local_clock/
clock_impls.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

//! Some useful built-in implementations of `LocalClock`.

use super::LocalClock;
use super::LocalClockDelta;
use super::LocalClockTime;
use parking_lot::Mutex;
use std::sync::Arc;
use std::time::SystemTime;

/// An implementation of [`LocalClock`] backed by [`std::time::SystemTime`].
///
/// # A note on Time Travel
///
/// The time reported by [`std::time::SystemTime`] may be radically altered by
/// external factors, such as the system operator manually setting the global
/// system clock. If this happens, `SystemTimeClock` will _also_ jump
/// forwards/backwards in time in-tandem, depending on how far the clock was
/// rolled back/forwards!
///
/// If this is something that concerns you, you might want to consider writing a
/// custom [`LocalClock`] implementation backed by something akin to Linux's
/// `CLOCK_BOOTTIME`, which provides a stable monotonically increasing clock
/// resilient against host suspends / resumes, and not subject to unexpected
/// negative / positive time jumps.
#[derive(Debug)]
#[cfg_attr(feature = "inspect", derive(inspect::Inspect))]
pub struct SystemTimeClock {
    offset_from_system_time: LocalClockDelta,
}

impl SystemTimeClock {
    /// Create a new [`SystemTimeClock`], set to the current [`SystemTime`].
    pub fn new() -> SystemTimeClock {
        SystemTimeClock {
            offset_from_system_time: LocalClockDelta::from_millis(0),
        }
    }
}

impl LocalClock for SystemTimeClock {
    fn get_time(&mut self) -> LocalClockTime {
        LocalClockTime::from(SystemTime::now()) + self.offset_from_system_time
    }

    fn set_time(&mut self, new_time: LocalClockTime) {
        self.offset_from_system_time = new_time - LocalClockTime::from(SystemTime::now());
    }
}

/// A mock implementation of [`LocalClock`], which is manually ticked via a
/// [`MockLocalClockAccessor`]. Useful for tests.
#[derive(Debug)]
#[cfg_attr(feature = "inspect", derive(inspect::Inspect))]
pub struct MockLocalClock {
    time: Arc<Mutex<LocalClockTime>>,
}

impl MockLocalClock {
    /// Create a new [`MockLocalClock`]
    pub fn new() -> Self {
        MockLocalClock {
            time: Arc::new(Mutex::new(LocalClockTime::from_millis_since_unix_epoch(
                1337,
            ))),
        }
    }

    /// Return a new [`MockLocalClockAccessor`], which can tick the clock.
    pub fn accessor(&self) -> MockLocalClockAccessor {
        MockLocalClockAccessor {
            time: self.time.clone(),
        }
    }
}

impl LocalClock for MockLocalClock {
    fn get_time(&mut self) -> LocalClockTime {
        *self.time.lock()
    }

    fn set_time(&mut self, new_time: LocalClockTime) {
        *self.time.lock() = new_time
    }
}

/// Handle to manually tick an instance of [`MockLocalClock`].
#[derive(Clone)]
pub struct MockLocalClockAccessor {
    time: Arc<Mutex<LocalClockTime>>,
}

impl MockLocalClockAccessor {
    /// Bump the amount of mock time that's passed.
    pub fn tick(&self, d: std::time::Duration) {
        let mut time = self.time.lock();
        *time = *time + LocalClockDelta::from_millis(d.as_millis().try_into().unwrap())
    }

    /// Bump the amount of mock time that's passed backwards in time.
    pub fn tick_backwards(&self, d: std::time::Duration) {
        let mut time = self.time.lock();
        *time = *time - LocalClockDelta::from_millis(d.as_millis().try_into().unwrap())
    }

    /// Get the current clock time.
    pub fn get_time(&self) -> LocalClockTime {
        *self.time.lock()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn naive_system_time() {
        let mut clock = SystemTimeClock::new();

        let time = clock.get_time();
        std::thread::sleep(std::time::Duration::from_secs(1));
        let new_time = clock.get_time();

        let delta = new_time - time;

        // cannot use assert_eq, because there is a *bit* of extra time elapsed
        // aside from the thread sleep.
        assert!(delta >= std::time::Duration::from_secs(1).into());
        assert!(delta < std::time::Duration::from_secs(2).into()); // sanity check
    }

    #[test]
    fn naive_set_time_backwards() {
        let mut clock = SystemTimeClock::new();

        clock.set_time(LocalClockTime::from_millis_since_unix_epoch(0));

        let time = clock.get_time();
        std::thread::sleep(std::time::Duration::from_secs(1));
        let new_time = clock.get_time();

        let delta = new_time - time;

        // cannot use assert_eq, because there is a *bit* of extra time elapsed
        // aside from the thread sleep.
        assert!(delta >= std::time::Duration::from_secs(1).into());
        assert!(delta < std::time::Duration::from_secs(2).into()); // sanity check
    }
}