Question

如何防止方法“test”中的引用类型变量“local”在工作时中途改变？除了制作它的深层副本之外，还有其他方法吗？我还认为“锁定”应该可以防止这种情况发生，但在这种情况下它不会发生。谁能开导我？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace ConsoleApplication3
{
    class Class1
    {
        public int Value = 0;
    }
    class Test
    {
        private static readonly object m_lock = new object(); 


        static void Main()
        {
            Class1 r1 = new Class1();
            r1.Value = 2;
            Console.WriteLine("MainThread Original Value: {0} ", r1.Value);

            ThreadStart starter = delegate { test(r1); };
            Thread subThread = new Thread(starter);
            subThread.Start();

            Thread.Sleep(1000);
            r1.Value = 1234;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);
            Thread.Sleep(1000);
            r1.Value = 4321;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);
            Thread.Sleep(1000);
            r1.Value = 5678;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);


        }

        static void test(Class1 r)
        {
            lock (m_lock)
            {
                Class1 local = r;
                Console.WriteLine("SubThread Original Values: {0}, {1}", local.Value, r.Value);

                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);

                Console.WriteLine("SubThread Final Values: {0}, {1}", local.Value, r.Value);
                Console.ReadLine();
            }
        }
    }
}

输出：

MainThread Original Value: 2
SubThread Original Values: 2, 2
Working... local value: 2
MainThread New Value: 1234
Working... local value: 1234
Working... local value: 1234
MainThread New Value: 4321
Working... local value: 4321
Working... local value: 4321
MainThread New Value: 5678
Working... local value: 5678
Working... local value: 5678
SubThread Final Values: 5678, 5678

我想要实现的输出（其中“local”不会受到主线程中发生的事情的影响）：

MainThread Original Value: 2
SubThread Original Values: 2, 2
Working... local value: 2
MainThread New Value: 1234
Working... local value: 2
Working... local value: 2
MainThread New Value: 4321
Working... local value: 2
Working... local value: 2
MainThread New Value: 5678
Working... local value: 2
Working... local value: 2
SubThread Final Values: 2, 5678

编辑：假设无法修改Class1，即它来自外部dll。

Answer 1

添加锁定在这里没有帮助。您这里只有一个Class1实例，因此所有线程都访问该单个对象。您需要为每个线程创建一个Class1实例，以便每个线程只有自己的Class1实例可供使用。

具体而言，test中读取Class1 local = r;的行是罪魁祸首。如果您将该行更改为阅读Class1 local = new Class1()，那么您将获得所期望的行为。

或者，除了您已经传递的实例之外，从test传入Main()个新的Class1实例。那会做同样的事情。如果要在将值传递给线程函数之前预先设置值，请执行以下操作：

static void Main()
    {
        Class1 r1 = new Class1();
        r1.Value = 2;
        Console.WriteLine("MainThread Original Value: {0} ", r1.Value);

        Class1 r2 = new Class1();
        r2.Value = 2;

        ThreadStart starter = delegate { test(r1, r2); };

        *rest of your code here*

而static void test(Class1 r)改为使用

static void test(Class1 tr, Class1 r) {
    Class1 local = r;

    *etc*

请注意，我已将r2而不是r1传递给test。

这是您的代码，已修复以显示与您正在寻找的输出相同的输出：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace ConsoleApplication3 {
    class Class1 {
        public int Value = 0;
    }
    class Test {
        private static readonly object m_lock = new object();


        static void Main() {
            Class1 r1 = new Class1();
            r1.Value = 2;

            Class1 r2 = new Class1();
            r2.Value = 2;

            Console.WriteLine("MainThread Original Value: {0} ", r1.Value);

            ThreadStart starter = delegate { test(r1, r2); };
            Thread subThread = new Thread(starter);
            subThread.Start();

            Thread.Sleep(1000);
            r1.Value = 1234;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);
            Thread.Sleep(1000);
            r1.Value = 4321;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);
            Thread.Sleep(1000);
            r1.Value = 5678;
            Console.WriteLine("MainThread New Value: {0} ", r1.Value);


        }

        static void test(Class1 r, Class1 tr) {
            lock (m_lock) {
                Class1 local = tr;
                Console.WriteLine("SubThread Original Values: {0}, {1}", local.Value, r.Value);

                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);
                Console.WriteLine("Working... local value: {0}", local.Value);
                Thread.Sleep(500);

                Console.WriteLine("SubThread Final Values: {0}, {1}", local.Value, r.Value);
                Console.ReadLine();
            }
        }
    }
}

输出：

MainThread Original Value: 2
SubThread Original Values: 2, 2
Working... local value: 2
MainThread New Value: 1234
Working... local value: 2
Working... local value: 2
MainThread New Value: 4321
Working... local value: 2
Working... local value: 2
MainThread New Value: 5678
Working... local value: 2
Working... local value: 2
SubThread Final Values: 2, 5678

如何防止另一个线程在方法运行时修改方法中的本地引用变量？

1 个答案: