我正在努力提高应用程序的性能。我们有很多Activator.CreateInstance调用引起了一些悲伤。
我们基于一个接口（ITabDocument）实例化了很多类，在浏览后我想到了使用这个代码：
与使用我们的Activator.CreateInstance代码相比，代码并不是更好（实际上速度稍慢）。
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>));
}
我想知道为什么会这样，我所做的只是：
ITabDocument document = CreateInstance<ITabDocument>(Type.GetType("[Company].Something"));
有没有更好的方法来创建有助于上述内容的对象？当你不确定具体的类型时，它有点难。
答案 0 :(得分：45)
我在这些之间做了一些基准测试（我会写下最基本的细节）：
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所说，编译表达式是最快的，并且大幅度提升。除(T)FormatterServices.GetUninitializedObject(typeof(T)) 之外的所有方法仅适用于具有默认构造函数的类型。
当你有一个每个泛型类型的静态类时，缓存已编译的结果委托是微不足道的。像：
public static class New<T> where T : new()
{
public static readonly Func<T> Instance = Expression.Lambda<Func<T>>
(
Expression.New(typeof(T))
).Compile();
}
请注意new约束。打电话给任何人
MyType me = New<MyType>.Instance();
除了第一次将类加载到内存中外，执行速度最快。
要有一个使用默认构造函数处理这两种类型的类，我采用混合方法，from here：
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;
}
也会以有效的方式处理价值类型。
请注意，(T)FormatterServices.GetUninitializedObject(t) string将失败。因此，对字符串进行特殊处理以返回空字符串。
答案 1 :(得分：15)
这可能有所帮助：Don’t use Activator.CreateInstance or ConstructorInfo.Invoke, use compiled lambda expressions：
// 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();
答案 2 :(得分：7)
问题是如果你要反复直接调用CreateInstance而不是将结果保存到某个地方并反复使用该结果，你可能应该继续并在内部进行缓存。
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();
}
答案 3 :(得分：3)
您可能会从生成相同代码中获得一些开销。
ILGenerator动态创建工厂代码。
创建一些您已经使用过的地图或Dictionary类型，并保留为该类型创建的工厂方法。
答案 4 :(得分：2)
2019年12月13日
nawfal's answer benchmarked
以NetCore3.1为基准，只是看到它仍然有多么必要。
[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 *
答案 5 :(得分：0)
构造委托的通用方法，直接调用构造函数。 使用给定委托类型的签名自动搜索给定类型的构造函数，并构造该类型的委托。代码在这里：
/// <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项目来源的一部分。使用它，您可以构造委托调用给定类型的任何构造函数，包括带参数的构造函数（ref和out参数除外）。
样本用法：
var newList = Constructor.Compile<Func<int, IList<String>>>(typeof (List<String>));
var list = newList(100);
构建委托后，将其存储在静态字典中或使用泛型参数的类的静态字段中。不要每次都构造新的委托。使用一个委托来构造给定类型的多个实例。