1 use crate::cmp::Ordering;
2 use crate::convert::TryInto;
6 use crate::time::Duration;
8 use core::hash::{Hash, Hasher};
10 const NANOS_PER_SEC: u64 = 1_000_000_000;
11 const INTERVALS_PER_SEC: u64 = NANOS_PER_SEC / 100;
13 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Hash)]
15 // This duration is relative to an arbitrary microsecond epoch
16 // from the winapi QueryPerformanceCounter function.
20 #[derive(Copy, Clone)]
21 pub struct SystemTime {
25 const INTERVALS_TO_UNIX_EPOCH: u64 = 11_644_473_600 * INTERVALS_PER_SEC;
27 pub const UNIX_EPOCH: SystemTime = SystemTime {
29 dwLowDateTime: INTERVALS_TO_UNIX_EPOCH as u32,
30 dwHighDateTime: (INTERVALS_TO_UNIX_EPOCH >> 32) as u32,
35 pub fn now() -> Instant {
36 // High precision timing on windows operates in "Performance Counter"
37 // units, as returned by the WINAPI QueryPerformanceCounter function.
38 // These relate to seconds by a factor of QueryPerformanceFrequency.
39 // In order to keep unit conversions out of normal interval math, we
40 // measure in QPC units and immediately convert to nanoseconds.
41 perf_counter::PerformanceCounterInstant::now().into()
44 pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
45 // On windows there's a threshold below which we consider two timestamps
46 // equivalent due to measurement error. For more details + doc link,
47 // check the docs on epsilon.
48 let epsilon = perf_counter::PerformanceCounterInstant::epsilon();
49 if other.t > self.t && other.t - self.t <= epsilon {
50 Some(Duration::new(0, 0))
52 self.t.checked_sub(other.t)
56 pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
57 Some(Instant { t: self.t.checked_add(*other)? })
60 pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
61 Some(Instant { t: self.t.checked_sub(*other)? })
66 pub fn now() -> SystemTime {
68 let mut t: SystemTime = mem::zeroed();
69 c::GetSystemTimePreciseAsFileTime(&mut t.t);
74 fn from_intervals(intervals: i64) -> SystemTime {
77 dwLowDateTime: intervals as c::DWORD,
78 dwHighDateTime: (intervals >> 32) as c::DWORD,
83 fn intervals(&self) -> i64 {
84 (self.t.dwLowDateTime as i64) | ((self.t.dwHighDateTime as i64) << 32)
87 pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
88 let me = self.intervals();
89 let other = other.intervals();
91 Ok(intervals2dur((me - other) as u64))
93 Err(intervals2dur((other - me) as u64))
97 pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
98 let intervals = self.intervals().checked_add(checked_dur2intervals(other)?)?;
99 Some(SystemTime::from_intervals(intervals))
102 pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
103 let intervals = self.intervals().checked_sub(checked_dur2intervals(other)?)?;
104 Some(SystemTime::from_intervals(intervals))
108 impl PartialEq for SystemTime {
109 fn eq(&self, other: &SystemTime) -> bool {
110 self.intervals() == other.intervals()
114 impl Eq for SystemTime {}
116 impl PartialOrd for SystemTime {
117 fn partial_cmp(&self, other: &SystemTime) -> Option<Ordering> {
118 Some(self.cmp(other))
122 impl Ord for SystemTime {
123 fn cmp(&self, other: &SystemTime) -> Ordering {
124 self.intervals().cmp(&other.intervals())
128 impl fmt::Debug for SystemTime {
129 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
130 f.debug_struct("SystemTime").field("intervals", &self.intervals()).finish()
134 impl From<c::FILETIME> for SystemTime {
135 fn from(t: c::FILETIME) -> SystemTime {
140 impl Hash for SystemTime {
141 fn hash<H: Hasher>(&self, state: &mut H) {
142 self.intervals().hash(state)
146 fn checked_dur2intervals(dur: &Duration) -> Option<i64> {
148 .checked_mul(INTERVALS_PER_SEC)?
149 .checked_add(dur.subsec_nanos() as u64 / 100)?
154 fn intervals2dur(intervals: u64) -> Duration {
155 Duration::new(intervals / INTERVALS_PER_SEC, ((intervals % INTERVALS_PER_SEC) * 100) as u32)
159 use super::NANOS_PER_SEC;
160 use crate::sync::atomic::{AtomicU64, Ordering};
163 use crate::sys_common::mul_div_u64;
164 use crate::time::Duration;
166 pub struct PerformanceCounterInstant {
167 ts: c::LARGE_INTEGER,
169 impl PerformanceCounterInstant {
170 pub fn now() -> Self {
174 // Per microsoft docs, the margin of error for cross-thread time comparisons
175 // using QueryPerformanceCounter is 1 "tick" -- defined as 1/frequency().
176 // Reference: https://docs.microsoft.com/en-us/windows/desktop/SysInfo
177 // /acquiring-high-resolution-time-stamps
178 pub fn epsilon() -> Duration {
179 let epsilon = NANOS_PER_SEC / (frequency() as u64);
180 Duration::from_nanos(epsilon)
183 impl From<PerformanceCounterInstant> for super::Instant {
184 fn from(other: PerformanceCounterInstant) -> Self {
185 let freq = frequency() as u64;
186 let instant_nsec = mul_div_u64(other.ts as u64, NANOS_PER_SEC, freq);
187 Self { t: Duration::from_nanos(instant_nsec) }
191 fn frequency() -> c::LARGE_INTEGER {
192 // Either the cached result of `QueryPerformanceFrequency` or `0` for
193 // uninitialized. Storing this as a single `AtomicU64` allows us to use
194 // `Relaxed` operations, as we are only interested in the effects on a
195 // single memory location.
196 static FREQUENCY: AtomicU64 = AtomicU64::new(0);
198 let cached = FREQUENCY.load(Ordering::Relaxed);
199 // If a previous thread has filled in this global state, use that.
201 return cached as c::LARGE_INTEGER;
203 // ... otherwise learn for ourselves ...
204 let mut frequency = 0;
206 cvt(c::QueryPerformanceFrequency(&mut frequency)).unwrap();
209 FREQUENCY.store(frequency as u64, Ordering::Relaxed);
213 fn query() -> c::LARGE_INTEGER {
214 let mut qpc_value: c::LARGE_INTEGER = 0;
215 cvt(unsafe { c::QueryPerformanceCounter(&mut qpc_value) }).unwrap();