线程安全的缓存库，用于.NET [英] Thread-safe cache libraries for .NET
问题描述
背景：
我保持若干的WinForms应用程序和类库，要么可能或已经这样做受益于高速缓存。我也知道了缓存应用程序块和的System.Web.Caching 命名空间（其中，从我收集的，也完全可以ASP之外使用。 NET）。
I maintain several Winforms apps and class libraries that either could or already do benefit from caching. I'm also aware of the Caching Application Block and the System.Web.Caching namespace (which, from what I've gathered, is perfectly OK to use outside ASP.NET).
我发现，虽然上述两种类是技术上的，即单个方法是同步的线程安全的，他们不是真的似乎并没有被设计特别针对多线程的情况。特别是，他们没有实现 GetOrAdd 方法的一个类似的新 ConcurrentDictionary 类在.NET 4.0中。
I've found that, although both of the above classes are technically "thread safe" in the sense that individual methods are synchronized, they don't really seem to be designed particularly well for multi-threaded scenarios. Specifically, they don't implement a GetOrAdd method similar to the one in the new ConcurrentDictionary class in .NET 4.0.
我认为这种方法是一种的原始的缓存/查找功能，显然框架设计者意识到这一点 - 这就是为什么在并发集合存在的方法。然而，除此之外，我没有使用.NET 4.0中的生产应用程序可事实，字典是不是一个成熟的缓存 - 它没有像过期，持久/分布式存储等功能
I consider such a method to be a primitive for caching/lookup functionality, and obviously the Framework designers realized this too - that's why the methods exist in the concurrent collections. However, aside from the fact that I'm not using .NET 4.0 in production apps yet, a dictionary is not a full-fledged cache - it doesn't have features like expirations, persistent/distributed storage, etc.
为什么这是很重要的：
在一个富客户端应用程序，一个相当典型的设计（甚至一些web应用程序）是启动pre-装载只要应用程序启动高速缓存，阻塞如果客户端请求数据还没有被加载（后来缓存以备将来使用）。如果用户是通过他的工作流程耕快，或者网络连接速度较慢，它的不寻常，在所有客户端要与preloader竞争，而且它真的没有很大的意义，要求相同的数据两次，特别是如果该请求是相对昂贵的。
A fairly typical design in a "rich client" app (or even some web apps) is to start pre-loading a cache as soon as the app starts, blocking if the client requests data that is not yet loaded (subsequently caching it for future use). If the user is plowing through his workflow quickly, or if the network connection is slow, it's not unusual at all for the client to be competing with the preloader, and it really doesn't make a lot of sense to request the same data twice, especially if the request is relatively expensive.
所以，我似乎只剩下了几个同样糟糕的选择：
So I seem to be left with a few equally lousy options:
-
不要试图使操作原子可言的，冒着被加载数据的两倍（也可能有工作在不同的副本两个不同的线程）;
Don't try to make the operation atomic at all, and risk the data being loaded twice (and possibly have two different threads operating on different copies);
连续访问缓存，这意味着锁定的整个缓存的只是加载的单个项目的;
Serialize access to the cache, which means locking the entire cache just to load a single item;
开始重新发明轮子，只是为了获得一些额外的方法。
Start reinventing the wheel just to get a few extra methods.
澄清：例如时间线
说，一个应用程序启动时，它需要装载3的数据集，每个需要10秒来加载。考虑下面两个时间表：
Say that when an app starts, it needs to load 3 datasets which each take 10 seconds to load. Consider the following two timelines:
00:00 - Start loading Dataset 1
00:10 - Start loading Dataset 2
00:19 - User asks for Dataset 2
在上述情况下，如果我们不使用任何种类的同步时，用户必须等待一个完整的10秒的数据，将可在1秒，由于code将看到，产品尚未加载到缓存中，并尝试重新装入。
In the above case, if we don't use any kind of synchronization, the user has to wait a full 10 seconds for data that will be available in 1 second, because the code will see that the item is not yet loaded into the cache and try to reload it.
00:00 - Start loading Dataset 1
00:10 - Start loading Dataset 2
00:11 - User asks for Dataset 1
在这种情况下，用户要求的数据是已经在缓存。但是，如果我们连续访问缓存，他将不得不等待另外9秒没有理由，因为缓存管理器（无论是）拥有的的特定的项目的被要求不认识，只有东西被请求和东西正在进行中。
In this case, the user is asking for data that's already in the cache. But if we serialize access to the cache, he'll have to wait another 9 seconds for no reason at all, because the cache manager (whatever that is) has no awareness of the specific item being asked for, only that "something" is being requested and "something" is in progress.
的问题：
是否有任何缓存库.NET（pre-4.0）的执行实施这样的原子操作，因为人们可能期望从一个线程安全的缓存？
Are there any caching libraries for .NET (pre-4.0) that do implement such atomic operations, as one might expect from a thread-safe cache?
或者，或者，有没有一些方法来扩展现有的线程安全的缓存来支持这样的操作，没有序列化到缓存（这违背用线程的目的访问首先安全的实现）？我怀疑是有，但也许我只是累了，忽略了一个显而易见的解决办法。
Or, alternatively, is there some means to extend an existing "thread-safe" cache to support such operations, without serializing access to the cache (which would defeat the purpose of using a thread-safe implementation in the first place)? I doubt that there is, but maybe I'm just tired and ignoring an obvious workaround.
还是......是有什么别的我丢失吗？是它只是标准的做法，让两个竞争线程steamroll彼此如果它们碰巧都可以请求相同的项目，在同一时间，在第一次或期满后？
Or... is there something else I'm missing? Is it just standard practice to let two competing threads steamroll each other if they happen to both be requesting the same item, at the same time, for the first time or after an expiration?
推荐答案
我知道你的痛苦，因为我
I know your pain as I am one of the Architects of Dedoose. I have messed around with a lot of caching libraries and ended up building this one after much tribulation. The one assumption for this Cache Manager is that all collections stored by this class implement an interface to get a Guid as a "Id" property on each object. Being that this is for a RIA it includes a lot of methods for adding /updating /removing items from these collections.
下面是我的CollectionCacheManager
Here's my CollectionCacheManager
public class CollectionCacheManager
{
private static readonly object _objLockPeek = new object();
private static readonly Dictionary<String, object> _htLocksByKey = new Dictionary<string, object>();
private static readonly Dictionary<String, CollectionCacheEntry> _htCollectionCache = new Dictionary<string, CollectionCacheEntry>();
private static DateTime _dtLastPurgeCheck;
public static List<T> FetchAndCache<T>(string sKey, Func<List<T>> fGetCollectionDelegate) where T : IUniqueIdActiveRecord
{
List<T> colItems = new List<T>();
lock (GetKeyLock(sKey))
{
if (_htCollectionCache.Keys.Contains(sKey) == true)
{
CollectionCacheEntry objCacheEntry = _htCollectionCache[sKey];
colItems = (List<T>) objCacheEntry.Collection;
objCacheEntry.LastAccess = DateTime.Now;
}
else
{
colItems = fGetCollectionDelegate();
SaveCollection<T>(sKey, colItems);
}
}
List<T> objReturnCollection = CloneCollection<T>(colItems);
return objReturnCollection;
}
public static List<Guid> FetchAndCache(string sKey, Func<List<Guid>> fGetCollectionDelegate)
{
List<Guid> colIds = new List<Guid>();
lock (GetKeyLock(sKey))
{
if (_htCollectionCache.Keys.Contains(sKey) == true)
{
CollectionCacheEntry objCacheEntry = _htCollectionCache[sKey];
colIds = (List<Guid>)objCacheEntry.Collection;
objCacheEntry.LastAccess = DateTime.Now;
}
else
{
colIds = fGetCollectionDelegate();
SaveCollection(sKey, colIds);
}
}
List<Guid> colReturnIds = CloneCollection(colIds);
return colReturnIds;
}
private static List<T> GetCollection<T>(string sKey) where T : IUniqueIdActiveRecord
{
List<T> objReturnCollection = null;
if (_htCollectionCache.Keys.Contains(sKey) == true)
{
CollectionCacheEntry objCacheEntry = null;
lock (GetKeyLock(sKey))
{
objCacheEntry = _htCollectionCache[sKey];
objCacheEntry.LastAccess = DateTime.Now;
}
if (objCacheEntry.Collection != null && objCacheEntry.Collection is List<T>)
{
objReturnCollection = CloneCollection<T>((List<T>)objCacheEntry.Collection);
}
}
return objReturnCollection;
}
public static void SaveCollection<T>(string sKey, List<T> colItems) where T : IUniqueIdActiveRecord
{
CollectionCacheEntry objCacheEntry = new CollectionCacheEntry();
objCacheEntry.Key = sKey;
objCacheEntry.CacheEntry = DateTime.Now;
objCacheEntry.LastAccess = DateTime.Now;
objCacheEntry.LastUpdate = DateTime.Now;
objCacheEntry.Collection = CloneCollection(colItems);
lock (GetKeyLock(sKey))
{
_htCollectionCache[sKey] = objCacheEntry;
}
}
public static void SaveCollection(string sKey, List<Guid> colIDs)
{
CollectionCacheEntry objCacheEntry = new CollectionCacheEntry();
objCacheEntry.Key = sKey;
objCacheEntry.CacheEntry = DateTime.Now;
objCacheEntry.LastAccess = DateTime.Now;
objCacheEntry.LastUpdate = DateTime.Now;
objCacheEntry.Collection = CloneCollection(colIDs);
lock (GetKeyLock(sKey))
{
_htCollectionCache[sKey] = objCacheEntry;
}
}
public static void UpdateCollection<T>(string sKey, List<T> colItems) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
if (_htCollectionCache.ContainsKey(sKey) == true)
{
CollectionCacheEntry objCacheEntry = _htCollectionCache[sKey];
objCacheEntry.LastAccess = DateTime.Now;
objCacheEntry.LastUpdate = DateTime.Now;
objCacheEntry.Collection = new List<T>();
//Clone the collection before insertion to ensure it can't be touched
foreach (T objItem in colItems)
{
objCacheEntry.Collection.Add(objItem);
}
_htCollectionCache[sKey] = objCacheEntry;
}
else
{
SaveCollection<T>(sKey, colItems);
}
}
}
public static void UpdateItem<T>(string sKey, T objItem) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
if (_htCollectionCache.ContainsKey(sKey) == true)
{
CollectionCacheEntry objCacheEntry = _htCollectionCache[sKey];
List<T> colItems = (List<T>)objCacheEntry.Collection;
colItems.RemoveAll(o => o.Id == objItem.Id);
colItems.Add(objItem);
objCacheEntry.Collection = colItems;
objCacheEntry.LastAccess = DateTime.Now;
objCacheEntry.LastUpdate = DateTime.Now;
}
}
}
public static void UpdateItems<T>(string sKey, List<T> colItemsToUpdate) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
if (_htCollectionCache.ContainsKey(sKey) == true)
{
CollectionCacheEntry objCacheEntry = _htCollectionCache[sKey];
List<T> colCachedItems = (List<T>)objCacheEntry.Collection;
foreach (T objItem in colItemsToUpdate)
{
colCachedItems.RemoveAll(o => o.Id == objItem.Id);
colCachedItems.Add(objItem);
}
objCacheEntry.Collection = colCachedItems;
objCacheEntry.LastAccess = DateTime.Now;
objCacheEntry.LastUpdate = DateTime.Now;
}
}
}
public static void RemoveItemFromCollection<T>(string sKey, T objItem) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
List<T> objCollection = GetCollection<T>(sKey);
if (objCollection != null && objCollection.Count(o => o.Id == objItem.Id) > 0)
{
objCollection.RemoveAll(o => o.Id == objItem.Id);
UpdateCollection<T>(sKey, objCollection);
}
}
}
public static void RemoveItemsFromCollection<T>(string sKey, List<T> colItemsToAdd) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
Boolean bCollectionChanged = false;
List<T> objCollection = GetCollection<T>(sKey);
foreach (T objItem in colItemsToAdd)
{
if (objCollection != null && objCollection.Count(o => o.Id == objItem.Id) > 0)
{
objCollection.RemoveAll(o => o.Id == objItem.Id);
bCollectionChanged = true;
}
}
if (bCollectionChanged == true)
{
UpdateCollection<T>(sKey, objCollection);
}
}
}
public static void AddItemToCollection<T>(string sKey, T objItem) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
List<T> objCollection = GetCollection<T>(sKey);
if (objCollection != null && objCollection.Count(o => o.Id == objItem.Id) == 0)
{
objCollection.Add(objItem);
UpdateCollection<T>(sKey, objCollection);
}
}
}
public static void AddItemsToCollection<T>(string sKey, List<T> colItemsToAdd) where T : IUniqueIdActiveRecord
{
lock (GetKeyLock(sKey))
{
List<T> objCollection = GetCollection<T>(sKey);
Boolean bCollectionChanged = false;
foreach (T objItem in colItemsToAdd)
{
if (objCollection != null && objCollection.Count(o => o.Id == objItem.Id) == 0)
{
objCollection.Add(objItem);
bCollectionChanged = true;
}
}
if (bCollectionChanged == true)
{
UpdateCollection<T>(sKey, objCollection);
}
}
}
public static void PurgeCollectionByMaxLastAccessInMinutes(int iMinutesSinceLastAccess)
{
DateTime dtThreshHold = DateTime.Now.AddMinutes(iMinutesSinceLastAccess * -1);
if (_dtLastPurgeCheck == null || dtThreshHold > _dtLastPurgeCheck)
{
lock (_objLockPeek)
{
CollectionCacheEntry objCacheEntry;
List<String> colKeysToRemove = new List<string>();
foreach (string sCollectionKey in _htCollectionCache.Keys)
{
objCacheEntry = _htCollectionCache[sCollectionKey];
if (objCacheEntry.LastAccess < dtThreshHold)
{
colKeysToRemove.Add(sCollectionKey);
}
}
foreach (String sKeyToRemove in colKeysToRemove)
{
_htCollectionCache.Remove(sKeyToRemove);
}
}
_dtLastPurgeCheck = DateTime.Now;
}
}
public static void ClearCollection(String sKey)
{
lock (GetKeyLock(sKey))
{
lock (_objLockPeek)
{
if (_htCollectionCache.ContainsKey(sKey) == true)
{
_htCollectionCache.Remove(sKey);
}
}
}
}
#region Helper Methods
private static object GetKeyLock(String sKey)
{
//Ensure even if hell freezes over this lock exists
if (_htLocksByKey.Keys.Contains(sKey) == false)
{
lock (_objLockPeek)
{
if (_htLocksByKey.Keys.Contains(sKey) == false)
{
_htLocksByKey[sKey] = new object();
}
}
}
return _htLocksByKey[sKey];
}
private static List<T> CloneCollection<T>(List<T> colItems) where T : IUniqueIdActiveRecord
{
List<T> objReturnCollection = new List<T>();
//Clone the list - NEVER return the internal cache list
if (colItems != null && colItems.Count > 0)
{
List<T> colCachedItems = (List<T>)colItems;
foreach (T objItem in colCachedItems)
{
objReturnCollection.Add(objItem);
}
}
return objReturnCollection;
}
private static List<Guid> CloneCollection(List<Guid> colIds)
{
List<Guid> colReturnIds = new List<Guid>();
//Clone the list - NEVER return the internal cache list
if (colIds != null && colIds.Count > 0)
{
List<Guid> colCachedItems = (List<Guid>)colIds;
foreach (Guid gId in colCachedItems)
{
colReturnIds.Add(gId);
}
}
return colReturnIds;
}
#endregion
#region Admin Functions
public static List<CollectionCacheEntry> GetAllCacheEntries()
{
return _htCollectionCache.Values.ToList();
}
public static void ClearEntireCache()
{
_htCollectionCache.Clear();
}
#endregion
}
public sealed class CollectionCacheEntry
{
public String Key;
public DateTime CacheEntry;
public DateTime LastUpdate;
public DateTime LastAccess;
public IList Collection;
}
下面是我如何使用它的一个例子：
Here is an example of how I use it:
public static class ResourceCacheController
{
#region Cached Methods
public static List<Resource> GetResourcesByProject(Guid gProjectId)
{
String sKey = GetCacheKeyProjectResources(gProjectId);
List<Resource> colItems = CollectionCacheManager.FetchAndCache<Resource>(sKey, delegate() { return ResourceAccess.GetResourcesByProject(gProjectId); });
return colItems;
}
#endregion
#region Cache Dependant Methods
public static int GetResourceCountByProject(Guid gProjectId)
{
return GetResourcesByProject(gProjectId).Count;
}
public static List<Resource> GetResourcesByIds(Guid gProjectId, List<Guid> colResourceIds)
{
if (colResourceIds == null || colResourceIds.Count == 0)
{
return null;
}
return GetResourcesByProject(gProjectId).FindAll(objRes => colResourceIds.Any(gId => objRes.Id == gId)).ToList();
}
public static Resource GetResourceById(Guid gProjectId, Guid gResourceId)
{
return GetResourcesByProject(gProjectId).SingleOrDefault(o => o.Id == gResourceId);
}
#endregion
#region Cache Keys and Clear
public static void ClearCacheProjectResources(Guid gProjectId)
{ CollectionCacheManager.ClearCollection(GetCacheKeyProjectResources(gProjectId));
}
public static string GetCacheKeyProjectResources(Guid gProjectId)
{
return string.Concat("ResourceCacheController.ProjectResources.", gProjectId.ToString());
}
#endregion
internal static void ProcessDeleteResource(Guid gProjectId, Guid gResourceId)
{
Resource objRes = GetResourceById(gProjectId, gResourceId);
if (objRes != null)
{ CollectionCacheManager.RemoveItemFromCollection(GetCacheKeyProjectResources(gProjectId), objRes);
}
}
internal static void ProcessUpdateResource(Resource objResource)
{
CollectionCacheManager.UpdateItem(GetCacheKeyProjectResources(objResource.Id), objResource);
}
internal static void ProcessAddResource(Guid gProjectId, Resource objResource)
{
CollectionCacheManager.AddItemToCollection(GetCacheKeyProjectResources(gProjectId), objResource);
}
}
下面是有问题的接口：
public interface IUniqueIdActiveRecord
{
Guid Id { get; set; }
}
希望这会有所帮助，我已经通过地狱和背部几次，终于抵达，作为解决方案，而对于我们来说是一个天赐良机，但我不能保证它是完美的，只是我们还没有发现一个问题呢。
Hope this helps, I've been through hell and back a few times to finally arrive at this as the solution, and for us It's been a godsend, but I cannot guarantee that it's perfect, only that we haven't found an issue yet.
这篇关于线程安全的缓存库，用于.NET的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
