MEF导出是否在每次请求时都缓存或发现
本文关键字:缓存 发现 请求 是否 MEF | 更新日期: 2023-09-27 17:52:40
如果我有一个MyClass类型,注册
[Export(typeof(Myclass))]
属性,和
[PartCreationPolicy(CreationPolicy.Shared)]
或
[PartCreationPolicy(CreationPolicy.NonShared)]
和稍后尝试调用
compositionContainer.GetExportedValue<Myclass>()
多次。
MEF会再次进行全局查找或者在内部缓存
是的,MEF执行一些缓存并广泛使用延迟初始化,如果您对MEF性能有疑问:
1)元数据(可组合部件、导出定义和导入定义)被缓存。例子:
public override IEnumerable<ExportDefinition> ExportDefinitions
{
get
{
if (this._exports == null)
{
ExportDefinition[] exports = this._creationInfo.GetExports().ToArray<ExportDefinition>();
lock (this._lock)
{
if (this._exports == null)
{
this._exports = exports;
}
}
}
return this._exports;
}
}
2)导出的值也被缓存:
public object Value
{
get
{
if (this._exportedValue == Export._EmptyValue)
{
object exportedValueCore = this.GetExportedValueCore();
Interlocked.CompareExchange(ref this._exportedValue, exportedValueCore, Export._EmptyValue);
}
return this._exportedValue;
}
}
当然,当使用CreationPolicy.NonShared
时,当您请求它时,将一次又一次地创建导出值。但即使在这种情况下,也不会执行"全局查找",因为元数据无论如何都是缓存的。
每次使用[PartCreationPolicy(CreationPolicy.NonShared)]
时都进行查找。然后你必须自己实现缓存。
默认实现是使用Singleton模式。这等于属性[PartCreationPolicy(CreationPolicy.Shared)]
。这是最佳实践。
更多信息,请阅读http://blogs.microsoft.co.il/blogs/bnaya/archive/2010/01/09/mef-for-beginner-part-creation-policy-part-6.aspx
虽然值/元数据可能被部分缓存,但做一些性能测试表明,每次调用GetExportedValue
时都会执行一些查找。因此,如果你有很多需要获取值的调用,你应该自己做缓存。
namespace MEFCachingTest
{
using System;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.ComponentModel.Composition.Primitives;
using System.Diagnostics;
using System.Reflection;
public static class Program
{
public static CompositionContainer Container { get; set; }
public static ComposablePartCatalog Catalog { get; set; }
public static ExportedClass NonCachedClass
{
get
{
return Container.GetExportedValue<ExportedClass>();
}
}
private static ExportedClass cachedClass;
public static ExportedClass CachedClass
{
get
{
return cachedClass ?? (cachedClass = Container.GetExportedValue<ExportedClass>());
}
}
public static void Main()
{
Catalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());
Container = new CompositionContainer(Catalog);
const int Runs = 1000000;
var stopwatch = new Stopwatch();
// Non-Cached.
stopwatch.Start();
for (int i = 0; i < Runs; i++)
{
var ncc = NonCachedClass;
}
stopwatch.Stop();
Console.WriteLine("Non-Cached: Time: {0}", stopwatch.Elapsed);
// Cached.
stopwatch.Restart();
for (int i = 0; i < Runs; i++)
{
var cc = CachedClass;
}
stopwatch.Stop();
Console.WriteLine(" Cached: Time: {0}", stopwatch.Elapsed);
}
}
[Export]
[PartCreationPolicy(CreationPolicy.Shared)]
public class ExportedClass
{
}
}
更多的变化,看看这个要点:https://gist.github.com/DanielRose/d79f0da2ef61591176ce
在我的电脑上,Windows 7 x64, .NET 4.5.2:
Non-Cached: Time: 00:00:02.1217811
Cached: Time: 00:00:00.0063479
使用MEF 2 from NuGet:
Non-Cached: Time: 00:00:00.2037812
Cached: Time: 00:00:00.0023358
在我工作的实际应用程序中,这使应用程序慢了6倍。