Java 多线程 竞争造成的异常

初始状态， 未使用线程同步机制，造成错误。

package com.kunpengku;import java.util.Random;import java.util.Stack;public class Welcome {    public static Stack<Integer> abc = new Stack();    public static void main(String[] args) throws Exception    {        for (int i=0;i<10;i++){            abc.push(i);        }        //多线程方式        Q q = new Q();        Q q2 = new Q();        q.start();        q2.start();    }}class Q extends Thread{    public static Stack<Integer> abc;    Q(){        this.abc = Welcome.abc;    }    public void run(){        try{            while(this.abc.size()>0){                Random random = new Random();                Thread.sleep(random.nextInt(1000));                int tmp = abc.pop();                System.out.println(Thread.currentThread() + String.valueOf(tmp));            }        }catch(InterruptedException e){            e.printStackTrace();        }    }}

终端输出

Thread[Thread-0,5,main]9Thread[Thread-1,5,main]8Thread[Thread-1,5,main]7Thread[Thread-0,5,main]6Thread[Thread-1,5,main]5Thread[Thread-0,5,main]4Thread[Thread-1,5,main]3Thread[Thread-1,5,main]2Thread[Thread-0,5,main]1Thread[Thread-1,5,main]0Exception in thread "Thread-0" java.util.EmptyStackException    at java.util.Stack.peek(Unknown Source)    at java.util.Stack.pop(Unknown Source)    at com.kunpengku.Q.run(Welcome.java:38)

解决方法 利用Lock 线程锁

package com.kunpengku;import java.util.Random;import java.util.Stack;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class Welcome {    public static Stack<Integer> abc = new Stack();    public static void main(String[] args) throws Exception    {        for (int i=0;i<10;i++){            abc.push(i);        }        //多线程方式二        Q q = new Q();        Q q2 = new Q();        q.start();        q2.start();    }}class Q extends Thread{    public static Stack<Integer> abc;    private static Lock lock = new ReentrantLock();    Q(){        this.abc = Welcome.abc;    }    public void run(){        lock.lock();        try{            while(this.abc.size()>0){                Random random = new Random();                Thread.sleep(random.nextInt(1000));                int tmp = abc.pop();                System.out.println(Thread.currentThread() + String.valueOf(tmp));            }        }catch(InterruptedException e){            e.printStackTrace();        }finally{            lock.unlock();        }    }}

主要增加了 30， 36， 48行。