Java 多线程竞争造成的异常

刺骨的言语ヽ痛彻心扉 2022-08-18 02:57 175阅读 0赞

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]9
    Thread[Thread-1,5,main]8
    Thread[Thread-1,5,main]7
    Thread[Thread-0,5,main]6
    Thread[Thread-1,5,main]5
    Thread[Thread-0,5,main]4
    Thread[Thread-1,5,main]3
    Thread[Thread-1,5,main]2
    Thread[Thread-0,5,main]1
    Thread[Thread-1,5,main]0
    Exception 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。