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July 27, 2024 16:46
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sans-io with coroutines
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| #![feature(stmt_expr_attributes, coroutines, coroutine_trait)] | |
| use std::ops::Coroutine; | |
| use std::pin::pin; | |
| use std::thread::sleep; | |
| use std::time::{Duration, Instant}; | |
| fn main() { | |
| let mut machine = pin!(make_machine()); | |
| let resp = machine.as_mut().resume(Input::ping(Instant::now())); | |
| println!("{resp:?}"); | |
| sleep(Duration::from_millis(150)); | |
| let resp = machine.as_mut().resume(Input::ping(Instant::now())); | |
| println!("{resp:?}"); | |
| } | |
| const NUM_PINGS_FOR_EVERY_PONG: u64 = 2; | |
| const MAX_DURATION_BETWEEN_PINGS: Duration = Duration::from_millis(200); | |
| fn make_machine() -> impl Coroutine<Input, Yield = Output, Return = ()> { | |
| return #[coroutine] | |
| move |mut input: Input| { | |
| let mut last_ping_at: Option<Instant> = None; | |
| let mut outstanding_pings = NUM_PINGS_FOR_EVERY_PONG; | |
| loop { | |
| let now = input.now; | |
| let since_last = last_ping_at.map(|l| now.duration_since(l)); | |
| let expired = since_last | |
| .map(|d| d > MAX_DURATION_BETWEEN_PINGS) | |
| .unwrap_or(false); | |
| if expired { | |
| // Failure | |
| return (); | |
| } | |
| match input.kind { | |
| Kind::Ping => { | |
| last_ping_at = Some(now); | |
| outstanding_pings -= 1; | |
| if outstanding_pings == 0 { | |
| last_ping_at = None; | |
| outstanding_pings = NUM_PINGS_FOR_EVERY_PONG; | |
| input = yield Output::Pong; | |
| } else { | |
| let expires_at = last_ping_at | |
| .map(|d| MAX_DURATION_BETWEEN_PINGS - now.duration_since(d)) | |
| .or(Some(MAX_DURATION_BETWEEN_PINGS)); | |
| input = yield Output::Wait(expires_at); | |
| } | |
| } | |
| Kind::Time => { | |
| let remaining = since_last.map(|d| MAX_DURATION_BETWEEN_PINGS - d); | |
| input = yield Output::Wait(remaining); | |
| } | |
| } | |
| } | |
| }; | |
| } | |
| struct Input { | |
| now: Instant, | |
| kind: Kind, | |
| } | |
| #[derive(Debug, PartialEq, Eq)] | |
| enum Kind { | |
| Ping, | |
| Time, | |
| } | |
| impl Input { | |
| fn ping(now: Instant) -> Self { | |
| Self { | |
| now, | |
| kind: Kind::Ping, | |
| } | |
| } | |
| fn time(now: Instant) -> Self { | |
| Self { | |
| now, | |
| kind: Kind::Time, | |
| } | |
| } | |
| } | |
| #[derive(Debug, PartialEq, Eq)] | |
| enum Output { | |
| Pong, | |
| Wait(Option<Duration>), | |
| } | |
| #[cfg(test)] | |
| mod tests { | |
| use super::*; | |
| use std::ops::CoroutineState::*; | |
| #[test] | |
| fn test_two_pings_to_a_pong() { | |
| let start = Instant::now(); | |
| let mut machine = pin!(make_machine()); | |
| let resp = machine.as_mut().resume(Input::ping(start)); | |
| assert_eq!( | |
| resp, | |
| Yielded(Output::Wait(Some(Duration::from_millis(200)))) | |
| ); | |
| let resp = machine | |
| .as_mut() | |
| .resume(Input::ping(start + Duration::from_millis(150))); | |
| assert_eq!(resp, Yielded(Output::Pong)); | |
| } | |
| #[test] | |
| fn test_too_late() { | |
| let start = Instant::now(); | |
| let mut machine = pin!(make_machine()); | |
| let resp = machine.as_mut().resume(Input::ping(start)); | |
| assert_eq!( | |
| resp, | |
| Yielded(Output::Wait(Some(Duration::from_millis(200)))) | |
| ); | |
| let resp = machine | |
| .as_mut() | |
| .resume(Input::ping(start + Duration::from_millis(250))); | |
| assert_eq!(resp, Complete(())); | |
| } | |
| #[test] | |
| fn test_no_second_ping() { | |
| let start = Instant::now(); | |
| let mut machine = pin!(make_machine()); | |
| let resp = machine.as_mut().resume(Input::ping(start)); | |
| assert_eq!( | |
| resp, | |
| Yielded(Output::Wait(Some(Duration::from_millis(200)))) | |
| ); | |
| let resp = machine | |
| .as_mut() | |
| .resume(Input::time(start + Duration::from_millis(250))); | |
| assert_eq!(resp, Complete(())); | |
| } | |
| } |
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