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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT | ||
// file at the top-level directory of this distribution and at | ||
// http://rust-lang.org/COPYRIGHT. | ||
// | ||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
// option. This file may not be copied, modified, or distributed | ||
// except according to those terms. | ||
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use fnv::FnvHashMap; | ||
use std::hash::Hash; | ||
use std::ops; | ||
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#[cfg(test)] | ||
mod test; | ||
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pub struct SnapshotMap<K, V> | ||
where K: Hash + Clone + Eq | ||
{ | ||
map: FnvHashMap<K, V>, | ||
undo_log: Vec<UndoLog<K, V>>, | ||
} | ||
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pub struct Snapshot { | ||
len: usize | ||
} | ||
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enum UndoLog<K, V> { | ||
OpenSnapshot, | ||
CommittedSnapshot, | ||
Inserted(K), | ||
Overwrite(K, V), | ||
} | ||
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impl<K, V> SnapshotMap<K, V> | ||
where K: Hash + Clone + Eq | ||
{ | ||
pub fn new() -> Self { | ||
SnapshotMap { | ||
map: FnvHashMap(), | ||
undo_log: vec![] | ||
} | ||
} | ||
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pub fn insert(&mut self, key: K, value: V) -> bool { | ||
match self.map.insert(key.clone(), value) { | ||
None => { | ||
if !self.undo_log.is_empty() { | ||
self.undo_log.push(UndoLog::Inserted(key)); | ||
} | ||
true | ||
} | ||
Some(old_value) => { | ||
if !self.undo_log.is_empty() { | ||
self.undo_log.push(UndoLog::Overwrite(key, old_value)); | ||
} | ||
false | ||
} | ||
} | ||
} | ||
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pub fn remove(&mut self, key: K) -> bool { | ||
match self.map.remove(&key) { | ||
Some(old_value) => { | ||
if !self.undo_log.is_empty() { | ||
self.undo_log.push(UndoLog::Overwrite(key, old_value)); | ||
} | ||
true | ||
} | ||
None => { | ||
false | ||
} | ||
} | ||
} | ||
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pub fn get(&self, key: &K) -> Option<&V> { | ||
self.map.get(key) | ||
} | ||
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pub fn snapshot(&mut self) -> Snapshot { | ||
self.undo_log.push(UndoLog::OpenSnapshot); | ||
let len = self.undo_log.len() - 1; | ||
Snapshot { len: len } | ||
} | ||
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fn assert_open_snapshot(&self, snapshot: &Snapshot) { | ||
assert!(snapshot.len < self.undo_log.len()); | ||
assert!(match self.undo_log[snapshot.len] { | ||
UndoLog::OpenSnapshot => true, | ||
_ => false | ||
}); | ||
} | ||
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pub fn commit(&mut self, snapshot: Snapshot) { | ||
self.assert_open_snapshot(&snapshot); | ||
if snapshot.len == 0 { | ||
// The root snapshot. | ||
self.undo_log.truncate(0); | ||
} else { | ||
self.undo_log[snapshot.len] = UndoLog::CommittedSnapshot; | ||
} | ||
} | ||
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pub fn rollback_to(&mut self, snapshot: Snapshot) { | ||
self.assert_open_snapshot(&snapshot); | ||
while self.undo_log.len() > snapshot.len + 1 { | ||
match self.undo_log.pop().unwrap() { | ||
UndoLog::OpenSnapshot => { | ||
panic!("cannot rollback an uncommitted snapshot"); | ||
} | ||
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UndoLog::CommittedSnapshot => { } | ||
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UndoLog::Inserted(key) => { | ||
self.map.remove(&key); | ||
} | ||
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UndoLog::Overwrite(key, old_value) => { | ||
self.map.insert(key, old_value); | ||
} | ||
} | ||
} | ||
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let v = self.undo_log.pop().unwrap(); | ||
assert!(match v { UndoLog::OpenSnapshot => true, _ => false }); | ||
assert!(self.undo_log.len() == snapshot.len); | ||
} | ||
} | ||
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impl<'k, K, V> ops::Index<&'k K> for SnapshotMap<K, V> | ||
where K: Hash + Clone + Eq | ||
{ | ||
type Output = V; | ||
fn index(&self, key: &'k K) -> &V { | ||
&self.map[key] | ||
} | ||
} |
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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT | ||
// file at the top-level directory of this distribution and at | ||
// http://rust-lang.org/COPYRIGHT. | ||
// | ||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
// option. This file may not be copied, modified, or distributed | ||
// except according to those terms. | ||
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use super::SnapshotMap; | ||
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#[test] | ||
fn basic() { | ||
let mut map = SnapshotMap::new(); | ||
map.insert(22, "twenty-two"); | ||
let snapshot = map.snapshot(); | ||
map.insert(22, "thirty-three"); | ||
assert_eq!(map[&22], "thirty-three"); | ||
map.insert(44, "fourty-four"); | ||
assert_eq!(map[&44], "fourty-four"); | ||
assert_eq!(map.get(&33), None); | ||
map.rollback_to(snapshot); | ||
assert_eq!(map[&22], "twenty-two"); | ||
assert_eq!(map.get(&33), None); | ||
assert_eq!(map.get(&44), None); | ||
} | ||
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#[test] | ||
#[should_panic] | ||
fn out_of_order() { | ||
let mut map = SnapshotMap::new(); | ||
map.insert(22, "twenty-two"); | ||
let snapshot1 = map.snapshot(); | ||
let _snapshot2 = map.snapshot(); | ||
map.rollback_to(snapshot1); | ||
} | ||
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#[test] | ||
fn nested_commit_then_rollback() { | ||
let mut map = SnapshotMap::new(); | ||
map.insert(22, "twenty-two"); | ||
let snapshot1 = map.snapshot(); | ||
let snapshot2 = map.snapshot(); | ||
map.insert(22, "thirty-three"); | ||
map.commit(snapshot2); | ||
assert_eq!(map[&22], "thirty-three"); | ||
map.rollback_to(snapshot1); | ||
assert_eq!(map[&22], "twenty-two"); | ||
} |