1 use crate::cmp::Ordering;
2 use crate::fmt;
3 use crate::mem;
4 use crate::sys::c;
5 use crate::sys_common::IntoInner;
6 use crate::time::Duration;
7
8 use core::hash::{Hash, Hasher};
9
10 const NANOS_PER_SEC: u64 = 1_000_000_000;
11 const INTERVALS_PER_SEC: u64 = NANOS_PER_SEC / 100;
12
13 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Hash)]
14 pub struct Instant {
15 // This duration is relative to an arbitrary microsecond epoch
16 // from the winapi QueryPerformanceCounter function.
17 t: Duration,
18 }
19
20 #[derive(Copy, Clone)]
21 pub struct SystemTime {
22 t: c::FILETIME,
23 }
24
25 const INTERVALS_TO_UNIX_EPOCH: u64 = 11_644_473_600 * INTERVALS_PER_SEC;
26
27 pub const UNIX_EPOCH: SystemTime = SystemTime {
28 t: c::FILETIME {
29 dwLowDateTime: INTERVALS_TO_UNIX_EPOCH as u32,
30 dwHighDateTime: (INTERVALS_TO_UNIX_EPOCH >> 32) as u32,
31 },
32 };
33
34 impl Instant {
now() -> Instant35 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()
42 }
43
checked_sub_instant(&self, other: &Instant) -> Option<Duration>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))
51 } else {
52 self.t.checked_sub(other.t)
53 }
54 }
55
checked_add_duration(&self, other: &Duration) -> Option<Instant>56 pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
57 Some(Instant { t: self.t.checked_add(*other)? })
58 }
59
checked_sub_duration(&self, other: &Duration) -> Option<Instant>60 pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
61 Some(Instant { t: self.t.checked_sub(*other)? })
62 }
63 }
64
65 impl SystemTime {
now() -> SystemTime66 pub fn now() -> SystemTime {
67 unsafe {
68 let mut t: SystemTime = mem::zeroed();
69 c::GetSystemTimePreciseAsFileTime(&mut t.t);
70 t
71 }
72 }
73
from_intervals(intervals: i64) -> SystemTime74 fn from_intervals(intervals: i64) -> SystemTime {
75 SystemTime {
76 t: c::FILETIME {
77 dwLowDateTime: intervals as c::DWORD,
78 dwHighDateTime: (intervals >> 32) as c::DWORD,
79 },
80 }
81 }
82
intervals(&self) -> i6483 fn intervals(&self) -> i64 {
84 (self.t.dwLowDateTime as i64) | ((self.t.dwHighDateTime as i64) << 32)
85 }
86
sub_time(&self, other: &SystemTime) -> Result<Duration, Duration>87 pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
88 let me = self.intervals();
89 let other = other.intervals();
90 if me >= other {
91 Ok(intervals2dur((me - other) as u64))
92 } else {
93 Err(intervals2dur((other - me) as u64))
94 }
95 }
96
checked_add_duration(&self, other: &Duration) -> Option<SystemTime>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))
100 }
101
checked_sub_duration(&self, other: &Duration) -> Option<SystemTime>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))
105 }
106 }
107
108 impl PartialEq for SystemTime {
eq(&self, other: &SystemTime) -> bool109 fn eq(&self, other: &SystemTime) -> bool {
110 self.intervals() == other.intervals()
111 }
112 }
113
114 impl Eq for SystemTime {}
115
116 impl PartialOrd for SystemTime {
partial_cmp(&self, other: &SystemTime) -> Option<Ordering>117 fn partial_cmp(&self, other: &SystemTime) -> Option<Ordering> {
118 Some(self.cmp(other))
119 }
120 }
121
122 impl Ord for SystemTime {
cmp(&self, other: &SystemTime) -> Ordering123 fn cmp(&self, other: &SystemTime) -> Ordering {
124 self.intervals().cmp(&other.intervals())
125 }
126 }
127
128 impl fmt::Debug for SystemTime {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result129 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
130 f.debug_struct("SystemTime").field("intervals", &self.intervals()).finish()
131 }
132 }
133
134 impl From<c::FILETIME> for SystemTime {
from(t: c::FILETIME) -> SystemTime135 fn from(t: c::FILETIME) -> SystemTime {
136 SystemTime { t }
137 }
138 }
139
140 impl IntoInner<c::FILETIME> for SystemTime {
into_inner(self) -> c::FILETIME141 fn into_inner(self) -> c::FILETIME {
142 self.t
143 }
144 }
145
146 impl Hash for SystemTime {
hash<H: Hasher>(&self, state: &mut H)147 fn hash<H: Hasher>(&self, state: &mut H) {
148 self.intervals().hash(state)
149 }
150 }
151
checked_dur2intervals(dur: &Duration) -> Option<i64>152 fn checked_dur2intervals(dur: &Duration) -> Option<i64> {
153 dur.as_secs()
154 .checked_mul(INTERVALS_PER_SEC)?
155 .checked_add(dur.subsec_nanos() as u64 / 100)?
156 .try_into()
157 .ok()
158 }
159
intervals2dur(intervals: u64) -> Duration160 fn intervals2dur(intervals: u64) -> Duration {
161 Duration::new(intervals / INTERVALS_PER_SEC, ((intervals % INTERVALS_PER_SEC) * 100) as u32)
162 }
163
164 mod perf_counter {
165 use super::NANOS_PER_SEC;
166 use crate::sync::atomic::{AtomicU64, Ordering};
167 use crate::sys::c;
168 use crate::sys::cvt;
169 use crate::sys_common::mul_div_u64;
170 use crate::time::Duration;
171
172 pub struct PerformanceCounterInstant {
173 ts: c::LARGE_INTEGER,
174 }
175 impl PerformanceCounterInstant {
now() -> Self176 pub fn now() -> Self {
177 Self { ts: query() }
178 }
179
180 // Per microsoft docs, the margin of error for cross-thread time comparisons
181 // using QueryPerformanceCounter is 1 "tick" -- defined as 1/frequency().
182 // Reference: https://docs.microsoft.com/en-us/windows/desktop/SysInfo
183 // /acquiring-high-resolution-time-stamps
epsilon() -> Duration184 pub fn epsilon() -> Duration {
185 let epsilon = NANOS_PER_SEC / (frequency() as u64);
186 Duration::from_nanos(epsilon)
187 }
188 }
189 impl From<PerformanceCounterInstant> for super::Instant {
from(other: PerformanceCounterInstant) -> Self190 fn from(other: PerformanceCounterInstant) -> Self {
191 let freq = frequency() as u64;
192 let instant_nsec = mul_div_u64(other.ts as u64, NANOS_PER_SEC, freq);
193 Self { t: Duration::from_nanos(instant_nsec) }
194 }
195 }
196
frequency() -> c::LARGE_INTEGER197 fn frequency() -> c::LARGE_INTEGER {
198 // Either the cached result of `QueryPerformanceFrequency` or `0` for
199 // uninitialized. Storing this as a single `AtomicU64` allows us to use
200 // `Relaxed` operations, as we are only interested in the effects on a
201 // single memory location.
202 static FREQUENCY: AtomicU64 = AtomicU64::new(0);
203
204 let cached = FREQUENCY.load(Ordering::Relaxed);
205 // If a previous thread has filled in this global state, use that.
206 if cached != 0 {
207 return cached as c::LARGE_INTEGER;
208 }
209 // ... otherwise learn for ourselves ...
210 let mut frequency = 0;
211 unsafe {
212 cvt(c::QueryPerformanceFrequency(&mut frequency)).unwrap();
213 }
214
215 FREQUENCY.store(frequency as u64, Ordering::Relaxed);
216 frequency
217 }
218
query() -> c::LARGE_INTEGER219 fn query() -> c::LARGE_INTEGER {
220 let mut qpc_value: c::LARGE_INTEGER = 0;
221 cvt(unsafe { c::QueryPerformanceCounter(&mut qpc_value) }).unwrap();
222 qpc_value
223 }
224 }
225