java GC如何清理相关的对象 [英] How does java GC clean inter related object

问题描述

任何人都可以告诉我什么会与彼此引用的对象？ java的GC如何解决这个问题？如果您有对象A和B，并且以下条件成立：

$ b

解决方案

$ b

• 引用B


• B引用A


• 没有其他对象引用它们中的任何一个


• 它们不是根对象（例如，常量池中的对象）

然后，这两个对象将被垃圾收集。这被称为循环引用。

这是因为标记和清除GC将扫描并找出所有可从根对象访问的对象。如果A和B在没有任何外部参考的情况下相互引用，则标记和扫描GC将无法将它们标记为可到达，因此将被选作GC的候选。

有许多不同的标记和扫描实现（天真标记和扫描，三色等）。但基本的想法是一样的。如果无法通过直接/间接引用从根目录访问对象，则会收集垃圾。

Could anyone please tell me what will be with objects that refer to each other? How does java's GC resolve that issue? Thanks in advance!

解决方案

If you have object A and B, and if the following conditions hold:

• A references to B
• B references to A
• No other objects reference to any one of them
• They are not root objects (e.g. objects in the constants pool etc)

then, these two objects will be garbage collected. This is called "circular reference".

This is because the mark-and-sweep GC will scan and find out all the objects that are reachable from the root objects. If A and B reference each other without any external reference, the mark-and-sweep GC won't be able to mark them as reachable, hence will be selected as candidates for GC.

There are a number of different mark-and-sweep implementations (naive mark-and-sweep, tri-colour etc). But the fundamental idea is the same. If an object cannot be reached from the root by direct/indirect references, it will be garbage collected.

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