time.rs.html -- source
Description: Source to the Rust file `src\libstd\sys\windows\time.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::cmp::Ordering;
    use crate::fmt;
    use crate::mem;
    use crate::sys::c;
    use crate::time::Duration;
    use crate::convert::TryInto;

    use core::hash::{Hash, Hasher};

    const NANOS_PER_SEC: u64 = 1_000_000_000;
    const INTERVALS_PER_SEC: u64 = NANOS_PER_SEC / 100;

    #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Hash)]
    pub struct Instant {
        // This duration is relative to an arbitrary microsecond epoch
        // from the winapi QueryPerformanceCounter function.
        t: Duration,
    }

    #[derive(Copy, Clone)]
    pub struct SystemTime {
        t: c::FILETIME,
    }

    const INTERVALS_TO_UNIX_EPOCH: u64 = 11_644_473_600 * INTERVALS_PER_SEC;

    pub const UNIX_EPOCH: SystemTime = SystemTime {
        t: c::FILETIME {
            dwLowDateTime: INTERVALS_TO_UNIX_EPOCH as u32,
            dwHighDateTime: (INTERVALS_TO_UNIX_EPOCH >> 32) as u32,
        },
    };

    impl Instant {
        pub fn now() -> Instant {
            // High precision timing on windows operates in "Performance Counter"
            // units, as returned by the WINAPI QueryPerformanceCounter function.
            // These relate to seconds by a factor of QueryPerformanceFrequency.
            // In order to keep unit conversions out of normal interval math, we
            // measure in QPC units and immediately convert to nanoseconds.
            perf_counter::PerformanceCounterInstant::now().into()
        }

        pub fn actually_monotonic() -> bool {
            false
        }

        pub const fn zero() -> Instant {
            Instant { t: Duration::from_secs(0) }
        }

        pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
            // On windows there's a threshold below which we consider two timestamps
            // equivalent due to measurement error. For more details + doc link,
            // check the docs on epsilon.
            let epsilon =
                perf_counter::PerformanceCounterInstant::epsilon();
            if other.t > self.t && other.t - self.t <= epsilon {
                Some(Duration::new(0, 0))
            } else {
                self.t.checked_sub(other.t)
            }
        }

        pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_add(*other)?
            })
        }

        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_sub(*other)?
            })
        }
    }

    impl SystemTime {
        pub fn now() -> SystemTime {
            unsafe {
                let mut t: SystemTime = mem::zeroed();
                c::GetSystemTimeAsFileTime(&mut t.t);
                t
            }
        }

        fn from_intervals(intervals: i64) -> SystemTime {
            SystemTime {
                t: c::FILETIME {
                    dwLowDateTime: intervals as c::DWORD,
                    dwHighDateTime: (intervals >> 32) as c::DWORD,
                }
            }
        }

        fn intervals(&self) -> i64 {
            (self.t.dwLowDateTime as i64) | ((self.t.dwHighDateTime as i64) << 32)
        }

        pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
            let me = self.intervals();
            let other = other.intervals();
            if me >= other {
                Ok(intervals2dur((me - other) as u64))
            } else {
                Err(intervals2dur((other - me) as u64))
            }
        }

        pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
            let intervals = self.intervals().checked_add(checked_dur2intervals(other)?)?;
            Some(SystemTime::from_intervals(intervals))
        }

        pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
            let intervals = self.intervals().checked_sub(checked_dur2intervals(other)?)?;
            Some(SystemTime::from_intervals(intervals))
        }
    }

    impl PartialEq for SystemTime {
        fn eq(&self, other: &SystemTime) -> bool {
            self.intervals() == other.intervals()
        }
    }

    impl Eq for SystemTime {}

    impl PartialOrd for SystemTime {
        fn partial_cmp(&self, other: &SystemTime) -> Option<Ordering> {
            Some(self.cmp(other))
        }
    }

    impl Ord for SystemTime {
        fn cmp(&self, other: &SystemTime) -> Ordering {
            self.intervals().cmp(&other.intervals())
        }
    }

    impl fmt::Debug for SystemTime {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("SystemTime")
             .field("intervals", &self.intervals())
             .finish()
        }
    }

    impl From<c::FILETIME> for SystemTime {
        fn from(t: c::FILETIME) -> SystemTime {
            SystemTime { t }
        }
    }

    impl Hash for SystemTime {
        fn hash<H : Hasher>(&self, state: &mut H) {
            self.intervals().hash(state)
        }
    }

    fn checked_dur2intervals(dur: &Duration) -> Option<i64> {
        dur.as_secs()
            .checked_mul(INTERVALS_PER_SEC)?
            .checked_add(dur.subsec_nanos() as u64 / 100)?
            .try_into()
            .ok()
    }

    fn intervals2dur(intervals: u64) -> Duration {
        Duration::new(intervals / INTERVALS_PER_SEC,
                      ((intervals % INTERVALS_PER_SEC) * 100) as u32)
    }

    mod perf_counter {
        use super::{NANOS_PER_SEC};
        use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
        use crate::sys_common::mul_div_u64;
        use crate::sys::c;
        use crate::sys::cvt;
        use crate::time::Duration;

        pub struct PerformanceCounterInstant {
            ts: c::LARGE_INTEGER
        }
        impl PerformanceCounterInstant {
            pub fn now() -> Self {
                Self {
                    ts: query()
                }
            }

            // Per microsoft docs, the margin of error for cross-thread time comparisons
            // using QueryPerformanceCounter is 1 "tick" -- defined as 1/frequency().
            // Reference: https://docs.microsoft.com/en-us/windows/desktop/SysInfo
            //                   /acquiring-high-resolution-time-stamps
            pub fn epsilon() -> Duration {
                let epsilon = NANOS_PER_SEC / (frequency() as u64);
                Duration::from_nanos(epsilon)
            }
        }
        impl From<PerformanceCounterInstant> for super::Instant {
            fn from(other: PerformanceCounterInstant) -> Self {
                let freq = frequency() as u64;
                let instant_nsec = mul_div_u64(other.ts as u64, NANOS_PER_SEC, freq);
                Self {
                    t: Duration::from_nanos(instant_nsec)
                }
            }
        }

        fn frequency() -> c::LARGE_INTEGER {
            static mut FREQUENCY: c::LARGE_INTEGER = 0;
            static STATE: AtomicUsize = AtomicUsize::new(0);

            unsafe {
                // If a previous thread has filled in this global state, use that.
                if STATE.load(SeqCst) == 2 {
                    return FREQUENCY;
                }

                // ... otherwise learn for ourselves ...
                let mut frequency = 0;
                cvt(c::QueryPerformanceFrequency(&mut frequency)).unwrap();

                // ... and attempt to be the one thread that stores it globally for
                // all other threads
                if STATE.compare_exchange(0, 1, SeqCst, SeqCst).is_ok() {
                    FREQUENCY = frequency;
                    STATE.store(2, SeqCst);
                }
                frequency
            }
        }

        fn query() -> c::LARGE_INTEGER {
            let mut qpc_value: c::LARGE_INTEGER = 0;
            cvt(unsafe {
                c::QueryPerformanceCounter(&mut qpc_value)
            }).unwrap();
            qpc_value
        }
    }