Question

我有以下类在浏览器和网络服务器之间执行缓存，并作为代理服务器。我给出了简单的类定义。

这里我在这节课中有三种方法。

RequestNewCacheFilePath返回唯一ID（在每次函数调用后递增1），用于将网络文件保存到磁盘中。
CommitNewCacheFilePath在文件下载后将唯一ID提交到字典中。直到下载它的id将为0到字典。

在RequestNewCacheFilePath函数中，一个字典项添加了值0.这意味着该资源正在进行资源下载。当文件下载完成时，字典会使用其实际的唯一缓存ID进行更新。但有时在CommitNewCacheFilePath函数中，调试断言在多线程场景中失败。

public class CacheManager
{
    const string INDEX_FILE_NAME = "index.txt";

    Dictionary<string, int> _dictResources = new Dictionary<string, int>();

    public IAppServer Server { get; private set; }

    object _syncCacheIdObject = new object();
    int _cacheId;

    public string CacheDirectoryPath { get; private set; }

    public CacheManager(IAppServer server)
    {
        server.ThrowIfNull("server");

        Server = server;

        CacheDirectoryPath = (server.Config as ProxyServerConfig).CacheDirectoryPath;
        if (CacheDirectoryPath.IsEmpty())
            CacheDirectoryPath = Path.Combine("C:\\", Application.ProductName);

        if (!Directory.Exists(CacheDirectoryPath))
            Directory.CreateDirectory(CacheDirectoryPath);

    }

    public int GetCacheId(string key)
    {
        int value;
        if (_dictResources.TryGetValue(key, out value))
            return value;
        else
            return -1;
    }

    public string RequestNewCacheFilePath(string key)
    {
        int cacheId;

        lock (_syncCacheIdObject)
        {
            cacheId = ++_cacheId;
        }

        lock (_dictResources)
        {
            if (_dictResources.ContainsKey(key))
                return null;
            else
            {
                _dictResources[key] = 0;
                return Path.Combine(CacheDirectoryPath, cacheId + ".cache");
            }
        }
    }

    public void CommitNewCacheFilePath(string key, string cachedFilePath)
    {
        int cachedId = int.Parse(Path.GetFileNameWithoutExtension(cachedFilePath));

        lock (_dictResources)
        {
            Debug.Assert(_dictResources[key] == 0);

            _dictResources[key] = cachedId;
        }
    }

    public void RevertNewCacheFilePath(string resourcePath)
    {
        lock (_dictResources)
        {
            _dictResources.Remove(resourcePath);
        }
    }
}

多线程逻辑问题

0 个答案: