java之学习多线程（四）

来源：互联网发布：淘宝c店运营编辑：程序博客网时间：2024/04/28 03:24

线程的同步与死锁

public class lock_line {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubMyThread3 Me = new MyThread3();new Thread(Me ,"one").start();    new Thread(Me ,"three").start();    new Thread(Me,"two").start();}}class MyThread3 implements Runnable{int ticket1 = 6;@Overridepublic void run(){for(int x = 0;x < 10;x++){if(this.ticket1 > 0){try {Thread.sleep(100);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println(Thread.currentThread().getName()+"卖票，ticket="+ this.ticket1--);}}}}

结果

one卖票，ticket=6
three卖票，ticket=5
two卖票，ticket=4
one卖票，ticket=3
three卖票，ticket=2
two卖票，ticket=1
one卖票，ticket=0
three卖票，ticket=-1
出现负数，说明在同一个时间段内有多个线程在运作，修改了ticket，使票数不为零的判断之后的ticket变为负数。

解决的方法就是：同步，是多个操作在同一个时间里只能有一个线程进行，其他线程要等待此线程完成后才可以继续执行。

方法一：同步代码块（ synchronized(同步对象){同步代码}）

public class lock_line {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubMyThread3 Me = new MyThread3();new Thread(Me ,"one").start();    new Thread(Me ,"three").start();    new Thread(Me,"two").start();}}class MyThread3 implements Runnable{int ticket1 = 6;@Overridepublic void run(){for(int x = 0;x < 10;x++){synchronized(this){if(this.ticket1 > 0){try {Thread.sleep(100);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println(Thread.currentThread().getName()+"卖票，ticket="+ this.ticket1--);}}}}}

方法二：同步方法

public class lock_line {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubMyThread3 Me = new MyThread3();new Thread(Me ,"one").start();    new Thread(Me ,"three").start();    new Thread(Me,"two").start();}}class MyThread3 implements Runnable{int ticket1 = 6;@Overridepublic void run(){for(int x = 0;x < 10;x++){this.test();}}public synchronized void test(){if(this.ticket1 > 0){try {Thread.sleep(100);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println(Thread.currentThread().getName()+"卖票，ticket="+ this.ticket1--);}}}

在此处说明一个问题，加入同步后程序会变慢许多，所以代码性能会减低，但数据安全性会很高。

多线程访问同一资源时一定要考虑到同步的问题，过多的同步会带来死锁。

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