openethereum/ethcore/db/src/cache_manager.rs

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// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.
// Parity Ethereum 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 Ethereum 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 Ethereum. If not, see <http://www.gnu.org/licenses/>.
//! Database cache manager
use std::collections::{VecDeque, HashSet};
use std::hash::Hash;
const COLLECTION_QUEUE_SIZE: usize = 8;
/// DB cache manager
pub struct CacheManager<T> {
pref_cache_size: usize,
max_cache_size: usize,
bytes_per_cache_entry: usize,
cache_usage: VecDeque<HashSet<T>>
}
impl<T> CacheManager<T> where T: Eq + Hash {
/// Create new cache manager with preferred (heap) sizes.
pub fn new(pref_cache_size: usize, max_cache_size: usize, bytes_per_cache_entry: usize) -> Self {
CacheManager {
pref_cache_size: pref_cache_size,
max_cache_size: max_cache_size,
bytes_per_cache_entry: bytes_per_cache_entry,
cache_usage: (0..COLLECTION_QUEUE_SIZE).into_iter().map(|_| Default::default()).collect(),
}
}
/// Mark element as used.
pub fn note_used(&mut self, id: T) {
if !self.cache_usage[0].contains(&id) {
if let Some(c) = self.cache_usage.iter_mut().skip(1).find(|e| e.contains(&id)) {
c.remove(&id);
}
self.cache_usage[0].insert(id);
}
}
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/// Collects unused objects from cache.
/// First params is the current size of the cache.
/// Second one is an with objects to remove. It should also return new size of the cache.
pub fn collect_garbage<F>(&mut self, current_size: usize, mut notify_unused: F) where F: FnMut(HashSet<T>) -> usize {
if current_size < self.pref_cache_size {
self.rotate_cache_if_needed();
return;
}
for _ in 0..COLLECTION_QUEUE_SIZE {
if let Some(back) = self.cache_usage.pop_back() {
let current_size = notify_unused(back);
self.cache_usage.push_front(Default::default());
if current_size < self.max_cache_size {
break
}
}
}
}
fn rotate_cache_if_needed(&mut self) {
if self.cache_usage.is_empty() { return }
if self.cache_usage[0].len() * self.bytes_per_cache_entry > self.pref_cache_size / COLLECTION_QUEUE_SIZE {
if let Some(cache) = self.cache_usage.pop_back() {
self.cache_usage.push_front(cache);
}
}
}
}