Nop中的Cache浅析

Nop中定义了ICacheManger接口，它有几个实现，其中MemoryCacheManager是内存缓存的一个实现。

MemoryCacheManager：

using System;
using System.Collections.Generic;
using System.Runtime.Caching;
using System.Text.RegularExpressions;

namespace Nop.Core.Caching
{
    /// <summary>
    /// Represents a manager for caching between HTTP requests (long term caching)
    /// </summary>
    public partial class MemoryCacheManager : ICacheManager
    {
        /// <summary>
        /// Cache object
        /// </summary>
        protected ObjectCache Cache
        {
            get
            {
                return MemoryCache.Default;
            }
        }
        
        /// <summary>
        /// Gets or sets the value associated with the specified key.
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="key">The key of the value to get.</param>
        /// <returns>The value associated with the specified key.</returns>
        public virtual T Get<T>(string key)
        {
            return (T)Cache[key];
        }

        /// <summary>
        /// Adds the specified key and object to the cache.
        /// </summary>
        /// <param name="key">key</param>
        /// <param name="data">Data</param>
        /// <param name="cacheTime">Cache time</param>
        public virtual void Set(string key, object data, int cacheTime)
        {
            if (data == null)
                return;

            var policy = new CacheItemPolicy();
            policy.AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(cacheTime);
            Cache.Add(new CacheItem(key, data), policy);
        }

        /// <summary>
        /// Gets a value indicating whether the value associated with the specified key is cached
        /// </summary>
        /// <param name="key">key</param>
        /// <returns>Result</returns>
        public virtual bool IsSet(string key)
        {
            return (Cache.Contains(key));
        }

        /// <summary>
        /// Removes the value with the specified key from the cache
        /// </summary>
        /// <param name="key">/key</param>
        public virtual void Remove(string key)
        {
            Cache.Remove(key);
        }

        /// <summary>
        /// Removes items by pattern
        /// </summary>
        /// <param name="pattern">pattern</param>
        public virtual void RemoveByPattern(string pattern)
        {
            var regex = new Regex(pattern, RegexOptions.Singleline | RegexOptions.Compiled | RegexOptions.IgnoreCase);
            var keysToRemove = new List<String>();

            foreach (var item in Cache)
                if (regex.IsMatch(item.Key))
                    keysToRemove.Add(item.Key);

            foreach (string key in keysToRemove)
            {
                Remove(key);
            }
        }

        /// <summary>
        /// Clear all cache data
        /// </summary>
        public virtual void Clear()
        {
            foreach (var item in Cache)
                Remove(item.Key);
        }

        /// <summary>
        /// Dispose
        /// </summary>
        public virtual void Dispose()
        {
        }
    }
}

缓存的添加，在需要的地方构建cache key然后调用ICacheManger接口存储起来：

 var cachedModel = _cacheManager.Get(cacheKey, () =>
            {
                var model = new List<BlogPostYearModel>();

                var blogPosts = _blogService.GetAllBlogPosts(_storeContext.CurrentStore.Id, 
                    _workContext.WorkingLanguage.Id);
                if (blogPosts.Count > 0)
                {
                    var months = new SortedDictionary<DateTime, int>();

                    var first = blogPosts[blogPosts.Count - 1].CreatedOnUtc;
                    while (DateTime.SpecifyKind(first, DateTimeKind.Utc) <= DateTime.UtcNow.AddMonths(1))
                    {
                        var list = blogPosts.GetPostsByDate(new DateTime(first.Year, first.Month, 1), new DateTime(first.Year, first.Month, 1).AddMonths(1).AddSeconds(-1));
                        if (list.Count > 0)
                        {
                            var date = new DateTime(first.Year, first.Month, 1);
                            months.Add(date, list.Count);
                        }

                        first = first.AddMonths(1);
                    }


                    int current = 0;
                    foreach (var kvp in months)
                    {
                        var date = kvp.Key;
                        var blogPostCount = kvp.Value;
                        if (current == 0)
                            current = date.Year;

                        if (date.Year > current || model.Count == 0)
                        {
                            var yearModel = new BlogPostYearModel
                            {
                                Year = date.Year
                            };
                            model.Add(yearModel);
                        }

                        model.Last().Months.Add(new BlogPostMonthModel
                        {
                            Month = date.Month,
                            BlogPostCount = blogPostCount
                        });

                        current = date.Year;
                    }
                }
                return model;
            });

这个ICacheManger的Get方法其实是个扩展方法，当获取不到缓存的时候调用Func<T>获取值，然后缓存起来：

using System;

namespace Nop.Core.Caching
{
    /// <summary>
    /// Extensions
    /// </summary>
    public static class CacheExtensions
    {
        /// <summary>
        /// Get a cached item. If it's not in the cache yet, then load and cache it
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="cacheManager">Cache manager</param>
        /// <param name="key">Cache key</param>
        /// <param name="acquire">Function to load item if it's not in the cache yet</param>
        /// <returns>Cached item</returns>
        public static T Get<T>(this ICacheManager cacheManager, string key, Func<T> acquire)
        {
            return Get(cacheManager, key, 60, acquire);
        }

        /// <summary>
        /// Get a cached item. If it's not in the cache yet, then load and cache it
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="cacheManager">Cache manager</param>
        /// <param name="key">Cache key</param>
        /// <param name="cacheTime">Cache time in minutes (0 - do not cache)</param>
        /// <param name="acquire">Function to load item if it's not in the cache yet</param>
        /// <returns>Cached item</returns>
        public static T Get<T>(this ICacheManager cacheManager, string key, int cacheTime, Func<T> acquire)
        {
            if (cacheManager.IsSet(key))
            {
                return cacheManager.Get<T>(key);
            }

            var result = acquire();
            if (cacheTime > 0)
                cacheManager.Set(key, result, cacheTime);
            return result;
        }
    }
}

Cache的移除。Nop缓存的移除比较有意思，它使用Pub/Sub模式来实现。

当你缓存一个Blog的列表，如果后面对某个Blog进行Update的时候，你就有两个选择：1.更新这个Blog的cache 2.移除所有关于Blog的cache。Nop选择的是后者，因为第一种方案实现起来的代价有点大，你可能需要给单独每个Blog指定一个Key来缓存起来，或者遍历所有关于Blog的cache。

当发生Blog的Update的时候，会发送一个通知事件：

  public virtual void UpdateBlogPost(BlogPost blogPost)
        {
            if (blogPost == null)
                throw new ArgumentNullException("blogPost");

            _blogPostRepository.Update(blogPost);

            //event notification
            _eventPublisher.EntityUpdated(blogPost);
        }
        

看一下EventPublish的实现 ：

 public interface IEventPublisher
    {
        /// <summary>
        /// Publish event
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="eventMessage">Event message</param>
        void Publish<T>(T eventMessage);
    }

using System;
using System.Linq;
using Nop.Core.Infrastructure;
using Nop.Core.Plugins;
using Nop.Services.Logging;

namespace Nop.Services.Events
{
    /// <summary>
    /// Evnt publisher
    /// </summary>
    public class EventPublisher : IEventPublisher
    {
        private readonly ISubscriptionService _subscriptionService;

        /// <summary>
        /// Ctor
        /// </summary>
        /// <param name="subscriptionService"></param>
        public EventPublisher(ISubscriptionService subscriptionService)
        {
            _subscriptionService = subscriptionService;
        }

        /// <summary>
        /// Publish to cunsumer
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="x">Event consumer</param>
        /// <param name="eventMessage">Event message</param>
        protected virtual void PublishToConsumer<T>(IConsumer<T> x, T eventMessage)
        {
            //Ignore not installed plugins
            var plugin = FindPlugin(x.GetType());
            if (plugin != null && !plugin.Installed)
                return;

            try
            {
                x.HandleEvent(eventMessage);
            }
            catch (Exception exc)
            {
                //log error
                var logger = EngineContext.Current.Resolve<ILogger>();
                //we put in to nested try-catch to prevent possible cyclic (if some error occurs)
                try
                {
                    logger.Error(exc.Message, exc);
                }
                catch (Exception)
                {
                    //do nothing
                }
            }
        }

        /// <summary>
        /// Find a plugin descriptor by some type which is located into its assembly
        /// </summary>
        /// <param name="providerType">Provider type</param>
        /// <returns>Plugin descriptor</returns>
        protected virtual PluginDescriptor FindPlugin(Type providerType)
        {
            if (providerType == null)
                throw new ArgumentNullException("providerType");

            if (PluginManager.ReferencedPlugins == null)
                return null;

            foreach (var plugin in PluginManager.ReferencedPlugins)
            {
                if (plugin.ReferencedAssembly == null)
                    continue;

                if (plugin.ReferencedAssembly.FullName == providerType.Assembly.FullName)
                    return plugin;
            }

            return null;
        }

        /// <summary>
        /// Publish event
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="eventMessage">Event message</param>
        public virtual void Publish<T>(T eventMessage)
        {
            var subscriptions = _subscriptionService.GetSubscriptions<T>();
            subscriptions.ToList().ForEach(x => PublishToConsumer(x, eventMessage));
        }

    }
}

很简单，只是获取所有的订阅，然后依次调用其中的PublishToConsumer方法。

那么订阅是在哪里呢？

首先这是Blog消息消费者的定义：

using Nop.Core.Caching;
using Nop.Core.Domain.Blogs;
using Nop.Core.Domain.Catalog;
using Nop.Core.Domain.Configuration;
using Nop.Core.Domain.Directory;
using Nop.Core.Domain.Localization;
using Nop.Core.Domain.Media;
using Nop.Core.Domain.News;
using Nop.Core.Domain.Orders;
using Nop.Core.Domain.Polls;
using Nop.Core.Domain.Topics;
using Nop.Core.Domain.Vendors;
using Nop.Core.Events;
using Nop.Core.Infrastructure;
using Nop.Services.Events;

namespace Nop.Web.Infrastructure.Cache
{
    /// <summary>
    /// Model cache event consumer (used for caching of presentation layer models)
    /// </summary>
    public partial class ModelCacheEventConsumer: 
       
        //blog posts
        IConsumer<EntityInserted<BlogPost>>,
        IConsumer<EntityUpdated<BlogPost>>,
        IConsumer<EntityDeleted<BlogPost>>
      
    {
        /// <summary>
        /// Key for blog tag list model
        /// </summary>
        /// <remarks>
        /// {0} : language ID
        /// {1} : current store ID
        /// </remarks>
        public const string BLOG_TAGS_MODEL_KEY = "Nop.pres.blog.tags-{0}-{1}";
        /// <summary>
        /// Key for blog archive (years, months) block model
        /// </summary>
        /// <remarks>
        /// {0} : language ID
        /// {1} : current store ID
        /// </remarks>
        public const string BLOG_MONTHS_MODEL_KEY = "Nop.pres.blog.months-{0}-{1}";
        public const string BLOG_PATTERN_KEY = "Nop.pres.blog";

        private readonly ICacheManager _cacheManager;
        
        public ModelCacheEventConsumer()
        {
            //TODO inject static cache manager using constructor
            this._cacheManager = EngineContext.Current.ContainerManager.Resolve<ICacheManager>("nop_cache_static");
        }


        //Blog posts
        public void HandleEvent(EntityInserted<BlogPost> eventMessage)
        {
            _cacheManager.RemoveByPattern(BLOG_PATTERN_KEY);
        }
        public void HandleEvent(EntityUpdated<BlogPost> eventMessage)
        {
            _cacheManager.RemoveByPattern(BLOG_PATTERN_KEY);
        }
        public void HandleEvent(EntityDeleted<BlogPost> eventMessage)
        {
            _cacheManager.RemoveByPattern(BLOG_PATTERN_KEY);
        }
    }
}

所有的Blog的key都采用统一的前缀，Nop.pres.blog。这样只要使用这个前缀就能清楚所有关于blog的缓存了。

这个类继承了3个接口所以有3个HandleEvent的实现，都是清楚blog相关的缓存。

这些消费者其实并未主动的去注册订阅，而是通过反射在启动的时候自动加载进IoC容器里的，当需要使用的时候通过接口直接取出来使用。

            //Register event consumers
            var consumers = typeFinder.FindClassesOfType(typeof(IConsumer<>)).ToList();
            foreach (var consumer in consumers)
            {
                builder.RegisterType(consumer)
                    .As(consumer.FindInterfaces((type, criteria) =>
                    {
                        var isMatch = type.IsGenericType && ((Type)criteria).IsAssignableFrom(type.GetGenericTypeDefinition());
                        return isMatch;
                    }, typeof(IConsumer<>)))
                    .InstancePerLifetimeScope();
            }
            builder.RegisterType<EventPublisher>().As<IEventPublisher>().SingleInstance();
            builder.RegisterType<SubscriptionService>().As<ISubscriptionService>().SingleInstance();

其中Pub/Sub是其中的精髓，非常值得学习。