[−][src]Struct arc_swap::cache::Cache
Caching handle for ArcSwapAny.
Instead of loading (or leasing or something) the Arc on every request from the shared storage, this keeps another copy inside. Upon request it only cheaply revalidates it is up to date. If it is, access is significantly faster. If it is stale, the full load is done and the cache value is replaced. Under a read-heavy loads, the measured speedup are 10-25 times, depending on the architecture.
There are, however, downsides:
- The handle needs to be kept around by the caller (usually, one per thread). This is fine if there's one global instance, but starts being tricky with eg. data structures build from them.
- As it keeps a copy of the Arc inside the cache, the old value may be kept alive for longer period of time ‒ it is replaced by the new value on load. You may not want to use this if dropping the old value in timely manner is important (possibly because of releasing large amount of RAM or because of closing file handles).
Examples
use std::sync::Arc; use arc_swap::ArcSwap; use arc_swap::cache::Cache; let shared = Arc::new(ArcSwap::from_pointee(42)); // Start 10 worker threads... for _ in 0..10 { let mut cache = Cache::new(Arc::clone(&shared)); std::thread::spawn(move || { // Keep loading it like mad.. loop { let value = cache.load(); do_something(value); } }); } shared.store(Arc::new(12));
Methods
impl<A, T, S> Cache<A, T> where
A: Deref<Target = ArcSwapAny<T, S>>,
T: RefCnt,
S: LockStorage,
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A: Deref<Target = ArcSwapAny<T, S>>,
T: RefCnt,
S: LockStorage,
pub fn new(arc_swap: A) -> Self
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Creates a new caching handle.
The parameter is something dereferencing into an ArcSwapAny
(eg. either to ArcSwap
or ArcSwapOption
). That can be ArcSwapAny
itself, but that's not very useful. But
it also can be a reference to it or Arc
, which makes it possible to share the
ArcSwapAny
with multiple caches or access it in non-cached way too.
pub fn arc_swap(&self) -> &A::Target
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Gives access to the (possibly shared) cached ArcSwapAny
.
pub fn load(&mut self) -> &T
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Loads the currently held value.
This first checks if the cached value is up to date. This check is very cheap.
If it is up to date, the cached value is simply returned without additional costs. If it is outdated, a load is done on the underlying shared storage. The newly loaded value is then stored in the cache and returned.
Trait Implementations
impl<A: Clone, T: Clone> Clone for Cache<A, T>
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fn clone(&self) -> Cache<A, T>
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default fn clone_from(&mut self, source: &Self)
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Performs copy-assignment from source
. Read more
impl<A, T, S> From<A> for Cache<A, T> where
A: Deref<Target = ArcSwapAny<T, S>>,
T: RefCnt,
S: LockStorage,
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A: Deref<Target = ArcSwapAny<T, S>>,
T: RefCnt,
S: LockStorage,
impl<A: Debug, T: Debug> Debug for Cache<A, T>
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Auto Trait Implementations
impl<A, T> Send for Cache<A, T> where
A: Send,
T: Send,
A: Send,
T: Send,
impl<A, T> Sync for Cache<A, T> where
A: Sync,
T: Sync,
A: Sync,
T: Sync,
Blanket Implementations
impl<T> From for T
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impl<T, U> Into for T where
U: From<T>,
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U: From<T>,
impl<T> ToOwned for T where
T: Clone,
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T: Clone,
impl<T, U> TryFrom for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T> Borrow for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T, U> TryInto for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,