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//
// A simple LRU cache used for tracking the cache items
//
// Authors:
// Miguel de Icaza (miguel@gnome.org)
//
// Copyright 2010 Miguel de Icaza
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
using System;
using System.Collections.Generic;
namespace System.Web.Caching
{
sealed class CacheItemLRU
{
public delegate bool SelectItemsQualifier (CacheItem item);
Dictionary<string, LinkedListNode <CacheItem>> dict;
Dictionary<LinkedListNode<CacheItem>, string> revdict;
LinkedList<CacheItem> list;
Cache owner;
// High/Low water mark is here to avoid situations when we hit a limit, evict an
// entry, add another one and have to evict again because the limit was hit. When we
// hit the high water limit, we evict until we reach the low water mark to avoid the
// situation.
int highWaterMark, lowWaterMark;
bool needsEviction;
public int Count {
get { return dict.Count; }
}
public CacheItemLRU (Cache owner, int highWaterMark, int lowWaterMark)
{
list = new LinkedList<CacheItem> ();
dict = new Dictionary<string, LinkedListNode<CacheItem>> (StringComparer.Ordinal);
revdict = new Dictionary<LinkedListNode<CacheItem>, string> ();
this.highWaterMark = highWaterMark;
this.lowWaterMark = lowWaterMark;
this.owner = owner;
}
public bool TryGetValue (string key, out CacheItem value)
{
LinkedListNode <CacheItem> item;
if (dict.TryGetValue (key, out item)) {
value = item.Value;
return true;
}
value = null;
return false;
}
// Must ALWAYS be called with the owner's write lock held
public void EvictIfNecessary ()
{
if (!needsEviction)
return;
for (int i = dict.Count; i > lowWaterMark; i--) {
var key = revdict [list.Last];
owner.Remove (key, CacheItemRemovedReason.Underused, false, true);
}
}
// Must ALWAYS be called with the owner's read lock held
public void InvokePrivateCallbacks ()
{
foreach (var de in dict) {
CacheItem item = de.Value.Value;
if (item == null || item.Disabled)
continue;
if (item.OnRemoveCallback != null) {
try {
item.OnRemoveCallback (de.Key, item.Value, CacheItemRemovedReason.Removed);
} catch {
//TODO: anything to be done here?
}
}
}
}
// Must ALWAYS be called with the owner's write lock held
public List <CacheItem> SelectItems (SelectItemsQualifier qualifier)
{
var ret = new List <CacheItem> ();
foreach (LinkedListNode <CacheItem> node in dict.Values) {
CacheItem item = node.Value;
if (qualifier (item))
ret.Add (item);
}
return ret;
}
// Must ALWAYS be called with the owner's read lock held
public List <CacheItem> ToList ()
{
var ret = new List <CacheItem> ();
if (dict.Count == 0)
return ret;
foreach (LinkedListNode <CacheItem> node in dict.Values)
ret.Add (node.Value);
return ret;
}
public void Remove (string key)
{
if (key == null)
return;
LinkedListNode <CacheItem> node;
if (!dict.TryGetValue (key, out node))
return;
CacheItem item = node.Value;
dict.Remove (key);
if (item == null || item.Priority != CacheItemPriority.NotRemovable) {
revdict.Remove (node);
list.Remove (node);
}
}
public CacheItem this [string key] {
get {
if (key == null)
return null;
LinkedListNode<CacheItem> node;
CacheItem item;
if (dict.TryGetValue (key, out node)){
item = node.Value;
if (item == null || item.Priority != CacheItemPriority.NotRemovable) {
list.Remove (node);
list.AddFirst (node);
}
return item;
}
return null;
}
set {
LinkedListNode<CacheItem> node;
if (dict.TryGetValue (key, out node)){
// If we already have a key, move it to the front
list.Remove (node);
if (value == null || value.Priority != CacheItemPriority.NotRemovable)
list.AddFirst (node);
else
revdict.Remove (node);
node.Value = value;
return;
}
needsEviction = dict.Count >= highWaterMark;
// Adding new node
node = new LinkedListNode<CacheItem> (value);
if (value == null || value.Priority != CacheItemPriority.NotRemovable) {
list.AddFirst (node);
revdict [node] = key;
}
dict [key] = node;
}
}
}
}
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