問題描述

我在另一個問題中看到了這個提示，想知道是否有人可以向我解釋這到底是如何工作的?

I saw this tip in another question and was wondering if someone could explain to me how on earth this works?

try { return x; } finally { x = null; }

我的意思是，finally 子句真的執(zhí)行 after return 語句嗎?這段代碼有多線程不安全?你能想到任何可以做的額外黑客行為嗎?這個 try-finally 破解?

I mean, does the finally clause really execute after the return statement? How thread-unsafe is this code? Can you think of any additional hackery that can be done w.r.t. this try-finally hack?

推薦答案

不 - 在 IL 級別，您不能從異常處理塊內(nèi)部返回.它本質(zhì)上將它存儲在一個變量中，然后返回

No - at the IL level you can't return from inside an exception-handled block. It essentially stores it in a variable and returns afterwards

即類似于:

int tmp;
try {
  tmp = ...
} finally {
  ...
}
return tmp;

例如(使用反射器):

static int Test() {
    try {
        return SomeNumber();
    } finally {
        Foo();
    }
}

編譯為:

.method private hidebysig static int32 Test() cil managed
{
    .maxstack 1
    .locals init (
        [0] int32 CS$1$0000)
    L_0000: call int32 Program::SomeNumber()
    L_0005: stloc.0 
    L_0006: leave.s L_000e
    L_0008: call void Program::Foo()
    L_000d: endfinally 
    L_000e: ldloc.0 
    L_000f: ret 
    .try L_0000 to L_0008 finally handler L_0008 to L_000e
}

這基本上聲明了一個局部變量(CS$1$0000)，將值放入變量中(在處理的塊內(nèi))，然后在退出塊后加載變量，然后返回它.反射器將其呈現(xiàn)為:

This basically declares a local variable (CS$1$0000), places the value into the variable (inside the handled block), then after exiting the block loads the variable, then returns it. Reflector renders this as:

private static int Test()
{
    int CS$1$0000;
    try
    {
        CS$1$0000 = SomeNumber();
    }
    finally
    {
        Foo();
    }
    return CS$1$0000;
}

這篇關(guān)于在 try { return x; 中真正發(fā)生了什么?} 最后 { x = null;} 陳述?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！