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// Copyright 2015, 2016 Ethcore (UK) Ltd. | ||
// This file is part of Parity. | ||
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// 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. | ||
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// 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. | ||
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// 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. | ||
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/// 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, | ||
} | ||
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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, | ||
} | ||
} | ||
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/// 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()) | ||
} | ||
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/// 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() | ||
} | ||
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/// 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); | ||
} | ||
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/// Clears everything; the queue is entirely reset. | ||
pub fn reset(&mut self) { | ||
self.pending = None; | ||
self.in_use.clear(); | ||
} | ||
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/// 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)) | ||
} | ||
} | ||
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/// 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() | ||
} | ||
} | ||
} | ||
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#[test] | ||
fn should_find_when_pushed() { | ||
let mut q = UsingQueue::new(2); | ||
q.push(1); | ||
assert!(q.find_if(|i| i == &1).is_some()); | ||
} | ||
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#[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()); | ||
} | ||
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#[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()); | ||
} | ||
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#[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()); | ||
} | ||
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#[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()); | ||
} | ||
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#[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)); | ||
} | ||
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#[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)); | ||
} | ||
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#[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()); | ||
} | ||
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#[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)); | ||
} | ||
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#[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); | ||
} | ||
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#[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); | ||
} | ||
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#[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)); | ||
} |