多线程的锁定

Question

我做了一个小测试是关于多线程的，但是结果与我期望的不同。
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;namespace ThreadTest
{
    
    public class LockCodeArea
    {
        private int count = 10;
        public void ReduceCount()
        {
            while (true)
            {
                lock (this) 
                {
                    Console.WriteLine("Current Count:{0}", count);
                    Console.WriteLine("Current thread HashCode is :{0}", Thread.CurrentThread.GetHashCode());
                    Thread.Sleep(100);
                    --count;
                    if (count > 0)
                        continue;
                    else
                        break;
                }
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            LockCodeArea testClass = new LockCodeArea();
            Thread firsThread = new Thread(new ThreadStart(testClass.ReduceCount));
            Thread secondThread = new Thread(new ThreadStart(testClass.ReduceCount));
            Console.WriteLine("Main HashCode is :{0}", Thread.CurrentThread.GetHashCode());
            Console.WriteLine("First thread Hashcode is :{0}",firsThread.GetHashCode());
            Console.WriteLine("Second thread HashCode is :{0}", secondThread.GetHashCode());
            firsThread.Start();
            secondThread.Start();
            if (!firsThread.IsAlive)
                Thread.Sleep(1000);
            Console.WriteLine("Press Any Key to Continue!");
            Console.WriteLine("Main HashCode is :{0}", Thread.CurrentThread.GetHashCode());
            Console.ReadLine();        }
    }
}
本来是希望使用Lock之后，只存在要么firstThread减数，要么secondThread减数，为什么会有firstThread和secondThead
交替减数的情况。我已经使用Lock锁定代码区了。？？？各位帮帮忙呀。

Answer 1

注意，lock锁定的块同一时间只有一个线程能访问，你目前的代码锁定的是while内的代码。也就是说有2个线程都到达了循环内，一个现成continue的时候另一个线程乘机执行Console.WriteLine....
如果要同一时间只有1个线程能执行整个循环，就要把整个循环（10次）都锁住，也就是说： public void ReduceCount()
        {
            lock (this)
            {
                while (true)
                {
                    Console.WriteLine("Current Count:{0}", count);
                    Console.WriteLine("Current thread HashCode is :{0}", Thread.CurrentThread.GetHashCode());
                    Thread.Sleep(100);
                    --count;
                    if (count > 0)
                        continue;
                    else
                        break;
                }
            }
        }注意，此时还是有2个线程进入了ReduceCount方法，但是只有先进入的线程执行了循环内的整个过程，然后break。这是等在方法口的另一个线程才执行该方法的代码（只有1次，因为count已经是0，超出了条件了）。
所以进一步修改代码，不让最后一次多余的执行显示出来：public void ReduceCount()
        {
            lock (this)
            {
                while (true)
                {
                    if (count > 0)
                    {
                        Console.WriteLine("Current Count:{0}", count);
                        Console.WriteLine("Current thread HashCode is :{0}", Thread.CurrentThread.GetHashCode());
                        Thread.Sleep(100);
                        --count;
                        continue;
                    }
                    else
                        break;
                }
            }
        }