有趣的多线程编程（3）——线程内部是如何进行的？

看一下以下两个例子的运行结果：
//TestThread.cs
using System;
using System.Threading;

public class Test
{
    static int count=0;
    
    static void Main()
    {
        ThreadStart job = new ThreadStart(ThreadJob);
        Thread thread = new Thread(job);
        thread.Start();
        
        for (int i=0; i < 5; i++)
        {
            count++;
        }
        
        thread.Join();
        Console.WriteLine ("Final count: {0}", count);
    }
    
    static void ThreadJob()
    {
        for (int i=0; i < 5; i++)
        {
            count++;
        }
    }
}

//InnerDataThread.cs

using System;
using System.Threading;

public class Test
{
    static int count=0;
    
    static void Main()
    {
        ThreadStart job = new ThreadStart(ThreadJob);
        Thread thread = new Thread(job);
        thread.Start();
        
        for (int i=0; i < 5; i++)
        {
            int tmp = count;
            Console.WriteLine ("Read count={0}", tmp);
            Thread.Sleep(50);
            tmp++;
            Console.WriteLine ("Incremented tmp to {0}", tmp);
            Thread.Sleep(20);
            count = tmp;
            Console.WriteLine ("Written count={0}", tmp);
            Thread.Sleep(30);
        }
        
        thread.Join();
        Console.WriteLine ("Final count: {0}", count);
    }
    
    static void ThreadJob()
    {
        for (int i=0; i < 5; i++)
        {
            int tmp = count;
            Console.WriteLine ("/t/t/t/tRead count={0}", tmp);
            Thread.Sleep(20);
            tmp++;
            Console.WriteLine ("/t/t/t/tIncremented tmp to {0}", tmp);
            Thread.Sleep(10);
            count = tmp;
            Console.WriteLine ("/t/t/t/tWritten count={0}", tmp);
            Thread.Sleep(40);
        }
    }
}

Read count=0 Read count=0 Incremented tmp to 1 Written count=1Incremented tmp to 1Written count=1 Read count=1 Incremented tmp to 2Read count=1 Written count=2 Read count=2Incremented tmp to 2 Incremented tmp to 3Written count=2 Written count=3Read count=3 Read count=3Incremented tmp to 4 Incremented tmp to 4 Written count=4Written count=4 Read count=4Read count=4 Incremented tmp to 5 Written count=5Incremented tmp to 5Written count=5Read count=5Incremented tmp to 6Written count=6Final count: 6

再比较下面这个例子：

//使用Monitor.Enter/​​Exit​​​ 
//MonitorThread.cs

using System;
using System.Threading;

public class Test
{
    static int count=0;
    static readonly object countLock = new object();
    
    static void Main()
    {
        ThreadStart job = new ThreadStart(ThreadJob);
        Thread thread = new Thread(job);
        thread.Start();
        
        for (int i=0; i < 5; i++)
        {
            Monitor.Enter(countLock);
            int tmp = count;
            Console.WriteLine ("Read count={0}", tmp);
            Thread.Sleep(50);
            tmp++;
            Console.WriteLine ("Incremented tmp to {0}", tmp);
            Thread.Sleep(20);
            count = tmp;
            Console.WriteLine ("Written count={0}", tmp);
            Monitor.Exit(countLock);
            Thread.Sleep(30);
        }
        
        thread.Join();
        Console.WriteLine ("Final count: {0}", count);
    }
    
    static void ThreadJob()
    {
        for (int i=0; i < 5; i++)
        {
            Monitor.Enter(countLock);
            int tmp = count;
            Console.WriteLine ("/t/t/t/tRead count={0}", tmp);
            Thread.Sleep(20);
            tmp++;
            Console.WriteLine ("/t/t/t/tIncremented tmp to {0}", tmp);
            Thread.Sleep(10);
            count = tmp;
            Console.WriteLine ("/t/t/t/tWritten count={0}", tmp);
            Monitor.Exit(countLock);
            Thread.Sleep(40);
        }
    }
}

结果与上例InnerDataThread.cs是不一样的，原因就在于Monitor的使用了。

Read count=0Incremented tmp to 1Written count=1 Read count=1 Incremented tmp to 2 Written count=2Read count=2Incremented tmp to 3Written count=3 Read count=3 Incremented tmp to 4 Written count=4Read count=4Incremented tmp to 5Written count=5 Read count=5 Incremented tmp to 6 Written count=6Read count=6Incremented tmp to 7Written count=7 Read count=7 Incremented tmp to 8 Written count=8Read count=8Incremented tmp to 9Written count=9 Read count=9 Incremented tmp to 10 Written count=10Final count: 10

下面使用lock来锁定线程：

// LockThread.cs
using System;
using System.Threading;

public class Test
{
    static int count=0;
    static readonly object countLock = new object();
    
    static void Main()
    {
        ThreadStart job = new ThreadStart(ThreadJob);
        Thread thread = new Thread(job);
        thread.Start();
        
        for (int i=0; i < 5; i++)
        {
            lock (countLock)
            {
                int tmp = count;
                Console.WriteLine ("Read count={0}", tmp);
                Thread.Sleep(50);
                tmp++;
                Console.WriteLine ("Incremented tmp to {0}", tmp);
                Thread.Sleep(20);
                count = tmp;
                Console.WriteLine ("Written count={0}", tmp);
            }
            Thread.Sleep(30);
        }
        
        thread.Join();
        Console.WriteLine ("Final count: {0}", count);
    }
    
    static void ThreadJob()
    {
        for (int i=0; i < 5; i++)
        {
            lock (countLock)
            {
                int tmp = count;
                Console.WriteLine ("/t/t/t/tRead count={0}", tmp);
                Thread.Sleep(20);
                tmp++;
                Console.WriteLine ("/t/t/t/tIncremented tmp to {0}", tmp);
                if (count < 100)
                    throw new Exception();
                Thread.Sleep(10);
                count = tmp;
                Console.WriteLine ("/t/t/t/tWritten count={0}", tmp);
            }
            Thread.Sleep(40);
        }
    }
}

结果如何？与MonitorThread.cs比较一下，再想想看。