mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
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186 lines
4.9 KiB
Rust
186 lines
4.9 KiB
Rust
// Copyright 2018 The Chromium OS Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE-BSD-3-Clause file.
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use std::collections::hash_map::IterMut;
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use std::collections::HashMap;
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use std::io;
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use std::ops::{Index, IndexMut};
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use std::slice::SliceIndex;
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/// Trait that allows for checking if an implementor is dirty. Useful for types that are cached so
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/// it can be checked if they need to be committed to disk.
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pub trait Cacheable {
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/// Used to check if the item needs to be written out or if it can be discarded.
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fn dirty(&self) -> bool;
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}
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#[derive(Clone, Debug)]
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/// Represents a vector that implements the `Cacheable` trait so it can be held in a cache.
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pub struct VecCache<T: 'static + Copy + Default> {
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vec: Box<[T]>,
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dirty: bool,
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}
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impl<T: 'static + Copy + Default> VecCache<T> {
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/// Creates a `VecCache` that can hold `count` elements.
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pub fn new(count: usize) -> VecCache<T> {
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VecCache {
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vec: vec![Default::default(); count].into_boxed_slice(),
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dirty: true,
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}
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}
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/// Creates a `VecCache` from the passed in `vec`.
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pub fn from_vec(vec: Vec<T>) -> VecCache<T> {
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VecCache {
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vec: vec.into_boxed_slice(),
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dirty: false,
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}
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}
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pub fn get<I>(&self, index: I) -> Option<&<I as SliceIndex<[T]>>::Output>
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where
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I: SliceIndex<[T]>,
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{
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self.vec.get(index)
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}
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/// Gets a reference to the underlying vector.
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pub fn get_values(&self) -> &[T] {
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&self.vec
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}
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/// Mark this cache element as clean.
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pub fn mark_clean(&mut self) {
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self.dirty = false;
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}
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/// Returns the number of elements in the vector.
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pub fn len(&self) -> usize {
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self.vec.len()
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}
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}
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impl<T: 'static + Copy + Default> Cacheable for VecCache<T> {
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fn dirty(&self) -> bool {
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self.dirty
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}
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}
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impl<T: 'static + Copy + Default> Index<usize> for VecCache<T> {
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type Output = T;
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fn index(&self, index: usize) -> &T {
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self.vec.index(index)
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}
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}
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impl<T: 'static + Copy + Default> IndexMut<usize> for VecCache<T> {
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fn index_mut(&mut self, index: usize) -> &mut T {
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self.dirty = true;
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self.vec.index_mut(index)
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}
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}
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#[derive(Clone, Debug)]
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pub struct CacheMap<T: Cacheable> {
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capacity: usize,
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map: HashMap<usize, T>,
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}
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impl<T: Cacheable> CacheMap<T> {
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pub fn new(capacity: usize) -> Self {
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CacheMap {
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capacity,
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map: HashMap::with_capacity(capacity),
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}
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}
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pub fn contains_key(&self, key: usize) -> bool {
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self.map.contains_key(&key)
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}
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pub fn get(&self, index: usize) -> Option<&T> {
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self.map.get(&index)
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}
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pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
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self.map.get_mut(&index)
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}
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pub fn iter_mut(&mut self) -> IterMut<usize, T> {
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self.map.iter_mut()
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}
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// Check if the refblock cache is full and we need to evict.
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pub fn insert<F>(&mut self, index: usize, block: T, write_callback: F) -> io::Result<()>
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where
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F: FnOnce(usize, T) -> io::Result<()>,
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{
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if self.map.len() == self.capacity {
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// TODO(dgreid) - smarter eviction strategy.
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let to_evict = *self.map.iter().next().unwrap().0;
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if let Some(evicted) = self.map.remove(&to_evict) {
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if evicted.dirty() {
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write_callback(to_evict, evicted)?;
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}
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}
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}
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self.map.insert(index, block);
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Ok(())
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}
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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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struct NumCache(pub u64);
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impl Cacheable for NumCache {
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fn dirty(&self) -> bool {
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true
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}
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}
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#[test]
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fn evicts_when_full() {
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let mut cache = CacheMap::<NumCache>::new(3);
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let mut evicted = None;
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cache
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.insert(0, NumCache(5), |index, _| {
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evicted = Some(index);
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Ok(())
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})
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.unwrap();
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assert_eq!(evicted, None);
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cache
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.insert(1, NumCache(6), |index, _| {
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evicted = Some(index);
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Ok(())
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})
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.unwrap();
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assert_eq!(evicted, None);
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cache
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.insert(2, NumCache(7), |index, _| {
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evicted = Some(index);
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Ok(())
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})
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.unwrap();
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assert_eq!(evicted, None);
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cache
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.insert(3, NumCache(8), |index, _| {
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evicted = Some(index);
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Ok(())
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})
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.unwrap();
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assert!(evicted.is_some());
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// Check that three of the four items inserted are still there and that the most recently
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// inserted is one of them.
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let num_items = (0..=3).filter(|k| cache.contains_key(*k)).count();
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assert_eq!(num_items, 3);
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assert!(cache.contains_key(3));
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}
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}
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