标签：ant thread run 执行 code demo 产生 exit get
单线程相当于一个人做一件事，而多线程程序中，当需要多个线程共享同一个数据时，一个线程对共享的数据进行修改时，在他没有完成相关操作之前不允许其他线程进行相关操作，否则会出现线程安全问题。
package pers.zhb.runnable; public class MyThread implements Runnable { private int tickets = 10; public void run() { while (true) { if (tickets > 0) System.out.println(Thread.currentThread().getName() + "售票窗口,售卖了" + tickets-- + "号票"); else System.exit(0); } } }
package pers.zhb.runnable; public class RunnableDemo { public static void main(String[] args) { MyThread mt=new MyThread(); Thread thread1 = new Thread(mt); Thread thread2 = new Thread(mt); Thread thread3 = new Thread(mt); Thread thread4 = new Thread(mt); thread1.start(); thread2.start(); thread3.start(); thread4.start(); } }
可以看出，10号票在被1号窗口卖出后，又被2号窗口卖了一次，显然这是不符合常理的。产生的原因是这样的：2号线程开始执行，tickets为10，进行了 if (tickets > 0)；语句的执行，可以继续往下执行了，但是他没有抢夺到CPU资源，接着是1号线程读取数据10，进行判断可以执行，1号线程执行完后，2号线程依旧没有抢夺到CPU资源，只能继续等待。接着是3号线程、0号线程进行相关操作。当2号线程抢夺到CPU资源时，他的数据还是10，就造成了有重复票的情况。
添加同步语句：
package pers.zhb.runnable; public class MyThread implements Runnable { private int tickets = 10; Object lock = new Object(); public void run() { synchronized (lock) { while (true) { if (tickets > 0) System.out.println(Thread.currentThread().getName() + "售票窗口,售卖了" + tickets-- + "号票"); else System.exit(0); } } } }
package pers.zhb.runnable; public class RunnableDemo { public static void main(String[] args) { MyThread mt=new MyThread(); Thread thread1 = new Thread(mt); Thread thread2 = new Thread(mt); Thread thread3 = new Thread(mt); Thread thread4 = new Thread(mt); thread1.start(); thread2.start(); thread3.start(); thread4.start(); } }
创建同步方法：
package pers.zhb.runnable; public class MyThread implements Runnable { private int tickets = 10; Object lock = new Object(); public void run() { while (true) lock(); } public synchronized void lock() { while (true) { if (tickets > 0) System.out.println(Thread.currentThread().getName() + "售票窗口,售卖了" + tickets-- + "号票"); else System.exit(0); } } }
package pers.zhb.runnable; public class RunnableDemo { public static void main(String[] args) { MyThread mt=new MyThread(); Thread thread1 = new Thread(mt); Thread thread2 = new Thread(mt); Thread thread3 = new Thread(mt); Thread thread4 = new Thread(mt); thread1.start(); thread2.start(); thread3.start(); thread4.start(); } }
可以对资源重复加锁：
package pers.zhb.runnable; import java.util.concurrent.locks.ReentrantLock; public class MyThread implements Runnable { private int tickets = 10; ReentrantLock lock = new ReentrantLock(); public void run() { while (true) { lock.lock(); if (tickets > 0) System.out.println(Thread.currentThread().getName() + "售票窗口,售卖了" + tickets-- + "号票"); else System.exit(0); } } }
package pers.zhb.runnable; public class RunnableDemo { public static void main(String[] args) { MyThread mt=new MyThread(); Thread thread1 = new Thread(mt); Thread thread2 = new Thread(mt); Thread thread3 = new Thread(mt); Thread thread4 = new Thread(mt); thread1.start(); thread2.start(); thread3.start(); thread4.start(); } }
标签：ant thread run 执行 code demo 产生 exit get
原文地址：https://www.cnblogs.com/zhai1997/p/11371536.html
