• 本代码描述如何确保当前一个线程使用某些资源时，同时其他线程无法使用该资源。
  

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

namespace ConsoleApplication3
{
 class Program
    {
        static void Main(string[] args)
        {
            #region 1.10
            var c = new Counter();
            var t1 = new Thread(() => Class1_10.TestCounter(c));
            var t2 = new Thread(() => Class1_10.TestCounter(c));
            var t3 = new Thread(() => Class1_10.TestCounter(c));
            t1.Start();
            t2.Start();
            t3.Start();
            t1.Join();
            t2.Join();
            t3.Join();
            Console.WriteLine("有问题的 counter类");
            Console.WriteLine("Total count:{0}",c.Count);//一个循环周期内先增1然后在减1，原则上最终结果是0，实际上可能是0，但是更多的是其他值（不确定）。原因：Counter是线程不安全的。
            Console.WriteLine("-----");

            Console.WriteLine("正确的 counter类");

            var c1 = new CounterWithLock();
            var tt1 = new Thread(() => Class1_10.TestCounter(c1));
            var tt2 = new Thread(() => Class1_10.TestCounter(c1));
            var tt3 = new Thread(() => Class1_10.TestCounter(c1));
            tt1.Start();
            tt2.Start();
            tt3.Start();
            tt1.Join();
            tt2.Join();
            tt3.Join();
            Console.WriteLine("Total count:{0}", c1.Count);

            #endregion
}
    public class Class1_10
    {
        public static void TestCounter(CounterBase c)
        {
            for (int i = 0; i < 10000; i++)
            {
                c.Increment();//增量
                c.Decrement();//减量
            }
        }
    }
    public class Counter : CounterBase
    {
        public int Count { get; private set; }
        //递增
        public override void Increment()
        {
            Count++;
        }
        //递减
        public override void Decrement()
        {
            Count--;
        }
    }
    public class CounterWithLock : CounterBase
    {
        private readonly object _syncRoot = new object();
        public int Count { get; private set; }
        //递增
        public override void Increment()
        {
            lock (_syncRoot)
            {
                Count++;
            }
        }
        //递减
        public override void Decrement()
        {
            lock (_syncRoot)
            {
                Count--;
            }
        }
    }
    public abstract class CounterBase
    {
        public abstract void Increment();
        public abstract void Decrement();

    }
}

1.10 使用C#中的lock关键字