一些文章在分析GC時(shí)，不可逾越的說到要先從根對象掃描出不可達(dá)對象，然后標(biāo)記那些不可達(dá)對象為垃圾。那么源頭根對象是什么玩意呢？

幾分鐘后google到比較可信源是http://stackoverflow.com/questions/8458886/what-is-a-rooted-reference。其解釋具體為：

GC roots are not objects in themselves but are instead references to objects. Any object referenced by a GC root will automatically survive the next garbage collection. There are four main kinds of root in .NET:

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1，A?local variable in a method that is currently running（GC發(fā)生時(shí)，當(dāng)前正在執(zhí)行的方法中那些本地變量）?is considered to be a GC root. The objects referenced by these variables can always be accessed immediately by the method they are declared in, and so they must be kept around. The lifetime of these roots can depend on the way the program was built. In debug builds, a local variable lasts for as long as the method is on the stack. In release builds, the JIT is able to look at the program structure to work out the last point within the execution that a variable can be used by the method and will discard it when it is no longer required. This strategy isn’t always used and can be turned off, for example, by running the program in a debugger.

2，Static variables（靜態(tài)變量）?are also always considered GC roots. The objects they reference can be accessed at any time by the class that declared them (or the rest of the program if they are public), so .NET will always keep them around. Variables declared as ‘thread static’ will only last for as long as that thread is running.

3，If?a managed object is passed to an unmanaged COM+ library through interop（非托管類似COM+一樣通過interop被使用的對象）, then it will also become a GC root with a reference count. This is because COM+ doesn’t do garbage collection: It uses, instead, a reference counting system; once the COM+ library finishes with the object by setting the reference count to 0 it ceases to be a GC root and can be collected again.

4，If?an object has a finalizer（實(shí)現(xiàn)了finalizer接口的對象）, it is not immediately removed when the garbage collector decides it is no longer ‘live’. Instead, it becomes a special kind of root until .NET has called the finalizer method. This means that these objects usually require more than one garbage collection to be removed from memory, as they will survive the first time they are found to be unused.

推薦【譯】.Net 垃圾回收機(jī)制原理（一），其中也提到了finalizer有重活機(jī)會(huì)。

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轉(zhuǎn)載于:https://www.cnblogs.com/wusong/p/3282283.html

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