85 lines
2.6 KiB
Rust
85 lines
2.6 KiB
Rust
// Copyright 2015, 2016 Ethcore (UK) Ltd.
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// This file is part of Parity.
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// Parity is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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// Parity is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with Parity. If not, see <http://www.gnu.org/licenses/>.
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//! Helper module that should be used to randomly squeeze
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//! caches to a given size in bytes
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//!
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//! ```
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//! extern crate heapsize;
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//! extern crate ethcore_util as util;
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//! use std::collections::HashMap;
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//! use std::mem::size_of;
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//! use heapsize::HeapSizeOf;
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//! use util::squeeze::Squeeze;
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//!
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//! fn main() {
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//! let initial_size = 60;
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//! let mut map: HashMap<u8, u8> = HashMap::with_capacity(initial_size);
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//! assert!(map.capacity() >= initial_size);
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//! for i in 0..initial_size {
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//! map.insert(i as u8, i as u8);
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//! }
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//!
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//! assert_eq!(map.heap_size_of_children(), map.capacity() * 2 * size_of::<u8>());
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//! assert_eq!(map.len(), initial_size);
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//! let initial_heap_size = map.heap_size_of_children();
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//!
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//! // squeeze it to size of key and value
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//! map.squeeze(2 * size_of::<u8>());
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//! assert_eq!(map.len(), 1);
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//!
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//! // its likely that heap size was reduced, but we can't be 100% sure
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//! assert!(initial_heap_size >= map.heap_size_of_children());
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//! }
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//! ```
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use std::collections::HashMap;
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use std::hash::Hash;
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use heapsize::HeapSizeOf;
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/// Should be used to squeeze collections to certain size in bytes
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pub trait Squeeze {
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/// Try to reduce collection size to `size` bytes
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fn squeeze(&mut self, size: usize);
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}
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impl<K, T> Squeeze for HashMap<K, T> where K: Eq + Hash + Clone + HeapSizeOf, T: HeapSizeOf {
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fn squeeze(&mut self, size: usize) {
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if self.is_empty() {
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return
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}
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let size_of_entry = self.heap_size_of_children() / self.capacity();
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let all_entries = size_of_entry * self.len();
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let mut shrinked_size = all_entries;
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while !self.is_empty() && shrinked_size > size {
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// could be optimized
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let key = self.keys().next().unwrap().clone();
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self.remove(&key);
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shrinked_size -= size_of_entry;
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}
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self.shrink_to_fit();
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// if we squeezed something, but not enough, squeeze again
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if all_entries != shrinked_size && self.heap_size_of_children() > size {
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self.squeeze(size);
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}
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}
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}
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