C# 中的线程、值类型和引用类型说明? [英] Threading in C# , value types and reference types clarification?

问题描述

在阅读 Jon Skeet 文章 和 这篇来自 msdn 的文章，我还有一个问题

After reading Jon Skeet article , and this article from msdn , I still have a question

假设我有这个代码:

  MyPerson mp = new MyPerson(); //Field

  int g=0; //Field

  public void DoWork ()
   {
      int i;
      MyPerson mp2 = new MyPerson();  
      ...
   }

现在假设我有 2 个线程.它运行 DoWork.(让我们暂时忽略竞争条件)

Now let's say I have 2 threads. which runs DoWork. ( let's ignore for now , race conditions)

• 他们会看到相同的 g 还是每个线程都有自己的项目??(价值)

• Will they both see the same g or each thread will have its own item ? ? ( value )

他们会看到相同的 mp 还是每个线程都有自己的项目?(实例)

Will they both see the same mp or each thread will have its own item ?? ( instance )

他们会看到相同的 i 还是每个线程都有自己的项目?(价值)

Will they both see the same i or each thread will have its own item ? ( value )

他们会看到相同的 mp2 还是每个线程都有自己的项目?(实例)

Will they both see the same mp2 or each thread will have its own item ? ( instance )

如果他们都看到相同的内容，我为什么需要 static ?

if they both see the same , why would I need static ?

我已经搜索了很多关于这个主题的内容，找不到找到 任何文章，其中指出:不同的线程、引用类型和值类型...)

I've searched a lot about this topic , and couldn't find any article which states : Different Threads ,ref types and value types... )

推荐答案

两个线程都没有简单地运行DoWork"；他们在特定对象上运行DoWork .如果两个线程是针对不同的实例创建的，那么 mp 和 g 将是完全独立的字段.如果两个线程是针对 same 实例创建的，则 mp 和 g 将共享 但 它不是保证线程将看到另一个线程所做的更改，除非您使用同步或 volatile 访问.

Neither thread simply "runs DoWork"; they run DoWork on a particular object. If the two threads are created targeting different instances, then mp and g will be completely separate fields. If the two threads are created targeting the same instance, then mp and g will be shared but it is not guaranteed that the threads will see changes made by the other thread unless you use synchronization or volatile access.

例如:

var obj = new SomeObject();
Thread thread1 = new Thread(obj.DoWork);
Thread thread2 = new Thread(obj.DoWork); // clearly targeting the same instance

对

var obj = new SomeObject();
Thread thread1 = new Thread(obj.DoWork);
obj = new SomeObject();
Thread thread2 = new Thread(obj.DoWork); // targeting a different instance

局部变量 i 和 mp2 严格针对每个线程.

The local variables i and mp2 are strictly specific to each thread.

附加说明:即使它们是单独的字段/本地，如果 ... 中的某些代码稍后重新分配 mp 或 mp2 引用同一个对象，那么他们就会为同一个对象争吵；将应用相同的同步/volatile 规则.

Additional note: even if they are separate fields/locals, if some of the code in the ... later reassigns mp or mp2 to refer to the same object, then they will be squabbling over the same object; the same synchronization / volatile rules will apply.

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