C# Lock锁保正多线程环境下的数据一致性

Posted 2021-06-23 何以解忧 `唯有暴富

C#中支持多线程，而多线程引发的一个比较突出的问题就是在同一个时间里，可能会有多个线程访问同一个资源，引起资源的竞争导致数据内容超出预期。

我们建立一个对象，然后在对象里增加一个线程id打印的方法，因为这个_threadId = threadId赋值没有锁，可以多线程访问，输出时可能被另一个线程改掉

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

namespace LockTest
{
    public class LockClass
    {
        private string _threadId;
        public void Test(string threadId)
        {
            _threadId = threadId;
            Random random = new Random();
            Thread.Sleep(random.Next(1000, 2000));
            Console.WriteLine("ThreadId:" + Thread.CurrentThread.ManagedThreadId.ToString() + " _threadId:" + _threadId + "第一层锁");
            Thread.Sleep(random.Next(1000,2000));
        }
    }
}

结果那是一片混乱

 

调用代码

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

namespace LockTest
{
    class Program
    {
        private static LockClass lockClass = new LockClass();
        static void Main(string[] args)
        {
            Thread t1;
            Thread t2;
            Thread t3;
            t1 = new Thread(SetInfo1);
            t2 = new Thread(SetInfo2);
            t3 = new Thread(SetInfo3);
            t1.Start();
            t2.Start();
            t3.Start();
        }

        public static void SetInfo1()
        {
            while (true)
            {
                lockClass.Test(Thread.CurrentThread.ManagedThreadId.ToString());
            }
        }
        //偶数线程
        public static void SetInfo2()
        {
            while (true)
            {
                lockClass.Test(Thread.CurrentThread.ManagedThreadId.ToString());
            }
        }

        public static void SetInfo3()
        {
            while (true)
            {
                lockClass.Test(Thread.CurrentThread.ManagedThreadId.ToString());
            }
        }

    }
}

我们给他加上锁看下结果如何，结果井然有序

代码

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

namespace LockTest
{
    public class LockClass
    {
        private object _sign = new object();
        private string _threadId;
        public void Test(string threadId)
        {
            lock (_sign)
            {
                _threadId = threadId;
                Random random = new Random();
                Thread.Sleep(random.Next(1000, 2000));
                Console.WriteLine("ThreadId:" + Thread.CurrentThread.ManagedThreadId.ToString() + " _threadId:" + _threadId + "第一层锁");
                Thread.Sleep(random.Next(1000, 2000));
            }
        }
    }
}

 如果我们在锁中加同一把锁会有什么事情发生么，lock 关键字可以用来确保代码块完成运行，而不会被其他线程中断。这是通过在代码块运行期间为给定对象获取互斥锁来实现的。在同一个线程内，锁中的同一把锁会被无视。

在lock内加lock

lock (_sign)  {

           lock (_sign){｝

｝

代码如下

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

namespace LockTest
{
    public class LockClass
    {
        private object _sign = new object();
        private string _threadId;
        public void Test(string threadId)
        {
            lock (_sign)
            {
                _threadId = threadId;
                lock (_sign)
                {
                    Random random = new Random();
                    Thread.Sleep(random.Next(1000, 2000));
                    Console.WriteLine("ThreadId:" + Thread.CurrentThread.ManagedThreadId.ToString() + " _threadId:" + _threadId + "第一层锁");
                    Thread.Sleep(random.Next(1000, 2000));
                }
            }
        }
    }
}

结果相同