java 利用cas算法模拟多线程并发抢票

傷城~ 2023-02-20 07:19 185阅读 0赞

### 利用cas算法实现。基于乐观锁。如果值发生冲突。加入异步线程递归进行抢（设置递归次数。防止死循环） ###

1、创建ThreadUtils类

/**
     * 线程副本，保证数据
     */
    public class ThreadUtils {
        private static ThreadLocal<Integer> threadLocal;
        static{
            threadLocal = new ThreadLocal();
        }
    
        public static void set(int value){
            threadLocal.set(value);
        }
    
        public static Integer get(){
            return threadLocal.get();
        }
    }

2、创建CasUtils类

/**
     * 基于cas原理实现高并发
     */
    public class CasUtils implements Runnable{
        /**
          * 私有内部类创建单例
         */
        private static class AtomicHolder{
            private static volatile AtomicInteger s = new AtomicInteger(ThreadUtils.get());
        }
    
        /**
         * 线程池
         */
        private  static ThreadPoolExecutor ex;
        static {
             ex = new ThreadPoolExecutor(
                    10,10,5,TimeUnit.SECONDS,
                    new ArrayBlockingQueue<Runnable>(1),
                    new ThreadPoolExecutor.DiscardOldestPolicy());
    
        }
    
        public CasUtils()throws Exception{
            int value = ThreadUtils.get();
            if(!AtomicHolder.s.compareAndSet(value,value)){
                /**
                 * 此处对于未赋值的进行其他操作
                 */
            }
        }
    
        @Override
        public void run() {
            System.out.println("我在抢票中..."+Thread.currentThread());
            try {
                int value = AtomicHolder.s.get();
                int si = 0;
                if(value-1>=0&&(si=AtomicHolder.s.decrementAndGet())>0){
                    /**
                     * 涉及业务可以写入消息队列
                     */
                    System.out.println("抢票成功..."+Thread.currentThread()+"========"+(si));
                }else{
                    /*if(value-1<0){
                        System.out.println("暂无票..."+Thread.currentThread()+"========"+(si));
                        return;
                    }*/
                    ex.execute(new Runnable() {
                        @Override
                        public void run() {
                            System.out.println("抢票循环..."+Thread.currentThread());
                            boolean isSubmit = true;
                            //设置抢票循环次数。
                            int time = 0;
                            while(isSubmit){
                                ++time;
                                int value = AtomicHolder.s.get();
                                //超过10次结束
                                if(time>=10){
                                    System.out.println("抢票结束【未抢到】..."+Thread.currentThread());
                                    isSubmit = false;
                                    break;
                                }
                                if(value-1>=0&&AtomicHolder.s.decrementAndGet()>0){
                                    /**
                                     * 涉及业务可以写入消息队列
                                     */
                                    isSubmit = false;
                                    System.out.println("抢票成功..."+Thread.currentThread());
                                }
                                try {
                                    Thread.sleep(200);
                                } catch (InterruptedException e) {
                                    e.printStackTrace();
                                }
                            }
                        }
                    });
                }
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

3、执行
    public static void main(String[] args) throws Exception {
        for(int i=0;i<100;i++){
            ThreadUtils.set(10);
            new Thread( new CasUtils()).start();
        }
    }

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