快速創建對象而不是 Activator.CreateInstance(type)

Question

我正在嘗試提高我們應用程序的性能。 我們有很多 Activator.CreateInstance 調用導致一些悲傷。

我們基於接口（ITabDocument）實例化了很多類，環顧四周后，我想到了使用以下代碼：

該代碼並不比使用我們擁有的 Activator.CreateInstance 代碼更好（實際上稍微慢一點）。

    public static Func<T> CreateInstance<T>(Type objType) where T : class, new()
    {
        var dynMethod = new DynamicMethod("DM$OBJ_FACTORY_" + objType.Name, objType, null, objType);
        ILGenerator ilGen = dynMethod.GetILGenerator();
        ilGen.Emit(OpCodes.Newobj, objType.GetConstructor(Type.EmptyTypes));
        ilGen.Emit(OpCodes.Ret);
        return (Func<T>)dynMethod.CreateDelegate(typeof(Func<T>));
    }

我想知道為什么會這樣，我所做的只是：

ITabDocument document = CreateInstance<ITabDocument>(Type.GetType("[Company].Something"));

有沒有更好的方法來創建可以幫助完成上述操作的對象？ 當您不確定具體類型時，它有點難。

Answer 1

我在這些之間做了一些基准測試（我會寫下最基本的細節）：

public static T Instance() //~1800 ms
{
    return new T();
}

public static T Instance() //~1800 ms
{
    return new Activator.CreateInstance<T>();
}

public static readonly Func<T> Instance = () => new T(); //~1800 ms

public static readonly Func<T> Instance = () => 
                                 Activator.CreateInstance<T>(); //~1800 ms

//works for types with no default constructor as well
public static readonly Func<T> Instance = () => 
               (T)FormatterServices.GetUninitializedObject(typeof(T)); //~2000 ms


public static readonly Func<T> Instance = 
     Expression.Lambda<Func<T>>(Expression.New(typeof(T))).Compile();  
     //~50 ms for classes and ~100 ms for structs

正如 CD 所說，編譯表達式是最快的，而且幅度很大。 除(T)FormatterServices.GetUninitializedObject(typeof(T))之外的所有方法僅適用於具有默認構造函數的類型。

當每個泛型類型都有 static class 時，緩存編譯的結果委托是微不足道的。 喜歡：

public static class New<T> where T : new()
{
    public static readonly Func<T> Instance = Expression.Lambda<Func<T>>
                                              (
                                               Expression.New(typeof(T))
                                              ).Compile();
}

注意new的約束。 調用任何東西

MyType me = New<MyType>.Instance();

除了第一次在 memory 中加載 class 之外，執行將是最快的。

為了讓 class 使用默認構造函數和不使用默認構造函數處理兩種類型，我采用了混合方法，從這里開始：

public static class New<T>
{
    public static readonly Func<T> Instance = Creator();

    static Func<T> Creator()
    {
        Type t = typeof(T);
        if (t == typeof(string))
            return Expression.Lambda<Func<T>>(Expression.Constant(string.Empty)).Compile();

        if (t.HasDefaultConstructor())
            return Expression.Lambda<Func<T>>(Expression.New(t)).Compile();

        return () => (T)FormatterServices.GetUninitializedObject(t);
    }
}

public static bool HasDefaultConstructor(this Type t)
{
    return t.IsValueType || t.GetConstructor(Type.EmptyTypes) != null;
}

也會以有效的方式處理值類型。

請注意， (T)FormatterServices.GetUninitializedObject(t)對於string將失敗。 因此，對字符串進行了特殊處理以返回空字符串。

Answer 2

這可能會有所幫助： 不要使用 Activator.CreateInstance 或 ConstructorInfo.Invoke，使用已編譯的 lambda 表達式：

 // Make a NewExpression that calls the ctor with the args we just created NewExpression newExp = Expression.New(ctor, argsExp); // Create a lambda with the New expression as body and our param object[] as arg LambdaExpression lambda = Expression.Lambda(typeof(ObjectActivator), newExp, param); // Compile it ObjectActivator compiled = (ObjectActivator)lambda.Compile();

Answer 3

問題是，如果您要直接一遍又一遍地調用 CreateInstance 而不是將結果保存在某處並一遍又一遍地使用該結果，那么您可能應該只提前 go 並在其中緩存。

internal static class DelegateStore<T> {
     internal static IDictionary<string, Func<T>> Store = new ConcurrentDictionary<string,Func<T>>();
}

public static T CreateInstance<T>(Type objType) where T : class
{
    Func<T> returnFunc;
    if(!DelegateStore<T>.Store.TryGetValue(objType.FullName, out returnFunc)) {
        var dynMethod = new DynamicMethod("DM$OBJ_FACTORY_" + objType.Name, objType, null, objType);
        ILGenerator ilGen = dynMethod.GetILGenerator();
        ilGen.Emit(OpCodes.Newobj, objType.GetConstructor(Type.EmptyTypes));
        ilGen.Emit(OpCodes.Ret);
        returnFunc = (Func<T>)dynMethod.CreateDelegate(typeof(Func<T>));
        DelegateStore<T>.Store[objType.FullName] = returnFunc;
    }
    return returnFunc();
}

Answer 4

2019 年 12 月 13 日
nawfal的答案基准化

以 NetCore3.1 為基准，只是看到這仍然是多么必要。

[MemoryDiagnoser, ThreadingDiagnoser]
[SimpleJob(runtimeMoniker: RuntimeMoniker.NetCoreApp31)]
[GenericTypeArguments(typeof(TestClass))]
public class ActivatorBenchmark<T> where T : new()
{
    [Benchmark(Baseline = true)]
    [Arguments(1_000)]
    [Arguments(1_000_000)]
    [Arguments(100_000_000)]

    public void ActivatorTest1(int x)
    {
        for (int i = 0; i < x; i++)
        {
            var t = new T();
        }
    }

    [Benchmark]
    [Arguments(1_000)]
    [Arguments(1_000_000)]
    [Arguments(100_000_000)]
    public void ActivatorTest2(int x)
    {
        for (int i = 0; i < x; i++)
        {
            var t = New<T>.Instance();
        }
    }
}

public class TestClass
{
    public string Name { get; set; }
    public int Id { get; set; }
    public string Email { get; set; }
}

public static class TestHelpers
{
    public static class New<T>
    {
        public static readonly Func<T> Instance = Creator();

        private static Func<T> Creator()
        {
            Type t = typeof(T);
            if (t == typeof(string))
                return Expression.Lambda<Func<T>>(Expression.Constant(string.Empty)).Compile();

            if (t.HasDefaultConstructor())
                return Expression.Lambda<Func<T>>(Expression.New(t)).Compile();

            return () => (T)FormatterServices.GetUninitializedObject(t);
        }
    }

    public static bool HasDefaultConstructor(this Type t)
    {
        return t.IsValueType || t.GetConstructor(Type.EmptyTypes) != null;
    }
}

.

// * Detailed results *
ActivatorBenchmark<TestClass>.ActivatorTest1: Job-RRTXQH(Runtime=.NET Core 3.1) [x=1000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 30.9925 us, StdErr = 0.1962 us (0.63%); N = 17, StdDev = 0.8088 us
Min = 30.2190 us, Q1 = 30.4151 us, Median = 30.4745 us, Q3 = 31.5188 us, Max = 32.7203 us
IQR = 1.1037 us, LowerFence = 28.7595 us, UpperFence = 33.1744 us
ConfidenceInterval = [30.2049 us; 31.7802 us] (CI 99.9%), Margin = 0.7876 us (2.54% of Mean)
Skewness = 0.96, Kurtosis = 2.4, MValue = 2
-------------------- Histogram --------------------
[29.944 us ; 30.909 us) | @@@@@@@@@@@
[30.909 us ; 31.555 us) | @@
[31.555 us ; 32.301 us) | @@
[32.301 us ; 32.996 us) | @@
---------------------------------------------------

ActivatorBenchmark<TestClass>.ActivatorTest2: Job-RRTXQH(Runtime=.NET Core 3.1) [x=1000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 7.0534 us, StdErr = 0.0144 us (0.20%); N = 14, StdDev = 0.0538 us
Min = 6.9228 us, Q1 = 7.0269 us, Median = 7.0687 us, Q3 = 7.0849 us, Max = 7.1367 us
IQR = 0.0580 us, LowerFence = 6.9399 us, UpperFence = 7.1718 us
ConfidenceInterval = [6.9927 us; 7.1142 us] (CI 99.9%), Margin = 0.0607 us (0.86% of Mean)
Skewness = -0.76, Kurtosis = 3.12, MValue = 2
-------------------- Histogram --------------------
[6.903 us ; 7.148 us) | @@@@@@@@@@@@@@
---------------------------------------------------

ActivatorBenchmark<TestClass>.ActivatorTest1: Job-RRTXQH(Runtime=.NET Core 3.1) [x=1000000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 27.6912 ms, StdErr = 0.0412 ms (0.15%); N = 13, StdDev = 0.1486 ms
Min = 27.5318 ms, Q1 = 27.6171 ms, Median = 27.6435 ms, Q3 = 27.7196 ms, Max = 28.0946 ms
IQR = 0.1025 ms, LowerFence = 27.4633 ms, UpperFence = 27.8734 ms
ConfidenceInterval = [27.5132 ms; 27.8691 ms] (CI 99.9%), Margin = 0.1780 ms (0.64% of Mean)
Skewness = 1.56, Kurtosis = 4.57, MValue = 2
-------------------- Histogram --------------------
[27.477 ms ; 28.150 ms) | @@@@@@@@@@@@@
---------------------------------------------------

ActivatorBenchmark<TestClass>.ActivatorTest2: Job-RRTXQH(Runtime=.NET Core 3.1) [x=1000000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 7.0697 ms, StdErr = 0.0239 ms (0.34%); N = 15, StdDev = 0.0927 ms
Min = 6.9195 ms, Q1 = 6.9889 ms, Median = 7.0681 ms, Q3 = 7.1187 ms, Max = 7.2497 ms
IQR = 0.1298 ms, LowerFence = 6.7942 ms, UpperFence = 7.3134 ms
ConfidenceInterval = [6.9706 ms; 7.1687 ms] (CI 99.9%), Margin = 0.0991 ms (1.40% of Mean)
Skewness = 0.22, Kurtosis = 2.08, MValue = 2
-------------------- Histogram --------------------
[6.887 ms ; 7.252 ms) | @@@@@@@@@@@@@@@
---------------------------------------------------

ActivatorBenchmark<TestClass>.ActivatorTest1: Job-RRTXQH(Runtime=.NET Core 3.1) [x=100000000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 2.7852 s, StdErr = 0.0093 s (0.33%); N = 15, StdDev = 0.0358 s
Min = 2.7426 s, Q1 = 2.7576 s, Median = 2.7693 s, Q3 = 2.8141 s, Max = 2.8629 s
IQR = 0.0565 s, LowerFence = 2.6728 s, UpperFence = 2.8989 s
ConfidenceInterval = [2.7469 s; 2.8235 s] (CI 99.9%), Margin = 0.0383 s (1.38% of Mean)
Skewness = 0.76, Kurtosis = 2.21, MValue = 2
-------------------- Histogram --------------------
[2.735 s ; 2.796 s) | @@@@@@@@@@
[2.796 s ; 2.876 s) | @@@@@
---------------------------------------------------

ActivatorBenchmark<TestClass>.ActivatorTest2: Job-RRTXQH(Runtime=.NET Core 3.1) [x=100000000]
Runtime = .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT; GC = Concurrent Workstation
Mean = 698.4029 ms, StdErr = 1.3760 ms (0.20%); N = 15, StdDev = 5.3292 ms
Min = 688.2649 ms, Q1 = 693.8483 ms, Median = 697.9546 ms, Q3 = 703.2100 ms, Max = 707.1939 ms
IQR = 9.3617 ms, LowerFence = 679.8057 ms, UpperFence = 717.2526 ms
ConfidenceInterval = [692.7056 ms; 704.1001 ms] (CI 99.9%), Margin = 5.6972 ms (0.82% of Mean)
Skewness = 0.09, Kurtosis = 2.08, MValue = 2
-------------------- Histogram --------------------
[686.374 ms ; 709.085 ms) | @@@@@@@@@@@@@@@
---------------------------------------------------

// * Summary *

BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
Intel Core i9-9980HK CPU 2.40GHz, 1 CPU, 16 logical and 8 physical cores
.NET Core SDK=3.1.100
  [Host]     : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
  Job-RRTXQH : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT

Runtime=.NET Core 3.1

|         Method |         x |             Mean |          Error |         StdDev | Ratio | Completed Work Items | Lock Contentions |       Gen 0 |     Gen 1 | Gen 2 |    Allocated |
|--------------- |---------- |-----------------:|---------------:|---------------:|------:|---------------------:|-----------------:|------------:|----------:|------:|-------------:|
| ActivatorTest1 |      1000 |        30.993 us |      0.7876 us |      0.8088 us |  1.00 |               0.0001 |                - |      4.7607 |         - |     - |     39.06 KB |
| ActivatorTest2 |      1000 |         7.053 us |      0.0607 us |      0.0538 us |  0.23 |               0.0000 |                - |      4.7760 |         - |     - |     39.06 KB |
|                |           |                  |                |                |       |                      |                  |             |           |       |              |
| ActivatorTest1 |   1000000 |    27,691.175 us |    177.9530 us |    148.5988 us |  1.00 |               0.0625 |                - |   4781.2500 |         - |     - |  39064.19 KB |
| ActivatorTest2 |   1000000 |     7,069.695 us |     99.0538 us |     92.6550 us |  0.26 |               0.0156 |                - |   4781.2500 |         - |     - |   39062.5 KB |
|                |           |                  |                |                |       |                      |                  |             |           |       |              |
| ActivatorTest1 | 100000000 | 2,785,181.093 us | 38,325.0183 us | 35,849.2459 us |  1.00 |               2.0000 |                - | 478000.0000 | 2000.0000 |     - | 3906418.4 KB |
| ActivatorTest2 | 100000000 |   698,402.860 us |  5,697.2360 us |  5,329.1981 us |  0.25 |               2.0000 |                - | 478000.0000 |         - |     - |   3906250 KB |

// * Hints *
Outliers
  ActivatorBenchmark<TestClass>.ActivatorTest2: Runtime=.NET Core 3.1 -> 1 outlier  was  removed, 2 outliers were detected (6.92 us, 9.73 us)
  ActivatorBenchmark<TestClass>.ActivatorTest1: Runtime=.NET Core 3.1 -> 2 outliers were removed (28.56 ms, 29.78 ms)

// * Legends *
  x                    : Value of the 'x' parameter
  Mean                 : Arithmetic mean of all measurements
  Error                : Half of 99.9% confidence interval
  StdDev               : Standard deviation of all measurements
  Ratio                : Mean of the ratio distribution ([Current]/[Baseline])
  Completed Work Items : The number of work items that have been processed in ThreadPool (per single operation)
  Lock Contentions     : The number of times there was contention upon trying to take a Monitor's lock (per single operation)
  Gen 0                : GC Generation 0 collects per 1000 operations
  Gen 1                : GC Generation 1 collects per 1000 operations
  Gen 2                : GC Generation 2 collects per 1000 operations
  Allocated            : Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
  1 us                 : 1 Microsecond (0.000001 sec)

// * Diagnostic Output - ThreadingDiagnoser *

// * Diagnostic Output - MemoryDiagnoser *

Answer 5

您可能會從生成相同代碼中獲得一些開銷。

ILGenerator為工廠動態創建代碼。

創建某種 map 或您已經使用過的類型的Dictionary ，並保留為該類型創建的工廠方法。

Answer 6

構造委托的通用方法，直接調用構造函數。 使用給定委托類型的簽名自動搜索給定類型的構造函數並構造該類型的委托。 代碼在這里：

/// <summary>
/// Reflective object construction helper.
/// All methods are thread safe.
/// </summary>
public static class Constructor
{
    /// <summary>
    /// Searches an instanceType constructor with delegateType-matching signature and constructs delegate of delegateType creating new instance of instanceType.
    /// Instance is casted to delegateTypes's return type. 
    /// Delegate's return type must be assignable from instanceType.
    /// </summary>
    /// <param name="delegateType">Type of delegate, with constructor-corresponding signature to be constructed.</param>
    /// <param name="instanceType">Type of instance to be constructed.</param>
    /// <returns>Delegate of delegateType wich constructs instance of instanceType by calling corresponding instanceType constructor.</returns>
    public static Delegate Compile(Type delegateType,Type instanceType)
    {
        if (!typeof(Delegate).IsAssignableFrom(delegateType))
        {
            throw new ArgumentException(String.Format("{0} is not a Delegate type.",delegateType.FullName),"delegateType");
        }
        var invoke = delegateType.GetMethod("Invoke");
        var parameterTypes = invoke.GetParameters().Select(pi => pi.ParameterType).ToArray();
        var resultType = invoke.ReturnType;
        if(!resultType.IsAssignableFrom(instanceType))
        {
            throw new ArgumentException(String.Format("Delegate's return type ({0}) is not assignable from {1}.",resultType.FullName,instanceType.FullName));
        }
        var ctor = instanceType.GetConstructor(
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, parameterTypes, null);
        if(ctor == null)
        {
            throw new ArgumentException("Can't find constructor with delegate's signature","instanceType");
        }
        var parapeters = parameterTypes.Select(Expression.Parameter).ToArray();

        var newExpression = Expression.Lambda(delegateType,
            Expression.Convert(Expression.New(ctor, parapeters), resultType),
            parapeters);
        var @delegate = newExpression.Compile();
        return @delegate;
    }
    public static TDelegate Compile<TDelegate>(Type instanceType)
    {
        return (TDelegate) (object) Compile(typeof (TDelegate), instanceType);
    }
}

是Yappi項目來源的一部分。 使用它，您可以構造委托調用給定類型的任何構造函數，包括帶參數的構造函數（ref 和 out 參數除外）。

示例用法：

var newList = Constructor.Compile<Func<int, IList<String>>>(typeof (List<String>));
var list = newList(100);

構建委托后，將其存儲在 static 字典或 class 的 static 字段中的某個位置，並帶有通用參數。 不要每次都構造新的委托。 使用一個委托來構造給定類型的多個實例。