对于C＃对象缓存 [英] Object cache for C#

问题描述

我在做一个文档查看器的一些文档格式。为了更方便，让我们说这是一个PDF阅读器，一个桌面应用程序。该软件的一个要求是在渲染的速度。所以，现在，我缓存图像的下一个页面，而用户是滚动浏览文档。

I'm doing a document viewer for some document format. To make it easier, let's say this is a PDF viewer, a Desktop application. One requirement for the software is the speed in rendering. So, right now, I'm caching the image for the next pages while the user is scrolling through the document.

这工作，用户界面​​是非常敏感，这似乎是一个应用程序能够使网页几乎立即....有代价的：内存使用率有时会到600MB。我缓存这一切在内存中。

This works, the UI is very responsive and it seems like the application is able to render the pages almost instantly....at a cost : the memory usage sometimes goes to 600MB. I cache it all in memory.

现在，我可以缓存到磁盘，我知道，但这样做，所有的时间明显要慢。我想这样做的是执行一些高速缓存（LRU），有些地方的缓存页面（图像对象）是内存，其中大部分是在磁盘上。

Now, I can cache to disk, I know, but doing that all the time is noticeably slower. What I would like to do is implement some cache (LRU?), where some of the cached pages (image objects) are on memory and most of them are on disk.

在我走上了这一点，是有什么在框架或某些库在那里，将帮我这个忙？这似乎是一个pretty的普通不过的问题。 （这是一个桌面应用程序，而不是ASP.NET）

Before I embark on this, is there something in the framework or some library out there that will do this for me? It seems a pretty common enough problem. (This is a desktop application, not ASP.NET)

另外，你有没有其他的想法，这个问题？

Alternatively, do you have other ideas for this problem?

推荐答案

我写了一个LRU Cache和一些测试情况下，随意使用它。

I wrote an LRU Cache and some test cases, feel free to use it.

您可以通过<一个源中读取href="http://samsaffron.com/archive/2009/08/21/Behaviour+driven+design+using+rspec+IronRuby+and+C">my博客。

有关懒惰（这里是负的测试用例）：

For the lazy (here it is minus the test cases):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LRUCache {
    public class IndexedLinkedList<T> {

        LinkedList<T> data = new LinkedList<T>();
        Dictionary<T, LinkedListNode<T>> index = new Dictionary<T, LinkedListNode<T>>();

        public void Add(T value) {
            index[value] = data.AddLast(value);
        }

        public void RemoveFirst() {
            index.Remove(data.First.Value);
            data.RemoveFirst();
        }

        public void Remove(T value) {
            LinkedListNode<T> node;
            if (index.TryGetValue(value, out node)) {
                data.Remove(node);
                index.Remove(value);
            }
        }

        public int Count {
            get {
                return data.Count;
            }
        }

        public void Clear() {
            data.Clear();
            index.Clear();
        }

        public T First {
            get {
                return data.First.Value;
            }
        }
    }
}

LRUCache

LRUCache

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LRUCache {
    public class LRUCache<TKey, TValue> : IDictionary<TKey, TValue> {

        object sync = new object();
        Dictionary<TKey, TValue> data;
        IndexedLinkedList<TKey> lruList = new IndexedLinkedList<TKey>();
        ICollection<KeyValuePair<TKey, TValue>> dataAsCollection;
        int capacity;

        public LRUCache(int capacity) {

            if (capacity <= 0) {
                throw new ArgumentException("capacity should always be bigger than 0");
            }

            data = new Dictionary<TKey, TValue>(capacity);
            dataAsCollection = data;
            this.capacity = capacity;
        }

        public void Add(TKey key, TValue value) {
            if (!ContainsKey(key)) {
                this[key] = value;
            } else {
                throw new ArgumentException("An attempt was made to insert a duplicate key in the cache.");
            }
        }

        public bool ContainsKey(TKey key) {
            return data.ContainsKey(key);
        }

        public ICollection<TKey> Keys {
            get {
                return data.Keys;
            }
        }

        public bool Remove(TKey key) {
            bool existed = data.Remove(key);
            lruList.Remove(key);
            return existed;
        }

        public bool TryGetValue(TKey key, out TValue value) {
            return data.TryGetValue(key, out value);
        }

        public ICollection<TValue> Values {
            get { return data.Values; }
        }

        public TValue this[TKey key] {
            get {
                var value = data[key];
                lruList.Remove(key);
                lruList.Add(key);
                return value;
            }
            set {
                data[key] = value;
                lruList.Remove(key);
                lruList.Add(key);

                if (data.Count > capacity) {
                    data.Remove(lruList.First);
                    lruList.RemoveFirst();
                }
            }
        }

        public void Add(KeyValuePair<TKey, TValue> item) {
            Add(item.Key, item.Value);
        }

        public void Clear() {
            data.Clear();
            lruList.Clear();
        }

        public bool Contains(KeyValuePair<TKey, TValue> item) {
            return dataAsCollection.Contains(item);
        }

        public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) {
            dataAsCollection.CopyTo(array, arrayIndex);
        }

        public int Count {
            get { return data.Count; }
        }

        public bool IsReadOnly {
            get { return false; }
        }

        public bool Remove(KeyValuePair<TKey, TValue> item) {

            bool removed = dataAsCollection.Remove(item);
            if (removed) {
                lruList.Remove(item.Key);
            }
            return removed;
        }


        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() {
            return dataAsCollection.GetEnumerator();
        }


        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
            return ((System.Collections.IEnumerable)data).GetEnumerator();
        }

    }
}

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