139 lines
3.2 KiB
Rust
139 lines
3.2 KiB
Rust
// Copyright 2015-2018 Parity Technologies (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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extern crate parking_lot;
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use std::collections::VecDeque;
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use std::ops::{Deref, DerefMut};
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use std::sync::atomic::AtomicUsize;
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use std::sync::atomic::Ordering;
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use parking_lot::{Mutex, MutexGuard};
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/// Implement to allow a type with a len() method to be used
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/// with [`LenCachingMutex`](struct.LenCachingMutex.html)
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pub trait Len {
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fn len(&self) -> usize;
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}
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impl<T> Len for Vec<T> {
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fn len(&self) -> usize { self.len() }
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}
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impl<T> Len for VecDeque<T> {
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fn len(&self) -> usize { self.len() }
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}
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/// Can be used in place of a `Mutex` where reading `T`'s `len()` without
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/// needing to lock, is advantageous.
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/// When the Guard is released, `T`'s `len()` will be cached.
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/// The cached `len()` may be at most 1 lock behind current state.
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pub struct LenCachingMutex<T> {
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data: Mutex<T>,
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len: AtomicUsize,
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}
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impl<T: Len> LenCachingMutex<T> {
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pub fn new(data: T) -> LenCachingMutex<T> {
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LenCachingMutex {
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len: AtomicUsize::new(data.len()),
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data: Mutex::new(data),
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}
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}
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/// Load the most recent value returned from your `T`'s `len()`
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pub fn load_len(&self) -> usize {
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self.len.load(Ordering::SeqCst)
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}
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pub fn lock(&self) -> Guard<T> {
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Guard {
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mutex_guard: self.data.lock(),
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len: &self.len,
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}
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}
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pub fn try_lock(&self) -> Option<Guard<T>> {
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Some( Guard {
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mutex_guard: self.data.try_lock()?,
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len: &self.len,
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})
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}
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}
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pub struct Guard<'a, T: Len + 'a> {
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mutex_guard: MutexGuard<'a, T>,
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len: &'a AtomicUsize,
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}
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impl<'a, T: Len> Guard<'a, T> {
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pub fn inner_mut(&mut self) -> &mut MutexGuard<'a, T> {
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&mut self.mutex_guard
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}
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pub fn inner(&self) -> &MutexGuard<'a, T> {
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&self.mutex_guard
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}
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}
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impl<'a, T: Len> Drop for Guard<'a, T> {
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fn drop(&mut self) {
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self.len.store(self.mutex_guard.len(), Ordering::SeqCst);
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}
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}
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impl<'a, T: Len> Deref for Guard<'a, T> {
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type Target = T;
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fn deref(&self) -> &T {
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self.mutex_guard.deref()
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}
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}
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impl<'a, T: Len> DerefMut for Guard<'a, T> {
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fn deref_mut(&mut self) -> &mut T {
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self.mutex_guard.deref_mut()
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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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use std::collections::VecDeque;
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#[test]
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fn caches_len() {
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let v = vec![1,2,3];
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let lcm = LenCachingMutex::new(v);
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assert_eq!(lcm.load_len(), 3);
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lcm.lock().push(4);
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assert_eq!(lcm.load_len(), 4);
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}
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#[test]
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fn works_with_vec() {
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let v: Vec<i32> = Vec::new();
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let lcm = LenCachingMutex::new(v);
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assert!(lcm.lock().is_empty());
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}
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#[test]
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fn works_with_vecdeque() {
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let v: VecDeque<i32> = VecDeque::new();
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let lcm = LenCachingMutex::new(v);
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lcm.lock().push_front(4);
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assert_eq!(lcm.load_len(), 1);
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}
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}
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