94 lines
3.3 KiB
Rust
94 lines
3.3 KiB
Rust
use std::sync::Arc;
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use tokio::sync::mpsc;
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use tokio::time::{Duration, Instant};
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use crate::state_store::{PersistState, StateStore};
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/// A handle the registry uses to request a persist. `mark_dirty(state)` records
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/// the latest snapshot and (re)arms the debounce timer.
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#[derive(Clone)]
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pub struct Persister {
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tx: mpsc::Sender<PersistState>,
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}
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impl Persister {
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pub fn mark_dirty(&self, state: PersistState) {
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// Best-effort; dropping a snapshot is fine because a newer one will arrive.
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let _ = self.tx.try_send(state);
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}
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}
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/// Spawn the debounce task. Returns the `Persister` handle.
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/// `debounce` is configurable so tests can use a short window.
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pub fn spawn(store: Arc<dyn StateStore>, debounce: Duration) -> Persister {
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let (tx, mut rx) = mpsc::channel::<PersistState>(64);
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tokio::spawn(async move {
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let mut latest: Option<PersistState> = None;
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let mut deadline: Option<Instant> = None;
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loop {
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let timer = async {
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match deadline {
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Some(d) => tokio::time::sleep_until(d).await,
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None => std::future::pending::<()>().await,
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}
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};
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tokio::select! {
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msg = rx.recv() => {
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match msg {
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Some(state) => {
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latest = Some(state);
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deadline = Some(Instant::now() + debounce);
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}
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None => {
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// channel closed: final flush then exit
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if let Some(s) = latest.take() { let _ = store.save(&s); }
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break;
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}
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}
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}
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_ = timer => {
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if let Some(s) = latest.take() { let _ = store.save(&s); }
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deadline = None;
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}
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}
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}
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});
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Persister { tx }
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use std::sync::atomic::{AtomicUsize, Ordering};
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use std::sync::Mutex;
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struct CountingStore {
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saves: AtomicUsize,
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last: Mutex<Option<PersistState>>,
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}
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impl StateStore for CountingStore {
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fn load(&self) -> anyhow::Result<PersistState> { Ok(PersistState::default()) }
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fn save(&self, state: &PersistState) -> anyhow::Result<()> {
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self.saves.fetch_add(1, Ordering::SeqCst);
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*self.last.lock().unwrap() = Some(state.clone());
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Ok(())
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}
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}
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#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
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async fn burst_coalesces_to_one_save() {
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let store = Arc::new(CountingStore { saves: AtomicUsize::new(0), last: Mutex::new(None) });
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let p = spawn(store.clone(), Duration::from_millis(80));
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// Fire several dirty signals rapidly.
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for v in 1..=5u32 {
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let mut s = PersistState::default();
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s.version = v;
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p.mark_dirty(s);
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tokio::time::sleep(Duration::from_millis(10)).await;
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}
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// Wait past the debounce window.
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tokio::time::sleep(Duration::from_millis(200)).await;
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assert_eq!(store.saves.load(Ordering::SeqCst), 1, "burst should coalesce to one save");
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assert_eq!(store.last.lock().unwrap().as_ref().unwrap().version, 5, "save uses the latest snapshot");
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}
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}
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