Tuesday, February 8, 2011

Caching in .NET 4

For a long time I have been using the caching application block in Enterprise Library when I needed some caching functionality inside my .NET application. You could also use  System.Web.Caching but it was not extensible,and not easy to use outside an ASP.NET context.

With the release of .NET 4 there is a finally a more mature caching system now included in the framework. This is known as System.Runtime.Caching.  The System.Runtime.Caching namespace contains types that let you implement caching in NET Framework applications.

The output caching functionality and types in the System.Runtime.Caching namespace are new in .NET Framework version 4. The classes in this namespace provide a way to use caching facilities like those in ASP.NET, but without a dependency on the System.Web assembly.

The caching types that are provided in this namespace offers the following features:

  • Caching is accessible to all .NET Framework applications, not just ASP.NET.

  • Caching is extensible.

  • You can create custom caching providers. For example, instead of using the default in-memory cache engine, you can create custom providers that store cache data in databases, in custom objects, or in the file system

The starting class is the abstract ObjectCache which has one concrete implementation the MemoryCache.  To use it first instantiate an instance of the MemoryCache(in this sample I’m using the default instance).  I can check if the cache contains an object using the .Contains method, I retrieve from the cache using the .Get method and I add to the cache using the .Add method.

//Create a cache instance
ObjectCache cache = MemoryCache.Default;     

//check the cache for a specific value
if (cache.Contains("CachedValueKey"))     
{         
//get an item from the cache
var value=cache.Get("CachedValueKey");     
}     
else    
{         
//add an item to the cache 
cache.Add("CachedValueKey", "Some value to cache", new CacheItemPolicy());     
} 

Important to notice is the CacheItemPolicy. In the sample I’m using the default policy but you can configure a lot of options:

  • AbsoluteExpiration: Set a date/time when to remove the item from the cache.
  • ChangeMonitors: Allows the cache to become invalid when a file or database change occurs.
  • Priority: Allows you to state that the item should never be removed.
  • SlidingExpiration: Allows you to set a relative time to remove the item from cache.
  • UpdateCallback & RemovedCallback: Two events to get notification when an item is removed from cache. UpdateCallback is called before an item is removed and RemovedCallBack is called after an item is removed.

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