如何理解在C#中使用异常处理“使用”的JITed代码

我在C#中编写了一个非常简单的类:

class DisposableClass : IDisposable {
    public void Dispose() { }
}


static void UsingClass() {                    // line 31
    using (var dc = new DisposableClass()) {  // line 32
        DoSomething(dc);                      // line 33
    }                                         // line 34
}                                             // line 35

我用WinDBG为JIT转储了本机代码:

0:000> !u 000007fe87d30120 
Normal JIT generated code
SimpleConsole.Program.UsingClass()
Begin 000007fe87d30120, size 80

c:\projects\SimpleConsole\SimpleConsole\Program.cs @ 32:
>>> 000007fe`87d30120 55              push    rbp
000007fe`87d30121 4883ec30        sub     rsp,30h
000007fe`87d30125 488d6c2420      lea     rbp,[rsp+20h]
000007fe`87d3012a 48896500        mov     qword ptr [rbp],rsp
000007fe`87d3012e 48c7450800000000 mov     qword ptr [rbp+8],0
000007fe`87d30136 488d0d6b47eeff  lea     rcx,[000007fe`87c148a8]
000007fe`87d3013d e8fe24665f      call    clr+0x2640 (000007fe`e7392640) (JitHelp: CORINFO_HELP_NEWSFAST) // new DisposableClass()
000007fe`87d30142 48894508        mov     qword ptr [rbp+8],rax

c:\projects\SimpleConsole\SimpleConsole\Program.cs @ 33:
000007fe`87d30146 488b4d08        mov     rcx,qword ptr [rbp+8]
000007fe`87d3014a e8d1beeeff      call    000007fe`87c1c020 (SimpleConsole.Program.DoSomething(System.Object), mdToken: 00000000
class DisposableClass : IDisposable {
    public void Dispose() { }
}


static void UsingClass() {                    // line 31
    using (var dc = new DisposableClass()) {  // line 32
        DoSomething(dc);                      // line 33
    }                                         // line 34
}                                             // line 35

012)
000007fe`87d3014f 90 nop
000007fe`87d30150 90 nop

c:\projects\SimpleConsole\SimpleConsole\Program.cs @ 35:
000007fe`87d30151 488b4d08 mov rcx,qword ptr [rbp+8]
000007fe`87d30155 4c8d1dc4feeeff lea r11,[000007fe`87c20020]
000007fe`87d3015c ff15befeeeff call qword ptr [000007fe`87c20020] // Call Dispose()
000007fe`87d30162 90 nop
000007fe`87d30163 488d6510 lea rsp,[rbp+10h]
000007fe`87d30167 5d pop rbp
000007fe`87d30168 c3 ret

// I could understand the code above (without exception thrown).

c:\projects\SimpleConsole\SimpleConsole\Program.cs @ 32:
000007fe`87d30169 55 push rbp
000007fe`87d3016a 4883ec30 sub rsp,30h
000007fe`87d3016e 488b6920 mov rbp,qword ptr [rcx+20h]
000007fe`87d30172 48896c2420 mov qword ptr [rsp+20h],rbp
000007fe`87d30177 488d6d20 lea rbp,[rbp+20h]

c:\projects\SimpleConsole\SimpleConsole\Program.cs @ 35:
000007fe`87d3017b 48837d0800 cmp qword ptr [rbp+8],0
000007fe`87d30180 7417 je 000007fe`87d30199
000007fe`87d30182 488d1597feeeff lea rdx,[000007fe`87c20020]
000007fe`87d30189 488b4508 mov rax,qword ptr [rbp+8]
000007fe`87d3018d 803800 cmp byte ptr [rax],0
000007fe`87d30190 488b4d08 mov rcx,qword ptr [rbp+8]
000007fe`87d30194 4c8bda mov r11,rdx
000007fe`87d30197 ff12 call qword ptr [rdx]
000007fe`87d30199 90 nop
000007fe`87d3019a 4883c430 add rsp,30h
000007fe`87d3019e 5d pop rbp
000007fe`87d3019f c3 ret

我可以毫无例外地理解代码(上面已经评论过),但抛出异常时代码是如何工作的?代码如何进入评论下面的代码?

更新:

有些人认为我们应该从IL开始,所以我粘贴下面的代码:

.method private hidebysig static 
    void UsingClass () cil managed noinlining 
{
    // Method begins at RVA 0x23bc
    // Code size 25 (0x19)
    .maxstack 1
    .locals init (
        [0] class SimpleConsole.DisposableClass dc
    )

    IL_0000: newobj instance void SimpleConsole.DisposableClass::.ctor()
    IL_0005: stloc.0
    .try
    {
        IL_0006: ldloc.0
        IL_0007: call void SimpleConsole.Program::DoSomething(object)
        IL_000c: leave.s IL_0018
    } // end .try
    finally
    {
        IL_000e: ldloc.0
        IL_000f: brfalse.s IL_0017

        IL_0011: ldloc.0
        IL_0012: callvirt instance void [mscorlib]System.IDisposable::Dispose()

        IL_0017: endfinally
    } // end handler

    IL_0018: ret
} // end of method Program::UsingClass

但我不认为这有帮助,因为IL几乎将所有内容保存在C#中,就像完整的try … finally语句一样.我想要了解的是本机代码如何处理异常.

最佳答案
抖动比“反汇编”窗口中显示的内容要多得多.例如,它生成一个表,描述局部变量的生命周期和存储.对于垃圾收集器非常重要,它需要该表来查找对象引用.

它会为异常生成一个展开表.它有一个非常理想的属性,它免费提供一个try语句.编写具有异常处理的代码时没有成本,输入try块不需要代码.所以你在反汇编中没有看到任何东西.没有简单的方法可以从调试器中找到该表.一个相当不错的描述他们is here.

转载注明原文:如何理解在C#中使用异常处理“使用”的JITed代码 - 代码日志