多线程学习笔记(七)

时间 2019-11-07

标签多线程学习笔记栏目 Java 繁體版

原文原文链接

在使用synchronized时,当一个线程获得一个对象锁后,再次请求此对象锁时是能够再次获得该对象锁的.这也证实在一个synchronized方法/块的内部调用本类的其余synchronized方法/块时,是永远能够获得锁的.ide

public class ThreadReenter {
    synchronized public void firstService() {
        System.out.println("This is the first service!");
        secondService();
    }

    synchronized public void secondService() {
        System.out.println("This is the second service!");
        thirdService();
    }

    synchronized public void thirdService() {
        System.out.println("This is the third service!");
    }
}

public class FirstThread extends Thread {

    @Override
    public void run(){
        ThreadReenter threadReenter = new ThreadReenter();
        threadReenter.firstService();
    }
}

public class Run {
    public static void main(String[] args) {
        FirstThread firstThread = new FirstThread();
        firstThread.start();

    }
}

运行结果:this

可重入锁的概念:线程

本身能够再次获取本身的内部锁.好比一个线程获取了某个对象的锁,此时这个对象的锁尚未释放,当这个线程想要获取这个对象的锁的时候仍是能够获取的,若是不能够锁重入的话,就会形成死锁.对象

注:可重入锁也适用于父子类继承的环境中.继承

public class ThreadReenter {
    public int i = 10;
    synchronized public void ancestor(){
        try{
            i--;
            System.out.println("the ancestor i = " + i);
            Thread.sleep(200);
        }catch (Exception e){
            e.printStackTrace();
        }
    }

}

public class SonOfThreadReenter extends ThreadReenter{
    synchronized public void Posterity(){
        try{
            while(i > 0){
                i--;
                System.out.println("the Posterity i = " + i);
                Thread.sleep(200);
                this.ancestor();
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

public class FirstThread extends Thread {

    @Override
    public void run(){
        SonOfThreadReenter sonOfThreadReenter = new SonOfThreadReenter();
        sonOfThreadReenter.Posterity();
    }
}

public class Run {
    public static void main(String[] args) {
        FirstThread firstThread = new FirstThread();
        firstThread.start();

    }
}

运行结果:同步

当存在父子类继承时,子类是彻底能够经过可重入锁调用父类的同步方法的.it