是MEF出口缓存或者发现在要求每一次？

问题描述

如果我有一类MyClass的，注册

[导出（typeof运算（MYCLASS））] 属性，以及

[PartCreationPolicy（CreationPolicy.Shared）]

或

[PartCreationPolicy（CreationPolicy.NonShared）]

和后来试图调用

compositionContainer.GetExportedValue＆LT; MYCLASS＆GT;（）多次

问：与第一个电话，我将通过MEF得到我的注册类 - llokup所有已注册的组件，然后试图找到一个注册的合同。问题是关于第二次等等 - 将MEF再做全局查找或缓存某处内部

解决方案

是的，MEF perfoms一些缓存，并广泛使用延迟初始化，如果你的问题是关于MEF的表现：

1）元数据（组合的部分，定义导出和导入定义）被缓存。例如：

 公共覆盖的IEnumerable＆LT; ExportDefinition＆GT; ExportDefinitions
{
    得到
    {
        如果（this._exports == NULL）
        {
            。ExportDefinition []出口= this._creationInfo.GetExports（）的ToArray＆LT; ExportDefinition＆GT;（）;
            锁（this._lock）
            {
                如果（this._exports == NULL）
                {
                    this._exports =出口;
                }
            }
        }
        返回this._exports;
    }
}
 

2）输出的值的被缓存过：

 公共对象值
{
    得到
    {
        如果（this._exportedValue == Export._EmptyValue）
        {
            对象exportedValueCore = this.GetExportedValueCore（）;
            Interlocked.CompareExchange（REF this._exportedValue，exportedValueCore，Export._EmptyValue）;
        }
        返回this._exportedValue;
    }
}
 

当然，使用 CreationPolicy.NonShared ，出口值变为一次又一次创建的时候，当你要求它。但是，即使在这种情况下，全局查找不进行，因为元数据被反正缓存

If I have one type MyClass, register with

[Export(typeof(Myclass))] attribute, and

[PartCreationPolicy(CreationPolicy.Shared)]

or

[PartCreationPolicy(CreationPolicy.NonShared)]

and later trying to call

compositionContainer.GetExportedValue<Myclass>() multiple times.

Question: with the first call, I will get my registered class via MEF - llokup all registered assemblies, then trying to find one registered contract. Question is about second time and so on - will MEF do global lookup again or it caches somewhere internally?

解决方案

Yes, MEF perfoms some caching and widely uses lazy initialization, if you question is about MEF performance:

1) metadata (composable parts, export definitions and import definitions) is cached. Example:

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) exported values are cached too:

public object Value
{
    get
    {
        if (this._exportedValue == Export._EmptyValue)
        {
            object exportedValueCore = this.GetExportedValueCore();
            Interlocked.CompareExchange(ref this._exportedValue, exportedValueCore, Export._EmptyValue);
        }
        return this._exportedValue;
    }
}

Of course, when using CreationPolicy.NonShared, exported value becomes created again and again, when you requesting it. But even in this case "global lookup" isn't performed, because metadata is cached anyway.

这篇关于是MEF出口缓存或者发现在要求每一次？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！