server: implement key expiration #13
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carllerche
commented
Mar 25, 2020
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| pub(crate) fn set(&self, key: String, value: Bytes, expire: Option<Duration>) { | ||
| let mut state = self.shared.state.lock().unwrap(); | ||
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| // Get and increment the next insertion ID. | ||
| let id = state.next_id; | ||
| state.next_id += 1; | ||
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| // By default, no notification is needed | ||
| let mut notify = false; | ||
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| let expires_at = expire.map(|duration| { | ||
| let when = Instant::now() + duration; | ||
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| // Only notify the worker task if the newly inserted expiration is the | ||
| // **next** key to evict. In this case, the worker needs to be woken up | ||
| // to update its state. | ||
| notify = state.next_expiration() | ||
| .map(|expiration| expiration > when) | ||
| .unwrap_or(true); | ||
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| state.expirations.insert((when, id), key.clone()); | ||
| when | ||
| }); | ||
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| // Insert the entry. | ||
| let prev = state.entries.insert(key, Entry { | ||
| id, | ||
| data: value, | ||
| expires_at, | ||
| }); | ||
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| if let Some(prev) = prev { | ||
| if let Some(when) = prev.expires_at { | ||
| // clear expiration | ||
| state.expirations.remove(&(when, prev.id)); | ||
| } | ||
| } | ||
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| drop(state); | ||
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| if notify { | ||
| self.shared.expire_task.notify(); | ||
| } |
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Setting the value, tracking expiration
carllerche
commented
Mar 25, 2020
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| impl Shared { | ||
| fn purge_expired_keys(&self) -> Option<Instant> { | ||
| let mut state = self.state.lock().unwrap(); | ||
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| // This is needed to make the borrow checker happy. In short, `lock()` | ||
| // returns a `MutexGuard` and not a `&mut State`. The borrow checker is | ||
| // not able to see "through" the mutex guard and determine that it is | ||
| // safe to access both `state.expirations` and `state.entries` mutably, | ||
| // so we get a "real" mutable reference to `State` outside of the loop. | ||
| let state = &mut *state; | ||
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| // Find all keys scheduled to expire **before** now. | ||
| let now = Instant::now(); | ||
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| while let Some((&(when, id), key)) = state.expirations.iter().next() { | ||
| if when > now { | ||
| // Done purging, `when` is the instant at which the next key | ||
| // expires. The worker task will wait until this instant. | ||
| return Some(when); | ||
| } | ||
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| // The key expired, remove it | ||
| state.entries.remove(key); | ||
| state.expirations.remove(&(when, id)); | ||
| } | ||
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| None | ||
| } | ||
| } | ||
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| impl State { | ||
| fn next_expiration(&self) -> Option<Instant> { | ||
| self.expirations.keys().next().map(|expiration| expiration.0) | ||
| } | ||
| } | ||
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| async fn purge_expired_tasks(shared: Arc<Shared>) { | ||
| loop { | ||
| // Purge all keys that are expired. The function returns the instant at | ||
| // which the **next** key will expire. The worker should wait until the | ||
| // instant has passed then purge again. | ||
| if let Some(when) = shared.purge_expired_keys() { | ||
| tokio::select! { | ||
| _ = time::delay_until(when) => {} | ||
| _ = shared.expire_task.notified() => {} | ||
| } | ||
| } else { | ||
| shared.expire_task.notified().await; | ||
| } | ||
| } | ||
| } |
|
I like it! |
EverlastingBugstopper
approved these changes
Mar 25, 2020
src/parse.rs
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| Frame::Integer(v) => Ok(v), | ||
| Frame::Simple(s) => atoi::<u64>(s.as_bytes()).ok_or(ParseError::Invalid), |
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might be worth having more descriptive variable names here instead of v and s. data is probably fine for all of them?
src/db.rs
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| data: Bytes, | ||
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| /// Instant at which the entry expires and should be removed from the | ||
| /// databaase. |
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nit
Suggested change
| /// databaase. | |
| /// database. |
| pub(crate) fn subscribe(&self, key: String) -> broadcast::Receiver<Bytes> { | ||
| use std::collections::hash_map::Entry; | ||
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| let mut state = self.shared.state.lock().unwrap(); |
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should this error be handled / can this be an .expect so readers know what went wrong?
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we could... it shouldn't happen in practice (mutex poisoning). I might punt this to a "polish" pass.
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To clarify, I think your point of better handling poisoned mutexes (or at least having comments) is good. We had the unwrap before and I don't know what the best answer is yet, so i am punting for this PR. I can open an issue to track.
src/db.rs
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| .map(|tx| tx.send(value).unwrap_or(0)) | ||
| .unwrap_or(0) |
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perhaps worth a comment noting what this is doing
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Also renames
Kv->Dbas it covers more than just pure "key-value" (subscriptions).