黑马程序员-学习日记（多线程间的通信）

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示例：

//将资源封装成对象
class Resour
{
    String name;
    String gender;
}

//将线程执行的任务封装成对象
class Input implements Runnable
{
       private Resour r;
    Input(Resour r)
    {
        this.r = r;
    }
    public void run()
    {
        int x =0;
        while(true)
        {
            if(x==0)
            {
                r.name = "Travis";
                r.gender = "male";
            }
            else
            {
                r.name = "张妙";
                r.gender = "女性";
            }
            x = (x+1)%2;
        }
    }
}

class Output implements Runnable
{
    private Resour r;
    Output(Resour r)
    {
        this.r = r;
    }
    public void run()
    {
        while(true)
        {
            System.out.println(r.name+" "+r.gender);
        }
    }
}

class myLock
{
    static Object lockA = new Object();
    static Object lockB = new Object();
}

 class mlpcDemo
{
    public static void main(String[] args)
    {
        Resour r = new Resour();
        Input in = new Input(r);
        Output out = new Output(r);
        Thread th0 = new Thread(in);
        Thread th1 = new Thread(out);

        th0.start();
        th1.start();
    }
}

于是，我们给赋值的代码块加上同步。这里要注意必须明确哪些代码是要同步的。

//将资源封装成对象
class Resour
{
    String name;
    String gender;
}

//将线程执行的任务封装成对象
class Input implements Runnable
{
    private Resour r;
    Object obj = new Object();
    Input(Resour r)
    {
        this.r = r;
    }
    public void run()
    {
        int x =0;
        synchronized(obj)
        {　　　　　　　　　　　while(true)
            {
                if(x==0)
                {
                    r.name = "Travis";
                    r.gender = "male";
                }
                else
                {
                    r.name = "张妙";
                    r.gender = "女性";
                }
                x = (x+1)%2;
            }
        }

    }
}

class Output implements Runnable
{
    private Resour r;
    Output(Resour r)
    {
        this.r = r;
    }
    public void run()
    {
        while(true)
        {
            System.out.println(r.name+" "+r.gender);
        }
    }
}

class myLock
{
    static Object lockA = new Object();
    static Object lockB = new Object();
}

 class mlpcDemo
{
    public static void main(String[] args)
    {
        Resour r = new Resour();
        Input in = new Input(r);
        Output out = new Output(r);
        Thread th0 = new Thread(in);
        Thread th1 = new Thread(out);

        th0.start();
        th1.start();
    }
}

表面上看，赋值代码块被加上了同步，但运行的结果依然出现了姓名和性别乱搭配的情况。

于是分析原因，定义同步有两个前提，首先Input和Output这两个线程并未使用同一个锁。

其次，仔细观察下列代码：

Thread th0 = new Thread(in);
Thread th1 = new Thread(out);th0.start();th1.start();

无论Input还是Output都只有一条线程在执行！

不过，解决这个问题也十分容易。给不同线程的同步函数加上相同的锁。

需注意的错误：

 1 public void run()
 2     {
 3         int x =0;
 4         synchronized(r)  //这样会使得线程永远走此同步函数内的代码块
 5         {
 6                 while(true)
 7                 {
 8                 if(x==0)
 9                 {
10                     r.name = "Travis";
11                     r.gender = "male";
12                 }
13                 else
14                 {
15                     r.name = "张妙";
16                     r.gender = "女性";
17                 }
18                 x = (x+1)%2;
19             }
20         }
21     }