has a
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/// `SystemTime` measurement earlier than the first**. In other words, an
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/// operation that happens after another operation in real time may have an
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/// earlier `SystemTime`!
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///
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/// Consequently, comparing two `SystemTime` instances to learn about the
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/// duration between them returns a [`Result`] instead of an infallible [`Duration`]
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/// to indicate that this sort of time drift may happen and needs to be handled.
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///
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/// Although a `SystemTime` cannot be directly inspected, the [`UNIX_EPOCH`]
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/// constant is provided in this module as an anchor in time to learn
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/// information about a `SystemTime`. By calculating the duration from this
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/// fixed point in time, a `SystemTime` can be converted to a human-readable time,
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/// or perhaps some other string representation.
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///
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/// The size of a `SystemTime` struct may vary depending on the target operating
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/// system.
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///
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/// Example:
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///
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/// ```no_run
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/// use std::time::{Duration, SystemTime};
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/// use std::thread::sleep;
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///
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/// fn main() {
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/// let now = SystemTime::now();
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///
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/// // we sleep for 2 seconds
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/// sleep(Duration::new(2, 0));
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/// match now.elapsed() {
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/// Ok(elapsed) => {
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/// // it prints '2'
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/// println!("{}", elapsed.as_secs());
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/// }
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/// Err(e) => {
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/// // an error occurred!
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/// println!("Error: {:?}", e);
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/// }
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/// }
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/// }
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/// ```
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///
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/// # Underlying System calls
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/// Currently, the following system calls are being used to get the current time using `now()`:
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///
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/// | Platform | System call |
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/// |:---------:|:--------------------------------------------------------------------:|
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/// | SGX | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
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/// | UNIX | [clock_gettime (Realtime Clock)] |
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/// | Darwin | [gettimeofday] |
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/// | VXWorks | [clock_gettime (Realtime Clock)] |
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/// | WASI | [__wasi_clock_time_get (Realtime Clock)] |
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/// | Windows | [GetSystemTimePreciseAsFileTime] / [GetSystemTimeAsFileTime] |
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///
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/// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
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/// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
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/// [gettimeofday]: http://man7.org/linux/man-pages/man2/gettimeofday.2.html
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/// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
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/// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
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/// [GetSystemTimePreciseAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime
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/// [GetSystemTimeAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime
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///
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/// **Disclaimer:** These system calls might change over time.
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///
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/// > Note: mathematical operations like [`add`] may panic if the underlying
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/// > structure cannot represent the new point in time.
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///
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/// [`add`]: SystemTime::add
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#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
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#[stable(feature = "time2", since = "1.8.0")]
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pub struct SystemTime(time::SystemTime);
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/// An error returned from the `duration_since` and `elapsed` methods on
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/// `SystemTime`, used to learn how far in the opposite direction a system time
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/// lies.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::thread::sleep;
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/// use std::time::{Duration, SystemTime};
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///
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/// let sys_time = SystemTime::now();
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/// sleep(Duration::from_secs(1));
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/// let new_sys_time = SystemTime::now();
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/// match sys_time.duration_since(new_sys_time) {
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/// Ok(_) => {}
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/// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
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/// }
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/// ```
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#[derive(Clone, Debug)]
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#[stable(feature = "time2", since = "1.8.0")]
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pub struct SystemTimeError(Duration);
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impl Instant {
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/// Returns an instant corresponding to "now".
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///
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/// # Examples
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///
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/// ```
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/// use std::time::Instant;
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///
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/// let now = Instant::now();
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/// ```
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#[stable(feature = "time2", since = "1.8.0")]
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pub fn now() -> Instant {
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let os_now = time::Instant::now();
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// And here we come upon a sad state of affairs. The whole point of
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// `Instant` is that it's monotonically increasing. We've found in the
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// wild, however, that it's not actually monotonically increasing for
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// one reason or another. These appear to be OS and hardware level bugs,
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// and there's not really a whole lot we can do about them. Here's a
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// taste of what we've found:
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//
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// * #48514 - OpenBSD, x86_64
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// * #49281 - linux arm64 and s390x
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// * #51648 - windows, x86
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// * #56560 - windows, x86_64, AWS
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// * #56612 - windows, x86, vm (?)
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// * #56940 - linux, arm64
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// * https://bugzilla.mozilla.org/show_bug.cgi?id=1487778 - a similar
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// Firefox bug
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//
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// It seems that this just happens a lot in the wild.
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// We're seeing panics across various platforms where consecutive calls
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// to `Instant::now`, such as via the `elapsed` function, are panicking
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// as they're going backwards. Placed here is a last-ditch effort to try
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// to fix things up. We keep a global "latest now" instance which is
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// returned instead of what the OS says if the OS goes backwards.
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//
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// To hopefully mitigate the impact of this, a few platforms are
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// excluded as "these at least haven't gone backwards yet".
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if time::Instant::actually_monotonic() {
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return Instant(os_now);
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}
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static LOCK: StaticMutex = StaticMutex::new();
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static mut LAST_NOW: time::Instant = time::Instant::zero();
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unsafe {
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let _lock = LOCK.lock();
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let now = cmp::max(LAST_NOW, os_now);
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LAST_NOW = now;
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Instant(now)
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}
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}
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/// Returns the amount of time elapsed from another instant to this one.
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///
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/// # Panics
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///
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/// This function will panic if `earlier` is later than `self`.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::time::{Duration, Instant};
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/// use std::thread::sleep;
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///
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/// let now = Instant::now();
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/// sleep(Duration::new(1, 0));
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/// let new_now = Instant::now();
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/// println!("{:?}", new_now.duration_since(now));
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/// ```
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#[stable(feature = "time2", since = "1.8.0")]
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pub fn duration_since(&self, earlier: Instant) -> Duration {
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self.0.checked_sub_instant(&earlier.0).expect("supplied instant is later than self")
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}
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/// Returns the amount of time elapsed from another instant to this one,
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/// or None if that instant is later than this one.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::time::{Duration, Instant};
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/// use std::thread::sleep;
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///
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/// let now = Instant::now();
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/// sleep(Duration::new(1, 0));
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/// let new_now = Instant::now();
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/// println!("{:?}", new_now.checked_duration_since(now));
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/// println!("{:?}", now.checked_duration_since(new_now)); // None
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/// ```
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#[stable(feature = "checked_duration_since", since = "1.39.0")]
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pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
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self.0.checked_sub_instant(&earlier.0)
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}
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/// Returns the amount of time elapsed from another instant to this one,
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/// or zero duration if that instant is later than this one.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::time::{Duration, Instant};
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/// use std::thread::sleep;
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///
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/// let now = Instant::now();
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/// sleep(Duration::new(1, 0));
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/// let new_now = Instant::now();
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/// println!("{:?}", new_now.saturating_duration_since(now));
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/// println!("{:?}", now.saturating_duration_since(new_now)); // 0ns
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/// ```
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#[stable(feature = "checked_duration_since", since = "1.39.0")]
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pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
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self.checked_duration_since(earlier).unwrap_or_default()
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}
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/// Returns the amount of time elapsed since this instant was created.
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///
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/// # Panics
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///
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/// This function may panic if the current time is earlier than this
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/// instant, which is something that can happen if an `Instant` is
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/// produced synthetically.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::thread::sleep;
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/// use std::time::{Duration, Instant};
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///
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/// let instant = Instant::now();
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/// let three_secs = Duration::from_secs(3);
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/// sleep(three_secs);
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/// assert!(instant.elapsed() >= three_secs);
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/// ```
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#[stable(feature = "time2", since = "1.8.0")]
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pub fn elapsed(&self) -> Duration {
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Instant::now() - *self
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}
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/// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be represented as
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/// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
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/// otherwise.
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#[stable(feature = "time_checked_add", since = "1.34.0")]
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pub fn checked_add(&self, duration: Duration) -> Option<Instant> {
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self.0.checked_add_duration(&duration).map(Instant)
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}
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/// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
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/// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
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/// otherwise.
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#[stable(feature = "time_checked_add", since = "1.34.0")]
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pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
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self.0.checked_sub_duration(&duration).map(Instant)
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}
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}
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#[stable(feature = "time2", since = "1.8.0")]
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impl Add<Duration> for Instant {
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type Output = Instant;
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/// # Panics
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///
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/// This function may panic if the resulting point in time cannot be represented by the
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/// underlying data structure. See [`Instant::checked_add`] for a version without panic.
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fn add(self, other: Duration) -> Instant {
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self.checked_add(other).expect("overflow when adding duration to instant")
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}
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}
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#[stable(feature = "time_augmented_assignment", since = "1.9.0")]
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impl AddAssign<Duration> for Instant {
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fn add_assign(&mut self, other: Duration) {
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*self = *self + other;
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}
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}
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#[stable(feature = "time2", since = "1.8.0")]
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impl Sub<Duration> for Instant {
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type Output = Instant;
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fn sub(self, other: Duration) -> Instant {
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self.checked_sub(other).expect("overflow when subtracting duration from instant")
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}
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}
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#[stable(feature = "time_augmented_assignment", since = "1.9.0")]
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impl SubAssign<Duration> for Instant {
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fn sub_assign(&mut self, other: Duration) {
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*self = *self - other;
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}
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}
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#[stable(feature = "time2", since = "1.8.0")]
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impl Sub<Instant> for Instant {
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type Output = Duration;
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fn sub(self, other: Instant) -> Duration {
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self.duration_since(other)
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}
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}
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#[stable(feature = "time2", since = "1.8.0")]
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impl fmt::Debug for Instant {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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self.0.fmt(f)
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}
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}
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impl SystemTime {
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/// An anchor in time which can be used to create new `SystemTime` instances or
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/// learn about where in time a `SystemTime` lies.
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///
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/// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
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/// respect to the system clock. Using `duration_since` on an existing
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/// `SystemTime` instance can tell how far away from this point in time a
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/// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
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/// `SystemTime` instance to represent another fixed point in time.
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///
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/// # Examples
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///
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/// ```no_run
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/// use std::time::SystemTime;
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///
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/// match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
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/// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
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/// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
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/// }
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/// ```
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#[stable(feature = "assoc_unix_epoch", since = "1.28.0")]
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pub const UNIX_EPOCH: SystemTime = UNIX_EPOCH;
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/// Returns the system time corresponding to "now".
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///
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/// # Examples
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///
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/// ```
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/// use std::time::SystemTime;
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///
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/// let sys_time = SystemTime::now();
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/// ```
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#[stable(feature = "time2", since = "1.8.0")]
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pub fn now() -> SystemTime {
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SystemTime(time::SystemTime::now())
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}
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/// Returns the amount of time elapsed from an earlier point in time.
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///
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/// This function may fail because measurements taken earlier are not
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/// guaranteed to always be before later measurements (due to anomalies such
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/// as the system clock being adjusted either forwards or backwards).
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/// [`Instant`] can be used to measure elapsed time without this risk of failure.
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///
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/// 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
|
|
///
|
|
/// ```no_run
|
|
/// 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);
|
|
/// ```
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
pub fn duration_since(&self, earlier: SystemTime) -> Result<Duration, SystemTimeError> {
|
|
self.0.sub_time(&earlier.0).map_err(SystemTimeError)
|
|
}
|
|
|
|
/// Returns the difference between the clock time when this
|
|
/// system time was created, and 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 may 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
|
|
///
|
|
/// ```no_run
|
|
/// 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);
|
|
/// ```
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
pub fn elapsed(&self) -> Result<Duration, SystemTimeError> {
|
|
SystemTime::now().duration_since(*self)
|
|
}
|
|
|
|
/// 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.
|
|
#[stable(feature = "time_checked_add", since = "1.34.0")]
|
|
pub fn checked_add(&self, duration: Duration) -> Option<SystemTime> {
|
|
self.0.checked_add_duration(&duration).map(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.
|
|
#[stable(feature = "time_checked_add", since = "1.34.0")]
|
|
pub fn checked_sub(&self, duration: Duration) -> Option<SystemTime> {
|
|
self.0.checked_sub_duration(&duration).map(SystemTime)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
impl Add<Duration> for SystemTime {
|
|
type Output = 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.
|
|
fn add(self, dur: Duration) -> SystemTime {
|
|
self.checked_add(dur).expect("overflow when adding duration to instant")
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time_augmented_assignment", since = "1.9.0")]
|
|
impl AddAssign<Duration> for SystemTime {
|
|
fn add_assign(&mut self, other: Duration) {
|
|
*self = *self + other;
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
impl Sub<Duration> for SystemTime {
|
|
type Output = SystemTime;
|
|
|
|
fn sub(self, dur: Duration) -> SystemTime {
|
|
self.checked_sub(dur).expect("overflow when subtracting duration from instant")
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time_augmented_assignment", since = "1.9.0")]
|
|
impl SubAssign<Duration> for SystemTime {
|
|
fn sub_assign(&mut self, other: Duration) {
|
|
*self = *self - other;
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
impl fmt::Debug for SystemTime {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
self.0.fmt(f)
|
|
}
|
|
}
|
|
|
|
/// 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.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```no_run
|
|
/// use std::time::{SystemTime, UNIX_EPOCH};
|
|
///
|
|
/// match SystemTime::now().duration_since(UNIX_EPOCH) {
|
|
/// Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
|
|
/// Err(_) => panic!("SystemTime before UNIX EPOCH!"),
|
|
/// }
|
|
/// ```
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
pub const UNIX_EPOCH: SystemTime = SystemTime(time::UNIX_EPOCH);
|
|
|
|
impl SystemTimeError {
|
|
/// Returns the positive duration which represents how far forward the
|
|
/// second system time was from the first.
|
|
///
|
|
/// A `SystemTimeError` is returned from the [`SystemTime::duration_since`]
|
|
/// and [`SystemTime::elapsed`] methods whenever the second system time
|
|
/// represents a point later in time than the `self` of the method call.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```no_run
|
|
/// use std::thread::sleep;
|
|
/// use std::time::{Duration, SystemTime};
|
|
///
|
|
/// let sys_time = SystemTime::now();
|
|
/// sleep(Duration::from_secs(1));
|
|
/// let new_sys_time = SystemTime::now();
|
|
/// match sys_time.duration_since(new_sys_time) {
|
|
/// Ok(_) => {}
|
|
/// Err(e) => println!("SystemTimeError difference: {:?}", e.duration()),
|
|
/// }
|
|
/// ```
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
pub fn duration(&self) -> Duration {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
impl Error for SystemTimeError {
|
|
#[allow(deprecated)]
|
|
fn description(&self) -> &str {
|
|
"other time was not earlier than self"
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "time2", since = "1.8.0")]
|
|
impl fmt::Display for SystemTimeError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
write!(f, "second time provided was later than self")
|
|
}
|
|
}
|
|
|
|
impl FromInner<time::SystemTime> for SystemTime {
|
|
fn from_inner(time: time::SystemTime) -> SystemTime {
|
|
SystemTime(time)
|
|
}
|
|
}
|