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| 1 | +use async_trait::async_trait; |
| 2 | +use std::ops::{Div, Mul}; |
| 3 | +use std::time::{Duration, SystemTime}; |
| 4 | +use tokio::time::{self, Instant}; |
| 5 | + |
| 6 | +use crate::SimulationError; |
| 7 | + |
| 8 | +#[async_trait] |
| 9 | +pub trait Clock: Send + Sync { |
| 10 | + fn now(&self) -> SystemTime; |
| 11 | + async fn sleep(&self, wait: Duration); |
| 12 | +} |
| 13 | + |
| 14 | +/// Provides a wall clock implementation of the Clock trait. |
| 15 | +#[derive(Clone)] |
| 16 | +pub struct SystemClock {} |
| 17 | + |
| 18 | +#[async_trait] |
| 19 | +impl Clock for SystemClock { |
| 20 | + fn now(&self) -> SystemTime { |
| 21 | + SystemTime::now() |
| 22 | + } |
| 23 | + |
| 24 | + async fn sleep(&self, wait: Duration) { |
| 25 | + time::sleep(wait).await; |
| 26 | + } |
| 27 | +} |
| 28 | + |
| 29 | +/// Provides an implementation of the Clock trait that speeds up wall clock time by some factor. |
| 30 | +#[derive(Clone)] |
| 31 | +pub struct SimulationClock { |
| 32 | + // The multiplier that the regular wall clock is sped up by, must be in [1, 1000]. |
| 33 | + speedup_multiplier: u16, |
| 34 | + |
| 35 | + /// Tracked so that we can calculate our "fast-forwarded" present relative to the time that we started running at. |
| 36 | + /// This is useful, because it allows us to still rely on the wall clock, then just convert based on our speedup. |
| 37 | + /// This field is expressed as an Instant for convenience. |
| 38 | + start_instant: Instant, |
| 39 | +} |
| 40 | + |
| 41 | +impl SimulationClock { |
| 42 | + /// Creates a new simulated clock that will speed up wall clock time by the multiplier provided, which must be in |
| 43 | + /// [1;1000] because our asynchronous sleep only supports a duration of ms granularity. |
| 44 | + pub fn new(speedup_multiplier: u16) -> Result<Self, SimulationError> { |
| 45 | + if speedup_multiplier < 1 { |
| 46 | + return Err(SimulationError::SimulatedNetworkError( |
| 47 | + "speedup_multiplier must be at least 1".to_string(), |
| 48 | + )); |
| 49 | + } |
| 50 | + |
| 51 | + if speedup_multiplier > 1000 { |
| 52 | + return Err(SimulationError::SimulatedNetworkError( |
| 53 | + "speedup_multiplier must be less than 1000, because the simulation sleeps with millisecond |
| 54 | + granularity".to_string(), |
| 55 | + )); |
| 56 | + } |
| 57 | + |
| 58 | + Ok(SimulationClock { |
| 59 | + speedup_multiplier, |
| 60 | + start_instant: Instant::now(), |
| 61 | + }) |
| 62 | + } |
| 63 | + |
| 64 | + /// Calculates the current simulation time based on the current wall clock time. |
| 65 | + /// |
| 66 | + /// Separated for testing purposes so that we can fix the current wall clock time and elapsed interval. |
| 67 | + fn calc_now(&self, now: SystemTime, elapsed: Duration) -> SystemTime { |
| 68 | + now.checked_add(self.simulated_to_wall_clock(elapsed)) |
| 69 | + .expect("simulation time overflow") |
| 70 | + } |
| 71 | + |
| 72 | + /// Converts a duration expressed in wall clock time to the amount of equivalent time that should be used in our |
| 73 | + /// sped up time. |
| 74 | + fn wall_clock_to_simulated(&self, d: Duration) -> Duration { |
| 75 | + d.div(self.speedup_multiplier.into()) |
| 76 | + } |
| 77 | + |
| 78 | + /// Converts a duration expressed in sped up simulation time to the be expressed in wall clock time. |
| 79 | + fn simulated_to_wall_clock(&self, d: Duration) -> Duration { |
| 80 | + d.mul(self.speedup_multiplier.into()) |
| 81 | + } |
| 82 | +} |
| 83 | + |
| 84 | +#[async_trait] |
| 85 | +impl Clock for SimulationClock { |
| 86 | + /// To get the current time according to our simulation clock, we get the amount of wall clock time that has |
| 87 | + /// elapsed since the simulator clock was created and multiply it by our speedup. |
| 88 | + fn now(&self) -> SystemTime { |
| 89 | + self.calc_now(SystemTime::now(), self.start_instant.elapsed()) |
| 90 | + } |
| 91 | + |
| 92 | + /// To provide a sped up sleep time, we scale the proposed wait time by our multiplier and sleep. |
| 93 | + async fn sleep(&self, wait: Duration) { |
| 94 | + time::sleep(self.wall_clock_to_simulated(wait)).await; |
| 95 | + } |
| 96 | +} |
| 97 | + |
| 98 | +#[cfg(test)] |
| 99 | +mod tests { |
| 100 | + use std::time::{Duration, SystemTime}; |
| 101 | + |
| 102 | + use crate::clock::SimulationClock; |
| 103 | + |
| 104 | + /// Tests validation and that a multplier of 1 is a regular clock. |
| 105 | + #[test] |
| 106 | + fn test_simulation_clock() { |
| 107 | + assert!(SimulationClock::new(0).is_err()); |
| 108 | + assert!(SimulationClock::new(1001).is_err()); |
| 109 | + |
| 110 | + let clock = SimulationClock::new(1).unwrap(); |
| 111 | + let now = SystemTime::now(); |
| 112 | + let elapsed = Duration::from_secs(15); |
| 113 | + |
| 114 | + assert_eq!( |
| 115 | + clock.calc_now(now, elapsed), |
| 116 | + now.checked_add(elapsed).unwrap(), |
| 117 | + ); |
| 118 | + } |
| 119 | + |
| 120 | + /// Test that time is sped up by multiplier. |
| 121 | + #[test] |
| 122 | + fn test_clock_speedup() { |
| 123 | + let clock = SimulationClock::new(10).unwrap(); |
| 124 | + let now = SystemTime::now(); |
| 125 | + |
| 126 | + assert_eq!( |
| 127 | + clock.calc_now(now, Duration::from_secs(1)), |
| 128 | + now.checked_add(Duration::from_secs(10)).unwrap(), |
| 129 | + ); |
| 130 | + |
| 131 | + assert_eq!( |
| 132 | + clock.calc_now(now, Duration::from_secs(50)), |
| 133 | + now.checked_add(Duration::from_secs(500)).unwrap(), |
| 134 | + ); |
| 135 | + } |
| 136 | +} |
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