C#高性能動態獲取對象屬性值


動態獲取對象的性能值,這個在開發過程中經常會遇到,這里我們探討一下何如高性能的獲取屬性值。為了對比測試,我們定義一個類People

public class People
{
    public string Name { get; set; }
}

 

然后通過直接代碼調用方式來取1千萬次看要花多少時間:

private static void Directly()
{
    People people = new People { Name = "Wayne" };
    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value = people.Name;
    }
    stopwatch.Stop();
    Console.WriteLine("Directly: {0}ms", stopwatch.ElapsedMilliseconds);
}

 

大概花了37ms:

 

 

反射

通過反射來獲取對象的屬性值,這應該是大家常用的方式,但這種方式的性能比較差。接下來我們來看看同樣取1千萬次需要多少時間:

private static void Reflection()
{
    People people = new People { Name = "Wayne" };
    Type type = typeof(People);
    PropertyInfo property = type.GetProperty("Name");
    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value = property.GetValue(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Reflection: {0}ms", stopwatch.ElapsedMilliseconds);
}

 

大概花了1533ms,果然要慢很多:

 

 

那既然反射慢,那還有沒有其它方式呢?

動態構建Lambda

我們知道可以動態構建Linq的Lambda表達式,然后通過編譯后得到一個委托,如果能動態構建返回屬性值的委托,就可以取到值了。所以我們想辦法構建一個像這樣的委托:

Func<People, object> getName = m => m.Name;

 

接下來我們就通過Expression來構建:

private static void Lambda()
{
    People people = new People { Name = "Wayne" };
    Type type = typeof(People);
    var parameter = Expression.Parameter(type, "m");//參數m
    PropertyInfo property = type.GetProperty("Name");
    Expression expProperty = Expression.Property(parameter, property.Name);//取參數的屬性m.Name
    var propertyDelegateExpression = Expression.Lambda(expProperty, parameter);//變成表達式 m => m.Name
    var propertyDelegate = (Func<People, object>)propertyDelegateExpression.Compile();//編譯成委托
    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value = propertyDelegate.Invoke(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Lambda:{0}ms", stopwatch.ElapsedMilliseconds);
}

 

然后我們測試一下,大概花了138ms,性能要比反射好非常多:

 

 

委托調用

雖然動態構建Lambda的性能已經很好了,但還是更好嗎?畢竟比直接調用還是差了一些,要是能直接調用屬性的取值方法就好了。

在C#中,可讀屬性都有一個對應的get_XXX()的方法,可以通過調用這個方法來取得對應屬性的值。可以使用System.Delegate.CreateDelegate創建一個委托來調用這個方法。

  • 通過委托調用方法來取得屬性值

我們定義一個MemberGetDelegate的委托,然后通過它來調用取值方法:

delegate string MemberGetDelegate(People p);
private static void Delegate()
{
    People people = new People { Name = "Wayne" };
    Type type = typeof(People);
    PropertyInfo property = type.GetProperty("Name");
    MemberGetDelegate memberGet = (MemberGetDelegate)System.Delegate.CreateDelegate(typeof(MemberGetDelegate), property.GetGetMethod());
    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value = memberGet(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Delegate: {0}ms", stopwatch.ElapsedMilliseconds);
}

 

然后我們測試一下,大概花了38ms,性能幾乎與直接調用一致:

 

但這個方法的限制在於需要知道返回類型,在返回類型未知的時候就顯得不那么方便了。

Emit

Emit可以在運行時動態生成代碼,我們可以動態構建一個方法,在這個方法里面調用取屬性值的方法:

private static void Emit()
{
    People people = new People { Name = "Wayne" };
    Type type = typeof(People);
    var property = type.GetProperty("Name");
    DynamicMethod method = new DynamicMethod("GetPropertyValue", typeof(object), new Type[] { type }, true);
    ILGenerator il = method.GetILGenerator();
    il.Emit(OpCodes.Ldarg_0);
    il.Emit(OpCodes.Callvirt, property.GetGetMethod());
            
    if (property.PropertyType.IsValueType)
    {
        il.Emit(OpCodes.Box, property.PropertyType);//值類型需要裝箱,因為返回類型是object
    }
    il.Emit(OpCodes.Ret);
    Func<People, object> fun = method.CreateDelegate(typeof(Func<People, object>)) as Func<People, object>;

    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value = fun.Invoke(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Emit:{0}ms", stopwatch.ElapsedMilliseconds);
}

測試一下,大概119ms,性能與動態構建Lambda編譯的委托接近:

 

 原文鏈接:http://www.zkea.net/codesnippet/detail/csharp-fast-get-property-value.html


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