C#线程安全使用(三)

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C#线程安全使用(三)

kiba518 2013-10-21 15:46:00 浏览677
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在讲CancellationTokenSource之前我决定先讲一下lock和Interlocked,如果能很好的理解这两个,再去理解CancellationTokenSource就会方便很多,由于我也是后起使用多线程,使用的时候就是直接运用FramWork4的东西,这样导致了很多东西学起来很吃力,当回顾了以前的知识点后,发现新出的东西如此好理解。

先看一下Lock的使用,下面是一个例子。

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

namespace LockConsole
{
    class Program
    {
        static object lockint = 0;
        static void Main()
        {
            Task[] tlist=new  Task[10];

            Thread[] threads = new Thread[10];
          
            for (int i = 0; i < 10; i++)
            {
             var action =   new Action<object>(Withdraw);
             Task t = new Task(action, i);
             tlist[i] = t;
                //Thread t = new Thread(new ThreadStart(acc.DoTransactions));
                //threads[i] = t;
            }
            for (int i = 0; i < 10; i++)
            {
                tlist[i].Start();
           
                //threads[i].Start();
            }
            Console.Read();
        }


        static void Withdraw(object i)
        {
            int amount = int.Parse(i.ToString());
            int  balance = 1000;

            lock (lockint)//删除lock就会造成 线程混乱
            {
                if (balance >= amount)
                {
                    Console.WriteLine("当前线程{0},当前状态{1}", Thread.CurrentThread.GetHashCode(), Thread.CurrentThread.ThreadState + "Balance before Withdrawal :  " + balance); 
                    Console.WriteLine("当前线程{0},当前状态{1}", Thread.CurrentThread.GetHashCode(), Thread.CurrentThread.ThreadState + "Amount to Withdraw        : -" + amount);
                    balance = balance - amount;
                    Console.WriteLine("当前线程{0},当前状态{1}", Thread.CurrentThread.GetHashCode(), Thread.CurrentThread.ThreadState + "Balance after Withdrawal  :  " + balance);
                   
                }
              
            }
        }

      
       
    }
   
    
}
View Code

输出结果如下,他的线程都是一个接一个的,线程11后是线程12,然后是13,14,11等。每个线程都是等到执行完了下一个才执行。

 

在看一下没有Lock的结果,如下图,线程是混乱的,12线程的函数没执行完13就开始了。

有了上面的例子,Lock就很好理解了,他是为了保障资源同一时间只被一个线程使用,虽然该例子中没有使用Lock的资源,但线程还是一个接一个的执行,因为使用了lock线程就会一个接一个执行。

 

接下来看一下interLock,这是一个MSDN的例子,我觉得不错,他的意思是,把usingResource作为一个锁,当多线程开始运行,函数UseResource()需要判断usingResource的值,当usingResource等于0的时候,当前线程不运行,否则运行,当本线程运行时,要修改usingResource的值为1,这样确保其他线程不运行,即同一时间只运行一个线程。

如果这样需求用到开发中,会出现一个问题,那就是当一个线程改变usingResource的值的一瞬间,别的线程读取了usingResource的值,那这个线程也被运行了。

这时就需要InterLock了。代码如下。

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

namespace MyInterlockedExchangeExampleClass
{
    class MyInterlockedExchangeExampleClass
    {
        //0 for false, 1 for true.
        private static int usingResource = 0;

        private const int numThreadIterations = 5;
        private const int numThreads = 10;

        static void Main()
        {
            Thread myThread;
            Random rnd = new Random();

            for (int i = 0; i < numThreads; i++)
            {
                myThread = new Thread(new ThreadStart(MyThreadProc));
                myThread.Name = String.Format("Thread{0}", i + 1);

                //Wait a random amount of time before starting next thread.
                Thread.Sleep(rnd.Next(0, 1000));
                myThread.Start();
            }
        }

        private static void MyThreadProc()
        {
            for (int i = 0; i < numThreadIterations; i++)
            {
                UseResource();

                //Wait 1 second before next attempt.
                Thread.Sleep(1000);
            }
        }

        //A simple method that denies reentrancy.
        static bool UseResource()
        {
            //0 indicates that the method is not in use.
            //原始值是0,判断是时候使用原始值,但判断后值为1,进行了设置
            if (0 == Interlocked.Exchange(ref usingResource, 1))
            {
                Console.WriteLine("{0} acquired the lock", Thread.CurrentThread.Name);

                //Code to access a resource that is not thread safe would go here.

                //Simulate some work
                Thread.Sleep(500);

                Console.WriteLine("{0} exiting lock", Thread.CurrentThread.Name);

                //Release the lock
                Interlocked.Exchange(ref usingResource, 0);
                return true;
            }
            else
            {
                Console.WriteLine("   {0} was denied the lock", Thread.CurrentThread.Name);
                return false;
            }
        }

    }

}
View Code

理解了lock和interlock后下一章讲解CancellationTokenSource。

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