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//! A sync RwLock that uses closures to avoid deadlocks.
use std::sync::Arc;
/// A clonable thread safe read write lock designed to make it hard to create dead locks
/// or hold long long lived locks.
pub struct RwShare<T>(Arc<parking_lot::RwLock<T>>);
impl<T> Clone for RwShare<T> {
fn clone(&self) -> Self {
Self(self.0.clone())
}
}
impl<T> Default for RwShare<T>
where
T: Default,
{
fn default() -> Self {
Self(Default::default())
}
}
impl<T> RwShare<T> {
/// Create a new shareable lock
pub fn new(value: T) -> Self {
Self(Arc::new(parking_lot::RwLock::new(value)))
}
/// Get a shared reference to the value. This will not block other readers
/// but will block writers.
/// This should never be used recursively or held over awaits
/// or held for a long time.
pub fn share_ref<R, F>(&self, f: F) -> R
where
F: FnOnce(&T) -> R,
{
let t = self
.0
// First we try to get a fair reader that won't starve writers.
.try_read_for(std::time::Duration::from_millis(100))
// The lock is taking a little longer then we'd like so print an info
// and try for a further 30 seconds.
.or_else(|| {
tracing::warn!(
"Took over 100ms to get a RwShare reader. Conductor might be over utilized"
);
self.0.try_read_for(std::time::Duration::from_secs(30))
})
// However if that fails we may be in a recursive reader dead lock so we will try for
// a recursive reader that may starve writers.
.or_else(|| {
tracing::warn!("Failed to get fair reader, trying for recursive reader");
self.0
.try_read_recursive_for(std::time::Duration::from_secs(60))
})
// Now we are probably at a deadlock or a really long held lock so print an error.
.or_else(|| {
tracing::error!(
"Failed to get a RwShare read lock for over 120s this could be a dead lock"
);
self.0
.try_read_recursive_for(std::time::Duration::from_secs(180))
})
.expect("Failed to take a read lock for over 5 minutes this must be a deadlock");
f(&t)
}
/// Get a mutable reference to the value.
/// This should never be used recursively or held over awaits
/// or held for a long time.
pub fn share_mut<R, F>(&self, f: F) -> R
where
F: FnOnce(&mut T) -> R,
{
// First try to get the write lock in under 100 ms.
let mut t = self
.0
.try_write_for(std::time::Duration::from_millis(100))
// If that fails try print an info and try for a further 120 seconds.
.or_else(|| {
tracing::warn!(
"Took over 100ms to get a RwShare writer. Conductor might be over utilized"
);
self.0.try_write_for(std::time::Duration::from_secs(120))
})
// Now we are probably at a deadlock or a really long held lock so print an error.
.or_else(|| {
tracing::error!(
"Failed to get a RwShare write lock for over 120s this could be a dead lock"
);
self.0.try_write_for(std::time::Duration::from_secs(180))
})
.expect("Failed to take a write lock for over 5 minutes this must be a deadlock");
f(&mut t)
}
}