弱引用的线程安全
使用 WeakReference 时，我们如何确定在 .IsAlive 和 .Target 调用之间没有收集目标？
例如：
if (myWeakReference.IsAlive)
{
// How can we be sure the object is still alive while here?
((MyType)myWeakReference.Target).Foo();
}
When using a WeakReference, how can we be sure than the target is not collected between the .IsAlive and .Target calls?
For example:
if (myWeakReference.IsAlive)
{
// How can we be sure the object is still alive while here?
((MyType)myWeakReference.Target).Foo();
}
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只需获取
Target并检查它是否不为空：IsAlive 的文档特别指出：
Just get the
Targetand check whether it's not null:The docs for
IsAlivespecifically say:“IsAlive”属性的唯一目的是用于以下情况：如果 WeakReference 的目标已被销毁，您希望采取一些操作，但又不想冒意外使其存活时间超过必要时间的风险。例如，如果
if (someWeakReference.Target == null) cleanup_related_object();垃圾收集器（无论出于何种原因）在评估 someWeakReference.Target 的代码之后立即触发，GC 就会注意到存在对该对象的强引用并阻止其收集。另一方面，说：
if (!someWeakReference.IsAlive) cleanup_related_object();不会有意外延长 someWeakReference 目标的目标生命周期的风险
The only purpose of the "IsAlive" property is for situations where you want to take some action if the target of a WeakReference has already been destroyed, but where you don't want to risk accidentally keeping it alive longer than necessary. If one were to say, e.g.
if (someWeakReference.Target == null) cleanup_related_object();and the garbage-collector were to (for whatever reason) trigger right after the code that evaluated someWeakReference.Target, the GC would notice that there existed a strong reference to that object and preclude its collection. On the other hand, saying:
if (!someWeakReference.IsAlive) cleanup_related_object();there would be no risk of accidentally prolonging the lifetime of the target of someWeakReference target
你不能。将 myWeakReference.Target 分配给变量，并检查是否为 null。
You can't. Assign myWeakReference.Target to a variable, and check for null.
你可以摆脱 if :)
(myWeakReference?.Target as MyType)?.Foo()
you can get rid of the if :)
(myWeakReference?.Target as MyType)?.Foo()