class MyClass
{
    private int _i;
    private object _locker = new object();

    public void DoSomething()
    {
        var b = 2;

        // some work that depends on b being 2

        lock(_locker)
        {
            _i = 3;
        }

        // some more work

        b = -1;

        // some more work
    }
}

我用这种方式,

//Usage:

var myobject = new MyClass();
new Thread(new ThreadStart(() => myobject.DoSomething())).Start();
new Thread(new ThreadStart(() => myobject.DoSomething())).Start();

以下序列可以发生吗？

Thread 1 is halfway through its work.
Thread 2 just starts. Sets b = 2. 
Thread 1 sets b = -1. 
Thread 2 is confused because it expected b to be 2 but its -1.

重要的一点是b是局部变量.两个线程是否可以访问b的同一个实例？我理解,对于实例变量_i,会发生这种情况.因此,锁定构造.但我不确定是否需要锁定局部变量.