C# 的对象缓存 [英] Object cache for C#

问题描述

我正在为某种文档格式做一个文档查看器.为方便起见，假设这是一个 PDF 查看器，一个桌面应用程序.对软件的一项要求是渲染速度.所以，现在，当用户滚动浏览文档时，我正在缓存下一页的图像.

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.

这很有效，UI 响应速度非常快，而且应用程序似乎几乎可以立即呈现页面......但代价是:内存使用有时会达到 600MB.我把它全部缓存在内存中.

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，但一直这样做会明显变慢.我想要做的是实现一些缓存(LRU?)，其中一些缓存页面(图像对象)在内存中，其中大部分在磁盘上.

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.

在我开始之前，框架或一些库中有什么东西可以为我做这件事吗?这似乎是一个相当普遍的问题.(这是一个桌面应用程序，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)

或者，您对这个问题有其他想法吗?

Alternatively, do you have other ideas for this problem?

推荐答案

我写了一个 LRU Cache 和一些测试用例，请随意使用.

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

您可以阅读 我的博客.

对于懒人(这里是减去测试用例):

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

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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