这个对象生命周期扩展闭包是一个C#编译器错误吗?

当我碰到C#编译器(如果有问题的话)的一些非常好奇的代码的时候,我正在回答关于closures(合法地)延长对象生命期的可能性的问题。

最短的repro我可以find如下:

  1. 在调用包含types的静态方法的同时创build一个捕获本地的lambda
  2. 将生成的委托引用分配给包含对象的实例字段。

结果:编译器创build一个闭包对象,该闭包对象引用创buildlambda的对象,当它没有理由时 – 委托的“内部”目标是一个静态方法,并且lambda创build对象的实例成员不需要当代表执行时,(而不是)被触摸。 实际上,编译器就像程序员没有理由地捕捉到了this

 class Foo { private Action _field; public void InstanceMethod() { var capturedVariable = Math.Pow(42, 1); _field = () => StaticMethod(capturedVariable); } private static void StaticMethod(double arg) { } } 

从发布版本生成的代码(反编译为“简单”C#)看起来像这样:

 public void InstanceMethod() { <>c__DisplayClass1 CS$<>8__locals2 = new <>c__DisplayClass1(); CS$<>8__locals2.<>4__this = this; // What's this doing here? CS$<>8__locals2.capturedVariable = Math.Pow(42.0, 1.0); this._field = new Action(CS$<>8__locals2.<InstanceMethod>b__0); } [CompilerGenerated] private sealed class <>c__DisplayClass1 { // Fields public Foo <>4__this; // Never read, only written to. public double capturedVariable; // Methods public void <InstanceMethod>b__0() { Foo.StaticMethod(this.capturedVariable); } } 

注意到<>4__this这个闭包对象的<>4__this字段被填充了一个对象引用,但永远不会被读取(没有理由)。

那么这里发生了什么? 语言规范是否允许? 这是一个编译器的bug /怪异的还是有一个很好的理由(我明显缺less)的封闭引用对象? 这使我感到焦虑,因为这看起来像一个封闭开发的程序员(像我一样)不知不觉地将奇怪的内存泄漏(想象如果委托被用作事件处理程序)引入程序。

    2 Solutions collect form web for “这个对象生命周期扩展闭包是一个C#编译器错误吗?”

    这肯定看起来像一个错误。 感谢您的关注。 我会研究它。 它可能已经被发现和修复。

    这似乎是一个错误或不必要的:

    我在IL lang中运行例子:

     .method public hidebysig instance void InstanceMethod () cil managed { // Method begins at RVA 0x2074 // Code size 63 (0x3f) .maxstack 4 .locals init ( [0] class ConsoleApplication1.Program/Foo/'<>c__DisplayClass1' 'CS$<>8__locals2' ) IL_0000: newobj instance void ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::.ctor() IL_0005: stloc.0 IL_0006: ldloc.0 IL_0007: ldarg.0 IL_0008: stfld class ConsoleApplication1.Program/Foo ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::'<>4__this' //Make ref to this IL_000d: nop IL_000e: ldloc.0 IL_000f: ldc.r8 42 IL_0018: ldc.r8 1 IL_0021: call float64 [mscorlib]System.Math::Pow(float64, float64) IL_0026: stfld float64 ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::capturedVariable IL_002b: ldarg.0 IL_002c: ldloc.0 IL_002d: ldftn instance void ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::'<InstanceMethod>b__0'() IL_0033: newobj instance void [mscorlib]System.Action::.ctor(object, native int) IL_0038: stfld class [mscorlib]System.Action ConsoleApplication1.Program/Foo::_field IL_003d: nop IL_003e: ret } // end of method Foo::InstanceMethod 

    例2:

     class Program { static void Main(string[] args) { } class Foo { private Action _field; public void InstanceMethod() { var capturedVariable = Math.Pow(42, 1); _field = () => Foo2.StaticMethod(capturedVariable); //Foo2 } private static void StaticMethod(double arg) { } } class Foo2 { internal static void StaticMethod(double arg) { } } } 

    在cl:(注意!!现在这个参考文件已经不存在了!)

     public hidebysig instance void InstanceMethod () cil managed { // Method begins at RVA 0x2074 // Code size 56 (0x38) .maxstack 4 .locals init ( [0] class ConsoleApplication1.Program/Foo/'<>c__DisplayClass1' 'CS$<>8__locals2' ) IL_0000: newobj instance void ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::.ctor() IL_0005: stloc.0 IL_0006: nop //No this pointer IL_0007: ldloc.0 IL_0008: ldc.r8 42 IL_0011: ldc.r8 1 IL_001a: call float64 [mscorlib]System.Math::Pow(float64, float64) IL_001f: stfld float64 ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::capturedVariable IL_0024: ldarg.0 //No This ref IL_0025: ldloc.0 IL_0026: ldftn instance void ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::'<InstanceMethod>b__0'() IL_002c: newobj instance void [mscorlib]System.Action::.ctor(object, native int) IL_0031: stfld class [mscorlib]System.Action ConsoleApplication1.Program/Foo::_field IL_0036: nop IL_0037: ret } 

    例3:

     class Program { static void Main(string[] args) { } static void Test(double arg) { } class Foo { private Action _field; public void InstanceMethod() { var capturedVariable = Math.Pow(42, 1); _field = () => Test(capturedVariable); } private static void StaticMethod(double arg) { } } } 

    在IL:(这个指针回来了)

     IL_0006: ldloc.0 IL_0007: ldarg.0 IL_0008: stfld class ConsoleApplication1.Program/Foo ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::'<>4__this' //Back again. 

    在这三种情况下,method-b__0()看起来都一样:

     instance void '<InstanceMethod>b__0' () cil managed { // Method begins at RVA 0x2066 // Code size 13 (0xd) .maxstack 8 IL_0000: ldarg.0 IL_0001: ldfld float64 ConsoleApplication1.Program/Foo/'<>c__DisplayClass1'::capturedVariable IL_0006: call void ConsoleApplication1.Program/Foo::StaticMethod(float64) //Your example IL_0006: call void ConsoleApplication1.Program/Foo2::StaticMethod(float64)//Example 2 IL_0006: call void ConsoleApplication1.Program::Test(float64) //Example 3 IL_000b: nop IL_000c: ret } 

    在所有这三种情况下,都提到了一种静态方法,所以它更加奇怪。 所以在这个小问题分析之后,我会说它是一个bug /不好。 !