openethereum/util/src/using_queue.rs

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2016-03-24 08:49:54 +01:00
// Copyright 2015, 2016 Ethcore (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/>.
//! Queue-like datastructure including notion of usage.
/// Special queue-like datastructure that includes the notion of
/// usage to avoid items that were queued but never used from making it into
/// the queue.
pub struct UsingQueue<T> where T: Clone {
/// Not yet being sealed by a miner, but if one asks for work, we'd prefer they do this.
pending: Option<T>,
/// Currently being sealed by miners.
in_use: Vec<T>,
/// The maximum allowable number of items in_use.
max_size: usize,
}
impl<T> UsingQueue<T> where T: Clone {
/// Create a new struct with a maximum size of `max_size`.
pub fn new(max_size: usize) -> UsingQueue<T> {
UsingQueue {
pending: None,
in_use: vec![],
max_size: max_size,
}
}
/// Return a reference to the item at the top of the queue (or `None` if the queue is empty);
/// it doesn't constitute noting that the item is used.
pub fn peek_last_ref(&self) -> Option<&T> {
self.pending.as_ref().or(self.in_use.last())
}
/// Return a reference to the item at the top of the queue (or `None` if the queue is empty);
/// this constitutes using the item and will remain in the queue for at least another
/// `max_size` invocations of `push()`.
pub fn use_last_ref(&mut self) -> Option<&T> {
if let Some(x) = self.pending.take() {
self.in_use.push(x);
if self.in_use.len() > self.max_size {
self.in_use.remove(0);
}
}
self.in_use.last()
}
/// Place an item on the end of the queue. The previously `push()`ed item will be removed
/// if `use_last_ref()` since it was `push()`ed.
pub fn push(&mut self, b: T) {
self.pending = Some(b);
}
/// Clears everything; the queue is entirely reset.
pub fn reset(&mut self) {
self.pending = None;
self.in_use.clear();
}
/// Returns `Some` reference to first block that `f` returns `true` with it as a parameter
/// or `None` if no such block exists in the queue.
pub fn find_if<P>(&self, predicate: P) -> Option<&T> where P: Fn(&T) -> bool {
if self.pending.as_ref().map(|r| predicate(r)).unwrap_or(false) {
self.pending.as_ref()
} else {
self.in_use.iter().find(|r| predicate(r))
}
}
/// Returns the most recently pushed block if `f` returns `true` with a reference to it as
/// a parameter, otherwise `None`.
/// Will not destroy a block if a reference to it has previously been returned by `use_last_ref`,
/// but rather clone it.
pub fn pop_if<P>(&mut self, predicate: P) -> Option<T> where P: Fn(&T) -> bool {
// a bit clumsy - TODO: think about a nicer way of expressing this.
if let Some(x) = self.pending.take() {
if predicate(&x) {
Some(x)
} else {
self.pending = Some(x);
None
}
} else {
self.in_use.last().into_iter().filter(|x| predicate(x)).next().cloned()
}
}
}
#[test]
fn should_find_when_pushed() {
let mut q = UsingQueue::new(2);
q.push(1);
assert!(q.find_if(|i| i == &1).is_some());
}
#[test]
fn should_find_when_pushed_and_used() {
let mut q = UsingQueue::new(2);
q.push(1);
q.use_last_ref();
assert!(q.find_if(|i| i == &1).is_some());
}
#[test]
fn should_find_when_others_used() {
let mut q = UsingQueue::new(2);
q.push(1);
q.use_last_ref();
q.push(2);
q.use_last_ref();
assert!(q.find_if(|i| i == &1).is_some());
}
#[test]
fn should_not_find_when_too_many_used() {
let mut q = UsingQueue::new(1);
q.push(1);
q.use_last_ref();
q.push(2);
q.use_last_ref();
assert!(q.find_if(|i| i == &1).is_none());
}
#[test]
fn should_not_find_when_not_used_and_then_pushed() {
let mut q = UsingQueue::new(3);
q.push(1);
q.push(2);
q.use_last_ref();
assert!(q.find_if(|i| i == &1).is_none());
}
#[test]
fn should_peek_correctly_after_push() {
let mut q = UsingQueue::new(3);
q.push(1);
assert_eq!(q.peek_last_ref(), Some(&1));
q.push(2);
assert_eq!(q.peek_last_ref(), Some(&2));
}
#[test]
fn should_inspect_correctly() {
let mut q = UsingQueue::new(3);
q.push(1);
assert_eq!(q.use_last_ref(), Some(&1));
assert_eq!(q.peek_last_ref(), Some(&1));
q.push(2);
assert_eq!(q.use_last_ref(), Some(&2));
assert_eq!(q.peek_last_ref(), Some(&2));
}
#[test]
fn should_not_find_when_not_used_peeked_and_then_pushed() {
let mut q = UsingQueue::new(3);
q.push(1);
q.peek_last_ref();
q.push(2);
q.use_last_ref();
assert!(q.find_if(|i| i == &1).is_none());
}
#[test]
fn should_pop_used() {
let mut q = UsingQueue::new(3);
q.push(1);
q.use_last_ref();
let popped = q.pop_if(|i| i == &1);
assert_eq!(popped, Some(1));
}
#[test]
fn should_pop_unused() {
let mut q = UsingQueue::new(3);
q.push(1);
assert_eq!(q.pop_if(|i| i == &1), Some(1));
assert_eq!(q.pop_if(|i| i == &1), None);
}
#[test]
fn should_not_pop_unused_before_used() {
let mut q = UsingQueue::new(3);
q.push(1);
q.push(2);
let popped = q.pop_if(|i| i == &1);
assert_eq!(popped, None);
}
#[test]
fn should_not_remove_used_popped() {
let mut q = UsingQueue::new(3);
q.push(1);
q.use_last_ref();
assert_eq!(q.pop_if(|i| i == &1), Some(1));
assert_eq!(q.pop_if(|i| i == &1), Some(1));
}