计时器、事件和垃圾收集:我错过了什么吗? [英] Timer, event and garbage collection : am I missing something?

问题描述

考虑以下代码:

class TestTimerGC : Form
{
    public TestTimerGC()
    {
        Button btnGC = new Button();
        btnGC.Text = "GC";
        btnGC.Click += (sender, e) => GC.Collect();
        this.Controls.Add(btnGC);

        System.Windows.Forms.Timer tmr = new System.Windows.Forms.Timer();
        tmr.Interval = 1000;
        tmr.Tick += (sender, e) => this.Text = DateTime.Now.ToString();
        tmr.Start();
    }
}

如果我没记错的话，在 tmr 变量超出范围后，Timer 不会在任何地方被引用，因此它应该有资格进行垃圾收集.但是当我点击GC按钮时，计时器继续运行，所以我猜它没有被收集......

If I'm not mistaken, after the tmr variable goes out of scope, the Timer isn't referenced anywhere, so it should be eligible for garbage collection. But when I click the GC button, the timer continues to run, so I guess it wasn't collected...

有没有人解释一下?

PS:这当然不是一个真正的程序，我只是想向某人证明一个观点......但我的证明没有奏效;)

推荐答案

好吧，我想我知道发生了什么......我用 Reflector 查看了 Timer 类的代码，然后我在 Enabled 属性的 setter 中找到以下指令:

OK, I think I know what's going on... I looked at the code of the Timer class with Reflector, and I found the following instruction in the setter of the Enabled property :

this.timerRoot = GCHandle.Alloc(this);

所以，当它启动时，定时器为自己分配一个GCHandle，这阻止了它被GC收集......

So, when it is started, the timer allocates a GCHandle for itself, which prevents its collection by the GC...

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