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Merge pull request #474 from Chronostasys/master

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fix: wrong condvar usage
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Niko Matsakis 2024-04-02 10:15:49 +00:00 committed by GitHub
commit 9a0a6518e7
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1 changed files with 15 additions and 5 deletions
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20
components/salsa-2022/src/storage.rs
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@ -48,6 +48,9 @@ struct Shared<DB: HasJars> {
/// Conditional variable that is used to coordinate cancellation.
/// When the main thread writes to the database, it blocks until each of the snapshots can be cancelled.
cvar: Arc<Condvar>,
/// Mutex that is used to protect the `jars` field when waiting for snapshots to be dropped.
noti_lock: Arc<parking_lot::Mutex<()>>,
}
// ANCHOR: default
@ -62,6 +65,7 @@ where
shared: Shared {
jars: Some(Arc::from(jars)),
cvar: Arc::new(Default::default()),
noti_lock: Arc::new(parking_lot::Mutex::new(())),
},
routes: Arc::new(routes),
runtime: Runtime::default(),
@ -135,19 +139,23 @@ where
loop {
self.runtime.set_cancellation_flag();
// Acquire lock before we check if we have unique access to the jars.
// If we do not yet have unique access, we will go to sleep and wait for
// the snapshots to be dropped, which will signal the cond var associated
// with this lock.
//
// NB: We have to acquire the lock first to ensure that we can check for
// unique access and go to sleep waiting on the condvar atomically,
// as described in PR #474.
let mut guard = self.shared.noti_lock.lock();
// If we have unique access to the jars, we are done.
if Arc::get_mut(self.shared.jars.as_mut().unwrap()).is_some() {
return;
}
// Otherwise, wait until some other storage entities have dropped.
// We create a mutex here because the cvar api requires it, but we
// don't really need one as the data being protected is actually
// the jars above.
//
// The cvar `self.shared.cvar` is notified by the `Drop` impl.
let mutex = parking_lot::Mutex::new(());
let mut guard = mutex.lock();
self.shared.cvar.wait(&mut guard);
}
}
@ -167,6 +175,7 @@ where
Self {
jars: self.jars.clone(),
cvar: self.cvar.clone(),
noti_lock: self.noti_lock.clone(),
}
}
}
@ -178,6 +187,7 @@ where
fn drop(&mut self) {
// Drop the Arc reference before the cvar is notified,
// since other threads are sleeping, waiting for it to reach 1.
let _guard = self.shared.noti_lock.lock();
drop(self.shared.jars.take());
self.shared.cvar.notify_all();
}