openethereum/util/memory_cache/src/lib.rs

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// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.
// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Parity. If not, see <http://www.gnu.org/licenses/>.
//! Lru-cache related utilities as quick-and-dirty wrappers around the lru-cache
//! crate.
// TODO: push changes upstream in a clean way.
extern crate heapsize;
extern crate lru_cache;
use heapsize::HeapSizeOf;
use lru_cache::LruCache;
use std::hash::Hash;
const INITIAL_CAPACITY: usize = 4;
/// An LRU-cache which operates on memory used.
pub struct MemoryLruCache<K: Eq + Hash, V: HeapSizeOf> {
inner: LruCache<K, V>,
cur_size: usize,
max_size: usize,
}
// amount of memory used when the item will be put on the heap.
fn heap_size_of<T: HeapSizeOf>(val: &T) -> usize {
::std::mem::size_of::<T>() + val.heap_size_of_children()
}
impl<K: Eq + Hash, V: HeapSizeOf> MemoryLruCache<K, V> {
/// Create a new cache with a maximum size in bytes.
pub fn new(max_size: usize) -> Self {
MemoryLruCache {
inner: LruCache::new(INITIAL_CAPACITY),
max_size: max_size,
cur_size: 0,
}
}
/// Insert an item.
pub fn insert(&mut self, key: K, val: V) {
let cap = self.inner.capacity();
// grow the cache as necessary; it operates on amount of items
// but we're working based on memory usage.
if self.inner.len() == cap && self.cur_size < self.max_size {
self.inner.set_capacity(cap * 2);
}
self.cur_size += heap_size_of(&val);
// account for any element displaced from the cache.
if let Some(lru) = self.inner.insert(key, val) {
self.cur_size -= heap_size_of(&lru);
}
// remove elements until we are below the memory target.
while self.cur_size > self.max_size {
match self.inner.remove_lru() {
Some((_, v)) => self.cur_size -= heap_size_of(&v),
_ => break,
}
}
}
/// Get a reference to an item in the cache. It is a logic error for its
/// heap size to be altered while borrowed.
pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
self.inner.get_mut(key)
}
/// Currently-used size of values in bytes.
pub fn current_size(&self) -> usize {
self.cur_size
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_works() {
let mut cache = MemoryLruCache::new(256);
let val1 = vec![0u8; 100];
let size1 = heap_size_of(&val1);
cache.insert("hello", val1);
assert_eq!(cache.current_size(), size1);
let val2 = vec![0u8; 210];
let size2 = heap_size_of(&val2);
cache.insert("world", val2);
assert!(cache.get_mut(&"hello").is_none());
assert!(cache.get_mut(&"world").is_some());
assert_eq!(cache.current_size(), size2);
}
}