synchronized测试-优快云博客

public class BeSynchronized {
    
    private BeSynchronized() {
    }

    public static BeSynchronized getInstance() {
        return getIns.INSTANCE.returnInstance();
    }

    public void runBeSynchronized() {
        System.out.println("Thread.currentThread().getName() enter = " + Thread.currentThread().getName());
        synchronized (this) {
            System.out.println("LocalDateTime.now()+Thread.currentThread().getName() = " + LocalDateTime.now() + "~~" + Thread.currentThread().getName() + "=run");
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    enum getIns {
        INSTANCE;
        private BeSynchronized beSynchronized;

        getIns() {
            beSynchronized = new BeSynchronized();
        }

        private BeSynchronized returnInstance() {
            return beSynchronized;
        }
    }
}

public class Main {

    public static void main(String[] args) {
       	/**
         * synchronized测试
         * */
        BeSynchronized beSynchronized = BeSynchronized.getInstance();
        for (int i = 0; i < 5; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    beSynchronized.runBeSynchronized();
                }
            }, i + "-Thread").start();
        }
    }

}

G:\jdk\bin\java.exe -javaagent:G:\IDEA\lib\idea_rt.jar=55057:G:\IDEA\bin -Dfile.encoding=UTF-8 -classpath G:\GITHUB\DesignPattern\target\classes Main
Thread.currentThread().getName() enter = 2-Thread
Thread.currentThread().getName() enter = 0-Thread
Thread.currentThread().getName() enter = 4-Thread
Thread.currentThread().getName() enter = 3-Thread
Thread.currentThread().getName() enter = 1-Thread
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:30:42.478178200~~2-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:30:45.490695100~~1-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:30:48.491333~~3-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:30:51.492005100~~0-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:30:54.492464200~~4-Thread=run

Process finished with exit code 0

运行结果可以看到，线程一窝蜂的全都进入runBeSynchronized方法，然后在进入接下来的代码块的时候，被 synchronized(this) 拿住，所以后面的this对象只能等前一个完成之后才能拿到锁，然后再进入代码块运行代码。从运行结果的时间相差3S也反馈了我们预想的结果。

做个对照试验试试，把 synchronized锁 拿掉，然后运行试试。

    public void runBeSynchronized() {
        System.out.println("Thread.currentThread().getName() enter = " + Thread.currentThread().getName());
//        synchronized (this) {
            System.out.println("LocalDateTime.now()+Thread.currentThread().getName() = " + LocalDateTime.now() + "~~" + Thread.currentThread().getName() + "=run");
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
//        }
    }

G:\jdk\bin\java.exe -javaagent:G:\IDEA\lib\idea_rt.jar=57653:G:\IDEA\bin -Dfile.encoding=UTF-8 -classpath G:\GITHUB\DesignPattern\target\classes Main
Thread.currentThread().getName() enter = 2-Thread
Thread.currentThread().getName() enter = 1-Thread
Thread.currentThread().getName() enter = 3-Thread
Thread.currentThread().getName() enter = 0-Thread
Thread.currentThread().getName() enter = 4-Thread
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:44:55.764253500~~3-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:44:55.764253500~~4-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:44:55.764253500~~0-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:44:55.764253500~~1-Thread=run
LocalDateTime.now()+Thread.currentThread().getName() = 2019-11-12T16:44:55.764253500~~2-Thread=run

Process finished with exit code 0