java--Thread

2023年6月26日 122次阅读

多线程

//一种方法是将类声明为 Thread 的子类。该子类应重写 Thread 类的 run 方法。接下来可以分配并启动该子类的实例(不推荐)

//另一种方法是声明实现 Runnable 接口的类。该类然后实现 run 方法。然后可以分配该类的实例，在创建 Thread 时作为一个参数来传递并启动。（推荐）


//使用方法二创建一个测试类
public class MyThread2 implements Runnable {
    @Override
    public void run() {
        // TODO Auto-generated method stub
        for(int i=0;i!=100;i++)
        {
            Thread t = Thread.currentThread();
            System.out.println(t.getName() + ":" + i);
        }
    }
}



//多线程
private static void method2() {
    MyThread2 m = new MyThread2();
    Thread t = new Thread(m);
    t.setName("Hei");
    t.start();
    
    Thread t2 = new Thread(m);
    t2.setName("Hello");
    t2.start();
}

多线程出现的问题

现象

//static void sleep(long millis):让当前线程停一会
public class Ticket implements Runnable{
    
    int ticket;
    public Ticket(int ticket)
    {
        this.ticket = ticket;
    }
    public void run() {
        // TODO Auto-generated method stub
        Thread t = Thread.currentThread();
        while(true)
        {
            if(ticket>0)
            {
                System.out.println(t.getName() + ":" + ticket);
                ticket--;
            }
            else
                break;
        }
    }
    
}


private static void method3() {
    Ticket tk = new Ticket(100);
    Thread t1 = new Thread(tk);
    Thread t2 = new Thread(tk);
    Thread t3 = new Thread(tk);
    
    t1.setName("售票口1");
    t2.setName("售票口2");
    t3.setName("售票口3");
    
    t1.start();
    t2.start();
    t3.start();
}

解决方法（增加mutex互斥锁）

public class Ticket implements Runnable{
    
    int ticket = 100;
    Object mutex = new Object();
    @Override
    public void run() {                // 注意
        // TODO Auto-generated method stub
        Thread t = Thread.currentThread();
        while(true)
        {
            synchronized(mutex)                //注意
            {
                if(ticket>0)
                {
                    System.out.println(t.getName() + ":" + ticket);
                    ticket--;
                }
                else
                    break;
            }
        }
    }
}

//或者（锁的位置不同）
public class Ticket implements Runnable{
    
    int ticket = 100;
    Object mutex = new Object();
    @Override
    public synchronized void run() {       // 注意
        // TODO Auto-generated method stub
        Thread t = Thread.currentThread();
        while(true)
        {
            if(ticket>0)
            {
                System.out.println(t.getName() + ":" + ticket);
                ticket--;
            }
            else
                break;
        }
    }
}
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