c# - 包装字符串的 WeakReference 会导致奇怪的行为

Question

我知道我应该只对大对象使用 Wea​​kReference，但我对以下场景感到好奇:

object obj = 1; //Int32

var wk = new WeakReference(obj);

Console.WriteLine(wk.IsAlive); //Prints: True

obj = null;

GC.Collect(2, GCCollectionMode.Forced, true);

Console.WriteLine(wk.IsAlive); //Prints: false, All Rigth!

到目前为止一切正常。

看这个:

object obj = "test"; //String

var wk = new WeakReference(obj);

Console.WriteLine(wk.IsAlive); //Prints: True

obj = null;

GC.Collect(2, GCCollectionMode.Forced, true);

Console.WriteLine(wk.IsAlive); //Prints: True, Why?

这是怎么回事？

Answer 1

来自String.Intern的评论:

The common language runtime conserves string storage by maintaining a table, called the intern pool, that contains a single reference to each unique literal string declared or created programmatically in your program. Consequently, an instance of a literal string with a particular value only exists once in the system.

因此，还有一个不能以编程方式发布的引用。稍微更改代码以在运行时生成一个实例会得到预期的结果:

object obj = new string(new char[] { 't', 'e', 's', 't' });
var wk = new WeakReference(obj);
Console.WriteLine(wk.IsAlive); //Prints: True
obj = null;
GC.Collect(2, GCCollectionMode.Forced, true);
Console.WriteLine(wk.IsAlive); //Prints: False