Shulou(Shulou.com)06/01 Report--

This article introduces the relevant knowledge of "What is the method used by WeakReference with GC". In the actual case operation process, many people will encounter such difficulties. Next, let Xiaobian lead you to learn how to deal with these situations! I hope you can read carefully and learn something!

We usually use strong references to objects. If there are strong references, GC will not recycle objects. Can we keep a reference to an object while allowing GC to reclaim it when needed? NET provides WeakReference to implement. Weak references allow you to keep references to objects while allowing GC to free objects and reclaim memory if necessary. For objects that are cheap to create but memory-intensive, consider weak references when you want to keep them, use them when your application needs them, and reclaim them when GC needs them. Weak references are easy to use, see the following code:

Object obj = new Object();

WeakReference wref = new WeakReference( obj );

obj = null;

The first line of code creates a new object, called Object A, obj is a strong reference to Object A. The second line then creates a new weakly referenced object with arguments that are strong references to object A, and the third line releases the strong references to object A. If GC were to reclaim, object A would be reclaimed.

How do I get a strong reference to object A? It's simple. Look at code 2:

Object obj2 = wref.Target;

if( obj2 != null )

{

//Do what you want.

}

else

{

//The object has already been recycled, if you want to use it, you must create a new one.

}

As long as the Target attribute displayed attaches a value to the weak reference, you get a strong reference to the object represented by the weak reference. Check the availability of an object before using it, however, because it may have been recycled. If you get null (Nothing under VB. NET), it means that the object has been recycled and can no longer be used, and you need to reassign one. If it is not null, you can use it boldly.

Next let's look at another version of WeakReference, see Code 3:

// public WeakReference(

// object target,

// bool trackResurrection

//);

Object obj1 = new Object();

Object obj2 = new Object();

WeakReference wref1 = new WeakReference( obj1, false );

WeakReference wref2 = new WeakReference( obj2, true );

Another version of WeakReference has two parameters, the first of which is the same as the version we used earlier. The second parameter lets us look at its prototype, bool trackResurrection, is a bool type, that is, whether to track resurrection. In the previous article, I mentioned that objects that need Finalize will have a resurrection before they are finally released. We can probably guess what the second parameter means. If our second parameter is false, this weak reference is a short weak reference. When GC is recycled, it finds that there is no reference to this object in the root, so it is considered useless. At this time, the tracking of this object by the short weak reference ends, and the Target of the weak reference is set to null. The constructor version of one of the previous arguments creates a weak reference that is short and weak. If the second argument is true, the weak reference is a long weak reference. Target is available until the object's Finalize method is executed. However, some member variables of this object may have been recycled, so use it carefully.

Now let's see how WeakReference is implemented. Obviously WeakReference cannot directly reference the target object. The get/set of the Target attribute of WeakReference is two functions that return a reference to the target object from somewhere, rather than directly returning or setting a private variable as we most often write. GC maintains two lists to keep track of two types of weakly referenced target objects. When a WeakReference object is created, it finds a place in the corresponding list to put the reference to the target object. Obviously, these two lists are not part of the root. During GC memory collection, if an object is to be reclaimed, the list of weak references is checked and if a reference to the object is saved, it is set to null.

public class AspPage : Page

{

private static ArrayList __ENCList = new ArrayList();

[DebuggerNonUserCode]

public AspPage()

{

base.Load += new EventHandler(this.Page_Load);

ArrayList list = __ENCList;

lock (list)

{

__ENCList.Add(new WeakReference(this));

}

}

}

"WeakReference with GC what is the method used" content is introduced here, thank you for reading. If you want to know more about industry-related knowledge, you can pay attention to the website. Xiaobian will output more high-quality practical articles for everyone!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.