2.8.4 错误的加锁

Posted 2020-10-23 anxbb

package 第二章.错误的加锁;

/**
 * Created by zzq on 2018/1/22.
 */
public class BadLockOnInteger implements Runnable{
    public static Integer i = 0;
    static BadLockOnInteger instance = new BadLockOnInteger();

    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object‘s
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p/>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see Thread#run()
     */


    /**
     * 得到的结果并不是2000000,在多线程的操作中出现了错误
     *
     * @param args
     * @throws InterruptedException
     */
    public static void main(String args[]) throws InterruptedException {
        Thread thread1 = new Thread(instance);
        Thread thread2 = new Thread(instance);
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(i);
    }

    public void run() {
        for (int j = 0; j < 1000000; j++) {
            synchronized (instance) {//这里同步的并不是同一个对象,因为i是以Integer关键字创建的
                //正确做法应该是 synchronized (instance)
                i++;
            }
        }
    }
}