LRU cache for dapps (#2006)

Conflicts:
	dapps/Cargo.toml
	dapps/src/lib.rs

dapps/src/apps/cache.rs

@@ -0,0 +1,128 @@
+// 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/>.
+
+//! Fetchable Dapps support.
+
+use std::fs;
+use std::sync::{Arc};
+use std::sync::atomic::{AtomicBool, Ordering};
+
+use linked_hash_map::LinkedHashMap;
+use page::LocalPageEndpoint;
+
+pub enum ContentStatus {
+	Fetching(Arc<AtomicBool>),
+	Ready(LocalPageEndpoint),
+}
+
+#[derive(Default)]
+pub struct ContentCache {
+	cache: LinkedHashMap<String, ContentStatus>,
+}
+
+impl ContentCache {
+	pub fn insert(&mut self, content_id: String, status: ContentStatus) -> Option<ContentStatus> {
+		self.cache.insert(content_id, status)
+	}
+
+	pub fn remove(&mut self, content_id: &str) -> Option<ContentStatus> {
+		self.cache.remove(content_id)
+	}
+
+	pub fn get(&mut self, content_id: &str) -> Option<&mut ContentStatus> {
+		self.cache.get_refresh(content_id)
+	}
+
+	pub fn clear_garbage(&mut self, expected_size: usize) -> Vec<(String, ContentStatus)> {
+		let mut len = self.cache.len();
+
+		if len <= expected_size {
+			return Vec::new();
+		}
+
+		let mut removed = Vec::with_capacity(len - expected_size);
+		while len > expected_size {
+			let entry = self.cache.pop_front().unwrap();
+			match entry.1 {
+				ContentStatus::Fetching(ref abort) => {
+					trace!(target: "dapps", "Aborting {} because of limit.", entry.0);
+					// Mark as aborted
+					abort.store(true, Ordering::Relaxed);
+				},
+				ContentStatus::Ready(ref endpoint) => {
+					trace!(target: "dapps", "Removing {} because of limit.", entry.0);
+					// Remove path
+					let res = fs::remove_dir_all(&endpoint.path());
+					if let Err(e) = res {
+						warn!(target: "dapps", "Unable to remove dapp: {:?}", e);
+					}
+				}
+			}
+
+			removed.push(entry);
+			len -= 1;
+		}
+		removed
+	}
+
+	#[cfg(test)]
+	pub fn len(&self) -> usize {
+		self.cache.len()
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	fn only_keys(data: Vec<(String, ContentStatus)>) -> Vec<String> {
+		data.into_iter().map(|x| x.0).collect()
+	}
+
+	#[test]
+	fn should_remove_least_recently_used() {
+		// given
+		let mut cache = ContentCache::default();
+		cache.insert("a".into(), ContentStatus::Fetching(Default::default()));
+		cache.insert("b".into(), ContentStatus::Fetching(Default::default()));
+		cache.insert("c".into(), ContentStatus::Fetching(Default::default()));
+
+		// when
+		let res = cache.clear_garbage(2);
+
+		// then
+		assert_eq!(cache.len(), 2);
+		assert_eq!(only_keys(res), vec!["a"]);
+	}
+
+	#[test]
+	fn should_update_lru_if_accessed() {
+		// given
+		let mut cache = ContentCache::default();
+		cache.insert("a".into(), ContentStatus::Fetching(Default::default()));
+		cache.insert("b".into(), ContentStatus::Fetching(Default::default()));
+		cache.insert("c".into(), ContentStatus::Fetching(Default::default()));
+
+		// when
+		cache.get("a");
+		let res = cache.clear_garbage(2);
+
+		// then
+		assert_eq!(cache.len(), 2);
+		assert_eq!(only_keys(res), vec!["b"]);
+	}
+
+}